LIBRARY OF CONGRESS. — ■ V Vl5 UNITED STATES OF AMERICA. II MODERN EXAMINATIONS OF STEAM ENGINEERS OR Practical Theory Explained and Illustrated. WKITTEN rOR ENGINEEES BY AN El^GINEEE. CO.nPRlSING rULL AND CO/nPLETE ANSWERS TO 300 QUES- TIONS EOR THE USE OE ENGINEERS AND ElRE/nEN, WHEN PREPARING TO AAICE APPLICATION TOR EXAMIN- ATION ro:^ U. S. GOVERNMENT AND STATE LICENSE: AND TOR THE INFORMATION or ENGINE BUILDERS. BOILER MAKERS, MACHINISTS, ETC. BY W. H. WAKEMAN, INSTRUCTOR IN STEAM ENGINEERING AT THE BOARDMAN /MANUAL TRAINING HIGH SCHOOL. NEW HAVEN, CONN. ASSOCIATE EDITOR "MACHINERY," NEW YORK. N. ^■. INSTRUCTOR ELM CITY STATIONARY EN- GINEERS' ASSOCIATION, N.A.S. E., NO. 10, OP CONN.. AND AUTHOR OE MANY EDITORIALS EOR MECHANICAL PUBLI- CATIONS. FIRST EDITION. BRIDGEPORT, CONN. XC^mu^s. AMERICAN INDUSTRIAL PUBLISHING CO 1895. ^ ^ X ^ h -tHi COPYRIGHTED BY W. H. WAKEMAN. 1895. All rig-hts reserved. PRESS OF THE UNION PUBLISHING CO., BRIDGEPORT, CONN. PRE FA CE, The author takes pleasure in presenting- to the steam engineers of America, a work treating* in a plain, practical way of a g-reat variety of subjects pertaining- to the engine and boiler rooms, con- taining valuable and important information for those who aspire to become competent engineers, and something more than starters and stoppers. The authorities quoted are reliable and up to date, and the formulas and rules given are fully explained, thus enabling all to understand and apply them. The Manufacturers Gazette, of Boston, Mass., originally published this work, one part appear- ing in each weekly issue for an entire year, and as it was very favorably received by steam and me- chanical engineers, boiler makers, machinists, draughtsmen, etc., it is now published in book form for the convenience of those who wish to use it in daily practice. That the benefits derived from it by the craft may be commeasurate with the labor of preparing this volume, is the sincere wish of THE AUTHOR. June 22nd, 1895. DEDICA TION. To those true friends among- the eng-ineers of the United States of America who have ever been ready to g-ive encourag^ement and support, to the efforts of the author for the elevation of the po- sition of the practical eng-ineer, this book is re- spectfully dedicated. W. H. Wakeman. New Haven, Conn., U. S. A. CONTENTS. CHAPTER I. Introduction. .A Right and a Wrong way to Prepare for Examination .." Book Engineers are not Always Despised.". .Theory will do Practice no Harm.. The Ceaseless Routine of the Engine Room is Rendered Less Monotonous by Devoting a Portion of the Time to Study. CHAPTER H. General Outline of Subjects that Should be Familiar to Applicants for Other than First Class Licenses. .They Should be able to give Details of the Plant that they are to Run, and be Ready to Tell what Course to Pur- sue in Case of Accident, and also be Ready to Explain the Construction and Operation of the Slide Valve. CHAPTER HL Much is Usually Expected From the Applicants for First Class Licenses. .They Should Thoroughly Understand the Meaning of the Terms "Lap" and "Lead," and Know what is Meant by Clearance, Compression, Cushion, Cut-off, and Understand How to Set all Kinds of Valves. .They Should also Understand How to Properly Reverse an Engine. CHAPTER IV. All Rules Given for Reversing an Engine are not Cor- rect. .Travel of the Crank and Wrist Pin Compared. . How to Find the Throw of an Eccentric . .The Effect of Reducing the Diameter of an Eccentric. .The Proper Size of Steam and Exhaust Pipes. » CONTENTS. CHAPTER V. The Proper Size of Steam and Exhaust Ports. .Diameter of Crank Shaft. .Size of Crank and Wrist Pins. .Diam- eter of Connecting Rods and Piston Rods. .Length and Diameter of Main Bearings. .The Value of a Counter- bore. CHAPTER VI. Condensing and Non-condensing Engines. .Absolute Back Pressures. .Difference Between an Automatic and a Throttling Engine. .Compound, Triple and Quadruple Expansion Engines. .Good and Bad Quali- ties of these Types. What will the Engine of the Future be ? CHAPTER VH. What is Meant by the Horse Power of an Engine ?. .How to Determine the Power of any Engine. .One and Eight Horse Power. .Diameter of Cylinder, Length of Stroke, Speed, and Mean Effective Pressure Should be Stated. CHAPTER VHL How to Ascertain the Area of a Piston. .Deducting One- Half the Area of the Piston Rod. .How to Determine the Speed, or the Diameter of the Piston When all Other Data is Given.. Short Rule for Finding the Square Root of Certain Numbers. CHAPTER IX. Explanation of the Rule for Extracting the Square Root of any Number. .To Determine the Necessary Mean Effective Pressure, When all Other Data is given. .How to Ascertain the Horse Power Constant of any Engine, and Showing the Value of the same. .Increasing the CONTENTS. S> Power of an Engine. . Limit of the Size of a new Cy- linder. . Boiler Capacity for the Engine Under the new Conditions. .Shall We add a Condenser ?. .Best Remedy for an overloaded engine. CHAPTER X. Determining the Speed of an Engine Before Steam is Ad- mitted to It. .Revolutions of the Governor. .Does the Engine Run the Governor, or Vice Versa. .To Calcu- late the Speed of the Governor when all other Data is furnished. .The Size of Pulleys and Speed of Shafting ..Why do We Use the Diameter of Pulleys Instead of the Circumference ? CHAPTER XI. The Ratio of Expansion. .Rule for Determining the Mean Effective Pressure Under Certain Stated Condi- tions. .Hyperbolic Logarithms and the Rule for Find- ing them from Common Logarithms. .Why the Num- ber lo is Used. .To Determine the Actual Point of Cut Off. .What is a Crank ?. .What is Meant by the Valve Gear of an Engine ? CHAPTER XII. What is a Fly Wheel ?. .How does it assist in Regulating the Speed of an Engine ?. .Rule to Determine the Weight of Rim.. What Does This Rule Recognize? .. Effect of a Heavy Rim on the Strength of the Wheel . .Rule for the AVeight of Entire Wheel . .Safe Limit of the Speed of Fly Wheels. .All Fly Wheels Should.be Carefully Balanced. .Bolting Split Wheels Together. CHAPTER XIII. Adding a Condenser to a Non-Condensing Engine.. Does it Increase the Mean Effective Pressure ?. .Re- 10 CONTENTS. ducing Boiler Pressure and Maintaining Mean Effective Pressure. .Reduction of Absolute Back Pressure. .Sav- ing Steam by use of Condenser. .Increasing the Con- densation on Account of Low Terminal Pressure. .De- termining the Point of Cut Off when the Mean Effec- tive and Initial Pressures are Given. CHAPTER XIV. From the Engine to the Boiler. .The Source of Power Must be Understood. .Reducing Common to Decimal Fractions. .Safe Working Pressure of a Steam Boiler. . Thickness of Plate and Strength of Joint Must be Taken Into Account. .Tensile Strength and Factor of Safety. .Other Rules for Safe Working Pressure.. Coefficient of Safety. .All Safe Pressure Rules are not Practical. .Four Rules Compared. .Aggregate Strain Caused by the Steam Pressure. CHAPTER XV. Boiler Seams. .The Weakest Part Must be Taken for the Calculation. .Pitch of the Rivets. .Strength of net Section of Plate. .Strength of the Rivets. .Comparing Strength of Joint and of Solid Plate. .Double Welt Butt Joints. CHAPTER XVI. Bracing Flat Boiler Heads. .Bracing from Head to Head and from Head to Shell. .Safe Load for Braces. .Ag- gregate Pressure on a Flat Head.. Braces Should be made Without Welds. .They Should not be Riveted to the Fire Sheets.. The use of Tee Irons. .Strength of Seams with Drilled and with Punched Holes. .Effect of Flanging the Boiler Heads CONTENTS. 11 CHAPTER XVII. Heating Surface Necessary for a Horse Power. .Square Inches on the Engine Cylinder and Square Feet on the Boiler Shell. .Hot and Cold Feed Water. .What Consti- tutes a Horse Power ?. .Determining the Heating Sur- face of a Boiler, .The Shell and the Heads. .Water Space of a Boiler. .The Steam Space Must Include the . Dome. .Foaming and Priming. .Removing Some of the Tubes and Putting in a Dry Pipe. .Value of a Sep- arator CHAPTER XVIII. Proper Size of Safety Valve for Any Boiler. .The Grate Surface and the Heating Surface. .English and French Rules.. U. S. Rule the Best. .Area of Opening. .Dif- ference Between Flat and Bevelled Seats. CHAPTER XIX. Areas of the Openings of Safety Valves Further Consid- ered. .Examples Illustrating the Same. . Proper Size of Pump for a Steam Plant. .Hot and Cold Water Pumps . .Water Needed in Winter and Summer. .Calculating the Capacity of a Pump. .How Water is Raised. .Limit of the Height to which a Pump can Lift Water, .Prac- tical Limit to the Same. CHAPTER XX. Advantage of Heating Feed Water. .Heating it by Ex- haust Steam. .Rule for Determining the Percentage of Fuel Saved. .Illustration of the Same.. Forced and Natural Draft. .Fan Blower and Steam Jet. .Efficiency of the System. .Designing Chimneys. .Rule for the Size of Chimney for any Plant. 12 CONTENTS. CHAPTER XXI. A General Knowledge of the Steam Engine Indicator is Necessary. .Description of the Instrument. .Slight De- fects Produce Serious Consequences. .The Admission and the Steam Lines. .The Expansion and the Counter- pressure Lines. .The Atmospheric and the Vacuum Lines. .Height and Weight of the Atmosphere. .The Forward Pressure is not the Mean Effective Pressure. . Three Ways of Ascertaining the Mean Effective Pres- sure. CHAPTER XXII. Rules for Locating the Theoretical Expansion Line.. Proving the Rule for Determining the Mean Effective Pressure. .Calculating the Water Consumption . .A Pound of Water Makes a Pound of Steam. CHAPTER XXIII. Explaining Rules for Calculating Water Consumption.. Pressure at the Point of Release. .Weight of a Cubic Foot of Steam. .Cubical Contents of the Cylinder. .The Horse Power Developed. .The Principle Involved Should be Understood . .Every Point Should be Taken Into Consideration. CHAPTER XXIV. Formula Used by the Massachusetts School of Technol- ogy . .Illustration of Its Application . .How Different Values were Obtained . .Small Differences will not Prevent the Applicant From Receiving a License. CHAPTER XXV. Comparison of Four Rules for Calculating Water Con- CONTENTS. 13 sumption. .A Rule which is Short but Requires a Table to Make it Complete. CHAPTER XXVI. Conclusion of the Subject of Water Consumption . .The Rate Maybe Changed Without Changing the Engine. . Light and Heavy Loads. .Reduction of Speed and De- creased Output of Machinery. CHAPTER XXVH. Conclusions Should not be Hastily Arrived At. .Initial Cylinder Condensation and Re-evaporation. .Exact Clearance not Always Known. .Causes for Improperly Located Expansion Lines. .Exposed Cylinders Should be well Covered with Some Non-Conductor. .A Badly Set Steam Valve and the Cause of it. .Counter Pressure and Compression Lines. .Concerning the Proper Amount of Compression. CHAPTER XXVIII. Direct Steam and Expansion .. Do we Save Fuel by Using Steam Expansively ?. . " Power Developed " and "Work Done".. When Absolute Pressures Should be LTsed . .An Easy Way to Prove a rule. .The Most Eco- nomical Pressure to Carry. .A High Boiler Pressure, Economical Under Certain Condition CHAPTER XXIX. Effect of Lowering the Boiler Pressure.. An Engine Should be Properly Proportioned For Its Work. .Prin- ciple on which a Compound Engine Operates. .Cylin- der Condensation an Unknown Quantity. .Why Piston Rods of Cross Compound Engines may be the same Diameter. 14 CONTENTS. CHAPTER XXX. Amount of Water Needed for a Surface Condenser. .Effect of Condenser on Temperature of Feed Water. .Explan- ation of Rule for Water Needed. .How to Calculate the Power Developed by a Compound Engine. .Water Rate for a Compound Engine. .Adding a Low Pressure Cylinder to a Simple Engine. CHAPTER XXXI. Water for a Jet Condenser. .Volume of Water in Steam . .Density and Weight are not the Same. .How to Cal- culate the Density From the Weight and Vice Versa. CHAPTER XXXH. Size of Injection Pipe. .Explanation of the Rule for De- termining it. .Water Above and Below the Condenser. . Great Care is Necessary when Indicating an Engine. . The Horse Should Always be put Before the Cart. CHAPTER XXXIII. Steam Heating for Buildings. .Three Systems in Use.. Explanation of the Difference Between Them. .Heating and Ventilating with the Same Apparatus. .Heating in Winter and Cooling in Summer with the Same Ma- chinery. CHAPTER XXXIV. Four Different Ways of Piping the Direct Radiation System for Steam Heating. .Cost and Efficiency Com- pared . .Angle Valves are Recommended. .Water Ham- mer. .Admitting Steam to the System. .How to Locate the Position of a Globe Valve. .Asbestos Wicking for Packing Valve Stems. CONTENTS. 15 CHAPTER XXXV. Radiating Surface Necessary to Heat a Room .. Heating and Cooling Surface. . Effect of Glass Surface.. Re- ducing all Wall Surface to a Common Standard. CHAPTER XXXVI. Difference in Temperatures to be Considered when Esti- mating the Radiating Surface for a Room. .Allowances to be Made.. Area of Main Steam Pipe. .Two Rules for this Purpose. .Heating Surface of the Boiler.. Efficiency of Direct Heating Surface, and Tube or Flue Surface. CHAPTER XXXVn. The Value of Exhaust Steam for Heating Purposes. .How to Calculate the Cost of the Same. .Heavy Back Pres- sure not a Necessity. .How to Arrange the Piping for Good Results. .A Trap is Advisable. .Live Steam May be used in the Same System. CHAPTER XXXVHI. Strength of Shafting. .Conditions to be Considered.. Diameter of Wrought Iron Shafting to Transmit a Given Horse Power. . Example Illustrating the Rule . . Power That a Shaft Will Safely Transmit. .Diameter and Power of Steel Shafting. .Cast Iron Shafting.. Formula for Crank Shafts for Compound Engines. CHAPTER XXXIX. Diversity of Opinion Concerning the Power of Belting. . A Good Formula. .Half Angle of Contact. .The Size of Pulley Is a Factor. .Speed of Belting. .Safe Load.. Formula for Breadth of Belt for a Given Horse Power . .Strength of Double and Single Belts. .Endless Belts Are Recommended. 16 CONTENTS. CHAPTER XL. Why Do Steam Boilers Explode?. .Superheated Water Theory.. Heat Generated When Fires Are Banked.. Effect of Opening the Throttling Valve to Start the Engine. .When Steam Boilers Explode. .Accumulation of Electricity. .Is Lightning a Factor?. .Pumping in Cold Water. .Effect of Heating Plates Red Hot. CHAPTER XLL More About Steam Boiler Explosions. .Is Low Water the Only Cause?.. What Becomes of the Water When a Boiler Explodes?. .Effect of a Ruptured Plate. .Other Theories. .The Real Cause for Explosions. .It is Better to Know Before Than After. .An Evaporative Test Does Not Always Demonstrate the Value of a Boiler. CHAPTER XLII. Steam Boiler Explosions Still Further Considered .. Bor- ing Holes in the Shell. .Improperly arranged Settings. . Insufficient Bracing. .Poorly Constructed Braces.. Boilers Wear Out. .Illustrating the Work Done by a Boiler. .Circulation of the Water. .Effect of Unequal Contraction. ."Nobody to Blame." CHAPTER XLIII. Necessity for Covering Steam Pipes. .Best Kind to L^se. . Air and Coal. .Process of Combustion. .Air Necessary to Burn a Pound of Coal. .Weight and Volume of Air. CHAPTER XLIV. The Bursting Pressure of a Boiler. .Thickness of Boiler Plate. .Strength of Shell Plates. .Explanation of Rules Given .. Elastic Limit of Boiler Heads.. Safe Working CONTENTS. 17 Pressure of a Head Without Braces. .Tensile Strength and Elastic Limit. .Tons and Pounds. .American and English Practice. CHAPTER XLV. Boiler Heads. .Cast Iron Dome Heads. .Deflection Within the Elastic Limit. .Improving the Qualit}^ of Cast Iron ..Spherical or Bulged Boiler Heads . .Increasing the Safe Working Pressure .. Head and Shell of the Same Thickness. .Tensile Strength and Elastic Limit Must not be Called the Same Thing. Strength of a Concave Head. .Modifying Conditions. CHAPTER XLVI. Wrought Iron Heads for Boilers. .Steel and Cast Iron Heads. .Rules to Determine Elastic Limit of Heads Made of Different Materials. .Clear Distance Apart of Braces. .Rules to Determine Thickness of Plate, Strength of Plate, and Pressure That May Safely be Carried.. Are the Braces Strong Enough to Carry Their Load . .Estimating the Strength of Threaded Stay Bolts CHAPTER XLVII. Bracing Boiler Heads. .Details of the Problem. .Locating the Braces. .Illustrating the Rule.. The Surface to be Braced and the Pressure to be Carried. CHAPTER XLVIII. Segments of Circles. .What is a Segment ?. .The Arc and the Chord. .Illustrating the Rule . .Segments May be Larger or Smaller Than a Semi-circle. .Measuring the Length of Curved Lines. .Square Inches Supported by a Boiler Brace. .Number of Braces Needed.. Re- ducing tne Number of Braces. 18 CONTENTS. CHAPTER XLIX. Strength of Tee Irons. .The Web and the Flange. .Ten- sion and Compression. .The Neutral Axis. .The Flange in Tension.. The Datum Line.. The Axis a Fixed Point. .Some Parts of the Beam More Effective Than Others. CHAPTER L. Compressive and Tensile Strength of Tee Irons. .Lo- cating the Center of the Tensile Stress. .The Centre of Compressive Resistance. .The Total Compressive Re- sistance. .No Formula Given. .A General Rule. CHAPTER LI. Calculating the Load on Tee Irons. .Distributing the Braces. .The Span or Distance Between Supports.. Braces May be Needed Below the Tubes. .Always be on the Safe Side. CHAPTER LII. Collapsing Pressure of Tubes. .Application of the Rule. . A Large Factor of Safety. .The Length of the Tube Must be Considered. .Safe Working Pressure of Tubes and Lap Welded Flues. .Comparison of Rules.. Ex- amples Illustrating the Same, .Rule to Determine Thickness of Flues. .All Parts of the Boiler will Stand the Designated Pressure. CHAPTER LIII. Conclusion of the Whole Matter. .Time Required to Make an Engineer. .Sometimes Ignorant Engineers Claim to Know it All. .A Key for the Storehouse. .Re- liable Rules Based on Common Sense. MODERN EXAMINATIONS OF STEAM ENGINEERS BY W. H. WAKEMAN. CHAPTER I. INTRODUCTION. — THEORY WILL DO PRACTICE NO HARM. This book is intended to g-ive information to those eng'ineers who wish to qualify themselves to pass examinations and take out licenses to run stationary eng^ines in those localities where such licenses are required. To many engineers, who are interested in the business by which they g^ain a livelihood, but who are employed in localities where no licenses are required, the idea of g-oing before a board of examiners, passing- an exam- ination and receiving aleg-al document with a larg-e seal thereon affixed, stating- that the owner is quali- fied to care for and manage steam eng-ines and boilers, is a very fascinating* one, and the desire for knowledg-e which will enable them to pass an exammination almost universal. The writer has been amused in noting* the way in which some of them expect to g-et the necessary 20 MODERN EXAMINATIONS information, for while they have a fair situation, and no license needed, they are content to merely wish that they possessed the qualifications called for in other places, and are too "shiftless" to study up the points, but when they secure a situa- tion where their knowledge of steam eng-ineering- is to be put to a test they are very active. They will come to you full of zeal for the new conditions under which they are to work, state that they want to get posted, and g-ive you the idea that they expect you to attach a hose to their brain, in some mysterious manner, and start up a pump, and pump them chock full of information in about half an hour. Some of them expect to get a list of questions that the inspector will ask them, together with the answers to the same, and having secured these, and learned them in the same way that a parrot or jackdaw learns to swear, that they can then go up to the pompous looking official who presides over the inspectors' department, and compel him to give one of the coveted prizes. Reader, did you ever attend school in your boy- hood days, where long lessons in spelling were allotted you, and becoming desperate on account of repeated failures, adopted a plan which you thought would enable you to go home when the other boys did? This plan was to note 5^our po- sition in the class (near the foot), and select the words which it would naturally be your turn to spell, and learn them thoroughly. But do you remember how you were seized with consterna- tion when you discovered that the teacher began at the other end of the class to give out the words, thus putting those to you that you had not even attempted to learn to spell? If you have been through this experience, you were probably OF STEAM ENGINEERS. 21 impressed with the idea that the only sure way was to learn the whole lesson. And so it will be with men who expect to learn a few questions and answers, and so get a first-class license, for they will find that the answers that they did not learn are just the ones that they will be required to g-ive, and consequently the only sure way, if a first-class license is needed, is to learn the whole lesson. The whole lesson did we say? That means a great deal, for probably none of us have accomplished that feat, and in this respect the comparison does not hold good, but at the same time, if all engineers who carefully read the whole of this series of articles will make themselves familiar with all the subjects treated of, together with those that may be suggested by them, they will not fear to go before any board of examiners, and submit themselves to a fair test as to their knowledge of engines, boilers, etc. Occasionally we meet a man who claims that he knows how to run an engine, but that he cannot tell others how it is done, but such an excuse ap- pears to be very unsatisfactory, for while we may not be able to express ourselves in as correct language as others do, still if we really know how these things are done, we can usually find some way to tell it to others. The fact is that there are many good men in charge of steam plants who were formerly firemen, and through faithfulness and sobriety have been promoted, and get along after a fashion, without really knowing anything of the theoretical part of the business. Such men can keep their plants clean, practice economy in the use of supplies, and are devoted to the in- terests of their employers, but at the same time just as soon as any question comes up which re- quires a little *' head-work" to settle, they are 22 MODERN EXAMINATIONS ever ready to call upon others to help them out of their troubles, although at other times they affect to despise them, on account of being what they are pleased to term "book engineers" or *' paper engineers." Well, we are of the opinion that the well-posted ones can stand it if the others can, for it is a well-known fact that these men speak dis- paragingly of their fellows to divert attention from their own defects. I trust none of my readers are ready to admit that they are in this class, but if there are any such, allow me to ask a few questions. As you now claim to understand the practical part of your business, do you think that it would detract from the knowledge already possessed if you should acquaint yourself with the theoretical part of your occupation? As you now know that it is well to have your safety valve weight set so that the valve will open when the gage indicates 80 pounds pressure, and find it a good plan to lift the valve from its seat once every day, would it do you any harm if you knew how to determine the area of said valve, and also how to calculate the pressure at which it should lift, all necessary data being given, and then compare it with the results obtained in practice? Are you aware that such knowledge will tend to lighten the work in the fire room, and relieve the monotony of the ceaseless routine of the engine room? We beg pardon for this digression, and will return to our subject. While a list of direct questions are necessary in examining a candidate, still it is not the intention of the writer to give a catechism at this time, but the subjects will be treated in a more general way, believing it to be the best plan. OF STEAM ENGINEERS. 23 CHAPTER II. GENERAL OUTLINE OF SUBJECTS THAT SHOULD BE FAMILIAR TO APPLICANTS FOR OTHER THAN FIRST CLASS LICENSES. Applicants for a license other than first class are expected to have a general knowledge of the plant which they are to have charge of, for in these cases the license is given to run a certain plant, and will not qualify a man to take charge of any plant that he may be hired to run. A misun- derstanding concerning this point has caused some rather embarrassing mistakes, for if a man conceives the idea that it would be a help to him in securing employment, provided he has a license to show, and, acting on the happy thought, ap- plies for one on general principles, about the first question that he will be asked will prove to be a hard one to reply to, for he will be asked to state where he is to be employed, and as this is the very question that is puzzling him in his own mind, he can scarcely be expected to give an intelligent reph^ But having secured a situation, his next care should be to get a good idea as to the details of his plant. He should know the diameter of the cylinder of his engine, the length of the stroke and the number of revolutions per minute. He should be able to state whether it is an automatic or an adjustable cut-oif, or one of the fixed, cut-off, throttling type; the size of the steam and exhaust pipes should be given, and a 24 MODERN EXAMINATIONS general description of the whole eng-ine prepared, so that almost any question as to the size of any of the parts can be answered. The boiler or boilers should also receive attention, and a gen- eral description of them be prepared, including- their diameter and leng-th, the thickness of the material of which they are composed, and whether they are of iron or steel, the number and the diameter of the tubes or flues in them, the size of the furnaces and the kind of setting- adopted. The boiler feeders should not be over- looked, but the diameter of the water pistons or plung-ers g-iven and the length of their stroke. Whether an injector is provided or not, and, if so, is it of the liftitig- or the non-lifting- type, and its rated capacity should be known ; this to be determined by reading- the maker's catalog-ue, and an opinion g-iven as to whether the capacity of each of them, in cases where more than one boiler feeder is provided, is sufficient for the needs of the plant. It will do no harm for the candidate to review some ordinary questions concerning- his every- day practice in the eng-ine and boiler room, and as to what he would do in cases of emerg-ency. He should remember that his first duty on entering his boiler room in the morning is to ascertain where the water level in the boiler is, this always to precede the opening of the damper. It is not sufficient to know that there was three gages there the night before, and that, as the floor is not flooded, it demonstrates that it is still there, for there are several ways whereby it might have made its escape unnoticed. Probably there are few engineers who have not at one time or another found less water in the boiler than they anticipated, and although month OF STEAM ENGINEERS. 25 after month slips away and the above-mentioned precaution seems entirely unnecessary, still it should never be neglected, for no one can tell when such neglect will cause serious damage to be done. This also should receive all due atten- tion before firing up a boiler after it has been cleaned. He may be asked what he would do in case that he accidentally allowed the water to get low while the engine is running, to which he should always reply that he would never allow such a thing to happen, and if it is sug'g-ested that even the best of engineers forget to attend to their duties at times, he should never admit that it is possible for him to forget so important a thing as that. If, however, the feed pipe should burst, thus allowing the water to escape faster than it can be replaced, he should run the pump to its full ca- pacity, and, provided he can open the furnace door without being scalded, he should cover the fire with fresh coal or damp ashes, for the writer believes that this is a much better plan than to attempt to draw it, as when a fire is disturbed, it gives out a very intense heat for a few minutes. Of course a pipe may burst in such a way as to fill the furnace with steam and scalding water, thus preventing' the fireman or engineer from banking it, but in that case it will be so deadened down that it will not be capable of injuring the boiler. The size of the safety valve should be noted, and an opinion formed as to whether it is large enough for the purpose intended or not, and it is well to bear in mind the fact that careful engi- neers try their safety valves at short intervals, in order to know that they are ready to open when needed. It is the dutv of an eng-ineer to bank his fire 26 MODERN EXAMINATIONS and shut down the plant whenever he is convinced that the boiler has developed a weakness, caused by a blister, a fractured plate, or any of the other ag*encies which work to cause its destruction, when such weakness has advanced sufficiently to warrant it, and no consideration should cause him to continue to run with a high pressure, thus en- dang-ering* lives and property. The applicant should familiarize himself with the construction and operation of the slide valve, as it is quite possible that he may be shown a model and asked to set it properly, and if he should find that it is so made that it cannot be set so as to work properly, it would not be the first time that an eng-ineer has been so tested. These questions, as will be noted, are of a plain, practical nature, and every man who claims to be an eng^ineer should be able to readily answer them. OF STEAM ENGINEERS. 27 CHAPTER III. DIRECTIONS TO THOSE WHO DESIRE A FIRST CLASS LICENSE. We now come to matters with which the candi- date for the honor of holding- a first-class license must be familiar, in order to be sure of passing* a satisfactory examination. But a small proportion of the licenses issued are for this class, because it is much easier to g^et one of the lower g^rade, which usually answers every purpose. The applicant is deterred from seeking- one by the fact that if he applies for one of a lower g-rade '^but which may be sufficient to answer his pur- pose), if he fails to pass the examination, he may try it ag-ain in a few days, but if he wants a first- class license, more will be naturally expected of him, and furthermore, if he cannot meet the re- quirements at his first trial, he may be oblig-ed to wait for three months before another trial will be g-ranted him, and in the meantime the situation that he wished to take will be secured by someone who has already passed the ordeal once, and con- sequently knows just what to expect. We would not be surprised if the examination were far less rig-id after a man has become well known to the inspector. It is perfectly natural in speaking- of the diif er- ent parts which constitute a steam plant to men- tion the eng-ine first, which rule will be followed here, and in enumerating- the parts of the eng-ine 28 MODERN EXAMINATIONS we usually speak of the valve, and the machinery which operates it, first, and therefore we w^ould say that it is well for the applicant for a license to be thoroughly familiar with the principles here involved. There is a g-reat difference in the ways that men go about learning these things, for some of them appear to know no other way than to learn just how the several parts of a certain valve gear are to be adjusted in relation to each other, without understanding any of the principles which lie at the foundation of their operation. For instance, a man of this stamp will take charge of an engine, and among the first things that he will do will be to note the position of the eccen- tric on the crank shaft, the exact length of the ec- centric rod, and also of all of the other parts which are adjustable, and mark them in such a way that he will be able to replace them, should they ever become disarranged from any cause. Nearly all valves if properly made have lap, and if properly set they will have lead. This state- ment naturally suggests the question, what is lap? Let us suppose that the steam ports, or passages leading from the steam chest into the cylinder, are lyi inches wide, and when the slide valve is placed in the centre of its travel, the ends of it being made to cover up these ports, each end of it laps over the ports one quarter of an inch. That part which laps over the edge of the port towards the end of the valve is called outside lap, and that part which projects over the part toward the in- side or middle of the valve is called inside lap. These may not be good proportions but will do for illustration. The object in putting outside lap on a slide valve is to save steam by cutting off the supply from the boiler before the piston reaches the end OF STEAM ENGINEERS. 29 of the stroke. The object soug-ht in putting- on inside lap is to close the exhaust port before the piston reaches the end of the return stroke, thus trapping- in some of the exhaust steam, (filling- the clearance), and raising- it to some considerable pressure, according- to the speed of the eng-ine and the judgment of the engineer. The effect is to make the eng-ine run quietly by bring-ing- the reciprocating- parts to rest, by the piston striking- ag-ainst a cushion, as it were, and also to save steam, for the portion of the wasteroom at the ends of the cylinder, which are thus filled with exhaust steam will not have to be filled with live steam.. The term lead, as applied to the working- of the steam eng-ine, is partially self-explanatory, for it means that the action of the valve in open- ing- must lead the action of the crank, taking- the dead centre as a starting- point; therefore if when the engine is on one of its centres the valve is open one-sixteenth of an inch, we say that it has one-sixteenth of an inch lead. Of course we mean that it must be open on the same end that the piston stands at, and care must be taken to see that the eccentric is set so that when the eng-ine is turned over in the direction that it is to run, the valve will continue to open, for it is possible to set it so that while it may g-ive the valve lead, still if the engine be turned over by hand, the valve will immediately close, and it is quite plain that it will not run even if steam is ad- mitted under those conditions. These principles apply to all valves of whatever form, size or description, and it makes no differ- ence whether they slide or rotate, lift or swing* to give opening of port. It is the same whether the steam is admitted over the end of the valve or 30 MODERN EXAMINATIONS throug-h the middle of it. Whatever devices are used to turn the rotary motion of the crank shaft into the reciprocating motion of the valves does not affect them, and if engineers would be mas- ters of this idea it would save much hard work in studying" out how to set different valves. I do not mean to say that the eccentric would be in the same position on the shaft in all of the cases, for it would not, but the motion which opens the valve must precede the motion of the crank in every case. The connections between the crank shaft and the valves are made in different ways, and this will effect the position of the eccentric, for if a rocker arm is hung* at the bottom the eccentric must be put in a certain position to do its work properly, but if the rocker arm is changed and hung* in the middle, the eccentric will have to be put in an en- entirely different place, but the principle is the same, for the motion of the valve must be in ad- vance of the crank. To explain just what to do to set the valves of every kind of engine that is built would fill the pages of a large book, but if the eng-ineer tinderstands these principles, and then will carefully examine the engine that he is to adjust, he will soon see how the desired result is to be obtained. To reverse the engine, put it on the centre, and note the amount of lead that the valve has. Loosen the set screws, and turn the eccentric in the opposite direction from that in which it is intended that the engine shall run, un- til the valve has the same lead on the same end. Tighten the set screws, and the valve will be properly set, assuming that it was so before. OF STEAM ENGINEERS. 31 CHAPTER IV. REVERSING AN ENGINE. — THROW OF THE ECCEN- TRIC. — STEAM AND EXHAUST PIPES. While on the subject of reversing" an eng'ine, it is proper to speak of rules given by others for this purpose, which do not ag"ree with the one just g'iven, for when the seeker after knowledge meets with two or more rules which do not agree, he is perplexed to know which one to believe. In two different books which give a so-called rule for doing this, one of which claims to be the only practical work published, I find the following instructions given: To reverse an engine, place it on the dead Centre, remove the steam chest cover, and note the amount of lead that the valve has. Loosen the set screws in the eccentric, and turn it in the opposite direction until the valve has the same lead on the opposite port; then the engine will run in the opposite direction. This is a mistake, for when an engine is to be started from the dead centre (or a little past the centre) it must take steam on the same end, regardless of the direction in which it is to run. If an engine is on one of its centres, and the valve admits steam to the opposite end of the cylinder from where the piston stands, how can it be started in either direction? In the first place, the whole volume of the cylinder must be filled with steam, which would constitute a very large clearance, to say the least, and then as the piston is already at 32 MODERN EXAMINATIONS the end of the cylinder, how can it be forced any further in that direction? In turning* an eng-ine over from one centre to the other, it is interesting to note the difference in the travel of the crank pin and the wrist pin. There is before me, as I write the explanation of this problem, in a book written for the purpose of instructing* engineers in their duties: "A crank pin travels 1.1416 times further than the piston each revolution, or 0.5707 times further each stroke. For example, take an engine with a 12-inch stroke, the piston travels 24 inches and the crank pin 37.6992 inches each revolution, or the piston travels 12 inches each stroke and the crank pin 13.6992 per single stroke of the pis- ton." This statement is a.bout as badly mixed up as it could be, for in the case of an engine with a 12-inch stroke, the crank would be 6 inches long, and in making a revolution it would describe a circle whose diameter is 12 inches, and whose circumference is 37.6992 inches, and in making a single stroke or half a revolution, it will travel through just one-half of that distance. A few points about the eccentric may be of interest at this point. An eccentric is to all intents and purposes a crank and a crank pin. The distance from the centre of the eccentric to the centre of the hole bored in it for the shaft represents the length of the crank, and twice this distance gives us the stroke or throw of the eccentric, just the same as twice the length of the crank of an engine gives us the stroke of it. It is seldom convenient to take eccentric off from its shaft and measure these distances, therefore if it is desired to find the throw of it, while in posi- tion, measure the distance from the shaft to the edge of eccentric on the heavy side, and also on OF STEAM ENGINEERS. 33 light side. Subtract one from the other and the remainder will be the throw of the eccentric. The diameter of the eccentric represents the diameter of the crank pin in this case, and although these proportions are very different from those used for the crank of an engine, still the principle is exactly the same. Sometimes engineers will ask this question: "If an eccen- tric is turned down, say from 10 inches in diam- eter to 9 inches, will it affect the travel of the valve?" We wish to ask a question. Suppose that we take an ordinary crank on an engine, and this crank projects beyond the crank pin to the extent of 3 inches. If we turn it off so that it ic: 1 inch shorter than it was before, without dis- turbing the crank pin, will it affect the stroke of the engine? Of all those who read this chapter, probably not one will claim that it would, because as we have not changed the distance between the centre of the crank shaft and the centre of the crank pin, and this distance is what determines the stroke of the engine, so in putting the eccen- tric in a lathe and turning it down an inch, we have not changed the throw of it, because we have not changed the distance between the centre of the eccentric and the centre of the hole for the shaft. The applicant for a license should be able to calculate the size of steam pipe needed for any engine, and the old-time rule for this is that it should be one-quarter the diameter of the cylin- der. This may do very well for the slow piston speeds formerly used, but if that is sufficient for a speed of 300 feet per minute it does not necessarily follow that it will give the best re- sults for a speed of 600 feet. There is no unqualified rule that will apply to all cases, for 34 MODERN EXAMINATIONS it is quite evident that an automatic engine will need a lar§*er steam pipe than a throttling- one of the same diameter will, for in the former case all the steam must be admitted before the cut-off valve closes, which may averag-e at quarter stroke, while in the latter case, with a cut-off fixed at three-quarter stroke, the pipe will be admitting- steam during- a space three times as long- as in the former to do the same work. Por an automatic engine running at a high piston speed, the pipe should be one-third diam- eter of the cylinder, but for a throttling one, if it is one-quarter the diameter of the cylinder, it will answer every purpose, for there is such a thing as having a pipe too large, causing greater loss from condensation. If the exhaust pipe is four-tenths of the diameter of the cylinder, it will be large enough to allow the steam to escape freely, with- out causing back pressure. A smaller pipe will answer every purpose if the engine has only a light load, but when this is increased to the full capacity of the machine, unless it is of ample size, it will cause unnecessary back pressure, and that at a time when it will be of the greatest disadvan- tage. OF STEAM ENGINEERS. 