UNIVERSITY OF CALIFORNIA ANDREW SMITH HALL1DIR r f HANDBOOK ON ENGINEERING. THE PRACTICAL CARE AND MANAGEMENT OF DYNAMOS, MOTORS, BOILERS, ENGINES, PUMPS, 1NSPIRA TORS AND INJECTORS, REFRIGERATING MACHINERY, HYDRAULIC ELEVATORS, ELECTRIC ELEVATORS, AIR COMPRESSORS, ROPE TRANSMISSION AND ALL BRANCHES OF STEAM ENGINEERING. BY HENRY C. TULLEY, Engineer and Member Board of Engineers, St. Louis. THIRD EDITION. lUO'J. and Enlarged. //^ Of SOLD BY HENRY C. TULLEY & CO., Wainwright Building, St. Louis, Mo. PRICE, $3.50. HALLIDIE Entered according to Act of Congress, in the year 1900, by HENRY C. TULLE Y, In the Office of the Librarian of Congress, at Washington. Copyrighted, 1902. NIXON-JONES PRINTING Co 215 PINB STREET, ST. Louis. INTRODUCTION. The object of the writer in preparing this work has been to present to the practical engineer a book to which he can, with confidence, refer to for information regarding every branch of his profession. Up to the date of the publication of this book, it was impossi- ble to find a plain and practical treatise on the steam boiler, steam pump, steam engine, and dynamo, and how to care for them; electric and hydraulic elevators, and how to care for them ; and all other work that an engineer is apt to come in contact with in his profession. An experience of over twenty-five years with all kinds of en- gines and boilers, pumps, and all other kinds of machinery, ena- bles the writer to fully understand the kind of information most needed by men having charge of steam engines of every descrip- tion, and what they should comprehend and employ. With this object in view, the writer has carefully made note of his past experience, and has also made note of things that came to his notice while visiting different engine rooms, and accord- ingly, has taken up each subject singly, excluding therefrom, everything not strictly connected with steam engineering. Particular attention has been given to the latest improvements in all classes of steam engineering and their proportioning, ac- cording to the best modern practice, which, it is hoped, will be of great value to engineers, as nothing of the kind has heretofore been published. This book also contains ample instructions for setting up, lining, reversing and setting the valves of all classes of engines. 116603 THE AUTHOR. (iii) CONTENTS. For Alphabetical Index to Subjects, see page 893. CHAPTER I. PAGE. THE ELEMENTARY PRINCIPLES OF ELECTRICAL MA- CHINERY 1 A permanent magnet ; 1 to 2 Two-bar magnet 3 to 6 A magnet needle 3 Magnetic lines of force ...... ....->.... 6 Lines of force 6 to 14 Magnetic force 13 To find the lifting capacity of a magnet 13 CHAPTER II. THE PRINCIPLES OF ELECTROMAGNETIC INDUCTION 14 to 22 The armature cores 23 to 27 CHAPTER III. TWO-POLE GENERATORS AND MOTORS 27 The simplest type of armature winding 27 to 29 Two-pole genera tors and motors 27 to 30 The g neral arrangement of the field and armature in a two-pole machine 33 to 36 The reason why brushes are set differently on motors than on dynamos 30 to 37 V VI CONTENTS. CHAPTER IV. PAGE. MULTIPOLAR MACHINES 38 Multipolar machines as to 39 Setting the brushes on a four-pole machine 40 Setting the brushes on an eight-pole machine 41 The lap and wave winding for four-pole machine 42 to 40 CHAPTER V. SWITCH BOARD, DISTRIBUTING CIRCUITS, AND SWITCH BOARD INSTRUMENTS 47 Generators of the constant potential . 47 to 48 The switch-board arranged for two generators of the shunt type 49 to 51 Switch-board for three-wire system 5G to 57 To wire a large building with a lighting and power system . 58 to 60 The ammeters GO Circuit breakers ..." . C>2 to 63 The electromotive in volts force, etc 63 CHAPTER VI. ELECTRIC MOTORS 64 Motors and their connections 64 to 73 The strength of an electric current, etc 73 The watt 73 The ampere 73 Candle power 73 CHAPTER VII. INSTRUCTIONS FOR INSTALLING AND OPERATING SLOW AND MODERATE SPEED GENERATORS AND MOTORS . . 74 To remove the armature 74 Assembling the parts .... 74 Filling the bearings 74 To complete the assembly 74 Starting 74 Care of commutator 75 CONTENTS. Vll PAGE. If commutator gives trouble , 76 General directions for starting dynamos . . . , 76, 77 Bringing dynamos to full speed 77 Connecting one dynamo with another 78 Switching dynamos into circuit 78 How dynamos may be connected together . . 78 Dynamos in parallel 79 'Directions for running dynamos and motors 80 Precautions in running dynamos 81 Personal safety 81 CHAPTER VIII. WHY COMMUTATOR BRUSHES SPARK AND' WHY THEY DO NOT SPARK 82 to 84 The way in which the current is shifted, etc 84, 85 Diagram illustrating the same 85 If the commutated coil, etc. 86 Even when the machine is properly proportioned, etc 87 Sparking 87 to 91 Noise 91 to 92 Heating in dynamo or motor . 93 to 94 The effect of the displacement of the armature 94 to 98 Table of carrying capacity of wires 99, 101 Insulation resistance .... 100 Soldering fluid .101 Table showing the size of wire of different metals that will be melted by currents of various strengths . 102 CHAPTER IX. INSTRUCTIONS FOR INSTALLING AND OPERATING APPA- RATUS FOR ARC LIGHTING, BRUSH SYSTEM 103 Theory of the Brush arc generator 103 Bipolar Brush arc generators 105 General data on bipolar Brush arc generators 10(5 Connections of No. 7 and No. 8 bipolar generators 107 Automatic regulator for bipolar Brush arch generators . . . . .108 Multipolar Brush arc generators 11U Vlll CONTENTS. PAGE. General data on multipolar Brush arc generate * Ill Method of suspending armature Ill Method of handling the magnet yoke 112 Setting the brushes 112 Care of commutator 114 Connections of multipolar Brush arc generators 114 Connections of Nos. 8, 9, 10 and 11 Brush arc generators, single circuit, clockwise rotation with form 1 regulator 115 Form 1 regulator for multipolar Brush arc generators ll(> Connections of Brush controller 118 Starting the multipolar Brush arc generator with form 1 regulator . 120 Form 2 regulator for multipolar Brush arc generators 120 Adjustment of form 2 regulator 123 Starting the multipolar Brush arc generator with form 2 regulator . 123 Form 3 regulator for multipolar Brush arc generators 124 Form 4 regulator for multipolar Brush arc generators 125 Ammeter 125 Instructions for installing and operating improved Brush arc lamps . 125 Connections for improved Brush arc lamps 128 Diagram of same ..." 128 Personal safety 129 Table showing relative resistance of metals at temperature of 70 degrees F 130 View of tlie Thomson-Houston Standard Arc dynamo arranged for right-hand rotation 131 CHAPTER X. INSTALLATION OF ARC DYNAMOS 131 Diagram of connections for arc lighting system 133 Diagram of connections for rheostat .134 View of controller for arc dynamos 135 Testing arc light dynamos 137 Diagram showing commutator segments and brush holders, etc. . . 138 Table of leads 140 Diagrams showing best position of air blasts and jets on L 1) and M D dynamos 141 Directions for setting the air blast, etc . 142 CONTENTS. ix PAGE. Some troubles which may be met and their causes reversal of polarity 142 Ring armatures 144 Standard plug switchboard for 6 circuits 147 Switchboards 147 View of the back of switchboard 148 View of meter for station use 149 Connections for watt meters for series arc circuits 149 Watt meters 150, 151 Instructions for the installation and care of arc lamps 151 View of interior of M arc lamp 150 Starting the lamps 152 Diagram of connections for M and K arc lamps 152 Instructions for repairing, testing and adjusting arc lights .... 153 Table of magnetizing force in ampere turns required per inch of length of magnetic circuit 159 CHAPTER Xa. INCANDESCENT WIRING TABLES 160 to 168 Amperes per motor table 169,170 Volts lost at different per cent drop 171,172 Amperes per lamp table 173 Approximate weight of " O. K." triple braided weatherproof copper wire . 174 Table showing difference between wire gauges in decimal parts of an inch 175 Electric light conductors table 176 CHAPTER XI. THE STEAM ENGINE 177 The selection of an engine 177 The gain by expansion 183 Table of cut-off in parts of the stroke 183 The steam engine governor 183 and 194 The fly-wheel 184 Horse power 185 Care and management of a steam engine 185 X CONTENTS. PAGE. Lubrication of an engine 18(> Selecting an oil for an engine 187 The piston packing 187 Crank-pins 188 Connecting rod brasses 189 Knocking in engines 189 to 190 The main bearings 190 to 192 Repairs of engines 191 Fitting a slide valve 191 Eccentric straps 192 Heating of journals 193 Automatic engines 194 To find the dead centers . . . . 195 View of tandem compound engine and its foundation 198 How to line an engine 199 to 203 View of twin tandem compound engine^ showing arrangement of piping 200 CHAPTER XIa. Directions for setting up ; adjusting and running the improved Cor- liss steam engene 205 Adjustment of Corliss valve gear with single and double eccentrics. 206 Adjustment with two eccentrics . . .215 The compound engine 222 Horse power of compound engine 232 Condensing engines 232 Condensers 235 Setting the piston type of valve 238 Setting the cut-off valve 243 Flat valve riding cut- off 245 CHAPTER XII. THE STEAM ENGINE CONTINUED . . 251 What is work 251 What is power 251 Horse power of an engine 252 General proportions of engine . 252 CONTENTS. XI PAGE. Rules for weights of fly-wheels 253 View of the Russell engine 254 Setting the valves of Russell engines 254 View of the Porter- Allen engine 258 Description of the Porter-Allen engine 259,271 Directions for setting the valves, and running the Porter-Allen engine 271, 273 Specifications for centrally balanced Centrifugal Inertia Governor 273, 275 The Armington and Sims engine 275 Setting the valve in an Armington and Sims engine 275 The Harrisburg engine 276 The care and management of the Harrisburg engine .... 276-281 The Mclntosh and Seymour High Speed engine 281 How to set the valves of an M. and S. engine . 281 The Ideal engine 283 Instructions for starting and operating Ideal engines .... 283, 291 Instructions for indicating Ideal engines 291, 292 The Westinghouse Compound engine 293 Instructions for starting and operating a Westinghouse Compound engine 292, 309 How to set the main valve on a Westinghouse engine .301 How to rebabbitt connecting rods 305 Some points on cylinder lubrication 309 Automatic lubricators 310, 312 Setting a plain slide valve with link motion 313,318 Valve setting for engineers 318, 322 View of a slide valve engine showing the point of taking steam . .321 View of a slide valve engine showing the point of cut-off . . . .321 View showing the position of the valve when compression begins 321, 322 CHAPTER XIII. TAKING CHARGE OF A STEAM POWER PLANT 323 Economy in steam power plants 327, 329 Priming in boilers 329 Table of properties of saturated steam 330 High pressure steam 332, 335 Using steam full stroke 335,337 XIV CONTENTS . 1'AGE. Zigzag riveting and chain riveting 4(58, 472 Single riveted lap joints, iron plates 469 Steel plates and steel rivets, S. R. L. J 470 Steel plates and steel rivets, D. R. L. J 471 Strength of stayed flat boiler surfaces 473 Boiler stays 474, 477 Riveted and lap welded flues 477, 481 Table of allowable steam pressure on flues 478, 479 Thickness of material required for tubes 481,486 Table of wrought-iron welded pipe 486 Pulsation in steam boilers 487, 488 Weight of square and round iron per lineal foot 488 Water columns for boilers . , 489 Steam gauges 489, 490 Safety valves 491, 499 Table of the rise of safety valves 494 Safety valve rules 497 Table of heating surfaces in square feet 501 Centrifugal force 501 CHAPTER XVIII, ' THE WATER TUBE SECTIONAL BOILER 502 The down draft furnace 503, 522 View of boiler setting and furnace common in the East 513 Vertical tubular boilers . . 514, 521 Proper water column connections 515 Table of pressures allowable in boilers 516 Eire line in boiler settings 520 Proper location of gauge cocks 521 Number of bricks required for boiler setting ... 522 Specifications for a sixty-inch 6-inch flue boiler ........ 524 Banking flres 531 Instructions for boiler attendants 532 Rules and problems anent steam boilers 536 Steam jets for smoke prevention 542 CONTENTS. XV CHAPTER XIX. PAGE. THE STEAM PUMP .... 544 The Worthington Compound pump 544 View of steam valves properly set 545 The Deaue steam pump 546 View of steam valves properly set 547 The Cameron steam pump 548 Explanation of steam end 548 View of steam valves properly set 548 The Knowles steam pump 550 Explanation of steam valves 550 View of steam valves properly set 552 The Hooker steam pump 553 Operation of the Hooker pump 553 View of steam valves property set 555 The Blake steam pump 555 Operation of the Blake pump 556 View of steam valves properly set 558 Miscellaneous pump questions and answers . . . ... . 559 and G03 How to set the steam valves of a duplex pump . 567 View of steam valves properly set 568 Proper pipe connections 569 View of pipe connections 570 Pumps refusing to lift water . . . . . 577 Corrosion in water pipes 579 Pumping acids 579 Selecting boiler for a steam pump 580 The Worthington water meter 581 Table of water pressure due to height 582 Table of decimal equivalents of IGths, 32n.ds and 64ths of an inch . 583 Capacity of tanks in U. S. gallons . 584 Capacity of square cisterns in U. S. gallons . . . . . . . . ". 585 Weight of water 585 Cost of water 587 Loss by friction of water in pipes 588 How water may be wasted 589 Ignition points of various substances 589 XV1U . CONTENTS. PAGE. Pure water 681 The temperature and pressure of saturated steam 684 Something for nothing . 686 Melting point of metals 687 Chimneys 688 to 694 Weight of steel smoke stacks per linear foot 694 CHAPTER XXIV. HORSE POWER OF GEARS 695 Table of H. P. of shafts 697 Prime movers 697 Wheel gearing . 698 The pitch line of a gear wheel 698 To find the pitch of a wheel 698 To find the chordal pitch 699 to 703 To find the diameter of a wheel 699 to 703 To find the number of teeth for a wheel "699 to 703 To find the proportional radius of a wheel or pinion 700 To find the diameter of a pinion 700 To find the circumference of a wheel 700 To find the number of revolutions of a wheel or pinion . . 700 to 70 1 Stress on gear teeth 705 A train of wheels and pinions 701 Table of diameters and pitches of wheels 701 Curves of teeth 705 Construction of gearing 706 Bevel wheels 707 Worm-screw ' ...... 708 Proportions of teeth of wheels 709 To find the depth of a cast-iron tooth 709 To find the horse-power of a tooth 710 Calculating the speed of gears 710 When time must be regarded 711 Table of weight of a square foot of sheet iron . . 712 Screw cutting 713 Transmission of power by manila rope 714,812,813 Decimal equivalents of one foot by inches 714 Table of transmission of power by wire ropes 715 and 8 14 CONTENTS. XIX CHAPTER XXV. PAGE. ELECTRIC ELEVATORS 716 The Otis elevator 716 Belt driven elevators 716, 725 Direct connected elevators 717, 730 The motor-starting switch 719 The elevator machine brake 720 The main hand rope 721 View of connections of gravity motor controller to elevator . . . 722 View of connections of gravity motor controller with separate rope attachment 723 Direct connected electric elevators 730 Automatic stops 733 View of circuit connections 734 The starting resistance 735 The switch lever 736 Cutting out the series field coils 737 The safety brake magnet 739 The proper care of machines 739, 779 How to start the car 74:3 The car switch 748 The slack cable switch 749 P^lectric control for private house elevators 749 View of wiring for private houses 750 The Sprague Electric Co.'s elevators 756 View of operative circuits for Sprague screw elevator . . . . . 762 The pilot motor " .763 Care of Sprague elevators 765 Directions for the care and operation of electric elevators .... 765 CHAPTER XXVI. HYDRAULIC ELEVATORS 769 How to pack hydraulic vertical cylinder elevators 769 How to set the hand cable on a iever machine 770 How to pack vertical cylinder valves 771 View of Otis vertical hydraulic elevator and valve chamber, and packing same 772 XX CONTENTS. PAGE. View of the Crane auxiliary and main valve, and operation of same . 775 Automatic stop valve 776 Leather cup packings for valves 784 Closing down elevators 784 Otis gravity wedge safety 777 Care of. Hale elevators 777 Water for use in hydraulic elevators 778,781 Otis differential and auxiliary valve 780 Elevator inclosures and their care 782 Standard hoisting rope with 19 wires to the strand 783 Cables, and how to care for them 783 Lubrication for hydraulic elevators 785 Belts, and how to care for them 786 Useful information 786 To find leaks in pressure tanks 786 Decimal equivalents of an inch 787 CHAPTER XXVII. THE DRIVING POWER OF BELTS 788 The average strain or tension at which belting should be run . . . 788 Rules and problems anent belting 788,71)7 Extracts from articles on belts, by It. J. Abernatliy 790 Transmitting power of belts 795 Table of horse-power of belts 790,799 Directions for adjusting belting 798 Horse power of belting '. 799 CHAPTER XXVIII. AIR COMPRESSORS, THERMOMETERS, THE METRIC SYS- TEM, AND ROPE TRANSMISSION 800 Losses in air compressors 800 Capacity of air compressors 800 Contents of a cylinder in cubic feet for each foot in length .... 801 The McKierman air compressor 801 The Bennett automatic air compressor 803 The Ingersoll-Sergeant air compressor . 803 The Pohle air lift system .807 CONTENTS . XXI 1'AGE, The metric system 80) Thermometers 811 Rope transmission . . 812 Horse-power transmitted by hemp ropes .. . . . . . . . . .813 To test the purity of hemp ropes 814 Wire rope data 814 CHAPTER XXIX. ALTERNATING CURRENT MACHINERY .815 The principles of alternating currents 815 Diagrams representing a generator of either continuous or alter- nating currents 817 Diagrams showing the relations between alternating currents and e.m.fs 821,825 One reason why alternating currents vary, etc 825 Diagrams showing the way in which sine curves are used, etc. . . 826 Polyphase currents '...." 832 Unbalanced three-phase currents, etc . . 834 Inductive action in alternating current circuits, etc 834 The angle of lag between the current, etc 837 By the use of condensers, etc 840 The general principle of construction of a condenser, etc. .... 841 Mutual induction 842 Transformers 844 The action in a transformer 846 The object in using transformers 849 Alternating current generators . 852 Diagram illustrating a simple alternating current generator . . .854 Alternator of the multipolar type 855 How alternating current generators are run . 859 If an alternator is of the multipolar type 854 A revolving field alternator 857 An inductor alternator 858 Alternating current generators 859 Alternators run in parallel 860 Starting alternators connected in parallel 861 The way in which synchronizing lamps are connected 863 Compensating and compounding alternators . . . . " . . . . . 864 2 HANDBOOK ON ENGINEERING. also upon the temper it is given. Generally speaking, the harder the steel the stronger the magnet. A bar of soft steel, or wrought iron, cannot be made into a permanent magnet of any noticeable strength, but if such a bar is covered with a coil of wire, as shown in Figs. 3 and 4, and a current of electricity is passed through the wire, the bar will be converted into a very strong magnet so long as the current flows. As soon as the electric current stops flowing through the wire, the magnetism of the bar will die out. Magnets of the last-named type are called electro-magnets, as they do not possess magnet properties except when the electric current flows around them. Electro-magnets, when energized by sufficiently strong electric currents, can be far more powerful than the permanent magnets, and on that account they are used in electric generators and motors. In addition to being stronger magnets, the electro-magnet has the advantage that it can be magnetized and demagnetized almost instantly, by simply cutting off the exciting electric current, and on this account they can be used for parts of electrical machines and apparatus, for which the permanent magnet would be entirely unsuited. If we test the attractive power of a magnet, we will find that it is greatest at the ends, the force at the middle point being scarcely noticeable. A bar such as Fig. 1 or Fig. 3 might hold a piece of iron weighing several pounds, if presented to either end, while at the middle point, it might not be able to sustain more than an ounce or two. Owing to this fact, the ends are called the poles of the magnet. If any magnet is suspended from its center, like a scale beam, and allowed to swing freely, it will be found that it will come to rest in a north and south position, and no matter how violently it may be moved around, it will always come to a state of rest with the same end pointing towards the north. On this ac- count, the ends are called north and south poles, the north pole being the end that points toward the north. HANDBOOK ON ENGINEERING. 3 If two-bar magnets are suspended side by side with the north end of one at the top and the north end of the other at the bottom, as is illustrated in Fig. 5, they will attract each other ; but if both magnets had the north end at the top, they will push away, as shown in Fig. 6. It is evident that there is a good reason for this difference in action, and this reason we can find out by experiment. a a a Fig. 5. Fig. 6. A magnet needle, such as is used in mariner's compasses, is simply a small magnet. If we place a magnet bar, as shown in Fig. 7, and then set near to it, in different positions, a compass containing a very small needle, we will find that in these several positions the direction of the needle will be about as is indicated by the small arrows marked I) on the curved lines a a; the point of the arrow being the north end, or pole of the needle. The reason why the needle will take up these positions is that the north end of the bar attracts the south end of the needle, and pushes away the north end, just as in Figs. 5 and 6, and the south end of the bar acts in the same way ; so that there is a tug of war going on, so to speak, between the attractions and repulsions of 4 HANDBOOK OX ENGINEERING. the two ends of the bar upon the two ends of the needle, the result being that the position assumed by the needle is the re- sultant of these several actions. When the needle is near the \ V .s v. Fig. 7. \ Fig. 8. north pole of the bar, its south end is attracted with the greatest force, and when near the south end of the bar, the north end ex- periences the greatest attraction. If we were to place the exploring needle in all possible posi- tions near the magnet and trace lines parallel with it, in these positions, we would obtain a large number of curves about the shape of those shown in Fig. 8. As these curves represent the direction into which the magnet needle is turned at the various points in the vicinity of the magnet, they represent the direction in which the combined forces of the two poles act at these two points, hence, these lines are called magnetic lines of force. HANDBOOK ON ENGINEERING. When two magnets are suspended as in Fig. 5, the lines of force of both will be in the same direction as is indicated in Fig. 9 by the arrow heads on the curves a a. That this is true can be seen from Fig. 7, in which it will be seen that the arrow heads point toward the south pole and away from the north pole. As the north pole of a magnet has an attraction for the south pole, we can readily see that there is an endwise pull in the lines of force, which tends to make them contract, like rubber bands, hence, we can imagine the lines a a in Fig. 9 to contract and thus draw the two magnet bars together. The repulsion of the two magnets, when the north poles are at the same end, is illustrated in Fig. 10. Here we see that the lines of force passing on the outside of the bars, as indicated by lines a a, are unobstructed, and can assume their natural posi- a JV s Fig. 9. Fig. 10. tion, but those that pass between the bars, along line c, are pressed out of position. If we assume that the lines of force make an effort to retain their position, like so many wire 6 HANDBOOK ON ENGINEERING. springs, then we can see that the repulsion is due to the effort that the lines make to assume their natural form in the space between the bars. Magnetic lines of force have no real existence, they simply in- dicate the direction in which the force acts, but if we keep this fact in mind, it helps us to understand magnetic actions, if we treat the lines of force as if they were something real. This fact will become more evident as we proceed. Lines of force always pass from the north to the south pole through the space between these poles, and through the magnet itself, they are assumed to pass from the south to the north pole. The form of the lines of force depends upon the relative position of the north and south poles. In Fig. 9 they are curved, as a s w E==E S jy Fig. 11. the magnets are placed side by side, but if the bars were arranged end to end, as in Fig. 11, the lines of force would be straight, as is shown at a. From the north end of the right side magnet, the lines of force would pass in curved line, as in Fig. 10, to the south pole of the magnet on the left side, thus completing the magnetic chain, or circuit, as it is called. If we take the two magnet bars of Fig. 11 and stand them on end, as in Fig. 12, and suspend a bent wire C in the manner shown, effects can be produced that are interesting and instruct- ive, as they illustrate the principle upon which generators and motors act. The wire should be journaled at D D, so as to swing with as little friction as possible, and its ends are to be con- nected with a battery J5, by means of fine wires a and b; a switch being provided at c so as to stop the flow of current when desired. HANDBOOK ON ENGINEERING. 7 I* the switch c is opened, so that no current flows through C, the latter will not be disturbed, and if we give it a swing, it will oscil- late back and forth, like a clock pendulum, and in a few seconds come to rest in the position in which it is shown. If the switch is closed, C will at once swing out of the stream of magnetic lines of force and will remain in that position as long as the current from the battery passes through it. The direction in which C Fig. 12. will swing will depend upon the direction of the current through it. If with the wires a and 6 connected with the battery, in the manner shown, the wire C swings to the right side, then if a is connected with e, and b with d, the direction of swing will be reversed ; that is, C will swing toward the left. From this experiment we see that the magnetic lines of force can develop a repulsive force against an electric current, and that the direction of the repulsion depends upon the direction of the 8 HANDBOOK ON ENGINEERING. electric current with respect to the direction of the lines of force. We now desire to know why this repulsion is developed, and this we can ascertain by the following experiments : If we arrange three wires as shown in Figs. 13, 14 and 15, so as to run north and south, the upper end being north, and place over these magnet needles D D D, pivoted at e e e, we will find that if there is no current flowing through the wire, the needle will point toward the north, or be parallel with the wire, as is Fig. 13. Fig. 14. Fig. 15. shown in Fig. 14. If the current runs through the wire from south to north, the north end of the needle will swing to the right, as in Fig. 15, and if the current runs through the wire from north to south, the north end of the needle will swing toward the left, as in Fig. 13. From this we see that an electric current can repel a magnet, and that the direction in which it repels it depends upon the direction of the current. If we stand the three wires on end, as shown in Figs. 16, 17 and 18, in which ABC represent the wires as seen from above, we will find out more about the relation between electric currents HANDBOOK ON ENGINEERING. and magnets. If we place four small magnet needles around each one of the wires, as shown at a a a a, we will find that those around the center wire, through which no current flows, will all a Fig. 16. Fig. 18. point toward the north, as shown, while those around the wire Fig. 16, through which a current flows upward, that is, away from the center of the earth, will point in a direction opposite to that in which the hands of a clock move; and in wire Fig. 18, in which the electric current flows down toward the center of the earth, the north ends of all the needles will point in the direction in which the hands of a clock move, that is, just opposite to those in Fig. 16. .(IP Fig. 19. Fig. 20. From these actions, we infer at once that when an electric current flows through a wire, the latter becomes surrounded with magnetic lines of force, as is illustrated in Figs. 19 and 20, 10 HANDBOOK ON ENGINEERING. and that there is a fixed relation between the direction of the current and that of the lines of force. At A, Fig. 19, the direc- tion of the lines of force is shown for a current moving up- ward, and at B, Fig. 20, the direction of the lines of force is that due to a current moving downward through the wire. Inasmuch as an electric current flowing through a wire is surrounded by magnetic lines of force, we can say that a com- plete electric current consists of two parts, one the current proper, which traverses the wire, and the other the magnetic casing which envelops the wire. It is the action between the latter part of the current and the lines of force of magnets that develops the current in a generator, or the power in a motor. With the aid of Figs. 21 and 22, we can now show how the force is developed that thrusts the wire to one side in Fig. 12. The lines of force of the magnet, which constitute what is called the magnetic field, will flow from the north pole at the top to the south pole at the bottom, as is shown in Figs. 21 and 22. If the electric current flows through the wire C from the back toward the front, the lines of force developed around it will have the direction shown in Fig. 21. As lines of force cannot flow in op- posite directions in the same space, the lines of the field will swing over to the left side of the wire, but in doing so they will be stretched out of the straight form, and they will also push the lines surrounding the wire out of their central position. Under these conditions, which are illustrated in Fig. 21, the effort made by the field lines to straighten out, together with the effort made by the wire lines to return to the central position, will develop a thrust between the wire and the field, and thus force the former out toward the right side. If the direction of the current through the wire is reversed so as to flow from front to back, the direction of the lines of force around the wire will be reversed, and will be as in Fig. 22. Under these conditions, the lines of force of the magnetic field will HANDBOOK ON ENGINEERING. 11 swing over to the right side of the wire, and thus the thrust will be in the opposite direction. Fig* J2 represents the principle of an electric motor in its sim- plest form, and from it we see that the force that causes the armature to rotate is developed by the repulsion between the mag- netism of the field magnet and the magnetism that surrounds the wires wound upon the armature. Fig. 21. Fig. 22. It is self-evident that if we undertake to force the wire C through the magnetic field in the opposite direction to that in which it swings, we will have to make an effort to do so ; that is, if we try to move the wire from right to left in Fig. 21, or from left to right in Fig. 22. we will have to apply power. Now nature is a strict accountant and does not allow any power to be lost ; therefore, all the energy we expend in moving the wire through the magnetic field must appear in some other form, and the form in which it appears is as an electric current that is generated in 12 HANDBOOK ON ENGINEERING. the wire. If we were to remove the battery in Fig. 12 and put in its place an instrument to indicate the presence of a current in the wire, we would find that >Vhen we move the latter in the opposite direction to that in which it moves under the influence of the current, we generate a current; that is, we convert the device into a simple electric generator. If in Fig. 21, we move the wire from right to left, the direction of the current generated in the wire will be the same as that of the current which causes the wire to swing in the opposite direction, that is, from back toward the front. As it is a poor rule that does not work both ways, we would naturally infer that if moving the wire from right to left develops a current from back to front, movement in the opposite direction would develop a current from front to back ; and such is actually the case. This fact can be demonstrated by Fig. 12. Suppose that in this figure we hold C stationary in the central position, and then pass a current through from back toward the front ; this current would exert a force to swing C to the right side. If we release the wire, it will swing to the right and as soon as it begins to move, the current will become weaker, show- ing that the movement of the wire developed therein a current in the opposite direction. If we force the wire over to the left side, the current flowing through it will begin to increase as soon as the wire moves. All the foregoing shows us that when a wire is moved through a magnetic field, a current will be generated in it if it forms part of a closed circuit, and it makes no difference whether there is a current already flowing in the wire or not. When the wire is caused to move through the magnetic field by a current flowing through it from an external source, the current developed in it will be in opposition to that which comes from the external source, and, as a consequence, the movement produces an actual reduc- tion of the strength of current flowing through the wire. The stronger the magnetic field and the greater the velocity of the HANDBOOK ON ENGINEERING. 13 wire, the stronger the current generated in opposition to the driv- ing current, and, therefore, the weaker the latter. It is on this account that if a motor is allowed to run free, the faster it runs the weaker the current through it becomes, as the actual current in every case can only be the difference between the main driving current and the one developed in the wire, which latter runs in the opposite direction. Magnetic force is measured in units that are based upon the centimeter grame second system which is too technical to be ex- plained in a few words. Briefly stated a unit of magnetic force will exert a pull of unit mechanical force at a unit distance. The force of magnets is measured either by the total force of the magnet, or by the force exerted by each unit of cross-section. When the measurement is based upon the total force of the mag- net, the unit is called a Maxwell ; thus we speak of the total flux of a magnet as so many maxwells. When the measurement is referred to the force per unit of cross-section, it is spoken of as the magnetic density, or density of magnetization, and the unit used is called a Gauss ; thus we speak of a magnet as having a density of so many gausses per square centimeter, or square inch of cross-section. The density of magnetization is deter- mined by a rule given on page 46. The lifting capacity of a magnet can be determined by the following rule : TO FIND THE LIFTING CAPACITY OF A MAGNET IN POUNDS. Multiply the area of cross-section of the magnet pole in square inches, by the square of the density of magnetization per square inch, and divide this product by 72 millions. This rule gives the pull for one pole. For horse shoe magnets double the figures. If the object lifted is not in contact with the poles the pull will be less than rule gives. 14 HANDBOOK ON ENGINEERING CHAPTER II. THE PRINCIPLES OF ELECTROMAGNETIC INDUCTION. By Electromagnetic Induction, I mean the induction of electric currents by magnetic action. In the preceding chapter it has been shown that if we move a wire through a magnetic field, an electric current will be generated in it, providing its ends are joined, so as to form a closed circuit. If the ends are not joined, then there will be no current developed, because, an electric current cannot flow except in a closed circuit. When the ends of the wire are not joined, the movement through the field develops simply an electromotive force. Electromotive force is that force which causes an electric current to flow when there is a circuit in which it can flow. Electromotive force is a long-winded name and on that account it is always abbreviated into e.m.f., so that here- after when these letters are used, it will be understood that they stand for electromotive force. Metals and all other substances that allow electric currents to flow through them are called conductors, while glass, mica, wood, paper and many other similar forms of matter that do not allow currents to flow through them are called insulators. The difference between conductors and insulators is only one of degree, for there is no known substance that is an absolute non- conductor of electricity ; that is, a perfect insulator ; and there is no substance that does not resist to some extent the passage of a current that is, there is no such thing as a perfect conductor. Some substances, like damp paper or wood, which stand midway between good conductors and good insulators, can be regarded as either one or the other, depending upon the service for which they are used. For currents of very low e.m.f., they would be in- HANDBOOK ON ENGINEERING. 15 sulators, but for currents of very high e.m.f., they would be conductors. The current that will flow through any circuit when impelled by an e.m.f., will have a strength that will depend upon the amount of resistance that opposes its flow. As all conducting materials are not of the same degree of conductivity, their relative values are determined by the amount of resistance they interpose to the flow of the current. The resistance of a conductor is measured in units called ohms ; the strength of current is measured in units called amperes, and the e.m.f. is measured in units called volts. The relation between these units is such that an e.m.f. of one volt will cause a current of one ampere to flow in a circuit having a resistance of one ohm. When a wire is moved through a magnetic field, the e.m.f. induced in it will be determined by the strength of the field and the velocity with which the wire moves, and will not be affected in any way by the resistance of the circuit of which the wire forms a part. If the resistance is very great, the strength of current generated will be very low,, and if the resistance is very low the current will be strong, but in either case the e.m.f. will be the same. If movement of the wire in one direction develops an e.m.f. in a given direction through the circuit, then movement of the wire in opposite direction will reverse the direction of the e.m.f. Thus, in Fig. 23, which represents a magnetic field between the poles N S, if wire a is moved from right to left, it will have induced in it an e.m.f. that will be from back to front, and if the direction of motion of the wire is reversed, the e.m.f. will also be reversed. This will be true whether the wire is near the N pole or S pole. This being the case, it can be seen that if a represents the end of a wire moving in the direction of arrow d, and 6 the end of a wire moving in the opposite direction, the e.m.f. 'sin these two wires will be in opposite directions. The 16 HANDBOOK ON ENGINEERING. direction of the e.m.f. in a will be up from the paper toward the observer, and the direction of the e.m.f . in b will be down through the paper. If these two wires are secured to a shaft placed in the center of the field, then by the continuous rotation Fig. 23. Fig. 24, of the shaft, the two wires can be made to revolve around the circular path shown. If these two wires are joined at the ends, as shown in Fig. 24, they will form a closed loop, and although the direction of the induced e.m.f. in the two sides will be opposite, when compared to a fixed point in space, they will be in the same direction so far as the loop is concerned ; that is, both e.m.f.'s will develop currents that will flow through the wire in the same directions. Returning to Fig". 23 it will be noticed that if the wires re- volve around the circular path at a uniform velocity, their move- ment in the direction of line c c will not be uniform, but will be the greatest when the wires are in the position shown, and least, when they cross the line c c. In fact, when the wires cross line c c their motion in the direction of this line will be zero, for this HANDBOOK ON ENGINEERING. 17 is the point where the direction of movement reverses. Now, the magnitude of the e.m.f . induced in the wire is proportional to the velocity in the direction of the line c c, hence, when the wires are crossing this line, the e.m.f. will be zero, and when they are one-quarter of a turn ahead of the line, the e.m.f. will be the highest. In Fig* 24 we see that in side a, the direction of the current is toward the front, and in b it is the reverse ; now, when a moves through half a turn, it will take the place of &, and the direction of the e.m.f. induced in it will be the same as in b in the figure ; that is, it will be the reverse of what it is when pass" ing in front of the pole N. This being the case, it is evident that each time the loop makes a half -revolution, the direction of the current generated in it reverses. Fig. 25. As the loop in Fig. 24 is closed, the current generated in it would be of no practical value, but if we cut the wire at one side and connects the ends with rings as shown at a and b in Fig. 25, then by means of collecting brushes c c we can take the cur- 18 HANDBOOK ON ENGINEERING. rent off through the wires d d. This current, however, would consist of a series of impulses that would flow in opposite direc- tions, each one starting from nothing and increasing to its greatest Fig. 26. strength when the loop reaches the position shown in the figure, ' and then declining and reaching the zero value when the loop reaches the vertical position. Such a current is called an alter- nating current, because it flows first in one direction and then in the opposite direction. All forms of machines that generate cur- rents by electromagnetic induction, develop alternating currents, but in the class of machines known as direct or continuous current, a rectifying device is used which rectifies the current before it reaches the external circuit. This rectifying device is called a commutator, and is illustrated in its simplest form in Fig 26. In this illustration it will be noticed that the ends of the wire, instead of being attached to two independent rings, placed side by side, are secured to two half-rings, placed opposite each other. The brushes c d, through which the current is taken off, are held stationary ; therefore, as can be readily seen, c will make contact HANDBOOK ON ENGINEERING. 19 with a during one-half of the revolution, and with b during the other half ; and this will also be the case with brush d. Now, as the half-rings with which the brushes are in contact change at each half revolution, it follows that by properly setting the brushes, they can be made to pass from one-half ring to the other at the very instant when the direction of the current in the loop reverses, so that through each brush there will be a succession of current impulses, but all in the same direction. The device shown in Fig. 25 is a perfect alternating current generator, and that shown in Fig. 26 is a perfect direct current generator. In both cases, however, the e.m.f. induced is so low as to be of no practical value. To obtain serviceable machines, capable of developing the e.m.f. and current strength required in practice, it is necessary to provide very strong mag- netic fields and to rotate in these a large number of loops of wire. In order that the operation of such machines may be understood, I will first show how the powerful magnetic fields are obtained. In Fig". 27 two wires are shown as seen from the end, these being marked A and B. The lines of force surrounding them are '^ifj 's / Fig. 28. Fig. 27. in directions that correspond to opposite directions of current in the wires. In wire A, the current flows away from the observer. As can be seen, the lines of force of both wires have to crowd into 20 HANDBOOK ON ENGINEERING. the space between the wires, for on the outside of A the two sets of lines would meet each other head on, and this would also be the case on the right side of wire B. This crowding of the lines of force into the space between the wires causes them to distort from their natural position and instead of being central with the wires, are eccentric to them. If we take a long wire through which a current is flowing and bend it into a loop, we will see that if the current flows out through one side, it will return through the other side, so that in the two sides of the loop the current will flow in opposite directions. This being the case, Fig. 27 can be regarded as showing the two sides of such a loop, and from it we find that the effect of such a loop is to concentrate within its interior nearly all the lines of force that surround the wire. In Fig* 28 the two wires A and B are surrounded with lines of force that correspond to the same direction of current. In this case it will be noticed that in the space between the wires the lines of force flow in opposite directions ; hence, only a few of the lines will follow this path, simply that number surrounding each wire that can traverse the space without encroaching upon the path of the lines belonging to the other wire. If the two wires are very near to each other, practically all the lines of force of both wires will join forces, so to speak, and pass around the two wires. Now, if we wind a wire into a coil of many turns, the direction of the current in the several turns will be the same, so that the lines of force of all the turns will combine into one large stream and circulate around the entire coil side, no matter how many turns of wire it may contain. From this it can be seen that if we have a current of say ten amperes, we can make it produce just as powerful magnetic effect as a current of one thousand amperes, by simply increasing the number of turns of wire in the coil. A current of ten amperes passing through a coil of wire containing one hundred turns, will have the same magnet- HANDBOOK ON ENGINEERING. 21 ism in effect, as a current of one hundred amperes passing through a coil of ten turns, or as a current of one thousand amperes pass- ing through a coil of a single turn. If we place at the side of a wire through which an electric current is flowing a piece of iron, as is shown in Fig. 29, the effect will be that the lines of force will no longer flow in circular paths, as indicated by the circle a, but will be deflected in the manner illustrated, by the presence of the iron. If, instead of Fig. 29. Fig. 30. the straight iron bar, we substitute a ring of iron, as in Fig. 30, nearly all the lines of force will be concentrated in the metal, and the magnetic field in the space (7, between the ends of the ring, will be vastly greater than at any other point. The explanation of these actions is that all forms of matter oppose the develop- ment of magnetic force, but some offer greater resistance than others. Iron, steel, nickel, and one or two other metals, offer less resistance to the magnetic lines of force than air, and are said to have a higher magnetic permeability. Nickel is only a slight improvement on air, but steel and iron are far superior, iron being of about two to three times the permeability of hard- 22 HANDBOOK ON ENGINEERING. ened steel, and about one thousand times the permeability of air, when magnetized to the density ordinarily used in practice. The iron in Figs. 29 and 30, therefore, becomes the path of the lines of force, because it interposes a much lower resistance. Owing to this difference in the resistance of iron and air, it is possible to make an iron magnet core of any desired form, and to con- centrate within it nearly all the lines of force developed by the current flowing through the wire wound upon it. The presence of the iron not only serves to concentrate the magnetism in it, but as it reduces the resistance opposing the development of the magnetism, it enables the field to be made vastly stronger than it could be with air alone, say a thousand times as great. If we make a magnet in the form of Fig. 31, with a coil of wire around the part 5, practically all the lines of force will flow to Fig. 31. the poles N /S, and will pass through the air space between them. If this air space is nearly filled with a cylindrical mass of iron, J., the strength of the magnet will be increased, for, by doing this, HANDBOOK ON ENGINEERING. 23 we replace air which is a poor magnetic conductor, by iron which is a far superior conductor. Electric motors and generators are made with a cylindrical mass of iron at A, which is the armature Fig. 32. Fig. 33. core, and the air space between it and the faces of the poles of the field magnet is made just sufficient to accommodate the wire coils, and by this means the field strength is increased as much as possible. The armature cores are sometimes made solid, as in Fig. 32, and sometimes as a ring, as in Fig. 33. When they are solid, the lines of force cross through them in straight lines, see Fig. 32 ; and when they are ring form, the lines follow the ring and do not penetrate the interior space. If the single loop of Fig. 24 is replaced by a coil containing many turns of wire, the e.m.f. induced in it will be increased in proportion with the number of turns of wire in the coil, so that by using such a coil in a field such as shown in Fig. 31, a high e.m.f. can be obtained. This e.m.f., however, would be alter- nating, and if the current were rectified by means of a commu- 24 HANDBOOK ON ENGINEERING. tator, it would not be of uniform strength, but would fluctuate from a maximum value to zero. Just how the current would fluctuate and how the construction can be changed so as to get rid of the fluctuation, we can explain by presenting a diagram that illustrates the alternating current as it flows in the armature coil, and the rectified current as it leaves the commutator. In Fig. 34, let the distance / 7i, h i, i n, along the line// represent half -revolutions of the coil, and let distances measured on the vertical line c d represent the strength of current, distances above/ being current flowing in one direction, and distances below /being for current flowing in the opposite direction. Let us con- sider the instant when the coil is passing the point where the e.m.f . induced is zero ; then this instant will be represented by the point /, at the left of the diagram, and the curve a will start from this point ; as at that instant, the current which it represents has no value. As the coil rotates, the current begins to grow, and this fact we indicate by causing curve a to gradually Fig. 34. f d Fig. 35. rise above the horizontal line. At the quarter turn, the current reaches its greatest strength, thus this forms the highest point of curve a, and is midway between / and h. From this point HANDBOOK ON ENGINEERING. 25 onward, the current declines and becomes zero, when the rotation of the coil has reached one-half of a revolution, which is repre- sented by the point h. In the next half -re volution, the current Fig. 36. Fig. 38. flows in the reverse direction, but has the same maximum strength and increases and decreases at the same rate ; therefore, the curve 6, drawn below the horizontal line, represents the reverse current ; and point i corresponds to one complete revolution, so that beyond i the curves a and b are repeated in systematic order. Now, if we provide a commutator to rectify this current, all we can accomplish is to turn curve b upside down and transfer it to the upper side of the horizontal line, as in Fig. 35 ; but, as will be seen, all we accomplish by this act is to obtain a current that flows always in the same direction, but at each half -revo- lution it drops down to a zero value. If we wind two coils upon the armature, placing them at right angles with each other, as is indicated by A and B in Fig. 36, then if the currents of these two coils are rectified, they will bear the relation toward each other shown at the upper line in Fig. 37, the a a curves in solid lines representing the current from the A coil, and the b b curves in broken lines, representing the current from the B coil. As will be seen, when one of these currents is zero, the other is at its greatest value, so that if we run both into 26 HANDBOOK ON ENGINEERING. the same circuit, the lowest value of the combined current would be equal to the maximum of either one of the single currents, and the maximum value would be equal to the sum of the two currents when the coils are on the eighths of the revolution. Fig. 37. This resulting current is shown on the lower line in Fig. 37 by the curve d d. From this curve we see that the number of fluctuations in the current has been doubled, but the variation in the strength is greatly reduced. If we wound four coils upon the armature, as indicated by A B C D, in Fig. 38, the number of undulations in the combined current would be again doubled, but the fluctuation would be very much less. If the number of coils is increased to twenty-five or thirty, the fluctuations in the current become so small a.s to be hardly worth noticing. With coils such as shown in Fig. 26, a separate commutator would have to be provided for each coil, and this would render the machine very complicated, if the number of coils were even six or eight ; hence, in actual machines, the winding of the coils is modified so as to be able to use a single commutator for any number of coils. This construction will be explained in the next chapter. HANDBOOK ON ENGINEERING. 27 CHAPTER III. TWO POLE GENERATORS AND MOTORS. The simplest type of armature winding is that used with ring cores, and is illustrated in Fig. 39. As will be seen, it is simply a continuous winding all the way around the circle, the end of the last turn of wire being connected with the beginning of the first turn, so as to form an endless coil. If wires are attached at a and 6, and a current is passed through, it will divide into two halves, one part flowing through the wire above a 6, and the other part through the wire below a b. In the upper half of the wire, the direction of the current in the front sides of the turns will be toward the center of the ring, as is indicated by the arrow heads, and in the lower half it will be away from the center. If, in- stead of attaching wires at a and l> we place stationary springs, so as to press against the wire, then we could revolve the ring, and still the current would enter and leave the wire at the same points. Small armatures are often made in this way, but for regular 28 HANDBOOK ON ENGINEERING. machines it is more desirable to provide a commutator as shown in Fig. 40 at C, and then the several segments can be connected with the wire at regular intervals. In the figure, the commutator is provided with twelve segments, and these connect with the armature wire at every fourth turn, so that the wire is divided into twelve coils of four turns each. The only difference between this diagram and a regular gen- erator armature of the ring type, is that it shows the wire coils spread out with a considerable space between them, and only in one layer, while in the actual machine, the wire is wound close together and generally, in several layers ; but no matter how many layers there may be, or how many turns in a coil, the principle of winding is the same. I have shown the ring winding first, because it is so simple that it can be understood with the most superficial explanation. The drum winding, which is used to a much greater extent, is the same in principle as the ring, but owing to the fact that the coils cross each other at the ends, it appears to be decidedly different. By the aid of Figs. 41 to 44, the drum winding can be made per- fectly clear. Fig* 41 shows a ring armature core with a single coil wound upon it ; and Fig. 42 shows a drum core, with a single coil wound upon it. In the ring, only one side of the coil appears upon the outer surface of the armature, but in the drum, as there is no open space for the coil to thread through, both sides of the coil must be placed upon the outer surface. The side B of the coil may be called the live side, as it is the one from which the ends project, and the lower side c, may be called the dead side. Since only the live side of the coil has ends to be connected, it can be readily seen that if in the drum winding we leave spaces between the live sides for the dead sides, and then connect the ends of the live sides by jumping over the dead side between them, that we will have the same order of connection as in the ring winding. HANDBOOK ON ENGINEERING. 29 Fig. 41. The dead side of each coil adjoins the live side of a coil that is, in reality, half a circumference away from it; thus, in Fig. 43, the live side of coil a is at the top and the dead side is at the bottom ; while the live side of coil n is at the bottom and the dead side is at the top. The live sides of these two coils are on opposite sides of the armature, so that the coil side to the right of a is simply Fig. 43, Fig. 44, 30 HANDBOOK ON ENGINEERING. the dead side of a coil whose live side is on the other side of the diameter. In Fig. 44 the two coils a and b are adjoining coils, for the coil side between them is the dead side of coil n. To con- nect the armature, therefore, we join end 2 of coil a with end 1 of coil Z>, and the end 2 of coil b would jump over a dead side and connect with end 1 of coil c. Coil c, however, would appear to be two coils ahead of &, just as 6 appears to be two coils ahead of a. In winding drum armatures, the coils are generally placed in pairs, as shown in Fig. 43 and also in Fig. 44. The object of this is simply to make the ends of the armature look more even- A drum armature can be wound out of a continuous wire, by simply making a loop to take the place of the ends 1 and 2 , and then skipping a space, as shown by coils a and b in Fig. 44. After the armature is half covered, there will be spaces left between the coils, these spaces being of the width of a coil ; we then proceed to fill up the vacant spaces, and when they are all filled, the last coil put in will be the proper position to connect with the first one wound. A little practice with a piece of twine and a wooden cylinder, will enable any one to find out in short order how to wind drum armatures. The two types of winding I have explained, are those used with two pole machines, motors as well as generators. I may here add that there is no difference, electrically, between a motor and a generator, and any machine can be used for either service. Motors, however, are somewhat modified in design so as to make them more suited to the work they have to perform. The modi- fication consists mainly in protecting the parts liable to be injured by objects falling upon them. The general arrangement of the field and armature in a two pole machine is shown in Fig. 31. The design can be changed in a vast number of ways, but it will always be two-pole, or bipolar, as it is called, if only two poles are presented to the armature. HANDBOOK ON ENGINEERING. 31 Generators and motors are arranged so that the current that magnetizes the field may be the whole current that flows in the circuit, or only a part of it. When the whole current passes through the field magnetizing coils, the machine is said to be of the series type ; this name being given because the armature wire and the field coils are connected in series, so that the current first passes through one and then through the other. If the field coils are traversed by only a portion of the current, the machine Fig. 45. Fig. 46. is said to be of the shunt type, owing to the fact that the field is supplied with a current that is shunted from the main circuit. Generators and motors are also arranged so that there are two sets of field coils and one is traversed by the whole current, and the other by a portion thereof. The best way to understand these different types of connection is by means of simple diagrams that show the wire coils of the field and the outline of the arma- ture. Such diagrams are presented in Figs. 45 to 50. Fig. 45 32 HANDBOOK ON ENGINEERING. represents the series connection, A being the armature, C the commutator, and M the field coil. The direction of the current is indicated by the arrow heads. Fig. 46 is the shunt connection, and the arrow heads show the direction of the currents in the case of a generator. As will be seen, at d the field current branches off from the main line and returns to it at a, after having passed through the field coil. Fig. 47 shows the type in which the field is magnetized by two sets of coils, one being in series with the main circuit and the other in shunt. As will be noticed, all the armature current passing out through wire cZ, goes through coil jp 7 , except the portion that is shunted at c, into the shunt coil M. This type of winding is called compound, being a combination of the series and shunt. When the shunt coil is connected as in Fig. 47. Fig. 48. Fig. 47, it is called a short shunt, and when as in Fig. 48, it is a long shunt. In the first case, the coil M shunts the armature only, and in the second, it shunts the coil F also. HANDBOOK OX EMJINKKHINU. 33 Figs* 49 and 50 show the shunt and compound types for motors, and as will be noticed, the only difference between them and the generator diagrams, is that the direction of the current d Fig. 49. Fig. 50. in the shunt coils is not the same. This difference in direction is due to the fact that in the generator the armature generates the current that passes through coil M; hence, at point d!, the cur- rent flows up to the main line and down to the field coil. In the motor, the current comes from an external source through main ft, and thus passes from a to the armature, and also to the field coil, thus traversing the latter in the opposite direction. In the series coil F, the direction of the current is the same in both machines. Generators are made so as to keep the strength of the current constant, and allow the voltage to vary as the demands of the service may require ; or they may be wound so as to keep the voltage constant and allow the current strength to vary. Machines 3 34 HANDBOOK ON ENGINEERING. of the first class are called constant current, and are used principally for arc lighting. Machines of the second class are called constant potential and are the kind used for incandescent lighting, for electric railways and for the operation of motors of every description. For constant current generators the series winding is used in connection with some kind of regulating device that prevents the current strength from varying more than the small fraction of an ampere. The shunt and compound windings are used for constant potential genera- tors. If the armature wire had no resistance, the shunt winding would enable a generator to maintain a constant voltage at its terminals, no matter how much the strength of the current might vary ; but armature without resistance cannot be made ; there- fore, a shunt- wound machine will develop a slightly lower voltage with full current than with a weak one, but the difference will not be more than three to five per cent. By the aid of the com- pound winding, the generator can be made so as to develop the same voltage with light or full load, and if desired, the voltage can be made to increase as the current increases. If a com- pound generator is so proportioned that the voltage is the same for weak and strong currents, it is said to be evenly-compounded, and if the voltage increases as the current increases, it is said to be over-compounded. If the voltage is five per cent higher, with full load than with no load, the generator is said to be over-com- pounded five per cent, and if the increase is ten per cent, it is said to be over-compounded ten per cent. The way in which a compound generator increases the volt- age can be readily understood from an examination of Fig. 47. The current that passes through the shunt coil Jf, is practically one of the same strength at all times ; therefore, the magnet- izing effect of this coil does not change. Through coil F the whole current passes, hence, the magnetizing effect of this coil increases as the current strength increases. Now the total field HANDBOOK ON ENGINEERING. 35 magnetism is that due to the combined action of the two coils, so that as the action of F increases, the strength of the field in- creases. If F has only a few turns of wire, it will only help slightly to magnetize the field ; therefore, its increased effect, due to increase in current, will not be very noticeable ; but if F has many turns, it will develop a large proportion of the field magnet- ism, and, under this condition, the change in current strength will make a decided change in the strength of the field, and thus in the voltage, for the voltage is directly proportional to the strength of the field. In motors, the coil F can be connected so as to act with coil MI or against it. If both coils act together, the motor is compound-wound ; and if F acts against M , the motor is differ- entially-wound. A compound- wound motor will slow down more with a heavy load than a simple shunt machine, but it will carry the load with a smaller current, and, on this account, this wind- ing is commonly used for elevator motors. A differential motor will hold up the speed better with a heavy load than a simple shunt machine, but it will take a correspondingly larger current to do the work. The differential winding is not used to any great extent, except in cases where it is desired to obtain as uniform a velocity as possible. In explaining 1 the principles of armature winding, it was shown that the commutator brushes must make contact with the com- mutator on the sides, that is, that in Fig. 51, they would be placed on the diameter n n. In actual machines, they are either ahead of this line, as in Fig. 52, or back of it, as in Fig. 53. The first position is that of the generator and the second that of the motor. The reason why the brushes have to be set ahead of line n n in a generator, and back of the line in a motor, is that the armature current develops a magnetization of its own, and this reacts upon the magnetism of the field so as to twist the lines of force out of their true path. If we look at Fig. 39, we can see 36 HANDBOOK ON ENGINEERING . that the direction of the current through the wires is such that the magnetizing effect produced upon the armature core is the same as it would be if the wire were wound in the way indicated by the vertical lines in Fig. 51. Now this current will develop a magnetization in the direction of line n n; that is, at right angles to the field magnetism. These two magnetic forces of the arma- ture and the field, engage in a tug of war, and the result is that the actual magnetization that acts upon the armature wire is the combined effect of the two. If the strength of the field magnetism Fig. 51 Fig. 52. is proportional to line c ., and the strength of the armature mag- netization is proportional to line < b, then the actual magnetiza- tion will be equal to line c d, and in the direction d d In Fig. 52, which represents a generator, if the current in the field coils passes over the front side in the direction of arrow ?', and the armature revolves in the direction of arrow d, then the armature current will be in the direction of arrow / and the armature mag- netization will be in the direction of arrow h. The field magneti- zation will be from j^to S, therefore, the resulting magnetization will be in the direction of line a a. Now the proper position for HANDBOOK ON ENGINEERING. 37 the brushes is on a line at right angles to the direction of the field, hence, they must rest upon line c c. If the machine is a motor, the only change effected will be that the direction of the armature current will be reversed, so that arrow./ will point downward instead of upward, and the magnetism of the armature will be directed to the right as shown by arrow c. Under these conditions, the actual direction of the field magnetism will be that of line b />, and upon line e e, at right angles to this the brushes must be set. 38 HANDBOOK ON ENGINEERING. CHAPTER IV. MULTIPOLAR MACHINES. The only difference between a bipolar and multipolar machine is, that the latter has two poles, and the former has two or more pairs of poles. In consequence of this difference in the number Fig. 54. of poles, the armature winding has to be slightly modified, as will be presently explained. Fig. 54 illustrates a four-pole machine HANDBOOK ON ENGINEERING. 39 and, as will be noticed, the N and 8 poles alternate around the circle. This arrangement is followed, no matter what the number of poles may be. The advantage of the multipolar construction is that it in. creases the capacity of the machine for a given size and weight- Figs. 55 to 57 illustrate the gain effected in weight. The first figure shows a two-polfe machine, the second a four-pole and the third an eight-pole, the three being of the same capacity. The poles of the second machine are half as wide as those of the first, as there are twice as many. The other parts are reduced in like proportion. In Fig. 57, the poles are one-quarter as wide as in Fig. 55. Fig. 56. Fig. 57. Fig. 55, as there are four times as many. On account of the reduction in the width of the poles, the armatures can be increased in diameter as the number of poles is increased, without increas- ing the outside dimensions of the machine, so that in reality, Fig. 56 is somewhat more powerful than Fig. 55, and Fig. 57 is still more powerful. The fields of multipolar machines are wound the same as those of the bipolar ; that is, as series, shunt or compound. Figs. 58 to 60 show the three types of winding for a four-pole machine and Fig. 61 is a diagram of compound winding for an eight-pole generator. The number of commutator brushes used is equal to the number of poles, although with one type of armature 40 HANDBOOK ON ENGINEERING. winding, two brushes are suilicient, no matter how many poles the machines may have. In practice, however, even with this winding, the number of brushes is generally made equal to the number of poles. With a four-pole machine the brushes can be connected in a simple manner, as shown in Figs. 58 to 60, but with a greater number of poles, two rings are generally provided, to which the brushes are connected in the manner shown in Fig. 61. Looking; at Fig* 54, it can be seen that if the current flows up from the paper, under the N poles, it will flow down through the paper, under the S poles ; hence, the armature coils in a four- pole machine must span only one-quarter of the circumference, and not one-half, as in the two-pole armature. For a six-pole armature, the coils must span one-sixth of the circumference, and for an eight-pole, one-eighth, and so on, for any higher number of poles. There are two types of winding for multipolar armatures, one being called the lap, or parallel winding, and the other the wave HANDBOOK ON ENGINEERING. 41 42 HANDBOOK ON ENGINEERING. or series winding. Fig. 62 is a diagrammatic illustration of the lap winding, and Fig. 63 of the wave winding, both for four poles. Fig. 62. The small circles around the outside of the armature represent bars or wires, which are connected with the commutator segments by means of the solid lines, and with each other at the opposite side of the armature, by means of the broken lines. If we start from coil side, or bar 1 on the left, and follow the connections as guided by the numbers, we will finally reach 32, and thus come back to left side brush a, which is the starting point, As will be seen, bar 1 connects at the back of armature, HANDBOOK ON ENGINEERING. 43 with bar 2, and then over the front, the connection runs in the backward direction, to bar 3 ; thence, forward again, at the back end, to bar 4, and again backward over the front, to bar 5. The connections, therefore, lap over each other and it is on this account, that it is called a lap winding. Figf* 63 shows the wave winding, and it will be noticed that if we start from bar 1 at the top, we advance around the right to bar 2, and then we go further ahead to bar 3, and in like manner advance to bar 4, the connections in every case advancing in the Fig. 63. same direction around the circle. It will be further noticed that the connections run zig-zag from side to side of the armature core 44 HANDBOOK ON as they advance, thus forming a wave-like path for the current-. and it is on this account that this stle of connection is cjilled wave winding. With the lap winding, the brushes a a are connected with each other, and so are the b I brushes. In the wave winding, two brushes set one-quarter of the circle from each other, will take the current off properly as indicated by a and b in Fig. 63, but four brushes can also be used. In Figf* 54, the brushes are shown midway between the poles, while in Figs. 62 and 63, they are opposite 'the poles. This dif- ference 'in position is due to the fact that in the last two named figures, the connections between the armature coils and the com- mutator segments do not run in radial lines from either side, but one connection bends backward and the other forward. In actual machines, the connections are run as in these diagrams, and in some cases, one of the sides runs in a radial direction ; there- fore, in some generators, the brushes are opposite the poles, and in others they are between them. Diagrams 62 and 63 show coils of a single turn, but by regard- ing the broken lines as representing the position of the end of the coil at front as well as the back of the armature, and the solid lines as simply the ends of the wire that connect with the com- mutator segments, they become accurate representations of coils of any number of turns. The coils of multipolar armatures are made on forms, and in the finished state are placed upon the armature core. Some coils are so formed as to bend down over the ends of the armature, and are then given the form at the ends, shown in Fig. 64, so they may fit into each other. In some machines, the coils do not bend down over the ends of the armature, but run out parallel with the shaft. Armatures so wound are sometimes said to have a barrel winding, and the coils, if laid out upon a flat surface., would present the appearance of Fig. 65 ; that is, if they con- HANDBOOK ON ENGINEERING. abed 45 Fig. 64. Fig. 65. tained more than one turn. If of the single-turn type, they would look like Fig. 66, if for a lap winding; and like Fig. 67, if for a wave winding, the ends d d being joined and then con- nected with the commutator segments. In connecting the field coils of multipolar machines, it is necessary to be careful not to make mistakes, so that some of the /, \ V abc m \_ s \ ab c ab d Fig. 67, 46 HANDBOOK ON ENGINEERING. coils will act to magnetize the field in the wrong direction. By studying Fig. 27 and the explanation of it, the direction of the magnetic lines of force with respcot to the direction of the current through the magnetizing coils, can be clearly understood, and then there will be no difficulty in determining the proper way in which to connect the coil ends, for all we have to do is to make the connections such that if one pole is N the one next to it is S. With two-pole machines, it is also necessary to be careful not to connect the field coils improperly; that is, if there is more than one coil, and in most machines this is the case. The current that energizes a magnet is called the magnetizing force and is measured in ampere turns. The ampere turns are obtained by multiplying the number of turns of wire in coil, by the amperes of current flowing through it. All forms of matter resist the development of magnetic force. This resistance is called magnetic reluctance. The reluctance of air is much greater than that of iron or steel, but is constant ; that of iron and steel is not. If one thousand ampere turns develop a certain magnetic density in a circuit composed wholly of air, two thousand ampere turns will double this density. In iron and steel it will require much more than double the ampere turns to double the magnetic density. If in a magnetic circuit ten inches long, 100 ampere turns develop a .certain density, it will require 200 ampere turns to develop the same density if the magnetic circuit is double the length. The table on page 209 gives the ampere turns required to develop different magnetic densities in magnetic circuits one inch long, composed of air, iron and steel. To find ampere turns required to develop any magnetic density in any magnet use following rule : Multiply the figures given in the table on page 159 ; for density required, by length of the magnetic circuit, and the product will be total number of ampere turns. HANDBOOK ON ENGINEERING. 47 .CHAPTER V. SWITCH-BOARDS, DISTRIBUTING CIRCUITS AND SWITCH- BOARD INSTRUflENTS. Generators of the constant potential type are made so as to develop a certain voltage at a given velocity, but in some cases it is not practicable to run them at the exact speed for which they are designed ; and in others, it is desired to vary the voltage slightly, hence, all machines are provided with means for chang- ing the e.m.f. slightly. This regulating device is also necessary in cases where the load is for a time light, and for the balance of the time heavy ; for, as we have shown, the voltage will vary to some extent with changes in the strength of the current. If the generator is at some distance from the points where the cur- rent is used, the drop of voltage in the lines will be greater with strong currents ; hence, when the load is heavy, it is necessary to increase the" voltage developed by the generator. As it is not advisable to change the speed of the engine, the variation of volt- age is obtained by changing the strength of the current that flows through the shunt field coils, and this is accomplished by providing a resistance that can be cut in or out of the shunt coil circuit, as is illustrated in Fig. 68, in which R represents the resistance, or field regulator, as it is called. When the lever is moved to the extreme left position, all the regulator resistance is cut out of the circuit, and then the voltage of the generator is the highest that can be obtained with the speed at which it is run- ning. When the lever is moved to the extreme right, all the resistance of the regulator is introduced into the shunt coil cir- cuit, and then the voltage is the lowest. By placing the lever in 48 HANDBOOK ON ENGINEERING. intermediate positions between the extremes right HIK-! left, differ- ent voltages may be obtained. To be able to operate a generator furnishing current to < sys- tem of distributing wires, it is necessary to have a number of (t d Fig. 68. instruments and other devices, included in the circuit, some of which are absolutely indispensable, and others of which are simply conveniences, and may be looked upon as luxuries. The various devices required are shown in Fig. 69. The generator is shown at Jf, and at e the field regulator is placed, audit is connected with one of the generator armature terminals and with one end of the shunt coil wires by means of wires d d. The wires c c run from the generator terminals to the voltmeter V, and thus enable us to see what the voltage is at all times. Wires a and b convey the current to the external circuit, with which they can be connected or disconnected by means of switches ,s.s- *.s. At A an ammeter is placed which indicates the strength of current in HANDBOOK ON ENGINEERING. 49 amperes. The ammeter can be placed in either a or 6, as the same strength current Hows in both. At// safety fuses are pro- vided, so as to open the circuit in case the current becomes so strong as to be capable of overheating the generator wire. If one of the line wires runs out into the open air, and is carried along on poles, we will have to provide a lightning arrester, as shown at /i, this being connected with the ground as at g. If both lines run into the open air, an arrester must be placed in both ; and if both are confined to the interior of a building, no arresters will be required. From the points m m branch circuits may be run off in as many directions as necessary, and by providing switches s s, these can be connected or disconnected from the main line when desired. This crude arrangement would enable us to operate the system successfully, but it would not be so convenient as a more methodi- cal grouping of the several devices and instruments. It repre- sents the way things were done in the early days of electric light- ing, but at the present time, instead of having the several parts scattered about in a helter-skelter fashion, they are all assembled 4 50 HANDBOOK ON ENGINEERING. upon a large panel, which is called a switch-board. Fig. 70 gives the general arrangement of wiring and location of devices for a simple board arranged for one generator feeding into five external \n \P Fig. 70. circuits. The ammeter and voltmeter are placed at the top of the board, and directly under these are arranged five switches, s, which control the external circuits. One of these circuits is indi- HANDBOOK ON ENGINEERING. 51 cated by the lines n _p, //, being safety fuses. The wires i i con- vey the main current from the generator to a circuit breaker Z>, which is simply a switch that is constructed so that it will open automatically when the current becomes too strong. From the circuit breaker, the current passes through wires a and b to the main switch jP 7 , and by wire c, it runs from here to the ammeter A and from the latter by wire d to a rod 1 which is called a bus bar. The upper side of the main switch is connected directly with bus 2. The voltmeter is connected with two busses by the wires e e. The field regulator is located back of the board at 72, and is connected in the shunt coil circuit by means of wires h h. The switch of the regulator R is connected with a hand -wheel on the front of the switch-board, so that the attendant can watch the voltmeter as he turns the wheel and thus see just what effect the movement is producing on the voltage. In addition to the devices shown in Fig. 70, we can, if desired, provide a recording ammeter, a recording voltmeter and a watt- meter ; the first two would give us a record of the amperes and volts for a certain length of time, generally 24 hours, and the last one would register the amount of electrical energy. We could also provide ammeters for each one of the distributing cir- cuits, so as to know the strength of current in each one. If we desire to arrange the switch-board for two generators, and these are of the shunt type, we will require no changes in Fig. 70, except to provide another regulator and a main switch and circuit breaker for the additional machine. This arrange- ment of board is suitable for a single compound wound generator, or any number of shunt wound machines, but if we have two or more compound generators, the connections between these and the bus bars will have to be somewhat modified. The modifications required in a switch-board for two or more compound generators can be made clear by the aid of Figs. 71 and 72. In the first figure, we can see that if the current return- 52 HANDBOOK ON ENGINEERING. ing from the main line through n divides into wires a and />, it will remain divided until it passes through the armatures and the F coils of the two machines, and thence through wires <> e, it will Fig. 71. reunite again in wire p. In Fig. 72, the two parts of the current will flow through wires d d to the single wire e, and then divide into wires//, and thus reach the coils F F, and. finally, through wires h /*, reach p. In Fig. 71, if the right side armature gen- erates more current than the other one, the F coil of that gener- ator will be traversed by the strongest current, for in each machine the strength of current in the armature and the F coil will be nearly the same. Now, if the right side machine generates the strongest current, it is because its voltage is the highest, but the fact that its F coil will be traversed by the strongest current will make its voltage still higher, thus increasing the difficulty. In Fig. 72, the current flowing through the two F coils will be the same, no matter how much the two armature currents may differ > HANDBOOK ON ENGINEERING. 53 for these come together in wire, ^, and passing from this to the two F coils, the current will divide in equal amounts. As can be seen, the effect of adding the wires d and //in Fig. 72. The equalizing connections run from generator .vires /to the main switches S, and thence to bus 1. The li wires of the generators run to one side of the circuit breakers D E. 54 HANDBOOK ON ENGINEERING. and thence to the middle blades of the S switches, and from these to the bus 2. The generator wires run to the outside blades of ff 1 LiI ff Fig. 73. the circuit breakers, and from these to the ammeters A A, and thence to bus 3. The voltmeters are connected with wires h and /, and thus indicate the e.m.f.'s of the generators. HANDBOOK ON ENGINEERING. 55 If another generator were added, it would be connected with the bus bars in the same way. In starting two or more compound-wound generators, one machine is started first, and then the second is run up to full speed, and its voltage is adjusted by means of the regulator 72, so as to be the same as that of the machine that is running. When the voltages of the two machines are equal, the main switch of the second machine is closed so as to connect it with the bus bars. This action will generally make a slight change in the voltage of the second machine, causing it to run up or down a trifle ; and as a result by looking at the ammeters, we will find that it is taking more or less than its share of the load. If such is the case, we manipulate the regulator R, until the loads are properly divided. Whether the voltage of the second machine will rise or fall after it is connected with the bus bars, will depend upon the extent to which it is compounded ; if slightly compounded, the voltage will drop, and if heavily compounded, it will rise. The switch-boards illustrated are adapted to what is called the two- wire system of distribution, but in cases where it is desired to transmit the current to a considerable distance, without using extra large wire, the three- wire system of distribution is employed. This system is illustrated in Figs. 74 to 76. Suppose we have two generators as indicated at G G in these diagrams, and let the direction of the current through both be from bottom toward the top ; then it is evident, that if we remove the middle wire 0, the lower machine will deliver current into the upper one, and if each generator develops an e.m.f. of 115 volts, the combined e.m.f. will be 230 volts, and this will be the pressure between the bottom and top wires; but the voltage between either wire and the center one will only be 115. Suppose we have a number of lamps connected between wire P and the center wire 0, and an equal number of lamps between and JV, as is shown in Fig. 74 ; then it is evident that the same amount 56 HANDBOOK ON ENGINEERING. of current will flow through both sets, and as a consequence, all the current that passes from the upper generator into wire /* will go directly through both sets of lamps to the lower wire N, and thus return to the lower side of the bottom generator. Under these conditions, the -lamps will be acted upon by 115 volts each, but the current will be driven through the circuit by a voltage of 230. Now, if the voltage is doubled, four times the number of lamps can be supplied with the same size wires ; hence, the cost of line wire per lamp will be reduced to one-fourth. Suppose, that instead of having the lamps equally divided as in Fig. 74, HANDBOOK ON ENGINEERING. 57 they are arranged as in Fig. 75 ; then since the current fed into the system from the upper wire/ 3 is only sufficient for five lamps; while there are seven lamps in the lower section, it follows that through wire O a current sufficient for two lamps must be sup- plied. The way in which the currents would flow in this case is clearly indicated by the arrows. In Fig. 74, it will be seen that if we removed the middle wire, the lamps would not be affected, for none of the current comes through it; but in Fig. 75, if we cut the middle wire, two of the lower lamps would be unprovided for. From this it will be seen that the object of the middle wire is simply to provide the extra current required for the side that carries the largest number of lamps. If the lights are so arranged that on both sides of the central wire the number is practically the same at all times, the center wire can be made very small, but such perfect balance cannot be obtained always, and on that accouut, the center, or neutral wire, as it is called, is made of the same size as the others, except in large systems, in which it is sometimes not more than one-third the size. As motors require large amounts of current, they are nearly always made to operate with a voltage of 230, and are connected with the outside wires of the system, as is shown in Fig. 76, in which a a a a and c c c c indicate lamps connected between the sides and the neutral wire, and ABC are motors connected across the outside lines. When a switch- board is arranged for two generators connected with a three-wire system, we use three bus bars, just as in Fig. 70, but discard the equalizing connection, and connect the generators with the busses in the same way as they are connected with wires N and P in Figs. 74 to 76. If we have a number of generators feeding into the three-wire system, then we connect each set with an equalizer bus; that is, provide two sets of busses, and the P and N busses of these two sets we connect 58 HANDBOOK ON ENGINEERING. with a third set in the proper order for the three-wire system, and from the latter busses the external circuits are fed. If we desire to supply a larger building with a lighting and power system, we can run the wires in almost any way, providing we make connections with the lamps and motors, but if we adopt Fig. 77. a systematic arrangement it will require less labor to operate the plant, and when anything goes wrong we will be able to locate the difficulty with much less trouble and in less time. The best way to accomplish this is by the use of small switch-boards located at different points in the building, these becoming centers HANDBOOK ON ENGINEERING. 59 of distribution, from which all the lamps are supplied. The general arrangement of such a system can be understood from Fig. 77, in which B represents the main switch-board, located in the engine room, and e e e the several floors upon which the lights are located. From the main switch-board we run up four lines, one to each floor, and locate secondary boards at C and D D D. We can also run out lines directly from the board to the lamp circuits as at c c c c. From the boards C (7, we run circuits to smaller boards, as shown at E, F, A, A, A, and b b b. From each one of these small boards we can run out circuits to the lamps. These small switch-boards are called panel boards or boxes, and also distribution boards. They are made of all sizes from eight or ten inches square, up ^to four or five feet, and are arranged to feed into one or two, or fifty or sixty circuits, supplying anywhere from five or six lights up to a thousand or more. The construction of distribution boards can be understood from Figs. 78 and 79, the first being arranged for the three- wire system, and the second for the two- wire. Fig. 78 is ar- ranged to feed ten circuits, and is provided with one main switch by means of which the entire box can be disconnected from the main line. The distributing circuits are provided with safety safety fuses on the outside wires , so that if anything goes wrong and the current increases to a dangerous point, the circuit will be open. No fuse is placed on the middle wire, as it is not neces- sary, and might result in cutting out both sides of the circuit when only one was disabled. Fig* 79 is a more complete panel, because each one of the six distribution circuits is provided with switch, so that it is pos- sible to disconnect any of the circuits without interfering with the others. In some cases a distribution board of this kind is the only thing that will answer the purpose, but in others, the more 60 HANDBOOK ON ENGINEERING. simple construction of Fig. 78 answers just us well. The fuses in Fig 78 are shown at E F. These fuses are sometimes made so that they can be used as switches that is, they can be pulled out Fig. 78. Fig. 79. of place and thus open the circuit, and if one blows out it can be removed and a new fuse be put in, and then it can be replaced, thus placing the disabled circuit in service without interfering with the others. The ammeters uud. voltmeters used on switch-boards depend for their operation upon the repulsion between magnetic lines of force. A great many different constructions are used, but most of them operate upon the principles illustrated in Fig. 80 or 81. If a small bar of iron c is placed between the poles of a permanent magnet, as in Fig. 80, it will be held in the horizontal position by the. attraction of the magnet. If it is surrounded by a stationary coil of wire 6, through which a current of electricity passes, then HANDBOOK ON ENGINEERING. 61 it will be under the intlueiice of two forces, one the attraction of the poles N S of the magnet, and the other the attraction of the lines of foice developed by the current flowing through coil b. The action of the latter will tend to swing the rod c into the ver- tical position. The force of the magnet will remain constant, but the force of the coil will vary with the strength of the current passing through it ; hence, the stronger the current the more the bar c will be swung around into the vertical position. If we pro- vide a small counter-weight, as shown in the illustration, to resist the action of the coil, we will have a means that will enable us to adjust the movement of the bar, so that it will swing around through a given angle for a given increase in current. If a pointer a is secured to c it will swing over the scale as shown, when r is rotated by the action of the coil. If coil & is mounted so that it may swing around the center pivot, we can discard bar c, for then as soon as a current traverses o, the lines of force developed around it will be attracted by Fig. 80. Fig. 81. those of the permanent magnet, and will exert a twisting force so as to place the axis of the coil parallel with the lines of force passing from N to S. In this case as in the previous case, the 62 HANDBOOK ON ENGINEERING. effort to twist b around will be proportional to the strength of the current, hence, the stronger the current the greater the swing. Ammeters and voltmeters are made on these principles, and the only difference in the two instruments is in the size of the wire used for the coils. Figs* 82 and 83 illustrate the principle upon which circuit breakers are made. In Fig. 82, suppose a current flows through magnet E, then it will attract the lever A, the latter being made Fig. 82. Fig. 83. of iron. If the current is weak it may not develop a sufficient attractive force in E to lift the weight Z>, and in that case A will remain where it is. If, however, the current is increased until E becomes strong enough to lift /), then A will move over toward the magnet, and the catch " a " falling behind it, will not allow it to return to its former position until placed there by hand. When A swings over, it carries B, and thus breaks the connec- tion with (7 and opens the circuit. Thus it will be seen that by properly adjusting the weight D and the magnet E, we can setthe device so as to open the circuit whenever the current reaches a certain strength. This is the principle upon which circuit break- HANDBOOK ON ENGINEERING. 63 era act, but such a device as Fig. 82 would be of no service for lighting circuits, because the distance by which C and B are separated is too small to break the current. By modifying the construction as in Fig. 83, we can obtain a device that will give a wide separation at the breaking point. In this construction, the lever A when drawn towards the magnet, strikes the catch a, so as to release lever jB, and then the weight D throws the latter down to the position shown in broken lines, thus giving a wide separation between F and C. By moving the weight on the lower arm at A, the device can be adjusted so as to act with different strengths of current. Circuit breakers as actually constructed, do not have the appearance of this diagram, but they operate on the principle illustrated by it. The electromotive in volts force developed in the armature of a motor, or generator, can be determined if we know the number of wires upon the outer surface, the number of maxwells of mag- netic flux that pass through the armature and the revolutions per second. The rule for the calculation is as follows : Multiply the number of wires on the outer surface of the arma- ture by the maxwells of magnetic flux and by the revolutions per second, and divide this product by 100,000,000. This is the rule for two pole armatures. For multipolar arma- tures with series, or wave winding, use same rule making the flux equal to the sum of the fluxes issuing from all the positive poles. For multipolar armatures with a lap, or parallel winding, use same rule but take the flux issuing from one pole only. To obtain the pull in pounds of a motor armature at one foot radius use the following rule : Multiply the number of wires on the outer surface of armature by the amperes of armature current, and by total number of max- wells of magnetic flux passing through armature, and divide this product by 852,000,000. See pages 13 and 46. 64 HANDBOOK ON ENGINEERING. CHAPTER VI. ELECTRIC MOTORS. Motors are made so as to run at a constant velocity, or for variable speed. For the latter type of machine, the field coils are wound in series, and for constant speed the shunt winding is used. A motor of either kind cannot be started successfully without placing an external resistance in the armature circuit, because, when the armature is at a standstill, there is nothing but the resistance of the wire to hold the current back, and as a result, if no extra resistance is provided, the first rush of current would be very great. As soon as the armature begins to revolve, an e.rn.f . is induced in its wires, and this acts in opposition to the e.m.f. of the line current ; that is, it acts like a back pressure, and holds the current back. On this account, the e.m.f. of a motor is called a counter e.m.f., and it is abbreviated into c. e.m.f. The way in which the external resistance is connected with a motor is illustrated in Fig. 84, in which M is the motor and R the external resistance. I) is a main switch, by means of which the motor is connected with the main line. This switch is closed first, and then switch F is moved to the right until it cov- ers the first contact of the resistance R. The current can then pass directly to the field shunt coils through wire e, and thence by wire a, return to the main line. The armature current, however, has to first pass through the resistance J, before it can reach wire IT and thus the armature. As soon as the armature begins to speed up, the switch F is advanced, step by step, and in a few seconds it is moved to the extreme right position, in which all the resistance R is cut out of the armature circuit. When F reaches this position, the motor should be running at full speed. HANDBOOK ON ENGINEERING. bO If the current should stop while the motor is running, the machine would stop, also, and then, if the current were turned on again, the motor would be caught with the armature connected across the line without an external resistance, and as it would be at a standstill, the current would rise to an enormous strength. To prevent this, the switch F is always opened whenever the motor stops. The attendant may forget to do this, however ; therefore automatic switches have been devised that will open themselves whenever the current dies out. Fig. 84 A simple switch provided with a resistance so as to be suited to start a motor, is called a motor-starter, and one that in addi- tion is provided with means for automatically flying to the open position whenever the current fails, is called an automatic under- load starter. If the motor is very much overloaded, its speed will slow down and the current will increase in strength. If the overload is suf- ficient, the current will become so strong as to be able to ourn out 5 66 HANDBOOK ON ENGINEERING. the armature ; hence, it is desirable to provide a circuit breaker that will open the circuit when the current becomes so strong as to be liable to burn out the machine. Motor-starters are made with a circuit-breaking attachment, and are then called automatic overload motor-starters. A device that combines the under and overload starter, features is called an automatic under and over- load starter, and by some people it is called a " no voltage " and " overload starter." When motors were first introduced, a great deal of trouble was experienced with the starters, owing to the fact that they were arranged so that when the motor was stopped, the connection with the field coils was broken. Now, the current flowing through the field coils objects to stop flowing when the connection is broken, and, consequently, it continues to flow between the end of switch Fin Fig. 84, and the last of the contacts of 72, until the distance is more than the e.m.f. of the current can overcome. Fig. 85. This action produces serious sparking at the last terminal, and in addition, produces a severe strain upon the insulation of the HANDBOOK ON ENGINEERING. 67 field coils, because, as the current is headed off in one direction, it tries to find an outlet in another. This action is what is Fig. 86. commonly called the "kick of the motor field." All this trouble can be obviated by connecting the starter with the motor in such a way that the field circuit is never opened, as is shown in Fig. 84. As this is quite an important point, I will present it in a more simple form in Fig. 85, in which it will be seen that the field coils and armature are permanently connected, so that when switch & opens the circuit, the field current can flow through the armature, until it dies out. All first-class concerns make motor starters with this connection, at the present time. Some of them add the curved contact e. Without this contact, it can be seen that when the switch S is moved to the top position, the 68 HANDBOOK ON ENGINEERING. resistance H is simply transferred from the armature to the field circuit, and that the current oing to the field coils has to pass through this resistance. As this resistance is insignificant in comparison with that of the shunt coils, it makes little difference whether it is left in the field circuit or not, but by the addition of e it can be cut out. Variable speed motors are always arranged so that the speed may be changed by hand as conditions may require. Trolley-car motors are of this type, and so are the motors used for printing presses, and many other kinds of work. Figs. 86 to 88 show arrangements by means of which the speed may be varied with series wound motors. In Fig. 86, E is the starting box and F is the speed regulator. In the act of starting, the switches are in the position shown. To start, the switch S and E is turned so as to close the circuit with the resistance R all included. S is moved toward the left as the armature speeds up, and reaches the last position when full' speed is attained. If the switch of F is now closed, a portion of the current 'will be diverted from the armature, and thus its rotating force will be reduced, and thereby its speed. This method of speed control is also arranged so that the two switches act together, so as to introduce resistance into the motor circuit, and at the same time divert more or less of the current around the armature. It is not used extensively, as all the current that passes through F is just so much thrown away. In Fig. 87 the speed is controlled by means of the switch F, ' which cuts out portions of the field coils and this changes the strength of the field. With this arrangement, if a portion of the field is cut out, the motor will run faster, because the c.e.m.f will be reduced, therefore, the armature current will be increased. To obtain a wide^ range of regulation, it is necessary to wind a large number of turns of wire on the field, so that with all the wire in service, the speed may be the lowest required. HANDBOOK O"N ION(J INKKRING. 69 Fig. 88 shows another arrangement that varies the strength of the field by diverting a portion of the current through switch F. It gives as wide a range of regulation as Fig. 87, but is not so economical. Figs- 86 and 88 cannot be used to regulate the speed of shunt motors, but Fig. 87 can. The first two named figures, if used Fig. 87. with a shunt motor, would simply afford a third path through which current could pass from one side of line to the other, that is, from the p to the n wires, but this would not materially affect the strength of current that would flow through the armature and field coils. They work with series wound motors, because the current is not shunted from wire p to wire n but simply from one side of the armature, or the field, to the other. 70 HANDBOOK ON ENGINEERING. Fig, 89 shows an arrangement by means of which a shunt motor can be made for variable speed. In this case, the switch Fig. 88. and resistance E is simply an ordinary starter, and F is a resist- ance that is introduced in the field circuit, so as to vary the strength of the field. With this arrangement the slowest speed is obtained when all the resistance of F is out of the circuit. The direction in which a motor runs can be reversed by sim- ply reversing the direction of the current through the armature. Any of the arrangements for varying the speed can be used in connection with reversible motors by arranging the switch so as HANDBOOK OX ENGINEE&ING. 71 to reverse the armature connections. Fig. ( .0 will give a fail- idea of the \v:iy in which :i reversing switcli is made. This repre- sents the type of switch used most generally for this purpose, and it is known as the cylinder switch. It is the kind used on trol- ley-cars. The vertical row of circles numbered from one to eleven represents stationary contact pieces, to which the terminals of the motor, the line and the, resistance are attached. The shaded parts 1> 7J are metal plates that are secured to the surface of a cylinder, that is so located that as it is turned in one direction or the other, these plates slide over the stationary con- tacts. If the cylinder is turned so that the plates on the right side slide over the contacts, the motor will run in one direction, and if the cylinder is turned in the other direction, the motor will be reversed. Suppose the right side plates slide over the con- Fig. 89. tacts, then the current f rom p will pass to contact 2, and thence to wire , and to the left-side of the field. Through wire d it will return from the field to contact 5, and by means of 12 HANDBOOK ON ENGINEERING. plates J^and T 7 , which are connected as shown at X 1 , it will reach contact 3 atid wire 6, which runs to the lower side of the arma- ture. From the top of the armature, through wire c, the current will return to contact 4 and through plates S and M and the con- nection X will reach contact 6 , which by one of the wires e con- Fig. 90. nects with the left-side of the resistance D. From the right-side of this resistance, the current will pass to contact 10, and thus to contact 11, through the cylinder plate, and in that way reach line wire n. If the cylinder is turned further around, contact 7 will be cov- ered by plate M, and this will cut one section of D. By a further HANDBOOK ON ENGINEERING. 73 movement, contact 8 will be covered, thus cutting out another section, and by continuing the movement, all of D can be cut out. If the cylinder is turned so as to slide the left-side plates over the contacts, the change effected will be that contact 5 will be connected with 4 instead of with 3, and contact 6 will be con- nected with 3 instead of 4, thus reversing the direction of the current through the armature. The strength of an electric current is measured in amperes. The electromotive force that drives an electric current through a circuit is measured in volts. The resistance that a wire or other circuit offers to the passage of an electric current th r ough it is measured in ohms. The unit of resistance, the Ohm, is the resistance oi a column of mercury about 40 inches long and about five hundredths of an inch in diameter, or, to be more exact, 106 centimeters long, and one millimeter in diameter. THE WATT. The watt is the unit of electric power the volt ampere, the power developed, and is equal to T Jg- of one horse power. A con- venient multiple of this is called the Kilowatt, written K. W., and is equal to 1,000 watts. THE AflPERE. The ampere is the practical unit of electric current, such a cur- rent [or rate of flow, or transmission of electricity] as would pass, with an electromotive force of one volt, through a circuit whose resistance is equal to one ohm ; a current of such a strength as would deposit from solution .006084 grains of copper per second. CANDLE POWER. The candle power is the unit of light ; and a standard candle is a candle of definite composition which with a given consump- tion in a given time, will produce a light of a fixed and definite brightness. A candle which burns 120 grains of spermaceti wax per hour, or two grains per minute, will give an illumination equal to one standard candle. 74 HANDBOOK ON -ENGINEERING. CHAPTER VII. INSTRUCTIONS FOR INSTALLING AND OPERATING SLOW AND MODERATE SPEED GENERATORS AND HOTORS. To remove the armature, take off the brush-holders, brush yoke, pulley and bearing caps and put a sling on the armature, as shown in accompanying illustration. A spreader of suitable length should be used and its location adjusted to prevent the rope from drawing against the flange or end connections. In assembling, marked parts of the machine should be assem- bled strictly according to the marking. Clean all connection joints carefully before clamping them together. Wipe the shaft- bearing sleeves and oil cellars perfectly clean and free from grit. Place the bearing sleeves and oil rings in position on the shaft and then lower the armature into place, taking care that the oil rings are not jammed or sprung. As soon as the armature is in position, pour a little oil in the bearing sleeves, put the caps on the boxes and screw them down snugly. The top field should next be put on and bolted firmly into position, and a level placed on the shaft to check the leveling of the foundation. Fill the bearings with the best grade of thin lubricating oil and do not allow it to overflow. Oil throwing is usually due to an excess of oil and can be avoided by care in filling the oil cellars. To complete the assembly, place the pulley on the shaft, draw up the set screws and put on the brush rigging and connection blocks. STARTING. Before putting on the belt, see that all screws and nuts are tight and turn the armature by hand to see that it is free and HANDBOOK ON ENGINEERING. 75 does not rub or bind at any point. Pat on the belt with the machine so placed on the rails as to have the minimum distance between pulley centers. Start the machine up slowly and see that the oil rings in bearings are in motion. As the machine comes up to speed, tighten the belt till it runs smoothly, and run the machine long enough without load to make sure that the bear- ings are in perfect condition. The bearings, when running, should be examined at least once a week. CARE OF COMMUTATOR. The commutator brushes and brush-holders should at all times be kept perfectly clean and free from carbon or other dust. Wipe the commutator from time to time with a piece of canvas lightly coated with vaseline. Lubricant of any kind should be applied very sparingly. 76 HANDBOOK ON ENGINEERING. t \ If a commutator when set up begins to give trouble by rough- ness, with attendant sparking and excessive heating, it is neces- sary to immediately take measures to smooth the surface. Any delay will aggravate the trouble, and eventually cause high tem- peratures, throwing off solder, and possibly displacement of the segments. No. sandpaper, fitted to a segment of wood, with a radius equal to that of the commutator, if applied in time to the surface when running at full speed (and if possible with brushes raised), and kept moving laterally back and forth on the commu- tator, will usually remedy the fault. DIRECTIONS FOR STARTING DYNAMOS. GeneraL Make sure that the machine is clean throughout, especially the commutator, brushes, electrical connections, etc. Remove any metal dust, as it is very likely to make a ground or short circuit. Examine the entire machine carefully, and see that] there are no screws or other parts that are loose or out of place. See that the oil-cups have a sufficient supply of oil, and that the passages for the oil are clean and the feed is at the proper rate. In the case of self -oiling bearings, see that the rings or other means for carrying the oil work freely. See that the belt is in place and has the proper tension. If it is the first time the machine is started, it should be turned a few times by hand, or very slowly, in order to see if the shaft revolves easily and the belt runs in center of pulleys. The brushes should now be carefully examined and adjusted to make good contact with the commutator and at the proper point, the switches connecting the machine to the circuit being left open. The machine should then be started with care and brought up to full speed, gradually if possible ; and in any case HANDBOOK ON ENGINEEKING. 77 the person who starts either a dynamo or a motor should closely watch the machine and everything connected with it, and be ready to throw it out of circuit if it is connected, and shut down and stop it instantly if the least thing seems to be wrong, and should then be sure to find out and correct the trouble before starting again. STARTING A DYNAMO. In the case of a dynamo it is usually brought up to speed either by starting up a steam-engine or by connecting the dynamo to a source of power already in motion. The former should, of course, only be attempted by a person competent to manage steam-engines and familiar with the particular type in question. This requires special knowledge acquired by experi- ence, as there are many points to appreciate and attend to, the neglect of any of which might cause serious trouble. For ex- ample, the presence of water in the cylinder might knock out the cylinder-head ; the failure to set the feed of the oil-cups properly might cause the piston-rod, shaft, or other part, to cut. And other great or small damage might be done by ignorance or care- lessness. The mere mechanical connecting of a dynamo to a source of power is usually not very difficult; nevertheless, it should be done carefully and intelligently, even if it only requires throwing in a friction-clutch or shifting a belt from a loose pul- ley. To put a belt on a pulley in motion is difficult and danger- ous, particularly if the belt is large or the speed is high, and should not be tried except by a person who knows just how to do it. Even if a stick is used for this purpose, it is apt to be caught and thrown around by the machinery, unless it is used in exactly the right way. It has been customary to bring dynamos to full speed before the brushes are lowered into contact with the commutator ; but 78 HANDBOOK ON ENGINEERING. this is not necessary, provided the dynamo is not allowed to turn backwards, which sometimes occurs from carelessness in starting, and might injure copper brushes by causing them to catch in the commutator. If the brushes are put in contact before starting, they can be more easily and perfectly adjusted and the e.m.f . will come up slowly, so that any fault or difficulty will develop gradually and can be corrected ; or the machine can be stopped, before any injury is done to it or to the system. In fact, if the machine is working alone on a system, and is absolutely free from any danger of short-circuiting any other machine or storage bat- tery on the same circuit, it may be started while connected to the circuit, but not otherwise. If there are a large number of lamps connected in the circuit, the field magnetism and voltage might not be able to " build up " until the line is disconnected an instant. If one dynamo is to be connected with another, or to a circuit having other dynamos or a storage battery working upon it, the greatest care should be taken. This coupling together of dynamos can be done perfectly, however, if the correct method is followed, but is likely to cause serious trouble if any mistake is made. SWITCHING DYNAHOS INTO CIRCUIT. Two or more machines are often connected to a common cir- cuit. This is especially the case in large buildings where the number of lamps required to be fed varies so much that one dynamo may be sufficient for certain hours, but two, three or more machines may be required at other times. The various ways in which this is done depending upon the character of the machines and of the circuit and the precautions necessary in each case make this a most important and interesting subject, which requires careful consideration. Dynamos may be connected together either in parallel (mul- tiple arc) or in series. HANDBOOK ON ENGINEERING. 79 DYNAMOS IN PARALLEL. In this case the + terminals are connected together or to the same line, and the terminals are connected together or to the other line. The currents (i. e. amperes) of the machines are thereby added, but the e.m.f. (volts) are not increased. The chief condition for the running of dynamos in parallel is that $heir voltages shall be equal, but their current capacities may be different. For example: A dynamo producing 10 amperes may be connected to another generating 100 amperes, provided the voltages agree. Parallel working is, therefore, suited to constant potential circuits. A dynamo to be connected in parallel with others or with a storage battery, must first be brought up to its proper speed, e.m.f., and other working conditions, otherwise, it will short-circuit the system, and probably burn out its armature. Its field magnetism must, therefore, be at full strength, owing to the fact that it generates no e.m.f. with no field magnetism. Hence, it is well to find whether the pole pieces are strongly magnetized by testing them with a piece of iron, and to make sure of the proper working of the machine in all other respects before connecting the armature to the circuit. It is a common accident for the field-circuit to be open at some point, and thus cause very serious results. In fact, a dynamo should not be connected to a circuit in parallel with others until its voltage has been tested and found to be equal to, or slightly (not over 1 or 2 per cent) greater than that of the circuit. If the voltage of the dynamo is less than that of the circuit, the current will flow back into the dynamo and cause it to be run as a motor. The direction of rotation is the same, however, if it is shunt- wound, and no great harm results from a slight difference of potential. But a compound-wound machine requires more careful handling. 80 HANDBOOK ON ENGINEERING. DIRECTIONS FOR RUNNING DYNAMOS AND MOTORS. In the case of a machine which has not been run before, or has been changed in any way, it is of course wise to watch it closely at first. It is also well to give the bearings of a new machine plenty of oil at first, but not enough to run on the arma- ture, commutator or any part that would be injured by it, and to run the belt rather slack until the bearings and belt have got- ten into easy working condition. If possible a new machine should be run without load or with a light one for an hour or two, or several hours in the case of a large machine ; and it is always wrong to start a new machine with its full load, or even a large fraction of it. ** This is true even if the machine has been fully tested by its manufacturer and is in perfect condition, because there may be some fault in setting 'it up, or some other circumstance which would cause trouble. All machinery requires some adjust- ment and care for a certain time to get it into smooth working order. When this condition is reached, the only attention required is to supply oil when needed, keep the machine clean and see that it is not overloaded. A dynamo requires that its voltage or current should be observed and regulated if it varies. The per- son in charge should always be ready and sure to detect the beginning of any trouble, such as sparking, the heating of any part of the machine, noise, abnormally high or low speed, etc. ; before any injury is caused, and to overcome it by following directions given elsewhere. Those directions should be pretty thoroughly committed to mind, in order -to facilitate the prompt detection and remedy of any trouble when it suddenly occurs, as is apt to be the case. If possible, the machine should be shut HANDBOOK ON ENGINEERING. 81 down instantly when any trouble or indication of one appears, in order to avoid injury and give time for examination. Keep all tools or pieces of iron or steel away from the machine while running, as they might be drawn in by the magnetism, and perhaps get between the armature and pole-pieces and ruin the machine. For this reason, use a zinc, brass or copper oil-can instead of iron or v ' tin " (tinned iron). Particular attention and care should be given to the commu- tator and brushes to see that the former keeps perfectly smooth and that the latter are in proper adjustment. (See Sparking.) Never lift a brush while the machine is delivering current, unless there are one or more other brushes on the same side to carry the current, as the spark might make a bad burnt spot on the commutator. Touch the bearing's and field-coils occasionally to see that they are not hot. To determine whether the armature is running hot, place the hand in the current of air thrown out from it by centrifugal force. Special care should be observed by any one who runs a dynamo or motor to avoid overloading it, because this is the cause of most of the troubles which occur. rjfcY, OF THE UNIVERSITY j >^ 82 HANDBOOK ON ENGINEERING. CHAPTER VIII. WHY COMMUTATOR BRUSHES SPARK AND WHY THEY DO NOT SPARK. I might give a long list of reasons why commutator brushes spark, and why they do not spark, but by such a procedure no light would be thrown on the subject, because the reasons would not be understood unless fully explained. I therefore propose to explain the subject and let the reader tabulate the reasons after digesting the explanation of the principles involved. Whenever an electric current is interrupted, a spark is pro- duced and it makes no difference how the current is generated, or what kind of a conductor it is flowing through. To break a current without a spark is not a possibility ; hence, if we desire to open a circuit without producing a spark, the only way to accomplish the result is by killing the current before the circuit is opened. The brushes resting on the commutator of a motor or a generator have to transmit to the armature and take away from it the current that is generated, in the case of a generator, or the current that drives the machine in the case of a motor. If the brushes were made so narrow that they could only make contact with one commutator segment at a time, it would be impossible to run the machine without producing very destruc- tive sparks. Commutators, however, are not made in this way. The insulation between the segments is narrow, and the brushes are wide enough to be always in contact with two segments, and part of the time with three. Suppose that the proportions are such that during most of the time the brush only touches two HANDBOOK ON ENGINEERING. 83 segments, as shown in Fig. 1. With these proportions it will be seen, that so long as there are two segments in contact with each brush, it is a possibility *or the current to be diverted through one of them only. Suppose that at the instant when the forward segment is passing from under the brush, all the current .flows through -the rear segment ; then it is quite evident that the first- named segment will break away from contact with the brush with- out making a spark, for there will be no current flowing from it to the brush. All the foregoing is self-evident, but it will be suggested that although the brush can break away from the front segment with- out producing a spark, it cannot do the same thing with the rear segment, for all the current is flowing through this one. While it is true that when the forward segment passed from under the brush all the current was flowing through the rear segment, it is not true that the current continues to follow this path. As soon as the front segment passes from under the brush, the rear one becomes the forward segment, and while it is advancing to the point where it must pass from under the brush, the current can be transferred to the next segment back of it which now plays the part of rear segment. Thus we see that to be able to run a machine without producing sparks at the commutator, all we have to do is to provide means whereby the current is transferred from one segment to the one back of it as the commutator revolves, so that when the segments pass from under the brush there is no current flowing through them. This result is accomplished more or less perfectly in all machines, made by responsible firms. There are machines on the market that have been designed by men that are not well enough posted in the principles of electrical science to obtain proper proportions, and these are not propor- tioned so as to shift the current from the forward to the rear segment as fast as the machine revolves ; such machines always produce more or less serious sparking. 84 HANDBOOK ON ENGINEERING. If a machine is accurately made and the armature coils and commutator segments are properly spaced and sufficient in num- ber, it is possible to get the brushes so there will be little or no spark at a given load ; but if the current strength be increased or reduced, the sparks will appear, and the more the current is changed the larger the sparks will be, the increasing' current producing the greatest sparking. The way in which the current is shifted from the front to the rear segment I will explain in connection with Fig. 1. In this figure, A represents a portion of the core of a ring armature. The shaft upon which it is mounted is shown at D, and P N are the corners of the poles between which it rotates. The small blocks C represent a portion of the commutator segments, which we have placed outside of the armature, so as to make the diagram as simple as possible. For the same reason I have shown the armature coils as made of two turns of wire each. The line F divides the space between the ends of the poles into two equal parts, and the line E divides the armature into two halves on which the directions of the induced currents is opposite. In all the coils to the right of line E the currents are induced in a direction away from the shaft, and in all the coils to the left of line E the currents flow toward the shaft, all of which is clearly indicated by the arrow heads placed upon the lines repre- senting the coils. The outline B represents the end of one of the brushes, and from the direction in which it is inclined it will be understood that the armature revolves in a direction counter to that of the hands of a clock. When the armature is in the position shown, the current flow- ing in the coils to the right of line E passes to segment 6, and thus reaches the brush, while the current flowing in the coils to the left of line E reaches segment a, and through this passes to the brush. As the brush rests upon segments a and b the coil with which they connect is short-circuited, and therefore a HANDBOOK ON ENGINEERING. 85 current can flow in it in any direction, or there may be no cur- rent. To be able to run without spark, or to obtain perfect commutation, as it is called, the current in this short-circuited coil, when in the position shown, should be zero, or nearly so. This coil, which is short-circuited by the brush, is called the corn- mutated coil, or the coil undergoing commutation. It will be noticed that this commutated coiMs in a position just forward of Fig. 1. the line E ; hence, the action of pole P will be to develop a current in it that will flow in the same direction as the current in the coils ahead of it, that is, in the coils to the left. Now if this current flowed through the brush, it would be in a direction contrary to that of the arrow at a; hence it would act to check the current flowing from the front segment a to the brush, and would divert it through the commutated coil to the rear segment 86 HANDBOOK ON ENGINEERING. b. If the action of pole P upon the eoramutated coil is sufficiently vigorous, the current developed in it will be as strong as the cur- rent in the coils ahead of it, by the time the end of the segment is about to break away from the brush ; and this being the case there will be no current from segment a to the brush, and conse- quently, no spark. If the action of pole P is not strong enough, then there will be a small current from segment a to the brush when they separate, and as a result, a small spark. If the action of pole P on the commutated coil is too vigorous, then the current developed in it will be too great, and it will not only divert all the current coining from 'the forward coils, through the commuta- ted coil to segment 6, but in addition will develop a local current that will circulate through the end of the brush, and, therefore, when the separation occurs, there will be a current flowing from the brush to the front segment, and consequently a spark. If the commutated coil were placed astride of line E, the action of pole P upon it would be no greater than that of pole JV, so that no current would be developed in it while undergoing com- mutation. The further the coil is in advance of line E, when short- circuited by the brush, the stronger the action of pole P upon it ; therefore, the strength of the current developed in the commutated coil can be increased by moving the brush further away from pole P. Hence, by trial, a point can be found where the current developed will be just sufficient for the purpose and no more. This is true, supposing the current developed by the armature to remain con- stant, but, if it varies, the current in the commutated coil will be either too great or too small. If, when the brushes are set, the armature is delivering a current of, say, twenty amperes, then the current flowing through the coils to the left of the brush will be ten amperes, and the current in the commutated coil will also be ten amperes. If the armature current increases to forty amperes, the current in the forward coils will be twenty amperes, and as that jn the commutated coils will still be ten amperes, it will have only HANDBOOK ON ENGINEERING. 87 one-half the strength required for perfect commutation. In prac- tice, however, it is found that if the commutator have a sufficient number of segments, and the proportions of the machine are such that the line E remains practically in the same position for all strengths of armature current, then, if the brushes are set so as to run sparkless with an average load, they will run so nearly spark- less with a heavy or light load as to make it difficult to detect the difference. Even when a machine is properly proportioned, the brushes may spark badly if they are not set in the proper position and with the proper tension. If the tension is not right, they will spark no matter where they are set. If the tension is too light, they will spark, because they will chatter and thus jump off the surface of the commutator. If the tension is too great, they will spark because they will cut the commutator, and then the latter will act as a file or grindstone and cut away particles from the brushes, and these will conduct the current from segment to seg- ment, as well as from the segment to the brush. Whenever a com- mutator is seen to be covered with fine sparks, some of which run all the way around the circle, it may be depended upon that the surface is rough, due in most cases to too much pressure on the brushes, and the remedy is to smooth it up and reduce the tension and set the brushes where they will run with the smallest spark. When the brushes begin to spark they rarely cure themselves and the longer they are allowed to run with a heavy spark the worse they will get. Of all the troubles which may occur, sparking is the only one which is very different in the different types of machines. In some its occurrence is practically impossible. In others, it may result from a number of causes. The following cases of sparking apply to nearly all machines, and they cover closed-coil dynamos and motors completely. Cause J. Brushes not set at the neutral point. 88 HANDBOOK ON ENGINEERING. Symptom* Sparking, varied by shifting the brushes with rocker-arm. Remedy* Carefully shift brushes backwards or forwards until sparking is reduced to a minimum. The usual position for brushes in two-pole mrchines is opposite the spaces between the pole-pieces. Cause 2* Commutator rough, eccentric, or has one or more " high bars " projecting beyond the others, or one or more flat bars, commonly called " flats," or projecting mica, any one of which causes brush to vibrate, or to be actually thrown out of contact with commutator. Symptom* Note whether there is a glaze or polish on the commutator, which shows smooth working ; touch revolving com- mutator with tip of finger-nail, and the least roughness is perceptible, or feel of brushes to see if there is any jar. If the machine runs at high-voltage (over 250), the commutator or brushes should be touched with a small stick or quill to avoid danger of shock. In the case of an eccentric commutator, careful examination shows a rise and fall of the brush when commutator turns slowly, or a chattering of brush when running fast. Remedy* Smooth the commutator with a fine file or fine sand- paper, which should be applied by a block of wood which exactly fits the commutator (in latter case, be careful to remove any sand remaining afterward ; and never use emery) . If bearing is loose put in new one. If commutator is very rough or eccentric, it should be taken out and turned off. Cause 3* Brushes make poor contact with commutator, Symptom* Close examination shows that brushes touch only at one corner, or only in front or behind, or there is dirt on sur- face of contact. Sometimes, owing to the presence of too much oil or from other cause, the brushes and commutator become very dirty and covered with smut. They should then be carefully cleaned by wiping with oily rag or benzine, or by other means. HANDBOOK ON ENGINEERING. 