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You __ may be charged a minimum fee of $75.00 for each non-returned or lost item. Theft, mutilation, or defacement of library materials can be causes for student disciplinary action. All materials owned by the University of Illinois Library are the property of the State of Illinois and are protected by Article 16B of Illinois Criminal Law and Procedure. TO RENEW, CALL (217) 333-8400. University of Illinois Library at Urbana-Champaign When renewing by phone, write new due date below previous due date. L162 al oe ie? | ara hw t ‘aT a rea i a ac Ay Ves) 4, wf er %, , i i ‘ ie ' & ¥ Lea ste ie AIR COMPRESSION AND TRANSMISSION McGraw-Hill Book Company Publisters of Books for Electrical World The Engineering and Mining Journal Engineering Record Engineering News Railway Age Gazette American Machinist Signal Engineer American Engineer Electric Railway Journal Coal Age Metallurgical and Chemical Engineering AIR COMPRESSION AND TRANSMISSION BY H. J. THORKELSON ASSOCIATE PROFESSOR STEAM AND GAS ENGINEERING UNIVERSITY OF WISCONSIN McGRAW-HILL BOOK COMPANY 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E. C. 1913 *,* ; - PC eater), CopyniGnt, 1913, BY THE McGraw-Hitt Boox Company 4 18 MAY 14 lh MoOlurg. rchitecture. /F/7A PREFACE This text is designed to present in logical order the fundamental _ principles dealing with the subject of the compression of air, and its transmission through ducts or pipes, together with such examples as will serve to illustrate their application. It is hoped that the presentation will make clear the methods to be followed in calculations dealing with air at various pressures, and that students and engineers will be better able to appreciate the advantages and limitations of the various systems of securing the pressures desired, and of using air as a means of transmitting energy, or for securing certain results which cannot be obtained under normal atmospheric pressure. The material offered consists of notes used for a number of years by the author in his classes. He wishes to acknowledge his indebt- edness to the many excellent texts on the subject which have been published, notably those of Richards, Saunders, Hiscox, Harris and Peele. The fundamental formule are to be found in most texts on Thermo- dynamics for Engineers. The author is particularly indebted to Prof. C. H. Peabody’s text on this subject, and to the lectures of F. W. O’Neill, F. D. Longacre, H. deB. Parsons and F. W. Towl, given at Columbia University in a course on Applied Thermo- dynamics of Air Compressors. The material on turbo-compressors is taken from articles on this subject in recent numbers of the Engineering Magazine by Franz zur Nedden. Permission to use this material has been courteously granted by these authors and their publishers. The author is also indebted to the editors of Compressed Air Magazine andto various manufacturers for cuts, and to his col- leagues, particularly Prof. A. G. Christie and Mr. W. C. Rowse, for assistance in preparing this text. | Healers April, 1913. 259994 ae low, A RA ee eee ean ‘ f 7 os INTRODUCTION HISTORICAL ACCOUNT OF MECHANICAL USES OF AIR The earliest writings describing mechanical uses of air are found in a book entitled ‘‘Pneumatics”’ by Hero of Alexandria, published about 200 B. C. An English translation of this by Bennet Wood- croft indicates.a very complete knowledge of many mechanical devices possessed by the Ancients, and shows various pumps, Hero’s steam turbine and many remarkable uses of air as a means of transmitting energy. Fic. 1.—Hero’s device for opening temple doors. One of the most interesting illustrations is a device for opening temple doors by fire on an altar illustrated in Fig. 1. The altar, E is hollow and a tube F passes through the altar and is attached to a leather bag, K. Beneath this a small weight LZ is suspended which is connected to the bag and to the pivots of the temple doors as shown. Weights LZ and B are so proportioned as to normally Vii vil INTRODUCTION close the doors. When a fire is lighted on the altar, the bag K will expand under the pressure of the heated air below the altar and, in doing so lift the weight L. Weight B then falls and causes the doors to open. If the fire is extinguished, the air under the altar will cool, contract, and the bag K will take the position indicated and weight B will be dropped, causing the doors to close. A somewhat similar device is also described in the same text using heated air under a similar altar to force water from one cham- ber into a pail, thus counterbalancing the weight and causing the temple doors to open. Many automatons are also described, in “which air is made use of to produce musical notes and cause water to flow from vessels or objects when certain changes in the mechanism take place. A-very interesting experiment, illustrated in most texts on physics, called ‘‘Hero’s Fountain” and in- vented by the author of the book ‘‘ Pneumatics,” consists of two globes, Fig 2, M and N, and a brass dish, D. The dish D communicates with the lower part of the globe N by a tube B and another tube A connects the two globes. A third tube passes through the dish D to the lower. part of the globe M@. This tube having been taken out, the globe M is partially filled with water, the tube is then replaced and water is poured into the dish. The water flows through Fic. 2.