35 CHAPTER V. STEAM AND EXHAUST PORTS. — DIMENSIONS OF DIF- FERENT PARTS OF AN ENGINE. The size of the steam and exhaust ports should receive due attention, and as the practice of the prominent eng"ine builders in desig'ning* them does not agree, it is rather puzzling- to any one who may seek to show that it will not do to depart from a rule that he may have adopted. One firm who manufacture a great many engines make the steam ports six per cent, of the area of the cylin- der and the exhaust ports 12 per cent, of it, while another high-grade engine builder makes them 8.7 per cent, and 10 per cent, respectively. These are good samples of their class, and from the re- sults obtained from them it is safe to say that the steam ports should have 10 per cent, of the area of the cylinder, and the exhaust ports 12 per cent, of the same. The reasons for this conclusion are as follows : The engines having a steam port area of six per cent., do not maintain the initial pressure to the point of cut-off while running at a piston speed of 500 feet, but the way that they exhaust the steam, even when very heavily loaded, is very satisfac- tory, while the engines with the 8.7 per cent, steam ports hold the steam line up remarkably well, al- though they are run at a slow speed, while an im- provement could be made in the exhaust ports, hence the conclusion that the steam port area 36 MODERN EXAMINATIONS may be made 10 per cent, of the cylinder area, and exhaust port area 12 per cent, of it, with g'ood re- sults. The diameter of the crank shaft should be one- half of the diameter of the cylinder, in order to be stiff enoug-h to avoid springing, with its accom- panying evils. Of course it is easy to find en- gines that have them smaller than "this, and still give no trouble, but on the other hand, those builders who take pride in showing that they put plenty of stock into their product adopt the above rule for size of crank shaft. If a deep key seat is cut in this shaft it weakens it materially, and to avoid this, at least one prominent maker (and perhaps more) has the shaft made larger where the fly wheel is to be lo- cated, so that the key way does not make it weaker than the main part of the shaft. If the diameter of the crank pin is .25 of that of the cylinder, it will give good results. As the wrist pin is supported at both ends, it is not necessary that it should be as large as the crank pin, so far as strength is concerned, but to make the wear on these pins as nearly equal as possible, it is frequently the custom to make them of the same diameter or nearly so. The connecting rod should be .23 of the diame- ter of cylinder in the middle and .18 of it in its smallest parts, and in order to reduce what is usually called the ** angularity of the connecting rod" as much as possible, its length should be six times the length of the crank. Sometimes we find a connecting rod made solid at one end and with the ordinary strap and key at the other end. This is done to keep the length of the rod, or, more properly speaking, the distance between the centre of the crank pin and the OF STEAM ENGINEERS. 37 centre of the wrist pin constant, for with the strap and key the wear tends to shorten this distance, and with the solid end it tends to leng"then it, so that it will always be the same, provided the brasses wear alike. The diameter of the piston rod should also be determined by the diameter of the cylinder, with perhaps some modification for very high steam pressures. With ordinary leng-ths in the case of a non-condensing- engine it should be made .15 of the diameter of the cylinder, for say 90 pounds or less, but if 130 pounds are to be required, .18 of it will be necessary for safety. It is the custom of some of the builders of me- dium-sized machines to make the length of the main bearing the same as the diameter of the cyl- inder. This is a very liberal allowance, still it is not necessary or practicable in the case of large engines. The lengths of the eccentric and valve rods are determined by the size of the engine, and their diameters vary greatly, and always will, for with a style of valve that works easy a light rod will answer every purpose, but with the same size of engine having a different valve it may require rods nearly twice as large as in the former case. When we speak of a counterbore in a cylinder we mean that it is bored larger at each end for a cer- tain distance, in order that the packing rings, as they slide back and forth in the cylinder, may not leave a shoulder at each end of it, which in the course of time would cause a pound when the engine passes its centres. As the rings pass partially over the edge of this counterbore, it is plain that a shoulder cannot be left there until the main part of the cylinder is 38 MODERN EXAMINATIONS worn to the full size of it, but by that time the cylinder will need reboring". Eng-ine builders frequently make the mistake of not counterboring" deep enough to allow the ring's to travel to it, which can sometimes be remedied by putting" in wider rings. OF STEAM ENGINEERS. 39 CHAPTER VI. CONDENSING AND NON-CONDENSING ENGINES. — DESCRIPTION OF DIFFERENT TYPES OF ENGINES. It will probably be necessary to explain the dif- ference between non-condensing* and condensing* engines, by stating that with the former steam is exhausted ag^ainst the atmosphere, while in the case of the latter it is exhausted into a condenser, and the air pump removes the pressure of the air, the effect of which is to reduce the back pressure. This will naturally suggest the question as to what the back pressure on an engine is, to which the engineer should reply that the steam acting on the piston to drive it forward gives us the for- ward pressure, and as there is always some pressure on the opposite side of the piston which tends to oppose its advance, this is very properly called back pressure, and the difference between these two is called the mean effective pressure. In giving the amount of these different press- ures it is customary to state what the average is for the whole stroke, or in other words what the mean pressure is. When the term back pressure is used, it is generally understood to mean the back pressure above the pressure of the atmos- phere, as for instance when we say that our engine is working under four pounds back press- ure, caused by heating the factory w^ith exhaust steam, we mean that there is four pounds back 40 MODERN EXAMINATIONS pressure above the atmosphere, but when mention is made of the back pressure absolute, we mean the total back pressure measured from a perfect vacuum. By initial pressure is meant the press- ure in the cylinder at the beg-inning* of the stroke, and by terminal pressure is meant the pressure existing- at the time that the exhaust valve opens to discharge the steam. The applicant for a license may be called upon to explain the difference between a throttling- and an automatic eng-ine, when he should reply that with a throttling- engine the point of cut-off is fixed, and the speed reg-ulated by a valve in the steam pipe, called the g-overnor valve, which admits more steam when the load is increased and less w hen it is decreased, but during- a fixed por- tion of each stroke (usually about three-quarters of it), while with an automatic engine the steam is admitted at nearly boiler pressure, and when suffi- cient has been admitted to complete the stroke it is quickly cut off. An adjustable cut-off eng-ine is one in which the speed is reg-ulated by throttling- the steam, and the point of cut-off is varied by means of a hand wheel on the outside of c\dinder. A compound eng-ine is one in which the steam is used in one cylinder, then exhausted into another, where it does more work, and is then exhausted into the atmosphere. A compound condensing- engine is a compound eng-ine with the condenser attached. A triple expansion eng-ine is one in which the steam is used in one cylinder (called the hig-h pressure cylinder) then exhausted into another called the intermediate, and then exhausted into another called the low pressure cylinder, and from thence into the atmosphere. If a condenser OF STEAM ENGINEERS. 41 is attached it is said to be a triple expansion con- densing- engine. A quadruple expansion engine is one in which four cylinders are used, the same steam passing through all of them, and then into the air, and if a condenser is added, it is called a quadruple ex- pansion condensing engine. The advantages and disadvantages of these sev- eral types may be summed up as follows: The throttling engine is used extensively for small mills and factories, on account of its simplicity and low first cost, but it is very wasteful of steam, and could not be tolerated for large powers where fuel is worth anything. The automatic engine is usually more complicated and consequently more liable to become deranged than the throttling engine, but is more economical in the use of steam, and for medium powers is very satis- factory. When a condenser is added it increases the complication, but reduces the consumption of fuel. An adjustable cut-off engine is a kind of a cross between an automatic and a throttling engine, but can be used to advantage where the load is rea- sonably constant during a part of the day, and is increased to a certain known extent during the remainder of it, for in that case the cut-off may be varied to suit the load. It is not probable that they will ever come into very general use for stationary work. The compound engine is economical in the use of steam only when the load is just right for it, but is expensive to run if the load is too light, and cannot be used to advantage if the load is a very heavy one. It is also complicated, and the first cost of it is large. The compound condensing engine is coming 42 MODERN EXAMINATIONS into very g-eneral use for large powers, on ac- count of its economy in the use of steam, and although it is complicated, and the first cost of it is very large, and intelligent supervision is abso- lutely necessary, still its economy more than overbalances these objections to its use. A high boiler pressure is essential to success. In the triple expansion condensing engine, the complication and first cost is increased, but owing to its greater economy it finds favor with some. The first cost of the quadruple expansion condensing engine is excessive, and the cost of keeping it in repair proportionately great. It requires the most intelligent supervision that can be procured, and its use is of necessity limited to the very largest powers, but where fuel is expen- sive it is a profitable investment. A very high boiler pressure is absolutely necessary in order to use the steam to good advantage. We sometimes wonder what sort of a machine the steam engineer of the future will be called upon to run. Will it have six, eight or ten cylin- ders? Just imagine an engine room containing an engine with ten cylinders, each one of which has four valves, with a total of 20 dash pots. It might do very well as long as everything is new and in good order, but how will it be when it has run for several years, with a record of only $1.37 spent for repairs, and the boss positively declin- ing to make any that year, because business is dull? And then, as a matter of course, the boiler pressure will have to be increased to a frightful extent, and boiler plates will compare favorably with the armor plates for the new cruisers that will be in course of construction at that time. But some will say that we have now reached the limit for all these things, but do not be too sure OF STEAM ENGINEERS. 43 of it, for you must remember that there were men who believed at one time that an engine could never be run at 150 revolutions per minute. 44 MODERN EXAMINATIONS CHAPTER VII. MEANING OF THE TERM "HORSE POWER." The term "horse power" is one that is very commonly used, but at the same time there are many eng-ineers, or men in charge of steam plants, that do not thoroug-hly understand it. Let us take for our starting- point a small en- g-ine made in the usual way, except that instead of a fly wheel it has a drum on the crank shaft, on which is wound a small wire rope. We have a piece of cast iron which weig-hs 33,000 pounds. We attach the end of the rope to the weigfht, and start up our eng-ine, which runs at 50 revolutions per minute. We time the weight as it goes up, and find that it rises just one foot per minute, with a mean effective pressure of 20 pounds in the cylinder. This is just one horse power. Now suppose that we attach two pieces of cast iron, each weighing 33,000 pounds, to the end of our wire rope, and start up the engine. It runs until the slack of the rope has been taken up, when it stops, and we discover that we cannot raise the two weights together. We now proceed to take the drum off from the crank shaft and put a gear wheel on in its place. We next put up a second shaft, on which we put the drum, and also a gear wheel just twice as large as the one on the crank shaft. We now start up the engine with its speed of 50 revolutions, and a mean effective pressure of 20 pounds, as before; we find that we OF STEAM ENGINEERS. 45 can just raise the two weights. Are we now using two horse power? Some will probably say yes, because we are raising just twice as much weight as we did be- fore, but in reality we are using just one horse power, as we did in the first experiment, for although we are raising twice the weight that we did before, it travels upward but one-half as fast, therefore the power consumed is the same in both cases. Now if we speed our engine up to 100 revolu- tions per minute with the same pressure as be- fore, our weights will travel upwards at the rate of one foot per minute, and then we shall be developing two horse power. If we increase the speed to 200 revolutions per minute with the same pressure, we shall raise the two weights at the rate of two feet per minute, and shall use four horse power to do it. We assume that the highest point of speed has been attained, and we still wish to do more work. Our next move is to increase our mean effective pressure to 40 pounds, and then we can raise four pieces of cast iron, each weighing 33,000 pounds, at the rate of two feet per minute, and shall con- sume eight horse power in doing it. By this explanation we trust that the meaning of the term "horsepower" is made plain, for it is 33,000 pounds raised one foot high in one min- ute, and it very naturally follows that to deter- mine the horse power of any engine we must ascertain the number of square inches in the sur- face of the piston, and multiply this number by the effective pressure acting on every square inch. This product must be multiplied by the number of feet that the piston travels per minute, and 46 MODERN EXAMINATIONS when we divide the product so obtained by 33,000 we shall know the horse power of the engine. We sometimes hear men say that they wonder how it is that such a small engine can do so much work, as for instance in the cases of the heavy road rollers that we see on our streets. The en- gines that drive them are small, but we do not always consider that while they are moving a heavy load still it travels but very slowly. If the same engine were put into a light wagon it could make it travel very swiftly, and few men that see it would consider it quite possible that it required fully as much power to drive the light wagon swiftly as it does to drive the heavy road roller slowly. We also hear men speak of putting on a small fly-wheel, and belting on to a large pulley on the main shaft, in order to get more power out of their small engine, but with a constant piston speed and mean effective pressure, the power of the en- gine is the same, regardless of the way in which it is connected to the machinery to be driven. In the foregoing illustrations the friction of the engine itself and of the gears was not spokea of, because it was unnecessary, for while it in- creases with speed and pressure, it has no effect on the raising of the weights, which represent the machinery in a factory. If a man says that he is running a 100 horse power engine, in reply to a question, what an in- definite answer it is. Take the case of the first illustration. There we had an engine of one horse power. In the last illustration we had an eight horse power engine, and yet it was just the same machine in both cases. It had not been en- larged in any of its parts, or strengthened in any way, and when it is shut down it will have exactly OF STEAM ENGINEERS. 47 the same appearance in both cases, and yet one day it is a one horse power machine and the next it is eig^ht times as large, if we were to judg'e by its rating-. It is just so with larger engines, for the principle holds good with them, as with smaller sizes. If an engineer is asked how large an engine he is running, and replies that it has a 20-inch pis- ton, a 4-foot stroke, and runs at 65 revolutions per minute, with a boiler pressure of 90 pounds, he conveys an intelligent idea of the machine in his charge, and if he adds that the mean effective pressure is usually about 35 pounds, the reply is complete, but not otherwise. 48 MODERN EXAMINATIONS CHAPTER VIII. CAECULATING THE HORSE POWER OF AN ENGINE. — SQUARE ROOT. The matter of fig'uring' the horse power of an eng"ine should be thoroughly understood by the applicant for a license, and by this we do not mean that he should simply know how to repeat the rule, but that he ought to be able to not only work out an example illustrating the workings of the rule, but if other questions are asked him on the subject he must be prepared to give a ready answer. To fully illustrate what is meant by the above, an example will be introduced here and worked out in full, so that it may te made plain. The horse power of an engine is required, the following data being given: Diameter of cylin- der, 18 inches; diameter of piston rod, 2.75 inches; stroke, 42 inches; speed, 65 revolutions per minute; mean effective pressure, 35 pounds. To find the area of a piston 18 inches in diameter we multiply 18 by 18, and the product by .7854, and find our answer to be 254.46 square inches. The area of a piston rod 2.75 inches in diameter is 5.93 square inches. Dividing this by two our quotient is 2.96. Subtracting this from the full area of the piston we have 254.46—2.96=251.5 square inches, which is the effective area of the piston. The area of the rod is to be deducted because the space occupied by it is not accessible for the steam to act upon, and we subtract but one-half OF STEAM ENGINEERS. 49 of it because it is on but one side of the piston, the whole of the other side being- effective. Mul- tiplying- the area of the piston by the speed, and this product by the mean effective pressure, and dividing- by 33,000, we have 251.5 X 455x35 -f- 33,000 = 121.37 horse power. This part of the problem is very easy to learn, but when it is pre- sented in another light, or perhaps it would be better to say that if other parts of data are g-iven, and other parts are to to be supplied by the can- didate, it may prove a stumbling- block to him, and undoubtedly will unless he has g-iven the matter some thoug-htful consideration. Suppose for instance, that he should be asked to state at what speed an eng-ine should be run whose cylin- der is 18 by 42 inches, with a mean effective press- ure of 35 pounds, in order to develop 121.37 horse power. In that case he would multiply 121.37 by 33,000, and divide the product by the mean effect- ive pressure, and the quotient so obtained by the area of cylinder or piston, 121.37 X 33, 000 -^- 35-=- 251.5=455 feet per minute. The piston travels seven feet per stroke and 455-^7=65 revolutions per minute. Suppose the question asked was, what the diam- eter of the piston should be if the stroke were 42 inches, the speed 65 revolutions, the mean effect- ive pressure 35 pounds, and the horse power developed 121.37? In this case he would multiply the power developed by 33,000, and divide the product by the mean effective pressure, and the quotient so obtained bv the speed in feet per minute: 121. 37x33, 000 --'35 --445 = 251. 5. To this must be added one-half of the area of the piston rod, which is 2.96, and 251.5+2.96=254.46 square inches. Now in ascertaining" the area of the piston, we multiply the diameter of it by itself 50 MODERN EXAMINATIONS and the product by .7854, consequently our next move in solving- the problem is to divide 254.46 by .7854 and the quotient is 324. We must now find the square root of 324. The following" rule for obtaining' the square root of any number that can be divided by four without a remainder is inserted here> because it will answer ever}^ purpose for man}^ of the numbers that en- g-ineers will use in making the above calculation. Divide the number by four and find the square root of the number so obtained. Multiply this by two and the product will be the desired square root. Applying- this rule to the case in hand we have 324-^4=81. This being' a small number it requires only a moment's consideration to show us that the square root of it is 9, and 9x2 — 18, therefore the square root of 324 is 18. If our cal- culation was for a 24-inch cylinder, the number that we wish to obtain the square root of w^ould be 576 instead of 324, and 576^4 = 144, and it needs but a moment to see that the square root of 144 is 12, and 12x2 = 24. And even if our engine were a 30-inch one, it would still be convenient to use this rule, for the number would then be 900, and 900^4^:225, and the square root of 225 is 15, and 15x2 = 30. There are, however, other sizes, both larger and smaller than these, which this rule will not answer for as well, and for such we can use the following- rule for whole numbers: (1) Point off from right to left, in orders or places of twos. (2) Ascertain the highest root in the first order and place it at the right of the number, as in long- division. (3) Square this root and subtract it from the first order. To the remainder annex the next order and double the root already found and place it to the left ':^f this dividend. (4) As- OF STEAM ENGINEERS. 51 certain how often this divisor is contained in all but the linal figure of the dividend, and place the quotient to the rig'ht of the root already obtained, and to the right of the trial divisor. (5) Multiply this divisor by the final figure in the root, and subtract as before. In like manner proceed until all the orders have been worked. In or- dinary business practice it is much more con- venient to take up a book of reference, which is usually at hand, and refer to the table containing the desired information, when the square root of a number is wanted; nevertheless, as this is some- thing of value to the engineer who wishes to become well posted, and as in the writer's opinion the rule, as given in some of the text books, is not readily understood, an explanation of its work- ings will be given in the next chapter. o2 MODERN EXAMINATIONS CHAPTER IX. TO INCREASE THE POWER OF AN ENGINE. EFP^ECT OF ADDING A CONDENSER. In order to illustrate the workings of the rule for extracting- square root of a number, and ap- plying- it to the case in hand, we will set down the number, which is 324, and our rule says: "First, point off from rig-ht to left in orders or places of twos." This bring-s our point between 3 and 2, g-iving- us 3 in the first and 24 in the second order. "Second, ascertain the hig-hest root in the first order," and that means to take the hig-hest num- ber which when multiplied by itself, the product will not exceed the number in the first order, "and place it at the rigfht of the number, as in long- division"; thus, 3.24(1. "Third, square this root," which means multiply it by itself, "and subtract it from the first order: 1x1 — 1 and our example is then as follows: 3.24(1 1 2 "to the remainder annex the next order" as follows : 3.24(1 1 224 "double the root already found, and place it to OF STEAM ENGINEERS. 53 the left of this dividend." The root already found is 1, and when it is doubled we have 2, and having" placed it to the left of this dividend our example stands thus: 3.24ri 1 2 j224 *'Pourth, ascertain how often this divisor is con- tained in all but the final fig-ure of the dividend." Now the final figure of our dividend is 4, and leav- ing- this off we would naturally say that 2 is con- tained in 22, 11 times, but this is not proper here, for it can in no case exceed 9, and as we can only assume a number for this place, and try it, in order to know whether it is correct or not, let us try 9, and place the quotient to the right of the root already obtained, and to the right of the trial divisor. When we have done this our exam- ple stands thus : 3.24(19 1 29)224 ^ *' Fifth, multiply this divisor by the final figure and subtract as before." This divisor is 29 and the final fig-ure in the root is 9, and 29x9 = 261. Now we cannot subtract 261 from 224, therefore we must try a lower number, and we will take 8. Our example is now as follows: 3.24(18 1 28)224 We now multiply 28x8 and our product is 224, which we subtract and find that we come out even, and the problem is solved : 54 MODERN EXAMINATIONS 3.24(18 1 28)224 224 The vsquare root of 324 being- 18, and therefore the piston must be 18 inches in diameter. Ag'ain, the diameter of the cylinder, the stroke, the speed and the horse power may be given, and the necessary mean effective pressure required. In this case we multiply the horse power devel- oped by 33,000, and divide the product by the speed, and this quotient by the area of the piston, the quotient so obtained being- the mean effective pressure. 121.37 x33,000-^455-^251.81=: 35 pounds. The horse power constant of an engine is found by multiplying- the effective area of the piston in square inches by its speed in feet per minute, and dividing- by 33,()00. The horse power may be de- termined bv multiplying- the horse power con- stant b}^ the mean effective pressure, if so desired. Sometimes an engine will not do the work re- quired of it, and it may be impracticable to increase the speed of it. In such a case if w^e can increase the mean effective pressure, we shall obtain more power w^ith which to drive machinery m direct proportion to the increase excepting- the increase in the friction of the eng'ine itself. This may be done bv increasing- the boiler pressure, or the size of the steam pipe, and making it more direct in reaching- the engine; by putting- on a more suitable governor; bv enlarging- the steam ports, or by lengthening the point of cut-off. To determine just which of these to do requires g-ood judg-ment, for it is quite plain that we shall not be OF STEAM ENGINEERS. 55 able to remedv the evil unless we know just where the trouble lies. If we g'et boiler pressure ap- proximately up to our throttling governor, with a full load on the engine, we shall know that our steam pipe is large enoug'h, and if practicable the boiler pressure should be increased. If we get boiler pressure in our steam chest we shall know that our pipe and throttling governor are not at fault, but if there is less pressure in the cylinder than in the steam chest, either the steam ports are not large enough, or the valve is not set properly. If our slide valve cuts off the steam at half-stroke, we can increase the mean ef- fective pressure by cutting some of the lap off from it, thus allowing* the steam to follow during a g'reater portion of the stroke. If this is done it will be necessary to reset the valv e. The ques- tion as to whether we will have boiler capacity sufficient for the new conditions must receive at- tention before alterations are made. Adding a condenser will make it possible to increase the mean effective pressure, but does not of itself in- crease the said pressure. If the mean effective pressure cannot be increased, or the engine speeded up, the power of it may be increased by putting* on a larg'er cylinder, but of course this cannot be carried to any very g'reat extent, for it is only fair to assume that when the engine was built the several parts were calculated for each other, with a certain marg-in for safety, and if we increase the size of the c\dinder verv much, the stress mav be too great for some other part to bear, and a wreck be the result. When an eng'ine is overloaded, the best way is to remov^e it, and put in a new one, adapted to the load to be carried. 56 MODERN EXAMINATIONS CHAPTER X. TO DETERMINE THE SPEED OF AN ENGINE BEFORE ADMITTING STEAM TO IT. — SIZE OF PUL- LEYS AND SPEED OF SHAFTING. Sometimes an eng-ine, especially if it be a small one, is shipped from the factory all ready to be put on to the foundation and belted up for use. In the absence of definite information, the pro- prietor would naturally ask the engineer that is to have charg-e of the machine how fast it is to run, and an inspector who is conducting" an examin- ation may ask a question, the reply to which will determine whether the engineer understands such matters or not. Of course any one could turn on the steam after the engine is ready to start, and when it is run- ning at full speed count the revolutions per minute and report the speed, but this may have to be de- cided on before the engine can be tried in this way. If the engineer will look the governor over carefully, he will find the number of revolutions that it is calculated to make stamped on it some- where, or at least this is the practice of the makers of the principal governors now used. The cut gears which transmit the motion of the governor shaft to the governor spindle and balls are both the same size, therefore they both > travel at the same speed. Now it should be re- membered that although the engine furnishes the OF STEAM ENGINEERS. 57 power to run the g^overnor, still the g'overnor de- termines the speed at which the eng-ine runs. Prom this it will be seen that the speed of the g'overnor pulley is the standard, and from this we must make our calculations. Let us suppose for illustration that the g'ov- ernor pulley is seven inches in diameter, and is to revolve 150 times per minute, and the pulley on the shaft is ten inches in diameter. How fast will the eng-ine run? 150x7-^-10 ==105 revolutions per minute. Sometimes there is no g'overnor pulley on the eng-ine but the required speed is known, and the question is as to what the diameter of the g'ov- ernor pulley should be. Suppose that the eng-ine is to run 90 revolutions per minute, and the pulley on the shaft is 18 inches in diameter, and the g'ov- ernor is stamped 120; 90x18^120 = 13.5 inches, which is the diameter of the pulley needed for the governor. But if we knew the speed of the eng-ine and wish to find the speed of the g-overnor the calcu- lation would be 90 X 18 -^ 13. 5 = 120 revolutions per minute. By the above examples, the workings of the following- rules are illustrated. To determine the speed of the driven pulley, multiply the speed of the driver by its diameter, and divide the product by the diameter of the driven. The quotient will be the required speed. To determine the diameter of a pulley required to run a shaft at a g-iven speed, multiply the speed of the driver by its diameter, and divide the pro- duct by the speed of the driven. The quotient will be the required diameter. If there are two lines of shafting- already located with the pulleys on, and the necessary 58 MODERN EXAMINATIONS Speed of the driven is kno^vn, and the required speed of the driver is desired, then multiplv the speed of the driven by its diameter, and divide the product by the diameter of the driver. The quotient will be the speed of the driver. These rules will enable the engineer to calculate the speed of any machine or line of shafting- in the mill or factory, excepting* that it does not take into account the slipping- of belts, and no rule can be formulated that will determine this accurately. These rules for calculating- the speed of shaft- ing- are based on the circumference of the pulleys over which the belt runs, althoug-h only the diam- eter is mentioned. This is done for simplicity, as when the diameters are used in both cases, the result is the same as if the circumference were broug-ht into the calculation. Suppose that we have one line of shafting- run- ning- 90 revolutions per minute on which is a pulley 36 inches in diameter. Prom this pulley, power is transmitted to another line of shafting* on which there is a 24-inch pulle3\ The belt con- necting* the two is 28 feet, three inches or 28.25 feet long-. Now if we take off the belt and stretch it out on the floor, and take a pulley that is 36 inches in diameter, and roll it along* leng-thwise of the belt, when we have traversed the whole leng-th of it, our 36-inch pulley will have revolved three times. If we take another pulley that is 24 inches in diameter and roll it over the belt in the same way, we shall see that it will revolve 4j^ times, therefore while the larg-e pulley revolves three times when on the shaft, the smaller one revolves Ayi times or 50 per cent. more. Fifty per cent, of 90 is 45, and 90+45 = 135, which is the speed of the 24-inch pulley. Or it may be done as an example in proportion OF STEAM ENGINEERS. 59 as follows: The circumference of the 36-inch pulley is 9.42 feet, and that of the 24-inch one 6.28 feet, and the larger one revolves 90 times per minute; therefore 6.28: 9.42: :90: 135. Ag-ain, if we work it out according* to the first rule g'iven for this purpose, we have 90x36^24 — 135, which demonstrates that all of the three ways are cor- rect. In this example we can readily see the end from the begfinning" without any fig-uring", but others involving* much different proportions may be worked out and proven in the same way. 60 MODERN EXAMINATIONS CHAPTER XI. HOW TO CALCULATE THE MEAN EFFCTIVE PRES- SURE. — SEVERAL KINDS OF CRANKS. In determining* the horse power of an eng'ine, three factors are necessary, namely: area, speed and pressure. The first two are easily ascer- tained, and so is the third, provided you have an indicator to do it with, but if an engineer is requested to tell how he would decide this point, he should reply that it can be done if the initial pressure, point of cut-off and back pressure are known, or at least a g-ood estimate of it may be g*iven. There are two ways of doing* this, and one of them is to take the g-iven data, and from it lay out an indicator card, and then determine the mean effective pressure from it, but as the matter of laying" out the theoretical expansion line will be spoken of in detail in another part of this book, it will not be explained here. The other way to do it is by calculation as follows : The initial pressure and point of cut-off being" g-iven, divide the leng-th of the stroke in inches by the number of inches traversed by the piston before the steam is cut-off. The quotient will be the ratio of expansion. Find the hyberbolic log-arithm of this quotient, and add 1 to it. Di- vide the sum so obtained by the ratio of expan- sion, and multiply the quotient by the absolute initial steam pressure. Prom this product sub- OF STEAM ENGINEERS. 61 tract the absolute back pressure, and the remain- der will be the mean effective pressure. For illustration let us take the case of an en- o-ine taking- steam at 80 pounds pressure, main- taining- it up to the point of cut-off, which takes place at one-quarter stroke, and assuming- that the valves and piston are tight. If the stroke of the eng-ine is 36 inches, and the cut-off at one- quarter stroke, then 36^4 = 9 inches, which is the distance travelled at quarter stroke; 36-=-9=4, which is the ratio of expansion. The h3^perbolic logarithm of 4 is 1.386, and adding one to it gives us 2.386, and 2. 386 -=-4 = .5965. The gage pressure being- 80 pounds, the absolute pressure is 80+14.7 =94.7 pounds; .5965x94.7 = 56.488 pounds aver- ag-e absolute pressure. As we assume in this case that there is no back pressure above the at- mosphere, we must subtraxt the atmospheric pressure, and 56.488 — 14.7 = 41.788 pounds mean effective pressure. A procf of the correctness of this rule will be given in the part treating of indi- cator cards. Some further explanation of the above may be of interest. The term "ratio of expansion" means the number of times that the steam is expanded or increased from its original volume. Thus if the cut-off takes place at one- third stroke, by the time that the piston has reached the end of the stroke the steam occupies a space three times as large as it did when cut off (excluding- clearance), and the ratio of expan- sion is said to be three. If the cut-off takes place at one-half stroke it is two, etc. Hyperbolic logarithms are a series of numbers by which arithmetical calculations are simplified. The logarithm of a number is the exponent of a power to which 10 must be raised to give that number. The number 10 is used because it is a conve- 62 MODERN EXAMINATIONS nient one, and not from necessity, as other num- bers mig-ht be taken as a base. To find the hyper- bolic log-arithm of a number, multiply the common log-arithm by 2.302585. Fortunately the books of reference which engineers use contain these in tabular form, so that no one thinks of fig-uring' them out in ordinary practice. In the above ex- ample the clearance is not taken into account, but when the rule is applied to any particular case the clearance in that case must be added to the stroke, and also to the space traversed by the pis- ton before the cut-off takes place, and it should be expressed in decimals of an inch. If the en- g-ine has a fixed or an adjustable cut-off, the point of cut-off may be determined by taking- off a cylin- der head, admitting steam to the steam chest, and turninof the en^-ine bv hand until the steam is shut off by the valve, when the distance may be noted on the guides. This should be done when the cvlinder is well warmed up, and the piston ring's may be tested by admitting steam to the oppo- site end, when the engine is on the centre. In the case of a slow-speed, long--stroke throt- tling engine, the initial pressure may be deter- mined by attaching- a steam gage to the steam chest, taking care to put a globe valve in the pipe, so that it mav be partially closed in order to pre- vent fluctuations of the pointer. The writer does not claim that the mean effec- tive pressure can be accurately determined in any other way than by using- a good indicator, but an approximation of it may be obtained as above stated. The elements of uncertainty are the tightness of the valve and piston under actual working conditions, the amount of compression, and also the exhaust opening. We all know what a crank is (althoug'h there are several kinds of OF STEAM ENGINEERS. 63 them), but if we were asked to tell what it is, some of us might be at a loss for a term to ex- press our meaning, unless we should remember that it is a device for converting the reciprocating' motion of the cross head into the rotary motion of the shaft. Some people evidently believe that there is a great loss of power in using the crank, and have made efforts to introduce some other de- vice that will answer the same purpose, but so far without success, and as a consequence the exprevS- sion that "the man who tries to improve upon the crank is a greater crank than the crank ever w£is, " is sometimes made use of. The term "valve gear" is used to designate all of the rocker arms, rods, cranks, etc., which form the connection between the eccentric and the steam and exhaust valves. A misunderstand- ing concerning' this is sometimes the cause of ludicrous mistakes, as, for instance, when a cer- tain man was told that the valve gear of the engine needed repairs, he thoug'ht that the bevel gears on the lower part of the governor needed attention, and when told that they were all right, said that they were the only gears on the machine. 64 MODERN EXAMINATIONS CHAPTER XII. RULES FOR DETERMINING THE WEIGHT OF FEY WHEEES. We have never discovered just why it was that a fly wheel received its name, but the fact remains that a wheel put on the crank shaft to answer the double purpose of helping* the engine to run steadv, and also to receive a belt for transmitting power, is so called. As the engine begins its stroke, it receives the steam at nearly the full boiler pressure. Soon it is cut off and begins to expand down, until when near the end of it there is but little pressure left, if the load is a light one. If there were no wheel on the shaft of a single engine, it would run at a very irregular speed, if it revolved at all, but as it is in practice the wheel causes the power stored up at the beginning of the stroke to be given out during the latter part of it, the result being economy in the use of steam and steady speed. After looking over the several specimens of fly wheels put on engines by their builders, we are caused to wonder if there has been any rule fol- lowed determining their size and weight. This is an open question, but nevertheless there are rules for this purpose which will give good results, one of which is as follows: 7,000,000--R2--D = P, in which R — revolutions per minute, D=diam- OF STEAM ENGINEERS. 65 eter of wheel, and P the number of pounds per horse power required in the rim of the wheel. This rule recognizes the fact that the efficacy of a wheel increases, not as its velocity, but as the square of its velocit}^ and as its diameter. This is shown by the way that the constant number 7,000,000 was obtained, which is as follows: An eng'ine having" a fly wheel which gave good results at a known load was taken, and dividing its weight by the horse power developed, and multiplying the quotient so obtained by the square of the number of revolutions per minute and by its diameter. Let us now explain and illustrate this rule, be- ginning by reading the formula as follows: Divide 7,000,000 by the square of the number of revolutions per minute, and the quotient b}^ the diameter of wheel. The quotient so obtained will be the number of pounds per horse power re- quired for the rim of the wheel. Por our example let us take the engine spoken of in Chapter 8, in which the diameter of c^dinder is 18 inches, the stroke 4-2, inches, speed 65 revo- lutions per minute, mean effective pressure 35 pounds, and horse power developed 121.37. It w^ll be necessary to assume the diameter of the wheel, and for convenience sake we will call it 15 feet. Apph^ing- the rule our first step is to square the number of revolutions per minute, and 65 X 65=4225. 7,000,000^4225=1656.8, and dividing this by the diameter of wheel we have 1656.8^15 = 110.45. The power developed is 121.37, and 110.45 X 121.37= 13,405.3165 pounds. This it must be remembered is for the rim of the wheel. Let us look for a moment at the foundation on which this rule is based. Let us suppose that this fly-wheel had been made for this engine, and 66 MODERN EXAMINATIONS is found to give good results. Taking this as a basis, we divide the weight by the power devel- oped, and multiply by the square of the number of revolutions, and by the diameter, 13,405.3165-^ 121.37x4225x15=6,999,768.75. This is not quite as much as the constant number given, but the difference is due to the fact that the fractions are not carried out indefinitely. There is another rule which may be preferred by some, and it is used bv many of our designers, as follows: Divide 12,000,000 by the sq lare of the diameter of the wheel in feet, and this quo- tient by the square of the number of revolutions per minute, and m_ultiply this quotient by the area of the cylinder in square inches and by the stroke in feet. Applying this rule as before, we have 12,000,000 -^ 225^4225x254.46x3.5 = 11, 221 pounds. This it should be remembered is to be the weight of the rim of the wheel, and is said to be sufficient to give good results for ordinary cases, but where the work is variable, as in rolling mills and some saw mills, the former is preferable, or may be exceeded, but it is well to bear in mind the fact that while in most cases where iron is used, to in- crease the amount of material used is to increase the strength of the machine, yet this does not apply to the rim of a fly wheel, owing* to the fact that when the weight is increased the tendency to burst is also increased. It may be well to speak of a rule for determin- ing the entire weight of wheel, and the following is one said to be used bv one of our most promi- D^X S nent engine-building firms : 785,400 — — =:W. D^XR^ d = diameter of cvlinder in inches, S = stroke in OF STEAM ENGINEERS. 