89 Occasionally a " glass-hard " carbon brush is met with. It is incapable of wearing to a good seat or contact and will only touch in one or two points, and should be discarded. Remedy* File, bend, adjust or clean brushes until they rest evenly on commutator, with considerable surface of contact and with sure but light pressure. It sometimes happens that the brushes make poor contact, because the brush-holders do not turn or work freely. Cause 4. Short-circuited coil in armature or reversed coil. Symptom. A motor will draw excessive current, even when running free without load. A dynamo will require considerable power even without any load. The short-circuited coil is heated much more than the others, and is very apt to be burnt out entirely ; therefore, stop machine immediately. If necessary to run machine to locate the short- circuit, one or two minutes is long enough, but it may be re- peated until the short-circuited coil is found by feeling the arma- ture all over. An iron screw-driver or other tool held between the field- magnets near the revolving armature vibrates very perceptibly as the short-circuited coil passes. Almost any armature, par- ticularly one with teeth, will cause a slight but rapid vibration of a piece of iron held near it, but a short-circuit produces a much stronger effect only once per revolution. The current pulsates and torque is unequal at different parts of a revolution, these being particularly noticeable when arma- ture turns rather slowly. If a large portion of the armature is short-circuited, the heating is distributed and harder to locate. In this case a motor runs very slowly, giving little power, but having full-field magnetism. Remedy. A short circuit is often caused by a piece of solder or other metal getting between the commutator bars or their con- nections with the armature, and sometimes the insulation between 90 HANDBOOK ON ENGINEERING. or at the ends of these bars is bridged over by a particle of metal. In any such case the trouble is easily found and corrected. If, however, the short-circuit is in the coil itself, the only real cure is to rewind the coil. One or more " grounds " in the armature may produce effects similar to those arising from a short circuit. Cause 5. Broken circuit in armature. Symptom* Commutator flashes violently while running, and commutator-bar nearest the break is badly cut and burnt ; but in this case 110 particular armature coil will be heated, as in the last case and the flashing will be very much worse, even when turn- ing slowly. This trouble, which might also be confounded with a bad case of " high-bar " or eccentricity in commutator (sparking), is distinguished from it by slowly turning the arma- ture, when violent flashing will continue if circuit is broken, but not with eccentric commutator or even with " high bar." Remedy* The trouble is often found where the armature wires connect with the commutator and not in the coil itself, and the break may be repaired or the loose wire may be resoldered or screwed back in place. If the trouble is due to a broken com- mutator connection and it cannot be fixed, then connect the dis- connected bar to the next by solder, or " stagger " the brushes ; that is, put one a little forward and the other back so as to bridge over the break. If the break is in the coil itself, rewinding is generally the only cure. Cause 6* Weak field-magnetism. Symptom* Any considerable vibration is almost sure to pro- duce sparking, of which it is a common cause. This sparking may be reduced by increasing the pressure of the brushes on the commutator, but the vibration itself should be overcome by the remedies referred to above. Cause 7* Chatter of Brushes. The commutator sometimes HANDBOOK ON ENGINEERING. 91 becomes sticky when carbon brushes are used, causing friction, which throws the brushes into rapid vibration as the commutator revolves, similarly to the action of a violin-bow. Symptom. Slight tingling or jarring is felt in brushes. Remedy* Clean commutator and oil slightly. This stops it at once. NOISE. Cause 8. Vibration due to armature or pulley being out of balance'. Symptom* Strong vibration felt when the hand is placed upon the machine while it is running. Vibration changes greatly if speed is changed. Remedy* The easiest method of finding in which direction the armature is out of balance is to take it out and rest the shaft on two parallel and horizontal A-shaped metallic tracks suffici- ently far apart to allow the armature to go between them. If the armature is then slowly rolled back and forth, the heavy side will tend to turn downward. The armature and pulley should always be balanced separately. An excess of weight on one side of the pulley and an equal excess of weight on the opposite side of the armature will not produce a balance while running, though it does when standing still ; on the contrary, it will give the shaft a strong tendency to "wobble." A perfect balance is only obtained when the weights are directly opposite, i. e., in the same line perpendicular to the shaft. Cause 9* Armature strikes or rubs against pole pieces. Symptom. Easily detected by placing the ear near the pole- pieces, or by examining armature to see if its surface is abraded at any point, or by examining each part of the space between armature and field, as armature is slowly revolved, to see if any 92 HANDBOOK ON ENGINEERING. portion of it touches or is so close as to be likely to touch when the machine is running. Or turn armature by hand when no current is on, and note if it sticks at any point. Remedy. Bind down any wire, or other part of the armature that may project abnormally, or file out the pole-pieces where the armature strikes, or center the armature so that there is a uni~ form clearance between it and the pole-pieces at all points. Cause tO* Singing or hissing of brushes. This is usually occasioned by rough or sticky commutator, or by tips of brushes not being smooth, or the layers of a copper brush not being held together and in place. With carbon brushes, hissing will be caused by the use of carbon which is gritty or too hard. Vertical carbon brushes, or brushes inclined against the direction of rotation, are apt to squeak or sing. A new machine will sometimes make noise from rough commutator, no matter how carefully it is turned off, because the difference in hardness between mica and copper causes the cut .of the tool to vary, thus forming inequali- ties which are very minute, but enough to make noise. This can be best smoothed by running. Remedy* Apply a very little oil or vaseline to the com- mutator with the finger or a rag. Adjust the brushes or smooth the commutator. Carbon brushes are apt to squeak in starting up, or at slow speed. This decreases at full speed, and can usually be reduced by moistening the brush with oil, care being taken not to have a ay drops, or excess of oil. Shortening or lengthening the brushes sometimes stops the noise. Run the machine on open circuit until commutator and brushes are worn smooth. HANDBOOK ON ENGINEERING. 93 HEATING IN DYNAHO OR MOTOR. General Instructions* The degree of heat that is injurious or objectionable in any part of a dynamo or motor is easily deter- mined by feeling the various parts. If the heat is bearable for a few moments, it is entirely harmless. But if the heat is unbear- able for more than a few seconds, the safe limit of temperature has been passed, except in the case of commutators in which solder is not used ; and it should be reduced in some of the ways that are given above. In testing with the hand, allowance should always be made for the fact that bare metal feels much hotter than cotton, etc. If the heat has become so great as to produce an odor or smoke, the safe limit has been far exceeded and the current should be shut off and the machine stopped immediately, as this indicates a serious trouble, such as a short-circuited coil or a tight bearing. The machine should not again be started until the cause of the trouble has been found and positively overcome. Of course neither water nor ice should ever be used to cool elec- trical machinery, except possibly the bearings of large machines, where it can be applied without danger of wetting the other parts. Feeling 1 for heat will answer in ordina^ cases, but of course, the sensitiveness of the hand differs, and it makes a very great difference whether the surface is a good or bad conductor of heat. The back of the hand is more sensitive and less variable than the palm for this test. But for accurate results a thermometer should be applied and covered with waste or cloth -to keep in the heat. In proper working the temperature of no parts of the machine should rise more than 45 C., or 81 F. above the tem- perature of the surrounding air. If the actual temperature of 94 HANDBOOK ON ENGINEERING. the machine is near the boiling point, 100 C., or 212 F., it is seriously high. It is very important in all cases of heating to locate correctly the source of heat in the exact part in which it is produced. It is a common mistake to suppose that any part of a machine which is found to be hot is the seat of the trouble. A hot bearing may cause the armature or commutator to heat or vice versa. In every case, all parts of the machine should be felt to find which is the hottest, since heat generated in one part is rapidly diffused throughout the entire machine. It is generally much surer and easier in the end to make observations for heating by starting with the whole machine perfectly cool, which is done by letting it stand for one or more hours or over night, before making the examination. When ready to try it, run it fast for three to five minutes, with the field magnets charged ; then stop, and feel all parts immediately. The heat will be found in the right place, as it will not have had time to diffuse from the heated to the cool parts of the machine. Whereas, after the machine has run some time, any heating effect will spread until all parts are equal in temperature, and it will then be almost impossible to locate the trouble. Excessive heating of commutator, armature, field magnets, or bearings may occur in any type of dynamo or motor, but it can almost always be avoided by proper care and working conditions. THE EFFECT OF THE DISPLACEHENT OF THE ARMATURE. If a machine is old, it is more than likely the shaft will be found out of center, and if this fact is discovered at a time when things are not working as they should, it is taken for granted this is the cause of the trouble. What is true of shafts out of the HANDBOOK ON ENGINEERING. 95 center is true of several other things that are liable to get out of place. For the present it will be sufficient to investigate just what effect the displacement of the shaft can have. Fig. \ illustrates an armature of a two-pole machine which is out of center in one direction, and Fig. 2 shows another two-pole armature out of center in a direction of right angles to that shown in the first figure. The condition shown in Fig. 1 could be produced by a heavy armature running in rather light bear- ings for several years, and the side displacement of Fig. 2 could be produced by the tension of an extra tight belt. The mechan- Fig. 1. Fig. 2. ical effect of both these conditions would be to increase the pres- sure on the bearings, as the part a of the armature would be drawn toward the poles of the field with greater force than the opposite side. The downward pull, due to the attraction of the magnetism, would be greater in Fig. 1 than the side pull in Fig. 2, supposing both armatures and fields to be the same in both cases, and the displacement of the shafts equal. This difference is due to the fact that in Fig. 1 the magnetism of both poles is concentrated at the lower corners on account of the shorter air gap ; hence both sides pull much harder on the lower side. In 96 HANDBOOK ON ENGINEERING. Fig. 2 the pull of the N pole is greater than that of the other, simply because in the latter the magnetism ia more dispersed, but the difference in the density on the two sides will not be very great. If the bearings of a machine, with the armature dis- placed, as indicated, have shown any signs of cutting, or if they run unusually warm, their condition will be improved by putting in new bearings that will bring the shaft central. If the armature is of the drum type, the displacement of the shaft will have no effect upon it electrically. This is owing to the fact that all the armature coils are wound from one side of the core to the other, and, therefore, at all times, every coil has one side under the influence of one pole and the other side under the influence of the opposite pole, and if one side is acted upon strongly by one pole, it will be acted upon feebly by the other. If the armature is of the ring type, then the displacement of the shaft will affect it electrically, for in a ring armature, the coils on one side are acted upon by the pole on that side, only, and as the magnetic field from one pqlewill be stronger than that from the other (that is, considering the action upon equal halves of the armature) , the voltage devel- oped in the coils on one side of the armature will be greater than that developed on the other side. The effect of the disturbance of the electrical balance will be that the brushes will spark badly, because the voltage of the cur- rent generated on one side of the armature will be greater than that of the current on the other side. Hence, when these two currents meet at the brushes, the strong one will tend to drive the weak one backward. If, while the armature is out of center, we wish to adjust the brushes so as to get rid of the excessive sparking, all we have to do is to set them to the right of the cen- ter line, as in Fig. 2, so that the wire on the left side will cover a greater portion of the circumference than the right. HANDBOOK ON ENGINEERING. 97 In a multipolar machine, the displacement of the armature will have the same effect mechanically as in the two-pole type ; multipolar armatures are connected in two different ways, one of which is called the wave or series winding, and the other the lap or parallel winding. In the first named type of winding, the ends of all the coils on the armature are connected with each other and with the commutator segments in such. a manner that there are only two paths through the wire for the current ; there- fore, these two armature currents pass under all the poles and the voltage of each current is the combined effect of all the poles. From this very fact, it can be clearly seen that it makes no difference what the distance between the several poles and arma- ture may be, for if some are nearer than the others, the only effect will be that these poles will not develop their share of the total voltage, but whatever their action may be, it will be the same on the coils in both circuits. When a multipolar armature is connected so as to form a parallel or lap winding, then the connections between the coil ends, and between these ends and the commutator segments, are such that as many paths are provided for the current as there are poles, and each one of these paths is located under one pole, and as a consequence, the voltage developed in it is proportional to the action of this pole. The diagram 3 illustrates a six-pole armature with the ends of the field poles, and the arrows a a, b 6, c c, indicate the six separate divisions of the coils in which the branch currents are developed. Now, it can be clearly seen that as the armature is nearer to the lower poles than to any of the others, the action of these will be the strongest. Hence, the cur- rents a a will be stronger than the others and will have a higher voltage. The two upper currents are weaker than the side ones and 7 98 HANDBOOK ON ENGINEERING. their voltage is also lower, so that, the current returning to the commutator through the brushes at the upper corners, will not divide equally, but the larger portion will be drawn into the coils on the side ; and as the upper coils will have to fight to hold their own, so to speak, there will be a disturbance of the balance that Fig. 3. is required for smooth running. The result will be heavy spark- ing at these brushes. In the.great majority of cases, if the brushes of a multipolar machine spark on account of tffe armature being out of center, the only cure is to reset the bearings, if they are adjustable, and if they are not, to put in new ones. HANDBOOK ON ENGINEERING. 101 Soldering 1 Fluid* . The following formula for soldering fluid is suggested : Saturated solution of zinc chloride, 5 parts. Alcohol, 4 parts. Glycerine, 1 part. Bell or Other Wires* a. Shall never be run in same duct with lighting or power wires. Table of Capacity of Wires* 1 73 fl IN w p OQ 1* 1 OQ H o> A cSO * "0^ 9 ^ii CQ K << 6 N ^ 35 19 1,288 ... ... ... 18 1,624 ... ... 3 17 2,048 ... ... ... 16 . 2,583 ... ... 6 15 3,257 ... ... ... 14 4,107 ... ... 12 12 6,530 ... 17 ... 9,016 7 19 21 ... 11,368 7 18 25 ... 14,336 7 17 30 ... 18,081 7 16 35 ... 22,799 7 15 40 ... 30,856 19 18 50 ... 38,912 19 17 60 ... 49,077 19 16 70 ... 60,088 37 18 85 ... 75,776 37 17 100 ... 99,064 61 18 120 .0. 124,928 61 17 145 157,563 61 16 170 102 HANDBOOK ON ENGINEERING . "3 K 8 198,677 01 15 200 250,527 61 14 235 296,387 91 15 270 373,737 91 14 320 413,639 127 15 340 When greater conducting area than that of B. & S. G. is re- quired, the conductor shall be stranded in a series of 7, 19, 37, 61, 91 or 127 wires, as may be required ; the strand consisting of one central wire, the remainder laid around it concentrically, each layer to be twisted in the opposite direction from the pre- ceding. / TABLE SHOWING THE SIZE OF WIRE OF DIFFERENT METALS THAI- WILL BE MELTED BY CURRENTS OF VARIOUS STRENGTHS. Strength of Current in Amperes. DIAMETER OF WIHE IN THOUSANDTHS OF AN INCH. Copper. Aluminum. Platinum. German Silver. Iron. Tin. 1 .002 .003 .003 .003 .005 .007 2 .003 .004 .005 .005 .008 .011 3 .004 .005 .007 .007 .010 .015 4 .005 .006 .008 .008 . .012 .018 5 .006 .008 .010 .010 .014 .021 10 .009 .012 .016 .016 .022 .033 15 .013 .016 .020 .020 .028 .044 20 .015 .019 .025 .025 .034 .053 25 .018 .022 .029 .029 .040 .062 30 .020 .025 .032 .032 .045 .069 35 .022 .028 .036 .036 .050 .077 40 .025 .030 .039 .039 .055 .084 50 .027 .033 .042 .042 .059 .091 60 .029 .035 .045 .045 .063 .098 HANDBOOK ON ENGINEERING. 103 CHAPTER IX. INSTRUCTIONS FOR INSTALLING AND OPERATING APPAR- ATUS FOR ARC LIGHTING, BRUSH SYSTEM. Theory of the Brush arc generator. The Brush Arc Gen- erator is of the open coil type, the fundamental principle of which is illustrated in Fig. 1. Two pairs of coils, placed at right angles Fig. I. on an iron core, are rotated in a magnetic field. The horizontal coils represented in the diagram are producing their maximum electromotive force, while the pair of coils at right angles to them is generating practically no electromotive force. The brushes are placed on the segments of the four-part commutator, so as to collect only the current generated by the two horizontal coils. The other coils are open circuited, or completely cut out of the circuit. 102 HANDBOOK ON ENGINEERING. H g CO o , , 930 ,880 40,232 3,200 68,480 5,000 107,000 ,890 40,446 3,250 69,550 5,050 108,070 ,900 40,060 3,300 70,620 5,100 109,140 ,910 40,874 3,350 71,090 5,150 110,210 ,920 41,088 3,400- 72,760 5,200 111,280 ,930 41,302 3,450 73,830 5,250 112,350 ,940 41,516 3,500 74,900 5,300 113,420 ,1)50 41,730 3,550 75,970 5,350 114,400 ,960 41,944 3,600 77,040 5,400 115,560 ,970 42,158 3,650 78,110 5,450 116,630 ,980 42,372 3,700 79,180 5,500 117,700 ,990 42,586 3,750 80,250 5,550 118,770 2,000 42,800 3,800 81 320 5,000 119,840 2,050 43,870 3,850 82,390 5,050 120,910 2,100 44,940 3,900 83,460 5,700 121,980 2,150 46,010 3.950 84,530 5,750 123,050 2/200 47,080 4,000 85,600 5,800 " 124,120 2,250 48,150 4,050 86,670 5,850 125,190 2,300 49,220 4,100 87,740 5,900 126,260 2,350 " 50,290 4,150 88,810 5,950 127,330 2,400 51,300 4,200 89,880 6,000 128,400 166 TABLE No. 2. HANDBOOK ON ENGINEERING, Feet x a x 10.70. Miles. Ft.x2xlO.70 Miles. Ft.x2xlO.70 Miles. Ft.x2xlO.70 i 564,960 4 451,968 n 847,440 112,992 4i 508,464 8 903,936 i& 169,488 5 564,960 M 960,432 2 2*25,984 Si 621,456 9 1,016,928 2i 282,480 6 677,952 0* 1,073,424 3 338,976 6* 734,448 10 1,129,920 395,472 7 .790,944 (A) Feet x 2 x 10.7 x Amperes = Circular nails. Volts lost Feetx 2x 10.7 x Amperes Tr . . (B) ^ -. .- -=Volts lost. ^ * .'iVSftll lai* TVI1 I C3 (C) Circular mils. Circular mills x volts lost = Amperes. Feetx 2 x 10.7 In calculating the sizes of wire as shown in the Incandescent Wiring Table a formula (A) has been used in which there is a constant 10.7, the number of circular mils in a copper wire which would have a resistance of one ohm for one foot of length. One ampere through one ohm resistance loses one volt. To determine the size of wire necessary for carrying a given current a given distance in feet, multiply the number of feet by 2 to obtain the actual length of circuit, multiply this product by the constant 10.7 and it will give the circular mils necessary for one ohm re- sistance, multiply this by the amperes and it gives the circular mils necessary for the loss of one volt. Divide this last result by the volts lost and it gives the circular mils necessary. Hence the formula "A." By simply transposing the terms we obtain formula " B," which can be ueed to determine the volts lost in a given length of wire of certain size carrying a certain number of amperes. HANDBOOK ON ENGINEERING. 167 Again, by another change in the terms, we obtain formula " C," which shows the number of amperes which a wire of given size and length will carry at a given number of volts lost. Table No. 2 has been arranged for the purpose of saving time in the use of these formulae. It shows the result of Feet x 2 x 10.7 for various distances over which it may be desired to trans- mit current. A few examples will assist in showing the use of the formulas and tables. Suppose we wish to distribute 300 16 c. p. 3.5 watt lamps of 110 volts at a distance of 490 feet with a loss of 10 per cent. Using formula A, 490 feet x 2 x 10.7 (find it in table No. 2) = 10486. 300 lamps of 110 volts = 152.7 amperes. (See table No. 3 for amperes per lamp, and multiply by 300.) 10 per cent loss on 110 volt system = 12.22 volts. (See table No. 4.) 10486 x 152.7 amperes = 1601212 circ. mite. ^ 12.22 volts lost 131032 circ. mils. In our table it shows the size of wire for this number of circ. mils, to be 00. To check this and determine exactly the volts lost in this cir- cuit by using No. 00 wire, use formula B, as follows: 10,486 x 152.7 amperes = 1601212 ~- 133079 circ. mils. = 12.03 volts lost. Suppose it is desired to distribute 1,000 lamps at a distance of 1950 feet by 3-wire system, viz., 220 volts, with a loss of 10 per cent. Using formula A, 1950 feet x 2 x 10.7 (see table) = 41730. 1000 lamps on 220 volt system = 291 amperes. (See table No. 5 for amperes per lamp, and multiply by 1000.) 168 HANDBOOK ON ENGINEERING. 10 per cent on 220 volt system = 24. 44 volts lost. (See table No. 4.) 41730 x 291 amperes = 12143430-:- 24.44 volts lost = 496867 circ. mils. 500000 circ. mils, the nearest commercial size, should be used. , Check this as before by formula B. 41730 x 291 amperes = 12 143430 -^-500000 circ. mils = 24.29 volts lost. Suppose we wish to deliver 100 h. p. to a 500 volt motor, at a distance of 4850 feet with 10 per cent loss : Again using formula A, 4850 feet x 2 x 10.7 = 103790. 100 h. p. at 500 volts = 160 amperes. (See table No. 3.) 10 per cent loss on 500 volts system = 55. 5 volts. (See table No. 4.) 103790 x 160. amperes = 16606400 -j- 55.5 volts = 299215 circ. mils. 300000 circ. mils, cable should be used. Check this as before by formula B. 103790 x 160 amperes = 16606400 -*- 300000 circ. mils = 55.35 volts lost. To ascertain how many amperes could be carried to a distance of 4850 feet with 500 volts with 10 per cent loss, use formula C : 4850 feet x 2 x 10.7 = 103790. 10 per cent loss on 500 volts system = 55.5 volts. 300000 circ. mils x 55.5 volts lost -~- 103790 = 160.42 am- peres, which as will appear by reference to table No. 3, will permit the use of 100 h. p. motor. HANDBOOK ON ENGINEERING. 169 Amperes per Motor, TABLE No. 8. H. P. Per Cent Efficiency Watts. VOLTS. 110 115 120 1 65 860 7.82 7.48 7.17 65 1148 10.4 9.98 9.57 2 65 2295 20.8 200 19.1 24 75 2487 22 6 21.6 20.7 $4 75 3480 31.6 30.3 29.0 5 80 4662 42 4 40.5 388 ft 80 6994 63 6 60.8 58.3 10 85 8776 79.8 76.3 73.1 15 85 13165 120. 114. 110. 20 90 16578 151. 144. 138. 25 90 20722 188. 180.. 173. 30 90 24867 2^6. 216. 207. 40 90 33155 301. 288. 276. 50 90 41444 377. 360. 345. 70 90 58022 528. 505. 484. 90 90 74600 678. 649. 622. 100 93 80215 729. 697. 668. 125 93 100269 912. 872. 836. 150 93 120323 1094. 1046. 1003. The above table is arranged to show the amperes per motor at dif- ferent voltages for several sizes of motors at efficiencies obtained in ordinary practice. 170 HANDBOOK ON ENGINEERING. Amperes per Motor. TABLE No. 8. VOLTS. 125 220 250 500 525 550 6.88 3.91 3.44 1.72 1.64 1.56 9.18 5.22 4.59 2.30 2.19 2.09 18.4 10.4 9.18 4.59 4.37 4.17 19.9 11.3 9.95 4.97 4.74 4.52 27.8 16.8 13.9 6.96 6.63 6.33 37.3 21.2 18.6 9.32 8.88 8.48 56.0 31.8 28.0 14.0 13.3 12.7 70.2 39.9 35.1 17.6 16.7 16.0 105. 59.8 52.6 26.3 25.1 23.9 133. 75.4 66.3 33.2 31.6 30.1 166. 94.2 82.9 41.4 39.5 37.7 199. 113. 99.4 49.7 47.4 45.2 265. 151. 133. 66.3 63.2 60.3 332. 188. 166. 82.9 79.0 75.4 464. 264. 232. 116. 111. 106. 597. 339. 298. 149. 142. 136. 642. 365. 321. 160. 153. 146. 802. 456. 401. 200. 191. 182. 963. 547.. 481. 241. 229. 219. The above table is arranged to show the amperes per motor at different voltages for several sizes of motors at efficiencies obtained in ordinary practice. HANDBOOK ON ENGINEERING. 171 Volts Lost at Different Per Cent Drop. Voltage at Lamp or Distribution Point, Top Row. TABLE No. 4. VOLTS 52 75 ICO 110 220 400 i% .261 .376 .502 .552 1.10 2.01 \% .525 .757 1.01 1.11 2.22 4.04 \l% .787 1-14 1.52 1.67 3.35 6.09 2% 1.06 1.53 2.04 2.24 4.48 8-16 H% 1.33 1.92 2.56 2.82 5.64 10.25 3% 1.61 2.31 3.09 3.40 6.80 12.37 4% 2.16 3.12 4 = 16 4.58 9.16 16.06 5% 2.73 3.94 5.26 5.78 11.57 21.05 K% 3.31 4.78 6.38 7.02 14.04 25.53 7% 3.91 5.G4 7.52 8.27 16.55 30.10 Z% 4.52 6o52 8.69 9.56 19.13 34.78 3% 5.14 7o41 9.89 10.87 21.75 39.56 10% 5.77 8o33 11.11 12.22 24.44 44.44 12% 7.09 10.22 13.63 14o99 29.99 54.54 13% 7.76 11.10 14.04 16.43 32.87 59.76 U% 8.46 12.20 16.27 17.90 35.81 65.1 15% 9.17 13.23 17.64 19.41 38.82 70.5 20% 13. 18.75 25. 27.50 55. 100. 25% 17.33 25. 33.33 36.66 73.33 133. The above table shows the loss in voltage between dynamos and distribution point at different per cents and for various voltages. 172 HANDBOOK ON ENGINEERING. Volts Lost at Different Per Cent Drop. Voltage at Lamp or Distribution Point, Top Row. TABLE No. 4. 500 600 800 1000 1200 2000 2.51 3 01 4.02 5 02 6.03 10.05 5 05 6.66 8.08 10.10 12.12 20.2 7.61 9.13 12.1 152 18.2 30.4 10 2 12.2 16.3 20 4 24.4 40.8 12 8 15 3 20.5 25.6 30.7 51.2 15.4 18.5 24.7 30.9 37.1 61.8 20.8 24.9 33.3 41.6 49 9 83.3 26.3 31.5 42.1 52.6 63.1 105. 31.9 38.2 - 51. 63.8 76.5 127. 37.6 45.1 60.2 752 90.3 150. 43.4 52.1 69.5 86.9 104. 173. 49.4 59.3 79.1 98.9 118. 197. 55.5 66.6 88.8 111. 133. 222. 61.7 74.1 98 8 123. 148. 247. 68.1 81.8 109. 136. 163. 272. 74.7 89.6 119. 149. 179. 298. 81.3 97.6 130. 162. 195. 325. 88.2 105. 141. 176. 211. 352. 125. 150. 200. 250. 300. 400. 166. 200. 266. 333. 400. 606. By adding the volts given .in the table to the voltage at motor or lamp the result shows the voltage necessary at dynamo for voltage required at point of distribution. HANDBOOK ON ENGINEERING. 173 H J I 03 +3 ,0 3 - $1 19 -8 I 8 ffl * bD O rt Cs! +J ' 3 d a 03 o ^ S a SH "IT; b a o a M & 1 h i d B! 03 O ^ 03 S 9 /-> .?* p, C .2 03 -1-3 OP 03 f3 en 3 0^ s. = l y ^ a . s 03 P O rO ^ D A S 03 | g 9 f, 1 O O t! a * 4 I" * d 03 03 <^ bo ^ ^ J3 3 s s-^ ^ ' * ^ ^ 03 O3 O? bD 40 S d 53 03 ill 52 fl "^ 03 oo rS *3 ^ 2 g o 3 <" 02 d ^ a 'E * 8 I 2 1 'O fe 03 i| r^ W fe a> O S T! ^ ci d 1 - g oi C3 ^ O ^' o 53 21 5 * cT |H|| -^ c3 O H k c3 .S be 03 II & .2 ^ d) S 3 8 3 03 .2 a 2 1 "S o S ?P3 O -i 03 s a >> l> * eo t- t- eo o eo >0 5 O CO ^H O 1-4 I-l i W W a S s . ci s> o Th QO CO 3S> O O CO O t^. -H <* t CC O O > 1 i i i N SJ CQ i> 41 T*I O 00 O 1 O5 O O O >-i i-t i-H 5 o "* iC >J ^^ CO ?D *M ^ CO C5 O CO 00 r- 1 i 1 N CO " ^5 Volts. >o cc >C 00 Ci O * 00 10 CO CO cq co 10 o t- o I ( co O W * O >! C5 1C O5 3 iQ O5 t^ 00 CO 00 t- <> co co t^ o r^ (M CO >O ^C 00 O 1 CO I ~ l * O CO 00 00 l^ SO O * CO Oi !> C5 -H 1^5 cq O ^f IM CM CO W5 t" OO i g CO o 2 00 O 3 O * 01 "* -^ CD M -f OS t^ O5 O O OS ^^ OD CO ~ CD CO CO * ?O CD b- (M IO 00 ^ ",_;_; _i c CO O * >O OS 1 ^ OS CO ^ rH^H * O OO O (M CO CO 00 (M CO OS ^ i-l -H r~l CM CD O CM O OO * >O b r-l ^ CO (M O CO i-t .-H i-( & oooooo QO O CD O * W i-H >-i M Tr*J g O Q M fl is III "j5 s5 S .0 fl-^ K js a -so || K 0} P w 3 o o * o MCO CQ 00 cj o S3 ^SoS ;_, to 22 000000 46 000000 00000 .43 .45 00000 0000 ".'46'" i454 .393 .4 .4 0000 000 .40964 .425 .362 .36 .372 '...... 000 00 .3648 .38 .331 .33 .348 00 .32495 .34 .307 .305 .324 o 1 .2893 .3 .283 .285 .3 1 2 .25763 .284 .263 .265 .276 2 3 22942 .259 .244 .245 .252 3 4 .20431 .238 .225 .225 .232 4 5 .18194 .22 .207 .205 .212 5 6 .16202 .203 .192 .19 .192 6 7 .14428 .18 .177 .175 .176 7 8 .12849 .165 .162 .16 .16 8 9 .11443 .148 .148 .145 .144 . . . . 9 10 .10189 .134 .135 .13 .128 10 11 .090742 . .12 .12 .1175 .116 11 12 .080808 .Ki9 .105 .105 104 ]2 13 .071961 .095 .092 .0925 .092 13 14 .064084 .083 .08 .08 .08 '"oss"" 14 15 .057068 .072 .072 .07 .072 .072 15 16 .05082 .065 .063 .061 .064 .065 16 17 .045257 .058 .054 .0525 .056 .058 17 18 .040303 .049 .047 .045 .048 .049 18 19 .03589 .042 .041 .039 .04 .04 19 20 .031961 .035 .035 .034 .036 .035 20 21 .028462 .032 .032 .03 .032 0315 21 22 .025347 .028 .028 .27 .028 .0295 22 23 .022571 .025 .025 .024 .024 .027 23 24 .0201 .022 .023 .0215 .022 .025 24 25 .0179 .02 .02 .019 .02 .023 25 26 .01594 .018 .018 .018 .018 .0205 26 27 .014195 .016 .017 .017 .0164 .01875 27 28 .012641 .014 .016 .016 .0148 .0165 28 29 .011257 .013 .015 .015 .0136 .0155 29 30 .010025 .012 .014 .014 .0124 .01375 30 31 .008928 .01 .0135 .013 .0116 .01225 31 32 .00795 .009 .013 .012 .0108 .01125 32 33 .00708 .008 .011 .011 .01 .01025 33 34 .006304 .007 .01 .01 .0092 .0095 34 35 .005614 .005 .0095 .009 .0084 .009 35 36 .005 .004 .009 .008 .0076 .0075 36 37 .004453 .0085 .00725 .0068 .0065 37 38 .C039b5 .008 .0065 .006 .00575 38 39 .003531 .0075 .00575 .0052 .005 39 40 .003144 .007 .005 .0048 0045 40 176 HANDBOOK ON ENGINEERING. Weather proof in- sulation. punoj J9d 399^1 g g punoj jod 590 j gaj Weather proof In sulation. J9d spunoj aad spunoj ootoc-i *o^ 10001 000 t-cc^ aocra -*' co*^sD *-*oo "* MCC'?! Otn J9d spunoj CCtM 1-I o -H CD.- 1C '-"- -I o >!< 99 k * ooo'l aad spunoj Safe Carryin Capacity in Amperes. ?! 1 C> (M O US 5O -H O M 1 ift CO ci 'jo irt rj as !- co -^ CO C^ 2^ rl r- ( rH r^ 5fio.Av pa 1C -CO lO t -CM * .60 -(M rH-r-l I32 g8 S8 Sg g38 >O CDl^- -^ ei JO H< OCO HANDBOOK ON ENGINEERING. 177 THE STEAM ENGINE. CHAPTER XI. THE SELECTION OF AN ENGINE. There are so many conflicting statements in regard to the merits and demerits of the several engines placed in the market that one is often confused in judgment, and scarcely knows how to proceed in the matter of selection, It is easy to advise that ' ' When you are ready to buy, select the best engine, for in the long run the best is the cheapest." No one would pretend to deny this as a general rule, yet there are circumstances which so materially modify this rule that it would seem to a casual observer to be entirely set aside. There are localities in which the price of fuel is so low that it scarcely war- rants the doubling of the price on an engine to save it ; and in such localities the owners usually want an engine of the very simplest construction ; hence, they almost invariably select an ordinary slide valve engine with a throttling governor. This selection is made for several reasons, among which are low first cost, simple in detail, remoteness from the manufacturer or from repair shops. For small powers in which it is desirable that the investment be as low as consistent with commercial success, the engine selected should be fitted with a common slide valve ; this will in general apply to all engines having cylinders eight inches or less in diameter. If upon a thorough canvass of the situation, it then be thought advisable to employ an automatic cut-off engine, the next ques- tion would probably be whether it shall be fitted with a positive, or some one of the various ' ' drop ' ' movements now in the market. 12 178 HANDBOOK ON ENGINEERING. For the smaller sizes, say 8 to 24 inches diameter of cylinder, it will perhaps be found more desirable to use an automatic slide cut-off, of which there are now several varieties offered through the trade. This style of engine has the advantage of being low- priced, efficient and economical. Small engines are usually required to run at pretty high speed ; there is a very decided advantage in this on the score of economy, as a small engine running at a quick speed will be quite as efficient as a large engine running at a slow speed, with the further advantage that the former will not cost in original outlay more than about two-thirds of the latter, while the cost of operat- ing will be no greater per indicated horse power. The slide valve is still used to the almost total exclusion of all other kinds in locomotives. It is doubtful whether a better valve for that particular use can be devised. It is simple, efficient, and readily obeys the action of the link when controlled or adjusted by the engineer. For. portable engines and the smaller stationary engines it leaves little to be desired in point of simplicity. One objection to a slide valve is that it cannot readily be made to cut off steam at, say, half-stroke or less, without interfering with the exhaust. In ordinary practice | to -| seems to be where most slide valves cut off as a minimum, perhaps J would repre- sent nearer the actual average conditions. It can easily be shown that this is very wasteful of steam, and consequently not economical in fuel ; but as there are cases in which the loss in fuel is fully gained by other advantages, the ordinary slide valve will, in all probability, continue to be used. High speed engines* The general tendency seems now to be in the direction of a horizontal engine with a stroke of medium length having a rapid piston speed and a rapid rotation of crank shaft, rather than a longer stroke with a less rate of revolution. This rapid movement of piston and crank shaft permits the use of HANDBOOK ON ENGINEERING. 179 small fly-wheels and driving pulleys, and thus very materially reduces the cost of an engine for a given power. To illustrate this, it may be said that a 16x48 inch engine using steam at 80 Ibs. pressure and cutting off J stroke, running at the rate of 60 revolutions per minute, may be replaced by an engine having a 13 x 24 inch cylinder, running at the rate of 200 strokes per minute, the pressure of steam and point of cut- ting off remaining the same, both engines being non-condensing, and representing the best example's of their kind. The differ- ence between 60 and 200 revolutions per minute in millwright work is very great, but there is a constantly growing demand for an engine which shall meet such a requirement whenever it shall present itself ; by this is not to be understood an engine which shall be used at either speed indiscriminately, but rather a type of engine which shall be economical in fuel, and shall be of a kind by which the rate of revolution may be such as to suit the millwright's work without loss of economy in working, and with- out excessive outlay for the engine itself in proportion to power developed. Slow speed engines are designed and built from a standpoint entirely different from that of high speed engines ; in the former case the reciprocating parts are made as light as possible, con- sistent with safety. The fly wheel is large in diameter and made with a very heavy rim, especially is this the case with auto- matic cut-off engines of long stroke and slow revolution of crank shaft. In high speed engines the reciprocating parts are often of great weight, in order to insure the utmost smoothness of running. The piston and cross-head are made of unusual weight that at the beginning of the stroke they may require a large part of the steam pressure to set them in motion ; this absorbing of power at the beginning of the stroke is for the purpose of temporarily storing it up in the reciprocating parts that it may be given off at the 180 HANDBOOK ON ENGINEERING. later portions of the stroke, by imparting their momentum to the crank ; thus at the beginning of the stroke, these reciprocating parts act as a temporary resistance, but once in motion they tend by their inertia to equalize the pressure on the crank pin, and so produce not only smooth running, but a very uniform motion. Results to be obtained in practice* The best automatic non- condensing engines furnish an indicated horse power for about three pounds of good coal^ depending somewhat upon the fitness of the engine for the work and the quality of the coal. With a condenser attached, a consumption as low as two pounds has been reported, but this is an exceptional result, 2 J pounds may be quoted as good practice. The larger the engine the better the showing, as compared with smaller engines. For ordinary slide valve engines, the coal burned per indicated horse power will vary from 9 to 12 Ibs., for the sake of illustra- tion, we will say 10 Ibs., and that the engine is of such size as would require for a year's run S3, 000 worth of coal; now, an ordinary adjustable cut-off engine with throttling governor, ought to save at least half that amount of coal, or say $1,500 per year ; if the best automatic engine were employed using 21 Ibs. of coal per horse power, a further saving of $750 per year could be effected, or between the two extremes $2,250 per year in saving of coal, without interfering in any way with the power, with the exception, perhaps, that the automatic engine will furnish a better power than the former engine. It is easy to see that it is true economy to buy the best engine and pay the extra cost of con- struction, if the saving of fuel is an element entering into the question of selection. The cost of an engine for any particular service is always to be taken into consideration, for it is possible to contract for a certain saving of coal at too high a price, not simply when paid out as the .original purchase money, but with this economy of fuel, the purchaser may have many vexatious and damaging HANDBOOK ON ENGINEERING. 181 delays caused by the breaking of the automatic mechanism of the engine. All such delays which would not have occurred to an ordinary or simpler engine, are to be charged against any saving credited to the engine which failed in producing a regular and constant power. Take a flouring mill for example, producing 400 barrels per day ; it is easy to see how a single day's stoppage would interfere with the trade and shipment by the proprieters, yet it would require a very small break in an engine that would require less than a day for repairs. This does not argue against high grade engines, but the pur- chaser should be certain that the engine when once on its founda- tions shall be as free from dangers of this kind as any other engine of similar economy. There are engines which from their peculiar construction appear to be very complex, and this objection is often urged against them, while the fact is the complexity is apparent rather than real. Take the Corliss engine, for example; it is doubtful whether there is another automatic cut-off engine in successful use in this or any other country which has cost less for repairs during the last ten or twenty years. It is true it contains a great many separate pieces in the valve mechanism, but the pieces themselves are simple, durable, easily accessible and always in sight. These several parts are not liable to excessive wear, but such as there is can lie readily adjusted. The engines to be preferred are those in which the valve ad justing mechanism is outside of the steam chest and which is in plain sight at all times when the engine is in motion. Location of engine. This will depend upon circumstances, but it is far from true economy to place an engine in a dark cellar, or in some inconvenient place above ground. The engine as the prime mover, should have all the care and attention which may be needed to insure regular and efficient working. Machinery in the dark is almost sure to be neglected. If the 182 HANDBOOK ON ENGINEERING. design of the building, or the nature of the business, is such that the engine must be located underground, there should be some provision for letting in the daylight ; the extra expense incurred will soon be saved by the order, cleanliness and fewer repairs required, following neglect. The engine should always be close to, but not in the boiler room. Many a high-priced engine has had its days of usefulness shortened by the abrasive action of fine ashes and coal dust coming in contact with the wearing surfaces. There should always be a wall or tight partition between the engine and fire room. The foundations for an engine should be large and deep. Too many manufacturers in marking dimensions of foundation drawings for engines, make them altogether too shallow. The stability of an engine depends more on the depth than on the breadth of the foundations. Stone should be used for founda- tions rather than brick, but if the latter must be used they should be hard burned and laid in a good cement rather than a lime mortar. If the bottom of the pit dug for the engine foundation be wet, or the soil uncertain in its stability, it is a good plan to make a solid concrete block about a foot and a half thick, on which the foundation may be continued to the top. If such a concrete block be made with the right kind of cement it will be almost as hard and solid as a whole stone. The most economical engine is the one in which high pressure steam can be used during such portion of the stroke as may be necessary, then quickly cut off by a valve which shall not inter- fere with the exhaust at the opposite end of the cylinder, and allow the steam to expand in the cylinder to a pressure which shall not fall below that necessary to overcome the back pressure on the piston. In general, the most successful cut-off engines use the boiler pressure for a distance of one-fifth to three-eighths of the stroke from the beginning ; at this point the steam is cut off and allowed to expand throughout the balance of the stroke. HANDBOOK ON ENGINEERING. 183 The gain by expansion consists in the admission of steam at a pressure much above the average required to do the work, and allowing it to follow but a small portion of the stroke, then ex- panding to a lower than the average pressure at the end of the stroke. The mean effective pressure on the piston is that by which the power of the engine is measured ; hence, it follows that the higher economy is to be reached, other things being equal, where the mean effective pressure on the piston is highest when com- pared with the terminal pressure, or the pressure at the end of the stroke. In order to get this, a high initial pressure is used ; the steam follows as short a distance as possible to keep the motion regular under a load, and then expanding down to as near the atmospheric pressure as possible. The following table exhibits at a glance the performance of a non-condensing engine cutting off at different portions of the stroke. The initial pressure of steam being in each case eighty pounds per square inch. CUT-OFF IN PARTS OF THE STROKE. 1 2 3 4 5 10 10 10 10 10 Mean effective pressure . 18 35 48 57 65 Terminal pressure . . . 11 20 30 39 48 Pounds water, per h'r per H. P 20 21 22 23 25 Fractions are omitted in the above table and the nearest whole number given. Governor* Any automatic device by which the speed of an engine is controlled may properly be called a governor. There 184 HANDBOOK ON ENGINEERING. are now two distinct methods by which the steam supplied to an engine is thus brought under control. The first is usually applied to slide valve engines having a fixed cut-off, and consists in the adjustment of a valve by which the pressure of steam in the cylinder is increased or diminished in order to maintain a con- stant rate of revolution with a variable load. The second device consists in a mechanism by which the whole boiler pressure is admitted to the cylinder, which is allowed to follow the piston to such portion of the stroke as will maintain a regular rate of revo- lution ; the steam is then suddenly cut off at each half revolution of the engine, thus furnishing a greater or less volume of steam at a constant pressure. Neither of these two varieties of governors will act until a change in the rate of revolution of the engine occurs, and this change will either admit more or less steam as it is faster or slower than that for which the governor is adjusted. The commonest form of a governor consists of a vertical shaft to which are hinged two arms containing at their lower ends a ball of cast iron ; as the shaft revolves the balls are carried outward by the action of what is commonly called centrifugal force ; the greater the rate of revolution the further will the balls be carried outward ; advantage is taken of this property to regulate the ad- mission of steam to the engine. The action of the balls and that of the valve include two distinct principles and should be consid- ered separately ; an excellent valve may be manipulated by an indifferent governor and so produce unsatisfactory results ; on the other hand, the governor mechanism may be satisfactory in its operation, but being connected with a valve not properly balanced, is likely to cause a variable rate of revolution in the engine. Fly- wheel. The object in attaching a fly-wheel to an engine is to act as a moderator of speed. The action of the steam in the cylinder is variable throughout the stroke, against which the rev- olution of a heavy wheel acts as a constant resistance and limits the variations in speed by absorbing the surplus power of the first HANDBOOK ON ENGINEERING. 185 portion of the stroke, and giving it out during the latter portion. The fly-wheel is simply a reservoir of power, it neither creates 1101* destroys it, and the only reason why it is attached to an engine is to simply regulate the speed between certain permitted variations which are necessary to cause the governor to act, and to equalize the rate of revolution for all portions of the stroke, thus convert- ing a variable reciprocating power into a constant rotary one. It is considered good practice to make the diameter of the fly-wheel four times the length of the stroke for ordinary engines, in which the stroke is equal to twice the diameter of the cylinder. This may be taken as a fair proportion in engine building, and furnishes a wheel sufficiently large to equalize the strain and reduce any variation in speed to within very narrow limits, if the engine is supplied with a proper governor. The greater the number of revolutions at which the engine runs, the smaller in diameter may be the fly-wheel, and it may also be largely reduced in weight for engines developing the same power. Horse-power* By this term is meant 33,000 pounds raised one foot high in one minute. The horse-power of an engine may be found by multiplying the area of the piston in square inches by the mean effective pressure ; this will give the total pressure on the piston ; multiply this total pressure by the length of the stroke of the piston in feet ; this will give the work done in one stroke of the piston ; multiply this product by the number of strokes the piston makes per minute, which will give the total work done by the steam in one minute ; to get the horse-power, divide this last product by 33,000. From this deduct, say, 20 per cent, for various losses, such as friction, con- densation, leakage, etc. CARE AND MANAGEHENT OF A STEAM ENGINE. It is to be supposed to begin with that the engine is correctly designed and well made, and that, after a suitable selection of an 186 HANDBOOK ON ENGINEERING. engine for the work to be done, nothing now remains except proper care and management. Lubrication* The first and all-important thing in regard to keeping an engine in good working order is to see that it is properly lubricated. This does not imply, neither is it intended to encourage, the use of oil to excess ; all that is needed is simply a film of oil between the wearing surfaces. It is marvelous how small a quantity of oil is required when of good quality and con- tinuously applied. There are several self -feeding lubricators in the market which have been tested for years and are a pronounced success ; these include crank-pin oilers, in which the oscillatory motion of the oil makes a very efficient self -feeding device, the flow being regulated by means of an adjustable opening to the crank-pin, or in the adjustment of a valve by which its lift is reg- ulated by each throw of the crank ; and in others by a continual flow through a suitable tube containing a wick or other porous substance. For stationary engines, it is desirable that the main body of the oiler be made of glass that the flow of oil may be closely watched and adjusted accordingly. For the reciprocating and rotary parts of the engine $ a modification of the above men- tioned oilers may be used. They are of various patterns and devices and many of them very good. It is also a good plan to have some device by which the cross-head at each end of each stroke will take up and carry with it a certain amount of oil ; for the lower half of the slide this is not difficult to arrange ; for the upper side an automatic feeder placed in the middle of the slides will provide ample lubrication. For oiling the main bearing there should be two separate devices, one an automatic glass oiler ; and in addition, a large tallow cup attached to the cap of the bearing. This cup should be filled with tallow mixed with powdered plumbago ; the open- ings from the bottom of the cup to the shaft should be not less than quarter-inch for small engines, and three-eighths to half -inch HANDBOOK ON ENGINEERING. 187 for larger ones ; so long as the main bearing runs cool the tallow will remain in the cup unmelted ; but if heating begins, the tallow will melt and run down on the surface of the revolving shaft, and thus provide an efficient remedy when needed. For oiling the valves and piston, a self -feeding lubricator should be attached to the steam pipe ; this by a continuous flow of oil will be found not only satisfactory in its practical working, but economical in the use of oil. In selecting 1 an oil for an engine, it is in general better to use a mineral rather than an animal oil, especially for use in the valve chest and cylinder. The objection to an animal oil, and espe- cially to tallow or suet, is that it decomposes by the action of heat, often coating the surface of the steam chest, the piston ends and the cylinder heads with a deposit of hard fatty matter ; or forms into small balls not unlike shoemaker's wax. There is no such decomposition and formation in connection with mineral oils, which may now be had of uniform quality and consistency, and at much lower prices than animal oils. The slide valve should be kept properly set and should be examined occasionally to see that the face and seat are in good condition. So long as this is the case, the valve mechanism and the valve itself must be let alone and not tampered with. The piston packing" will need looking after occasionally to see that it does not gum up and stick fast, which it is very likely to do when the cylinder is lubricated with tallow or animal oil. The rings should fit the cylinder snugly and should be under as little tension as possible and insure perfect contact. If the rings are set out too tight they are liable to scratch or cut the cylinder ; if too loose, the steam will blow through from one end of the cylinder, past the piston and into the other. In adjusting the springs in the piston, care must be exercised that the adjust- ments are such as will keep the piston rod exactly central, to prevent springing the rod, or causing excessive wear on the stuf- 188 HAND BOOK ON ENGINEERING. fing box. There are several packings which do not require this adjustment, the rings being narrow, and either expanding by their own tension or by means of springs underneath. The only thing to be done with such a packing is to keep it clean, and when lubricated with a mineral oil this is not a difficult matter. If it groans, take rings out and file sharp edges off. The stuffing boxes whether for the piston or valve-stem need to be looked after carefully, and to prevent leaking, will require tightening from time to time. There are several kinds of ready- made packings in the market, containing rubber, canvas, garlock, soapstone, asbestos and other substances which form the basis of a good durable packing. These can be had in sizes suitable for all ordinary purposes, and their use is recommended. In the absence of any of these, a packing made of clean manila or hemp fiber will serve a useful purpose. Formerly it was the only sub- stance used, but is being gradually superseded by the other kinds mentioned above. In packing the small and delicate parts, auch as a governor stem, a good packing is made by pleating together three or more strands of cotton candle-wick. This is soft, pliable, free from anything like grit, and will not get hard until soaked with grease and baked into a brittle fiberless substance not easily described. Crank-pins. There are few things more troublesome to an engineer than a hot crank-pin, and it is sometimes very difficult to get at the real reason why it heats. Among the principal rea- sons for heating are: the main shaft is not " square " with the engine, or, that the pin is not properly iitted to the crank ; or, perhaps, it is too small in diameter defects which are to be remedied as soon as practicable. Heating is often caused by the boxes being keyed too tightly, or by insufficient lubrication. There are now several good self -feeding lubricators in the market which will supply the oil to a crank-pin continuously ; these are recommended rather than the old style of oil cup, which way HANDBOOK ON ENGINEERING. 189 not only uncertain, but doubtful in its action. Many trouble- some crank-pins have been cured of heating by this simple matter of constant lubrication. When the crank-pin is rather small for the engine and the load variable, there is a possibility of having a hot pin at any time ; it is advisable to have ready some simple and effective expedient to be applied when it does occur ; for this there is perhaps nothing better and safer than a mixture of good lard oil and sulphur. Connecting rod brasses. -In quick running engines the brasses should be litted metal to metal ; or, if this is not desir- able, several strips of tin or sheet brass should be inserted be- tween them and keyed up tight. This gives a rigidity to a joint which is difficult to secure when the brasses have a certain amount of play in the strap. It is a common practice to bore the brasses slightly larger than the pin, so that when fitted to it the hole shall be slightly oval, and thus permit a freer lubrica- tion than is secured by a close fit around the whole circum- ference. Knocking. There are several causes which, combined or singly, tend to produce knocking in steam engines. In most cases the, difficulty will be found to be in the connecting rod brasses ; but whether in the crank-pin end or at the cross-head is not easily determined in all cases. A very slight motion will often produce a very disagreeable noise ; the remedy is, in most cases, very simple, and consists in simply tightening the brasses by means of the key or other device that may have been pro- vided for their adjustment. In adjusting a key it is the common practice to drive it down as far as it will go, marking with a knife blade the upper edge of the strap, then drive the key back until it is loose ; after which drive it down again, until the line scratched on the key is within J or 1 inch of the top of the strap. The size of the strap joint and the judgment of the per- son in charge must decide the best distance. This may be done 190 HANDBOOK ON ENGINEERING. at both ends of the connecting rod. On starting the engine, the cross-head and crank-pin must be carefully watched, and upon the slightest indication of heating, the engine should be stopped and the key driven back a little further. A slight warmth is not particularly objectionable, and will, as a general thing, correct itself after a short run. Knocking is sometimes occasioned by a misfit, either in the piston, or cross-head and the piston rod. These connections should be carefully examined, and under no circumstances should lost motion be permitted at either end of the piston rod. If the means of securing are such that the person in charge can properly fasten the piston to the rod, he should see that it is kept tight ; if not, then it should be sent to the repair shop at once, as there is no telling when an accident is likely to overtake an engine with a loose piston. The connection between the piston-rod and cross-head is usu- ally fitted with a key -and furnishes a ready means of tightening the joint, if proper allowance has been made for the draft of the key. In case there has not, the piston-rod and cross-head should be filed out so that the draft of the key will insure a good tight joint when driven down. The main bearing should be examined and if there should be too much lateral movement of the shaft, the side boxes might then be adjusted until the shaft turns freely, but has no motion other than a rotary one. The cap to the main bearing should also be carefully examined, as it may need screwing down and thus prevent an upward movement of the shaft at each stroke ; this applies more particularly to quick running engines. Engines which have been in use for some time are likely to have a knock caused by the piston striking the head. This is brought about by having a very small clearance in the cylinder and in no^ providing, by suitable liners, for the wear of the connecting rod brasses, In a case of this kind, liners should be inserted behind HANDBOOK ON ENGINEERING. 191 the brasses in the connecting rod, or new brasses put in, which will restore the piston to its original position. Knocking 1 may be caused by defects in the construction of the engine ; such, for example, as not being in line, the crank-pin not at right angles to the crank, the shaft may be out of line, etc. Whenever the cause is one in which it can be shown that it is a constructive defect, there is but one remedy, and that is the re- placing of that part, or the assembling of the whole until perfect truth is had in alignment of all the parts. This will require the services of an experienced engineer but all improperly fitting pieces should be replaced by new ones as a safeguard against accident, which is likely sooner or later to overtake badly fitting pieces. If the boiler is furnishing wet steam, or priming, so as to force water into the steam pipe, it will collect in the cylinder and will not only cause knocking, but on account of its being practically incompressible there is danger of knocking out a cylinder head, bending the piston-rod, or doing other damage to the engine. The cylinder cocks should be opened to drain any collected water away from the cylinder. Repairs* Whenever it is necessary to make repairs the work should be done at once ; oftentimes a single day's delay will in- crease the extent and cost fourfold. If an engine is properly designed and built, the repairs required ought to be very trivial for the first few years it is run, if it has had proper care. It may be said in reply to this " true, but accidents will happen in spite of every care and precaution." That accidents do occur is true enough ; that they occur in spite of every care and precaution is not true. In almost every case, accidents may be traced directly back to either a want of care, negligence, or to a mistake. Fitting- slide-valves* -7" The practice of fitting a slide-valve to its seat by grinding both together with oil and emery, is wrong and should never be resorted to. The proper way to fit the sur- 192 HANDBOOK ON ENGINEERING. faces is by scraping ; this insures a more accurate bearing to begin with, and will also be entirely free from the fine grains of emery which find their way and become imbedded in the pores of the casting, and are thus liable to cut the valve face and destroy its accuracy. The scraping of the valve and seat has a beneficial effect by causing the removal of the fine particles of iron, which are loosened by the action of the cutting tool in the planing machine, and which ought to be fully removed before the engine leaves the manufacturers' hands. Aside from this, it is doubtful whether the scraping amounts to anything practically, for the reason that the cylinder and valve are fitted cold, and their relative positions are distorted by the action of the heat of the steam, once the engine is in use. The scraping which simply renders the valve face and seat smooth and hard is all that is sufficient to begin with, and may be re-scraped after the valve has been in use a few days, should it be found necessary, which will not often -be the case in small and ordinary sized engines. Eccentric straps are likely to need repairs as soon as any- thing about an engine. They should be carefully watched at all times. If they are likely to run hot, it is also probable there is more or less abrasion or cutting going on, and if prompt measures are not taken to arrest it r they are likely to cut fast to the eccentric, and a breakage is sure to occur. When the straps begin to heat, the bolts should be slackened a little, and at night, or perhaps at noon, the straps should be taken off and all cuttings carefully removed with a scraper (not with a file) ; the rough surfaces on the eccentric should be removed in the same manner. The straps should be run loose for a few days, gradually tightening as a good wearing surface is obtained. The main bearing, if neglected, is a very troublesome journal to keep in order. The repairs generally needed are those which HANDBOOK OX EXCJINKKKING. 11)3 attend overheating and cutting. The shaft, whenever possible, should be lifted out of the bearing, and both the shaft, bottom of main bearing and side boxes, carefully scraped and made perfectly smooth. It sometimes occurs that small beads of metal project above the surface of the shaft which are often so hard that neither a scraper nor file will remove them ; chipping is then resorted to and the fitting completed with a file and line emery cloth. Heating of journals* A very common cause for the heating of journals having brasses and boxes composed of two halves, is that both halves alter their shape from causes attending their wear. Thus, most engineers will have noticed that, although there is no wear between the sides of a brass and the jaws of a box, yet in time the brass becomes a loose fit in the box. Now, since the sides of the brass have, when fitted, no movement in the box, it is evident that this cannot have proceeded from wear be- tween those surfaces, and it remains to find what causes this looseness. Most engineers will also have observed that though the bottom or bedding surfaces of a brass .and of the box may have been carefully filed to fit each other when new, yet if in the course of time the brasses be taken out and examined, and more especially the bottom brass that receives the weight, the file marks will become effaced on all parts where the surfaces have bedded together well, the surface having a dull bronze and condensed appearance. This is caused by the vibrations under pressure hav- ing condensed the metal. Now, this condensation of the metal moves or stretches it, and causes the sides of the brass to move away from the sides of the box, and, consequently, to close upon the journal, creating excessive friction that may often, and very often does, cause heating. It is for this reason that on such brasses the sides of the brass boxes are, by a majority of engi- neers, eased away at and near the joint, and it follows from this cause the same easing away is a remedy. Governor* It not inf req uently occurs that after an ordinary 13 194 HANDBOOK ON ENGINEERING. throttling engine has been used a few years, the speed becomes variable to such a degree that it interferes with the proper run- ning of the machinery. This occurrence can generally be traced directly to the governor. When it does occur, the governor should be taken apart and thoroughly examined ; if the needed repairs are such as can be easily made in an ordinary repair shop, they should be made at once ; if not, a new governor should be purchased. The price of governors is now so low that it is better and more economical to buy a new one than lose the time and pay the bills for repairing an old one. AUTOMATIC ENGINES. In the care and management of this class of engines, it is diffi- cult to say just what particular attention they need, owing to the variety of styles and the peculiarities of each. As a rule, how- ever, they require first, to be kept well oiled ; second, to be kept clean ; third, to be kept well packed ; and fourth, to be let alone nights and Sundays. There is little doubt that there has been more direct loss resulting from a ceaseless tinkering with an engine than results from legitimate wear and tear to which the engine is subjected. The writer does not wish to be understood as saying that builders of this class of engines are infallible ; it might be difficult to prove any such assertion in case it was made ; but it may be said with truth, that the engines of this class now in the market are carefully designed, well proportioned, of good materials and workmanship, and as examples of mechanism are entitled to take very high rank. The writer knows of several engines of this class which have not cost their owners for repairs so much as five dollars in five years' constant use. It is essential to the economical working of these engines that the cut-oft' mechanism be in good order and properly adjusted. Whenever the valves need resetting, the final adjustment should be made HANDBOOK ON ENGINEERING. HIT) with a load on the engine and with the indicator attached to the cylinder, the valves being set by the card rather than by the eye. No general rule can be given for setting the valves, as the prac- tice varies with the size and speed of the engine ; nor is any rule needed, for the indicator will furnish all the data required. The adjustments may then be made so as to secure prompt admission, sharp cut-off, prompt release, and the proper compression. TO FIND THE DEAD CENTERS. When setting the valve of an engine by measuring the lead, as is the usual method, it is necessary that the crank be accurately placed on the dead centers at each end of the stroke. Sometimes an engineer, when adjusting the valves of his engine, will attempt to place the crank on the dead center by watching for the point at which the travel of the cross-head stops, or by the appearance of the connecting-rod as related to the crank. These methods are totally unreliable for obtaining accurate results, especially the first one mentioned. The travel of the cross-head and the piston near the point of reversal of motion is very slow when compared with the valve. The velocity of travel of the valve is at nearly its maximum amount when the crank is on the dead center, and a slight error in finding the dead center point makes a very appre- ciable error in the position of the valve, with a subsequent error in its proper setting. There are several methods for finding the dead center. The method that can be recommended and the one that should always be used when the dead center of an engine is to be found is that familiarly known as " tramming." The dead centers when found by this method, are geometrically accurate, no matter if the engine is out of level or if the shaft is above or below the axis of the cylinder. Some simple tools are required which are generally available, with the exception of the trams, which may be readily UN; HANDBOOK ON KN(J IX KK1JI N(I . made for the purpose. Two trams are required, one of which should be 6" or 7" long and the other about 24" or 30", as the condition may require. The smaller tram may be made of {" steel wire with the points turned over at right angles to the body, so as to project about 1". The points should be sharpened so that a hair line may be drawn by them. The larger tram should be made from rod of at least f " diameter and the points made in the same way as for the smaller tram. Oftentimes, the long tram Finding the Dead Center. is made with one leg longer than the other, on account of being handier to reach some stationary part, but this is a minor point, which has nothing to do with the principle to be described. The other tools required are a light hammer, a prick-punch, a pair of 10" or 12" wing dividers and a hermaphrodite caliper, or a scrib- ing block. A piece of chalk will also be found convenient to facilitate scribing lines on the metal parts with the trams or dividers. Having the necessary tools, we are ready to begin operations, you may start at either end of the stroke, as circumstances may favor. The fly-wheel is turned so that the crank stands at about the angle shown in the accompanying illustration, which HANDBOOK ON ENGINEERING. 1<>7 may, however, l>e approximated as the operator may desire. The effort made, being to give sweep enough to the cross-head to allow accurate measurements and still not have such an excessive arc on the fly-wheel as to make its bisection difficult. A prick mark is made on the guides, or some convenient sta- tionary point, as at /;?, and an arc struck on the cross-head with the small tram. At the same time, an arc is scribed on the rim of the fly-wheel at 6r, using some convenient point for the lower point of the tram as at K. The fly-wheel is now turned until the crank passes the center and the cross-head travels back until the scribed line will coincide exactly with the point of the tram when held in the same position as in the first case. When this point has been reached, the wheel is stopped and a second arc is scribed on the fly-wheel rim at F with the tram ,/. The herma- phrodite caliper, or the scribing block, is now used to scribe a concentric line I) E on the fly-wheel rim and the arc C F is bisected with the dividers. When the center // has been accur- ately located, it should be carefully prick-marked. The scribing of the concentric line D E is a refinement that is not strictly necessary if care be taken to locate the points of the dividers at the same distance from the outer periphery of the wheel in each instance when finding the center H. The marks left by the lathe tool will sometimes be plain enough for a guide. When the center H has been found, the fly-wheel is turned so that the point of the tram will fall into the prick-mark // when its lower end is in the stationary point K. When this condition is effected, the crank is exactly on the dead center and the position of the valve may be taken with confidence that its location at the dead center point is accurately found. The same procedure is followed to place the crank on the dead center at the opposite end of the stroke. The cut on page 198 is an elevation of Tandem Compound Engine, showing engine erected on brick foundation. It also shows a line through cylinders ; also a line over the shaft. 198 HANDBOOK ON ENGINEERING. HANDBOOK ON ENGINEEKING. These lines are used in the erection of a new engine, or to line up an old one, or with an engine that is out of line. The cut also shows how the foundation is made; also how the anchor bolt is fastened. The cut on page 200 shows how to pipe a Twin Tandem Compound Condensing Engine. The plan shows two receivers, heaters, relief valves, gate valves, etc., and is so arranged that either side can be run independently of the other. It also shows how to line a pair of these engines up by following the lines and noting the distance between each line. An engineer would have no trouble in lining up a pair of these engines. HOW TO LINE AN ENGINE. The method followed when lining different types of engines, such as vertical, horizontal, portable, etc. : The method followed in lining any piston engine is essentially the same in all cases, as far as determining when adjustments are needed. The method of making the adjustments after the char- acter and amount of them is determined, depends entirely on the construction of the engine, and will necessarily have to be deter- mined in each individual case. Lining an engine consists of ad- justing the guides so they shall be parallel to the bore of the cylinder, and in such a position that the center of the piston socket of the cross-head shall coincide with the axis of the cylin- der. Under these conditions only, can the piston and cross-head travel through the stroke freely, and without distorting any of the parts. After this adjustment has been made, the truth of the right-angle position of the shaft must be determined as being "out of square; "this will make an engine run badly, and is often the unsuspected cause of much trouble to engineers. We will assume that we have an engine with four-bar or locomotive guides, and that the connecting rod, cross-head, back cylinder 200 HANDBOOK ON ENGINEERING. rr HANDBOOK ON KNUINKKKING 201 head and piston have been removed. If the engine is of the horizontal type, the iirst step will properly be to ascertain if the engine is level on the foundation, and if not, proceed to make it so. After having leveled the engine, stretch a smooth linen line, as shown in Fig. 1, through the bore of the cylinder and the stuffing box, to a point beyond the shaft, where it should be attached to an iron rod driven into the floor. The other end is fastened to a cross-bar bolted across the face of the cylinder to fig. % two of the studs, as shown in Fig. 4, or the bar may preferably be somewhat longer than one-half of the diameter of the cylinder, and with a saw cut for a short distance lengthwise at the inner end. In this case, it is held by only one of the cylinder studs and can be somewhat more easily adjusted. The line or cord is adjusted to approximately the proper position, and is drawn taut and fastened through the cross-bar by being tied to a short stick that is too long to pass through the hole. In this position it is held by the friction, and can be readily adjusted to the required position. An assistant is required to move the line in the direc- tions indicated, as the work proceeds, and then you are ready to center it in the cylinder. The only tool required for this purpose is a light pine stick of slightly less length than the radius of the 202 HANDBOOK ON ENGINEERING. bore, and it should have an ordinary pin pushed into the head for a u feeler." Now adjust the line in the cylinder so that the head of the pin will just tick the line from four points of the counter- bore, which is always the part of the cylinder to work from, as it is not affected by the wear. The line should then be adjusted to the center of the other end of the cylinder, but not from the stuffing box, as this is likely to be out of center somewhat. Make the adjustment at this end from the counterbore, if pos- sible, the same as in the first instance, and then it will be neces- sary to try the position of the line in the back end of the cylinder, as the changes made at the other end will affect it slightly. After the line is truly centered, you are ready to adjust the guides. With some types of cross-heads, it is possible to use the cross- head for determining the proper location of the guides, but with the ordinary form, such as shown in Fig. 2, this cannot be done, but you will need a tool similar to that shown in Fig. 3, which consists simply of a piece of flat iron long enough to reach across the guides, and having a hole drilled and tapped in the center for the thumb-screw. This thumb-screw is adjusted so that its point is the same distance from the lower side of the bar, as the lower face of the wings of the cross-head are from the center of the piston socket. To find this distance, lay a straight edge across the end of the cross-head and draw the line A B, and then, hav- ing found the center of the hole, the measurement may be accur- ately taken. The lower guides are now adjusted by the tool, so that the point of the screw will tick the line throughout the length, and then the top guides are put in position with the cross- head in place and adjusted for a proper working fit. Before removing the line from the cylinder, however, the shaft should be tested for the truth of its right-angle position, which may be done by calipering between the crank disc and the line at the points H and 7. If the distances are equal, the shaft is square with the bore of the cylinder, providing, of course, that HANDBOOK ON ENGINEERING. 203 the disc is faced true with the slmft. If there is any doubt as to its accuracy, turn the shaft as nearly half way around as the crank-pin will admit without disturbing the line. Then caliper the distance of a point on the disc that will not be far removed from the first position, thus reducing the chance for error. If the shaft shows " out," move the outward bearing until the meas- urements show equal in both positions. The horizontal truth of the shaft can be found by laying a level on it, and if "out," raise or lower the out-board bearing until the level shows fair. Work of this kind requires skill and patience and belongs prop- erly to the sphere of the chief engineer. It requires a delicacy of touch and an appreciation of what is meant by close measurement that can come only through experience. In .centering the line, one should be able to detect when it is as little as T ^Q- of an inch out of center. A piece of ordinary tissue paper is about .00125 inch thick. A man should be able, therefore, to adjust a line so accurately that if the " feeler," with one or more pieces of the paper under it, just clips the line, it will miss the line when one thickness is removed. While it may not always be necessary to work as closely as this, a person cannot expect to line up engines successfully until he has a full knowledge of what this degree of accuracy means. 204 HANDBOOK ON ENGINEERING. HANDBOOK ON ENGINEERING. 205 CHAPTER XIa. DIRECTIONS FOR SETTING UP, ADJUSTING AND RUNNING THE IMPROVED CORLISS STEAM ENGINE. Location of foundation* The foundation must beat right angles with main line shaft. If main line shaft is not already in position, then foundation must be set by two points, located and connected with a line parallel with the buildings, and at right angles to an imaginary line through center of cylinder. Foundation plans should show all center lines. If a templet is furnished to locate the foundation accurately for the mason, the center line of engine cylinder and guides and right angle for crank center are drawn thereon. Cap Stones* Examine carefully the lap faces of cap stones and, if necessary, have them trimmed off by cutter or mason, so that each is true and level, and in exactly the plane shown in formation plan. Cylinders and frame* Put engine cylinder and frame in position and bolt them together. Lining off crank shaft and out-end bearing* Stretch a line at right angles to main center line, through main bearing to represent center line of crank shaft. See that this line is exactly in the center and level. By this line place out-end bearing square and true. Put crank shaft in its bearings after bottom box has been placed in main bearings. Insert quarter boxes and adjusting wedges into main bearing and put cap on. To ascertain that shaft is at exact right angles to main center line, turn engine shaft until the crank pin comes nearly to the main 206 HANDBOOK ON ENGINEERING. center line, then with a pair of calipers, or rule, measure from shoulder of crank-pin to line, and after noting this distance, turn the crank back towards opposite center until pin is in same relative position to line, and measure again. If both measurements do not correspond, out-end bearing must be moved either way as required, until measurements show equal. Then take up slack around shaft in main bearing, being careful not to force the adjusting wedge too tight. Fly- wheels. The fly-wheel is next placed on shaft and firmly keyed in position. Placing valve gear. Steam and exhaust valve covers or bon- nets on valve gear side are next bolted to place, taking care that no dirt or foreign substance gets between the surface underneath the covers. Valve stems are inserted from opposite or front of cylinder and the valves put in after them, the F head of valve stem entering slot in valve. Couple up all valve gear parts, i. e., disc plate, valve-stem cranks, valve-connecting rods, dash pots and dash-pot rods, valve-rod rocker, eccentric and straps on crank-shaft, first and second eccentric rods. The dash pots should be thoroughly cleaned and oiled before putting in place. ADJUSTMENT OF CORLISS VALVE GEAR WITH SINGLE AND DOUBLE ECCENTRICS. A brief description of the essential parts of the Corliss engine valve gear will assist in obtaining a clear conception of the subject. When a single eccentric drives both steam and exhaust valves the range of cut-off is limited to about half the piston stroke. This will become obvious by considering the following necessary conditions : HANDBOOK ON ENGINEERING. 207 After the eccentric has reached the extreme of its throw as shown in Fig. 2 in either direction all valve gear motions are reversed . Fig. 2. The steam valve must be released before the eccentric motion is reversed, for if the hook does not strike the knock-off cam during its forward motion, it cannot strike it during its return motion. The maximum exhaust opening, or the middle of the exhaust period, must occur when the eccentric is at the extreme of its throw as in Fig. 2. Now, in order to release the expanded steam in the cylinder before the commencement of the return stroke and to secure the exhaust closure a little before the end of the return stroke, the middle of the exhaust period or the extreme of the eccentric throw must evidently occur before the middle of the return stroke, and, therefore, the extreme throw of the eccentric in the opposite direction must occur before the middle of the forward stroke, and the valve must be released before this point is reached if released at all. It will be understood from the foregoing that late release and late exhaust closures are conditions imposed by the single eccentric valve gear, and these conditions agree very well with moderate rotative speed ; but at higher speed earlier release and 208 HANDBOOK ON ENGINEERING. more compression may be required. This may be effected by moving the eccentric forward on the shaft, but the reversing of the steam valve motion would then occur at an earlier stage of the forward stroke and the range of cut-off would be correspond- ingly shortened. Earlier exhaust closure could be had by giving the exhaust valve more lap, but this would involve a later release of the expanded steam at the end of the stroke. On the other hand, shortening the exhaust lap would give earlier release but insufficient or no compression. In Fig's* 3 and 4 similar capital letters of reference indicate the same parts of the mechanism. Fig. 3 shows all the essential parts of the valve gear. The steam valves work in the chambers S S and the exhaust valves work in the chambers E E. The double-armed levers D D work loosely on the hubs of the steam bonnets ; they are con- nected to the wrist-plate B by the rods K K, the levers M M are keyed to the valve stems J J", and are also connected by the rods to the dash pots P P. The double-armed levers D carry at their outer ends what are called steam hooks, F F, these being pro- vided with hardened steel catch plates, which engage with arms ' M Jf, making the arm Jtf and the hook F work in unison until steam is to be cut off. At this point another set of levers or cams G 6r, which are connected by the cam rods H H, to the governor, come into play, causing the catch plates on the hooks F to release the arms MM. the outer ends of which are then pulled downwards by the dash-pot plunger, causing the steam valves to rotate on their axis and thus cut off steam. These are the essential fea- tures of the Corliss gear. The exhaust valve arms N are connected to the wrist-plate by the rods L L, and it is seen that all the valves receive their motion from the wrist-plate B; the latter receives its motion from the hook-rod A; this rod is generally attached to a rocker arm not shown ; to this arm the eccentric rod is HANDBOOK ON ENGINEERING 209 H 210 HANDBOOK ON ENGINEERING. also attached. The rocker arm is usually placed about mid- way between the wrist-plate and eccentric, and in the center of its travel stands in a vertical position. The setting of the valves is not a difficult matter, when, on the wrist-plate, its support, valves and cylinder, the customar/ marks have been placed for finding the relative positions of wrist-plate and valves. G- Fig. 4. Now, referring to Fig. 4, when the back bonnets of the valve chambers have been taken off, there will generally be found a mark or line, r, on the end of each steam valve s s, coinciding with the working or opening edge of each valve ; another line, , will be found on each face of the steam valve chamber coinciding with the working edge of the steam port. The exhaust valves and their chambers are marked in a similar way, i. e., the line u on the end of each exhaust valve coincides with the working edge of the valve, and the line a;, on the face of ^ach exhaust valve HANDBOOK ON ENGINEERING. 211 chamber, coincides with the working edge of the exhaust port. On the hub of the wrist plate will be found three lines n, c, n, placed in such a way that when the line c coincides with the line b on wrist plate, the wrist plate will stand exactly in the center of its motion, and when the line b coincides with either of the lines n, n, the wrist plate will be at one of the extreme ends v or w of its travel. In setting the valves, the first step will be to set the wrist- plate in its central position, so that the lines b and c will coin- cide, and fasten the wrist-plate in this position by placing a piece of paper between it and the washer R on its supporting pin. Now set the steam valves so that they will have a slight amount of lap, that is to say, the lines r, r, must have moved a little beyond the lines , t. The amount of this lap depends much on individual preference and experience ; it ranges from A to J ^ or sma ^ engines, and from J- to | inch for compara- tively large engines. This lap is obtained by lengthening or shortening the rods TTTTby means of the adjusting nuts. Now place the exhaust valves e, e, by lengthening or shorten- ing the rods L L by means of the adjusting nuts, in a position so that the working edges will just open the exhaust ports, or, in other words, place the lines u and x in line with each other as indicated in illustration. The next step will be to adjust the rocker arm. Set this arm in a vertical position by means of a plumb line, and connect the eccentric rod to it ; then turn the eccentric around on the shaft, and see that the extreme points of travel are at equal distances from the plumb line. To secure this a little adjustment in the stub end of the eccentric rod may be necessary. Now connect the hook rod A to the wrist- plate. The paper between the wrist- plate and the washer on the supporting pin should now be taken out, so that the wrist-plate which is connected to the valves can be swung on its pin. Now turn the eccentric around on the shaft 212 HANDBOOK ON ENGINEERING. in order to determine the extreme points of travel of the wrist- plate. If all parts have been correctly adjusted, the line b will coincide with the lines ??, n, at the extreme points of travel ; if this is not the case, the hook rod will have to be adjusted at its stub end so as to obtain the desired equalized motion of tbe wrist-plate. The next step will be to set the valves correctly with reference to the position of the crank ; to do this the length of the rods A", K, L, and L must not be changed, but the following mode of procedure should be followed : Place the crank on one of its dead centers (see page 195) and turn the eccentric loosely on the shaft in the direction in which the engine is to run, until the steam valve nearest to the piston shows an opening or lead of ^ to ^ inch. After the proper lead has been given to this valve, secure the eccentric, and turn the shaft with eccentric in the same direc- tion in which the engine is to run until the crank is on the oppo- site dead center, and notice if the opening or lead at this end of the cylinder is the same as on the other steam valve ; if not, shorten or lengthen slightly, as may appear necessary, the con- nection between the wrist-plate and eccentric. Of course much adjustment in the length of these connections is not admissible without resetting the valves with reference to the wrist-plate. The compression on an engine is a very important factor, upon which cool and quiet running depends. With exhaust valves line and line about 5 per cent compression is secured, which is equal to 1 J' for 36" stroke and 2" for 42" stroke. In case more compression is desired, the exhaust valves must be given a little lap. To set the exhaust valves for a given compression, say, 2 inches, first measure off 2 inches from the ends of the cross- head travel as shown in Fig. 5 (not from the ends of the guide). Then turn the crank in the direction it is to run until the end of the crosshead reaches the line on the guide. Adjust the exhaust valve corresponding to this end of the stroke so that it just closes HANDBOOK ON ENGINEERING. 213 the port. Turn the crank over the center and back on the return stroke until the opposite end of the cross-head reaches the line on the opposite end (to the first mark) of the guide. Then adjust the exhaust valve corresponding to this end of the stroke so that it just closes the port. Both exhaust valves will then close the ports when the piston reaches a point 2 inches from the working end of the guide and the engine will then have exactly 2 inches Fig. 5. compression. If this is found to be too much or too little, as determined by the running qualities of the engine, it may be varied either way by adjusting the length of the rods L and L, being careful to turn each nut exactly the same amount. The only thing which remains now to be done is to adjust the cam rods H, //, to produce an equal cut-off at each end of the cylinder. On the column of most Corliss engine governors will be found a stop device, sometimes in the form of a loose pin, some form of cam motion or movable collar. This device is for the purpose of preventing the governor from reaching its lowest position, for when it reaches the latter position the valves should not hook on. Should the governor belt break or become iiieffect- 214 HANDBOOK ON ENGINEERING. ive, the governor will stop and reach its lowest position on the column, thereby bringing the safety cam Y in underneath the inner member of the hook F which prevents the latter from engaging arm M, and as the valves cannot hook on when it is in this position the admission of steam to the cylinder is entirely shut off and the engine will come to a standstill. It will be apparent that the stop on the governor column should be removed or otherwise rendered inoperative as soon as the engine has attained full speed, and should again be placed in active position when stopping the engine in the usual way. As the stop just mentioned determines the lowest position of the governor at which the valves should hook up, it should be kept in place while the foregoing adjustments are being made. Next, unhook the reach rod from the wrist plate and by means of the starting bar move the wrist plate over until the lines b and n are nearly opposite each other. The head end valve should now have opened the' port to nearly the limit, which may be ascertained by the marks on the ends of the valve. Now, adjust the governor rod H so that the projection or cam on the disk G operated by the governor will come in contact with the inner member of the steam hook F, so that the valve will be tripped or released when the marks b and n are exactly in line. As all governors do not move an equal amount to produce a given change in the point of cut-off, it will be safer to hook the reach rod on the wrist-plate and have the engine turned in the direction in which it is to run, until the head end valve is released, than to adjust the cut-off with the use of the starting bar only. To prove the correctness of the cut-off adjustment, raise the gover- nor balls to a position where they probably would be when at work and block them there ; then, with the connections made between the eccentric and the wrist-plate, turn the engine shaft slowly in the direction in which it is to run, and when the valve is released, measure upon the slide the distance which HANDBOOK ON ENGINEERING. 215 the crosshead has moved from its extreme position. Continue to turn the shaft in the same direction, and, when the other valve is released, measure the distance through which the crosshead has moved from its extreme position, and if the cut-off is equalized, these two distances will be equal to each other. If they are not, adj ust the length of the cam rods until the points of cut-off are equal distances from the beginning of the stroke. Replace the back bonnets and see that all connections have been properly made, which will complete the setting of the valves. Fig. 6, ADJUSTMENT WITH TWO ECCENTRICS. In order to obtain a greater range of cut-off in Corliss engines a separate steam and exhaust eccentric is used. With two eccen- trics the admission and exhaust valves can be adjusted independ- ently, and steam may be cut off anywhere, nearly to the end of the stroke. The work of setting the valves of a Corliss engine having two 216 HANDBOOK ON EXGI MAKING. HANDBOOK ON ENGINEERING. 217 eccentrics is not particularly complicated as many engineers seem to think. After inspecting the type of releasing gear employed and knowing in which direction the engine is to run, finding the direction in which to turn the eccentric becomes a very simple matter. When setting the steam valves we have one eccentric to turn as in the case of the single eccentric engine, and when set- ting the exhaust valves another eccentric must be turned, but this does not add complication to the work, although it requires a little more time. The work of centralizing the positions of the various parts, equalizing the movements and setting and adjust- ing the valve gear is practically the same as with the single eccen- tric engine. Set the wrist-plate central as shown in Fig. 6, and adjust the valve rods ; but in this case the steam valves are set with negative lap which is usually a little less than half the port opening. The first step is to set the exhaust eccentric (as it is generally placed next to the bearing). To do this turn the engine until the piston is in the position shown in Fig. 7, so as to obtain a compression of about 5 per cent of the stroke. Then turn the exhaust eccentric loosely on the shaft in the direction the engine is to run, until the exhaust valves are line and line. Then secure the eccentric and turn the engine on the other end in the same position to prove the correctness of the other exhaust valve. The next step is to set the steam eccentric ; place the crank on either one of its dead centers, then turn the steam eccentric loosely on the shaft until the steam valve on the same end the piston is, has the required opening or lead, which varies from -^" to T y. These directions apply to engines in which the reach rod from the eccentric is connected to the wrist-plate above the center pin /, Fig. No. % 3. When the reach rod is connected to wrist- plate below the pin /, the eccentric should be turned the opposite direction to that in which the engine is to run. 218 HANDBOOK ON ENGINEERING. HANDBOOK ON ENGINEERING. 219 The arrangement of the steam rods in Fig. 3 is in every re- spect satisfactory in connection with a single eccentric valve gear, for in that case a slow initial valve motion is imperative, and it is obtained by the lateral movement of the radius rod. But with two eccentrics quicker initial motion is feasible and desirable, and it is obtained by reversing the valve motion as in Fig. 6. Sepa- rate eccentrics require separate wrist-plates, which are usually placed on the same pin. Fig. 9. Figs* 8 and 9 show how the eccentrics may be placed on the shaft. The steam eccentric is at point 4, Fig. 8, the exhaust eccentric is at point 1, Fig. 9, and the crank is at its dead center at G. Individual eccentric circles are shown for the sake of clear- ness. An imaginary motion of the eccentric will point out the various events. Referring to Fig. 8, near point 2, at the end of 220 HANDBOOK ON ENGINEERING. the throw, the hook connects with the steam valve ; at point 3 the steam edges are at the point of separating and the eccen- tric motion 2-3 determines the initial valve motion. When the eccentric is at point 4 the crank is at its dead center as shown. At point 5 the steam wrist-plate is in its central position and in that position the valve does not cover the port, as with the single eccentric gear, but the port is open to a certain extent, determined by the eccentric motion 3-5. Point 7 marks the end Fig. 10. of the throw, and the corresponding position of the crank is at C l at about three-quarters of the piston stroke, and the limit of cut- off is a little later. If the hook does not strike the knock- off cam the valve will remain open until closed by the return stroke of the eccentric at point 9, near the middle' of the return piston stroke. The exhaust action is discernible, Fig. 8. HANDBOOK ON ENGINEERING. 221 It is similar to the single eccentric action, bat with this differ- ence, that the release at point 5 occurs at about 95 per cent of the stroke, and the exhaust is also cut off at about 95 per cent of the return stroke at point 8. The motion of the exhaust valve after it has closed the port is determined by the eccentric motion 8-2-^5, and full period of exhaust opening is obtained by the eccentric motion 5-7-8. In case the exhaust valve motion is designed and set with lap, Fig. 10 shows the effect lap has on the exhaust valves. The lap when wrist-plate is central is determined by motion A-B. It will be Fig. 11. noticed that the compression begins at A at about 90 per cent of the stroke, and the release at E occurs at 98 per cent of the return stroke and the exhaust opening E, (7, A, is shortened. Where lap is used on the exhaust valve it has the effect of making earlier compression and later release. A valve gear designed to be operated by a single eccentric cannot very well be made to cut off much later than at half stroke, even when a separate exhaust eccentric is added. For the slow initial valve motion requires at least half the throw of the eccentric, and the other half is not sufficient for a late cut-off, and it will readily be seen from an inspection of Figs. 4 and 6, that a quicker initial valve motion in 222 HANDBOOK ON ENGINEERING. Fig. 4 would involve radical changes in the valve gear. However, the range of cut-off may be extended by moving the eccentric back, sacrificing the lead, and to this there is no objections when it does not involve later release. The advantage gained by a second eccentric would consist in more compression and earlier release. After setting the valves and making the final adjustment, if it is convenient an indicator should be applied to the engine when at work to verify the adjustment of the valves for the best possible conditions for"economical operation. Fig. 10 indicates position of eccentric at J cut off which can be extended some by giving the steam valves a little more nega- tive lap, but as this shortens the amount of lap when closed, it may cause leakage in the steam valves. COMPOUND ENGINE. The compound engine is practically two single engines con- nected together and so arranged that the exhaust steam from one engine passes into and becomes the " live " steam for the other, in other words the first, or high pressure cylinder receives its supply of steam from the boiler and the second or low pressure cylinder receives its supply from the high pressure cylinder. The object of the compound engine is to enable the steam to expand to the lowest possible pressure with the least loss by condensation. When steam expands its temperature decreases, so that by the time the piston reaches the end of the stroke the temperature of the steam and consequently the tem- perature of the cylinder walls is considerably below the temper- ature of the incoming steam. The fresh steam of hight empera- ture coming from the boiler comes in contact with the walls of the cylinder which have been cooled to the temperature of the exhaust steam, and the result is a considerable portion of the fresh steam is condensed, the latent heat serving to reheat the HANDBOOK ON ENGINEERING 223 224 HANDBOOK ON ENGINEERING. cylinder walls. It will be understood that were it possible to keep the cylinder at a higher temperature, less steam would be condensed in warming it at each stroke and consequently more steam would be available for useful work. In the compound engine the steam is expanded partly in one cylinder and partly in the other so that the difference between the temperatures of the incoming and exhaust steam in each cylinder is greatly reduced. By this means steam may be expanded from a given initial pres- sure to a given final pressure with a loss of nearly twenty-five per cent less than would be incurred were the same expansion to take place in a single cylinder. It is due principally to avoiding the loss by cylinder condensation that the compound engine, considered as a type of engine, can perform nearly twenty-five per cent more work with the same weight of steam than can be obtained when the steam is expanded in one cylinder only. In order to utilize the low pressure steam escaping from the high pressure cylinder it is necessary to provide a larger area of piston so that the low pressure steam acting on a large sur- face will do as much work as the high pressure steam acting on a smaller area. It is for this reason that the low pressure cylinder of compound engines is always made larger than the high pressure cylinder. The required size of low pressure cylinder for a given' size of high pressure, depends upon the number of times the steam is to be expanded, the initial steam pressure and the nature of the work the engine is intended for. For steady loads the difference in the size of the two cylinders may be greater than where the load is constantly changing between wide limits as nearly always occurs in street railway service. Compound engines, as this term is generally employed, are built of two types, the tandem compound, Fig. 1, and the cross compound, Fig. 2. In the tandem compound the work of both pistons is transmitted to the crank through one piston rod, cross- head and connecting rod, while in the cross compound there are HANDBOOK OX ENGINEERING 225 226 HANDBOOK ON ENGINEERING. two complete engines placed side by side, the cranks of which are generally set 90 degrees apart. It will be seen that in the tandem compound engine it makes but little difference from the mechanical standpoint whether the work is divided evenly between the two cylinders or not because both pistons move in unison and drive the same crank. In the cross compound engine it is necessary, in order to secure a uniform turning effort at the shaft, to have the work divided as nearly equally between the two cylinders as the conditions will permit. In the tandem com- pound engine the principal consideration is the proper working of the steam, and the sizes of the cylinders are determined by the number of expansions to be effected in both cylinders, or the total number of expansions, as it is called, and the initial pressure. As the equal division of the work between the two cylinders in compound engines is essential, the ratio of the cylin- ders is generally for noncondensing 21 to 1 for 100 Ibs., 2J to 1 for 125 Ibs., and 3 to 1 for 150 Ibs. initial pressure, and for con- densing 3 to 1 for 100 Ibs., 3J to 1 for 125 Ibs., and 4 to 1 for 150 Ibs., initial pressure. The number of expansions required in a compound engine is represented by the quotient of the absolute initial pressure divided by the absolute terminal pressure. If steam is to be used at 105 pounds gauge pressure and is to be expanded down to 10 pounds 105 + 15 absolute in the low pressure cylinder, there will be r^ = 12 expansions. A simple rule for finding the ratio of the area of cylinders for noncondensing, is to divide the absolute initial pres- sure by the terminal pressure which equals the expansions in both cylinders and the square root of total expansions equals the ratio of cylinders. For example : 150 Ibs. initial pressure plus 15 Ibs. equals 165 Ibs. absolute initial pressure divided by 16 Ibs. terminal pressure equals 10.3 total expansions, and the square root of 10.3 equals HANDBOOK ON ENGINEERING. 227 3.2 equals ratio of cylinders. Care should be taken in non- condensing engines so that the ratio of the low pressure cylinder is not too large, as in such cases the steam in low pressure cylin- der would expand to less than the atmospheric pressure, and thus make loops on indicator card, which would incur a serious loss. The calculation of the diameters of cylinders for a compound condensing engine when the data are given, follows. Take an engine that is to develop 500 horse power with an initial pressure of 105 pounds gauge, or 120 pounds absolute, the steam to be expanded to a terminal pressure of 6 pounds absolute. The total expansion of steam in both cylinders is 120 -f- 6 =20. Expansion in each cylinder = -^20=4. 47. Point of cut-off in each cylinder, per cent of stroke 4.47 22.3 per cent, 1 -|- hyp. log. of expansion in each cylinder = 1 -j- hyp. log. 4.47 = 2.497. Terminal and back pressure in high pressure cylinder, and the 120 initial pressure in the low = j^p = 26.8 pounds. Mean effective pressure in h. p. cyl. = 26.8 X 2.497 26.8 = 40.11 pounds. Mean effective pressure in 1. p. cyl. (assuming 3 Ibs. back press.) = 6 X 2.497 3 = 11.98 pounds. If half the work is to be done in each cylinder, which is de- sirable in cross compound engines, each cylinder must do 250 horse power of work. Assuming the piston speed to be 600 feet per minute, the area of the low pressure cylinder is 33000 X H. P. 33,000 X 250 Piston speed~X~effective P*es7. 600 X H-98 = ' U7 ' 7 sc * uare inches = 38 ins. diameter. QO nnrj \/ Area of high pressure cylinder by same rule is : ! _ 600X40.11 = 342.3 square inches = 21 inches diameter. 228 HANDBOOK ON ENGINEERING. Ratio of cyl. = 40.11 11.98 = 3.3 to one. The clearance and the areas of the piston rods have not been taken account of by separate processes in the foregoing calcu- lations. These should always be included when making calcu- lations involving the pressure and expansion of steam in engine cylinders. The method of finding the number of expansions taking place in a compound engine may be readily -understood by referring to the diagram, Fig. 3. The shaded area in the / Vol. Vo/s, Fig. 3. smaller cylinder represents the initial volume of steam in the high pressure cylinder, that is to say, this represents the volume of steam taken from the boiler for one stroke, or during one-half revolution. The point of cut-off is at one-third stroke and the area of the low pressure cylinder is three times that of the high pressure cylinder. It will be seen that when the low pressure piston moves to one-third stroke the volume of the cylinder V behind the piston is equal to the volume of the entire high pres- sure cylinder. This shows that the capacity or contents of the low pressure cylinder is three times that of the high so that for every HANDBOOK ON ENGINEERING. 229 volume of steam and therefore for every expansion taking place in the high pressure cylinder there will be three volumes, and three expansions taking place in the low pressure cylinder. This shows why the total number of expansions in a compound engine is the number in the high pressure cylinder multiplied by the number in the low pressure cylinder. In the diagram, Fig. 8, when the small piston reaches the end of the stroke the steam will have expanded three times, that is, it will occupy three times the space it did at the point of cut-off. Now when the large piston reaches the end of the stroke each of the three volumes a, a and a, Fig. 4, will have been expanded three more times and the total will be 3X3=9 expansions, that is, the original volume a, Fig. o, will then occupy nine times the space it did when & 0* Fig. 4. first let into the high pressure cylinder. To find the number of expansions in a compound engine multiply the number of expan- sions in the high pressure cylinder by the number in the low, or multiply the number of expansions in the high pressure cylinder by the ratio of cylinder areas ; the product will be the number required. Again referring to Fig. 4, it will be seen that the low pressure cylinder must receive a high-pressure cylinderful of steam at each 230 HANDBOOK ON ENGINEERING. stroke otherwise the pressure in the receiver and the back pressure on the high pressure piston will rise too high and a loss of power will result, or if the pressure be too low in the larger cylinder the small piston will drive the larger one which will again result in loss of power. It has been shown that the volume of both cylinders vary in proportion to the areas, that is, if the areas are as 1 to 3 then when both pistons have reached, say, one-third stroke the volume of one will be 3 times the volume of the other, and when the larger piston in this case travels one-third of the stroke the capacity of the low pressure cylinder behind the piston will then be equal to the whole of the smaller cylinder and will be capable of containing all the steam used during a full stroke of the smaller piston, or a high-pressure cylinderful of steam. This steam then expands during the remaining two- thirds of the stroke. Now it will be readily understood that if a cut-off valve were pro- Hls\ Pressure Diaeram. X lev Preuurt Diaoram. ^7+snos. 2/*r& . Fig. 6. vided on the low pressure cylinder and is set to cut off at less than one-third stroke (with a ratio of cylinder areas 1 to 3) the low pressure cylinder will not take a high pressure cylinderful of steam when steam is cut off, and the pressure in the receiver must necessarily rise. Reducing the volume of steam entering the low pressure cylinder apparently tends to lessen the work done by the larger piston and consequently more work must apparently be HANDBOOK ON ENGINEERING. 231 done by the high pressure piston. This in turn causes a later cut-off in the small cylinder as shown in Fig. 5, dotted lines, which serves to neutralize the effect of the higher back pressure so that while the cut-off has been made later, the mean effective pressure remains practically the same. The higher backpressure on the small piston means a higher initial pressure in the low pressure cylinder, see Fig. 6 dotted lines, which causes more power to be developed in the latter cylinder. Thus it is seen that, within certain limits, shortening the cut-off in the low pres- sure cylinder puts more of the load upon the low pressure piston. On the other hand when the low pressure piston is doing more work than the high pressure, the cut-off in the low pressure cylinder may be lengthened. This permits the low pressure cylinder taking more steam and consequently the receiver pressure and the back pressure on the high pressure piston are reduced and the work done by the high pressure piston is thus increased. By manipulating the cut-off on the low pressure cylinder the load on the two pistons may be equalized or very nearly so except when the engine is considerably underloaded or overloaded. The range of maximum economy is not as great with the compound as with the simple engine, that is to say, the load may be varied more widely from the point where the best economy is obtained, in the simple engine than in the compound which is due to the large difference in cylinder areas in the latter engine. At very early cut-off both the high pressure and the low pressure cylinders work the steam very similarly to the simple engine and as the loss by cylinder condensation increases with an increase in the range of temperatures it follows that an underloaded compound engine is but little if any more economical than a simple engine working with a similar initial point of cut-off. In compound automatic cut-off engines the point of cut-off will be nominally the sa*me in both cylinders, we say nominally (in name only) because the initial pressure and the extent of the 232 HANDBOOK ON ENGINEERING. vacuum have some influence upon the receiver pressure and the mean effective pressure in the low pressure cylinder. In most compound engines in which the cut-off mechanism of both cylin- ders are operated by a single governor, provision is made for adjusting the cut-off of the low pressure cylinder relative to that in the high, so that while the nominal cut-off may be, say, one- fourth stroke, the actual points of cut-off maybe one-fourth in the high pressure and -$ in the low pressure cylinder, the governor, however, varying both points of cut-off as the load changes. HORSE POWER OF COMPOUND ENGINE. Little can be done in finding the horse power of compound en- gines without the indicator because of the uncertainty of the points of cut-off and consequently of the back pressure and mean effec- tive pressures. The mean effective pressure in each cylinder may be computed by using assumed data, by the same rules given for simple engines, but it will readily be understood that assumed data furnishes assumed results only. Knowing the mean effective pressure areas and speed of the pistons the horse power of a compound engine is found as follows: Multiply the areas of the high pressure piston by its mean effective pressure and divide by the area of the low pressure piston, then add this quotient to the mean effective pressure in the low pressure cylinder.* Call this answer 1. Multiply the area of the low pressure piston by the piston speed in feet per minute and by answer 1, and divide the last product by 33,000 ; the quotient will be the indicated horse power. CONDENSING ENGINES. It has been explained that the atmosphere exerts a pressure of about 15 Ibs. per square inch on all surfaces with which it * This quantity is to be taken as the M. E. P. when finding steam con- sumption of compound engine. HANDBOOK ON ENGINEERING. 233 is in contact. The atmosphere is in contact with one side of mi engine piston when the exhaust is open", and, consequently, the steam in pushing the piston forward, has to overcome this atmospheric pressure of 15 Ibs. per square inch. The useful pressure of steam is, therefore, whatever pressure there is above the pressure of the atmosphere, and this is the pressure that the steam gauge shows. When the gauge says 60 Ibs. we really have 75 Ibs., but 15 Ibs. of it does not count, because it is balanced by the atmospheric pressure on the other side of the piston. If we had sixty-pound steam pressing on the pis- ton and could get rid of the atmospheric pressure on the side of the piston, the steam would exert a force of 75 Ibs. per square inch, a very respectable gain, indeed. We might remove the air pressure by pumping it out, but the amount of power required in doing the pumping would be equal precisely to all gain hoped for, plus the friction of the pump ; therefore, there would be an actual loss in the operation. But there is another way of remov- ing the air pressure. It has been explained that a cubic inch of water vaporizes and expands into a cubic foot of steam at atmos- pheric pressure. If, after getting this cubic foot of steam, we take the heat out of it, we again turn it into the cubic inch of water. Assume the engine cylinder to hold just a cubic foot of steam, and assume that the stroke is complete and ready for the exhaust valve to open and permit this foot of steam to escape, and assume that this cubic foot of steam has expanded down to atmospheric pressure, that is, 15 Ibs., absolute pressure. Now, instead of opening the cylinder to the atmosphere, we dose the cylinder with cold water. The heat leaves the steam and goes into the water and the steam turns to water, leaving in the cylinder the condensed steam in the form of a cubic inch of water. The steam formerly filled the cylinder, and now it fills but a cubic inch of it, consequently, we have produced in the cylinder u vacuum which has the effect of adding about 15 Ibs. 234 HANDBOOK ON ENGINEERING. per square inch, to the force of the steam on the other side of the piston, by virtue of removing that much resistance to its forward motion. The heat which was in the steam has gone into the con- densing water, except the trifle that remains in the cubic inch of condensed water. We must get this condensed water out of the cylinder, and it will be an advantage to pump it back into the boiler, for it is pure and it is hot. This is the general principle of the condensing engine. It gives us the grand advantage of a heavy increase in the useful pressure acting to push the piston forward ; it gives us pure water for use in the boiler, and it saves in the feed-water the heat that would otherwise go out of the exhaust pipe. But it is not practicable to condense the steam in the cylinder by dosing the cylinder with cold water. In practice, the steam is allowed to go into a separate condensing vessel, called the condenser. The condenser is precisely the opposite of the boiler. The boiler is the machine for putting heat into the steam to vaporize it, and the condenser is the machine for taking heat out of the steam and turning it into water again. In the condensing engine, one of these machines is pushing on the piston and the other machine is pulling on the piston. The gain by condensing is so great that it is a profitable piece of business to apply a condenser to any large non-condensing engine. The condenser requires a pump to withdraw the water of condensation, and this pump must be in reality an air-pump. In practice, they employ an air-pump and condenser combined in one structure, separate from the engine, and driven either by rod connection from the engine, or by a belt from the engine, or by an independent steam pump. The arrange- ment will depend much upon the situation. The belt-driven pump permits of the condenser being set in any convenient position independent of the engine. HANDBOOK ON ENGINEERING. 235 CONDENSERS. When steam expands in the cylinder of a steam engine, its pressure gradually reduces and ultimately becomes so small that it cannot profitably be used for driving the piston. At this stage, a time has arrived when the attenuated vapor should be disposed of by some method, so as not to exert any back pressure or resistance to the return of the piston. If there were no atmos- pheric pressure, exhausting into the open air would effect the desired object. But, as there is in reality a pressure of about 14.7 pounds per square inch, due to the weight of -the super- incumbent atmosphere, it follows that steam in a non-condensing engine cannot economically be expanded below this pressure, and must eventually be exhausted against the atmosphere, which exerts a back pressure to that extent. It is evident that if this back pressure be removed, the engine will not only be aided by the exhausting side of the piston being relieved of a resistance of 14.7 pounds per square inch, but moreover, as the exhaust or release of the steam from the engine cylinder will be against no pressure, the steam can be expanded in the cylinder quite, or nearly, to absolute of pressure, and thus its full expansive power can be obtained. Contact, in a closed vessel, with a spray of cold water, or with 'one side of a series of tubes, on the other side of which cold water is circulating, deprives the steam of nearly all its latent heat, and condenses it. In either case the act of condensation is 236 IIAXDKOOK OX ENGINEERING. almost instantaneous. A change of state occurs mid the vapor steam is reduced to water. As this water of condensation only occupies about one sixteen-himdredths of the space filled by the steam from which it is formed, it follows that the remainder of the space is void or vacant, and no pressure exists. Now, the expanded steam from the engine is conducted into this empty or vacuous space, and, as it meets with no resistance, the very limit of its usefulness is reached. The vessel in which this condensation of steam takes place is the condensing chamber. The cold water that produces the con- densation is the injection water ; .and the heated water, on leaving the condenser, is the discharge water. To make the action of the condensing apparatus continuous, the flow of the injection water and the removal of the discharge water, including the water from the liquefaction of the steam, must likewise be continuous. The vacuum in the condenser is not quite perfect, because the cold injection water is heated by the steam and emits a vapor of a tension due to the temperature. When the temperature is 110 degrees Fahr. , the tension or pressure of the vapor will be represented by about 4" of mercury ; that is, when the mercury in the ordinary barometer stands at 30", a barometer with the space above the mercury communicating with the condenser, will stand at about 26". The imperfection of vacuum is not wholly traceable to the vapor in the condenser, but also to the presence of air, a small quantity .of which enters with the injection water and with the steam ; the larger part, however, comes through air leaks and faultly connections and badly packed stuffing boxes. The air would gradually accumulate until it destroyed the vacuum, if provision were not made to constantly withdraw it, together with the heated water by means of a pump. The amount of water required to thoroughly condense the steam from an engine is dependent upon two conditions : the total heat and volume of the steam, and the temperature of the injection HANDBOOK ON ENGINEERING. 237 water. The former represents the work to be done, and the latter the value of the water by whose cooling agency the work of con- densation of the steam is to be accomplished. Generally stated, with 26" vacuum, the injection water at ordinary temperature, not exceeding 70 Fahr., from* 20 to 30 times the quantity of water evaporated in the boilers will be required for the complete liquefaction of the exhaust steam. The efficiency of the injection water decreases very rapidly as its temperature increases, and at 80 and 90 Fahr., very much larger quantities are to be employed. Under the conditions of common temperature of water and a vacuum of 26" of mercury, the injection water necessary per H. P. developed by the engine, will be from 1J gallons per minute when the steam admission is for one-fourth of the stroke, up to two gallons per minute, when the steam is carried three-fourths of the stroke of the engine. 238 HANDBOOK ON ENGINEERING. SETTING THE PISTON TYPE OF VALVE. The simple piston valve admitting steam between the pistons is, in operation, the reverse of the plain D slide valve, which ad- mits steam at the outer edges, or ends of the valve. To make this still clearer it may be said that were the live steam to enter through the exhaust cavity of the D slide valve its operation and the position of the eccentric relative to the crank would be iden- tical to that piston valve. Fig. 1 illustrates the similarity of action and eccentric positions were these conditions to obtain. In these types of valve, as ordinarily employed, the steam is admitted at the ends of the slide valve, and between the pistons or at the middle of the piston valve. The change from the end to the middle of the valve necessitates a change in the position of the eccentric relative to the crank in order to have the direc- tion of rotation remain the same. The positions of the eccentric when driving the simple D valve, and the piston valve, are indi- HANDBOOK ON ENGINEERING. 239 cated in Fig. 2. It will be noticed that the crank revolves in the same direction in both cases, and that when the crank leaves the dead center, moving in the direction of the arrow, the same port, viz., the one at the head end of the cylinder, will be opened at the same time and to the same extent. This proves the positions as shown to be correct and illustrates why the eccentric must be moved in the same direction the engine is to run with theZ) valve, and in the opposite direction with the piston valve, in order to secure the same direction of rotation in the engine. Fiff.2 f When setting valves it is a good plan to obtain as much uni- formity of methods as possible, because of the liability to con- fusion when methods involving different movements of the eccentric are employed. In all the directions that follow it is assumed that the crank is placed on the dead center (sae page 195) nearest the cylinder so that when setting the different styles of valves, the same steam port will always be opened first, namely, the one at the head end of the cylinder. The engine, it will be 240 HANDBOOK ON ENGINEERING. seen, is thus treated as though it contained but one steam port, which greatly simplifies matters. In order to show that each particular form of valve of the same type does not require different methods for its proper adjustment, both the simple piston valve andjthe main valve of the round riding cut-off are illustrated together, the same directions applying to both. Where marks appear upon the valve stem, or seat, it becomes an easy matter to set a valve quickly and correctly but when these do not appear a different method must be pursued for obtaining them. First remove the chest covers at both ends of the chest .eyM of Gape*- Me f c/r efc Fig. 3 and also the valve (both styles) from the chest and lay it upon a clean place on the floor, or bench. Procure a piece of sheet steel about y 1 ^ inch thick and file it to the form shown in Fig. 3. Make the length of the gauge thus formed equal to the thickness of the piston on the valve plus the lead, which may betaken as -^ inch. Replace the valve in the chest and connect it to the valve stem. Turn the eccentric from one extreme position to the other and see that the valve opens the ports an equal amount. It is not necessary that the ports be opened exactly wide, the object being to secure exactly the same opening at each end of the valve. If the head end port is opened farther than the other, the eccentric HANDBOOK ON ENGINEERING. 241 rod should be lengthened an amount equal to one-half the differ- ence, and should the port at the crank end be opened farthest, tte eccentric rod should be shortened a like amount. Turn the eccentric to the extreme position farthest from the cylinder. Then place the small end of the gauge against the inner edge of the port, and with a scriber make a fine line (a) on the seat as shown in Fig. 4. Remove the gauge, and turn the eccen- tric in the same direction the engine is to run until the end of the valve reaches the fine line on the seat. Secure the eccentric to the shaft, being careful not to move the eccentric in either direc- tion. Now turn the crank in the direction it is to run UDtil the eccentric reaches the extreme position nearest the cylinder. The gauge is now placed against the edge of the opposite port and a fig. 4 fine line drawn on the seat, at the end of the gauge, in the same manner as shown in Fig. 4. Turn the crank to the dead center farthest from the cylinder when the end of the valve should have just reached the line on the seat. If it does not, the crank should be turned sufficiently to enable the distance between the valve and the mark, being measured. The eccentric rod is then to be adjusted so as to move the valve a distance equal to one- half of what the valve lacks of exactly reaching the line on the seat. The valve will then open both ports to the extent of the 10 242 HANDBOOK ON ENGINEERING. lead when the crank occupies the exact dead centers. It is very desirable to have a method of setting the valve without removing the chest covers. By the aid of simple gauges this can be readily accomplished. Take a piece of steel wire and sharpen the ends and bend into the form shown in Fig 5. With a prick punch make a mark (&) on the guide block, place one end of gauge in this mark and make another mark (c) where the opposite end of the gauge touches the valve stem. This gauge enables the valve stem being disconnected from the valve stem guide block, and the chest cover put on, and the stem afterward con- nected up again in exactly the same position (see page ). Having made this second gauge, place the crank on the exact dead center nearest the cylinder. Then make a prick punch mark (c?) on the stuffing box, place one end of the gauge in this mark and then make a second mark (e) where the other end of the gauge touches the valve stem. It will readily be seen that when testing the setting of- the valve all that is necessary is to place the crank on the dead center nearest the cylinder, then place the gauge the mark (d) on the stuffing-box, and have the eccentric moved until the punch mark (e) on the valve stem falls under the point of the gauge. The valve will then have opened the port to the extent of the lead, because it was in this position when the gauge and the marks were first made. If the punch marks are nicely made and not too large the extent of the lead opening may be measured at both ports, by turning the crank to the opposite dead center and making a second punch mark (/) on the valve stem by means of the gauge. These two guages should be carefully preserved from injury and from being mislaid so that in case of emergency, such as the slipping of an eccentric, the latter can be returned to its correct position without unnecessary loss of time. HANDBOOK ON ENGINEERING. 243 SETTING THE CUT=OFF VALVE. The following directions are applicable to both the flat slide and the round types of cut-off valves. The point of latest cut-off is seldom known exactly by the average engineer because of its unimportance while the engine is in running order, and as this point varies with different engines it is advisable to discard it as an element in valve setting. First place the main valve in its position of mid-travel, that is, place it centrally over the ports. This may be accomplished by finding the center between the punch marks (/) and (e) on the valve stem, bringing the center mark g under the point of the gauge in the manner shown in Fig. 5. The travel of the cut-off valve must first be equalized which is accomplished by turning the cut-off eccentric to its extreme positions and noting the travel of the cut-off valve over the ports of the main valve. The cut-off eccen- tric rod should be lengthened or shortened so that the cut-off valve will travel evenly over the ports in the main valve. This, of course, is obtained by measuring the distance from the edge of the ports in the main valve to the ends of the cut-off valve when the latter occupies its extreme positions. First, assume the engine to have a fixed, or a hand-adjusted cut-off, and that the cut-off valve is to be set to cut off steam at 244 HANDBOOK ON ENGINEERING. one-half stroke. Place the crank on the dead center (see page 195) and the full part of the cut-off eccentric the same. Then measure off one-half the length of the stroke from the end of the cross-head as in Fig. 6 and make a light line / on the guide. Turn the engine in the direction it is to run until the end of cross-head reaches the line / on the guide. The piston will now have com- pleted one-half its stroke. Turn the cut-off eccentric in the direction the engine is to run until the cut-off valve opens the port in the main valve wide and just closes the port again in the main valve. Secure the cut-off eccentric to the shaft at this point. Turn the crank over to the opposite d^ad center and far enough beyond the center so that the same end of the crosshead will have again reached the line (/) on the guide as in Fig. 6. The piston will now have completed one-half of the return stroke and the cut-off valve should have just closed the port in the main valve. If the cut-off valve has moved too far, or not far enough, measure the amount it lacks of just closing the port and then adjust the cut-off eccentric rod an amount equal to one-half the amount of HANDBOOK ON ENGINEEKING. 245 the discrepancy. The cut-off valve will then close the port in the main valve at exactly the same point in both forward and return strokes. When an automatic cut-off engine, in which the cut-off eccentric is operated by a shaft governor, first block out the weights to their extreme position or against the stops, the travel of the cut-off valve having been previously equalized in the manner explained above. Then turn the crank to the dead center, preferably the one nearest the cylinder, and turn the full port of the cut-off eccentric to the same position as a starting point. Then turn the eccentric in the direction the engine is to run until the cut-off valve opens the port in the main valve to the extent of the lead or from -fa to -f^ inch. Secure the governor wheel to the shaft at this point. Turn the crank to the opposite dead center and see that the cut-off valve has opened the port in the main valve to the same extent. If it has not done so, adjust the length of the eccentric rod an amount equal to one-half the differ- ence between the two. lead openings. Take out the blocks and the work will be completed. It will readily be understood that, were the speed of the engine to reach a point, where the governor weights strike the stops, the cut-off valve will admit only steam enough to fill the clearance, which should always be done, because while it does not tend to accelerate the speed it does prevent forming a vacuum in the cylinder, and from drawing in whatever may happen to be in the vicinity of the end of the exhaust pipe. The point of latest cut-off will then take care of itself and will occur at that point for which the valve and gear were designed. FLAT VALVE RIDING CUT-OFF. In medium and slow speed engines it is very desirable to have a uniform point of release and constant compression. If the engine is of the automatic cut-off variety the point of cut-off will 246 HANDBOOK ON ENGINEERING. necessarily change with each change of load, and if the steam is released, and the point of compression determined by the valve effecting the out-off , it is plain that as the cut-off varies, the point of exhaust and of compression must also vary proportionately. In order to secure a uniform amount of lead, a constant point of release and of compression, it is necessary that the valve deter- mining these points be given a constant travel. Then in order to produce a variable cut-off a separate cut-off valve must be pro- vided. This is the object of the riding cut-off. The main valve determines the lead, point of release and point of exhaust closure and as the travel of the main valve relative to the crank is un- changeable these functions always remain the same. The duty of the cut-off valve is simply to close the ports in the main valve, and it determines the point of cut-off only. It will be seen, there- fore, that with this arrangement of valves, constant lead, exhaust Ftg.r opening and constant compression are secured while the point of cut-off is constantly changing with the load. Keeping these fun- damental facts in mind, it is readily seen that the main valve of the riding cut-off is, in operation, exactly the same as the ordi- nary D slide valve having a fixed travel. In the riding cut-off the travel of the cut-off valve is fixed, so far as length of stroke is concerned, but the times of closing the ports in the main valve are variable and are determined either by hand adjustment or by the governor, depending upon whether the engine is a throttling or an automatic cut-off engine. The points of cut-off are changed by rolling the cut-off eccentric around on the shaft. HANDBOOK ON ENGINEERING. 