—Hero’s tHe tube B into the lower globe and expels the air fountain, | Which is forced into the upper globe. The air being compressed acts upon the water and makes it jet out as shown. If it were not for the resistance of the atmosphere and friction, the liquid would rise to a height above the water in the dish equal to the difference of the level of the water between the two globes. Although a knowledge of this wonderful method of transmitting energy has been known for centuries, it is only within comparatively recent years that it has been used to any considerable extent in practical work. Its modern use dates from the construction of the Mt. Cenis tunnel completed in 1871. The work on this tunnel, which is about 8 miles long, had progressed very slowly from 1857 to 1861, the tunnel headings having been drilled by hand labor with an average advance in each of the two headings of about 1 1/2 ft. per day. Machine drills driven by compressed air were introduced and the speed rose to 4 3/4 ft. per day, and later when dynamite was INTRODUCTION 1X introduced, the cut was increased to 6 ft. per day. Sommeiller deserves the honor for solving, in this work, many of the initial problems of compressed-air production and use. The type of com- pressor used is illustrated in Fig. 3. A natural supply of water was used for compressing the air. The water was conducted in a sluice A through a valve C, compressing the air which is in D and forcing it into the reservoir H. When this was done the valve C was automatically closed and the water in D allowed to escape and be replaced by a new supply of air at atmospheric pressure. This Fic. 3.—Sommeiller’s compressor. was in turn compressed and forced into the reservoir E, giving not a continuous but an intermittent flow of air. This compressor furnished air at 80-lb. pressure, but only gave an efficiency of 50 per cent., that is, only one-half of the available energy was turned into useful work. Although the value of compressed air for machine drills for tunnel work was clearly demonstrated in the building of Mt. Cenis tunnel, it was some time before this was applied to mining work. One of the earliest tests for mining work was made at the Calumet and Hecla copper mine in Michigan in 1878, and the advantages in lower costs and higher speeds were so clearly demonstrated that its use for this work has since become almost universal. One of the most important of modern applications of compressed air is to be found in the braking of trains. George Westinghouse, in 1869, designed his first “straight air brake,’ which was later changed to the “automatic” type of air brake. This apparatus has x INTRODUCTION been improved and perfected to such an extent that its operation is truly marvelous and its application world wide. Railroad men were among the first to appreciate the uses of com- pressed air in shop and structural work, and its application to manufacture and other allied arts has since become so universal that a mere recital of the modern applications of compressed air would become tedious. One of the largest manufacturers of air compressors has recently published a partial list of various ap- plications of compressed air for which they have furnished compres- sors. This list includes over sixty different industries, with a great many different uses of compressed air in each. While compressed air has many advantages over other systems of transmitting energy, it has also certain disadvantages and limita- tions which should be clearly understood. In order to appreciate these, it is necessary to study in detail the nature and characteristics of air and the fundamental principles governing its generation, distribution, and application. CONTENTS PREFACE. INTRODUCTION CHAPTER I CHARACTERISTICS OF AIR . Air—Vapor in air—Free acs aye air—Effect af pressure on aiite perature. CHAPTER II FUNDAMENTAL DEFINITIONS Reeth Hine Dewersel cai perakiressA bsolute Renimeracire —B.t.u.—Effects of heat—Energy in air—Specific heat—Specific heat at constant pressure—Specific heat at constant volume—Real specific heat—Apparent specific heat. CHAPTER III CHARACTERISTIC AND ENERGY EQUATIONS FOR AIR . Boyle’s law—Law of Charles—Characteristic equation for perfects gases —Numerical value of R—Weight of air—Relation between specific heats—Work of isothermal change—Exponential change—Work of adiabatic change—Relations between P, v and T for adiabatic and exponential change—Computation of intrinsic energy. CHAPTER] LV GRAPHICAL DIAGRAMS AIR Construction of isothermal curves—Construction of exponential curves—Heat added or taken away for isothermal change—Heat added or taken away for exponential change—Difference between isothermal and adiabatic compression—Temperatures due to adiabatic com- pression—Work done by a compressor—Exponential compression— Isothermal compression. CHAPTER V AT PRESSURES BELOW THE ATMOSPHERE : Ae Venturi vacuum pump—Sprengle air Bee ueacurines vacuums— Condenser pumps—Wheeler combined pump—Size of water and air pumps—Steam cylinder size—U. S. Navy air pumps—Edwards air pump—lIndustrial uses of vacuums—Salt evaporating effects—Con- centration of liquids—Evaporation of cane juice—Vacuum cleaners— Syphon. xl vii Io 18 26 xll CONTENTS CHAPTER VI Arr AT Low PRESSURES Uses of air at low Botan eer Me arise sais for ion ea eet ey ce forges—Air