67 inches, D = diameter of wheel in feet, R = revolu- tions per minute. This formula sig'niiies that the constant whole number 785,400 is to be multiplied by a fraction whose numerator is found by multipl3dng' the diameter of the cylinder in inches by itself, and the product by the stroke in inches. The denominator is determined by multiplyino* the diameter of the wheel in feet by itself, and also by the square of the number of revolutions per minute. The final product will be the weight of the entire wheel. Applying' this rule or formula to the case in hand we find the square of the diameter of the cylinder in inches to be 324. The stroke is 42 inches, and 324x42=13,608, which is the numer- ator of the fraction. The diameter of the wheel is 15 feet, and the revolutions per minute 65, therefore 15x15x65x65=950,625, which is the denominator, and the fraction then reads 13,608 950,625 and by dividing- each part by nine, or in other words by cancellation, it mav be reduced to 1512 ^ 105,625 In order to multiply our constant whole num- ber by this fraction, we must multiply it by the numerator and divide the product so obtained bv the denominator: 785,400x1512^105,625=11242.8 pounds for the entire wheel. We g-ive these rules just as we find them, trust- ing* that the examples have been worked out in such a way as to be plain and easily understood by the engineer of limited education, in order 68 MODERN EXAMINATIONS that he may make comparisons for himself. The first one is from a well known authority, while the second and third are from another source usually accepted as reliable. The results obtained differ widely, and it is proper that they should, for no one rule will apply to every case, for if we have a long-stroke, slow- speed eng-ine, running- a rolling- mill or a sawmill, or any other kind of a mill where the load varies g-reatly, it will need a heavier wheel than a hig-h speed eng-ine running- a dynamo or any other ma- chinery that operates in such a way as to make the load practically constant will; therefore, when a wheel is desig-ned, the kind of work that it is intended for must be taken into consideration. If the rim of a sound wheel is never run at a g-reater speed than 5000 feet per minute it will be within safe limits, but in desig-ning- a plant it would be well to make it less than this if possible. All fly wheels should be carefully balanced be- fore being- put into service, as it will tend to cause the engine to run steadier, the bearing's to run cooler, and the wheel will be safer. In bolt- ing- tog-ether the sections of a wheel, g-ood judg-- ment should be used, in order to avoid unneces- sary stress in screwing- up the nuts. OF STl^AM ENGiNEER&3. 69 CHAPTER XIII. BEFORE AND AFTER ADDING A CONDENSER. — IS THE MEAN EFFECTIVE PRESSURE EFFECTED BY IT? Reference has been made in a preceding- chapter to the practice of adding' a condenser to a non- condensing engine, and as the candidate for a li- cense will probably be called upon to answer some questions concerning- this appendag-e to an engine, he should g-ive the matter some attention. In a certain work on steam eng-ineering, which lies before me, I find the statement that in ordi- nary practice if we add a condenser we shall raise the mean effective pressure by 12 pounds. This authority does not tell us what becomes of this increase of 12 pounds, or how we can use it up. A careful consideration will show any one that to run a certain machine will require a certain mean effective pressure in the cylinder, and whether we have a condenser in use or not does not affect this pressure in the least. If we start up another machine the mean effective pressure will be increased at once, and it will be just the same whether we use a condenser or not. This refers to ordinary practice. If, however, we had an engine using steam whole stroke, and maintaining boiler pressure up to the end of the stroke, running* non-condensing- and without a g-overnor, then by adding- a con- denser we could increase the mean effective press- sure by putting on a condenser, but this is not 70 MODERN EXAMINATIONS ordinary practice, and in fact is seldom, if ever, found in every-day use. Assuming- this to be the case, the percentage of g-ain in pressure may be calculated as follows: Multiply the reduction in back pressure by 100, and divide by the mean effective pressure. Sup- pose that our boiler pressure is 80 pounds, and our mean effective pressure 80 pounds also. We reduce the back pressure by 12 pounds and 12 X 100=1200, and dividing- 1200 by 80 gives us 15, which is the percentag-e of g-ain in mean effective pressure. The above conditions are the only ones under which a condenser adds to the mean effective pressure. In ordinary practice, if our initial pressure is 80 pounds and our cut-off at one-third stroke, if we add a condenser and thereby reduce the abso- lute back pressure by 12 pounds, our g-overnor immediately reduces the forward pressure by 12 pounds, and as the mean effective pressure is always the difference between the forward and the back pressure, and they are both reduced alike, the mean effective pressure is just the same as it was before. This is a theory that has been proven to be correct in practice, many times over. If it is desired to know how much the addition of a condenser will allow us to reduce the boiler pressure, and maintain the orig-inal point of cut- off, the following- is a simple formula for express- ing- it : PxS p'X(H. P.+l) in which P =mean effective pressure, S stroke in feet, p'= point of cut-off, plus clearance expressed in feet, H. P. = hyperbolic log-arithm of ratio of expansion, P' =boiler pressure. OF STEAM ENGINEERS. 71 It sig*nifies that the mean effective pressure multiplied by the stroke in feet will g-ive us what we may term our first product. The point of cut- off, or in other words the distance travelled by the piston before the cut-off valve closes, in feet, plus the clearance, multiplied by the hyperbolic log-arithm of the ratio of expansion plus 1, will o-ive us our second product. Dividing* the first product by the second gives us the desired boiler pressure. Now if we assume that the initial and boiler pressure are both 80 pounds, the cut-off at one- quarter stroke, and not taking the clearance into account, which will affect the result but a very little, the mean effective pressure will be 41,788 pounds. The stroke is 3.5 feet and the cut-off is at one-quarter stroke. 3.5-^4=. 875. The ratio of expansion is 4, the hyperbolic logarithm of which is 1.386 adding 1 to it equals 2.386. The problem is then as follows: 41.788x3.5 = 70 pounds. .875x2.386 It is assumed that the condenser will reduce the absolute back pressure by 12 pounds. In case that the question is asked, as to how much the consumption of steam will be reduced by adding a condenser, maintaining' our initial press- ure, the answ^er is expressed in the following for- mula, assuming- the ratio of expansion to be six. Iv-i-R=l, in which L equals length of stroke in feet, R equals ratio of expansion ^assumed), 1 equals point of cut-off in feet. Applying" this to the case in hand, we find that 3.5-^6 =.583 feet, or .583 of 12 inches equals 6.996 inches. By this we see that whereas the steam followed the piston for 10.5 inches of the stroke before the condenser 72 MODERN EXAMINATIONS was made use of, it is now cut off at 6.996 inches, and therefore the volume admitted is less in direct proportion. If we were to calculate the amount saved fi.g'ur- ing" from these two volumes, we should have a simple problem in proportion, as the whole stroke would be taken as 100. 10.5: 6.996: :100:66.6. This is solved by multiplying- 6.996 by 100 and dividing- the product by 10.5. In other words, the consumption of steam would be reduced from 100 to 66.6 per cent., a saving of 33.4 per cent, on the face of it, as we sometimes say. It is possible that this would not be realized in practice, for while the volume admitted, as shown by the indicator, is as above stated, still, as the terminal pressure is less, the condensation would be more, which of course would effect the saving- in coal. In regard to the formula for determining the point of cut-off we would say, that as we have but one factor to start with, namely the length of the stroke in feet, and from this we must ascertain the other two, it is necessary to assume one of them and try it. If it does not prove to be cor- rect we must try another. In this case we as- sumed the ratio of expansion to be six, and the way to prove whether it is correct or not is as follows: Taking- the data which we now have, we must determine the mean effective pressure from it, by the rule given in Chapter 11 of this book. The cut-off is at one-sixth stroke, therefore the ratio of expansion of 6. The logarithm of 6+1= 2.7918 and dividing by six we have .4653 as a quo- tient. The initial pressure is 80 pounds by the gage, to which we must add the atmospheric pressure; 80+14.7=94.7, and .4653x94.7=44.06 pounds mean pressure. If the condenser re- OF STEAM ENGINEERS. 73 moves 12 pounds of the back pressure due to the atmosphere, we shall 2.7 pounds left, and 44.06 — 2.7=41.36 mean effective pressure. As it origin- ally was 41.788 pounds, the difference is but a fraction of a pound, and is practically identical. If it was not we should have to assume another ratio of expansion and try ag'ain. The author would state, in parenthesis, that he has indicator cards in his possession which prove these con- clusions to be correct in a remarkable degree. 74 MODERN EXAMINATIONS CHAPTER XIV. SAFE WORKING PRESSURE OF A STEAM BOILER. Having- devoted a larg-e portion of the preceding- chapters to answering- questions concerning- the eng-ine, we will now turn our attention to the boiler, but in doing- this what a transformation we have made. Prom the contemplation of the brig-ht, symmetrical eng-ine, we turn to the black, sooty and dirty boiler, but the man who aspires to be a licensed eng-ineer and to hold a first-class certifi- cate to that eifect, will find that there are many questions to be answered concerning- the "source of power," and that a knowledg-e of its construc- tion, the streng-th of the materials of which it is constructed, the comparative streng-th of the seams, of the manner in which it is braced, and other points concerning- it will be necessary. The first thing- that we will take up for consideration in detail will be the way to calculate the safe work- ing- pressure of any boiler. For illustration suppose that a boiler is made of iron three-eig-hths of an inch thick, the long-i- tudinal seams are double riveted, and the diameter of the shell is 60 inches. To this case the follow- ing- formula for determining- the safe working- pressure of a double riveted boiler will apply. Tx. 70x10,000 R safe working- pressure, in which T= thickness of iron in decimals of an inch, and R= radius, or OF STEAM ENGINEERS. /O one-half of the diameter. Then .375 X .70x10,000 -f- 30= 87.5 pounds safe working- pressure. Our first step in solving- this problem is to reduce Ys to decimals of an inch by setting- down 100 and dividing- it b}^ the denominator of the fraction, which in this case is eig'ht, and adding* ciphers to our dividend (100) until we can divide by eig-ht without a remainder. We find that by adding- one cipher our quotient is .125, which is one-eigfhth of an inch expressed in decimals, and by mtiltiplying- by three we have .375. This may also be done by adding- ciphers to the numerator and dividing- by the denominator. By adding- three ciphers, we can divide without a re- mainder and by pointing- off as many decimals in our answer as we have added ciphers we g-et the same result, 3,000-^8= .375 as before. We do this because the streng-th of boiler plate is estimated at a certain amount per square inch of sectional area, or in other words, a bar one inch square will require a certain amount of stress to cause it to break in two. As our plate is but three-eig-hths of an inch thick, it is proper that we should take that as a basis for our calculation. We multiply by .70 because the riveted seam is never as strong- as the solid plate, and where there are two rows of rivets it is estimated to possess .70 of the streng-th of the solid plate. We next multiply by 10,000 because g-ood boiler iron has a tensile strength of 50,000 pounds to the square inch of sectional area, and taking- one-fifth of this for a safe load g-ives us ihe number 10,000. If the tensile streng-th is 60,000 pounds and the factor of safetv 5 then we should have 60,000-i-5= 12,000 instead "of 10,000 and if it is 40,000, then 40,000--5 =8,000 pounds. The number that we 76 MODERN EXAMINATIONS divide the tensile strength by is called the factor of safety. "We divide b}^ one-half of the diameter, because in this case we have calculated the streng-th of but one side of the boiler, taking- one inch of its leng^th and therefore must not calculate on the whole diameter. This rule is probably as g-ood a one as can be found, as it takes into consideration all of the elements in the case except one, and that is it does not recog-nize the fact that all double-riveted seams do not possess the same streng-th. It is g-iven to us in this form because Fairburn found by experimenting* with double riveted seams that 30 per cent, of the streng-th of the solid plate was lost in punching-, but this does not g-o to show that all seams are alike, simply because they have two rows of rivets in them. Having- g-iven a rule which the writer considers to be a g-ood one, he wishes to speak of some others, and express an opinion concerning* them. Here is one that is published by a firm whose name is calculated to inspire confidence. Multiply twice the thickness of the iron by the tensile streng-th of sheet, and divide the product by diam- eter of shell in inches. Divide this product by six. For double riveted seams add 20 per cent. This rule apparently assumes that it is safe to carry but one-sixth of the bursting- pressure in every-day practice, but when we examine a little closer, we find that it is not as safe as it looks to be. It will be noted that the whole streng-th of the sheet is taken, no deduction being- made for the loss of streng-th due to the sing-le riveted joint. With this rule the factor of safety is but 3.5, which we consider altog-ether too small for the averag-e boiler. For the purpose of comparison, let us assume OF STEAM ENGINEERS. 77 the elements of the preceding- case and try it. Thickness of iron, .375; tensile, 50,000 pounds; diameter, 60 inches. Applving- this rule, we have .375 X 2 x50,000^60--6= 104.16 pounds for a boiler with sing*le riveted seams. Adding- 20 per cent, for double-riveted seams, we have 104.16+20.83= 124.99 pounds for safe load. Would not the aver- ag-e intellig-ent eng-ineer doubt the expediencv of carrying" 125 pounds pressure on such a boiler? Another authority g-ives us the following- formula: SBt2 =P DC in which S= tensile strength of plate. B= strength of joint. t= thickness of plate. D= diameter of shell. C= coefficient of safety. The ^'coefficient of safet}^" means the "factor of safety" which we assume to be 5. Now this formula, although it looks rather com- plicated, is really not so when explained. If we assume the elements of the preceding case it would stand as follows: 50.000 X. 70 X. 375x2 • =87-5 pounds. 60x5. It will thus be seen that this rule is identical with the first one quoted, although it appears in quite a different way. The following rule is also given us for determ- ing the safe working pressure. Divide the thick- ness of the plate in inches by the diameter of the boiler in inches, and multiply the quotient bv 7600 for an iron boiler with single riveted seams, and 9000 for double riveted seams. Applying- 78 MODERN EXAMINATIONS this to the case in hand we have .375-^60x9000= 56.25. Probably this is a "safe" pressure to carry on such a boiler, judg-ing- by the pressures that are safely carried on such boilers in every- day practice. Here are four rules g^iven us for determining- the pressure that it is safe to carry on a boiler of g-iven dimensions, which g^ives us three widely different results, and which of these are we to adopt? The first and third rules, g-iv- ing" 87.5 pounds for an answer, are undoubtedly the proper ones to adopt. The second one shows the eifect of competition as to who can allow the hig-hest pressure to be carried without disaster, while the fourth one is many years behind the times, and is not consistent with g'ood practice. We cannot tell how hig-h a pressure it is safe to carry until we know the actual streng^th of the seams based on the size and pitch of rivets, etc. In Chapter 15, due attention will be g-iven to this important factor, as in the preceding- cases we have only assumed that the seam possessed 70 per cent, of the streng-th of the solid plate. In a certain book, claiming- to g-ive correct rules and instructions to eng-ineers and firemen, I find the following-: "Rule to find ag-g-regate strain caused by the pressure of steam on the shells of boilers. Multiply the circumference in inches by the leng-th in inches; multiply this answer by the pressure in pounds." This is incorrect, for while such a rule will g-ive the total pressure on the shell of a boiler, it is not a proper way to determine the strain (stress) on the shell, as that is determined by multiplying- the diameter in inches by the leng-th in inches. OF STEAM ENGINEERS. 79 CHAPTER XV. STRENGTH OF THE SEAMS IN A BOILER. In considering' the streng'th of any riveted seam, it is very plain that it cannot be taken at an^^thing more than the weakest part of it. This may be in the rivets or it may be in the plate, or rather what is left oi it after it is punched or drilled. No joint can possess more streng-th than that due to the material left between the first row of holes, for it will make no difference whether there are one or two additional rows of rivets. The double welt butt joint owes its efficiency to this fact larg'ely, for in this case the rivets in the first row ma}^ be set wide apart, thus increasing* the net section of plate at this point. Suppose that we take up the illustration used in Chapter 14, in which the plate was 3-8 or .375 thick, the tensile strength of it 50,000 pounds, and assume the pitch of the rivets to be 3 1-16 inches (3.0625 inches) their diameter, when in position, 15-16 or .9375 inch. Now the pitch of the rivets mean the distance from the centre of one rivet hole to the centre of the next one, therefore when we wish to calculate the streng-th of this section of the plate, before the holes are punched, we must multiply the width of it by its thickness, which will gfive us the sectional area, and by mul- tiplying* the product so obtained by the tensile streng*th of iron, we shall have the streng-th of the section of solid plate. After the holes have been punched, as one-half 80 MODERN EXAMINATIONS of each hole is included in the section designated by the pitch of rivets, we must deduct the diam- eter of one hole from the section, when we wish to calculate the strength of what is called the net section of plate. Illustrating- the above ideas we have 3.0625 X. 375x50,000 =57,421 pounds, which is the strength of the solid plate. Deducting the diameter of one rivet hole, we have 3.0625 — .9375 X. 375x50, 000 =39, 843 pounds, strength of net section of plate. As we have now determined the strength of plate, at seam, let us calculate the strength of the rivets in the joints. In the sec- tion that we have taken there are two rivets in- cluded, for although in taking the pitch of the rivets, we include but one-half of two rivets in the first row, still, as there is another rivet directly between these two located in the second row, we must calculate on two rivets. The area of one is .69 and 69x2=1.38. If we take the strength of the iron in the rivets as being the same as that in the plate we must multiply 1.38 by 50,000 and our product is 69,000 pounds, which is the strength of the rivets. Again we find a difference of opinion among' ex- perts, for while some tell us that the iron in the rivets should be taken as the same as that in the plate, others claim that it is less, put- ting' it about .8 of it. If we should adopt this idea, we must multiply 69,000 by .8, giving' us a product of 55,200 pounds as the strength of rivets. The net section of plate is therefore the weakest, and by dividing 39,843 by 57,421 our quo- tient is found to be .69, or in other words, our double-riveted seam possesses 69 per cent, of the streng'th of the solid plate. In our original cal- culation we assumed it to be 70 per cent., which is near enough for practical purposes, under the OF STEAM ENGINEERS. 81 conditions named, but if the rivets were larg-er or smaller, or had a different pitch, the results would be different as a matter of course. By this we see that all the details of the joint must be given before we can tell the strength of it. Another rule for determining strength of net section of plate is expressed by the following formula: P-D =Plate, P in which P equals pitch of rivets and D equals diameter of holes. Applying this to the case in hand, we have 3.0625— .9375 • =69 per cent, of solid plate. 3.0625 Another rule for determining streng-th of rivets is expressed bv the following formula: AxR — =Rivets, PXT in which A equals area of rivets, R equals number of rows, P equals pitch of rivets and T thickness of plate. Apph^ing this to the joint that we have been considering, we have: .69x2 3. 0625 X. 375 eq vials 1.2 times the strength of solid plate. We have already shown that the strength of the section of plate is 57,421 pounds and 57,421x1.2= 68,905 or very nearly 69,000 pounds as before. This shows that the net section of plate is the weakest, as did our former calculation. These rules do not apply to the double welt butt joint, as now made for boilers of larg'e diameter, 82 MODERN EXAMINATIONS calculated to carry high steam pressures, for the first row of rivets are spaced much farther apart than is ordinarily done, or in other words given a greater pitch. The effect of this is to greatly increase the strength of the weakest part of the joints, namely the section of plate between the rivets, in the first row. Under any circumstances liable to be found in practice, the rivets in this joint are much stronger than the plate is, but if it is desired to calculate the strength of rivets it may be done by taking a section extending from the centre of rivet in the first row to the centre of the next one in the same row, and estimate it as a single-riveted joint. To this must be added the strength of the rivets in the second and third rows, for a section of the same width, and add the two together. In order to familiarize himself with these calcula- tions, the candidate for a license should practice on different problems along this line, supplying data himself. OF STEAM ENGINEERS. 83 CHAPTER XVI. BRACING FLAT SURFACES IN A BOILER. In the ordinary tubular boiler, the longitudinal seam is the one by which the strength of the whole structure is usually calculated, for the tubes strengthen the heads greatly, and from the nature of the case the curvilinear seams are sub- jected to much less stress than the others are. There is, however, a space on each head above the tubes, which must be held by braces, aud also a space below them in those boilers which have a manhole in lower part of front head, as all of them should have. It is a very good plan to have these braces extend from one head to the other, as they strengthen the shell in that case, without adding any unnecessary stress to the iron in the braces. Another reason is that they then are in a position to hold to the best advantage, as a brace standing at an ang-le greater or less than 90 degrees cannot hold as much stress on the heads as one that stands at right angles to the heads. Where they are put on from head to shell, their efficiency decreases as their length is made less, which fact is not always taken into consideration, judging by the way some boilers are constructed. In designing this part of a tubular boiler, it is necessary to take into consideration the surface to be braced, the pressure that it will be called upon to withstand, and the size of the braces. We are told that braces in a steam boiler should not be made to withstand a pull exceeding 6,000 8-1- MODERN EXAMINATIONS pounds per square inch of sectional area. If braces were made of iron one inch square it would be much less trouble to estimate their capacity, but as they are usually made of round iron, it is necessary to reduce them to square inches. A piece of round iron l}i inches in diam- eter contains a square inch of iron, practically, but if a brace is made of round iron 1.5 inches in diameter we must ascertain its area by squaring- its diameter and multiplying- by .7854, thus: 1.5 X 1. 5 X. 7854 = 1. 767 square inches. Now if each square inch of section may be depended upon to bear a stress of 6,000 pounds, in order to ascer- tain how much it will do to put on a brace 1.5 inches in diameter, we must multix3ly 1.767 by 6,000, and our product is 10,60^ pounds. Suppose that we find that we have a flat surface on one of our boiler heads, containing- 700 square inches of surface, and we wish to carry 90 pounds of steam pressure. By multiphnng- 700 by 90 we find that we have a load of 63,000 pounds to pro- vide for, and as each brace will hold 10,602 pounds, by dividing- 63,000 by 10,602 our quotient is found to be 5.94, therefore we shall need to put in six braces, in order to make the head safe. Braces should be very carefully inspected be- fore being- put into service, in order to guard ag-ainst defects in the iron, especially where they are welded, and we note with pleasure that braces are now in the market that have no welds in them, as we believe that this is a step in the rig-ht direc- tion. We wish to call attention to the fact that in cal- culating- the stress on a brace extending- from head to head, it is proper to take the surface on one head only, and not on both of them. This does not seem to be g'enerally understood by en- OF STEAM ENGINEERS. 85 g-ineers, althong-h much has been said on the sub- ject. The writer recalls an instance where he made this statement before a society of en- g-ineers, and one of them remarked in an exceed- ing-ly sarcastic manner that in his boiler there was a pressure on both of the heads. Well, what of it? We never doubted the truth of the state- ment, but as that fact has no bearing" on the idea that in calculating- the load on the brace, we must take the surface on one head only, we made no reply. If the brace extends from head to shell, there is just as much stress on it as if it extended from head to head. A brace should never be put from head to shell on the lower part of a tubular boiler, for where it is riveted to the shell it makes a place for scale to collect, and the flat part of a brace so put in prevents the water from coming- in contact with the iron of the shell, and that too in about the hottest part of the boiler. It is customary to rivet pieces of T iron to the flat head to be braced and then attach the braces to them. This, of course, g-reatly streng-thens the heads, and makes a g-ood anchoragfe for one end of the braces. It may not be out of place here to remark that where the rivet holes are drilled the sheets are strong-er than where they are punched, because punching- disturbs the fibres of the iron, but when drilled the edg-es of the holes are more sharply defined, therefore the rivets will shear more easily. However, the difference is in favor of the drilled holes. In calculating- the area of a boiler head to be braced it is not necessary to take into consid- eration the whole surface exposed to pressure, for the flanges impart stiffness to it, to a limited 86 MODERN EXAMINATIONS extent, according- to the thickness of the head. If it is 9-16 or ^^ inch thick it will do to leave a space of two inches from the shell, out of the cal- culation. This will receive further consideration in another chapter. OF STEAM ENGINEERS. 87 CHAPTER XVII. THE HORSE POWER OF A BOILER. — PRIMING AND FOAMING. This book would not be complete unless it con- tained instructions as to the proper way to calcu- late the horse power of a boiler. We occasion- ally see it stated in print that in the case of a tubular boiler 15 square feet of heating- surface constitutes a horse power. This may be correct and it may not be, for it will depend much on other conditions. In a preceding- chapter the proper way to calculate the horse power of an engine was illustrated and explained. Prom the data there given it will be seen that while the size of the cylinder is an important factor in solving- the problem, still that of itself does not determine the horse power of the engine, but other things must be taken into consideration. The square inches on the inside surface of the cylinder does not tell us the power of the ma- chine, neither does the square feet on the outside surface of a boiler tell us the power of it, for in either case it will depend on how much heat is ap- plied, etc. The only proper way to determine the horse power of a boiler is by the amount of water that it will evaporate per hour under given condi- tions. It will evidently make a difference whether this water is to be evaporated into steam of 10 pounds pressure or of 150 pounds pressure, for in one case it will require much more heat than in the other. bo MODERN EXAMINATIONS Ag-ain, it will make a difference whether the water to be converted into steam is hot or cold when it is delivered into the boiler. If it is put in at a temperature of 40° it will need more heat to convert it into steam than it will if it enters at 212°. From this it will be seen that some stand- ard must be adopted in order to bring- all of the different conditions under which boilers are run, to a common basis for the purpose of comparison. The standard usually adopted is the evaporation of 30 pounds of water per hour from a tempera- ture of 100° into steam at 70 pounds pressure. Now ag-ood tubular boiler, well set and properly run, will develop a horse power for each 15 square feet of heating- surface without doubt, and some of them are developing- nearly two-horse power for each 15 square feet of heating- surface, while others require 20 or more. Some firms who man- ufacture boilers allow one square foot of g-rate surface for each 36 feet of heating- surface, and this works very well in practice. The candidate for a license should bear in mind that no inflexible rule can be g-iven for determin- ing- the heating- surface of a boiler, as, for in- stance, some writers say take one-half of the sur- face of the shell of the boiler and two-thirds of the heads. This is evidently a mistake, althoug-h perhaps not a very serious one in its conse- quences, for if the brick setting* does not come in contact with the shell until it is above the centre line of boiler, then more than one-half of the shell is available as heating- surface. Many boilers are set in this way. To this should be added the internal surface of all of the tubes or flues. Ag-ain the area of one head up to the water line should be determined, and the combined area of the holes cut for the tubes subtracted from it. i OF STEAM ENGINEERS. 89 This will g'ive the heating" surface in the heads when multiplied by two. The water space of the boiler is that part of it which is occupied by the water, and is found by ascertaining- the area of one head up to the water line, as before referred to, and subtracting* the com- bined area of the holes cut for the tubes. Mul- tiply this by the leng-th of the boiler in inches and divide by 1728. This will g'ive the number of cubic feet of water in it. To chang-e to g-allons multiply by 7.5. To find weig-ht multiply the number of g-allons by 8.33. The steam space of a tubular boiler is found by ascertaining- the area of one of the heads above the water line, and mul- tiplying- it by the leng-th of the boiler in inches. Divide by 1728. If there is a dome the cubical con- tents must be added to the above. Por rules to determine areas of seg-ments of circles, see Chap- ter 48. When an eng-ineer says that his boiler "foams," it is g-enerally understood that he means that the water froths up into the steam space, so that it is almost impossible to tell where the true water level is. It is a dang-erous fault, and is usually caused by foul water or too small a steam space. Sometimes chang-ing- from salt to fresh water, or vice versa, will cause a boiler to foam. When we say that a boiler "primes," we usually mean that more or less water is continually carried oif with the steam, causing- it to be what is called "wet steam." When the report of an evaporative test is g-iven, it is unreliable unless the condition of the steam is known, for water carried off in this way is not evaporated, but when it is so counted, causes the boiler to be credited with g-reater efficiency than it is entitled to. If an uprig-ht boiler primes it may sometimes be 90 MODERN EXAMINATIONS stopped by removing- some of the tubes, thus in- creasing* the steam space. If it is a tubular boiler, and the priming- is excessive it may be stopped by putting- in a dry pipe. Priming- is a source of loss of fuel, and may result in injury to the eng-ine. Nearly all boilers prime more or less, and it may g-o on undetected for years, unless the steam is tested, as the glass g'ages give no in- timation of it. Generally boilers furnishing steam for auto- matic engines prime less than if the engine is a throttling one, taking steam nearly whole stroke. A separator is a device forming a part of the steam pipe, and is applied for the purpose of catching the water in the steam, and preventing it from going to the engine. Water so entrapped may be returned to the boiler at a high tempera- ture. 1 OF STEAM ENGINEERS. 91 CHAPTER XVIII. SAFETY VALVES. There are several rules relating* to safety valves which an eng-ineer who hopes to receive a first- class license should be familiar with, the first one that we shall call attention to being- the one, or rather several, for determining- the proper size of valve for any boiler. As we believe that the rule adopted by the United States Government is a very g-ood one, we shall speak of that first, and it says that we must allow one square inch of safety valve area for each two square feet of g-rate sur- face, in the case of a common lever valve, and allow one square inch of valve area to each three square feet of g-rate surface, if the pop valve is adopted. This refers to boilers using- natural draught, and for such it will be ample. We believe that the grate surface is the proper base for the calculation, rather than the heating- surface, for if the g-rate surface is large in pro- portion to the heating- surface, then if the size of valve was calculated from the latter, it might not be sufficient for the purpose intended, and become a danger valve instead of a safety valve. The English rule is to allow one-half square inch of valve area for each square foot of g-rate surface, which is identical with the above for natural draught and lever valve. Another one said to be Prof. Rank- ine's is to allow .006 of a square inch of valve area for each pound of water evaported per hour. It is rather a difficult manner to design a valve 92 MODERN EXAMINATIONS by this rule, for who can tell how much water the boiler will evaporate in advance? We could g-ive what migfht be called "a shrewd guess," but that would not fill the bill. Another one, said to be the French rule, is as follows: Multiply the grate surface in square feet by the number 22.5. This g-ives number one. Add the number 8.62 to the steam pressure al- lowed. This g-ives number two. Divide one by two and the quotient will be the area of the valve in square inches. This rule embodies a correct principle, for it takes into account the steam pressure to be carried, which it may be well to do, for steam of a high pressure will escape into the atmosphere more rapidly than steam of a low pressure will, the openings being the same size, therefore we shall need a larger valve for a boiler that IS to carry a low pressure of steam. It may be well to note, however, that the rule is defective in that the first number given should be much larger than it is to give correct results. For illustration, suppose that we have a 54-inch boiler with a grate surface of 25 square feet, to carry 80 pounds steam pressure. Applying the rule, we have 25x22.5=562.5; 80+8.62=88.62; 562.5^88.62 = 6.34 square inches valve area, which is just about one-half what it should be. A rule adopted by the German government takes into account the heating surface of boiler, and pressure to be carried, but as it is not com- plete without a table it will not be inserted here. If the candidate gives the first rule mentioned probably it will be all that will be required of him. We think that it is not generally understood that a valve having a bevelled seat will not give as large an opening as one having a level one will, and at first thought it will appear as if it would be OF STEAM ENGINEERS. 93 the same in both cases, for although the valve and seat may be on an angie of say 45°, does not the valve lift just the same, thus bringing- all parts of it at the same distance from the seat as if there was no bevel to be taken into account? If any one who is interested will draw a sketch of a valve and seat on an ang-le and represent the valve as lifted one-quarter inch from its seat, they can easily see that the distances measured at rig-ht ang-les to the seat, between the valve and the seat, is less than one-quarter inch, and as this is what determines the area of an opening, it must of necessity be less than a flat valve and seat would give. To determine what the area of open- ing will be the following rule is given, provided the angle is at 45° : Multiply the diameter of the valve by the lift, and this product by 2.22. Mul- tiply the square of the lift by 1.11. Add the two products and their sum will be the required area of the opening of valve in square inches. The rule for determining the area of opening of any valve, with a bevelled seat, at whatever angle it may stand, provided, of course, that the lift of the valve is less than the depth of the seat, is as follows: Mtiltiply the diameter of the valve by the lift, and this product by the sine of the angle of inclination and this product by 3.1416. This gives what may be termed the first product. Multiply the square of the lift by the square of the sine of the angle of inclination, and multiply the- product so obtained by the co-sine of the angle of inclination, and this product by 3.1416. This gives what may be termed the second product. Add the first and second products to- gether and their sum will be the area of the open- ing in square inches. If both valve and seat were flat, then all that we should have to do would be 94 MODERN EXAMINATIONS io multiply the circumference of the valve by its Lift and the product would be the area of the opening- in square inches. As these rules may not be fully understood by some, they will be illus- trated and fully explained in Chapter 19. OF STEAM ENGINEERS. 95 CHAPTER XIX. MORE ABOUT SAFETY VALVES. — HOT AND COLD WATER PUMPS. Por the purpose of illustrating- the rules given in Chapter 18 for calculating- the area of safety valve opening's we shall g-ive one example, in order that the results may be compared. The author finds that in many works g-iving- these rules, dif- ferent examples are g-iven for each rule, but this is not at all necessary, and, in fact, is a detriment, for if two rules are g-iven for solving* the same problem the results should at least very nearly ag-ree. Let us take a valve four inches in diam- eter with a seat bevelled to an ang-le of 45°, and assume that the lift is one-fourth of an inch. Applving- the fi'rst rule w^e find that 4x.25x 2.22=2^^22 which is our first product: .25x.25x 1.11 = .069375, which is our second product. Add- ing- these two together we find that 2. 22+. 069375 =2.289 square inches. It may be expressed in an abbreviated form as follows: DxLx2.22=A. L2 xl.ll=B. A+B=R, in which D=diameter of valve, L=lift of valve, A=first product, B = second product and R = area of opening-. Apply- ing- the second rule we find that 4x.25x.707x 3.1416=2.2211, which is the first product; 707x 707 X. 25 X. 25 X. 707x3.1416 = . 0693 which is our second product. When this product is written out in full it requires 17 decimal places to express it, but the result is not materially chang-ed by omitting 13 of them. 2.2211+.0693 =2-2904 square 96 MODERN EXAMINATIONS inches area of opening'. It may be expressed as follows: D XL XSX 3.1416 = F. L^ x S^ x C X 3.1416 = P. F+P=A, in which D= equals diam- eter of valve, L=lift of valve, S=sine of ang-le of inclination, C=co-sine of ang^le of inclination, F= first product, P= second product, A= area in square inches. If the valve and seat were flat, then we could make use of the third rule as fol- lows: 12.5664x25=3.1416 square inches. This rule may be expressed as follows: Cxiv = A, in which C= circumference, L=lift and A = area of opening* in square inches. We wish to call attention to the fact that the valve with a flat seat g^ives 37 per cent, more opening" than the one with a bevelled seat, at a 45-deg-ree ang-le, the lift being' the same in both cases, and as the ang^le decreases (from the perpendicular) the opening" g-rows less. The candidate should be familiar with rules for determining' the pressure at which a valve will blow off at under stated conditions; for telling* the leng-th of lever for a certain valve, and also the weig*ht required on a lever of g-iven leng"th to allow the valve to open at a stated pressure, and also should be ready to assume data for examples illustrating' all of these rules. He should also look up matters in connection with boiler feeders, and one of the inost difficult questions to g-ive a proper reply to, is how to de- termine the proper size of pump for a battery of boilers. Not that there is any lack of rules for this purppse, the most prominent one being- to provide a pump capable of delivering- one cubic foot or 7.5 g-allons of water per hour for each 15 square feet of heating- surface. This is usually sufficient, and oftentimes larg-ely in excess of what will be used at any time. How- OF STEAM ENGINEERS. 