247 The farther the cut-off eccentric is set in advance of the crank the earlier in the stroke will steam be cut off, and, the nearer together the two eccentrics are set, the later will the cut-off occur. The main valve is generally designed to cut off steam at |- or J stroke, so that if the cut- off valve and main valve move together the point of cut-off will be determined by the main valve and will occur at % or J stroke. Now if the cut-off eccentric (c) be set ahead of the main eccentric (m) as in Fig. 7, it will reach the end of its stroke and start back again before the main eccentric has com- pleted the stroke, thus the cut-off valve moves in one direction and the main valve in the opposite direction and that point in the piston stroke at which the centers of the two valves meet will be the point of cut-off. If the cut-off eccentric be set nearly oppo- site the main eccentric it is evident that when the main valve reaches one-half of the outward stroke the cut-off valve will have reached nearly one-half of the return stroke and the cut-off will occur at about this point in the piston stroke, which will be approximately one-fourth stroke. Figs When setting the valves, first equalize the port opening of the main valve. This is accomplished by turning the main eccentric from one extreme position to the other seeing that both ports in the valve seat leading into the cylinder are opened exactly the same amount. It is not necessary that these ports be opened exactly wide ; the object is to see that both ports are opened to the same extent when the eccentric is in its extreme positions. 248 HANDBOOK ON ENGINEERING. Having equalized the travel of the main valve place the crank on the dead-center, see page 195, and turn the full side of the main eccentric to a corresponding position. Then turn the eccentric in the direction the engine is to run until the port in the main valve, corresponding to the position of the crank or piston, opens the port leading into the cylinder to the amount of the lead, which may be taken as -J^- inch. Now, before moving the engine make a gauge of the form shown in Fig. 8. Put a punch mark on the stuffing-box, and, placing one end of the gauge in this mark, draw a fine line on the valve stem at the opposite point of the gauge. Turn the crank to the opposite dead-center and note the amount of lead opening. If it is not the same as first obtained adjust the eccentric ^rod to the extent of one-half the difference. Then place the gauge in the punch mark on the stuffing-box and draw a fine line at the opposite point of the gauge. Turn the crank back again to its first position and note the lead. If it is found to be equal at both ends, apply the gauge again and this time make a light punch mark at the outer point of the gauge. Then put a similar punch mark on the fine line representing the lead at the opposite end of the valve travel. By means of these marks it will be possible to set the main valve correctly without removing the steam chest cover. Now divide the distance between the two punch marks and put a third punch mark at the middle. Turn the crank around in the direction the engine is to run until the middle punch mark falls under the outer point of the gauge. The main valve will now be at the middle of its travel. The travel of the cut-off valve must now be equalized so that the latter valve will travel equal distances be- yond the ports in the main valve. This is accomplished in pre- cisely the same manner as with the main valve. Having equalized the travel of the cut-off valve, turn the crank in the direction the engine is to run until the cross-head reaches the point in the stroke at which the cut-off is to occur, which is to be de- HANDBOOK ON ENGINEERING. 249 signaled by a line drawn on the guide. Now turn the cut-off eccentric in the same direction until it reaches its extreme position. Continue to move the eccentric until the cut-off valve just closes the port in the main valve. Secure the cut-off eccentric to the shaft at this point. Then turn the crank around until the cut- off takes place on the return stroke and see if it corresponds to the point on the previous stroke. If not, adjust the length of the cut-off eccentric rod an amount equal to one-half the differ- ence. It is important to be able to set the cut-off valve also without taking off the steam chest cover. One punch mark only is re- quired for this. Place the main valve in its position of mid- travel by means of the gauge. Then put a punch mark on the stuffing-box of the cut-off valve stem and, placing the gauge in this mark, put another at the opposite end of the gauge on the cut-off valve stem. See Fig. 8. This method furnishes a simple and quick means of setting both the -main and cut-off valves when an eccentric slips. All that is necessary is to place the crank on the dead-center and bring the proper punch mark under the point of the gauge. Then bring the main valve to its position of mid-travel and with the gauge bring the cut-off valve to its proper position. The foregoing directions for setting the cut-off eccentric apply to the hand-adjusted gear only. When the cut-off eccentric is operated by the governor, the travel is equalized in precisely the same manner as when hand-adjusted. After equalizing the travel of the cut-off valve, place the crank on the dead-center. The main valve, which is invariably set first, will now open the port, corresponding to the .position of the piston to the extent of the lead. Next block out the governor weights against the stops. Turn the full side of the cut-off eccentric to correspond to that of the crank as a starting-point. Then turn the cut-off eccentric (governor wheel), around on the shaft in the direction the engine 250 HANDBOOK ON ENGINEERING. is to run until the port in the main valve is opened to the extent of the lead. Secure the governor wheel to the shaft. Turn the crank to the opposite dead-center and see that the cut-off valve opens the port in the main valve to the same extent. If the difference is slight it may be equalized by adjusting the length of the cut-off eccentric rod an amount equal to one-half the differ- ence of the lead openings. Should the difference be great, say, one-half inch, that is, should the cut-off valve lack one-half inch of opening the port in the main valve, it indicates that the cut-off valve is too long, which is apt to be the case where two cut-off valves are employed on the same stem. The valve may be shortened by moving the two parts closer together, moving each part one-fourth of the amount the cut-off valve lacked of opening the port in the main valve. Then begin over again to set the cut-off eccentric and if the adjustments have been carefully made it will open the ports correctly at both ends of the main valve. After fastening the main eccentric and the governor wheel securely to the shaft remove the blocks from the governor weights and the job will be finished. When the valve gear contains a rocker-shaft of the construc- tion shown on page 322, the eccentric must be turned in the opposite direction to that in which the engine is to run, until the main valve opens the port leading into the cylinder, to the extent of the lead. HANDBOOK ON ENGINEERING. 251 CHAPTER XII. THE STEAM ENGINE. CONTINUED. Work consists of the sustained exertion of force through space. The unit of work, the foot-pound, is a force of one pound exerted through one foot space. The work done in lifting one pound ten feet, or ten pounds one foot, is ten-foot pounds. Power is the rate of work, or the number of foot-pounds ex- erted in a unit of time. The unit of power is the horse-power, and equals 33,000 foot-pounds exerted in a minute, or 550 foot- pounds exerted in a second, or 1,980,000 foot-pounds exerted in an hour. An engine developing fifty-horse power, exerts 27,500 foot-pounds per second, 1,650,000 foot-pounds in a minute. It could raise (friction neglected) 41,250 pounds forty feet in one minute. A belt running over a pulley at 4,000 feet per minute, pulling with a force of 240 pounds (fair load for a 4-inch belt) will transmit 240x4.000 oo Ann equal thirty horse- power (nearly). oo ,uUO If moving at 1,100 feet per minute, the result would be 240x1,100 equal eight horse-power. A gear-wheel, the cogs of which transmit a pressure of 1,800 pounds (fair load for 1J" pitch 6" face) to the cogs of its mate, the periphery velocity of the wheels being ten feet per second, transmits 1,800 x 10 equal thirty-three horse power nearly. 252 HANDBOOK ON ENGINEERING. If speed was 360 feet per minute, it would transmit 1,800x360 o t > ~~~ equal twenty horse-power nearly. The horse-power developed by a steam engine consists of two primary factors, Piston Speed and Total Awr /V^.s.s/, and from the eccentric rod to the eccentric rod head at E F, on the valve-slide end, and a tram is furnished with the engine, or a new tram can be made with exactly three inches distance between the points, which will suffice. 282 HANDBOOK ON ENGINEERING. In case the tram marks become lost, or, owing to wear of the valve gear, the length of connection is altered, the proper procedure is to put the engine on one center, and then on the A Sectional Cut of Mclntosh and Seymour High-Speed Engine, Showing -Valve and Governor. other, and observe the leads which occur when the governor is in the normal position of rest, as shown. The lead on the crank end should be three times as much as the lead on the head end, if the connection between the valve and eccentric is of proper length. When the valve is set this way, the cut-off on the two ends of the cylinder will be approximately equal at one-quarter cut-off on the smaller size engines having inside governors. Preliminary to adjusting connections between the valve and eccentric, care should be taken that the mark on eccentric G H, corresponds to the mark on the pendulum. In examining the steam leads, as described above, it should be noted that the surface B on the valve has nothing to do with the steam distribution, but it is merely to give ample wearing sur- face, and that the steam is admitted to the cylinder through the port which is between B and the steam edge which is at A, and the lead should be measured between this steam edge and the HANDBOOK ON ENGINEERING. 283 of the port leading to the cylinder. On engines of larger size having outside governors, a similar method should be em- ployed in setting the valves, except that the trams are four inches from point to point, and should be used between the valve-rod slide and valve-rod, and the eccentric rod and the eccentric rod head at governor end, instead of slide end, as above. INSTRUCTIONS FOR STARTING AND OPERATING IDEAL ENGINES. Before starting- engine* Open cylinder cocks and throttle valves sufficiently to warm the cylinder and valve. Place sufficient oil in the basin under the crank so it will stand one inch above the bottom of crank discs. When receiving a new engine from the shops with visible stuffing-box and water drain , before you lill the crank case with oil, previous to starting, pour water in opening Fig. 1. in frame into pocket under piston rod stuffing-box, until water overflows through trap connected therewith attached to outside of frame. Fill cylinder lubricator and start it to feeding. Fill oil 284 HANDBOOK ON ENGINEERING. pump, and pour engine oil into pocket on main bearings. Fill eccentric oiler -and start it feeding. After the steam chest and cylinder are warm, turn the engine over by hand to see that all is free and right to start. Open the throttle valve gradually, start eny'iir xlmvly. After the engine is up to speed, pump five or six strokes of oil into cylinder with oil pump. ' The oil should flow in streams through both pipes on the crank cover into the pockets of the main shaft bearings. This oil passes from the main bearings through the crank pin and is distributed over cross-head pin and slides. Occasionally clean out the oil passages in crank pin. Supply, as needed, a little fresh oil to the basin, and if the oil in the engine bed becomes thick, gritty or dirty, so as not to flow freely through oil passages, draw it off and replace with fresh oil. Filter the old oil and use it over continuously. Use a pure mineral oil that will not thicken by the churning it receives. Serious damage and cutting of the cylinder and valve will result from allowing the lubricator to cease feeding, even for a few minutes. If your engine is a new one from the shops, feed plenty of oil through the lubricator and oil pump for the first few weeks after starting. Use one drop of oil per minute for each ten horse-power, or ten drops per minute for 100 horse-power engine, for the first thirty days ; after which, one-half this amount will be sufficient, if the oil is of good quality. If your boiler is priming or foaming, use double the quantity of oil to protect the cylinder and piston from cutting. A little graphite fed into cylinder is very beneficial. The governor* Fill the cups on governor bearing with grease and give the cap J turn every day. Screw the cap to the stuffing- box on dash pot loosely, only using your hand to turn the cap. The governor should be taken apart every two or three months and bearings cleaned with coal oil to remove gum. If governor HANDBOOK ON ENGINEERING. 285 has a dash pot, it should be refilled with glycerine once or twice a year. Oil may be used in the dash pot in place of glycerine, unless the engine is in a cold room where the oil is liable to congeal. To refill dash pot, unscrew cover on end. In taking 1 the governor apart, allow the sliding block which holds the end of the governor spring to remain with its outer edge on a line with a mark across the face of the slide, and in re- adjusting the spring, place the same tension on it as before, which can be ascertained by measuring the length of the thread through the nuts before slacking up the spring. If you have trouble with springs breaking it is because you are working them under too much tension. The speed of the governor is changed by moving the weight on the lever. To increase the speed of the engine, move the weight on the governor lever near to the fulcrum pin. To reduce the speed, move the weight out toward the end of the lever. Tightening the spring will also increase the speed, but will cause the engine to " race," unless at the same time the block which holds the end of the spring, is moved toward the center of the wheel. The proper way to change the speed is by moving the weight, allowing the spring to remain in its marked position. Moving the block, which holds the spring, towards the rim of the wheel, will make the governor more sensitive and regulate more closely ; but if moved too far, this will cause the governor to " race." Moving the block towards the hub of the wheel has a tendency to stop the " racing," but if moved too far the speed of the engine will be reduced with the increased load. If any of the bearings of the governor bind, or require oiling or cleaning, the governor will "race." These bearings should be kept clean and in good condition and the stuffing-box to the dash pot must not be screwed up tight, as that will cause the governor to " race " when set for close regulation. The face of the slide is marked with a line where the outer 286 HANDBOOK ON ENGINEERING. edge of block which holds the spring should be. Figures stamped on the face of the slide, give length of end of eye-bolt extending through nuts. This gives the right tension to the spring. Tightening the* spring will give closer regulation, but will cause the governor to " race " if the spring is too tight. " Racing " caused by over-tension of spring, can be stopped by moving block nearer to center of wheel. To set valve. Should you wish to ascertain if the steam valve is properly set, proceed as follows : Take off the cover or elbow on outer end of steam chest, so you can have access to end of valve. Turn the engine over until the valve has traveled as far as it will go towards end of steam chest. Then measure from the end of steam chest to the end of the valve, and this distance should be represented by the figures in inches and fractions on end of steam chest. If measurements do not agree, set valve by screwing the valve stem at the ball joint. Square, braided flax packing is the best kind for piston rod and valve stem. Don't screw the glands up tight; allow them to leak a little. The valve stem has only exhaust steam don't pack it tight. Screw it up by hand only. Screwing the piston rod gland up tight may cause the piston to thump or pound the cylinder, and heat and cut the piston rod. Safety caps* The safety caps attached to drip valve under the cylinder are intended to break, in order to save damage to the engine if water enters cylinder. They will protect the engine from breaking if the amount of water is not too large to pass through the valves and pipes. If they break, they have accom- plished their purpose and new ones should be attached. Eccentric* Take up lost motion by reducing the brass liners between the lugs on eccentric strap, and unscrew and dis- connect the ball joint on the eccentric rod to see that the eccen- tric strap will turn freely on the eccentric. If a close fit it will heat, cut, seize and break the eccentric rod or valve stem. Allow HANDBOOK ON ENGINEERING. 287 the eccentric strap to run loose ; no harm if it knocks a little. It will not wear out of round on account of running loose ; it is dangerous to run with the strap snug. Ball joint, Take up lost motion in the ball joint, on the valve stem, by unscrewing the joint at eccentric rod and turning or liling off the face of the brass part attached to the valve stem, so as to allow the male part to screw in a greater distance. Connecting rod* Take up the lost motion on the crank pin bearing by removing the cap and taking out two of the steel liners ; take one from each side, put the cap back and set the nuts up snug. Disconnect the cross-head end of the rod by re- moving cross-head pin, and try lifting the rod up and down to see that it does not pinch the crank pin. If it pinches the pin when the bolts are drawn up snug, place the liners back or substitute thinner ones. Always screw the cap back solid on the liners, and keep in sufficient liners so the cap will not pinch the pin when the bolts are screwed down snug. NEVER RUN THE ENGINE WITHOUT HAVING THE CAP- SCREWED UP SOLID AGAINST THE ROD, with liners between if needed, to make the proper fit. If you remove some .of the liners be sure to take out an equal amount from each side, for if you take out more on one side you are liable to throw the cap at an angle in tightening up the bolts, which, in time, will cause the bolt to break and is liable to wreck the engine. The brass in the cross-head end of the connecting rod is set up by a wedge. This wedge is drawn down by the steel bolt until the brass is forced solid against the shoulders in the end of the connecting rod, which prevents any movement of the brass. The upper bolt is used to lock the wedge in position ; also in withdrawing the wedge when the brass is to be removed. To take up lost motion in the cross-head end of the connecting rod, remove the brass and file an equal amount, even and square, from each edge of the brass, so as to allow the brass part to come up to the pin. When filing the brass, try the pin in the rod 288 HANDBOOK ON ENGINEERING. and do not file enough to allow the brass to pinch the .pin when the wedge is screwed down solid. If, by mistake, too much is filed off, put in a sheet of copper or sheet brass liner, so the wedge may be drawn snug without pinching the pin. Cross-head. For adjusting the lower cross-head slide, take out the cross-pin, turn cross-head J round with the lower brass slipper opposite opening in engine frame ; loosen nuts and insert paper or thin metal strips between cross-head and slipper. The top slide will never require adjustment. The lower slide should run five years before requiring lining or adjustment. Turn the cross-head pin | way around every three months. This will prevent it wearing out of round. Main bearing's; To take up lost motion in the main shaft bearings, remove the cap and file, scrape or plane an equal amount from each of the babbitt metal liners or strips which are in the main bearings under the inside edge of the cap. Remove the metal evenly, so the liners will remain of equal thickness at each end. Do not remove enough from the liners to allow the cap to pinch the shaft when the nuts are screwed down snug. If, by mistake, too much metal is removed, put in paper strips on .top of the liners so the cap can be screwed down solid without pinching the shaft. You can tell when the cap pinches the shaft by turn- ing the engine over by hand ; it will not turn freely when the cap is too tight. With proper care the main bearings will run two years before requiring adjustment. NONE OF THE BEARINGS OF THE ENGINE SHOULD BE SO TIGHT AS TO PREVENT TURNING THE ENGINE FREELY OVER BY HAND. Always test the engine in this manner after adjusting bearings. If a bearing- heats, stop the engine immediately, take out shaft or box, clean out the cuttings, scrape smooth, clean out oil pass- ages and run bearings loose. Heating or cutting will never occur if liners are put in so caps cannot be set up to pinch the bearings and they receive proper HANDBOOK ON ENGINEERING. 289 lubrication with oil five from grit or dirt. After adjusting any of the bearings, run the engine for a few minutes ; then stop the engine and feel the bearings which have been adjusted to see if they are running cool. This precaution may obviate having to shut down your engine while performing regular duty. Do not allow your engine to run with bearings so loose as to thump or pound, as this will cause the bearings to wear out of round. If the shaft or wheels run out of true or wabble, it is because the main bearings are loose and should be taken up. The engine will run smooth and noiseless if bearings are properly adjusted. THE STEAfl CHEST. Fig. 2 shows a section through cylinder and valve. The steam chest is bored out and fitted with a pair o' cylinders or bushings, which have supporting bars across the ports, to prevent any pos- sibility of the valve catching upon the ports. The valve is of the hollow piston type a hollow tube with a piston at each end. The live steam is entirely upon the outside 19 290 HANDBOOK ON ENGINEERING. of this piston, pressing equally on each end ; the exhaust steam is entirely on the inside of the piston, so the valve is perfectly bal- Fig. 3 is a Tandem Compound. auced and can easily be moved by hand when under full boiler pressure. Fig* 4 is a cross-section of cylinder and valve of the Tandem Compound engine. The cylinders of the Ideal Compound engine in Fig. 4, the stuffing-box between the two cylinders, is dispensed with entirely. It is replaced by a long sleeve of anti-friction metal. This sleeve is light and free to adjust itself central with the rod. Grooves are turned on the inner surface, so as to form a water packing. Both valves of engine are controlled by the same governor on the same stem, moving together and varying in stroke as the load and steam pressure vary. This gives the advantage of automatic cut-off in both cylinders and dispenses with the complication of double eccentrics, rock arms, slides and stuffing-boxes. The high-pressure cylinder has a piston valve, same as used in all ideal engines. For the low-pressure valve in order to bring it HANDBOOK ON ENGINEERING . 291 into line with the high-pressure valve and keep clearance spaces at minimum, which thus gives a quick and wide opening at. the beginning of the stroke, in order to reduce the pressure on exhaust end of high-pressure piston. Fig. 4. The cover of this valve is held in place by springs and will lift and prevent excessive pressure in the cylinder from water or other causes. FOR INDICATING IDEAL ENGINES. The illustration (page 292) shows the reducing motion at- tached to engine ready for taking indicator cards. To apply the Ideal Indicator Rig: Screw slotted stud in cross-head pin, first removing the cap screw. Set the slot per- pendicular to line of motion of cross-head. Set cross-head exactly in center of its travel. Fasten on top of bed where oil funnel is placed, first removing the oil funnel. Lever should be adjusted so it will travel in slot without strik- 292 HANDBOOK ON ENGINEERING. ing bottom, or passing out at top. Make sure that lever will travel freely in slot without binding. Select a hole on string carrier that will give the necessary motion to indicator drum. Fig. 5. With string attached from indicator through hole, so adjust this carrier that lines drawn on polished surface shall come exactly parallel with string. Make all adjustments while cross-head is in center of its travel. POINTS ON STARTING AND RUNNING A WESTINGHOUSE COMPOUND ENGINE. In the compound engine, the automatic governor is located on the shaft inside an inclosed case tilled with oil, whi^h forms the center of one band wheel. Its action varies the travel of the valve in accordance with the amount of work demanded of the engine. The other end of the shaft carries an ordinary band-wheel, or combination pulley, of any required diameter and HANDBOOK ON ENGINEERING. 293 face. Set up the engine as directed, keeping the combination pulley, or band-wheel, as close to the engine as possible. Work the wheel on by turning it around while the shaft is held station- ary . Do not attempt to drive it on. The above is a cut of the Westinghouse Compound Engine. In order to put on the governor case with its band- wheel, it will be necessary to first remove the lid or cover of the case, so as to get at the set screws and key way. It is to be put on carefully and should not be driven on hard enough to in any way injure the shaft. The keys are to be carefully fitted to their places, and this should be done by a competent mechanic. It is not pos- sible, in every case, lor the wheels to be put on the engine to 294 HANDBOOK ON ENGINEERING . '.-J: which they belong and keys fitted in their proper places, for various reasons ; therefore, the keys are left as they come from the planer, a triile full of the required size, so that a little filing will bring them to a good fit. If the keys are not fitted in well and carefully at the start, they may become the cause of a great deal of subsequent trouble ; but if this be well done at the beginning, there will be no trouble afterwards. It is the practice of some to tie a tag to each key, designating which one is intended for the governor case wheel and for the band wheel. It is im- portant they should not be put in the wrong places. If the band wheel key should be a trifle too long, no harm will result ; but if the governor case key be too long, it will protrude through the case and bind the eccentric so that the latter will not have free movement across the shaft, and this will seriously attract the regulation of the engine. The key in the governor case should be from J" to J" shorter than the hub in the governor case, to prevent this possibility. When the keys are well fitted they should be driven home with a degree of tightness depending on the size of the engine, and the set screws should be pulled down hard and fast to hold them. The keys are not intended to lit top and bottom, but must fit exactly sideways. After the governor ^ase with its wheel is properly located on the shaft, the key fitted and set screws pulled down hard and fast, the governor case lid is to be put on, having a paper gasket, both on its outer edge and at the hub, to prevent leakage of oil past these surfaces ; and it is to be bolted up tightly in its place, and the governor case completely fdled with cylinder or Dalzell crank- case oil, through a connection provided for this purpose. Turn the engine over by hand to make sure that everything is free. Before starting the engine for the first time, oil both pistons thoroughly by taking off the relief valves and pouring oil into the ports. This oil will work through the valve and oil it also. Swing aside the bonnets from the crank case, and see that the HANDBOOK ON ENGINEERING. 295 latter is clean and free from the cinders and dust of travel, which o-enerallv find their way into the interior. When found to be per- O / / fectly clean, supply oil and water according to the following directions : Pour in water until it makes its appearance at the outlet of the overflow cup ; then pour in one gallon of Westinghouse crank-case oil for every 10 H. P. of the rating of the engine for the smaller compounds, and about half this amount for the larger ones. This will raise the water and oil in the interior to such a level as to almost touch the crank-shaft, so that the connecting rods will be plunged into the liquid at every revolution. Takeoff the eccentric strap , clean it thoroughly, also clean the hollow eccentric rod, then oil and replace it. Be liberal in the use of oil all over the engine, at least for the first few days. Remember that there are two large cylinders and a valve to be lubricated and that the low-pressure cylinder gets its oil only through the high-pres- sure cylinder. The engine should now be ready to start. Fill the automatic lubricator on the steam pipe with good cylinder oil ; fill the side oil cups over the main bearing with Westing- house crank-case oil, and open the drip-cocks over each main bearing, so that the drip is continuous and regular at the rate of about 2 to LO drops per minute from each cup, according to the size of the engine. If undue service is required of the engine, so that the main bearings show signs of heating, the amount should be increased. Start the automatic lubricator; give the eccentric strap some direct lubrication from a squirt can, and start the cup over the rocker arm to feeding from each cock. To start the engine. the throttle valve being closed, open the drain cocks in the throttle-valve and steam and exhaust pipes, blow them out thoroughly and then close them. Open both cylin- der drain cocks ; raise the check valve on the crank case by set- ting the handle down ; open the by-pass valve. Turn the engine rouod until the high-pressure piston is on the upper^center. Now, open the throttle-valve slightly, for the purpose of warming up the 296 HANDBOOK ON ENGINEERING, steam-chest and valve equally, as otherwise the valve, by heating quickest, may expand and bind. The engine being on its center will not start. When sufficiently warmed up, say in three minutes by your watch, close the throttle value for an instant and bar the engine off the center. Then open the throttle- valve quickly, but not too far, which will insure the engine passing the first center. As soon as the engine is up to speed, close the by-pass valve tight and keep it closed thereafter. When the water is thor- oughly worked out of both cylinders, close the cylinder cocks and keep them closed, and at the same time, close the check valve and open main throttle- valve gradually until it 'is wide open. Never attempt to regulate the speed of the engine by the throttle- valve. In stopping the engine, open the cylinder cocks, check valves and by-pass valve and close the throttle slowly, so as to allow the engine to lose speed by degrees. Do not stop suddenly, as the momentum of the pistons and fly-wheels, at standard speed, is great, and the strain thrown on the connecting rods and crank- shaft, in being suddenly stopped, is unnecessary and may, in time, become injurious. In general, it is well to run a new engine empty (that is with no belts on) in order to be certain that everything is right ; then, if the performance is all right, the belts can be thrown on. With a compound engine properly adapted to its work, not overloaded, and running under proper conditions, the duty of the engineer may be said to be merely nominal. Nevertheless, this engine, when it requires the attention of an engineer, needs the proper kind of attention. One competent man can operate a very large number of these engines. What is meant in this con- nection by the terms ' ' properly adapted ' ' and ' ' proper condi- tions," is: a load corresponding to a mean effective pressure in the high-pressure cylinder not exceeding -one-half of the boiler pressure ; a boiler pressure as high as possible, the engine erected HANDBOOK ON ENGINEERING. 297 in compliance with the directions given, and the directions as to lubrication followed carefully. The wear is constant in one direction, namely, downward. The steam acts only on the upper side of the pistons. The two crank-pins are exactly opposite each other. Each piston in its downward stroke raises the other piston. The direction of the wear on all the bearings being downward, the lost motion may be considerable without detriment to the quiet running of the engine. In starting and stopping the engine, however, the accumulated lost motion will cause a noise, inasmuch as this motion is taken up at each revolution ; the greater the amount of lost motion, the greater this noise will be in starting and stopping. The cause of this is apparent ; the crank, while the engine is stopping, must pull the piston down and the effect of lost motion then becomes similar to that in a double-acting engine. The effect of this action is not conducive to good wear or long service. It allows a shock to come on the connecting rod strap with con- siderable force ; this wear, therefore, should be taken up fre- quently, but it can be allowed to accumulate to a greater degree than will be possible in any double-acting engine. The wear is taken up on both ends of the connecting rod at once, by the upper bolt at the lower end. The engineer on opening the crank case will see a bolt with a squared end and a lock nut ; with the large end of the socket- wrench, he will slack off the lock nut, and then with the small end of the wrench he will turn the bolt to the left until the brasses come up solid ; then slack off half a turn and set up the lock nut. The construction of the rod and the way in which a single wedge is made to take up both ends of the rod at once, is evident from the cut. The piston wrist-pins, if worn or cut, should never be dressed off or turned down, as they will not fit the bushing or have a proper bearing. Order a new pair, and throw the old ones away. When the babbitt is about worn out of the main bearing shells, they can be 298 HANDBOOK ON ENGINEERING. re-babbitted and put back again. The cylinder packing rings will, after much wear, become unfit for service, and will allow steam to blow past the pistons into the crank-chamber. There will be at all times, when the engine is running loaded, a small amount of vapor arising in the crank-case. This does not necessarily indicate that there is a leakage of steam past the pistons, as the heat generated by the splashing of the water on the hot pistons and cylinders, and by the leakage of the hot water of condensation past the pistons, will heat up the water contained in the crank-case, until it vaporizes slightly. New packing rings can be easily sprung into place by the engineer. The principal duties of the engineer will be to see that the automatic lubricator, which oils the cylinders and valve and the oil cup over the rocker arm, perform their work properly and regu- larly. Feed slowly, drop by drop, according to the requirements of the engine. The engineer must also see that the oil tanks on the sides of the engine are supplied with oil and fed slowly, drop by drop, into each main bearing. The inclosed construction of the engine, whereby all oil used in lubrication is completely distributed on the wearing surfaces and is prevented from wasting, renders it unnecessary for the engineer to pay as close attention to this engine as to any other, as it, in a sense, lubricates itself. The crank-case bonnets should be removed regularly, preferably every morning, as it is the work of Only a few minutes. The interior of the engine should be examined to make sure that no nuts or bolts (of which there are the fewest possible number) have worked loose, bushings worn out, or lost motion become unduly great ; this internal examination is absolutely imperative, at least, once a week. The proper drainage of water in the steam pipes should demand his attention, to prevent any entrainment, resulting from the foaming of the boilers or from any other cause. Entrained water is always a prolific source of trouble in steam engineering ; it is particularly HANDBOOK ON ENGINEERING. 299 troublesome in all piston valve engines, even with Westinghouso engines, which are provided with water relief valves. The engineer should become thoroughly acquainted with his engine so as to understand its operation and principle, and be at all times familiar with its precise condition. All adjustments being made in the shop before shipment, it is unnecessary for the engineer to set any valves or take any part in the adjustment of a new engine ; but as wear occurs, he must be able to intelligently make the needful adjustments of wearing parts. After an engine has run a long time, the downward wearing of the reciprocating parts will have the effect of throwing the valve slightly out of adjustment. That is to say, it will draw the valve gear downward with the shaft, and favor one cylinder more than the other. The valve, therefore, will require resetting occasionally, but not at all fre- quently. It should be adjusted by lengthening the eccentric rod, just the amount to which the shaft is worn downwards. MAIN BEARING. MAIN BEARING. The main shaft bearings are now made adjustable. There is a slight difference of construction here in the various sizes, occasioned by limited space in the castings ; but they are all alike in this respect, that the bottom half of the main bearing is stationary, being turned off on its outer shell eccentric with the shaft journal and held down firmly by a long set screw on each 300 HANDBOOK ON ENGINEERING. side, which prevents it from rotating or from rattling loose. The top half of the main bearing is adjustable downwards, so as to follow up any wear either of the babbitted bearing or of the shaft. In the 8 anctl3x8 and ( J and 15x9 engines, this top half of main bearing is adjusted downwards by three set screws located at the apexes of a triangle, and the bearing is locked firmly by three tap bolts oppositely placed so as to hold it secure after adjustment, In the case of all larger sizes of compound en- gines, the downward adjustment is made by wedges bearing on the inclined tops of the upper half of the bearing. These wedges are moved and locked by a tap bolt in each end, which passes through and draws against the shell of the crank-case head. The top half of main bearing is drawn up and locked in position after adjustment by tap bolts which pass down through the top shell and are screwed into the bearing. Some of these bolts and wedge screws are inside of the crank-case, and adjustment must, there- fore, be made while the engine is standing idle. It is customary to mark with an arrow head on the outside of the crank-case head to indicate which way the wedge will move to tighten up. The proper condition of the compound engine, while perform- ing its work, is one of perfect quiet, without leaks of steam past any joint and without noise. Any noise in the engine, after it has attained full speed, may be immediately accepted as an indi- cation that something is wrong and the engineer should familiar- ize himself with it, so as to be able to discover the cause and the remedy. Hot bearings may be said to be unknown in this engine ; occasionally, however, they have been met with but they are always traceable to the use of improper oil ; dirt and grit in the oil ; the filling up of oil grooves, or the wearing out of the oil grooves in the main bearing shells ; or to worn out or broken packing rings in the piston. The eccentric strap is the only point liable to run dry, and the engineer should see that the oil cup feeds with certainty. All joints in the governor are bushed and HANDBOOK ON ENGINEERING. 301 these bushings are provided with sufficient oil hples ; they can readily be replaced with new ones when necessary. In replacing bushings, always be careful to provide ample oil-holes, the same as were in the old removed bushings, and observe the same pre- caution in the case of other repairs. As above stated, it is the duty of an engineer to know in what condition every part of his engine is at all times. All wearing parts should be examined from time to time, so they can be re- placed before they are entirely worn out, and damage is done. It is too late to find out that a bushing needs replacing after it has been worn entirely through and the pin has cut into the solid metal. While the engine is built of the very best materials and with the greatest care, and while the means and the opportunity for lubrication are the best known, yet it is not claimed that it possesses any miraculous virtues by which it will run on for- ever without any attention and without repairs. Nowhere is the old proverb more forcibly demonstrated than in the case of machinery, that " A stitch in time saves nine." The wearing parts of the engine are few, are easily reached and placed, and the engineer who waits until same accident happens to announce that he has long neglected the proper inspection of the part which could, at the proper time, have been replaced at a trifling cost, is not worthy of being placed in charge of any machine more complicated than a wheel-barrow. The same principle will apply with equal force to machinery of every type. There is a proper time to replace worn parts and a time it is too late to replace them. HOW TO SET THE MAIN VALVE. The only exact and final setting of the valve is by means of the indicator. As the valves are permanently set and all adjust- ments made before the engine is shipped, it is not supposed that 302 HANDBOOK ON ENGINEERING. the engineer will have occasion to reset them. Should the neces- sity for setting the valves arise, however, the following method will be sufficiently accurate : Break joints and take off the throttle- valve. The steam ports in the bushing will then be seen through the steam connection S. (This opening is on the side in fact, but is here shown on the top for convenience.) Bring the high- pressure piston exactly to the top of its stroke by turning the shaft in the direction the engine runs. This may be ascertained B by either taking off the water relief valve and measuring through its port, or more conveniently, by bringing the middle of the key- way in the shaft exactly over the center of the shaft. The key- ways are planed exactly with the cranks, so that the position of the key way is the position of the high-pressure piston. With this piston at the top of its stroke, the valve edge a a, should show about y L of an inch port or lead, and be moving towards the right as you stand behind the engine. If out, it may be brought to position by screwing the valve-stem into or out of the valve which is tapped to receive it. Be sure and set the jam nut solid when through. HANDBOOK ON ENGINEERING. 303 After a test of n compound engine has been completed with the indicator, and the valve has in this manner been accurately adjusted, marks are scored on the end of the rocker arm, at its junction with its supporting bracket, in order to show the extreme points of oscillation of the rocker arm. If, therefore, in starting up a new compound engine, the eccentric rod is too long or too short, these marks will not coincide when the engine is turned round by hand, to examine this point. The eccentric rod must then be adjusted with the nuts provided for that purpose, until the scored lines on the rocker arm will coincide exactly. When this rod has thus been proven correct, the engine should then be put by hand on the dead center, with the high-pressure piston at the top of its stroke. In order to prove this upright position of the high-pressure piston exactly, two lines are scored on the faced-off end of the crank-box head on the high-pressure side, to which marks the keyway in the main shaft must be brought exactly. Then remove the back head from the steam chest and measure the distance from the rear end of main valve to the end of the steam chest, while the engine is in this position. This distance measured will be found stamped with steel figures on the finished face of the steam chest, underneath the back head. If the valve has not been disturbed, the measurement thus taken will agree with the figures. If it has been disturbed, the valve must be adjusted to correspond with the measurement. ADJUSTHENT OF ECCENTRIC STRAP AND CONNECTING ROD. Before starting" the engine for the first time, the eccentric strap must be taken off and both the strap and eccentric carefully cleaned and lubricated with clean oil. The eccentric rod is hollow and might contain dirt or other injurious matter, and should be examined and thoroughly cleaned before putting on the engine. There must be a sufficient number of liners between the 304 HANDBOOK ON ENGINEERING. joints of the strap, so that when the bolt is pulled up hard and tight the eccentric strap will still be free to run without binding. After the bolt has been tightened, take hold of the strap and shake it back and forth to be sure that it is free. If it binds in the least, it is certain to heat or cut either itself or the eccentric or probably both. When the upper ball joint on eccentric rod becomes worn it should be adjusted to take up the lost motion promptly. As to the connecting rods, the lost motion should be simply taken up without binding. No possible good, but much harm, can come from too tight an adjustment, GENERAL INSTRUCTIONS FOR HOHE REPAIRING. How to put in new bushings and cut the oil holes and grooves* When new bushings are shipped to fill repair orders, they are turned to gauge so as to fit tightly in their respective places. A very careful mechanic may, by the use of a wooden block and hammer, be able to drive in bushings 'properly. The much safer course, however, is to use a bolt which passes through the bushing, and a nut and washer ; by screwing up the nut and taking reasonable care, the bushing is thus drawn surely and gradually into place. After the bushing is in place, the oil grooves must then be cut into it with a half-round chisel and hammer. The oil-holes must then be drilled ; these latter should be large and free ; no harm can come from having them too large, but much trouble will result if they are too small. The oil should have very free access through these holes to the grooves. We have conducted a long series of experiments to determine what form or style of oil groove would produce the best lubrication, and consequently, the most satisfactory results in each bushing, and, therefore, urge that grooves be cut in new bushings in strict accordance with the grooves and oil holes as shown in the old HANDBOOK ON ENGINEERING. 305 bushing which has been removed. This course is safer and bet- ter than to try experiments of your own. How to rebabbitt connecting rods* Connecting rods may be re-babbitted at home, if preferred. You should provide yourself with a plug, preferably of cast-iron, turned to the exact diameter of the shaft or crank-pin and squared accurately on the end. A perfectly true surf are is then required on which to lay the rod, so that the plug will stand in its proper position, exactly square with the rod. The original length of -the rod must be known, and will be furnished by us on application, by stating the number of your engine. The center of the plug must then be placed at the proper distance from the center of the eye of the connecting-rod pin, and the babbitt metal poured into place. Moistened lire-clay will be found very convenient for confining the molten babbitt metal within its proper limits. After cooling, the babbitt metal should be dressed with chisel and file. Bear in mind that heavy service is required of these connecting rods, and that the engines run at higher speeds than is possible in any other type of engine, hence, nothing but first-class babbitt metal, or '" genuine " babbitt metal, as it is called in the trade, will answer the purpose. I would, however, advise that the brasses be sent to the shop to be re-babbitt, and that duplicates be kept on hand, if necessary. How to rebabbitt main bearing shells* This is a very diffi- cult piece of work to do at home, and it is not recommended that you attempt it ; it cannot possibly be done accurately by any one without special appliances for the purpose. The lines of the bab- bitt, internally, when complete, must be exactly parallel with the outside lines of the shell, else the shaft cannot lie on its bearings with equal contact throughout the length of the shell. The lack of equal contact will cause the shaft to bind, and in all probabil- ity, the limited bearing surface will cause friction and heating. The only way in which main bearing shells can be properly re- babbitted at home, is to first provide yourself with what is called on 306 HANDBOOK ON ENGINEERING. a "jig," which is simply a special device that holds the main bearing shell and the central plug in their relative positions, ex- actly, while the babbitt metal is being poured. After cooling, the ends of the shell should be dressed and the oil-holes and grooves must be properly cut, exactly as they existed when the shell was new. A simple and more satisfactory method, would be for each owner of an engine to purchase an extra pair of main bearing shells ; in this way, while one pair of shells is in use in the engine, the other pair may be sent in for rebabbitting, with- out the loss of time, and at trifling cost. Use nothing but iirst- class " genuine " babbitt metal in the main bearing shells. How to repair worn or badly scored wrist-pins* Instruc- tions on this point are very simple: Don't! If, on examina- tion, you find you have allowed the wrist-pins at the upper ends of the connecting rods to become worn, or even badly scored, it is recommended that, having bought a new pair of wrist-pins and rebabbitted the brasses, you immediately take out the old pins and throw them away. It is useless to attempt . to repair worn wrist-pins. If you turn them down until they present a smooth exterior (as some have proudly announced they have done) the diameter of the pin is so reduced that it will not fit the brasses and the reduced bearing surface will soon destroy it. Or, if you attempt to use a badly scored wrist-pin in new brasses, it will cut them out so rapidly that it would be more economical in the end for you to buy new wrist-pins than to attempt to use the old ones. The service on the wrist-pin of any engine is extremely heavy. These pins are made with the besi possible care, using the best selected materials, and after machin- ing them they are ground in special machinery. The brasses are lined with the finest possible babbitt metal and should last a long time under heavy duty if properly lubricated ; yet, the use of an improper oil in the crank-case either volatile or gritty nul- lities all these precautions. Therefore, if you lind on examina- HANDBOOK ON ENGINEERING. 307 tion, that the wrist-pins in your engine have become badly worn or badly scored, I would urge you to throw them away and buy new ones. Where the inclosed form of governor is used, the governor case is to be filled completely full of good cylinder oil, or with James Dalzell & Son., Ltd., Crank-case oil. Use nothing else. A nipple is screwed into the face of the inner case and extends through the first flange of the wheel in a radial direction. This nipple is closed by a cap. Turn the engine around till this nipple is on top and fill the case entirely full through the opening. The joint at the outer rim of the case, also the joint on face of hub, is made with a paper gasket. The oil is prevented from escaping along the spindle of the eccentric and out past the eccentric by a leather packing ring fitting around the spindle and between the 308 HANDBOOK ON ENGINEERING. eccentric and the face of the case. If, after service, this should leak oil when the engine stands still, you must pack it tighter by putting in a thicker packer-ring of leather, so it shall be held tightly in its place and prevent the passage of oil. Be careful in locating the governor case on the shaft, so that the average posi- tion of the eccentric rod shall be vertical and that its extreme positions shall be alike on each side of a vertical line drawn through the center of eccentric. Be very careful as to the lubrica- tion of the eccentric strap at the start. After it runs for a few weeks and gets a good surface, it will require little attention beyond regular oiling. When you start the engine, be sure to put plenty of oil on the eccentric direct, by hand. The best means for lubricating the valve and pistons is an Automatic Sight Feed Lubricator, which is treated of elsewhere. It is manufactured in a variety of forms, many of which are very effective in their working. With a good cylinder oil, the number of drops per minute can be regulated so as to effect the greatest economy of oil and distribute it in such a way as to do the engine the greatest amount of good. Any other system of lubri- cating the cylinders is defective. It will not suffice to give the engine an hour's supply of oil at one dose and then allow it to run without any cylinder lubrication for the remainder of that hour. The construction of the Westinghouse engine is such as to be favorable to the economy of oil in this direction, because the pistons moving up and down in a vertical direction do not have the same tendency to wear as in the case of a horizontal engine, where the heavy piston-head drags back and forth. These im- mense bearing surfaces, moreover, reduce the amount of pres- sure per square inch to a minimum. The Automatic Lubri- cator is to be attached to the steam-pipe, within easy reach of the engineer, so that it can be refilled without loss of time. With each lubricator is packed specific directions for starting and operating it, which should be followed carefully. It may HANDBOOK ON ENGINEERING. 309 be well to note here that, in order to get the best results and avoid trouble, no other than a first-class cylinder oil should be used in the cylinders. Approximately, one pint of cylinder oil per day for every fifty horse-power, and pro- portional, will be required for engines, depending on the amount of work to be done. The lubricator furnished on each engine will serve as a partial index of the quantity of oil required. These cups are not intended to hold over 8 to 10 hours' supply in any case. Feed regularly and slowly. The use of Valvoline, or 600 W. Vacuum Cylinder Oil, made by the Vacuum Oil Co., Rochester, N. Y., is recommended, although there are others who make a first-class article. SOME POINTS ON CYLINDER LUBRICATION. 44 In the first place, use the best automatic feed cup that can be secured. Don't be satisfied with the old-fashioned direct feed, or a cheap automatic. A good cup will save many a hun- dred per cent on its cost in a year. Don't get the kind which, on account of its peculiarity of feed, is adapted for a light oil only ; you will then be shut out from using a dark oil, which may be far more serviceable and economical in every respect. Get a cup where the drop of oil cuts off square and passes either down or up through a glass tube into the steam pipe. This kind will feed oil perfectly ; if yours is not this kind, it will pay you to change it." "Take good care of your cup. Don't let it leak around the glass tubes or other joints, for if it does the water will escape as it condenses, and the oil will clog up the escape pipe and stop feeding. Use in it only the best grades of cylinder oil, made by large manufacturers of established reputation. Don't run in your cylinders any kind of poor stuff that may be offered, because it is cheap ; it is a dangerous experiment. Feed a good 310 HANDBOOK ON ENGINEERING. oil sparingly don't drench the cylinder. Too much oil is as bad as water in the cylinder. Engineers have been known to run a couple of quarts per day of cheap oil into an ordinary sized cylinder, and thought they were doing just right ; this is positive abuse of an engine. In almost all cases where too much oil is fed, cut it down. Two to four drops per minute on engines from 50 to 150 H. P. are all that is necessary, if the oil is good. Just enough to do the work and no more, will afford best results. As long as the valve stem does not cause trouble, you may know the valves are working smoothly and that you are giving oil enough. AUTOMATIC LUBRICATORS. An Automatic Sight Feed Lubricator should be furnished with every engine, which enables the engineer to see the oil as it is fed drop by drop to the engine. The construction of these lubricators is such that the steam entering a chamber is condensed and this water of condensation finds its way into another com- partment of the lubricator, wherein is contained the oil to be fed to the engine. The drop of water, by reason of its greater spe- cific gravity, seeks the 'bottom of this oil compartment and forces out an equivalent bulk of oil into the steam pipe, whence it is carried by the current of steam into the cylinders and is distrib- uted upon the wearing surfaces intended to be lubricated. This method insures regularity and economy. There are numerous automatic lubricators made by various manufacturers throughout the country, many of which will per- form their functions successfully. I have used several of the best types, and consider any of them suitable for the purpose ; jut herewith is submitted, with description of the cup I have been using for some years. This is the up-feed cup, showing an external view and sec- tional view of the same. Attachment is made to the steam-pipes HANDBOOK ON ENGINEERING. 311 at the points F and .A". In operation, the condensing chamber F provides for the condensation of steam which enters at the pipe F. This water of condensation passes down through the valve D and through the tube P shown in the section and discharges into the bottom of the oil vessel A. This vessel is filled with oil when the cup is started, the height of oil being shown in the index glass J. THE ''DETROIT" LUBRICATOR. The operation is as follows : The valve N being opened, the valve D is opened and the drop of water is allowed to pass from the condensing chamber F downward through the water tube and into the bottom of the oil chamber A, where it displaces a drop of oil of equal bulk on account of its greater gravity, and this drop of oil is forced out past the valve E, making its appearance in the feed glass H, as it starts on its way to the steam-pipe. It is carried by the current of steam to the engine and lubricates the valve and the pistons. When the oil cup is empty, the valve D 312 HANDBOOK ON ENGINEERING. is closed and the drain valve G is opened, which will allow tin- water in the oil chamber to be blown out preparatory to the re- filling at the plug (7. By opening the valves G and D, steam will be blown through the sight glass ,7, thereby clearing the same from any clogging up of the oil, which would disfigure it. The amount of oil to be fed by the lubricator will be regulated by the valve Z>, controlling the amount of water admitted, and the valve E controlling the discharge of the oil into the sight glass. The valve N is to be left wide open in operation and its object is to provide for the accidental breaking of the glass //. Sketch showing proper method of attaching cup to prevent the oil from dropping into the well, and not going into the cylinder. These cups should be attached to the steam pipe, in strict ac- cordance with the instructions contained in the box in which the lubricator is packed. The greatest enemy to proper performance is leakiness ; all joints must be absolutely tight, otherwise the HANDBOOK ON ENGINEERING. 313 water of condensation, instead of performing its duty of displac- ing the oil, will ooze out at the leaks and the cup will refuse to work. In most cases, provision is made for a column of water which may stand 12" or more in height and enable the cup to work more positively, by giving it a greater pressure in the dis- placement chamber, due to the height of the column. A suitable oil is essential to the proper working of such a lubricator, as well as to the proper lubricating of a steam-engine. An improper oil will not feed through the cup as it should, on account of its dis- position to disintegrate and go off in bubbles, when exposed to the heat of the steam. SETTING A PLAIN SLIDE VALVE WITH LINK NOTION. The setting of a slide valve operated by a link motion does not differ materially in principle from the method pursued when setting the ordinary slide valve driven by one eccentric. A link motion may be considered as a means of driving a valve by two independent eccentrics, either of which controls the functions of the valve wholly or in part, according to the position of the link. Thus when the link is in either extreme position, the eccentric driving that end of the link in line with the link-block pin may be considered as being entirely in control of the valve action, and, vice versa, when the link occupies the other extreme position of its throw, as actuated by the reverse lever, the other eccentric becomes possessed of the controlling" function. Practically, however, the operation of the link motion is very complicated and the movement of one eccentric materially modifies the action of the other. Since the interfering action is least at the extreme positions of the link and greatest in mid-gear, the plan is followed of setting the valve with the link in full gear both forward and backward motion, and, as before stated, the procedure is on the theory of independent action of the eccentrics. 314 HANDBOOK ON ENGINEERING. In the accompanying diagram, a link motion is shown driving a plain slide valve without the intervention of a rocker. Each eccentric is set with reference to the crank-pin, the same as it would be with a simple slide-valve engine. The eccentric A is set on the shaft with the same angular advance, QMO, as would be required for an ordinary engine to run in the direction indi- cated by the arrow. Now, since the crank pin is at (7, if it were necessary to reverse the simple engine with one eccentric, it would be necessary to change the position of the eccentric so that instead of being ahead of the bottom quarter line QM, it would be ahead of the top quarter line PM by an amount of angular advance made necessary by the lap and lead of the valve. Therefore, the eccen- tric would come in the position of the eccentric A 1 , or with its center line coinciding with MN, giving it the angular advance PMN. Now it should be clear that if an engine is to be equipped with two eccentrics, so that it may run with equal facility in either direction, they will occupy the positions A and A 1 . We will suppose that an engine having a link motion is to be over- hauled and the valve" motion to be properly set. This will mean that the eccentrics will be properly located for the correct angular advance, and that the eccentric rods will be adjusted to the right length. When these conditions are obtained, the valve should HANDBOOK ON ENGINEERING. 315 perform its functions properly in both forward and backward motions, and also when the link is " hooked up." Before starting to set the valve, it is best to take a general survey of the valve motion parts and see if the eccentrics are somewhere near the proper location on the shaft relative to the crank-pin. If they are obviously much out of position, they should be shifted and adjusted as near the correct position as possible by the eye ; doing this at the beginning will often save confusion and much time. The dead centers will be found by the method given on page 195. The operation should be carefully performed, as upon it depends the success of the work. After having found the dead centers and having them marked so that no mistake will occur when "catching" them with the tram, the valve positions may be taken for the four positions , that is, front and back centers in forward motion, and the front and back centers in backward motion. Put the reverse lever in full gear in one motion or the other, whichever is most convenient, and turn the fly-wheel in the direction the engine would run for the given reverse lever position. Suppose the link stands in the position shown in the diagram, the fly-wheel should be turned in the direc- tion indicated by the arrow until the dead center is reached, which is known when the tram drops into the prick mark. The position of the valve is then noted and a measurement taken. If the valve shows the steam port open, measure the distance with a steel scale, or it may be done by sharpening a stick wedge-shaped and shoving it into the opening. By noting the depth to which it goes at the valve face the opening can be readily measured on the removal of the wedge. We will suppose the distance is found to be y m The measurement should be set on a sheet of paper laid out as follows : FORWARD MOTION. BACKWARD MOTION. Front center, Front center, Back center. Back center, |" lead. 316 HANDBOOK ON ENGINEERING. It will be seen that the valve opening is set down a being H" lead, and as being on the back center in the backward motion. After having verified the measurement taken, the engine can be '" turned over " in the same direction as before until the opposite dead center is caught by the tram. It may be found Hint the valve does not show open in this position but covers the steam port. To find the position of the valve edge relative to the steam port, scribe a line in the valve seat face along the edge of the valve and then turn the fly-wheel until the valve uncovers the steam port. The distance the valve laps over when the crank i on this dead center can then be readily measured. Suppose the distance is found to be J". It is set down on the log as follows : FORWARD MOTION. IJAOKWA Rl> MOTION. Front center. Front center, J" blind. Back center. Back center, |" lead. The valve position is put down as being J" blind, which is the same as saying that it has |" negative lead, and is fully as com- prehensive as the latter term. The reverse lever should now be thrown into the opposite gear and the measurements taken for both front and back centers the same as has been described for the backward motion. It may now be supposed that when all the measurements have been taken the log reads as follows : FORWARD MOTION. BACKWARD MOTION. Front center, ,J" blind. Front center, |" blind. Back center, -f^" lead. Back center, |" lead. When in forward motion, the valve is open T 5 " on the back center and lacks J" of being open when the crank is on the front center. The total lead due to the angular position of the eccentric is -f^" minus J" T V'. One-half the total lead should be given to each edge of the valve so that it will be necessary to lengthen the eccentric rod JB 1 , -^" -f- *." = ^" to get the valve HANDBOOK ON ENGINEERING. 317 into its proper position. A little reflection will show the reason for lengthening the eccentric rod B l . In speaking of the front and back centers, they are taken to coincide with the crank and head ends of the cylinder. When the piston is at the crank end of the cylinder, the crank is on the front center. By referring to the log it will be seen that to adjust the backward eccentric rod 72, it will also be necessary to lengthen it. The valve is J" blind on the front center and has | " lead on the back center. The total lead is, therefore, f" minus J" J". One-half J" = J", which being added to the amount the valve is lapped on the front center, makes J", or the amount the eccentric rod B will have to be lengthened to make the valve open equally at each end of the piston stroke. The opening the valve has when the crank is on the centers is called the lead and in the ease of the backward motion, it is found that after the eccentric rod is lengthened, the lead is J", which is too much for most cases and in this one we can assume that 3 ^" would be about right. Before explaining the adjustment of the eccentric for the cor- rect angular advance, it will be in order to call attention to the necessity of making the adjustment for the eccentric rod lengths first. The eccentric rods are lengthened or shortened, as the case may require, by inserting or removing liners between the eccentric rods and straps at R. Other forms of construction provide different means for adjustment, but the principle is the same in each. It will be noted that the correct length for the two motions is obtained by adjusting the eccentric rod corre- sponding to that motion. Any attempt to correct an irregularity by changing the length of the valve rod F will result erroneously, unless both eccentric rods require the same amount of movement and in the same direction. After having adjusted the eccentric rods to the correct lengths, the angular advance of the eccentric A can be changed. Place the crank on a dead center and have the reverse lever thrown in the backward motion and then 318 HANDBOOK ON ENGINEERING. loosen the set screws that hold the eccentric to the shaft and turn it towards the crank until the valve shows open ^ 2 ", and then tighten the set screws on the shaft. After all the adjustments have been effected, it is always advisable to turn the engine over again and catch all the dead centers, so that the correctness of the adjustments can be verified. After taking the new log, it will usually be found that some slight irregularities have been introduced, especially if any of the adjustments have been consid- erable, as the changes made for one motion will affect the other slightly. The link motion shown in the cut is so connected that the lead increases as the link is shifted towards the center. If the eccen- tric rods be oppositely connected to the link, the engine will run in an opposite direction for a given reverse lever position and the lead will decrease as the lever is shifted towards the center. The link motion for hoisting engines is quite commonly connected in this manner, for the reason that the engine will stop when the lever is put on the center, which is not the case when connected as shown. Of course, in such a case, the admission and cut-off take place at the same position in the stroke and the compression is high, but with a light load the engine will run on the center, which is considered objectionable in the case of the hoisting engine. VALVE-SETTING FOR ENGINEERS. Plain slide-valve* The plain slide-valve, while the simplest valve made, is perplexing to one who has not made a study of it. Unless one understands the principles of the valve and its connections, he will probably meet with trouble when he attempts to set it. We will first place the engine (see p. 195) on the dead center, and will simply explain the other steps that have to be taken. In the first place, it should be understood what result is obtained by adjusting the position of the eccentric HANDBOOK OX ENGINEERING. 319 and the length of the valve stem. The position of the eccentric, when the valve is set. depends upon which way the engine is to run and whether the valve is connected directly to the eccentric or whether it receives its motion through a rocker which reverses the motion of the eccentric. When the valve is direct connected, the eccentric will be ahead of the crank by an amount equal to 90, plus a small angle called the angular advance. When a reversing rocker is used, the eccentric will be diametrically opposite this position, or it will have to be moved around 180 and will follow instead of lead the crank. Shifting the eccentric ahead has the effect of making all the events of the stroke come earlier, and moving it backwards has the effect of retarding all the events. Lengthening or shortening the valve stem cannot hasten or retard the action of the valve, and its only effect is to make the lead, or cut-off, as the case may be, greater on one end than on the other. The general practice is to set a slide-valve so that it will have equal lead. The lead is the amount that the valve is open when the engine is on the center. To set the valve, therefore, put the engine on the center, remove the steam-chest cover so as to bring the valve into view, and adjust the eccentric to about the right position to make the engine turn in the direction desired. Now make the length of the valve-spindle such that the valve will have the requisite amount of lead, say ^ of an inch, the amojLint, however, depending 'upon the size and speed of the engine. Turn the engine over to the other center and measure the lead at the end. If the lead does not measure the same as before, correct half the difference by changing the length of the valve-stem, and half by shifting the eccentric. Suppose, for example, that the lead proved to be too great on the head end by half an inch. Lengthening the valve-stem by half of this, or J inch, would still leave the lead J inch too much on the crank end. That is to say, the valve would then open too soon at both head and crank ends, and to correct this, the eccentric would 322 HANDBOOK ON ENGINEERING. end, towards which the piston is moving, has just commenced, and the exhaust is about to take place from the other end. AT POINT OF TAKING STEAM. I Fig. 4. Fig* 4 shows the position of eccentric and valve in an engine with a rocker-arrn. AT POINT Or CUT- OF FT Fig. 5. Fig. 5 shows the position of valve and eccentric at point of cut-off. POS/T/ON WHEN COMPRESSION BEGINS. Fig. 6. Fig 1 * 6 shows point 01 compression. HANDBOOK ON ENGINEERING. I CHAPTEK XIII. TAKING CHARGE OF A STEAfl POWER PLANT. It is frequently the case that an cugineer, en assuming charge of a steam power plant, proceeds as though lie were thoroughly familiar with the condition of the engine, boiler and entire sur- roundings. He plunges headlong into his duties, without first taking his bearings. A skillful physician on taking a case, would not proceed in this manner ; neither would a lawyer. The physi- cian would feel the patient's pulse, look at his tongue, take his temperature, observe his color and ask a number of questions, all for the purpose of enabling him to make a correct diagnosis of the patient's ailment. The first duty of ah engineer, when he takes charge of a plant, is to ascertain the arrangement and con- dition of the plant. Since the boiler is the most important mem- ber of the plant, it should be the first to engross his attention, and it, together with its connections, should be examined as closely as time and surrounding conditions will permit. He should look the boiler all over, internally and externally, if possible, in view of 324 HANDBOOK ON ENGINEERING mud, scale, grooving, pitting and defective braces. The furnace should be examined next, in view of burnt-out brickwork, grate bars and door linings. It may be that the furnace has distorted or cramped proportions, or it may be too large. The bridge wall may be so constructed as to huddle the ilames in one spot on the fire sheets of the boiler; or it may be of such shape and in such condition as to cause the ignited gases to become dissipated in the combustion chamber. Even the combustion chamber itself may require the service of a bricklayer. He should next examine the safety valve and see that it is of ample capacity to relieve the boiler of surplus steam, and that it is in thorough working order. The first duty of an engineer when entering his plant at any time, is to ascertain how the water in the boiler stands, or, in other words, just how much water the boiler contains. He should open the gauge cocks first and note what comes from each in turn ; then open the cocks or valves connecting the glass gauge and note the water line there shown. He should also blow the water column out, in case any sediment may have choked any of the passages, which would be liable to give a false impression as to the actual quantity of water contained in the boiler. Should the water be found at tho correct height, he may now proceed to get up steam ; open the damper, pull down the banked fire and spread it evenly over the grate, adding a quantity of green fuel. Allow the steam to rise slowly ; do not force it. This applies especially to raising steam in a boiler which has been cold, as the expansion of the parts of the boiler due to the heat should take place slowly and evenly; otherwise, the life of the boiler will be shortened. While waiting for the steam to come up to the desired point, the engineer should now get his engine ready for the day's run. Fill all the oil cups and cylinder lubricator, so as to be ready to operate as the engine starts. With a hand oil squirt can, go around all the small brasses, connections, etc., and, in a word, well lubricate all the parts where friction takes place. If HANDBOOK ON P]NG1NKKKIN(}. you have an oil pump for your cylinder and valves, it would be well to inject a small quantity of cylinder oil before the engine is started, while the stop-valve is open, during the time the engine is being " warmed up." After the engine cylinder is warmed through, the fire should again be looked at, and dealt with according to the indications. Of course, the water gauge glass must be looked at frequently, not only while raising steam in the morning, but at all times while the boiler is in operation. Everything being in readiness, the engine is started slowly at first, the speed being gradually increased until the limit is reached. The day's run is now fairly commenced. A boiler should be blown down one gauge every morning before starting the day's run to get rid of the mud, scale or anything that is held in mechanical suspension in the water. Before starting in the morning and at noon is the best time to do this, as the sediment has settled to the bottom during the night, after the circulation of the water has stopped. When blowing a boiler down, always remember to open the blow- valve slowly be careful not to blow too long, and then to close the valve slowly. An engineer or attendant cannot be too careful in handling the many appliances with which a steam plant is equipped. The principal things to which an engineer should give his attention during the operation of his boiler day by day are, as follows : The maintenance of the water at the proper level, as near as pos- sible, and avoiding fluctuations in the pressure of steam. See that the firing is done correctly and economically so as to obtain from every pound of coal all that is possible under the con- ditions existing. The raising of the safety valve from its seat, at least once daily ; the blowing out of the water column twice daily, or oftener, if the water used is very dirty ; the frequent opening of the water gauge cocks, or try cocks, as they are sometimes called, and not depending entirely on the gauge glass for the correct height of water ; the blowing down cf t,he boiler HANDBOOK ON ENGINEERING. one gauge every day ; the keeping of all valves, cooks, fittings, steam and water-tight, clean and in good working order. When shutting down the plant for the night, the fires should be cleaned out and the live coals shoved back on the grates and banked; that is, green coal should be thrown upon them, suffi- ciently thick to cover all the glowing fuel. Pump in the water until it reaches the top of the glass gauge. This should be done to insure a sufficient quantity from which to blow down in the morn- ing, and also to allow for any small leaks. Then close the cocks or valves connecting the glass gauge. Should this glass break dur- ing the night and the valves be left open, there would not be much water to start with in the morning. Leave the damper open a little, just sufficient to allow the gases which will rise from the banked fires to escape up the chimney. Finally, make sure that all the valves about the plant which should be closed, are closed ; and all those which should be left open, are open. Of course, the foregoing is applicable to a plant where there is no night engineer. But in any case, no matter how many assistants an engineer may have under his control, he should be familiar with all details of the plant under his charge. One of the most important points in connection with the opera- tion of a steam boiler, is the preventing of corrosion, both internally and externally. One of the best aids to secure the well working and longevity of the steam boiler, or, in fact, the whole plant, is by being regular and punctual in a certain course of treatment, which has been proven to N be effectual and beneficial in its results. All conditions do not require the same methods of treatment; therefore, it is absolutely necessary that the engineer in charge familiarize himself with all the conditions under which his plant is running, for then, and then only, can he intelligently prescribe and act accordingly. Above all, let him remember the adage, " Eternal vigilance is the price of safety/* especially where a steam boiler is concerned. HANDBOOK ON ENGINEERING. 327 ECONOMY IN STEAM PLANTS. In these days of close figuring upon expense in office buildings and manufacturing plants, what may at first appear insignificant items may actually make all the difference between a good margin of profit and an actual loss. The fuel expense is one of the largest in the operation of the majority of plants, and any reduction which can be made in the amount of fuel used, while maintaining the same amount of power, is considered a direct gain. The evaporation of more than nine pounds of water per pound of coal, is looked upon with suspicion by many, as it is not thought possible to obtain more than this amount in even the best designed and well regulated furnaces and boilers, especially when the firing is done by hand. The actual value of the fuel depends upon the way in which it is used, fully as much as on any other factor. The heat unit in the coal should be as much as possible utilized, as in one pound of good steam coal there is about 14,000 B. T. U., and about 10,000 of this amount can be utilized, so that 4,000 heat units are lost. The mixture of gases in a furnace depends upon the amount of air used. One pound of coal requires, theoretically, about twelve pounds of air to burn completely. But, in practice, about twice this amount is required in the present boiler furnace. To have good combustion coal requires a good draft. The gases are con- sumed near the fire, and the waste gases carry the heat to the boiler on their way to the stack. The boiler ought to have suffi- cient heating surface, or the hot wasted gases ought to travel a sufficient distance to be cooled down to about 350 degrees Fah- renheit ; which temperature is found high enough to produce a good draft in a stack of, at least, 100 feet high. How a bad draft will unnecessarily increase the coal bill, is this: That of all the fuel burnt to perform certain work, ascer- tained proportion is consumed to keep the heat of the furnace up 328 HANDBOOK ON ENGINEERING. to say, 212 degrees Fahr., without making any steam whatever which is available for work. This quantity varies from 20 to 30 per cent, according to conditions, which are affected by various causes, such as leakages of steam, air, or water. Now, the only available power for work which we get from our fuel is the margin between this, say thirty per cent required for the said purpose, and what we generate above that. An engineer should notice the general condition of his boiler or boilers, and the equipments of same ; he should examine the boiler both inside and outside, ascertain the dimension of grates, heating surfaces, and all im- portant parts. The area of heating surfaces is to be computed from the outside diameter of water-tubes, and the inside diameter of fire-tubes. All the surfaces below the main water level which have water on one side and products of combustion on the other, are to be considered as water-heating surfaces. If he finds that the boiler does not come up to what he thinks it should, he should put the boiler and all its appurtenances in first-class condition. Clean the heating surfaces inside and outside of boiler, remove all scale from flues and inside of boiler ; remove all soot from inside of flues, all ashes from the flame-bed or com- bustion chamber, and all ashes from smoke connections. Close all air leaks in the masonry and poorly fitted cleaning door. See that the damper in britching or smoking-flue will open wide and close tight. Test for air leaks through the crevices, by passing the flame of a candle over cracks in the brick work. A good, attentive fireman, who understands his business and will keep his bars properly covered without choking his fires, is really worth double the wages of an ignorant or inattentive one, as his coal bills would certainly prove. All an engineer can do is to keep the steam piston and valve or valves tight. Also the drains from his engine, and all drains on steam traps in the plant tight : also, his engine cleaned and well-oiled, and not keyed up too tight. If in a heating plant, he should see that the back pressure valve is HANDBOOK ON ENGINEERING. 329 at all times tight, as it does not take much of a leak to show a difference in his coal bill at the end of a month. He should keep all valves in the pumps in his plant tight, and see that the pump piston is packed, but not too tight. After a pump is packed, you should be able to move it back and forth by hand ; if the pump valves leak he can take them out and smooth them up with sand- paper. He should see that the feed- water to the boiler is at least 208 degrees Fahrenheit ; if it is under 204 degrees, his heater is not right, as the poorest heater will heat the feed- water to 204 ; it would be well to overhaul the heater it may be full of scale ; or, if an open heater, the spray may be off. In most first-class plants, the feed-water is 212 Fahrenheit. PRIMING. The term priming is understood by engineers to mean the passage of water from the boiler to the steam cylinder, in the shape of spray, instead of vapor. It may go on unseen, but it is generally made manifest by the white appearance of the steam as it issues from the exhaust-pipe as moist steam, which has a white appearance and descends in the shape of "mist, while dry steam has a bluish color and floats away in the atmosphere. Priming also makes itself known by a clicking in the cylinder, which is caused by the piston striking the water against the cylinder head at each end of the stroke: Priming is generally induced by a want of sufficient steam-room in the boiler, the water being car- ried too high, or the steam-pipe being too small for the cylinder, which would cause the steam in the boiler to rush out so rapidly that, every time the valve opened, it would induce a disturbance and cause the water to rush over into the cylinder with the steam. 330 HANDBOOK ON ENGINEERING. TABLE OF PROPERTIES OF SATURATED STEAM. Pressure in h pounds per square Inch above vacuum II Temperature in degrees Fahrenheit. Total heat in heat units from water at 32. Heat in liquid from 32 in units. Heat of vapor- ization or latent heat in heat units. till 111! Volume of one pound in cubic feet. Factor of equivalent evaporation at 212. Total pressure above vacuum. 1 101.99 1113.1 70.0 1043.0 00299 334.5 .966 1 2 126.27 1120 5 94 4 1026.1 0.00576 173 6 .9738 2 3 141.62 1125.1 109.8 1015.3 00844 118.5 .9786 3 4 153 09 1)28.6 121 4 1007 2 01107 90 33 .9822 4 5 162.34 1131 5 130.7 1000 8 01366 73 21 .9852 5 6 170.14 1133.8 138 6 995.2 0.01622 61 65 .9876 6 7 176 90 1135.9 145.4 990.5 01874 53.39 .9897 7 8 182 9-2 1137 7 151.5 986 2 0.02125 47.06 .9916 8 9 188.33 1139 4 256 9 982.5 0.02374 42 12 .9934 9 10 193.25 1140 9 161 9 979 0.02621 38.15 .9949 10 15 213 03 1146.9 181 8 965 1 0.03826 26.14 1.0003 15 20 227 95 1151.5 196 9 964 6 0.05023 19 91 1.005 20 25 240.04 1155.1 209 1 946.0 0.06199 16.13 1 0099 25 30 250 . 27 115S.3 219 4 938.9 07360 13.59 .0129 30 35 259.19 1161. H 228.4 93 2. b 08508 11.75 .0157 35 40 267 . 13 1163 4 236 4 927.0 0.09644 10.37 .0182 40 45 274.29 1165.6 243 s6 92-2.0 0.1077 9.285 .0205 45 50 280.85 1167 6 250.2 9)7 4 1188 8.418 .0225 60 55 286 89 1169 4 256.3 913 1 0.1-299 7 698 .0245 55 60 292.51 1171.2 261 9 909 3 1409 7.097 .0263 60 65 297 77 117-2.7 267.2 905.5 0.1519 6 583 .0280 65 70 302 71 1174.3 272.2 902 1 C.1628 6 143 .0296 70 75 307 38 1175.7 276.9 898 8 0.1736 5.760 0309 75 80 311 80 1177.0 281.4 81)5 6 0.1843 5.436 .0323 80 85 316.02 1178 3 285.8 892.5 0.1951 5 126 0337 85 90 320.04 1179.6 290 889 6 0.2058 4.859 .0350 90 95 3-23.89 ]180 7 294.0 886 7 0.2165 4.619 .0362 95 100 3-27.58 1181.9 297 9 884.0 0.2271 4.403 .0374 100 105 331 13 1182.9 301 6 881 3 2378 4.206 .0385 105 110 334 56 1184 305 2 878 8 2484 4 026 0396 110 115 337.86 1185 308.7 876 3 0.2589 3 862 .0406 115 120 341.05 1186.0 312.0 874.0 0.2695 3.711 0416 120 125 344 . 13 1186 9 315.2 871.7 0.2800 3.571 .0426 125 130 347.12 1187 8 318.4 869.4 0.2904 3 444 .0435 130 140 352.86 1189.5 324.4 865 1 3113 3 212 0453 140 150 358.26 1191.2 330.0 861 2 3321 3 Oil 0470 150 160 363.40 1192.8 335.4 867.4 3530 2 833 .0486 160 170 368 29 1194.3 340.5 853 8 0.3737 2.676 .0602 170 180 372.97 1195 7 345.4 850.3 0.3945 2.635 .0517 180 I'.K) 377.44 1197.1 350.1 847 0.4153 2.408 0531 190 200 381.73 1198 4 354.6 843 8 0.4359 2.294 0545 200 2-25 391 79 1201.4 365.1 836.3 0.4876 2.051 0576 225 250 400.99 1204.2 374.7 829.5 0.5393 1.854 0605 250 275 409 ,50 1-206.8 383.6 823 2 0.5913 1.691 0632 275 300 417.42 1209.3 391 9 817 4 0.644 1 553 0657 300 3-25 424.82 1211.5 391) 6 811 9 0.696 1 437 0680 325 350 431 90 1213.7 406.9 806.8 0.748 1.337 0703 350 375 438 40 1215.7 414 2 801 5 0.800 1.250 0724 376 400 445.15 1217.7 421.4 796 3 0.853 1.172 0745 400 5UO 466.57 1224.2 444 3 779.9 1.065 .939 0812 600 HANDBOOK ON ENGINEERING. 331 The gauge pressure is about 15 pounds (14.7) less than the total pressure, so that in using this table, 15 must be added to the pressure as given by the steam gauge. To ascertain the equivalent evaporation at any pressure, multiply the given evap- oration by the factor of its pressure, and divide the product by the factor of the desired pressure. Each degree of difference in temperature of feed-water makes a difference of .00104 in the amount of evaporation. Hence, to ascertain the equivalent evaporation from any other temperature of feed than 212, add to the factor given as many times .00104 as the temperature of feed-water is degrees below 212. For other pressures than those given in the table, it will be practically correct to take the pro- portion of the difference between the nearest pressures given in the table. Example : If a boiler evaporates 3000 Ibs. of water per hour from feed-water at 200 degs. Fah. into steam at 100 Ibs. per sqr. in. by the gauge, what is the equivalent evaporation " from and at" ? Ans. 3159.24 Ibs. Operation : Temperature of feed-water = 200 degs. Then, 212 200 = 12 = difference in temperature. Then, 15 added to the gauge pressure = 115. Looking in the above table we find the factor 1.0406. Then, .00104 X 12= .01248. And, 1.0406 .01248 1.05308 Then, 3000 X 1.05308 = 3159.24 Ibs. the equivalent evapo- ration. The H. P. of this boiler would be 91.57. HANDBOOK ON ENGINEERING. HIGH PRESSURE STEAM. It is generally believed that high-pressure steam is cheaper to use and costs but little more to generate than low pressure steam. A study of a table of the properties of saturated steam, to be found on another page in this book, will show why high-pressure steam is economical to generate, and a few calculations will prove instructive by showing what may be excepted from its use. To generate one pound of steam at 25 Ibs. pressure, absolute, requires an expenditure of 1,155 thermal units, and to generate steam at 200 Ibs. pressure, absolute, requires 1,198 thermal units, or an increase of only 43 thermal units for an increase of 175 Ibs. pressure. Further investigation shows that the temperature of steam at 25 Ibs. pressure is 240 and at 200 Ibs. pressure, 382, the difference, 142, being the number of degrees that the tem- perature of steam js raised with an expenditure of 43 thermal units. To put it in another way, the temperature of the steam has been raised nearly 60 per cent, with an increase of less than 4 per cent in the number of thermal units. It is con- venient to consider that the generation of steam takes place by two different steps, one of which is raising the water from 32 to the temperature corresponding to the pressure of the steam, and the other is giving off the steam at this pressure, which process absorbs a quantity of heat that becomes latent or non-sensible. At 25 Ibs. pressure, the sensible heat required to raise one Ib. of water from 32 to 240 is 209 units, and to raise it from 32 to 382 degrees, the temperature of steam at 200 Ibs. pressure requires 355 thermal units. The increase in the sensible heat of the water, there- fore, is 355 minus 209 = 146 units, or about the same as the tem- perature increase for these two pressures, which is 142. It is thus clear that the total increase in the number of heat units in steam raised from 25 Ibs. to 200 Ibs. pressure is small (43 as found HANDBOOK ON ENGINEERING. 333 above) because the latent heat absorbed in the formation of the steam decreases as the pressure increases. It requires less heat to generate steam from water raised to 382 at 200 Ibs. pressure, than from water previously raised to 240 at 25 Ibs. pressure. To generate higher pressure steam, therefore, we must first apply enough heat to bring the water to a temperature corresponding to the higher pressure. This heat will be nearly proportionate to the increase in temperature. Then enough heat must be applied to the water to generate the steam, the amount of heat required for this purpose decreasing as the pressure increases. The combined result of these two processes is that it takes only a very small increase in the total heat to pro- duce the higher pressure steam. The idea may be suggested that if this higher pressure is obtained at the cost of so small an expen- diture of heat, it would not be reasonable to expect a large gain in economy from it, since it is not possible for the steam to do a greater amount of work than the equivalent of the heat which it contains. This would be true were it not for the fact that the larger part of the heat in the steam is rejected during the ex- haust. To illustrate, suppose an engine to exhaust at atmos- pheric pressure, or at about 15 Ibs., absolute, and tha the steam is saturated. As may be determined from the steam tables, there would be ejected 1,147 heat units per pound of steam, or 51 heat units less than were found to be in a pound of steam at 200 Ibs. pressure. That is to say, under the above assumption, there are available only 51 heat units per pound of steam to do the work in the engine cylinder when the steam pressure is 200 Ibs. But we also found that the increase in the heat units in raising the steam pressure from 25 to 200 Ibs. was 43, and hence the increase in proportion to the number available is large, although the increase in proportion to the total number required 334 HANDBOOK <>\ ENGINEERING. to generate the steam is small. This shows why high-pressure steam is economical to generate and profitable to use. It should be stated that the only way in which the full benefit can be de- rived from high pressure-steam is by using the steam expansively, keeping the terminal pressure at release as low as possible. I will not take the space to give the calculations to prove this, but will compare a few results of calculations. Suppose steam to be used in a theoretically perfect engine at the pressure of 25 Ibs., 50 Ibs., 100 Ibs. and 200 Ibs. We will assume that in each case the cut-off is at one-third stroke, giving three expansions'and a terminal pressure of one-third the initial pres- sure. The steam consumptions will then be, respectively, about 161, IG, 151, and 14 Ibs. per horse-power, showing that gain from the increase in pressure is very slight. On the other hand, suppose the expansions to be carried to the atmospheric pressure in each case. The consumptions will then be about 27, 15, 1] and 8 Ibs. respectively", showing a marked decrease. Still another point should be mentioned in relation to the relative gain that is to be expected with the increase in pressure. Comparing the last iigure, it will be observed that the decrease in consumption when the pressure increased from 25 to 50 Ibs- was 27 minus 15 = 12 Ibs., or 44 per cent. Again, when the pressure doubled from 50 to 100 Ibs., the consumption decreased only 4 Ibs., or 27 per cent; and when the pressure was again doubled to 200 Ibs., the consumption only decreased 3 Ibs., or about 27 per cent. It is evident from this that the saving from an increase in steam pressure grows less as the pressure increases, and this is found to be the case in actual practice. There is another reason for this, also, coming from the losses incident to cylinder condensation and re-evap*oration, which is 1 more marked where there is a wide range in pressures than where the pressures are more uniform throughout the stroke. It is found that where the steam pressure is much above 100 Ibs. gauge pres- HANDBOOK ON ENGINEERING. 335 sure, no gain will result from a further increase in pressure with- out compounding, the advantage of the compound engine being that the extremes of temperature in the cylinders are not so great as with a simple engine. USING STEAfl FULL STROKE. The steam engine is nothing in the world but an enlargement upon the end of the steam pipe, containing a piston against which the steam in the boiler may press. The piston moves a certain distance, and then the steam is allowed to press upon its other side, while the steam on the first side is allowed to flow into the atmosphere and go to waste. The slide-valve is the device or- dinarily employed to admit the steam, alternately, to opposite sides of the piston, and to permit the free outflow of steam from the reverse side of the piston. As the steam presses upon the piston the piston moves forward with a force equal to the pressure of steam per square inch, multiplied by the number of square inches of piston surface. Steam occupies the entire space from the sur- face of the water in the boiler, to the piston of the engine. The steam space, therefore, includes the steam space of the boiler, the steam pipe, the steam chest, and the cylinder space upon one side of the piston. As the piston moves, the entire steam space be- comes a little larger, by reason of the cylinder space becoming longer. Thus it will be seen that all of the steam in the boiler and pipe and engine, would expand a trifle and the pressure become somewhat reduced, were it not for the fact that new steam is made by the fire as fast as the piston moves forward. By this means the steam is maintained at about uniform pressure. It will be seen that the pressure is produced upon the piston by the generation of new steam from the water, that is, the fire causes the water to generate a quantity of steam, and this quantity of steam forces its way into the other steam, exerting a force upon the whole body of steam and pushing the piston ahead. HANDBOOK ON ENGINEERING. If an engine piston has a surface of 100 square inches and a stroke of ten inches, it follows that the piston will yield a thousand cubic inches additional steam space by its movement during one stroke, and consequently, the fire will be called upon to produce 1,000 cubic inches of new steam for each single stroke of the engine. If the pressure of the steam be eighty pounds to the square inch, the engine piston will move with the force of 8,000 pounds. When the engine has completed one stroke, we find an amount of power exerted equal to 8,000 pounds moved ten inches, and we then open the exhaust valve and empty into the atmosphere 1,000 cubic inches of eighty-pound steam. We keep on doing this for each stroke. Now your attention is par- ticularly called to the fact that when we empty the steam out of the cylinder, it is just as good as when it went into the cylinder; that is, it was 1,000 cubic inches of steam at a pressure of eighty pounds to the square inch, and when it goes into the atmosphere it will expand into over 6,000 cubic inches, at fifteen pounds pressure to the square inch, or the same pressure as the atmos- phere. This 1,000 cubic inches of steam which we dumped out of the cylinder, is precisely the same quality of steam as the steam which we have penned up in the boiler; and which we have to be making new all the time in order to keep the engine run- ning. Such is the operation of the steam engine which receives its steam the full length of the stroke ; and such an engine may be described briefly, as a very wasteful machine which throws away steam as good as it receives it, and which requires the gen- eration of a cylinder full of full pressure steam for each stroke. It should be readily understood that when the piston has com- pleted its stroke, and just before the exhaust valve is opened to allow the steam to escape, the cylinder contains 1,000 cubic inches of steam at eighty pounds pressure, which it is capable of expanding into many thousand cubic inches at constantly de- creasing pressure. The first step in the improvement of such an HANDBOOK ON ENGINEERING. 337 engine would be to so arrange things as to get some benefit from this enormous power of expansion. The full stroke engine does not get one-half of the power before it throws 'the steam away. The engine which we would have referred to would yield a power of 8,000 pounds moved ten inches at each single stroke; oo,000 pounds moved one foot in one minute is a horse-power ; 66,000 pounds moved half a foot would be the same. An engine using steam full stroke is such an extravagant contrivance that w r e, now- adays, seldom find them in use. There are certain classes of engines built, fitted with link motions for driving the valve, and they are arranged so as to carry their steam full stroke, but pro- vision is also made for quickly hooking up the link and suppress- ing the full-stroke feature. SLIDE VALVE ENGINES. If we have an engine arranged to receive its steam full stroke and to dump the steam out into the air in as good condition as it was received, and we wish to get some of the benefits of the expansive power of the steam, there is a simple way of doing it and without any great change in the engine, and that is, to lengthen out the slide valve so that after the cylinder is half full of steam, the valve will shut and let no more steam enter. Dur- ing the balance of the stroke, the entire power comes from the gradual expansion of the steam shut up in the cylinder, and it will be readily seen that whatever power we succeed in getting out of the expansion of the steam, is pure gain. The lower the pres- sure of the steam is when it is exhausted into the air, the more it has expanded, the more power we have gotten out of it, and the more we have gained. It may be said in a few words, that all slide-valve engines are now arranged to work their steam expans- ively. But it is, unfortunately, found that the slide-valve pos- sesses a peculiar defect which prevents the system being carried very far. We can lengthen out a slide-valve so as to cut the '22 338 HANDBOOK ON ENGINEERING. steam off at any desired point of the stroke, and we must then increase the throw of the eccentric in order to properly operate the long valve. x But the minute we do this we lind that we have interfered, to a certain extent, with the proper operation of the exhaust. No matter what we do about the admission of steam or about cutting off before the end of the stroke, we must arrange our exhaust to take place at a certain point at the end of the stroke. It is found in practical operations that this necessary quality of the slide-valve prevents our arranging it to cut off the steam properly at an earlier point than about five-eighths or three- quarter stroke. The consequence is, that an engine with two-feet stroke. will receive steam 18 inches, then have (5 in. of expansion. It may be fairly said, in a general way, that about all the slide- valve engines now manufactured, cut off the steam at about five- eighths or three-quarters stroke ; and it may be further said that this is about all we can get put of a slide-valve engine. Even the trifling expansion got from such engines as this, represents an immense amount of money in the course of a year in large establishments, but it is not good enough for anyone who seeks even a decent investment of money, in power-getting appliances. REGULAR EXPANSION ENGINES. A liberal expansion of steam being desirable and the slide- valve proving totally incapable of providing for such expansion, the first step in the desired direction is to totally discard the slide-valve. The Corliss valve is a cylindrical piece, oscillating in a cylindrical hole. The valve does not fill this hole, but seats against one side only. Hence, the fitting qualities are about the same as with the slide-valve and, in fact, the principle is about the same, the Corliss representing a portion of the slide-valve, rolled into the form of a cylinder and operating in a concave seat. We must not only discard the slide-valve arrangement, but in the valve arrangement which we select, we must secure an abso- HANDBOOK ON ENGINEERING. 339 lute independence between the steam admission part of the sys- tem and the exhaust part. The slide-valve is one chunk of cast iion, letting in and cutting off steam at its outside edges, and opening and closing the exhaust by its inside edges. When one of these valve edges moves, everything else has to move. There is, consequently, no independence of action. In the Corliss engine there are parts to let steam into the cylinder and to quit letting it in at the proper time, and there are valves to let it out at the proper time, and they are perfectly independent of each other in all of their movements. The consequence of this arrangement is, that the steam valve may open, steam flow into the cylinder, the valve suddenly shut and chop the steam off short, the piston move forward in its stroke by the expansion of the confined steam, and finally, be let out by the opening of the exhaust valve, which has all the time stood ready for the dis- charge. Here we have a regular expansion engine. We can cut the steam off as early in the stroke as we desire, and hence, have any degree of expansion we desire. And we can do this without interfering with the exhaust valves. It is found, in practice, that an engine cutting off at about one-fifth of its stroke and expanding the other four-fifths, will yield the fairest practical economy. AUTOMATIC CUT-OFF ENGINES. In order that those not posted may understand what is meant by the term " Automatic Cut-off Engines," we will have to go back a step. Take, for instance, a full-stroke engine. It ought to be well understood how the ordinary governor does its work. Sup- pose, for instance, that there is no governor, and that we regulate the speed of the engine by having a man stand at the throttle-valve all the time. If the engine runs too fast, he shuts the throttle- valve a little. This makes the steam pipe so small that the steam eannot flow fast enough to keep the pressure up, and consequently, 338 HANDBOOK ON ENGINEERING. steam off at any desired point of the stroke, and we must then increase the throw of the eccentric in order to properly operate the long valve. "But the minute we do this we find that we have interfered, to a certain extent, with the proper operation of the exhaust. No matter what we do about the admission of steam or about cutting off before the end of the stroke, we must arrange our exhaust to take place at a certain point at the end of the stroke. It is found in practical operations that this necessary quality of the slide-valve prevents our arranging it to cut off the steam properly at an earlier point than about five-eighths or three- quarter stroke. The consequence is, that an engine with two-feet stroke. will receive steam 18 inches, then have 6 in. of expansion. It may be fairly said, in a general way, that about all the slide- valve engines now manufactured, cut off the steam at about live- eighths or three-quarters stroke ; and it may be further said that this is about all we can get put of a slide-valve engine. Even the trifling expansion got from such engines as this, represents an immense amount of money in the course of a year in large establishments, but it is not good enough for anyone who seeks even a decent investment of money, in power-getting appliances. REGULAR EXPANSION ENGINES. A liberal expansion of steam being desirable and the slide- valve proving totally incapable of providing for such expansion, the first step in the desired direction is to totally discard the slide-valve. The Corliss valve is a cylindrical piece, oscillating in a cylindrical hole. The valve does not fill this hole, but seats against one side only. Hence, the fitting qualities are about the same as with the slide-valve and, in fact, the principle is about the same, the Corliss representing a portion of the slide-valve, rolled into the form of a cylinder and operating in a concave seat. We must not only discard the slide-valve arrangement, but in the valve arrangement which we select, we must secure an abso- HANDBOOK ON ENGINEERING. 339 lute independence between the steam admission part of the sys- tem and the exhaust part. The slide-valve is one chunk of cast iron, letting in and cutting off steam at its outside edges, and opening and closing the exhaust by its inside edges. When one of these valve edges moves, everything else has to move. There is, consequently, no independence of action. In the Corliss engine there are parts to let steam into the cylinder and to quit letting it in at the proper time, and there are valves to let it out at the proper time, and they are perfectly independent of each other in all of their movements. The consequence of this arrangement is, that the steam valve may open, steam flow into the cylinder, the valve suddenly shut and chop the steam off short, the piston move forward in its stroke by the expansion of the confined steam, and finally, be let out by the opening of the exhaust valve, which has all the time stood ready for the dis- charge. Here we have a regular expansion engine. We can cut the steam off as early in the stroke as we desire, and hence, have any degree of expansion we desire. And we can do this without interfering with the exhaust valves. It is found, in practice, that an engine cutting off at about one-fifth of its stroke and expanding the other four-fifths, will yield the fairest practical economy. AUTOMATIC CUT-OFF ENGINES. In order that those not posted may understand what is meant by the term " Automatic Cut-off Engines," we will have to go back a step. Take, for instance, a full-stroke engine. It ought to be well understood how the ordinary governor does its work. Sup- pose, for instance, that there is no governor, and that we regulate the speed of the engine by having a man stand at the throttle-valve all the time. If the engine runs too fast, he shuts the throttle- valve a little. This makes the steam pipe so small that the steam eannot flow fast enough to keep the pressure up, and consequently, 340 HANDBOOK ON ENGINEERING. the speed goes down. If the engine runs too slow, he opens the throttle- valve and lets the steam flow free, so as to maintain higher pressure. Thus it will be seen that the man at the throttle regulates the engine by altering the pressure with which the steam acts upon the engine. An ordinary engine governor is simply a man at the throttle. When the engine runs too fast the balls fly out, the governor valve shuts a little and the pressure of steam entering the engine is reduced, and so on through all the changes continually taking place. All steam engines, in which the regulation of steam is effected by means of a governor operat- ing upon a throttle, are called throttling engines. They operate by reducing the pressure of the steam admitted to the engine, and thereby taking so much of the vitality out of the steam. It is entirely the wrong way to do it. After once spending our money to get up pressure in the boiler, we should make the greatest possible use of that pressure, so long as we are taking the steam from the' boiler. It is, therefore, desirable that the full boiler pressure should be admitted to our cylinder ; and the question arises as to how we shall be able to regulate the speed if we do not tinker with this pressure. The Automatic Engine regulates the speed by the simple act of altering the point of cut-off. If the engine is cutting off at one-fifth stroke, we get a power equal to the incoming force of steam for one-fifth of the stroke, and the expansion of the steam for the other four-fifths of the stroke. If the engine runs too slow we cut the steam off a little later and thereby increase the average pressure during the expansion. The Automatic Engine, then, is an engine which cuts off the steam at an earlier point in the stroke, if the engine runs too fast, and cuts it off at a later point if it runs too slow. It is the duty of the governor to say just when the steam valve should close and not let any more steam into the cylinder. In the Cor- liss Engine the steam valves open wide at the beginning of the stroke and let full boiler pressure smack in against the piston. HANDBOOK ON ENGINEERING. After the piston has advanced to, say one-fifth of its stroke, the valve shuts up as quick as a flash and the expansion begins. If the engine starts too slow, the governor will hold the steam valve open a trifle longer, but will not interfere with its full opening at the beginning of the stroke, or with its flash-like closing when the cut-off is to take place. During all these operations of the governor and the admission valves, the exhaust valves are let entirely alone, and they continue their work unchanged. It will thus be seen that the expansion engine makes provision for the utmost economy in the use of steam, and with the automatic fea- ture added to it, provides that this economy shall not be sacrificed for the purpose of regulating the speed. THE GARDNER SPRING GOVERNORS. Construction* Two balls are rigidly connected to the upper ends of two flat, tapering, steel springs the lower ends of the springs being secured to a revolving sleeve which receives rotation through mitre gears ; links connect the balls to an upper revolv- ing sleeve, which is free to move perpendicularly. The valve stem passes up through a hollow standard upon which the sleeves revolve, and is furnished with a suitable bearing in the upper sleeve ; the closing movement of the valve is upward, and is obtained in the following manner : The balls at the free ends of the springs furnish the centrifugal force and the springs are the main centripetal agency (gravity is not employed). As the balls fly outward, under the centrifugal influence, they move in a curved horizontal path which may be described as an arc, modified by a radius of changing length the radius being represented by the length and position of the springs ; the links represent a radius of lesser length, Awhile the sleeve to which the lower ends of the links are pivoted, being free to rise and fall, nullifies the effect of the links in determining the arc in which the balls travel. As the 342 HANDBOOK ON ENGINEERING. balls move outward in their peculiar path, the sleeve is drawn up- ward by the links, and, as the balls move inward, the sleeve is pushed downward. The change of speed is obtained by increas- THE GARDNER STANDARD GOVERNOR CLASS "A" WITH AUTOMATIC SAFETY STOP AND SPEEDER. ing or decreasing the centripetal resistance, and accomplished by the action of a spiral spring pivoted against the lever, and by means of a shaft and arm against the valve-stem in the direction to open the valve ; a thumb-screw is used to adjust the compres- HANDBOOK ON ENGINEERING. 343 sion. A convenient Sawyer's lever is attached to the shaft, and a reliable automatic safety stop is furnished when desired. The cut on the preceding page represents the Gardner Standard Governor, Class "A." This is a Gravity Governor, having an Automatic Safety Stop and Speeder. It is made in sizes from 1J inches to 16 in., and is especially adapted to the larger type of stationary engines. In action, the centrifugal force of the pendulous balls is opposed by the resistance of a weighted lever, the speed being varied by the position of the weight. The Automatic Safety Stop is very simple in construction and reliable in action. It is accomplished by allowing a slight oscillation of the shaft bearing, which is sup- ported between centers and held in position by the pull of the belt ; a projection at the lower part of the shaft bearing supports the fulcrum, of the speed lever. If the belt breaks or slips off the pulley, the support of the fulcrum is forced back, so as to allow the fulcrum to drop and instantly close the valve. The valve is not affected by steam current and both valve and seats are made of special composition, that effectually resists wear and the cutting action of the steam. The workmanship is of the highest class, all parts being made by the duplicate system, with special machinery. The cut on the following page represents Class " B " Gov- ernor a combination of the gravity and spring actions. They are made in sizes from f to 10 inches inclusive, and are adapted to all styles of engines. They are provided with Speeder and Sawyer's Lever, but are not automatic. In the Class " li " Governor the centrifugal force of the pendulous balls operates against the resistance of a coiled steel spring, inclosed within a case and pivoted on the speed lever by means of a screw ; the amount of compression of the spring can be changed so as to give a wide range of speed. A continuation of the Speed Lever makes a convenient Sawyer's hand lever, which controls the valve by 344 HANDBOOK ON ENGINEERING. means of a cord. Sizes J to li in., inclusive, have an adjustable frame, which can be set at any desired angle in relation to the THE GARDNER STANDARD GOVERNOR CLASS "B." valve chamber. The valve and chamber are the same as used on Class " A " Governor, and they are made with the same care and style of workmanship. HANDBOOK ON ENGINEERING. 345 CHAPTER XIV. A FEW REHARKS ON THE INDICATOR. The steam-engine indicator is an instrument designed to show the steam pressure in the cylinder at all points in the stroke. It consists primarily, of a piston of known area capable of moving in a cylinder and resisted by a coil spring of known strength. To this piston is attached, by means of suitable piston rod and levers, a pencil capable of tracing a line corresponding to the motion of the indicator piston. This line is traced on a paper slip attached to the drum of the indicator, which drum is con- nected to some moving part of the engine in such a way as to have a back and forward movement, coincident with the steam piston of the engine. By referring to the above selected view of an indicator, which is generally recognized as the best known, the construction will be readily understood. Of-TH, JA 34() HANDBOOK ON ENGINEERING. THE USE OF THE STEAH ENGINE INDICATOR IN SETTING VALVES AND THE INVESTIGATION OF SOME OF THE DE- FECTS BROUGHT OUT BY THE INDICATOR CARDS. The steam-engine indicator has come into such general use that to-day there are but few men running engines who are not familiar with its construction and manner of attachment to en- gines, and the method of calculating horse-power from cards. The indicator is attached to pipes tapped into the cylinder heads, or into the barrel of the cylinder opposite the counterbore, beyond the travel of the piston rings. The indicator consists of a cylin- der with piston and compression spring and a drum attached to a coiled spring, used for returning the same. The pressure of steam on the piston of the indicator compresses the spring above it. The motion of the piston is carried by a piston-rod to a pencil motion, which multiplies the motion of the spring some five or six times. The springs "are marked 20, 40, 80, etc. This meaning that 80 Ibs. pressure per square inch on the indicator piston (or whatever the spring may be marked) will cause the pencil at the end of the pencil-arm to move an inch. The pencil marks on paper, which is fastened on a drum. This drum is moved by the cross-head of the engine, through some form of reducing motion, such as pantograph, laz} r -tongs, brumbo pulley, etc. To obtain the horse-power, we first need the mean pressure equiva- lent to the variable pressure on the card. This is most easily found by dividing the area of the card by the length, giving the height of a rectangular card of equivalent area, and then multi- plying this height by the scale of the spring. The mean effective pressure per square inch on the piston, times the area of the pis- ton in square inches, times the speed of the piston in feet per minute, divided by 33,000, gives the horse-power. If there is a loop at either end of the card, the area of this loop is to be sub- tracted from the larger area before finding the mean height of HANDBOOK ON ENGINEERING. 347 the card, since such a loop represents work opposed to the work- ing side of the piston. In getting areas by means of a planimeter, no attention need be given to the loops. By following the lines in order, as drawn by the indicator pencil, the loops will be sub- tracted from the main card, for if the main body of the card is traced in a right-handed rotation, the loops will be traced in a left-handed rotation. DIAGRAM ANALYSIS. Figs* \ and 2 are from throttling engines ; the former repre- senting good performances for that class of engine, and the latter, Fig. 1. in some respects which the engineer will readily recognize, bad performances. 'US HANDBOOK ON ENGINEERING. Figs* 3, 4> and 5, are from automatics ; Fig. o representing what is now considered rather too light a load for best practical economy ; Fig. 4 about the best load, and Fig. 5 is from a con- densing engine. Line A B is the induction line, and B C the steam line ; both together representing the whole time of admission. C is about the point of cut-off, as nearly as can be determined by inspection. It is mostly anticipated by a partial fall of pres- sure due to the progressive closure of the valve. The usual method is, to locate it about where the line changes its direction of curvature. C D is the expansion curve. 1) is the point of exhaust. D E is the exhaust line, which begins near the end of the stroke and terminates at the end of the stroke, or, at latest, before the piston has moved any considerable distance on its return stroke. The principal defect of Fig. 2 is, that this line occupies nearly all the return stroke. E F is the back pressure line, which, in non-condensing engines, should be coincident with, or but little above, atmospheric pressure. In Fig. 5 it is below the atmos- pheric line to the extent of the vacuum obtained in the cylinder. Some authorities would call it the vacuum line in Fig. 5 but that name properly belongs to a line representing a perfect vacuum. F is the point of exhaust closure (slightly anticipated by rise of pressure) and F A the compression curve, which, joining the admission line at A, completes the diagram proper, forming a closed figure. G G is the atmospheric line traced when the piston of the indi- cator is subject to atmospheric pressure, above and below alike. Some pull the cord by hand when tracing it, to make it longer than the diagram. H H is the vacuum line, which, when re- quired, is located by measurement such a distance below the atmospheric line as to represent the atmospheric pressure at the time and place, as nearly as can be ascertained. The mean HANDBOOK ON ENGINEERING. 349 atmospheric pressure at the sea level is 14.7 pounds. For higher altitudes, the corresponding mean pressure may be found by multiplying the altitude by .00053, and subtracting the product from 14.7. When a barometer can be consulted, its reading in inches multiplied by .49 will give the pressure in pounds. Fig. 2. 1 is the clearance line, representing by its distance from the nearest point of the end of the diagram at the admission end, as compared with the whole length, the whole volume of clearance known to be present. Its use is mainly to assist in constructing a theoretical expansion curve by which to test the accuracy of the actual one. Calculating mean effective pressure* Since the simplification and popularization of the planimeter, no engineer who has occa- 350 HANDBOOK ON ENGINEERING. sion to compute the." indicated horse-power " (1HP) of engines should be without one ; for, if properly handled, the results obtained by them are more accurate and more quickly obtained than by any other process. The diagram is pinned to a smooth board covered with a sheet of smooth paper, the pivot of the leg pressed into the board at a point which will allow the tracing point to be moved around the outline of the diagram without forming unnecessarily extreme angles between the two legs, and a slight indentation made in the line at some point convenient for begin- ning and ending ; for it is vitally important that the beginning and ending shall be at exactly the same point. The reading of the wheel is taken, or it is placed at zero, and the tracing point is HANDBOOK ON ENGINEERING. 351 passed carefully around the diagram, following the lines as closely us possible, moving right-handed, like the hands of a watch. The reading obtained (by finding the difference between the two, if the wheel has not been placed at zero) is the area of the diagram in square inches, which, multiplied by the scale of the diagram, and divided by its length in inches, gives the mean effective pressure. The process of finding 1 the mean effective pressure by ordinates* Divide the diagram into 10 equal parts as shown by the full lines in Fig. 4 : but I wish to call attention to a frequent mistake, viz.. Fig. 4. making all the spaces equal. The end ones should be half the width of the others, since the ordinates stand for the centers of 352 HANDBOOK ON ENGINEERING. equal spaces. Ten is the most convenient and usual number of ordinates, though more would give more accurate results. The aggregate length of all the ordinates (most conveniently measured consecutively on a strip of paper) divided by their number, and multiplied by the scale of diagram, will give the mean effective Fig. 5. pressure. A quick way of making a close approximation to the mean effective pressure of a diagram is, to draw line a 6, Fig. 6, touching at a, and so that space d will equal in area spaces c and e, taken together, as nearly as can be estimated by the eye. Then a measure,/, taken at the middle, will be the mean effective pressure. With a little practice,. verifying the results with the planimeter, the ability can soon be acquired to make estimates in HANDBOOK ON ENGINEERING. 353 this way with only a fraction of a pound of error with diagrams representing some degree of load. With very high initial pres- sure and early cut-off, it is not so available. Fig. 6. The indicated horse-power. IHP is found by multiplying together the area of the piston (minus half the area of the piston- rod section, when great accuracy is desired), the mean effective pressure and the travel of the piston in feet per minute, and dividing the product by 33,000. It is sometimes convenient to know the HP constant of an engine, which is the HP for one revolution at one pound mean effective pressure. This multiplied by the mean effective pressure, and by its number of revolutions per minute, gives the IHP. THEORETICAL CURVE. Testing expansion curves. It is customary to assume that steam, in expanding, is governed by what is known as Mariotte's law, according to which its volume and pressure are inversely pro- 23 354 HANDBOOK ON ENGINEERING. portioual to each other. Thus, if a cubic loot of steam at, say, 100 pounds pressure be expanded to 2 cubic feet, its pressure will fall to 50 pounds, and proportionately for all other degrees of expansion. The pressures named are " total pressures ; " that is, they are reckoned from a perfect vacuum. A theoretic ex- pansion curve which will conform to the above theory may be \ K 10 Fig. 7. traced by the following method: Referring to F'^. 7, having drawn the clearance and vacuum lines as before explained, draw any convenient number of vertical lines, 1, 2, 3, 4, 5, etc., at equal distances apart, beginning with the clearance line and num- ber them as shown. Decide at what point in the expansion curve HANDBOOK ON ENGINEERING. of the diagram you wish the theoretic curve to coincide with it. Suppose you choose line 10, on which you find the indicated pres- sure to be 25 pounds. Multiply this pressure by the number of the line (10) and divide the product (250) by the numbers of each of the other lines in succession. The quotients will be the pressures to be set off in the lines. Thus, 250 divided by 1) gives 27.7, the pressure on line 9 ; and so for all the others. The same curve may also be traced by several geometric methods, one of which is as follows, referring to Fig. 8 : - E Fig. 8. Having drawn the clearance and vacuum lines as before, select the desired point of coincidence, as a, from which draw the perpendicular a A. Draw A B at any convenient height above or near the top of the diagram, and parallel to the vacuum line D C. From A draw A C and from a draw a b parallel to D (7. and from 356 HANDBOOK ON ENGINEERING. its intersection with A B, erect the perpendicular b r, locating the theoretical point of cut-off on A B. From any convenient num- ber of points in A B (which may be located without measurement) as E, F, G, H, draw lines to 0, and also drop perpendiculars E e, F f, G g, Hli, etc. From the intersection of E C with b c, draw a horizontal to e, and the same for each of the other lines F C, G (7, H C; establishing points e,/, f lore. But, -jj of 48 = 1.')^, or 13.71 inches nearly, so that, instead of catting off at 12 inches with 80 Ibs. boiler pressure, we are cutting off at 13.71 inches and using 63 cubic feet more 452. 4 x 13,71x 2 x 70 steam per minute. Thus, = 503, nearly. 1728 And, 503 minus 440 =63, that is, we must use 63 cubic feet more of steam per minute at 80 Ibs. boiler pressure, in order to get 46 more horse-power, which means the evaporation of more water per minute, and the burning of more coal per hour. HOW TO INCREASE THE HORSE=POWER OF AN ENGINE HAVING A THROTTLING GOVERNOR. There are three ways in which this can be done, also. We will take, for example, a plain slide-valve engine 10 x 16 inches, making 150 re volutions per minute, with T 9 ^ cut-off, and M. E. P. say 31|- Ibs. per square inch, with a boiler pressure of 60 Ibs. by gauge. The governor pulley on the main shaft 6 inches in diameter, and the pulley on the governor shaft 4 inches in diameter. The horse-power of this engine is about 30. Thus, - - = 2f ft., and 150 x 2| = 400 ft., the piston speed. 1 2i 10 x 10 x .7854 x 31.5 x 400 Then, : 30 horse-power, nearlv. 33000 It is now desired to run the engine at 180 revolutions per minute in order to develop 6 horse-power more. In order to obtain these results, the governor pulley must be enlarged, so as to make the governor balls revolve in the same plane at 180 revo- lutions per minute, that they now do at 150 revolutions. Thus, 4:6:: 150: 225, that is, the governor balls are now making 225 revolutions per minute. And 150:180::4:4.8. Con- sequently, the governor pulley must be increased to 4.8 inches in 384 HANDBOOK ON ENGINEERING. diameter. Then, 4.8 : 6 : : 180 : 225, that is, the governor balls, after the change, making the same number of revolutions as before. At 180 revolutions per minute, the piston speed is 480 feet per minute. Thus,- fJL = 2f . And, 180x2f = 480. Then, 78 ' 54 x 31 ' 5 x 48 = 36 horse-power, nearly. It might 33000 seem from the above that we are getting 6 horse-power more for nothing ; but such is not the case. For, cutting off at T 9 is equivalent to cutting off at 9 inches of the stroke. 78.54x9x2x150 Then, _ _= 123 cubic ft., nearly. 1728 78.54x9x2x180 1728 147 minus 123 = 24. So that for 6 horse-power more, we are using 24 cubic feet more of steam per minute, at 31.5 Ibs. M. E. P., which means more water evaporated per minute and more coal burned per hour. If the boiler pressure may be safely increased, we can get 6 horse-power more out of the engine without increasing its speed, by running the boiler pressure up to 75 Ibs. by gauge. Thus 75 Ibs. boiler pressure would give about 37.8 Ibs. M. E. P. with T 9 F cut-off: Then, ?8.54 x 37.8 x 400 = 86 ho Qwer nearly . 33000 In this case no change should be made in the governor, nor in the speed of the engine. We can also get 6 horse-power more out of this engine by cutting off later, say at f , in order to get 37.8 Ibs. M. E. P. But a later cut-off is not desirable, because it is not economical of steam, and besides, it would require a new valve, new eccentric, or a change in the length of a rocker arm, if not a change of the valve- seat, because the travel of the valve would have to be increased. HANDBOOK OX ENGINEERING. 385 HOW TO INCREASE THE HORSE=POWER OF AN ENGINE HAVING A SHAFT GOVERNOR. Suppose it is desired to increase the speed of the engine from 250 to 275 revolutions per minute, cutting off at i stroke. In this case the governor springs should be so adjusted that the throw of the eccentric will be the same at 275 revolutions that it was at 250 revolutions. This will require an increased consumption of steam per minute at the same initial cylinder pressure as before making the change, consequently more fuel will be required. If the speed of the engine is not to be changed, an increase of the horse-power may be obtained by increasing the initial cylinder pressure, if the condition of the boiler will so permit. Or, the initial cylinder pressure may remain unchanged and the governor springs and levers so adjusted as to give a later cut-off, say at | or -f s of the stroke, or whatever may be required to offset the increased per- manent load, the speed of the engine remaining unchanged. Any one of the changes above described would necessitate an increased consumption of fuel. HOW TO LINE THE ENGINE WITH A SHAFT PLACED AT A HIGHER OR A LOWER LEVEL. We will suppose the latter shaft not yet in place, but to be represented by a line tightly drawn. From two points as far apart as practicable, drop plumb lines nearly, but not quite, touching this line. Then by these strain another line parallel with the first, and at the same level as the center line of tli* 1 engine, and at right angles with this stretch another represent- ing this center line, and extend both each way to permanent walls on which their terminations, when finally located, should be care- fully marked, so they can at any time be reset. The problem is to get the latter line exactly at right angles with the former. Everything depends upon the accuracy with which this right 25 386 HANDBOOK ON ENGINEERING. angle is determined. It is done by the method of right-angled triangles. There are two ways of applying this method. In the first, one end of a measuring line is attached to some point of line No. 1, and its other end is taken successively to points on line No. 2 on opposite sides of the intersection, as illustrated in the following figure, in which A B is a portion of line No. 1, and C I) of line No. 2, the direction of which is to be determined. B F and B G are the same measuring line fixed at JB, and applied to the line C I) successively at the points F and (*. The dis- tances B Fand B G being, therefore, the same, when E F is equal to E G, the lines A B and C D are at right angles with each other. In the second, application is made of the law that the square of the hypothenuse of a right-angle triangle is equal to the sum of the squares of the other two sides. Thus 3 2 -f- 4 2 = 5 2 . So if the above figure E B = 4, E F = 3, and B F= 5, the angle at E is a right-angle. Any uru't of measure may be used, a foot is generally the convenient one ; so any multiple of these numbers may be taken; as, for example, 6, 8 and 10. Respecting the comparative advantages of these two ways, the situation will often determine which is to be preferred. In the former, the diagonal HANDBOOK ON ENGINEERING. 