for cupolas—Air for ventilation—Fans or blowers—Classi- fication—Definitions—Measurement of draft—Fan efficiency—Flow of gas through an orifice—Loss of head due to friction in ducts—Usual velocity in ducts—Notation of symbols—Pipe losses—Rotary blowing machines—Blower pressures and capacities—Power for rotary blowers —Mechanics of the fan—Effect of outlet on capacity—Work required to move a volume of gas—Design°of fans—Description of fans—Centrif- ugal fans—Fan blast or steel plate machine—Housing—Cone wheel fans—Turbine blast or “‘Sirocco” fan. CHAPTER VII PISTON COMPRESSORS Action of piston Nes ernie tt: eid oF pictow compressor— Effect of clearance—Methods of reducing clearance—Suction line— Compression line—Wet and dry compression—Actual compression— Cards for air compressors. CHAPTER VIII EFFICIENCIES AND ENERGY COMPENSATION Volumetric Efficiency—Apparent volumetric Brrcienmt ernie dave metric efficiency—Cylinder efficiency—Efficiency of compression— Mechanical efficiency—Net efficiency—Blower efficiency—Energy com- pensation—Hydraulic compensator—Lever compensator—Weight com- pensator—Straight line compressor—Duplex compressor, CHAPTER Ix MULTI-STAGE COMPRESSION . Advantage of multi-stage Compr eceionen Dress Teed ford various stages—Intercoolers—Types of intercoolers—Cooling surface and capacity—Intercooler pressure—Effect of clearance on volumetric efficiency. CHAPTER X DETAILS OF PISTON AIR COMPRESSORS Classification of valves—Mechanical tee ince valves pete Effect of changing discharge pressure—Automatic valves—Valve area— Forms of Poppet valves—Piston-inlet valves—Semi-mechanical valves —Regulators, unloading devices, etc.—Belt regulator—Westinghouse governor—Norwalk regulator—Combined governor and regulator— Nordberg governor—Unloading devices—Clearance unloader. CHAPTER XI TURBO-COMPRESSORS . Design of turbo- eerarecenre = alone blower The Rae blower— 38 69 i. 89 98 113 xX CONTENTS Cooling turbo-compressors—Cooling devices—Expansion of casing— Runners—Balancing axial thrust—Balance by counter-position— Balancing by diminishing back area—Balancing by balancing piston— Stuffing-boxes—Coupling compressors—Rateau multiplicator—Mixing blower. CHAPTER XII HypDRAULIC COMPRESSION OF AIR Aerie et Trompe—Frizell’s renvecccm Baloche end Ncrahniass compressor— Arthur compressor—Taylor compressor—-Taylor compressor at Magog, Quebec—Taylor compressor at Ainsworth, B. C.—Taylor compressor at Victoria Mine, Mich.—Phenomena of hydraulic air compression— Losses of hydraulic compression. CHAPTER XUHI EFFECT OF ALTITUDE AND COMPRESSOR TESTS . Effect of altitude on capacity—Effect of mlutuder on arent between altitude and volume—Compressor tests—Mode of conducting the tests—Results of the tests—Tests of plant No. 1—Test of plant No. 2—Test of plant No. 3—Test No. 4—Summary. CHAPTER XIV RECEIVERS. MEASUREMENT AND TRANSMISSION OF COMPRESSED AIR Receivers—Measurement of air and gases—Standards of measure- ments—Volumetric meters—Velocity meters—St. John’s meter— Venturi meter—Thomas meter—Meter comparisons—Pipe lines— Dresser coupler—Hammon coupler—Pipe-line formule—Reheating— Stoves. Cin b LE Rea, THE SELECTION AND CARE OF AIR COMPRESSORS Available power—Valve gear—Size and type of eorneeeore Cone pressed air explosions—Lubricating compressors—Cleaning valves— Inlet connections. APPENDIX A—ComMoN LOGARITHMS APPENDIX B—-NAPERIAN LOGARITHMS APPENDIX C—HyYGROMETRY . INDEX xlil 129 140 159 179 184 188 IQI 201 254 >; oF So 74 . i bet poe a a le vie Py St, Sar i ee Lane AIR COMPRESSION AND TRANSMISSION CHAPTER I CHARACTERISTICS OF AIR Air.—Air is a mechanical mixture of several gases, principally oxygen and nitrogen, its average composition by volume being as follows: INI ECOO CliINede mapatie ey eer ee ter enes fee ee Uta ety a’ FOVAO RV PCD nee heey tar ie are Ne ha hth, tava gh ae casks 20.63 INGUCOUSAVADOLE eri eete ek Die ni cet ane Ween eh Okina 0.84 Ar pOuiceacit CAS merger i ee Nh oars Geeks 0.04 By weight it contains about 77 parts of nitrogen to 23 parts of oxygen. There may be, in addition to the above, local impurities in the atmosphere, the principal ones being ammonia and sul- phuretted hydrogen. The carbonic acid gas arises principally from the respiration of animals and the processes of combustion, but, notwithstanding the enormous continual production of this gas, the composition of the atmosphere does not vary, for plants in the process of growth decompose the carbonic acid, assimilate the carbon, and restore to the atmosphere the oxygen, which is being continually consumed in the processes of respiration and combustion. Vapor in Air.—The vapor of water is always present in the atmos- phere and when the air contains as much of this vapor as it possibly can, it is said to be saturated. The amount of vapor present in the air when saturated will vary with the temperature, as shown in Table I, taken from the Smith- sonian Institution Reports. 1 2 AIR COMPRESSION AND TRANSMISSION TABLE I.