97 ever, it is well to have a pump large enough to do its work easily, for pumps should not be expected to run at the speeds given them in the maker's catalogue, as they are excessive. A good direct- acting pump will run at a very slow speed, and it is well to run it at from 25 to 50 strokes per minute, instead of from 100 to 300 as listed in some cata- logues. There is no way to tell in advance just how much water will be needed to operate a plant, but when the amount of coal consumed is known, then under average conditions the number of pounds of coal burned will be the number of gal- lons required. This of course, would not apply to plants that are used for heating purposes dur- ing the winter, and returning the water of con- densation by means of some trap, or other auto- matic arrangement, and for running an engine also, as the amount of water needed in the winter season is practically no more than what is needed in the summer time, although the amount of coal burned may be much greater. It is a very convenient way to refer to a pump manufacturer's catalogue when it is desired to know the capacity of a pump, but if it is desired it may be calculated by multiplying the diameter of water plunger by itself, and the product by .7854. By multipl5nng the product so obtained by the length of the stroke and dividing the product by 231 the number of gallons per stroke may be known. The formula is as follows: AxL =G 231 in which A=area of piston, L= length of stroke in inches, and G= gallons contained. If a part of this space is occupied by a piston rod it must be dedncted from the above. If any form of injector 98 MODERN EXAMINATIONS is to be used as a boiler feeder the capacity of it must be determined by experiment, or by consult- ing the manufacturer's catalogue. It ma}^ be well to remember that the capacity of an injector is much greater when the water is delivered to it under pressure than it is when it must lift its supply from a well or tank. A pump will take water much hotter than an in- jector (if the supply is above the pump,) because the steam supplying the injector must be con- densed and the water must be cold enough to do this. Hot water cannot be lifted as cold water can, because when the pump removes a part of the atmospheric pressure the partial vacuum is at once filled with vapor instead of a solid body of water. The only diiference between a hot water and a cold water pump is that if it is to be used for cold water only it is customary to make the valves of soft rubber, which answers every pur- pose; but if hot water is to be used, then the valves should be made of metal in order to insure durability. Sometimes hard rubber valves are used, but metal ones are better. It should be remembered that a larger pump will be required to pump hot water for a given plant, than for the same one if the water is to be cold when pumped. Theoretically, a pump that is perfect in every way should just raise a column of water 33.947 feet high at sea level, or rather it should create a perfect vacuum, and then the pressure of the atmosphere on the surface of the water outside of the pipe should force it up, but perfection is rarely obtained in worldly matters, and pumps are no exception to the general rule, therefore they should never be expected to ele- vate water more than 25 feet, and they will work better if it is even less than this. OF STEAM ENGINEERS. 99 CHAPTER XX. HEATING THE FEED WATER. — PROPER SIZE OF CHIMNEY FOR A STEAM PLANT. Under ordinary conditions water cannot be heated above 212° by exhaust steam without back pressure on the eng*ine (above the atmospheric pressure). A good form of heater, properly pro- portioned for the work that it has to do, will heat the water nearly as hot as this in every-day prac- tice, and in some cases water is delivered at the boiling- point almost constantly. This saves re- pairs on the boilers, by avoiding- excessive con- traction caused by pumping- cold water into a hot boiler. This alone will be of enoug-h value to repay the cost of a heater several times over, and we cannot g-ive a rule for calculating- just what this saving- will be, but the per cent, saved bv utilizing- a portion of waste heat in the exhaust steam may be determined by subtracting- the tem- perature of the water as it enters the heater from its temperature as it leaves the heater, and divid- ing- the remainder by the total heat of the steam in the boiler. For an example, suppose that we have water en- tering- at 40° P., and leaving- at 212°, and are using* steam at 70 pounds pressure; 212—40 = 172 Steam at 70 pounds pressure contains a total heat of 1210°; 172^1210 = . 14, or in other words the saving would be 14 per cent, on all of the fuel used over what it would be if the water were pumped in cold. 100 MODERN EXAMINATIONS In the case of a sing"le boiler using* 1% tons of coal per day, the cost of which is $3.50 per ton, the total saving* on fuel for one year of 300 days would be 3.50xl.50x.l4x300 = $220. It is not surprising, therefore, to note the very large num- ber of heaters that are manufactured at the present time, and that the variety of styles offered is so very great. If a heater is not giving satis- factory results an improvement may be made by covering it with some non-conducting covering, but the best results cannot be obtained unless the heater is large enough to allow the water to pass through it at a very slow rate of speed, that it may have time to take up the heat before it is dis- charged. In testing the heat of feed water, a valve near the heater should be opened, and the water allowed to run on to the bulb of a ther- mometer. If the candidate is asked to tell the difference between forced and natural draught he should state that by natural draught is meant the circu- lation of air through an ordinary chimney, caused by the difference in the weight of air on the out- side and the air and gases on the inside. The latter being the lightest are forced upward by the weight of the former, hence the draught is called natural. If a fan blower or steam jet is used to force the air and g'ases up throug'h the chimney, the draught is said to be forced. If the gases, or rather the products of combustion which are in the chimney are very hot they will be very light, and if they are very light they will ascend quickly, or in other words, the draught will be very strong. Thus may we reason from cause to effect as far as the draught is concerned, but when we go a little farther we see at once that if these products OF STEAM ENGINEERS. 101 of combustion are very hot, it means a loss of heat, which in turn means money thrown away. Now, if we close our ash-pit doors, and supply the air necessary for combustion by means of a pipe led into the ash pit, which, if supplied by a fan, and we regulate the discharg'e of air so that we can g"et just enoug-h to burn the required amount of coal or, in other woids, to keep up steam, it is plain that we can create a draught, and a strong* one, too, without depending- on hav- ing- a larg-e amount of heat g-o up the chimney to make it. To get the full advantage of this ar- rangement, we must have a large amount of heat- ing surface to absorb the heat. Prom this it will be seen that forced draught is more economical than natural draught is, provided all the condi- tions are right for it. The author does not wish to be quoted as being an advocate of using forced draught under the conditions sometimes found where it is used, for he is not. Such conditions are that the natural draught is used as long as it is sufficient to make steam enough to run with, and then the forced draught is substituted, simply because a stronger draught can be secured by so doing. We do not believe in running a plant in this way, as it is not economical in the use of fuel, and it also tends to wear out boilers much faster than when they are used under proper conditions. In designing chimneys it is a good idea to make the area equal to the combined area of the tubes discharging into it, plus 10 per cent, for a round chimney or 20 per cent, for a square one. The height of it will depend on the surroundings to a great extent. It should not be less than 80 feet, and if there are high buildings in close proximity to it, then it must be carried up higher. Some- 102 MODERN EXAMINATIONS times the area of the chimney is determined by the amount of coal burned on the grates per hour, as follows: First determine the necessar\^ height of chimney. Then multiply the pounds of coal that it is desired to burn per hour by the constant whole number 15. Divide the product so obtained by the square root of the height of the the chimney. The quotient will be the area of the chimney in square inches. For illustration, suppose that we have decided to erect a chimney 120 feet high, and wash to burn 12 pounds of coal per hour per square foot of grate surface, our grate being six feet square: 6x6 = 36 square feet of grate; 36x12 =432 pounds of coal per hour; 432x15=6480. The square root of 120 is 10.95, and 6480^10.95= 591.7 square inches. By consulting a table we find that a circle 27.5 inches in diameter contains 593.95 square inches, which is near enough for all practical purposes, therefore the diameter of our round chimney or stack should be 27.5 inches. Or 591.7-^.7854 = 753.3 and the square root of 753.3 is 27.45, which gives us the diameter practically the same as before. OF STEAM ENGINEERS. 103 CHAPTER XXI. DESCRIPTION OF THE SEVERAL PARTS OF AN IN- DICATOR DIAGRAM. In this connection, a general knowledge of the steam engine indicator, its construction, utility, use and care is essential. The applicant should be able to give readily a description of the principles on which it works, tell the names of the different parts of an indi- cator card, explain how defects in engines are de- tected by it, and give full instructions as to how to calculate the mean forward pressure from it, also the back pressure, and explain how to lay out the perfect expansion line, and estimate the water consumption from the card. The indicator consists of a small cylinder, in which there is a nicely fitted piston made so as to be steam tight without the use of packing rings of metal, and by means of suitable connections this piston operates a pencil, which draws the card on a piece of paper, and to the intelligent engineer this card tells just what is transpiring in the cylinder, so far as variations in the pressure are concerned, as plain as if they were written out by a typewriter. The indicator card does not tell us everything that we wish to know along this line, for in reality it is but a steamgage, telling us how much press- ure we have at all parts of the stroke, taking the line of perfect vacuum as a basis. Its principal 104 MODERN EXAMINATIONS use is to tell whether the valves are set rig'ht or not, and to measure the power developed b}^ the eng"ine. If a small card is taken at one time and a larg-er one at some other time, the difference be- tween the two represents the difference in the load at the time w^hen they were taken, other con- ditions being- the same. The indicator is of necessity a delicate instru- ment, and as such needs to be well taken care of, for even slight defects in it lead to conclusions that are erroneous, sometimes seriously so. A full description of all of the parts of a card is not necessary here, but mention of them by way of a reminder may be of interest. The admission line shows how and when the steam is admitted, the steam line shows how the amount admitted compares with the amount re- quired to g-et best results, the expansion line helps to locate leaks, the line of exhaust opening* tells us when the exhaust valve releases the steam, the counter-pressure line tells us how much back pressure we have, and the compression line tells us when the exhaust valve closes. After a card consisting- of the above lines is taken, the steam is shut off, and another line drawn, which is called the atmospheric line. Prom this a perfect vacuum line is located by measuring- downward, using- the scale correspond- ing- to the spring- used in the instrument when the card w^as taken. In places that are near the sea coast or situated on low ground inland, it is cus- tomary to put it at 14.7 pounds below the atmos- pheric line, but the author received a letter a short time ag-o, from a friend, who lives where the atmospheric pressure is but 11.5 pounds, so that when a card is taken from his engine, the vacuum line must be drawn 3.2 pounds higher up than is OF STEAM ENGINEERS. 105 ordinarily done. We know of no inflexible rule for calculating- this pressure by the heig-ht, for the air g-rows lig-hter very fast as we ascend, and moreover, it is not always of the same density or weig-ht in the same place, the variations being' indi- cated bv the barometer and the thermometer. 106 MODERN EXAMINATIONS Scientific observations made by a party travel- ing* to the Rocky Mountains show that at an eleva- tion of 6000 feet above sea level, the pressure was 11.48 pounds; when a point a little more than 14,000 feet high was reached it was 7.1 pounds. What we ordinarily call forward pressure of the steam on the piston is found as illustrated by Fig-. 1, in which S is the steam line of a card, E the expansion line, A the atmospheric line and V the line of perfect vacuum. Prom the point 1 draw a line 3 to the atmospheric one, and at rig^ht ang-les to it. Prom the point 2 draw a similar one, 4. The space enclosed by 3 on the right, the steam and expansion lines on the top, 4 on the left and A on the bottom represent the forward press- ure as we usually speak of it. If we wish to ob- tain the absolute forward pressure the lines 3 and 4 must be continued down to the vacuum line V, and this line then becomes the boundary on the bottom instead of the line A. What we usually call the back pressure on the piston is represented by the space enclosed by the line 3 on the right, and the counter pressure and compression lines C C on the top, the line 4 on the left and the line A on the bottom. If we wish to obtain the absolute back pressure, we must take the line V as the boundary of the lower side of the space. The difference between the two, namely, the forward and the back pressure, is the mean effective pressure. There are at least three ways of finding the mean effective pressure from the card, and one of them is to divide the length of it into 10 parts, and ascertain the aver- age height of the upper line above the lower one, measured on the scale corresponding to the spring used in the indicator when the card was taken. OF STEAM ENGINEERS. 107 . Another way is by using- the planimeter to trace over the card, and note the readings of the ver- nier. Then divide the number of the spring- used by the leng-th of the card, and mtiltiply the quotient by the reading- of the vernier. The product will be the mean effective pressure. Another way is to beg-in the tracing- with the planimeter, at some point at the right-hand side of the card, and g-oing- over it in the direction traveled by the hands of a watch, until the start- ing- point is reached. Then cause the tracer to travel in a perpendicular line until the vernier stands at zero or 0. The distance between the two points measured on the corresponding scale is the mean effective pressure. 108 MODERN EXAMINATIONS CHAPTER XXII. RULES FOR LAYING OUT THE THEORETICAL EX- PANSION LINE. In Chapter 11 we promised to g-ive a rule for la^dng" out the theoretical expansion line, and now is a g-ood time to do it. Referring- to Fig. 2, which is an ordinary indi- cator card, we will first draw the vacuum line V at a point 14.7 pounds below the atmospheric line, and the clearance line B at a point far enough from the admission line to represent the percent- ag-e of clearance. We will now make a dot on the expansion line at D and from it draw a line parallel to the atmospheric line, represented by D P. Now draw another line from D at right angles to the atmospheric line, as at D G. . Next from the point P draw lines 1, 2, 3, 4, 5, 6 and 7. Prom the points where these lines cross the line D P erect perpendicidar lines 0, 0, 0, 0, 0, 0, and from the points 1, 2, 3, 4, 5, 6 and 7 draw horizontal lines. The points where these lines intersect are the points w^here the expansion line should be. Por cards where the point of cut-oif is short, a very convenient way of laying* out the expansion line may be found illustrated in Pig. 3, in which the vacuum line is drawn in its proper place as be- fore, and also the clearance line. Draw the first vertical line through the point of cut-off, and the others the same distance apart that this is from OF STEAM ENGINEERS. 109 the clearance line. Starting* from the point of cut-off draw lines to the base of the vertical lines as shown. Where the slanting lines intersect the vertical ones are the points through which the expansion line must pass, as shown in the figure. The rule that was given in Chapter 11 for de- 110 MODERN EXAMINATIONS termining the mean effective pressure when the initial pressure and point of cut-off are known is a g-ood one, and this rule it may be remembered g-ave us a mean effective peessure of 41.788 pounds under stated conditions, but wishing- to demon- strate the matter to our own satisfaction we con- OF STEAM ENGINEERS. Ill structed a theoretically perfect card, but without the clearance line for convenience, assuming- the spring- to be 40. "We then carefully measured off the ordinates, and obtaining- the mean effective pressure from them found it to be 42 pounds. We then went over it with a planimeter and found the reading- of the vernier to be 5.16. The length of the card is five inches; 40^5x5.16=41.28 pounds. Going- over it again with a planimeter and after returning- to our starting- point, travel- ing- in a vartical line until the vernier stood at zero, and measuring- the distance between the two points, we found that the mean effective pressure was 41.5 pounds, and so we believe that the rule which calculated it to be 41.788 was correct. It is quite possible that cards may be furnished the candidate for a license which were taken from engines whose valves were improperly set, and he may be required to tell what the trouble was with them, and what the remedy is. Among- other thing-s that are shown by the card, we are told that from it we can calculate the amount of water used by the eng-ine in developing- power. This calculation is founded principally on the fact that if we know what the pressure of the steam is at the end of the stroke, we can ascertain what its weig-ht is from tables published for that purpose. As a pound of water evapo- rated into steam will still weig-h a pound, if we know the weig-ht of the steam it is ail easy matter to calculate how much water it took to make that steam. But after we have made all our calculation along this line the question naturally arises as to whether this will account for all of the water or not. A moment's reflection will convince us that it does not Suppose that 10 per cent, of the steam 112 MODERN EXAMINATIONS is condensed upon being- admitted to the cylinder. What then? The amount so lost is immediately replaced by more steam from the boiler, the pressure is created and maintained, and as the indicator is simply a steam g'ag-e, it can g'ive no in- timation of the loss of steam, or rather of water, from this cause. There is also a loss from radia- tion and other causes, so that when the water con- sumption is calculated from the card, and then a comparison made with the amount actually pumped into the boilers and they do not ag-ree, there is always some one ready to decry ^'theory " and claim that practice alone is of value. Where the water consumption is calculated from the card, it is not always proper to take the actual terminal pressure as showing- the amount of steam used, for the exhaust valve may open before the piston reaches the end of its stroke, and so cause the pressure to fall much more rapidly than it would were the fall due to expansion alone. Prom this it will be seen that the expansion line should be continued to the end of the stroke, and the terminal pressure measured from it, or usually it will be all right to take the pressure at the point of release, as the difference will be very small. Care should be taken to measure this pressure from the line of perfect vacuum. The water consumption may also be calculated from the pressure at the point of cut-off. Rules will be ofiven and explained at length in succeeding" chapters. OF STEAM ENGINEERS. 113 CHAPTER XXIII. CALCULATING THE WATER CONSUMPTION OF AN ENGINE FROM AN INDICATOR DIAGRAM. Our first move in explaining- the rule or rules for calculating- the water consumption by the card, or the water accounted for by the indicator, will be to draw the card Fig. 4. We have drawn it full size, in order that it may be the more readily understood. We believe that this card was taken from an engine whose cylinder is 24 inches in diameter, and the stroke is 48 inches, and the speed is 65 revolutions per minute. There was a No. 40 spring- in the indicator when it was taken. The point 2 is the point of cut-off, 3 is the point of release, 5 the point of compression, V the vacuum line, and 1 and 4 are lines drawn for Convenience in making- measurements. A few moments consideration will show that the pressure of the steam, taken for the purpose of calculating- the water consumption, must be reckoned from that existing- at the point of re- lease 3, or perhaps, more properly speaking-, what the pressure would be if the expansion line were extended until it intersected the dotted line 4, which means the end of the card. It will answer every purpose in a majority of cases to take it at point of release, as the difference will be unap- preciable. We repeat, then, that it is proper to take the pressure at the point of release, for it makes no 114 MODERN EXAMINATIONS difference what the initial pressure is, or where the point of cut-off is located, or how much steam was admitted after the cut-off valve closed, for the pressure existing* after all of these operations have taken place is that which indicates the weight of the steam, and from this we must . OF STEAM ENGINEERS. 115 decide the amount of water required. In this case the absolute pressure at 3 is 27 pounds. Referring- to *'A Manuel of Rules, Tables and Data for Mechanical Engineers, "by D. K. Clark, we find that one cubic foot of this steam weig-hs .0673 pounds. We must now ascertain how many cubic feet of steam at this pressure we are using* per hour, and we shall be able to tell how much the whole of it weig-hs, and the number of pounds ac- counted for, per horse power. Prom this it may be seen that the cubical contents of the cylinder must be ascertained, but the space occupied by the piston rod will not be taken out, as it will affect the result but very little. The area of a 24-inch circle is 452.39 square inches. The stroke is 48 inches; 452.39x48=21,714.72 cubic inches, which is the volume of the cylinder reckoned by the stroke, but asthe clearance must be filled with steam at each stroke it must be taken into account. It is stated at four per cent. 21,- 714.72 X. 04=868.58, and 21,714.72+868.58=22,583.3 cubic inches for each stroke. As the eng-ine runs 65 revolutions each minute, this space must be filled with steam 130 times during- each 60 seconds ; 22,583.3X130=2,935,829 cubic inches, and by divid- ing this number by 1728 we have 1699 cubic feet of steam used per minute. As one cubic foot weig-hs .0673 pound we multiply ag-ain and 1699 X. 0673= 114.3427 pounds per minute. As we wish to know the amount per hour we multiply by 60 and our product is 6860.56 pounds per hour. This then is the total amount of water accounted for by the indicator, according- to this mode of calculating- it. Our next move is to determine the horse power developed. The horse power constant is 7.13, and the mean effective pressure is 52.4, therefore 7.13x52.4= 116 MODERN EXAMINATIONS 373.6-horse power. Dividing* the total weight of the w^ater accounted for by the horse power devel- oped we have 6860.56-^373.6= 18.35 pounds of water per horse power per hour. This it wnll be noted is a very fair performance for a non-condensing engine. To some engineers this calculation may seem to be a very elaborate one, requiring many figures to put it in the proper form for inspec- tion, and it is hoped that the matter has been made plain step by step as it has progressed, and while no one can be expected to carry all these figures in his head, and draw them out to order when wanted, still if any one who is not thor- oughly familiar with the manner of solving such problems will study out the principle involved it will make what appeared to be a hard lesson to start wnth an easy one at the finish, and such cal- culations have an attraction for the engineer who is thoroughly interested in his business, as they tend to relieve the monotony of the ceaseless routine of w^ork in the engine and boiler-room, and furthermore the author will say, while speak- ing for himself, that these matters possess a fas- cination which is equalled by few others and excelled by none. But to return to the subject. However lengthy the above calculation may seem it is incomplete, as it does not take into consider- ation all of the factors which form a part of the complete whole. It will answer for all practical purposes, and is by no means to be despised, but a formula will now be referred to which embraces every point that can effect results, a most thorough and complete rule, and in fact, it may be termed a masterpiece. OF STEAM ENGINEERS. 117 CHAPTER XXIV. MORE ABOUT CALCULATING THE WATER CONSUMP- TION OF AN ENGINE. We will first give the formula as we find it for determining- the water accounted for per horse power per hour at the point of release. This formula is said to be used in the Massachusetts Institute of Technology: 13750 (R+E Wr)— (H+E Wh)= M.E.P. number of pounds of steam accounted for at re- lease, in which, together with another formula using pressure at point of cut-oif, the following symbols are made use of : ME P= mean effective pressure; C=portion of stroke completed at cut- off expressed in decimals; E=per cent, of clear- ance or the volume of clearance compared with the volume of the cylinder; R= proportion of stroke completed at release; H=propor- tion of stroke uncompleted at compression; Wc= weight of one cubic foot of steam at cut-off pressure; Wh=weight of one cubic foot of steam at compression pressure; Wr= weight of one cubic foot of steam at release pressure. An explanation of this formula is as follows: The constant whole number 13,750 is to be divided by the mean effective pressure, and the quotient so obtained we will set down by itself, calling it our first answer. To R we must add E, and mul- 118 MODERN EXAMINATIONS tiply their sum by Wr, and the product so ob- tained we will call our second answer. To H we must now add E, and multiply their sum by Wh, and this product we will call our third answer for convenience. Subtract the third from the second and multiply the remainder by the first. The product will be the pounds of water per horse power, per hour, at release pressure. We will now work out an example by this formula, taking- for illustration the card shown in Fig-. 4, Chapter 23, and when we substitute for the symbols their values taken from this card, our formula is as follows: 13750 f .%4+.04 X .0673)— (.071+.04 x .0411)= 16 53 52.4 pounds of water per horse power per hour. This is somewhat less than the result ob- tained by a former rule, but from the conditions stated it is only reasonable to suppose that it would be from the start, for the simple reason that while the first rule given counts all the steam lost, when it is released by the exhaust valves, this rule takes into account the fact that a portion of it is saved by the closing- of the exhaust valve before the completion of the return stroke, in other words by compression. In order to avoid any misunderstanding- on the part of those who are not familiar with such com- putations as these, we shall now offer a full ex- planation of the way in which the figures were ob- tained. The total leng-th of the card is 5.25 inches, and by measuring- from the end of the card to the point 3, we find that 27-28ths of the stroke has been completed when the exhaust valve opens, and reducing* it to a decimal fraction, we have .964. That is how we obtained R. The OF STEAM ENGINEERS. 119 clearance is estimated at 4 per cent, of the volume of *.the cylinder, judging- by the distance from the piston to cylinder head when on the centre, plus the volume of the ports, etc. Thus we obtained E. Wr was obtained from a table in the manual referred to previously by D. K. Clark. By meas- uring" from the point 5 to the end of the card, we find it to be three-eig-hths of an inch, or one-four- teenth of the whole stroke. 1-14= .071. In this way we obtained H. Wh was obtained from Clark's manual. If it is desired to obtain the water accounted for by the indicator at the point of cut-off, the following- formula should be used: 13750 (C+E W6-)— (H+E W^)= M.E.P. pounds of water per horse power per hour. When we substitute for the symbols their values as determined by the card Pig-. 4, we have the fol- lowing-: 13750 (.25+.04 X .2586;— (.071+.04 x .0411)= 18.48 52.4 pounds per horse power per hour at the point of cut-off. The process is as follows: 13750^52.4=262.4, which is our first answer. . 25+. 04 X. 2586= .074994, which is our second answer. .071+.04X .0411= .004562. .074994— .004562 X 262.4= 18.48 pounds. In this case the author has pursued his usual policy of illustrating- several rules g-iven, by using- the same data for all. It is a policy not always looked on with favor, as it shows up the difference too well, but as we are seeking- after knowledg-e, and as this book is written for the purpose of imparting* the same, it is better to look at these matters in their true 120 MODERN EXAMINATIONS lig-ht. When two or more rules are g-iven by g-ood authority it is often a difficult task to decide which one is correct, but if the candidate is well versed in his favorite, and can explain it in detail, probably no inspector would refuse him a license on account of small differences in the results ob- tained. Some further comparison will be made in the next chapter. OF STEAM ENGINEERS. 121 CHAPTER XXV. STILL MORE ABOUT CALCULATING THE WATER CONSUMPTION. The following- formula may be used for calcu- lating- the water accounted for at the point of cut- off: vs w =p H. P. In which V=volume of cylinder up to point of cut-off in cubic feet, S= number of strokes per hour, W=weig-ht of one cubic foot at cut-off pressure (absolute), H. P. = the horse power de- veloped, and P=the pounds of water per horse power. Assuming- the elements of the preceding- case, and again referring- to Pig*. 4, Chapter 23, we find that the area of the cylinder is 452.39 square inches. The cut-off takes place at 12 inches, and 452.39 Xl2yl728= 3.14 cubic feet. The speed is 65 revolutions per minute, or 7800 strokes per hour. The pressure at cut-off is 113 pounds, and the weig-ht of one cubic foot is .2586 pound. It was developing- 373.6 horse power. Then 3. 14 X 7800 X. 2586 ^373. 6= 16.95 pounds per horse power per hour. It will be noticed that w^e have not taken the clearance into account so far, for the reason that we wish to raise the question as to whether it should be a factor in the calculation, inasmuch as 122 MODERN EXAMINATIONS it is filled by compressing- the exhaust steam. As it is generally conceded that the amount of clear- ance in the cylinder will effect the economy of the machine, and some authorities at least deem it proper to recog-nize it when making* calculations, we should like to present another question con- cerning* it. In this case it is four per cent., that is, it possesses .04- of the volume of the whole cylinder, but if we are using* the volume of it up to the point of cut-off only, is it proper to call it the same? As we have reduced the entire volume under consideration to one fourth of what it was, and have not reduced the volume of the clearance, is it not proper to say that the percentage is four times as much, or 16 per cent? Viewing it in this light then we have 16.95 pounds per hour ; adding 16 per cent to it makes it 19.66 per horse power per hour. Putting the re- sults of the four rules together we have for the 1st rule, taking pressure at release, 18.36 pounds 2d " " *' *' " 16.53 3d " " *' " cut-off 18.48 4th " " " " " 19.66 Of course rules No. 1 and 2 should be classed to- gether, as the conditions are the same, and the difference in the results are not so large as they at first appear to be, for it is but 82 gallons per hour, even for this large engine, or less than 22 gallons for each 100 horse power developed. Rules No. 3 and 4 may be compared, and the dif- ference between the results is but 53 gallons per hour, or less than 15 gallons for each 100 horse power developed. In the rules No. 2 and 3 it will be noted that the water consumption is calculated directly from the card, without bringing the size of the cylinder into the calculation at all. This can be done OF STEAM ENGINEERS. 123 where the rate onh^ is required, as in this case, and shortens up the process materially. We wish to emphasize this, for the answer so obtained is the amount of water accounted for per one horse power per hour, and if the whole amount accounted for is desired (when employing- 124 MODERN EXAMINATIONS rulCvS 2 and 3), it must be multiplied by the power developed. In this book it has been one of the objects of the author to dispense with the use of tables as far as possible, but there is one which makes the calculation of the amount of water ac- counted for by the indicator such a simple matter that it is worthy of notice. This table w^as originally prepared by Mr. E. W. Thompson for the American Machinist, and in its orig-inal form is very full and complete, em- bracing* the terminal pressures from three to 60 pounds absolute, both included, advancing by tenths of a pound, but for all practical purposes the whole and half pounds are sufficient. To use the table, first ascertain the absolute terminal pressure and take the number opposite to it in the table, which is to be divided by the mean effective pressure. The quotient so obtained w^ll be the pounds of dry steam accounted for per horse power per hour. For the purpose of illustrating the utility of this table, let us refer to Pig. 5, which is a reproduction of a card shown in Pig. 4. The pressure at the point of release is 27 pounds absolute. The number in the table which is op- posite 27 is 927.990. The mean effective pressure of this card is 52.4 pounds; 927.990--- 52.4= 17.71 pounds dry steam per horse power per hour, or in other words, w^ater accounted for by the indi- cator. This as it stands is uncorrected for clearance and compression. If it is desired to do this, draw the dotted line, 6, in the figure, through the point of release parallel to the atmospheric line, and also the two vertical lines representing the ex- treme ends of the card. Ascertain the distance from the end of the card at the left to the place where the dotted line crosses the compression OF STEAM ENGINEERS. 125 line at 7. Multiply the pounds of water already accounted for by this distance in inches, and divide the product by the distance between the two vertical dotted lines. The quotient will be the water accounted for per horse power per hour, corrected for clearance and compression. Applying- the above we find that 17.71x5.1875 = 91.8706, and dividing" this by 5.25, we find our 126 MODERN EXAMINATIONS quotient is 17.50 pounds. In many cases found in practice, however, the conditions will be some- what different than with this card, an illustration of them being- shown in Fig-. 6. In this case the terminal exceeds the compression pressure (both being- absolute); therefore it will be necessary to extend the compression line as shown and pro- ceed as before. The data in this case is as follows : Release pressure 28 pounds; number opposite 28 in table is 960.120, and the mean effective pressure is 19 pounds; 960.120^19=50.53 pounds per horse power per hour. To correet for clearance and compression: The distance from the end of card at 8 to where the dotted line crosses the compression line is 3}i or 3.875 inches, and from the same point to other end of card is 3 11- 16 or 3.6875 inches; 50.53x3.875=195.8037 and dividing- this Ly 3.6875 g-ives us a quotient of 53.1 pounds per horse power per hour. It will be noted that this amount exceeds that obtained at first, which is what mig-ht be expected, as the compression is less than the terminal pressure. T. P. Number. T. P. 117-300 3-5 153-880 4.5 189-750 5-5 225. 240 6.5 260.540 7.5 295-440 8.5 330.030 9.5 364-400 10.5 398.640 II. 5 432.720 12.5 466.570 13.5 500. 220 14.5 533-850.. 15-5 Number. 135-748 171-945 207.598 242.970 278.063 312.800 347.273 381.570 4T5.725 449.688 483.435 517.070 550.638 OF STEAM ENGINEERS. T. P. Number. T. 567-360 16 600.780 17 633960 18 666. 900 19 699.800 20 732.690 21 765-380 22 798. 100 23 830.640 24 863.250 25 895.700 26 927.990 27 960. 120 28 992.380 29 1024. 500 30 1056.480 31 1088.320 32 1120.350 , S3 1152-260 34 1184.050 35 1215.720 36 1247.640 37 1279.460 38 1311-180 39 1342. 800 40 1374-320 41 1405.740 42 1437-060 43 1468. 720 44 1500.300 45 1531-800 46 1563-220 47 1594-560 48 1625.820 49 1657.000 50 1688. 100 51 1719. 120 52 1750-060 53 1780.920 54 127 P. Number. .5. .. 584.100 •5 . 617.400 ■5 . 650.460 •5 • 683.378 •5 . 716.270 •5 . 749.060 •5 • 781.763 •5 . 814.393 •5 . 846 965 •5 • 879.495 •5 . 911.865 •5 • 944-075 -5 . 976.268 •5 . 1008.458 •5 . 1040.508 -5 . 1072.418 •5 • 1104.350 •5 . T136.420 •5 . 1168.170 •5 . 1199.900 •5 . 1231.693 -5 - 1263.563 ■5 • 1295.333 •5 . 1327.003 •5 • 1358-573 •5 . 1390.043 •5 • 1421.413 •5 . 1452.900 -5 . 1484.520 •5 . 1516.060 •5 - 1547-520 -5 . 1578.900 •5 . 1610.200 •5 . 1641.420 5- . 1672.560 •5 . 1703.620 5- . 1734.600 •5- . 1765.500 •5- . 1796.320 128 MODERN EXAMINATIONS T. P. Number. T. P 55 1811.700 55.5 56 1842.960 56.5 57 1874.160 57.5 58 1905-300 58.5 59 1936.380 59.5 60. . . . 1967.400 60.5 Number. 1827.338 1858.568 1889.738 1920,848 1951.898 1983.888 OF STEAM ENGINEERS. 129 CHAPTER XXVI. CONCLUSION OF THE SUBJECT OF WATER CON- SUMPTION. There is still another style of card to which we wish to apply the rule, which makes use of a table, an illustration being- shown in Pig". 7. In this case the cut-off is very short, and as a consequence the terminal, or, more properly speaking, the release pressure, is below the atmosphere. This makes no difference, so far as determining- the water ac- counted for is concerned, but inasmuch as it may prove a stumbling'-block to some reader, we have deemed it best to introduce it at this point. Where the steam is expanded below^ the pressure of the atmosphere, and the exhaust valve is opened before the end of the stroke, the pressure rises instead of falling-, or, in other words, is just the reverse of what takes place w^hen the release pressure is above the atmosphere, therefore, the rule which tells us to continue the expansion line to the end of the card, carr^dng- it out in the same manner that it would have been carried out, pro- vided the exhaust valve had not opened before the completion of the stroke, applies to this case as well as to others which have been illustrated. As the release and terminal pressure are so much be- low the compression, we must continue the com- pression line downward as shown at 9 in the fig-ure. Applying- the rule w^e find that the termin- al pressure is 10.5 pounds absolute. The number 130 MODERN EXAMINATIONS Opposite 10.5 in the table is 381.57. The mean effective pressure is 10.25 pounds; 381. 57 -=-10. 25 = 37.22 pounds of water accounted for per horse power per hour uncorrected for clearance and compression. The distance from the end of the diagram at the OF STEAM ENGINEERS. 131 left to the point where the two lines cross at 10 is 3.875 inches, and the total leng-th of the card is 4.25 inches; 37.22x3.875^4.25=33.93 pounds cor- rected for clearance and compression. The en- gine from which this card was taken is one of the best made, and its builder has a world-wide repu- tation as a builder of first class machines, and yet the water rate is hig-h, and its efficiency low ac- cordingly, but what is the cause of it? Simply because it is underloaded. Suppose that more machinery should be put into the factory which is run by this engine until the terminal pressure would be 25 pounds instead of 10.5 pounds as at present. Then the water consumption would be reduced to about 20 pounds, although no change had been made in the engine. This shows the loss due to running an underloaded engine, but at the same time the machines in that factory are all running up to full speed, which could not be said if the engine had a heavy load to carry, for there would be times when the speed would be reduced, causing the output to be lessened, which would be a greater loss than is caused by what fuel is wasted under the present conditions, and this is a leak that cannot be detected by the indicator. Concerning a rule for calculating the water rate in the case of a compound engine, would say that we know of no better one than rule No. 1 as al- ready given for a simple engine, but in using it the high-pressure card should be made use of, and care taken to divide the total amount of water ac- counted for by the total power developed in both cylinders. The first rule mentioned, in w^hich the table given in Chapter 25 is used, may be applied to the case of a compound engine, using the diagram 132 MODERN EXAMINATIONS from the low pressure cylinder for the calcu- lation. These rules are useful for the purpose of making" comparisons of different engines, and also of the performance for the same eng-ine under varying conditions. OF STEAM ENGINEERS. 133 CHAPTER XXVII. CAUSES FOR DEFECTIVE INDICATOR DIAGRAMS. While the indicator points out many defects in valve setting-, and also in the construction of the steam engine, still when a card is taken and found to be imperfect, it is not wise to "jump to a conclu- sion" as to the cause of the trouble, as there may be more than one cause for it. Take for instance, the case of a card or diagram that shows a higher terminal pressure than should be according to the ways of laying out the theoretical expansion line illustrated in Chapter 22. We would naturally conclude that the steam valve leaked, thus admit- ting more steam after the cut-off had taken place, and raising the expansion line accordingly, but such a conclusion might be an erroneous one, as the defect may be due to re-evaporation, that is, there may be water in the steam w^hen first ad- mitted to the cylinder, or it may be due to initial cylinder condensation, by which we mean that the cylinder walls may have been cooled down by a low terminal pressure during the previous stroke, so that when steam is again admitted, although it may have been dry, still the effect of this lower temperature is to cause some of the incoming steam to be condensed at once, but after the cut- off has taken place and the pressure grows less as the piston advances, this water of condensation is again evaporated by the heat present, and hence the expansion line is raised. 