387 being the same line, fixed at B and brought successively to the points F and 6r, its length is immaterial, though generally the longer the better ; and the only point to be determined is the equality of E F and E G, which may be compared with each other by marks* on a rod. In the latter, the proportionate lengths, 3, 4 and 5. or their multiples, must be exactly measured. It is better adapted to places where a floor is laid and the meas- urements can be transferred by trammels. The result should be verified by repeating the operation on the opposite side of the intersection at E, and when so verified we have, in fact, the first process, without the additional and unnecessary trouble of deter- mining the relative lengths of the lines. Care should be taken when a measuring line is used, to avoid errors from its elasticity . On this account, a rod is often employed. Points on the lines are best marked by tying on a white thread. HOW TO LINE THE ENGINE WITH A SHAFT TO WHICH IT IS TO BE COUPLED DIRECT. In this case, it is supposed that the engine bed and the bear- ings for the shaft are already approximately in position. They are leveled by a parallel straight edge and a spirit level. To line then) horizontally, a line must be run through the whole series of hearings and continued to a permanent wall at each end, and its terminating points, when determined, carefully marked, as already directed. A piece of wood is tightly set in each end of each bearing and the surfaces of these are painted white or chalked. Then the middle of each piece being found by the compasses, two fine lines are drawn across it, equally distant from the middle, and having between them a space a little wider than the thickness of the line. This being then strained, nearly touching those blocks; or, if long, having its sag supported by them, the two marks on each block must be seen, one on each side of the line, with the line of white between. 388 HANDBOOK ON ENGINEERING. HOW TO SET A SLIDE VALVE IN A HURRY. Open your cylinder cocks ; then open the throttle slightly, so as to admit a small amount of steam to the steam-chest. Roll your eccentric forward in the direction the engine runs, until steam escapes from the cylinder cock at the end where the valve should begin to open. Now screw your eccentric fast to the shaft. Roll your crank tojthe next center and ascertain if steam escapes at the same point, at the opposite end of the cylinder. If so, ring your bell and go ahead. You are all right and can run until an opportunity occurs to you to open your steam-chest and examine your valve. DO YOU DO THESE THINGS? A writer in a contemporary asks and answers the following pertinent questions : - Do you take a squirt-can in one hand and project a stream of oil as far as you can throw it, in order to save going to the oil hole itself ? If you do, don't do it any more ; willful waste is downright robbery. Do you use an oil can at all for oiling, except on emergency, or for the moment ? If you do, don't do it any more, for much better lubrications can be had by automatic apparatus. Do you keep an old tin coffee pot full of suet on the steam- chest, and every tiine you have nothing else to do, pour a dipper- ful into the steam-chest? If you do, stop it and get a sight-feed cup, which will save you the labor of slushing the cylinder and save the cylinder and valve-seats, the piston and follower, and all other places touched by the grease. HANDBOOK ON KN<; INHERING. 389 Do you feed the boiler until the water is out of sight in the glass, then shut off the feed, put in a big fire and sit down in a dark corner with a four-horse brier pipe and smoke, until you happen to think that maybe the water is low? If you do these things you should notify the coroner that some day his services will be needed, but it is better to cease the prac- tice mentioned before the coroner comes. Do you stop leaks about the boiler as fast as they occur, or do you wait until the places sound like a snake's den before, you stir? If you do, you waste heat, 'which is the same word as money, only differently spelled. Every jet of hot water leaking from a steam boiler is just so much money thrown away, and if it was your money you would be bankrupt in a short time, in some boiler rooms. Do you take a screw wrench and yank away at a bolt or nut under steam pressure? If you do, there will come a time, sooner or later, when you will do so once too often, and either kill yourself or some one else. Bolts and nuts are liable to strip or break if tampered with under pressure, and they never tell any one beforehand when they are going to do it. Do you attempt to stop pounding in the engine by laying for the crank-pin as it comes round, and trying to hit the key once in a while? If you do, ask the strap and neck of the connecting-rod how he likes it, when you don't hit the key and do hit the oil cup? Do you pack the piston by taking it out of the cylinder, lay- ing it on the floor, setting out the rings, and then when the piston will not go into the cylinder, try to batter it in with a four-foot stick of cord wood? If you dQ, you should reform, and pack the piston in the cylinder where it belongs, being sure to get it central by meas- uring from the lathe center in the end of the piston rod. 390 HANDBOOK ON ENGINEERING. Do you put a new turn of packing on top of the old, lisird- burned stuff when the piston rod leaks steam ? If you do, you will have a scored piston rod and broken gland bolts some day. Packing under heat and pressure gets so hard that it cuts like a file when left in the stuffing box, and as one begins to leak all the old stuff should be pulled out and new put in its place. Fig. 1. Fig. 2. THK TRAVEL OF A SIDE VALVE. 4 The travel of a slide valve is found as follows : The maximum port opening at the head end, plus the maximum port opening at the crank end, plus the lap at the head end, plus the lap at the crank end. Therefore If" -f- If" -f- " + f" =4J", the re- quired travel: of valve. Incidentally, it may be well to mention that the travel of a valve may also be obtained from the eccentric, by subtracting the thin part of the eccentric from the thick part as per Fig. 1, or again, by taking twice the distance between the center of rotation and center of the eccentric. This distance on the eccentric is the end valve travel, and is termed the " throw " of the eccentric. In the above question, the travel may also be HANDBOOK ON ENGINEERING. 391 found by the aid of the diagram, Fig. 2, which is explained as follows: From the center A, with a radius of J inch (lap), describe a circle B C D. From any point, in the circumference, say 12, lay off the distance B E equal to the maximum port open- ing. If" ; from the center A, with a radius A E, describe the circle E F G; the diameter of the circle .E F G is equal to the travel of the valve, which is 4J". Let the readers try this with another set of figures, to prove the correctness of the diagram. LOSS OF HEAT FROM UNCOVERED STEAM PIPES. The following table shows the loss of heat through naked steam pipes, wrought iron, of standard sizes. The best covering for a steam pipe is hair felt from one to two inches thick, depending on the diameter of the pipe, say one inch thick for pipe from 1 to 4 inches in diameter, and two inches or more for larger pipes. Such covering will save at least 96 per cent. Cheaper coverings will save from 75 to 90 per cent. The chief value of the table is as an aid in estimating the saving that can be made by covering the pipe. The money loss by naked pipe being known, the sav- ing can be estimated and the cost of the covering will decide its value as an investment. TABLE OF MONEY LOSS FROM 100 FEET OF NAKED STEAM PIPE, FOR ONE YEAR OF 3000 WORKING HOURS. fl STEAM PRESSURES. | 50 60 70 80 90 100 fc^ 0.5 Ibs. Ibs. Ibs. Ibs. Ibs. Ibs. 1 $13.15 $13.70 $14.20 $14.66 $15.08 $15.47 U 16.58 17.29 17.92 18.49 19.02 19.51 if 18.98 19.78 20.51 21.17 21.77 22.33 2 23.72 24.73 25.63 26.45 ' 27.21 27.91 2JL 28.72 29.94 31.03 32.03 32.94 33.79 3 8 34.97 36.45 37.78 38.99 40.10 41.14 4 44.96 46.86 48.57 50.13 51.56 ,02.89 5 55.57 57.92 60.04 61.96 63.73 65.38 6 66.27 69.08 71.60 73.89 76.01 77.96 392 HANDBOOK ON ENGINEERING. RULES AND PROBLEMS APPERTAINING TO THE STEAM ENGINE. To find the H. P. of a simple non-condensing engine : Rule* Multiply the net area of the piston in square inches, by the mean effective pressure in pounds per square inch, and by the velocity of the piston in feet per minute, and divide the last product by 33,000. The quotient will be the gross H. P. Sub- tract from this from ten to twenty per cent for friction in the engine itself, and the remainder will be the delivered H. P. Example* The area of the piston is 500 sqr. ins. Half the area of the piston-rod is 5 sqr. ins. The M. E. P. is 50 Ibs. per sqr. in. The stroke is 3 feet, and the revolutions per minute 125. The friction is 10 per cent. What is the delivered H. P. of the engine? Ans. 506.25 H. P. Operation* 3 ft. X 2 = 6 ft. twice the stroke. Then, 500 5 =495 sqr, ins. net area of piston. And, 125 X 6 = 750 ft. the piston speed per minute. ^495X50X750 33,000 Then, 562.5 X .90 = 506.25. The delivered H. P. For a condensing engine: Add the vacuum to the M. E. P. and proceed as above. The M. E. P. is the average pressure in the cylinder, less the back pressure. To find the H. P. of a compound noncondensing engine : The usual method of calculating the H. P. of a multiple cyl- inder engine is to assume that all the work is done in the low pressure cylinder alone, and that such a M. E. P. is obtained in that cylinder as will give the same H. P. as is given by the whole engine. Rule* Find the ratio of areas of the high and low pressure cylinders, when of the same stroke, as they usually are, and HANDBOOK ON ENGINEERINO. 393 multiply it by the number of expansions in the high pressure cylinder, for the total number of expansions in both cylinders. Find -the hyperbolic logarithm corresponding to this result and add 1 to it, and divide the sum by the total number of expan- sions. Multiply this result by the absolute steam pressure, and subtract the back pressure. Subtract again the loss in pressure between cylinders, and the remainder will be the M. E. P. Then multiply the net area of the low pressure cylinder by this M. E. P. and by the piston speed in feet per minute and divide by 33,000. Deduct the friction in the engine itself and the remainder will be the delivered H. P. Example. Given a tandem compound engine with cylinders 20" and 32" diameter, and 4 feet stroke, making 75 revolutions per minute, boiler gauge pressure 125 Ibs. per sqr. in., J cut-off in high pressure cylinder, back pressure 15J Ibs. per sqr. in., drop in pressure between cylinders 15 per cent, and friction in engine 10 per cent. What is the H. P. delivered of this engine? Ans. 338.4 H. P. Operation* Neglecting the areas of the piston rods, we have : - 20 X 20 X .7854 = 314.16 sqr. ins. area of high pressure cylinder. And, 32 X 32 X .7854 = 804,2 sqr. ins. area of low pressure cylinder. * Then, 804.2 -i- 314.16 = 2.56 = the ratio between cylinders. And, 2.56 X 4 = 10.24 = the total number of expansions. The hyperbolic logarithm of 10.24 = 2.328. (Seetableonp. 397.) And, 1 + 2.328 = 3.328. Then, 3.328 4- 10.24 = .325. Also, 125 -f- 15 140 Ibs., the absolute pressure. And, .325 X 140 =45.5 Ibs., forward pressure. And, 45.5 15.25 = 30.25 Ibs., the M. E. P. 394 HANDBOOK OX ENGINEERING. And, 30.25 X .85 = 25.7 Ibs. -^ the M. E. P. less the " drop." 804.2 X 25.7 X 8 X 75 Then, - =376 H. P. nearly. 33,000 And, 376 X .90 = 338.4 H. P. delivered. For a compound condensing engine, proceed as above, except that the condenser pressure, due to impaired vacuum, only should be subtracted from the forward pressure. To find the linear expansion of a wrought-iron pipe or bar : Rule* Multiply the length of the pipe or bar in inches by the increase in temperature, and by the constant number .0007, and divide the last product by 100. Example* Given a 6 inch wrought-iron pipe 75 feet long. Steam pressure 150 Ibs. by gauge. Temperature of pipe when put up 60 degs. Fah. What is its linear expansion? Ans. 2 ins. nearly. Operation. The diameter of the pipe cuts no figure. Then, 150 Ibs. pressure = 366 degs. And, 366 60 = 306 degs. Also, 75 X 12 = 900 inches length of pipe. The,. 306 X900X .0007 =1>9a78ineh- For copper, use the constant number .0009 ; for brass, use .00107 ; for fire-bjick, use .0003, and proceed as above. To find the proper diameter of steam pipe for an engine : - The velocity of steam flowing to an engine should not exceed 6,000 feet per minute. Rule. Multiply the area of the~piston in square inches by the piston speed in feet per minute, and divide by 6,000 ; and divide again by .7854, and extract the square root for the diameter of the pipe and take the nearest commercial size. Example* Given a 20" X 48" Corliss engine making 72 revo- lutions per minute. What should be the diameter of its steam pipe? Ans. 6 inches. HANDBOOK ON ENGINEERING. 395 Operation* 20 X 20 X .7854 r=314.16 sqr. ins. And, 48 " X 2 X 72 = 576 ft. the piston speed. 12 And. 314 - 16X576 = 30.15. 6,000 Then, = 6.1". Take 6" pipe. To find the water consumption of a steam engine : The most reliable method for determining this, is to make an evaporation test, that is, to measure the water fed to the boiler in a given time and delivered to the engine in the form of steam. But as this method entails considerable trouble and expense, it is frequently figured from indicator diagrams. This plan, however, does not insure correct results, because the amount of water ac- counted for by the indicator is considerably less than it should be owing to cylinder condensation and leakage, so that it might be possible that only 80 per cent of the water passing through the cylinder would be accounted for by the indicator. But the cal- culation, used in connection with an evaporation test, will reveal the extent of the losses caused by cylinder condensation and leakage, by deducting the amount of water found by computation from the amount of water fed to the boiler while making an evaporation test. Rule. Divide the constant number 859,375 by the M. E. P. of any indicator card, and divide this quotient by the volume of its total terminal pressure, the result will be the theoretical con- sumption in pounds of water per horse power per hour. The constant number 859,375 is found as follows: Compute the size of an engine that will give just one horse- power at one pound M. E. P. per square inch, thus: Area of piston equals 412.5 sqr. inches. Stroke equals 4 feet, and revolutions per minute equal 10. 396 HANDBOOK ON ENGINEERING. Then, the piston speed is (4 X 2 X 10) 80 feet per minute. 412.5 X 1X80 And ' -88^00- To find how much water it would take to run this engine one hour, allowing 02 1 Ibs. to the cubic foot of water, proceed as follows : Twice the stroke equals 90 .inches. Then, - equals 2 2. 9 10 GO cubic feet for one revo- 1728 . lution. And, 22.91600 X 10 equals 229.1000 cubic feet for 10 revolu- tions, or for one minute. Then, 229.1000 X 60 X 02J equals 859,375 Ibs. of water used per hour. T SCALE 40 M. E. P. 13 7. 6 LBS. Fig. 1 is not an actual indicator card, but answers to illustrate the rule. A A is the atmospheric line, and from A to A is the whole stroke. VV is the vacuum line. Points (a) and (?>) are equally distant from the vacuum line. The point (a) is taken at or very near the point of release. HANDBOOK ON ENGINEERING. 397 Example. From the indicator card Fig. 1 compute the water consumption, the M. E. P. being 37.6 Ibs. per square inch, the scale of spring used in the indicator being 40, the distance from point (a) to point (fr) being 3.03 inches, the stroke A A being 3.45 inches, and the pressure at point () being 25 Ibs. per sqr. inch absolute. Ans. 20.14 Ibs. Operation* 859,375 ~- 37.6 = 22,855.7. Now, the absolute pressure at point (//) is 25 Ibs., and steam tables give 996 as the volume of steam at this pressure, that is, steam at this pressure has 996 times the bulk of the water from which it was generated. Then, 22,855.7 -f- 996 = 22.94 Ibs. of water. But as the period of consumption is represented by (6) (a), AA being the whole stroke, the following correction is required : The distance from point (a) to point (b) is 3.03 ins. Then, 22.94 X 3.03 = 69.5080. And the whole stroke or length of line AA is. 3. 45 ins. Then, 69.5080 -^-3.45 = 20.14* Ibs. of water per indicated horse power per hour. TABLE OF HYPERBOLIC LOGARITHMS. NO. LOGARITHM. NO. LOGARITHM. NO. LOGARITHM. 1.25 .22314 5. 1.60943 9.5 2.25129 1.0 .40546 5.25 1.65822 10. 2.30258 1.75 .55961 5.5 1.70474 10.24 2.328 2. .69314 5.75 1.74917 11. 2.39789 2.25 .81093 6. 1.79175 12. 2.48490 2.5 .91629 6.25 1.83258 13. 2.56494 2.TS .01160 6.5 1,87180 14. 2.63905 3. .09861 6.75 1.90954 15. 2.70805 3.25 .17865 7. 1.94591 16. 2.77258 3.5 .25276 7.25 1.98100 17. 2.83421 3.75 .32175 7.5 2.01490 18. 2.89037 4. .38629 7.75 2.04769 19. 2.94443 4.25 .44691 8. 2.07944 20. 2.99573 4.5 .50507 8.5 2.14006 21. 3.04452 4.75 .55814 9. 2.19722 22. 3.09104 398 JIANDHOOK ON* ENGINEERING. THE STEAM BOILER. CHAP T K R XVI. THE FORCE OF STEAM AND WHERE IT COMES FROH. If water he heated it will expand somewhat, and will finally burst forth into vapor. The vapor will expand enormously, and naturally occupy more space than the water from which it is formed. 'A cubic inch of water will make a cubic foot of steam : that is, the water has been expanded by heat to seventeen hundred times its original bulk. The steam is very elastic; the water was not. When we say that a cubic inch of water will form a cubic foot of steam, we mean that it will do so when the steam is allowed to rise naturally from the water without any confinement. If the steam is confined, as it would be in a boiler, it could not expand, and consequently would not. If the steam is allowed to rise into the atmosphere from an open vessel, the pressure of the steam would be precisely the same as the pressure of the atmosphere, that pressure being about fifteen pounds to the square inch. An ordinary steam gauge only takes notice of the pressure above the atmospheric pressure. When the hand of the steam gauge stands at zero, it indicates that there is no pressure above the ordinary pressure of the atmosphere. An ordinary steam gauge not connected with anything has the atmosphere acting upon it in both directions, the same as the atmosphere acts upon everything when it can reach both sides. If the air be pumped out of the steam gauge, the atmosphere will then act upon one side, and the hand will move backward until it stands at fifteen points less than nothing. In this condition the steam gauge indicates the absolute zero of pressure. If now the air be allowed to re-enter where it was pumped out, it will begin to exert its pressure upon the steam HANDBOOK ON ENGINEERING. 399 gauge, and the hand will move forward ; when the full air pressure is on, the gauge hand will stand at its usual zero. To go into this matter in order that it may be understood that the real pressure of steam is always fifteen pounds greater than ordinary steam gauges indicate. In all of the finer cal- culations relating to the action of steam, its total pressure must be known, and this total pressure is to be counted from the absolute zero. The real pressure of steam is always the steam gauge pressure, plus fifeeen pounds. When a steam gauge shows lifty pounds, the steam really has a pressure of sixty-five pounds. The fifteen pounds of this pressure is nullified by the atmospheric pressure, and the steam gauge shows us our useful pressure. As before stated, a cubic inch of water will make a cubic foot of steam at atmospheric pressure; that is, fifteen pounds to the sq uare inch, abolute pressure, or zero by the steam gauge. If this cubic inch of water was made into steam in a boiler holding just a cubic foot, the steam gauge would show zero. If the boiler was only large enough to hold half a cubic foot, the steam would all be in the boiler, and being confined in half its natural space, it would have double pressure. It would have an absolute pres- sure of thirty pounds to the square inch, and the steam gauge would indicate fifteen pounds. If this steam was then allowed to pass into a chamber holding a cubic foot, the steam would expand until it filled the chamber, and its pressure would go down again to fifteen pounds absolute. N In short, the pressure is in reverse proportion to the amount of space it occupies. The pressure of steam may be doubled by compressing the steam into one-half its former volume, and so on. After water is turned into steam, the steam may be made hotter, but it is not very much expanded. The pressure of steam is increased by forcing more steam into the space occupied. If a boiler contains steam at 50 Ibs. pressure, we may increase the pressure by adding more steam, and thus compressing all the 400 HANDBOOK ON ENGINEERING. steam that the boiler contains. In the ordinary operation of a steam boiler, the fire turns the water into steam and the more steam there is made and confined, the greater the pressure will be. If the steam is constantly (lowing out of the boiler into an engine, the pressure in the boiler must be kept up by continually making new steam to take the place of that drawn off. If we make steam as fast as it is drawn off, and no faster, the pressure will remain the same. If we make steam faster than the engine draws it off, the pressure will rise, and if it is drawn off faster than we make it, the pressure will go down. The pressure of the steam is due to its desire to expand into a larger body, and it acts outwardly in every direction against everything upon which it presses. If we crowd GOO cu. ft. of steam in a boiler, which will only hold 100 cu. ft., the steam will be held compressed into one-sixth its natural bulk, and will thus have a pressure of 90 Ibs., and the steam gauge will show 75 Ibs. If a hole 1 in. square be cut in the boiler, and a weight of 75 Ibs. be laid over the hole, the steam will just lift the weight. If the atmospheric pressure could be removed from one sq. in. of the top of the weight, the steam would then be capable of lifting a 90 Ib. weight. The force which this steam will exert to lift a weight, or any similar thing against which it acts, will equal the pressure per square inch multiplied by the number of square inches which the steam acts upon. It will thus be readily under- stood that if we lead a pipe from the boiler and lit a piston in the pipe, the steam will tend to force this piston out of the pipe. THE ENERGY STORED IN STEAM BOILERS. A steam boiler is not only an apparatus by means of which the potential energy of chemical affinity is rendered actual and avail- able, but it is also a storage reservoir, or a magazine, in which a quantity of such energy is temporarily held ; and this quantity, HANDBOOK ON T ENGINEERING. MM enormous, is directly proportional to UK; weight of water and of steam which the boiler at the time contain**. The energy of gunpowder is somewhat variable, but a cubic foot of heated water under a pressure of GO or 70 Ibs. per square inch, has about the same energy as one pound of gunpowder ; at a low red heat, it has about forty times this amount of energy. The letters B. T. U. are the initial letters of the words British .Thermal Unit, and are used as abbreviations of those words. The British Thermal Unit is the unit of heat used in this country and England, and may be said to be the amount of heat required to raise the temperature of one pound of pure water from 60 to 61 degrees Fahr. It is often necessary to distinguish between B. T. U. used in this country and the French thermal unit used in France and most of the countries of Europe. The French ther- mal unit is called the calorie, and is the heat required to raise the temperature of one kilogram of water one degree centigrade. Safety at high pressure depends entirely upon the design, material, and workmanship, and it is a question that may be re- garded as settled long since, that a steam boiler properly con- structed and designed for a working pressure of 150 pounds is as safe as a properly constructed boiler designed for eighty pounds, with the chances in favor of the high pressure, for the reason that less care is taken in selecting boilers for the ordinary pressure, as anything in the shape of a boiler is regarded, by careless people, as good enough for the lower pressures, with which they have become so familiar as to become almost too careless. SPECIAL HIGH PRESSURE BOILERS. The extending use of compound steam engines, which make necessary the employment of high steam pressures, calls for steam boilers specially designed to successfully operate under working pressures ranging from 100 to 160 pounds. These boilers must be safe and economical and of such construction as to afford 26 402 HANDBOOK ON ENGINEERING. access for examination and repair, moderate in first cost and maintenance and of simplest possible form. Fortunately, the controlling conditions are not difficult to meet, and there are sev- eral well-tried and approved types of steam boilers from whi<5h to make your selection, choice being governed by the space tit dis- posal, arrangement of plant, kind of fuel and other circum- stances. TYPES OF BOILERS. Four types that are very succesfully used, and they represent good practice for high pressure work, being respectively the Hori- zontal Tubular, and Vertical Fire Box Tubular Boilers. The Fire Box Locomotive Tubular Boiler may safely be added to this list and gives most excellent satisfaction. THE WATER TUBE BOILER. Steam boilers must be designed with reference to the pres- sure of steam to be carried, and when so designed and constructed are quite as safe at one pressure as another, preference being given to the type that is simplest in form and the least liable to destruction, not so much by reason of the pressure carried as by failure to provide for the strains of expansion and contraction within itself. HORSE POWER OF BOILERS. In determining the proper size or evaporating capacity of a boiler to supply steam for a given purpose, it is necessary to con- sider the number of pounds of dry steam actually required per hour at the stated pressure. The standard horse power rating for any steam boiler is 34^ pounds of water evaporated (made into steam) from feed water at 212 per hour. The total pounds steam required for your purpose per hour on this basis divided by 34 J will give the standard boiler horse power required. Maim- HANDBOOK ON ENGINEERING. 403 facturers of steam boilers sometimes rate the horse power of their boilers by so many square feet of heating surface per horse power ; 8 to 15 sq. ft. of heating surface, they figure, equals one horse power. This rating does not represent the actual capacity of the steam boiler, the only safe guide being the evaporative perform- ance in pounds of steam from water at 212 to steam at 212. Some boilers will evaporate this with 8 sq. ft., some requiring from 15 to 18 sq. ft., hence, the absurdity of rating horse power of boilers of unlike construction by the square feet of heating surface. But as the practice is an old one in the case of the well-known tubular boiler, so deservedly popular and used more, than any other kind, good practice is to allow approximately as follows : Allow for each Horse Power Steam for Heating, etc 15 sq. ft. heating surface. For Plain Throttle Engine, ... 15 " " For Simple Corliss Engine ... 12 " " For Compound Corliss Condensing .10 " Hence, a boiler for heating purposes or furnishing steam for Plain Slide engine with 1,500 sq. ft. surface, equals . 100 H.P. For Simple Corliss Engine, same boiler " . 125 H. P. For Compound Engine ' k . 150 H. P. The best method is to compare, boilers with their evaporative ofliciency and not by heating surface. The following is an approximate consumption of steam per indicated horse power per hour for engine : Plain Slide Engine 60 to 70 pounds. High Speed Automatic Engine 30 to 50 " Simple Corliss Engine 25 to 35 " Compound Corliss Engine 15 to 20 u Triple Expansion Engine 13 to 17 " 404 HANDBOOK ON KXC-JIXKKKING. depending upon the horse power, steam pressure, condition of engine, load, etc. Each pound of first-class steam coal consumed under a well- proportioned steam boiler, well managed, should evaporate 10 pounds of steam from water 212 to steam at 212. The average boiler throughout the country, with ordinary fuel and manage- ment, ranges from 5 to 8 pounds steam per pound of coal, and it would scarcely be safe to make fuel guarantees per horse power of engine without a counter guarantee on the part of the pur- chaser, when his old boiler is used, that the fuel economy is based on an evaporative efficiency of a given pounds water evaporated per pound of coal per hour of his boiler. The usual practice is to ignore the boiler altogether and guarantee pounds of steam per indicated horse power per hour used by the engine. This affords an exact method and is not hampered by unknown con- ditions and places all tests on an equal or comparative basis. fHE RATING OF BOILERS. It 'is considered usually advisable to assume a set of practically attainable conditions in average good practice, and to take the power so obtainable as the measure of the power of the boiler in commercial and engineering transactions. The unit generally assumed has been usually the weight of steam demanded per horse power per hour by a fairly good steam engine. ' In the time of Watt, one cubic foot of water per hour was thought fair ; at the middle of the present century, ten pounds of coal was a usual figure, and live pounds, commonly equivalent to about 40 Ibs. of feed water evaporated, was allowed the best engines. After the introduction of the modern forms of engine, this last figure was reduced 25 per cent, and the most recent improvements have still further lessened the consumption of fuel and of steam. By general consent the unit has now become thirty pounds of dry steam per HANDBOOK ON ENGINEERING. 405 hoj'se power per hour, which represents the performance of uon- condensing engines. Large engines, with condensers and com- pound cylinders, will do still better. A committee of the American Society of Mechanical Engineers recommended thirty pounds as the unit of boiler power, and this is now generally accepted. They advised that the commercial horse power be taken as an evaporation of 30 Ibs. of water per hour from a feed water temperature of 100 Fahr. into steam at 70 Ibs. gauge pres- sure , which may be considered equal to 34J Ibs. of water evapo- ration, that is, 34 i Ibs. of water evaporated from a feed water temperature of 212 Fahr. into steam at the same temperature. This standard is equal to 33,305 British thermal units per hour. A boiler rated at any stated power should be capable of developing that power with easy firing, moderate draught and ordinary fuel, while exhibiting good economy, and at least one-third more than its rated power to meet emergencies. WORKING CAPACITY OF BOILERS. The capacity or horse-power of a boiler, as rated for purposes of the trade, is commonly based upon the extent of heating surface which it contains. The ordinary rating was for a long time 15 sq. ft. of surface per horse-power. At the present time most of the stationary boilers are sold on the basis of from 10 to 12 sq. ft. per horse-power, the power referred to being th % e unit of 30 Ibs. evaporation per hour. This method of rating is arbi- trary, inasmuch as it is independent of any condition pertaining to the practical work of the boiler. The fact that 10 or 12 sq. ft. of surface is sold for one horse-power is no guarantee that this extent of surface will have a capacity of one horse-power when the boiler is installed and set to work. The boiler in service and the boiler in the shop are two entirely different things, and where one passes to the other, the trade rating disappears. New 4_. 19. Total refuse, dry pounds equals . 20. Total combustible (dry weight of coal, item 18, less refuse, item 19) . *21. Dry coal consumed per hour *22. Combustible consumed per hour . hours, hours. Sq. ft. Sq. ft. Sq. ft. Ibs. Ibs. in. in. deg. deg. deg. deg. deg. Ibs. per cent. Ibs. per cent. Ibs. Ibs. Ibs. HANDBOOK OX ENGINEERING. 413 RKSri/l'S OK CALORIMKTRIC TESTS. 23. Quality of steam, dry steam being taken as unity . 24. Percentage of moisture in steam . . . percent. 2T). 'Number of degrees superheated . . . cleg. * WATER. 2<>. Total weight of water pumped into boiler and apparently evaporated .... Ibs. 27. Water actually evaporated, corrected for quality of steam I DS . 2*. Equivalent water evaporated into dry steam from and at 212 F Ibs. *2i>. Equivalent total heat derived from fuel in B. T. U B. T. U. *30. Equivalent water evaporated in dry steam from 212 F. per hour ... Ibs. - ECONOMIC EVAPORATION. 31. Water actually evaporated per pound of dry coal, from actual pressure and temperature . Ibs. 32. Equivalent water evaporated per pound of* dry coal, from 212 F Ibs. 33. Equivalent water evaporated per pound of combustible from and at 212 F. . Ibs. COMMERCIAL EVAPORATION. 34. Equivalent water evaporated per pound of dry coal with one-sixth refuse, at 70 Ibs. gauge pressure, from temperature of 100 F., equals item tests 33 X. 0.7249 pounds Ibs. t corrected for inequality of water level and of steam pressure at beginning and end of test. 414 HANDBOOK ON ENGINEERING. RATE OF COMBUSTION. 35. Dry coal actually burned per sq. foot of grate-surface per hour Per sq. ft. of grate Consumption of dry surface coal per hour. Coal Per sq. ft. of water assumed with one- [ heating surface . sixth refuse. Per sq. foot of least area for draught. *36 *37 *38 39, *40. *41. *42, KATE -OF EVAPORATION. Water evaporated from and at 212 F. per square foot of heating surface per hour. Per sq. ft. of grate Water evaporated per hour from temperature of 100 F. into steam of 70 Ibs. gauge pres- sure. surface Per sq. ft. of heat- ing surface Per sq. ft. of least area for draught. COMMERCIAL HORSE POWER. 43. On basis of 30 Ibs. of water per hour evaporated from temperature of 100 F. into steam of 70 Ibs. gauge pressure (34J Ibs. from and at 212) . . . 44. Horse-power, builders' rating at sq. ft. per horse-power 45. Per cent developed above or below rating Ibs. Ibs. Ibs. Ibs. Ibs. Ibs. Ibs. H. P. per cent. * NOTE. Items 20, 22, 33, 34, 36, 37, 38 are of little practical value. For if the result proves to be less satisfactory than expected on the actual coal, it is easy for an expert fireman to decrease No. 20 by simply taking out some partly consumed coal in cleaning fires, and thus make a fine showing on that simply ideal or theoretical unit, the u pound com- bustible." The question at issue is always what can be done with an actual coal, not the " assumed coal " of Hems 34, 36, 37 and 38, HANDBOOK ON ENGINEERING. 415 DEFINITIONS AS APPLIED TO BOILERS AND BOIUBR flATERIALS. Cohesion is that quality of the particles of a body which causes them to adhere to each other, and to resist being torn apart. Curvilinear seams* The curvilinear seams of a boiler are those around the circumference. Elasticity is that quality which enables a body to return to its original form after having been distorted, or stretched by some external force. Internal radius* The internal radius is one-half of the diam- eter, less the thickness of the iron. To find the internal radius of a boiler, take one-half of the external diameter and substract the thickness of the iron. Limit of elasticity* The extent to which any material may be stretched without receiving a permanent " set." Longitudinal seams* The seams which are parallel to the length of a boiler are called the longitudinal seams. Strength is the resistance which a body opposes to a disinte- gration or separation of its parts. Tensil strength is the absolute resistance which a body makes to being torn apart by two forces acting in opposite direc- tions. Crushing strength is the resistance which a body opposes to being battered or flattened down by any weight placed upon it. Transverse strength is the resistance to bending or flexure, as it is called. Torsional strength is the resistance which a body offers to any external force which attempts to twist it round. Detrusive strength is the resistance which a body offers to being clipped or shorn into two parts by such instruments as shears or scissors. Resilience or toughness is another form of the quality of 416 HANDBOOK ON strength; it indicates that a body will manifest ;i m-tain degree of flexibility before it can be broken ; hence, that body which bends or yields most at the time of fracture is the toughest. Working strength. The term " working strength " implies a certain reduction made in the estimate of the strength of ma- terials, so that when the instrument or machine is put to use, it may be capable of resisting a greater strain than it is expected on the average to sustain. Safe working pressure, or safe load* The safe working pros- sure of steam-boilers is generally taken as * of the bursting pres- sure, whatever that may be. Strain in the direction of the grain, means strain in the direc- tion in which the iron has been rolled : and in the process of man- ufacturing boiler-plates, the direction in which the libres of the iron are stretched as it passes between the rolls. Stress. By the term " stress " is meant the force which acts directly upon the particles of any material to separate them. HEAT AND STEAM. The steam engine is a machine for the conversion of heat into power in motion. The heat is generated by the combustion of fuel ; the transmission is accomplished through the agency of steam ; the power is made available and brought under control by means of the engine. The effect of heat upon water is to vaporize, it, if there be inten- sity enough, the heat will, under proper conditions, cause water to boil; the vapor produced by boiling is called steam, and steam under pressure is a product which is the end and aim of that por- tion of that steam engine known as the boiler and furnace. The steam engine then is to be considered as a form of the heat engine ; of which the furnace, boiler, and the engine itself are to be regarded as separate portions of the same mechanism. HANDBOOK ON ENGINEERING. 417 The conditions demanded upon economic grounds to secure the highest ellicioncy in the steam engine are: , 1. A proper construction of the furnace so as to secure the perfect combustion of fuel. 2. The heat generated in the furnace must be transferred to the water in the boiler without loss. 3. The circulation in the boiler must be so complete that the heat from the furnace may be quickly and thoroughly diffused throughout the whole body of water. 4. The construction of an engine that will use the steam with- out loss of heat, except so much as may be necessary to perform work required of the engine. 5. The recovery of heat from exhaust steam. 6. The absence of friction and back pressure in the working of the engine. It is superfluous to say that these conditions are not fulfilled in any engine of the present day. At best the combustion of fuel is only approximately perfect, the losses being due to several, causes, among which are, unburned fuel falling through the spaces in the grates and mingling with the ashes. This, with, some kinds of coal, and improper firing, amounts to a large percentage of the furnace waste. It is not possible with any present method of setting boilers to transfer all the heat of the furnace to the water in the boiler ; nor can there be, for the reason that the temperature of the escaping gases must not be lower than that of the steam in the boilers, or direct loss will result in the radiation of heat from the tubes or flues in the boiler, by thus reheating the gases to the steam temperature. If the steam pressure is 80 Ibs. per square inch above the atmosphere, the cor- responding temperature due to this pressure is 324 Fahr. The temperature of the escaping gases ought not, therefore, to be less than 350 Fahr., where they leave the boiler flues or tubes to pass off into the chimney. If the temperature of the furnace be taken 27 - 418 HANDBOOK OX ENGINEERING. at 2,000 Fahr., and the escaping gases at 400 Kahr., it will be seen that one-fifth of the heat generated in the furnace is passing off without performing work. This is a very great loss, and these figures understate, rather than correctly give, the loss from this one source. Efforts have been made to utilize the tempera- ture of these waste gases by making them heat feed water by means of coils, or by that particular disposition of pipes and connection known as an economizer. Others have turned it into account by making it heat the air supplied the fuel on the grates. Any heat so reclaimed is money saved, provided it does not cost more to get it than it is worth in coal to generate a similar quan- tity of heat. It is doubtful whether the loss in this particular direction can be brought below 20 per cent of the fuel burned, at least, by any method of saving now known. The loss by bad firing and by a bad construction of furnace is often a large one. It has been demonstrated experimentally that 20 to 30 per cent of fuel can be saved by a proper construc- tion and operation of the furnace. The direct causes of loss are, too low temperature of furnace for properly burning fuels, espe- cially such as are rich in hydro-carbon gases ; or, by the admis- sion of too much cold air over or back of the fire ; or, by the admission of too little air under the fire so that carbonic oxide gas is generated instead of carbonic acid gas, the former being a product of incomplete, the latter the product of complete combustion. The relative heating powers of fuel burned, resulting in the production of either of these two gases being as follows : Heat Units. 1 pound of carbon burned to carbonic acid gas . . 14,500 1 pound of carbon burned to carbonic oxide . . . 4,500 Units of heat lost by burning to carbonic oxide . 10,000 It will be seen that here is an enormous source of loss, and all that is required to prevent it is a proper construction of furnace. HANDBOOK ON ENGINEERING. 419 Smoke is u nuisance which ought to be prohibited by stringent legislation. There is no good reason for its polluting presence in the atmosphere, defiling everything with which it comes in con- tact. Smoke regarded as a source of direct loss is greatly over- estimated ; the fact is, the actual amount of coal lost to produce smoke is very trilling. The presence of smoke indicates a low temperature of f ur.nace or combustion chamber ; if the temper- ature were sufficiently high and the furnace properly constructed, smoke could not be generated. The prevention of smoke is easily accomplished, and with it a more economical combustion of hydro-carbon fuels. Radiation* A considerable loss of heat occurs by radiation from the furnace walls ; this may be prevented in part by making the walls hollow, with an air space between. If a force blast is used the air may be admitted at the back end of the boiler-setting and by passing through between the walls will become heated, and if conveyed into the ash pit at a high temperature will greatly assist combustion and thus tend to a higher economy. Air required. In regard to the quantity of air required, it will vary somewhat with the fuel used, but in general, 12 pounds of air are sufficient to completely burn one pound of coal ; prac- tically, however, 15 to 25 pounds are furnished, being largely in excess of that which the fire can use, and must pass off with the gases as a waste product. This surplus air enters cold and leaves the furnace heated to the same temperature as that of the legitimate and proper products of combustion, and thus directly operates to the lowering of the furnace temperature. Measurement of heat* A heat unit is that quantity of heat necessary to raise the temperature of one pound of water one degree, from 39 to 40 Fahr., this being the temperature of the greatest density of water. A thermal unit, a heat unit, or unit of heat, all mean the same thing. Experiments have been made to determine the mechanical equivalent of a heat unit, and it is 420 HANDBOOK ON ENGINEERING. found to be equal to 772 pounds raised one foot high. This is sometimes called "Joule's equivalent," after Dr. Joule, of England ; it is also known as the dynamic value of a heat unit. Knowing the number of heat units in a pound of coal enables us to calculate the amount of work it should perform. Let us suppose a pound of coal to be burned to carbonic acid gas, and to develop during its combustion 14,000 heat units, then : 14,000x772 equals 10,808,000 foot pounds. That is to say, if one pound of coal were burned under the above conditions it would have a capacity for doing work repre- sented by the lifting of ten millions of pounds one foot high against the action of gravity. Suppose this to be done in one hour, then we should expect to get from one pound of coal an equivalent of 5.45 H. P. It is well known that only a very small fraction of such equivalent is secured in the very best modern practice. The question is, where does this heat go, and why is it so small a portion of it is actually utilized ? The losses may be accounted for in several ways, and, perhaps, as follows : The heat wasted in the chimney . . . . 25 per cent. Through bad firing . 10 " Heat accounted for by the engine (not indicated) 10 " Heat by exhaust steam ....... 55 " 100 per cent. This is about 2 pounds of coal per hour per indicated horse power, which is regarded as a very high attainment, and is seldom reached in ordinary cut-off engines. It requires good coal, good firing, and an economical engine to get an indicated horse power from two pounds of coal burned per hour. As coal varies in quality it is a better plan to deduct the ashes and other incombustible matter, and take the net combustible as a basis of comparison. The best coal when properly burned HANDBOOK ON ENGINEERING. 421 is capable of evaporating 15 pounds of water from and at a temperature of 212 Fahr. The common evaporation is about half that amount, and with the best improved furnaces and care- ful management, it is seldom that 10 pounds of water is exceeded, and is to be regarded as a high rate of evaporation. In experi- mental tests, 12 pounds have been reported, but it is doubtful whether there is any steam boiler and furnace which is con- stantly yielding any such results. Circulation of water in a boiler is a very important feature to secure the highest evaporative results. Other things being equal, the boiler which affords the best circulation of water will be found to be the most economical in service. Circulation is greatly hin- dered in some boilers by having too many tubes ; in others, by introducing in the water space of the boiler too many stays and making the water spaces too narrow. To secure the highest economy there must be thorough circulation from below upwards, in, the boiler. There is no doubt that a great deal of heat is lost because the construction is such as to hinder a free flow of water around the tubes and sides of the boiler. The construction of an engine that will use steam without loss of heat, except so much as may be necessary to perform work required of it, is a physical impossibility. Among the sources of loss ill an engine are : radiation, condensation of steam in un- jacketed cylinders, and the enormous loss of heat occasioned by exhausting the steam into the atmosphere. Radiation is usually classed among the minor losses in a steam engine. There is a considerable loss of heat caused by radiation from steam boilers and pipes exposed to the atmosphere, and not protected by a suitable covering. Much of this heat may be saved by employing a non-conducting material as a covering, which, though not preventing all radiation, will save enough heat to make its application economical. It is well known that some bodies conduct and radiate heat less rapidly than others, but it 422 HANDBOOK ON ENGINEERING. must not be understood thut the absolute value of such it Cover- ing is inversely proportioned to the conducting power of the material employed, because, in its application, the outer surface is enlarged and the radiation will be going on less actively at any given point, but the enlarged surface exposed reduces somewhat the apparent gain. SELECTION OF A BOILER. The selection of a boiler for a particular service will naturally suggest the following questions : - 1. What kind of a boiler shall it be? 2. Of what material shall it be made? 3. What size shall it be in order to furnish a certain power? In reply to the first question, it is to be expected there will be wide differences of opinion, varying with the locality, usage, and service for which it is intended. One of the first things to be taken into account in the selection of a boiler is the quality of water to be used in it for generating steam. If the water is pure, then it makes little difference what kind of boiler be selected, so far as incrustation affects selection. If the water is hard and will deposit scale upon evaporation, then a boiler should be selected which will admit of thorough inspection and removal of any deposit formed within it. For hard water, the ordinary tine boiler will* be found a good one, as it is favorable to a thorough circulation of water, and permits easy access to all parts of it for examination and clean- ing. It does' not, however, present the extent of heating surface for a given space that tubular boilers offer ; but with hard water the boiler is quite as economical if kept in good condition. The difficulty with tubular boilers when used in connection with hard water is that the tubes will in a short time become coated with scale ; this prevents the transmission of heat, not only, but impairs the circulation of the water around them. HANDBOOK ON ENGINEERING. 423 Both of these are opposed to economy in the fact that it requires more coal to generate a given weight of steam in the first case; and second, by reason of deficient circulation the plates over the (ire are likely to become overheated and burnt and so become dangerous ; thus directly contributing to accident or disaster. The matter of circulation in boilers is one which should have careful sit tendon in making a selection. There is little trouble in this regard with any of the ordinary types of boilers so long as they are clean and new, and properly proportioned. Nor is there likely to be any difficulty thereafter if the water is soft and clean. Circulation is often seriously impaired by putting in too many tubes in a boiler, the effect of which is to so fill up the space that the heated particles of water forcing their way upwards from below meet with so much resistance that they can hardly over- come it, and the result is that a boiler does not furnish from one- fourth to one-half as much steam for a given weight of fuel as it should, from this very cause. Boilers intended for use in distant localities where the facilities for repairs are meager or entirely wanting, and fuel low priced, should be of the simplest description. Cylinder boilers or two- flue boilers will perhaps be found most suitable. These are largely used by coal miners, blast furnaces, saw mills, and other branches of industry, which must, of necessity, be removed from the larger towns and engineering work shops. In selecting a boiler for a mill of any kind where they burn shavings or offal, or any other place in which the fuel is of a similar description and the firing irregular, there should be large water capacity in the boiler that it may act as a reser- voir of power in much the same way that a fly wheel acts as a regulator for a steam engine. It is a common notion among wood- workers that firing with shavings or light fuel is " easy on the boiler." There is abundant iveason to doubt this. The suddenness and rapidity with which an intense fire is kin- 424 HANDBOOK ON ENGINEERING. died in the furnace, filling all the furnace space and the tubes with flame, and with an intense heat which envelops all within the limits of draft opening, continuing thus for a few minutes only, and as suddenly going out, can hardly be regarded as the ideal furnace. Yet there are thousands of just 'such furnaces at work, and it is altogether probable that little or no change will be made in them by this class of manufacturers, at least in the near future. In regard to the selection of a boiler for this service, we are brought back again to the question of hard or soft water. The decision should be largely influenced by this, but whatever type of a boiler is selected there should be a surplus of boiler power of at least 20 per cent, that is, if a 50 horse-power boiler is needed to do the Work, put in one of 60 horse-power; this will prevent the fluctua- tions of speed in the engine which are sure to follow a reduction of boiler pressure. This increase in boiler power ought not to be simply that of tube surface, but should also include extra water space. The reserve power of a boiler is in the water heated up to a temperature corresponding to the steam pressure ; when this pressure is lowered, the water then gives off steam corresponding to the lower pressure ; the more water the more steam ; and in this way the water in the boiler stores up heat when overtired, to give it off again when the fire is low, and so acts a regulator of pressure, a thing that extra tube surface cannot do. This kind of firing is apt to induce priming, and for this reason a boiler should be selected having a large water surface. Horizontal boilers are, in general, to be preferred over vertical ones for mills, because of the larger water surface exposed in proportion to the heating surface. If a tubular boiler is selected, the water Hue above the tubes should be not higher than two-thirds the diameter of the boiler measured from the bottom, and the boiler should be made having the upper edge of the top row of tubes at least three inches below this ; there should also be a clear space up through the center of HANDBOOK ON ENGINEERING. 425 the boiler of sufficient width to insure a perfect circulation of water. Horizontal tubular boilers are to be recommended when pure soft water is used. They combine at once the qualities of great strength without excessive bracing, large heating surface, high evaporative capacity without liability to priming, and are conve- nient of access for external and internal examination when set in the furnace. Fire box boilers, or locomotive boilers, as they are commonly called, are best adapted for small powers and with a fuel which deposits but little soot in the tubes. This kind of boiler is sup- plied with portable or agricultural engines and is very well adapted for that particular service. In canvassing the desirability of this kind of a boiler for stationary use, we must again refer to the kind of water to be used in it. If the water is soft and clean there is then no particular objection to a boiler of this construc- tion being used for small powers ; if the water is hard and will form scale, it ought not to be chosen, but a flue boiler selected instead. Vertical boilers are used in great numbers for small engines, heating, etc. They have the merit of being compact and low priced. A common defect in the construction of this kind of boiler is that too many tubes are put in the head in the lire box, thereby preventing a proper circulation of water between them. This defect in construction induces priming, with all its attendant annoyances and dangers. This style of boiler is not suited to hard water, but pure soft water only. These boilers should be provided with hand holes above the crown sheet and around the bottom of the water legs ; at least three at each place mentioned. In regard to the material of which a boiler shall be made there is but the simple choice between iron and steel. Steel for boilers should not be of too high tensile strength ;. 55,000 to 60,000 pounds tensile strength per square inch makes 426 HANDBOOK ON ENGINEERING . the best boilers. If the steel is of too high a grade it will take :i temper, and, therefore, is utterly unlit for use in steam boilers : if the steel is of too low tensile strength it is apt to be loose or spongy. Among the advantages steel possesses over iron may be mentioned the circumstance that it is a practically homogeneous material when properly made and rolled, consequently, it is nearly as strong in one direction as it is in another. In this respect, steel is superior to iron plate of equal thickness, because the latter is made up of several pieces of iron welded together and in rolling into the plate it becomes fibrous, and thus of unequal strength, being greatest in the direction of the liber, and least, when tested across it. BOILER TRIMMINGS. The common trimmings to a steam boiler are a safety valve, feed and blow-off pipe, steam pipe, gauge cocks, glass water gauge and steam gauge ; to which may be added a steam drum or dome and a mud drum. There are numerous other devices which are attached to boilers such as safety gauges, alarms, fusible plugs, automatic dampers, etc. ; many of these are very serviceable and are well liked by those using them. Safety valves should always be large enough to permit the escape of all the steam a boiler is capable of making and each boiler should have its own safety valve rather than connecting two or more boilers together, and depending on one valve for the whole. The valve and seat should be made of hard gun metal, or any other composition that will not rust and stick fast. At one time it was quite a common thing to see a brass valve fitted to a cast-iron seat ; this is wrong, for the rusting of the iron would lix the valve so tightly that the boiler would be in constant danger of rupture from over pressure. For stationary boilers the common ball and lever safety valves are generally used. For stationary boilers it is immaterial whether the safety valve be fitted with a ON ENGINEERING. 427 lever and weight, or whether it In 1 fitted with a spring. The former is the usual manner of loading a safety valve and has but few objections. For portable engines and locomotives safety valves are loaded with springs, which by suitable adjustment may be made to blow off at any desired pressure. The following 1 rule is that enforced by the U. S. Government in fixing the area of satetv valves for ocean and river service, when the ordinary lever and weight safety valve is employed : Rule* When the common safety valve is employed it shall have an area of not less than one square inch for each two square feet of grate surface. Another rule is to multiply the pounds of coal burned per hour by 4 ; this product is to be divided by the steam pressure, to which a constant number 10 is added. KXAMPLK: What would be the proper area for a safety valve for a boiler having a grate surface 5 feet square and burning 12 pounds of coal per hour per square foot of grate ; the steam pressure being 75 pounds per square inch? 5x5 equal 25 square feet of grate. 25 x 12 equal 300 Ibs. of coal per hour. 800x4 equal 1200. 75 plus 10 equal 85 equal steam pressure with 10 added, then 1200/85 equal 14.11 inches area, or 4| inches diameter. A feed pipe should be at least twice the area over that which is regarded as simply necessary to supply the boiler with water, as sediment or scale is likely to form in it, which will materially re- duce its area. In localities where the water is hard the feed pipes should be disconnected near the boiler and examined occa- sionally to ascertain whether or not scale is forming in them. In general, the sizes of feed pipes leading from the pump to the boiler are fixed by the size of tap used by the maker of the pump. It is not well to reduce the diameter of the pipe and the size should be the same throughout. Care should be exer- 428 HANDBOOK ON ENGINEERING. cised iii putting pipes in place that no strain be brought upon them by imperfect fitting, as it is certain to lead to leaky joints at some time or other. It is also desirable that the pipes be as short and straight as possible. Feed pipes should never be placed under ground if it is possible to make any different disposition of them. In locating pipes it is desirable to arrange for the expansion of the boiler, as well as for that of the pipes themselves. In select- ing a pump it should have a much larger capacity than that needed to supply the boiler, as there are many things which affect the working of a pump, such as a defective suction pipe, leaky valves, etc. It is the practice of most manufacturers to give the capacity of their pumps in gallons of water delivered per minute, from which it is easy to select a suitable size ; but the speed given in the tables at which the pump is to run is generally faster than that which it is desirable to run them. As a general thing, and without referring to any particular maker or design, it is a good plan to select a pump having four times the capacity actually needed for the boiler ; then the speed may be reduced to half that given in the table, and will require less repairs, and will be a more satisfactory purchase in the long run. In selecting an injector or inspirator, the size should not greatly exceed that actually required to supply the boiler. In making the steam connections the pipes should start from the steam space of the boiler and should not be branches merely from the other steam pipes ; neither should the diameters of the pipes be less than that which the instrument calls for. The pipes should be as short and straight as practicable ; abrupt bends should always be avoided in the suction pipes. If the water is taken from a place in which there are floating particles of wood, leaves, etc., a strainer should be used; a large sheet metal box with perforated sides, makes a good strainer ; the openings ought not too greatly exceed an eighth of an inch in diameter, and should be several times the area of the suction pipe. HANDBOOK ON ENGINEERING. 429 A check valve -should bo fitted with a valve between it and the boiler, so that in the event of its not working satisfactorily it may be taken apart, cleaned and replaced without stopping for exami- nation or repairs. The blow-off pipe should be so arranged that it will entirely drain the boiler of water ; it is also a good plan to set a boiler with a slight inclination toward the blow-off pipe that it may be thoroughly drained ; an inclination of two inches in twenty feet works well in practice. The blow-off pipe is usually fitted at the back end of the boiler. The steam pipe may be connected at any convenient point on the top of the boiler. If the boiler is to furnish steam for an engine only, the common practice is to make the diameter of the pipe one-fourth that of the cylinder. The steam pipe should be as short and straight as possible. If bends are to be introduced in steam pipes it is better to have a long curved bend than the abrupt right-angle fitting usually employed for the purpose. It is also a good plan to provide a stop-valve r .xt to the boiler to shut off the steam and prevent it condensir^- in the steam pipe at night, or other long stoppages. The gauge cocks should not be less than three in number, and may be of any of the various kinds now in the market. For stationary boilers, the Mississippi gauge cock is, perhaps, as good as any. For portable engines a compression gauge-cock is, perhaps, the best. The lower gauge-cock should be at least 2" above the tubes or crown sheet, the middle 2" above the first ordinary water line, the upper 2" above the 2 on 2" to 3", de- peudhig on the size of the boiler. A glass water gauge should be provided for each boiler and should be so located that the water level in the boiler when at the lower end of glass shall be one inch above the top of flue. When glass gauges are so fitted the fireman can always tell at a glance, just how much water he has above the flues or crown sheet ; it 430 HANDBOOK ON ENGINEERING. also permits the easy test of accuracy by try ing the gauge-cocks witli the water at a certain known level. Too much dependence must not be placed on the glass water-gauge alone, hut should he used in connection with the gauge-cocks. A steam gauge is a very important appendage to a steam boiler, and should be chosen with special reference to accuracy and durability. The ordinary gauges now in the market are the bent tube and the diaphragm gauges. It matters little which of the two kinds is selected, provided it is a good and first-class gauge. A steam gauge should be compared with a standard test gauge at least once a year, to see that it is correct. The importance of this will be fully apparent when it is known that it furnishes the only means by which the fireman is to judge of the steam pressure in the boiler. A siphon should be attached to every gauge, and provision should also be made for draining the gauge or siphon, to prevent freezing when steam is off the boiler. Neglect of this may endanger the accurate reading of the steam gauge and render it useless. Steam dome* This is a reservoir for steam riveted to the upper portion of the shell and communicated by a central opening with the steam space in the boiler. When this reservoir forms a separate fixture and is attached to the boiler by cast or wrought iron nozzles, it is then called a steam dram. The latter answers all the purposes for stationary boilers that the former does, and is to be preferred because of the smaller openings in the shell of the boiler. A considerable number of boiler explosions have been traced directly to the weakness of the shell, caused by the large opening in and imperfect staying of the shell underneath the dome. When a dome is employed and has a large hole under- neath, the strength of the shell is impaired in two ways: 1. By reducing the longitudinal sectional area of shell through the cen- ter of opening cut for it, which weakness cannot wholly be made good by a strengthening ring around the opening. 2. By causing HANDBOOK ON ENGINEERING. 431 a tension equal to that on the crown area of steam dome, upon the annular part of the shell covered by the llange of the dome. The weakest part of the boiler shell will be where the distance from rivet hole at the base of the dome to edge of plate is least. It is difficult, owing to the complex nature of the strains, to form a rule whereby to determine how much the strength of the shell is impaired by using a dome ; but it is quite apparent from gen- eral experience that they are in many cases a source of weakness, and the larger the dome connection with the shell, the greater the liability to rupture. This tendency to rupture is due to the fact that the dome, with its connecting flange, is practically inelastic ; that portion of the shell of the boiler covered by the dome is, as soon as the pressure is introduced on both sides of the plate, simply a curved brace. The pressure of the steam in the boiler has a tendency to straighten the shell under the dome and thus brings about a series of complex strains which are not easily rem- edied by any system of bracing, so that on the whole it is prefer- able to use a small connecting nozzle with a drum above it, rather than to rivet a large dome directly to the shell. Dry pipe* - This is a pipe having numerous small perforations on its upper side, and inserted in "the upper part of the steam space of the boiler. This pipe does not dry the steam, but acts mechanically by separating the steam from the wetter when the latter is in a violent state of agitation, and is liable to be carried in bulk toward or into the steam pipe. The object of these numer- ous small holes in the pipe is that a small quantity of steam may be taken from a large number of openings at one time, and thus carried over a larger extent of surface than that afforded by a single opening, and by this single device checking the tendency to priming. Steam boiler furnaces are receiving more attention now than perhaps ever before. The question of economy of fuel is being closely studied, and there is now an effort to save much of the 432 HANDBOOK ON ENGINEERING. heat which had formerly been allowed to go to waste. The main thing in furnace construction is to get perfect combustion. With- out this there must be of necessity a great loss constantly going on. There are some losses which it is difficult to prevent, for example the loss by the admission of too much air in the ash pit ; the loss by incomplete combustion ; the loss occasioned by the heated gases escaping up the chimney ; the loss by radia- tion ; but, chief among these, is that of incomplete combustion. To burn a pound of coal requires about twenty-four pounds of air, or, say 300 cubic feet. Most boiler settings permit from 200 to 300 feet to pass through the fire. It is needless to point out the great source of loss arising from this one cause alone. This may be prevented in a measure by having a suitable damper in the chimney, and regulating the flow of escaping gases by it, instead of the ash pit doors. If the furnace is so constructed that the fuel is imperfectly burned, so that carbonic oxide instead of car- bonic acid gas is formed, the loss is very great. This results often from too little air supply and too low temperature in the furnace. The furnace doors should be provided with an opening leading into the space between the door proper and the liner ; this opening ought to have a sliding or revolving register by which the admission of air may be controlled. By this means, the quantity of air admitted above the fire may be adjusted to its needs by a little attention on the part of the fireman. The liner to the furnace door should have a number of small holes in it, rather than a solid plate, with a space around the edges. Great care should be exercised in the construction of furnace walls, that the materials and workmanship be good throughout. The entire structure should be brick. The outer walls may be of good hard red brick, but the interior walls, around the furnace and bridge wall, should be of fire brick. The best quality of fire brick for withstanding an intense heat are very, very strong and tenacious ; the structure is open and they are free from black HANDBOOK ON ENGINEERING. 433 srx)ts, due to sulphuret of iron in the clay ; if well burned they will not be very light colored on the outside, and will have a clear ring when struck. Fire brick should be dipped in a thin mortar made of tire clay, rather than in a lime and sand mortar, such as is used in ordinary red brickwork. Inlaying up these portions of a boiler furnace requiring fire brick, provision should be made in the original wall for leplaciug the* fire brick and without disturbing the outer brickwork. CARE AND MANAGEMENT OF A BOILER. It is not enough that a boiler be of approved design, made of the best materials, and put together in the best manner ; that it have the best furnace and the most approved feed and safety apparatus. These are all desirable, and are to be commended, but cleanliness and careful management are quite essential to get- ting high results, and are also conducive to long use in service. Pumps* Special attention should be given at all times to the feed and safety apparatus ; the pumps should be in good working order ; it is preferable that they be independent steam pumps rather than pumps driven by the engine, or by a belt ; they should be kept well packed and the valves in good condition . Firing* Kindle a fire and raise steam slowly ; never force a lire so long as the water in the boiler is below the boiling point. The fire should be of an even height, and of such a thickness as will be found best for the particular fuel to be burned, but should be no thicker than actually necessary. In regard to the size of coal used, that will depend upon circumstances. If anthracite coal is used, it should not, for stationary boilers, be larger than ordinary stove coal. For bituminous coal, which is always shipped in lumps as large as can be conveniently handled, the size will vary somewhat in breaking, but it may in general be used in larger lumps than anthracite. If the coal is likely to cake in burn- 23 434 HANDBOOK ON ENGINEERING. ing, the fire should be broken up quite frequently with a slice biir, or it will fuse into a large mass in the center of the furnace a:id lower the rate of combustion. If the coal is likely to form a con- siderable quantity of clinker, or enough to become troublesome, it may be advantageous to increase the grate area and thus lower the rate of combustion per square foot of grate, and have M Hie of less intensity. The lire should be kept free from ashes, and the ash pit should be kept clean. Whenever the fire door of a steam boiler furnace is opened, the damper should be closed to prevent the sudden reduction of temperature underneath, which is likely to injure the boiler by contraction, and thus render it likely to spring a leak around the riveted joints. Some firemen are very careless in this respect, and there is little doubt that many a dis- agreeable job of repairing a leaky seam might be prevented by this simple precaution. Gauge cocks should be used constantly to keep them free from any accumulation of sediment. It is a very common practice to rely wholly on the indications of the glass water gauge for the water level in the boiler. This is all wrong and should be dis- continued, if once begun. The glass water gauge serves a very useful purpose, but it should not be wholly relied on in practice. In using the ordinary gauge cocks, the ear more than the eye, detects the water level, and thus acts as a check on the indications given by the glass gauge. Water gauges should be tested several times during the day to see that they are clear, and to keep them free from any sediment likely to form around the lower opening to the water in the boiler. If this is not attended to, the water gauge is likely to indicate a wrong water level and a serious accident may be the result. Steam or pressure gauges are likely to become set after long use and should be tested at least once, or better still, twice a year by a standard gauge known to be correct. They should also be HANDBOOK ON ENGINEERING. 435 tested every few days if the boilers are constantly under steam by turning off the steam and allowing the pointer to run back to zero. If there are two or more boilers set together in one battery, and each boiler has its own steam gauge, and which will, starting from the zero point, indicate the same pressure on all the gauges, they may be assumed to be correct. Blow-off cocks or valves should be examined frequently and should never be allowed to leak. In general a cock is to be pre- ferred to a valve, but both is safer than one ; if the latter is selected it should be some one of the various ;i straight-way valves," of which there are now several in the market. If the cock is a large one, and especially if it has either a cast iron shell or plug, it should be taken apart after each cleaning out of the boilers, examined, greased with tallow and returned. Blowing 1 out* This should be done at least once a day, except in the very rare instances in which water is used that will not form a scale. The water should not be let out of a boiler or boilers until the furnace is quite cold, as the heat retained in the walls is likely to injure an empty boiler directly by overheating the plates, and indirectly by hardening the scale within the boiler. Bad effects are likely to follow when a boiler is emptied of its water before the side walls have become cool ; but greater injury is likely to result when cold water is pumped into an empty boiler heated in this manner. The unequal contraction of the boiler is likely to produce leaky seams in the shell and to loosen the tubes and stays. It is a better plan to allow the boiler to remain empty until it is quite cold, or sufficiently reduced in tem- perature to permit its being filled without injury. Many boilers of good material and workmanship have been ruined by the neglect of this simple precaution. Fusible plugs should be carefully examined every six months, as scale is likely to form over the portion projecting into the water space. It is only a question of time when this scale 436 HANDBOOK ON ENGINEERING. would form over the end of the plug, and thick enough to with- stand the pressure of steam and thus fail in the accomplishment of the very object for which it was introduced. This applies espe- cially to the fusible plugs inserted in the crown sheets of portable engine boilers. Cleaning tubes* This should be done every day if bitumin- ous coal is used. A portable steam jet will be found an extremely useful contrivance which will keep them reasonably clean by blow- ing out the loose soot and ashes deposited in the tubes. Every two or three days, or at least once a week, a tube scraper or stiff brush should be used to take out all the ashes or soot adhering to the tubes and which cannot be blown out with the jet. Flues may be cleaned the same way but will not require to be done so frequently. Low water* If from any cause the water gets low in the boiler, bank the fire with ashes or with fresh coal as quickly as possible, shut the damper and ash pit doors and leave the fire doors wide open ; do not disturb the running of the engine but allow it to use all the steam the boiler is making ; do not under any circumstances attempt to force water in the boiler. After the steam is all used and the boiler cooled sufficiently to be safe, then the water may be admitted and brought up to the reg- ular working height ; the damper opened and the fires allowed to burn and stearn raised as usual ; provided, no injury has been done the boiler by overheating. Foaming and priming are always troublesome and often danger- ous. Some boilers prime almost constantly, because of their bad proportion, and will require the constant care of the person in charge, especially at such times as the engine may be using the steam up to the full capacity of the boiler. In a case of this kind, an increase in pressure will often check, but will not entirely prevent it ; nothing short of an increase of water surface, or a better circulation of water, or a larger steam room will afford a HANDBOOK ON ENGINEERING. 437 complete remedy. If the foaming or priming is due to a sudden liberation of steam, or on account of impure feed water it may be checked by closing the throttle valve to the engine and opening he lire door for a few minutes. The surface blow may be used with advantage at this time, by blowing off the impurities collected on the surface of the water. The feed pump may be used if necessary, but care should be exercised that too much cold water be not forced into the boiler, and thus lose time by having to wait for the accumulation of the regular steam pressure required for the engine. The dangers attending foaming or priming are r. the laying bare of heating surfaces in the boiler, and of breaking down the engine by working water into the cylinder. The com- monest damage to the engine being either the breaking of a cylin- der head, or the cross-head, or the breaking of the piston. Wbeu boilers are new and set to work for the first time priming is a very frequent occurrence ; in fact, it may be said that for the first few days there is always more or less of it. All that is needed during this time is a little care on the part of the attendant to see that the water is kept up to the require^ level in the boiler ; it is also recommended that the throttle valve to the engine be partially closed to prevent any very great variation of pressure in the boiler, and thus prevent water passing over with the steam in such quantities as to become dangerous. If a boiler continues to prime after it has had a week's work and then thoroughly cleaned, the causes are to be attributed to other than the grease and dirt in it, which are inseparable from the manufacture. As already said, priming may be caused by a sudden reduction of pressure ; that is, a boiler may be working smoothly and well with say 80 pounds pressure ; if an increase of load be suddenly applied to an engine so as to reduce the pressure to 70 or 60 pounds, this sudden reduction of pressure will almost always cause priming ; the less the steam space in the boiler, the greater the tendency to prime, and the greater the 438 HANDBOOK ON ENGINEERING. difficulty in checking it. The only permanent cure for this is more boiler power; as a temporary expedient, the engine should be throttled sufficiently to make the drain upon the boiler con- stant instead of intermittent. If the duty required of an engine is irregular, the steam pressure should be carried higher ; in any case similar to the above, it is recommended that the pressure be increased to i)0 or 100 pounds and the throttling to begin with the increased drain upon the boiler. But this is at best a mere makeshift, and a larger boiler power becomes imperative both on the score of economy and safely. WATER FOR USE IN BOILERS. Water is never pure, except when made so in a laboratory or by distillation ; the impurities may be divided into four classes : 1. Mechanical impurities. 2. Gaseous impurities. 3. Dissolved mineral impurities. 4. Organic impurities. (a) Mechanical impurities may be both mineral and organic. The commonest suspended impurity in water is mud or sand ; these may be removed by filtration or by allowing the water to stand long enough to let theiri settle to the bottom of the tank or cistern and then carefully drawing the water from the top, and without disturbing the bottom. (b) Gaseous impurities in water vary somewhat according to the localities from which they are obtained. The commonest gases found in the water are an excess of oxygen, nitrogen and carbonic acid. These have no effect on water intended for steam boilers. (c) Dissolved mineral impurities in water are of the most varied description, and are almost always found in it. Among these are found salts of iron, sulphate and carbonates of lime; sulphate and carbonates of magnesia ; salt and alkalies, such as soda, potash, etc. ; acids, such as sulphuric, phosphoric, and others. All of these are more or less injurious to steam boilers. The most objectionable are the salts of lime and magnesia, which impart to water that property known as hardness. When such HANDBOOK ON ENGINEERING. 4? 9 water is used in a steam boiler a scale will gradually form, which will, in a short time, become very troublesome. (d) Organic impurities are present, to a certain extent, in most waters. They are sometimes present in the water in suffi- cient quantities to give it a very decided color and taste. The presence of organic matter in wa,ter is often dangerous to health, and maybe a means of spreading contagious diseases, but has little or no bad effect yi any water used for steam boilers. In general, water is regarded by engineers as being either soft, hard or salt. Ebullition* Is the motion produced in a liquid by its rapid conversion into vapor. When heat is applied to the bottom of a boiler, the particles of water in contact with the plates become heated and immediately expand, and becoming specifically lighter, pass upwards through the colder body of water above ; the heat of the furnace is in this way diffused throughout the Avhole body of water in the boiler by a translation of the particles of water from below upwards, and from top to bottom in regular succession. After a time this liquid mass becomes heated to a degree in which there is a violent agitation of the whole body of water, steam is given off and it is said to boil. The temperature at the boiling point of water, at ordinary atmospheric pressure, is 212 Fahr., and increases as the pressure of steam above it increases. Distilled water for boilers i not to be recommended without some reservation. Chemically pure water, and especially water which has I teen redistilled several times, has a corrosive action on iron which is often very troublesome. The effect on steel plates by the use of water several times redistilled, such, for example, as that supplied for heating buildings, is well known ; information is yet wanting which shall point with certainty to the exact change which the water undergoes and explain why its action on or affinity for steel is so greatly intensified. It has been suggested as a means of neutralizing this corrosive action of the water, to 440 HANDBOOK ON ENGINEERING. introduce with the feed other water, which shall have the prop- erty of forming a scale and continuing it long enough and at such intervals as will permit the formation of a thin scale in the interior of the boiler. However objectionable this may seem at first sight, it is at present the best practical solution of the difficulty. Scale is a bad conductor of heat and is opposed to economical evaporation. It is estimated that a thickness of half an inch of hard scale firmly attached to a boiler plate will require a temper- ature of about 700 Fahr. in the boiler plate in order to raise and maintain an ordinary steam pressure of 75 pounds. The mis- chievous effects of accumulated scale in the boiler, especially in the plates immediately over the fire, are : (1) preventing the water from coming in contact with the plates, and thus directly con- tributing to the overheating of the latter; and (2) by causing a change of structure in the plates and the consequent weakening brought about by this continual overheating, which would, in a short time, render an iron or a steel plate wholly unfit for use in a steam boiler. The two principal ingredients in boiler scale are lime and magnesia. The lime, when in combination with carbonic acid, forms carbonate of lime ; when in combination with sulphuric acid, it then becomes sulphate of lime. This is also true of magnesia. Carbonate of lime will form in the boiler as a loose powder which is held mechanically in suspenion ; while in this stage it may be blown out of the boiler without injury to it ; but it is seldom that a pure carbonate is formed in the boiler as there are other impurities in the water with which it combines to form a hard scale. This is especially true in such waters as also contain sulphate of lime in solution. This fine powder (carbonate of lime), will form a hard scale should any adhere to tHe sides or bottom of a boiler ; in any case where the boiler is blown out dry while the furnace walls are still hot; and this, in itself, forms an excellent reason why boilers should stand until the furnace walls HANDBOOK ON ENGINEERING. 441 are cold before blowing out. When emptied, nearly or all of this slushy deposit may be washed out of the boiler by means of a hose. Sulphate of lime is not so easily got rid of, as it is]heavier than carbonate of lime and adheres to the plates while the boiler is at work. It is the most troublesome scale steam engineers have to deal with ; it is very difficult to remove and by successive layers becomes dangerous, on account of the thickness to which it eventually accumulates. The carbonates of lime and magnesia may be largely arrested by passing the feed water through a suitable heater and lime extractor. It must be apparent to every one that any device which will accomplish this is a very desirable attachment to a steam boiler. As it is not possible to eliminate all the foreign matter in the water from it, recourse is often had to the use of solvents and chemical agencies for the prevention of scale. Some of these are very simple and within easy reach ; others are sur- rounded by an atmosphere of uncertainty and the real nature of the compound is hidden under a meaningless trade-mark. For carbonate of lime, potatoes have been found to be very service- able in preventing the formation of scale ; its action appears to be that of surrounding the particles of lime with a coating of starch and gelatine, and thus preventing the cohesion of these particles to form a mass. Various astringents have been used for this purpose, such as extracts of oak and hemlock bark, nutgalls, catechu, etc., with varying success. Carbonate of soda has been used and with very great success in some localities, not only in preventing, but in actually removing scale already formed. It acts on carbonate of lime not only, but on the sulphate afso. It is clean, free from grit, and is quite unobjectionable in the boiler ; one or more pounds per day, de- pending on the size of the boiler, may be admitted through the pump with the feed water ; or admitted in the morning before 442 HANDBOOK ON ENCUXKKKING. firing up, by simply mixing with water and pouring into the boiler- through the safety valve or other opening. Tannate of soda has been similarly employed and is an excel- lent scale preventive. It will also act as a solvent for scale already formed in the boiler, acting on sulphate as well as carbon- ate of lime. Crude petroleum has been found very beneficial in removing the hard scale composed principally of sulphate of lime. Zinc in steam boilers. The employment of zinc in steam boilers, like that of soda, has been adopted for two distinct objects: (1) to prevent corrosion, and (2) to prevent and remove incrustation. To attain the first object, it has been used chiefly in marine boilers, and for the second, chiefly in boilers fed with fresh water. In order that the application of zinc in marine boilers may be effective, it is necessary that the metallic contact should be insured. If galvanic action alone is relied upon for the protection of the plates and tubes, it will doubtless be diminished materially by the coating of oxide that exists between all joints of plates, whether lapped or butted, and also between the rivets and the plates. Assuming the preservative action of zinc to be proved when properly applied, we have now two systems for preventing the internal decay of marine boilers, viz. : allowing the plates and tubes to become coated with scale, and employing zinc. It remains to decide which of these two systems is the best with respect to economy and practicability. We come now to consider the use of zinc for preventing and removing incrustation. At one time it was considered that the action of zinc in pre- venting incrustation was physical or mechanical. The particles of zinc, as it wasted away, were supposed to become mixed amongst the solid matter precipitated from the water, in such a manner as to prevent it adhering together, so as to form a hard scale ; or the particles of zinc were supposed to become deposited HANDBOOK ON ENGINEERING. . 443 upon the plates, and so prevent the scale from adhering to them* Then it was suggested that the zinc acted chemically, and now, it is the generally received opinion that its action is galvanic in preventing incrustation as well as in preventing corrosion. When the water contains an excess of sulphates or chlorides over the carbonates, the acid of the former will form soluble salts with the oxide of zinc, the surface of the zinc will be kept clean, and the galvanic current, to which the efficiency of the zinc is due, will be maintained. On the other hand, should there be a preponderat- ing amount of carbonates, the zinc will be covered first with oxide, then with carbonates and its useful action arrested and stopped. It is quite as important that the zinc should be in metallic con- tact with the plates when used to prevent incrustation, as when employed to prevent corrosion. The application of zinc for the former purpose should never be attempted without first having the water analyzed in order to ascertain whether it is likely to be effective. The use of zinc in externally fired boilers should be attempted with great caution, as when efficacious in preventing the formation of a hard scale, it is liable to produce a heavy sludge that may settle over the furnace plates and lead to over- heating. On the whole we cannot but regard the evidence as to the effect of zinc upon incrustation as being very conflicting. Leaks should be stopped as soon as possible after their dis- covery ; the kind of leak will indicate the treatment necessary. If it occurs around the ends of the tubes, it may be stopped by expanding the tubes anew ; if in a riveted joint, it should be care- fully examined, especially along the line of the rivets and care should be exercised in determining whether there is a crack extending from rivet to rivet along the line of the holes ; should this prove to be the case, the boiler is then in an extremely dangerous condition and under no circumstances should it be again fired up until suitable repairs have been made which will in sure its safety. 444 HANDBOOK ON ENGINEERING. Blisters occur in plates which are made up of several thick- nesses of iron and which from some cause were not thoroughly welded before the final rolling into plates. When such a plate comes in contact with the heat of the furnace the thinnest portion of the defective plate " buckles " and forms what is called a blister. As soon as discovered, there should be thorough exami- nation of the plate and if repairs are needed there should be as little delay as possible in making them. If the blister be very thin and altogether on the surface it may be chipped and dressed around the edges ; if the thickness is equal or exceeds Jg" the blister should be cut off and patched, or a new plate put in. Patching boilers* When a boiler requires patching it is bet- ter to cut out the defective sheets and rivet in a new one ; or if this cannot be done, a new piece large enough to cover the defect in the old sheet may be riveted over the hole from which the defective portion has been cut. If this occurs in any portion of the boilei subject to the action of tire, the lap should be the s-ame as the edges of the boiler seams, and should be carefully calked around the edges after the riveting. Whenever the blisters occur in a plate, patching is a comparatively simple thing as against the repairs of a plate worn by corrosion. In the latter case, the defective portions of the plate should be entirely removed and the openings should show sound metal all around and of full thick- ness. If this cannot be obtained within a reasonable sized open- ing then the whole plate should be removed. It often occurs that a minor defect is found in a plate and at a time when it is not convenient to stop for repairs; in such an event a " soft patch " is often applied. This consists of a piece of wrought iron carefully fitted to that portion of the boiler plate needing repairs ; holes are fitted in both plates and patch, and " patch bolts " provided for them. A thick putty consisting of white and red lead with iron borings or filings in them placed evenly over the inner surface of the patch, which is then tightly HANDBOOK ON ENGINEERING. 445 bolted to the boiler plate. This is best but a temporary make- shift and ought never to be regarded as a permanent repair. A mistake is often made of making a patch of thicker metal than that of the shell of the boiler needing it. A moment's reflection ought to show the absurdity of putting on a T 5 F or | patch on an old i inch boiler shell; yet it is not so rare as one would imagine. A piece of new iron T 3 ^" thick will, in most cases, be found to be stronger than that portion of a J" old plate needing repairs. Inspection* A careful external and internal examination of a boiler is to be commended for many reasons. This should be as frequent as possible and thoroughly done ; it should include the boiler not only, but all the attachments which affect its working or pressure. Particular attention should be paid to the examina- tion of all braces and stays, safety valve, pressure gauges, water gauges, feed and blow-off apparatus, etc. ; these latter refer more particularly to constructive details necessary to proper manage- ment and safety. The inspection would obviously be incomplete, did it not include an examination into the causes of " wear and tear," and determine the extent to which it had progressed. Among the several causes which directly tend to rendering a boiler unsafe, may be mentioned the dangerous results occasioned by the overheating of plates, thus changing the structure of the iron from fine granular, or fibrous, to coarse crystalline. This may easily be detected by examination, and will in general be found to occur in such cases where the boilers are too small for the work, are fired too hard, or have a considerable accumulation of scale or sediment in contact with the plates. Blistered plates are almost instantly detected at sight, so also is corrosion, from whatever cause it may have proceeded. Corrosion of boiler plates* Iron will corrode rapidly when subjected to the intermittent action of moisture and dryness. Land boilers are less subject to corrosion than marine boilers. The corrosion of a boiler may be either external or internal. Ex- 446 HANDBOOK ON ENGINEERING. ternal corrosion may, in general, be easily prevented by carefully caulking all leaks in the boiler ; by preventing the dropping cf water on the plates, such, for example, as from a leaky joint in the steam pipe or from the safety valve. A leaky roof, by allow- ing a continual or occasional dropping of water on the top of a boiler, especially if the boiler is not in constant use, would pro- mote external corrosion. Sometimes external corrosion is caused by the use of coal having sulphur in it, and acts in this way : The sulphur passes off from the fire as sulphurous oxide, which often attaches to the sides of a boiler ; so long as this is dry no especial mischief is done ; but if it comes in contact with a wet plate the sulphurous oxide is converted into sulphuric acid over so much of the surface as the moisture extends; this acid attacks, and will, in time, entirely destroy the boiler plate. Internal corrosion is not so easily accounted for and is very difficult to correct, especially when it occurs above the water line. It is generally believed to be due to the action of acids in the feed water. Marine boilers are especially subject to internal corrosion when used in connection with surface condensers. A few years ago it was generally supposed to be due to galvanic action but that idea is now almost entirely given up. From the fact that boilers using distilled water fed into them from surface condensers are more liable to internal corrosion than other boilers, has led to the theory that it is the pure water that does the mischief, and that a water containing in slight degree a scale-forming salt, is to be preferred to water which is absolutely pure. Whatever maybe the truth or falsity of this theory, it is a well established fact that distilled water has a most pernicious action on various metals, especially on steel, lead and iron. This action is attributed to its peculiar property, as compared with ordinary water, of dissolving free carbonic acid. One of the worst features in connection with internal corrosion is that its progress cannot be easily traced on account of the boiler being closed while at work. As it does not HANDBOOK ON ENGINEERING. 447 usually extend over any very great extent of surface, the ordinary hydraulic test fails to reveal the locality of corroded spots ; the hammer test, on the contrary, rarely fails to locate them, if the plates are much thinned by its action. Testing boilers* It is the general practice to apply the hydraulic test to all new steam boilers at the place of manufacture, and before shipment. The pressure employed in the test is from one and ti half to twice the intended working steam pressure. This test is only valuable in bringing to notice defects which would escape ordinary inspection. It is not to be assumed that it in any way assures good workmanship, or material, or* good design, or proper proportions ; it simply shows that the boiler being tested is able to withstand this - pressure without leak- ing at the joints, or distorting the shell to an injurious degree. Bad workmanship may often be detected at a glance by an expe- rienced person. The material must N be judged by the tensile strength and ductility of the sample tested. The design and pro- portions are to be judged on constructive grounds, and have little or nothing in common with the hydraulic test. The great majority of buyers of steam boilers have but little knowledge on the sub- ject of tests, and too often conclude that if they have a certified copy of a record showing that a particular boiler withstood a test of say, 150 Ibs., it is a good and safe boiler at 75 to 100 Ibs. steam pressure. If the boiler is a new one and by a reputable maker, that may be true ; if it has been used and put upon the market as a second-hand boiler, it may be anything but safe at half the pressure named. By the hydraulic test, the braces in a boiler may be broken, joints strained so as to make them leak, bolts or pins may be sheared off, or so distorted as to be of little or no service in resisting steam when pressure is on. Hammer test. The practice of inspecting boilers by sounding with a hammer is, in many respects, to be commended. It requires some practical experience in order to detect blisters and 448 HANDBOOK ON ENGINEERING. the wasting of plates, by sound alone. The hammer test is especially applicable to the thorough inspection of old boilers. It frequently happens in making a test that a blow of the hand hammer will either distort it, or be driven entirely through the plate ; and it is just here that the superiority of this method of testing over, or in connection with the hydraulic test, becomes fully apparent. The location of stays, joints and boiler fittings all modify and are apt to mislead the inspector if he depends upon sound alone. There is a certain spring of the hammer and a clear ring indicative of sound plates, which are wanting in plates much corroded or blistered. The presence of scale on the inside of the boiler has a modifying action on the sound of the plate. When a supposed defect is discovered, a hole should be drilled through the sheet by which its thickness may be determined, as well as its condition. In order to thoroughly inspect a boiler, the inspector should crawl into the boiler (when it is possible to do so) and he should look for pitting and grooving of plates, test all braces, and examine all inlets and outlets. HANDBOOK ON ENGINEERING. 449 CHAPTER XVII. USE AND ABUSE OF THE STEAM=BOILER. Steam-boilers* A steam-boiler may be defined as a close vessel, in which steam is generated. It may assume an endless variety of forms, and can be constructed of various materials. Since the introduction of steam as a motive power a great variety of boilers has been designed, tried and abandoned ; while many others, having little or no merit as steam generators, they have their advocates and are still continued in use.- Under such cir- cumstances, it is not surprising that quite a variety of opinions are held on the subject. This difference of opinion relates not only to the form of boiler best adapted to supply the greatest quantity of steam with the least expenditure of fuel, but also to the dimensions or capacity suitable for an engine of a given num- ber of horse-power ; and while great improvements have been made in the manufacture of boiler materials within the past fifteen years, yet the number of inferior steam-boilers seem to increase rather than diminish. It would be difficult to assign any reasonable cause for this, except that, of late years, nearly the whole attention of theoretical and mechanical engineers has been directed to the improvement and perfection of the steam-engine, and practical engineers, following the example set by the leaders, devote their energies to the same object. This is to be regretted, as the construction and application of the steam-boiler, like the steam-engine, is deserving of the most thorough and scien- tific study, as on the basis of its employment rest some of the most important interests of civilization. Until quite recently, the idea was very generally entertained that the durely mechanical skill required to enable a person to join 29 450 HANDBOOK ON ENGINEERING. together pieces of metal, and thereby form a steam-tight and water-tight vessel of given dimensions, to be used for the gen- eration of steam to work an engine, was all that was needed ; experience has shown, however, that this is but a small portion ol the knowledge that should be possessed by persons who tarn theii attention to the design and construction of steam-boilers, as the knowledge wanted for this end is of a scientific as well as of a mechanical nature. As the boiler is the source of power and the place where the power to be applied is first generated, and alsc the source from which the most dangerous consequences may arise from neglect or ignorance, it should attract the special attention of the designing and mechanical engineer, as it is well known that from the hour it is set to work, it is acted upon by destroy- ing forces, more or less uncontrollable in their work of destruc- tion. These forces may be distinguished as chemical and mechanical. In most cases they operate independently, though they are frequently found acting conjointly in bringing about the destruction of the boiler, which will be more or less rapid accord- ing to circumstances of design, construction, quality of material, management, etc. The causes which most affect the integrity of boilers and limit their usefulness are either inherent in the mate- rial, or due to a want of skill in their construction and manage- ment ; they may be enumerated as follows : First, inferior material ; second, slag, sand or cinders being rolled into the iron ; third, want of lamination in the sheets ; fourth, the overstretching of the fiber of the plate on one side and puckering on the other in the process of rolling, to form the circle for the shell of a boiler ; fifth, injuries done the plate in the pro- cess of punching ; sixth, damage induced by the use of the drift- pin ; seventh, carelessness in rolling the sheets to form the shell, as a result of which the seams, instead of fitting each other exactly, have in many instances to be drawn together by bolts, which aggravates the evils of expansion and contraction when the HANDBOOK ON ENGINEERING. 451 boiler is in use : eighth, injury done the plates by a want of skill in the use of the hummer in the process of hand-riveting; ninth, damage done in the process of calking. Other causes of deterioration are unequal expansion and con- traction, resulting from a want of skill in setting ; grooving in the vicinity of the seams ; internal and external corrosion ; blowing out the boiler when under a high- pressure and filling it again with cold water when hot ; allowing the lire to burn too rapidly after starting, when the boiler is cold ; ignorance of the use of the pick in the process of scaling and cleaning ; incapacity of the safety- valve ; excessive firing ; urging or taxing the boiler beyond its safe and easy working capacity ; allowing the water to become low, and thus causing undue expansion ; deposits of scale accum- ulating on the "parts exposed to the direct action of the fire, thereby burning or crystallizing the sheets or shell ; wasting of the material by leakage and corrosion ; bad design and construction of the different parts ; inferior workmanship and ignorance in the care and management. All these tend with unerring certainty to limit the age and safety of steam boilers. On account of want of skill on the part of the designer and avarice on the part of the manufacturer, or perhaps both reasons, boilers are sometimes so constructed as to bring a riveted seam directly over the fire, the result of which is that in consequence of one lap covering the other, the water is prevented from getting to the one nearest the fire, for which reason the lap nearest the fire becomes hotter and expands to a much greater extent than any other part of the plate ; and its constant unequal expansion and contraction, as the boiler becomes alternately hot and cold, inevitably results in a crack. Such blunders are aggravated by the scale and sediment being retained on the inside, between the heads of the rivets, which should be properly removed in cleaning. The tendency of manufacturers to work boilers beyond their capacity, especially when business is driving, is too great in this 452 HANDBOOK ON ENGINEERING. country ; and no doubt many boiler explosions may be attributed to this cause. Boilers are bought, adapted to the wants of the manufactory at the time, but, as business increases, machinery is added to supply the demand for goods, until the engine is overtasked, the boiler strained and rendered positively danger- ous. Then again, it not unfrequently occurs that engines in manufactories are taken out and replaced by those of increased power, while the boilers used with the old engine are retained in place, with more or less cleaning and patching, as the case may require. Now, it is evident to any practical mind that boilers constructed for a twenty-horse power engine are ill adapted to an engine of forty-horse power, more especially if those boilers have been used for a number of years. In order to supply sufficient steam for the new engine, with a cylinder of increased capacity, the boiler must be worked beyond its safe working pressure, consequently excessive heating and pressure greatly weaken it and endanger the lives of those employed in the vicinity. The danger and impracticability of using boilers with too limited steam-room may be explained thus : Suppose the entire steam-room in a boiler to be six cubic feet, and the contents of the cylinder which it supplies to be two cubic feet ; then at each stroke of the piston one-third of all the steam in the boilers is discharged, and consequently, one-third of the pressure on the surface of the water before that stroke is relieved ; hence, it will be seen that excessive fires must be kept up in order to generate steam of sufficiently high temperature and pressure to supply the demand. The result is that the boilers are strained and burned. Such economy in boiler power is exceedingly expensive in fuel, to say nothing of the danger. Excessive firing distorts the fire- sheets, causing leakage, undue and unequal expansion and con- traction, fractures, and the consequent evils arising from external corrosion. Excessive pressure arises generally from a desire on the part of the steam-user to make a boiler do double the work for HANDBOOK ON ENGINEERING. 453 which it was originally intended. A boiler that is constructed to work safely at from fifty to sixty pounds was never intended to run at eighty and ninety pounds ; more especially if it had been in use for several years. Boilers deteriorated by age should have their pressure decreased, rather than increased. One of the first things that should be done in manufacturing establishments would be to provide sufficient boiler power and, in order to do this, the work to be done ought to be accurately cal- culated and the engine and boilers adapted to the results of this calculation. Steam users themselves are frequently to blame for the annoyances and dangers arising from unsafe boilers and those of insufficient capacity. From motives of false economy the v are too easily swayed in favor of the cheaper article, simply because it is cheap, when they should consider they are purchasing an article which, of almost all others, should be made in the most thorough manner and of the best material. In view of the fearful explosions that occur from time to time, every steam user should secure for his use the best and safest. The object of a few dollars as between the work of a good, responsible maker and that of an irresponsible one, should not for one moment be entertained. It is very bad policy for steam-users to advertise for estimates for steam-boilers, or to inform all the boiler-makers in the town or city that a boiler or boilers to supply steam for an engine of a certain size is needed, because in this way steam-users frequently find themselves in the hands of needy persons, who, in their anxiety to get an order, will sometimes ask less for a boiler than they can actually make it for ; consequently, they have to cheat in the material, in the workmanship, in the heating-surface and in the fittings. As a result, the boiler is not only a continual source of annoyance, but, in many instances, an actual source of danger. The most prudent course, and in fact the only one that may be expected to give satisfaction, is to contract with some responsible 454 HANDBOOK ON ENGINEERING. manufacturer that has an established reputation for honesty, capability and fair dealing, and who will not allow himself to be brought in competition with irresponsible parties for the purpose of selling a boiler. There are thousands of boilers designed, con- structed and set up in such a manner as to render it utterly impossible to examine, clean or repair them. Generally, in such cases, in consequence of imperfect circulation, the water is expelled from the surface of the iron at the points where the extreme heat from the furnace impinges, and, as a result, the plates become overheated and bulge outward, which aggravates the evil, as the hollow formed by the bulge becomes a receptacle for scale and sediment. By continued overheating, the parts become crystallized and either crack or blister; this, if not attended to and remedied, will eventually end in the destruction of the boiler. Many boilers, to all appearance well made and of good material, give considerable trouble by leakage and fracture, owing to the severe strains of unequal expansion and contraction induced by the rigid construction, the result of a want of skill in the original design. DESIGN OF STEAM=BOILERS. It has become a general assertion on the part of writers on the steam-boiler that the most important object to be attained in its design and arrangement is thorough combustion of the fuel. This is only partially true as there are other conditions equally important, among which are strength, durability, safety, economy and adaptability to the particular circumstances under which it is to be used. However complete the combustion may be, unless its products can be easily and rapidly transferred to the water, and unless the means of escape of the steam from the surfaces on which it is generated is easy and direct, the boiler will fail to produce satisfactory results, either in point of durability or economy of fuel. HANDBOOK ON KN(! IN KER1NG. 455 Strength means the power to sustain the internal pressure to which the boiler may be subjected in ordinary use, and under careful and intelligent management. To secure durability, the material must be capable of resisting the chemical action of the minerals contained in the water, and the boiler ought to be designed so as to procure the least strain under the highest state of expansion to which it may be subjected be so constructed that all the parts will be subjected to an equal expansion, con- traction, push, pull and strain, and be intelligently and thoroughly cared for after being put in use. These objects, however, can only be obtained by the aid of a knowledge of the principles of mechanics, the strength and resistance of materials, the laws of expansion and contraction, the action of heat on bodies, etc. The economy of a steam boiler is influenced by the following con- ditions: cost and quantity of the material, design, character of the workmanship employed in its construction, space occupied, capa- bility of the material to resist the chemical action of the ingredi- ents contained in the water, the facilities it affords for the transmission of the heat from the furnace to the water, etc. The safety of any structure depends on the designer's knowledge of the principles of mechanics, the resistance of materials and the action of bodies as influenced by the elements to which they are exposed ; and in the case of steam boilers, the safety depends on the judgment of the designer, the quality of the material, the character of the workmanship and the skill employed in the man- agement. Safety is said to be incompatible with economy, but this is undoubtedly a mistake, as an intelligent economy includes permanence and seeks durability. Adaptability to the peculiar purposes for which they are to be used is one of the first objects to be sought for in the design and construction of any class of machines, vessels or instruments, and it is undoubtedly this that gave rise to the great variety of designs, forms and modifications of steam boilers in use at the present day, which are, with very 456 HANDBOOK ON few exceptions, the result of thought, .study, investigation and experiment. FORMS OF STEAfl BOILERS. According to the well-known law of hydrostatics, the pressure of steam in a close cylindrical vessel is exerted equally in all directions. In acting against the circumference of a cylinder, the pressure must, therefore, be regarded as radiating from the axis, and exerting a uniform tensional strain throughout the inclosing material. Familiarity with steam machinery, more especially with boil- ers, is apt to beget a confidence in the ignorant which is not founded on a knowledge of the dangers by which they uro contin- ually surrounded ; while contact with steam, and a thoroughly elementary knowledge of its constituents, theory and action, only incline the intelligent engineer and fireman to be more cautious and energetic in the discharge of their duties. Many regard steam as an incomprehensible mystery ; and although they may employ it as a power to accomplish work, know little of its character or capabilities. Steam may be managed by common sense rules as well as any other power ; but if the laws which regulate its use are violated, it reports itself, and often in louder tones than is pleasant. If steam-boilers in general were better cared for than they are, their working age might be greatly in- creased. Deposits of incrustation, small leaks and slight cor- rosion, are too often neglected as matters of little consequence, but they are the forerunners of expensive repairs, delay and disaster. SETTING STEAM-BOILERS. While engineers differ very much in opinion respecting the best manner of setting boilers, they all readily allow that the results obtained, as regards economy of fuel and the generation of steam, HANDBOOK ON ENGINEERING. 457 depend in a great measure on the arrangement of the setting. Particularly is this the case with horizontal tubular boilers, and there have been numerous plans introduced to obtain a maximum of steam with a minimum of fuel. Some of the most practical designs and best laid plans are frequently rendered useless for want of knowledge on the part of those whose duty it is to exe- cute or carry them out. This has perhaps been more frequently the case as regards the setting of steam boilers than any other class of machines, as it is customary for owners of steam boilers to depend too much on the knowledge of masons and bricklayers ; consequent!}', a great many blunders have been made which necessitated changes in the size of gratebars, alteration of brick- work, alteration of flues, chimney, etc., with a list of other annoy- ances, such as insufficiency of steam, poor draught, or something else. In setting or putting in boilers, all the surface possible should be exposed to the action of the heat of the fire, not only that the heat may be thus completely absorbed, but that a more equal ex- pansion and contraction of the structure may be obtained. Long boilers are often hung by means of loops riveted to the top of them and connected to crossbeams and arches resting on masonry above them, by means of hangers. This is a very mischievous arrangement, unless turn-buckles, or some other contrivance, are used to maintain a regular strain on all the hangers, as long boil- ers exposed to excessive heat are apt to lengthen on the lower side and relieve the end hangers of any weight; consequently, the whole strain is transmitted to the central hanger, which has a tendency to draw the boiler out of shape in many instances inducing excessive leakage, rupture, and, eventually, explosion. DEFECTS IN THE CONSTRUCTION OF STEAM BOILERS. The following cuts illustrate some of the mechanical defects that impair the strength and limit the safety and durability of 458 HANDBOOK ON ENGINEERING. steam boilers. All punched holes are conical, and unless the sheets are reversed after being punched, so as to bring the small sides of the holes together, it will be impossible to till them with the rivets. Fig. 1 shows the position of the rivet in the hole without the sheets being reversed ; and it will be observed that, as very little of the rivet bears against the material, the ex- pansion and contraction of the boiler have a tendency to work it loose. It is apparent that such a seam would not possess over one-third the strength that it would if the holes in the sheets Fig. 1. Fisr. o. Fig. 5, Fig. 6. were reversed and thoroughly filled with the rivet, as shown in Fig. 2. Fig. o represents what is known in boiler-making as a blind-hole, which means that the holes do not come opposite each other when the seams are placed together for the purpose of riveting. Fig. 4 shows the position of the rivet in the blind-hole after being driven. It will be observed that the heads of the rivet, in consequence of its oblique position in the hole, bear only on one side, and that even the bearing is very limited, and through the expansion and contraction of the boiler, is liable to HANDBOOK ON ENGINEERING. 459 work loose and become leaky. Such :i seam would be actually weaker than that represented in Fig. 1. Fig. 5 shows the metal distressed and puckered on each side of the blind-hole in the sheets, which is the result of efforts on the part of the boiler- maker, by the use of the drift-pin, to make the holes correspond for the purpose of inserting the. rivet. Fig. 6 shows the metal broken through by the same means. Now, it will be observed that nearly all the above defects are the result of ignorance and carelessness, showing a want of skill in laying out the work, as well as a want of proper appliances for that purpose. The evils arising from such defects are greatly aggravated by the fact that they are all concealed, frequently defying the closest scrutiny, and are only revealed by those forces which unceasingly act on boilers when in use. Such pernicious mechanical blunders ought to be condemned, as they are always the forerunners of destruction und death. There can be no reason why boilers should not be constructed with the same degree of accuracy, judgment and skill as is considered so essential for all other classes of machinery. IMPROVEMENTS IN STEAM=BOILERS. Until quite recently the steam boiler has undergone very little improvement. This arose, perhaps, from the fact that men of intelligence and mechanical genius directed their thoughts and labors to something more inviting and less laborious than the construction of steam boilers. Consequently, that branch of mechanics was left almost entirely to a class of men that had not the genius to rise in their profession or improve much in anything they attempted. As a result ignorance, stupidity and a kind of brute force were the predominant requirements in the construc- tion of the steam boiler ; but within the past few years this state of things has been changed, as some very important improvements have been made, not only in the manufacture of the material of which boilers are made, but also in the mode of constructing 460 HANDBOOK ON ENGINEERING. them. The imposing, powerful and accurate boiler machinery in use at the present time is an evidence that the attention of emi- nent mechanics and manufacturers is directed to the steam boiler, and that in the future its improvement will keep pace with that of the steam engine. Boiler-plate is now rolled of sufficient dimensions to form the rings for boilers of any diameter with only one seam, obviating the necessity of bringing riveted seams in contact witk the fire, as was usually the case in former times. In the manner of laying off the holes for the rivets, accurate steel gauges have taken the place of the old-fashioned wooden templet, thereby removing the evils induced by blind-holes, and obviating the necessity of using the drift-pin. So, also, in the method of bending the sheets to form the requisite circle with a better class of machinery, the work is now mo re accurately performed. The old process of chip- ping is, in nearly all the large boiler-shops, superseded by planing the bevels on the edge of "the sheet, preparatory to calking. Recent improvements in " calking " have resulted in perfect immunity from the injuries formerly inflicted on boilers in that process. In most establishments of any repute in this country, riveting is done by machinery, which is (as is well known to all intelligent mechanics) very much superior to hand-riveting. It is only small shops that enter into rivalry to secure orders and build cheap boilers, using poor material and an inferior quality of mechanical skill, that use the same old crude appliances in many cases the merest makeshifts that were in use a quarter of a century ago, and constructed without regard to any of the rules of design that are considered so essential in appliances for the construction of all other classes of machinery. Every engineer should inform himself on the subject of the safe working pressure of boilers, and when he finds the limit of safety has been reached, he should promptly inform his employer and use his influence to have the boiler worked within the bounds of safety. HANDBOOK ON ENGINEERING. 461 To find the heating surface of a water tube boiler : Rule. Add the combined outside area of the tubes in square feet to one-half the area of the shell of the steam drum in square feet and the sum will give the total heating surface.. Example J* What is the heating surface of a water tube boiler having fifty tubes, each three inches outside diameter and fifteen feet long, and the steam drum thirty-two inches in diameter and fifteen feet long ? Operation. 3 X 3.1416 equals 9.4248 inches, the circumfer- ence of one tube. 15 X 12 equals 180 inches the length of one 9. 4248 X 180 tube. - TTT - equals 11.781 square feet in one tube, and 11.781 X 50 equals 589.05 square feet of heating surface in fifty 32 X 3. 1410 tubes. Then, - ^ - equals 8.3770 linear feet the circum- ference of the steam drum and 8.3770. X 15 equals 125.004 square 125.064 feet of heating surface in steam drum, and ~ equals 62.832 square feet, half the heating surf ace of steam drum. Then, 589.05 plus 02.832 equals 651.882 square feet, the total heating surface. Answer. STRENGTH OF RIVETED SEAflS. The strength of a riveted seam depends very much upon the arrangement and proportion of the rivets ; but with the best design and construction, the seams are always weaker than the solid plate, as it is always necessary to cut away a part of the plate for the rivet holes, which weakens the holes in three ways : 1st, by lessening the amount of material to resist the strains; 2d, by weakening that left between the holes; 3d, by disturbing the uniformity of the distribution of the strains. 462 HANDBOOK ON FA ? , For steel plates and steel rivets : 23 X (V X n . P = 28 XT- + d ' Example, for single-riveted joint : Given, thickness of plate \ inch, diameter of rivet = if inch. In this case, ?i=l. Then Example, for double-riveted joint : Given, thickness of plate i inch, diameter of rivet = J inch, n = 2. Then 2 = ^5 inches. FOR DISTANCE FROM CENTER OF RIVET TO EDGE OF LAP. 3 X <* ~2~ Example : Given, diameter of rivet (d) = | inch ; required, the distance from center of rivet to edge of plate. E= 3X ^= 1.312 inches, ^ for single or double riveted lap joint. FOR DISTANCE BETWEEN ROWS OF RIVETS. The distance between lines of centers of rows of rivets for double, chain-riveted joints (F) should not be less than twice the diameter of rivet, but it is more desirable that V should not be less than t SO 466 . HANDBOOK ON ENGINEERING. Example under latter formula: Given, diameter of rivet = inch, then For ordinary, double, zigzag -riveted joints, 10 Example : Given, pitch = 2 .85 inches, and diameter of rivet = | inch, then r= IXJH^ il> =1 . 4 7inche , DIAGONAL PITCH. For double, zigzag-riveted lap joint. Iron and steel. (ij> -f 4d ~Jo~ pjxample: Given, pitch = 2. 85 inches, and d = % inch, then MAXIMUM PITCHES FOR RIVETED LAP JOINTS. For single-riveted lap joints, maximum pitch =(1.31 X T) + lf . For double-riveted lap joints, maximum pitch =(2.62 X T) -f 1| . Example: Given a thickness of plate = J inch, required, the maximum pitch allowable. For single-riveted lap joint, maximum pitch = (1.81 X 4-) + If = 2.28 inches. For double-riveted lap joint, maximum pitch = (2.62 X |) + 14 = 2.935 inches. o The following tables, taken from the handbook of Thomas W. Traill, entitled "Boilers, Marine and Land, their Construction HANDBOOK ON ENGINEERING. 467 and Strength," may be taken for use in single and double riveted joints, as approximating the formulas of the British Board of Trade for such joints : IRON PLATES AND IRON RIVETS. DOUBLK-RIVKTKI) LAP JOINTS. Distance between rows Center of of rivets. Thickness Diameter Pitch of rivets to of plates. of rivets. rivets. edge of plates. Zigzag Chain riveting. riveting. r d P E V V 1 6" 1 2.272 .937 1.145 1.750 u 3 2 2.386 .984 1.202 1.812 l" ft 2.500 1.031 1.260 1.875 tt P 2.613 1.078 .317 1.937 "i L (i" 2.727 1.125 .374 2.000 l| n 2.826 1.171 .426 2.062 i" 13. 2.886 1.218 .465 2.125 if 2.948 1.265 .504 2.187 "A % 3.013 1.312 .544 2.250 11 If 3.079 1.359 .585 2.312 1 It ; 3.14-6 1.406 .626 2.375 H 1.453 .667 2.437 ti \* 3.284 1.500 .709 2.500 il laV 3.355 1.546 .751 2.562 ^ liV 3.426 1.593 .794 2.625 M 1-3*- 3.498 1.640 1.836 2.687 6 U 3.571 1.687 1.879 2.750 il l- 3 5 2 - 3.645 1.734 1.923 2.812 1 1W 3.718 1.781 1.966 2.875 If 1- 3 L 3.793 1.828 2.009 2.937 ft 14 3.867 1.875 2.053 3.000 II l- 3 a- 3.942 1.921 2.096 3.062 l-5 d - 4.018 1.968 2.140 3.125 468 HANDBOOK ON ENGINEERING. ZIGZAG RIVETING. CHAIN RIVETING. -f~M o -e-- HANDBOOK ON ENGINEERING. IRON PLATES AND IRON RIVETS. SINGLE-RIVETED LAP JOINTS, 469 7 i ^ \% p .- . LET C^ (i) ^!Q^. i g w V> \J/ 'uT ^ /a ^ 1 Thickness of Diameter of Pitch of Center of rivets to plates. rivets. rivets. edge of plates. T - d P E j 1 ft .524 .937 A 2_L 3 2 .600 .984 A .676 .031 II .753 .078 | .829 .125 If .905 .171 .981 .218 |i 2.036 .265 i 1 2.077 .312 II !! 2.120 .359 i if 2.164 .406 if 11 2.210 .453 | i 2.256 .500 f 2 i- 1 - 2.304 .546 16 hV 2.352 .593 3 2 2.400 .640 lr 2.450 .687 2.5. 2.500 .734 IB l^Sj 2.550 .781 il J_i. 2.601 .828 i* ll 2 2.652 .875 if l- 3 a. 2.703 .921 it h 5 e 2.755 .968 470 JIANDHOOK ON ENGINEK1M N(! . STEEL PLATE AND STEEL RjVETS. SINGLE-RIVETED LAP JOINTS. -** i* -i- Thickness of plates. Diameter of . rivets. Pitch of rivets. Center of rivets to edge of plates. T rf P i H 1.562 .031 2 .633 .078 JL.! ;] .704 .125 11. ft .775 .171 .846 .218 if 3 2 .917 .265 la .988 .312 I! fl 2.036 .359 L II 2.071 .406 li 2.108 .453 A 1 2.146 .500 II 2.186 .546 1-jL 2.227 .593 2JL 1-^- 2.269 .640 fl l| 2.312 .687 |f H & 2 2.356 .734 2.400 .781 25 2.445 .828 rl 2.500 .875 2- 1A 2.562 .921 |* 1-5.. 2.623 .968 25 Ifl 2.687 2.015 a If' 2.750 2.062 HANDBOOK ON ENGINEERING. 471 STEEL PLATE AND STEEL RIVETS. DOUBLE -RIVETED LAP JOINTS. Distance between rows Center of of rivets. Thickness Diameter Pitch of rivets to of plates. of rivets. rivets. edge of plates. Zigzag Chain riveting. riveting. T ." \L cos# D equals diameter of the stay. A " area in square inches to be supported. P " pressure, per square inch. L " safe load per square inch of stay section. B " angle between the shell and the stay. Using" the preceding problem as an example and referring to the same diagram, we have angle B equal to 15, and all the other dimensions as previously given. Therefore, equals 7000 X .96593 The diameter of the stay, when the above is simplified, is .9526", or practically 1". A rule for finding the pitch of stays for any flat surface is given below. J. A safe formula for the strength of stayed fiat surfaces is that given by Unwin's machine design. When the spacing of the stays is desired, assuming that it is the same in each direc- tion, we have, a equals 8 t \2p HANDBOOK ON ENGINEERING. 477 where a equals spacing of stays or rivets in inches,/ equals safe working strength of the plate, t equals thickness of plate, and p equals boiler pressure. Expressed as a rule, this reads : Divide the safe strength of the plate by twice the pressure ; extract the square root of the quotient and multiply the final result by three times the thickness of the plate. The result will be the spacing of the stays in inches. For example, boiler pressure 100 pounds, plate 1/2 inch thick, safe strength of plate, 10,000 pounds per square inch ; 2p equals 2 x 100 equals 200 ; f/2p equals 10000/200 equals 50; V 50 equals 7.07; ot equals 3/2 equals 1-1/2 equals 1.5; 7. 07 x 1.5 equals 10.0 for the spacing. In making such a calculation care must be exercised not to assume too high values for the strength of the plate. It is not safe to count on more than (50,000 pounds for the strength of steel plates and 40,000 for iron . The working strength must be taken not higher than 1/6 of this, or 10,000 for steel and 6,666 for iron, and lower values still would be better, say ( J,000 for steel and 6,000 for iron. 2* The safe pressure for a boiler to carry, so far as the flat, stayed surfaces are concerned, may be found from the above formula by transposing it a little, as follows: 9 f 2 f p equals ~^T Now, applying this to the above example, we have p equals 9 x.5 2 x 10000 9 x .25 x 10000 ~l&xTlOL25~~ 6q 2x110.25 after re ~ 22500 duction equals equals 102, or substantially the pressure Z ZO ,ooooonooooooooo5ooooo aJ'C O ta *- >~> *^ O f* g Over 6 and not over 7 inches. E o O a 1 Is Is Is Least thickness allowab Greatest length of sections allowable, 5 feet. ::..:: : : . : : : : : : : 9 ^ Over 7 and not over 8 inches. ................ ^g^S. . p.g] ......... . . ^ Over 8 and not over 9 inches. '' ' * ' .40 of material le. : : * -.-,-,-. ~ ^ : 3*| :::-:- ' : : ' ^ OWOSCDt * J ' orj : ::*?. .::::' . . : : : . . ^ ^ Over 12 aud not over 13 inches. Is ::;-,:: : : 8SS83a8S8 : : : : : S? | :::::: gg-s---^.-; : : | | ; S|| Over 13 and not over 14 inches. I* :::; ::::::' i> Over 14 and not over 15 inches. Is Is . . . . 5 o . j : : ^gSSS2SS: : : : : : : |l| : : . .:.:::.: ^^ ^ Over 15 and not over 16 inches. : : : issSS^SgHsiii: : : : : : : : 32 : : ::::::; : : : - ::::;:::: g-g^ Over 16 and not over 17 inches. Is . j ; ?,^32%$&t%l :;::::::?