—GRAINS VAPOR IN 1 CU. FT. OF AIR SATURATED WITH MOISTURE (7,000 Grains=1 lb. Avoir.) es 4 | I | 2 3 4 5 6 7 8 9 10 0.481 | 0.505 | 0.529 | 0.554 | 0.582 | 0.610] 0.639] 0.671} 0.704) 0.739 nme) 0.7767 (02816) 1028504] OF S060) 0.0408 OnOS Sir. 0321.07 Om teal cio meter tou: 20 Te235e) Le2O4 a) Las S on Le 416 fd 4 Ose eee S 5 0 mn Os ele OO 7imeLeye7 oi eos 30 T.035' || 2.022 192.1130) 26104 152527900102), 200\e2, 457920550127 040|n2n7A0 40 2.849 | 2.955 | 3.064 | 3.177 | 3.294 | 3.414) 3.539] 3.667) 3.800) 3.936 50 4.076 | 4.222 | 4.372 | 4.526 | 4.685 | 4.849] 5.018] 5.191] 5.370] 5.555 60 52745 | 5. O4L, |) O20A2) 46. C408 On5OS nis On7O27. O00 7 624 Tl 7A COTE 76 70 7.980 | 8.240\| 8.508 | 8.782 129.066) |.0.356) 02 6551) 0.002) 50.277) 10.007 80 10.934 |LE275 |Lt 026 111. O87 12.350) (12) 730) tan 27103).520/Ta Os TANenG 90 I4.790 |15.234 |15.6809 |16.155 |16.634 |17.124\17.626|18.142/18.671|19.212 This shows the number of grains of vapor present in each cubic foot of air when the air is saturated. As there are 7,000 gr. in a 0 20 40 60 80 100, Temperature, Degrees Fahrenheit Fic. 4.—Water present in saturated air. pound avoirdupois, these weights can be easily converted into pounds. This data is shown graphically in Fig 4. Free Air.—Free air is air at the pressure and temperature of the atmosphere. This is a term used extensively in texts on compressed air and in rating the capacity of a compressor. It can be shown experimentally (Boyle’s Law) that if a cubic CHARACTERISTICS OF AIR 3 foot of free air at sea-level (14.7 lb.) is compressed to a pressure of 44.1 lb. by the gauge, or 4 atmospheres absolute, and allowed to cool to the temperature of the atmosphere, the compressed air will occupy one-fourth its original volume; if compressed to a pressure of 58.8 lb. gauge, or 5 atmospheres absolute, and allowed to cool to the temperature of the atmosphere, it will occupy one-fifth of its original volume. Figure 4 shows the weight of moisture which may be held in 1 cu. ft. of air at different temperatures, if saturated, and is true no matter what pressure the air may be under. It is evident then, that if a volume of free saturated air be com- pressed into a smaller space and kept at the same temperature, part of the vapor it originally contained must be precipitated for the reason that 1 cu. ft. of air at a certain temperature can only hold a definite weight of vapor when saturated, whether compressed or at atmospheric pressure. If saturated air is compressed to 5 atmospheres, or 73.5 lb. per square inch absolute, and allowed to cool to atmospheric tempera- ture, its volume will be reduced to one-fifth of its original volume and 1 cu. ft. of compressed air will contain the moisture content Obes CU eit, Of iree alr. TABLE II—POUNDS OF WATER PRECIPITATED PER CUBIC FOOT OF COM- PRESSED AIR AFTER COMPRESSION AND COOLING OF SATURATED FREE AIR (Pressures) Temp. Ga. 29.4 4AM foSOnO pLO2-07 147.0) 30725 1735 20] 2205.0 of Abs. 44.1 CO om (aay pO LOL giigole 2: 7A0u 7 | 2210.9 air Atm. 3 4 5 8 Er 26 5 I51 fo) .OOOI | .0002| .0003} .0005] .0007| .0017| .0035| .Oo105 IO .0002 | .0003] .0004| .0008] .ooII| .0027| .0055| .o165 20 .0004 | .0005] .0007) .0013| .0018) .0045) .0090] .0270 30 .0006 | .0008) .COII] .0020} .0028) .0070] .0140]} .0420 40 .0008 | .0012) .0016} .0028} .0040} .0100| .0200] .o600 50 .0012 | .0017} .0023| .0041| .0058] .0145| .0290] .0870 60 0016 | .0025| .0033] .0057| .0082] .0205| .o410] .1230 70 10023 de. CO84) 0045), .0070| JO1I4! .02351 30570" 22770 80 .003I | .0048| .0062] .o109] .0156] .0390] .0780] .2340 go SOOA2 she: GOOS4 =. O0GA |) .OT43! (O2TIh 20527. 1055) 23305 (For a further discussion on moisture in the air see Appendix C.) 4 AIR COMPRESSION AND TRANSMISSION When reduced to the temperature of the atmosphere, the moisture held in suspension per cubic foot of the compressed air cannot exceed the moisture held in suspension per cubic foot of the free air, and in consequence the remaining moisture will be precipitated. This will represent for each cubic foot of compressed air a weight of water equivalent to four times the weight held in suspension. These weights have been calculated for various temperatures and pressures as shown in Table IT. Dry Air.—Air is said to be “dry” when water evaporates and moist objects dry rapidly, and the air is ‘““moist”’ when they do not dry rapidly and when the least lowering of temperature brings about deposits of moisture. The terms are therefore relative ones, but the expression “dry air,’”’? when used with reference to com- pressed air, is usually understood as air containing less than half the amount of moisture that is contained in “‘saturated”’ air. Effect of Pressure on Temperature.—It is well known that air can be made to expand by the application of heat. The altar trick of the Egyptians illustrates this as does the modern hot-air engine. Before friction matches came into general use, fire was often produced by means of an air plunger-pump, which consisted of a cast-iron barrel weighing several pounds with a bore about 3/8 in. in diameter, in which a steel piston fitted rather tightly. The end of the piston had a small cavity for receiving a piece of punk, and by pushing the barrel down on the piston the air in the barrel was compressed and its temperature rose high enough to ignite the punk. If heat is generated by compressing air, it is natural to expect that if compressed air be allowed to expand the temperature of the air will fall. This is exactly what does happen in compressed-air motors, and if the compressed air contains much moisture, the temperature may fall so low that this moisture is frozen and collects as a frost in the exhaust pipe. Frost may even collect to such an extent as to clog the exhaust pipe and stop the motor. ‘The methods used to overcome this obstacle will be dis- cussed later in detail. The principal characteristics of air to be considered in discussing its mechanical uses are: pressure, temperature, volume, weight and humidity. The relations existing between the temperature and humidity have been considered, but before considering the other character- istics mentioned, it is necessary to state clearly certain fundamental _ definitions. CHAPTER II FUNDAMENTAL DEFINITIONS Work.