134 MODERN EXAMINATIONS Again, it is often inconvent to ascertain the exact clearance, so that the best that we can do is to approximate it, and if it is really more than we have calculated on, then the actual expansion line will be above the theoretical one, althoug-h no steam has been admitted since the cut-off took place. On the contrary, if the actual is below the theoretical expansion line, it may be due to the fact that, in estimating- the volume of the clear- ance, an error has been made in calling* it more than it really is, so that the only cause for differ- ence betw^een the. two lines is this error in the be- g-inning" of the process. However, if the engineer is satisfied that no error exists here, the fall in the expansion line points to a leak in the piston, for, as it is pushed forward, some of the steam passes by it, over into the other part of the cylin- der hence the undue fall in pressure. Or it may be that the exhaust valve leaks, thus allowing* some of the steam to pass out to the exhaust pipe with- out doing- its share of the work. There is at least one other reason for this fall in the line which will only apply to extreme cases, and that is excessive condensation, after a cut-off has taken place. If an eng-ine is located in a very cold place, without suitable protection by lag-g-ing- or covering* with some non-conductor, and the weather is cold, then the condensation is g-reat, and will cause the line to fall when no defect exists in the eng-ine itself. If the line falls in a proper manner for a time and then suddenly rises, it shows that the steam valve is reopened, thus admitting- another charg-e of steam, before the completion of the stroke. In the case of some eng-ines it is not such an easy matter to lo- cate the cause of such distortion as mig-ht be sup- posed. A certain engine having valves which are OF STEAM ENGINEERS. 135 actuated in a similar manner to the Corliss valve, was found to be in a bad condition. A diagram taken from it showed that the steam valve re- opened at about five-eighths of the stroke. An examination of the eccentric showed that it was in its proper place. On the hub of the jim-cranks which operated the steam valve was a mark which corresponded to a similar mark on a collar located on a sleeve which formed a bearing- for the valve stem. With the engine on the centre, these marks were found to be in such a position as to form one continuous line, thus showing that the valve w^as properly set. Still, when another diagram was taken, it was very plain that the valve reopened as before. When the bonnet on the other side of the cylinder was taken off to compare the marks on valve and cylinder, it was found that they did not agree, thus showing plainly that the valve was not properly set, and at the same time pointing out the fact that it was due to a twist in the valve stem. If the expansion line falls very suddenly at say three-quarters stroke, it indicates that the ex- haust valve opens sooner than than it ought to. If the counter-pressure line rises suddenly before it is time for compression to begin, it indicates that the exhaust valve is closed sooner than it ought to be, and if the compression exceeds the initial pressure, it also shows that the exhaust valve closes too soon, and this is not only a wasteful condition of affairs, but a dangerous one as well. It is wasteful because it causes the point of cut-off to be lengthened to run the same amount of machinery, causing a direct waste to that ex- tent, and it is dangerous because it brings a greater pressure to bear on the cylinder head than has been calculated on in some cases, and 136 MODERN EXAMINATIONS also because if there should be water carried over for any cause, and the cylinder is not perfectly drained during* the return stroke, there is more reason to believe that the effect will be disastrous than if the compression is light, under normal conditions. No inflexible rule can be given for the amount of compression that will give best results, but it is only reasonable to assume that the greater the speed the greater will be the com- pression advisable, other conditions being equal. OF STEAM ENGINEERS. 137 CHAPTER XXVIII. POWER DEVELOPED BY DIRECT STEAM AND BY EXPANSION. The indicator diagram enables us to tell, in ad- dition to other things, how much of the work done is furnished by steam direct from the boiler, and how much is furnished by the expansion of this steam. Suppose that we take an indicator card in which the admission line is at the left hand and the ex- pansion line at the right hand. We will draw a perpendicular line from the point of cut-off down to the line of perfect vacuum. Now all of the space at the left of our perpendicular line between the steam line and the vacuum line represents the work by direct steam pressure, and all of the space at the right of the perpendicular line be- tween the expansion line and the vacuum line represents the work done by the expansion of the steam. It has been claimed that when we take into ac- count the work done by direct steam pressure we should stop there, as that is all that there is to it, and that to figure in the expansion of the steam is to claim to get double duty out of it, but we do not see how it is possible for this claim to be made good, for when the steam is cut off in the cylinder it is not all used up at once, for the force in it at the point of cut-off has been supplied di- rectlv from the boiler, as none of the benefits of 138 MODERN EXAMINATIONS the expansive qualities of it have been made use of, so far as performing* work in the cylinder is concerned, and if it were immediately exhausted at this point there is no doubt that it would re- quire more coal to devolop 100-horse power than it does at present. The proportion of the work done during- ex- pansion, to that done during- the time that the steam is admitted to the cylinder up to the point of cut-off, is represented by the hyperbolic log-ar- ithm of the ratio of expansion. Suppose that the ratio of expansion is four, the hyperbolic log-ar- ithm of which is 1.3863. Then if we call the amount of work done previous to cut-off unity, or in other words call it one, then the work done during- expansion will be 1.3863, hence the rule. To find the work done during- expansion, multiply the hyperbolic logarithm of the ratio of expansion by the work done during- the period of full steam. The product will be the work done during- expan- sion. The words "power developed " may be in- serted instead of the words "work done," if so desired, for althoug-h the terms are not inter- changeable as a rule, still it must be remembered that this is an example in proportion only. It should not be forgotten that such rules do not always take account of clearance or compres- sion, and that the pressures are all absolute, as is always the case when the full power developed by the engine is to be calculated. To demonstrate the correctness of this rule may seem to be a complicated operation to some engineers, but in reality it is a very simple one. It may be done as follows : Draw a theoretically perfect card, v/ithout clear- ance or compression, putting the cut-off at one- quarter stroke, making the initial pressure 80 OF STEAM ENGINEERS. 139 pounds above the atmosphere, or 95 pounds abso- lute. Now draw a perpendicular line from the point of cut-of to the vacuum line. Having* done this, the author took a planimeter and carefully measured the area of the space representing- the work done prior to the cut-off point and found it to be 2.96 square inches. Now, as the cut-off took place at one-quarter stroke, the ratio of expansion is 4, the hyperbolic logarithm of which is 1.3863. By multiplying- 2.96 by 1.3863, we find that the product is 4.10, which should be the area of the space representing" the work done by expansion. As the actual reading- of the plainimeter was 4.14, it proves that the rule is correct, for we do not expect that these reading's will always agree ex- actly, and a difference of .04 in a case like this is not of enough importance to be taken into ac- count. Some writers tell us that if w^e are running* an automatic engine, we should carry such a press- ure on our boilers that the steam in the cylinder will expand down to atmospheric pressure at the end of the stroke. Others claim that it is better to have about five pounds above the atmosphere. Probably either one will give g-ood results within reasonable limits, but with a very light load, if we should attempt to lower the boiler pressure to meet this requirement, it would be so low that it would prove to be unprofitable, for althoug-h when we expand the steam below the pressure of the atmosphere the condensation is excessive, still it proves to be a less evil than to run with a low boiler pressure. If we were running- with a gage pressure of 75 pounds on the boilers, and the load is such as to g-ive a high terminal press- ure, say 35 pounds absolute, if we raise the boiler pressure to 100 pounds, the expense for fuel will 140 MODERN EXAMINATIONS be much less, taking- it for granted that the boilers are safe at the hig-her pressure. In the case of a compound condensing* engine there are other matters to take into consideration, which do not apply to a simple engine. OF STEAM ENGINEERS. 141 CHAPTER XXIX. SIMPLE AND COMPOUND ENGINES. If we are running- a simple, non-condensing-, automatic eng-ine, and for any cause wish to raise the terminal pressure, all that we have to do is to lower the boiler pressure, and the desired result is obtained, and that is all that there is to it; but if we have a compound condensing- eng-ine and the terminal pressure in the high pressure cylinder is too low to g-ive g-ood results, there are several things to be taken into consideration. Let us follow the operation and note the results. If the terminal pressure in the hig-h pressure cylinder is very low, then but little steam will be left to g-o to the low pressure cylinder, and an uneven distri- bution of the load is a natural consequence. Now if we can raise this terminal pressure it will make a difference, and so we proceed to lower the boiler pressure. Assuming- that the load is a constant one, the first thing* that we notice is that the point of cut-off is lengfthened, and the steam is not expanded down as low as it was formerly. We now have more steam g-oing- to the low press- ure cylinder, and its mean effective pressure is raised accordingly, but as the mean effective press- ure of the two cylinders taken together is a con- stant factor under conditions named, this increase is not needed, and the effect of it is to cause the engine to make an effort to increase its speed, but this effort is promptly checked by the governor, 142 MODERN EXAMINATIONS which shortens the point of cut-off, the effect of which is to reduce the mean effective pressure in the hig-h pressure cylinder, and also in the low pressure, and as our terminal pressure in this cylinder is now raised, we shall need more water to condense the steam, as a hig-her pressure means more heat to dispose of, and thus more work is put upon the air pump. In addition to this, as even now the point of cut-off is longer than it was before the boiler pressure was re- duced, more steam will be needed on this end of the machine also. Now the question is, have we gained enough to offset the loss? A due consideration of these facts will explain the necessity of having an engine of this kind properly proportioned for the work that it will be required to do, and for the power that it will be called upon to develop. Of course it is always well to have even a simple engine of a suitable size, but as we add on cylinders the desirability of it increases. Another question that the indicator helps us to decide, in the case of a compound engine, is whether it pays to run a compound engine or not. Suppose that we have a simple, non-condensing engine, in which there is no back pressure above the atmosphere. The conditions are such that the horse power constant is 2.5 Now if we com- pound the engine, that is, add another C3dinder, say twice the diameter of the first one, we may have caused a back pressure of six pounds in the high pressure cylinder. This will of necessity cause the mean forward pressure to be increased by six pounds, and consequently this cylinder will be called upon to furnish 2.5x6 = 15-horse power more than it did before, and this is required to overcome the increased back pressure. OF STEAM ENGINEERS. 143 If this were not put to some use, the compound- ing" would be a dead loss, but as the extra steam so used is to be utilized further, it changes the the conditions. As the low pressure cylinder is twice the diameter of the high pressure, it follows that the horse power constant will be four times as great, ignoring the areas of the piston rods, so that 2.5x4 = 10. Now, if by creating an additional back pressure of six pounds, calling for 15-horse power to over- come it, we can secure steam enough to run our low pressure cylinder, securing for it a mean effective pressure of three pounds, then it shows on the face of it that it pays to compound, for when we trade off 15 horse power and get 30 in return for it, we are on the safe side, to say the least. It is assumed that the extra water needed will not have to be bought of the local corporation monopoly, provided we wish to add a condenser to this engine. The indicator does not tell us everything that we wish to know in this connection, however, for it does not point out the difference in cylinder condensation, which is often referred to as X on account of its being an unknown quantity, but as the terminal pressure in the high pressure cylin- der is higher, it is only reasonable to suppose that the condensation will be less in proportion as the difference between the initial and the ter- minal pressure is less. If we now add a condenser, and thereby remove a large part of the back pressure on the large piston, we shall make another improvement, for the air pump deals with this atmospheric press- ure in a more economical way than the piston can, therefore it is good policy to make the second cylinder much larger than the first, the ordinary 144 MODERN EXAMINATIONS limit being" twice the diameter, or four times the area, but a more common practice is to make them as 16 is to 30 inches, or as 22 is to 40 inches, respectively, in diameter. For cross compounds it is customary to make the piston rods of the same diameter, notwithstanding- the great difference in the size of the pistons, on account of the differ- ence in the mean effective pressures acting on them. OF STEAM ENGINEERS. 145 CHAPTER XXX. CALCULATING THE AMOUNT OF WATER NECESSARY TO SUPPLY A SURFACE CONDENSER. Some time ago a friend in another state re- quested the writer to inform him how much water he would need, provided he added a condenser to his eng-ine. He stated that it was a compound engine, gave the diameters of the cylinders, length of the stroke and pressure carried on the boiler. As the point of cut-off was not given, nor any data from which the terminal pressure could be calculated, it was not possible to give an in- telligent answer. This then is another matter that the indicator helps us to decide, namely, the volume of circulating water that will be required for any engine under stated conditions. This problem we intend to illustrate and ex- plain in full, beginning with a formula given us for this purpose: 1114+.3T-/ =V. t'-t" In which T=temperature of steam entering con- denser, /=temperature of feed water, ^'^ —temper- ature of water of condensation discharged, and /"=temperature of circulating water, all in de- grees P., and V=volume of water. This formula may be read as follows: To the constant number 1114 add .3 of the temperature 146 MODERN EXAMINATIONS of the steam as it enters the condenser (expressed in deg-rees Fahrenheit). Prom the sum so ob- tained, subtract the temperature of the feed water. Divide the remainder by the temperature of the water of condensation as discharg-ed, minus the temperature of the circulating- water before it is taken up by the circulating- pump. The quo- tient will be the volume required ; or, in other words, it will be the number by which you must multiply the number of pounds that is required per hour to g-enerate the steam that is used in operating- the eng-ine. The product will be the nnmber of pounds needed per hour to supply the condenser. In calculating- the amount of water that will be needed it is well to remember that while it is a g-ood idea to continue to pump the feed water throug-h a heater, still it must not be expected that it will be as hot as formerly, as the pressure in the exhaust pipe wnll be g-reatly reduced by the condenser and air pump. Also that after the con- denser has been added the back pressure will be reduced, thus requiring- less forward pressure, the consequence being- that the terminal pressure will be less (as before stated), making- the tem- perature of the exhaust steam as it g'oes to the condenser lower than when it is exhausted into the atmosphere. Therefore w^e may safely as- sume a lower temperature for it, or if we choose to take it as we find it, whatever error there is will be on the safe side, as the result so obtained will be more than what is actually needed, but the difference will not be g-reat. We now call attention to Fig. 8, Avhich consists of diagrams from the hig-h pressure cylinder of a compound condensing- eng-ine, the data being- as follows: Diameter of cylinder 12 3-16 inches, OF STEAM ENGINEERS. 147 stroke 36 inches. Diameter of piston rod 2}i inches. Net area of piston, obtained by subtract- ing" one-half area of rod from area of piston 114.9033 square inches. Horse power constant Fi<5.8. 1.5041. Mean effective pressure of right hand card, 20 pounds, left hand card 23 pounds, and of both tog-ether 21.5 pounds. Indicated horse power 32.338, terminal pressure (absolute), rig-ht hand card 25, left hand card 28 pounds, the averag-e being- 26.5 pounds. Pig-. 9 consists of cards from the low pressure cylinder of the same eng-ine, the data being- as follows: Diameter of cylinder 20 inches, stroke 36 inches, diameter of rod 3 inches, net area of piston 310.6257 square inches, horse power constant 4.0663, mean effective pressure, rig-ht hand 10.5 pounds, left hand 10 pounds, and of both tog-ether 10.25 pounds. Indicated horse power 41.679, terminal pressure of rig-ht hand 7.5 pounds, of left hand eight pounds, the average being 7.75 pounds. 148 MODERN EXAMINATIONS In determining" the horse power developed by this or any other compound or compotmd con- densing eng-ine, all that is necessary is to add to- gether the horse power developed in the two cvlinders. In this case it is 32.3384-41.679= 74.017 horse power. The initial pressure is but 80 pounds. As the lowest terminal pressure is 7.5 pounds, we will assume that the feed-water is heated to 130°, that the steam as it enters the con- denser has a temperature of 180°, the temperature OF STEAM ENGINEERS. 149 of the water of condensation discharged is 100°, and that of the circulating* water 70°. Our prob- lem, therefore, is as follows: 1114+.3X 180-130 =34.6 volumes. 100-70 We w^ould call attention to the fact that if the temperature of the discharged water is 110°, the value of V will be 25.95, instead of 34.6 as above, which will make a great difference in the work of the circulating pump, and will be quite an object when the supply of water is limited. The next step is to ascertain the amount of water that this engine calls for per hour, which we will do by one of the rules already explained, and that may be found in Chapter 23. The high pressure cylinder has an area of 116.6766 square inches, and its length is 36 inches. 116.6766x36=4200.3576. Add ^ve per cent, for clearance and we have 4200.3576+210.0178=4410.- 3754 cubic inches. Dividing this by 1728 gives us 2.5523 cubic feet per stroke, and as this engine runs 72 revolutions per minute, we have 144 strokes to calculate on, and 2.5523x144=367.5312 cubic feet per minute. The average terminal pressure of these cards is 26.5 pounds. The weight of one cubic foot of steam at 26 pounds pressure is .0650 pound, and at 27 pounds it is .0673 pound, therefore .0650+ .0673— 2= .06615 pound, which is the weight at 26.5 pounds pressure; 367.5312 X. 06615 =24.3121 pounds per minute, and multiplying this by 60 gives us 1458.726 pounds per hour. One gallon of water weights 8.3 pounds, and 1458.726-^8.3 = 175.75 gallons per hour, which is the water ac- counted for by the indicator. 150 MODERN EXAMINATIONS Referring" to a preceding- part of this calcula- tion, we find that we need 34.6 volumes, and 175.75x34.6=6080.95 g-allons per hour. It may be of interest to note the efficiency of this engine, and as the indicator accounts for 1458.726 pounds of steam per hour, and as the total horse power developed is 74.017, we divide the former by the latter, and our quotient is 19.7 pounds of steam per horse power per hour. If this were a larger engine, using steam at say 130 povinds pressure, and with a load for which it is adapted, we should expect a g-reater efficiency; or, in other words, less steam per horse power per hour would be used, but when we consider the size of it, the low initial pressure of 80 pounds and the slow speed, we admit that it is doing* very well. It was formerly a simple engine, but as the load was increased the low pressure cylinder was added and it is now g-iving good satisfaction, using less fuel than before, and doing the work easily. OF STEAM ENGINEERS. 151 CHAPTER XXXI. THE AMOUNT OF WATER NECESSARY FOR A JET CONDENSER. — DENSITY OF STEAM. As will be noted the formula g-iven in Chapter 30 applies to the use of a surface condenser, and it will no doubt be of interest to explain the for- mula g'iven us for use in the case of a jet con- denser, as many of them are in use, and still more will be used in the future. We shall first give a formula to determine the amount of water that will be required to reduce steam of any given pressure to water of a stated temperature, as follows: S+L-D =V D-I In which S = sensible heat of the steam, L=latent heat of steam, D=temperature of discharg'ed water, I=temperature of injection water, and V = volume of water as compared with that which it required to generate the steam. When written out in full this will read as fol- lows: Add the sensible and latent heat of the steam expressed in degrees F. together, and from the sum so obtained subtract the temperature of the discharged water. Divide the remainder by the number obtained by subtracting the tempera- ture of the injection water from the temperature of the discharg'ed water, and the quotient will be the volume required. We will now apply this to 152 MODERN EXAMINATIONS the case mentioned, and illustrated in Chapter 30, Fig's. 8 and 9, but we must take the steam as it leaves the low pressure cylinder for the con- denser, as that is what we must condense. The lowest terminal pressure here is 7.5 pounds, and as it is but 8 pounds at the other end, the differ- ence in temperature being- but 3°, we will take the lowest as before. If the difference was g^reater we should take the averag-e. Substituting for the symbols their values, we have 180+988-100 =35.6 volumes. 100-70 The diag"rams call for 175.75 g-allons per hour, which is one volume, and 35.6 volumes equal 175.75x35.6 = 6256.7 g-allons per hour. When the temperature of the steam is g-iven, instead of the pressure, the formula is as follows : l+T-t =V. t—w In which /=latent heat, T = temperature of steam, /=temperature of discharg-e, zf = temperature of condensing- water, and V = volumes. Substituting- for the symbols their values as above, we have 988+180-100 =35.6 volumes. 100-70 This operation is practically the same as the one preceding- it, but both are g-iven in order to cover all the g-round. The next question that naturally sug-g-ests itself in this connection is, how shall we determine the area of the pipe that is to convey this injection water to the condenser? It may be determined by the following* formula: OF STEAM ENGINEERS. 153 A C =X V In which A = volume of water required for g-ener- ating" the steam used, expressed in cubic inches per second, C = number of volumes of water re- quired for condensation, V=velocity due to flow in feet per second and X = areain square inches. This is a very innocent looking- formula, but it will require some patience on the part of any one not familiar with it, in order to fully understand the meaning of every part of it. However, it is not ver}^ complicated, although the explanation ma}^ seem somewhat lengthy. The first step is to read the formula, in order to avoid the possibility of a misunderstanding here, which we will do as follow^s: Multiply A by C and divide the product by V, and the quotient will be the area of the pipe in square inches. We will now determine the value of A by use of the following rule: To compute volume of water in a given volume of steam, multiply the volume of steam in cubic feet by its density, and the product will be the volume of water in cubic feet. By re- ferring to Chapter 30 we see that the engine from which the diagrams illustrated there were taken calls for 367.5312 cubic feet of steam per minute, but as the time mentioned in this problem is sec- onds, we will divide by the number of seconds in a minute, and 367.5312-^-60 = 6.12552 cubic feet per second. Here a few words concerning the density of steam will not be out of place, for in the tables of properties of saturated steam that are published in the various books of reference, there is one column under the heading of "Densit}^ or weight of one cubic foot." This may mislead the casual 154 MODERN EXAMINATIONS reader into thinking- that density and weight are synonomous terms, but such is not the case, for the weight refers to the actual weig-ht of a cubic foot of steam, while density means the weig-ht of it as compared with the weight of a cubic foot of water, and taking- this as 62.5 pounds, it is a prob- lem in proportion as follows: As 62.5 is to 1, so is the weight of the steam as to its density. In the case in hand, the pressure is 26.5 pounds ab- solute, as before shown, and we have already demonstrated that a cubic foot at this pressure weig-hs .06615 pound, therefore 62.5 : 1 : : .06615 : .0010584, which is the density at stated pressure. As will be noted, the process consists of simply dividing- the weig-ht of the steam per cubic foot by 62.5, although this does not explain the reason for the proceeding-, as when viewing it as an ex- ample in proportion, and it therefore follows that when the density is g-iven and the weig-ht desired, the process is reversed, or in other words, sub- stitute multiplication for division, so that the density multiplied by 62.5 will g-ive the weight. OF STEAM ENGINEERS. 155 CHAPTER XXXII. DETERMINING THE AREA OF INJECTION PIPE. Proceeding- with our problem we have 6.12552 X .0010584 = .006483 cubic feet of water per second. As we wish to have it in cubic inches, we multiply by the number of cubic inches in a cubic foot, and .006483x1728 = 11.2 cubic inches per second. Adding- 10 per cent, for leakage of valves, etc., makes it 12.32, which is, therefore, the value of A. The value of C is 35.6 as demonstrated in Chapter 31. In determining- the value of V, it is necessary to know the vacuum in the condenser, and in this case it is stated at 25 inches. To reduce to pounds, divide by 2.04, and 25h-2.04 = 12.25 pounds. To ascertain flow of water in feet per second due to this vacuum, multiply by 2«31 in the case of fresh water, 12.25x2.31 = 28.29 feet. To this must be added the vertical distance or heig-ht from centre of opening* in condenser to surface of water above the condenser, assuming that it is above it. This is not stated on the diagrams taken from this engine, but we will assume it to be eight feet. Then 28.29+8 = 36.29 feet per second. Thus we have established the value of V in the formula, and when we substitute for the symbols their values, it stands as follows: 12.32x35.6 =12.1 36.29 156 MODERN EXAMINATIONS square inches, or practically a pipe four inches in diameter will be needed for this case, provided the water supply is near at hand, but if a long pipe is necessary, a larger size should be used. The author would call attention to the fact that this formula is a modification of one found in a certain standard book of reference, but it will answer for all ordinar}^ conditions, and for small and medium-sized engines. It may be well to write it A C = X V D in which case D would be a variable factor, to be changed to suit certain conditions, at the judg- ment of the engineer. There is another wa}^ to determine the value of A, as follows: The amount accounted for by the indicator is 175.75 gallons per hour. Dividing this by 60 gives us 2.929 gallons per minute, and dividing this quotient by 60 gives us .0488 gallons per second. As there are 231 cubic inches in a gallon, .0488x231 = 11.2 cubic inches per second, and adding 10 per cent, makes it 12.32 as before. Here it will be noted that the value of V is calculated on a fresh water basis, but if salt water is to be used, as we may with a surface con- denser, then we must multiply the vacuum in pounds by 2-24, instead of 2.31, for, as salt water is heavier, it does not require so high a column to correspond to a stated amount of vacuum. And again we have assumed that the water of condensation is above the condenser, but it often is below it, which changes the conditions, for in the former case the distance in feet must be added to the height due to the vacuum, as it helps the water in its passage, but in the latter case, with OF STEAM ENGINEERS. 157 the supply below the condenser, it must be sub- tracted from it, as it tends to retard the flow of the water. Suppose then that we assume that we are to use sea water, which is eight feet below the centre of the opening* in condenser. In that case the value of V would be 12.25 X 2.24-8=^19.44, making- the problem stand thus: 12.32x35.6 =22.56 19.44 square inches, or in other words, requiring- a pipe about ^ve inches in diameter. This conclusion is only a reasonable one, for every eng-ineer knows that when a pump has the water delivered to it under pressure, the pipe may be much smaller than when it must be raised in the ordinary way. From the foreg-oing' calculations it will be seen that it is very necessary to take g-reat care in taking- a diag-ram from an eng-ine, to see that the indicator is in good order and that it is well lubricated. The paper should be smooth and toug-h, althoug-h not necessarily g-lazed. The pencil should be sharp that it may make a fine line, and so adjusted that it will not bear too hard, for in that case the card or diag-ram will be distorted, and prove worse than useless. It is for the best interests of every man now in charg-e of a steam plant or who expects to be in the future, to understand the use of this instru- ment, for although the engineer in charge of a small plant may not see the need of such knowl- edge, as he may be laboring- under the impression that it is only necessar\^ for those who are run- ning large engines, yet if the opportunity should present itself for him to be advanced to a more responsible position, provided he understood the indicator, it would not be a proper time for him 158 MODERN EXAMINATIONS to begin to learn then, for while he would be getting- posted on the subject, another man would secure the position. Qualify for the position first, and seek the same afterward. Always keep the horse before the cart, and never attempt to reverse the order. 'i OF STEAM ENGINEERS. 159 CHAPTER XXXIII. THREE SYSTEMS OF STEAM HEATING FOR BUILD- INGS. It is well for the applicant for a license to un- derstand something" of steam heating- systems, and their application to use in every day practice, as this will be necessary in many cases, for this apparatus will be under care of the eng-ineer, and, althoug-h he may be able to run a certain system from day to da3% provided nothing" unusual hap- pens, still, it is much better for him to under- stand the principle on which it works, for then he can more readily detect the cause of failure of any part of it to work. The writer well remem- bers presenting- the question: "What is the mean- ing- of the term indirect radiation?" before an assembly of eng-ineers, and not one of them could g-ive a satisfactory reply, therefore it may be well to g-ive a description of the three principal sys- tems of heating- building-s, namely, direct radia- tion, indirect radiation and direct-indirect radia- tion. The first is just what its name applies, and that is that the heat is radiated directly into the room to be warmed from coils or radiators located in said room. The pressure may be hig-h or low, and steam or hot water may be used, but so long- as the radiators are in the room to be heated, and are not connected with any system of ventilation, this system is known as direct radiation. 160 MODERN EXAMINATIONS The indirect radiation system is one in which the air is warmed by coils or banks of pipes located in some place outside of the room to be heated, and then forced by means of a fan into rooms where it is needed, or small separate radi- ators may be placed near the bottom of the flues leading- into the rooms, when, as the air becomes heated, it naturally rises, and thus can be utilized. It is quite evident that the fan is to be pre- ferred, as it makes the circulation positive, and does not depend on circumstances, such as "which way the wind blows," etc. From the nature of the system it will be noted that it can only be used in connection with some system of ventilation. The direct-indirect system, as its name indi- cates, is something* of a combination of the other two systems, for it is one in which the radiators are partly or wholly within the room to be heated, and are in direct connection with some system of ventilation. The indirect system is used at the present time for heating- factories more than ever before, and the apparatus is very simply, consisting- of a large coil or bank of pipe through which the exhaust steam from the engine circulates, or when it is not running-, live steam from the boiler is intro- duced. The coil is encased in a jacket of sheet iron, or of something- more substantial if it is very large, and a fan blower forces the cold air into this jacket, where it is heated, and is then led away by means of suitable pipes to the different rooms where it is needed. The fan is often run by a small independent engine, and so equipped that the speed may be varied at will. One great advantage of this system is that while it heats it also ventilates, and in summer time cool air may be forced throug-h, and the rooms rendered more OF STEAM ENGINEERS. 161 comfortable. Care should be taken to have the inlet for air in such a place as to secure that which is pure and wholesome, as the odor of the rooms will be unpleasant otherwise. The direct-indirect system reminds one of a factory, the main part of which has been out- grown by the business carried on therein, and to provide necessary room, additions are built on from time to time, until the whole affair has a patched-up appearance. So it is with this system, for while there is no doubt about its giving- good results in many cases, still it is not as symmetri- cal as the others, and involves unnecessary com- plications. The direct radiation system for steam is prob- ably used more than any other for heating- public buildings, and as there is more than one wa}^ to pipe up this system, we would call attention to this fact and to some of the methods adopted. We frequently hear the question asked: "Can the water of condensation from coils and radiators be returned to the boiler without the use of some mechanical contrivance made for this purpose?" To this we would reply that it can and is done in many places, and we see no objection to it. Of course the radiators must be above the water line of the boiler, and it is a good plan to have the piping so arranged that the cold water which fills the returns when steam is first turned on may be blown out into the sewer (through suitable con- nections), and when the body of water is in mo- tion and circulation established, the blow-off valve may be closed, when the water will be returned to the boiler. The author is aware that this has been tried, and in some cases proved a failure, but wherever it has there is some straight reason for it. It is necessary to maintain boiler pressure in 162 MODERN EXAMINATIONS the radiators, and if there are so many of them that the opening in the dome or the intermediate pipes are not large enough to supply sufficient steam to do this, then the water of condensation cannot return to the boiler, unless it is pumped in. This is the principal cause of failure. If some of the radiators must be located lower than the water line, it will be necessary to provide a pump or trap to return the water of condensa- tion. OF STEAM ENGINEERS. 163 CHAPTER XXXIV. COMPARISONS OF SYSTEMS FOR STEAM HEATING. The system of direct radiation for steam heat- ing- may be piped up in four different ways as follows : (1) A main steam pipe is continued from the dome of boiler up to the highest floor of the building- to be heated. From this pipe, which is commonly called a riser, steam is taken for ra- diators located on each floor, and separate return pipes are provided for each, which are not con- nected tog-ether until fhey are broug-ht down below the hydrostatic level. (2) A riser is put up and connected in the same way as before, but the drip pipes are all connected into one pipe, called the return riser, in the same way that steam is taken from the steam riser, and thus returned to the boiler. (3) The steam riser is provided as before, which is also made to do duty as a return riser until it reaches the point where it is con- nected into the horizontal steam pipe from boiler. Here a tee is used instead of an elbow, and the re- turn pipe is continued down until it is below the hydrostatic level, when it is carried in a horizon- tal direction to the boiler. (4) A sing-le pipe is the only connection between boiler and radiator, in which the steam passes along- the upper part of it, and the water of condensation returns along- the lower part of it. As a matter of course all of the pipes in this circulation must incline towards the boiler, or else it will not work at all. 164 MODERN EXAMINATIONS System No. 1 is to be recommended above the others, for it gives practically a positive circula- tion, and especially where low steam pressure is to be used, and in places where it will be run b}^ persons who are not experts, as there should be no trouble in expelling the air, and preventing* all of the disagreeable cracking noises frequently heard in other systems, caused by steam coming in contact with water, etc. Its first cost is a little more than either of the others. No. 2 is used much in large buildings, and gives fair results when properly put up and cared for. It requires less labor and material, consequently the expense is less. In No. 3 much larger pipes must be used, and for that reason the cost in some cases will equal that of No. 2, and the results will be less satisfac- tory. The same objections apply to No. 4, and therefore it is not to be recommended except for small jobs, or w^here for some special reason it may be desirable. Where Nos. 1 or 2 are used care must be taken to provide a drip connection, so that no water can collect in the vertical steam supply pipe or steam riser, for it must be remembered that the flow of steam through this pipe is often very slow, and consequently the condensation is excessive. It is not intended to give a complete description of the details of piping for these systems, as it would require a volume of reading matter and many illustrations, but the few hints and sugges- tions here offered will be found of practical use, as for instance it is better to use angle valves wherever practicable, as they give full opening, cause less friction and save the use of an elbow. Where a valve must be located in a straight pipe, a straight-way valve is preferable, but if for OF STEAM ENGINEERS. 165 any reason a g'lobe valve must be used, then do not place the stem in a vertical position, for if it is, the water running- along* the bottom of the pipe will be trapped there, owing- to the construction of the valve, and much unnecessary strain will be brought to bear on the pipe by the hammering- action of this water. Pieces of pipe that have been broken by this ac- tion, under an ordinary working- steam pressure, have afterward been tested, and withstood 1000 pounds pressure applied in a careful and steady manner. When steam is first admitted to a system of piping-, the valve should be opened very slowly, as the first steam that enters will be condensed, causing- what is called "water hammer," therefore it should be admitted as carefully as possible. If a g-lobe or angle valve is used, it is much easier to tell just when it beg-ins to open than it is in the case of a g-ate valve, and, as it frequently happens that we only wish to admit a little steam to a radi- ator in moderate weather, this is one thing- in their favor. This refers to radiators having- inde- pendent drips. The eng-ineer who is systematic and careful about his work, and takes pride in seeing- it prop- erly done, always likes to have a valve stem placed in either a vertical or horizontal position, and with a g-lobe valve, the latter is the best of the two, but neither one of them are just rig-ht so far as service is concerned, for if the former plan is adopted, the water will be trapped in the pipe, owing- to the construction of the valve, and if the latter is, the water will stand in the bonnet and leak out around the stem, therefore if the stem is inclined upward slig-htly it will g-ive the best re- sults, but at the same time does not look as well. 166 MODERN EXAMINATIONS Valves should be put on with the bottom towards the source of pressure, so that when they are shut there will be no steam on the stuffing- box, for otherwise the valve cannot be packed without re- lieving* the whole system of pressure. Asbestos wicking- for packing" valve stems is far preferable to the ordinary candle wicking often used for that purpose. a OF STEAM ENGINEERS. 