| : : ::.::::.. a ^^ Over 17 and not over 18 inches. Is . ; tta^38486K: ; : ; ; ; : | ; 3?| : .-a^^^^,^^,.,^^,-: : ::::::: gg| osKiSw^o'SScSow^- '.'..'.'.'.'. a an * Over 18 and not over 19 inches. Is lis : : : :::::::'"** ^ Over 19 and not over 20 inches. ^SS55i^s:s:sSK : : : : : : : : : : : il ~* weD * a, HANDBOOK ON ENGINEERING, 479 ength of sec lowable, 3 ft Great tion ness of ma lowable. Least thi terial saqoui fg aoAoqou jut? gg JOAQ << eoqouj fig J8AO 10U DQB e-g J8AQ saqouj Aoioa Ig J8AQ saqoai aAo^ou pu Og J9AQ Og JOAO 1OU put? 66 ^ A O saqouj saqoui 85 JOAO ion put? iz aaAQ -saqout IZ IQA.O ion PUB 92 J8AQ soqoui JAOIOU puw GZ JOAQ | ob a) < &OQ saqom <& 43AO ?oa put? f & JOAQ PUB g JOAQ soqoui 5J J3AO -JOU put? 2 put? 05 JfAQ pojtnboi jo : SGSSg^SS . 00 000 00 cflcacoccafl c^q ooooowooooo S S5 ?- -5r, 5 .5 -?5 5 ss^iss 480 HANDBOOK ON KN .1(55 15 .2T)9 n .109 i .165 16 .270 3 .109 8 .165 1 Tubes, water pipes and steams pipes, made of steel manufac- tured by the Bessemer process, may be used in any marine boiler when the material Irom which pipes are made does not contain more than .06 percent of phosphorus and .04 per cent of sulphur, to be determined by analysis by the manufacturers, verified by them, and copy furnished the user for each order tested ; which analysis shall, if deemed expedient by the Supervising Inspector- G-eneral, be verified by an outside test at the expense of the manufacturer of the tubes or pipes. No tube increased in thick- ness by welding one tube inside of another, shall be allowed for use. Seamless copper or brass tubes, not exceeding three-fourths of an inch in diameter, may.be used in the construction of water tube pipe boilers or generators, when liquid fuel is used. There may also be used in their construction copper or brass steam drums, not exceeding 14 inches in diameter, of a thickness of material not less than five-eighths of an inch, and copper or brass steam drums 12 inches in diameter and under, having a thickness of material not less than one-half inch. All the tubes and drums referred to in this paragraph shall be made from ingots or blanks drawn down to size without a seam. Water-tube boilers or gen- HANDBOOK ON ENGINEERING. 483 erators so constructed may be used for marine purposes with oone other than liquid fuel. Lap-welded Hues not exceeding inches in diameter may be made of any required length without being made in sections. And till such lap-welded flues and riveted flues not exceeding 6 inches in diameter may be allowed a working steam pressure not to exceed 225 Ibs. per square inch, if deemed safe by the inspectors. Lap- welded Hues exceeding inches in diameter and not exceeding 10 inches in diameter, and not exceeding 18 feet in length, and required to carry a steam pressure not exceeding 60 Ibs. per square inch, shall not be required to be made in sections. Lap-welded ^ud riveted flues exceeding inches in diameter and not exceeding 10 inches in diameter, and not exceeding 18 feet in length, and required to carry a steam pressure exceeding 00 Ibs. per square inch, and not exceeding 120 Ibs. per square inch, may be allowed, if made in sections not exceeding 5 feet in length and properly fitted one into the other, and substantially riveted. On all boilers built after July 1st, 181)0, a bronze or brass- seated stop-cock or valve shall be attached to the boiler between all check valves and all steam and feed pipes and boilers, in order to facilitate access to connections. Where such cocks or valves exceed 1 inches in diameter, they must be flanged to boiler. The stop-valves attached to main -steam-pipes may, however, be made of cast-iron or other suitable material. The date referred to above applies to this paragraph only. All copper steam-pipes shall be flanged to a depth of not less than four times the thickness of the material in the pipes, and all such flanging shall be made to a radius not to exceed the thickness of the material in such pipes. And all such pipes shall have a thickness of material according to the working steam pressure 484 HANDBOOK ON ENGINEERING. allowed, and such thickness of material shall be determined bv the following rule : Rule* Multiply the working steam pressure in pounds per square inch allowed the boiler by the diameter of the pipe in inches, then divide the product by the constant whole number 8000, and add .0625 to the quotient; the sum will give the thick- ness of the material required. Example* Let 175 Ibs. working steam pressure per square inch allowed the boiler, 5 inches = diameter of the pipe, 8000 a constant. Then we have : -f- .0625 = .1718 -f- thickness of material in decimals of oOOO an inch. The llanges of all copper steam pipes over three inches in diameter shall be made of bronze or brass composition, and shall have a thickness of material of not less than four times the thickness of material in the pipes plus .25 of an inch ; and all such flanges shall have a boss of sufficient thickness of material projecting from the back of the flange a distance of not less than three times the thickness of material in the pipe ; and all such flanges shall be counter-bored in the face to lit the flange of the pipe ; and the joints of all copper steam pipes shall be made with a sufficient number of good and substantial bolts to make such joints at least equal in strength to all other parts of the pipe. The terminal and intermediate joints of all wrought iron and homogeneous steel feed and steam pipes over 2 inches in diameter and not over 5 inches in diameter, other than on pipe or coil boilers or steam generators, shall be made of wrought iron, homo- geneous steel, or malleable iron flanges, or equivalent material ; and all such flanges shall have a depth through the bore of not HAM >n<>< >K ON KNGIXKKIMNG. -IS.") less than that equal to one-half of the diameter of the pipe to which any such flange may be attached ; and such bores shall taper slightly outwardly toward the face of the flanges ; and the OIK Is of such pipes shall be enlarged to lit the bore of the ilanges, and they shall be substantially beaded into a recess in the face of each flange. But where such pipes are made of extra heavy lap-welded steam pipe, the Ilanges may be attached with screw threads ; and all joints in bends may be made with good and substantial malleable iron elbows, or equivalent material. All feed and steam pipes not over 2 inches in diameter may be attached at their terminals and intermediate 'joints with screw threads by Ilanges, sleeves, elbows, or union couplings ; but where the ends of such pipes at their terminal joints are screwed into material in the boiler, drum or other connection having a thickness of not less than ] inch, the flanges of such terminal joints may be dispensed with. Where any such pipes are not over one inch in diameter and any of the terminal ends are to be attached to material in the boiler or connection having a thickness of less than i inch, a nipple shall be firmly screwed into the boiler or connection against a shoulder, and such pipe shall be screwed firmly into such nipple. And should inspectors deem it necessary for safety, they may require a jam nut to be screwed onto the inner end of any such nipple. The word ' ' terminal ' ' shall be interpreted to mean the points where steam or feed pipes are attached to such appliances on boilers, generators or engine, as are placed on such to receive them . All lap-welded iron or steel steam-pipes over 5 inches in diam- eter, or riveted wrought-iron or steel steam-pipes over 5 inches in diameter, in addition to being expanded into tapered holes and substantially beaded into recess in face of flanges, as provided in preceding paragraph for steam and feed-pipes exceeding 2 inches and not exceeding 5 inches in diameter, shall be substantially and / 486 HANDBOOK ON ENGINEERING. firmly riveted, with good and substantial rivets, through the hubs of such flanges ; and no such hubs shall project from such flanges less than 2 inches in any case. Steam-pipes of iron or steel, when lap- welded by hand or machine, with their flanges welded on, shall be tested to a hydro- static pressure of at least double the working pressure of the steam to be carried and properly aiinealed after all the work requiring fire is finished. When an affidavit of the manufacturer is furnished that such test has been made and annealed, they may be used for marine purposes. WROUGHT IRON WELDED PIPE. DIMENSIONS, WEIGHTS, ETC., OF STANDARD SIZES FOR STEAM, GAS, WATER, OIL, ETC. 1 inch and below are butt- welded, and tested to 300 pounds per square inch hydraulic pressure. li inch and above are lap-welded, and tested to 500 pounds per square inch hydraulic pressure. i 3 oa g^i Jo ^ 1 2 v> '~- 3 h 0) QJ 2^ if f 3J ^ Is eg %$|8 |*| Iljg vi (3 "c - "" ^ -g_o ^ r3^ 2.2 .ss SI bc^ a> sj *2 < -~'2 _bco *o c5 h ^ ~ '~- bt ~ 'c c - '- '~ '** C ^ *5 ^ 2 ai Hi 3ES-7 a^ X<5 |0n3o ^ *^ o * & M * H* - 'M * ft ^ Inch. Inches. Inches. Feet. Inches. Inches. Feet. Lbs. Lbs .40 1.272 9.44 .012 .129 2500. .24 27 .0006* 005 .54 1 . 696 7.075 049 229 1385. .42 18 .0026 .021 .67 2' 121 5.657 .110 . 358 751.5 .56 18 .(J057 .047 84 2.652 4 502 .196 . 554 472.4 .84 14 .0102 .085 1.05 3.299 3.637 .441 .866 270. 1.12 14 .0230 .190 1 1 31 4.134 2.903 .785 1.357 166.9 1.67 114 .0408- .349 1 66 5.215 2.301 1 227 2 . 164 96.25 2.25 III .0638 .527 li 1.9 5.969 2.01 1.767 2.835 70.65 2.69 Hi . 0918 .760 2* 2.37 7.461 1.611 3 141 4.430 42.36 8.66 ll| .1632 1.356 2.87 9.032 1.328 4 908 6.491 30.11 5.77 8 .2550 2.116 3 5 3 5 10.996 1 091 7.068 9.621 19.49 7.54 8 .3673 3.049 3* 4. 12.566 .955 9.621 12.566 14.56 9.05 8 .4998 4-155 4 4.5 14.137 .849 12.566 15.904 11.31 10.72 8 .6528 5.405 4* 5. 15.708 .765 15.904 19.635 9.03 12.49 8 .8263 6.851 5 5.56 17.475 .629 19.635 24.299 7.20 14.56 8 1.020 8.500 6 6.62 20.813 .577 28.274 34.471 4.98 18.76 8 1.469 12.312 7 7.62 23 954 .505 38.484 45.663 3.72 23.41 8 1.999 16.662 8 8 62 27.096 .444 50.265 58.426 2.88 28.34 8 2.611 21.750 9 9 68 30.433 .394 63.617 73.715 2.26 34.67 8 3.300 27.500 10 10.75 33.772 .355 78.540 90 792 1.80 40.64 8 4.081 34.000 ANDHOOK o\ ENGINEERING. 487 PULSATION IN STRAfl-BOILERS. Pulsation i' 1 steam-boilers, though not discernible to the eye, as in animated nature, goes on intermittently in some boilers whenever they are in use. It is induced by weakness and want of capacity in the boiler to supply the necessary quantity of steam, and sometimes is caused by the boiler being badly de- signed, thereby admitting of a great disproportion between the heating-surface and steam-room. Boilers are frequently found in factories that were originally not more than of sufficient capacity to furnish the necessary quantity of steam, but, as business increased, it became necessary to increase the pressure and also the speed of the engine; or, perhaps to replace it with a larger one, which has to be supplied with steam from the same boiler.. The result is, each time the valve opens to admit steam to the cylinder, about one-third of the whole quantity in the boiler is admitted, thus lowering the pressure ; the next instant, under the influence of hard firing, or, perhaps, a forced draught, the steam is brought to the former pressure, and so on ; this lessening and increasing the pressure continues while the engine is in motion, which has an effect on the boiler similar to the breathing of an animal. Trie strains induced by this pulsation are transmitted to the weakest places, viz., the line of the rivet holes, and that marked by the tool in the process of calking ; the result is, the plate is broken in two, as shown in the above cut. The manner in which the break takes place may be illustrated by filing a small nick, or drilling a small hole, in a piece of hoop or band- iron, and then bending back 488 HANDBOOK OX ENGINEERING. and forth, when it will be discovered that the material will break just at that point, however slight the nick or small the hole may be. Pulsation is frequently very severe in the boilers of tug- boats when commencing to start a heavy tow, and also in loco- motives when starting long trains. Some frightful explosions of the boilers of tug-boats and locomotives have occurred under such circumstances. Pulsation, if permitted to continue, is sure to effect the destruction of the boiler. It is always made mani- fest by the vibrations of the pointers on steam gauges, or an unsteadiness in the mercury column. It may be remedied, to a certain extent, by adding a larger steam dome, but this has a tendency to weaken the boiler and render it more unsafe. Tho only sure preventive of such a silent and destructive agent is to have the boiler of sufficient capacity in the first place. WEIGHT OP SQUARE AND ROUND IRON PER LINEAR FOOT. SIDE OK DIAM. Weight, Square. Weight, Round. SIDE OR DIAM. Weight, Square. Weight. Round. SIDE OR DIAM. Weight, Siju.-uv. Weight, Uouinl. tV .013 .01 2 13.52 10.616 5 84.48 66.35 1 .053 .041 * 15.263 11.988 k 93.168 73.172 ft .118 .093 i 17.112 13.44 h 102.24 80.304 1 .211 .165 1 19.066 14.975 I 111.756 87.776 i .475 .373 h 21.12 16.588 I .845 .663 t 23.292 18.293 6 121.664 95.552 1 1.32 1.043 I 25.56 20.076 i 132.04 103.704 * 1.901 1.493 I 27.939 21.944 i 142.816 112.16 I 2.588 2.032 1 154.012 120.96 3 30.416 23.888 i 3.38 2.654 i 35.704 28.04 7 165.632 130.048 1 4.278 3.359 4 41.408 32.515 \ 177.672 139.544 5.28 4.147 t 47.534 37.332 h 190.136 149.328 | G.39 5.019 3 203.024 1 of). 456 h 7.604 5.972 4 54.084 42.464 I 8.926 7.01 1 61.055 47.952 8 216.336 169.856 i 10.352 8.128 I 68.448 53.76 1 11.883 9333 3 76.264 59.9 9 273.792 215.04 HANDBOOK ON ENGINEERING. 489 WATER COLUHNS. Every boiler should be equipped with a safety water column. Next to keeping the steam pressure within the limits of safety, the most important point to be observed in operating steam boilers is the maintenance of the proper water level. If the water level is too low, there is danger of burning the tubes and plates and ? perhaps, of wrecking the boiler ; if it is too high, water is liable to be carried along with the steam and cause damage in the engine, while a constant variation in the water level produces a waste of fuel and unsteady pressure, and impairs the life of the boiler. Safety water columns have been devised for the purpose of insuring owners of steam boilers against accidents of this kind. They are so ar- ranged that any variation in the water level beyond reasonable lim- its will be loudly proclaimed by means of a suitable steam whistle. STEAM-GAUGES. The object of the steam-gauge is to indicate the steam pressure in the boiler, in order that it may not be increased far above that at which the boiler was originally considered safe ; and it is as a provision against this contingency that a really good gauge is a necessity where steam is employed, for no guide at all is vastly better than a false one. The most essential requisites of a good steam-gauge are, that it be accurately graduated, and that the material and workmanship be such that no sensible deterioration may take place in the course of its ordinary use. The pecuniary loss arising from any considerable iluctuation of the pressure of steam has never been properly considered by the proprietors of engines. If steam be carried too high, the surplus will escape through the safety-valve, and all the fuel consumed to produce such excess is so much dead loss. On the other hand, if there be at any [time too little steam, the engine will run too slow, antf. every lathe, loom, or other machine driven by it, will lose its speed and, of course, its effective power in the same pro- 490 HANDBOOK ON .KNiJINEKKIXfJ. portion. A loss of one revolution in ten at once reduces the pro- ductive power of every machine driven by the engine ten per cent, and loses to the proprietor ten per cent of the time of every workman employed to manage such machine. In short, the loss of one revolution in ten diminishes the productive capacity of tin- whole concern ten per cent, so long as such reduced rate con- tinues ; while the expenses of conducting the shop (rent, wages, insurance, etc.) all run on as if everything was in full motion. A variation to this amount is a matter of frequent occurrence, and is, indeed, unavoidable, unless the engineer is afforded facilities to prevent it. A very little reflection will satisfy any one that it must be a very small concern, indeed, in which a half- hour's continuance of it would not produce a result more than enough to defray the cost of a very expensive instrument to pre- vent it. If the engineer, to avoid this loss, keeps a surplus of steam constantly on hand, he is constantly wasting the steam, and consequently, fuel, thus incurring another loss, which, though less alarming than the first, will yet be serious and render any instrument most desirable which can prevent it. It is, there- fore, of great importance to the proprietors of engines to have an instrument which can constantly indicate the pressure in the steam-boilers with accuracy. This would enable the engineer to keep his steam at a constant pressure, thus avoiding waste of fuel on the one hand, and the still more serious loss of the productive power of the shop on the other. An instrument, therefore, con- stantly indicating the pressure of steam, reliable in its character, and, with ordinary care, not subject to derangement, is evidently a desideratum both to the engineer and proprietor. - The impor- tance of such an instrument, as a preventive of explosion, and of the frightful consequences to life and limb and ruinous pecuniary results of such disaster, is obvious on the slightest consideration : but the value of the instrument, in the economical results of its daily use, is by no means properly appreciated. HANDBOOK ON E\ . "^ w> fl ^ > . j " O fl ^ > ""5 c x i -t~ ^ S S m S* 3 'SJa ^ 2i W *J =t._^' W ^^ 5 ^ ^ ! - Tl <* S|| aq =s S c ^" iy "H..C O nj 2 O o . '" rt o "c . bs-fl ? fl | =*-! O O gg| s a* '^=5 s E,"S OhH Sc2 O|H <2 /. -_ ^ . .' ^ ^ Q - . . !H "J * .. i . IH -5~ 1?^ r* ^ 1'^ a; a 1 !y^S 2-S5 fi S^^s 0.25 .022794 10 .005698 70 .001015 0.5 .021164 20 .003221 80 .000892 1 .018515 30 .002244 90 .000796 2 .014814 40 .001723 100 .000719 3 .012345 50 .001398 150 .000481 4 .010582 60 .001176 200 .000364 5 .009259 ' TABLE OF COMPARISON BETWEEN EXPERIMENTAL RESULTS AM) THEORETICAL FORMULAE. Boiler Pressure. 45 pounds. Boiler Pressure, 75 pounds. ,i.,.., in , r JAreu of open- BnrfSw '"K fund by 1 experiment. Area of open- ing according to formulae. Heating Surface. Area of open- ing found by experiment. Area of open- ing according to formulae. S(|. Ft. S(j. ins. . Sq. Ins. Sq. Ft. Sq. Ins. Sq. Ins. 100 .089 .09 100 .12 .12 20(1 j .180 .19 200 .24 .24 500 ! .45 .48 500 .59 .59 1000 .89 .94 1000 1.20 1.18 2000 ' 1.78 1.90 2000 i 2.40 2.37 5000 4.46 4.75 5000 6.00 5.95 496 HANDBOOK ON ENGINEERING. Now, if we compare the area of openings, according to these experiments, with Zeuner's formula, which is entirely theoretical, it will be observed that the results from the two sources are almost identical, or so nearly so as not to' make any material difference. In the absence of any generally recognized rule, it k> customary for engineers and boiler-makers to proportion safety- valves according to the heating surface, grate-surface, or horse- power of the boiler. While one allows one inch of area of safety-valve to 66 square feet of heating surface, another gives one inch area of safety-valve to every four horse power ; while a third proportions his by the grate-surface it being the custom in such cases to allow one inch area of safety-valves to 2 square feet of grate-surface. This latter proportion has been proved by long experience and a great number of accurate experiments, to be capable of admitting of a free escape of steam without allowing any material increase of the pressure beyond that for which the valve is loaded, even when the fuel is of the best quality, and the consumption as high as 24 pounds of coal per hour per square foot of grate-surface, providing, of course, that all the parts are in good working order. It is obvious, however, that no valve can act without a slight increase of pressure, as, in order to lift at all, the internal pressure must exceed the pressure due to the load . The lift of safety-valves, like all other puppet- valves, de- creases as the pressure increases ; but this seeming irregularity is but what might be required of an orifice to satisfy appearances in the flow of fluids, and maybe explained as follows: A cubic foot of water generated into steam at one pound pressure per square inch above the atmosphere, will have a volume of about 1,600 cubic feet. Steam at this pressure will flow into the atmosphere with a velocity of 482 feet per second. Now, suppose the steam was generated in five minutes, or in 300 seconds, and the area of an orifice to permit its escape as fast as it is generated be re- HANDBOOK ON ENGINEERING. 497 quired, 1600 divided by 482 x 300 will give the area of the orifice, 1|- square inches. If the same quantity of water be generated into steam at a pressure of 50 pounds above the atmosphere, it will possess a volume of 440 cubic feet and will flow into the atmos- phere with a velocity of 1791 feet per second. The area of an orifice, to allow this steam to escape in the same time as in the first case, may be found by dividing 440 by 1791x300, the result will be ^ square inches, or nearly -J- of a square inch, the area required. It is evident from this that a much less lift of the same valve will suffice to discharge the same weight of steam under a high pressure than under a low one, because the_steam under a high pressure not only possesses a reduced volume, but a greatly increased velocity ; it is also obvious from these consider- ations, that a safety-valve, to discharge steam as fast as the boiler can generate it, should be proportioned for the lowest pressure. RULES. Rule. Yor finding the weight necessary to put on a safety- valve lever when the area of valve, pressure, etc., are known : Multiply the area of valve by the pressure in pounds per square inch ; multiply this product by the distance of the valve from the fulcrum ; multiply the weight of the lever by one-half its length (or its center of gravity) ; then multiply the weight of valve and stem by their distance from the fulcrum ; add these last two prod- ucts together, subtract their sum from the first product, and divide the remainder by the length of the lever ; the quotient will be the weight required. EXAMPLE, Area of valve. 12 in 65 13 8 Pressure, (>5 Ibs 12 16 4 Fulcrum, 4 in. . . ......... 780 208 32 498 HANDBOOK ON ENGINEERING. Length of lever, 32 in 4 13 Weight of lever, 13 Ibs, Weight of valve and stem, 8 Ibs 3120 208 240 32 32)2880 240 90 Ibs. Rule for finding the pressure per square inch when the area of valve, weight of ball, etc., are known: Multiply the weight of ball by length of lever, and multiply the weight of lever by one-half its length (or its center of gravity) ; then multiply the weight of valve and stem by their distance from the fulcrum. Add these three products together. This sum, divided by the product of the area of valve, and its distance from the fulcrum, will give the pressure in pounds per square inch. EXAMPLE. Area of valve, 7 in 50 12 Fulcrum, 3 in 30 15 Length of lever, 30 in 1500 180 18 Weight of lever, 12 Ibs 180 Weight of ball, 50 Ibs. . . . . . . . 18 7 Weight of valve and stem, 6 Ibs 21)1698 3 80.85 Ibs. 21 Rule for finding the pressure at which a safety-valve is weighted when the length of the lever, weight of ball, etc., are known : Multiply the Jength of lever in inches by the weight of ball in pounds ; then multiply the area of valve by its distance HANDKOOK ON KNCJINNKKING. 499 from the fulcrum ; divide the former product by the latter; the quotient will be the pressure in pounds per square inch. EXAMPLE. Length of lever, 24 in . 52 7 Weight of ball, 52 Ibs. 24 Fulcrum, 3 in. . . 208 21 Area of valve, 7 in 104 21)1248 59.42 Ibs. The above rule, though very simple, cannot be said to be exactly correct, as it does not take into account the weight of the lever, valve and stem. Rule for finding center of gravity of taper levers for safety- valves : Divide the length of lever by two (2); then divide the length of lever by six (6), and multiply 'the latter quotient by width of large end of lever less the width of small end, divided by width of large end of lever plus the width of small end. Subtract this product from the first quotient, and the remainder will be the distance in inches of the center of gravity from large end of lever. EXAMPLE. Length of lever 36 in. Width of lever at large end 3 " Width of lever at small end 2 " 36 divided by 2 = 18 minus 1.2 = 1(5.8 in. 36 divided by 6 = (I X 1 <> divided by 5 = 1.2. Center of gravity from large end, 16.8 in. The safety-valve has not received that attention from engi- neers and inventors which its importance as a means of safety 500 HANDBOOK ON ENGINEERING . so imperatively deserves. In the construction of most other kinds of machinery, continual efforts have been made to secure and insure accuracy ; while in the case of the safety-valve, very little improvement has been made either in design or fitting. It is difficult to see why this should be so, when it is known that deviations from exactness, though trifling in themselves, when multiplied, not only affect the free action and reliability of machines, but frequently result in serious injury, more partic- ularly in the case of safety-valves. Safety-valves should never be made with rigid stems, as, in consequence of the frequent inaccuracy of the other parts, the valve is prevented from seating, thereby causing leakage ; as a remedy for which, through ignorance or want of skill, more weight is added on the lever, which has a tendency to bend the stem, thus rendering the valve a source of danger instead of a means of safety. The stem should, in all cases, be fitted to the valve with a ball and socket joint, or a tapering stem in a straight hole, which will admit of sufficient vibration to accommodate the valve to its seat. It is also advisable that the seats of safety-valves, or the parts that bear," should be as narrow as circumstances will permit, as the narrower the seat the less liable the valve is to leak, and the easier it is to repair when it becomes leaky. All compound or complicated safety-valves should be avoided, as a safety-valve is, in a certain sense, like a clock any complication of its parts has a tendency to affect its reliability and impair its accuracy. It has been too much the custom heretofore for owners of steam boilers to disregard the advice and suggestions of their own en= giueers and firemen, even though men of intelligence and experi- ence, and to be governed entirely by the advice of self-styled experts and visionary theorists. HANDBOOK ON ENGINEERING. 501 Table of Heating Surface in Square Feet, Diam. of Boiler in inches 24 30 32 34 36 38 40 42 44 48 5 Heating surface of shell per foot of length. 4.19 5.24 5.57 5.93 6.28 6.63 6.98 7.73 7.68 8.38 Diameter of Tube or Flue in inches. 2 24 3 3* 4 44 5 G 7 8 Whole External Heating surface per foot length. .524 .655 .785 .916 1.05 1.18 1.31 1.57 1.83 2.09 50 52 54 5G 58 60 62 64 66 68 70 72 8.73 9.08 9.42 9.77 10.12 10.47 10.82 11.17 11.52 11.87 12.22 12.57 9 10 11 12 13 14 15 16 17 18 19 20 2.36 2.C2 2.88 3.14 3.40 3.66 3.93 4.19 4.45 4.71 4.96 5.24 CENTRIFUGAL FORCE. The centrifugal force of a body depends upon its weight W in pounds ; distance R in feet it is from the center of rotation, and the number of revolutions N it makes about that center each WR N* minute and equals Multiply the weight in pounds by radius in feet, by square of number of revolutions, and divide by 2933 = centrifugal force in pounds. 502 HANDBOOK ON ENGINEERING. CHAPTER XVIII. THE WATER TUBE SECTIONAL BOILER. The water tube sectional boiler has been a growth of many years and of many different minds. There are some two and a half million horse-power in daily service in the United States alone, and the number is rapidly increasing. Large orders for this type of boiler have often been repeated, adding proof that its principles are correct and appreciated by those having them in use and in charge. This being the case, purchasers should note well the points of difference in the various water tube boilers claiming their attention, and particularly see that the claims made for them are embodied in their actual construction. The general principles of construction and operation of this class of steam boilers are now well known to engineers and steam users. In selecting a water tube boiler there are several vital points to be considered : 1st. Straight and smooth passages through the headers of ample area, insuring rapid and uninterrupted circulation of the water. 2d. The baffling of the gases (without throttling or impeding the circulation of the water) in such a way that they are com- pelled to pass over every portion of the heating surface. 3d. Sufficient liberating surface in the steam drums to insure dry steam, with large body of water in reserve to draw from. 4th. A steam reservoir or steam drum. 5th. Simplicity in construction ; accessibility for cleaning and inspection. 6th. A header, which in its design provides for the unequal expansion and contraction. HANDBOOK ON ENGINEERING. 503 Illustration above is that of a Horizontal Safety Water Tube Boiler, manufactured by the John O'Brien Boiler Works Company, of St. Louis, U. S. A. Down draft furnace* A great many of these boilers are fit- ted with the down draft furnaces, and the above illustration shows the style of same, together with the manner in which they are connected. A full and complete description of these furnaces is given on page 522. Description* In construction, this type of boiler consists 504 HANDBOOK ON ENGINEERING. simply of a front and rear water leg or header, made approx- imately rectangular in shape, overhead combination steam and water drum or drums and with circulating water tubes, as shown in cut, which extend between and connect both front and rear headers, being thoroughly expanded into the tube sheets. The tubes are inclined on a pitch of one inch to the foot and the rear header being longer than the front one, the overhead drum connecting both headers lies perfectly level when the boiler is set in position. The connection of the headers with the combined steam and water drum is made in such a manner as to give prac- tically the same area as the total area of the tubes, so there is no contraction of area in the course of circulation ; and extending between and connecting the inside faces of the water legs, which form end connections between these tubes and the com- bined steam and water drums or shells, placed above and parallel with them, also a steam drum above these, assures absolutely dry steam and a large steam space, also a large water space. The water legs are made larger at the top, about 11 inches wide, and at the bottom about 7 inches wide, which is a great advantage, allowing the globules of steam to pass quickly up the water legs to the steam and water drums. The water, as it sweeps along the drums, frees itself of steam ; then it goes down the back connec- tion until it meets the inclined tubes, meeting on its passage a gradually increasing temperature, till the furnace is again reached, where the steam formed on the way is directly carried up in the drum as before. The tubes extend between and connect both the front and rear headers and are thoroughly expanded into the tube sheets. Opposite the end of each tube there is an oval hand-hole slightly larger than the tube proper through which it can be withdrawn. It will be noted that the throat of each water leg is 11 times the total tube area. The rapid and unimpeded circulation tends to keep the inside surface clean and floats the scale-making sediment along until it reaches the back HANDBOOK ON ENGINEERING. 505 water leg, where it is carried down and settles in the bottom of leg, where it is blown off at regular intervals. Steadiness of water level. The large area of surface at water line and the ample passages for circulation, secure a steadiness 506 HANDBOOK ON ENGINEERING. of water level unsurpassed by any boiler. This is a most im- portant point in boiler construction and should always be consid- ered when comparing boilers. The water legs are stayed by hol- low stay-bolts of hydraulic tubing of large diameter, so placed that two stays support each tube and hand-hole and are subjected to only very slight strain. Being made of heavy material, they form the strongest parts of the boiler and its natural supports. The water legs are joined to the shell by flanged and riveted joints and the drum is cut away at these two points to make connection with in- side of water leg, the opening thus made being strengthened by special stays, so as to preserve the original strength. The shells are cylinders with heads dished to form part of a true sphere. The sphere is everywhere as strong as the circular seam of the cylinder, which is well known to be twice as strong as the side seam ; therefore, the heads require no stays. Both the cylinder and the spherical heads are, therefore, free to follow their natural lines of expansion when put under pressure. The illustration on page 505 plainly shows the formation of the front water leg or header in this type of water tube boiler. It will be seen that the hand plates are all oval in shape, allow- ing each one to be removed from its respective hole ; also, the manner of bracing with hollow stay-bolts is shown. Note that the feed pipes for supplying furnace are equipped with oval hand plates to facilitate cleaning. Walling in, In setting the boiler, its front water leg is placed firmly on a set of strong, cast-iron columns bolted and braced to- gether by the door frames and dead-plates and forming the fire front. This is the fixed end. The rear water legs rest on rollers which are free to move on cast-iron plates firmly set in the ma- sonry of the low and solid rear wall. Thus the boiler and its walls are each free to move separately during expansion or contraction, without loosening any joints in the masonry. On the lower, and between the upper tubes, are placed light HANDBOOK ON KN<; IN BERING. 507 fire-brick tiles. The lower tier extends from the front water leg to within a few feet of the rear one, leaving there an upward pass- age across the rear ends of the tubes for the flame. The upper tier closes into the rear water leg and extends forward to within a few feet of the front one, thus leaving an opening for the gases in front. The side tiles extend from side walls to tile bars and close up to the front water leg and front wall, 'and leave open the final uptake for the waste gases. The gases being' thoroughly mingled in their passage between the staggered tubes, the combustion is more complete, and the gases impinging against the heating surface perpendicularly, in- stead of gliding along the same longitudinally, the absorption of the gas is more thorough. The draft area, being much larger than in lire tube boilers, gives ample time for the absorption of the heat of the gases before their exit to the chimney. DESCRIPTION OF THE HEINE SAFETY BOILER. The boiler is composed of lap-welded wrought-iron tubes ex- tending between and connecting the inside faces of two " water legs," which form the end connections between these tubes and a combined stearn and water drum or ' ' shell ' ' placed above and parallel with them. (Boilers over 200 horse-power have two such shells.) These end chambers are of approximately rectangular shape, drawn in at top to fit the curvature of the shells. Each te composed of a head plate and a tube sheet FLANGED ALL AROUND AND JOINED AT BOTTOM and sides by a butt strap of same material, strongly riveted to both. The water legs are further stayed by hollow stay-bolts of hydraulic tubing of large diameter, so placed that two stays support each tube and hand-hole and are subjected to only very slight strain. Being made of heavy metal, they form the strongest parts of the boiler and its natural supports. The 508 HANDBOOK ON ENGINEERING. water legs are joined to the shell by flanged and riveted joints, and the drum is cut away at these two points to make connection with inside of water leg, the opening thus made being strength- ened by bridges and special stays so as to preserve the original strength. 48 HANDBOOK ON ENGINEERING. f>()9 The shells ai'e cylinders with heads dished to form parts of a true sphere. The sphere is everywhere as strong as the circle seam of the cylinder, which is well known to be twice as strong as its side seam. Therefore, these heads require no stays. Both the cylinder and its spherical heads are, therefore, free to follow their natural lines of expansion when put under pressure. Where flat heads have to be braced to the sides of the shell, both suffer local distortions where the feet of the braces are riveted to them, making the calculations of their strength fallacious. This they avoid entirely by their dished heads. To the bottom of the front head a flange is riveted, into which the feed-pipe is screwed. This pipe is shown in the cut with angle valve and check valve attached. On top of shell, near the front end, is riveted a steam nozzle or saddle, to which is bolted a tee. This tee carries the steam valve on its branch, which is made to look either to front, rear, right or left ; on its top the safety valve is placed. The saddle has an area equal to that of stop valve and safety valve combined. The rear-head carries a blow-off flange of about same size as the feed flange, and a manhead curved to fit the head, the manhole supported by a strengthening ring outside. On each side of the shell a square bar, the tile-bar, rests loosely in flat hooks riveted to the shell. This bar supports the side tiles, whose other ends rest on the side walls, thus closing the furnace or flue on top. The top of the tile-bar is two inches below low water line. The bars ' rise from front to rear at the rate of one inch in twelve. When the boiler is set, they must be exactly level, the whole boiler being then on an incline, i. e., with a fall of one inch in twelve from front to rear. It will be noted that this makes the height of the steam space in front about two-thirds the diam- eter of the shell, while at the rear the water occupies two-thirds of the shell, the whole contents of the drum being equally divided between steam and water. The importance of this will be ex- plained hereafter. 510 HANDBOOK ON ENGINEERING. The tubes extend through the tube sheets, into which llicv .-in- expanded with roller expanders ; opposite the end of each and in the head-plates, is placed a hand-hole of slightly larger diarn- eter than the tube, and through which it can bo withdrawn. These hand-holes are closed by small cast-iron hand-hole plates, which, by an ingenious device for locking, can be removed in, a HANDBOOK ON KN< J I NKEKI \(J . 511 lew seconds to inspect or clean ;i tube. The accompanying cut shows these hand-hole plates marked //. In the upper corner one is shown in detail, If 2 being the top view, 7/ 3 the side view of the plate itself, the shoulder showing the place for the gasket. //' l is the yoke or crab placed outside to support the bolt and nut. Inside of the shell is located the mud drum />, placed well below the water line, usually parallel to and 3 inches above the bottom of the shell. It is thus completely immersed in the hot- test water in the boiler. It is of oval section, slightly smaller than the manhole, made of strong sheet-iron with cast-iron heads. It is entirely inclosed except about 18 inches of its upper portion at the forward end, which is cut away nearly parallel to the water line. Its action will be explained below. The feed- pipe F enters it through a loose joint in front ; the blow-off pipe N is screwed tightly into its rear-head, and passes by a steam- tight joint through the rear-head of the shell. Just under the steam nozzle is placed a dry pan or dry pipe A. A deflection plate L extends from the front head of the shell, inclined up- wards, to some distance beyond the mouth or throat of the front water leg. It will be noted that the throat of each water leg is large enough to be the practical equivalent of the total tube area, and that just where it joins the shell it increases gradually in width by double the radius of the flange. Erection and walling in. In setting the boiler, its front water leg is placed firmly on a set of strong cast-iron columns, bolted and braced together by the door frames, deadplate, etc., and forming the fire front. This is the fixed end. The rear water leg rests on rollers, which are free to move on cast-iron plates firmly set in the masonry of the low and solid rear wall. Wherever the brickwork closes in to the boiler, broad joints are left which are filled in with tow or waste saturated with fireclay, or other refractory but pliable material. Thus the boiler and its walls are each free to move separately during expansion or con- HANDBOOK ON ENGINEERING. traction without loosening any joints in the masonry. On the lower, and between the upper tubes, arc placed light fire-brick tiles. The lower tier extends from the front water leg to within a few feet of the rear one, leaving there an upward passage across the rear ends of the tubes for the flame, etc. The upper tier closes in to the rear water leg and extends forward to within a few feet of the front one, thus leaving the opening for the gases in front. The side tiles extend from side walls to tile bars and close up to the front water leg and front wall, and leave open the final uptake for the waste gases over the back part of the shell, which is here covered above water line with a rowlock of firebrick rest- ing on the tile bars. The rear wall of the setting and one paral- lel to it arched over the shell a few feet forward, form the uptakes. On these and the rear portion of the side walls is placed a light sheet-iron hood, from which the breeching leads to the chimney. When an iron stack is used, this hood is stiffened by L and T irons so that it becomes a truss carrying the weight of such stack and distributing it to the side walls. Longitudinal section of Heine Boiler and its operation* The boiler being filled to middle water line, the fire is started on the grate. The flame and gases pass over the bridge wall and under the lower tier of tiling, finding in the ample combustion chamber space, temperature and air supply for complete combus- tion, before bringing the heat in contact with the main body of the tubes. Then, when at its best, it rises through the spaces be- tween the rear ends of the tubes, between rear water leg and back end of the tiling, and is allowed to expand itself on the entire tube heading surface without meeting any obstruction. Ample space makes leisurely progress for the flames, which meet in turn all the tubes, lap round them, and finally reach the second uptake at the forward end of the top tier of tiling, with their temperature reduced to less than 900 ^Fahrenheit. This has been measured here, while wrought iron would melt just above the lower tubes at II AM) MOOR ON ENGINEERING. r>i3 rear end, showing a reduction of temperature of over 1,800 Fahr. between the two points. As the space is studded with water tubes, swept clean by a positive and rapid circulation, the absorp- tion of this great amount of heat is explained. The gases next travel under the bottom and sides of shell and reach the uptake at just the proper temperature to produce the draft required. This varies, of course, according to chimney, fuel required, etc. With boilers running at their rated capacity, 450 Fahrenheit are A furnace that is used in the East a great deal. seldom exceeded. Meanwhile, as soon as the heat strikes the tubes, the circulation of the water begins. The water nearest the surface of the tubes becoming warmer, rises, and as the tubes are higher in front, this water flows towards the front water leg where it rises into the shell, while colder water from the shell falls down the rear water leg to replace that flowing forward and upward through the tubes. This circulation, at first slow, in- 33 514 HANDBOOK ON ENGINEERING. creases in speed as soon as steam begins to form. Then the speed with which the mingled current of steam and water rises in the forward water leg will depend on the difference in weight of this mixture, and the solid and slightly colder water falling down the rear water leg. The cause of its motion is exactly the same as that which produces'draft in a chimney. Plain Vertical Tubular Boiler- This cut shows the place for gauge cocks and water glass in an upright boiler. HANDBOOK ON ENGINEERING. 515 060OCHDOOOO ooooo, ooooo ooooo ooooo ooooo ooooo oooo oooo O ^ft-rfk O The above cut shows the water-column iu its proper place. HANDBOOK ON ENGINEERING. juao aod OS OinSSOJJ fsl 60,000 ten strengt 1-6, 10,00 }U9O JOd ^uoo J9d OS -*S88&SS8S88SS3832S5BS e _ oo t- 1^ Li mo; 'at gTojj ; 2; :; r 38! icooocoi^-'-H-^c^ co^o-''^ioi^*oO' ^co-^'OO' tjccor -rf/Dci -* -5 -52 o O !- -< 3 M eo rio ooB t2S * 35 o 01 r-S5 r-. i occD-J aeco;e-ocD^Hr -^< t- 5 S Ss fi f-F-ao 35 o o H o 2 55 t^ooooos o ^ t~ CO QO CO c> SO r~- CD I OS ^ O5 * ^XMQOO-^TtlC-. * jo 00 00 0> OJ J3 ~ O O a c HANDBOOK ON ENGINEERING. 519 to ):o :$ co o M < * 10 <* m -M -* i-ccoox> (iot--f-*coi~co^sio--ootOi i IO--KH HOt>j ^o 2^1* f X W 1 sfi^'i cc b tc>^ O o 5 rt 72"x22' 18" 10,500 2,500 18 bu. 88 8 9 bbl. 72"x20' 18" 10,000 2,300 18 bu. 80 8 8 bbl. 72"xl8' 18" 9,500 2,200 17 bu. 72 7 8 bbl. 60"x20' 18" 9,500 2,200 17 bu. 80 7 8 bbl. 60"xl8' 18" 9,000 2,000 16 bu. 72 7 8 bbl. 54"x20' 18" 8,700 ,900 15 bu. 80 6 8 bbl. 54"xl8' 18" 8,000 ,800 15 bu. 72 6 8 bbl. 54"xl6' 18" 7,500 ,700 14 bu. 64 6 7 bbl. 48"xl8' 18" 7,500 ,600 14 bu. 72 6 7 bbl. 48"xl6' 18" 7,200 ,500 14 bu. 64 5 7 bbl. 42"xl8' 18" 7,000 ,400 12 bu. 72 5 7 bbl. 42"xl6' 18" 6,500 ,300 12 bu. 64 4 7 bbl. If 13" wall i less on Red Brick. THE DOWN DRAUGHT FURNACE. The down draught furnace is noted for being one of the best smoke preventing furnaces in the market, while at the same time the cheapest kind of coal can be used. The down draught furnace made a good smoke record, even with overworked boilers, doing variable work, and with a marked economy in fuel. My experience with the down draught furnace, I feel safe in saying that smoke from boiler furnaces can now be abated by practical means, without hardship, no matter what the type of boiler. Directions for firing the Down Draught Furnace* When firing the furnace, throw the coal evenly over the entire grate surface, from 6 to 8 inches in depth, a little heaviest at the rear end of the furnace. Do not put in too much coal burn more air ; and economize with your fuel and HANDBOOK ON ENGINEERING. 523 do not pile up the coal in front near the door. Never fire any fresh coal on the lower grates ; let in air below the lower grates. When poking the fire, run the slice-bar down between the water grates and back the full length of the grates ; then raise the slice- bar and gently shake the coal, and then pull it out without stir- ring up the fire. Never turn the fire over so that black coal gets down upon the water grates, unless there is a large clinker to re- move. Never give the top grates a general cleaning, so as to leave a portion of the grates uncovered and the remainder with a hot fire on them, as this causes an uneven expansion in the differ- ent tubes forming the water grates, and is liable either to bend the tubes or strip off the threads where they enter the drums. When the top fire becomes clogged with clinkers so that you can- Down Draught Furnace. not keep up steam, run in the slice-bar and raise the clinkers to the top of the fire ; remove the large clinkers, leave the small ones alone, and put on afresh fire. The lower grates must have proper 524 HANDBOOK ON ENGINEERING. attention. The coals must be raked over evenly and all holes filled up, particular care being taken that the grates are perfectly covered all over. If considerable coals have accumulated on the . ja"*L i~r J. iv-4 View of the Down Draught Furnace. lower grates and the air spaces are closed with ashes or clinkers, the slice-bar must be used and the clinkers raised up and turned over and the larger ones removed. It is best to remove the clink- ers every two or three hours, leaving the coals to burn up. SPECIFICATIONS FOR ONE SIXTY-INCH HORIZONTAL SIX= INCH FLUE BOILER. General directions* There will be one boiler 20 feet long from out to out of heads and 60 inches inside diameter. Material, quality, thickness, etc* Material in shell of the above named boiler to be made of homogeneous flange steel T 5 ^" thick, having a tensile strength of not less than 60,000 Ibs. to HANDBOOK ON ENGINEERING. 525 526 HANDBOOK ON ENGINEERING. the square inch of section, with not less than 56 per cent ductil- ity, as indicated by contraction of area at point of fracture under test, or by an elongation of 25 per cent in length of 8 inches. Heads must be J" thick and of the same quality of steel as that in the shell. All plates and heads must be plainly stamped with the maker's name, and tensile strength. Tubes, size, number and arrangement* The boiler must contain 18-6" lap-welded flues, riveted to the heads with Ten " rivets in each head ; said flues must be made of charcoal iron of the best American make, standard thickness, equal to the National Tube Works Company's make. All flues must have at least 3 inch clear space between them, and not less than 3 inches between flues and shell. All flanging of heads must be free from flaws or cracks of any description, and properly annealed in an annealing oven before riveting to the boiler. If 4-inch flues are wanted in place of 6 -inch, the boiler must have 44 best lap- welded tubes, 4" in diameter and 20 feet long, set in vertical and horizontal rows, with a clear space between them, vertically and horizontally of 11", except the central vertical space, which is to be 4 inches. Holes for tubes to be neatly chamfered off on the outside. Tubes to be set with a Dudgeon expander, and beaded down at each end. Riveting* The longitudinal seams of the boiler must be above the fire line, and have a TRIPLE row of rivets ; all rivets to be J" in diameter ; and all rivets to be of sufficient length to form upheads equal in size to the pressed heads of same. The rivets in the longitudinal seams must be spaced 31" apart from center to center, anc[ the rows of same to be pitched 2 T 3 ^" apart from center to center, so as to give an efficiency of the joint of T 7 6 Q per cent of the solid plate. Transverse seams to be single riveted with same size rivets as those in the longitudinal seams pitched 2" apart from center to center. Care must be taken in punching and drilling holes that they may come fair in HANDBOOK ON ENGINEERING. 527 construction; the use of adrift-pin to bring blind, or partially blind holes in line will be sufficient cause for the rejection of the boiler. Calking* The edges of the plates to be planed and beveled before making up the boilers, and the calking to be done with round nose tools, pneumatically driven ; no split or wedge calk- ing will be allowed. Bracing. There must be 22 braces in the boiler, one inch area at least, be nine above the flues on the front head and nine similar ones on the back head, none of which shall be less than 3' 6" long, made of good refined iron and securely riveted to the heads ; the other end to be extended to the shell of boiler and riveted thereto with two J'' rivets. Care must be exercised in the setting of them, so they may bear uniform tension. There must be two braces below flues, one on each side of manhead, and riveted to the heads with two J" rivets. The back end of brace to be ex- tended backward to side of shell and riveted thereto by means of two J" rivets ; and two braces in back end above flues, one on each side and riveted the same as the other two below flues. Manholes* The boiler to have two manholes of the Hercules or Eclipse pattern, same to be of size 10" x 15", one located in front head, beneath the flues, and the other in rear head above the flues, and each to be provided with a lead gasket, grooved lid, two yokes and two bolts. The proportion of the whole to be such as will leave" it as strong as any other portion of the head of like area. Steam drum* The boiler must be provided with one steam drum 30" in diameter by 5' in length r shell plates of which are to be T y thick and heads |" thick, of the same quality of material as that in the boiler. The heads must be bumped to a radius so as to give as near as practicable equal strength as to that in the shell without bracing. The longitudinal seams of the drum are 528 HANDBOOK ON ENGINEERING. to be doubly riveted with ^" diameter rivets, pitched 2^" jipnrt from center to center, so as to give an efficiency of the joint of TO\ P er cen ^ ^ the solid plate. Manhole in drum. The drum must be provided with Her- cules or Eclipse Patented Manhole, same to be of size 10" x 15", located in the center of one head, and to be provided with a grooved lid, lead gasket, two yokes and two bolts. The propor- tion of the whole to be such as will leave it as strong as any other portion of the head of like area. To attach to boilers. The steam drum must be attached to the boiler by means of two flange steel connecting legs, 8" in diameter by 12" in length, and securely riveted to boiler and steam drum shell. Mud drum. Boiler must be provided with one mud drum 24" in diameter and of sufficient length so that each end may come flush with the outside of the boiler walls on each side ; the quality and thickness of steel to be the same as that specified for the steam drum, and all seams to be single riveted ; said mud drum to be provided with one Hercules or Eclipse Patent Manhole in one end, and to be of size 9" x 14", supplied with a grooved lid, lead gasket, two yokes and two bolts. To attach to boiler. The mud drum is to be attached to boiler by means of 8" diameter steel connecting leg, about 16" in length, properly riveted to boiler and mud drum shells. Flanges. The boiler to have one 8" wrought steel flange riv- eted on top of steam drum ; one wrought steel flange 4" in diam- eter, about 5 feet from front end of boiler for safety valve one 2" wrought steel flange on after end of boiler over the center of mud leg for supply pipe - all flanges to be threaded ; 2" hole in mud drum for blow-off ; also 2 1 J" holes, one on top of boiler and one on end near bottom of boiler for water column. Fusible plugs. To have two fusible plugs ; one inserted in shell from inside on second sheet, or about 5' from forwardend, 1 HANDBOOK ON ENGINEERING. inch above flues ; one plug inserted in top of flue, not more than three !;eet from after end. Trimmings* Furnish one 4" spring or dead weight safety valve, 4" diameter ; one water combination column ; provide same with two 1J" valves for the steam and water connections between the boiler and column, and one 1" valve for blow-pipe ; said blow- pipe to be connected with ashpit ; said combination barrel to be 4'' diameter, 18'' long, and made of cast-iron. Also, furnish one water gauge having a J" x 15" Scotch glass tube, bodies polished with wood wheels and guards, rods, bodies threaded " ; three gauge cocks " register pattern, polished brass bodies ; one steam gauge with 10" dial ; one 2" brass feed valve with 2" check valve ; one 2" globe valve for blow-off from m.ud drum ; also one asbestos packed stop-cock for same, so as to insure against the possibilities of a leak through the blow-pipe. Water column to have crosses in place of ells. Crosses to have brass plugs. Castings, grates, doors, etc* The boiler must be provided with a heavy three-quarter fire front of neat design, having double tiring and ashpit doors, anchor bolts for anchoring fire fronts in place, heavy deadplates, a full set of lire liners 0" deep for sup- porting firebrick on end, front and rear bearing bars ; a full set of ordinary grate bars 4 ft. long, soot door and frame for cleaning out rear ashpit ; a full set of skeleton arch plates ; 12 heavy buck staves 9 i' long, provided with tie rods, nuts and washers, heavy back stand with plate and expansion roJlers ; also furnish wrought plates to cover mud drum. Fire tools* Furnish in addition to above two sets of fire tools consisting of two pokers, two hoes, two slice-bars, two claws, and one six inch flue brush with j." pipe for handle. Breeching* Boiler must have a breeching fitted to front head and fastened thereto by means of bolts, stays and suitable pieces of angle iron, bent to conform to circle of boiler. The underside of breeching is to run across the head between the lower flues and 34 530 HANDBOOK ON ENGINEERING. the manhole, leaving the manhole freely exposed ; the siaes of breeching are to be made of T 3 " steel, the front and dooi> of J" steel ; said doors to be hung by means of strap hinges, rrovided with suitable fastenings so as to give free access to all flues when open. Uptake and damper* An uptake having an area of 1221 square inches must be fitted to top of breeching. vSaid uptake must be of convenient form for attaching to a stack 40" in diam- eter and provided with a close-fitting damper having a steel hand attachment, so that same may be operated convenient!}' from the boiler room floor. Smoke stack. There is to be provided for the above boiler one smoke stack 40" in diameter by 90 feet in height, half of which is to be made of No. 8, and the other half of No. 10 best black sheet steel throughout, and supplied with two sets of four guy rods, each consisting of f" galvanized wire cable guy strand with turn buckles for same. In general* The above-mentioned boiler must be made of strictly first-class material and workmanship throughout, and sub- jected to a hydrostatic pressure of 150 pounds to the square inch before leaving the works of the manufacture. Painting boiler breeching* Smoke stack and boiler front, steam and mud drum, and all trimmings, to have two good coats of coal tar. Masonry* Boiler to be set in good substantial masonry, of hard burned brick and good mortar, made of clean, sharp sand and fresh burned lime. Walls to be 18" thick. The outside walls to be laid up of selected hard burned brick, with close joints struck smooth and rubbed down. The sides, end and bridge walls, and boiler front, to have a foundation of 24" wide and 12' deep, laid in Portland cement. The ash pit to be paved with hard burned brick set on edge firmly, imbedded in Portland cement. For a distance of seven feet in front of the boiler and HANDBOOK ON ENGINEERING. 531 continuing across entire width of front of boiler setting to be paved with hard burned brick set on edge, firmly imbedded in sand. The walls to be carried up to the full height and a row- lock course of brick 4" thick to be carried over top of boiler from side wall to side wall, extending the whole length of boiler, and the entire arch to be plastered over on the outside with mortar. The bridge walls to be 24", carried up to within 6" of under side of boiler. The top of bridge wall to be of fire brick and made in the form of an inverted arch, conforming to the shell of the boiler. The space under boiler and back of bridge wall to the back end of boiler, to be filled in with earth or sand and the top paved with brick, and taper ing from bridge wall back to back end to 12" at back end, and in a similar form and shape, that is, inverted arch. The uptake for returning the smoke and heat at back end of boiler, to be arched over from rear wall against the back head of boiler 2" above the tubes, the arch being made of arch fire brick, and backed up with red brick. Furnace to be lined throughout with first quality fire brick, dipped in fire clay with close joints and fire brick rubbed to place, from a point 2" below grates, to where it safes in against boiler, and to be continued fire brick as far back as the rear end of setting and across rear end of same ; it being the intent that all interior surfaces of the setting with which the heat comes in contact, shall be faced with fire brick. Every sixth course to be a header course. Smoke connections* The connection from boiler to chimney to be made of No. 12 black iron, with cleaning door and damper in same. BANKING FIRES. Different engineers pursue different methods in banking fires. One method is to push the fire back one-third towards the bridge wall, and clean off the grate in front. Then shovel in from 150 to 300 Ibs. of fine coal on top of the fire, closing ash-pit doors 532 HANDBOOK ON ENGINEERING. and leaving furnace doors open, with damper open enough to let the gases escape. Others bank after this fashion but close all doors and air holes, leaving the damper partially open. Another method is to level the fire all over the grate, and shovel in from 150 to 500 Ibs. of fine coal, depending on the size of the grate, and then cover the whole surface with wet ashes to a good depth, so that no fire nor flame can be seen, then close the ash-pit doors, leaving the furnace doors ajar, and leave the damper partially open so that the gases may escape. In the morning, rake out the ashes, clean the fire, and throw in fresh coal. INSTRUCTIONS FOR BOILER ATTENDANTS. The following instructions apply more particularly to horizontal return tubular boilers, although in a general way they are appli- cable to all types of boilers. Never start a fire under a boiler until you are positively certain that there is sufficient water in the boiler, at least two gauges of water. Do not trust to the water gauge alone, but try the gauge cocks also, and try them at intervals during the day, be- cause the water-gauge pipe connections may be choked and cause a false water level. Before starting a fire be sure that the blow-off cock is closed and not leaking. Before it is time to start the engine, pump up three gauges of water, and blow off one gauge, in order to get rid of mud and other sediment. If the boiler has a surface blow-off, commonly called a ;; skimmer," blow off the scum before stopping the engine for the day. When the day's work is done, leave three gauges of water in the boiler, to allow for leakage and evaporation during the night. Never raise steam hurriedly. Sudden changes of temperature may produce fractures, or start leaks. HANDBOOK ON ENGINEERING. 533 In starting a iire in a furnace, a good plan is to cover the grate with a thin layer of coal and to place the shavings and wood on the coal and then light the shavings. The advantage of placing a covering of coal on the grate before the wood and shavings, is that it is a saving of fuel, as the heat that would be transmitted to the bars is absorbed by the coal, and the bars are also protected from the extreme heat of the fresh lire. Lift the safety-valve, if of the lever pattern, every morn- ing while raising steam, and satisfy yourself that it is in good working order, and that the pi is set at the proper point on the lever. The most disastrous explosions have occurred with boilers whose safety-valves had been stuck down or overloaded. Keep the boiler shell free of soot. Soot is a very good non- conductor of heat, and considered worse than scale inside of a boiler. Keep your boiler tubes free from soot and dust. Choked tubea impair the draft.' The tubes should be cleaned twice a week, or oftener. Soot collects also in a stack or chimney and in the connection between the" breeching "and stack, and interferes with the draft. Open your boiler every two weeks, or, as often as necessary, depending on the kind of feed-water used, and clean out the mud and scale. At the same time examine all of the stays, and see that they are taut and in good order. Also, look for pitting around the mud-drum connection, and for grooving in the side seams. Examine all outlets and pipe connections, and look for indications of " bagging " in the furnace sheets. Clean off the fusible plugs both inside and outside of the boiler. A fusible plug covered with soot on the fire side, and with scale on the water side, is no longer a " safety plug." Renew the filling in safety plugs, at least once a year. They are filled with pure Banca tin. 534 HANDBOOK ON ENGINEERING. Be perfectly satisfied that your boiler is in good condition internally before you close it up. Just as soon as you have fastened the man-head in its place, turn on the feed-water until you get at least three gauges of water. Fires have been built under empt}^ boilers, and will be again, if you forget to turn on the feed water after cleaning out. Do not empty a boiler while it is under steam pressure, but allow it to get cold before letting the water run out. If you are in a great hurry and can't wait for the boiler to cool down, nor for the- brickwork or anything else to cool down, draw the fire and open the furnace and ash-pit doors, then turn on the feed water, and from time to time blow out, until the steam gauge shows no pressure ; then shut .off the feed-water, raise the safety valve, open the blow-off cock, then open up the boiler. Before opening a man -hole, lift the safety-valve, so as to be sure that there is neither pressure nor vacuum in the boiler. Look well after the brick-work surrounding your boiler, and stop all cracks in tne walls with mortar or cement, as soon as discovered. They impede the draft, and cool the plates of the boiler, causing a waste of fuel. See that the bridge- wall is in perfect condition, because a gap in the bridge wall might cause a ' ' bag ' ' in the boiler by concen- trating the flames on one spot. Never allow any bare places on the grate, nor any accumulation of ashes, or dead coal in the corners of the furnace, as such places admit great quantities of cold air into the furnace, and render the combustion very imperfect. In firing with anthracite coal, do not poke and stir up the fire, as with soft coal, but let it alone. In firing soft slack coal, fire very lightly but frequently, carry- ing a thin fire. In firing 1 with soft lump coal, carry a thick fire, say from six to eight inches deep, according to the size of the furnace. HANDBOOK ON ENGINEERING. 535 In firing up, you may spread the fresh coal evenly all over the grate, or, you may push the live coals back towards the bridge- wall, leavings thin bed of live coals near the furnace doors, and spreading the fresh coal on top of it. This is called carrying a coking fire. Some prefer the one and some the other method of firing. In case you should find the water in the boiler out of sight, and a heavy fire in the furnace, don't get rattled, and don't lose your head. Open the furnace doors, and close the ash-pit doors, and cover the fire with wet ashes, or damp clay, completely smothering it. Let everything else alone, including the safety valve and the engine. Now wait until the boiler cools down and the gauge shows no pressure, then turn on the feed-water. On the other hand, if there is but very little fire in the furnace, you may draw the fire, instead of covering it with ashes or clay. If your boiler foams badly and you are uncertain as to the water level, stop the engine, and the true water level will show itself at once. If your boiler primes and water is carried over to the engine, it shows that there is want of sufficient steam room in the boiler. Either put a dry-pipe in the boiler, or, increase the steam pressure if the boiler will safely stand it. Never attempt to calk a leaky seam in a boiler under steam pressure, because the jar caused by the hammer blows might cause a rupture of the seam. Better to be on the safe side always when repairs are required in a steam boiler, and wait until the boiler is cold. The above applies to steam pipes and valve casings, also. Never open any steam valves suddenly, nor close them sud- denly either, because it is highly dangerous to do so, particularly if there is considerable water in the pipes. The effect is the same as water hammer in water pipes. Smoke is caused by too little air supply, or by the flames being 536 HANDBOOK ON ENGINEERING. prematurely cooled. Therefore, after firing up with fresh coal, it might be necessary to leave the furnace doors ajar in order to supply sufficient air above the fuel. Remember that it takes nearly 24 cubic feet of air for the proper combustion of one pound of soft coal. Hard coal does not require so much. Each and every boiler in a battery should have its own inde- pendent safety-valve and steam gauge. If you are obliged to force your fire, watch your furnace sheets for indications of " bagging," if the water space below the lowest row of tubes is cramped. Water-tube boilers are less liable to suffer from the effects of forced fires than shell boilers. With an intensely hot fire under a shell boiler, the furnace sheets are liable to bag, unless there is ample water space be- tween the shell of the boiler and the bottom row of tubes. The use of mineral oil to remove or prevent boiler scale, is not to be recommended.. Have your feed water analyzed, and use a scale preventer adapted to its requirements. By all means endeavor to secure a steady furnace temperature, and a steady steam pressure, for herein lies much economy of fuel. Fluctuations are wasteful. Put a damper in your chimney and adjust it to the needs of your furnace. Try to prevail on your employer to put in a shak- ing grate. It will enable you to carry a steady furnace temper- ature, and also enable you to keep the air spaces in your grate free and open without breaking up your fire. RULES AND PROBLEMS RELATING TO STEAM BOILERS. To find the safe working pressure : U. S* Rule. Multiply one-sixth (|) of the lowest tensile strength found, stamped on any plate in the cylindrical shell, HANDBOOK ON ENGINEERING. 537 by the thickness expressed in inches or parts of an inch of the thinnest plate in the same cylindrical shell, and divide by the radius or half diameter also expressed in inches and the result will be the pressure allowable per square inch of surface for single riveting ; to which add 20 per cent for double riveting, when all the holes have been " fairly drilled " and no part of such hole has been punched. . A. S. of M. E. Rule. First, find the tensile strength of the solid plate between the centers of two adjacent rivet "holes. Call this factor A. Next, find the tensile strength of the solid plate between the centers of two adjacent rivet holes, less the diameter of one rivet hole. Call this factor 13. Next, find the shearing strength of the rivets. Call this factor C. Now divide whichever is the smaller factor 13 or C by A, and the quotient will give the strength of the joint as compared with the solid plate expressed as a percentage. Then multiply the tensile strength of the plates by the thickness of plates in frac- tional parts of an inch and multiply this product by the per- centage as found above, and divide this last product by the radius of the shell in inches, and the quotient will be the bursting pressure. Divide this quotient by the factor of safety and the result will give the safe working pressure. Example* What is the safe working pressure for a steel boiler 60 inches in diameter, with side seams double riveted, tensile strength" of plates 60,000 Ibs. per sqr. in., thickness of plate | inch. Diameter of rivet holes f inch, pitch of rivets 3J inches, shearing strength of rivets 38,000 Ibs. per sqr. in., and factor of safety 5 ? Ans. By U. S. rule, 150 Ibs. per sqr. in. By A. S. of M. E. rule, 106^ Ibs. per. sqr. in. 538 HANDBOOK ON ENGINEERING. Operation by U. S. rule: 60,000 -~- = 10,000. And, 10,000 X | = 3750. 3750 And, -gjj- = 125. And, 125 X .20 =25. Then, 125 +.25 = 150. Operation by A. S. of M. E. rule: f" = .375". #" = .9375". Then, 60,000 X 3J X .375 73,125 Ibs., the strength of the solid plate between the centers of two adjacent rivet holes. Call this factor A. Also, 3J = 3.25. Then, 3.25 .9375 = 2.3125. And, 60,000 X 2.3125 X .37552,031.25 Ibs. the strength of the plate between-two adjacent rivet holes. Call this facto.r B. Then, .9375 X -9375 X .7854 = .69029 of a square inch, the area of one rivet hole. There are two rows of rivets. Then, .69029 X 2 = 1.38058 sqr. ins. the area of two rivet holes combined. Then, 38,000 X 1.38058 =52,462.04 Ibs., the resistance of rivets to shearing. Call this G. Now since B is less than (7, divide 52,031.25 by 73,125 and get as a quotient .71 + , thus showing the strength of "the joint to be more than 71 per cent of the strength of the solid plates. Then, 60.000 X. 875 X. 71 _ M9K ^ per sqr< fa>| the 30 bursting pressure. And, 582 ' 5 = 106.5 Ibs. per sqr. in., the safe working 5 pressure. HANDBOOK ON ENGINEERING. 539 To find the horse power of a horizontal return tubular boiler, from its heating surface : Rule* Find the heating surface in square feet, of the shell of the boiler, measuring from one fire line to the other. Next find the internal heating surface of all the tubes in square feet. Add the two results together and divide their sum by 12, and the quotient will be the H. P. approximately. The heads are omitted. Example* What is the H. P. of a horizontal return tubular boiler 60 inches in diameter and 20 feet long, with 44 four-inch tubes each 20 feet long, the distance from fire line to fire line being 9 feet? Ans. 86.65 H. P. Operation* The internal diameter of a 4-inch tube is 3.732 inches. Then, 20 X 9 = 180 square feet of heating surface in the shell. And, 8 ' 782 X 3 ' 1416 -B .9770376 ft., the circumference of 12 one tube in feet. And, .9770376 X 20 X 44 = 859.793 -f sqr. ft., the total heating, surface of the tubes. Then, 180+859.793 = 86.65 nearly. 12 To find the factor of evaporation : Rule* From the total number of heat units in one pound of steam at the given pressure, subtract the number of heat units in one pound of the feed water at its given temperature, and divide the remainder by 965.7, which is a constant. Example* A boiler evaporates 6,000 Ibs. of water per hour from feed-water at 210 degrees into steam at 125 Ibs. gauge pres- 540 HANDBOOK ON ENGINEERING. sure, what is the equivalent evaporation ''from and at," and what is the H. P. of the boiler? . Ans. Equiv. evap. 6276 Ibs. H. P. 182, nearly. Operation* The total number of heat units in steam at 125 Ibs. per sqr. in. gauge pressue is 1221.5351. The number of heat units in feed-water at 210 degrees equals 210.874. The latent heat of steam at atmospheric pres- sure, equals 965.7. Then, 1221.5351 210.874 = 1010.6611. And, 1 >1Q - 6 ^ 11 = 1.046, the factor of evaporation. And, 6000 X 1-046 = 6276 the equivalent evaporation. Then, = 181.9 H. P. ' 34.5 To find how many pounds of steam at a given absolute pressure will flow through an orifice of one square inch area in one sec- ond : Rule. Divide the absolute pressure by the constant number 70. Example. How many pounds of steam at 85 Ibs. per sqr. in. gauge pressure, will flow through an orifice one inch in diameter, in one second ? Ans. 1.122 Ibs. Operation* A hole 1 inch in diameter has an area of .7854 of a sqr. inch. And 85 + 15 =100 Ibs. absolute. 100 X .7854 Then, --- ^ -=1.122. The weight of a cubic foot of steam at 100 Ibs. per sqr. in. 1.122 absolute pressure is .2307 of a pound. Then, -3307 == 4t86 cubic feet. HANDBOOK ON ENGINEERING. 541 To find the width of a reinforcing ring for a round hole in a flat surface, when the ring must contain as many square inches as were cut out of the plate, and when the ring and the plate are of the same thickness : Rule* Find the area of the hole in square inches and multi- ply it by 2. Divide this product by .7854 and extract the square root of the quotient for the diameter of the ring over all. Sub- tract the diameter of the hole from the diameter over all, and divide the remainder by 2 for the width of the ring. Example* What should be the width of a reinforcing ring for a hole 10 inches in diameter, the metal cut out, and the metal in the ring being | in. thick? Ans. 2 T *g- inches. Operation. 10 X 10 X .7854 = 78.54 sqr. ins. area of hole. And, 78.54 X 2 = 157.08 sqr. ins. in both hole and ring. 157.08 And < And, V 200: ^ 14 - 142 +- And, 14.14210=4.142. 4.142 Then, ^ = 2.071" or practically To find the width of a reinforcing ring for an elliptical manhole in a flat surface, when the ring must contain as many square inches as are contained in the hole, and the metal cut out and metal in the ring are of the same thickness : Rule* Square the short diameter of the hole and add to it six times the short diameter multipled by the long diameter, and to this product add the square of the long diameter, and extract the square root of the sum. From this root subtract the sum of the short diameter added to the long diameter, and divide the re- mainder by 4 for the width of the ring. Example. What should be the width of a reinforcing ring for a manhole 11" X 15"? Ans. 2 inches. 542 HANDBOOK ON ENGINEERING. Operation. 11" X H" = 121. And, 11 X 15 X 6 =990. And, 15 X 15 = 225. Then, 121 + 990 + 225 = 1336. And, V 1336 = 36.551. And, 11 + 15 = 26. Then, 36.551 26 = 10.551. 10.551 And, T =2.637 -f- ins. the width of the ring, or, prac- tically 2iJ ins. Then, 2.637X2=5.274". And, 11 + 5.274 = 16.274" short diameter of ring over all. And, 15 -f 5.274 = 20.274" long diameter over all. Proof: 20.274 X 16.274 X .7854= 259.13 + square inches area of hole and ring. And, 15 X 11 X .'7854 = 129.59 + sqr. ins. area of hole alone. Then, 259.13129.59 = 129.54. THE AHOUNT OF STEAM USED WITH VALVE OPEN WIDE, WITH STEAH JETS AS A SMOKE PREVENTIVE. STEAM JETS. Given two boilers with separate furnaces, having 4 steam jets in each furnace, and each jet T \ inch in diameter, the steam pres- sure being 100 Ibs. per sqr. inch by the gauge. How many pounds of steam at this pressure will flow through the 8 nozzles in 12 hours? Answer. 1739 Ibs. nearly. Operation : T V" = .0625 ". Then, .0625 X -0625 X .7854 = .003067968750 sqr. inch, area of 1 jet. HANDBOOK ON ENGINEERING. 543 And, .003067968750 X 8 == .02454375 sqr. inch, the com- bined area of 8 jets. Also, 100 + 15 = 115 Ibs. per sqr. inch, the absolute steam pressure . And, = 1.64 Ibs. of steam per second that will flow 70 through an orifice of 1 square inch area. Then, 1.64 X .02454375 = .04025175 Ibs. of steamier second flowing through the 8 jets. Again: There are 43,200 seconds in 12 hours. Thus: 12X60X60^43,200. Then, .04025175 X 43,200 = 1738.8756 Ibs. of steam will flow through 8 jets in 12 hours' time. Taking a high speed automatic cut-off engine using 20 Ibs. of steam per H. P. per hour, the 8 steam jets would waste enough steam in 12 hours to run A 10 H. P. engine for 8% hours. A 20 " " " 4J- " A 40 " " " 2J * An 80 " " " 1J*. ' Thus^lO X- 20 = 200. -, 1739 And. _ = 81 nearly. 200 20 X 20 = 400. 1739 ' 4QO~ * n y ' 80 X 20 = 1600. 544 HANDBOOK ON ENGINEERING THE STEAM PUMP. CHAPTER XIX The Worthington Compound Pump. THE WORTHINGTON COMPOUND PUMP. In the arrangement of steam cylinders here employed, the steam is used expansively, which cannot be done in the ordinary form. Having exerted its force through one stroke upon the smaller steam piston, it expands upon the larger during the return stroke, and operates to drive the piston in the other direction. This is, in effect, the same thing as using a cut-off on a crank engine, only with the great advantage of uniform and steady action upon the water. HANDBOOK ON ICNGINEERING. 545 Compound cylinders are recommended in any service where the saving of fuel is an important consideration. In such cases, their greater first cost is fully justified, as they require 30 to 33 per cent less coal than any high-pressure form on the same work. The above illustration is a sectional view of the Worthington Compound Pump This cut shows the steam valves properly set. On the larger sizes, a condensing apparatus is often added, thus securing the highest economical results. Any of the ordinary forms of steam pumps can be fitted with compound cylinders. It should be remembered that, as the compounds use less steam their boilers may be reduced materially incize and cost, compared with those required by the high-pressure form. This principle of expansion without condensation cannot be used with advantage wnere the steam pressure is below 75 Ibs. 35 546 HANDBOOK ON ENGINEERING The Deane Pump. The above is a~ sectional view of the DEANE DIRECT ACTING STEAM PUMP. The operation of the steam valves* In the Deane Steam Pump a rotary motion is not developed by means of which an HANDBOOK ON ENGINEERING. 547 eccentric cnn be made to operate the valve. It is, therefore, necessary to reverse the piston by an impulse derived from itself at the end of each stroke. This cannot be effected in an ordinary single-valve engine, as the valve would be moved only to the cen- ter of- its motion, and then the whole machine would stop. To overcome this difficulty, a small steam piston is provided to move the main valve of the engine. In the Deane Steam Pump, the lever 90, which is carried by the piston rod, comes in contact This cut shows the valves properly set. with the tappet when near the end of its motion, and by means of the valve-rod 24, moves the small slide-valve which operates the supplemental piston 9. The supplemental piston, carrying with it the main valve, is thus driven over by steam and the engine reversed. If, however, the supplemental piston fails accidentally to be moved, or to be moved with sufficient prompt- ness by steam, the lug on the valve-rod engages with it and compels its motion by power derived from the main engine. 548 HANDBOOK ON ENGINEERING, ' SECTIONAL VIEW OF CAMERON" STEAM PUMP The above is a sectional view of the steam end of a Cameron pump. Explanation: A. is the steam cylinder ; (7, the piston ; D, the piston rod ; Z/, the- steam chest; F, the chest piston or plunger, the right-hand end of which is shown in section ; 6r, the slide valve ; H, a starting bar connected with a handle on the outside ; II are reversing valves ; TT/rare the bonnets over reversing valve chambers ; and E E are exhaust ports leading from the ends of steam chest direct to the main exhaust, and closed by the revers- ing valve II; Nis the body piece connecting the steam and wau>v HANDBOOK ON ENGINEERING. 549 Operation of the Cameron Pump: Steam is admitted to the steam chest, and through small holes in the ends of the plunger; F fills the spaces at the ends and the ports E E as far as the reversing valves //; with the plunger F and slide valve G in position to the right (as shown in cut), steam would be admitted to the right-hand end of the steam cylinder -A, and the piston C would be moved to the left. When it reaches the reversing valve I it opens it and exhausts the space at the left-hand end of the plunger F, through the passage E ; the expansion of steam at the right-hand end changes the position of the plunger F, and with it the slide valve G, and the motion of the piston C is instantly reversed. The operation repeated makes the motion continuous. In its movements, the plunger F acts as a slide valve to shut off the ports E E, and is cushioned on the confined steam between the ports and steam chest cover. The reversing valves / / are closed immediately the piston C leaves them , by pressure of steam on their outer ends, conveyed direct from the steam chest. Operation. Supposing the steam piston C moving from right to left: When it reaches the reversing valve I it opens it and exhausts the space on the left-hand end of the plunger F, through the passage E, which leads to the exhaust pipe ; the greater pres- sure inside of the steam chest changes the position of the plunger F and slide valve G, and the motion of the piston C is instantly reversed. The same operation repeated at each stroke makes the motion continuous. The reversing valves //are closed by a pres- sure of steam on their large ends, conveyed by an unseen passage direct from the steam chest. When a pump is first connected, remove the bonnets K K and valves / / and blow steam through to remove any dirt, oil or gum that may be lodged in the steam ports. Take valve F, valve G and // out and wipe off with clean waste, and then oil and put back. Then see that the pack- ing is not too tight. When a Cameron pump has been run a long time, the plunger F becomes worn and leaks enough steam tQ 550 HANDBOOK ON ENGINEERING. cause the valve F to become balanced. The effect of this is, the pump will remain on the end ; to overcome this, take out plunger F, or piston, as it is called by some, and drill the little hole that you will find in the ends of same a little larger, say about one- fourth larger ; that will increase the pressure on both ends of plunger F ' ; as soon as the piston comes in contact Avith valve 1 the steam is exhausted to exhaust pipe. 30-* The above is a sectional cut of THE KNOWLES DIRECT ACTING STEAH PUMP. Explanation of steam valves, etc. The Knowles, in fact, all first-class direct acting steam pumps, is absolutely free from what is termed a " dead center," when in first-class order. This feature in the Knowles Pump is secured by a very simple and ingenious mechanical arrangement, i. e., by the use of an auxiliary piston which works in the steam chest and drives the main valve. This auxiliary or " chest piston," as it is called, is driven backward and forward by the pressure of steam, carrying HANDBOOK ON ENGINEERING. 551 with it the main valve, which valve, in turn, gives steam to the main steam piston that operates the pump. This main valve is a plain slide valve of the B form, working on a Hat seat. The chest piston is slightly rotated by the valve motion ; this rotative move- ment places the small steam ports, I), E, F (which are located in The Knowles Direct Acting Steam Pump. the under side of the said chest piston), in proper contact with corresponding ports A B cut in the steam chest No. 31. The steam entering through the port at one end: and filling the space between the chest piston and the head, drives the said piston to the end of its stroke and, as before mentioned, carries the main slide valve with it. When the chest piston has traveled a certain distance, a port on the opposite end is uncovered and steam there enters, stopping its further travel by giving it the necessary 552 HANDBOOK ON ENGINEERING. cushion. In other words, when the rotation motion is given to the auxiliary or valve driving piston by the mechanism outside, it opens the port to steam admission on one end, and at the same time opens the port on the other end to the exhaust. 'is This cut shows the valves properly set. Operation of the Knowles Pump is as follows : The piston rod, with the tappet arm, moves backward and forward from the impulse given by the steam piston. At the lower part of this tappet arm is attached a stud or bolt, on which there is a friction roller. This roller coming in contact with the " rocker bar" at the end of each stroke, operates the latter. The motion given the " rocker bar " is transmitted to the valve rod by means of the connection between, causing the valve rod to partially rotate. This action, as mentioned above, operates the chest piston, which carries with it the main slide valve, the said valve giving steam to the main piston. The operation of the pump is complete and HANDBOOK ON ENGINEERING. 553 continuous. The upper end of the tappet arm does not come in contact with the tappets on the valve rod, unless the steam pres- sure from any cause, should fail to move the chest piston, in which case the tappet arm moves it mechanically. NOTICE. 1. Should the pump run longer stroke one way than the other, simply lengthen or shorten the rocker connection (part 25) so that rocker bar (part 23) will touch rocker roller (20) equally distant from center (22). 2. Should a pump hesitate in making its return stroke, it is be- cause rocker roller (20) is too low and does not come in contact with the rocker bar (23) soon enough. To raise it, take out rocker roller stud (20 A), give the set screw in this stud a suffi- cient downward turn, and the stud with its roller may at once be raised to proper height. o. Should valve rod (77) ever have a tendency to tremble, slightly tighten up the valve rod stuffing box nut (28). When the valve motion is properly adjusted, tappet tip (16) should not quite touch collar (15) and clamp (27). Rocker roller (20), coming in contact with rocker bar (23) will reverse the stroke. Operation and construction of the HOOKER DIRECT-ACTING STEAM=PUMP. The parts being in position, as shown, the steam on being ad- mitted to the center of the valve chamber, brings its pressure to bear on the main and supplemental flat slide valve 4 and 7, and also within the recess in the center of the supplemental piston 6. The recess incloses the main valve 4, so that this valve will move with the supplemental piston whenever the steam is supplied to 554 HANDBOOK ON ENGINEERING. and exhausted from each end of this piston. The live steam passes through the left-hand ports A 1 U 1 , driving the main piston 2 to the right, and the exhaust passes out through the right-hand ports A and C under the cavity in the main valve 4 to the atmos- phere. As the main piston nears the right hand port, the valve lever 13, which is attached to the piston rod 3, brings the dog 1 7, in plate 16, in contact with the valve arm _Z, and moves the sup- plemental valve 7 to the right, thus supplying live steam to the right of the supplemental piston 6', and exhausting from the left through the ports e e. As the supplemental piston incloses the main valve, this valve is carried with it to the left. Steam now enters the right-hand ports A B and is exhausted from the left- hand main port A. The engine commences its return stroke and the operation just described becomes continuous. As the main piston (2) closes the main port (A) to the right, it is arrested on compressed exhaust steam. The main valve 4 having closed the auxiliary ports (B) leading to that end of the main cylinder, the HANDBOOK ON ENGINEERING. 555 This cut shows the steam valves properly set. steam being supplied through both the main and auxiliary ports, but released through the main ports only. BLAKE STEAM PUHP. Description of the Blake Steam Pump* The Blake Steam Pump is absolutely positive in its action ; that is to say, the operation at the slowest speed under any pressure, is perfectly continuous, and the pump is never liable to stop as the main valve passes its center, if the pump is in good order. An ingenious and simple arrangement is used in the Blake Pump to overcome the " dead center," as will be seen from the engravings. Operation of the Blake Steam Pump* The main or pump driving piston A could not be made to work slowly were the main valve to derive its movement solely from this piston ; for 556 HANDBOOK ON ENGINEERING. when this valve had reached the center of its stroke, in which position the ports leading to the main cylinder would be closed, The Blake Steam rump. no steam could enter the cylinder to act on said piston, con- sequently, the latter would come to rest, since its momentum would be insufficient to keep it in motion, and the main valve would remain in its central position or kt dead cen- ter." To shift this valve from its central position and admit steam in front of the main piston (whereby the motion of the piston is reversed and its action continued), some agent independent of the main piston must be used. In the Blake Pump, this independent agent is the supplemental or valve-driving piston B. The main valve, which controls the admission of steam to, and the escape of steam from, the main cylinder, is divided into two parts, one of which, (7, slides upon a seat on the main cylinder, and, at the same time, affords a seat for the other part, HANDBOOK ON ENGINEERING. 557 D, which slides upon the upper face of C. As shown in the en- graving, D is at the left-hand end of its stroke, and C at the opposite, or right-hand end of its stroke. Steam from the steam- chest J is, therefore, entering the right-hand end of the main cylinder through the ports E and //, and the exhaust is escap- ing through the ports H l and E 1 , K and M, which causes the Sectional views of steam cylinder, valves, etc., of the Blake Steam Pump. main piston A to move from right to left. When this piston has nearly reached the left-hand end of its cylinder the valve motion 558 HANDBOOK ON ENGINEERING. (not shown) moves the valve-rod 7 J , and this causes C, together with its supplemental valve 11 and S 8 1 (which form, with (1, one casting) to be moved from right to left. This movement causes steam to be admitted to the left-hand end of the supplemental cylinder, whereby its piston 11 will be forced toward the right, carrying D with it to the opposite or right-hand end of its stroke ; for the movement of /S y closes N (the steam port leading to the This cut shows the valves properly set. right-hand end), and the movement of S 1 opens N l (the port leading to the opposite, or left-hand end). At the same time the movement of opens the right-hand end of the cylinder to the exhaust through the exhaust ports X and Z. The ports C and D now have positions opposite to those shown in the engrav- ings, and steam is, therefore, entering the main cylinder through the ports E l and H l , and escaping through the ports //, E, K and Jf, which will cause the main piston A to move in the op- HANDBOOK ON ENGINEERING. 559 posite dhvction, or from left to right, and operations similar to those already described will follow, when the piston approaches the right-hand end of its cylinder. By this simple arrangement the pump is rendered positive in its action ; that is, it will in- stantly start and continue working the moment steam is admitted to the steam chest. The main piston A cannot strike the head of the cylinder, for the main valve has a head ; or, in other words, steam is always admitted in front of said piston just before it reaches either end of its cylinder, even should the supplemental piston B be tardy in its action and remain with D at that end, toward which the piston A is moving ; for C would be moved far enough to open the steam port leading to the main cylinder, since the possible travel of C is greater than that of D. The supple- mental piston B cannot strike the heads of its cylinders, for in its alternate passage beyond the exhaust ports X and X, it cushions on the vapor intrapped in the ends' of this cylinder. MISCELLANEOUS PUHP QUESTIONS. Q. What is a pump? A. It is hard to get a definition that will cover the whole ground. A pump may be said to be a mechanical contrivance for raising or transferring fluids ; and as a general thing consists of a moving piece working in a cylinder or other cavity ; the device having valves for admitting or retaining the fluids. Q. What two classes of operations are included in the term "raising" fluids? A. They may be raised by drafting or suc- tion, from their level to that of the pump ; they may be raised from the level of the pump to a higher level. Q. Do pumps always "raise" by either method, from one level to a higher one, the liquid which they transfer? A. No ; in many cases the liquid flows by gravity to the pump ; and in some it is delivered at a lower level than that at which it is received. 560 HANDBOOK ON ENGINEERING. Q. Where a pump is not used for raising a liquid to a higher level, for what is it generally used? A. To increase or decrease its pressure. Q. What classes of liquids are handled by pumps ? A. Air, ammonia, lighting gas, oxygen, etc. Q. Name some liquids which are handled by pumps? A. Water, brine, beer, tan liquor, molasses, acids and oils. Q. Where it is not specified whether a pump is for gas or for liquid, which is generally understood? A. Liquid. Q. What gas is most frequently pumped? A. Air. Q. What liquid is generally understood if none other is speci- fied for a pump? A. Water. Q. Can pumps handle. hot and cold liquids? A. Yes; though cold are easier handled than hot. Q. What is the difference between a fluid and a liquid? A. Every liquid is a fluid ; every fluid is not a liquid. Air is a fluid ; water is both a fluid . and a liquid. Every liquid can be poured from one vessel to another. SUCTION. Q. What causes the water to rise in a pump by so-called suction? A. The unbalanced pressure of the air upon the surface of the liquid below the pump, forces the water up into the suction pipe when the piston is withdrawn from the liquid. Q. How much is the pressure of the atmosphere ? A. At the sea level about 14.71bs. per square inch, or 2116.8 Ibs. per square foot. Q. In what direction is this pressure exerted ? A. In every direction equally. Q. What tends to prevent the water from being lifted? A. The force of gravity, which is the result of the attraction of the earth's center. HANDBOOK ON ENGINEERING. 5 HI Q. In what direction does the force of gravity act? A. In radial lines towards the center of the earth. Q. With what force does this gravity act? A. That depends upon the substance upon which it is acting. Q. Why do you refer to the level of the sea in speaking of the pressure of the air and the weight of water? A. Because the air pressure becomes less as, in rising above the sea level, we recede from the center of the earth, and the weight of a given quantity of water or any other substance becomes less than it is at the level of the sea, as we approach to or recede from the center of the earth. Q. How is it that the weight of any substance becomes less if you go either above or below the sea level? A. The farther you go from the earth, the less its attraction and the less a given body will weigh upon a spring balance. The farther down into the earth you go, the nearer you get to the center of the earth, at which, there being attraction upon all sides, any body would weigh nothing. Going from the surface of the earth towards its center, then, a body weighs less and less upon a spring balance. Q. Why do you specify a spring balance? A. Because in weighing by counterpoise, both the body to be weighed and the counterpoise by which it is weighed, would change their weights in the same proportion, as the position with regard to the center of the earth was changed. Q. What are the causes which principally prevent pumps from lifting up to the normal maximum? A. Friction ; leakage of air into the suction, chokes in the suction pipe. Q. Can a liquid be "drafted" without the expenditure of work ? A. No ; in drafting a liquid to the full height to which it can be drafted, at least as much power must be expended as, would lift the same weight of liquid that height by any mechan- ical means ; only the amounts of friction being different. Q. Then what advantage is there in having a pump draft its 36 562 HANDBOOK ON ENGINEERING. water to the fall possible height, over having it force the water the full height? A. Convenience in having the pump higher up. Q. Can a pump throw water higher or farther, with a given expenditure of power, where it flows in, than where it must draft its water? A. Yes; on the same principle that it can throw farther or force harder when the water is forced to its suction side than where it merely flows in. Q. What is the use of the suction chamber? A. To enable the pump barrel to fill where the speed is high; to prevent pounding, when the pump reverses. Q. Upon what does the lifting capacity of a pump depend? A. When the pump is in good order its lifting capacity depends mainly upon the proportion of clearance in the cylinder and valve chamber to the displacement of the piston and plunger. Q. Which will lift further, an ordinary piston pattern pump or a plunger pump? And why? A. Other things being as nearly equal as they can be made between these two pumps, the piston pump will lift the farther of the two, because the plunger pump has the most clearance. Q. What is the advantage of the suction chamber? A. To assist the pump in drafting, especially at high speed. Q. What is the advantage of the air chamber? A. To make the stream steady. Q. What difficulty is v sometimes met with in using an air chamber? A. Where the pressure is very great sometimes the air is absorbed by the water, and thus the cushion is detroyed. FORCING. Q. What will be the volume of the air in the air chamber of a force pump, when the pump is forcing against a head of 67.6 feet? A. It will be reduced to half its ordinary volume, because it will be at the pressure of two atmospheres. HANDBOOK OX ENGINEERING. 563 The above cut shows a pump with a removable cylinder or liner, and is packed with fibrous packing set out by adjustable set screws and nuts. This style of a pump is the best for small water-works or elevators, or where a pump is used where the water is muddy or sandy. To find the horse power necessary to elevate water to a given height : Multiply the total weight of the water in pounds by the height in feet and divide the product by 33,000 (an allow- ance of 25 per cent should be added for water friction, and a further allowance of 25 per cent for loss in steam cylinder.) The heights to which pumps will force water when running at 564 HANDBOOK ON ENGINEERING. 100 feet piston speed per minute, and the suction and discharge pipes being of moderate length, will be found by dividing the area of the steam piston by the area of the water piston, and multi- plying the quotient by the steam pressure. Deduct 40 per cent for friction and divide the remainder by .434. Example* To what height will an 8-inch steam piston, with a 5-inch water piston, force water, the steam pressure being 80 Ibs. by gauge? .Ans. 283 ft. nearly. Operation. Area of steam piston = 50. 2G sq. ins. ' 4 " water " 19.63 " " Then, ^ = 2.56. And 2.50 X 80 = 204.80 Ibs. iy.63 , Then, 204.80 less 40% = 122.88 Ibs. 1 22 HH And, ' = 283 -f feet. An allowance must be made where long pipes are used. The normal speed of pumps is taken at 100 piston feet per minute, which speed can be considerably increased if desired. For feeding 1 boilers, a speed of 25 to 50 piston feet per minute is most desirable. A gallon of water, U. S. Standard, weighs 8 Ibs. and contains 231 cubic inches. A cubic foot of water weighs 62.425 Ibs. and contains 1,728 cubic inches, or 7J gallons. Doubling the diameter of a pipe increases its capacity four times. Friction of liquids in pipes increases as the square of the velocity. To find the area of a piston, square the diameter and multiply by .7854. HANDBOOK ON ENGINEERING. 565 Boilers require, for eacli nominal horse-power, about one cubic foot of feed water per hour. In calculating horse power of tubular or flue boilers, consider 15 square feet of heating surface equivalent to one nominal horse- power. To find the pressure in pounds per square inch of a column of water, multiply the height of a column in feet by .434. Approximately, we say that every foot of elevation is equal to one-half Ib. pressure per square inch ; this allows for ordinary friction. The area of the steam piston, multiplied by the steam pressure, gives the total amount of pressure that can be exerted. The area of the water piston, multiplied by the pressure of water per square inch, gives the resistance. A margin must be made between the power and the resistance to move the pistons at the required speed say from 20 to 40 per cent, according to speed and other conditions. To find the capacity of a cylinder in gallons : Multiplying the area in inches by the length of stroke in inches will give the total number of cubic inches ; divide this amount by 231 (which is the cubical contents of a gallon of water) and quotient is the capacity in gallons. To find quantity of water elevated in one minute running at 100 feet of piston speed per minute : Square the diameter of water cylinder in inches and multiply by 4. Example: Capacity of a five-inch cylinder is desired. The square of the diameter (5 inches) is 25, which, multiplied by 4, gives 100, which is gallons per minute, approximately. Q. " What is the reason that a steam pump of the horizontal double acting type should throw an intermitting stream under pressure, like the stream from milking a cow, only not quite so bad as that? 1 have tried valves of different sizes, with different amount of rise, springs or valves of different tension, different 566 HANDBOOK ON ENGINEERING. kinds of packing in water piston, .and different sized water ports or passages, without any apparent difference." A. Steam pumps of the horizontal double-acting type are not alone in throwing an intermitting stream. The same thing shows up in vertical single- acting pumps ; and all horizontal double-acting pumps do not so behave. The steam fire engine shows that no type of pump is exempt from ' squirting/' Q. How may this squirting be lessened? A. By increasing the suction valve area ; by giving more suction chamber and more air chamber. ##'* * * * * # * Q. What is a sinking pump? A. One which can be raised and lowered conveniently, for pumping out drowned mines, etc, Q. Into what main general classes may reciprocating cylinder pumps be divided? A. Into single acting and double acting. Q. What is a single acting reciprocating pump? A. One in which each reciprocation or single stroke in one direction causes one influx of fluid, and each reciprocation or single stroke in the opposite direction causes one discharge of fluid. In other words, the pump, as regards its action, is single ended. Q. What is a double acting reciprocating pump? A. One in which each end acts alternately for suction and discharge. Re- ciprocation of the piston in one direction causes an influx of fluid into one end of the pump from the source, and a discharge of fluid at the opposite end ; on the return stroke the former suction end becomes the discharge end. In other words, the pump is double ended in its action ; or is ' l double-acting." Q. What is the special advantage of having double-acting pump cylinders? A. The column of water is kept in motion more constantly, and hence there is less jar ; smaller pipes may be used. **# * * * * * * * N .$ Q. How may those pumps which are driven by steam against a HANDBOOK ON ENGINEERING. 567 steam piston be divided ? A. Into those which have a fly wheel and those which have no fly wheel. Q. Into what classes may those pumps which are driven by steam, without a flywheel, be divided? A. Into direct acting and duplex. Q. What is the advantage of a fly wheel steam pump? A. Steadiness of action ; the capability of using the steam expan- sively. Q. What are the disadvantages of fly wheel pumps? A. Great weight ; inability to run them very slowly without gearing down from the fly wheel shaft, as the wheel must run comparatively rapidly. Q. What is a direct-acting steam pump? A. One in which there is no rotary motion, the piston being reversed by an impulse derived from itself at or near the end of each stroke. There is but one steam cylinder for one water cylinder ; the valve motion of the steam cylinder being controlled by the action of the steam in that cylinder. HOW TO SET THE STEAfl VALVES ON A DUPLEX PUMP. The steam valves on Duplex pumps generally have no outside lap, consequently, when in its central position, it just covers the steam ports leading to the opposite ends of cylinder. By lost motion is meant, the distance a valve-rod travels before moving the valve; if the steam-chest cover is off the amount of lost motion is shown by the distance the valve can be moved back and forth before coming in contact with the valve- rod nut. The object of lost motion is to allow one pump to almost complete its stroke before moving the valve of its fellow engine. As the steam piston is nearing the end of its stroke, it moves the valve of its fellow engine, admitting steam and start- ing its fellow engine as it lays down its own work ; in other words, 568 HANDBOOK ON ENGINEERING. the other picks it up. The amount of lost motion required is enough to allow each piston to complete its stroke ; in other words, if there was no lost motion, as each piston would pass the center of their travel, they would move the valve of their fellow engine, and the result would be a very short stroke. This cut shows the steam valves properly set. To set the steam valves, move the steam piston towards the steam cylinder head until it comes in contact with the head ; mark with a scribe on the piston-rod at the face of the stuffing-box follower on steam end ; then move the piston to its contact stroke on the opposite end and make another mark on the piston-rod, exactly half way between the face of the stuffing-box follower on the steam end, and the first mark. Then move the piston back until the middle mark is at the face of piston-rod stuffing-box follower on the pump end. This operation brings the piston exactly in the middle of the stroke. Then take off the steam HANDBOOK ON ENGINEERING. f)69 chest cover, place the slide-valve in the center, exactly over the steam ports. Place the slide-valve nut in exact center between the jaws of the slide-valve, screw the valve-rod through the nut until the eye on the valve-rod head comes in line with the eye of the valve-rod link ; slip the valve-rod head pin through head and the valve is set. Repeat the same operation on the other side of the pump. Where a pump is fitted with four hexagon valve-rod nuts, two either end of the slide-valve, instead of one nut in the center of the valve, set and lock these hexagon nuts at equal dis- tances from the outer end of the slide-valve jaws, allowing a little lost motion, varying from J" on high-pressure pumps, to, say, J" on low service pumps, on each side of valve ; if the steam piston hits the head, take up some of your lost motion ; if the steam piston should not make a full stroke, give more lost motion. THE BEST MANNER OF ARRANGING PIPE CONNECTIONS. For the purpose of showing good arrangement, the following cut is presented. On long lifts it is necessary to provide the suction pipe S with a foot-valve F. By the use of a foot-valve, the pipe and cylinders are constantly kept charged with water, allowing the pump to start without having to free itself and the suction pipe of air. In case of a long lift, the vacuum chamber V is also essential. This may be readily constructed by using a tee in place of the elbow E, extending the suction pipe and placing a cap upon the top. In order to keep the water back when the pump is being examined or repaired, a gate valve should be placed in the delivery pipe. It sometimes happens that, either purposely or through a leak in the foot-valve, the suction chamber becomes empty. For the purpose of charging the suction pipe and cylin- der a " charging pipe " P is placed outside the check valve, connecting the delivery pipe D with the suction. In order that 570 HANDBOOK ON EX(! INHERING. the pump, in starting, may free itself of air, a check valve (7 and a " starting pipe" A should be provided. This pipe may be ARRANGEMENT OF PIPE CONNECTIONS. led to any convenient place of discharge. After the pump has started, the valve in the starting pipe should be closed gradually. Faulty connections are generally the cause of the improper action HANDBOOK ON ENGINEERING. 571 of a pump. Great care should, therefore, be taken to have everything right before starting. A very small leak in the suc- tion will cause a pump to work badly. Q. What is the peculiarity of the duplex type? A. There are two steam cylinders and two water cylinders ; the piston of one of these cylinders works the valve of the other cylinder, and vice versa. Neither half can work alone. This name is entirely arbitrary. Q. How would you call a pumping machine in which there are two steam cylinders, each operating a water cylinder in line with it ; each half being a perfect pumping machine independent of the other side? A. A " double " pump. Q. Can a direct acting steam pump use steam expansively? A. Not to any extent ; in fact, there would be danger of sticking upon the centers in most cases, if there was lap and expansion. Q. What is the reason that a single cylinder engine cannot well reverse itself without a fly wheel, by means of the ordinary single D valve? A. Because when the valve was at mid-travel, both ports of the valve seat would be closed by the valva faces, and neither exhaust nor admission take place. Q. What means are employed in a direct acting steam pump to move the valve? A. A small supplementary piston is used; this supplementary piston being actuated by the main piston in any one of several different ways. Q. What are the principal ways of working the supplementary piston from the main piston? ,A. (1) The main piston strikes the tappet of a small valve, which opens an exhaust passage in one end of the cylinder, containing a supplementary piston, and having live steam pressing upon both ends of the supplementary piston ; (2) by the main piston striking a rod passing through the cylinder head, and moving a lever which controls the motion of the part of the main valve to which is attached the valves which moves the supplementary piston ; (3) the main piston rod carries a tappet arm, which twists the stem of the supplementary piston, 572 HANDBOOK ON ENGINEERING. thus uncovering ports which cause its motion ; (4) a projection upon the main piston rod engages the stem and operates the valve which moves the supplementary piston, but if that valve should not, by means of its steam passages, cause quick enough or sure enough motion of the supplementary piston, a lug upon this stem moves the supplementary piston. Q. In the first of these four classes, what is the principal element in the valve motion? A. A difference in area between the eduction port of the supplemental piston and its induction port Q. What is the principal feature in the second class? A. A regular slide valve letting steam upon alternate ends of the sup- plemental piston. Q. In the third class, what is the main feature? A. A twist- ing motion in the supplemental piston. Q. In the fourth class, what is the principal feature? A. Movement of the supplemental piston by steam controlled by a slide valve, and by the mechanical action of the slide valve itself if its steam distribution is defective. Q. .What are the objections to most pumps of the direct acting type? A. The unbalanced condition of the auxiliary pistons in the exhaust side, causing a loss of steam when the parts are worn, the choking up of the small ports for the auxiliary pistons, by the gumming and caking of the oil therein. Q. Can the ordinary direct acting steam pump use steam expansively? A. No. Q. How may this be done? A. By compounding. Q. What is to be taken into consideration in the use of com- pound steam pumps? A. That they are designed for a certain range of pressure say from 80 to 120 pounds boiler pressure, and will do their best work between these pressures. Q. Have all direct-acting steam pumps intermittent valve motion? A, No; there are some which have continuous valve motion, HANDBOOK ON ENGINEERING. 573 Q. In most direct-acting steam pumps, are the auxiliary piston heads made together or in separate pieces? A. Together. Q. They are in contact with the steam in the chest? A. Yes. Q. What should be said about the location of a pump? A. It should be as near the source of supply as is convenient. Q. What may be said about convenience in repairs? A. The pump should have room left upon all sides ; and upon both ends equal to its length, for the removal of the piston rods in case of repairs. Q. If the floor is not strong enough, how may a good founda- tion be made ? A. By digging two or three feet into the ground and building up the proper height with stone or brick laid in strong cement, with a cap stone. Q. What may be said about suction pipes? A. They must be as large as possible ; the longer they are the greater in diameter they should be ; they should be as straight as possible, and as free from bends and valves ; they must be air-tight ; they must not be allowed to get obstructed by foreign substances. Q. What may be said about the area of strainer holes? A. They should have an aggregate area about live times that of the suction pipe. Q. Where are foot valves necessary ? A. Upon long suctions or high lifts. Q. Should two pumps take their suction from one pipe ? A. It should be avoided, unless the pipe is very large ; and in case both suctions should be arranged so that one of the pumps should not have to draft at right-angles to the flow of water going to the other pump. Q. What arrangement should be made where it is necessary to have two pumps draft from one Suction ? A. There should be a Y connection. Q. What is a good way to reduce the friction in suction pipes where tfrere are many bends? A. To use bends of wrought- 574 HANDBOOK ON ENGINEERING. iron pipe of as long a radius as possible r instead of cast-iron elbows. Q. What may be said about the lower end of the suction pipe? A. It should generally have a strainer ; and if the lift is over 12 to 15 feet, should have a foot valve. Q. What is a good thing to do witli the discharge pipe near the pump? A. To put a valve in it near the pump, to keep the water in the pipe when the water end is to be opened for inspection or repairs. Q. What provision should be made for priming the pump? A. There should be a pipe with a stop valve in it connected from the discharge pipe beyond this check valve, or from some other source of supply, to the suction pipe, for the purpose of priming the pump. Q. When the pump is in position for piping, what care should be taken? A. That the pipes are of proper length, so as not to bring any undue strain upon them in connecting them to the pump, as in that case they will be liable to give trouble by breaking or working the joints loose and leaking. Q. Does any pipe have an effective diameter as great as its nominal diameter? A. No; because the sides retard the flow of the liquid ; there is a neutral film of liquid which practically does not move. Q. Upon what does the thickness of this lilmof liquid depend ? A. Upon the viscosity (commonly miscalled the " thickness ") of the liquid ; upon the roughness, material and diameter of the pipe ; the pressure, etc. Q. When long lines of pipe are used, should the diameter of the pipe be the same all the way along, or should there by sections be decreasing diameter, as the distance from the pump increases? A. Most emphatically, the pipe diameter should remain constant clear out to the end. HANDBOOK ON ENGINKKKING. 575 TAKING CARE OF A PUMP. Q. What can be said about taking care of a pump? A. In places where an inferior grade of labor is employed, oil and dirt are sometimes found covering the steam chest and pump to the depth of an inch in thickness ; stuffing boxes are allowed to go leaky and get loose ; the valve motion is never looked after ; lost motion is never taken up, and the pump will be let run in a slip- shod way for months, until some accident occurs. This will sometimes exist in places where the engine is well taken care of. Q. Should not as good care be taken of a steam pump as of an engine? A. Yes. It is a steam engine, and the fact that it has generally but little adjustability, should not render it liable to lack of care. Q. What is a very common thing for pump runners to do when anything happens? A. To condemn the pump at once without finding out the cause of the trouble. Q. What is one reason of this? A. The man who understands an ordinary engine, will often become quite perplexed when he examines the steam end of a direct acting steam pump, because he does not comprehend the principal feature of its construc- tion that all direct acting steam pumps which have no fly wheels and cranks, must generally have an auxiliary piston in order to carry them over the "dead center." A direct acting steam pump is really a double engine; a plain, flat slide, valve admitting steam to a small piston, which in turn operates the main valve, which gives steam by the usual arrangement to the main piston. Q. What would save firemen and engineers much trouble with steam pumps? A. If they would take the trouble to examine their pumps carefully, and find out the way their valves were arranged and actuated. Q. Upon what does the successful performance of a pump 576 HANDBOOK ON KNiilNKKRTNG. depend, in great measure? A. Upon its proper selection from among the many patterns differing from each other in size, pro- portion and general arrangement. Q. What may be said about the selection of pumps? A. Pumps are often selected improperly for their work. As an illus- tration, a man who wishes to use a circulating pump for a surface condenser, where the water pressure upon the pump cylinder will never exceed 5 to 10 pounds, will buy a pump intended for boiler feed work, and having its steam cylinder about three times the area of its pump cylinder. Q. What will be the result in such a case? A. There will be little or no pressure in the steam cylinder when working on the condenser ; and while there is pressure sufficient to move the main piston, there is not enough to operate the auxiliary piston with positiveness. Q. In ordering a pump, or in asking estimates, what informa- tion should be given? A. In ordering a pump, it is to the inter- est of the purchaser to fully inform the maker or seller on the following questions : 1st. For what purpose is the pump to be used? What is the average steam pressure? 2d. What is the liquid to be pumped ; and is it hot or cold, clear or gritty, fresh, salt, alkaline or acidulous? 3d. What is the maximum quantity to be pumped per minute or hour? 4th. To what height is the liquid to be lifted by suction, and what is the length of the suction pipe, and the number of elbows or bends? 5th. To what height is the liquid to be pumped, and what is the length of discharge pipe? Q. How can an engineer familiarize himself with the direction of the auxiliary steam and exhaust passages? A. By means of a piece of wire. Q. What is the special thing to look after in duplex pumps? A. That all packings are adjusted uniformly on both sides. Q. What would be the result of having the packings different HANDBOOK OX ENGINEERING. 577 i>pon the two sides of a duplex pump? A. The machinery would run unsteadily. (J. If :i pump works badly, what should be about the first thing to look at? A. The connections. Q. When a pump is first connected, what should be done? A. It should be blown through to remove dirt ; if it be of the class which will permit of removing the bonnets and blowing through, that should be done. Q. What pump piston speed is recommended for continuous boiler feeding service? A. About 50 feet per minute. Q. What may be said about the care and use of steam pumps of all kinds? A. It is important that the pump be properly and thoroughly lubricated ; that all stulling-box, piston and plunger packings be nicely adjusted ; not so tight as to cause undue fric- tion ; nor so slack as to leak badly. Q. In which end of a steam-pumping machine is there most likely to be trouble? A. In the water end. Q. If a pump slams and hammers in its water end, is it neces- sarily defective in its water cylinder? A. No; it may be that there is no suction chamber, or not enough ; or sometimes it slams because the suction pipe is not large enough. Q. What are very common defects in cheap grades of pumps i A. Too little valve area in the pump end; too great lift for the valves. Q. What are the principal causes of pumps refusing to lift water from the source of supply? A. Among these maj r be mentioned leaky suction pipes, worn out pistons, plungers, pack- ings or water valves ; rotten gaskets on joints in piping or pump ; and sometimes a failure to properly prime the pump as well as the suction pipe. Q. What is one great cause of a pump refusing to lift water when lirst started? A. It often happens that a pump refuses to lift water while the full pressure against which it is expected to 37 578 HANDBOOK ON ENGINEERING. work is resting upon the discharge valves, for the reason that the air within the pump chamber is not dislodged, but only compressed, by the motion of the plunger. It is well, therefore, to arrange for running without pressure until the air is expelled and water follows ; this is done by placing a valve in the delivery pipe and providing a waste delivery, to be closed after the pump has caught water. Q. Sometimes when starting, the water may not come for a long time ; what is the best thing to do in this case? A. First, open the little air cock, which is generally located in the top of the pump, between the discharge valves and the air chamber, to let off any accumulation of air which may there be confined under pressure. Very often, by relieving the pump of this air pressure, it will pick up its water by suction and operate promptly. Q. What precaution must be taken in priming the pump? A. The air cock, which should be provided at the top of the pump, should be opened to allow the escape of the air from the suction pipe and from the pump, and then the valve in the priming pipe should be opened. The pump should then be started slowly, as it aids in more completely filling the pump cylinders, which otherwise, might not occur and the pump might fail to lift water. Q. Is there any advantage in having air in the suction? A. Sometimes a small amount of air let into the suction will cause less jarring when the duty is very heavy. Q. What may be said about pumping hot water? A. Where the hot water is very hot, it should gravitate to the pump, instead of an attempt being made to draft it. Q. In the plunger pumps, what is about the only wearing part of the water end? A. The packing of the plunger stuffing-boxes. Q. How can a pump be prevented from freezing? A. By having draining cocks and opening them when the pump is idle. HANDBOOK ON ENGINEERING. Q. What may be said about leather piston packing for water cylinders? A. For cold water, or sandy, gritty water, the leather packing has many points to commend it ; it makes a tight piston, and one that is the least destructive to pump cylinders. Q. What is the best way to handle the square packing mostly employed, which is composed of alternate layers of cotton and rubber? A. Cut the lengths a trifle short, then there will be room for the packing to swell and not cause too much friction. I have known pistons where this precaution has not been taken to be fastened so securely in the cylinder by the swelling of the dry packing, that full steam pressure could not move them. Q. What is the remedy in such a case? A. Remove the follower, take out the different layers of packing and shorten their lengths. Q. What is the reason that some soft waters corrode pipes so often? A. Because they contain a large proportion of oxygen. Q. Will a pump with a 6" water cylinder and a 6" steam cylin- der force water into a boiler, the discharge from water cylinder being 4" diameter; boiler pressure, 80 Ibs.? A. A pump with a 6" water cylinder and 6" steam cylinder will not force water into the boiler which supplies it, no matter what the steam pressure, nor what the size of discharge pipe. It will not move. The pressures would be equalized and there would be nothing to over- come friction of steam and water in pipes and cylinder. The foregoing case supposes that the water is to be lifted to the pump ; or at least that there shall be no head ; also, that there shall be no fall from pump to boiler. If there were sufficient head or fall to overcome all the various frictions, and no lift, the pump would apparently work ; but really, the water piston would be dragging the steam piston along. Q. How may acids be pumped? A. By what is known as blowing up ; that is, by employing a pump to put pressure upon 580 HANDBOOK OX KNCIINKKKI N(J . the acid in a closed vessel, thereby forcing it through a pipe placed in the bottom of the vessel. Q. .In case any wearing part of :i pump gets to cutting, what should be done? A. If it is not practicable to stop the pump nor to reduce its speed, the part which is getting damaged should be given very liberal oiling. Q. What is the best oil for this purpose? A. That depends on the nature of the cutting surfaces, and on the pressure therein : the mineral oils are generally more cooling than others, although they have .less body to resist squeezing. CALCULATING THE BOILER FOR A STEAM PUMP. The amount of work which a boiler has to do is very easy of determination. Given the largest number of gallons which a pump will be required to pump per minute, and the height in feet from the surface of the well from which the water is drawn, to the point of discharge, you can easily tell by multiplying by 8J the weight in pounds of one gallon the number of foot pounds of power consumed per minute in lifting the water, adding a cer- tain percentage for friction of the machine and of water in the pipe, we have the total number of foot pounds consumed per minute, and this divided by 33,000 will be the horse power consumed . The allowance for friction will vary with the style, size and condition of the pump, the size of the pipe, and, above all, the manner in which the pipe is connected up, the number of right angle turns, etc. This may be arrived at in another way. A column of water 2.o feet in height exerts a pressure of one pound. Allowing the .3 for friction, we can, by dividing the total left in feet by two, get at the pressure per square inch, which is being exerted against the water piston or plunger, and multiplying by the number of HANDBOOK ON ENGINEERING. 581 square inches in that piston gives the total pressure against which the pump is working. This multiplied by the piston speed in feet minutes, and divided by 33,000, will give the lift in horse power. In this case, as in the other, the lift must be calculated from the surface of the supply, and not from the pump, when the pump is lifting its supply. If the water flows to the pump it must be calculated from the height of the water cylinder. An allowance of, say, 25 per cent, should be made above the horse power thus shown, in order to provide for contingencies, and to be on the safe side. In selecting & boiler to do this work, it must be borne in mind that a boiler which is sold for a certain horse power, is supposed to be able to furnish that power in connection with a good steam engine , and they are not apt to be overrated . Now , the steam pu m p as usually built, does not approach in economy the ordinary steam engine, and, therefore, a boiler which will develop twenty-five horse power in connection with a good engine would be too small for a pump which was required to do the same amount of work. The evaporation of 30 pounds of water per hour from feed at 100 degrees Fahr. into steam of 70 Ibs. pressure, has'been adopted by several authorities as a horse power. Any good automatic cut-off will run on this amount of water, and if an estimate can be made of the comparative performance of the pump under consideration, a close approximation to the desired size of boiler can be made. THE WORTHINQTON WATER METER. The counter registers cubic feet; one foot being 7 T 4 ^ gallons, United States standard. It is read in the same way as registers of gas meters. The following example and directions may be of use to those unacquainted with the method : If a pointer is between two figures, the smaller one must invariably be taken. Suppose the pointers of the dials to stand as in the engraving. 582 HANDBOOK ON ENGINEERING. The reading is 6,874 cubic feet. From the dial marked ten w- get the figure 4 ; from the next, marked hundred, the figure 7 ; from the next, marked thousand, the figure 8 ; from the next, marked ten thousand, the figure 6. The next pointer being between ten and 1, indicates nothing. By subtracting the read- ing taken at one time, from that taken at the next, the consump- tion of water for the intermediate time is obtained. TABLE OF PRESSURE DUE TO HEIGHT. ressure nch. ressure nch. 1 2 a ressure nch. fl 3 . ll ^ ft'"] Is ft . ii ft": *i ft . | ft'" i ^"t | ft"! 05 O5 5T OJ M a? OJ S' ' Ml J 1C C/l 9 > W O5 OD "3 si oJ '-> i 5 3 ^ c3 Vi ^ *3 t. ' -3 ^ * 03 - & ft a? &ft ! 0) S.& OJ CTft cu 0) && g S-^ i P y cr ft fc w fe H I SH H M H H a 1 0.43 15 6.49 30 12.99 45 19.49 60 25 99 75 32.48 90 38.98 5 2.16 20 8 66 35 15 16 50 21.65 65 28 15 80 34 65 95 41 15 10 4 33 25 10.82 40 17.32 55 23.82 70 30 32 85 36.82 100 48 31 HANDBOOK ON ENGINEERING. 583 TABLE OF DECIMAL EQUIVALENTS OF 8ths, 16ths, 32ds AND 64ths OF AN INCH. 8ths. 32ds. 64ths. 64ths. 1 .125 r/ 2 .03125 - 6 L 4 - -H .015625 || = .546875 1 = .25 - 3 \ = .09375 a; .046875 .578125 i .375 36,- .50 ,& = .15625 .21875 | = .078125 || = .109375 .609375 .640625 1 BD .625 & = .28125 f\ r= .140625 .671875 1 .75 = .34375 (Td .171875 AJ - .703125 1 . .875 H 3s .40625 -_ .203125 H . - . .734375 ft .46875 .234375 \ .765625 = .53125 =1= .265625 \ = .796875 I6ths. 32 = .59375 L rr= .296875 I = .828125 I* .65625 64 .328125 s . __ .859375 uf = .0625 .71875 || 33- .359375 1; .890625 A = 1875 = .78125 |f s .390625 64 ^ .921875 I = .3125 = .84375 H = .421875 64 == .953125 .4375 .90625 H - .453125 .984375 A .5625 .96875 31 6 4 .484375 1L = .6875 II 6 4 - .515625 16 .8125 tj = .9375 LATENT HEAT OF LIQUIDS, UNDER A PRESSURE OF SO INCHES OF MERCURY. (TREATISE OX HEAT, BY THOMAS BOX.) Latent Heat in Units. Increase of Tempe- rature of Liquid, if Heat bad not become Latent. Water 966 966 Regnault 457 735 Ure Ether 313 473 a Oil of Turpentine. . . Ntiphthti . . 184 184 390 443 < tt The Boiling Point of different Liquids varies; and the Boiling Point of a liquid varies with the pressure. 584 HANDBOOK ON ENGINEERING. Z 2 1 I < 3 9 -* O O > '-> M t- .-HOaSCOCOO'*OO ,_,^.-i,-i;>4S ^ < 00 O t^ (M O " O o ^^ 1*11 a **. o Q, HANDBOOK ON ENGINEERING. 585 CAPACITY OF SQUARE CISTERNS IN U. S. GALS. 5X5 5X 5X7 5X8 5X9 5X10 6X6 6X7 6X8 6X9 6X10 5 ft.. 935 1122 1309 1496 1683 1870 1346 1571 1795 2020 2244 54ft.. 1028 1234 1440 1645 1851 2057 1481 1728 1975 2221 2469 G ft.. 1122 1346 1571 1795 2019 2244 1615 1885 2154 2423 2693 (54 ft.- 1215 1459 1702 19*5 2188 2431 1750 2042 2334 2625 2917 7 ft.. 1309 1571 1833 2094 2356 2618 1884 2199 2513 2827 3142 74 ft.. 1403 1683 1963 2244 2524 2800 2019 2356 269313029 3366 H ft.. 1496 1795 2094 2393 2693 2992 2154 2513 2872 3231 3592 S4ft.. 1589 1907 2225 2543 2861 3179 2288 2670 3052 3433 3816 '.) ft.. 1683 2020 2356 2693 3029 3366 2423 2827 3231 3635 4041 94ft.. 1776 2132 2487 2842 3197 3553 2558 2984 3412 3837 4265 10 ft.. 1870 2244 2618 2992 3366 3470 2692 3142 3591 4039 4489 1 XH 6X1217X77X8 7X9 7X10 7XH 7X12 8X8 8X9 5 ft.. 24G8 2693 1832 2094 2356 2618 2880 3142 2394 2693 54 ft. . 2715 2962 20162304 2592 2880 3168 3456 2633 2962 <; ft.. 2962 3231 21992513 2827 3142 3456 3770 2872 3231 64 ft.. 3209 3500 2382'2722 3063 3403 3744 4084 3112 3500 7 ft.. 3455 3770 25652932 3298 3665 4032 4398 3351 3770 74ft.. 3702 4039 27483141 3534 3927 4320 4712 3590 4039 8 ft.. 3949 4308 2932'3351 3770 4189 4608 5026 3830 4308 84ft.. 4196 : 4577 31153560 4005 4451 4896 5340 4069 4578 y ft.. 4443 4847 329813769 4341 4712 5184 5655 4308 4847 94 ft.. 4689 5116 3481,3979 4576 4974 5472 5969 4548 5116 10 ft.. 4936 5386 3664 4188 4712 5236 5760 6283 4788 5386 WEIGHT OF WATER. 1 cubic inch 12 cubic inches 1 cubic foot (salt) . . 1 cubic foot (fresh) 1 cubic foot .03617 pound. .434 pound. 64. 3 pounds. 62.425 pounds. 7.48 U. S. Gallons. NOTE. The center of pressure of a body of water is at two-thirds the depth from the surface To find the pressure in pounds per square inch of a column of water, multiply the height of the column in feet by .434. Every foot elevation is called (approximately) equal to onS-half pound pressure per square inch. 586 HANDBOOK ON ENGINEERING. SHOWING U. S. GALLONS IN GIVEN CUBIC FEET. NUMBER OF Cubic Feet. Gallons. Cubic Feet. Gallons. Cubic Feet. Gallons. 