—Work is a force overcoming resistance, and is measured in foot-pounds. A force of 10 lb. exerted for a distance of 4 ft. represents 104 or 4o ft.-lb. of work, or a 1oo-lb. weight lifted 3 ft. represents 300 ft.-lb. of work, etc. Energy.—Energy is the ability to do work and may be measured in the same units. Energy may exist in a number of forms, for example: a water-fall, heat, light, electricity, the wind, etc. The source of all energy is the sun, but unfortunately this energy, as it reaches the earth, is not in the most suitable form for all of the work of the world. It is the province of the engineer to change available energy into the desired form with as few losses and as few changes as possible. Most of the energy required in commercial enterprises is supplied by coal, but the burning of coal represents the use of energy from the sun which reached the earth ages ago. It is only a question of time when other sources of energy than coal will have to be provided in greater abundance than at present and the attention of scientific investigators is being called to the importance of a more direct method of getting energy from the sun and of using other available forms of energy with fewer changes than are now necessary. Heat.—Heat may be defined as a form of energy, without at this time going into any discussion regarding its characteristics or effects. Power.—Power is defined as the rate of doing work. The engi- neers’ unit being the horse-power, or 33,000 ft.-lb. of work per minute. Temperature.—Temperature is an indication of the direction in which heat will flow if it has an opportunity to do so. That is, heat will naturally flow from a hot to a cold body. Temperature does not represent the heat energy that a substance contains. Absolute Temperature.—Temperature in engineering work is 5 6 AIR COMPRESSION AND TRANSMISSION usually measured on the Fahrenheit thermometer in which the freezing-point of water at atmospheric pressure is 32° and the boil- ing-point is 212°. As the temperature falls, the vibration of the molecules becomes less rapid and the energy contained in any substance decreases. That point at which the vibration of the molecules ceases is called absolute zero. From a study of the property of gases, it is evident that this point is about 460° below the zero-point of the Fahrenheit scale. The absolute tempera- ture, then, is the sum of the temperature Fahrenheit and 460°. B.t.u.—Amounts of heat are measured in British thermal units. A B.t.u. is the amount of heat required to raise the temperature of t lb. of water from 63° to 64° F. The mechanical equivalent of this is about 778 ft.-lb. This is usually represented by the letter J, and its reciprocal, or as by A. Effects of Heat.—If heat is applied to a substance, many of its characteristics may change. Its pressure may change, temperature may change; its volume, conductivity, elasticity, etc., may also be affected by the application of heat. However, all these effects may be classified into two groups: internal changes and external changes. This may be represented by an equation as follows: Heat applied = internal energy changes + external energy changes. The internal changes may be represented in part by changes of temperature which mean an increase in the velocity with which the molecules vibrate back and forth. This energy expressed in heat units may be represented by S. If a substance is of such a nature that expansion takes place when heat is applied, then the molecules must be separated farther apart against whatever mutual attraction exists between them. This also represents an internal application of energy and can be represented by the letter L. } If external work is done, as in the expansion of any substance at constant pressure, this work can be measured by the product of the pressure in pounds per square foot and the change in volume measured in cubic feet. The product in foot-pounds can be repre- sented by the letter W, and its heat equivalent as AW. If the heat supplied in B.t.u. is represented by Q, the equation Q=S+L+4AW, in which each term is measured in B.t.u. may be considered as a fundamental energy equation. Energy in Air.