167 CHAPTER XXXV. DETERMINING THE RADIATING SURFACE NECES- SARY TO HEAT A ROOM OR BUILDING. If the candidate for a license is called upon to g"ive a rule for determining the heating or radiat- ing- surface necessary to warm a certain room, he should reply that there can be no inflexible rule given for such a purpose, as it will depend largely upon the conditions existing in each individual case, such as the location of the room, the manner in which the walls are built, the number and size of windows that it contains, and the temperature that must be maintained in it. There are, how- ever, rules that may be used for the foundation of such a calculation. The following is said to be in use among some of the steam fitters who put in heating apparatus, and many consider that it g'ives good results. Multiply the length, breadth and height of the room, in feet, together, and from the product so obtained cut oif two figures from the right hand, and call the remainder square feet of heating sur- face, or, as some might call it, radiating surface. This is for a high pressure S3^stem, but for a low pressure one additions must be made according to the judgment of the engineer in charge, for an exposed room will need more heat than one that is well protected, and if there are many windows in it, that will also be a consideration, for glass is a good conductor of heat. For an illustration I 168 MODERN EXAMINATIONS shall take a room in the immediate vicinity of where this is written. It is 30.5 feet long, 17 feet wide and 11 feet high ; 30.5x17x11=5703 cubic feet. As about two- thirds of this room is exposed, we will add 50 per cent, on this account, and we have 5703+2851= 8554. Cutting- oif the two right hand figures leaves 85 square feet of heating surface, or about 247 feet of one inch pipe. This rule, however, is not a very satisfactory one, as it does not take into account all existing conditions. It may be called a "rule of thumb." Now while a glazed window admits the heat of the sun, if it is shining directly on it, more than a brick wall or other opaque surface will, still, if the sun is not shining on it, then the glass be- comes an important factor in the calculation, as it will cool off the room much faster than brick walls, sheathing or lath and plaster will. The following rule has the endorsement of an eminent authority on steam heating: Divide the difference in temperature between that at which the room is to be kept and the coldest outside atmosphere, by the difference between the temperature of the steam pipes and that at which you wish to keep the room, and the quotient will be the square feet, or fraction thereof, of plate or pipe surface to each square foot of glass or its equivalent in wall surface. We will now explain the way to reduce wall sur- face to its equivalent in glass surface, and for this purpose we will introduce the following table from "Steam Heating for Buildings," by William J. Baldwin. Table of approximate power for transmitting heat, of various building substance compared with each other: OF STEAM ENGINEERS. 169 Window glass looo Oak and walnut sheathing on walls 66 to loo White pine and pitch pine 80 to 100 Lath and plaster walls, good 75 to loo Lath and plaster walls, common , 100 to 105 Common brick (rough) 150 Common brick (hard finish) 200 Common brick (hard finish, hollow walls). . 150 Sheet iron iioo to 1200 "In fio-uring- wall surface, etc., multiply the superficial area of the wall in square feet by the number opposite the substance in the table and divide by 1000 (the value of glass). The product is the equivalent of so many square feet of g-lass in cooling power, and may be added to the win- dow surface and treated in the same way." Let us now apply this rule to the case of the room mentioned before and note the result. It is 17x30.5 feet, so that there are 518.5 square feet in the ceiling-, and the same amount in the floor, making' 1037 square feet in both. This surface is taken into account because the room is in an iso- lated building- comparatively, there being- no other rooms above or below it to assist in keeping- it warm. In the sides of this room there are 30.5x11x2 = 671 feet. In the ends 17 X 11 X 2= 374 feet, mak- ing- 2082 square feet in all. A part of this is glass surface and the remainder is hard pine sheathing, and as the two represent different values, we must separate them and reduce them to a common standard. There are seven windows, each con- taining- 11 square feet of glass, and one sash door with nine feet. 11x7+9 = 86 square feet; 2082- 86 = 1996. Thus we have 86 square feet of g-lass, and 1996 square feet of hard pine sheathing- to pro- vide for. 170 MODERN EXAMINATIONS The latter we will reduce to its equivalent in g-lass surface, and add the two together. As this table tells us that the pitch pine sheathing- is valued at from 80 to 100 we will take it at 90 for an average. 1996x90^1000 = 179, which is the surface of the sheathing in the room reduced to its equivalent in glass surface. To this must be added 86 feet of glass surface, and 179+86 = 265 square feet. OF STEAM ENGINEERS. 171 CHAPTER XXXVI. AREA OF MAIN STEAM PIPE FOR DIRECT RADIAT- ING SYSTEM OF STEAM HEATING. — SIZE OF BOILER REQUIRED. We will now proceed to assume conditions in order to enable us to finish working* out the ex- ample presented in Chapter 35. Assuming* that the coldest outside temperature is at zero, or at 0°, and we wish to warm the room so that the thermometer will stand at 70°, we have 70°— 0= 70°. And here the question presents itself as to what we shall do if the coldest outside tempera- ture were taken at 10° below zero. In that case we would subtract the difference, as before, and add 10 to the remainder. A practical way to de- cide it is to take a thermometer in hand and calcu- late or count the difference in deg^rees. If we carry 60 pounds pressure on our heating pipes, the temperature will be 307°. The temperature of the room being- 70, we have 307-70=237, and 70 --237 =.295. Add 50 per cent, for ventilation, air leaks, etc., and .295-[-.147 = .442, which is the number of square feet of heating suface needed for each square foot of glass sur- face, or its equivalent. In this case it is 265, and 265 X. 442= 117 square feet, or about 340 feet of one-inch pipe. Now let us assume different con- ditions and compare results. Suppose that the difference between the inside and outside temper- atures is 70°, and we are using steam at two 172 MODERN EXAMINATIONS pounds pressure. Then we would have 219—70= 149, and 70 -=-149 ==.47. Add 50 per cent, as be- fore, and it brings it up to .705 square feet of radiating' surface for each square foot of g"lass surface, or its equivalent, 265 X. 705= 186 square feet, or about 540 feet of one-inch pipe. Now suppose that we wish to estimate what piping", boiler capacity, etc., will be needed to heat a building- containing- 12 rooms like the one before mentioned, the system to be direct radiation, and low pressure, say two pounds. In such a case we would not fig-ure in the floors and ceiling-, as they would not be exposed as in the case of an isolated room; 2082 — 1037=1045 square feet in the sides and ends of one room. In 12 rooms there would be 1045x12=12,540 square feet. In each room there would be 86 square feet of g-lass, and 86x12 =1032 square feet; 12,540-1032x11,508 square feet of pine sheathing- to be reduced to its equiva- lent in square feet of g-lass, and 11,508x90-^1000 =1035; 1032+1035=2067 square feet of g-lass, or its equivalent. Assuming- a difference of outside and inside temperatures amounting- to 70° as before, and a difference between the pipe and the room of 149°, and our multiplier is found to be .47, or if we wish to add the 50 per cent, here it makes it .705. Now 2067 X. 705 =1457 square feet oi radiating' sur- face needed, which would be about 4229 feet of one-inch pipe. Our next move is to determine the area of the main steam pipe, w^hich, of course, must be based on the number of square feet of radiating* surface that it must supply steam for, and to the number already obtained must be added the surface con- tained in the main itself. This we can only assume, but if we call it 20 per OF STEAM ENGINEERS. 173 cent, of the other, it will answer our purpose. This amounts to 291 square feet, and 1457+291 = 1748 square feet. Competent authorities tell us, and practice shows them to be correct, that for each 100 square feet of heating- surface in the building-, the main steam pipe should contain the area of a one-inch pipe, or .7854 of a square inch. 1748--100 = 17.48x.7854 = 13.7 square inches. Now the actual internal area of what we ordinarily call a four-inch pipe is stated at 12.7 square inches. Therefore a four-inch pipe will answer our purpose. Another w^ay to tell what the diameter of the main steam pipe should be, is as follows : Having- found the number of square feet of heating- sur- face needed, extract the square root of it, and one-tenth of this number will be the desired diam- eter. The square root of 1748 is 41.8+ and one- tenth of this is 4.18, or a four-inch pipe as before. Probably many building-s of this size are supplied with steam by a smaller pipe than this, but it does not necessarily follow that the best results are obtained thereby. In regard to the amount of heating- surface in the boiler that will be needed to supply steam for these rooms, if there is one square foot of sur- face exposed to the direct action of the tire, for each six square feet of radiating- surface, it will be sufficient for the conditions before mentioned, provided the firing- is attended to in a proper manner. This would call for a boiler containing about 300 square feet of direct heating surface. If a portion of it is tube or flue surface, a large allowance must be made, as its efficiency is much less. If a horizontal multitubular boiler is to be used, it should be four feet in diameter and 12 feet long, having, say 36 three-inch tubes. This 174 MODERN EXAMINATIONS g-ives 150 feet of direct heating* surface, and about 300 feet of tube surface. It should be noted that the data given here is for a system of direct radiation for steam. I OF STEAM ENGINEERS. 175 CHAPTER XXXVII. HEATING WITH EXHAUST STEAM. Occasionally we meet an eng-ineer who does not appreciate the value of exhaust steam for heating" purposes, as they allow it to g^o to waste, or at least they only utilize a portion of it in heating" the feed water, and althoug"h it does not pay to cause excessive back pressure on the eng-ine, still if the system of piping is properly arrang-ed, all of the exhaust steam left after passing" throug"h the heater, may be used during" the winter season with very little detriment on account of back pressure. The cost of such steam in any case may be calculated in the following" way : Ascertain the horse power constant of the en- g-ine, and multiply it by the back pressure due to the weig-hting" of the back pressure valve. The result will be the horse power expended in forc- ing* the exhaust steam around the factory. Sup- pose that we have an eng;ine 24x60 inches running" at 60 revolutions per minute. When the back pressure valve is up or open, the back pressure is one pound above the atmosphere, and when it is down or closed, it is two pounds above it, what do^s it cost to use the exhaust steam for heating"? The horse power constant for this eng-ine is 8.225, so that when we multiply it by the one pound additional back pressure caused by closing" the back pressure valve, and forcing" the steam throug-h the heating- pipes, we see that we can util- ize a larg-e volume of steam at a very slight cost. 176 MODERN EXAMINATIONS If the piping is properly arranged this can be accomplished, but at the same time we do not recommend that any engineer figure it up in his own case on this basis, unless he knows just what the back pressure is, for it is quite possible to have matters so arranged that it will cause 10 pounds back pressure instead of one. In many cases the exhaust pipe is carried up to the top of the factory, even when it is a high one, in order to get the exhaust steam away from the windows, and if it is provided with ample drips, or rather drip pipes, located at its lowest point, the steam may be carried up and cause very little back pressure, as it does not take much to force steam up, but, on the other hand, it requires much more to raise water. Cases can be found where the drip pipe is located at some point con- venient of access, without regard to whether it is at the lowest point or not. While such an arrangement may not cause any part of the exhaust pipe to entirely fill with water, still if there are two or three inches of water standing in an eight-inch pipe it will cause the steam at the end of the exhaust pipe to appear very wet, giving rise to the idea that the boiler primes badly, when such is not the case, and caus- ing unnecessary back pressure on the engine. With the exhaust pipe carried up at one end of the building, and tees having been put in at suita- ble places, say eight feet above each floor, if the ceiling is high enough to admit of it, then nipples may be put m, and other tees connected, from which branch pipes may be carried to either side of the room, where they are connected into a coil on eacli side. This is preferable to one large coil over the centre, not only on account of a better distribution of the heat, but because by placing OF STEAM ENGINEERS. 177 valves at the inlet and outlet of each coil, one of them may be shut off in moderate weather, and where the building* is so situated that the sun shines on one side of it during* the forenoon, and on the other side during* the afternoon, the steam may be put on the coldest side of room, thus nearly equalizing* the temperature of the same. These coils should all g^radually incline from the main exhaust pipe toward the other end of the rooms, allowing* them a pitch of about one-half inch for every 10 feet in leng-th. At the other end of the factory there should be a vertical pipe of about one-quarter of the diameter of the exhaust pipe, into which all the drips from the coils should be connected. The lower end of this pipe should be attached to a g-ood steam trap, for then no steam will be blown out near the windows. In this pipe, above the hig*hest drip connection, there should be a valve, and from the valve the pipe should be continued up throug-h the roof. Thus the air will be readily removed when the engine is started and the back pressure valve is closed, and the trap will take care of all of the water. If ib is desired to put on live steam when the engine is not running-, the valves near the exhaust pipe may be closed, and also the hig-hest valve in the vertical drip pipe, or what mig'ht be called the main return riser, and the live steam turned on at pleasure. 178 MODERN EXAMINATIONS CHAPTER XXXVIII. DIAMETER AND HORSE POWER OF SHAFTING. A knowledg-e of the streng-th of shafting- of various kinds may be required in this connection, and it is well to remember that a shaft of wroug^ht iron or any other material will transmit a g^iven horse power under certain conditions and last for years, while the same shaft would soon fail under other conditions, althoug^h the power transmitted is the same in both cases, or even less in the latter. The following' formula is g'iven us for determin- ing- the diameter of a wroug-ht-iron shaft to transmit a g'iven horse power under favorable conditions, namely, as in the case of a main shaft in a mill or factory, where it is well supported, not subjected to excessive strain from belts being- tighter than they should be and kept in line. It is one that agrees as well with g-ood practice as anv that can l:e found: 3 /50 I. H. P. V ^d n in which I. H. P. is the indicated horse power to be transmitted, n = number of revolutions, and d = diameter of shaft. It reads as follows: Multi- ply 50 by the indicated horse power, and divide the product bv the number of revolutions per minute. The cube root of the quotient is the diameter of the shaft in inches. For example let us take the case of a shaft made it I OF STEAM ENGINEERS. 179 of wrought iron which we wish to have tramsmit 138 horse power, running- at 115 turns per minute. Substituting' for the symbols their values in this case we have : 3 /50X138 V 115 3.914 inches, or as the sizes ordinarily run, we would call it a 3 15-16 inches shaft. If the size of shaft and number of revolutions are g-iven, and the power that it will transmit is required, the formula is as follows: .02 n d^=I. H. P., which reads, multiply .02 by the number of revolutions per minute, and the product by the cube of the diameter. The product so obtained will be the horse power that the shaft will transmit. Suppose that we have a 3^ inch wroug'ht-iron shaft whose speed is 100 revolutions per minute, and we wish to know how much power it will safely transmit: .02x100x3.5x3.5x3.5 = 85.75 indicated horse power. It will be noted that the power increases directly as the speed is increased, for if this shaft should be run at 200 revolutions, it would easily transmit 171.50 horse power. If the shaft is made of steel instead of wroug-ht iron the formula is as follows, the letters denoting- the same as in the preceding*: 3 /31.25 I. H. P. V =^^ n Assuming* the elements of the preceding* case, except that the shaft is made of steel, and substi- tuting- for the svmbols their values, we have: 3 /31.25X138 180 MODERN EXAMINATIONS 3.4 — inches nearly. If the size of shaft and speed is g-iven. and the power that it will transmit is re- quired in the case of a steel shaft, the formula is as follows: .03^ n d^=^L H. P. With a shaft running- at 100 revolutions per minute, whose diameter is 3.5 inches we would have .032 X 100 X 3.5x3.5x3.5 = 137.2. (The author's experience with steel shafts has been that they are apt to prove treacherous as they sometimes break under very light loads, on account of hidden flaws). If we wish to use a cast iron shaft, the formula for determining- the diameter of it is as follows : 3 783.5 I. H. P. V — -^ n the letters denoting- the same as above. Assum- ing- the elements of a preceding- case, and substi- tuting- for the symbols their values gives us the following: 3 783.5x138 115 4.641 inches, which is the diameter of the cast iron shaft. If the number of revolutions per minute, and the diameter is given, and the power that it will transmit required, the formula is as follows: .012 n d3=I. H. P. Assuming the ele- ments of a preceding case and we have .012 X 100 X 3.5x3.5x3.5 = 51.45 indicated horse power. The foregoing rules and formula do not apply to crank shafts of steam engines, propeller shafts, or other conditioas where the service required is severe. For determining the size of crank shaft for compound engines, with cranks set at an angle of 90° we have the following formula for wrought iron: OF STEAM ENGINEERS. 181 ^A/D^p+dnS 15 XS = 2468 diameter of shaft, in which D is the diameter of high pressure cylinder, in inches, p is the boiler or steam chest pressure above a vacuum, d is the diameter of low pressure cylinder in inches, and S is the stroke in inches. This may be read as follows: Square the diameter of the hig-h press- ure cylinder, and multiply by the steam-chest pressure absolute. To this product add the square of the diameter of the low pressure cylin- der multiplied by 15 and divide their sum by 2468. Multiply the quotient by the stroke in inches, and extract the cube root of the product which will be the diameter of the shaft in inches. Por the sake of illustrating" this formula we will suppose that a cross compound engine with cylinders 20 and 40 inches in diameter, respectively, and a stroke of 48 inches to be operated under a pressure of 140 pounds absolute, is to be used, and we wish to know what the diameter of the crank shaft should be. Substitute for the symbols their values and we have the following: 3 7202x140+402x15 X 48 = 11.6 inches nearlv. 2468 In practice a 12 inch shaft would be used. As we wish to make every part of this book plain as we proceed, we will give the solution of this problem in detail. The diameter of the hig'h pressure cylinder is 20inches, which being squared gives us 20x20=400. The absolute pressure is 140 pounds, and 400X140=56,000. The diameter of the low pressure cylinder is 40 inches, which 182 MODERN EXAMINATIONS being squared gives us 40 X 40 := 1600, and multiply- ing by 15 makes it 24,000. This is to be added to our first product, and 56,000+24,000 = 80,000, and 80,000-- 2468=32.41. This is to be multiplied by the stroke in inches, and 32.41x48 = 1555.68, the cube root of which is 11.6 nearly. OF STEAM ENGINEERS. 183 CHAPTER XXXIX. WIDTH, SPEED AND HORSE POWER OF BELTING. Probably there are few subjects connected with steam eng^ineering" concerning- which there is a g-reater diversity of opinion than as to a proper rule for determining- the horse power that a belt will transmit, and also for g'iving- the proper width of belt to transmit a g-iven amount of power. The writer does not expect to settle the question b}^ anything that may be written here, but at the same time does not hesitate to give a formula that takes into consideration all, or nearly all of the factors in the case. It is taken from Nystrom's Mechanics and is to determine the power that a belt will transmit, and is as follows : BdnZS 15,000,000 = H. P., in which B= breadth of belt in inches; d equals diameter of the smallest pulley in inches ; n= revolutions per minute of the smallest pulley ; Z=half angle of contact of belt on smallest pul- ley; S=safe working strength of belt in pounds per inch of width, for ordinary single leather belt is taken at 100 pounds, and H. P. = the horse power that can be easily transmitted. For ex- ample, we will take the case of a belt 48 inches wide, running over pulleys of which the smaller one is 54 inches in diameter, and revolves 200 times per minute. Half angie of contact is 85 184 MODERN EXAMINATIONS degrees, and safe load 100 pounds per inch of width. Our problem then becomes: 48x54x200x85x100 = 293.7 15,000,000 horse power. The reason for taking- the width of belt into account is because each inch or fraction thereof will transmit a certain amount of power. The diameter of smaller pulley is taken because that effects the friction of the belt. The speed of it is noted because that effects the power trans- mitted directly, just the same as the speed of shafting- effects it. The term "half ang-le of con- tact" may need some explanation. The rim of the pulley is a circle, and accordingly contains 360 deg-rees. If both of the pulleys were the same size, and there was no sag- to the belt, it would lap around one-half of this circle, or 180 deg-rees, but as the other pulley is assumed to be larg-er than this one, and the belt sag's a trifle (which is a help in some cases, and a detriment in others), the ang-le of contact is taken at 170 deg-rees, and one- half of this is 85 deg-rees. The safe load is deter- mined by experiment, but for belts in g-ood order may be taken at 100. The divisor is a constant number. If we wish to determine the breadth of belt necessary to transmit a g-iven horse power, our formula becomes 15,000,000 H. P. dnZS breadth, the letters meaning- the same as before. Assuming- elements of the preceding- case, we have 15,000,000X293.7 -= 48 inches. 54x200x85x100 OF STEAM ENGINEERS. 185 These formulae apply to leather belts in good order, running* on clean iron pulleys. There are several possible conditions which tend to modify them, as, for instance, if a double belt is running- over wooden pulle3^s, or iron pulleys covered with leather, the efficiency will be g*reater, and if the belts are hard and dry, and running- over pulleys that are very roug'h, or extraordinarily smooth on their faces, the efficienc}^ will be decreased. If we have a g-ood double belt instead of a sing-le one, the value of S will be doubled, or taken at 200 pounds, and according-lv the horse power that it will transmit will be doubled and 293.7x2=587.4 horse power. This assumes that the belt will not slip on the pulley even if the load is increased until the full safe working- strain on the belt is reached. If a belt is cemented and riveted tog-ether, or in other words is made *' endless," it will be much strong-er than if it is laced in the usual way, for reasons that are plain to ever}^ eng-ineer who has g-iven the matter any consideration. 186 MODERN EXAMINATIONS CHAPTER XL. STEAM BOILER EXPLOSIONS. The applicant should be well posted as to the causes, or perhaps we mig-ht be allowed to sa}^ the cause of steam boiler explosions, and also as to the theories which have been advanced at one time or another, for the same, but which can hardly be called correct ones in view of other facts in the same connection. Take for instance the theory of superheated water as an active ag-ent in this matter. The advocates of this theory claim that g-lobules of water absorb the heat of the fire in the furnace, and that while in a state of rest they are harmless, but when they rise to the surface and burst from some unknown cause thev develop a vast amount of energ-y, so much in fact, that no boiler can withstand the accumulation of it. This is said to be the condition of thing's when w^e shut down our engines, for while they are at rest it is assumed that the heat is being* g-enerated in the furnace, very much the same as when the machinery is in motion, and as the eng'ine is not taking- it, it is silently stored up for future use or abuse. So far as our observation and practice have been teachers, they have taug-ht us that when a fire is properly banked previous to shutting' down the eng'ine there is very little heat g-enerated to g-o anywhere. We are well aware that in places where it is necessary to force fires almost up to OF STEAM ENGINEERS. 187 shutting--down time the brickwork, arch plate, dead plate and other parts not in contact with water are at a high temperature, and some steam will be generated by this heat after the fires are banked, but even then the only effect that we will have noticed is that the lever safety valve slowly lifts as the pressure accumulates, and the surplus passes out into the atmosphere, and we cannot see how it can do any more harm to the boiler than if the steam was used by the eng'ine. But we are told that when the throttle valve is opened to start the engine the pressure on the top of the water is relieved, and it therefore rises and is converted into steam of great force, so that no gage can indicate it. We wonder how it is that anyone can still advo- cate this theory after they have stood by the side of one of our first class passenger locomotives, as they stand at a station ready to start out on a swift journe3^ with its train of half a dozen coaches, for while it waits the heat is being rapid- ly absorbed by the water, and the pressure rises until the safe working pressure is reached, when the pop safety valve opens with such celerity as to cause the unsuspecting' casual observer to give an involuntary jump, but no explosion takes place, and in addition to all this, certain kinds of engines are started up several times each day, and sudden- ly, too, but no explosion follows. Cases can be cited, it is true, where explosions have taken place just after the engine was started up, but what does that signify? Boilers appear to burst just as easily and as frequently, too, when the eng'ine for which they furnish steam have been running* an hour or two, as they do when they are just started, and sometimes they explode during* the night when no steam is being used, and others ex- 188 MODERN EXAMINATIONS plode when they never were used for supplying an engine. We are told that electricity accumulates in a boiler until it finally gets so full of it that an explosion follows, but it appears as if in order to hold a large volume of electricity, a boiler would of necessity have to be set so that it would be in- sulated from all surrounding objects and we never saw a boiler set in that way to be used for ordinary purposes. We suppose that if a boiler were carrying a heavy pressure and should be struck by lightning that the concussion together with the heavy pressure might cause an explosion, but that is a different thing. The favorite cause ascribed is that there was not sufficient water in the boiler to prevent the catastrophe, for it is claimed that the water having got low, the plates became red hot, and when cold water was pumped in, it immediately flashed into steam, which ac- cumulated faster than the safety valve could dis- pose of it, hence the trouble. The first point that we wish to call attention to in this connection is this: "Do the plates of an ordinary boiler contain heat enough to cause a large body of water to evaporate so rapidly?" Is this not worthy of consideration? The second point is that in the case of an ordinary tubular boiler, the water would have to be very low before the plates could get red hot, and if the feed enters through the bottom of the shell the boiler would have to be entirely empty before cold water could be pumped on to the red hot sheets? We do not advance the claim nor make the assertion that in- sufficiency of water cannot cause a boiler to ex- plode, for we believe that it will under certain conditions. If the iron in a boiler becomes red hot, it is not OF STEAM ENGINEERS. 189 SO strong" as it is when as hot as normal condi- tions, while in use make it, and then it might g-ive out under .an ordinary working- pressure, but an examination of the wreck would surely disclose the cause of the disaster. Experiments have been made to show the truth or falsity of the red hot sheet theory, and in every instance where the cold water was pumped on to the red hot plates, a very natural result followed, and that is that the plates cooled off. The rise in pressure was very slight, or else conspicuous on account of its absence in every instance. 190 MODERN EXAMINATIONS CHAPTER XIvI. STEAM BOII^ER EXPLOSIONS CONTINUED. If the plates are allowed to gfet red hot while the boiler is under a full working- pressure, and they g-ive out on this account, there would be an elongation of the iron, or perhaps we oug'ht to call it a reduction of the cross section at the point of rupture, which would prove, in connec- tion w4th the g-eneral appearance of the iron, that the plates were red hot if such were the case. However, the sheets in a boiler may be ruined by low water, without causing- them to g-et red hot, for if they are not covered for a short time at once, and the practice is persisted in, the streng-th of the iron will be lessened, and in time it may be- come unable to sustain an ordinary working- pressure. Many persons appear to think that low water is the one and only cause of the explosion of steam boilers, and of these we wish to ask a ques- tion. Suppose that you have a chain that is cap- able of sustaining- a weig'ht of 4000 pounds and no more. If you attempt to lift a weig-ht of 6000 pounds wdth it, as a matter of course one or more of the links in it are broken, and the weig-ht is not lifted. Now if you had so arrang-ed matters that the chain was covered with water when the strain was put upon it would it have made it any strong-er than when no water was near it? Undoubtedly you will reply in the neg-ative, but did you ever OF STEAM ENGINEERS. 191 rei3.ect that if more strain is put upon the iron in a boiler than it can stand that it will break in two, just the same as the iron in the chain did when it was taxed beyond its strength? If a boiler is safe at 80 pounds pressure, and you attempt to carry 150 pounds on it, do not be surprised if the result is disastrous, notwithstanding- your boiler is full of water, even to its hig-hest part. Some people appear to think that if a boiler had three g'ag'es of water in it when it exploded, the water would all be there afterwards, forg-etting- that when the pressure is so suddenly relieved, a portion of it will flash into steam and float away. On the other hand, those who advocate the idea that all of the water will always flash into steam under such conditions are not wholly rig-ht, for it cannot be converted into steam unless there is heat enoug-h stored in it to cause it to evaporate, and the necessary heat is not alwa3^s present. Some claim that if a boiler does explode when there are three g'ag^es of water in it, the result will not be disastrous, for as soon as the pressure is relieved, the water will simply run out, and that is all that there is to it, but while some weak boilers may have g'iven out under a low pressure, and the result been as above mentioned, still there was some special cause for it, and it is the ex- ception rather than the rule. There are several other theories which have been advocated at various times in the past, with a greater or less deg-ree of enthusiasm, but which have failed to secure recog-nition by theoretical and practical steam eng-ineers, and consequently have been laid on the shelf. The real cause for all boiler explosions is simply that the structure was not strong' enoug-h to stand the strain put upon it. 192 MODERN EXAMINATIONS Of course we shall proceed to specify the differ- ent reasons for this state of things, and call atten- tion to some of the practices of boiler makers and boiler users, that work together in perfect har- mony to bring- about these catastrophes which some people think originate in mystery and end in uncertainty. We saw an article in an alleged funny paper some time ago, which deprecated the practice of telling what caused a boiler to explode, after it had gone up in a cloud of dust, and expressed a wish that hereafter we might be informed of the dangerous condition of affairs just before the de- parture of the source of power, so that we should have time to get out of the way. A good sugges- tion, truly, but while it is not possible to tell just when the last straw wdll be laid on the camel's back, still we can point out things that should be avoided because they eventually lead to trouble. There is great rivalry among boiler makers at the present time, as to who can furnish a certain plant for the least money, or build a boiler that will evaporate more water than any other extant, and sometimes it appears as if they w^ere endeavor- ing to outdo all others in presenting unique designs. Some of these are not so planned as to be dur- able in practice, although they may show a high duty when tested for economy. It is not intended to specify any particular kind or style, but some of them are so designed that unequal contraction and expansion cause more strain on the several parts than the steam pressure does, which shortens the life of the fabric, and is a defect which is apt to cause trouble before it is discov- ered in practice. The design may be such as to necessitate the OF STEAM ENGINEERS. 193 use of larg"e, flat surfaces, which are alwa^^s to be avoided as much as possible, as they are weak points and must be strengthened with braces and stays, unless said parts are made of cast iron, and then it is almost impossible to g'uard against blow holes and excessive strains caused by the action of the metal itself in cooling after it is cast. If it is necessary to cut larg'e holes in the shell, as it is with some kinds, it is a source of weakness even after the edges have been reinforced by riveting cast-iron frames on them. 194 MODERN EXAMINATIONS CHAPTER XLII. STEAM BOILER EXPLOSIONS CONCLUDED. In some other kinds, series of holes are bored in the shell, into which tubes of some kind or de- scription are expanded, which, without doubt, g-reatly weakens the shell. In others great de- pendence is placed on bolts, which are expected to hold g-ood sized parts tog'ether against the direct pressure of steam, which is also a weak point. Still others are so made that parts above the water line are exposed to the action of the products of combustion on their way to the chim- ney, and although it is expected that those products will be comparatively cool by the time that they reach these exposed parts, still they are sometimes hot enough to do much harm. Poorly constructed boilers are the cause of many explosions, and under this head may be mentioned defective riveting, which is probably the most difficult fault for the running engineer to discover, for boilers have been run for years, and passed several inspections by agents of the insurance company, by whom they are pronounced all rig-ht, and afterwaid, through some mishap, or in some accidental way, it has been discovered that several rivets in a single seam were defective, and undoubtedlv had been so from the time that the boiler was built. If the sheets are punched or drilled separately it sometimes happens that the holes do not come fair when they are put to- gether, and to remedy the trouble the drift pin is OF STEAM ENGINEERS. 195 inserted and made to do regular duty, ,the result being- that the iibres of the iron are disturbed, and sometimes the plate is cracked. In either of the above cases the result is that there is a weak spot there, and when the wreck is examined after the explosion we are told just where the initial rupture was. In other cases not enough braces are put in to make the boiler safe under the pressure that it is designed to carr}^ or the}^ I'^^a-v be improperh^ lo- cated, so that some of them have more strain on them than they can safeh^ carr}^ or one or more of them might be defective and break, thus caus- ing- an excessive load to be put upon the others, causing' them to g*ive out also. Sometimes the braces on a flat surface may be in g'ood order and properly located at that end of them, but at the other end they may be bunched together, which concentrates the strain Jn one place more than it ought to, and trouble follows. Disastrous ex- plosions have been caused by this defective ar- rang-ement of these important parts. Sometimes braces are made in such a wav that when a heavy load is put upon them thev will straig'hten out, thus increasing' their length, allowing the head to bulg'e out before thev really perform the work that they were intended for. Some defects in the iron or steel of which the plates are made are so well covered up as to escape detection until they are put into use, but even if a boiler is well designed and properly constructed after it has been used for a time it will show signs of wear. Some steam users evidently are not aware of this fact, for they seem to be of the opinion that because a boiler is made of iron or steel it can never wear out; but when we consider the work that thev h^ive to do, and the influences 196 MODERN EXAMINATIONS that are at work to cause their destruction, even when well managed and cared for, it is not surprising' that the\^ do not last forever. Take for illustration the case of an ordinary tubular boiler furnishing' steam for an automatic, non- cendensing- eng'ine, developing- 100 horse power. Every hour there are 3000 pounds of water pumped into this boiler, or 15 tons every ten hours. Enoug'h heat must be g'enerated under it to evaporate this larg'e amount of water, and of course it must pass throug'h the iron before it can reach the water. If the plates were always clean it would not be so bad, but when a hard scale has accumulated on 'hem it requires more heat to do the work, as scale is a non-conductor of heat, and consequently the life of the iron is burned out sooner. The fact that this water cir- culates rapidh^ must not be lost sig'ht of, for that portion which is directly over the fire rises as it becomes heated, and must be replaced by that from cooler parts, and this is kept up as long' as the boiler is in use. It is an old saving' that the "g'entle waves wear the solid rock," and will they not wear on iron just as well? In manv cases the scale acts as a protector, and so is of some value, but neverthe- less we notice that the inspectors report some cases of internal g'rooving* nearly every month. But what do we find where boilers are not used in an intelligfent manner? How is it when the fires are drawn, the hot water blown out, and the cold water immediately run into them? The top is covered with brickwork, which retains the heat, while the lower part is cooled oif by the water, which causes it to contract or shorten, and so it is not to be wondered at, when the seams must be caulked or the tubes expanded. Even when one OF STEAM ENGINEERS. 197 boiler of a battery is allowed to cool off, and is then filled with cold water, and the steam is turned into it from the other boilers, the effect is just as bad; yet this is often done in some places. In addi- tion to all this and more that mig-ht be added, inter- nal corrosion is getting- in its work of weakening- the shell, heads and tubes, and when at last the crystalized plates gfive out, or, in other words, an explosion occurs, we are told that the fireman was careless and let the water g*et low, or that some mysterious ag-ency has been at work which is beyond the power of man to control, therefore nobody is to blame. 198 MODERN EXAMINATIONS CHAPTER XLIII. STEAM PIPE COVERINGS. — COMBUSTION OF FUEL. If the question is asked as to what kind of a covering- for steam pipes is the most efficient, it will be safe to reply that on general principles that covering which is the most porous, or in other words which allows the greatest quantit}^ of air to be confined within its limits, will prove the best. As for the need of a covering of an}^ kind that has been established by many experiments at different times and under various circumstances, and while in bare pipes the condensation is some- times as great as half a pound of steam per hour per square foot of surface exposed, when the same pipes have been properly covered, this has been reduced to about one-eighth of a pound in the same time. Excessive condensation is not only expensive, but dangerous in some cases, for with high speed engines w^ith small clearance, if the steam pipe is long, the water of condensation may not do harm of itself, although it will prove an annoyance, but if the boilers prime, even slightly, the two together may wreck the engine, when neither one alone would do it. The porous covering must be in turn covered with some sub- stance that will not admit air through it, for while the air space is well known to be an excellent non- conductor of heat, still it must be remembered that this must be a dead-air space, for if it can circulate around the pipes its efficiency will be very low, or perhaps no better than none at all. OF STEAM ENGINEERS. 