0.1 0.75 50 374.0 9,000 67,324.6 0.2 1.50 60 448.8 10,000 74,805.2 0.3 2.24 70 523.6 20,000 149,610.4 0.4 2.99 80 598.4 30,000 224,415.6 0.5 3.74 90 673.2 40,000 299,220.7 0.6 4.49 100 748.0 50,000 374,025.9 0.7 5.24 200 1,496.1 60,000 448,831.1 0.8 5.98 300 2,244.1 70,000 523,636.3 0.9 6.73 400 2,992.2 80,000 598,441.5 1 7.48 500 3,740.2 90,000 673,246.7 2 14.9 600 4,488.3 100,000 748,051.9 3 22.4 700 5,236.3 200,000 1,496,103.8 4 29.9 ' 800 5,984.4 300,000 2,244,155.7 5 37.4 900 6,732.4 400,000 2,992,207.6 6 44.9 1,000 7,480.0 500,000 3,740,259.5 7 52.4 2,000 14,961.0 600,000 4,488,311.4 8 59.8 3,000 22,441.5 700,000 5,236 363.3 9 67.3 4,000 29,922.0 800,000 5,984,415.2 10 74.8 5,000 ' 37,402.6 900,000 6,732,467.1 20 149.6 6,000 44,883.1 1,000,000 7,480,519.0 30 224.4 7,000 52,363.6 40 299.2 8,000 59,844.1 From the above any cubic feet reading can readily be converted into U. S. gallons, as follows: How many gallons are represented by 53,928 cubic feet? 50,000 cubic feet = 374,025.9 gallons. 3,000 " " = 22,441.5 " 900 " " = 6,732.4 " 20 " < = 149.6 " 8 59.8 53,928 cubic feet = 403,409.2 gallons. HANDBOOK ON ENGINEERING. 587 SHOWING COST OF WATER AT STATED RATES PER 1OOO GALLONS. Number of Cubic Feet. COST PER 1000 GALLONS. 5 Cents. 6 Cents. 8 Cents. 10 Cents 15 Cents. 20 Cents. 25 Cents. 30 Cents. 20 $0 007 $0.009 $0.012 $0.015 $0.021 $0.030 $0.037 $0.045 40 0.015 0.018 0.024 0.030 0.045 0060 0-075 0.090 60 0.022 0.027 0.036 0.045 0.066 0.090 0.112 0.135 80 0.030 0.036 0.048 0.060 0.090 120 0.150 0.180 100 0.037 0.049 0.060 0.075 0.111 0.150 0.187 0.224 200 0.075 0.090 0.120 0.150 0.225 0.299J 0.374 0.449 300 0.112 0.135 0.180 0.224 0.336 449, 0.561 0.673 400 0.150 0.180 0.239) 0.299 0.450 0.598 0-748 0.898 500 0.188 0.224 0.299 0.374 0.564 0.748 0-935 1.122 600 0.224 0.269 0.359 0.449 0.448 0.898 1.122 1-346 700 0-262 0.314 0.419 0.524 0-786 1.047 1-309 1-571 800 0.299 0.350 0.479 0.598 0.897 1.197 1-496 1-795 900 0.337 0.404 0.539 0.673 1.011 1 346 1.683 2-020 1,000 0-374 0.449 0.598 0-748 1-122 1 496 1.870 2.244 2,000 0.748 0.898 1.197 1.496 2.244 2.992 3-740 4-488 3,000 1.122 1.346 1-795 2-244 3.366 4.488 5.610 6-732 4,000 1.496 1-795 2-393 2.992 4.488 5.984 7.480 8.976 5,000 1.870 2.244 2-992 3-740 5.610 7.480 9-350 11-220 6,000 2.244 2.692 3-590 4-488 6.732 8.976 11.220 13.464 7,000 2.615 3-141 4-189 5-23b 7.854 10.472 13-090 15.708 8,000 2.992 3.590 4-787 5-984 8-976 11.9*8 14.961 17-953 9,000 3.366 4.039 5-385 6.732 10-098 13.464 16-831 20.197 10,000 3.74 4.488 5-984 7-480 11.122 14.961 18.701 22.441 20,000 7.48 8.976 11.968 14.961 22.443 29.992 37-402 44.882 30,000 11.22 13.46 17.95 22-44 33.664 44.88 56.10 67-32 40,000 14-96 17.95 23-94 29.92 44.885 59.84 74-10 89.77 50,000 18.70 22.44 29.92 37.40 56.103 74.80 93-50 112.20 60,000 22.44 26.92 35.90 44.88 67-323 89.76 112.20 134.64 70,000 26.18 31-41 41.89 52-36 78.543 104.72 130.90 157-08 80,000 29.92 35.90 47-87 59.84 89.766 119.68 149.61 179-53 90,000 33.66 40.39 53.85 67-32 100.986 134 64 168-31 201.97 100,000 37.40 44.88 59.84 74.80 111.22 149.61 187-01 224-41 200,000 74.81 89.76 119.68 149.61 224.43 299 22 374.02 448-82 300,^00 112.20 134.64 179.53 224.41 336.64 448.83 561-03 673.24 400,000 149.61 179.53 239.37 299.22 448-86 598.44 748.05 897- 6H 500,000 187.01 224.41 299.22 374.02 561.03 748.05 935.06 1122-07 600,000 224.41 269.29 359.06 448 83 673-23 897.66 1122.07 1346.49 700,000 261.81 314.18 418.90 523.63 785-43 1047.27 1309.08 1570.88 800,000 299-22 359.06 478.75 598.44 897-66 1196 88 1496-10 1795.32 900,000 336.62 403.94 538.59 673.24 1009-80 1346.49 1683.11 2019.73 1,000,000 374.02 448.83 598.44 748.05 1122.06 1498.10 1870.12 2244.15 588 HANDBOOK ON ENGINEERING. oo-^ : t ::::::::: I :::;:::::: i ig oSSSs p V JG 5 a . ;;;;;;;;;.; o od'o-ocoodd g ^ a : : : . . : :. <- :<=> " -H?sIJiot2 :::::::: o o o o o o c o - * ; . ; . i- it -^g - . S -0 COi-HplCMSOiOt^r-nfiOilftO h di fl 0} fe E 3 %2 $> M o 1 ^ HP - . ..^-*OOO5 c0t*"COCO'''' ...- _ -o5ood*oi : o "^ a 1-1 ** ; .:;..;:. V j= ...ooo^o^ r4-fi ^-7- ::::;:::.: "1 "^^ "^Sc5wS X! CO ^xi x-iwo^oo ::.:::::::-.::::::::.:::::: 01 3 5 ecot-^o-- oo .H "ssss ::;;;;; : ;;:;; : :;;;;; : ; ; : ; : : ; ; JOd injoi HANDBOOK ON ENGINEERING. 589 " SHOWING HOW WATER MAY BE WASTED. GALLONS DISCHARGED PER HOUR THROUGH VARIOUS SIZED ORIFICES UNDER STATED PRESSURES. ca S-g Diameters of Orifices in Inches and Fractions of an Inch. o 5 a 2 - j3 3 o> O 05 {2 p_, en 4 I 4 1 1 1 U j-J 15 2 -. cr 1 C 00 inch inch,inch inch inch inch inch inch inch inch 20 8.66 300 720 1260 1920 2760 4920 7380 11100 15120 19740 40 17.32 450 960 1800 2760 3960 6720 10920 15720 21360 27960 60 25.99 540 1200 2160 3480 4800 8580 13380 19200 26220 34260 80 34.65 620 1380 2460 3840 ! 5580 9840 15480 22260 30300 39540 100 43.31 690 1560 2760 4320! 6240 11040 17280 24900 33900 44280 120 51.98 780 1780 3000 4740 6840 12120 18960 27240 37440 48480 140 60.64 816 1860 3300 5IOO| 7320 13020 20160 29460 39080 52320 150 64.97 840 1920 3420 5280 7620 13560 21180 30480 41460 54120 175 75.80 900 2040 3660 5700 8220 14640 22800 32880 44940 58560 200 86.63 960 2220 3900 6120 8760 15600 25020 35880 47880 62580 235 101.79 1080 2460 4320 8280 11160 17100 26760 38520 52260 68460 The pressure or head of water is taken at the orifice, no allowance being made for friction in the pipe. In practical calculations to deter- mine the height which water can be thrown, the head consumed by the friction of the water in flowing from the source to the orifice must be considered. IGNITION POINTS OF VARIOUS SUBSTANCES. Phosphorus ignites at 150 Fahr. Sulphur- {? " 500 " Wood " " 800 " Coal " 1000 Lignite, in the form of dust, ignites at Canuel Coal, Coking < 'oal, Anthracite, 150 " 200 " 250 " 300 " 590 HANDBOOK ON ENGINEERING. CONTENTS IN CUBIC FEET AND IN U. S. GALLONS. (FROM TRAUTWEIN) Of 231 cubic inches (or 7.4805 gallons to a cubic foot) ; and for one foot of length of the cylinder. For the contents for a greater diameter than any in the table take quantity opposite one -half said diameter, and multiply it by 4. Thus, the number of cubic feet in one foot length of a pipe 80 Inches In diameter is equal to 8.728X4=34.912 cubic feet. So also with gallons and areas. For 1 foot in For 1 foot in For 1 foot in c M length. S ^ a <* length. c M 2> a>-i -fl ; O 5.C "S GJ '** ^ so 3 . _ * tu '** 03 aoS . "oj-C s "a} "^* OQ 5 So fl S l -23 * sag i S 03 +* n a g S a 3 Q 05 03 gs Sj--- 5 sf 0) 1*1 111 fil ~ 5 f sSs |ii 5 1 |1| ,2^.c t O"3 co "o "5 T o T3 O"5 03 "o . .0208 0003 .0026 . .5625 .2485 1 859 19. 583 1 969 14.73 5-16 .0260 .0005 .0040 7. .5833] .2673 1 999 | .625 2 074 15 52 4 .0313 .0008 .0057 .6042 .2868 2 144 20 .666 2.182 16.32 7-16 .0365 0010 .0078 .6250 .3068 2.295 i .708 3.292 17.15 } 0417 .0014 .0102 i .64581 .3275 2.450 21 750 2 405 17 99 9-16 0469 .0017 .0129 8. 6667 .3490 2.611 i .792 2.521 18.86 11-16 .0521 .0573 0021 .0026 .0159 0193 i .6875 .3713 .7083 .3940 2 777 2 948 833 875 2.640 2.761 19.75 20.65 i .0625 .0031 .0230 | .7292) .4175 3.125 23 ' 1.917 2.885 22.58 13-16 .0677 0031 .0270 9. .7500 .4418 S 305 i 1.958 3 012 31.53 3 .0729 .0042 0312 i .7708! .4668 3 492 24. 2.000 3 142 23.50 15-16 .07811 .9048 0359 i .79171 .4923 3 682 25. 2.083 3.409 25.50 1. .0833 0055 .0408 1 .8125 .5185 3.8791 26. 2.166 3.687 27.58 .1042 .0085 .0638 10. .8333 .5455 4 0811 27. 2 250 3.976 29 74 j .1250 -0123 .0918 i 8542 .5730 4.286 28. 2 333 4.276 31.99 a .1458 .0168 1250 .8750 .6013 4.498 29. 2 416 4 587 34.31 2, .1667 .0218 .1632 3 .8958 .6303 4.714 30 2.500 4.909 36.72 .1875 .0276 .2066 11. .9167 .6600 4.937 31 2 583 5.241 39.21 i .2083 .0341 .2550 1 .9375 .6903 5.163 32. 2 666 5 585 41.78 | .2292 .0413 3085 9583 .7213 5 395 33. 2.750 5.940 44.43 3. .2500 .0491 .3673 3 .9792 .7530 5.633 34 2.833 6 305 47.17 .2708 .0576 .4310 12. I Foot. .7854 5 876 35. 2.916 6.681 49.98 i .29171 .0668 .4998 i .042 .8523 6 375 36. 3 000 7 069 52.88 i .3125 .0767 .5738 13. .083 .9218 6.895 37. 3.083 7.468 55.86 4. .3333 .0873 .6528 i .125 .9940 7.435 38 3 166 7.876 58.92 .3542 .0985 .7370 14. .167 1 069 7.997: 39. 3 250 8 296 62.06 i .3750 .1105 .8163 i .208 1.147 8.578; 40. 3.333 8.728 65 29 a .3958 1231 .9205 15. .250 1.227 9.180 41. 3.416 9.168 68.58 5. .4167 .1364 .020 i .292 1.310 9.801 42. 3.500 9.620 71.96 .4375 .1503 .124 16. .333 1.396 10.44 43 3.583 10.084 75.43 i .4583 1650 .234 J .375 1.485 11.11 44. 3 666 10.560 79 00 | .4792 .1803 .H49 17. 417 1.576 11.79 45. 3.750 11.044 82 62 6. .5000 .1963 .469 i .458 1 670 12.50 46. 3.833 11.540 86.32 .5208 .2130 .594 18. .500 1.767 13.22 47. 3.916 12.048 90.12 * .5417 .2305 .724 i .542 1.867 13.97 48. 4.000 12.566 94.02 HANDBOOK ON ENGINEERING. 591 CHAPTER XX. THE INJECTOR AND INSPIRATOR. The energy of motion of a body is well known to be the prod- uct of its mass by the half square of its velocity ; hence, it is possible to communicate to a body of little weight a large amount of energy by moving it fast enough, and in fact, the energy of motion would only be limited by the speed which can be given the body. In this way a small weight of steam flowing from an orifice into a properly shaped jet of water is condensed, while the velocity of the steam is greater than if flowing into air ; the energy thus communicated is made sufficiently great by increasing the weight of steam, which can be done by increasing the area of the steam way, until we find such jet pumps adapted to many purposes. There are, however, two which are of interest to us in this connection, the well-known injector and inspirator, with the large family of lifting and non-lifting varieties, all differing in details as to form of nozzles, area of passages, distances between nozzles, and that class of instruments in which, after a certain energy and velocity have been reached, the operation is repeated. These might be called " consecutive " instruments. The illustrations in this book show some of the simplest and adjustable kinds. Within a few years the principle of increase of energy by increase of mass or velocity has been applied by in- creasing the mass of steam used until we find that not only can a few pounds weight of steam put into a boiler a good many more pounds of water at a much higher temperature than it had, but that in a non-condensing engine it is possible, by using the ex- haust in part, to put into the boiler at a much higher pressure 592 HANDBOOK ON ENGINEERING. and temperature, a weight of water which is still greater tlian that of the steam moving it. When the injector first made its appearance it was, by many, considered as almost a paradox, especially by those who looked at the question as one of hydrostatics only. That steam from a boiler could put water back into it at the same pressure, and over- come the friction of the passages without the aid that a steam pump had of a difference of piston areas, was to them a puzzle. The use of exhaust steam at atmospheric pressure for the purpose of putting water into a boiler at a pressure of 150 Ibs. per square inch, would be to such minds utterly incomprehensible. The use of an injector and inspirator, has this to recommend them, that the feed-water cannot be introduced into the boiler cold or nearly so, but must be warmed by contact with the steam, and the value of this has been already shown. In small boilers where no heater is used, an exhaust injector is better than a pump, and so is an ordinary injector ; but the former includes in itself an exhaust heater, saving a portion of heat from the exhaust, besides taking the power as heat also ; while, with the common injector, the heat for power and raising temperature are both derived from the live steam in the boiler. The latter portion of heat is, of course, directly returned to the boiler without loss, but that for power is necessarily expended. As to the amount of power used by pump and injector compared with each .other, it would seem that the pump is most efficient. There have been many comparative trials of pump and injector, but the results have usually been unsatis- factorv from contained discrepancies. RANGE OF THE INSPIRATOR AND INJECTOR. The steam pressure at which an injector will start and the highest steam pressure at which it will work constitute what is termed the " range " of an injector, and the inspirator varies with the vertical lift and the temperature of the feed water. HANDBOOK ON ENGINEERING. It must also be borne in mind that the same style of construc- tion in an injector and inspirator, while it confines them to about a specific range between its lowest starting and highest working points, permits of variation as to what the lowest starting point shall be. A style of construction which gives a range (on say a 2-foot lift) of 25 Ibs. to 155 Ibs. would permit of a range of 35 Ibs. to 165 Iks. (in fact, to a little higher than 165 Ibs.). Different manu- facturers, therefore, vary as to the starting point in their stand- ard machines aiming to cover the range which they deem most desirable. Nearly all have adopted about 25 Ibs. on a 2-foot lift, as lowest starting point. The World. POSITIVE OR DOUBLE TUBE INJECTORS. As before stated, this class of injector is provided with two sets of tubes or jets, one set adapted to lift the water and deliver it to 88 594 HANDBOOK ON ENGINEERING. the second set, which forces the water into the boiler. By this arrangement, it is apparent that inasmuch as the lifting jets supply a proportionate amount of water with varying steam pres- sures, a wider range is obtainable than with an automatic in- jector. In the following cases, it is better to use the double tube injectors : 1. Where the feed water is of too high a temperature to be handled by the automatic injectors. 2. When a great range of steam variation is accompanied by the condition of a long lift. The World Injector is one of the best and most popular of the double tube type of injectors. It is entirely self contained. It is supplied even with its own check valve and operated entirely by a single lever, a quarter of a turn of which starts the lifting, after which the completion of the single revolution sets the injector working to boiler. GENERAL SUGGESTIONS FOR PIPING=UP INJECTORS AND INSPIRATORS AND SUGGESTIONS THAT SHOULD BE CAREFULLY FOLLOWED WHEN MAKING PIPE CONNEC= TIONS. i Steam* Connect steam pipe with highest parts of boiler and never connect with a steam pipe used for any other purpose. I would recommend a globe valve being placed in the steam pipe next to boiler which can be closed in case it is desired to take off the injector. At all other times it can be left open. When the steam connection is made, be sure and take off the injector before the steam is turned on the machine. Then blow out the steam pipe with at least forty pounds steam, which will remove all dirt and scale. Suction* This pipe must be tight, and if there is a valve in it the stem must be well packed. To test the suction pipes for leaks, plug up the end of the pipe HANDBOOK ON ENGINEERING. 595 and then screw on a common iron cap on the overflow ; or if you do not have one, unscrew cap X, and place a piece of wood on top of valve P; replace the cap and the wood will hold the valve from rising ; then turn on the steam which will locate all leaks. All pipes, whether steam, suction or delivery, must be of the same or greater size than the corresponding branch of each injec- tor. Have all piping as short and as straight as possible, and especially avoid short turns. 59 () HANDBOOK ON ENGINEERING. If any old pipe is used, see that it is not partially filled or stopped up with rust. If the injector or inspirator has to lift the water very high or draw it very far, have the suction pipe a size or two larger than called for by the suction branch of the injector or inspirator. Have the water supply (suction) pipe independent of any other connection. , The suction pipe must be absolutely air tight ; the slightest leak, in most cases, will prevent the injector or inspirator from forcing water into the boiler. Always place a globe valve in the suction pipe as close to the injector as possible, and place it so that it will shut down against the water side and see that the stem is packed tight. When using the injector or inspirator as NON-LIFTING;, put two globe valves in the suction, one close to the injector, the other us far from it as you can conveniently, keeping the one farthest from the injector or inspirator tolerably close throttled. This will surely repay you for your trouble. The check valve may be next to boiler with a valve between it and boiler, the further from injector the better. If the injector forces through a heater, place check valve between injector and heater. Also place a valve between heater and check valve so you can take check valve out if necessary. Size of pipes* If injector or inspirator has over 10 feet lift, or a long draw, use suction pipe from strainer to valve a size larger than the connection on injector, reducing when you reach the valve. In all other cases, use for all pipes same size as injector connection. Blow-off* Always blow out steam thoroughly BEFORE CON- NECTING INJECTOR, so as to remove any dirt, rust or scale that may be in the pipes. Caution* The suction pipe must be ABSOLUTELY TIUHT throughout. To make sure that it is so, test the suction as directed. HANDBOOK ON ENGINEERING. 597 DIRECTIONS FOR CONNECTING AND OPERATING THE HANCOCK INSPIRATOR. 41 Stationary " Pattern. Connect as shown by cut above steam, suction and delivery. For full instructions, see page 588. For a lift of 5 ft., 15 Ibs. steam pressure is required. " 4 10 " 20 " " " " " " 15 " 25 ' l " " tl " " 20 " 35 " " " " " " 25 " 45 " " " " Operation* Open overflow valves Nos. 1 and 3 ; close forcer steam valve No. 2 and open the starting valve in the steam pipe. When the water appears at the overflow, close No. 1 valve ; open No. 2 valve one-quarter turn and close No. 3 valve. The inspir- ator will then be in operation. NOTE. No. 2 valve should be closed with care to avoid damag- ing the valve seat. When the inspirator is not in operation, both overflow valves Nos. 1 and 3 should be open to allow the water to drain from it. No adjustment of either steam or water supply is necessary for varying steam pressures, but both the temperature and quantity of the delivery water can be varied by increasing or reducing the water supply. The best results will be obtained from a little experience in regulating the steam and water supply. If the suction pipe is filled with hot water, either cool off both it and the inspirator with cold water, or pump out the hot water by opening and closing the starting valve suddenly. To locate a leak in the suction pipe, plug the end, fill it with water, close No. 3 valve and turn on full steam pressure. Examine the suction pipe and the water will indicate the leak. If the inspirator does not lift the water properly, see if there is a leak in the suction pipe. Note if the steam pressure corresponds to the lift as above speci- fied, and if the sizes of pipe used are equal in size to inspirator connections. If the inspirator will lift the water, but will not de- liver it to the boiler, see if the check valve in the delivery pipe is 598 HANDBOOK ON ENGINEERING. in working order and does not " stick." Air from a leak in the suction connections, will prevent the inspirator from delivering the water to the boiler, even more than it will in lifting it only. If No. 1 valve is damaged, or leaks, the inspirator will not work properly. No. 1 valve can be easily removed and ground. THE HANCOCK STATIONARY INSPIRATOR. STEAM Feed to Boiler. Suction. WATER Overflow. To remove scale and deposits from inspirator jets or parts, disconnect the inspirator and plug both the suction and delivery outlets with corks. Open No. 2 valve and fill the inspirator with a solution of one part muriatic acid and ten parts water. Allow this solution to remain in the inspirator over night, then wash it thoroughly in clear water. NOTE. It is not gerierally necessary to return an inspirator for repairs. The repair parts required can be ordered and the inspirator readily put in order. HANDBOOK ON ENGINEERING. 599 TO DISCOVER CAUSE OF DIFFICULTIES. WHEN INJECTOR FAILS TO GET THE WATER. 1. The supply may be cut off by: (a) Absence of water at the source, (b) Strainer clogged up. (c) The suction pipe, hose or valve stopped up ; or if a hose is used, its lining may be loose (a frequent cause of trouble). 2. A large leak in the suction (note that a small leak will pre- vent injector from working, but not from getting the water). 3. Suction pipe or water very hot. Open drip-cock, turn steam on slowly, then shut it off quickly. This will cause the cool air to rush into the suction pipe and cool it off. Repeat if necessary. 4. Lack of steam pressure for the lift; or, in some instances, too much steam pressure. If the steam pressure is ven r high, the injector will get the water more readily if the steam is turned on slowly and the drip-cock left open until the water is got. IF THE INJECTOR GETS THE WATER BUT DOES NOT FORCE IT TO THE BOILER. 1. No globe valve on the suction with which to regulate the water, or else the supply water not properly regulated. 2. Dirt in delivery tube. 3. Faulty check valve. 4. Obstruction between injector and check valve, or between check valve and boiler. 5. Small leak in suction pipe admitting air to the injector along with the supply water. It is ten to one this is the cause of the difficulty every time. 6. Be sure you understand the directions for starting before you condemn the injector. 600 HANDBOOK ON ENGINEERING. IF THE INJECTOR STARTS BUT " BREAKS." 1. Supply water not properly regulated. If too much water, the waste or overflow will be cool; if too little, the water will lie- very hot. 2. Leaky supply pipe admitting air to the injector. It is ten to one this is the cause of difficulty. The suction must be air tight; test as directed. MODE OF CONNECTING The above illustration shows the mode of connecting the Pen- berthy Injector. 3. Dirt or other obstruction, such as lime, etc., in delivery tube. . 4. Connecting steam pipe to pipe conducting steam to other points besides the injector, or not having suction pipe inde- pendent. HANDBOOK ON ENGINEERING. fiOl f>. Sometimes a globe valve is used on the suction connection that has a loose disc, and after starting the disc is drawn down, thus partially closing the valve; it is, of course, equivalent to giving the injector too little water. To remedy this, take the globe valve off and reverse it end for end. To clean* To clean injector, unscrew plug O, and the re- movable jet Y (which rests in it) will follow the plug out. Turn on steam (not less than forty pounds) and all dirt will be blown out. Examine all passages and drill holes and see that no dirt or scale has lodged in them. Replace jet by setting it in the plug (which acts as a guide) and screw into place tightly. Be c ireful not to bruise any jets, and use no wrenches on body of injector. PRICE LIST, CAPACITY, HORSE POWER, ETCo Size. Price. Pipe Connections. Capacity per Hour. 1 to 4 ft. lift, 50 to 75 Ibs. Pressure. Horse Power. Steam. Suction. Delivery, Maximum. : Minimum. OO. . A $16 00 * i 18 00 i n. 30 g 120 al. 55 gal. 70 " 4 to 8 8 to 10 A A 20 00 A 165 90 " 10 to 15 B 25 00 | 250 135 15 to 25 lili . 30 00 ; 340 165 25 to 35 C 40 00 1 475 300 35 to 50 cc. .. 45 00 1 575 350 50 to 60 D 55 00 i 750 400 60 to 95 DD .. HO 00 i J 920 500 95 to 162 E 75 00 1300 700 120 to 150 EK . 90 00 i H 1740 900 \ 165 to 230 F 110 00 2" 2" 2 2270 1100 230 to 290 FP 125 00 2 2 - 2 2820 1400 1 290 to 365 ! To test for leaks, Plug up end of water supply pipe, then fit a piece of wood into cap Z, so that when screwed down it will hold the valve P in place, then turn on steam and it will locate leak. Do not fail to do tli,i$ in case of any trouble. TO START AND STOP INJECTOR. To start* Open full the globe valve in water supply first, and then globe valve in steam pipe wide open. If water issues from overflow, throttle the valve //until discharge stops. Reg- 602 HANDBOOK ON ENGINEERING. ulate injector with water supply valve, not by steam valve. When water supply is above the injector, in starting open steam valve first. To stop* Close the steam valve. The water valve H need not be closed unless the injector is used as a non-lifter, or lift is considerable. The following table gives the number of British thermal units in a pound of water at different temperatures. They are reckoned above 32 degs. Fan., because, strictly speaking, water does not exist below 32 degs. Fan., and ice follows another law. WATER BETWEEN 32 AND 212 FAH. i J ~ 1 "d 5 10 'd s ""d . 2 -a 2 1 flg 2 o 2 a S 1 2 c g 5 1 9 ~^ o 5 ** o ^ ' O d *** fc| V ^ o s ^ P< -*J a 60 O ~ ** " % - a 4-> a "bC O Pta a bo w a a 83 l_i ~* S OJ .. S-q 55 t. 7* *^ Sa rf n T Lrf 13 0) :3 QJ gj w 5 * 03 "5 si Ba ^ ao - a a 3a a Hfc Ba a 32^ 00 62.4-2 110 78 00 61.89 115 1'3 26 61.28 179 147. at 60 57 35 3.02 62.42 112 80 00 61 86 146 114 27 61.26 180 148.54 60 55 40 8.06 62.42 113 81 01 61.84 147 115 2o 61.24 181 149.55 60.53 45 13.08 62 42 114 82.02 61 83 148 116 29 61.22 182 150.56 60 50 50 18.10 62.41 115 83.02 61 82 149 117 30 61.20 183 151 57 60.48 52 20.11 62 40 116 84.03 61 80 150 118 30 61.18 184 152 58 60.46 54 22.11 62.40 117 85.04 61 78 151 119 31 61.16 185 153 58 60 44 56 24 11 62 39 118 86 05 61.77 152 120 32 61.14 186 154 59 60 41 58 26.12 62 38 119 87.06 61 75 153 121 33 61.12 187 155 60 60.39 60 28 12 62.37 120 88.06 61 74 154 122.34 61.10 188 156 61 60.37 62 30 . 12 62.36 121 89 07 61 72 155 123.34 61.08 189 157 62 60.34 64 32.12 62 35 122 90.08 61.70 156 124 35 61.061 190 158 62 60.32 66 34 12 62 34 123 91.09 61.08 157 125.36 61.04 191 159.63 GO 29 63 36.12 62.33 124 92 10 61.67 158 126.37 61.02! 192 160.63 60 27 70 3 11 H2 31 125 93 10 61 65 159 127.38 61.00 193 161.64 60 25 72 40.11 62.30 126 94 11 61.63 160 128 38 60.98 194 162 65 60 22 74 42.11 62 28 127 95 12 61.61 161 129 39 60.96 195 163.66 60.20 76 44 11 32.27 128 96.13 61 60 162 130 40 60.94 196 164.66 60 17 78 46 10 62.25 129 97.14 61.58 163 131.41 60.92 197 165.67 60 15 80 43.09 62.23 130 98 14 61.56 164 132.42 60.90 198 166.68 60.12 82 50.08 02.21 131 99 15 61.54 165 133.42 60.87 199 167.69 60 10 84 52.07 62.19 132 100.16 61.52 166 134 43 60.85 200 168.70 60.07 86 54 06 62 17 133 101.17 61 51 167 135.44 60.83 201 169.70 60.05 88 56 05 62.15 134 102 18 61.49 168 136.45 60.81 202 170 71 60.02 90 53 04 62.18 135 103.18 61.47 169 137. 4K 60.79 203 171 72 60.00 92 60.03 62 11 136 104 19 61.45 170 138.46 60.77 204 172.73 59.97 94 62 02 62.09 137 105.20 61.43 171 139 47 60.75 205 173.74 59.95 96 64 01 62 07 138 106.21 61.41 172 140 48 60.73 206 174 74 59 92 98 66 01 62.05 139 107.22 61.39 173 141.49 60.70 207 175.75 59 89 100 68.01 62 02 140 103 22 61.37 174 142 50 60 68 208 176 76 59 87 102 70.00 62 00 141 109.23 61 36 175 143.50 60.66 209 177.77 59.84 104 72.00 61.97 142 110 24 61 34 176 144.51 60.64 210 178.78 59.82 106 74.00 61.95 143 111 25 61 32 177 145.52 60.62 211 179.78 59.79 108 76 00 61.92 144 112.26 61.30 178 146 53 60.59 212 180.79 59 76 HANDBOOK ON ENGINEERING. 603 To find the number of gallons of water delivered by a steam pump in one minute, when the diameter and stroke of water piston, and the number of strokes per minute are given : Rule* Square the diameter of water piston and multiply the result by .7854. Multiply this product by the stroke of the water piston in inches ; and multiply this product by the number of strokes per minute, and divide the result by 231. Example* How many gallons of water per minute will a steam pump deliver, whose water cylinder is 6 inches in diameter and 12 inches stroke, making 60 strokes per minute? Ans. 88.128 galls. Operation : 6 X 6 X .7854 28.2744. 28.2744 X 12 X 60 And, -~23i~ - = 88.128. To find the relative proportion between the steam and water pistons. Rule* Multiply the area of the pump piston by the resistance of the water in pounds per square inch ; and divide the product by the pressure of steam in pounds per square inch. The quotient will give the area of steam piston in square inches to balance the resistance. To this quotient add from 30 to 100 per cent of it- self, depending on the speed of the pump, and divide the sum by .7854, and extract the square root of the quotient for the diameter of the steam piston. Example* What should be the diameter of the 'steam piston to force water against a pressure of 125 pounds per square inch, the diameter of water piston being 6 ins. and the steam pressure 60 Ibs. per square inch? Ans. 10J inches. Operation: 6X6 .7874 = 28.2744 sqr. ins. And, 28.2744 X 125 = 3534.3 pounds the total resistance. 3534.3 Then, :^r = 58.9 square inches the area of steam piston. 604 HANDBOOK ON ENGINEERING. We will add 50 per cent for friction in pump and in delivery pipe, and for a moderate speed of pump. Then, 58.0 X .50 = 29.45. And, 58.1) + 29.45=88.35, 88.35 And, r-vKA = 112.49 sqr ins. Then, ^J 112.49 = 10.6 ins. the diameter of the steam piston. To find the pressure against which a pump can deliver water, when the diameter of steam piston, pressure of steam in pounds per square inch, and diameter of water piston are given : Rule* Multiply the area of steam piston by the pressure of steam in pounds per square inch, and divide the product by the area of the pump piston, and deduct from 30 to 50 per cent for friction in the delivery pipe and in the pump itself. Example* The area of the steam piston is 112 square inches, and the area of water piston is 28 square inches, and the steam pressure is 60 Ibs. per square inch, against what pressure can the pump deliver water, the resistance from friction being 48 per cent? Ans. 125 Ibs. per sqr. in., nearly. 112X60 Operation: gg And, 240 X -48 = 115.20. Then, 240 115.20 = 124.8. To find the steam pressure required when the diameter of the steam piston, the diameter of the water piston, and the resistance against the pump in pounds per square inch are given : Rule. Multiply the area of water piston by the resistance on the pump in pounds per square inch, and divide the product by the area of the steam piston. HANDBOOK ON ENGINEERING. 605 Example* The resistance against the pump, including fric- tion, is 240 pounds per square inch. The area of steam piston is 112 square inches, and the area of water piston is 28 square inches. What pressure of steam is required to operate the pump? Ans. 60 Ibs. per sqr in. ~ 240 X 28 , n Operation: - = 60. LL4 Now anything over 60 Ibs. will operate the pump, and the faster it is run the higher must be the pressure above 60 pounds. To find the diameter of water piston when the diameter of steam piston, the steam pressure in pounds per square inch, and the resistance against the pump piston in pounds per square inch are given : Rule. Multiply the area of steam piston in square inches by the steam pressure in pounds per square inch, and divide the product by the resistance in pounds per square inch on the water piston. Example* The resistance against the pump, including fric- tion, is 240 pounds per square inch ; the area of steam piston is 112 square inches, the steam pressure is 60 pounds per square inch, what should be the diameter of water piston? Ans. 6 inches. Operation : - X 6 = 35.65 sqr. ins. Call it 36 sqr. ins. Then, ^ = 6. To find the horse power required in a steam pump to feed a boiler with a given number of pounds of water per hour against a given pressure of steam : Rule. Multiply the velocity of flow of water in feet per min- ute by the total pressure against which the water is pumped in pounds per square inch, and divide the product by 33,000, and the quotient will be the horse power. 606 HANDBOOK ON ENGINEERING. Example* What horse power is required to feed a boiler with 600 gallons of water per hour against a total resistance of 112 Ibs. per square inch, including the friction in the delivery pipe, lift of water in suction pipe, weight of check valve, and friction in the pump itself? Ans. 1 H. P. nearly. Operation: 600 X 231 = 138,600 cubic inches of water per hour. 138,600 And, gQ =2310 cubic inches of water per minute. 2310 And, :- =192.5 feet per minute, the velocity of the water. The total resistance is 112 Ibs. per sqr. in. Then, 192.5 X 112 = 21560 foot pounds. 21560 And ' 3^000 = -663H.P. Now add say 50 'per cent and we have .653 X .50 = .3265. And, . 653 -f .3265 = .9795. This pump will feed a boiler as shown above, or it will deliver 600 gallons of water per hour under a head of 258 feet. 112 Thus, -^^ = 258. To find the horse-power of boiler required to furnish steam for a pump running at its fullest capacity. Role* Multiply the number of gallons of water delivered by the pump in one minute by 8-J. Multiply this product by the total height in feet to which the water is to be lifted, measuring vertically from the source of supply to the point of delivery, and divide the result by 33,000. Add from 50 to 75 per cent to the quotient for loss from friction of water in the pipe, friction in the pump, waste of steam in the cylinder, and other contingencies, a ud the result will give the horse power of boiler required. HANDBOOK ON ENGINEERING. 607 Example* What horse-power of boiler is required to run a steam pump lifting 800 gallons of water per minute to a height of 103 ft. from the source of supply? Ans. 50 H. P., nearly. Operation : 800 X 8J = 6667 Ibs. of water. And, 6667 X 163 = 1,086,721 footpounds. 1,086,721 And, --- - 33 H. P., nearly. Then, 33 X .50=16.50. And, 33 -f 16.5 = 49.5. To find the diameter of discharge nozzle for a steam pump, when the diameter and stroke of the water piston and the number f strokes per minute are given, and the maximum flow of water in feet per minute is given : - Rule* Find the cubic contents of the water cylinder for one stroke in cubic feet, and multiply it by the number of strokes per minute. Multiply this product by 144 and divide the result by the velocity of the water in feet per minute, and the quotient will be the area of pump nozzle in square inches. Example* The diameter of water cylinder is 10 inches, and the stroke of piston is 12 inches, and the speed is 50 strokes per minute. The velocity of water required is 500 feet per 'minute, what should be the diameter of pump discharge nozzle ? Ans. 3 J ins., nearly. Operation: 10 X 10 X .7854 = 78.54 sqr. ins. area of piston. And, 78.54 X 12 = 942.48 cubic inches in the cylinder for one stroke. 942.48 And, - ^pft = .5454 of a cubic foot for one stroke. And, .5454 X 50 == 27.27 cubic feet for 50 strokes per minute. 27.27 X 144 Then, - ^TTX - = 7.8537 sqr. ins. the area of the nozzle. 000 And, J 7 - 8537 = 3.1 ins. the diameter. 608 HANDBOOK OX KXGIXKKRINC}. To find the approximate size of suction pipe when its length does not exceed 25 ft. and when there are not more than two elbows in the same : Rule. Square the diameter of water cylinder in inches and multiply it by the speed of the piston feet in per minute ; divide this product by 200, and divide this quotient by .7854 and extract the square root, and the result will be the diameter of suction pipe, except for very small pipes when it should be made larger than the size given by the rule, in order to lessen the friction of the moving water. Example* The diameter of water cylinder is 6 ins., the stroke of piston is 12 ins., and the number of strokes per miuute is 60, what should be the diameter of suction pipe? Ans. 4 ins. n 6X0X60 Operation : r- And, 1Q>8 == 13.75. ' .7854 Then, ^/13.75 = 3.7 ins. There is no pipe of this size made, so take 4-inch pipe. To find the velocity in feet per minute necessary to discharge a given number of gallons of water per minute through a straight smooth iron pipe of a given diameter, regardless of friction : Rule* Reduce the gallons to cubic feet and multiply by 144, and divide the product by the area of the pipe in square inches. Example* What should be the velocity of the water to dis- charge 100 gallons of water per minute through a 4-inch pipe? Ans. 149 ft. per minute. ^ 100X231 Operation : : ^ lo cubic feet. 1728 And, 13 X 144 = 1872 cubic inches placed in a continuous line. Then, 4 X 4 X .7854 ='= 12.5664 square inches, the area of pipe. And, - = 12.5664 HANDHOOK ON KMJINKKRING. 609 To find the velocity in feet per minute of water flowing through a pipe of given diameter, when the diameter of water cylinder and speed of piston in feet per minute are given : Rule* Multiply the area of water cylinder in square inches by the piston speed in feet per minute, and divide the product by the area of the pipe in square inches. Example* The diameter of water cylinder is 8 ins., and the piston speed is 100 ft. per minute, and the diameter of discharge pipe is 4 ins., what is the velocity of the water in the discharge pipe? Ans. 400 ft. per minute. Operation: 8 X H X .7854 = 50.26 sqr. ins. area of the water piston. And, 50.26 X 100 = 5026. The area of the pipe is 12.56 sqr. ins. T,,, "=. To find the number of gallons of water discharged per minute through a circular orifice under a given head : Rule, Find the velocity of discharge in feet per second and multiply it by 60, then multiply this product by the area of the orifice in square feet, and multiply this last product by 7.48, and the result will be the gallons discharged per minute. Example. How many gallons of water will be discharged per minute through an orifice 4 inches in diameter under a head of 81 feet? Ans. 2829.7 galls. Operation: -^81 = 9. And, 9 X 8.025 = 72.225 feet per second, the velocity of discharge. The factor 8.025 is a con- stant for any head, and is found thusly: - v '2 X32.2 == 8.025. Or, the velocity of discharge may be found in this manner : > /2~X"32^2~x"8l = 72.22 feet per second, that is, the veloc- ity in feet per second equals the square root of the acceleration 39 610 HANDBOOK ON ENGINKKKING. due to gravity multiplied into the head in feet. Continuing the operation, we have : 72.225 X 60 = 4333.5 feet per minute. And ; 4 X 4 X -7854 = 12.5664 sqr. ins. area of orifice. And, * = .0873 of a square foot, the area of orifice, 144 also. Then, 4333.5 X -0873 = 378.3 cubic feet. And, 378.3 X 7.48 = 2829.7 galls. NOTE. With a ring orifice only 64 per cent of the above amount of water would be discharged, and with a funnel-shaped orifice only 82 per cent. To find the number of gallons of water discharged per minute under a given pressure in pounds per square inch : Rale* Divide the given pressure in pounds per square inch by .433 in order to get the head in feet, and then proceed accord- ing to the foregoing rule. Example* How many gallons of water will be discharged per minute through an orifice one square inch in area, under a pres- sure of 35.073 Ibs. per square inch? Ana. 81 galls, per minute. 35.073 Operation: 433" =81 ft., head equivalent to the given pressure. And, V2X32.2 X81 = 72.225 ft. per second the velocity. And, 72.225 X 60 = 4333.5. Also, rjj = .00694 of a square foot, equals the area of the orifice. And, 4332.5 X .00694 == 30.07449. And, 30.07449 X 7.48 == 224.9 galls. Then, deducting 64 per cent, we have: > 224.9 X . 64 = 143.9. And, 224*9 143.9=81. A HANDBOOK ON ENGINEERING. 611 To find the area of orifice in square ins. necessary to discharge a given number of gallons of water per minute under a given head in feet : Rule. Divide the number of gallons by the constant number 15.729 multiplied into the square root of the head, and the result will be the area of orifice in square inches. Example* What must be the area of orifice to discharge 1778.5 gallons of water per minute under a head of 81 feet? Ails, 12.56 sqr. ins. Operation: V^ = 9 - And, 9 X 15.729 = 141.6. 1778.5 Then ' -T4T6 = 12 - 56 ' To find how many gallons of water will flow through a straight smooth iron pipe in one minute under a given pressure in pounds per square inch, or head in feet : Rule* Multiply the inside diameter of the pipe hi feet by the head in feet, and divide the product by the length of pipe in feet. Extract the square root of the quotient and multiply it by 48, and the product will be the velocity of flow in feet per second. Multiply this result by 12 to reduce it to inches, and by 60 for the flow per mmute, and multiply again by the area of the pipe in square inches, and divide by 231 for the gallons discharged per minute. Example* How many gallons of water will be discharged per minute through a 4-inch pipe 2000 feet long, under a head of 92 feet? Ans. 230 galls, per minute. Operation : 4 ins. = .33 of a foot. And, 92 X .33 = 30.36. 30.36 And ' 2000" = 612 HANDBOOK ON ENGINEERING. And, V>5 = .1225. Then, .1225 X 48 X 12 = 70.56 ins. per second. And, 70.56 X' 60 =4233.60 ins. per minute. Then, 4 X 4 X .7854 12.56 sqr. ins. the area of the pipe. And, 4233.60 X 12.56 =53174.016 cubic ins. 53174.016 Then, -- = 230.2. Example. Assume two wells A and B with their mouths on a level. Well A is 26 ft. deep, and well B is 40 ft. deep. Well A is fed by natural springs and has a depth of water of 5 feet. The distance between the wells is 600 feet. How many gallons of water will a 1 inch pipe, laid perfectly straight and level, syphon over in one minute providing well B is always pumped dry, and that the pipe extends into well A 26 feet, and into well B 38 feet, using bends instead of elbows? Ans. 4 galls, per minute. Operation* The head equals 38 feet. The diameter of the pipe equals .0833 foot. Then, 600 -f 38 + 26 =664 ft. total length ot pipe. And, 38 X .0833 = 3.1654. 3.1654 And > -664- And, V -0047 = .068. Then, .068 X 48 = 3.264 ft. velocity per second. And, 3.264 X 60 = 195.840 ft. velocity per min. The area of pipe equals .7854 sqr. inch. Then, 195.840 X .7854 = 153.8127. And, 153.8127X7.48 = 1150.52. 1150.52 And, ~TZi~~ 8 nearly, gallons. HANDBOOK ON ENGINEERING. 613 Deducting 50 per cent on account of 2 bends and friction, we have 4 gallons per minute syphoned over. To find the head in feet due to friction in a pipe running full : - Rule, Multiply the length of the pipe in feet by the square of the number of gallons per minute, and divide the product by 1,000 times the 5th power of the diameter of the pipe in inches. The quotient less 10 per cent is the head in feet necessary to over- come the friction. NOTE. The head is the vertical distance from the surface of the water in the tank or reservoir, -to the center of gravity of the lower end of the pipe, when the discharge is into the air, or, to the level surface of the lower reservoir when the discharge is under the water. Example* A 2-inch pipe 100 feet long and running full, discharges 50 gallons of water per minute, what is the head in feet due to friction? Ans. 7.029 feet. Operation : 2 X 2 X 2 X 2 X 2 = 32 = the 5th power of the diameter of the pipe. And, 50 X 50 = 2500. And, 2500 X 100 = 250,000. Also, 32 X 1,000 = 32,000. 250,000 Then > And, 7.81 less 10 percent of itself equals 7.029. The resistance to the flow of water in pounds per square inch, due to friction, is found by dividing the friction head by 2.3. 7.029 Thus, 2Q3 =3.051bs. To find the size of pump required to feed a boiler of a given capacity : 614 HANDBOOK ON ENGINEERING. Rule. Multiply the number of pounds of water evaporated per pound of coal by the number of pounds of coal burned per sqr. foot of grate surface per hour, and multiply this product by the number of square feet of grate surface in the boiler furnace. This will give the number of pounds of water evaporated by the boiler in one hour. Divide this by 60 to find the evaporation per minute, and divide again by 8i in order to get the evaporation in gallons per minute ; add from 10 to 15 per cent to the last result for leakage and other contingencies, and select a pump that will deliver the gross number of gallons of water per minute at any speed that may be desired, usually taken, however, at 100 feet per minute. Example* What should be the dimensions of the water end of a steam pump, and what should be the speed of piston to sup- ply a boiler having a grate surface of 20 square feet, and burning 15 pounds of coal per square foot of grate, and evaporating 9 pounds of water per pound of coal per hour ? Operation ;20X15X9 2700 pounds of water evapo- rated per hour. And, = 45 Ibs. of water evaporated per minute. 60 And, = 5.4 galls, per minute. Then, 5.4 plus 10 per cent of itself, equals 6 galls, nearly per per minute. Referring to a pump maker's catalogue we find that a single pump 3|" X 2|" X 5", making 90 strokes per minute, will do the work, or, a duplex pump 3" X 2" X 3", making 100 strokes per minute will do the work equally as well. Again, adding 10 per cent to the pounds of water evaporated per minute we have, 45 + 4.5 =49.5 pounds. And, 49.5 X 27.71 = 1371.64 cubic inches displacement in the water cylinder per minute, and at 90 strokes per minute we have 15.24 cubic inches displacement per stroke. HANDBOOK OX ENGINEERING. 615 Thus, 15.24 which is all that is required for our yo boiler. Now, taking the above single pump we have: 2.25 X 2.25 X .7854 X 5 = 19.8 cubic inches displacement per stroke. And, taking the duplex pump we have: 2 X 2 X .7854 X 3 X 2 = 18.8 cubic ins. displacement for each double stroke of the piston, or, plunger, showing that either pump is of ample capacity to feed the boiler at a fair piston speed. To find the duty of a pumping engine when the number of pounds of coal burned, the number of gallons of water pumped, the pressure in pounds per square inch against which the pump piston works, and the height of suction are given : Rule* Find the head in feet against which the pump works, by multiplying the pressure by 2.3, add the suction in feet to this head in order to get the total head. Multiply the gallons of water by 8J to get the pounds of water deliv- ered. Then multiply the total number of pounds of water by the head in feet, and divide the product by the number of pounds of coal divided by 100, and the result will give the duty in foot pounds. The duty of a pumping engine is the number of pounds of water raised one foot high for each 100 pounds of coal burned. Example* What is the duty of an engine pumping 2,890,000 gallons of water in 12 hours against a pressure of 30 pounds per sqr. inch, the suction being 12 feet, and coal burned 24,470 pounds? Ans. 8,070,426 foot pounds. Operation: 30 X 2.3 = 70 nearly the head in feet. And, 2,890,000 X 8J = 24,083,333 pounds of water. Also, 70 -f 12 = 82 ft. total lift of water. And, 24,083,333 X 82 = 1,974,833,306 Ibs. of water lifted one foot high in 12 hours. 616 HANDBOOK ON ENGINEERING. And, M74.883.806 = 8,070,426. To find the horse power of a pumping engine : Rule* Divide the number of pounds of water raised one foot high in one minute by 33,000. Example* What is the H. P. of the pumping engine given in the above example? Ans. 83.11 H. P. Operation: 12 X 60 = 720 minutes. And, 1 ' 974 ' 888 ' 8QG = 2,742,824 Ibs. of water raised one foot 720 high in one minute,, Then, 2,742,824 = 83>n> 33,000 To find the capacity of a pump to feed a boiler it is necessary to know how much water the boiler is capable of evaporating per minute or per hour. Each horse power of boiler capacity corre- sponds to an evaporation of thirty pounds of water per hour. It is good practice to operate a pump slowly and continuously, and for this reason the pump running at its normal speed should be capable of supplying about twice as much water as the boiler evaporates under usual conditions. To find the diameter of water cylinder to deliver a certain num- ber of gallons of water per minute, when the stroke of the piston and the number of strokes per minute are given : - Rule. Multiply the number of gallons by 231, and divide the product by the stroke of the piston, and divide this quotient by the number of strokes per minute, and divide this last quotient by .7854, then extract the square root of the result for the diameter of the water piston. Example* A battery of boilers evaporate 100,000 pounds of water in one hour, what should be the diameter of water cylinder to supply this battery, the stroke of piston being 12 inches and making 100 strokes per minute? Ans. 7 inches. HANDBOOK ON ENGINEERING. 617 100,000 Operation: gx = 1666| pounds of water evaporated in one minute. L666| And, 7rj =200 galls, evaporated in one minute. Then following the above rule we have : 200X231 =46200. 46200 And, -jg = 3850. 3850 And ' "iOO' 38 ' 5 ' 38.5 And ' 77854^ Then, j/49 = 1" the required diameter. To determine the H. P. of boiler a steam pump of given dimensions will supply when the number of strokes per minute are given : Rule* Multiply the area of the piston is square inches by the stroke of piston in inches, and this product divided by 231 will give the gallons per stroke. Multiply this quotient by the num- ber of strokes per minute for the number of gallons per minute, and by 60 for the number of gallons per hour. Multiply this product by 8^ to find the number of pounds of water per hour delivered by the pump, and divide this product by 30 for the H. P. of boiler the pump will supply. This rule is based upon the assumption that the full capacity of the water cylinder is deliv- ered at each stroke, no allowance being made for slippage, leak- age, or short strokes. Example* The water piston of a steam pump is 6 inches in diameter and has a stroke of 12 inches, making 100 strokes per minute, what H. P. of boiler will the pump supply? Ans. 2448 H. P. 618 HANDBOOK ON ENGINEERING. Operation: 6 X 6 X .7854 ^28.2744 sqr. ins. area of piston. And, 28.2744 X 12 = 339.2928 cubic inches for one stroke. 339.2928 And, QQ^J =* 1.4688 galls, per stroke. And, 1.4688 X 100 = 146.88 galls, per minute. And, 146.88 X = 8812.8 galls, per hour. And, 8812.8 X 8-i = 73,440 pounds of water per hour. 73440 Then, QA = 2448 H. P. of boilers. oU Watt allowed one cubic foot (62 Ibs.) of water per H. P. per hour. Then taking this allowance instead of 30 as above, we 73440 would have, - = 1175 H. P. of boilers which the above pump would be suitable for, and which could be run very slowly, thus prolonging the life of the pump. Even though a suction pipe should be perfectly air tight, a perfect vacuum cannot be formed in it, because water contains air, and even the coldest water gives off some vapor tending, to impair the vacuum . Twenty-eight feet is a very good lift for a pump taking its water by suction. HANDBOOK ON ENGINEERING. 619 CHAPTER XXI. MECHANICAL REFRIGERATION. About the first thing asked by persons who are becoming interested in the subject of refrigerating and ice-making is, " Tell me how the thing is done? " Mechanical refrigeration, primarily, is produced by the evapo- ration of a volatile liquid which will boil at low temperature, and by means of a special apparatus the temperature and desired amount of refrigeration is placed under control of the operator. Simplest Apparatus Brine Tank or Concealer A, -* Elemental Refrigerating Apparatus. Fig. 1. The simplest form of refrigerating mechanical apparatus consists of three principal parts: ^4, an ''evaporator," or, as sometimes called, a " congealer," in which the volatile liquid is vaporized ; B, a combined suction and compressor pump, which 620 HANDBOOK ENGINEERING. sucks, or properly speaking, " aspirates " the gas discharged by the compressor pumps, and under the combined action of the pump pressure and cold condenser, the vapor is here reconverted into a liquid, to be again used with congealer. You now see the function of the compressor pumps and condensers. PRINCIPLES OF OPERATION. The action of all refrigerating machines depends upon well- defined natural laws that govern in all cases, no matter what type of apparatus or machine is used, the principle being the same in all ; while processes may slightly vary, the properties of the par- ticular agent and manner of its use affecting, of course, the efficiency or economic results obtained. Water Supply Condenser C FRICK COMPAQ Yg 1 ENGINEERS Compression Refrigerating Apparatus Three Parts UU LI U U UJU EXPANSION^- Brine Tank or Congealer A. Fig. 2. Outline drawing of mechanical compression system OPERATION OF APPARATUS. (See Fig* 2*) The apparatus being charged with a sufficient quantity of pure ammonia liquid, which we will, for simplicity, assume to be stored in the lower part of the condenser C', a small cock or expansion valve controlling a pipe leading to the congealer HANDBOOK ON KNCJ1NKKUING. or brine t:mk J, is slightly opened, thus allowing tlxe liquid to pass in the same oitice as a tube or flue in strain boiler :md having precisely the same function, it may be called heating or steam-making service. The amount of water capable of being boiled into steam in a boiler depends upon the square feet of heat- ing surface, temperature of lire and pressure of steam ; and the same is true of the capacity of heating surface pre- sented by the coils in the evaporator. The heat is transmitted through the coils from surrounding substance to the ammonia liquid, which is boiled into a vapor the same as water is boiled into steam in a steam boiler; as previously explained, the heat thus becomes cooler ; the amount taken up and made negative being in proportion to the pounds of liquid ammonia evaporated. FUNCTION OF THE RUHR AND CONDENSER. The office of the compressor, pump and condenser is to re- convert the gas after evaporation into a liquid, and make the original charge of ammonia available for use in the same -appa- ratus, over and over again. It will appear to the reader, after having carefully followed the text, that the pump and condenser might be dispensed with, but these conditions may only be eco- nomically realized when the, at present, expensive ammonia liquid can be obtained in great quantities and at less cost than the process of reconverting the vapor into a liquid by compression machinery and condenser on the spot. WHAT DOES THE WORK. The real index of the amount of cooling work possible is the number of pounds of ammonia evaporated between the observed range of temperature. To make the above clear, we will add that each pound of ammonia during evaporation is capable of storing up a certain quantity of heat, and that the simplest forms 622 HANDBOOK ON ENGINEERING. of refrigerating apparatus might consist, as shown by engraving, of two parts, to wit : A congealer and a tank of ammonia. In this apparatus the ammonia is allowed to escape from the tank into the congealer as fast as the coils therein are capable of evapo- rating the liquid into a gas. When completely evaporated the resulting vapor is allowed to escape into the atmosphere, which means it is wasted, the supply being maintained by furnishing fresh tanks of ammonia as fast as contents are exhausted. This process, while simple, would be tremendously expensive, costing at the rate of about $200 per ton, refrigerating or ice-mel ting- capacity. To recover this gas and reconvert to a liquid on the spot in a comparatively inexpensive manner, is the object to be obtained. MECHANICAL COLD EASILY REGULATED. This being under the control of the cock or valve leading from the condenser (called an expansion valve). As the gas begins to form in the evaporator, the compressor pump B is set in motion at such a speed as to carry away the gas as fast as formed, which is discharged into the condenser under such pressure as will bring- about a condensation and restore the gas to the liquid state ; the operation being continuous so long as the machinery is kept in motion. UTILIZING THE COLD. To utilize the cold thus produced for refrigerating, two meth- ods are in use, the first of which is called the brine system ; the second is known to the trade as the direct expansion system, both of which I will now proceed to explain at some length. BRINE SYSTEM. In this method, the ammonia evaporating coils are placed in a tank which is filled with strong brine made of salt, which is well known not to freeze at temperature as low as zero. This is the brine HANDBOOK ON ENGINEERING. 623 tank or cougealer A. The evaporating or expansion of the ammo- nia in these coils robs the brine of heat, as heretofore explained, the process of storing cold in the brine going on continuously and being regulated, as required, at the gas expansion valve. To practically apply the cold thus manufactured, the chilled brine or non-freezing liquid is circulated by means of a pump through coils of pipe which are placed on the ceilings or sides of the apart- ments to be refrigerated, the process being analogous to heating rooms by steam. THE BRINE COOLS THE ROOMS. The cold brine in its circuit along the pipes becomes warmer by reason of taking up the heat of the rooms, and is finally returned to the brine tank, where it is again cooled by the ammo- nia coils, the operation, of course, being a continuous one. DIRECT EXPANSION SYSTEM. By this method, the expansion or evaporating coils are not put in brine tanks, but are placed in the room to be refrigerated, and the ammonia is evaporated in the coils by coming in direct con- tact with the air in the room to be refrigerated, no evaporating tank being used. RATING OF THE MACHINE IN TONS CAPACITY. For the information of the unskilled reader, 1 will state that machines are susceptible of two ratings ; that is, either their capacity is given in tons of ice they will produce in one day (24 hours), called ice-making capacity ; or they are rated equal to the cooling work done by one ton of ice-making per day (24 hours), called .refrigerating capacity. DIFFERENCE IN THESE RATINGS. Ordinarily the ice-making capacity is taken at about one-half of the refrigerating capacity, but this is only approximate, and 624 HANDBOOK ON ENGINEERING. the tons of ice a refrigerating machine will make depend upon the initial temperature of the water to be frozen. UNIT OF CAPACITY. The unit of capacity is one ton of ice made from water at o2 Fahr., into ice at 32, per day, which is equal to 284,000 Ibs. of water cooled one degree, or 284,000 heat units, and is the tonnage basis for refrigerating capacity as well as ice made from water at 32. THE PREPARATION OF BRINE. Fig. 1. There are two methods in general use, which I will explain. Fig. 1 shows one of the methods, which consists of allowing water to percolate through a body of salt. Take a large water-tight barrel or cask, and tit a false bottom HANDBOOK ON ENGINEERING. or wooden grating six or eight inches above the bottom ; this can be made of strips of wood about an inch square, and placed not over one-half inch apart. This false bottom should be supported by two strips of boards, each six inches in width, placed on edge and nailed to the bottom. These boards should have several holes bored near their bottoms to permit a free passage of water. The water inlet should be below the false bottom. A single thickness of burlap should be stretched across the top of the false bottom and tacked to sides of barrel. The outlet pipe for the brine should be four or five inches below the top of the barrel. The water is supplied at the bottom from a convenient hose or faucet. The supply pipe should be of about 1J in. diameter ; and the outlet pipe about 1J in. diameter. If it is necessary to make brine faster than can be accomplished with one barrel, lit up two or more extra barrels. To make brine, fill the barrel above the false bottom with salt and turn on the water. The salt dissolve s rapidly and more must be shoveled in on top. The barrel must be kept full of salt or the brine will not be of full strength. No stirring is necessary. Keep skimming off all waste matter rising to the top. The brine outlet should be provided with a strainer of some kind to prevent chips, etc., from running out with the brine. Brine should not be made any stronger than is necessary to prevent it from freezing. Fig. 2 is the other method of brine-making. This method is a water-tight box, say four feet wide, 8 feet long and 2 feet high, with perforated false bottom and compartment at end. Locate the brine-maker at a point above the brine tank.C onmct the space under the false bottom with your water supply, extending the pipe lengthwise of the box, being perforated at each side to insure an equal distribution of water over the entire bottom surface ; use a valve in water supply pipe. Near the top of the brine- maker, at end compartment, put in an overflow with large strainer to keep back the dirt and salt, and connect with this a pipe, say three 40 626 HANDBOOK ON ENGINEERING. inches in diameter, with salt catcher at bottom, leading into the brine tank. Use a hoe or shovel to stir the contents. When all is ready, partly fill the box with water, dump the salt from the bags Salt Gauge Complete Brine Mixing Arrangement Fig. 2. on the floor alongside and shovel into brine-maker or dump direct from the bags into the brine-maker as fast as it will dis- solve. Regulate the water supply to always insure the brine being of the right strength as it runs into the brine tank. This point must be carefully noticed. Filling the brine tank with water and attempting to dissolve the salt water directly therein is not satisfactory, as quantities of salt settle on the tank bottom coils, forming a hard cake. It is a good plan, when desired to strengthen the brine, to suspend bags of salt in the tank, the salt dissolving from the bags as fast as required ; or the return brine from the pumps may be allowed to circulate through the brine- maker, keeping same supplied with salt. INSULATION OF BUILDINGS. The insulation of buildings used for the preservation and storage of substances subjected to mechanical refrigeration, is a HANDBOOK ON ENGINEERING 627 INSULATING BUILDINGS AND COLD STORAGE ROOHS. No 1 14. inch Brick , 4 " Air Space ,9 " Brick Cement Wash Pitched -2"x 3"Studding Tar Paper -TT&G. Board 2*x 4"Studding -1''f&. G. Board -Tar-Paper ~- TT&'G. Board 14 Brick 4" Pitch &.-Ashea -.4"' Brick 4" Air Space 14" Brick No 2 36" Brick Wall Pitch fSheathing Air Space 2"x 4"Studding T'Sheathing Mineral Wool 2"x 4"Studding 1"Sheathing No 3 Various Aooroved Methods, 628 HANDBOOK ON ENGINEERING. matter of vital importance, when viewed from an economic stand- point. It is true that by employment of a large surplus of refrigerating- power, poor insulation with its entailed great loss of negative heat is wastefully overcome, and a certain amount of cooling work can be accomplished ; but this is t\ bad way to reach a result ; it is like pumping out a leaky ship and keeping ever- lastingly at it, when the best way is to stop the leak and be done with the pumping it is a preventable loss. Poor insulation is like paying interest on borrowed capital, which is earning nothing for the borrower, a never-ceasing and useless drain upon the machinery and pocket-book of the user. PERFECT INSULATION. Perfect insulation is when there is absolutely no transfer of heat through the walls of a building ; but this is scarcely pos- sible. If it were, once cooling of the contents of a room would suffice ; for there being no loss, they would continue at the same temperature for an indefinite period. If all articles placed in the room thereafter were previously cooled to the temperature of the room before placing therein, no work need be done thereafter in the room itself. A large percentage of the actual work of a refrigerating machine is required to make up for transfer of heat through the walls, floors and ceilings occasioned by improper insulation, and the amount may be experimentally determined by proper instruments. Owing to difference in construction, exposure and insulation of building, you will find a great dif- ference in economy of performance and work done by the same machine in use by different parties in the same line of business ; and what a given machine and apparatus will do in one place is no certain guide for another place somewhat sim- ilar ; the insulation, exposure, and method of handling the business are mainly responsible for the difference. HANDBOOK ON ENGINEERING. 629 As shown by the engraving, screw into the ammonia flask a piece of bent one-quarter inch pipe, which will allow a small bot- tle to be placed so as to receive the discharge from it. This test bottle should be of thin glass with wide neck, so that quarter-inch pipe can pass readily into it, and of about 200 centimeters capac- ity. Put the wrench on the valve and tap it gently with a ham- mer. Fill the bottle about one-third full and throw sample out in order to purge valve, pipe and bottle. Quickly wipe off mois- ture that has accumulated on the pipe, replace the bottle and open Testing for Water by Evaporation. valve gently, filling the bottle about half full. This last operation should not occupy more than one minute. Remove the bottle at once and insert in its neck a stopper with a vent hole for the escape of the gas*. A rubber stopper with a glass tube in it is the best, but a rough wooden stopper, loosely put in, will answer the purpose. Procure a piece of solid iron that should weigh not less than eight or ten pounds, pour a little water on this and place the bottle on the wet place. The ammonia will at once begin to boil, and in warm weather will soon evaporate. If any residuum, pour it out gently, counting the drops carefully. Eighteen drops are about equal to one cubic centimeter, and if the sample taken 630 HANDBOOK ON ENGINEERING. amounted to 100 cubic centimeters, you can readily approximate the percentage of the liquid remaining. Sectional View of lo-ton Refrigerating Machine, regular pat- tern . Frick Company 's Eclipse Refrigerating Machine, with Placer Slide-Valve Throttling Machine. LUBRICATION OF REFRIGERATING MACHINERY. It is well to speak of this, for the reason that it is an important subject ; and some users of machinery think that a cheap, low 29 HANDBOOK ON ENGINEERING. 631 grade of oil is really the cheapest. To disabuse their minds of this idea and suggest the necessity of high grade oils, both on the score of economy and to keep the machinery at all times in efficient running order, is the object of this article. First-class refrigerating machinery calls for the use of at least three- different kinds of oil, Nos. 1, 2 and 3, each of high grade: No* f. For use in the steam cylinder, and is known in the trade as cylinder oil. This ranges in price from 50c. to $1 per gallon. Good cylinder oil should be free from grit, not gum up the valves and cylinder, should not evaporate quickly on being subjected to heat of the steam, and when cylinder head is removed, a good test is to notice the appearance of the wearing surfaces ; they should be well coated with lubricant which, upon application of clean waste, will not show a gummy deposit or blacken. Use this oil in a sight feed lubricator with regular feed, drop by drop. No* 2* For use of all bearing and wearing surfaces of machine proper an oil that will not gum, not too limpid, with good body, free from grit or acid and of good wearing quality, flowing freely from the oil cups at a fine adjustment without clogging, and a heavier grade should be used for lubricating the larger bearings. No. 3* For use in compressor pumps. This oil should be what is called a cold test, or zero oil, of best quality. Best paraffine oil is sometimes used ; as also a clear West Vir- ginia crude oil. This oil, when subjected to a low temperature, should not freeze. EFFECTS OF AMMONIA ON PIPES. Ammonia has no chemical effect upon iron ; a tank, pipe or stop-cock may be in constant contact with ammonia for an in- definite time and no action will be apparent. The only protec- tion, therefore, that ammonia-expanding pipes require is from corrosion on the outer surface. As long as the pipes are covered 632 HANDBOOK ON ENGINEERING. with snow or ice, corrosion does not occur ; the coating of ice thoroughly protects them from the oxidizing effect of the atmos- phere ; but alternate freezing and thawing requires protected sur- faces, which are best obtained by applying a coat of paint every season . Expansion coils having to Withstand but a maximum working pressure of thirty pounds per square inch, are constructed with such absolute security, in whole and in detail, as to make them one of the most perfect pipe constructions on a large scale ever applied in practice. POSITION OF TANK TO BE EMPTIED.. TO CHARGE THE SYSTEM WITH AMMONIA. Position of the tank should be as shown, the outlet valve pointing upwards and the other end of the tank raised 12" to 15". The connection between the outlet valve of the tank and the inlet cock of the system should be a |" pipe. In charging, open valve of the tank cautiously to test connection ; if this is tight, open valve fully; start machine and run slowly till tank is empty. The tank is nearly empty when frost begins to appear on it ; run the machine till suction gauge reaches atmospheric pressure. If it holds at this pressure when machine is stopped, the tank is empty; if not, start up again. In disconnecting, close the valve on the tank first, the inlet cock of the system. Weigh tank HANDBOOK OX ENGINEERING. 633 before and after emptying ; each standard tank contains from 100 to 110 pounds of ammonia. PROCESS OF MECHANICAL REFRIGERATION. The process of mechanical refrigeration is simply that of removing heat, and mechanism is necessary, because the rooms and articles from which the heat is to be removed are already as cold, or colder than their surroundings, and consequently, the natural tendency is for the heat to flow into them instead of out of them. The fact that a body is already cold does not prevent the removal of more heat from it and making it still colder. The term cold describes a sensation and not a physical property of matter ; the coldest bodies we commonly meet with are still possessed of a large quantity of heat, part of which, at least, can be abstracted by suitable means. The only means by which heat can be removed from a body is to bring in contact with it a body colder than itself. This is the function that ammonia performs in mechanical refrigeration. It is so manipulated as to become colder than the body we wish to cool. The heat thus abstracted by it is got rid of by such further manipulation that (while still retaining the heat it has absorbed) it will be hotter than ordi- nary cold water, and therefore, part with its heat to it. Ammonia thus acts like a sponge. It sops up the heat in one place and parts with it in another, the same ammonia constantly going backward and forward to fetch and discharge more heat. The complete cycle of operation comprises three parts : 1st. A compression side , in which the gas is compressed. 2d. A t'OH w Diameter and Nominal Horse Power. 20" 26" 30" 34" 36" 40" 44" 50" 54" 58" 60" 64" 72" 78" 70ft. 80ft. 90ft. 100 ft. 110ft. 120 ft. 40 50 60 75 100 120 130 150 150 175 175 200 200 225 250 300 340 360 375 400 425 430 455 500 500 550 600 600 650 700 750 825 900 930 990 1050 IRON CHIMNEY STACKS. In many places iron stacks are preferred to brick chimneys. Iron chimneys are bolted down to the base so as to require no stays. A good method of securing such bolts to the stack is shown in detail in the figure on page 693. Iron stacks require to be kept well painted to prevent rust, and generally, where not bolted down, as here shown, they need to be braced by rods or wires to surrounding objects. With four such braces attached to an angle iron ring at f the height of stack, and spreading laterally at HANDBOOK ON ENGINEERING. least an equal distance, each brace should have an area in square inches equal to T Q^Q- the exposed area of stack (dia. x height) in feet. Stability or power to withstand the overturning force of Holding down Bolts and Lugs. the highest winds, requires a proportionate relation between the weight, height, breadth of base, and exposed area of the chimney. This relation is expressed in the equation in which d equals the average breadth of the shaft ; h = its height ; b = the breadth of base all in feet ; W == weight of IN LBS., and C = a coefficient of wind pressure per o CHIMNEY 694 HANDBOOK ON ENGINEERING. square foot of area. This varies with the cross-section of the chimney, and = 56 for a square, 35 for an octagon and 28 for a round chimney. Thus a square chimney of average breadth of 8 feet, 10 feet wide at base and 100 feet high, would require to weigh 56x8x100x10=448.000 Ibs., to withstand any gale likely to be experienced. Brickwork weighs from 100 to 130 Ibs. per cubic foot; hence, such a chimney must average 13 inches thick to be safe. A round stack could weigh half as much, or have less base. WEIGHT OF SHEET LAP RIVETED STEEL SMOKE STACKS, PER FOOT, THICKNESS. DIA. No. 18 No. 16 No. 14 No. 12 No. 10 N T o. 8 A" *Y' 1" 4 - 3 y A" ti" 1" W * H" 1" 12" 14" 8 94 10 11* 13 154 17 20 21 24* 291 314. 36} 37 42 42 48* 47 84 i 52* 62i 58 67 63 73* 68} 79} 73* 85 78} 91 84 97 16" ioj 13 17* 23 28 34 42 49 56 63 70 77 84 91 98 105 112 18" 14* 19} 26 31* 38} 47 55 63 71 79 86 94 102 110 118 126 20" 13* 16 22 2;} 35 4-2* 52 60 69 78 86 95 104 113 121 131 138 22" 1*4 24 i 31* 38* 46J 54 6:5* 73 82 91 99 108 118 137 146 24" 15* 19* 26* 34} 42 51 59 68* 78* 88 98 108 118 128 137 147 157 26" 16* 21 28J 37 45* 551 63 73* 84 94 105 115 126 137 147 158 Ifi8 28" 18 22* 31 40 49 59* 67 78 891 100 111 122 134 145 156 167 179 20" 32" | 33 35 45* 52* 56 68 71 75 83 i 95" 100* 106* 113 118 125 130 138 142 150 154 163 166 175 178 188 190 201 34" 28 37 48} 59* 72i 80 93* 106 119 132 146 160 173 186 199 21-2 36" 29* 39 51 63 764 85 100 114 128 143 158 173 188 202 216 230 38" * " 31* *14 531 66* 801 90 105 120 135 151 166 182 1.98 213 227 242 40" 83| 43* 56* 70 85 94 110 126 142 158 174 191 208 224 239 254 42" 35 45} 59* 73i 89} 98 115 132 149 166 183 200 217 234 250 266 44" 36} 48 62 77" 93* 103 121 138 155 173 191 209 227 245 262 279 48" 38* 50} 65 80* 971 107 126 144 162 181 199 218 237 255 273 291 48" 40 524 68 84 102 112 131 150 169 188 208 227 247 266 284 303 50" 54f 71 871 106} 116 136 156 176 195 216 236 258 277 296 315 52" 57 74 91 110* 121 142 162 182 203 224 '245 266 287 307 3'28 54" 77 94* 124 147 168 189 211 233 254 276 298 319 349 58" 80 98 119 133 158 180 202 225 248 270 294 317 340 363 68" 83 102 1231 137 164 186 209 232 256 280 304 327 351 375 60" 86 106 127* 142 169 192 215 240 264 289 314 338 362 387 62" 89 110 1311 146 174 198 222 247 273 298 324 349 374 400 64" 92 114 136 151 179 204 229 255 281 307 333 359 385 412 HANDBOOK ON ENGINEERING. 695 CHAPTER XXIV. HORSE=POWER OF GEARS. To determine the horse-power which any gear-wheel will trans- mit, four facts are required to be known : 1st. The kind of wheel, whether spur, bevel, spur mortise, or bevel mortise. 2d. The pitch. 3d. The face. 4th. The velocity of pitch circle in feet per second. Generally, the fourth fact is not known. It can be found if the pitch diameter of the wheel in inches and the number of revo- lutions per minute are given, for it can be obtained from them by the following rule : Rule* Given the pitch diameter in inches and the number of revolutions per minute ; to find the velocity of pitch line in feet per second. First, multiply the pitch diameter (in inches) by the number of revolutions per minute. Second, divide the product thus found by 230. The quotient i.s the velocity required. Example. What is the velocity of the pitch circle of a gear-wheel in feet per second, the pitch diameter = 43 inches, the revolutions per minute = 125 ? 43 x 125 divided by 230 = 23.4 feet per second. Table \ shows the greatest horse-power which different kinds of gears of 1-inch pitch and 1-inch face will safely transmit at various pitch-line velocities. To find the greatest horse-power which any other pitch and face will safely transmit, the following rule can be used : Rule* Given, the pitch (in inches), face (in inches), velocity of pitch circle (in feet per second) , and kind of gear ; to find the greatest horse-power that can be safely transmitted. First. Find the horse-power in Table 2, which the given kind 696 HANDBOOK ON ENGINEERING. of wheel with 1-inch pitch and 1-inch face will transmit at the given velocity. Second. Multiply the pitch by the face. Third. Multiply the horse-power found by the product of pitch by face. The final product is the horse-power required. Example. What is the greatest horse-power that a bevel- wheel, 43" pitch diameter, 2" pitch, 6" face, and 125 revolutions' per minute will safely transmit? From previous example, we have found the pitch-line velocity to be 23.4 feet per second, which is nearest to a velocity of 24 feet per second in Table 1. First, the horse-power which a bevel wheel of 1" pitch and 1' face will transmit is. (from table) at this velocity 4.931. Second, the product of pitch by face is 2x6 = 12. Third, 12 x 4. 931 =-59.17 horse-power. Answer. Whenever it is desirable to know about the average horse- power that any wheel will transmit, | or * of the results obtained by the rule above should be taken. TABLE 1. TABLE SHOWING THE HORSE-POWER WHICH DIFFERENI KINDS OF GEAR WHEELS OF ONE INCH PITCH AND ONE INCH FACE WILL TRANSMIT AT VARIOUS VELOCITIES OF PITCH CIRCLE. 1 2 3 4 5 Velocity of pitch circle in ft. per sec. Spur Wheels. Spur Mortise Wheels. Bevel Wheels. Bevel Mortise Wheels. 2 1.338 .047 .938 .647 3 1.756 .971 1.227 .856 6 2.782 1.76 1.76 1 363 12 4.43 3.1 3.1 2.16 18 5.793 4.058 4.058 2.847 24 7.052 4.931 4.931 3.447 30 8.182 5.727 5.727 4.036 36 9.163 6.314 6.414 4.516 42 10.156 7.102 7 . 102 4.963 48 10.083 7.680 7.680 5.411 HANDBOOK ON ENGINEERING. NOTE. When velocities are given, which are between these in Table, the horse-power can be found by interpolation. Thus, the horse-power for spur wheels at 14 feet velocity is found as follows : 14 minus 12 = 21 5.793 minus 4.43 = 1.363. 18 " 12 = 6 J Then | of 1.363 = .454 and .454 -f 4.43 = 4. 884 horse-power. TABLE 2. SHAFTING, HORSE- POWER TRANSMITTED BY VARIOUS SHAFTS, AT 100 REVOLUTIONS PER MINUTE UNDER VARIOUS CON- DITIONS. 1 2 3 4 1 2 3 4 Shafts Shafts Diameter of Shaft. Line Shafts. Shaft as a Prime Mover. Under Slight Bending Diameter of Shaft. Line Shafts. Shaft as a Prime Mover. Under Slight Bending Strain. Strain. & .7 .4 1.3 3H 40. 20. 80- w 1.3 .7 2.6 3{f 49. 25. 97. 1-Z_ 2.4 1.2 4.7 4^ 70. 35. 139. ]JJL .3.8 1.9 7.6 4f& 96. 48. 192. 1 JL| 5.8 2.9 11.5 5- K 126. 64. 256. 9-1- 8.3 4.2 16.6 5 J L f 167. 84. 334. ft 11.5 5.8 23. e- L ^ 266. 133. 532. 2fl 15.5 7.8 31. 7 J L ^ 399. 200. 797. tt 20. 10. 40. 8 J 570. 285. 1139. 3ft 4 26. 33. 13. 17. 51. 65. 9 1 783. 392. 1566. This table states the horse-power that various sizes of shafts will safely transmit at 100 revolutions per minute under various conditions. Prime movers are those shafts in which the variation above and below the average horse-power transmitted is great, also where the transverse strain due to belts or heavy pulleys is large, such as jack-shafts, crank-shafts, etc. 696 HANDBOOK ON ENGINEERING. of wheel with 1-inch pitch and 1-inch face will transmit at the given velocity. Second. Multiply the pitch by the face. Third. Multiply the horse-power found by the product of pitch by face. The final product is the horse-power required. Example. What is the greatest horse-power that a bevel- wheel, 43" pitch diameter, 2" pitch, 6" face, and 125 revolutions' per minute will safely transmit? From previous example, we have found the pitch-line velocity to be 23.4 feet per second, which is nearest to a velocity of 24 feet per second in Table 1. First, the horse-power which a bevel wheel of 1" pitch and 1' face will transmit is (from table) at this velocity 4.931. Second, the product of pitch by face is 2 x 6 = 12. Third, 12 x 4.931 59. 17 horse-power. Answer. Whenever it is desirable to know about the average horse- power that any wheel will transmit, | or J of the results obtained by the rule above should be taken. TABLE 1. TABLE SHOWING THE HORSE-POWER WHICH DIFFERENT KINDS OF GEAR WHEELS OF ONE INCH PITCH AND ONE INCH FACE WILL TRANSMIT AT VARIOUS VELOCITIES OF PITCH CIRCLE. 1 2 3 4 5 Velocity of pitch circle in ft. per sec. Spur Wheels. Spur Mortise Wheels. Bevel Wheels. Bevel Mortise Wheels. 2 1.338 .047 .938 .647 3 1.756 .971 1.227 .856 6 2.782 1.76 1.76 1 363 12 4.43 3.1 3.1 2.16 18 5.793 4.058 4.058 2.847 21 7.052 4.931 4.931 3.447 30 8.182 5.727 5.727 4.036 36 9.1G3 6.314 6.414 4.516 42 10.156 7.102 7 . 102 4.963 48 10.083 7.680 7.680 5.411 HANDBOOK ON ENGINEERING. NOTE. When velocities are given, which are between these in Table, the horse-power can be found by interpolation. Thus, the horse-power for spur wheels at 14 feet velocity is found as follows : 14 minus 12 = 2 j minus 4 . 48= ^gg. 18 " 12 = 6 J Then f of 1.363 = .454 and .454 -j- 4.43 4.884 horse-power. TABLE 2. SHAFTING. HORSE- POWER TRANSMITTED BY VARIOUS SHAFTS, AT 100 REVOLUTIONS PER MINUTE UNDER VARIOUS CON- DITIONS. 1 2 3 4 1 2 3 4 Shafts Shafts Diameter of Shaft. Line Shafts. Shaft as a Prime Mover. Under Slight Bending Diameter of Shaft. Line Shafts. Shaft as a Prime Mover. Under Slight Bending Strain. Strain. if .7 .4 1.3 W 40. 20. 80- w 1.3 .7 2.6 sir 49. 25. 97. 2.4 1.2 4.7 W' 70. 35. 139. 1 4"-^' .3.8 1.9 7.6 4ffc" 96. 48. 192. 1 JL|/ 5.8 2.9 11.5 5- V 126. 64. 256. -iV 8.3 4.2 16.6 5J L f" 167. 84. 334. 2-j2g/ 11.5 5.8 23. " 266. 133. 532. 2tt' 15.5 7.8 31. 7 J t" 399. 200. 797. 2f ' 20. 10. 40. 8 J t" 570. 285. 1139. w 26. 13. 51. 9 r 783. 392. 1566. 33. 17. 65. This table states the horse-power that various sizes of shafts will safely transmit at 100 revolutions per minute under various conditions. Prime movers are those shafts in which the variation above and below the average horse-power transmitted is great, also where the transverse strain due to belts or heavy pulleys is large, such as jack-shafts, crank-shafts, etc. 698 HANDBOOK ON ENGINEERING. WHEEL GEARING. The pitch line of a wheel is the circle upon which the pitch is measured, and it is the circumference by which the diameter, or the velocity of the wheel, is measured. The pitch is the arc of the circle of the pitch line, and is determined by the num- ber of teeth in the wheel. The true pitch (chordal), or that by which the dimensions of the tooth of a wheel are alone determined, is a straight line drawn from the centers of two contiguous teeth upon the pitch line. The line of centers is the line between the centers of two wheels. The radius of a wheel is the semi-diameter running to the periphery of a tooth. The pitch radius is the semi-diameter running to the pitch line. The length of a tooth is the distance from its base to its ex- tremity. The breadth of a tooth is the length of the face of wheel. The teeth of wheels should be as small and numerous as is consistent with strength. When a pinion is driven by a wheel, the number of teeth in the pinion should not be less than eight. When a wheel is driven by a pinion, the number of teeth in the pinion should not be less than ten. The number of teeth in a wheel should always be prime to the number of the pinion ; that is, the number of teeth in the wheel should not be divisible by the number of teeth in the pinion, without a remainder. This is in order to prevent the same teeth coming together so often as to cause an irregular wear of their faces. An odd tooth introduced into a wheel is termed a hunting-tooth or cog. TO COMPUTE THE PITCH OP A WHEEL. Rule* Divide the circumference at the pitch-line by the num- ber of teeth. Example. Awheel 40 in. in diameter, requires 75 teeth; what is its pitch ? 3.1416x40 , fir . K - . = 1.6755 in. 75 HANDBOOK ON ENGINEERING. 699 TO COMPUTE THE CHORDAL PITCH. Rule* Divide 180 by the number of teeth, ascertain the sin. of the quotient, and multiply it by the diameter of the wheel. Example. The number of teeth is 75 and the diameter 40 in. ; what is the true pitch ? 180 75 = 2 24' and sin. of 2 24' = .04188, which x 40 = 1.6752 in. TO COMPUTE THE DIAMETER OF A WHEEL. Rule* Multiply the number of teeth by the pitch, and divide the product by 3.1416. Example. The number of teeth in awheel is 75, and the pitch 1.675 in. ; what is the diameter of it? 75x1.675 3.1416 40 in. TO COMPUTE THE NUMBER OF TEETH IN A WHEEL. Divide the circumference by the pitch. TO COMPUTE THE DIAMETER WHEN THE TRUE PITCH IS GIVEN. Rule. Multiply the number of teeth in the wheel by the true pitch, and again by .3184. Example. Take the elements of the preceding case. 75 x 1.6752 x .3184 = 40 in. TO COMPUTE THE NUMBER OF TEETH IN A PINION OR FOLLOWER TO HAVE A GIVEN VELOCITY. Rule, Multiply the velocity of the driver by its number of teeth, and divide the product by the velocity of the driven. Example. The velocity of a driver is 16 revolutions, the number of its teeth 54, and the velocity of the pinion is 48 ; what is the number of its teeth ? H! 4 = 18 teeth. 48 \ 700 HANDBOOK ON ENGINEERING. 2. A wheel having 75 teeth is making 16 revolutions per min- ute. What is the number of teeth required in the pinion to make 24 revolutions in the same time ? 24 TO COMPUTE THE PROPORTIONAL RADIUS OF A WHEEL OR PINION. Rule* Multiply the length of the line of centers by the num- ber of teeth in the wheel for the wheel, and in the pinion for the pinion, and divide by the number of teeth in both the wheel and the pinion. TO COMPUTE THE DIAMETER OF A PINION, WHEN THE DIAMETER OF THE WHEEL AND NUMBER OF TEETH IN THE WHEEL AND PINION ARE GIVEN. Rule* Multiply the diameter of the wheel by the number of teeth in the pinion, and divide the product by the number of teeth in the wheel. Example. The diameter of a wheel is 25 in., the number of its teeth 210, and the number of teeth in the pinion 30 ; what is the diameter of the pinion ? 25x30 210 = 3.57 in. TO COMPUTE THE CIRCUMFERENCE CF A WHEEL. Multiply the number of teeth by their pitch. TO COMPUTE THE REVOLUTIONS OF A WHEEL OR PINION. Multiply the diameter or circumference of the wheel or the number of its teeth, as the case may be, by the number of its revolutions, and divide the product by the diameter, circumfer- ence, or number of teeth in the pinion. Example. A pinion 10 in. in diameter is driven by a wheel HANDBOOK ON ENGINEERING. 701 2 ft. in diameter, making 46 revolutions per minute ; what is the number of revolutions of the pinion ? 2 x 12x46 10 110.4 revolutions. TO COMPUTE THE VELOCITY OF A PINION. Rule* Divide the diameter, circumference or number of teeth in the driver, as the case may be. by the diameter, etc., of the pinion. WHEN THERE IS 1. SERIES OR TRAIN OF WHEELS AND PINIONS. Rule* Divide the continued product of the diameter, circum- ference, or number of teeth in the wheels by the continued product of the diameter, etc., of the pinions. Example. If a wheel of 32 teeth drive a pinion of 10, upon the axis of which there is one of 30 teeth, driving a pinion of 8, what are the revolutions of the last ? 32 30 960 K) X "8 == scT = =12 revolutions. Ex. 2. The diameters of a train of wheels are 6, 9, 9, 10 and 12 in. ; of the pinions, 6, 6, 6, 6, and 6 in. ; and the number of revolutions of the driving shaft or prime mover is 10 ; what are the revolutions of the last pinion ? 6 x 9 x 9 x 10 x 12 x 10 583200 =. =_ tb revolutions. 6x6x6x6x6 7776 TO COMPUTE THE PROPORTION THAT THE VELOCITIES OF THE WHEELS IN A TRAIN WOULD BEAR TO ONE ANOTHER. Rule* Subtract the less velocity from the greater, and divide the remainder by one less than the number of wheels in the train ; the quotient is the number, rising in arithmetical progression from the less to the greater velocity. 702 HANDBOOK ON ENGINEERING. Example. What should be the velocities of three wheels to produce 18 revolutions, the driver making 3? 18 minus 3 = 15^ = ^ g = number to be ftdded to velocity of the 3 minus 1=2 driver = 7. 5 + 3 = 10. 5 and 10.5 -f- 7.5 = 18 revolutions. Hence, 3, 10.5 and 18 are the velocities of the three wheels. GENERAL ILLUSTRATIONS. 1. A wheel 96 inches in diameter, having 42 revolutions per minute, is to drive a shaft 75 revolutions per minute, what should be the diameter of the pinion ? 96x42 _ =53.76 in. 75 2. If a pinion is to make 20 revolutions per minute, required the diameter of another to make 58 revolutions in the same time. 58 divided by 20 = 2.9 = the ratio of their diameters. Hence if one to make 20 revolutions is given a diameter of 30 in., the other will be 30 divided by 2.9 = 10.345 in. 3. Required the diameter of a pinion to make 12i revolutions in the same time as one of*32 in. diameter making 26. 32x26 66.56 in. 12.5 4. A shaft having 22 re volutions per minute, is to drive another shaft at the rate of 15, the distance between the two shafts upon the line of centers is 45 in. ; what should be the diameter of the wheels ? Then, 1st, 22 -f- 15 : 22 : : 45 : 26.75 = inches in the radius of the pinion. 2d. 22 -f 15 : 15 : : 45 : 18.24 = inches in the radius of the spur. 5. A driving shaft, having 16 revolutions per minute, is to drive a shaft 81 revolutions per minute, the motion to be com- municated by two geared wheels and two pulleys, with an inter- mediate shaft ; the driving wheel is to contain 54 teeth, and the HANDBOOK ON ENGINEERING. 703 driving pulley upon the driven shaft is to be 25 in. in diameter ; required the number of teeth in the driven wheel, and the diameter of the driven pulley. Let the driven wheel have a velocity of V 16x81=36 a mean proportional between the extreme veloci- ties 16 and 81. Then, 1st, 36 : 16 : : 54 : 24 = teeth in the driven wheel. 2d. 81 : 36 : : 25 : 11.11 = inches diameter of the driven pulley. 6. If, as in the preceding case, the whole number of revolutions of the driving shaft, the number of teeth in its wheel and the diameter of the pulley are given, what are the revolutions of the shafts? Then, 1st, 18 : 16 : : 54 : 48 = revolutions of the intermediate shaft. 2d. 15 : 48 : : 25 : 80 = revolutions of the driven shaft. TO COMPUTE THE DIAMETER OF A WHEEL FOR A GIVEN PITCH AND NUMBER OF TEETH. Rule* Multiply the diameter in the following table for the number of teeth by the pitch, and the product will give the diam- eter at the pitch circle. Example. What is the diameter of a wheel to contain 48 teeth of 2.5 in. pitch? 15.29x2.5 = 38.225 in. TO COMPUTE THE PITCH OF A WHEEL FOR A GIVEN DIAMETER AND NUMBER OF TEETH. Rule* Divide the diameter of the wheel by the diameter in the table for the number of teeth, and the quotient will give the pitch. Example. What is the pitch of a wheel when the diameter of it is 50.94 in., and the number of its teeth 80? 50.94 704 HANDBOOK ON ENGINEERING. PITCH OF WHEELS. A TABLE WHEREBY TO COMPUTE THE DIAMETER OF A WHEEL FOR A GIVEN PITCH, OH THE PITCH FOR A GIVEN DIAMETER. From 8 to 192 teeth. g 03 .c 1 ^ 1 a 1 JS 1 "8 03 S "o o> I M - 03 i O OJ I S S d^"" 1 03 6 6 a d^" 1 45 d I 55 5 fe 5 * 5 fc 5 fc 5 8 2.61 45 14.33 82 26.11 119 37.88 156 49.66 9 2.93 46 14.65 83 26.43 120 38.2 157 49.98 10 3.24 47 14.97 84 26.74 121 38.52 158 50.3 11 3.55 48 15.29 85 27.06 122 38.84 159 50.61 12 3.86 49 15.61 86 27.38 123 39.16 160 50.93 13 4.18 50 15.93 87 27.7 124 39.47 161 51.25 14 4.49 51 16.24 88 28.02 125 39.79 162 51.57 15 4.81 52 16.56 89 28.33 126 40.11 163 51.89 16 5.12 53 16.88 90 28. H5 127 40.43 164 52.21 17 5.44 54 17.2 91 28.97 128 40.75 165 52.52 18 5.76 55 17.52 92 29.29 129 41.07 166 52.84 19 6.07 56 17.8 93 29.61 130 41.38 167 53.16 20 6.39 57 18.15 94 29.93 131 41.7 168 53.48 21 6.71 58 18.47 95 30.24 132 42.02 169 53.8 22 7.03 59 18.79 9 30.56 133 42.34 170 54.12 23 7.34 60 19.11 97 30.88 134 42.66 171 54.43 24 7.66 61 19.42 98 31.2 135 42.98 172 54.75 25 7.98 62 19.74 99 31.52 136 43.29 173 55.07 26 8.3 63 20.06 100 31.84 137 43.61 174 55.39 27 8.61 64 20.38 101 32.15 138 43.93 175 55.71 28 8.93 65 20.7 102 32.47 139 44.25 176 56.02 29 9.25 66 21.02 103 32.79 140 44.57 177 56.34 30 9.57 67 21.33 104 33.11 141 44.88 178 56.66 31 9.88 68 21.65 105 33.43 142 45.2 179 56.98 32 10.2 69 21.97 106 33.74 143 45.52 180 57.23 33 10.52 70 22.29 107 34.06 144 45.84 181 57.62 34 10.84 71 22.61 108 34.38 145 46.16 182 57.93 35 11.16 72 22.92 109 34.7 146 46.48 183 58.25 36 11.47 73 23.24 110 35.02 147 46.79 184 58.57 37 11.79 74 23.56 111 35.34 148 47.11 185 58.89 38 12.11 75 23.88 112 35.65 149 47.43 186 59.21 39 12.43 76 24.2 113 35.97 150 47.75 187 59.53 40 12.74 77 24.52 114 36.29 151 48.07 188 59.84 41 13.06 78 24.83 115 36.61 152 48.39 189 60.16 42 13.38 79 25.15 116 36.93 153 48.7 190 60.48 43 13.7 80 25.47 117 37.25 154 49.02 191 60.81 44 14.02 81 25.79 118 37.56 155 49.34 192 61.13 HANDBOOK ON ENGINEERING. 705 TO COMPUTE THE STRESS THAT MAY BE BORNE BY A TOOTH. Rule* Multiply the value of the material of the tooth to re- sist transverse strain, as estimated for this character of stress, by the breadth and square of its depth, and divide the product by the extreme length of it in the decimal of a foot. TO COMPUTE THE NUMBER OF TEETH OF A WHEEL FOR -A. GIVEN DIAMETER AND PITCH. Rule* Divide the diameter by the pitch , and opposite to the quotient in the preceding table is given the number of teeth. TEETH OP WHEELS. Epicycloidal* In order that the teeth of the wheels and pin- ions should work evenly and without unnecessary rubbing fric- tion, the face (from pitch line to top) of the outline should be determined by an epicycloidal curve, and the flank (from pitch line to base) by an hypocycloidal. When the generating circle is equal to half the diameter of the pitch circle, the hypocycloid de- scribed by it is a straight diametrical line, and consequently the outline of a flank is a right line and radial to the center of the wheel. If a like generating circle is used to describe face of a tooth of other wheel or pinion respectively, the wheel and pinion will operate evenly. Involute* Teeth of two wheels will work truly together when surfaces of their face is an involute ; and that two such wheels should work truly, the circles from which the involute lines for each wheel are generated must be concentric with the wheels, with diameters in the same ratio as those of the wheels. Curves of teeth* In the pattern shop, the curves of epicy- cloidal or involute teeth are defined by rolling a template of the generating circle on a template corresponding to the pitch line, a scriber on the periphery of the template being used to define 45 706 HANDBOOK ON ENGINEERING. the curve. Least number of teeth that can be employed in pin- ions having teeth of following classes, are : involute, 25 ; epicycloidal, 12 ; staves or pins, 6. CONSTRUCTION OF GEARING. If the dimensions of two wheels are determined, as well as the size of the teeth and spaces, the wheel is drawn as shown in figure. The starting- point for the division of the wheels is where the two pitch circles meet in A. It is advisable to determine the exact diameters of the wheels by calculation, if the difference between them is remarkable ; for any division upon two circles of unequal size by means of a divider, is incorrect, because the latter measures the chord instead of the arc. From the point A we construct the epicycloid (7, by rolling the circle A upon JB, as its base line. That short piece of the epi- cycloid, from the pitch line to the face of the tooth, is the curva- ture for that part of the tooth and the wheel B. This curvature obtained for one side of the tooth, serves for both sides of it, and also for all the teeth in the wheel. The lower part of the tooth, or that inside the pitch-line, is immaterial to the working of the wheel; this may be a straight line, as shown by the dotted lines which are in the direction of the diameters, or may be a curved line, as is seen in the wheel A. This line must be so formed as not to touch the upper or curved part of the tooth. The root of HANDBOOK ON ENGINEERING. 707 the tooth, or that part of it which is connected with the rim of the wheel, is the weakest part of the tooth, and may be strengthened by filling the angles at the corners. The curvature for the teeth in the wheel A is found in a similar manner to that of B. The pitch circle A serves now as a base line, and the circle B is rolled upon it, to obtain the circle D. This line forms the curvature for the teeth of J., and serves for all the teeth in A also for both sides of the teeth. In most practical cases the curvature of the teeth is described as a part of a circle, drawn from the center of the next tooth, or from a point more or less above or below that center, or the radius greater or less in strength than the pitch of the wheel. Such circles are never correct curves, and no rule can be established by which their size and center meets the form of the epicycloid. BEVEL WHEELS. If the lines C A and B C represent the prolonged axes, which are to revolve with different or similar velocities, the position and sizes of the wheels for driving these axes are determined by the dis- tance of the wheels from the point C. The diame- ters of the wheels are as the angles a and b and inversely as the number of revolutions. These angles are, therefore, to D be determined before the wheels can be drawn.' By measuring the distances from C to the line E, or from C to -F, the sizes of the wheels are determined. These lines E, F and D jP, are the diameters for the pitch lines ; from them the form 708 HANDBOOK ON ENGINEERING. of the tooth is described on the beveled face of the wheel. If the form of the tooth is described on the largest circle of the wheel, all the lines from this face run to the point O, so that when the wheel revolves around its axis, all the lines from the teeth concentrate in the point (7, and form a perfect cone. Curvature, thickness, length and spaces are here calculated as on face wheels ; the thickness is measured in the middle of the width of the wheel. WORM-SCREW. If a single screw A works in a toothed wheel, each revolution of the screw will turn the wheel one cog ; if the screw is formed of more than one thread, a corresponding number of teeth will be moved by each revolution. With the increase of the number of threads, the side motion of the wheel and screw is accelerated ; and when the threads and num- ber of teeth are equal, an angle of 45 is required for teeth and thread, provided their diameters also are equal. This motion causes a great deal of friction and it is only resorted to where no other means can be employed to produce the required motion. In small machinery, the worm is frequently made use of to produce a uniform, uninterrupted motion ; the screw, in such cases, is made of hardened steel and the teeth of the. wheel are cut by the screw which is to work in the wheel. If the form of the teeth in the wheel is not curved and its face is concave so as to fit the thread in all points, the screw will touch the teeth but in one point and cause them to be liable to breakage, HANDBOOK ON ENGINEERING. 709 PROPORTIONS OF TKKTH OF WHEELS. Tooth* Iii computing the dimensions of a tooth, it is to be considered as a beam lixed at one end, the weight suspended from the other, or face of the beam ; and it is essential to con- sider the element of velocity, as its stress in operation, at high velocity with irregular action, is increased thereby. The dimen- sions of a tooth should be much greater than is necessary to resist the direct stress upon it, as but one tooth is proportioned to bear the whole stress upon the wheel, although two or more are actually in contact at all times ; but this requirement is in consequence of the great wear to which a tooth is subjected? the shocks it is liable to from lost motion when so worn as to reduce its depth and uniformity of bearing, and the risk of the breaking of a tooth from a defect. A tooth running at a low velocity may be materially reduced in its dimensions compared with one running at high velocity and with a like stress. The result of operations with toothed wheels, for a long period of time, has determined that a tooth with a pitch of 3 inches and a breadth 7.5 inches will transmit, at a velocity of 6.66 feet per second, the power of 59.16 horses. TO COMPUTE THE DEPTH OF A CAST-IKON TOOTH. 1. When the stress is given. Rule* Extract the square root of the stress, and multiply it by .02. Exaiwple. The stress to be borne by a tooth is 4886 Ibs. ; what should be its depth? 1/1886 x .02 = 1.4 in. 2. When the horse-power is given. Rule. Extract the square-root of the quotient of the horse- power divided by the velocity in feet per second, and multiply it by ,466, 710 HANDBOOK ON ENGINEERING. Example. The horse-power to be transmitted by a tooth is 60, and the velocity of it at its pitch-line is 6.66 feet per second ; what should be the depth of the tooth ? 60 x .466 = 1.898 in. 6.66 TO COMPUTE THE HORSE -POWER OF A TOOTH. Rule* Multiply the pressure at the pitch-line by its velocity in feet per minute, and divide the product by 33,000. CALCULATING SPEED WHEN TIME IS NOT TAKEN INTO ACCOUNT. Rule* Divide the greater diameter, or number of teeth, by the lesser diameter or number of teeth, and the quotient is the number of revolutions the lesser will make, for one of the greater. Example. How many revolutions will a pinion of 20 teeth make, for 1 of a wheel with 125? 125 divided by 20 = 6.25 or 6J revolutions. To find the number of revolutions of the last to one of the first, in a train of wheels and pinions : Rule* Divide the product of all the teeth in the driving by the product of all the teeth in the driven ; and the quotient equals the ratio of velocity required. Example 1. Required the ratio of velocity of the last, to 1 of the first, in the following train of wheels and pinions, viz. : pinions driving the first of which contains 10 teeth, the second 15, and third 18. Wheels driven, first teeth 15, second 25, 10xl5x 18 and third 32. ^ ^ ^- = .225 of a revolution the wheel 1.0 X 20 X O ij will make to one of the pinion. Example 2. A wheel of 42 teeth giving motion to 1 of 12, on which shaft is a pulley of 21 inches diameter, driving 1 of 6 ; HANDBOOK ON ENGINEERING. 711 required the number of revolutions of the last pulley to 1 of the 42x21 first wheel. ^ == 12.-25 or 12J revolutions. NOTE. Where increase or decrease of velocity is required to be communicated by wheel- work, it has been demonstrated that the number of teeth on each pinion should not be less than 1 to 6 of its wheel, unless there be some other important reason for a higher ratio. WHEN TIME MUST BE REGARDED. Rule* Multiply the diameter or number of teeth in the driver by its velocity in any given time, and divide the product by the required velocity of the driven ; the quotient equals the number of teeth or diameter of the driven, to produce the velocity required. Example 1. If a wheel containing 84 teeth makes 20 revolu- tions per minute, how many must another contain, to work in contact, and make 60 revolutions in the same time: 80x20 divided by 60=27 teeth. Example 2. From a shaft making 45 revolutions per minute and with a pinion 9 inches diameter at the pitch-line, I wish to transmit motion at 15 revolutions per minute ; what, at the pitch-line, must be the diameter of the wheel? 45 x 9 divided by 15 = 27 inches. ExampleS. Required the diameter of a pulley to make 16 revolutions in the same time as one of 24 inches making 36. 24 x 36 divided by 16 = 54 inches. The distance between the centers, and the velocities of two wheels being given, to find their proper diameters : R a le. Divide the greatest velocity by the least ; the quo- tient is the ratio of diameter the wheels must bear to each other. Hence, divide the distance between the centers by the ratio -f 1 ; the quotient equals the radius of the smaller wheel ; and subtract 712 HANDBOOK ON ENGINEERING. the radius thus obtained from the distance between the centers; the remainder equals the radius of the other. Example. The distance of two shafts from center to center is 50 in. and the velocity of the one 25 revolutions per minute, the other is to make 80 at the same time ; the proper diameters of the wheels at the pitch line are required. 80 divided by 25 = 3.2, ratio of velocity, and 50 divided by 3.2 + 1 = 11.9, the radius of the smaller wheel; then 50 minus 11.9 =y 38.1, radius of larger ; their diameters are 11.9 x 2 = 23.8 and 38.1x2 = 76.2 in. To obtain or diminish an accumulated velocity by means of wheels and pinions, or wheels, pinions and pulleys, it is necessary that a proportional ratio of velocity should exist, and which is thus attained ; multiply the given and required velocities together ; and the square root of the product is the mean or proportionate velocity. Example. Let the given velocity of a wheel containing 54 teeth equal 16 revolutions per minute, and the given diameter of an intermediate pulley equal 25 in., to obtain a velocity of 81 revolutions in a machine ; required the number of teeth in the intermediate wheel and diameter of the last pulley. 7 81x16 == 36 mean velocity ; 54 x 16 divided by 36 = 24 teeth, and 25x36 divided by 81 = 11.1 in., diameter of pulley. TABLE OF THE WEIGHT OF A SQUARE FOOT OF SHEET IRON IX POUNDS AVOIRDUPOIS. No. 1 is T 5 ^ of an inch ; No. 4, J ; No. 11, J, etc. No. on wire gauge, 1234 5 6 7 8 9 10 11 12 Pounds avoir., 12.5 12 11 10 9 8 7.5 7 6 5.68 5 4.62 No. on wire gauge, 13 14 15 16 17 18 19 20 21. 22^ Pounds avoir., 4.31 4 3.95 3 2.5 2.18 1.93 1.62 1.5 1.37 HANDBOOK ON ENGINEERING. 713 SCREW-CUTTING. In a lathe properly adapted, screws to any degree of pitch, or number of threads in a given length, may be cut by means of a leading screw of any given pitch, accompanied with change wheels and pinions ; coarse pitches being effected generally by means of one wheel and one pinion with a carrier, or intermediate wheel, which cause no variation or change of motion to take place ; hence, the following : Rule* Divide the number of threads in a given length of the screw which is to be cut, by the number of threads in the same length of the leading screw attached to the lathe, and the quotient is the ratio that the wheel on the end of the screw must bear to that on the end of the lathe spindle. Example. -Let it be required to cut a screw with 5 threads in an inch, the leading screw being of i inch pitch, or containing 2 threads in an inch ; what must be the ratio of wheels applied? 5 divided by 2 = 2.5, the ratio they must bear to each other. Then suppose a pinion of 40 teeth be fixed upon for the spindle ; 40 x 2.5 = 100 teeth for the wheel on the end of the screw. But screws of a greater degree of fineness than about 8 threads in an inch are more conveniently cut by an additional wheel and pinion, because of the proper degree of velocity being more effectively attained, and these, on account of revolving upon a stud, are commonly designated the stud- wheels, or stud-wheel and pinion ; but the mode of calculation and ratio of screw are the same as in the preceding rule. Hence, all that is further neces- sary is to fix upon an^ three wheels at pleasure, as those for the spindle and stud-wheels ; then multiply the number of teeth in the spindle-wheel by the ratio of the screw and by the number of teeth in that wheel or pinion which is in contact with the wheel on the end of the screw ; divide the product by the stud-wheel in contact with the spindle- wheel, and the quotient is the number of teeth required in the wheel on the end of the leading screw. 714 HANDBOOK ON ENGINEERING. Example. Suppose a screw is required to be cut containing 25 threads in an inch, and the leading screw, as before, having two threads in an inch, and that a wheel of 60 teeth is fixed upon for the end of the spindle, 20 for the pinion in contact with the screw-wheel, and 100 for that in contact with the wheel on the end of the spindle ; required the number of teeth in the wheel for the end of the leading screw. , 60x 12.5x20 25 divided by 2 = 12.5, and _ -j^ = 150 teeth. Or suppose the spindle and screw wheels to be those fixed upon, also any one of the stud- wheels, to find the number of teeth in the other. 150x100 60 x 12. 5 x 20 = 20 teeth, or = 100 teeth. 60x12.5 150 Transmission of Power by Manilla Rope, power Transmitted. Horse- Feet per minute .... 1000 1500 2000 2500 3000 3500 4000 4500 5000 Diameter of Rope . f (( a i " .' 14 " " 14 " " . l| u " . 2 U 34 6* 74 10 13 2| *S 74 11 15 194 a 104 15 20 26 44 8 13 18 25 33 54 10 15 22 30 39 64 11 18 26 35 46 7 13 20 30 40 52 8 15 23 34 45 59 9 16 26 37 50 65 Decimal Equivalents of One Foot by Inches. 4 4 1 1 2 * ' '* 5 .0208 .0417 .0626 .0833 .1667 .2500 .3333 .4167 6 7 8 9 10 11 12 .5000 .5833 .6667 .7510 .8333 .9167 1.000 HANDBOOK ON ENGINEERING. 715 TABLE OF TRANSMISSION OF POWER BY WIRE ROPES. This table is based upon scientific calculations, careful observations and experience, and can be relied upon when the distance exceeds 100 feet. We also find by experience that it is best to run the Wire Rope Transmission at the medium number of revolutions indicated in the table, as it makes the best and smoothest running transmission. If more power is needed than is indicated at 80 to 100 revolutions, choose a larger diameter of sheave. Diameter of Sheave in ft. Number of Revolutions. Diameter of Rope. ' Horse- Power. Diameter of Sheave in ft. Number of Revolutions. Diameter of Rope. Horse - Power. 3 80 1 3 7 140 A 35 3 100 8 3i 8 80 26 3 120 1 4 8 100 i 32 3 140 *i 8 120 1 39 4 80 1 4 8 140 1 45 4 100 i 5 9 80 {At \ 47 i 48 4 120 1 6 9 100 {At 1 58 / 60 4 140 i 7 9 120 {A i 1 69 / 73 5 30 ft 9 9 140 fM 1 82 I 84 5 100 A 11 10 80 {l tt 1 64 / 68 5 120 -h 13 10 100 (I ft \ 80 / 85 5 140 & 15 10 120 {! H \ 96 J 102 6 80 h 14 10 140 {Hi \112 (119 6 100 h 17 12 80 {ftj \ 93 jf 99 6 120 h 20 12 100 {HI \116 / 124 6 140 h 23 12 120 (in \140 J 149 7 80 A 20 12 120 i 173 7 100 A 26 14 80 {.H 1141 /148 -7 120 A 30 14 100 {' \176 /185 716 HANDBOOK ON ENGINEERING. CHAPTER XXV. ELECTRIC ELEVATORS. In factories, warehouses and business buildings, freight, and in some instances passenger elevators, are operated by machines that are arranged to be driven by a belt. Such machines are variously called belted elevators, factory elevators and sometimes warehouse elevators. In factories where there is a line of shafting kept running continuously, they are driven from it. As a rule the elevator machine is driven from a countershaft which latter is belted to the line shaft. Very often the elevator machine is driven directly from the line shaft. As the line shaft runs always in the same direction, the only way in which the elevator machine can be made to run in both directions is by the use of two belts, one open and the other crossed, or some form of gearing that will accomplish the same result. The common practice is to use double belts. Either one of these belts can be made to drive by using friction clutches, or by having tight and loose pulleys, and a belt shifter. The latter arrangement is the most common. In buildings where there is no line of shafting, power for oper- ating the elevator machine must be derived from some kind of motor installed expressly for the purpose. Nowadays electric motors are very extensively used for this purpose, and the com- bination of an elevator machine and an electric motor to drive it is very generally called an electric elevator, although in reality it is not such, but simply a belted elevator machine driven by an electric motor. It has become so common, however, to call such com- binations electric elevators, that true electric elevators are generally designated as " direct connected electric elevators." HANDBOOK ON ENGINEERING. 717 The first impression would be that in the combination of a belted elevator machine, and an electric motor to drive it, as the motor simply furnishes the power to set the machine in motion, there can be nothing about the combination that requires any special elucidation. Such a conclusion, however, would not be correct, for there are several ways in which the combination can be arranged, and in what follows I propose to explain these several combinations, pointing out the important features of each. The simplest way in which a motor can be installed to drive an elevator, is to arrange it so as to drive the counter shaft con- tinuously, in which case the elevator is stopped and started by throwing the belts on the tight or the loose pulley. Although this is a very simple arrangement, it is not desirable unless the elevator is kept in service all the time. In buildings where the elevator is used only at intervals, a great amount of power is wasted if the shafting is kept running all the time ; hence it is desirable to arrange the motor so that it can be stopped when the elevator is stopped, and started whenever the elevator is to be used. If the motor is arranged so as to run all the time, it is provided with a simple motor-starting switch, the same as is used for any motor installed to operate machinery of any kind. If the motor is started and stopped whenever the elevator is started and stopped, it is necessary to provide a motor-starter that can be operated from the elevator car. A very common way of arranging a motor to start and stop with the elevator is illustrated in the diagram In this diagram the elevator car is shown at (7, with the lifting ropes running over the sheave F at the top of the elevator shaft, and then down and around the drum A of the elevator machine. This drum is driven by means of screw gearing, as a rule, with driving pulieys on the screw shaft as shown at B The 718 HANDBOOK ON ENGINEERING. driving motor is shown at Jf, and the counter-shaft to which it is belted is at D. In this arrangement the elevator machine is pro- vided with a tight center pulley and loose pulleys on the two sides. The belts are shown on the loose pulleys, one being open and the other being crossed . The countershaft carries a drum wide enough to allow for the side movement of the belts when one or the other is shifted upon the tight center pulley by the belt shifter s. To operate the elevator car, a hand rope is provided which HANDBOOK ON ENGINEERING. 719 runs up the elevator shaft at one side of the car from bottom to top of building. This rope is shown in the diagram at Z, and runs around two small sheaves a a. The lower one of these sheaves is provided with a crank pin which moves the connecting rod 6, and thus rocks the lever r, and thereby moves the belt shifter s. To cause the car to ascend the hand rope I is pulled down, and to make the car descend, the hand rope is pulled up. As will be seen from this explanation, the lower sheave a will rotate in one direction when the hand rope is pulled to make the car go up, and in the opposite direction when the rope is pulled to make the car run down. In the diagram, sheave a is shown in the stop posi- tion, therefore when the hand rope is pulled down so as to make the car run up, the sheave will turn in a direction opposite to the movement of the hands of a clock, and thus the belt shifter will be moved to the right, and the open belt will be run onto the tight center pulley. If the hand rope is pulled up sheave a will rotate in the direction of the hands of a clock, and the belt shifter will move toward the left and thus shift the crossed belt onto the tight pulley. The rope p is a stop rope and is connected with the two sides of the hand rope in the manner shown, so that when the car is running in either direction, if p is pulled hard it will bring I to the position shown in the diagram, and thus stop the car. This rope can be dispensed with, but the objection is that in pulling the hand rope I to stop the car it may be pulled too far and then the car will not only be stopped but it will be caused to run in the opposite direction. The motor starting switch is shown at E, the line wires being connected with the two top binding posts. The lever c c is in one piece and is independent of lever e, but both swing around the same pivot. At w, a dash pot is provided which acts to prevent the too rapid movement of lever e. As will be noticed, lever c has a projection which holds lever e up. The operation of this motor starter is as follows : When the hand rope I is pulled in 720 HANDBOOK ON ENGINEERING. either direction, the rope h draws lever c towards the left and causes it to make contact with the switch jaw j. In this way the current from the upper binding post which is connected with j through wire #, passes to lever e, and thus to the starting resist- ance, which is indicated by the dotted lines t, to binding post &, from where it goes to the motor armature through wire c?, and re- turns through the other wire d to the upper binding post at the right side, which is connected with the opposite side of the main line, thus completing the circuit. The field current branches off from the upper end of the starting resistance t and reaches the field coils through wire /, and through the lower wire / reaches the return armature wire d and thus the opposite side of the cir- cuit. When the rope h pulls lever c over toward the left, the lever e does not follow it, as it is held up by the dash pot m. The weight on the end of .e gradually overcomes the resistance of the dash pot, and thus causes lever e to move downward slowly. The velocity at which e moves downward is graduated by adjusting the opening in the dash pot through which the oil flows. From the foregoing it will be seen that the starter E is made so as to accomplish automatically just what a man accomplishes when he moves the lever of an ordinary motor-starter ; that is, it first closes the circuit through the motor, by bringing lever c into contact withj; and then allows lever e to move slowly so as to cut the resistance i out of the armature circuit gradually. When the elevator is stopped, by pulling the hand rope / to the stop position, the rope h slacks up and then the weight on the end of lever c causes it to descend, and thus return lever e to the posi- tion shown in the diagram, and also to break the circuit between c and j. The elevator machine A is provided with a brake which is actuated by the belt shifter s, so that when the belts are shifted upon the side pulleys, as shown in the diagram, the brake is put on, and thus the machine is stopped. As soon as the belt shifter HANDBOOK ON ENGINEERING. 721 moved to set the car in motion the brake is raised, so as to allow the machine to run free. This arrangement is used very extensively, although the motor- sttrtiug switch is not always made in strict accordance with the on^ shown at E. In fact, there are a great many different designs on the market, but they all accomplish the same result, although the means employed may be very different. Although it is very advantageous to have the motor arranged as in Fig. 1, so that it may be stopped and started together with the elevator, there is one objection to it which is sometimes re- garded as serious, and that is, that as it requires a great amount of power to start an elevator from a state of rest, the motor will take a very strong current in the act of starting. To get around this objection, it is a common practice to provide a separate rope for starting the motor, and then when it is desired to use the ele- vator, the motor rope is pulled first, and in half a minute or so, the main hand rope is pulled. In this way the motor gets a start ahead of the elevator, and the headway of the motor armature helps to set the elevator car in motion, so that the current taken by the motor to start the elevator is very much reduced. When a separate rope is used to start the motor in advance of the elevator, the starter E, or the levers connecting with it, are made so that while the motor can be started independently of the elevator car, when the main hand rope is pulled to stop the car, it also stops the motor. If this arrangement were not provided, the operator might stop the elevator and forget to stop the motor, in which case the latter would keep on running and waste power. The main hand rope I is provided with stops at top and bottom of the elevator shaft, so that the car may be stopped auto- matically should the operator forget to pull the hand rope at the proper time. It is the universal practice with elevator machines of the type shown in Fig. 1 to counterbalance the elevator car, but I have not shown a counterbalance in this diagram as it would only serve 46 722 HANDBOOK ON ENGINEERING. to complicate its appearance, and it is not necessary to show it ae the electrical features .will be the same whether there is a counter- balance or not. This diagram also shows a separate rope h fcr actuating the starter E, but in actual machines E is generaly CONTROLLER CLCYATQR DIAGRAM -SHOWING CONNECTIONS GRAVITY MOTOR CONTROLLER ELEVATOf? MOTOR operated from the lower sheave a, which also actuates the belt- shifter. Fig* 2 is a diagram that shows the way in which one of the various motor starters in actual use is connected with the motor HANDBOOK ON ENGINEERING. 723 and the operating hand rope. In this illustration A is the lower sheave a of Fig. 1, and F represents the hoisting drum and E the diiving pulleys of the elevator machine, G being the lifting ropes from which the car is suspended. The sheave A is rotated DIAGRAM OF CONNECTIONS OF A GRAVITY MOTOR CONTROLLER. W/TH SEPCRATE ROPE ATTA CHMCNT. CT'ia -O MOTOR. through one quarter of a turn in either direction by the pull on the hand rope B, and when so rotated shifts the belt shifter and also lifts the brake from the brake-wheel. At the same time the crank pin C pulls up the connecting rod, and thus the upper end 724 HANDBOOK ON ENGINEERING. of rod c, which takes the place of lever c in Fig. 1. In this way the switch blades in the lower end of c are raised into con- tact with the clips jj, which take the place of contact,; in Fig. 1, and thus the circuit is closed. A projection s on c holds ohe switch e in the upper position, but when c is raised, s goes up with it, and then e is free to descend by the force of gravity accing upon the weight w. The dash pot m is set so as to retard the movement of e as much as may be desired. The outer end of e glides over the contacts i in its downward movement, and thus cuts out of the armature circuit the starting resistance. This resistance is contained in the controller box. Fig*. 3 shows the same type of controller as in Fig. 2, but it is arranged so that the motor may be started ahead of the elevator. The separate motor-starting rope is shown at-//". When this rope is pulled, it elongates the spiral spring A" which is connected with the stud G fixed in the upper end of rod c. The rope // is pulled up enough to stretch K until the lever Dis lifted, H being attached to its outer end L When D is lifted sufficiently, its inner end dis- engages the stud G, and allows it to slide upward in the slot shown in dotted lines, in the lower end of the connecting rod. In this way the motor is started ahead of the elevator machine. If now the elevator machine is started, by pulling on the main hand rope FF^ the crank pin C" on the hand rope sheave will lift the connecting rod (7, and when it reaches its upper position, the catch-lever D will drop into the position shown in the illustration, and thus lock the stud 6r, so that when the elevator is stopped, the rotation of the hand rope sheave will push rod C downward and thus stop the motor, as well as shift the belts and stop the elevator machine. In the three illustrations shown the motor is run always in the same direction and the reversing of the direction of rotation of the hoisting drum is effected by the use of double belts and a belt shifter, or friction clutches which cause one or the other of HANDBOOK ON ENGINEERING. 725 the belts to do the driving. The way in which machines of this type are installed can be more fully understood from Fig. 4, 726 HANDBOOK ON ENGINEERING. This figure shows the position of the motor, the countershaft and the elevator machine with reference to the elevator shaft. This illustration is so clear that an explanation of it would be superfluous. In relation to the installation of elevator plants of this type all that need be said is that the motor must be of the shunt type, the same as those used for driving machines of any kind. A series wound motor, such as are used for electric railway cars, must not be used. Shunt wound motors cannot run above a certain speed, unless forced to do so by power applied from an external source, and in such an event they become generators of electricity and thus resist rotation. On this account, when they are used for elevator service, they not only move the elevator car, but when the latter is descending under the influence of a heavy load and tends to run away, the motor at once begins to act as a gen- erator, and is thus converted into a brake which holds the car and prevents it from attaining a speed much above the normal ; in fact, the difference between the car velocity when lifting a heavy load, and when running down under the influence of a similar load is hardly enough to be noticed by any one not familiar with the elevator. The motor in these combinations is to be given the same care as those used for other purposes ; that is, it must be kept clean and the brushes properly set so as to run with as little spark as is possible. The controller switch requires more attention than the motor starters used with stationary motors, for the simple reason that it is used to a much greater extent. Every time the elevator is started or stopped the controller switch is actuated, hence, the switch levers are subjected to a considerable amount of wear, and the contacts are liable to become rough, either by cutting or by being burned on account of making imperfect contact. On this account the contact must be well examined at least once every day, and if burned or rough must be smoothed up. It is also HANDBOOK ON ENGINEERING. 727 necessary to see that all parts of the controller are properly se- cured, that none of the screws or pins are working out, and that the contacts and switch levers are not out of their normal posi- tion. As electric motors can be run as well in one direction as the other, and as all that is required to make any motor reversible is to provide a reversing switch, it can be seen at once that by mak- ing use of such a switch, the direction of movement of the ele- 728 HANDBOOK ON ENGINEERING. vator car can be reversed by simply reversing the motor, and thus do away with the complication of a countershaft and tight and loose pulleys. Owing to this fact elevator machines are now made so as to be used with reversing motors. These are usually called single-belt machines. The way in which such machines are connected with the motor and the type of controller required can be understoood from the diagram Fig. 5. As will be seen, the principal difference in the machine itself is that the tight and loose pulleys are replaced by a single tight pulley which is only wide enough to carry the driving belt. Usually an extra pulley is provided for the brake, and this brake is mechanically operated in the same manner as upon machines provided with shifting belts. Another modification which is sometimes used, but is not shown in the diagram, is the arrange- ment of a brake so that same is operated by a magnet instead of by mechanical means. With this arrangement the magnet is arranged so that when the machine is in motion, the current passing through the magnet coil acts to lift the brake, and when the machine stops, the magnet lets go, and the brake goes on. By arranging the brake in this way it becomes perfectly safe ; for if the brake magnet fails to act, the brake will not be raised, and the .machine will not move ; that is, failure of the device to work properly will not permit the elevator car to move, thus call ing attention to the fact that something is out of order. The operation of the reversing controller is as follows : the current from the line wires passes along the dotted connections h h to the contact ?',, i,i. The upper left hand i contact is con- nected with the lower right hand one, and the upper right hand with the lower left hand. The switch lever c is connected with lever e by means of the two springs r r, so that c may be moved either up or down without carrying e with it. The curved con- tact o is connected with j and the stud around which c and e swing is connected with &, while g is connected with the ends of HANDBOOK ON ENGINEERING. 729 the starting resistance n n by means of the wire /and the two wires s s. If the hand rope I is pulled so as to carry lever c upward, the current from the left side line wire will pass through upper left side i contact, to o, and thence to j and through wire b to the motor armature and returning through the other b wire will reach g and then'pass through / and lower s to lower end of n and thence to lever e and the inner end of lever c, which will be rest- ing on the upper right side i contact, thus reaching the right side line wire. The current for the field magnet coils will be drawn from j through wire d and back to k through the other wire d. As lever c has been moved upward, the upper spring r will be compressed, and the lower one will be stretched, hence a force will be exerted to move e downward over the lower contacts n and thus cut out the starting resistance, As in the case of the con- troller in Fig. 1 the dash pot m by its resistance retards the move- ments of e, so as to cut out the resistance as gradually as may be desired. In the chapter on stationary motors it is shown that to prevent destructive sparking, when the starting switch is opened, the armature and field coils are connected so as to form a permanently closed loop. This style of connection is used in the non-revers- ing controller of Fig. 1, but it cannot be employed with a revers- ing controller, because both ends of the armature circuit must be free, so that they may be reversed when the direction of rotation is reversed. As this connection cannot be made, a very common expedient resorted to to prevent serious sparking when the switch is opened is to connect a string of incandescent lamps across the terminals of the field circuit, as is indicated at v v v. These lamps, together with the field coils, form a closed circuit, so that when the switch is opened, the field can discharge through the lamps, and thus avoid sparking at the controller contacts. The only objection to this arangement is that all the current that passes through the lamps is wasted, but by placing two or three 730 HANDBOOK ON ENGINEERING. in series the loss is reduced to an insignificant amount. Another way in which the sparking is subdued, but only to a slight ex- tent, is by connecting the brake magnet coil with the binding posts j and fc, which is the simplest and most generally used con- nection. The brake magnet coil together with the field coils form a closed loop when connected with J and fc, but when the main cir- cuit is opened, the currents flowing in the two coils meet each other at J and k flowing in opposite directions, hence they both follow along the main circuit and try to jump across the gaps at the switch, and thus produce about as much sparking as if they were connected independently of each other. In tracing out the path of the current when lever c is moved upward, it was shown that the left side line went directly to the upper commutator brush. Now when c is moved downward, this same line wire runs to the lower commutator brush since the connections between the two upper i contacts and the two lower ones are crossed. To reverse the direction of rotation of a motor all that is required is to reverse the direction of the current through the armature, that through the field remaining unchanged, hence it will be seen that by cross- ing the connections between the upper and lower i contacts, the direction of rotation of the motor is reversed when the c lever is moved in opposite directions. DIRECT CONNECTED ELECTRIC ELEVATORS. The machines explained in the foregoing pages are simply combinations of an electric motor and a belt driven electric ma- chine, but, as already stated, they are commonly spoken of as 44 electric elevators." In what follows it is proposed to explain the construction and operation of true electric elevators, which are called ' ' direct connected machines ' ' to distinguish them from the combinations so far described. There are many designs of direct connected electric elevators HANDBOOK ON ENGINEERING. 731 now upon the market, and it would be out of tbe question to un- dertake to describe all of them in the space that can be devoted to the subject in this book. On that account the discussion will be confined to the designs that are most extensively used. The explanations here given, however, will be sufficient to enable any Fig. 6. one to understand the operation of any of the machines not de- scribed because the difference in the principle of operation is only slight. 732 HANDBOOK ON ENGINEERING. Perhaps the type of direct connected electric elevator that is most extensively used is the Otis drum elevator with hand rope control which is illustrated in Fig. 6. This machine has been upon the market for twelve years or more, and is stili one of the standard Otis machines. It is called a hand rope control machine because the starting and stopping is controlled by the movement of a hand rope that passes through the elevator car. In the illustration, the sheave around which the hand rope passes can be seen located on the front end of the drum shaft. In a modification of the design, this sheave is mounted upon a sep- erate shaft but the way in which it acts is the same as in the pres- ent design. When the hand rope is pulled the sheave is rotated and the horizontal bar, running from it to the controller box, which is mounted on top of the motor? shifts the starting switch so as to run the machine in the direction de'sired. At the same time, the vertical lever ex- tending upward from the side of the brake wheel, lifts the brake and thus frees the motor shaft so that it may revolve unobstructed. The motor carries a worm on the end of the armature shaft which gears into the under side of a worm wheel mounted upon the drum shaft. This worm wheel runs in a casing seen just back of the hand rope sheave wheel. The sheave mounted upon the shaft directly above the drum is for the purpose of guiding the coun- terbalance ropes which run up from the back of the drum. In some buildings these ropes can be run up straight from the back of the drum, but in most cases they must run up in the elevator shaft in the space between the car and the side of the shaft. As these ropes wind upon the drum from one side to the other, the guiding sheave mast move endwise on the shaft, hence it is called a traveling, or vibrating sheave. The levers seen projecting to the right of the machine from a small shaft just above the drum are what is called a slack cable stop, and their office is to stop the machine if the lifting cable becomes slack through the w^ HANDBOOK ON ENGINEERING. 733 ing of the car in the elevator shaft or any other cause. These levers are held in the position shown when the lifting ropes are tight, but drop out of position if the rope slackens up, and in dropping they release a lever which holds the weight seen under the hand rope sheave. The movement of this lever operates a catch that engages with the hand rope sheave and thus the hori- zontal bar that operates the brake and the controller switch is brought to the stop position and the rotation of the hoisting drum is stopped. The hand rope has fastened to it at the top and bottom of the elevator shaft stops that are moved by the car when it reaches either end of its travel, and thus the elevator machine is stopped automatically. This arrangement is the same as that used with the belt driven machines already described, but as an additional safety, a stop motion is provided on the machine itself, so that if the stops on the hand rope become displaced, the car will still be stopped automatically at the top and bottom landings. This stop motion is seen on the end of the shaft, just in front of the hand rope sheave, and consists of a nut that travels on the shaft as the latter revolves. At both sides of the screw there are projection cases upon the inclosing frame, which are struck by the traveling nut when it comes near enough to either end. When the nut strikes the projection, the hand rope sheave is revolved with the shaft and thus the machine is stopped. To understand this ac- tion it must be remembered that the hand rope sheave does not revolve except when turned by the pull on the hand rope or by the action of the slack cable stop or the traveling nut. The controller box on top of the motor contains the starting resistance, the starting and reversing switch, and also a magnet to actuate a switch that gradually cuts out the starting resistance. The way in which the switches act to start and stop the motor can be readily explained by the aid of the diagram Fig. 7. This shows the circuit connections ia the simplest possible 734 HANDBOOK ON ENGINEERING. form. In this diagram all the wires whose presence would make SAFETY MAGNET FOR BRAKE ON MACHINE SHUNT FIELD the drawing confusing have been removed, but the manner in HANDBOOK ON ENGINEERING. 