—Air may be treated as a perfect gas or as a sub- - stance in which there is no mutual attraction existing between the molecules. In this case L=O, and the fundamental equation FUNDAMENTAL DEFINITIONS © 7 when applied to air becomes Q=S+AW. That is, if heat is applied to air the effect of that heat (Q) will be either to increase its tem- perature (S) or to cause the air to expand and do work (AW), or both. However, of the heat energy given to the air, the only por- tion that can be stored up in the air itself (internal energy) will be that portion which is used in increasing the temperature of the air. In other words, the internal energy of air depends upon its temperature alone. This statement is very important and should be thoroughly appreciated by the engineer working with compressed air. At first thought, it does not seem possible that there is no more energy in the air (internal or intrinsic energy) if at atmospheric pressure than if the air is compressed and at the same temperature as the atmosphere. This, however, is the case, as shown by the above equations. Although 1 lb. weight of air at a pressure of 1,000 Ib. per square inch at the temperature of the atmosphere has no more internal energy than 1 lb. of air at atmospheric pressure and temperature, still the energy contained in the air under pressure is available for use, while that under atmospheric pressure is not, for in the first case the compressed air may expand, suffer a loss of pressure and also of temperature, cool to a point below the temperature of the atmosphere, and in that way give up a portion of its internal energy. The greater the fall of pressure during expansion, the greater the fall of temperature, and hence the greater the amount of internal energy available for use. Some engineers are under the impression that the energy used in compressing air is actually stored up in the air. This, however, is far from true, the internal energy in compressed air depends on its temperature alone, and that part of this internal energy that may be available for use will depend upon the fall of pressure and hence of temperature that is permissible. Specific Heat.—The specific heat of a substance in English units is the amount of-heat required to increase the temperature of 1 |b. of the substance by one degree, and is usually represented by C. Specific Heat at Constant Pressure.—The specific heat at con- stant pressure (Cp) is the amount of heat required to increase the temperature of 1 lb. of the substance one degree F. the pressure remaining constant. Specific Heat at Constant Volume.—The specific heat at constant volume Cy is the amount of heat required to increase the tempera- 8 AIR COMPRESSION AND TRANSMISSION ture of 1 lb. of the substance one degree, the volume remaining constant. . As external work is done during a change at constant pressure, it is quite clear that the former specific heat is greater than the latterthatusy-C p. eC: Real Specific Heat.—The real specific heat of a substance is the amount of heat required to merely increase the temperature of 1 lb. of the substance, one degree F. that is, this excludes any energy that may be used in doing external or other work. Apparent Specific Heat.—The apparent specific heat is the amount of heat required to increase the temperature of 1 lb. of the substance one degree F. including heat used in doing external or other work at the same time. This is, therefore, usually greater than the real specific heat. From the fundamental equation Q=S-++AW, it is ap- parent that, if all the heat applied is to be used in raising tempera- ture, AW =O and Q=S. This condition can only exist if there is no change in volume. For a perfect gas, and hence for air, the real specific heat is equal to the specific heat at constant volume, that is, Co. These specific heats are measured in heat units, but may be ex- pressed in foot-pounds by multiplying by the mechanical equivalent of a heat unit or 778 ft.-lb., or J. When this is done, the specific heat is represented by K, that is, AED and JC p=K »p. TABLE III.—C, FOR AIR AT VARIOUS PRESSURES AND TEMPERATURES Pressures in atmospheres and pounds per square inch absolute Temperatures Fahrenheit I 10 20 40 70 100 LAND eet A TLDs 294 lb. 588 lb. | 1,029 lb. | 1,470 lb. 212° On2202 0. 2389 0. 2408 0.2446 Oresr2 0.2583 Bo ONz275 O.2419 0.2465 O12 512 0.2773 0. 2986 —58° ON238O0umO. 2455 3. 0.25720 (One 755m mons TOMImOnd laa — 148° 07238010) FO. 2585" 1. °O,, 2004 mt O es 00 MMO eA OT ie ce meee — 238° O72424 Cl OAS TOS Ul GORSO4S Arr ee aia ie eee tent —274° 02240791 AOL 4147 Spree. ie meee aeaegp noid eee ae sire ee FUNDAMENTAL DEFINITIONS 9 The specific heat of air at constant pressure, (C p) is usually taken as 0.2375 B.t.u., and the specific heat at constant volume, (Cy) as ; : G 0.1689 B.t.u. The ratio of these two specific heats, Ce. Or 1.405; Vv is frequently used as shown later in compressed-air calculations. As a matter of fact, the specific heat of air at constant pressure is not the same under all conditions, as it increases with increasing pressures or decreasing temperatures, as shown in Table III given by Prof. Linde. CHAPTER III CHARACTERISTIC AND ENERGY EQUATIONS FOR AIR The principal characteristics of air to be studied are its pressure, volume and temperature. Pressure may be measured in pounds per square inch or pounds per square foot, and in the equations that follow, absolute pressure is used. This is the sum of the pressure of the atmosphere and the pressure shown by the gage. When measured in pounds per square inch, the pressure will be indicated by p. When measured in pounds per square foot, it will be indicated by P. Volumes are measured in cubic inches or cubic feet, usually thelatter. If the volume of a1 lb. weight in cubic feet is considered, it will be represented by v. If the total volume of any weight in cubic feet is considered, it will be represented by V. Temperature may be measured on the Fahrenheit scale, and when so done is indi- cated by ¢. If absolute temperature is considered, it will be repre- sented by 7. TF-=t-+-460. Boyle’s Law.