199 A covering- made of straw, well protected from the outside air, has proved very efficient on ac- count of the larg-e air space that it formed, while a reg-ular air space covering- has proved a failure, because the air was allowed to circulate. A test was once made on a steam pipe of medium length, but which was rather larg-e for the service re- quired, to determine how much steam was con- densed in its passage to the engine, and it was demonstrated that in cool w^eather fully 25 per cent, of the steam g-enerated was lost, or con- densed before it reached its destination. When the pipes were well protected this was reduced to about three per cent. Much attention has been g-iven to this matter lately, and several first-class coverings are in the market, and ma}^ be procured at reasonable expense. The air that we breathe is composed of ox^^gen and nitrogen, and the coal that the engineer is ex- pected to make steam with is composed of carbon and hydrog-en. We are of the opinion that some of the coal that we have to burn contains larg-e quantities of other matter, and that some of the air that we breathe is diluted with foreign sub- stances, but, however, these are the principal in- gredients with which we have to deal. When we have a good lire in our boiler furnace there is a process of rapid oxidation going on which we call combustion. To carry out this process the car- bon and hydrogen in the fuel combine with the ox3^gen in the air, and when we g-et the proper combination, or, in other words, the rig-ht quali- ties of these tog-ether, the result is perfect combustion. When we consider that the air is composed of oxygen 21 parts and nitrog-en 79 parts b}^ volume; or oxygen 77 parts and nitrog-en 23 parts by weight, and when we consider that the 200 MODERN EXAMINATIONS air that supplies our furnaces is supplied by vol- ume, or, in other words, accordino- to the space vacated by the products of combustion, we see that we must take in much that we do not need, in order to g-et what we do want. It is customarv, however, to speak cf the number of pounds of air that we need to burn a pound of coal, and we are told that average coal chemically consumes 10.7 pounds of air for each pound of combustible, but ordinarily a g^reat deal more than this is used, as we practicallv never realize such results in prac- tice. Again, when we consider that when oxygen and hydrogen are present in the right proportions for it, they combine to form water, instead of fire, and in that case more heat must be taken to evap- orate this water, which, of course, is a loss. An- other authority tells us that the minimum amount of air that will be needed for the best grades of coal is 12 pounds of air for each pound of coal as we find it, and as each pound of air at a tempera- ture of 62° F. occupies 13.14 cubic feet of space, we see that each pound of coal needs 13.14x12 = 157.68 cubic feet of air when burned under the most favorable conditions, and these conditions are not present in an ordinary boiler furnace. On the contrary, many times the conditions are such that 24 pounds, or 315.36 cubic feet, are used for each pound of coal disposed of. From the above it will be seen that if the candidate for a license is asked how many pounds of air is disposed of for each pound of coal consumed, he should reply: "From 12 to 24 pounds, according to conditions." OF STEAM ENGINEERS. 201 CHAPTER XLIV. BURSTING PRESSURE OF STEAM BOILERS, THICK NESS AND TENSILE STRENGTH OF BOILER PLATE. In addition to what was said in Chapters 14, 15 and 16 concerning- the streng-th of a boiler, the following- will be found of value to the engineer. They were taken from standard works on steam eng-ineering-, but as such formula are g-iven in a very condensed form, often without ex- amples by way of illustration, the averag"e engi- neer finds it rather hard work to understand them. The author needs no one to tell him this, for he knoAvs it b}^ experience, and if he can suc- ceed in putting matter in more extended form, so that it may be more readily applied by his asso- ciates in the profession of steam eng-ineering, one of his objects will be accomplished. The following are given for determining the bursting pressure, thickness of plate, and tensile streng-th of plate, respectively : 4480 / ^^ d dt> 4480 6^ dp =t 4480 ^^ in which /^thickness of plate in decimals of an 202 MODERN EXAMINATIONS inch, ir=tensile streng'th of plate in tons per square inch, d in which /= thickness of head in inches, 6-= tensile stress of the head in tons per square inch at the the elastic limit, <^= diameter of the boiler, and/ = pounds per square inch. Applying this to the case in hand, and substi- tuting for the symbols their values, and our for- mula becomes 204 MODERN EXAMINATIONS 815 X. OX 11. 16 =75.8 60 pounds. Using- 5 as a factor of safety gives us 15.16 pounds as the safe working- pressure of such a head without braces or sta3^s. An explan-' ation of the way that we obtain the value of S in this case is in order. As before noted, we take tensile streng-th of the iron at 50,000 pounds, or 22.32 tons, and as the elastic limit is one-half of this, we divide 22.32 by 2, and the quotient is 11.16 tons. As even numbers are often used in these calculations, the value of S is taken at 12 tons, which is proper here, whence the following- formula is derived: For an iron head / 10,000—==^ d and for a steel head 11,500—=/ d in which /= thickness of head in inches, ^=diam- eter of the boiler, and /=bulg-ing- pressure in pounds per square inch. Making use of the former, we have .5 10,000— =83 60 pounds bulg-ing- pressure, or 16.6 pounds safe working- pressure. This is a trifle more than we obtained by a preceding- formula, but this increase is due to the fact that elastic limit is taken at 12 tons, which makes the tensile strength 24 tons or 53,760 pounds, instead of 50,000 pounds as we as- sumed. The terms "pounds" and "tons" are OF STEAM ENGINEERS. 205 both used here in order that the reader may fully understand both of them, but we prefer "pounds" wherever practicable, as it ag*rees with American practice, while the ton is more frequently used by the English eng*ineer. 206 MODERN EXAMINATIONS CPAPTER XLV. FLAT, CONCAVE AND CONVEX BOILER HEADS. If the head of the boiler that we took for illus- tration were made of steel instead of iron we would use the following- formula: t 11500—=^ d in which the symbols refer to the same elements as in that given for an iron head. Applying* this g-ives us .5 11500— =95.45 60 pounds, and with a factor of safety of five, the result is 19.09 pounds. Suppose that this boiler is equipped with a dome 24 inches in diameter, and this dome has a cast iron head two inches thick. If we wish to know how much this will bulg-e at the centre, without exceeding- the elastic limit, we can use the following- formula to deter- mine it : d — =B 44 and when we wish to determine the pressure that will do this we use the following-: t 4000— =j6 d In which <:/= diameter of head, 3 = deflection at OF STEAM ENGINEERS. 207 the centre, within the elastic limit, /^thickness of head in inches, and ^= pressure in pounds per square inch. Applying- these we have 24 " 2 — =.545 inch, and 4000— =332 44 24 pounds bulging* pressure, or 66.4 pounds safe working" pressure. According' to the above this head is much weaker than other parts of the boiler, but there are several thing's to be taken in consideration which effect the result. The formula is based on the assumption that cast iron has an elastic streng-th of five tons per square inch of sectional area, as being* an averag^e, but while some very poor specimens have shown even less streng-th than this, other g-ood specimens possess double this streng-th, and exceptionally g-ood ones have demonstrated that it requires 17 tons to break them, which w^ould make the allow- able pressure more than three times that g-iven by the formula. Remelting' the iron improves its quality, and without doubt none but the very best cast iron that can be procured should ever be used in boiler construction. This material possesses but very little elasticity, so that the tensile strength is but little more than the elastic strength. Usually the steam nozzle is cast on the dome head, and while the hole tends to make the part w^eak, still the raised portion of the nozzle reinforces it, and in a g'reat measure counteracts its bad effects. If it is necessary to drill holes in such heads to make minor steam connections they should be located as far apart as possible. The foreg-oing- formulas refer to flat heads, and ordinarily these are what the eng-ineer has to deal with, but it may be well for him to understand 208 MODERN EXAMINATIONS how to calculate the pressure that a spherical head will stand, or in other words a head made in convex form, or in the engineer's vernacular, "a bulg-ed head." Such a head cannot very well be used for a tube sheet on a boiler, but there are other places where such heads are used. Their streng-th may be determined by use of this formula 8960 t s V in which ^=pressure in pounds per square inch, ^'=thickness of the head in inches, ^= elastic streng-th of head in tons per square inch, r= radius of the head, and ^'= versed sign or rise of the head in inches. Assuming- elements of the preceding- case, except that the head is bulg"ed out six inches at the centre and made spherical in form by the boiler makers, instead of being- flat, and substi- tuting for the symbols their values, our formula becomes 8960 X. 5x11. 16 -:320 30^' 6 pounds, elastic limit, or 64 pounds safe working pressure. Having explained the way to read many of the formula which appear in the preceding' chapters of this book, I have considered it necessary to ex- plain those in this chapter further than to give the figures which illustrate their application, but OF STEAM ENGINEERS. 209 as the one just g-iven looks rather formidable, a full explanation may be advisable. The number 8%0 is to be multiplied by the thickness of the head in inches or parts of an inch, and the product by the elastic strength in tons per square inch, and this we may term our first product. The radius, or one-half of the diameter of the head is to be multiplied by itself and the product divided b}^ the rise of the head in inches. To this quotient add the rise of the head and the sum will be our second product. Divide the first by the second and the quotient will be the elastic limit in pounds per square inch. Thus we see that by giving' the head a spherical form, the rise of the segment being six inches, we have increased the safe working press- ure from 15.16 pounds in the flat head to 64 pounds in the spherical one. A careful study of these formulas will show that in calculating' the safe working' pressure of the shell, the ultimate tensile strength of the iron is used, while for the heads the elastic strength is taken, but if we wish to make a comparison of the strength of the shell of a boiler, made without seam or weld, and of a spherical head, we must take the same quantity for both, which ma}^ be stated at 24 tons tensile strength. In this case both shell and head must be of the same thickness in order to make the comparison proper. If a 60-inch boiler shell is made of iron one-half inch thick we find that it will take 4480 X .5x24-^60=8% pounds to burst it, and if the head is spherical, the rise of it being eight inches, it will require 8960 X .5x24= 107520; 30x30^8+8 = 120.5; 107520^120.5=892 pounds to rupture it, therefore if the rise of the spherical head is made one-eighth of the diameter of the shell, or one- 210 MODERN EXAMINATIONS fourth of its radius, approximately, both head and shell will possess equal streng-th. Care should be taken to avoid confounding- the tensile streng-th of the iron in these calculations with its elastic limit. A careful study of these problems will show that, if the wrought iron head of a plain cylinder boiler should be made concave, it would be much strong'er than either a flat or a convex one, for the reason that the pressure tends to compress the iron, and the same authority that tells us that the ultimate tensile streng-th of iron in tension is about 24 tons, also tells us that "the resistance to compression is an indefinite quantity." From this it would appear to the casual reader that the streng'th of a concave head is so g-reat as to be almost unknown, but when we consider that the concave head will not retain its form under great pressure, and if it did, it would bring- an excesive stress to bear on that part of the shell which immediately surrounds it, we see that there are modifying* conditions present. OF STEAM ENGINEERS. 211 CHAPTER XLVI. WROUGHT IRON, STEEL AND CAST IRON BOILER HEADS. It may be well to give a separate formula to de- termine the elastic limit of streng'th of spherical boiler heads when made of wroug'ht iron, steel or cast iron. They are as follows : 108,000 t V for a wroug-ht iron head. 125,000 / =p +v V *^or a steel head, and 45,000 =p +v for a cast iron head. In the above formulas the elastic limit of the metal is taken at 12 tons for wroug'ht iron, 14 tons for steel and 5 tons for cast iron, and the explanation found in Chapter 45 will apply here. In the 60 inch wroug'ht iron boiler that we have taken for illustration in work- 212 MODERN EXAMINATIONS ing out and applying" these rules and formula there are some flat surfaces which will need to be braced, as for instance the heads above and below the tubes, and when these are not strengfthened except b}^ the braces, the following- formula may be safely used : 407 / ^^ =p a in which / = thickness of the plate in inches, .9 = strengfth of the plate in tons per square inch at the elastic limit, ^ = maximum elastic pressure in pounds per square inch, and 2 inches wide, and this five-inch space is well within the limits of what the head will safely bear of its own thickness, as previously explained. The O represents another space five inches wide, and P is another four-inch tee iron, while Q is a space 2}4 inches wide, which is supported b}'^ the tee iron. By adding- tog-ether the above, it will be seen that w^hile the radius of this circle is 26.5 inches, 25.5 inches are here provided for, leaving a small segment only one inch in height out of the 236 MODERN EXAMINATIONS calculation, but as its area is small, and our factor of safety in calculating- on the other elements is larg-e, this will not materially affect the result. Let us now see how much pressure the tee iron N will be called upon to support. By drawing* a line throug-h its centre extending* from side to side of the circle represented by the dotted lines, we find that the averag*e leng*th of this line is 47.5 inches, which we will call 48 inches for convenience in calculating*. The space that it has to support is nine inches wide, as already explained, there- fore 48x9 = 433 square inches, and as we are to carry 87.5 pounds pressure, 432x87.5=37,800 pounds. We will make our braces of round iron F«6 18 .^^ ^=o>'-^^ ^ ^^ p l^v // o ^>s ff H n 1 C- n /> 1^ inches in diameter, the area of which is 1.767 square inches, and as we are not to exceed a pull of 6000 pounds per square inch on our braces, 1.767x6000 = 10,602 pounds, which is the limit for each brace; 37,800^10,602=3.56, so that we shall OF STEAM ENGINEERS. 237 need four braces. By ptittingf one brace six inches each side of the centre of this iron, and another one 12 inches from each of these, we find that they are evenly distributed, and that the g-reatest span or distance between supports is 12 inches. This is how we determined the value of Iv in the formula. In putting- in these braces it would be well to run the two nearest the centre from head to head, and the two outside ones from head to shell. In determining- the space to be supported by the upper tee iron, we find that its averagfe length is about 32.25 inches. By locating* one brace in the centre of this iron, and one each side of it at a distance of 11 inches, our load will be properly distributed, and as the span here is less than in the case of the lower one, w^e are on the safe side. As the space to be supported by the tee iron is 32.25 inches long* and 9 inches wade, it contains 290.25 square inches, and the total pressure on it is 25,396 pounds. As each brace is safe under a pull of more than 10,000 pounds, the marg-in is larg-e enoug-h to cover every conting-ency. As shown in Chapter 50, this span of 12 inches has an ultimate streng-th of 95,470 pounds. Tak- ing* one-half of this as the elastic limit, and using* a factor of safety of -^\e, as before, we find the safe load to be 9547 pounds. Let us see whether our working- load exceeds this or not. The span is 12 inches long-, and it supports a space nine inches wide; 9x12 = 108 square inches, and multi- plying* by the pressure gives us 108x87.5=9450, which is a trifle less than the safe load. With the upper tee iron the working* load will be less than this, showing* that we are still on the safe side. If the lower row of tubes are so low down that only a hand hole can be put in each head, below 238 MODERN EXAMINATIONS the tubes, then no braces will be needed here, but if a manhole is put in the front head, then braces will be needed according' to conditions, but usu- ally two are enough, and they should extend from head to head, as it is poor practice to rivet a brace to the shell directly over the fire, It may be the opinion of some readers that such a boiler is safe under a much higher pressure than this, and their opinion may be based on the fact that they know of similar boilers that are doing it, but what does that signify? A certain gentle- man wanted to hire a coachman, and advertising the fact, was soon called upon by several appli- cants for the position. He submitted to each one in turn the following question: '* Suppose that I eng'ag'e you to drive for me, and while riding with my wife and family we should come to the vicinity of a precipice. How near could you drive to the edge of it and escape accident?" The first one said that he could approach within a yard of it and get away safely. He was told that if his services were required he would be notified. The second one said that he could drive within a foot of it and yet be safe. He received the same reply as the first one. The third one said that he was such a complete master of his business that he could cause the carriage wheels to roll within one inch of the edge and still not go over it. He received the same reply as his predecessors. The fourth one said that he would keep just as far away from it as circumstances would allow. He was engaged at once. OF STEAM ENGINEERS. 239 CHAPTER LII. SAFE WORKING AND COLLAPSING PRESSURE OF TUBES AND FLUES. In some of the works on steam boilers there is very little said concerning* the collapsing- pressure of tubes and flues. This may be partly accounted for by the fact that in the ordinary tubular boiler, with three or four-inch tubes, the col- lapsing- pressure of them is so much g-reater than the bursting" pressure of the shell and heads, that they (the tubes) are practically out of the ques- tion. As an illustration of the truth of the above statement, we introduce the following- formula: 4480 S T =P D in which S = collapsing- pressure in tons per square inch of section of metal, T— thickness of tube in inches and D = the external diameter in inches. The vakie of S is obtained by the following' rule: Prom 25 subtract 2| times the diameter of the tube. For a 3 inch tube it will be 2f X3=8 and 25—8 = 17 tons. For a 4 inch tube it will be 2f X 4 = 10.64 and 25-10.64 = 14.36 tons. We will apply this to the case of a 4 inch tube .125 inch thick and when we have substituted for the symbols their values, our formula becomes 4480 X 14. 36 X. 125 = 2010 240 MODERN EXAMINATIONS pounds collapsing* pressure. Or the following may be used as it is at times more convenient. 112,000 T 12,000=P D By this we mean that if 112,000 is divided by the diameter of the tube and 12,000 subtracted from the quotient, then by multiplying* the remainder by the thickness of the tube, the product will be the collapsing- presure in pounds. Applying- this to the four inch tube as before we have 112,000 .125X 12,000=2000 4 pounds collapsing- pressure. This is practically the same as with the preceding- formula. Using- a factor of safety of 10, which corresponds to a factor of five when based on the elastic limit, the safe working* pressure of this tube is 200 pounds, and if it were a three-inch tube it would be 316 pounds. The foreg-oing* rules apply to small round tubes not more than 18 feet long-, but not to large flues. The United States Treasury rules for finding the strength of lap-welded flues, when the diam- eter is not less than seven inches or more than 16 inches, may be expressed by the following form- ula: T4400 = P R in w^hich T=thickness of flue, R = radius of flue in inches, and P = the pressure that may safely be carried. This, however, is subject to modifica- tions, one of w^hich is that the leng-th must not ex- ceed 18 feet, for when they are longer than this a reduction in the pressure carried must be made OF STEAM ENGINEERS. 241 amounting- to three pounds for each foot or frac- tion thereof over 18 feet. When the pressure is between 60 and 120 pounds, the flue must be made in lengths not to exceed five feet, and riveted to- g-ether in a substantial manner, or corrug-ated, the effect of which is practically the same. If the flue is more than 16 inches and less than 40 inches in diameter, the same formula may be used, except that instead of using- the constant number 4400 we must substitute the number 2840. Applying- the formula to a flue 14 inches in diam- eter and one-quarter of an inch thick, and substi- tuting* for the symbols their values, our formula becomes .25x4400 =157 pounds 7 for a leng-th of 18 feet or less, but if it were 22 feet long-, the pressure would be 157 — 12 = 145 pounds. Applying- the latter to a flue 24 inches in diam- eter, less than 18 feet long-, and three-eighths of an inch thick, the pressure would be .375x2840 =88.7 pounds. 12 The rule given by the same authority to determine the thickness of a flue for a given pressure, is ex- pressed by the following formula: RP =T 4400 the letters denoting the same factors as in the two previous ones. Applying this to thel4-inch flue we have 242 MODERN EXAMINATIONS 7x157 =.25 inch. 4400 Previous to 1892 the United States Treasury rules specified that the flues of a boiler should be made in lengths not exceeding three feet, in which case the following applies : 89,600 T^ =P LD in which T=thickness, Iv=length of sections in feet, D = diameter in inches, and P = safe working pressure. Applying this to our 14-inch flue, our formula becomes 89600 X. 25 X. 25 =133 pounds. 3X14 Thus it will be seen that every part of this boiler is abundantly able to withstand the pressure to be put upon it, for the shell has a large margin, the braces are not overloaded, neither are they spaced so far apart as to introduce an element of danger, and even if flues are put into it instead of tubes, it is still safe under the designated pressure. OF STEAM ENGINEERS. 243 CHAPTER LIII. CONCLUSION. We have now arrived at the conckiding* chapter of this book, in which we have called attention to calculations that engineers are supposed to under- stand when they aspire to positions in places where a strict license law is in force. Occasion- ally we meet a man who claims that all of the du- ties of an engineer can be learned in a month. If we were to proceed to argue the case, we might be tempted to assert that possibly that portion of the business that he is familiar with could be learned within the specified time, but such argu- ments are not always profitable. It is the author's experience that those engi- neers who study the most are the ones who are willing to allow that there is much more for them to learn, while oftentimes those who never spend any money or time in getting posted in the theo- retical part of their business are the ones who claim to know it all. The author is willing to ad- mit that the more a man studies steam engineering the more he will feel that there is more beyond, and that it is better further on, and this, too, after having spent several years in patient study, re- search and endeavors to improve every oppor- tunity to gain knowledge on the subject. It was our privilege some time ago to visit a panorama representing one of the greatest battle- fields known to history. At the entrance we pur- chased a key explaining the entire view in detail. 244 MODERN EXAMINATIONS but at first we were contented to gaze at the grand spectacle as a whole. Soon tiring* of this we were about to depart, but opening- the key and looking up the meaning of one part after another, and calling to mind the facts that they pictured to us, we soon found that, together with a friend, we were intensely interested, and when more than two hours had passed away, we had mastered only a portion of what was before us, but could not stay longer at that time. Shortly afterward, while conversing with a person who lived in that vicinity, we spoke of the grandeur of the sight, and of the wide extent of its teachings, but were coolly informed that it could all be understood in 15 minutes time. So it is with some men in charge of steam plants, for they understand only what may be termed the superficial part of the business in which they are engaged, and consequently think that it can all be learned in a few weeks, but when they get a key to it (and we believe this to be a proper term, for it unlocks one of the doors to the storehouse of knowledge) and make use of it, they soon discover their mistake. It has been one of the objects of the author to make every subject treated of as plain as possible, and to in- troduce only those rules and formulas which are sanctioned by good authorities and that are based on common sense. OF STEAM ENGINEERS. 245 I IN D E X TO 300 EXAMINATION Questions and Answers (The number after each question denotes the number of the page on which the answer to the question will be found.: 1. What is lap ? 28 2. What is lead ? 29 3. What is clearance ? 119 4. Explain how to set valves ? 29 5. Explain how to reverse an engine ? 30 6. Which travels the farthest, the crank pin or wrist pin ? 32 7. What is an eccentric ? 32 8. How do you find the throw of an eccentric?. . 32 9. Does it change the throw of it to reduce its outside diameter ? 33 10. How do you determine the proper size of steam pipe? ,. . .34-172 11. How do you determine the proper size of ex- haust pipe? 34 12. How do you determine the proper size of steam ports? 35 ^46 MODERN EXAMINATIONS 13. How do you determine the proper size of ex- haust ports? 35 14. What should be diameter of crank shaft?. . . .36-180 15. What should be the diameter crank pin? ^6 16. What should be the diameter of wrist pin?. ... $6 17. What should be the diameter of connecting rod? ^6 18. How long should the connecting rod be to give good results. ^6 19. How large should the piston rod be? 37 20. . What should be the length of the main bear- ing? 37 21. How would you determine the length of the eccentric rod ? 37 22. How would you determine the length of the valve rod ? , 37 23. What is the counterbore? . . . 37 24. What is the counterbore for? 37 25. What is the difference between a non-condens- ing and a condensing engine? 39 26. What is the forward pressure?. . 39 27. What is the back pressure? 39 28. What is the mean effective pressure? 39-106 29. What is the back pressure absolute? 40 30. What is the initial pressure? 40 31. What is the terminal pressure? 40 32. What is a throttling engine? 40 ^;^. What is an automatic engine? 40 34. What is an adjustable cut-off engine? 40 35. What is a compound engine? 40 36. What is a compound condensing engine? 40 OF STEAM ENGINEERS. 247 37. What is a triple expansion engine? 40 38. What is a triple expansion condensing engine? 40 39. What is a quadruple expansion engine? 41 40. What is a quadruple expansion condensing en- gine ? 41 41. What are the advantages and the disadv^antages of the before mentioned types? 41 42. What is a horse power? 45 43. How do you determine the horse power of an engine? 45 44. How do you find the area of a circle? 48 45. State how to determine the speed of engine, the size of cylinder, mean effective pressure and horse power being given? 49 46. State how to determine the diameter of the piston of an engine, the stroke, revolutions, mean effective pressure and horse power be- ing given? 49 47. How do you find the square root of a number? 50 48. How would you determine the necessary mean effective pressure to do a certain amount of work, all other data being given? 54 49. How do you find the horse power constant?. . 54 50. How would you increase the mean effective pressure of an engine? 54 51. Is there any other way of increasing the power of an engine ? 55 52. How would you determine the speed that an engine is intended to run at? 56 53. . How would you determine the proper size of governor pulle}^ ? 57 54. Explain how to figure speed of shafting? 58 55. How would you determine the mean effective pressure of an engine without an indicator? 60 248 MODERN EXAMINATIONS 56. What is the ratio of expansion? 60 57. What are hyperbolic logarithms? 61 58. How would you tell whether the valves and piston are tight or not? 62 5.9. What is a crank ? 62 60. What is meant by the valve gear of an engine 63 61. How do you ascertain the necessary weight for the rim of a flywheel? 64 62. How is the constant whole number 7,000,000 obtained ? 66 6;^. What is a flywheel for? 64 64. Give the formula for obtaining the weight of the entire wheel? 66 65. What is the safe limit of speed for flywheels?. . 68 66. How do you determine the percentage of gain in pressure due to adding a condenser?. ... 70 67. If a condenser is added how much can we re- duce the boiler pressure and keep the point of cut-off and mean effective pressure con- stant? 70 68. What is the theoretical saving by adding a con- denser? 71 69. How would you determine the point of cut-off to give a certain mean effective pressure?. . 71 70. How would you prove this rule? 72 71. How would you determine the safe working pressure of a boiler?. 74 72. What is meant by the pitch of the rivets? 79 73. How Avould you determine the strength of a section of solid plate? 79 74. How do you determine the strength of net sections of plate? 80 75. How do you calculate the strength of rivets in a joint? 80 OF STEAM ENGINEERS. 249 76. How do you calculate the strength of a double welt butt joint? 81 77. What part of the ordinary tubular boiler is usually calculated to be the weakest?. 83 78. Is it a good plan to have braces extend from head to head ? 83 79. Give the reasons? 8;^ 80. Why are pieces of T iron riveted to boiler heads? 85 81. How much stress is usually allowed for braces in boilers per square inch of sectional area? 83 82. How W(3uld you determine the safe load for a round brace i 1-2 inches in diameter? 84 83. How do you determine the number of braces necessary for a flat surface? 84 84. Is the stress on a brace extending from head to head greater than if it was only from head to shell? 85 85. Is it a good plan to brace from head to shell on the lower part of a tubular boiler? 85 86. Why not? 85 87. Which makes the strongest joints, punched or drilled holes? 85 88. Give the reason why? 85 89. Is it necessary to calculate on the whole surface of a head exposed to pressure, when laying out braces for it? 85 90. How do you determine the horse power of a boiler? 87 91. How many square feet of grate surface should be allowed per square foot of heating sur- face ? 88 92. How do you find the heating surface of a boiler? 88 250 MODERN EXAMINATIONS 93. What is the water space of a boiler, and how- do you ascertain it? 89 94. How would you reduce it to gallons? 89 95. How would you determine the weight of the water in it? 89 96. How do you determine the cubical contents of the steam space? 89 97. What is meant by the term "foaming," and what causes it? 89 98. What is meant by priming? 89 99. What is a separator? 90 100. How would you determine the proper size of safety valve for a boiler? 91 loi. How would you determine the area of opening of a safety valve v^ith a seat beveled at an angle of 45 degrees? 93 102. How would you determine the area, if the angle were greater or less than 45 degrees? 93 103. How would you determine the area of opening of a flat valve and seat? 93 104. Give an example illustrating the above rules?. . 95 105. What is the difference in the area of opening, between a valve with a seat beveled at an angle of 45 degrees and one with a flat seat? 96 106. How would you determine the proper size of pump for a steam plant? 96 107. Hov/ do you calculate the contents of the water cylinder of a pump ? 97 108. Is the capacity of an injector increased by sup- plying it with water under pressure? 98 109. Can hot water be lifted as cold water is? 98 no. Will an injector take hot water like a pump?. . 98 III. What is the difference between a hot water and cold water pump? 98 OF STEAM ENGINEERS. 251 112 How high can a pump raise cold water by suc- tion? 98 113. How hot can water be heated by exhaust steam? 99 114. How do you calculate the saving made by heat- ing the feed water? 99 115. How would you test the temperature of feed water? 100 116. What is the difference between natural and forced draught? 100 117. Which is the most economical? loi 118. How would you determine the area of a chim- ney for a steam plant ? loi 119. What is a steam engine indicator? 103 120. What are its principle uses? 104 121. How does it show the difference in the load on an engine? 104 122. Name the lines or parts of an indicator card?. . 104 123. How do you locate the line of perfect vacuum? 104 124 Is there any way to determine the pressure of the atmosphere from height about sea level? 105 125. How do you locate the atmospheric line? 104 126. Explain the way to lay out the theoretical ex- pansion line? 108 T27. How do you determine the M. E. P. by the planimeter ? iii 128. Is it possible to calculate the water consump- tion from the card ? iii 129. Does the amount so obtained agree with the amount actually used? 112 130. Give reasons for the discrepancy? 112 131. Explain the theory of calculating the water consumption from the card? 113 132. Give an example and explain it in detail? 113 252 MODERN EXAMINATIONS 133. How do you determine the volume of steam used by an engine in a given time? 115 134. Give a formula which takes into account the saving by compression? 117 135. Illustrate a way to change common fractions into decimals ? 75 136. How do you ascertain the portion of the return stroke uncompleted at compression? 119 137. Give formula for determining water consump- tion from pressure at cut-off? 119 138. Is the percentage of clearance the same when taking volume at cut-off as when taking it at release? 122 139. Can the rate of water consumption be obtained directly from the card without knowing the horse power developed? 122 140. When so obtained, how do you find the total accounted for? 123 141. Give another rule for calculating the water consumption? 124 142. Give an example illustrating the rule as applied to an ordinary card? 124 143. What difference does it make if the terminal pressure exceeds the compression? 126 144. How does this rule work if the release pressure is below the atmosphere? 129 145. If the release pressure is below the atmospheric pressure, what is the effect of opening the exhaust valve before the completion of the stroke ? 129 146. In this case what shall we do with the compres- sion line? 129 147. If the water rate is high, is it always due to the engine itself ? 131 148. Why is it better to have an engine under-loaded than over-loaded? 131 OF STEAM ENGINEERS. 253 149. Give a rule for calculating the water rate in the case of a compound engine 131 150. For what purpose are these rules useful? 132 151. If the diagram shows a higher terminal pressure than it should, where would you look for the trouble ? 133 152. Explain the meaning of the term "re-evapora- tion ?" 133 153. What is meant by initial cylinder condensation? 133 154. What causes it? 133 155. If the actual expansion line is below the theo- retical one, where would you look for the trouble ? 134 156. If a steam engine is in an exposed place in cold weather and the cylinder is not properly cov- ered, what is the effect? 134 157. What will cause the expansion line to rise sud- denly? 134 158. If the expansion line falls suddenly, where would you expect to find the cause of it? 135 159. If the counter pressure line rises suddenly, where would you look for the cause of it? 135 160. Does excessive compression affect the economy of an engine? 135 161. Is it dangerous? 135 162. Can you give a rule for the amount of compres- sion to be given that will apply in all cases? 136 163. What general rule applies? 136 164. How can we determine the power developed by direct steam and expansion? 13'/ 165. How do we know that the steam does. work after the cut-off has taken place? 137 166. How can we shorten up this calculation? 138 167. Give a rule for determining the work done dur- ing expansion ? 138 254 MODERN EXAMINATIONS i68. Are the terms "work done" and "power de- veloped" interchangeable? 138 169. Do such rules take account of clearance and com- pression? . 138 170. Are the pressures used in such calculations abso- lute? 138 171. How would you prove the above mentioned rules ? 138 172. What pressure should we carry on our boiler to insure the best economy with an automatic engine? 139 173. Does this apply to underloaded engines? 139 174. Does it apply equally well to a compound con- densing engine? 141 175. What is the effect in a simple non-condensing engine if we lower the boiler pressure? 141 176. What effect does it have in a compound condens- ing engine? 141 177. How does the indicator assist us in deciding on the economy of the compound condensing engine? 142 178. If we lessen the difference between the initial and the terminal pressures, what is the re- sult? 143 179. Does it increase the efficiency of the compound engine to add a condenser? 143 180. Give the reason for it? 143 181. What are the comparative sizes of cylinders in ordinary practice for this style of engine?. . . . 144 182. Does the indicator card enable us to determine the amount of water needed for the con- denser ? 145 183. Give a formula for determining the volume of circulating water needed 145 184. What does the volume mean in this connection? 146 OF STEAM ENGINEERS. 255 185. Is it a good plan to use a feed water heater with a surface condenser? 146 186. What effect does the condenser have on the temperature of the feed water? 146 187. Give reasons for it 146 188. Give an illustration from practice of the applica- tion of this formula 146 189. Flow do you determine the power developed by the compound engine? 148 190. If a simple engine is overloaded, will it pay to add a low pressure cylinder? 150 191. Give formula for amount of water needed to run a jet condenser 151 192. Illustrate and explain the use of the same? 152 193. Give formula for use when temperature of steam is given instead of its pressure 152 194. How shall we determine the area of injection pipe? 152 195. What is the meaning of the term "density of steam?" 153 196. If density is given, how would you determine the weight? 154 197. How do you change the vacuum in inches to pounds? 155 198. How do you determine the flow of water in feet per second due to a stated vacuum? 155 199. Does it make a difference whether the injection water is above or below the condenser? 156 200. Is the formula an inflexible one? 156 201. Does the quality of the injection water affect the result ? 156 202. What precautions should be taken when indicat- ing an engine ? 157 203. Is a knowledge of the indicator of value to the running engineer? 157 256 MODERN EXAMINATIONS 204. Name the systems in use for heating buildings.. 159 205. Describe them in detail 159 206. Why is the use of a fan recommended? 160 207. Can the water of condensation be returned with- out a pump? 161 208. Explain the principle cause of the failure of water to return? 161 209. In how many ways may systems of direct radia- tion be piped? 163 210. Describe them 163 211. Which is the best?. . , 164 212. What are the objections to the others? 164 213. How should globe valves be connected? 165 214. Give a rule for determining the radiating surface necessary to heat a room 167 215. What objections are there to the use of this rule? 168 216. Give a rule that takes into account all of the conditions 168 217. Give a rule for reducing Avail surface to its equivalent in glass surface 168 218. Give an illustration of the way to estimate the heating surface necessary for a building. ... 172 219. Give a rule for determining the area of a main steam pipe 172 220. Give another rule for the same purpose 173 221. About how much direct heating surface of a boiler will be needed for a given case? 173 222. Does it pay to use exhaust steam for heating purposes? 175 223. How would you estimate the cost of it? 175 224. Does it necessarily cause excessive back press- ure on an engine to use the exhaust for this purpose? 175 OF STEAM ENGINEERS. 257 225. Give a formula for determining the diameter of wrought iron mill shafting to transmit a given amount of power 178 226. If the diameter and speed are given, how would you determine the power that it will transmit? 179 227. Give a formula for determining the diameter of steel shafting 179 228. If the diameter and speed are given, how would you determine the power that it will transmit? 180 229. Give a formula for determining the diameter of cast iron shafting 180 230. If the diameter and speed are given, how would you determine the power that it will transmit? 180 231. Do these rules apply to crank shafts of steam engines ? 180 232. Can you give a formula that does apply to them? 181 2;^^. Give an illustration of the working of this formula 181 234. Can you give a rule that will determine the power that a belt will transmit? 183 235. What is the safe working strength of leather belting? 183 236. What is meant by the term "half angle of con- tract ?" 184 237. Why is it not taken at 90 degrees? 184 238. Give a formula for determining the breadth of belt to transmit a given horse power. ...... 184 239. To what kind of belts do these formula apply?. . 185 240. Mention conditions that will modify them 185 241. What theories are advanced to account for boiler explosions? 186 242. Explain the superheated water theory 186 243. Can electricity accumulate in an ordinary boiler? 188 258 MODERN EXAMINATIONS 244. What is the effect of pumping cold water on to red hot boiler plates? 189 245. What is the effect of heating boiler plates red hot? 188 246. If a boiler fails on account of the plates being red hot, will an examination of the wreck dis- close the fact? 189 247. What will be the appearance of the iron after a rupture from this cause? 190 248. What becomes of the water in a boiler when it explodes? 191 249. Because a boiler shows a high duty when tested does it prove that it is a good one to pur- chase? 192 250. What effect does it have on the shell of a boiler to bore holes in it and expand tubes or pipes into them? 194 251. What is the effect of defective riveting? 194 252. Of the use of the drift pin? 194 253. Of an insufficient number of braces?. 