735 which they are connected will be readily understood from the following explanation : The main switch, which connects the motor circuits with the line, is located at the upper left hand corner of the diagram, the main line wires being marke -|- and . When this switch is closed, the motor circuits are connected with the line, but the motor circuit itself is not closed so long as the switch M remains in the position shown. When this switch is turned about one quarter of a revolution in either direction, one end will ride over the upper contact and the other one over the lower contact. The reversing drum and switch M are mounted on the same spindle and move together. They are located within the con- troller box, on top of the motor, and are moved by the horizontal bar ; see Fig. 6. The shaded portions of the drum, on which the brushes h and i rest are made of insulating material so that when switch M and the reversing drum are in the position shown the motor circuit is open at two points. This is the position of these parts when the machine is stopped. The starting resistance is shown above the reversing drum, and in the machine it occupies the space at the back of the con- troller box, shown on top of the motor in Fig. 6. The segment R is a series of contacts that are connected with the resist- ance in the resistance box ; No. 2 contact being con- nected with point 2 on the resistance and so on for all the other numbers. The switch arm N is moved over the contacts R by a magnet that is represented by the spiral L. The motor arma- ture and the shunt and series field coils are shown at the bottom of the diagram. The motor is compound wound, it being made so for the purpose of keeping the starting current as low as possi- ble. The path of the current through the wires is as follows : Sup- pose the reversing drum and the M switch are revolved in the direc- tion in which the hands of a clock move, then brushes g and i will rest on one segment, and h and k will rest on the other segment. 736 HANDBOOK ON ENGINEERING. As switch M will now be closed, the current will flow to brush g and through the reversing drum segment to brush i; then it will follow the wire to the right side /of the armature and pass- ing through the latter will reach wire E and thus brush ft, from which it will pass to brush ~k. From this brush the current will go to and through magnet L and by wire C ' and switch N will reach contact No. 10. As this contact is connected with point 10 of the resistance the current will reach the latter and will pass through the whole of it, coming out at the opposite end C. This end is connected with contact C, so that from this segment the current can flow through wire G to the end F of the series field coils, and passing through these to end H, will find its way to wire /, and thus return to the opposite side of the main line. From this explanation it will be seen that the current will pass through the motor armature, and then through the whole of the resistance in the resistance box, and then through the series field coils, and finally reach the other side of the main line. From the switch M another current will branch off and run to binding post D, and thence through the shunt field coil to binding post JTand thus to wire/, and through the latter to the opposite of the main line. The switch lever ^V is in some cases arranged so that the mag- net L acts to hold it upon contact 10 and a spring acts to carry it forward toward contact A; in other cases the magnet is wound with two coils, one of which pulls N in one direction and the other pulls it in the opposite direction, the two coils being so pro- portioned that N moves gradually from contact 10 toward con- tact A. If we take the spring arrangement, then magnet L will pull N back toward contact 10, and the spring will pull it forward. As the starting current is very strong, ^will be held on contact 10, but as the current weakens, the spring will begin to overpower the magnet, and N will slide oVer contact 9 and then 8 and 7 and so on to contact A. As contact 9 is connected with the point 9 HANDBOOK ON ENGINEERING. 737 of the resistance, when JV reaches it, the section of the resistance between points 10 and 9 will be cut out. When N reaches con- tact 7 the resistance between points 10 and 7 will be cut out for the latter point is connected with contact 7. As all the contacts are connected with the corresponding points of the resistance, when N reaches contact C, all the resistance in the resistance box will be cut out of the circuit. As will be noticed, contact B is connected with the center point G of the series field coil so that when N reaches contact B one-half of the series coils will be cut out in addition to the whole of the resistance box. When N reaches contacted the current will pass directly to wire/, and thus cut out all the series field coils and then the motor will run as a plain shunt- wound machine, and its speed will be the highest it can attain. If the reversing drum and switch M are now revolved to the position shown in the diagram, the circuit through. the motor will be broken and the machine will come to a state of rest. If the reversing drum and M are now revolved in the opposite direction, that is, contrary to the movement of the hands of a clock, the brushes g and h will rest on one of the revolving drum segments, and i and k on the other segment. If the path of the current is now traced it will be found that it will enter the armature through wire E, and the left side, instead of through wire /, as in the pre- vious case. It will also be found, however, that the current after passing through the armature will reach the series field coils through F, which is the same path as before, so that the direction of the current has been reversed through the armature only, which is what is required to reverse the direction of rotation of the motor. Whichever way the switch M and the reversing drum are turned, the direction of the currents through the series field coils and the shunt field coil will be the same, and only the arma- ture current will be reversed. Cutting out the series field coils not only increases the speed 47 738 HANDBOOK ON ENGINEERING. of the motor, but obviates the danger of the car attaining a dan- gerously high speed if the load is being lowered. A shunt wound motor will run as a motor up to a certain speed, but if the veloc- ity is forced above this point by driving the machine by the ap- plication of external power, then the motor will begin to act as a generator, and as it takes power to run a generator the motor will begin to hold back. Now if an elevator car is running down with a heavy load, the load will draw the car down, and unless a resistance of some kind is interposed, the speed will become greater and greater as the car descends, and by the time it reaches the bottom of the shaft it may be running at a velocity almost equal to that attained by a free fall. The power required to drive the motor when acting as a generator serves to hold the car back, for the current developed increases very rapidly with increase of speed, so that an increase of speed of ten or fifteen per cent above the normal running velocity will be about as much as can be reached even with an extra heavy load. Although the motor will act as a generator and hold the car so that it cannot attain a dangerous speed when descending under the influence of a heavy load, it will only accomplish this result when the circuit is closed ; for if the circuit is open there will be no power generated ; hence, no power will be absorbed by the motor. As can be readily seen, it is possible for the circuit out- side of the motor to become broken by the melting of a fuse or some other cause, and if this occurs when the car is coming down with a heavy load there might be a serious accident. To obviate such mishaps the main switch is made with a magnet b which holds the switch closed so long as current passes through it. but allows the switch to swing open if the line current disappears. This switch on this account is called a potential switch, because it is arranged to be actuated by the difference of potential be- tween the two sides of the line. When the line current fails, and the potential switch opens, the blade m comes ink) contact with n HANDBOOK ON ENGINEERING. 739 and thus the circuit for the motor armature is closed through the resistance wire s which is connected with contact 7. This con- nection short circuits the armature through a resistance sufficient to keep it from being burned out, but not enough to prevent the motor from acting as a brake and holding the car down to a safe speed. The wire c c which runs from magnet b of the potental switch, it will be noticed, connects with a coil marked safety brake mag- net. This magnet acts normally to hold the brake off when the machine is running, but if the current passing through it dies out, then it acts to put the brake on. Now, as has already been ex- plained, when the current is flowing in the main line, there is a current passing through coil b of the potential switch ; hence, there is a current passing through the coil of the safety magnet for the brake ; but if the line current fails the current through the brake magnet will also fail and the brake will go on ; so that the car will be doubly protected, one protection being the short cir- cuiting of the motor circuit through wire s, and the other the ap- plying of the brake by reason of the failure of the current to flow through the safety brake magnet. As to directions for the proper care of these machines, very little need be said, as they are simple and substantial in con- struction and give very little trouble. The motor proper requires the same attention as is given to any stationary motor, that is, the commutator and all other parts must be kept as clean as pos- sible and the brushes must be properly set. As to the other parts, all that need be said is that the bearings must be well lubri- cated and free from grit. They must be tight enough to not al- low the parts to play, but at the same time care must be taken that they are not so tight as to heat up or cut. All bolts and nuts must be re*gularly examined and kept tight, so that they may not work loose or out of place. The most important point to observe, however, is not to undertake under any circumstances 740 HANDBOOK ON ENGINEERING. to tinker with the sheave wheel and the gears that connect it with the horizontal bar that operates the brake and- controller switches. Neither must the brake or the switches be disturbed. All that is to be done to the latter is to keep the contacts bright and clean. If any of these parts, from the sheave wheel to the controller switches, get out of set, so that the machine will not run satisfactorily, do not undertake to readjust them, but send for an expert from the elevator company. If any of these parts are removed or shifted there is danger of their not being put back in their proper position, and if they are misplaced a very serious accident may be the result. If the proper adjustment of these parts is destroyed, the elevator will not stop automatically at the top and bottom landings, but will run too far at one end and stop short of the mark at the other ; hence, the car may either strike violently against the floor or run at full speed into the overhead beams, and in either case the results might be very serious. Even elevator experts have to go cautiously in adjust- ing the position of the sheave wheel and the parts connected with it. The fact that those not thoroughly posted in the operation of these elevators should not tamper with the hand rope sheave and its connections, is not at all unfortunate, for it is next to impos- sible for them to get out of place ; but special caution is advised at this point, because there are many men who are apt to take it for granted that if the machine runs poorly from some trifling cause that they have not been able to locate, the trouble must be due to some defect in the adjustment of the several parts of the operating sheave and its connections. They will then proceed to pull the machine apart, and when they put it together again they are very liable to get it connected wrong, and if such should be the case the first trip made by the elevator might end seriously. Although the machine described in the foregoing works in an entirely satisfactory manner, it has been superseded almost en- HANDBOOK ON ENGINEERING. 741 tirely in first-class installations of recent date by machines that are controlled by means of a small switch in the car instead of the hand rope. There are several types of such elevators made by the Otis Company, one of the latest designs being shown in Fig. 8. Fig. 8. As will be noticed at once, this machine is different in several respects from" the hand rope control machine shown in Fig. 6. As the machine is controlled by the movement of a switch in the car, the brake cannot very well be actuated mechanically, hence a magnetic brake is provided, the magnet being seen at the top of the stand to the right of the motor. The automatic stopping de- vices and the slack cable stop are also arranged so as to act upon U \MMUH K ON :u<-. \\lr uM \vithm tlu - 8< ftt tho ftvnt OTul i^f UU, Tt^ t>^ of iuohino N tu on top of thfc moliWr* g^nv is not ooumvuM nuvhHnXonll^v with HUV of llie movii^r jvirts v^f UM . U OHU IH> Uvntxxi HI auv vvu\vi\iout |K>iut, *vl is then with tho motor artii&turv. tioUt o\>ils aiul with tho I 11 VMMIOOK ON l\\ t ,lM t IM\ 748 magnet and automatic stop switches \\\ moans of oopp. i \\ Pho controller used \\ilh this t\pe of maehino is arranged alter I ho fashion of a switchboard, the switches hoiiuv located on tho front.. Mud the eonnoelino vrites, together \\ith the start inu rwist .moo, hoini; .'it I ho haek. Hie >\\itfios :uv :u't u.-Uod l>\ ini\Mi>-> of . Miui on th:il :uvonnt llu> ilo\itv i- cMllod :i in:i"jn-t o ili:vr:un i>f llu 1 \virinn' t-oniuMMions \\ilh this i-on- (rollor is nioro i'oiuplicMloil than tluU for llu> IIMIK! ro|H> i i onlrolhr. but for tlio jMirposo i>t siiuplil vin^ tho lr:i\\ in^ as nnu . sihlo 1 l:ivo iviuovi'il all llu 1 i-oiiiu'i'tions that air not actually necossaiN for a j>roptr iiiuliM-staiuIin^ of tlu> ^MUM-al arran-MMin'Ml of tho I'in'iiits. 1'his simplitiod diagram i- sho\\n in V\^. 1>. The front of tlu i-onlrolU'r ix slu\\n in Ki^. 10. and tho l:u-U of s.'imo in Fio;. 11. tho starting rosistanoo loin^ ronio\>d in tlii* illustratii>n so as to atToi'd a oU-ar \io\vof tho \\ in> oonnoot ions. Tho sido of tho starting n^i-tanoi" oan lo soon in Fii>\ 10. In this la^t nainod illn.-t rat ion, all tho s\viiclu's arc 1 in tho position they tako \vhon tho olo\ator is stoppod. Tho t\\o lar^o s>\iioli'x oniMthor sido at tho bottom of thohoanl aro t ho starting s\\ itches. one noting to run tho oar up and tho othor ono to run it do\\n. Tho t\\o -inallor switcho^ oooupx \\\g tho o-iilor of tho U>Itoni panol of tho hoard ami the two Bitches in tho upper corner are for tho purpose of aecelorat \ug tho volooitx of tho motor wlion it is Started. 'When tho motor starts, tlioro is a resiM;mce in tho annatur*' oiivuit, ami the current, nfior passing through the arm:i- ture is passed tiirou^h ^iM'ii's I'u-ld coils. After tho motor has started, the Martin^ resistance is out. out, and then tho series lield ooils are out out. so that \\henthofull speed is a'tainod.tho motor is a simple shunt-wound machine. In this ivspoot tho arrangement of tho motor circuits is the same as in tho hand rope controller maohino. When it ' s desired to start tho car. a small s\\itch in the latter is moved ;o\vard tho riirht or loft . according to 1 he direct ion in 744 HANDBOOK ON ENGINEERING. which the car is to move. To run the car up, the car switch is turned to the left, and this movement sends a current through the magnet of the lower right side magnet on the controller board. Fig. 10. This magnet then lifts its plunger and the two discs mounted upon the latter come into contact with the stationary connectors located just above them, and then the current can find its way through HANDBOOK ON ENGINEERING, 745 the motor circuits in the proper direction to produce the upward motion. The four small switch magnets on the controller board are connected in separate circuits that are in parallel with each Fig. 11. other, and in shunt relation to the armature of the motor. When the motor first starts, the counter electromotive force developed by the armature is not as great as when it is running at full speed, 746 HANDBOOK ON ENGINEERING. because a portion of the electromotive force of the line current is used to force the current through the starting resistance and through the series field coils. When a portion of the starting resistance is cut out the armature counter electromotive force is correspondingly increased. When more of the starting resistance is cut out, the counter electromotive force is further increased. It is still further increased when the series field coils are cut out. Now the current that passes through the magnets of the four small switches on the controller board increases as the counter electromotive force of the motor armature increases. The mag- nets are so adjusted that as the currents passing through them increase one after the other will lift its plunger and then the con- nections made by the discs at the lower end of these plungers will cut out successively the sections of the starting resistance and the sections of the series field coils. The two small tubes at the top of the controller board are safety fuses, and the line wires are connected with their upper ends. By the aid of the foregoing explanation of the way in which the controller acts, the following description of the wiring diagram (Fig. 9) will be easily understood. In this diagram the line wires come in at the top of the controller and are marked -}- and . The motor is shown at the bottom of the diagram, the circle A representing the armature, and the coil B is the brake magnet. The stop motion switch is placed on the elevator machine, in one of the casings at the front end of the drum, and is actuated by the automatic stop mechanism which stops the car at the top and bottom landings. The car switch is shown in the upper left hand corner of the diagram, and the curved lines J represent the wires that connect it with the motor and the controller board. These wires are placed within a flexible cable that is attached to the side of the elevator shaft half the way up from the bottom, the cable being long enough to reach the car when at either end of the shaft. The limit switch in the car is for the purpose of stop- HANDBOOK ON ENGINEERING. 747 ping the motor, if the car reaches either end of its travel without being stopped by the operator, or the action of the stop motion switch. This switch is closed under ordinary conditions, so that the current in wire C can flow all the way to the lower contact a of the car switch. If it is desired to run the car down, the car switch is turned to the right, and then wire C is connected with wires D ' and FD. The stop motion switch is normally in the position shown so that the current in wire D ' can pass to D and following this wire it will reach contact DO which is under the lower disc of the right side starting switch. Through the disc this contact is connected with the corresponding contact on the other side of the disc, and this latter contact is connected with a wire that carries the current to the magnet of the left side starting switch. Considering now the main current in the + line it can be seen that it can flow down to the line near the bottom of the controller portion of the diagram, and which terminated in the -f- contacts of both the starting switches, but can go no further so long as the discs on the plungers of the magnets are in the lower position. As soon, however, as the current coming from the car switch passes through the magnet of the left side switch, as just explained, the plunger will be lifted, and then the disc will connect the -f- contact with the /S2 contact, and also with a smaller contact B. When this connection is made, the main cur- rent can flow from contact S2 to contact $2 of the right side switch , and thence through the connecting disc to contact I -which is connected by wire .to binding post I; the latter being con- nected with the right side armature terminal I. After passing through the armature the main current reaches binding post E and through the connecting wire the contact E at the top of the left side starting switch, and as the plunger of this switch is in the raised position, the current can pass to contact R and thus reach the upper end R of the starting resistance in the resistance box. 748 HANDBOOK ON ENGINEERING. From the end F of the starting resistance, the main current flows to binding post F and then to the F end of the series field coils, and from end H to binding post // and to the line wire at the top of the diagram. The current for the shunt field is taken from the contact S2 at the bottom of the left-ride starting switch, and passes to point 4 and thence to D and to the D end of the shunt field coil, and through this coil to end // of the series coil, and thus to the line. The current for the brake magnet starts from the small contact B at the bottom of the left-side starting switch. The car switch when moved will first cover contact D' so that the main current will follow the path outlined above, but as soon as the car switch covers contact FD, the current passing- through wire FD in the cable will reach the stop-motion switch and pass to F, and thus to magnet No. 1 at the upper left hand corner of the controller board. The lifting of this switch will cause its disc to connect the contacts RR' and thus the current will pass to point R' of the resistance and cut out the upper sec- tion. The current from contact B at the bottom of the left-side starting switch passes through the magnet coils of the three switches, Nos. 2, 3 and 4. Now soon after the first section of the starting resistance is cut out, No. 2 magnet becomes strong enough to lift its plunger, and then the current from the right side, contact R, at the top of the left-side switch, will pass to contact R of No. 2 switch, and thus to R2 and to point R'2 of the resistance, thereby cutting out two sections. In this way the current through magnet of switch No. 3 will be increased and the plunger will be lifted so that the current will be able to pass from the R contact of this switch to the G contact, and thus to binding post G and to the center of the series field coils, thereby cutting out one-half of these coils. In this way the current through coil of No. 4 magnet will be farther increased, so that it will be able to lift its plunger, and thus form a direct connection from contact G of switch No. 3 and the main wire leading to the line. HANDBOOK ON ENGINEERING. 749 Thus it will be seen that the four switches, 1,2, 3 and 4, will act one after the other. This same operation is repeated if the car switch is moved to the right, so as to run the elevator down, the only difference being that the starting switch at the right side of the board will be lifted, but the action of the four smaller switches will be the same. In addition to the operating circuits described in the foregoing there are wires that connect the slack cable switch with the motor circuits and other connections by means of which the elevator may be run from the controller board whenever desired. These con- nections are not shown in Fig. 9, as they would complicate the drawing, and it is not thought advisable to complicate the explan- ation of the main part of the system for the sake of introducing the minor details. This type of electric control is used for elevator building in- stalled in office buildings, and others placed where the car is oper- ated by a regular attendant. For private house elevators and for dumb waiters it is necessary to modify the controlling system so that the car may be operated not only from within, but also from any of the floors of the building. It is further necessary that the circuit connections be such that if the car is operated from any floor, it will run to that floor, whether above or below it, and further, so that if it is being operated by a person within the car it cannot be operated by any one else from any of the landings. It must also be arranged so that if the car is set in motion from any floor it cannot be stopped or interfered with in any way by a person at another floor. For the purpose of safety the system must also be arranged so that the car cannot move away from any floor until the landing door is closed. This feature is necessary to guard against people falling through the open doorway into the elevator shaft. Although it would appear difficult to accomplish all these results without resorting to great complications, as a matter of fact the system used by the Otis Company is decidedly 750 HANDBOOK ON ENGINEERING, DOOR CONTACTS HANDBOOK ON ENGINEERING. 751 simple. At each floor of the building a push button is placed, and by pressing this for an instant the cur is set in motion wher- ever it may be, providing it is not being used by some other per- son, and when it reaches the floor from which it has been operated it will stop automatically. If the elevator is operated from the car, a button is pushed that corresponds to the floor at which it is desired to stop, the car will then begin to move, and when the floor is reached it will stop. If the passenger after stepping out of the car forgets to close the landing door, the elevator cannot be moved away from the landing by the manipulation of any of the push buttons on the various floors or within the car. The way in which all these results are accomplished can be made clear by the aid of Fig. 12, which is a simplified diagram of the wiring. In this diagram most of the parts are marked with their full name. The floor controller is a drum which is revolved by the elevator machine and its office is to shift the connections of the wires 11, 22, 33, 44, from one side of the circuit DU to the other as the car ascends and descends in the elevator shaft. This shifting of these connections is necessary to cause the car to run down if above the landing from which it is operated, and to run up if it is below the landing. The actual position of the floor con- troller with reference to the elevator machine can be seen in Fig. 13 in which the floor controller is located back of the motor and is driven from the drum shaft by means of a chain and sprocket wheel. In the diagram Fig. 12 it will be noticed that the drum surface is divided into two segments and upon one rests the brush of wire D while upon the other rests the brush of wire U. The twelve contacts shown at G form the operating switch. The center row marked m n o p are movable, and the four contacts above them as well as the four below are stationary. The center row of con- tacts m n o p are moved upward by a magnet represented by the coil D and they are moved downward by another magnet repre- 752 HANDBOOK ON ENGINEERING. sented by the coil U. From this it will be seen that if a current comes from the floor controller through wire D the movable con. tacts of G will be lifted and will connect with the top row, while if the current comes from the floor controller through wire 7, the movable contacts will be depressed and will make connections with the lower row of contacts. The main switch that connects the motor circuits with the main line is shown at S. As will be noticed, a wire marked d -{- II runs from the -j- wire to the right side of the diagram, where the landing and the car push buttons and their connections are shown. This wire runs from top to bottom of the elevator shaft and is con- nected with switches that are closed when the landing doors are closed, and open when the doors are open. These switches are indicated by the four circles marked door contacts, the diagram being for a building four stories high. If the door contacts are closed, the current can pass as far as the wire marked + which runs through the flexible cable to the car. In the car there is a switch in this wire and further on a gate contact, which is closed when the car door is" closed. If these switches are closed, the current can return from the car through wire A and run as far as the center of the diagram under the main switch S. The floor controller is shown in the position corresponding to the car at the bottom of the shaft. Suppose now that the landing push button I is pressed for a second, then the wires B and I will be connected, and the current in wire A will pass to wire B and through the push button to wire I and thence to wire II. The coil between wire I and wire II is a magnet, and as soon as the current passes through it, it draws the contact to the right and thus provides a path for the current direct from wire A to wire M, so that the push button may be raised without opening the circuit. The current in wire II will pass through the floor controller to wire {/and thus through magnet U of the operating switch G. This magnet will then draw down the movable contacts m n o />, and the main line HANDBOOK ON ENGINEERING. 753 current from the -f- wire will pass from contact m to wire ra' and through wiie m' to point 10, hence through wire w 1 to the acceler- ating, or starting resistance, and to wire F which leads to th3 series field coils. Returning from these coils through wire // to magnet switch 2 and thence wire n' to contact w, and as this con- Fig. 14. tact is pressing against the one directly below it, the current will flow through the connection to wire E and thus to the armature ; returning from the latter through wire / and wire o' to the contact below o and thus to o and through the permanent connection to contact p and to the lower right hand contact which is connected 48 754 HANDBOOK ON ENGINEERING. with wire r which runs to the side of the main switch. The shunt field current is derived from wire m' and returns to contact p and thus to wire r through wire p' ', as can be clearly traced. The brake magnet current starts from the left side contact of G through wire -{- B and returns directly to the lower end of wire r. The magnet switches 1 and 2 act in the same manner as those in diagram Fig. 9, that is, by the increase in the counter electro- motive force of the armature which causes the current that passes through them to increase in strength. When magnet I closes its switch, the current passes from wire w' to wire F and thus the accelerating resistance is cut out. When magnet 2 closes its switch the current passes from wire m" directly to ri and thus to the armature without going through the series field coils ; thus the latter are cut out. Returning now to the operation of the floor controller it will be seen that as the current is flowing through wire II the circuit will be broken if the controller is rotated until the gap at the top comes under the brush of wire II. Now the floor controller drum begins to turn as soon as the elevator machine moves, and it is so geared to the elevator drum that when the car comes op- posite the first floor the brush of wire II will be over the upper gap, and then the circuit will be open and the magnet U will be de-energized and allow switch O to move back to the stop position . If button No. 4 is pressed instead of No. 1 the car will not stop until the gap at the top of the floor controller drum comes under the brush wire 44, for the circuit between this wire and wire U will be closed until that position is reached. If the car is run up to the fourth floor, as the gap at the top of the floor controller drum will then be under the brush of wire 44, the brushes of wire 11, 22 and 33 will rest upon the same segment as the brush of wire D; therefore, if with the car at the top floor a button is pressed at any one of the lower floors HANDBOOK ON ENGINEERING. 755 the current will pass from its corresponding wire to wire D and thus through magnet coil D and to wire r' and wire r. The cur- rent passing through magnet D will draw the movable contacts of the operating switch 6 upward, and thus set the elevator machine in motion in the opposite direction from that in which it runs when the U magnet is energized. In tracing out the circuits from the floor push buttons as just explained it will be noticed that if any one of them is depressed, the current in wire A will flow through wire B to the button de- pressed, and then enter the wire returning from that button. When the car buttons are depressed the current in wire A will pass to wire C and then through the button in the car to the proper return wire ; that is, to one or the other of the wires 1, 2, 3, 4. After entering one of these four wires the current follows the same path as it does when one of the floor buttons is depressed. The magnet B' in the B wke, and the magnet C' in the C wire, are for the purpose of preventing in- terference between a person operating the elevator from within the car and another one at one of the landings. The B' switch is actuated by a magnet that is wound with two coils that act in opposition to each other. These coils are shown to the left of B' '. When the elevator is operated from one of the floor push buttons the current in wire A passes through both the coils on the magnet of switch B' and as one coil counteracts the other the switch is left closed and the current passes directly to wire B. It the elevator is operated from within the car the current from wire A in passing to wire C passes through one of the coils of the -mag- net that actuates switch B ', hence this switch is opened and the connection with wire B is broken, so that if now any one of the floor buttons is pressed it will have no effect as the circuit is opened at switch B'. The current flowing through wire C passes through a magnet that acts to close the switch C' and thus allow a portion of the current to pass directly to wire r. This current 756 HANDBOOK ON ENGINEERING. will continue to flow even after the car has stopped at the landing, providing the door is not opened. As soon as the door in the car, or the lauding door, is opened the circuit is broken either in wire Hor in wire A, and then the car cannot be moved until the doors are closed. If it were not for switch C' it would be possi- ble for a person at one end of the landings to move the car if he pressed the button during the short interval of time between the stopping of the car and the opening of the landing door. The opening of the door would stop the car, but by this time it might be a foot or two away from the floor level. The current that passes from switch C' to wire r is kept down to a small amount by passing it through a high resistance which in the diagram is marked 700 w. The electrical portion of the Otis electric elevators has been supplied for many years to four or five of the leading companies, which were controlled by the Otis, and during the last two or three years it has been supplied to practically all the prom- inent makers, as these are now part and parcel of this company ; hence the descriptions given in the foregoing are more than likely to cover any case met with in practice, for although there are numerous small manufacturers, the sum total of their elevators in use is comparatively small. The only electric elevators in addition to those described in the foregoing that have come into extensive use are those made by the Sprague Electric Co. These maehines are of two different types, one being the ordi- nary drum design, and the other the screw machine. The drum machine is similar in its main features to the same type of ma- chine of other makers, and it is only in the minor details of con- struction that any radical difference can be noted. In the means employed for controlling the motion of the motor, however, there is a decided difference. In all the Sprague elevators the car is controlled electrically, hand rope control not being used in any HANDBOOK ON ENGINEERING. 757 758 HANDBOOK ON ENGINEERING. case. The drum machines are arranged like those of other makes, so that the motor is connected with the main line whether the car is going up or down, and acts as a motor or as a generator ac- cording to the conditions of the load ; that is if the load is lifted, the machine acts as a motor, and if the load is lowered, the ma- chine acts as a generator and holds the car back. With the screw type of machine, the arrangement is different, the motor acting as such in raising the load, but on the descent the motor is dis- connected with the main line and acts as a generator, developing a current that circulates in a circuit formed by the motor connect- ing the wires, and which is entirely independent of the main line. In the drum machine, when the motor acts as a generator in lowering a load, the current it generates is sent back into the main circuit, and at all times the machine is connected with the main line, while with the screw type the motor is only connected with the mainline when the load is lifted. The general appearance of the screw type of Sprague elevator is shown in Fig. 14. This illustration represents two machines, one placed on top of the other. In buildings where there is an abundance of floor space, the machines are all set directly upon the floor, but where floor space is limited, they are stacked two, three and even four high. As can be clearly seen in Fig. 14, a long screw is coupled to the end of the motor armature shaft. This screw threads through a nut that is mounted in a cross head that carries a number of sheaves around which the lifting ropes pass. At the extreme end of the machine other sheaves are mounted, these being held in stationary supports. The sheaves carried by the cross head travel from one end of the machine to the other as the screw is rotated. When they are drawn away from the stationary sheaves the elevator car is raised, and when they move toward the sta- tionary sheaves the elevator is lowered. In this respect the action is just the same as in a horizontal cylinder hydraulic ele- vator. HANDBOOK ON ENGINEERING, 759 Fig. 15, HAND BOOK ON ENGINEERING. The nut carried by the traveling cross head is so arranged that when the latter reaches the end of its travels at either end of the screw, the nut is released and then rotates with the screw with- out moving the cross head. This forms a perfect top and bottom limit stop, for even if the motor continues to run, the car cannot be carried beyond the positions corresponding to the points at which the n"ut slips around in the cross head. The brake for holding the machine is mounted upon the outer end of the armature shaft, and can be seen at Fig. 14 at the ex- treme right hand side. This brake is actuated by a magnet that releases it, and a spring that throws it on. When the current is on, the brake is lifted and when the current is off the brake goes on. In this respect, the action is the same as in all other electric elevators. The operation of the motor is controlled by a small switch in the car, which is connected with the motor circuits by means of wires contained in a flexible cable, just like the Otis electrically controlled machines. The controller consists of a main switch ? which is moved by a "small motor called a pilot motor, and a num- ber of smaller magnetic switches whose action will be presently explained. All these parts are mounted upon a switchboard, and present the appearance shown in Fig. 15. The pilot motor and main switch are located at the top of the board, and the magnet switches cover the space below, while the starting and regulating resistance is mounted on the back of the board. The complete wiring diagrams for these machines is decidedly complicated owing to the fact that there are numerous switches and devices whose office is to afford additional safety, or to ren- der the control more perfect. When all the parts that are not actually necessary to illustrate the system are removed, however, the diagram becomes quite simple and can be readily understood. Such a diagram is shown in Fig. 16. This diagram shows the motor together with the screw and sheaves, the elevator car, the HANDBOOK ON ENGINEERING. 761 counterbalance, and the operating switches. The wires marked' -f- and are connected with the main line. The switch in the car is connected with the controller by means of four wires, marked c b d and s. The lower one of these wires, marked s, is connected with the stud around which the car switch swings. When the car switch is moved onto the upper contact, it connects wire s with wire c and then the car runs up. When the car switch is moved down onto the lower contact, wire s is connected with wire d, and then the car runs down. When the car switch is placed in the central position wire s is connected with wire b and then the elevator stops. The two switches marked " up limit," "down limit," are for stopping the car automatically at the top and bot- tom landings. Normally the up limit switch is closed and the down limit switch is open. With these switches in this position, which is the position in which they are shown in the diagram, the current from the -f- wire can pass through the up limit switch to wire fc, and thence through wire I to the armature of the motor, and then through the field coils, and reach wire ra. It cannot go beyond this point until the switch C is moved. This is the main operating switch, which in Fig. 15 is seen at the top of the board, the contacts being arranged in two circles. The pilot motor that rotates the arm of this switch, which is clearly shown in Fig. 15, is represented in this diagram, Fig. 16, at A. As will be seen in this diagram, this motor has a field provided with two magnetizing coils, one for the up motion, and one for the down motion, and in addition it is provided with a brake to stop it quickly and hold it when not in use. The portion of the diagram marked B is the reversing switch. Let us suppose now that the car switch is moved upward, so as to cause the elevator to ascend, then wire s will be connected with wire c. From the -{- wire a current will pass through wire a to s and thus to c, and through magnet e of switch $, thus closing this switch so as to connect wires h and i. The current in wire c will 762 HANDBOOK ON ENGINEERING. pass to B and through the connecting plate u will reach the end of the up field coil of the pilot motor, and then pass through the armature of this motor, and finally through the magnet that re- leases the brake. The pilot motor will now rotate the reversing switch B so that the contact plates will jnove toward the left. This movement will bring plate w under the ends of wires s and i, thus permitting a current from s to pass to i, and as switch g is BRAKE RCLCASC 3PRAGUE PRATT SCREW ELEVATOR closed this current will reach wire h and thus the magnet J, thereby lifting the plunger switch that closes the gap between wire q and the -- wire. As the arm of the main switch C moves with the reversing switch J3, this arm will ride over the contacts on the right side, marked " t^res." and thus the current from wire ra will be able to reach wire q after passing through the up resistance. HANDBOOK ON ENGINEERING. 763 If the car switch is left on the upper contact, the pilot motor will continue to rotate until the arm of switch C reaches the top of the resistance contacts, marked Full up. When this point is reached, the contact plate u of the reversing switch B will pass from under wire c and the terminal of the up field of the pilot motor, and then this motor will stop rotating. If the car switch is not kept on the upper contact very long, the pilot motor can be stopped with the arm of switch C at some intermediate point on the resistance contacts, thus by the time during which the car switch is kept upon the upper contact, the amount of resistance cut out of the motor circuit can be con- trolled and thereby the speed of the car can be controlled. In this operation it will be noticed that the motor is connected with the main line and that the current enters through the -f- wire and passes out through the wire. If now we turn the car switch downward, the s wire will be connected with the d wire and by following the latter to the reversing switch B it will be seen that through connecting plate v it is connected with wire z which leads to the end of the down field of the pilot motor, thus setting the latter in motion in the opposite direction so as to shift the contact plates of B toward the right, and at the same time rotate the arm of the main switch C to the left, thereby making contact with the contacts of the down resistance. With the arm of C in this position, it will be seen that the current in wire I can flow through the motor armature and field and through wire ra to the arm of switch C and through the down resistance to wire n and thus back to wire Z, thereby forming a closed circuit within the motor wires and connections, and disconnected from the main line except on the side of the + wire. The rotation of B causes the connecting plate x to ride upon the terminals of wires s and t, and thus a current is sent through the brake magnet so as to lift the brake, and allow the elevator machine to run. When the pilot motor moves the arm of C so far as to reach the top of the down 764 HANDBOOK ON ENGINEERING. resistance, the contact plate v of the reversing switch B will pass beyond the terminals of wires d and z, thus breaking the circuit of the pilot motor and bringing the latter to a stop. When the reversing switch B is in the stop position, as shown in the diagram, the terminal of wire b does not rest upon a con- necting plate but when the switch is rotated for the up motion, the terminal of b rests on plate v so that if the car switch is turned to the stop position, the current from wire b will pass to wire z and thus reverse the direction of rotation of the pilot motor, and return the switches to the stop position. If the car is running down, when the car switch is turned to the stop position, the current from wire b will pass to wire z and thus reverse the direction of rotation of the pilot motor, and return the switches to the stop position. If the car is running down, when the car switch is turned to the stop posi- tion, the wire b will ride over the plate u and thus the current will pass through the pilot motor through the up field and thus rotate the switches back to the stop position. In each case, as will be noticed, whenever the current flows through wire b it ener- gizes coil / and thus opens switch g. When the car is running up the current for the brake magnet passes from wire i through the switch which is energized by the main current flowing in wire q. When the car runs too far down, and closes the down limit switch, the motor circuit becomes closed through wires j>, r and &, thus giving another path for the current generated by the motor arma- ture and thereby increasing the resistance to rotation. The controller for the Sprague drum machines is very similar to the one just described. It is operated by a pilot motor, and in so far as the controller switchboard is concerned looks the same. The only - difference is that rendered necessary by the fact that in lowering as well as in raising the load, the motor is connected with the line. This requires a slight change in some of the wire connections. HANDBOOK ON ENGINEERING . 765 The electrical parts of the Sprague elevators require very little attention other than to keep them clean and all the contacts bright and in proper adjustment, so that when moved a good contact may be made. Of the mechanical portion, the drum machines require about the same attention as other machines of this type. As to the screw machines, the part that requires most attention is the screw and the nut. As can be readily understood, if the nut were solid, the friction against the screw would be very great; therefore, to reduce this friction, the nut is made so as to carry a large number of friction balls. These run in a groove cut in the side of a thread and roll between the thread and the screw and the thread in the nut. A tube is attached to the nut to provide a path through which the friction balls can pass from the end of the thread to the beginning, thus making an endless path in which they move. As these friction balls are subjected to a heavy pres- sure, there is more or less danger of their giving trouble and on that account the thread on the screw should be carefully examined and kept as clean and free from grit as possible. Under favorable conditions these screws run very well, the wear being trifling, but in some instances they are liable to cut badly, hence they should be closely watched. DIRECTIONS FOR THE CARE AND OPERATION OF THE ELECTRIC ELEVATORS. Whenever the attendant wishes to handle the machine to clean, adjust, repair or oil it, he should see that the current is shut off at the switch, and thus prevent all possibility of accident. Cleaning. Keep the entire machine clean. Clean the com- mutator and other contacts and brushes carefully with a clean cloth and keep them free from grease and dirt. If the face of the rheostat on which the rheostat arm brushes work becomes burnt, clean with a piece of fine sand-paper (No. 0), or if necessary use 766 HANDBOOK ON ENGINEERING. a fine file. Keep all contacts smooth. Try the rheostat arm when cleaning to be sure that it moves freely off contacts. Oilingf, Oil the drum shaft bearings with good heavy oil. Oil the worm and gear by filling the chamber around them with a mixture of two parts of good castor oil and one part good cylinder oil. Keep this chamber filled to the top of worm or mark on gauge glass, adding a little each day as it is used. The end thrust bearings of the machine are automatically oiled from this chamber. This should be drawn off every two or three months and replaced by fresh oil. Oil the motor bearings with dynamo oil. These are automatically oiled, but should occasionally be supplied with fresh oil. Lubricate the commutator, rheostat face, drum switch and contacts VERY SPARINGLY with a cloth moistened with oil. Care should be taken not to supply too much oil to these parts. Keep the oil dash-pot, if any, sufficiently filled with oil to allow the rheostat arm to move quickly on to the first con- tact and to retard this movement beyond this contact. The best oil for this purpose is fish oil, or some thin oil that is not readily affected by changes in temperature. If an air dash-pot is used, keep it slightly oiled so as to keep the packing soft. Keep all parts of the elevator, including sheaves, guides, cables, etc., clean and well oiled. Operating. Before switching the current on to the machine, be sure that the operating lever is in its central position. To ascend, draw the lever the full throw to the up. To descend, draw the lever the full throw to the down. To run at slow speed, bring the lever toward the center according to the speed desired. To stop, bring lever to slow speed when within four feet of landing, and to its central position when close to it. In this way, the operator can make accurate stops. When starting (machines on which the solenoid is used) if the current is admitted to the motor too rapidly, thereby starting the car with a jerk, or momentarily dim- ming the lights on the circuit, check the speed with which the HANDBOOK ON ENGINEERING. 767 resistance is cut out of the armature circuit by slightly easing off the weight which acJbs in opposition to the core of the small solenoid. This solenoid controls a valve in the dash-pot and thereby regulates its speed in proportion to the current passing. If a governor starter is used and the current is admitted too rapidly, tighten the governor spring on the armature shaft, or close the vent in air dash-pot. If the car refuses to ascend with a heavy load, immediately throw the lever to the center and reduce the load, as in all probability it is greater than the capacity of the elevator. If it refuses to ascend with a light load, throw the lever to the center and have the fusible strip examined. If, in descending, the car should stop, throw the lever to the center and examine safeties, fusible strip and machine, and before starting, be sure that the cables have not jumped from their right grooves. If the car refuses to move in either direction, throw the lever on the center and have the fusible strips examined. Never leave the car with- out throwing the lever to the center. If the car should be stalled between floors, it can be either raised or lowered by raising the brake and running it by turning the brake-wheel by hand. Such a stoppage might be caused by the current being shut off at the station, undue friction in the machine, too heavy a load, fuses burnt out, or a bad contact of the switches, binding posts or elec- trical connections. If the car by any derangement of cables or switch cannot be stopped, let it make its full trip, as the auto- matic stop will take care of it at either end of the travel. The bearings should be examined occasionally to insure no heating and proper lubrication. General directions* Have the machine examined occasionally by someone well posted in electric motors and elevators. The attendant should inspect the machine often. All brushes and switches should be sufficiently tight to give a good contact, but no tighter. None of the brushes should spark when in their 768 HANDBOOK OX ENGINEERING. normal position. When the brushes become burnt dress with sandpaper or file, or, if necessary, replace with new ones. If brushes spark, dress with sandpaper or file to a good bearing, and, if necessary, set up springs, but do not make the ten- sion such as to interfere with their ready movement. Adjust commutator brushes gradually for least sparking. These should be close to the central position. Contacts and brushes should be kept clean and smooth and lubricated sparingly. While replacing a fusible strip, be sure that main switch is open, and be careful not to touch the other wire with your tool or otherwise, as such contact would be dangerous. Never put in a larger fuse than the one burnt. Inspect the worm and worm-wheel occasion- ally through hand-holes in casing, to see that they are well lubri- cated, and that no grit gets into the oil. They should show no wear. The stuffing box on the worm shaft should be only tight enough to keep the oil from leaking out of the worm chamber. Be sure that all parts are properly lubricated, and that none of the bearings heat. To make sure that the car and machinery run freely, lift brake lever and then rotate worm shaft by pulling on the brake wheel. The empty car should ascend without any exer- tion. Keep operating cables properly adjusted. Open main switch when the elevator is not in service. HANDBOOK ON ENGINEERING. CHAPTER XXVI. HYDRAULIC ELEVATORS. The purpose of these pages is to furnish such instructions and information as will be of use to engineers in the handling of eleva- tor machinery. To accomplish this end, cuts and sectional views of cylinders and valves of the different types of elevator machin- ery made by the different elevator companies, are herein produced, so as to make the different elevators plain to the engineer. It must be borne in mind that the one point of paramount impor- tance for the successful operation of an elevator is proper care and management ; a lack of thorough knowledge of the machine and lack of attention in this respect shortens the life of the ma- chine and often makes extensive repairs necessary. HOW TO PACK HYDRAULIC VERTICAL CYLINDER ELEVATORS. Packing vertical cylinder piston from top* Run the car to the bottom and close the gate valve in the supply pipe. Open the air cock at the head of the cylinder, and also keep open the 49 770 HANDBOOK ON ENGINEERING, Showing how to set the rope on the lever elevator ; the sheave* want to be on the center of the travel, as shown. HANDBOOK ON ENGINEERING. 771 valve in the drain pipe from the side of the cylinder long enough to drain the water in the cylinder down to the level of the top of the piston. Now remove the top head of the cylinder, slipping it and the piston rods up out of the way, and fasten there.. If the piston is not near enough to the top of the cylinder to be accessible, attach a rope or small tackle to the main cables (not the counter-balance cables) a few feet above the car, and draw them down sufficiently to bring the piston within reach. Remove the bolts in the piston follower by means of the socket wrench .furnished for that pur- pose. Mark the exact position of the piston follower before re- moving it, so that there will be no difficulty in replacing it. On removing the piston follower you will find a leather cup turned upwards, with coils of |-inch square duck packing on the outside. This you will remove and clean out the dirt ; also clean out the holes in the piston through which the water acts upon the cup. If the leather cup is in good condition, replace it, and on the outside place three new coils of |-inch square duck packing, being careful that they break joints, and also that the thickness of the three coils up and down does not fill the space by J inch, as in such case the water might swell the packing sufficiently to cramp it in this space, thus destroying its power to expand. If too tight, strip off a few thicknesses of canvas. Replace the piston follower and let the piston down to its right position. Replace the cylinder head and gradually open the gate valve in the supply pipe, first being sure that the operating valve is on the down stroke or it is so the car is coming down. As soon as the air has escaped before closing the air cock to make sure the air is all out of the cylinder, make a few trips, and the elevator is ready to run. Packing the vertical cylinder valves* To pack the valve, run the car to the bottom and close the gate valve in the supply pipe. Then throw the operating valve for the car to go up, open the air cock at the head of the cylinder and the valve in the drain pipe at the bottom, and the water will drain out of the cylinder. 772 HANDBOOK ON ENGINEERING* SECTION OF ELEVATOR CYLINDER AND VALVE SHOWING WORKING PARTS. OTIS VRTICAL HYDRAULIC PASSENGER AND FREIGHT MACHINE A shows the position of the valve at rest. B shows the position of the valve when the car is goin up or hoisting. C shows the position of the valve when the car is coming down or lowering. HANDBOOK ON ENGINEERING. 773 When the cylinder is empty, reverse the valve for the car to run down, so as to let the water out of the circulating pipe. In cases of tank pressure, where the level of the water in the lower tank is above the bottom of the cylinder, the gate valve in the discharge pipe will have to be closed as soon as the water in the cylinder is on a level with that in the tank, allowing the rest to pass through the drain pipe to the sewer. As soon as the water has all drained off, take off the valve cap and remove the pinion shaft and sheave, marking the position of the sheave and the relation which the teeth on the pinion bear to the teeth on the rack before removing. You can now take out the valve plunger and put the new cup leather packings on in the same position as you find the old ones. Replace all the parts as iirst found. Before refilling the cylinder, close the valves in the drain pipes, but leave the air cock at the head of the cylinder open and be careful that the operating valve is in position for the car to go down. Gradually open the gate valve in the supply pipe. When the cylinder has filled with water and the air has escaped, close the air cock and open the gate valve in the discharge pipe. Packing piston rods. Close the gate valve in the supply pipe. Remove the followers and glands to the stuffing boxes and clean out the old packing. Repack with about eight turns of i inch flax packing to each rod, and replace glands and followers. Screw down the followers only tight enough to prevent leaking. Packing Otis Vertical Piston from bottom* Remove the top stop-button on hand rope and run the car up until the piston strikes the bottom head in cylinder. Secure the car in this posi- tion by passing a strong rope under the girdle or crosshead and over the sheave timbers. When secured, close the gate valve in the supply pipe, open the air cock at the head of the cylinder, and throw the operating valve for the car to go up. Also open the valve in the drain pipe from the side of the cylinder, and from the lower head of the cylinder, thus allowing the water to drain 774 HANDBOOK ON ENGINEERING. out of the cylinder. When the cylinder is empty, throw the valve for the car to descend in order to drain the water from the cir- culating pipe. In case of tank pressure, where level of water in lower tank is above the bottom of the cylinder, the gate valve in the discharge pipe will have to be closed as soon as the water in the cylinder is on a level with that of the tank, allowing the rest to pass through the drain pipe to the sewer. When the water is all drained off, remove the lower head of the cylinder, and the piston will be accessible. Remove the bolts in the piston follower by means of the socket wrench, which is furnished for that pur- pose. Before removing the piston head, mark its exact position, then there will be no difficulty in replacing it ; also be careful and not let the piston get turned in the cylinder, so as to twist the piston rods. On removing the piston follower, you will find a leather cup turned upwards, with coils of J in. square duck packing on the outside. This you will remove and clean out the dirt ; also clean out the holes in the piston, through which the water acts upon the cups. If the leather cup is in good con- dition, replace it and on the outside place three new coils of | inch square duck packing, being careful that they break joints and also that the thickness of the three coils up and down does not fill the space by J inch, as in such case the water might swell the packing sufficiently to cramp it in this space, thus destroying its power to expand. If too tight, strip off a few thicknesses of canvas. Replace the piston follower and cylinder head, and the cylinder is ready to refill. Close the valves in the drain pipes, leave the air cock open at the head of the cylinder and the oper- ating valve in the position to descend, and open gate valve in the discharge. Slowly open the gate valve in the supply pipe, allow- ing the cylinder to fill gradually and the air to escape at the head of the cylinder. When the cylinder is full of water, leave the air cock open and put the operating valve on the center. The car can then be untied, the stop button can be reset, and the elevator is ready to use. Make a few trips before closing the air valve. HANDBOOK ON ENGINEERING, 775 The above cut is the Auxiliary Valve for Crane Hydraulic Passenger Elevators. The operation of this valve is explained as follows : D repre- sents the supply inlet ; E, the discharge outlet ; F, the opening 776 HANDBOOK ON ENGINEERING. to the cylinder ; 6r, the pilot valve ; H, the pilot valve supply pipe to the motor cylinder ; N and J", the attachment by which the valve is operated. Fig. 1 represents the valve on centers, or the car at rest at any floor between limits of travel. It will be noticed in cut that the plunger heads A and B are on either side of the central opening. The water is then entirely cut off from the machine and the pilot valve covers the port C. To start the car up, water is admitted to the cylinder /through the inlet I). This is accomplished by pushing on the connection in which opens the port C in the pilot valve 6r, allowing the water in the motor cylinder I to flow into the discharge E. The flow is regu- lated by the screw K. The pressure in the motor cylinder I being relieved, the valve plunger moves to the right under the difference in pressure upon the plunger A and L, L being of smaller diameter than A. Supply is thus admitted to the cylin- der through F. To start the car down, pull on the connection J. The port C in the pilot valve chest is opened, allowing water from the pilot supply H to flow into the motor cylinder 7. The pressure on head forces the plunger B to move to the left. Water is thus allowed to pass out from F to the discharge E. If a slow movement of the car is desired, connection J is removed to the right or left for either up or down, and only enough to open the main valve slightly to give the desired speed. This speed is maintained by the lever being moved on its fulcrum P, thus necessitating the valve O- covering port C. AUTOriATIC STOP VALVE. The stop valve M is opened automatically by the machine as the elevator starts from the top or bottom landing, giving free flow of water to the cylinder. As the car reaches the upper or lower limit -of travel, the valve is automatically closed, so that the car stops gradually at the terminals. HANDBOOK ON ENGINEERING. 777 OTIS GRAVITY WEDGE SAFETY. J. Under the car is a heavy hardwood safety plank, on each end of which is an iron adjustable jaw, inclosing the guide on the guide post. In this jaw is an iron wedge, withheld from con- tact with the guide in regular duty. Under the wedge is a rocker arm, or equalizing bar, with one of the lifting cables attached independently at each extremity. The four lifting cables, after being thus attached, pass over a wrought iron girdle at the top of the car. Each cable carries an equal strain, and the breakage of any one cable puts the load on the other cables, which throws the rocker out of equilibrium and forces the wedges on both sides instantly and immovably between the iron jaws of the safety plank and the side of the guides, stopping the car. It may be raised to any position by the unbroken cables, though it cannot be lowered until a new cable is put on. 2, Any cable will always stretch before it breaks, which will throw the equalizing safety-bar out of equilibrium and force the wedges on both sides into position. No other safety device will give warning in advance. CARE OF HALE ELEVATORS. Keep the guide springs on the girdle above, and the safety plank below the car adjusted, so that the car will not wabble, but not tight enough to bind against guides. When cables are draw- ing alike, the equalizing bars on a passenger elevator should be horizontal, and the set screws free from contact with the finger shaft, but adjusted so that one of them will come in contact with the finger shaft when the equalizing bar is tipped a certain amount either way. If the safety wedges should be thrown in, or rattle, when descending, the cause would be from the stretch- ing or breaking of one of the cables, the action of the governor, or from weakness of either the spring on the finger shaft, 778 HANDBOOK ON ENGINEERING. safety-wedge or gummy guides. In the first case, if occa- sioned by the cable stretching, the cable should be examined thoroughly, and if it shows weakness, a new one put on, otherwise, it can be shortened up, as stated above. In the sec- ond case, the car had probably attained excessive speed and the governor simply performed its proper function. In the third case, new springs should be put on and the guides kept clean, for it often happens that the guides are so dirty that the springs cannot well prevent the wedges catching. All the safeties should be kept clean and in good order, so that they will quickly respond when called upon to perform their duty. To loosen the wedges when thrown in, throw the valve for the car to ascend. If the wedges are thrown in above the top landing, remove the button on the hand cable and run the car up until the piston strikes the bottom of the cylinder. If this is not sufficient to loosen the wedges, the car will 'have to be raised by a tackle. Keep all nuts properly tightened. If traveling 1 or auxiliary sheave bushing is worn so that sheave binds, or the bushing is nearly worn through, turn it half round, and thus obtain a new bearing. If it has been once turned put in a new bushing. See that the piston rods draw alike. If they do not, it can be discerned by trying to turn the rods with the hand, or by a groaning noise in the cylinder. However, this groaning may also be caused by the packing being worn out, in which case the car would not stand stationary. See that all supports remain secure and in good condition. WATER FOR USE IN HYDRAULIC ELEVATORS. In hydraulic elevator service little heed is usually given to the quality of water with which the system is operated. Much loss of power by friction and many dollars spent annually in repairs can be avoided by a little thought and action on this subject. In order to prove the truth of this statement, one has only to obtain HANDBOOK ON ENGINEERING. 779 two samples of water, oue of soft water and the other of what is commonly known as hard water. For example, take rain water as the first sample and water from the well as the second. Now rub your hands briskly together while holding them immersed in one, and then in the other of these samples. You will instantly realize that the quality of water used in elevator service has much to do with the efficiency of the hydraulic machinery. Water from the service pipes of the city water-works always contains more or less sand and other gritty substances, in suspension, and this grit acts much the same on the packing and metal parts of the appar- atus as does a sand blast. Some engineers, having realized the evil effects of water in the state that it is generally used, have attempted to remedy the matter by replacing the water which is lost by leakage or evaporation by the addition of the water which is discharged from the steam traps of the plant ; and as this has been distilled, it is almost chemically pure thus the man who uses distilled water in an elevator system instead of the water containing grit, is simply getting out of one difficulty into another. It is a well-known fact in chemistry that pure water is a solvent for every known substance, and will especially attack iron to a large degree. Whenever it is practicable, the water for elevator use should be passed through a filter to remove grit before being allowed to pass into the surge tank. In many cases, however, it would be difficult for the engineer to convince the owner of the advisability of buying and installing a filter for this purpose. A simple and somewhat inexpensive remedy is within reach of all the plentiful use of soap will obviate many of the evil effects of hardness of the water, will double the life of the packing, will reduce the loss by friction, and will, to a large extent, prevent the chattering of the pistons, making the elevators run much smoother. In laboratory practice, the degree of hard- ness or softness of water is determined by the amount of pure 780 HANDBOOK ON ENGINEERING. OTIS DIFFERENTIAL AND AUXILIARY VALVE. HANDBOOK ON ENGINEERING. 781 soap that is necessary to mix with the water to form a lather, or to precipitate a certain quantity of carbonate of lime and other substances. This same action, on a larger scale, takes place when soap is introduced into an elevator tank, and while the oily portion of the soap forms an emulsion with the water, of great lubricating properties, the gritty matter is precipitated and can be gotten rid of through means of a blow-off in the bottom of the tank. The cheapest and most convenient form in which to obtain soap for this purpose, is the soap powder extensively manufac- tured by various firms and which can be purchased for about four cents per pound. In a plant of six elevators, with usually a storage capacity of some 8,000 gallons, it is a good practice to use about twenty pounds of this soap each week. The soap should be at first dissolved in about ten times its weight of boil- ing Water, and when cold it will form a stiff soft soap. The practice of putting in the refuse oil collected from the drip pans is of little value ; it will not mix with the water, but floats on the surface. It rarely gets low enough to enter the suction pipes of the pumps, and has little or no tendency to precipitate the solid matter that is held in suspension in the water. If car settles, the most probable cause is that the valve or pis- ton needs repacking. If packing is all right, then the air valve in the piston does not properly seat. If the car springs up and down when stopping, there is air in the cylinder. When there is not much air, it can often be let out by opening the air cock and running a few trips, but when there is considerable air, run the car to near the bottom, placing a block underneath for it to rest upon, then place the valve for the car to descend. While in this position-, open the air cock and allow the air to escape. This may have to be repeated several times before the air is all removed. Keep the cylinder and connections protected from frost. Where exposed, the easiest way to protect the cylinder is by an 782 HANDBOOK ON ENGINEERING. air-tight box, open at the bottom, at which point keep a gas jet burning during cold weather. Where there is steam in the build- ing, run a coil near the cylinder. Keep stop buttons on hand cable properly adjusted, so that the car will stop at a few inches beyond either landing, before the piston strikes the head of the cylinder. Regulate the speed desired for the car by adjusting the back stop buttons, so that the valve can only be opened either way suffi- ciently to give this speed. Occasionally try the governor to see that it works properly. Keep the machinery clean and in good order. ELEVATOR INCLOSURES AND THEIR CARE. Elevator inclosures, while intended for protection to passen- gers, are often carelessly neglected and are often a source of danger, unless looked after and taken care of in a proper manner. It is of the utmost importance that no projection of any kind shall extend into the doorways for clothing of passengers to catch on, thus endangering their lives. The door should move freely to insure their action at the touch of the operator. See that all bolts and screws are tight, and replace at once all that fall out, otherwise, the doors and panels may swing into the path of the elevator cage and be torn off, and probably injure some one, thus placing the owner liable to damages. Elevator doors that are automatic in their closing are the best, but all operators should be held strictly responsible for accidents occurring from the carelessness of leaving doors open. All inclosures should be equipped with aprons above the doors to the ceiling and as close to the cage as possible, to prevent passengers from falling out or extending their person through to be caught by ceilings or beams in the elevator shaft. As a rule, proprietors of buildings take a pride in keeping their inclosures and cars in a neat condition, as they are considered an ornament to the building for the purpose for which they are intended, and no expense is spared in the HANDBOOK ON ENGINEERING. 783 line of art; so it is recommended that they be kept free from dampness. Dust with a feather duster and use soft rags for cleaning. Never use any gritty substance, soaps or oils. If they become damaged, have the maker repair and relacquer them. STANDARD HOISTING ROPE WITH 19 WIRES TO THE STRAND. fej 3 Diameter. Circumfer- ence in inches. Weight per foot in IDS. of rope with hemp center. Breaking strain in tons of 2000 IDS. Proper working load in tons of 2000 Ibs. Circumfer- ence of new Manilla rope of equal strength. Minimum size of drum or sheave in feet. 1 24 61 8.00 74 15 14 13 2 2 6 6.30 65 13 13 12 3 H 54 5.25 54 11 12 10 4 H 5 4.10 44 9 11 84 5 14 41 3.65 39 8 10 74 54 H 4| 3.00 33 64 94 7 6 14 4 2.50 27 54 8i 64 7 N 34 2.00 20 4 n 6 8 i 84 1.58 16 3 66 5J 9 1 2| 1.20 11.50 24 $1 44 10 1 24 0.88 8.64 U 41 4 104 2 0.66 5.13 14 31 34 104 A U 0.44 4.27 1 34 21 101 4 14 0.35 3.48 4 3 24 lOa A If 0.29 3.00 1 21 2 101 1 14 0.26 2.50 4 24 14 Operating Cable or Tiller Rope, 1 in. diam.; | in. diam.; 4 in. diam.; I in. diam. Cables, and how to care for them* Wire and hemp ropes of same strength are equally pliable. Experience has demonstrated that the wear of wire cables increases with the speed. Hoisting ropes are manufactured with hemp centers to make them more pliable. Durability is thereby increased where short bending 784 HANDBOOK ON ENGINEERING. occurs. All twisting and kinking of wire rope should be avoided. Wire rope should be run off by rolling a coil over the ground like a wheel. In no case should galvanized rope be used for hoisting purposes. The coating of zinc wears off very quickly and corrosion proceeds with great rapidity. Hoisting cables should not be spliced under any circumstances. All fastenings at the ends of rope should be made very carefully, using only the best babbitt. All clevises and clips should fit the rope perfectly. Metal fastenings, where babbitt is used, should be warmed before pouring, to prevent chilling. Examine wire ropes frequently for broken wires. Wire hoisting ropes should be con- demned when the wires (not strands) commence cracking. Keep the tension on all cables alike. Adjust with draw-bars and turn- buckles provided. Leather cup packings for valves* Leather for cups should be of the best quality, of an even thickness, free from blemish and treated with a water-proof dressing. The cups should be of sufficient stiffness to be self-sustaining when passing over per- forated valve lining When ordering cups, the pressure of water carried should be specified, as the stiff cups intended for high- pressure would not set out against the valve lining when low pres- sure is used. Water* Water for use in hydraulic elevators should be per- fectly clear and free from sediment. A strainer should be placed on the supply pipe and water changed every three months, and the system washed and flushed.- Closing down elevators* If an elevator is to be shut down for an indefinite period, run the car to the bottom and drain off the water from all parts of the machine ; otherwise, a freeze is likely to burst some part of the machinery. If the machine is of the horizontal type, grease the cylinder with a heavy grease ; if vertical, the rods should be greased. Oil cables with raw linseed oil. HANDBOOK ON ENGINEERING. 785 LUBRICATION FOR HYDRAULIC ELEVATORS. The most effectual method of lubricating the internal parts of hydraulic elevator plants where pump and tanks are used, is to carry the exhaust steam drips from the foot of the pump exhaust pipe to the discharge tank, thus saving the distilled water and cylinder oil. This system is invaluable when water holding in solution minerals is used, as these minerals greatly increase cor- rosion. Horizontal machines operated by city pressure are best lubricated with a heavy grease applied either mechanically or by means of a piece of waste on the end of a pole. The former method serves as a constant lubricator, while in the latter case, greasing is often neglected, and in consequence packing lasts but a short time. Lubrication of worm gearing* Oils with a body, such as cylinder and castor oils, are best suited to the purpose. A com- position of two parts castor to one part cylinder oil of the very best quality, makes a desirable lubricant, for the following rea- sons : cylinder oil being heavy with ample body, on becoming warm runs freely to the point of contact between the worm and the gear and lubricates readily. On the other hand, castor oil when cool, or only slightly warm, retains its body and makes an excellent lubricant. Upon becoming heated, castor oil thickens, thus rendering it objectionable. By the combination, efficient lubrication is obtained at all temperatures. Lubrication of cables* A good compound for preservation and lubrication of cables is composed of the following : Cylinder oil, graphite, tallow and vegetable tar, heated and thoroughly mixed. Apply with a piece of sheepskin with wool inside. To prevent wire rope from rusting, apply raw linseed oil. Lubrication of guides* Steel guides should be greased with good cylinder oil. Grease wood strips with No. 3 Albany grease or lard oil. Clean guides twice a month to prevent gumming. 50 786 HANDBOOK ON ENGINEERING. Lubrication of overhead sheave boxes* In summer use a heavy grease. In winter, add cylinder oil as required. BELTS AND HOW TO CARE FOR THEM. The work required of an elevator belt is most severe and we might say extraordinary character, running as it does over a jarge to a small pulley and beneath an idler, so situated as to giv3 the small pulley as much belt surface as possible. The belt runs forward and backward as the cage descends and ascends, thereby causing a certain amount of slip. It is imperative that a belt performing such service should be of the very best quality. The following are the specifications : The stock should be strictly pure oak-tanned, cut in such a manner that the center of the hide will form the center of the belt. Each piece should have all stretch thoroughly removed. The belt should be short lap, none of the pieces to exceed 4' 2" in length, including the laps. Lock lap should be made, which makes a perfect splice. Under no circumstances should a straight lap be used. The cement should be of the very best quality and pliable to such an extent that it will allow for the short turn taken by the belt in passing under the idler and around the small pulley. As a precaution against laps coming apart from accident or other cause, belts should be riveted, as the rivets will hold lap together until defect may be seen and remedied. Owing to the high speed, laced belts should never be used, as the laces are sure to be cut by running over the small pulleys. Castor oil makes a very reliable dressing for belts. It renders them pliable, thus improving the adhesive qualities. USEFUL INFORMATION. To find leaks in elevator pressure tanks in which air is con- fined, paint round the rivet heads with a solution of soap and the leak will be found wherever a bubble or suds appear. To ascer- tain the number of gallons in cylinders and round tanks, multi- HANDBOOK ON ENiSIXKKUING. 787 ply the square of the diameter in inches by the height in inches ply the square of the diameter in inches by the height in inches and the product by . 0034 = gallons. Weight of round wrought iron : Multiply the diameter by 4, square the product and divide by 6: the weight in pounds per foot. To find the weight of a casting from the weight of a pine pattern, multiply one pound of pattern by 16.7, for cast-iron, and by 19 for brass. Ordinary gray iron castings = about 4 cubic inches to the pound. Water* A gallon of water (U. S. Standard) contains 231 cu. in. and weighs 8^ Ibs. A cubic foot of water contains 7 gal- or 1728 cu. in. and weighs 62.425 Ibs. A t; Miner's inch" is a measure for the flow of water and is the amount discharged through an opening 1 inch square in a plank 2 in. in thickness, under a head of 6 in. to the upper edge of the opening ; and this is equal to 11.625 U. S. gal. per minute. The height of a column of fresh water, equal to a pressure of 1 Ib. per sq. in., is 2.304 feet. A column of water 1 ft. high exerts a pressure of .433 Ibs. per sq. in. The capacity of a cylinder in gallons is equal to the length in inches multiplied by the area in inches, divided by 231 (the cubical contents of one U. S. gal. in inches). The velocity in feet per minute, necessary to discharge a given volume of water in a given time, is found by multiplying the number of cu. ft. of water by 144 and dividing the product by the area of the pipe in inches. Decimal Equivalents of an Inch. 1*16 1-8 3-16 1-4 5-16 3-8 7-16 1-2 .0025 .125 .1875 .25 .3126 .375 ! .4375 .5 9-16 5-8 11-16 3-4 13-16 7-8 15-16 .5625 .625 .6875 .75 .8125 .875 1 -9375 788 HANDBOOK ON ENGINEERING. CHAPTER XXVII. THE DRIVING POWER OF BELTS. The average strain or tension at which belting should be run, is claimed to be 55 pounds for every inch in width of a single belt, and the estimated grip is one-half pound for every square inch of contact with pulley, when touching one-half of the circumference of the pulley. For instance a belt running around a 36-inch pul- ley would come in contact with one-half its circumference, or 56J inches, and allowing. a half-pound per inch, would have a grip 28J pounds for each inch of width of belt. nECHANICAL PROBLEMS AND RULES. Problem 1. To find the circumference of a circle or a pulley : Solution. Multiply the diameter by 3.1416 ; or, as 7 is to 22 so is the diameter to the circumference. Problem 2. To compute the diameter of a circle or pulley: Solution. Divide the circumference by 3.1416; or multiply the circumference by .3183 ; or as 22 is to 7, so is the circumfer- ence to the diameter, equally applicable to a train of pulleys, the given elements being the diameter and the circumference. Problem 3. To find the number of revolutions of driven pulley, the revolution of driver, and diameter of driver and driven being given : Solution. Multiply the revolutions of driver by its diameter, and divide the product by the diameter of driven. HANDBOOK ON ENGINEERING. 789 Problem 4. To compute the diameter of driven pulley for any desired number of revolutions, the size and velocity of driver being known : Solution. Multiply the velocity of driver by its diameter and divide the product by the number of revolutions it is desired the driven shall make. Problem 5. To ascertain diameter of driving pulley : Solution. Multiply the diameter of driven by the number of revolutions you desire it shall make, and divide the product by the number of revolutions of the driver. 0. Rule for finding length of belt wanted: Add the diame- ters of the two. pulleys together, divide the result by two, and multiply the quotient by 3 1/7. Add the product to twice the distance between the centers of the shafts, and you have the length required. FOR CALCULATING THE NUMBER OF HORSE-POWER WHICH A BELT WILL TRANSMIT, ITS VELOCITY AND THE NUMBER OF SQUARE INCHES IN CONTACT WITH THE PULLEY BEING KNOWN. Divide the number of square inches of belt in contact with the pulley by two, multiply this quotient by velocity of the belt in feet per minute and divide the product by 33,000 ; the quotient is the number of horse-power. Example. A 20-inch belt is being moved with a velocity of 2,000 feet per minute, with six feet of its length in contact with the circumference of a four-foot drum ; desired its horse- power. 20 x 72 equal 1,440, divided by two, equals 720 x 2,000 equal 1,440,000 divided by 33,000 equal 43| horse-power. Rule for finding width of belt, when speed of belt in feet per minute and horse power wanted are given : For single belts, Divide the speed of belt by 800. The horse- power wanted divided by this quotient, witt/give'the width of belt required. 790 HANDBOOK ON ENGINEERING. Example. Required the width of single belt to transmit 100 horse-power. P^ngine pulley 72" in diameter. Speed of engine, 220 revolutions per minute. 800) 4146 (speed of belt per minute). 5,18)100.00 (horse-power wanted). 19" width of belt required. For double belts* Divide the speed of belt in feet per minute by 560. Divide the horse-power wanted by this quotient for the width of belt required. Example. Required the width of double belt to transmit 500 horse-power. Engine pulley 72" in diameter. Speed of engine, 220 revolutions per minute. 560)4146 (speed of belt per minute). 7.4)500.00 (horse-power wanted). 67|" width of belt required. EXTRACTS FROM ARTICLES ON BELTS. BY II. .T. ABERNATHEY. Although there is not near as much known in general about the power of transmitting agencies as there should be, still it seems that almost any other method or means is better understood than belts. One of the chief difficulties in the way of a better knowledge of the belting problem, is the relation that belts and pulleys bear to each other. The general supposition, and one that leads to many errors, is that the larger in diameter a pulley is, the greater its holding capacity the belt will not slip so easily, is the belief. But it is merely a belief, and has nothing to sustain it, unless it be faith, and faith without work is an uncertain factor. I would HANDBOOK ON ENGINEERING. 791 like here to impress upon the minds of all interested, the following immutable principles or law : 1. The adhesion of the belt to the pulley is the same the arc or number of degrees of contact, aggregate tension or weight being the same without reference to width of belt or diameter of pulley. 2. A belt will slip just as readily on a pulley four feet in diam- eter, as it will o'n a pulley two feet in diameter, provided the conditions of the faces of the pulleys, the arc of contact, the ten- sion, and the number of feet the belt travels per minute are the same in both cases. 3. A belt of a given width and making two thousand, or any other given number of feet per minute, will transmit as much power running on pulleys two feet in diameter as it will on pulleys four feet in diameter, provided the arc of contact, tension and conditions of pulley faces all be the same in both cases. It must be remembered, in reference to the first rule, that when speaking of tensions, that aggregate tension is never meant unless so specified. A belt six inches wide, with the same tension, or as taut as a belt one inch wide, would have six times the aggre- gate tension of the one inch belt. Or it would take six times the force to slip the six inch belt as it would the one inch. I prefer to make the readers of this, practical students. I want them to learn for themselves. Information obtained in that way is far more valuable, and liable to last much longer. In order that the reader may more fully understand whether or not a large pulley will hold better than a small one, let him provide a short, stout shaft, say three or four feet long and two inches in diameter. To this shaft firmly fasten a pulley, say 12 in. in diameter, or any other size small pulley" that may be convenient. The shaft must then be raised a few feet from the floor and firmly fastened, either in vices, or by some other means, so that it will not turn. It would IK- better, of course, to have D ' E L '., OF THE J\ 792 HANDBOOK ON ENGINEERING. a suiooth-faced iron pulley, as such are most generally used. So far as the experiment is concerned, it would make no difference what kind of a pulley was used, provided all the pulleys experi- mented with be of the same kind, and have the same kind of face finish. When the shaft and pulleys are fixed in place, procure a new leather belt and throw it over the pulley. To one end of the belt attach a weight, equal, say, to forty pounds or heavier, if desired for each inch in width of belt used ; let the weight rest on the floor. To the other end of the belt attach another weight, and keep adding to it until the belt slips and raises the first weight from the floor. After the experimenter is satisfied with plaxing with the 12 in. pulley, he can take it off the shaft and put on a 24 in., a 3.6 in., or any other size he may wish ; or, what is better, he can have all on the shaft at the same time. The belt can then be thrown over the large pulley and the experiment repeated. It will then be found if pulley faces are alike, that the weight which slipped the belt on the small pulley will also slip it on the large one. The method shows the adhesion of a belt with 180 degrees contact, but as the contact varies greatly in practice, it is well enough to understand what may be accomplished with other arcs of contact. But, after all, many are probably at a loss how to account for some obser- vations previously made. They have noticed that when a belt at actual work slipped, an increase in the size (diameter) of the pulleys remedied the difficulty and prevented the slipping. A belt has been known to refuse to do the work allotted to it, and continue to slip over pulleys two feet in diameter, but from, the moment pulleys were changed to three feet in diameter there was no further trouble. These observed facts seem to be at variance with and to contradict the results of the experiments that have been made. All, however, may rest assured that it is only apparent, not real. The resistance to slippage is simply a unit of useful effect (or HANDBOOK ON ENGINEERING. 793 that which can be converted into useful effect). The magnitude of the unit is in proportion to the tension of the belt. The sum total of useful effect depends upon the number of times the unit, is multiplied. A belt 6 inches wide and having a tension equal to 40 Ibs. per inch in width, and traveling at the rate of 1 foot per minute, will raise a weight of 240 Ibs. 1 foot high per minute. If the speed of the belt be increased to 136.5 feet per minute, it will raise a weight of 33,000 Ibs. per minute, or be transmitting 1 horse-power. The unit of power transmitted by a belt is rather more than its tension, but to take it at its measured tension is at all times safe, and 40 to 45 Ibs. of a continuous working strain is as much, perhaps, as a single belt should be subjected to. A little reflection will now convince the reader that a belt transmits power in proportion to its lineal speed, without reference to the diameter of the pulleys. Having arrived at that conclusion, it is then easy to understand why it is that a belt working over 36-inch pulley will do its work easy, when it refused to do it and slipped on 24-inch pulleys. If the belt traveled 800 feet per minute on the 24-inch pulleys, on the 36-inch it would travel 1,200 feet, thus giving it one-half more transmitting power. If, in the first instance, it was able to transmit but 8 horse-power, in the second instance it will transmit 12 horse-power. All of which is due to the increase in the speed of the belt and not to the increase in the size of the pulleys ; because, as has been shown, the co-efficient of friction, or resistance to slippage, is the same on all pulleys with the same arc of belt contact. There is no occasion for elaborate and perplexing formulas and intricate rules. They serve no useful purpose, but tend only to mystify and puzzle the brain of all who are not familiar with the higher branches of mathematics, and it is the fewest number of our every-day practical mechanics who are so familiar. In all, or nearly all treatises on belting, the writer will tell you that at 600, 800 or 1,000 feet per minute, as the case may be, a belt one 794 HANDBOOK ON ENGINEERING. inch wide, will transmit one horse-power ; and yet, when we come to apply their rules in practice, no such results can be obtained one time in ten. The rules are just as liable to make the belt travel 400, 1,000 or 1,600 per minute per horse-power as the' number ,of feet they may give as indicating a horse-power. I have adopted, and all my calculations are based upon the assumption that a belt traveling 800 feet per minute, and running over pulleys, both of which are the same diameters, will easily transmit one horse-power for each inch in width of belt. A belt under such circumstances would have 180 degrees of contact on both pulleys without the interposition of idlers or tighteners. The last proposition being accepted as true and the basis cor- rect, the whole matter resolves itself into a very simple problem, so far as a belt with 180 degrees contact is concerned. It is simply this : If a belt traveling 800 feet per minute transmit one horse-power, at 1,600 feet, it will transmit two horse-power ; or if 2,400 feet, three horse-power, and so on. It is no trouble for any one to understand that, if he understands simple multiplica- tion or division. It is not, however, always the case that both pulleys are the same size, and as soon as the relative sizes of the pulleys change, the transmitting power of the belt changes ; and that is the rea- son why no general rule has ever, or ever will be made for ascer- taining the transmitting capacity of belts under all circumstances. When the pulleys differ in size, the larger of the two is lost sight of it no longer figures in the calculations the small pulley, only, must be considered. To get at it, the number of degrees of belt contact on the small pulley must be ascertained as nearly as possible and use for a guide, for getting at the transmitting power, the next established basis below. Of course, the experi- menter can make a rule for every degree of variation, but it would require a great many, and is not necessary. I use five divisions, as follows : HANDBOOK ON ENGINEERING. 795 For 180 degrees useful effect .... 100 For 157. 1 , " 92 For 135 84 For 112.i " y (J For 1)0 " .... .<; 1 The experimenters may find that my figures are under obtained results, which is exactly what they are intended to be, more especially at the 90 degree basis. I wish to make ample allow- ance. To ascertain the power a belt will transmit under the first-named conditions : Divide the speed of the belt in feet per minute by 800, multiply by its width in inches and by 100. For the second, divide by 800, multiply by width in inches and by .92. Third place, divide by 800, multiply by width in inches and by .84. Fourth place, divide by 800, multiply by width in inches and by .76. Fifth place, divide by 800, multiply by width in inches and by .64. As an example: What would be the transmitting power of a 16-inch belt traveling 2,500 feet per minute by each of the above rules ? 1st: 2,500 divided by 800 equal 3.125x 16 & 100 equal 50 h. p. 2d: 2,500 800 " 3.125 x 16 & .92 equal 46 " 3d: 2,500 800 " 3.125 x 16 & .84 equal 42 " 4th: 2,500 800 " 3.125 x 16 & .76 equal 38 " 5th: 2,500 800 " 3. 125 x 16 & .64 equal 32 " As I have said, if the degrees of contact come between the divisions named above, in order to be on the safe side, calculate from the first rule below it, or make an approximate as you like. If the above lesson is studied well and strictly used, there can be no excuse for any mechanic putting in a belt too small for the work it has to do, provided he knows how much there is to do, which he ought, somewhere near at least. 796 HANDBOOK ON ENGINEERING. HORSE-POWER TRANSMITTED BY LEATHER BELTS. DRIVING POWER OF SINGLE BELTS. Speed in Feet per Width of Belt in Inches. Minute. 2 3 4 5 6 8 10 12 14 H. P. H. P. H. P. H. P. H. P. H. P. H. P. H. P. H. P. 400 1 H 2 2& 3 4 5 6 7 600 1J 2! 3 sl 4 2 6 7* 9 101 800 2 3 4 5 6 8 10 12 14 1,000 H 3! 5 6 i 7* 10 121 15 17i 1,200 3 H 7 9 12 15 18 21 1,500 1,800 31 4* 5| 6| 2 9 I 114 lit 15 18 18| 221 22 2 L 27 .261 311 2,000 5 H 10 in 15 20 25 30 35 2,400 6 9 12 15 18 24 30 36 42 2,800 3,000 7 H 10* 111 14 15. 17i j 21 18| 221 28 30 35 87* 42 45 49 521 3,500 8| 13 17* 22 26 35 44 521 61 4,000 10 15 20 25 30 40 50 60 70 4,500 ill 17 22 28 34 45 57 69 78 5,000 IS 19 25 31 37 50 621 75 87 DRIVING POWER OF DOUBLE BELTS. Speed in Width of Belts in Inches. Feet per Minute. 6 * 8 10 12 14 16 18 20 24 H. P. H. P. H. P. | H. P H. P. H. P. fl. P. H. P H. P. 400 44 5| 74 8* 10 H4 13 H4 174 600 6* 81 11 13 15 174 194 22 26 800 4 111 14* 174 20 23 26 29 344 1,000 11 \\ 184 ! 214 25i 29 324 36 434 1,200 13 "I 22 26 30i 344 39 44 524 1,500 164 21| 274 j 32^ 38 434 49 544 654 1,800 191 26 32| j 39 454 52 59 654 784 2,000 21| 29 361 | 434 504 58 654 724 87 2,400 26 34| 44 52^ 604 694 784 88 105 2.800 30| 40L 51 61 71 81 914 102 122 3,000 32 \ 43i 54i I 65^ 76 874 98 108 131 3,500 38 50} 63 \ 76 89 101 114 127 153 4,000 43i 68| 72| ! 87 101 116 131 145 174 4,500 49 65 82 98 114 131 147 163 196 5,000 541 72| 91 i 109 | 127 145 163 182 218 HANDBOOK ON ENGINEERING. 797 Example. Required the width of a single belt, the velocity of which is to be 1,500 feet per minute ; it has to transmit 10 horse- power, the diameter of the smaller drum being four feet with five feet of its circumference in contact with the belt. 33,000 x 10 equal 330,000, divided by 1,500 equal 220, divided by 5 equal 44, divided by 6 equal 1\ inches, the required width of belt. Directions for calculating the number of horse power which a belt will transmit. Divide the number of square inches of belt in contact with the pulley by two ; multiply this quotient by the velocity of the belt in feet per minute ; again we divide the total by 33,000 and the quotient is the mumber of horse-power. Explanations. The early division by two is to obtain the number of pounds raised one foot high per minute, half a pound being allowed to each square inch of belting in contact with the pulley. Example. A six-inch single belt is being moved with a velocity of 1,200 feet per minute, with four feet of its length in contact ^with a three-foot drum. Required the horse-power. 6x48 equal 288, divided by 2 equal 144 x 1,200 equal 172,- 800, divided by 33,000 equal, say, 5J horse-power. It is safe to reckon that a double belt will do half as much work again as a single one. Hints to users of belts. 1. Horizontal, inclined and long belts give a much better effect than vertical and short belts. 2. Short belts require, to be tighter than long ones. A long belt working horizontally increases the grip by its own weight. 3. If there is too great a distance between the pulleys, the weight of the belt will produce a heavy sag, drawing so hard on the shaft as to cause great friction at the bearings ; while, at the same time, the belt will have an unsteady motion, injurious to itself and to the machinery. 4. Care should be taken to let the belts run free and easy, so HANDBOOK ON ENGINEERING^. as to prevent the tearing out of the lace holes at the lap ; it also prevents the rapid wear of the metal bearings. 5. It is asserted that the grain side of a belt put next to the pulley will drive 30 per cent more than the flesh side. 6. To obtain a greater amount of power from the belts the pul- leys may be covered with leather ; this will allow the belts to run very slack and give 25 per cent more durability. 7. Leather belts should be well protected against water and even loose steam and other moisture. -8. In putting on a belt, be sure that the joints run with the pulleys, and not against them out. 9. In punching a belt for lacing, it is desirable to use an oval punch, the larger diameter of the punch being parallel with the belt, so as to cut out as little of the effective section of the leather as possible. 10. Begin to lace in the center of the belt and take care to keep the ends exactly in line and to lace both sides with equal tight- ness. The lacing should not be crossed on the side of the belt that runs next the pulley. Thin but strong laces only should be used. 11. It is desirable to locate the shafting and machinery so that belts shall run off from each other in opposite directions, as this arrangement will relieve the bearings from the friction that would result where the belts all pull one way on the shaft. 12. If possible, the machinery should be so planned that the direction of the belt motion shall be from the top of the driving to the top of the driven pulley. 18. Never overload a belt. 14. A careful attention will make a belt last many years, which through neglect might not last one. DIRECTIONS FOR ADJUSTING BELTING. In lacing cut the ends perfectly square, else the belt will stretch unevenly. Make two rows of holes in each end ; put the HANDBOOK ON F.XC I N .-IKKI N < ', . ends together and lace with lace leather, as shewn in the cuts below. For wide belts, in addition, put a thin piece of leather or I rubber on the back to strengthen the joint, equal in length to the width of the belt, and sew or rivet it to the belt. In putting on belting, it should be stretched as tight as possible, and with wide belts, this can be done best by the use of belt clamps. HORSE POWER OF BELTING. To ascertain horse-power which belts will transmit, multiply width of belt by diameter of pulley (in inches), by revolutions of pulley (per minute), by number in table (corresponding to the pull the belt can exert per inch of width). Example. 10" single horizontal belt, 36" pulley, 200 revolu- tions, pull taken at 50 Ibs. 10" x 36" x 200 x 0.0004 = 28.8 horse-power. The pulls which belts 1" wide will transmit are as follows : Single horizontal belts (pulleys nearly same diameter) 50 Ibs. Double " 100 Single vertical " 40 Double " " " 60 Single belts (large to very small pulleys) .... 10 Double " " " .... 15 Quarter twist, single belts 25 " ** double " ... 40 HANDBOOK ON ENGINEERING . CHAPTER XXVIII. [CAPACITY OF AIR COHPRESSORS. To ascertain the capacity of an air compressor in cubic feet of free air per minute, the common practice is to multiply the area of the intake cylinder by the feet of piston travel per minute. The free air capacity of the compressor, divided by the number of atmospheres, will give the volume of compressed air per minute. To ascertain the number of atmospheres at any given pressure, add 15 Ibs. to the gauge pressure ; divide this sum by 15 and the result will be the number of atmospheres. The above method of calculation, however, is only theoretical and these results are never obtained in actual practice, even with com- pressors of the very best design working under the most favor- able conditions obtainable. Allowances should be made for losses of various kinds,' the principal losses being due to clear- ance spaces, but in machines of poor design and construction other losses occur through imperfect cooling, leakages past the piston and through the discharge valves, insufficient area and improper working of inlet valves, etc. The writer has seen com- pressors where losses through imperfections and improper working conditions ranged from 15 to 25 per cent, while under favorable conditions and with the average compressor, the loss averages from 8 to 12 per cent. So that to get sufficiently accurate results in finding capacity of the compressor, "subtract 12 per cent from above computation, which gives nearly accurate figures. The following table will be found useful for quickly ascertaining the capacity of an air compressor, also to find the cubical contents of any cylinder, receiver, etc. The first column HANDBOOK ON ENGINEERING. 801 is the diam. of cylinder in inches. The second shows the cubical contents in feet, for each foot in length. Contents of a Cylinder in Cubic Feet for Each Foot in Length. a g M Q J2 Cubic Contents. l's rt J3 5 Cubic Contents. P 5 Cubic Contents. aS 5*8 S Cubic Contents. Diam. Inches. Cubic Contents. i .0055 6 .1963 11 .6600 20 2.182 36 7.069 U .0085 64 .2130 H4 .6903 204 2.292 37 7.468 ii .0123 64 .2305 H4 .7213 21 2.405 38 7.886 II .0168 SI .2485 HI .7530 214 2.521 39 8.296 2 .0218 7 .2673 12 .7854 22 2.640 40 8.728 24 .0276 M .2868 124 .8523 224 2.761 41 9.168 *i .0341 74 .3068 13 .9218 23 2.885 42 9.620 21 .0413 71 .3275 134 .9940 234 2.885 43 10.084 3 .0401 8 .3490 14 1.069 24 3.012 44 10.560 34 .0576 84 .3713 144 1.147 25 3.142 45 11.044 34 .0668 84 .3940 15 1.227 26 3.400 46 11.540 31 .07H7 81 .4175 154 1.310 27 3.687 47 12.048 4 .0873 9 .4418 16 1.396 28 3.976 48 12.566 4* .0985 94 .4668 164 1.485 29 4.587 44 .1105 94 .4923 17 1.576 30 4.909 . . ...... 41 .1231 91 .5185 174 1.670 31 5.241 5 .1364 10 .5455 18 1.767 32 5.585 64 .1503 104 .5730 184 1.867 33 5.940 .. 54 .1650 104 .6013 19 1.969 34 6.305 5 .1803 101 .6303 194 2.074 35 6.681 To find the capacity of an air-cylinder, multiply the figures in the second column by the piston travel in feet per minute. This applies to double-acting air cylinders. In the case of single- acting air cylinders, the result should be divided by 2. THE McKIERMAN DRILL COMPANY'S AIR COHPRESSOR. The air-cylinder and water-jacket are one complete casting. The heads are made with hoods and provision made for cool air in- take. 51 802 HANDBOOK ON ENGINEERING. The atmosphere valves are bronze, of poppet form. There- fore, there is no vacuum and the cylinder fills absolutely with free air. The valves are closed by mechanical means. The discharge valves are self-acting, are made of bronze. All of them are free to inspection without removal or disturbance of other parts. The cooling apparatus, or heat-preventing device, is extremely effective. Water jacket completely surrounds the cylinder, water is forced to wash the walls and is kept in rapid motion from bot- tom to top, from end to end, absorbing heat rapidly. It enters the jacket at bottom, flows from end to end, around partitions, back and forth and up. Follows natural laws in absorbing, retaining and dispelling the heat of air. Regulation of pressure and speed is entirely automatic. The regulating device is the only one by which the air weighs the steam admitted to the cylinder. Throttle may be thrown wide open at start, then the regulator takes absolute control, governing the speed from highest to lowest rate, varying the speed for HANDBOOK ON ENGINEERING. 803 variable amounts of air which may be required and in such man- ner as to keep the pressure constant. i IN SECTION. AiK-tja-i*'jt*- EM' KIEVATK I Snu'ir.G VALVE*. The Bennett Automatic Air Compressor. Ingersoll-Sergeant Air Compressor, 804 HANDBOOK ON ENGINEERING. INGERSOLL-SERGEANT AIR COMPRESSOR, This engine, a cut of which is shown above, is fitted with In- gersoll-Sergeant Air Compressor Cylinders, and in connection with the Pohle Air Lift System, has double the supply of water, using only one- half the fuel previously required. The steam cylinders are of the Duplex Corliss condensing type and con- necting tandem, and on each side are two Ingersoll-Sergeant Air Cylinders and two Conover Water Cylinders. .When the engine SECTIONAL VIEW OP AIR CYLINDER WITH VERTICAL LIFT VALVES, USED CLAS5 "E" AND "F" COMPRESSORS. is in operation, the air cylinders raise the water by the Pohle Air Lift System, from the wells to a tank at the surface, and from there it is taken by the water cylinders and forced to the stand- pipe. The cost of this combination compares favorably with the old plan of using separate compressors and water pumps, each with their own steam cylinders, and the saving in attendance, friction and foundation commends its use. The engines run at a fixed moderate speed and the regulation of the air and water is effected by passing the water from suction to discharge when the tank is too low and by mechanically unloading the air cylinders HANDBOOK ON ENGINEERING. 805 with a pressure regulator when the tank is too full. The regula- tion is cbne mechanically, with floats at the top and bottom of the 'eceiving tank. This combination can also be furnished with Straight Line Compressors ; the advantage of the Duplex is that should it be necessary, the one side of the engine can be discon- nected and the other side made to do the work. As will be seen, the inlet valves which are on the lower side of the cylinder are offset, thus preventing their being sucked into the cylinder and wrecking the compressor. They are made out ol a solid piece of steel and are extremely durable, because they are placed vertically, work in a bath of oil and do not slide on their seats. Both the inlet and discharge valves, being in the cylinder, allow the heads to be thoroughly water- jacketed, and this is an important feature when it is remembered that the heat of compression is greatest at the end of the stroke. The cylinder is, therefore, completely water- jacketed. The valves are arranged so that the air can be taken from outside of the engine room, which increases the efficiency of the machine 8 to 15 per cent, and are easily accessible. The two inlet valves are located in the piston, and, with the tube, are carried back and forth with the piston. The valve on that face of the piston which is toward the direction of move- ment is closed, while the one on the other face is open. This is exactly as it should be in order to force out the compressed air from one end of the cylinder while taking in the free air at the other ; when the piston has reached the end of its travel there is, of course, a complete stop while the engine is passing the center, and an immediate start in the other direction. The valve which was open immediately closes. There is no reason for its remain- ing open any longer, and it closes at exactly the right time, its own weight being all that is necessary to move it. The valve on the other side is left behind by the piston and the free air is admitted to that end of the cylinder for compression on the 806 HANDBOOK ON ENGINEERING. return stroke. No springs are used, and there is none of the throttling of the incoming air, and none of the clattering or hammering so noticeable with poppet-valves. As there is nothing to make the valve move faster than the piston, it stays behind until the piston stops, leaving the port wide open for the admission DETAILS OF PISTON INLET AIR CYLINDER. A. Circulating Water Inlet. D. Oil Hole for Automatic Oil Cup. G. Piston Inlet Valv B. Circulating Water Outlet. 'E. Air Inlet (through piston inlet? pipe). H. Discharge Valva. C. -Water Jacket Drain Pipe. F. Air Discharge (showi&g flange)? J.-Water Jacket. Sectional Cut of Ingersoll & Sargeant Single Compressor, of air. It is well known that while the fly-wheel and, of course the crank, rotate at a uniform speed, the movement of the pistoi is not uniform, but gradually increases in speed from the star" till the crank has reached half -stroke, when it gradually slows u{ till the crank is on the center, and at this moment of full stoj the valve gently slides to its seat. HANDBOOK ON ENGINEERING. The above is what is called the Pohle Air Lift System. 808 HANDBOOK ON ENGINEERING. The illustrations on page 807 shows the method of pumping water by air. A compressor in connection with the air-lift sys- tem of pumping water by direct air pressure. The pump con- sists of a water pipe and an air pipe, the latter discharging the air into the former at its bottom, through a specially designed foot-piece. The natural levity of the air compared with the water, causes it to rise and, in rising, to carry the water with it in the form of successive pistons, following one another. This system of pumping has found a large range of application and is of peculiar service in connection with deep well pumping. For this purpose, the absence of mechanical parts many feet below the surface, offers a commanding advantage. Method No. 1 and No. 2 is almost alike, consisting of placing the air and water pipes alongside of one another in the well, connecting them at the bottom with an end piece. Method No. 3 consists of placing a water discharge pipe into the well ; the air passing down into the well through the annular space between the well casing and the water pipe. Method No. 4 consists in using the well casing as the water discharge pipe, and simply putting an air pipe down into the well, with a specially designed foot-piece attached at the bottom through which the air escapes. HANDBOOK ON ENGINEERING. 809 CHAPTER XXVIII. CONTINUED. THE METRIC SYSTEM. It frequently happens that an engineer, in reading books and papers devoted to steam engineering, is confronted -with terms taken from the metric system, which he does not understand. I give below a few of the metric system terms most commonly used, with their values in feet and inches, also, gallons, quarts, pounds, tons, etc. A French meter is 30.37079 inches long, or a little less than 39f inches. It is generally taken, for convenience in fig- uring, at 39.37 inches. 1 decimeter is -f^ of a meter, or, 3.937 inches nearly. 1 centimeter is yj^ " " " .3937 " " 1 millimeter is T ^o- " " " .03937 " " ALSO. 1 decameter equals 10 meters, or, 32.80 feet nearly. 1 hectometer " 100 " "328 " " 1 kilometer " 1000 " " 3280 " " .. APPLICATION. 1. An engine shaft is 5 meters long, what is its length in feet and inches? Ans. 16 ft. 4J ins. nearly. Operation : 39 _L 3 J ><_? = 16.4 ft. nearly. \a 2. An engine cylinder is 10.3 decimeters in diameter, how much is this in inches? Ans. 40J ins. nearly. Operation: 3.937 X 10.3 = 40.55 ins. nearly. 810 HANDBOOK ON ENGINEERING. 3. A piston-rod is 8.7 centimeters in diameter, how much is this in inches ? Ans. 3| ins. nearly. Operation : .3937 X 8.7 = 3.42 ins. nearly. 4. A chimney is 5.1 decameters tall, how much is this in feet and inches? Ans. 167 ft. 3 ins. nearly. Operation : 32.80 X 5.1 = 167.28 ft. 5. How many miles are there in 30.2 kilometers? Ans. 18^ miles nearly. Operation : There are 5280 ft. in a mile. Then, 828 >< 8Q - 2 ^ 18.7 miles. 5280 6. A valve has 2 millimeters lead, how much is this in frac- tional parts of an inch? Ans. ^ in. nearly. Operation: .03937 X 2 = .07874. And, .07874 X 6"4 = / nearly. 7. How many square feet in a circle whose diameter is one meter? Ans. 8* nearly. n 39.37 X 39.37 X .7854 Operation : - = 8.45. 144 8. The cylinder clearance is 1.1 cubic decimeter, how many cubic inches in the clearance? Ans. 67 nearly. Operation: 3.937 X 3.937 X 3.937 X 1.1=67.12+ ALSO. 1 gramme equals 15.433 grains, or 1 ounce nearly. 1 kilogramme equals 2.2047 pounds avoirdupois. I tonne equals 1.1024 tons of 2000 Ibs. ALSO. 1 litre equals 1.0566 quarts. HANDBOOK ON ENGINEERING. 811 CONSEQUENTLY. 1 U. S. gallon equais 3.79 litres nearly. 1 U. S. pint equals .4732 litres nearly. 1. A main shaft weighs 800 kilogrammes, how much is this in avoirdupois pounds? Ans. 1763J Ibs. nearly. Operation: 2.2047 X 800 = 1763.76. 2. An engine weighs 12 tonnes, how much is this in U. S. tons of 2000 Ibs. each? Ans.. 13J tons nearly. Operation: 1.1024 X 12 = 13.2288. 3. A tank contains 9000 litres of water, how much is this in U. S. gallons? Ans. 2377.35 galls. 1.0566 X 9000 Operation: r Because 4 quarts equal 1 gallon. THERMOMETERS. In the U. S* the Fahrenheit scale is the one in most common use, although in our laboratories and for scientific purposes it is displaced by the Reaumer and Centigrade scales. Fahrenheit's scale marks the boiling point by 212 degrees, and the freezing point by 32 degrees above zero. The Reaumer scale marks the boiling point by 80 degrees, and the freezing point by zero. The Centigrade, or Celsius scale, marks the boiling point by 100 degrees, and the freezing point by zero. So that, reckoning from the freezing point of Fahrenheit, 180 degrees Fah. equal 80 degrees Reaumer, and 100 degrees Centigrade. Bearing in mind that Fahrenheit's zero is 32 degrees below the freezing point, one scale may readily be converted into another. To convert degs. of Reaumer into those of Fah. Rule* Multiply by 9, divide by 4, and add 32. I/ MA. <> Example! ''' i<"ti< ( /< ( .IH| b AM*, Operation* MX* 720, *' / A. 'i, IM (HO. it i ' 4 To 00WJft titt dtff / 04 (/V-ntiKrwl*' into n>"<' .i i Rule, Multiply \iy ti, .i. " nil 0MM oi MHntlMftlon f/i IKI Armr>^ MM M I llii( "' i< M)(!^ of DM '"CM ftliftll !< on ilin np|" ' t "* f " i" HAND ,.,,1,1, Mia lltn . ,n, f< , ||HJ ih,t y . ol '" ' '',. I* '' 'II il . ipp,,. .. i. , i, i. ofchi ' " i" it In motion MI,- woi kluj " i I', Mill, | , .Ml (I ll'pl> lit. Mil, I |1 ' |\l |" ,|i-ini. i, . ill Hilt |'0|M I li. p.-. ,1 .-I il., i, r , li,.ul.| M.., , . . . I MOO IV. -t p. i nmmi. -, iin.l Ilih MJUMM! jl\ bill '-'^l IVKUlUllI ii r rii, pi ,, HI ! i, .mi to iii,- itiuuhi i ni ,.! \\\ kyi '"n, -I !.,> ,1, limi, l\ i ....... I I ....... l\ ...... bill UOlUtltl il.ilii \ .'i bhl .op up Ilio Mlm-lv MM.) ulitMt lli muni- i -'i -|" , , , .1 ill. ........ .-oihl MI i\ be ntliti ! '"' '!' 'i"^ '" li d "''' ' '' '" ii..ni.i A(|| b< I- H Hum lo .1 i > 00 ili'im. III ili |>\N ' i. v , .MM.- nx .... , . lv Ml1 ''' i'" u ' ' ' '" """' ' 'M M l ..... '"i i. -p.. \\IIMI Ih, . I..-4M limit IOA do^i. --i -I,. , ..... ...... , ,, ,,,.( (linn ',< ' - I- y III,- ili'inirli-i .pi \ phi IMiin ill li 1 . . 1 Mlitnl,' I'- '1 l| n |M i 1 1 .n ll, M ' W.OVI lO.Nfl ii, yo u 1 i ' VIMHI U 7.11(1 1 n i ,i M MM 1 MM.A4 1 >< ' UI.N7 1 ' 4. IK) d.wii II mi 1 , M IM (III " | , MM 1 4.74 ivun ' ' 11 i, 4H.AII i. in 7,4 IW Mil n i VII HU i 1 (1 , I, 1 1 , UII.MII Kl , ' I.MMI 1 ' I M i , , i i i 7.MV , 10 UH.IIU M.lil ' ' 1 III, III III mi 11 H 117, Ml ' f| 1 to i in 1, UII.7U MU.tfll HUM , M.vin ' M.MW li.fi ' Mil, MM 814 HANDBOOK ON ENGINEERING. TO TEST THE PURITY OF ROPE. A simple test for the purity of manila or sisal rope is as fol- lows : Take some of the loose fiber and roll it into balls and burn them completely to ashes, and, if the rope is pure manila, the ash will be a dull grayish black. If the rope be made from sisal the ash will be a whitish gray, and if the rope is made from a com- bination of manila and sisal the ash will be of a mixed color. WIRE ROPE DATA. HOISTING ROPE. PATENT FLATTENED STRAND. HERCD- LES. foo s. II br flo 13.5 22.5 32 40.5 56 r,7 84 124 168 211 '2(50 CRUCI- BLE. per fo cents. ' 181 24 30 :'>'.', 50 59J 86 121 144 182 8i 21 26 34 43 52 74 109 | 104 140 i 120 176 1 1 152 9 1.5 ^ 38 47 56 81 I, s* ^ I-S 19 WIRE ROUND STRAND. HERCU- LES. is* ** *^ ft-* CKUCI- BLE. rP 12.5 20 29 36 50 60 77 113 157 191 238 8.8 13.6 19.4 26 34 42 50 72 96 124 156 *>. = HANDBOOK ON ENGINEERING. 815 ALTERNATING CURRENT MACHINERY. CHAPTER XXIX. THE PRINCIPLES OF ALTERNATING CURRENTS. The actions of alternating currents are not so easily under- stood as those of continuous currents and to most men not familiar with the subject they appear to be a mystery that can only be fathomed by those who are well versed in the higher branches of mathematics. As a matter of fact, when we once get on the right track, alternating current actions present no more difficulty to the man of fair mental ability, who is willing to work to learn, than the more simple continuous current actions. What makes alternating currents difficult to .understand is, that in con- sequence of the ever-changing strength of Mie current, inductive actions are developed that react upon the uirrent itself so that it becomes impossible to determine the magnitude of the current, the e.m.f. or the energy flowing in the circ'iit by the simple rules used for continuous currents. As the strength of an alternating current is constantly changing the magnitude of the inductive actions is constantly changing, and this fact further increases the difficulty of the subject. In studying the principles of continuous currents we learn that when a conductor is moved across a magnetic field an e.m.f. is developed in it ; and thus we understand the operation of a gen- erator, as we know that when the armature revolves, it carries the conductors upon its surface through the magnetic flux that issued from the poles of the field. We further learn that iiuis- 816 HANDBOOK ON ENGINEERING. much as the magnitude of the e.m.f. is increased by increasing the strength of the magnetic flux, or the number of conductors on the armature or the velocity of rotation, that one or all these factors must be increased to increase the voltage. Thus we come to consider that to induce a high e.m.f. we must have a strong magnetic field. Now one of the first things that the student of alternating currents finds out is that in an alternating current circuit, the strongest e.m.f. induced by the action of the current itself, comes at the very time when the magnetic field is the weakest, and this appears to him to completely upset all the principles of continuous currents; but in reality it does not. To be able to get over this stumbling block successfully it is necessarv to realize that the magnitude of the e.m.f. induced in a conductor that is moved through a magnetic field is not depend- ent upon the strength of- the magnetic field, but upon the rate, or rapidity with which the conductor cuts the magnetic flux. Now it so happens that in a continuous current generator, the rapidity with which the conductors cut the magnetic flux increases with increase in the strength of the magnetic field, or the velocity of rotation, and thus it comes about that in this case, the increase in the induced e.m.f. appears to be due to increase in armature velocity or field strength when in reality it is due to increase in the rate at which the conductors cut through the magnetic flux. The magnetic flux developed by an alternating current alternates precisely as the current does, and, as will be clearly explained presently, this magnetic flux cuts through any conductors in its path, and the rate at which it cuts them is the greatest at the in- stant when the direction of the flux is changing, and this is the instant when the flux is nothing, so that the e.m.f. induced by the magnetic flux developed by an alternating current is the greatest at the very instant when the magnetic field has a zero strength. The foregoing facts can be made more clear by refer- ence to diagrams. HANDBOOK ON ENGINEERING. 817 Fig* I is a simple diagram that can be taken to represent a genera- tor, either of continuous or alternating currents. The dark circles A A, B B and C C represent the sides of three loops of wire which may be regarded as wound upon the surface of an armature. JV jjz Fig. 1, The vertical lines represent a magnetic flux passing between the Held poles Pand JV. If the armature upon which the three loops are mounted is rotated, e.m.fs., will be induced in each one of the loops, but the magnitude of these e.m.fs. will not be the same. If we take the instant when the loops are in the position shown, the e.m.f . in A A will be zero, while that in C C will be the highest and that in B B will be seven-tenths of tb at in G C. Now all these coils rotate at the same velocity being mounted upon the same armature, and all move through a magnetic field of the same strength, yet, in A A no e.m.f . is developed while in B B the e.m.f. is only seven-tenths of that developed in C C. The question is, why this difference? The answer is, that while loops A A move just as fast as C C they do not cut the magnetic flux 52 818 HANDBOOK ON ENGINEERING. because they are moving in a direction parallel with the lines of force, the vertical lines, hence, the rate at which the magnetic flux is cut by them is zero, therefore the e.m.f. developed is zero. In B B the e.m.f. is seven-tenths of that developed in G (7, because the sides of this loop are moving in a direction that is not directly across the magnetic flux, but forms an angle of 45 degrees with it, so that their actual velocity in a direction parallel with A A is seven-tenths of the velocity of C C in this same direction. From the foregoing it will be seen that when we get down to a close examination of Fig. 1 we find that the magnitude of the e.m.f. developed in the several loops is directly proportional to the rate at which the sides of the loop cut through the magnetic flux. Let us now consider Fig. 2. In this diagram, circle A repre- sents a wire, seen end on, through which an alternating current is flowing. An alternating current is one that flows first in one direction, and then in the opposite direction, and continues changing the direction in which it flows at regular intervals of time. Now it is self-evident that if a current flows through a wire in alternate directions, it must stop flowing in one direction before it can flow in the opposite direction, that is at the instant when the direction of flow is changing, there can be no current. Such being the case, when the current begins to flow in either direction, it must increase in strength gradually up to a certain point, and then begin to decrease, so as to reduce to nothing at the instant when the direction of flow changes. As is explained in the section on continuous currents, when a current of elec- tricity flows through a wire, a magnetic flux is developed around the wire and this can be represented by lines of force drawn in the form of circles, as in Fig. 2. If there is no current flowing through the wire there is no magnetic flux, therefore, if wo consider the instant when a current begins to flow, we can imagine HANDBOOK ON ENGINEERING. 819 that at this instant the magnetic flux begins to expand outward from the wire, and since the circular lines are drawn to represent this flux we can assume that these expand outward, like the rip- ples on the surface of a pond when a pebble is thrown into the water. So long as the current flowing through the wire increases in strength, just so long will the magnetic circles of force expand, but when the current reaches its greatest strength the circular lines of force will become stationary, and will remain so if the current remains at its maximum strength; but if the current begins to reduce in strength as soon as it reaches its maximum, then the circular lines of force will begin to contract immediately after they stop expanding, just as a swing will begin to move backward the instant it stops swinging forward. If the circles B and C in Fig. 2 represent two wires parallel with J., it is evident that the magnetic circles of force when they move outward from A will cut through B and C in one direction, and when they contract back upon A they will cut through these two wires in the opposite direction. When these circular lines of force cut through the wires B G they will induce e.m.fs. in the latter, and if these e.m.fs. are positive when the lines of force ex- pand, they will be negative when the lines contract. When the current reaches its maximum strength and the circular lines of force become stationary for an instant, they will not cut the wires B and C and at this instant there will be no e.m.f. induced in these wires. Now the circular lines of force become stationary at the very instant when the current flowing through the wire reaches its greatest strength and is on the point of reducing, so that at this instant the e.m.f. induced in the wires B and C is zero. The highest e.m.f. induced in B and C occurs at the instant when the current flowing through A is changing its direction, or, in other words, at the instant when there is no current. Just before the current reduces to zero, the circular lines of force are contracting upon wire A, and the instant after the cur- 820 HANDBOOK ON ENGINEERING. rent reduces to zero and changes its direction, these lines of force will be expanding so that in the first case the lines of force will sweep over wires B and G in a direction toward A, and in the second case they will sweep over these wires in a direction away from A. From this fact it might be inferred that the e.m.f. induced in the two cases would be in opposite direc- tions, but this is not so, owing to the fact that the lines of force change in direction when the current changes, so that if while contracting they are directed clockwise, as soon as they begin to expand they will be directed counter clockwise. As a result of this change in the direction of the lines of force when they change from contracting to expanding, the e.m.fs. induced in B and C are in the same direction before the lines stop contracting and after they begin to expand. The circular lines of force stop con- tracting and begin to expand at the same instant, so that the inductive action developed by the contracting lines is followed up without a break by the expanding lines. In alternating currents such as are actually used in practice, the rate at which the strength of the current changes is the greatest when it is just beginning to grow, and when it is reduced almost to zero, and on this account the highest e.m.f. induced in wires B and C occurs at the instant when the direction of the current is changing, that is, when the current is zero. Alternating currents can be de- veloped in which the rate of change in the current is not the greatest just when they begin to grow and when they are reduced nearly to zero and with such currents the highest e.m.f. induced in wires B and C would not come at the instant when the current is zero, but would come at the instants when the change in the current is the most rapid. In every kind of alternating current, however, the instant when the e.m.f. induced in B and C is zero is the instant when the current reaches the maximum value, and begins to decrease, for this is the only instant when the circular lines of force are HANDBOOK ON ENGINEERING. 821 immovable ; it being the instant when they are about to change from expanding to contracting, while still flowing in the same direction. When the current becomes zero, the lines of force change from contracting to expanding but at this instant they also change their direction so that the new expanding circular lines of force take up the work if inducing an e.m.f. in the wires B and (7 at the very point where the contracting lines leave off. The circular lines of force developed by the current flowing in A cut through this wire as well as through B and (7, hence, they induce an e.m.f. in A; that is an alternating current induces an e.m.f. in its own circuit as well as in adjoining circuits. The action upon adjoining wires is called mutual induction, and that upon its own wire is called self-induction. These e.m.fs. act in a direction opposite to that of the current that induces them. The relations between alternating currents and e.m.fs. can be shown by means of diagrams, the simplest of which are con- FigJS structed in the manner shown in Fig. 3. In diagrams of this type the line T represents time, thus if a point is assumed to move from in the direction of T at a uniform velocity of say one foot per second, then a length of one inch will represent an interval of time of one-twelfth of a second. Distances measured in the vertical direction, along $ represent the magnitude of 822 HANDBOOK ON ENGINEERING. the current or e.m.f. Positive currents and e.m.f. are indicated above the time line T and negative currents and e.m.fs. below this line. Thus the wave line A A A can represent an alternating current or e.m.f. or an alternating magnetic flux. This curve it will be seen is above T from Oto6, and below T from b to d, being again above from d to T. The two sections of the curve from to d constitute one cycle, or two alternations. The portions between the lines a, a 5, b c, c d are called quarter cycles or quarter periods. The time from to d is called one period, and if this is equal to one-tenth of the distance that represents one second, then there are ten periods to one second. This fact is indicated by saying that the periodicity of the current is ten, or that its frequency is ten. The frequency of alternating currents in common use ranges between 20 and 130. The curve A A in Fig. 3 represents a current or e.m.f . that increases or decreases at a certain rate, but for a current varying at some other rate it would be necessary to use a curve of differ- ent shape to correctly represent it. Thus if the current does not increase so fast when rising from the zero value, but increases faster when nearing its maximum value we will require a modifica- tion of the curve such as is indicated by .B, in which the slope is more gradual on the start, and near the middle becomes more steep. If on the other hand the current increases more rapidly on the start, and less rapidly as it approaches the maximum value, we will have to use a curve something like C which is steeper at the ends and flatter at the middle. The actual form of curve required to correctly represent an alternating current depends upon the rate at which the current varies, and this rate depends upon the construction of the machine in which it is generated. For the purpose of simplifying calcula- tions it is necessary to assume that the rate of variation of a cur- rent is such that it can be represented in a diagram such as Fig- 3 by some form of curve that can be drawn in accordance with HANDBOOK ON ENGINEERING. 823 some fixed rule. The curve A A is of circular form, but there are few alternating current generators that develop currents that such a curve can properly represent. If a current alternates in equal intervals of time, and the rate of variation is the same when it is flowing negatively as when it is flowing positively, then it can be represented by a curve that is of symmetrical construction, such as A A in which the intervals of time &, b d are equal and the curves above the line T are of the same shape as those below it. Such a current is called a symmetrical periodic current, and it is the only kind with which we have to do in practice. It can be readily understood, however, that the current can be far from regular, that is, the time during which it flows positively can be more or less than the time during which it flows negat' Ty, and the rate of variation in the two instances can be different. The curves in Figs. 4 and 5 illustrate currents of this kind. In Fig. 4 the positive impulses of the cur- rent are longer than the negative, as is shown by the greater length of lines a, b c as compared with a b. It will also be seen that the rate of variation is different as is indicated by the difference in the form of the portions A A and B B of the curve. In Fig. 5 the irregularity is still greater, as all the time intervals Oa, a 6, b c, c cZ, are different, as are also the portions A B C D E of the curve. 