— Boyle’s law for perfect gases, which was determined by experiment, states that the product of the pressure and volume of a perfect gas is a constant if the temperature is constant. ‘That is, PV1= pod2= p3ds, etc., if the temperature is constant, or PiVi= PoVeo, etc, Or P3,=P oto. Law of Charles.—The law of Charles states that the volume varies inversely as the temperature, if the pressure is kept constant. Or Vie Ce : ; m =7, etc., if the pressure is constant. Leads Characteristic Equation for Perfect Gases.—Combining these two Piri uN Povo be T > : a constant is obtained. This constant will be indicated equations, which were determined by experiment, or Bal ie Lael oe as R and the above equation as Pyv,:=RT}. Numerical Value of R.—The value of this constant (R ao 7) will 1 vary with the gas considered. For example: As 1 lb. weight of oxygen at 32° F. and 14.7 lb. absolute pressure occupies 12.21 cu. ft., the | 10 - CHARACTERISTIC EQUATIONS FOR AIR 1a 14.7 X144 X12.21 reais eA In the same way, as the volume of 1 lb. weight of air at this tempera- ture and pressure is 12.39 cu. ft., the value of this constant for air is 14.7 X144 X12.39 | 460+ 32 mice 1V1 _ Pode Weight of Air.—In the equation, “Pin i meeepierne dey Keven a, this may be multiplied by the number of pounds of air, giving the equation SA aA E ss, 3, in which w represents the number of pounds of air. This equation is of great assistance in determining the weight of air in a certain receiver. For example: If a receiver 3 {t. in diameter by ro ft. high, and having, therefore, a volume of 70.68 cu. ft., contains air at a temperature of 70° F. and a gauge pres- sure of 143.3 lb., or 158 lb. absolute, the weight of air contained in the réceiver if the pressure of the atmosphere is 14.7 lb. per square Pr vie tso 144 70.08 53.321 §3-3X(460+70) 9°91” Relation between Specific Heats.—If 1 lb. of air contained in a vertical cylinder having a weighted piston above is heated, the temperature of the air will increase and, as the pressure is kept con- stant, the heat absorbed, may be expressed as the product of the amount of heat required to cause a change of one deg. F. and the actual change in temperature measured in degrees F. or as CONC intB tiesony ke (haa) eit expressed in mechanical units; where 7; and J, are the initial and final temperatures respectively. S, the energy required to cause the increase in temperature alone, is Cy(T2—T}) in heat units; K,(T2—71), if expressed in foot-pounds. W, the external work, must be P:(v2—21), where Pj represents the pressure on the piston in pounds per square foot; v1 and v2 the initial and final volumes of the air respectively in cubic feet, but as Pu= RT this may be expressed as R(T2—T7)); that is, the heat energy ap- plied, or 77830=K.(T2—T1)+R(T2—T;), in foot-pounds. But the heat energy applied may also be represented by the expression, K »(T2—T71), hence: K »(T2—T3) =K,(T,—-T,)+R(T2—-T1) K p=K.+R, or R=K p—Ky=778(Cp—Cv) = 778(0.2375 —0.1689) = 53.3 If expansion of air takes place in a perfectly non-conducting value of this constant for oxygen will be inch will be 12 AIR COMPRESSION AND TRANSMISSION cylinder, Q of the equation Q=S+AW must equal O, and hence W= — or W = —7785; that is, during an adiabatic expansion of air, as it is called, the temperature falls and the amount of energy used in doing work during the expansion will be given by the expression K,(T1—T>2) in foot-pounds. As no heat energy is given to the substance nor taken from it during this change, all the work that is done must be done at the expense of the internal energy. The principal relations known to exist between Kp and Kv for air are as follows: K» he, eee K, K p=KytR=Kot53-3 K p—Kv=53-3 Work of Isothermal Change.—From the characteristic equation for air, it is evident that if the temperature is a constant, PV = ?P 1 PV= RPV, = PVo Fic. 5.—Isothermal change of air. constant, or PiVi=P2V2=P3V3, etc. That is, if a certain volume of air is compressed to one-half its original volume isothermally, its pressure will be doubled, while if its volume is reduced to one- fourth its original volume, its pressure will be quadrupled, etc. This relation follows the path shown by the isothermal curve of the chart, Fig. 5, the equation being that of an equilateral hyperbola. In order to find the work done during an isothermal compression, it is necessary to find the area under the compression curve drawn | on a PV diagram or plane, this area representing the work done CHARACTERISTIC EQUATIONS FOR AIR 13 expressed in foot-pounds. ‘The fundamental expression for any area on a pressure—volume diagram is given by the expression, Area=work = { PdV with the isothermal curve PV =P1V,, hence pan, and V2 Ve w= { Pav ea | dV V V 1 Vi Ve. hence, W =P1V, loge = Vi where P, represents the maximum pressure in pounds per square foot and V; the minimum total volume of the compressed air in cubic feet, V2 the total volume in cubic feet occupied by the air before compression. This also represents the work done by any number of pounds of air expanding at constant temperature from an initial volume of V; cu. ft. to a final volume of V2 cu. ft. If 1 Ib. of air expands in this way the work done will be represented by the equation P21 loge = or as P\vi= RT), this may be written RT; loge . As the relation P1v,;=P2v2 applies to this isothermal change, | Py 2 Ps To illustrate the application of this formula, suppose it is required to find the work done as 1 lb. of air expands at constant temperature of 120° F. from a pressure of 150 lb. per square inch absolute to 30 lb. per square inch absolute the work done will be: : ae the equation may also be written Pv; loge si or RT, loge ISOX144 53.3X(120+460) loge peat It is evident that the ratios of pressures in pounds per square inch is the same as the ratios of pressures in pounds per square foot. 53-3 X 580 Xloge 5 =53-3 X 580 X 1.6094, or 49,800 ft.