195 254. Of improperly located braces? 195 255. Of improperly constructed braces? 195 256. Will a boiler wear out the same as any other structure? 195 257. What is the effect of blowing off a boiler and immediately refilling it with cold water?. ... 196 258. What kind of covering is the best for steam pipes ? 198 259. How much steam may be condensed in un- covered pipes? 198 260. Why is excessive condensation a detriment?. . . . 198 261. What is air composed of? 199 262. What is combustion? 199 OF STEAM ENGINEERS. 259 263. How is this process carried on? 199 264. What is the minimum amount of air required to burn a pound of coal?. . 200 265. About how much is needed under average con- ditions? 200 266. Give a formula to determine the bursting press- ure of a boiler 201 267. For the necessary thickness of the shell 201 268. For strength of plates 201 269. If the strength of boiler plate is stated in pounds, how would you reduce it to tons? 202 270. Give a formula for determining the distance that a boiler head may be bulged without exceed- ing the elastic limit 203 271. Give a rule for calculating this pressure if the head is of wrought iron 203 272. Also for a steel head 204 273. Why is it preferable to use the term "pounds" in these calculations, rather than "tons?". . . . 205 274. Give a rule for determining the bulging pressure of a cast iron head 206 275. How does the elastic limit of cast iron compare with its tensile strength? 207 276. How do you calculate the elastic limit of spher- ical boiler heads? 208 277. What must the rise of a spherical head be to make it as strong as the shell is when both are of the same thickness and made of the same material? 209 278. Is a concave head stronger than a flat one?. ... 210 279. Why?....... 210 280. State the conditions which modify the strength of concave heads? 210 260 MODERN EXAMINATIONS 281. Give a rule for determining the proper distance apart of braces or stays in a boiler 212 282. What is meant by ''clear distance apart" of braces or stays in a boiler? 212 283. Give a rule for determining the pressure that a flat head will safely carry 212 284. For the proper thickness of a flat head 213 285. Illustrate the difference between a steel head and one of wrought iron in this connection?. ... 214 286. Give a rule for determining the diameter of a brace that will safely withstand the same pressure that the flat surface of the head will. 214 287. In the case of a threaded stay bolt, how shall we calculate the diameter? 215 288. Give a rule for ascertaining the distance on a head which is supported by the flange 217 289. To what extent do tubes impart stiffness to the head of a boiler? 218 290. How would you reduce the number of braces necessary for a boiler head not otherwise supported ? 218 291. What is meant by the "segment of a circle?". . 221 292. How would you determine the area of a segment that is less than a semi-circle? 221 293. When it is greater than a semi-circle? 222 294. Explain and illustrate the way to calculate the strength of tee irons 225 295. What is the neutral axis of a piece of tee iron? 227 296. Are braces required below the tubes? 238 297. As boilers are usually constructed, which is the strongest, the shell or the tubes? 239 298. Give rules for calculating the collapsing pressure of tubes 239 299. For the safe working pressure of flues 240 300. Give a rule for determining the thickness of flues, to withstand a given pressure 242 OF STEAM ENGINEERS. 261 I N D B X. ?^'o. of Question. Page. Absolute pressure used 170. Adjustable cut-off engine 34. Air, composition of 261 . Air required to burn a pound of coal. . . . 264, Angle of contact 236 , Area of circle 44 , Area of opening of safety valve 101-102-103-104-105 , Area of chimney 118 Area of injection pipe 194 Area of main steam pipe 10-219-220 Atmosphere, pressure of 124 Atmospheric line 125 Automatic engine -^^ Automatic engine, pressure for best econ- omy 172 Axis, neutral 295 34- 40 199 200 184 48 93 lOI 152 -172 105 104 40 227 Back pressure 27-29 Back pressure, caused by heating building .224 Bearing, main 20 Belt, breadth of for given horse power. ... 238 Belt, power that it will transmit 234 Belt, safe working strength of 235 39-40 •175 • 37 .184 .183 .18-. 262 MODERN EXAMINATIONS No. of Question. Page. Blowing off boilers 257 196 Boiler, direct heating surface of 221 173 Boiler, explosions, cause of 241 191 Boiler, heads, tee irons riveted to 80 85 Boiler, heads, pressure necessary to bulge 271—272—274. .203-206 Boiler, heads, elastic limit of 270 203 Boiler, heads, elastic limit of, spherical. . 276 208 Boiler, heads, concave 278-279-280 210 Boiler, heads, difference between iron and steel 285 214 Boiler, heads, supported by flange 288 217 Boiler, heads, tubes impart stiffness to. . . . 289 218 Boiler, horse power of 90 87 Boiler, plates 269 202 Boiler, plates, effect of pumxping cold water on 244 189 Boiler, plates, effect of heating red hot .... 245 188 Boiler, plates, failure of red hot 246 189 Boiler, pressure for best economy 172 139 Boiler, pressure, effect of lowering. ... 175-176 141 Boiler, safe working pressure of . 71 . . . 74-202 Boiler, shell, effect of boring holes in. . , . 250 194 Boiler, shell, necessary thickness of 267 201 Braces below tubes 296 237 Braces, diameter of 286 214 Braces for part of head exposed to pressure 89 85 Braces from head to head 78-85-86. . . .83-85 Braces, insufficient number of . 253. ..... 195 Braces, improperly located . . 254 195 Braces, improperly constructed 255 195 Braces, necessary for fiat surface . St, 84 Braces, proper distance apart 281 213 Braces, safe load for 82 84 OF STEAM ENGINEERS. 263 '^(^- (if Question. Page. Braces, stress on 84 85 Braces, stress allowed on 81 83 Bursting pressure of boilers 266 201 Building, necessary heating surface for. . 218 167 Building, systems for heating. ... ; 204 159 Cast iron shafting, diameter of 229 180 Cast iron shafting, power it will transmit 230 180 Cast iron, elastic limit of 275 207 Cast iron head, bulging pressure of 274 206 Chimney, area of 118 loi Circle, area of 44 48 Circle, segment of a. 291-292—293 220 Circulating water needed 183 145 Clearance 3-169. . . .29-119-138 Coal, air to burn one pound of 264-265 200 Collapsing pressure of tubes 298 239 Compression, effect of excessive 160 135 Compression, line 146 129 Compression, rule for 162-163 136 Compression, return stroke uncompleted at 136 119 Compression, saving by 1 34 117 Common fractions 135 75 Compound engine 35-189. . .40-148 Compound engine, water rate for 149 131 Combustion 262 199 Constant, horse power. 49 54 Connecting rod, diameter of 17 2>^ Connecting rod, length of 18 36 Condensing engine 25-36-38-40. . . . 39-41 Condenser, theoretical saving by adding a. . 68 71 Condenser, water needed for a 182-191 . . 145-15 1 264 MODERN EXAMINATIONS No. of Question Condenser, percentage of gain by adding. . 66 Condenser, surface 185 Condensation, water of 207 Condensation in steam pipes 260 Consumption of water 128 Counter pressure line 159 Counterbore 23-24 Covering for steam pipes 258 Crank 59 Crank pin 6 Crank pin, diameter of 15 Crank shafts 231-232-233 Crank shafts, diameter of 14 Cut-off, consumption of water at 137 Cut-off engine 34 Cut-off to give mean effective pressure. . . . 69 Cylinder condensation 153 Cylinder, comparative sizes for compound engine 181 Cylinder, effect of not covering 156 Cylinder, low pressure 190 Page. 70 146 161 198 113 135 37 198 63 Z^ 36 180 36 119 40 71 ^Z3 143 134 150 Defective riveting 251 194 Density of steam 195-196 153 Diagram, too high terminal pressure on. . . . 151 133 Diameter of crank shafts 14-231 . . .36-180 Direct heating surface 221 173 Direct radiation 209-210— 211 163 Double welt butt joint 76 81 Drilled holes 87 85 Drift pin 252 194 I OF STEAM ENGINEERS. 265 ^o. of Question Eccentric 7-8 Eccentric, effect of reducing diameter of . . 9 Eccentric rod, length of 21 Elastic limit of boiler heads. . 270-271-272-276 Elastic limit of cast iron 275 Electricity, accumulation of 243 Engine, adjustable cut-off 34 Engine, automatic t,2> Engine, compound 35-189 Engine, compound condensing 36-1 76-1 77-1 79 Engine, compound, water rate of 149 Engine, compound, to determine power of 189 Engine, crank shafts of 14-231-232-233 Engine, diameter of piston for 46 Engine, horse power of 43 Engine, indicator 119 Engine, in exposed place 156 Engine, precautions when indicating 202 Engine, quadruple expansion 39 Engine, quadruple expansion condensing. . 40 Engine, speed of 45-52 Engine, steam used by in a given time. ... 133 Engine, to reverse an 5 Engine, throttling 32 Engine, triple expansion 37 Engine, triple expansion condensing 38 Engine, to increase mean effective press- ure of 50 Engine, to determine mean effective press- . ure of 55 Engine, underloaded and overloaded 148 Exhaust pipe, proper size of 11 Exhaust ports, proper size of 13 Page. ■ ■ 32 • • 33 ■ ' 31 03-208 . . 207 . .188 . . 40 . . 40 40-48 40-141 131 148 36-180 49 45 103 134 157 41 41 49-56 115 30 40 40 40 54 60 131 34 35 266 MODERN EXAMINATIONS No. of Question. Page. Exhaust steam for heating. . 113-222-223-224. . .99-175 Exhaust valve 145 129 Expansion line 157-158. . 134-135 Expansion line, theoretical 126 108 Expansion, ratio of 56 61 Expansion, work done by 164-167 137 Explosions, theories advanced to account for , 241 191 Feed water, to calculate saving by heating 114 99 Feed water, temperature of 115-186-187. .100-146 Flat surfaces, braces for 83 84 Flat surfaces, to determine safe pressure. . 283. .203-212 Flat heads, to determine proper thickness of 284 213 Flow of water 198 155 Flues, safe working pressure of 299 241 Flues, thickness of 300 241 Fly wheels 61-62-63-64-65 64 Foaming, cause of 97 89 Forced draft 116 100 Forward pressure 26 39 Fractions, to change common to decimals. . 135 75 G Governor pulley, to find size of 53 57 Grate surface per square foot of heating surface 91 88 H Head, boiler 270-271-272-274-276 277—278—279—280. .203—206 OF STEAM ENGINEERS. 267 A77. of Question. Head, boiler, difference between steel and iron 285 214 Head, boiler, part of supported by flange. . 288 217 Head, boiler, part of supported by tubes. . 289 218 Head, boiler, proper thickness of flat. . . . 284 213 Head, boiler, to reduce number of braces for 290 218 Heating buildings, systems in use for. . 204-205 159 Heating feed water, to calculate saving by 114 99 Heating purposes, exhaust steam for 222-223-224 175 Heating surface of boiler 92-221 . . .88-173 Heating surface necessary for a building. . 218 167 Heater, feed water, with surface condenser 185 146 Horse power, belt to transmit a given. . . . 238 184 Horse power constant, how to find the. ... 49 54 Horse power of an engine 43 48 Horse power of a boiler 90 87 Horse power, what is a 42 45 Hyperbolic logarithms 57 61 Indicator card, parts of an 122 104 Indicator diagram, shows water needed for condenser 182 ...... 145 Indicator, is knowledge of necessar}^ 203 157 Indicator on compound condensing engine 177 142 Indicator, the steam engine 119 103 Indicating engine, precautions to be taken 202 157 Initial cylinder condensation 153-154 133 Initial pressure 30-178. . .40-143 Injector, increasing capacity of 108 98 Injector, using hot water in no 98 Injection water 199-200-201 . . 156—157 268 MODERN EXAMINATIONS No. of Question. Page. Irons, neutral axis of tee 295 227 Irons, strength of tee 294 225 jr Jet condenser, water necessary to run 191-192 151 Joints 75-87 . . . .81-85 Joint, double welt butt 76 81 Lap, what is i 28 Lead, what is 2 29 Line of perfect vacuum, to locate 123 104 Line, theoretical expansion 126 108 Logarithms, hyperbolic 57 61 M Main bearings, length of 20 37 Main steam pipe, to determine area of 219-220. .172-173 Mean effective pressure. 28-67-69. .39-70-71 Mean effective pressure, to determine the 48-55-127. .54-60-107 Mean effective pressure, to increase 50. 54 Mill shafting 225 178 N Natural draft 116 100 Neutral axis of tee irons 295 227 Non-condensing engine 25 39 Pipes, best covering for . 258 198 Pipe, size of steam 10-219-220. . .34-172 Pipe, size of exhaust 11 34 OF STEAM ENGINEERS. ^69 A'o. of Question. Page. Piston rod 19 37 Pitch of rivets 72 79 Plate, to determine strength of solid. . 73-268. . .79-201 Plate, to determine strength of net section 74 80 Ports, size of exhaust 13 35 Ports, size of steam 12 35 Power of an engine. 43-51 • • • -48-54 Power that shafting will transmit 226-228-230 179 Power that belts will transmit 234 183 Pressure, bursting of boiler 266 201 Pressure, bulging of cast iron head 274 206 Pressure, collapsing of tubes 298 239 Pressure, mean effective 28-67-69. .39-70-71 Pressure, mean effective, to increase the. . 50 54 Pressure, mean effective, to determine with- out the indicator 55 60 Pressure, mean effective, to determine by planimeter 127 107 Pressure, of the atmosphere 124 105 Pressure, safe working of boiler 71 • • .74-202 Pressure, safe working of flues 299 240 Pressure, that flat head will carry 283 211 Pressure, terminal 31 40 Pulley, size of governor 53 57 Pump, cold water 1 1 1 98 Pump, height to which it will raise cold water 112 98 Pump, to calculate contents of water cylin- der of 107 97 Pump, to calculate size for a steam plant. . 106 96 Punched holes 87 85 Priming 98 89 Q Quadruple expansion engine 39-40 41 270 MODERN EXAMINATIONS No. of Question Radiation, direct 209 Radiating surface necessary for a room.. 214 Ratio of expansion 56 Re-evaporation 152 Reverse an engine 5 Rim of fly wheels 61 Riveting, defective 251 Rivets, pitch of 72 Rivets, strength of 75 Root, square 47 Rule for distance on boiler head supported by flange 288 Rule for power that a belt will transmit. . 234 Rule for size of steam pipe 10-219-220 Rule for work done during expansion 164-167 Rule for water consumption 141-142 Page. .163 . 167 . 61 •133 • 30 . 64 .T94 • 79 . 80 • 50 . 217 .183 34-172 •137 .117 Safe load of braces 82 84 Safe working pressure of boiler 71. . .74-202 Safe working pressure of flues 299 ..... . 240 Safety valve, to determine size of 100 91 Safety valve, to determine area of opening 101-102-103— 104-105 93 Segment of a circle 291-292-293 220 Separator, what is a 99 90 Shaft, diameter of crank 14-231 . . .36-180 Shafting, speed of 54 57 Shafting, to determine diameter of 225-227-229-231-232 178 Shafting, to determine power it will trans- mit 226—228—230 179 vShell, to determine thickness of 267 201 OF STEAM ENGINEERS. 271 JVo. of Question. Page. Speed of engine, to determine 45-52. . . .49-56 Speed of fly wheels 65 68 Spherical boiler heads, elastic limit of. . . . 276 208 Square feet of heating surface 91-92 88 Square root of numbers 47 50 Stays 281-282-287 . .212-215 Steam 133-164-165-195-222-259 T15-137-153-175-199 Steam engine 156 134 Steam engine indicator 119 103 Steam pipes, best covering for 258 198 Steam pipes, to determine size of 10-219-220. . . .34—172 Steam ports, to determine size of 12-13 35 Steam plant, to determine size of pump for 106 96 Steam plant, to determine size of chimney for 118 loi Steam space, to determine cubical contents of 96 89 Steel head 272-285 204-21 1 Strength of double welt butt joint 76 8r Strength of leather belting 235 183 Strength of net section of plate 74 80 Strength of rivets 75 80 Strength of section of solid plate 73-268. . .79-201 Strength of tee irons 294 225 Super heated water 242 186 Surface condenser 185 146 T Tee irons 80—294-295 . , 85—225—227 Temperature 1 15-186-193 . . roo-146-152 Tensile strength of cast iron 275 207 Terminal pressure 31-143-151—178. .40—126—133—143 Theoretical expansion line 126 108 Throttling engine -^2 40 Triple expansion engine 37—38 40 Tubes 250-289-296-297-298 . . 194-2 18-237-239 D L^ncovered pipes 259. ..... 199 Uncovered pipes, best covering for 258. 198 272 MODERN EXAMINATIONS V A'o. of Question. Page. Vacuum, flow of water into a 198 155 Vacuum, in inches, to change to pounds. . 197 ; 155 Vacuum, line of perfect 123 104 Valve, exhaust 145 129 Valve, gear 60 ()2> Valve, globe 213 165 Valve, how to set 4 29 Valve rod, to determine length of 22 37 Valve, safety 101-102-103-104-105 93 Valve, to determine tightness of 58 62 Volume of circulating water 183 145 Volume of steam 133 115 W Wall surface 217 168 Water consumption from diagram . . . 128-129-130-131-132-137-139-141 113 Water, cylinder of pump 107 97 Water, flow of 198 155 Water, heating the feed 114 99 Water heated by exhaust steam 113 99 Water, hot . 109-110-111 98 Water rate, cause of high 147 131 Water rate in compound engine 149 131 Water required for condenser 1 82-1 91 . . 145-15 1 Water space of boiler 93-94-95 89 Water superheated 242 186 Water, to test the temperature of feed .... 115 100 Water, volume of circulating 183 145 Wrist pin, diameter of 16 1^6 Wrist pin, travel of 6 32 Wrought iron boiler head 271 203 Wrought iron shafting, to determine diam- eter of 225 178 Wrought iron shafting, to determine power it will transmit 226 179 ADVERTISEMENTS. 1 W. A. FOSKETT, President. E. B. Beechek, Vice-President. N. P. Bishop, Treasurer C. E. Rounds, Secretary THE FOSKETT & BISHOP CO., ENGINEERS AND CONTRACTORS. Power Plants, Fire Extinguishing and Heating Apparatus, PLUMBING AND GAS FITTING. Manufacturers of the G. & J. R. Bolton Hot Water Heaters. STEAM TRAPS, STEAM SPECIALTIES. Agents for the General Fire Extinguisher Co. WROUGHT AND CAST IRON PIPE AND FITTINGS FOR STEAM, WATER AND GAS. Main Office and Factory, GRAND AND RAILROAD AVES., NEW HAVEN, OONN. New York Office, 114 Liberty Street. 11 ADVERTISEMENTS. See That 212° ? NATIONAL-:- FEED WATER HEATER ^p^DOES IT. Great Efficiency, Entire Durability, Low First Cost. Copper Coils. No inside joints to leak. No straight tubes to leak. No back pressure is possible. No contact of the water with the shell or iron. No chance for grease in the boiler. Economy of Goal Is Assured. OUR RECORD IS: 700,000 Horse-Power in Daily Use. The National Pipe Bending Gg., 35 LLOYD STREET, NEW HAVEN, CONN. ADVERTISEMENTS. Ill C. S. MERSICK & CO., DEALERS IN- ENGIINEERS Tools 8 Supplies, Nos. 286-292 STATE STREET, NEW HAVEN, CONN. A Complete Indicating Outfit. THE BATCHELDER AD- JUSTABLE SPRING STEAM ENGINE INDICATOR. Always ready for use at any speed or pressure. The "Ideal" Eeducing Wheel. A simple, accurate and' conven- ient reducing- motion for an}- leng-th stroke. THOMPSON & BUSHNELL CO., Sole Manufacturers. no Liberty St., New York. PATKNTED. Catalog-ue sent upon application. IV ADVERTISEMENTS. vi'vS^, YOUR HEART were not working- properly, you would not lose any time in looking- for a remed5\ But you let your engine hammer away with the valves all out of adjustment, and make no attempt to remedy the defects. We have onlj^ space here to sug-g-est that you g-et our catalogue of the Robertson- ThomiDson Indicator, $40. "VICTOR" REDUCING WHEEL (S15 and Standard Averag-mg- Planimeters ($15, , making- the most complete outfit now offered for any price. THE HINE ELIMINATOR, designed to sep arate water from steam — thus preventing the dang-er of a bursted cylinder head — also ensuring- better lubrica- tion. Will as effectually extract the oil from exhaust steam so you can use returns for boiler feeding-. " "SPENCER Damper Regu- lators will con- trol the heavi- est dampers, with least vari- ation in press- ure. Send for a Catalogue of these anJ a number of other high grade specialties. 1*#|J AT'Q The sale of "EUREKA" packing is larg-er than any ^p^M other made? It fills the bill where all others fail for ■ "JJ^L both steam, water and air. Get a sample box and try REASON for yours3lf. WE MANUFACTUKE- Feed V/ater Heaters, Steam Separators, Exhaust Pipe Heads, Reliance Water Columns, Steam Flue Cleaners, Waste Oil Filters, Oil Extractors, Shaking Crate Bars, Reducing Valves, Square Flax Packing. HINE & ROBERTSON CO. 68 CORTLANDT STREET, NEW YORK. ADVERTISEMENTS. tneering PUBLISHED MONTHLY. FREDERICK KEPPY, M. E., Editor and Business Manager. The wonderful developments in the practical application of steam and Elec- tricity make it necessarj' that every one engaged in mechanical work of all branches of industry should keep thoroughly informed on the subjects. ^^Aiiierican Eng-ineering-^^ is published monthly, and always contains the latest and most important Engi- neering, Electrical, and general Mechanical News. It is not possible in a few lines to tell you what our plans and aims are for the future; will simply say that we will improve with each number, and make a paper alike, creditable to the profession and ourselves. Every number is illustrated with new and original plates and engravings. We shall be pleased to send you a specimen copy on receipt of five cents in postage stamps, or, what is better, send us fifty cents In stam^.s, and we will send the paper to you for one year, postage prepaid. And as a free Premium we will also send you a Valuable Fifty-cent Book, #^^ THE ENGINEERS' MANUAL **# Containing a vast amount of practical information which comes into daily use in the boiler and engine room. The work treats on engines and boilers, pumps and pumping machinery, together with safety valves, injectors, steam appliances, etc., etc. Also contains valuable rules and tables necessary for use of engineers and firemen. Second edition, 12mo. cloth, postpaid. SUBSCRIPTION DEPARTMENT. American Industrial Publishing Company, Bridgeport, - - - conn. " McLELLAN'S GUAGE GLASS CUTTER." PATENT APPLIED FOR. The Simplest, Best and Cheapest. FULL NICKEL PLATED, - - 75 cents each. WM. McLELLAN, Stamford, Conn. VI ADVERTISEMENTS. <^D^CR V STEAM GAGE V^riWOD 1 andVALVECO SOLE PROPRIETORS AND MA^fUFACTURERS OF Crosty Pop Safety Valves, Water Relief Valves, Improved Steam Gages, Safe- ty Water Gages, Recording Gages, Gage Testers, Counters, Etc. ORIGINAL SINGLE BELL CHIME WHISTLES. CROSBY STEAWI ENGINE INDICATOR, With Sargent's Electrical Attachments, by which any number of diagrams can be taken simultaneously. BOSWORTH FEED WATER REGULATOR, For maintaining an even Water line in fast-steaming- boilers. BRAN DEN VALVES, Made of rubber with wire coil insertion, for all kinds of steam and power pumps of standard make. All kinds of Pressure and Vacuum g-ag-es used in the various arts. Main Office and Works, BOSTON MASS, U. S. A. Branches: New York, Chicago and London, Eng. GUY C. HUNT, Pres. W. C. HUNT, Treas. ESTABLISHED 1865. AMERICAN INDUSTRIAL PUBLISHING CO.. PUBLISHERS OF SCIENTIFIC BOOKS, ■ RELATING TO » STEAM. THE STEAM ENGINE, MECHANISM. MACHINERY, Electricity, Engineering, and Steam and Hot Water Heating. THE BEST SELECTED STOCK IN THE COUNTRY. Svibscriptions taken for any American or ■■■ ' — ■ —■ English Publication on the above Subjects. Bridgeport, Conn ADVERTISEMENTS. Vll ro^^<^ C^eo I Roberts & Brosjnc Telephone call, 1127- 38 How did yo\j vote f'or Qovcnor?) x^e Best WHY? Because there i s no other machine that does its work so satis- factorily as hun- dreds can tes- tify. of courae" Evidence Of this fact is that in Six Years we have never been called upon to renev^ or repair a sing-le part of the many sold throug-hout the country. We not only DEAL IN GOVERNORS but we sell every conceivable thing- in the line of Supplies for Engineers. STEAM. WATER. GAS. ELECTRIC. SEND FOR OUR CATALOG UE.^a—— : George I. Roberts & Bros., : -INCORPORATED.- 471 & 473 FOURTH AVENUE, ISEW YORK CITY. Vlll ADVERTISEMENTS. WM. L. SHEAHAN. THOS. J. GROARK. S heahan & G rqark, PRACTICAL Engineers, Plombers, STEAM and CASPITTERS. Personal Attention Given to Modernizing Defective Plumbing. The Heating of Private Residences by Steam and Hot Water a Specialty. Engineers' Supplies. 285 <& 287 STATE STREET, ^tsiX'.?,' - - NEW HAVEN, CONN. FACTORY WORK SOLICITED. ESTIMATES GIVEN. ALL WORK GUARANTEED. ADVERTISEMENTS. IX CATALOGUE 0!' Practical Hand Books, FOR ENGINEERS, FIREMEN, MACHINISTS AND STEAM-USERS. American Industrial PuMishing Co., PUBLISHERS OF SCIENTIFIC BOOKS RELATING TO Steam, the Steam Engine, Mechanism, Machinery, Electricity, Engineering, and Steam and Hot Water Heating. BRIDGEPORT, CONN., U. S. A. We will supply any of the books named in the following- pages; or any other American or English publication, by mail, postage prepaid, on receipt of the publi- cation price. j^S^Onr large, illustrated catalogue, 130 pages, ■will he sent to any address in the vjorld, postage prepaid, on receipt oj 10 cents in stamps. When sending for catalogue, state whether you are a Locomotive, Stationary, Marine or an Electrical Engineer. A CATECHISM OF THE STEAM-ENGINE in its Vari- ous Applications in the Arts, to which is now added a Chapter on Air and Gas Eng-ines, and another devoted to useful Rules, Tables, and Memoranda. By John Bourne, C. E. New edi- tion, much enlarg-ed, and mostly rewritten. Illustrated by 212 Woodcuts, for the most part new in this edition. 12mo. Cloth, $2.00. HAND-BOOK OF THE STEAM-ENGINE, containing^ all the Rules required for the Rig-ht Construction and manag-ement of Engines of Every Class, with the Easy Arithmetical Solu- X ADVERTISEMENTS. tion of those Rules. Constituting- a Key to the " Catechism of the Steam-Eng-ine. " Illustrated by 67 Woodcuts and numer- ous Tables and Examples. By John Bourne, C. E., author of " A Treatise on the Steam-Eng-ine," "A Treatise on the Screw-Propeller, " "A Cathechism of the Steam-Eng-ine, " etc. 12mo. Cloth, $1.75. HAND-BOOK OF CALCnLATIO:N^S. for Engineers, Fire- men and Machinists. By N. Hawkins, M. E. This work is carefully edited, in plain lang-uag-e and everyday fig-ures. Size 6x9 inches, weight 2>^ lbs., 336 pages, 150 illustrations ; strongly and handsomely bound in green silk cloth. Contains every calculation, rule and table necessary to be known by the engineer, fireman, or steam user. Price, $2.50. MAXIMS AND INSTRUCTIONS, for the Boiler Room. By N. Hawkins, M. E., deals with the following subjects: Boil- ers, pumps, steam heating, plumbing, piping, engineers' exam- inations, safety valves, valves, injectors, etc. Size 6x9 inches, nearly 200 illustrations, 331 pages; bound uniform with " Cal- culations. " Price, $2.50. USE AND ABUSE OF THE STEA3I BOILER, including its care and management. With illustrations. By Stephen Roper, engineer. This is the only book ever published in this country devoted exclusively to steam boilers. ' It contains illus- trations of all kinds of steam boilers now in use, whether stei- tionary, locomotive, fire or marine ; and also of sectional or patent boilers, with an elaborate description and explanation of the same. The safe working and bursting pressures of all classes of boilers ; the safe external and collapsing pressure of flues ; the horse-power of steam boilers ; relative proportion of heating to grate surface, and the strength of materials of which boilers are generally constructed, are fully discussed : nth ed. revised. 18mo, tucks, gilt edge. $2.00. ENGINEER'S HANDY BOOK, containing a full explana- tion of the steam engine indicator, and its use and advantages to engineers and steam users. With formulae for estimating the power of all classes of steam engines ; also facts, figures, questions and tables for engineers who wish to qualify them- selves for the United States Navy, the Revenue Service, the Mercantile Marine, or to take charge of the better class of sta- tionary steam engines. 14th edition, 1 vol. 16mo, 675 pages, tucks, gilt edge $3.50. THE PRACTICAU STEAM ENGINEER'S GUIDE, in the design, construction and management of American stationarj^ portable and steam fire engines, steam pumps, boilers, injec- tors, governors, indicators, pistons and rings, safety valves and steam gauges, for the use of engineers and firemen. By Emory Edwards. 10th edition. Illustrated by 119 engrav- ings. In one volume of 420 pages. Price, $2.50. ADVERTISEMENTS. XI THE AMERICAN STEAM ENGINEER. Theoretical and practi- cal ; with examples of the latest and most approved American practice, in the desigfn and construction of steam eng-ines and boilers of every description. For the use of eng-ineers, ma- chinists, boiler makers and students. By Emory Edwards, M. E. Illustrated by 77 engraving-s. 12mo, 419 pag-es. $2.50. The Engineers' Manual. Compiled by the New Haven stationary Eng-ineers' Association, No. 2. Containing" a vast amount of practical inforination which comes into daily use in the boiler and eng-ine room. The work treats on eng-ines and boilers, pumps and pumping- machinery, tog-ether with safety valves, injectors, steam appliances, etc., etc. Also contains valuable rules and tables necessary for use of eng-ineers and firemen. Second edition, 12mo., cloth, postpaid, 50 cents. A History of the Growth of the Steam Engine. By Robert H. Thurston, L.L. D., Director of Sibley Colleg-e, Cornell University, etc. With 163 illustrations. (Interna- tional Scientific Series). 12mo. $2.50. How to Run Engines and Boilers, a useful hand book of practical instruction for young- eng-ineers and steam users. By Egbert Pomeroy Watson. With a portrait of the au- thor. Third edition. 139 pages, fully illustrated, 16mo. , cloth. Price, $1.00. The Corliss Engine and Its Management. A practical hand book on the Corliss engine. By John T. Henthorn an^ C. D. Thurber. Synopsis of contents. Introduction and histori- cal, steam jacketing-, indicator cards, the g-overnor, valve g-ear and eccentric, valve setting-, tables for lap of steam valves, the air pump and its manag-ement, lubrication, care of main driv- ing- g-ears, heating- of mills by exhaust steam, eng-ine founda- tions and materials. Third edition, enlarged. 96 pages, 24 illustrations, 16mo., cloth. Price, $1.00. Practical Treatise on Injectors as feeders of steam boilers, for the use of the master mechanic and engineers in charge of loco- motive, marine and stationary boilers. Contains many illus- trations and is a thorough and up to date treatise on the sub- ject. By George N. Nissenson, engineer. i2mo. , paper. Price, 50 cents. Steam Boilers. A practical treatise on boiler construction and examination, for the use of practical boiler makers, boiler users, and inspectors ; and embracing in plain figures all the calculations necessary in designing or classifying steam boil- ers. By Joshua Rose, M. E. Illustrated by 73 engravings ; 250 pages. 8vo. Price, $2.50. XU ADVERTISEMENTS. Modern Steam Engines. An elementary treatise upon the steam engine, written in plain lang-uag-e ; for use in the workshop as well as in the drawing- office. Giving full explanations of the construction of modern steam engines ; including diagrams showing their actual operation. Together with complete but simple explanations of the operations of various kinds of valves, valve motions and link motions, etc., thereby enabling the or- dinary engineer to clearly understand the principles involved in their construction and use, and to plot out their movements upon the drawing board. By Joshua Rose, M. E. Illustrated by 422 engravings. 4to., 320 pages. Price, S6.00, Practical Application of the Indicator. By Lewis M. El- lison, C. E. A most complete and comprehensive treatise on indicators, with reference to the adjustment of valve gear on all style of engines. Written in simple language by a practi- cal engineer. Illustrated by 100 engravings ; 200 pages. Handsomely bound in cloth. Price, $2.00. The Steam Engine and the Indicator. Their origin and pro- gressive development ; including the most recent examples of steam and gas motors, together with the indicator, its princi- ples, its utility, and its application. By William Barnet Le Van. Illustrated by 205 engravings, chiefly of indicator cards ; 469 pages. 8vo. Price, $4.00. Indicator Practice ^^^d steam engine economy. With plain direc- tions for attaching the indicator, taking diag-rams, computing the horse power, drawing the theoretical curve, calculating steam consumption, determining economy, locating derange- ment of valves, and making all desired deductions. By Frank F. Hemenway, associate editor American Machinist. Price, $2.00. Slide Valve Gears. An explanation of the action and construc- tion of plain and cut-off slide valves. Analysis by the Bilgram diagram; 79 illustrations. By Frederick A. Halsey. 12mo. , cloth. Price, $1.50. Slide Valve Practically Explained. Embracing simple and complete practical demonstration cf the operation of each ele- ment in a slide valve movement, and illustrating the effects of variations in their proportions, by examples carefully selected from the most recent and successful practice. By Joshua Rose, M. E. ; 100 pages, 35 engravings. 12mo. , cloth. Price, $1.00. The Modern Machinist. By Johx T. Ushkr, Machinist. Specially adapted to the use of machinists, apprentices, de- signers, engineers and constructors. A practical treatise em- bracing the most approved methods of modern machine shop practice, embracing the applications of recent improved appli- ADVERTISEMENTS. XI 11 ances, tools and devices for facilitating", duplicating" and expe- diting" the construction of machines and their parts. A new book from cover to cover. The author, for many years in some of the largest machine shops in th:s country and Eng-land, is fully familiar with all details of machinery. His articles, from time to time published in the "American Machinist," "Machinery'-, " etc., have been universally approved and highly spoken of. He hiis recently visited many of the larg-est ma- chine shops in this countr}^ looking" into m:iny new methods, which are introduced in this work. It is the latet^t, cheapest, and best book ever published. It cannct f^iil to be of great help to the master mechanic as well as to the apprentice, and the price puts it within the reach of all in any way interested in the subject. Every illustration in this book represents a new device in machine shop practice, and the engravings have been made specially for this book. 8vo. , 320 pages, 250 illus- trations. Price, $2.30. Mechanical Drawing- Self-Taug^ht. Comprising- Instructions in the selection and preparation of drawing" instruments, ele- mentary instruction in practical mechemical drawing; to- g-ether with examples in simple g-eometry and elementary mechanism, including- screw threads, g-ear wheels, mechanical motions, engines and boilers. By Joshua Kose, M. E. Illus- trated by 330 engravings, 313 pag-es 8vo. Price, $4.00. Haswell's Mechanics' and Engineers' Pocket Book. New edition ; co-ntaining much new matter, with ad- ditional pages. Mechanics' and Engineers' Pocket Book of tables, rules, and formulas pertaining to mechanics, mathe- matics and phj^sics, with areas, squares, cubes and roots, &c. ; logarithms, steam and tlie steam engine, naval architec- ture (including displacement of vessels, cables, chains, an- chor, &c., &c. ) ; masonry, steam and the steam engine, steam vessels, mills, &c. ; limes, mortars, cements, &c. ; or- thography of technicEil words and terms, &c., &c. Fifty- seventh edition, revised and enlarged. By Charles H. Has- WELL, civil, marine and mechanical engineer, member of American Society of Civil Engineers, and Academy of Sci- ences, New York ; Institutions of Civil Engineers and of Naval Architects, England, &c., &c. Pages 982. 12mo., leather, pocket book form. $4.00. English and American Mechanic. An every day hand book for the workshop and factory. Containing several thousand re- ceipts, rules and tables indispensable to the mechanic, the arti- san and the manufacturer. A new, revised, enlarged and im- proved edition. Edited by Emory Edwards, M. E. Frank B. Van Cleve. 12mo., cloth. Price, $2.00. American Plnnibing". By Alfred Revill. For master plumbers, architects, builders, apprentices, householders. A XIV ADVERTISEMENTS. compendium of practical plumbing- from solder making- to hig-h class open work. The only work on plumbing- containing- a complete drainag-e system, elevation and plan, for use of archi- tects and plumbers. This work tells how to make joints of all kinds, how to make traps, how to make bends, how to set fix- tures, how to provide for varying- head of water, how to run pipes, how to arrang-e vents, how to find defects, how to make repairs, how to test plumbing- work, laws and rules g-overning- plumbing-. Form of specifications. In short it gives in detail everything of importance, g-reat or small in modern plumbing ; 225 pages devoted to the very latest improved sanitary methods and appliances used in plumbing; 138 illustrations, large 12mo., cloth. Price, $2.00. Steam Heating for Buildings, or Hints to Steam Fitters. By W. J. Baldwin, being a description of steam heating appar- atus for warming and ventilating private houses and large buildings, with remarks on steam, water, and air in their rela- tion to heating, to which are added miscellaneous tables. Il- lustrated. 12mo., cloth. Price, $2.50. Hand Book of Land and Marine Engines, including the modeling, construction, rt:nning and management .of land and marine en- gines and boilers. With illustrations. By Stephen Roper, engineer. Ninth edition. 12nio. , tucks, gilt edge. Price, $3.^50. Hand Book of Modern Steam Fire Engines. With illustrations. By Stephen Roper, engineer. Second revised edition. 12mo. , tucks, gilt edge. Price, $3.50. Catechism of the Marine Steam Engine, for the use of engineers and firemen. By Emory Edwards, M. E. Illustrated by 63 engravings, including examples of the most modern engines. Fifth edition, thoroughly revised, with much additional matter. In one volume. 12mo. , 414 pages. Price, $2.00. The American Marine Engineer. Theoretical and practical, with examples of the latest and most approved American prac- tice, for the use of marine engineers and students. By Emory Edwards. Illustrated by 85 engravings. One vol., 12mo., 440 pages. Price, $2.50. Belting. A treatise on the use of belting for the transmission of power ; with numerous illustrations of approved and actual methods of arranging main driving and quarter-twist belts and of belt fastenings. By John H. Cooper, M. E. Third edition. One vol. Demy8vo. Price, $3.50. Electricity for Engineers. By Charles Desmond. Especially adapted for engineers' use. A clear and comprehensive trea- tise on the principles, construction and operation of dynamos, motors, lamps, indicators and measuring instruments ; also a ADVERTISEMENTS. XV full explanation of the electrical terms used in the work. Third edition. Revised and enlarg-ed. Illustrated by 130 en- g-raving-s. Two parts, in one volume. 12mo. , 425 pages. Price, $2.50. Theoretical and Practical Ammonia Refrigeration. A work of reference for eng-ineers and others employed in the manage- ment of ice and refrigerating machinerj". By Ityld I. Red- wood, Assoc. M. Am. Soc. of M. E. ; M. Soc. Chem. Indus., Eng. 150 pages, 15 illustrations, and 25 pages of tables. 12 mo., cloth. $1.00. Catechism of the Locomotive, by Matthias N. Forney. The new edition is about twice the size of the original book, has cor- rect drawing-s of every part of the locomotive and of the different classes of the locomotives used in this country. It is written in such lang-uag-e as an eng-ineer or a fireman can easily under- stand, and it is believed that a study of this book will enable him to thoroug-hly know his business. There is no popular treatise in the English lang-uag-e which g-ives so clear, simple and complete a description of the construction and working of the locomotive engine. $3.50. Progressive Examinations of Locomotive Engineers and Fire- men, by John A. Hill. It contains 300 questions and answers to them. Seventeen colored plates showing position and color of every signal carried on eng-ine or train. Standard Code. Adopted as official examination on Railroads. Invaluable to engineers and firemen, and tells every young man with an am- bition to run a looomotive, just what he ought to know to start with and what he must learn before promotion. Send 50 cents (U. S. Stamps are good) for this neat book, pocket form, round covers, red and g"old. Hand-Book of the Locomotive, including the construction of Eng-ines and Boilers, and the construction, management and running- of locomotives. By Stephen Roper. 14th edition, re- vised. 18mo. , tucks, g-ilt edg-e. $2.50. Modern American Locomotive Engines, their design, construc- tion and management. A practical work for practical men. By Emory Edwards, M. E. Illustrated by 78 engravings. One volume of 383 pages, 12mo. $2.00. Locomotive Engine Running and Management, a treatise on Locomotive Engines, showing- their performance in running different kinds of trains with economy and despatch, etc. By Angus Sinclair. Illus. 12mo. $2.00. Air Brake Practice, '^y J- E. Phalex, of the Northern Pacific R, R. An exhaustive treatise on the Air Brake ; explains in simplest language how to operate it under all conditions. An XVI ADVERTISEMENTS. eng-ineer writes us: "The took on Air Brake Practice has been a source of invaluable information to me ; it is worth ten times the price you ask for it." Price, $1.25. Alexander's Ready Reference, by s. A. Alexander, for en- g-ineers and firemen, This book contains more valuable infor- mation in fewer words, and is easier understood by railroad men than any other book now in print, because it is written in the same manner that railroad men talk to each other, and by one who has had fort}" -two years' practical experience. It is a g-old mine to locomotive firemen aiming- at promotion. Price, $1.50. Modern Locomotive Construction, by j. G. A. Meyer, associate editor cf the " American Machinist." With many illustrations and fully up with the tim.es. Price, $10.00. Gardenier's Ready Help for Locomotive Engineers and Firemen, being- an educational chart for locomotive engineers and firemen seeking" promotion, for the scholars and students, and for the help of the examiner when employing- or promoting- new men, and is a ready help to eng-ineers while on the road. It comprises a remedy for every conceivable break-down or disorder that may occur to a locomotive, contains 600 questions and answers on the locomotive and air-brake. With a g-reat ainount of infor- mation of immense value to locomotive eng-ineers and firemen. Square 16mo. cloth, 117 pages. Price, $1.00. Hot Water Heating, Steam and Gas Fitting, by Jas. J. Lawier, for plumbers, steam fitters, architects, builders, apprentices, and householders, containing- practical information oE all the principles involved in the construction of Steam or Hot Water Plant, and how to do Gas Fitting. The illustrations show the latest and best appliances used for all systems. Complete plans for different kinds of building-s, with reg-ular working draw- ing's — the principles of circulation of hot water in a heating sys- tem illustrated and explained in the most comprehensive way. How to properly estimate on steam and hot water work. How to set up a steam and hot water plant from the foundation of the boiler to the bronzing of the radiators. Noises in water and steam pipes explained, and how to find and remedy them. The one and the two pipe system of steam heating illustrated. Gas fitting explained in all its branches, from the tapping of the main pipe in the street to the burners in the house. Large 12 mo., cloth, 300 pages, elegantly illustrated. Price, postpaid, to any address, $2. 00.