824 HANDBOOK ON ENGINEERING. The alternating currents developed by alternating current generators have such a rate of variation that they can be repre- sented in diagrams by means of what is known as a sine curve. s This curve is not a perfectly true- representation of practical alternating currents, but it comes so near to it that calculations based upon the assumption that the sine curve represents the actual variation, do not depart from the truth by more than two or three per cent, and in some cases less than that. As the sine curve is commonly used to represent alternating currents we will show HANDBOOK ON ENGINEERING. 825 how it is constructed by the aid of Fig. 6. In this diagram dia- metrical lines a b c are drawn on the circle J3, dividing it into any desired number of equal parts. A distance T on the hor- izontal line is divided into an equral number of equal parts and perpendicular lines a a are drawn at these divisions. From the points where the liness a b c cut the circle lines are drawn parallel with T as shown at e f g and the points where these cut the corresponding perpendicular lines a a form points of the sine curve A A. The distance T can be made anything desired without affecting the character of the curve, the only difference being that if it is short the curve will be more pointed than if it is long. One reason why it is assumed that alternating currents vary in accordance with a sine curve is that if the variation is at this rate the e.m.f. induced by the magnetic flux developed by the current will also vary in accordance with the sine curve, so that the current, the magnetization and the induced e.m.f. can be rep- resented by sine curves, and thus the process of calculating the effect of the induced e.m.f. upon the strength of the current can be greatly simplified. By looking at Fig. 1 it can be seen at once that if the loop A A is revolved at a uniform velocity, and the magnetic field between the poles P and N is of uniform strength at every point, the e.m.f. induced in A A will vary in strict accordance with the variations of the sine curve A A of Fig. 6, for in the position A A the e.m.f. will be zero, and in position C C it will be the maximum, while in any in- termediate position such as B B it will be equal to the actual velocity of the sides of the loop measured in the direction parallel with AA , and this velocity is equal to the distance of the side of the loop from the horizontal line A A. Now the height of the sine curve A A in Fig. 6 at any point is also equal to the distance from the end of the corresponding line in circle B from the horizontal HANDBOOK ON ENGINEERING. line, that is, the distrance e e' from the horizontal line to the curve is the same as the distance e e on the circle. The complete sine curve from to T is traced by following the rotation of the radius of the circle through one complete revolu- tion. On that account this distance T is taken to represent one revolution, and is divided into 360 degrees, the same as the circle. Half the distance, or d, is equal to 180 degrees, and one-quarter the distance is 90. The vertical lines a a in Fig. 6 are 30 degrees apart. The way in which sine curves are used to represent alternat- ing currents and e.m.fs. is shown in Fig. 7. In this diagram, let the curve A represent an alternating current flowing through a wire. As is fully explained in the foregoing, this current will develop an alternating magnetic flux, and this flux will increase and decrease as the current increases and decreases, that is, it will keep in time with the current, or in step with it, as it is com- monly expressed. Such being the case, the curve A can be used to represent the magnetic flux as well as the current, providing we assume a proper scale for both. Looking at the half circle to the left of the figure, it will be seen that curve A is described by HANDBOOK ON ENGINEERING. 827 a radius rotating around the middle circle. Remembering what was said in connection with Fig. 2 as to the time relation between the magnetic flux and the e.m.f . induced thereby, we will realize that at the instant when the flux is zero, the induced e.m.f. must be at the maximum value, and it will act in opposition to the e.m.f. that drives the current through the wire, hence, in the diagram, it will have to be drawn below line T. Let the maxi- mum value of this induced e.m.f. be equal to c, then for all other values it will be correctly represented by the sine curve .B, which is traced by the rotation of the radius of the inner circle. At the instant of time 0, the magnetic flux is zero, hence the radius of the middle circle from which curve A is traced must be in the direction of line T. At this same instant the induced e.m.f. is at the maximum value hence the radius that traces curve B must be in the vertical position parallel with O c. From this we see that in relation to time the curves A and B that repre- sent the magnetic flux and the induced e.m.f. are one-quarter of a cycle apart, that is the induced e.m.f. is 90 degrees behind the magnetization, and also 90 degrees behind the current that flows through the wire. No kind of electric current, whether continuous or alternating, can flow through a circuit unless there is an e.m.f. to drive it, and this e.m.f. must be sufficient to impel the current against all resistances of any kind that it may encounter. The e.m.f. that impels a current through an alternating current circuit is called the impressed e.m.f. In Fig. 7 it is evident that the impressed e.m.f. must be sufficient not only to overcome the actual resistance that opposes the flow of the current represented by curve A, but also sufficient to overcome the opposing action of the induced e.m.f. represented by curve B. Now the e.m.f. required to overcome the resistance that opposed the flow of the current can be represented by the curve A, in precisely the same 828 HANDBOOK ON ENGINEERING. way as this curve represents the magnetization ; hence, the curve C which represents the impressed e.m.f . must at every point be equal, in height, from the line T, to the sum of the heights of the curves A and .B, when these two curves are on opposite sides of T, or to their difference when they are on the same side. At the instant it is clear that as the current is zero, the impressed e.m.f. C must be of the value c' to balance the induced e.m.f. B for if it were not, there would be a current flowing negatively under the influence of e.m.f. B. At any instant between C and d, the impressed e.m.f. C must be equal to the sum A and 5, that is, the distance from C to the time line T must be equal to the distance between the curves .4 B measured on the same vertical line. At the instant d the induced e.m.f. is zero, hence the impressed e.m.f. is equal to the distance of curve A above line T. For any interval of time between d and e, the impressed and the in- duced e.m.fs. are acting together, so that the first named, that is, curve (7, need only be equal to the difference between A and B. By studying the diagram Fig. 7 it will be seen that the curve O, which represents the impressed e.m.f., is described by the rotation of the radius of the outer circle at Z>, and in order that this e.m.f. may have the value of c' at the instant 0, it is nec- essary for the describing radius at this instant to be in the posi- tion 6. From this it will be seen that the impressed e.m.f. is not in time with the current but in advance of it by a time interval that is equal to the angle formed by the radius b with the line T. If two alternating currents, e.m.f. or magnetic fluxes are in time with each other they are said to be in phase, but if they are not in time they are out of phase. In Fig. 7 the current, the impressed e.m.f. and the induced e.m.f. are out of phase with each other. The impressed e.m.f. leads the current, and the latter leads the induced e.m.f. This relation is also expressed by say- HANDBOOK OX ENGINEERING. 829 ing that the current lags behind the im- pressed e.ra.f. and the induced e.m.f. lags behind the current. The current and the impressed e.m.f. can never be out of phase by an angle as great as 90 degrees, but the phase difference can be any angle less than this. The induced e.m.f. is always 90 degrees out of phase with the current. The induced e.m.f. in the circuit in which the current flows is called the self-induction. The relations between the impressed e.m.f., the current and the self-induc- tion both in magnitude and phase are clearly shown in Fig. 8, which is simply an enlarged view of the left side of Fig. 7. The radius A of the outer circle is the impressed e.m.f. The radius B of the middle circle is the cur- rent, and the radius C of the inner circle is the self-induction. The magnitude of any one of these three quantities at any instant of time is equal to the distance from the end of the line to the horizontal line. The radius B which represents the current is on the horizontal line, hence the current at the instant represented by the diagram is zero. The self-induction G has a value at this instant equal to the length of the ime, that is, it is at the maximum value, and as it is below the horizontal line it is negative. The impressed e.m.f. A, has the value of a a, and being above the horizontal line, it is positive. The phase relation and also the magnitude of these quantities is also shown in Fig. 9, which is constructed from Fig. 8 by remov- ing the self-induction to the position of line a a. From Fig. 9 it Fig.8 830 HANDBOOK ON ENGINEERING. CURRENT. Figs RESISTANCE. Fi/JO can be seen that if we know two of the quantities we can always determine the other one by sim- ply constructing a right angle triangle. The self-induction acts tc oppose the flow of current, hence it is equivalent to th( addition to a certain amount oi resistance to the circuit, but.a;- can be seen from the diagrams- it cannot .be added directly, after the fashion in which numbers are added. To add it properly it must be placed at right angles to the resistance. If the self-induction is divided by the strength of the current, we get a quantity that can be compared with the resistance, and this quantity is called the reactance and is measured in ohms precisely as the resistance is. The flow of current in a continuous current circuit is opposed by the resistance only, but in an alternating current circuit it is opposed by the resistance and the reactance and the combined effect of these two is called the impedance of the circuit. The relation between resistance, reactance and impedance is the same as that between impressed e.m.f., current and self- induction, and is shown in Fig. 10. The reactance multiplied by the current gives the self -induction. The impedance multiplied by the current gives the impressed e.m.f. HANDBOOK ON ENGINEERING. 831 The resistance multiplied by the current gives the e.m.f. in phase with the current, which is also called the active e.m.f. A sine curve diagram, such as is shown in Fig. 7, serves very well to enable the learner to under- stand the relation between the current and e.m.fs. but when this relation has been fully mastered, what is known as a clock dial diagram becomes more convenient, specially if we desire to represent several currents and their e.rn.fs. Fig. 8 is virtually one-half of a clock dial diagram. A regular clock dial diagram to represent a single alternating current is shown in Figs. 11. 12, 13. The radius A represents the current, and is Fi/Jg Fig. 2 3 supposed to rotate at a velocity equal to the frequency of the current. The strength of the current for any instant of time is obtained by measuring the distance from the horizontal line S S to the end of the radius at that particular instant as indicated by line a a in Fig. 12. If A is above the line S S the current is positive, and if it is below S S the current is negative. At the instant when A is in the vertical position, as in Fig. 13, the current is at its maximum value, and when A is horizontal as in Fig. 11 the current is zero. If we desire to find the relation between the current and impressed e.m.f. or the self-induction, we draw radial lines of the proper length to represent these e.m.fs. and in the proper angular position with reference to the current and then assume them to be locked together when they 832 HANDBOOK ON ENGINEERING. are rotating so that the distances from the ends of each one to the line S S at any instant gives the values of the quantities at this instant. Diagrams of this type are specially valuable for the represen- tation of polyphase currents. Currents of this type are commonly spoken of as a two-phase current, or a three-phase current, or a polyphase current. Now there are no multiplephase currents. What is improperly called a two-phase current is a combination or two simple alternating currents so timed that they are out of phase with each other by one quarter of a period, or revolu- tion. This constitutes a system of two-phase currents. Three simple alternating currents so timed as to be out of phase with each other by one-third of a period, constitute a system of three phase currents. In the first case we have two currents, and in the second we have three currents. These currents in either system are connected so as to act together in the same system of circuits. If the phase relations are not such as given above, they cannot constitute true, two or three-phase systems. FijfJj. Fif.16 The phase relations for the two-phase system are shown in Fig. 14 and for the three-phase system in Fig. 17. The two currents A B in Fig. 14 are at right angles with each other, and the three currents in Fig. 17 are 120 degrees apart, or one-third of a period, or cycle. To obtain the values of the two currents in HANDBOOK OX ENGINEERING. 833 Fig. 14 at any particular instant, they are rotated together as is indicated in Figs. 15 and 16. The values will be equal to the lines a a and b b. In the same way the values of the three currents in a three-phase system are obtained for any instant as is illustrated in Figs. 18 and 19. For the transmission of the currents of a two-phase system, three or four wires can be used. In the three-phase system, if the three currents are equal, three wires are sufficient, but if these currents are not equal a fourth wire is required to carry the surplus a current as it may be called. When the three currents of a three- phase system are equal it is called a balance system, but if they are not equal the system is unbalanced. In Figs. 17 to 19 the three currents are drawn of equal length and it will be found that in every position in which the lines can be placed the sum of the two currents on one side of line S S will be just equal to the cur- rent on the other side, so that if the current is flowing away from the generator through one wire, it will divide up and return through the other two, and provide for each wire just the amount of current required. Thus in Fig. 17 the current flowing in A is zero, and the positive current in B is equal to the negative current in C. In Fig. 18 the two positive currents a a and b b in lines A B, are just equal to the one negative current in C,* and this is also the case in Fig. 19. 834 HANDBOOK ON ENGINEERING. Unbalanced three-phase currents are seldom used, but when they are, a fourth wire is run from the point where the three circuits A B C are joined, to a corresponding point at the genera- tor end of the circuit, and then any excess or deficiency of current that is not provided for by the three regular circuit wires is taken through the fourth wire. The point where the three wires join, at the center of the circle, is called the neutral point, and the wire connecting then is the neutral wire. Two and three-phase systems are used almost exclusively for the transmission of power to great distances, and for this work only three wires are used. Polyphase systems can be formed of any number of currents, but they would be of no practical value, owing to increased com- plications, and on that account are not used. In addition to the one, two and three-phase systems, explained in the foregoing, the only system that has been used to any extent is the ' ' monocyclic, ' ' which was introduced by the General Electric Company. This system may be described as a sort of cross between the single phase and the polyphase systems. It consists of two currents, 90 degrees out of phase, just as in a two phase system, but in- stead of the two currents being equal, one of them is four times the strength of the other. The armature coils of the generators that furnish these currents are so connected with each other that the two currents, as fed into the line wires, constitute an unbalanced three-phase system. This arrangement of the generator coils will be found more fully explained in the section on ' ' Alter- nating Current Generator," and the object of the " monocyclic " system will be found explained in the section on " Transmission Systems." Inductive Action in Alternating Current Circuits. In Fig. 20 let G represent an alternating current generator that impels an alternating current through the circuit A A. This current as already explained will develop a magnetic flux around the wire such as is indicated at C D. This flux will develop a self-indue- HANDBOOK ON ENGINEERING. 835 tive e.m.f . in the circuit and thus retard the current, so that the actual amount of current flowing will be less than it would be in a continuous current circuit acted upon by an impressed e.m.f. of the same magnitude. As will be noticed, the direction of the flux at C and D is such that they oppose each other, that is the lines C and D flow through the space between the two sides of the loop A A in opposite directions, and on that account the lines G can only extend to the center of the space, while lines D will occupy the upper half. This being the case it is evident that if the cir- cuit wires are brought closer together as indicated by the lines B J3, the magnitude of the magnetic flux that will surround each wire will be correspondingly reduced as is indicated by the lines a a. The self -inductive e.m.f. developed in the circuit will be propor- tional to the magnitude of the flux that surrounds the wire, hence the nearer the two sides are brought to each other the less the ' self-induction, and if the two wires could be placed side by side the inductive effect would be practically nothing. From this it A wmr will be seen that if an alternating current is transmitted to a dis- tance the nearer the line wires to each other the smaller the self- induction developed in them. In an alternating current circuit the self-induction developed in every portion is not the same, and the total effect is equal to the sum of the several effects. For example in Fig. 21 let A A A represent a circuit that is fed by a generator at G. The self- 836 HANDBOOK ON ENGINEERING, induction on the line A will be small, specially if the wires are placed near each other. If a number of incandes- cent lamps are connected at C the self-induction of these will be practically nothing. If at B we place some kind of device that is provided with wire in the form of coils, then at this point a large self-induction will be developed, for then the magnetic flux from each turn of wire in the coil will be able to cut Jl through many other turns, and thus greatly increase the inductive action. To determine the total amount of inductive action in this circuit, so as to ascertain the amount of current that will flow through it, we will have to find the total impedance of the circuit, and this we do by finding the impedance of each part and then adding these impedances, but all this operation is carried out not in the way in which we add figures, but in the manner shown in Fig. 10. The diagram Fig. 22 illustrates the operation. By actual measurement we can find the resistance of the line A in ohms and we can mark it down on the diagram as o a. By calculation, we find the reactance of line A and mark it down as a a', thus we obtain the impedance of o a' of the line. Next, we find the resistance of the lamps C which we mark down at a' 6, and from b draw b b' equal to the reactance of the lamps, thus obtaining the impedance a' &', of the lamps. We now draw b' c. equal to the resistance of B and c c' equal to the reactance of HANDBOOK ON ENGINEERING. 837 B and thereby obtain the impedance b' c' of B. We now join o -"b B with c' and obtain the line C which is the total impedance of the circuit, and line B, which is the total reactance, while line A is the total resistance. A glance at the diagram will show that the total impedance C is less than the sum o a! a' b' and b' c' if these were added in the ordinary way, so that the total impedance of a circuit can be less than the direct 'sum of the impedances of its several parts. Fig.23 The angle of lag between the current and impressed e.m.f. in an alternating circuit plays a very important part in determin- ing the actual amount of energy that is transmitted. In a continuous current circuit the energy is always equal to the 838 HANDBOOK ON ENGINEERING. product of the volts by the amperes but in an alternating circuit it may be equal to this product and it may not be as much as one per cent of this product. What proportion of the product of the volts by the amperes will represent the actual energy trans- mitted will .depend upon the angle of lag between the current and the impressed e.m.f., the greater this angle the less the en- ergy. The way in which the angle of lag affects the amount of energy flowing in the circuit can be made clear by means of Figs. 23 to 25. In these figures, curve A represents the impressed e.m.f. and curve B is the current, while the shaded curves repre- sent the energy. In Fig. 23 the impressed e.m.f. and the current are shown in phase with each other, and as a result the curves C which represent the energy are drawn above line T, thus show- ing that all the energy is positive, and it is equal to the direct product of the volts by the amperes. In Fig. 24 the current and impressed e.m.f. are drawn out of phase 90 degrees. Starting from 0, the e.m.f. is positive while the current is negative, curve B being below line T. This means that the current and e.m.f. act against each other hence the energy represented is negative. After the first quarter of a period, the current becomes positive HANDBOOK ON ENGINEERING. 839 and then the energy is positive. Thus for the first half period we heave two energy curves, D negative, and C positive, both of these are equal and, therefore, just offset each other, so that the net energy flowing in the circuit during this time is zero. As will be seen, during the following half periods, the same operation is re- peated, so that the actual result is that energy is putinto the circuit during one quarter period, and during the next quarter it is taken Fig.25 out, and the actual energy flowing through the circuit is nothing. The action is the same as when a swing is set in motion, during the first half of each swing energy is accumulated by the descent of the weight, but during the next half it is all absorbed in lifting the same weight, and unless we supply from outside enough en- ergy to overcome the friction the swing will soon come to a standstill. In an alternating current circuit, if the impressed e.m.f. and the current were out of phase 90 degrees no energy would be introduced into the circuit, hence, no current at all could flow, but if the angle is a trifle less than 90, say 89, a suf- ficient amount of energy can be put into the circuit to overcome the resistance loss, and then a strong current will sway back and forth that is not capable of doing any work. A current of this 840 HANDBOOK ON ENGINEERING. kind is called a wattless current as it carries no energy. The rea- son why it carries no energy is that the self-induction very nearly balances the impressed e.m.f. so that the effective e.m.f. is very small, in fact it is just enough to force the current against the resistance of the circuit. In Fig* 25 the current and imprissed e.m.f. are shown out of phase by an angle of 45 degrees, and as will be seen the shaded curves G which represent positive energy, are much larger than those below line T, which represent negative energy. The difference between these two is the actual energy flowing in the circuit. It can be clearly seen that the smaller the angle of lag between the current and impressed e.m.f. the larger the shaded curves above line T and the smaller those below the line ; hence, the greater the energy flowing in the circuit. By the use of condensers, the effect of self-induction can be counteracted, and in" that way the lag of the current can be re- duced and thus the energy in the circuit can be increased. A condenser is a device that is so constructed as to be able to re- ceive a very large electriostatic charge. To explain the nature of electrostatic charges so that they may be understood we may say that bodies arranged so as to hold a charge will carry this charge upon their surface. Thus we can picture to the mind's eye the charge as flowing over the surface until it completely covers it. When a condenser is used in an alternating current circuit, it is charged and discharged each time the current alternates, and the time relation of the charging and discharging currents is such as to be directly opposite to the current that would flow under the effect of the self-induction, or, to put it in another way, the e.m.f of the condenser current is 180 degrees -out of phase w r ith the self-induction. Now, by properly proportioning the condenser it can be made to just balance the self-induction, and then we get the relations illustrated in Fig. 26 in which curve B represents the self-induction, curve C the condenser e.m.f. which HANDBOOK ON ENGINEERING. 841 is directly opposite and of equal magnitude. Curve A represents the impressed e.m.f . as well as the current, both being in phase with each other. The general principle of construction of a condenser is illus- trated in Fig. 27, in which the plates A B represent the condenser, and G the generator that provides the current, the connecting wires being S S. A device of this kind, if placed in a continuous B Fig.27 current circuit, will simply prevent the ilow of current ; but when connected in an alternating current circuit, if of the proper pro- portions, will act as if it did not break the circuit. This is because 842 HANDBOOK ON ENGINEERING. the large surfaces on the plates A B act as reservoirs and accumu- late all the current that flows into them during the short time each impulse lasts. When the current reverses, the charge in the con- denser runs out together with the generator current. We can thus consider that if a positive impulse of the current fills plate A and empties plate B, a negative impulse will reverse the operation. Mutual induction* In connection with Fig. 2 it was shown that when an alternating current flows through a wire, the alter- Fig.28 nating magnetic flux that surrounds the wire, if it cuts through any other wires running parallel with it will induce e.m.fs. in them. The direction and phase of these e.m.fs. will be the same as that of the self-induction in the wire carrying the current. If we have two wires running parallel with each other and alternat- ing currents flow through, then the action of wire No. 1 upon wire No. 2 will be the same as that of No. 2 upon No. 1. This action is called mutual induction, and it is made use of in the HANDBOOK ON ENGINEERING. 843 construction of an apparatus used for transforming alternating currents which is commonly called a transformer. By the aid of Fig. 28 the principles of mutual induction can be made quite clear. In this diagram suppose that the circle A rep- resents one wire through which an alternating current is flowing, and circle B represents another wire carrying an alternating cur- rent. If these two wires are some distance apart, it is clear that a considerable portion of the magnetic flux of A will not cut through B, and in like manner that a considerable portion of the flux of B will not cut though A, as is indicated by Fig.29 the dotted circles at a a a. In any case, however, some of the flux of one wire will cut through the other. From this it follows that the effect of the current in each wire upon the other wire will be less than that upon itself, but the closer the wires are to each other the nearer equal the effects will be. When it is desired to avoid the effects of mutual induction as far as possible the wires must be separated to the greatest distance, and when we desire to make the mutual inductive effect the greatest, we must bring the wires as close 844 HANDBOOK ON ENGINEERING. together as possible. The inductive effect of wires upon each other in some cases produces very objectionable results, for example when telephone wires are run side by side for any distance the inductive action of one wire upon the other serves to render the conversation indistinct. Why this is so it can be appreciated at once from an inspection of Fig. 29, which shows a pole carrying four wires. Telephone currents are not alter- nating but they pulsate and thus produce the same effect as if they were alternating. In Fig. 29 the circles drawn around each one of the wires as will be seen cut through all the other wires. If the two upper wires belong to one circuit and the two lower ones to another, then if one set of wires are crossed at every three or four poles so that the wire running on the right side for a certain distance will then be changed over to the left side, the inductive actions will be counteracted to a very great extent and this method is followed in stringing telephone wires. It is also used in regular alternating current circuits when interference between different circuits is to be avoided. With regards to the two wires belonging to the same circuit, it is advantageous to string them as close together as possible, for in this case, the effect of mutual induction is to neutralize the effect of self-induction. Referring to Fig. 20 it can be seen at once that if the magnetic flux at (7 develops a self- induction in lower A toward the right, it will develop an induc- tion in upper A also towards the right, but with reference to the wire itself this induction will be just opposite to that in the lower side so that the two will counteract each other. Thus to reduce the reactance of the line, the two sides of the circuit must be placed as near together as is practicable. Transformers* A transformer is an apparatus in which the principle of mutual induction is utilized for the purpose of gener- ating a second current by the inductive action of a primary current. Referring to Fig. 28 it can be seen that if wire B is HANDBOOK ON ENGINEERING. 845 closed upon itself the e.m.f. induced in it by the magnetic flux issuing from A will cause a current to flow and then this current, which is brought into existence by the inductive action of the current in A, will in turn develop a magnetic flux that will react upon wire A in precisely the same manner as if the current were not induced in J5, but it came from an independent source. In a transformer, the wire is wound in the form of compact coils, and one of these coils, which is called the primary, is connected with an alternating current circuit. The current flowing through this coil induces a current in the other coil which is called the second- ary. The general construction of a transformer can be under- ,,c^Vf I ' ^r^ V . \ M- '/C Fig.30 stood from Fig. 30. An iron core C is provided upon which are wound two coils marked A and B. The coil A which is the prim- ary, is connected with an alternating current circuit, and thus the iron core C is strongly magnetized. The presence of the iron core C serves to greatly increase the magnetic flux but does not in any way interfere with its alternating properties, so that it increases and decreases and changes its direction in precisely the same manner as the flux that surrounds a single wire. The flux de- 846 HANDBOOK ON ENGINEERING. veloped by A, swells out as indicated by the lines a a a and cuts through the .side of the secondary coil B. If the circuit through this coil is close an alternating current will be generated in it, and this current will develop a magnetic flux that will swell out and cut the side of the primary coil A. The e.m.f. induced in A by the flux of B will be in opposition to the self-induction de- veloped by its own flux, hence, if the circuit through B is open, the current flowing through A will be small because the self- induction will counteract the impressed e m.f. so as to leave but a small effective e.m.f. As soon as the circuit through B is closed, the inductive action of this coil upon A will offset to a certain extent the self-induction and thus assist the impressed e.m.f .in forcing more current through A. The more the current through B is increased, the stronger its action upon A and as a result the more the self-induction of A will be neutralized and the stronger the primary current will become. This action which occurs in a perfectly natural manner serves to make the trans- former a self-regulating apparatus, so that if a strong current is required in the secondary circuit, a strong current passes through the primary so as to furnish the energy necessary to develop the strong secondary current. If no current is drawn from the secondary, the primary current is reduced to nearly nothing. To explain fully the action in a transformer would require a rather lengthy discussion of the principles involved, but the action, in a general way, can be made clear without going deeply into the theory. In explaining the phase relation of the current the self-induction and the impressed e.m.fs. in connection with Fig. 8 it was shown that the angle between the self-induction and the current is 90 degrees, and that the angle between the current and the impressed e.m.f, can be anything from zero up to nearly 90 degrees. If the current is passed through transformers or other iDductivc devices, the current will lag considerably Suppose U lags 10 degrees then the total angle between the un- HANDBOOK ON ENGINEERING. 847 pressed e.m.f. and the self-induction will be 100 degrees. Now in a transformer the e.m.f. induced in the secondary coil is in phase with the self-induction in the primary coil, hence, with the above angles it would be 100 degrees behind the impressed e.m.f. in the primary coil. Now if the secondary current lags as much as the primary, it will be 110 degrees behind the primary im- pressed e.m.f. and the magnetic flux developed by this current will induce an e.m.f. in the primary coil 90 degrees behind itself or 200 degrees behind the primary impressed e.m.f. This e.m.f. induced in the primary coil by the action of the sec- ondary current not only counteracts the self-induction in the primary coil, but in addition changes the phase relation between the primary current and its impressed e.m.f., making the angle smaller. This change in the phase relation between the current and impressed e.m.f. results, in turn, in a change of the phase relation of the secondary current, and this change in the phase of the secondary makes a corresponding change in the phase of the primary. If we were to trace up the action back and forth from primary to secondary currents we would finally arrive at the true phase relation of the currents and e.m.fs. inboth circuits but this is a complicated and unnecessary process of reasoning. We can easily see that the current induced in the secondary coil will have a certain phase relation with respect to the primary current, and we can further see that the combined magnetizing effect of the two currents, the primary and secondary, is the same as that of a single current having a phase intermediate between the phases of these two. Following this course of reasoning we have only one inductive action to deal with and this is in such a phase relation that as it increases it decreases the self- inductive e.m.f. in the primary and thus permits more current to pass through this coil, and this increase in current in the primary causes a corresponding increase in the secondary current. When the secondary current is very small the self-induction in the 848 HANDBOOK ON ENGINEERING. primary is very great and as a result the lag of the primary current is increased and its strength is decreased. As the sec- ondary current ^increases, the self-induction in the primary decreases, and the lag of the primary current reduces while the current strength increases. The strength of the secondary current is varied by varying the resistance in the secondary circuit ; if this resistance is reduced the current is increased. To make a transformer as perfect as possible it is necessary to place the primary and secondary coils in such a position that the mutual induction between them may be the greatest pos- sible, that is so that all the magnetic flux developed by the primary coil may cut through the secondary and all the flux of the secondary may cut through the primary. If the coils are arranged as in Fig. 30 it can be seen at once that all the flux of A will not cut through B and in like manner all the flux of B will not cut' thro ugh A. It is not possible to arrange the coils so that all the flux of one coil will pass through all the turns of wire on the other coil, but this condition can be very nearly realized. If one-half of coil A is wound on each side of the core G and then the B coil is wound in two parts directly over the A coils the chance for the flux of one coil to not pass through the other coil will be greatly reduced. The flux that does not pass through the opposite coil is called a leakage flux, thus in Fig. 30 the lines a that pass through coil A but not through B constitute the leakage from coil A and in like manner the flux of coil B that does not pass through A is the leakage of B. The leakage flux represents just so much mag- netism thrown away, hence the effort of the designer is to arrange the coils so as to reduce it to the smallest amount possible. If the two coils were wound together, that is, if we took the wires and wound them side by side forming a single coil, the leakage would be practically nothing, but this construction cannot be used as with it .there would be great danger of the insulation between HANDBOOK ON ENGINEERING. 849 the coils giving away, and this would destroy the transformer. This form of winding can be approximated to by winding each coil in many sections and placing these in sandwich fashion upon the iron core as is shown in Fig. 31 in which the sections forming one coil are shaded, and those of the other coil are not. This is the construction that is followed generally in large transformers. In the majority of designs, however, the primary and secondary coils are wound one over the other. Transformers are used for the purpose of changing the voltage of the current. The name transformer is misleading, as it creates the impression that the device transforms the current, when as shown in the foregoing it does nothing of the kind, it simply generates a secondary current which is in no way connected with the primary. When electric energy is transmitted to a consider- able distance by means of alternating currents, the voltage used is much higher than is required for the operation of lamps or motors, hence, at the receiving end of the line this cur- rent is passed through transformers and secondary currents are generated in these that are of the voltage desired. The voltage 54 850 HANDBOOK ON ENGINEERING. of the secondary current is controlled by the number of turns of wire placed upon the secondary coils. Roughly speaking, if the primary coil has ten times as many turns as the secondary the voltage of the secondary current will be one-tenth of that of the primary. If the primary voltage is 2000 and the secondary is 100 the primary coil will have twenty times as many turns of wire as the secondary. Transformers that deliver a secondary current of lower volt- age than the primary are called lowering transformers, while those that deliver a secondary of higher voltage are called raising transformers. For distributing current to consumers, lowering transformers are used. But in long distance transmission plants, where the current in the transmission line has ane.m.f. of any- where from 10,000 to 30,000 volts, raising transformers are used at the power house, and these take the current from the generators, which may be of 1,000 or 2,000 volts and deliver to the line a secondary current of 10,000 or more volts. Transformers cannot be used with continuous currents for the simple reason that as these currents do not fluctuate the magnetic flux developed by them remains stationary and, therefore, there is no inductive action. A medium size transformer is shown in Fig. 32. The com- plete transformer is seen at the right side of the illustration. In the center is shown the lower part of the iron core, with the wire removed from one leg, this wire being shown on the left. The iron plates at the bottom of the figure form the upper part of the iron core. The iron core of a transformer is built up out of sheet iron. It could not be made a solid mass, for, if it were, secondary cur- rents would be induced in it, and thus the energy in the primary current would be used up in developing useless currents with iron core. The sheet iron laminations are insulated from each other, so as to prevent the development of currents in the core. HANDBOOK ON ENGINEERING. 851 As can be seen from the illustration the wire wound on each leg of the core belongs in part to the primary and in part to the secondary circuit. If the primary wire is proportioned so that it is proper for^a 1,000 volt current when the parts on the two legs are connected in series, then it can be made proper for 500 volts Fig. 32. by connecting the two parts in parallel. If the secondary coils will develop a voltage of 100 when both parts are connected in series, they will develop 50 volts if both parts are connected in parallel, but in this case the current will be doubled. The transformer as shown to the right in Fig. 32, is complete, but for the purpose of protecting the wire an outer casing is pro 852 HANDBOOK ON ENGINEERING. yided. For high voltage transformers, this casing is made water tight and is filled with oil so as to improve the insulation of the apparatus. Very large transformers are provided with means for cooling them. In some, air is forced through the coils and iron core. In others, coils of pipe are placed within the casing and water circulates through these. Alternating 1 current generators. In alternating current gen- erators the field is magnetized permanently by means of a con- tinuous current. This current is obtained, generally, from a small continuous current generator that is called an exciter. Some alter- nators as a rule of small capacity are provided with a commu- tator to rectify a portion of the current the machine generates so as to provide a continuous current to magnetize the field. An alternating current cannot be used to magnetize the field because the field magnetism must remain unchanged. Alternators are also arranged so that the field is magnetized by the combined action of the two continuous currents above mentioned, that is, by the current from a separate exciter and the current derived from the armature. Alternators excited in this manner are called compound machines and are the counter- part of the continuous current generator. Alternators that are excited by the current from a separate exciter alone are the coun- terpart of the plain shunt wound continuous current generator. There are several other ways in which the field can be magnet- ized to make an alternator of the compound type, and the most important of these will be found fully explained under the head- ing of "Compensated Generators." The object of compound winding in alternators is the same as in continuous current generators, that is, to keep the voltage con- stant and not allow it to drop as the current strength increases. Large alternators used in central stations are always of the com- pound type. The way in which alternating current generators act can be HANDBOOK ON ENGINEERING. 853 understood from the diagrams Figs. 33 to 37. In Fig. 33 P and N represent the poles of the field magnet of a two-pole machine. The armtaure is provided with a single coil of wire marked a. When this coil is in the position shown, no e.m.f. will be induced in it, but as it begins to rotate from this position an e.m.f. will begin to be induced, and this will increase in mag- nitude until one quarter of a revolution has been made, when it will be at the maximum value. During the next quarter revolu- tion the e.m.f. will gradually reduce, becoming zero when the half turn is completed. During the next half turn the e.m.f. will again rise to a maximum and fall to zero, but it will be oppositely H Fig. 33. Fig. 34, Fig 35. directed, so that if during the first half turn the e.m.f. is posi- tive, during the next half it will be negative, and this operation will be repeated for each revolution of the armature. Thus it will be seen that if the armature revolves ten times in a second, the frequency of the current generated will be ten, and in any case the frequency will be equal to the number of revolutions the armature makes in a second. This is true for a two-pole machine, if the generator has four poles the frequency of the current will be equal to twice the number of revolutions per second and for any greater number of poles the frequency will be equal to the number of revolutions of the armature per second multiplied by half the number of poles. Alternating current generators are always made with a large number of poles so that the frequency required may be obtained without running the armature at too great a speed. 854 HANDBOOK ON ENGINEERING. The diagram Fig. 33 illustrates a simple alternating current generator, or what is called a single-phase generator. A single- phase machine is one that has one coil on the armature for each pair of poles in the fields and generates one alternating current. Fig. 34 illustrates diagrammatically a two-phase generator. A two-phase generator is an alternating current generator that gene- rates two alternating currents that are out of phase with each other by 1 one-quarter of a period, that is, by 90 degrees. Such a generator is provided with two coils or sets of coils for each pair of poles and these are placed at right angles to each other in a two-pole machine and so that the sides of one set come opposite the centers of the other set, in multi polar machines. In Fig.. 34 it will be seen that coil a is in the same position as the coil in Fig. 33, hence no e.m.f. is being induced in it. Coil &, however, is in the position in which the induced e.m.f. is of the maximum value, thus it will be seen that as the armature revolves the e.m.f. in one coil will rise toward the maximum while that in the other coil will be decreasing toward zero. Fig. 35 illustrates a three-phase generator. A three-phase generator is a machine that generates three alternating currents that are out of phase with each other by an angle of 120 de- grees, or one-third of a period. Such a machine has three coils or sets of coils for each pair of field poles. In Fig. 35 it will be seen that coil a is in the position in which no e.m.f. is generated, and if we assume that the armature is re- volving in the direction of the hands of a clock, then the e.m.f. induced in coil b is very near the maximum value, but is still increasing, and will become the maximum when the coil reaches the horizontal position. In coil c the e.m.f. has passed the maximum and is reducing toward zero, which value it will reach when the coil reaches the vertical position, or the position in which a now is. If an alternator is of the multipolar type the coils will be dis- HANDBOOK OJS T ENGINEERING. 855 posed in the manner shown in Fig. 36. If it is a single-phase machine it will have one set of coils only, those marked A. If it is a two-phase generator it will have two sets of coils, the addi- Fig. 36. tional set being placed in the position snown in broken lines and marked B. In this construction the machine appears to have as many A coils as there are poles and the same number of B coils, which is in contradiction to the statement made above, that a single- phase machine has one coil for each pair of poles. The truth, however, is that each coil in Fig. 36 is virtually one-half of a coil. Fig. 37 shows the way in which the coils are arranged in a three-phase generator of the multipolar type, the three sets of coils being marked ABC. In monocyclic generators the coils 856 HANDBOOK ON ENGINEERING. are arranged as in Fig. 36, but they differ from the two-phase winding in that the B coils are one-quarter the size of the A coils. In actual generators the armature coils are seldom given the form shown in these diagrams, but whatever the form may be the prin- ciple of winding is the same. In an alternator the armature coils forming one set are connected in series with each other, and the entering end of the first coil and the leaving end of the last coil are connected with collector rings mounted upon the armature shaft, and the current is taken from these by means of brushes similar to the commutator brushes of Fig. 38. continuous current machines. In monocyclic generators one end of the B set of coils is connected with the middle point of the A set, and the three remaining ends are connected with col- lector rings. This is the arrangement with generators of what is known as the revolving armature type, which is the HANDBOOK ON ENGINEERING. 857 one illustrated in Fig. 33 to 37. There is another type in which the outer part which is stationary is the armature and the revolving part is the field. Machines of this kind are called re- volving field alternators. The principle of operation is the same in both types, but the revolving field type has the advantage that as the armature is stationary, no collector rings and brushes are required to take off the current. All that is necessary is to pro- vide binding posts to which- the ends of the armature coils are con- nected, and from these the external circuit wires are run off. A revolving field alternator is shown in Fig. 38. In machines of this type, the field magnetizing coils are mounted on the periphery of the revolving part, hence the current that traverses them must pass through collector rings mounted upon the shaft. These rings are clearly shown in the illustration, the collector brushes being held, insulated from each other, by the stand located in front of the rings. Thus it will be seen that this type of machine requires collector rings, just the same as the revolving armature type, but the difference between the two is that in the latter the whole armature current passes through the collector rings, and on that account they must be made very large, while in the revolving field machines they can be made small, as only the field current passes through them, and this is only from one to two per cent of the armature current. There is still another type of alternating current generator in which the wire on the field as well as the armature is held station- ary. Such machines are called inductor generators. The revolv- ing portion of such generators is simply a mass of iron formed like a very large pinion with correspondingly large teeth. When this part revolves the ends of the teeth sweep over the armature coils, running as close to them as they can without touching. The magnetic flux developed by the field coil issues from the ends of the teeth and cuts through the armature coils thus inducing e.m.fs. in them. It will be seen that the difference between this type of 858 HANDBOOK ON ENGINEERING. generators and the revolving armature type is that instead of re- volving the armature coils through the stationary field flux, the latter is revolved and the armature coils are held stationary. The \ Fig. 39. difference between the inductor generator and the revolving field type is that in the latter the field is magnetized by a number of coils and these are rotated together with the field poles, while in the inductor machine there is a single field magnetizing coil and this remains stationary, the part that revolves being what might be called the poles. An inductor alternator is shown in Fig. 39. The small machine mounted on the right side of the base is the exciter that HANDBOOK ON ENGINEERING. 859 furnishes the field magnetizing current. The outer casing of the machine holds a ring built up of sheet iron laminations, which constitutes the armature and supports the armature coils. The large teeth, or polar projections which are well shown in the illustration are carried by the revolving part, and when rotating cause the magnetic flux to sweep over the armature coils. The field coil is placed back of these polar projections. Alternating current generators are run singly, or they may be connected in parallel, but they cannot be run in series. If an attempt is made to run them in series, one of the machines will act as a motor and will be driven by the current generated by the other. When alternators are connected in parallel it is necessary that they run at exactly the same velocity, if they are identical in construction. If the generators are not of the same construe-* tion then their velocities will depend upon the number of poles each one has. Machines of different size and even design, can be connected in parallel, providing the frequency of the currents they generate are the same. To make the frequency the same it is necessary that the velocity of each machine multiplied by the number of poles it has be equal to the same number. Thus if one machine has twice as many poles as the other, it must run at one-half the velocity. The velocity of alternators connected in parallel must be equal, absolutely, and not practically so ; that is, if two machines are alike, and one runs at 1000 revolutions per minute, the other must run at 1000 and it cannot run at 999 or 1001. Since such extreme accuracy in speed is necessary it might be inferred that it is practically impossible to run alter- nators in parallel unless their shafts are coupled together, or they are connected through spur gearing with the same driving shaft. As a matter of fact, however, alternators can be run in parallel even if one is driven by a steam engine and the other by a water wheel, and they may be side by side or several miles apart. The reason why this is the case is that when the machines are in oper- 860 HANDBOOK ON ENGINEERING. ation, the current holds them in step. If several generators are feeding into the same circuit, and one machine tends to lag behind the others, its current reduces and thus the speed in- creases as less power is required to drive it. If the tendency to lag increases, the machine begins to act as a motor, and is driven by the current from the other machines. While it is possible to run alternators in parallel under almost any conditions providing they are speeded so as to generate cur- rents of the same frequency and nearly the same voltage, entirely satisfactory results cannot be obtained unless the angular motion is uniform, that is, unless the velocity of rotation is the same at all points of the revolution. If a steam engine has a light fly- wheel the velocity of the shaft will not be the same at all points of the revolution, but will be the slowest when the crank is passing the- center, and the fastest when at half stroke. This fact is clearly shown by the irregular motion of the paddle-wheels of river boats driven by a single engine. If two alternators are driven by two engines whose rotative motion is not uniform and the engines are so timed that one is on the center when the other is at half -stroke, then the action of the two alternators will be irregular, for when one machine is rotating at the highest velocity the other will be ro- tating at the lowest. This uneven action of the alternators may be compared with the work of two horses hitched to a wagon and pulling unevenly. If both horses pull together all the time the whiffle-tree will remain straight and the wagon will be drawn along smoothly ; but as soon as the horses begin to pull unevenly the whiffle-tree will be jerked back and forth and the motion of the wagon will be irregular. In this case the horses soon tire out because they work against each other part of the time. The action between two alternators that do not rotate with uniform velocities is practically the same as that of two horses that do not work together ; the machine that runs ahead not only sends a HANDBOOK ON ENGINEERING. 861 current into the main circuit, but in addition backs up a cur- rent through the other generator, thus wasting energy by causing a strong current to flow back and forth between the two machines. To overcome this difficulty engines made to drive alternators are provided with extra heavy flv wheels, so that the momentum may be sufficient to keep the speed up to the normal point while the crank is passing the center. With small alternators that have only a few poles and are driven by high-speed engines, the effect of irregular motion is not so great as in large machines having many poles, hence the large slow-speed engines used to drive alternators having a large num- ber of poles, must be provided with excessively large flywheels to run in a satisfactory manner. The reason why alternators with a large number of poles require greater regularity in motion to give satisfactory results, can be easily understood. Suppose we have a pair of two-pole machines driven by engines whose flywheels are 25 ft. in circumference. Suppose, further, that the irregularity in motion is such that each engine when running at the faster velocity, gets three inches ahead of the other. Then the advance in position will be one per cent, and consequently the currents of the two generators will run ahead and behind each other one per cent at each quarter of a revolution. Now, if these same two engines drive two twenty- pole alternators, then the irregularity in motion will be multiplied ten times, because one-tenth of a revolution will give one cycle of current, and the current of each machine will run ahead and fall behind the other ten per cent, instead of one per cent. Starting alternators connected in parallel : In starting con- tinuous current generators that are connected in parallel all we have to do is to set one machine in operation and then after the second one is running up to full speed, we adjust its field regu- lator until the voltage is the same as that of the first machine, or one or two volts higher. . We then throw the switch and connect 862 HANDBOOK ON ENGINEERING. it with the switchboard. In starting alternators that are con- nected in parallel we have to do more than this, we must not only adjust the second machine so that its voltage is the same as that of the first, but we must bring it up to the proper speed and get its current in phase with that of the first generator before we connect it with the switchboard. To accomplish all this with certainty, devices are used that are called synchronizers, or phase indicators. These devices consist generally of a couple of small transformers one of which is connected with the circuit of each generator. The secondary wires of these transformers are connected with each other and one or two incandescent lamps are connected in this circuit. When the second machine is started up, as its speed is much lower than that of the generator already in operation the frequency of the secondary current of its transformer will be much lower than that of the first machine, and as a result the lamps in the circuit of the two transformers will flicker rapidly. As the second machine builds up its speed the flickering of the lamps will become slower. When the two generators are running at nearly the same speed the flickering will be replaced by rather long periods of darkness and light. During the periods when the lamps are lighted the current generated by one of the transformers is in such a direction as to act in series with the current of the other and thus draw the current through the lamp. When the lamps are dark it is because the currents of the two transformers are in opposition to each other and thus no current passes through the lamps. The second generator is connected with the switch- board during one of the periods of darkness or brightness, de- pending upon the way in which the transformers are connected. The second generator will not be running at exactly the proper speed when it is connected with the switchboard, but as soon as it is connected the currents of the two machines acting upon each other will at once draw the second machine into step with the first one, and they will continue to run in step even if the power HANDBOOK ON ENGINEERING. 863 driving one of the machines should fail. In the latter case, the first machine would not only furnish current for the main cir- cuit, but would in addition drive the second machine as a motor. The way in which synchronizing lamps are connected in single or polyphase circuits is clearly illustrated in the diagram Fig. 40. To Bus Bars. Synchronizing l vP : M/WVf ansfbrmers on Tempor wry TPS.TSwiCch. a OP 76 Generator. Fig. 40. The three upper lines are connected with the main bus-bars on the switchboard and the lower lines run to the generator that is to be synchronized. The left side of the diagram shows the connec- tions for synchronizing a single-phase generator. In such a case, the middle wire running to the bus-bars and to the generator would not be used. The synchronizing transformers would have their primary coils connected with the side wires in the manner shown by lines //and g g. When the generator current is in synchro- nism with that in the bus-bars, the primary currents in the two synchronizing transformers will flow in the direction of the arrows a a, and the secondary currents will be in the direction of arrows c, that is, in opposition to each other, so that no current will pass through the synchronizing lamps. If the connections of one of 864 HANDBOOK ON ENGINEERING. the transformers are reversed, either in the primary or secondary, the two secondary currents will flow through the lamps in the same direction as indicated by the arrows d on the right side of the diagram. Thus it will be seen that the synchronizing lamps can be arranged so that they will light up when the generator current is in phase with the bus-bar current, or they may be arranged so as to be dark at this instant. Generally they are arranged so as to be bright when the current is in phase and the switch connect- ing the generator with the switchboard is closed at the instant when the lamps appear to be brighter. When two and three-phase generators are started up the first time a temporar}^ synchronizing arrangement is connected in the manner shown on the right side of Fig. 40. The synchronizing lamps on the left side will show that the current flowing in the two side wires is in synchronism, but this does not show that the other currents also synchronize. To make sure that the temporary transformer is properly connected the connections e are made first, and if the lamps on both sides of the diagram become dark and bright together, the connections are correct. The connections are then broken and are transferred to the middle wire ; then when all the currents are synchronized, all the lights will light up together. Generally the internal connections of synchronizing transformers are properly made, and the correct connection of the terminal wires is clearly indicated so that mis- takes in making connections are not very liable. Compensating and compounding alternators. Continuous current generators are provided with a compound field winding for the purpose of maintaining the voltage uniform as the arma- ture current increases. Alternating current generators are compounded for the same purpose. If the field of an alternator is excited by a current derived from an exciter the voltage of the machine will drop as the strength of the current generated in the armature increases. A part of the drop is due to the fact HANDBOOK ON ENGINEERING. 865 that the increased current absorbs more voltage in passing through the armature coils. The balance of the drop is produced by the reaction of the armature current upon the field. As the current of the exciter that magnetizes the field remains constant, the magnetization produced by it remains constant. The cur- rent flowing in the aternator armature acts to demagnetize the field, and, as its action increases as the strength increases it follows that the stronger the current becomes the weaker the field will be, and, as a result, the lower the voltage of the cur- rent generated in the alternator armature. If a portion of the current of the alternator armature is recti- fied by being passed through a commutator and is used to assist the exciter current to magnetize the field then the field magnetism will increase as the armature current increases, because the action of the rectified current will increase. Thus by the com- pound action of the exciter current and the rectified armature current, the magnetism of the field of the alternator can be made to increase as the armature current increases, and in this way the voltage is increased so as to compensate for the greater drop of voltage on the armature coils, the result being that the voltage impressed upon the wire remains practically the same for all strengths of current. The above results can be obtained providing the phase relation between the current and the impressed, or line e.m.f. does not change ; but if the phase relation is continually changing such perfect regulation cannot be realized. The reason why changes in the phase of the current interfere with the regulation is that the same strength of armature current will produce different de- grees of reaction on the field magnetism with different phase relations. If the lag of the current is increased the reaction upon the field will be increased, and in like manner a decrease in the lag will reduce the reaction upon the field. Several arrangements are used for obtaining field magnetizing currents that will com- 55 866 HANDBOOK ON ENGINEERING. pensate for variations in the lag of the current as well as for va- riations in strength. Alternators provided with such arrange- ments are called " Compensated Generators." The way in which a field magnetizing current is obtained that will compensate for variations in lag as well as in current strength is by using a por- tion of the armature current to vary the strength of the current generated by an exciter, the exciter being provided with coils through which the current taken from the armature is passed. These coils are so disposed that their governing action upon the exciter is proportional to the lag of the current as well as its strength, hence the current that the exciter sends through the field coils of the alternator is at all times sufficient to compensate for variations in the strength and phase of the armature current. If an alternator is single-phase, one commutator is sufficient to rectify the portion of .the armature current and to magnetize the field. For a two-phase machine, two commutators are required and for a three-phase, three commutators. To obviate using two and three commutators in polyphase generators, trans- formers are employed, two transformers for two-phase and three transformers for three-phase. The recording currents of these transformers are combined into one, and this com- bined current is passed through a single commutator to be recti- fied. In some cases only one of the currents of a two or three- phase generator is rectified, but with most machines, if they are connected in parallel, care must be taken to have the circuits from which the rectified current is taken properly connected with each other ; if not, one armature will short circuit the other. This is due to the fact that when alternators are run in parallel the rectified currents for the field coils are connected with each other through equalizer wires, in a manner similar to that used with continuous current generators. The ordinary connections for two generators in parallel are shown in the diagram Fig. 41. HANDBOOK ON ENGINEERING. 867 As will be seen, the field-magetizing currents derived from the commutators are connected with each other through the equalizer switches, hence, to avoid short circuiting the armature through the equalizer connections, if the commutator rectify one current only, CONNECTIONS OF COMPOSITE FIELD ALTERNATING GENERATORS FOR RUNNING IN MULTIPLE Synchr o.r;r.g Plug Fig. 41. the two rectified currents must be in phase with each other. The rheostats shown in each field circuit are for the purpose of adjusting the voltage of each generator independently. The use of transformers to transform the portion of the arma- ture current that is rectified is no objection against polyphase machines, because, even with single phases, the armature voltage is generally so high that a transformer is used so as to obtain a secondary current of low voltage to pass through the field coils. Alternating Current Motors* From the foregoing it can be understood that an alternating current generator can be used as a motor providing it is supplied with the same kind of currents, 868 HANDBOOK ON ENGINEERING. that is, with a continuous current to magnetize the field, and with an alternating current for the armature. A single-phase alter- nator will run as a motor if connected in a single-phase circuit. Two-phase generators will act as two-phase motors, and three- phase generators will act as three-phase motors. With either one of these three types of machines a continuous current will be required to magnetize the field. Two and three-phase ma- chines can be run with a single alternating current, by connect- ing one of the armature circuits only, or all the circuits may be used if they are connected in parallel. When an alternator is used as a motor it is called a synchro- nous motor, because it runs in synchronism with the generator that supplies the current. A simple alternator (single-phase ma- chine) becomes a single-phase synchronous motor, and a two or three-phase generator becomes a two or three-phase syn- chronous motor. A single-phase synchronous motor will not start up of its own accord, but must be set in motion and run up to nearly its full speed before it will begin to act as a motor. If it is started up without a load when it comes rather near to its full speed it will give a sudden jump and swing into step with the current and then continue to run at this velocity. If it is started with a full load it will not fall into step with the current until its speed is very nearly up to the proper point. Synchronous motors are never started under load, they are always started light. Two and three-phase synchronous motors can be started with- out outside assistance. Synchronous motors are generally pro- vided with a self-starting motor, to set them in motion, or else they are arranged so as to be self -starting by being converted, jn the act of starting, into some form of motor that is self- starting. Fig. 42 shows a synchronous motor of large size provided with an induction motor of much smaller capacity to start it. HANDBOOK ON ENGINEERING. 869 This motor is of the revolving field type, and, as will be seen, is precisely the same as the same type of generator. 1000 H. P. TWO-PHASE REVOLVING FIELD SYNCHRONOUS MOTOR. Fig. 42." Owing to the fact that synchronous motors are not self -starting, they are generally used only where large power is required, unless they happen to be made so as to be self -starting, then they are used in small sizes. A synchronous motor, when running, will keep in step with the current, no matter how much the load may vary, provided it is not made greater than the capacity of the machine. If the load is made so great that the motor cannot carry it, the armature will be pulled out of step with the current and will imme- diately come to a stop. On this account, motors of the synchronous type are not well adapted to operate cranes or similar machines in which there is a liability of greatly overloading the machine occasionallv. 870 HANDBOOK OX ENGINEERING. The current developed by an alternating current generator will lag behind the impressed e.m.f. as has been fully explained in the foregoing. If this curreutis passed through a second machine, that acts as a motor, the latter will tend to generate a current that flows in opposition to that of the generator ; hence, in this current the lag will be in the opposite direction of that of the current that drives it. That is when the machine acts as a motor its whole action as a generator is reversed. Owing to this fact, if a synchronous motor is placed at one end of a circuit, and a generator at the other, the motor will act to neutralize the self-induction of the generator, and thus to bring the current in the circuit, and the impressed e.m.f. into phase with each other. Thus, a synchro- nous motor can be made to act in the same way as a condenser, to reduce the lag of the current. Power factor. In an alternating current circuit, it is very important to reduce the lag of the current as far as possible because the actual amount of energy carried by the current depends upon the angle of lag, as was fully explained in connection with Figs. 23 to 25. In a continuous current circuit the power is always equal to the product of the volts by the amperes, but in an alternating current circuit this product is not a measure of the power. It is called the apparent power, or the volt-amperes. The actual power is equal to the amperes multi- plied by the e.m.f. in phase with the current, or the active voltage, as it is called. The ratio between the true power and the volt- amperes is called the power factor. The power factor can be obtained by dividing the true power by the volt-amperes, and it may range from 100 per cent when the current and impressed e.m.f. are in phase down to five or ten per cent when the angle of lag is nearly 90 per cent. In actual working circuits the power factor ranges between about 95 and 75 per cent. Any kind of device that has a low reactance, as, for example, incandescent lamps, acts to keep the angle of lag of the current small, and thus HANDBOOK ON ENGINEERING. 871 the power factor high. Devices having large reactance, such as transformers, and induction motors act to increase the angle of lag of the current, and thus to reduce the power factor. Devices that develop a negative reactance, that is, which cause the current to lead the impressed e.m.f., such as condensers and synchronous motors, can be used in circuits in which transformers and similar devices are operated so as to counteract these and thereby keep up the percentage of the power factor. Induction and other types of motors* In addition to the synchronous motors just explained, the only type of machine that requires notice here is the induction motor. This is by far the most extensively used of all alternating current motors, and from the manner in which it acts it has a greater range of adaptability than any other type. It may be well to mention here, however, that a plain motor, such as those used with continuous currents, can be made to operate with alternating currents providing the field cores are made laminated, instead of solid castings. If the field is solid the motor will not run if connected in an alternating current circuit because the large mass of iron constituting the field cannot be magnetized and demagnetized as fast as the current alternates. If we take hold of a freight car and try to shake it we will fail in the effort, simply because the bulk is too great to be set in motion rapidly. If, however, we take hold of the side of a light buggy and shake it we will be able to produce a very vigorous movement, simply because the bulk is light. In the same way, if we attempt to alternate the magnetic polarity of large masses of iron \re fail because the bulk is too great, but if v e divide the mass up lato many thin sheets we will have no diffi - cu'ty in causing its polarity to change rapidly. Alternating cur- rent motors of this kind which are called commutator motors, hfeve been made, but they are not used or manufactured for com- mercial purposes at the present time, because they are fur inferior to other types. They are open to two objections, one of which 872 HANDBOOK ON ENGINEERING. is that they spark considerably and the other is that they will not give much more than one-third the power that the same machine will develop if supplied with a continuous current. The reason why they give such small power is that on account of the many turns of wire on the field the inductive action is very great, hence the reactance is very high, and as a result the current lags exces- sively so that the power factor is very low, therefore, although the current is strong, the actual energy carried by it is comparatively small. Several other types of alternating current motors have been devised, but they have never got beyond the experimental stage. Principle of the induction motor- Induction motors are made for single and polyphase currents. When in operation the Fig. 43. Fig. 44. principle of action is the same in all, but in the act of starting the single-phase machine is different from the others. Single-phase induction motors will not start of their own accord unless provided with special starting arrangements. The most common way of arranging a single-phase induction motor so as to be self-starting is to provide a set of starting coils that virtually convert it into a HANDBOOK ON ENGINEERING. 873 two-phase machine in the act of starting. When the motor is under way the starting coils are cut out, although in some cases they are left in circuit all the time. The principle of the induc- tion motor can be explained by the aid of the diagrams Figs. 43 to 46. These diagrams illustrate the action in a two-phase machine which is the one most easily understood. The single-phase induction motor is the most difficult one to ex- plain or to understand, so we will leave it for the last. In an induction motor, the stationary part, which is called the stator, and sometimes the field, is provided with coils that are connected with the operating circuits. The rotating part which is called the rotor and sometimes the armature, is provided with coils that are short circuited upon themselves and are not connected with the operating circuits. The principle of operation generally stated is that the currents in the stator develop an in- ductive action upon the coils of the rotor thus developing currents in these, the action being substantially the same as that in a transformer. On that account the stator is also called the primary member, while the rotor or armature is commonly called the secondary member. The primary currents passing through the coils of the stator, develop a magnetic flux and the secondary currents induced in the coils of the rotor also develop a magnetic flux, these two fluxes are at an angle with each other, and, hence, there is a strong attraction exerted between them, the magnetism of the rotor making an effort to place itself parallel with that of the stator. The magnetism of the stator rotates, on account of being developed by alternating currents, and the magnetism of the rotor in trying to place itself parallel with that of the stator also rotates, chasing the latter around the circle but never overtaking it. In Fig. 43 let A A represent two coils connected in one of the circuits of a two-phase system, and let B B represent two other coils connected in the other circuit of this same system. Suppose 874 HANDBOOK ON ENGINEERING. we consider the instant of time when the current flowing through the A A coils is at its maximum value, then at this very same instant the current in the B B coils will be zero. The current in the A A coils is then the only magnetizing current acting upon the ring at this instant. Suppose the direction of the current through A A is such as to develop a magnetic flux that will traverse the space in the center of the ring in the direction of arrow C. As the current in the A A coils begins to decrease, that flowing in the B B coils will begin to increase. Let the direction of the current in the B B coils be such as to send a magnetic flux through the center of the ring in the direction of arrow C in Fig. 45. This magnetization will act upon that developed by the current in the A A coils and will have a tendency to twist it around into the direction of arrow C in Fig. 44. When the current in the A A coils has reduced and the current in the B B coils has increased until they are both equal, then each one will act with equal force Fig. 46. to establish a magnetization in its own direction , and the result will be that the actual direction of the magnetic flux will be as indicated by arrow C in Fig. 44. Thus we see that by the decrease in the strength of the current in the A coils and the HANDBOOK ON ENGINEERING. 875 increase in the strength of the current in the B B coils until they are both equal, the magnetic flux has been rotated from the position of arrow C in Fig. 43 to its position in Fig. 44. Now as the variation in the currents progresses, and that in A A becomes weaker, while that in B B becomes stronger, the direction of the magnetic flux will be still further rotated so that when the current in B B reaches the maximum value, and that in A A becomes zero, the direction of the flux will be that of arrow C in Fig. 45. As we advance beyond this instant of time, the current in B B will begin to reduce, while that in A A will begin to increase, but its direction will be the opposite of what it was in Fig 43, so that when the currents in the two sets of coils become equal again, the direction of the magnetic flux will be that of arrow C in Fig. 46. When the current in the A A coils reaches the maximum and that in B B becomes zero, the flux will have rotated through one-half of a revolution and arrow G will be in the vertical position but pointing downward. If we follow the action of the currents further we will find that as a result of the continuous increasing and decreasing and changing of direction, the magnetic flux indicated by arrow C will continuously rotate keeping time with the frequency of the currents. Now if we suppose that an armature upon which a number of coils are wound in a diametrical position, is placed within the field ring, and is held stationary, we will see at once that the rotating magnetic flux will cut through its coils and develop e.m.fs. in them. The currents developed in these coils on the stationary armature will be alternating, hence, they will develop a magnetic flux in the armature that will rotate, and keep time with the rotating flux developed by the field coils. Both these fluxes act inductively upon the field and armature coils, their combined effect being equal to that of a single flux located 90 degrees in advance of the e.m.f. induced in the armature coils, hence, somewhat more than 90 degrees ahead of 876 HAND BOOK OX ENGINEERING. the armature current. If we hold the armature by means of a brake, and free this slightly, so that the armature may revolve slowly, it will at once follow around after the rotating field, but as its magnetization is developed by currents that are induced by the action of the field magnetism, it will matter little how fast the armature may revolve, its magnetization will never be able to overtake that of the field. As can be judged from the foregoing explanation, an induction motor is not a synchronous machine, and its armature can never at- tain a velocity equal to that of the rotating field. If the resistance of the armature coils is macte very low, it may reach a velocity very near to that of the rotating flux. The difference between the velocity of the rotating flux and that of the rotating armature is called the slip of the motor. If the motor is designed for constant speed, the resistance of the armature- coils is made, very low, and then when the machine is running free, the speed of the armature may run up to 99 or 99 J per cent of the speed of the rotating field, and when the maximum load is put on it may not drop lower than 94 or 95 per cent. If a motor is designed in this way the pull of the armature when it starts up will be small and will gradually increase until the speed is about nine-tenths of the maximum when it will again begin to decrease. If it is desired to make a motor that will give a strong pull when it starts up, its armature coils must have more resistance, and then it will pull harder on the start, but as fast as the speed builds up the pull will reduce. From this it will be seen that in- duction motors that are made so as to run at nearly a constant speed, say to vary five or six per cent between full load and run- ning free, will not give a strong pull in the act of starting, hence they will have to be started without a load. If a motor is to be made to start under a full load it must be proportioned so that it will not run at a constant speed, but will gradually reduce its velocity as the load is increased. HANDBOOK ON ENGINEERING. 877 Induction motors, if very small, are started by connecting them directly with the operating circuits, but if they are of any capacity they must be provided with some kind of starting resist- ance so as to keep the starting current down within safe limits. One way of starting is to introduce resistance into the primary circuits, but this results in reducing the strength of the field, and thus the pull of the armature. Another way is to intro- duce resistance into the armature coil circuit. This is the best method, because it enables the motor to start up with a strong pull. Three-phase induction motors act in precisely the same way as the two-phase, the only difference being that the rotation of the Held flux is produced by the increase and decrease in the strength of three currents flowing through three sets of coils equally spaced around the circle instead of by the increase and decrease in two currents flowing in two sets of coils equally spaced around the circle. In the single-phase induction motor, the magnetic flux developed by the single alternating current traversing a single set of coils on the field combines with the magnetic flux developed by the armature current, to develop a rotatingfield and this acting upon the armature coils produces rotation in precisely the same way as in the two- phase machine. This is the action that takes place after the armature is set in motion, but if the load is increased and the armature speed is reduced the rotating field begins to become irregular, and by the time the armature velocity is reduced to about one-half, the rotating flux becomes so irregular in its move- ment, that the armature pull begins to reduce very rapidly, and the machine comes to a standstill. Owing to this fact single- phase induction motors cannot be used in cases where it is de- sired to start with a strong pull, or where a wide range of speed variation is desired. To make a single-phase induction motor self -starting, it is wound 878 HANDBOOK ON ENGINEERING. with two sets of coils, like the diagrams Figs. 43 to 4fi, and the current from the single-phase circuit is passed through these two sets of coils in parallel branches, and in one of the branches the reactance is greatly increased, so as to make the current in this branch lag much more than in the other. In this way a phase displacement is obtained between the two currents, and this pro- duces a corresponding displacement in the magnetic fluxes devel- oped by the two sets of coils, so that their combined action develops a rotating field. This field does not rotajte at a uniform rate, like the field of a two-phase motor, but it is uniform enough for the purpose of setting the machine in motion. To increase the reactance in th,e auxiliary starting coils, all that is necessary is to wind them with many turns of fine wire, and this is an arrangement very commonly employed, but, in some cases, sep- arate coils are placed in the auxiliary circuit to obtain the required reactance. There are other ways in which single-phase induction motors are made self -starting, but they are not very extensively used. While induction motors are very satisfactory machines, being adapted to every kind of work, even to the operation of railway cars, they have the objection of being highly inductive devices that act to greatly increase the lag of the current, and thereby to reduce the power factor. On this account they are often used in connection with synchronous motors so that the latter may coun- teract their inductive effect, and thus keep the power factor high. The small motor shown in Fig. 42, is an induction motor. Induction motors are made in many different designs, and as large as 300 to 400 H. P., but as a rule they are confined to much smaller capacities ; synchronous motors being used for the large* sizes. Rotary transformers and rotary converters* A rotary transformer is a machine by means of which a continuous current may be obtained from an alternating current. A rotary con- HANDBOOK ON ENGINEERING. 879 verter is a machine for accomplishing the same result. The essential difference between the two is that the first is driven by an alternating current and generates a continuous current, while the second changes an alternating into a continuous current. As a result of this difference the rotary transformer can be used to obtain a continuous current of any desired voltage from an alternating current of any given voltage ; but in the rotary con- verter, as the action is to convert the alternating into a con- tinuous current, the voltage relation is fixed so that for a given alternating current voltage we will get a corresponding contin- uous current voltage. Both these machines can be used in the reverse order, that is to transform or convert a continuous into an alternating current. B c c Fig. 47. Principle of the rotary transformer* The principle of the rotary transformer is illustrated in Fig. 47. In this diagram A represents a continuous current armature, and B is an alternating current armature. If both these are provided with suitable magnetic fields then if continuous current is passed through A it will become a motor and will drive B and generate therein a single alternating current or a number of them according to the way in which the armature is wound. Thus B may become a single or a polyphase generator. It can further be seen that the 880 HANDBOOK ON ENGINEERING. voltage of the currents generated by B is in no way connected with the voltage of the current that drives A, and depends wholly upon the way in which B is wound. If B is connected with an alternating current circuit, then it will run as a synchronous motor and drive A and the latter will generate a continuous current. This machine if driven by a continuous current will be self -starting, but if driven by an alternating current it will have to be started. If driven by an alternating current its speed will be controlled by the frequency of the current, but if driven by a continuous current its speed will vary with the magnitude of the load placed upon it. n / A C ( u C y b \ J a i Fig. 48. Fig. 49. Figs. 48 and 49 illustrate the principle of operation and the construction of a rotary converter. The armature A is of the continuous current type, having a commutator (7. If it is a two- pole machine, then if wires are connected with diametrically opposite segments of the commutator as is indicated in Fig. 49 by the arrows, and these are connected with the collector rings a a, brtfshes c c placed on these rings, will take of a true alter- nating current if the armature is placed in a suitable field and is driven. While alternating current can be taken from the brushes c c, a continuous current can also be taken from the brushes b b HANDBOOK ON ENGINEERING. 881 which bear upon the commutator C. Thus, this machine, if driven, becomes a combination generator which will deliver a continuous and an alternating current at the same time. Machines of this type are constructed and are called double current generators. If the brushes c c are connected with a single-phase circuit, and the armature is placed in a suitable field, it will rotate and from the b b brushes of the commutator a continuous current can be drawn. If the brushes b b are connected with a continu- ous current circuit, an alternating current will be delivered through the brushes c c. If four wires are connected with four commutator segments one quarter of the circumference apart, and these are connected with four collector rings, then from these rings two alternating cur- rents 90 degrees out of phase can be obtained. Thus, with four connections with the commutator segments the machine can convert two phase currents into one continuous current, or one continuous current into two phase currents, thatis into two alter- nating currents 90 degrees out of phase. If wires are connected with three commutator segments one- third of the circumference apart, and these are connected with three collector rings, then the machine will become a three-phase converter, and if connected with a three-phase system will deliver one continuous current or if connected with a continuous current circuit will deliver the three currents of a three-phase system. The rotary converter, as will be seen from the foregoing, actually changes a continuous current into one or more alternat- ing currents, or one or more alternating currents into one con- tinuous current, and in every case there is a direct electrical con- nection between the continuous and the alternating current cir- cuits. As this type of machine simply converts the current of one type into current of the other type it is quite, evident that there must be a fixed relation between the strength of the alternat- 56 882 HANDBOOK ON ENGINEERING. ing and continuous currents and also between the voltages. An alternating current if of the sine type, will have an effective value of 70.7 per cent of its maximum value, for the amperes as well as the volts. So that if we have a continuous current of 70.7 amperes and 70.7 volts, we must have an alternating current of 100 amperes maximum value and 100 volts maximum value to be equal to it, and if the energy is also to be equal, the current ia the alternating current circuit must be in phase with it e.m.f ., that is the power factor must be 100. In a rotary converter the voltage of the continuous current is equal to the maximum voltage of the alternating current and the strength of the continuous current is equal to one-half the maxi- mum strength of the alternating current. Thus if the maximum voltage of the alternating current is 1,000 volts, the voltage of the continuous current will be 1,000, and if the maximum strength of the alternating current is 100 amperes the strength of the contin- uous current will be 50 amperes. This arises from the fact that the rotary converter does not develop energy, as it drives itself, hence, the energy in the continuous current cannot be more than that in the alternating, in fact it will be a trifle less owing to the energy absorbed in driving the machine. Now if the alternating e.m.f. and current have the maximum values of 1,000 volts and 100 amperes, their effective values will be 707 volts and 70.7 amperes, and the product of these two will be the energy in watts. Thus 707 X 70.7 = 50,000 watts. Now if the voltage of the continuous current is 1,000, its strength must be 50 amperes, less the amount absorbed in overcoming the friction of the machine. Fig. 50 shows a rotary converter of large size. Alternating Current Distributions* The principal advantage of alternating over continuous currents is that they can be used for transmitting energy to much greater distances, owing to the fact that a high voltage can be used to transmit the main current over the wire, and at the receiving end this current can be passed HANDBOOK ON ENGINEERING. 883 through transformers, from which secondary currents of low volt- age may be obtained. In a few instances, low voltage alternating ROTARY CONVERTER. Fig. 50. currents are used for distributing current over small areas. The general arrangement of circuits and apparatus for a three-phase system of this kind is illustrated in the diagram Fig. 51. IB Fig. 51. The generator is shown at the extreme left. At a an induction motor is connected with the circuit. At b an " arc" light is connected in the secondary circuit of a small transformer. At c 884 HANDBOOK ON ENGINEERING a number of incandescent lamps are connected. At d the circuit is used to drive a rotary transformer, which develops a continuous current to charge storage batteries at e. The three solid line wires constitute the main circuit and all the apparatus is connected with them. The broken line above these is the neutral wire and is connected with the incandescent lamps only. If the number of these lamps in each circuit is the same, as is shown on the diagram, no current will pass to the neutral wire, but if in one of the circuits there are more lamps than in the other, the excess of current will pass to or from the neutral wire. Systems of this type are operated at voltages rang- ing between 200 and 600. The diagram, Fig. 52, shows the way in which the circuits are arranged when the distance of transmission is from one to three or four miles, For such cases, the voltage generally used is 2300. The generator at the left develops currents that pass directly to the main line. At a an induction motor is connected directly to the main line. At b transformers are used to develop secondary currents of low voltage to supply the circuit wjres c from which the motor d and incandescent lamps e are fed. At f a series transformer is used to develop a secondary current o^ constant strength to operate the arc lamps g. The difference be- tween a series transformer and the ordinary type is that the former is provided with a mechanical regulator, actuated by the current which maintains the secondary current of constant strength and varies the voltage in accordance with the number of HANDBOOK ON ENGINEERING. 885 lamps in service. At h another set of transformers are used to develop low voltage secondary currents, which pass through a rotary converter i, and are converted into a continuous current to feed the incandescent lamps atj. The diagram 53 illustrates the arrangement of circuits and apparatus for long distance transmissions, which may range all the way from five or six miles up to one hundred or more, the greatest distance covered up to date being 145 miles. To trans- mit current to great distances with a small loss in the trans- mission lines, it is necessary to use very high voltages, ranging from 10,000 to 60,000, and as it is not advisable to construct Fig. 53. generators to develop such high pressures, raising transformers are employed to develop the line current. These transformers are shown in Fig. 53 at a. The generator develops currents at 1,000 volts, and this passing through the primary coils of the trans- formers at a induces secondary currents which may have any voltage desired, say, 20,000. These secondary currents pass to the transmission lines b 6, which may extend a distance of ten, twenty or more miles and may deliver all their energy at the end of the line or drop part of it at intermediate points. The trans- formers at c and also those at I develop secondary currents of any lower voltage that may be required ; thus, those at c develop secondary currents for the circuits d, which may be of, say, 1,000 volts. The motor e is shown connected directly with d, but 886 HANDBOOK ON ENGINEERING. motor g and lamps i, k require a still lower voltage, hence the currents in d are passed through a second set of transformers at /, li and j. The three transformers at I develop secondary cur- rents of sufficiently low voltage to be passed through the rotary converter m, and thus provide a continuous current for the trolley road as shown. STARTING. When the armature is turning, see that the oil rings in the bearings are in motion. When the machine is up to speed and all switches are open, lower the brushes on the commutator and col- lector, making sure that each bears evenly and squarely on the surface. Turn the rheostat until all resistance is in, then close the switch in the exciter circuit. Set the exciter brushes properly and adjust the voltage of the exciter to the proper point. The alternator rheostat may then be turned gradually over until the proper alternating voltage is indicated. The main circuit of the machine may now be closed. The commutator brashes should be adjusted at a non-sparking position. If there is any load the voltage should increase slightly. If it decreases, it shows that the series coils and the separately excited coils are opposing each other, unless this decrease is caused by a drop in speed. If it is found that the coils are opposing each other, unclamp the brush- holder yoke of the alternator and move its commutator brushes backward or forward one and one-half segments in a three-phase machine, and one segment in a two-phase machine. A position giving maximum voltage will be found from which any motion, forward or backward, diminishes the voltage. Having once de- termined the correct setting of the brushes, they may generally remain unchanged, unless the generator is subject to great varia- tion of load when in some machines, slight movements may be found desirable. HANDBOOK ON ENGINEERING. 887 PARALLEL RUNNING OF ALTERNATORS. TYPES SUITABLE FOR PARALLEL OPERATION. If the speeds are exactly adjusted, any two alternators of the same frequency will operate together in parallel. The maximum angular displacement that may take place between two machines in parallel without causing objectionable phase difference decreases with increased number of poles. For this reason high frequen- cies are, generally speaking, less favorable to parallel operation than lower frequencies. Machines of the highest frequencies ordinarily used can, however, be successfully run in parallel if the mechanical arrangements are suitable. DIVISION OF LOAD. Machines to operate in parallel must run at such speeds as will give exact equality of frequency. If the prime mover running one machine tends to produce a lower frequency than that run- ning the other, the machines cannot carry equal loads. When two alternators operate in parallel, each must carry an amount of load proportionate to the power received from its prime mover. If one engine or water-wheel governs in such a manner as to give more power than the other, this machine must carry more load, no matter what the field excitation may be. If under such conditions the field excitations are correct, both machines will de- liver current to the line in approximately the proportions in which they receive power from their prime movers. If the field adjust- ments are incorrect, there will be idle currents between the machines in addition to the currents which go to the line. COMPOUND ALTERNATORS. When compound alternators are operated in parallel, equalizer connections should be used so that the rectified alternating 888 HANDBOOK ON ENGINEERING. current can properly distribute itself into the fields of all the machines. Without equalizers, an unstable condition may exist which will render parallel operation unsatisfactory. This applies particularly in the case of machines driven from the same source of power. The greater the amount of compounding, the greater will be the tendency to instability. BELTED MACHINES. If two machines are belted to separate prime movers, their parallel operation is dependent upon the governing of the prime movers. If they are belted to the same source of power, their parallel operation depends upon the proportions of pulleys and belts, and upon the tension and friction of the latter. Under such conditions the pulleys and belts must be adjusted with great nicety, so that both machines will tend, with proper belt tension, to run at exactly the same frequency. Even where pulleys are of exactly the correct dimensions, a slight difference in the thick- ness of belts may cause considerable cross currents or unequal division of load. DIRECT COUPLED MACHINES. With such machines, engines must not only be adjusted to run at synchronous speed, but must also be provided with fly- wheels large enough to prevent appreciable variations of fre- quency within each revolution. Inequalities of speed, due to insufficient fly-wheel effect, will cause periodic cross currents between dynamos, or will entirely prevent their operation in parallel. The greater the number of poles in a direct coupled machine, the less the angular speed variation necessary to cause trouble. High speeds are much more desirable with direct coupled alter- nators than low speeds, and low frequencies present less diffi- HANDBOOK ON ENGINEERING. 889 culties than high. The desirabilty of high speeds with direct coupled alternators cannot be too strongly stated. While an increase of fly wheel effect will equalize the angular irregularities of an engine's motion, it cannot bring about such good results as would be brought about by a similar reduction of angular error effected through an increase of speed. While the large fly- wheel steadies the motion, it may tend to prevent correction of the angular error through the effect of the cross currents. Cross currents which flow in machines having light fly-wheels may have an effective tendency to hold them together ; while machines with very heavy fly-wheels may tend to act independently of each other as far as angular variations are concerned. These matters should be carefully considered in installing direct connected alternators. Where engines operate at the same speed and have the same number of cranks, this trouble can sometimes be overcome by synchronizing the engines themselves so that the impulse in both come together. When the fly-wheel effect is insufficient, the frequency will fluctuate and this fluctua- tion may cause serious trouble if synchronous motors or rotary converters are connected to the circuit. When the cranks of two engines coupled to alternators are synchronized, any fluctuation of frequency which is due to lack of fly-wheel effect will still exist, although it may not affect parallel running. Where alternators have to be operated in parallel by engines to which they are directly coupled, it is generally desirable to use engines having -as many cranks as possible, so that the crank efforts will be well distributed throughout the revolution, and will not tend to produce an irregularity of motion. STARTING. When a machine driven by a separate engine is thrown in parallel with others which are carrying load, the throttle should be partly closed so that it can just run at synchronous speed with- 890 HANDBOOK ON ENGINEERING. out carrying load. After it is in step with the other machines, load can gradually be taken on by giving it more steam. If this is carefully done the voltage on the circuit is not disturbed by the addition of the new machine. When a belted machine is to be thrown into parallel with others driven by the same shaft, its belt tension should first be reduced, which will tend to admit enough slip to bring it into step with the loaded machines. After it is thrown in it will gradually take load as the belt is tightened. SHUTTING DOWN. In shutting down machines operating singly, both the gener- ator and exciter field resistance should be cut in by turning the rheostat before the line switch is opened. When two or more generators are running in parallel on the bus-bars, one may be shut down at any time. The equalizer switch should be opened first, then the load reduced by throttling the engine or by slacking the belt. As soon as the load is prac- tically off, open the main switch. CARE OF MACHINES. With high voltage machines it is absolutely essential that they be kept scrupulously clean. Small particles of copper or carbon dust, may be sufficient to start a disastrous arc. The commutator collector should receive careful attention and be wiped thoroughly every day. From time to time the machine should be thoroughly over- hauled and given a coating of air-drying japan after cleaning. Machines of the rotary field type are so constructed that it is a comparatively easy matter to get at every part of the armature coils. In a large station it is recommended that an air compres- sor be installed so that a hose can be led to the machine and the dust thoroughly blown out. HANDBOOK ON ENGINEERING. 891 It is advisable to have rubber mats in front of high tension switchboards and on the floor at the commutator-collector end of the generator. If it is necessary to adjust the brushes while the machine is in operation, the attendant should stand on the mat and it is also recommended that he wear rubber gloves. Both commutator and collector rings require a very slight amount of vaseline. In applying it a dry stick with a little chamois leather tied to one end may be used, so that there will be no danger of coming in contact with the brushes. With the brushes properly set and all screws firmly tightened into place, the generators should require very little -attention while running. It is well to note from time to time whether the oil rings are working properly. ALPHABETICAL INDEX. ARMATURE cores, 23, 27. Armature winding, 27, 29. Armature, arrangement of the field and, 33. Ammeters, the, 60. Ampere, the, 73. Armature, to remove the, 74. Assembling the parts, 74. Assembly, to complete the, 74. Armature, effect of displacement of, 94. Automatic regulator, etc., 108. Ammeter, 125. Arc lamps, 125, 151. Arc dynamo, the Thomson-Houston, 131. Arc dynamos, installation of, 131. Arc lighting system, connections for, 133. Arc dynamo, controller for an, 135. Air blasts and jets on L. D. and M. D. dynamos, 141. Arc lamp, view of interior of M., 150. Arc lamps, connections forM. &K., 152. Arc lights, repairing, testing, etc., 153. Automatic cut-off engines,, 339, Armington and Sims engine, and setting the valves of same, 275. Automatic lubricators, 310. Automatic cut-off engine, card from an, 350. Attendants, instructions for boiler, 532. Acids, pumping, 579. Ammonia, a few tests for, 629. Ammonia, effect of on pipes, 631. Ammonia, to charge the system with, 632. Automatic stops for electric ele- vators, 733. Auxiliary valves, hydraulic ele- vator, 775. Air compressors, losses in, 800. Air compressors, capacity of, 800. Air compressor, the McKierman, 801. Air compressor, the Bennett auto- matic, 803. Air compressor, the Ingersoll-Ser- geant, 803. Air lift system, the Pohle, 807. Alternating current machinery, 815. Alternating currents, the principles of, 815. Alternating currents, diagrams rep- resenting a generator of either continuous or, 817. Alternating currents and e.m.fs., diagrams showing the relations between, 821-825. (893) 894 INDEX. Alternating currents, why they vary etc., 825. Alternating current circuits, induc- tive action in, 834. Angle of lag between the current, etc., 837. Alternating current generators, 852. Alternating current generator, dia- gram illustrating a simple, 854. Alternator of the multipolar type, 855. Alternating current generators, how they are run, 859. Alternators connected in parallel, starting, 860. Armature, the effect of displace- ment of the, 94, 98. . Amperes, per motor, table, 169 ; 170. Amperes, per lamp, table, 173. Alternator of the multipolar type, 855. Alternator, a revolving field, 857. Alternator, an inductor, 858. Alternating cu rrent generators, 8 52 . Alternators run in parallel, 860. Alternators connected in parallel starting, 861. Alternators, compensating and com- . pounding, 864. Alternating current distributions, 882. Alternators, parallel running of, 887. Alternators, compound, 887. BRUSHES, why set differently, etc., 36, 37. Brushes, setting, on a 4-pole ma- chine, 40. Brushes, setting, on an 8-pole ma- chine, 41. Building, to wire a large, etc., 58, 60. Breakers, circuit, 62, 63. Bearings, filling the, 74. Brushes, why they spark, 82, 84. Brush arc lamps, connections for improved, 128. Brasses, connecting rod, 189. Bearings, the main, 190, 192. Boilers, priming in, 329, 648. Boiler, the steam, 398. Boilers, energy stored in steam, 400, 401. Boilers, special high pressure, 401. Boilers, types of, 402. Boilers, horse power of, 402, 404. Boilers, the rating of, 404. Boilers, working capacity of, 405, 406. Boiler tests, code of rules for mak- ing, 407, 414. Boilers, and boiler material, defi- nitions as applied to, 415. Boiler, selection of a, 422, 425. Boiler trimmings, 426, 432. Boiler, care and management of a, 433, 437. Boilers, water for use in, 438, 448. Boiler, use and abuse of the steam, 449, 453. Boilers, design of steam, 454, 455. Boilers, forms of steam, 456. Boilers, setting steam, 456, 457. Boilers, defects in the construction of steam, 457, 459. Boilers, improvements in steam, '459, 461. INDEX. 895 Boiler surfaces, strength 01 stayed flat, 473. Boiler stays, 474, 477. Boilers, pulsation in steam, 487. Boilers, water columns for, 489. Boiler, the water-tube sectional, 502. Boiler setting and furnace, view of, 513. Boilers, vertical tubular, 514, 521. Boilers, table of pressures, allow- able in, 516. Boiler settings, fire line in, 520. Boiler setting, number of bricks required for, 522. Boiler, specifications for a sixty- inch 6-inch fiue, 524. Banking fires, 531. Boiler attendants, instructions for, 532. Boilers, rules and problems anent steam, 536. Blake steam pump, the, 555. Blake pump, operation of the, 556. Boiler for a steam pump, selecting, 580. Brine system, 622. Brine, the preparation of, 624. Buildings, insulation of, 626. Boilers, foaming in, 648. Boiler, in case of low water in a 649. Boilers, rating by feed water, 676 Bevel wheels, 707. Belt driven elevators, 716, 725. Brake, the elevator machine, 720. Brake magnet, the safety, 739. Belts and how to care for them, 786. Belts, the driving power of, 788. Belting, strain or tension on, 788. Belting, rules and problem sanent, 788, 797. Belts, extracts from articles on, 790. Belts, transmitting power of, 795. Belts, table of horse-power of, 796, 799. Belting, directions for adjusting, 798. Bennett automatic air compressor, 803. CORES, the armature, 23, 27. Circuits, distributing, 47. Constant potential, generators of the, 47, 48. Circuit breakers, 62, 63. Current, the strength of an elec- tric, 73. Candle power, 73. Commutator, care of, 75. Commutator gives trouble, if the, 76. Commutator brushes, why they spark, 82, 84. Current, the way it is shifted, 84, 85. Commutated coil, etc., if the, 86. Controller, diagram showing con- nections of Brush, 118. Controller for arc dynamo, view of, 135. Commutator segments and brush holders, 138. Cut-off in parts of the stroke, table of, 183. Crank-pins, 188. ' Connecting rod brasses, 189. Centers, to find the dead, 195. Compound engine, view of tandem, 198. 896 INDEX. Compound engine, the Westing- house, 293. Cylinder lubrication, 309. Cut-off, view of a slide valve engine showing point of, 321. Compression begins, view showing the position of slide valve, when, 321, 322. Card from a throttling engine, 347. Card from an automatic cut-off engine, 350. Calculating mean effective pressure, 351. Curve, the theoretical, 353, 357. Card from a Corliss engine, 357. Card, a stroke, 358. Card, a steam chest, 359. Cards, eccentric out of place, 360, 361. Cards, eccentric, 361, 365. Cards from " Eclipse " ice machine plant, 371, 373. Corliss engine, how to increase the power of a, 381, 382. Code of rules for making boiler tests, 407, 414. Centrifugal force, 501. Cocks, proper location of gauge, 521. Compound pump, the Worthington, 544. Cameron steam pump, the, 548. Corrosion in water pipes, 579. Condenser, function of the pump , and, 621. Cold, mechanical, easily regulated, 622. Cold, utilizing the, 622. Capacity, unit of, 624. Compressor, view of the " Eclipse,' 635. Compressor pumps, 636. Compressor, view of double acting, 640, 644. Chimneys, 688, 794. Chordal pitch, to find the, 699, 703. Curves of teeth, 705. Circuit connections, view of, 734. Coils, cutting out the series field, 737. Car, how to start the, 743. Car switch, the, 748. Cable switch, the slack, 749. Cables and how to care for them, 783. Cylinder, contents of same in cubic feet for each foot in length, 801. Compressor, the McKierman air, 801. Compressor, The Bennett auto- matic air, 803. Compressor, The Ingersoll-Ser- geant Air, 803. Current machinery, alternating, 815. Currents, the principles of alternat- ing, 815. Currents, diagrams representing a generator of either continuous or alternating, 817. Currents and e.m.fs., diagrams showing the relations between alternating, 821, 825. Currents vary, etc., one reason why alternating, 825. Curves are used, etc., diagrams showing the way in which sine, 826. Currents, polyphase, 832. INDEX. 897 Currents, etc., unbalanced three- phase, 834. Current circuits, etc., inductive action in alternating, 834. Current, etc., the angle of lag be- tween the, 837. Condensers, etc., by the use of, 840. Condensers, etc., the general prin- ciple of construction of a, 841. Current generator, diagram illus- trating a simple alternating, 854. Current generators are run, how alternating, 859. Currents, field magnetizing, 867. Converters, rotary, 878. DYNAMOS, general directions for starting, 76, 77. Dynamos to full speed, bringing, 77. Dynamo with another, connecting one, 78. Dynamos into circuit, switching, 78. Dynamos, how connected together, 78. Dynamos in parallel, 79. Dynamos and motors, directions for running, 80. Dynamos, precautions in running, 81. Dynamo or motor, heating in a, 93, 94. Dynamo, view of the Thomson- Houston standard arc, 131. Dynamos, installation of arc, 131. Dynamo, view of controller for an arc, 135. Dynamos, diagrams showing best position of air blasts and jets on L D and M D, 141. Dead centers, to find the, 195. Down draft furnace, the, 503, 522. Deane steam pump, the, 546. Duplex pump, how to set the steam valves of a, 567. Decimal equivalents of 16ths, 32ds, and 64ths, of an inch, table of, 583. Decimal equivalents of one foot by inches, 714. Decimal equivalents of an inch, 787. ELECTRICAL MACHINERY, the ele- mentary principles of, 1. Electromagnetic induction, the principles of, 14, 22. Electromotive in volts, force, etc., the, 63. Electric motors, 64. Electric light conductors table, 176. Electric current, etc., the strength of an, 73. Engine, the steam, 177. Engine, the selection of an, 177. Expansion, the gain by, 183. Engine, care and management of a steam, 185. Engine, lubrication of an, 186. Engine, selecting an oil for an, 187. Engines, knocking in, 189 to 190. Engines, repairs of, 191. Eccentric straps, 192. Engines, automatic, 194. Engine, view of a tandem com- pound and its foundation, 198. Engine, how to line an, 199, 203. Engine, view of a twin tandem compound; showing a rrangemem of piping, 200. Engine, horse power of an, 252. 898 INDEX. Engines, general proportions of, 252. Engine, view of the Kussell, 254. Engine, setting the valves of a Russell, 254. Engine, view of Porter- Allen, 258. Engine, description of the Porter- Allen, 259, 271. Engine, directions for setting the valves and running Porter-Allen, 271,273. Engine, the Armington and Sims, 275. Engine, the Harrisburg, 276. Engine, the Mclntosh and Sey- mour, 281. Engine, the Ideal, 283. Engine, the Westinghouse com- pound, 293. Engine, view of a slide valve (showing point of taking steam), 321. Engin , view of a slide valve (showing the point of cut-off), 321. Engines, condensing, 232. Engines, slide valve, 337. Engines, regular expansion, 338. Engines, automatic cut-off, 339, 340. Engines, the difference in the action of throttling and automatic en- gines, 375, 379. Engines, economy of steam, 380. Engine, how to increase the power of a Corliss, 381, 382. Engine, how to increase the power of a throttling, 383. Engine, how to increase the power of a shaft governor, 385. Engine, how to line an (with a shaft placed at a higher or a lower level), 385, 387. Engine, how to line an (with a shaft to which it is to be coupled direct, 387. Engine, rules and problems apper- taining to the steam, 392, 395. Engine, to find the water consump- tion of a steam, 395, 397. Engine, best economy in running an, 650. Expansion of steam, 654. Engine, taking up lost motion m an, 654. Engines, feed water required for small, 676. Electric elevators, 716. Elevators, electric, 716. Elevator, the Otis, 716. Elevators, belt driven, 716, 725. Elevators, direct connected, 717, 730. Elevator machine brake, the, 720. Elevator, view of connections of gravity motor controller to, 722. Elevators, electric control, for pri- vate house, 749. Elevators, the Sprague Electric Co.'s, 756. Elevator, view of operative circuits for Sprague screw, 762. Elevators, care of Sprague, 765. Elevators, directions for the care and operation of electric, 765. Elevators, hydraulic, 769. Elevators, how to pack hydraulic vertical cylinder, 769. Elevator, view of Otis vertical hy- draulic, 772. > IttDEX. 899 Elevators, care of Hale, 777. Elevators, water for use in hy- draulic, 778, 781. Elevator inclosures and their care, 782. Elevators, lubrication for hydraulic, 785. FORCE, magnetic lines of, 6. Force, lines of, 0, 14. Force, magnetic, 13. Field and armature in a two-pole machine, general arrangement of, 33, 36. Fly-wheel, the, 184. Fly-wheels, rules for weights of, 253. Flues, riveted and lap welded, 477. Flues, table of allowable steam pressure on, 478. Force, centrifugal, 501. Furnace, the down draft, 503. Fire-line in boiler settings, 520. Fires, banking, 531. Friction of water in pipes, loss by, 588. Foaming in boilers, G48. Feed-water required for small en- gines, G76. Feed-water, heating, 070. Feed-water, rating boilers by, 070. Feed-water and steam, weights of, 077. Feed-water heaters, 678. Feed-water heaters, gain by use of, 680. Field coils, cutting out the series, 737. Fluid, soldering, 101. GENERATORS and motors, two-pole, 27, 30. Generators of the constant poten- tial, 47, 48. Generators of the shunt type, the switch board arranged for two, 49. Generators andmotors, instructions for installing and operating slow and moderate speed, 74. Governor, the steam engine, 183- 194. Governor, specifications for cen- trally balanced centrifugal iner- tia, 273. Governor, the Gardiner spring, 341. Governor, the Gardiner standard, 342. Gauges, steam, 489. Gauge-cocks, proper location of, 521. Gears, horse power of, 695. Gearing, wheel, 698. Gear-wheel, pitch line of a, 698. Gear-teeth, stress orr, 705. Gearing, construction of, 706. Gears, calculating the speed of, 710. Gauges, wire, 175. HORSE-POWER, 185, 238. Harrisburg engine, the, 276. Hyperbolic logarithms, table of, 397. Heat and steam, 410. Heating surface in square feet, table of, 501. Hooker steam pump, the, 553. Hancock inspirator, directions for connecting and operatingthe, 597. Heating feed-water, 676. Heaters, feed-water^ 678. 900 INDEX. Heat, units of, required to convert one pound of water, etc., 679. Horse-power of gears, 695. Horse-power of shafts, 697. Hydraulic elevators, 769. Hydraulic vertical cylinder eleva- tors, how to pack, 769. Hydraulic elevators, water for use in, 778. Hydraulic elevators, lubrication for, 785. IDEAL engine, the, 283. Indicator, a few remarks on the, 345. Indicator, the use of, in setting valves, 346. Iron per lineal foot, weight of square and round, 488. Instructions for boiler attendants, 532. Ignition points of various sub- stances, 589. Injector and inspirator, the, 591. Injector, the first appearance of the, 592. Injectors, general directions for piping, 594. Injectors, care and management of, 599. Inspirator, directions for connect- ing and operating, 597. Insulation of buildings, 626. Insulation, perfect, 628. Iron, table of weight of a square foot of sheet, 712. Ingersoll-Sergeant air compressor, the, 803. Inductive action in alternating cur- rent circuits, etc., 834. Induction, mutual, 842. Ice-making plant, a complete, 639, 640. Incandescent wiring tables, 160 to 168. Insulation resistance, 100. JOURNALS, heating of, 193. Joints, maximum pitches for riveted lap, 466. Joints, double riveted lap, 467. Joints, single riveted lap, 46<). KNOCKING in engines, 189. Knowles, steam pump, the, 550. LINES of force, magnetic, 6. Lines of force, 6, 14. Lamps, connections for improved brush arc, 128. Lighting system, diagram of con- nections for arc, 133. Leads, table of, 140. Lamps, instructions for the instal- lation and care of arc, 151. Lamp, view of interior of M arc, 150. Lamps, starting the, 152. Lamps, diagram of connections for M and K arc, 152. Lights, instructions for repairing, testing, and adjusting arc, 153. Lubrication of an engine, 186. Lubricators, automatic, 310. Link motion, setting a plain slide valve with, 313. Lining an engine with a shaft placed at a higher-or lower level, 385. Lining an engine with a shaft to which it is to be coupled direct, 387. INDEX. 901 Logarithms, table of hyperbolic, 397. Lap joints, maximum pitches for riveted, 466. Lap joints,, double riveted, 467. Lap joints, single riveted, 469. Lubrication of refrigerating ma- chinery, 630. License, some practical questions usually asked of engineers when applying for, 646. Lead, what is valve, 653, 666, 668. Lap on a valve, what Is, 654, 666, 670. Lost motion in an engine, taking up, 654. Line shaft, instructions for lining up extension to, 672. Lamps are connected, the way in which synchronizing, 863. Load, division of, 887. MAGNET, a permanent, 1 to 2. Magnet, two-bar, 3 to 6. Magnet needle, a, 3. Magnetic lines of force, 6. Magnetic force, 13. Magnet, to find the lifting capacity of a, 13. Motors, two-pole generators and, 27. Multipolar machines, 38, 39. Motors, electric, 64. Motors and their connections, 64, 73. Motors, instructions for installing and operating slow and moderate speed generators and, 74. Motors, directions for running dynamos aud, 80, Meter for station use, view of, 149. Meters, Watt, 150,, 151. Main bearings, the, 190. Mclntosh and Seymour engine, 281. Mclntosh aud Seymour engine, how to set the valves of a, 281. Miscellaneous pump questions and answers, 559, 603. Meter, the Worthington water, 581. Machines for ice making, rating, 638. Metals, melting points of, 687. Manila rope, transmission of power by, 714, 812, 813. Motor controller, view of connec- tions of gravity, 723. Magnet, the safety br-ake, 739. Machines, the proper care of, 739, 779. Motor, the pilot, 763. Metric system, the, 809. McKiermau air compressor, 801. Mutual induction, 842. Motors, induction and other types of, 871. Motor, principle of the induction, 872, 877. Motors, three-phase induction, 877, 878. Machines, belted, 888. Machines, direct coupled, 888. Machines, care of, 890. NEEDLE, a magnet, 3. Noise in dynamos, 91, 92. OTIS elevator, the, 716. Otis vertical hydraulic elevator and valve chamber, view of, 772. Otis gravity wedge safety, 777. 902 INDEX. PRECAUTIONS in running dynamos, 81. Personal safety, 81. Polarity, reversal of, 142. Plug switchboard, standard for 6 circuits, 148. Piston packing, 187. Pins, crank, 188. Piping, arrangement of, etc., 200. Power, what is, 251. Porter-Allen engine, view and de- scription of the, 258 j 273. Power plant, taking charge of a steam, 323. .Priming in boilers, 329. Pipes, loss of heat from uncovered steam, 391. Pressure allowable on flues, 478. Pipe, table of wrought-iron welded, 486. Pressures allowable in boilers, table of, 510. Pump, the steam, 544. Pump, the Worthington compound, 544. Pump, the Deane steam, 54G. Pump, the Cameron steam, 548. Pump, the Knowles steam, 550. Pump, the Hooker steam, 553. Pump, the Blake steam, 555. Pump questions and answers, mis- cellaneous, 559, 503. Pump, how to set the valves of a duplex, 567. Pipe connections, proper, 569. Pipe connections, view of, 570. Pumps refusing to lift water, 577. Pipes, corrosion in water, 579. Pumping acids, 579. Pump, selecting a boiler for a steam, 580. Pipes, loss by friction in water, 588. Pump and condenser, function of, 621. Pumps, compressor, 036. Pipe arrangement for vaults, 037. Practical questions usually asked, etc., 640. Pumps do not work, reasons why, 647. Priming in boilers, 048. Piping, simplicity in steam, 074. Pipe to order, cutting, 075. Pure water, 081. Prime movers, 097. Pitch line of a gear wheel, 698. Pitch, to tind the chorda!, 699, 703. Pinion, to find the proportional radius of a wheel or, 700. Pinion, to find the diameter of a,700. Pinion, to find the number of revo- lutions of a wheel or, 700, 701. Pinions, a train of wheels and, 701. Pitches of wheels, table of, 704. Pilot motor, the, 703. Pressure tanks, to find leaks in, 786. Pohle air lift system, the, 807. Polyphase currents, 832. Piston, to test a (for leakage of steam, 669. Power factor, 870. REGULATORS for Brush arc genera- tors, 120 to 125. Rod brasses, connecting, 189. Repairs of engines, 191. Rules for weights of fly-wheels, 253. Russell engine, view of the, 240, 254. INDEX. 903 Regular expansion engines, 338. Rules and problems appertaining to the steam engine, 31)2, 395. Riveted seams, strength of, 461, 466. Riveted lap joints, max murn pitches for, 466, 469. Rules and problems anent steam boilers, 536. Rules and problems anent the steam pump, 603, 617. Refrigeration, mechanical, 619. Rating of ice machines in tons capacity, 623. Ratings, difference in the, 623. Refrigerating machinery, lubrica- tion of, 630. Refrigeration, process of mechan- ical, 633. Rating machines for ice making, j 638. Refrigerating plant, a complete, 642. Reasons why pumps do not work, 647. Rating boilers by feed water, 676. Rope, the main hand, 721. Resistance, the starting, 735. Rope, standard hoisting, 783. Rules and problems anent belting, 788, 797. Rope transmission, 714, 812, 813. Ropes, horse power transmitted by hemp, 813. Ropes, to test the purity of hemp, 814. Rope data, wire, 814. Rheostat, diagram of, connections for, 134. Rotary transformers and convert- ers, 878. Rotary transformer, principle of the, 879. SWITCH boards, 76. Starting the generator, 76. Sparking, 87, 91. Switchboard for 6 circuits, 147. Switchboard, view of back of, 148. Starting the lamps, 152. Steam engine, care and manage- ment of the, 185. Selecting an oil for an engine, 187. Straps, eccentric, 192. Steam power plant, taking charge of a, 323. Steam power plants, economy in, 327, 329. Steam, high pressure, 332, 335. Steam, using same full stroke, 335, 337. Slide valve engines, 337. Steam engines, economy of, 380. Slide valve, how to set in a hurry, 388. Slide valve, the travel of a, 390. Steam pipes, loss of heat from uncovered, 391. Steam, heat and, 416, 421. Seams, strength of riveted, 461, 466. Stayed flat boiler surfaces, strength of, 473. Stays, boiler, 474, 477. Steam gauges, 489, 490. Safety valves, 491, 499. Safety valve rules, 497. Steam jets for smoke prevention, 542. Smoke prevention, 542. 904 INDEX. Substances, ignition points of vari- ous, 589. Steam, expansion of, 654. Steam, weights of feed water and, 677. Steam, the temperature and pres- sure of saturated, 684. Something for nothing, 686. Stacks, weight of steel smoke (per lineal foot), 694. Shafts, table of the horse power of, 697. Stress on gear teeth, 705. Screw, the worm, 708. Sheet-iron, table of weight of a square foot of, 712. Screw-cutting, 713. Switch, the motor starting, 719. Stops, automatic, 733. Switch lever, the 736. Switch, the car, 748. Switch, the slack cable, 749. Sprague Electric Co.'s elevators, 756. Sprague screw elevator, view of operative circuits for, 762. Sprague elevators, care of, 765. Steam, the force of, etc., 398, 400. Starting direct coupled machines, 886, 889. Shutting down, 890. Soldering fluid, 101. TWO-BAR magnet, 3, 6. Two-pole generators and motors, 27, 30. Thomson-Houston standard arc dynamo arranged for right hand rotation, view of, 131. Table of leads, 140. Table of cut-off in parts of the stroke, 183. Fitting a slide valve, 191. Theoretical curve, the, 353, 357. Throttling and automatic engines, 374, 379. Travel of a slide valve, 390. Types of boilers, 402. Trimmings,, boiler, 426, 432. Table of allowable steam pressure on flues, 478, 479. Tubes, thickness of material re- quired for, 481, 486. Table of the rise of safety valves, 494. Table of heating surface in sq. ft. 501. Table of water pressure due to height, 582. Tanks, capacity of, in U. S. gal- lons, 584. Testing for water in ammonia, 629. Taking up lost motion in an engine, 654. Table showing the units of heal required to convert one pound of water at the temperature of 32 F. into steam at different pres- sures, 679. Table showing the gain by the use of feed water heaters, etc., 680. Temperature, and pressure of sat- urated steam, the, 684. Table of diameters and pitches of wheels, 704. Teeth, curves of, 705. Teeth of wheels, proportions of, 709. Tooth, to find the depth of a cast iron, 709. INDEX. 905 Tooth, to find the H. P. of a, 710. Transmission of power by manila rope, 714, 812, 813. Table of transmission of power by wire ropes, 715, 814. Tanks, to find the leaks in, pres- sure, 786. Transmitting power of belts, 795. Table of horse power of belts, 796, 799. Thermometers, 811. Transformers, 844. Transformer, the action in a, 846. Transformers, the object in using, 849. Tables, incandescent wiring, 160 to 168. Table of amperes per motor, 169, 170. Table of volts lost at different per cent drop, 171, 172. Table of amperes per lamp, 173. Table of copper wire, 174. Table of wire gauges, 175. Table of electric light conductors, 176. Table of carrying capacity of wires, 99, 101. Table of properties of water be- tween 32 and 212 Fall., 679. UNBALANCED three-phase currents, etc., 834. Useful information, 786. VALVE, fitting a slide, 191. Valve setting for engineers, 318, 322. Valve, the travel of a slide, 390. Valves, safety, 491, 499. Valve lead, what is, 653, 666, 668. Valve gear, describe the Corliss engine, 654. Valve, what is lap on a, 654, 666, 670. Valve motion, direct and indirect, 668. Valves, how to pack vertical hy- draulic elevator cylinder, 771. Volts lost at different per cent drop, 171, 172. WATT, the, 73. Watt meters, connections for, etc., 149. Watt meters, 150. Work, what is, 251. Westinghouse engine, the, 293, 301. Water consumption of an engine, to find the, 395. Water columns for boilers, 489. Water column connections, proper, 515. Worthington water meter, the, 581. Water, weight of, 585. Water, cost of, 587. Water may be wasted, how, 589. Wheel, to find the diameter of a, 699. Wheel, to find the number of teeth for a, 699. Wheel, to find the circumference of a, 700. Wheels, bevel, 707. Worm screw, 708. Wiring for private houses, view of, 750. Wiring tables, 160 to 168. 906 INDEX. Wire, approximate weight of Wires, table of carrying capacity " O. K." triple braided weather proof copper, 174. Wire gauges, difference between, 175. of, 99, 101. Water, table of properties of water, etc., 002. ZIGZAG riveting and chain rivet- ing, 408, 472. ^-- ~ _^,^-^ ^-- -^X/X^. z^ ^ .Jr ~~^_^^_^^ ^_^^ ^^^^