-lb. A table of logarithms to the base e, or hyperbolic or Naperian logarithms as they are called, is given in Appendix B. This is for numbers from 1 toro. If it is desired to obtain other logarithms as for the number 0.12, this is equal to the loge of 1.2 minus the loge 14 AIR COMPRESSION AND TRANSMISSION of ro, or the loge of ee In the same way the loge of 25 is the same as the loge of (2.5 X10), or the loge of ro plus the loge of 2.5. Work of Exponential Change.—When the equation of the com- pression line is unknown, it may be represented by the equation PV”=a constant, where z is the unknown exponent (Fig. 6). F 1 Pyns PV, "= PV" Fic. 6.—Exponential change of air. PV"=P,V," and par Substituting in the formula for work Ve V2 V2 : d w= frav,we | Davie gen | poner | V-"dV Vi 1 1, n artes Ln pas ee Mee as Pi Va Pa Vere P2Vo—PiVi_ PiVi-—PoVo2 I—n N—TI P, represents the maximum pressure and P, the minimum pressure in pounds per square foot, and V; the minimum total volume of the compressed air in cubic feet and V2 its volume in cubic feet before compression. The above expression for work also represents the number of foot-pounds of work that will be done by any number of pounds of air expanding according to a change of pressure and volume repre- sented by Pai =LfsV 5". If 1 lb. of air expands in this way the work done will be represented by the equation ya P ate _ ROT 2). n—I N—I As Pyvy" =P vq", Pove=P 01 (°:) V2 CHARACTERISTIC EQUATIONS FOR AIR 15 From this it is evident that the equation may also be written: Pv (*) ‘| Piven es) =| SLY mes he > or as Tle nN—-TI V2 n—I ) 1 As an illustration suppose it is required to find the work done as 1 lb. of air expands according to the equation Pyv\)*=Po2""4 from an initial pressure of 180 lb. per square inch absolute and a - volume of 1.2 cu. ft. to a final pressure of 15 lb. per square inch absolute, the work done will be oe ga | | ee eres = I—0.083 ye Neem 180 AT =77,760[1 —0.492] =77,760 X0.508 = 39,502 ft.-lb. Work of Adiabatic Change.—If a change takes place in a cylinder surrounded by non-conducting walls preventing energy in the form of heat from entering or leaving the cylinder, this change is called adiabatic. , During an adiabatic expansion of 1 lb. of air, the work done may be represented by the equation Ky(71—T+2), as for such a change AW =—S or W=—778S, and S=C»(T2—T)). As Pa Rt and Po,=RT > K (P01 —P 202) K»(%i—T,)= R but R=K p—Ky KyPii—Pod2) _ P1i1— P22 GOK Kp Kee This expression must equal the expression for work under an ex- ponential curve, viz.: then Ky (T,—T2) = Pi1—Pove n—I hence for an adiabatic change of 1 lb. of air, the exponent in the equation P11” =P v2” must equal —; that is, Ky Kp Kp Py, Ke =PypKo and for w lb. Kp Kp PV Ko PV Kk» =PsV; acae 16 AIR COMPRESSION AND TRANSMISSION Relations Between P, v and T for Adiabatic and Exponential Change.—This shows the relations existing between P and v for an adiabatic change. In order to find the relations between Pand T or v and T for such a change, it is necessary to turn to the charac- teristic equation Pu=RT, or P44 Pods P3033 Ty ah T 2 cs T3 Ey peels then PRE But as P4013-49 = Povo! 495 i ‘- 2) 1+405 then es & : VN om Oal (**) 0-405 Ty Equating ("*) Sais and : Te vas © 1.405 As Fat Pi) van ey ie nao gph ened Bee teeth Vo . h ) 1.405 2 then & = ence : T, (a 28825 Tae (*) 0.405 Or, P, te - In the same way for changes represented by the exponential equation P41” =P2v”. ("2 pieaae eb S eee V1 CoN De ae P» RS Computation of Intrinsic Energy.—These equations enable calculations to be made of temperature changes during adiabatic compression and are used in calculating the heat curves of the chart, Fig. ri. During an adiabatic expansion of air all the work that is done must be doneat the expense of the intrinsicenergy. This can be shown from the equation Q=S+AW, which becomes O=S+AW for an adiabatic change, for from the definition Q must equal zero. This being true, Weare or a measure of the work done would give also CHARACTERISTIC EQUATIONS FOR AIR 17 a measure of the change in intrinsic energy. That is, if the initial pressure and volume of w Ib. of air is known, the equation Eee overeat) too VOW tet 1h oP ToL IeA0 Saat 0.405 will be a measure of the intrinsic energy available. In this equation P, and P2 represent respectively the initial and final pressures in pounds per quare foot. If v; and ve be used representing the specific volumes, that is, the volumes occupied by 1 lb. weight, then the equation given represents the work done and the change of internal energy of 1 lb. weight only; but if V;and V2 be used representing the initial and final volumes occupied by all the air concerned in the expansion, the PiVi—P2V2 Fhe ° ° : ° gee _will represent the entire amount of intrinsic energy available for use in expansion of w lb. from:pressure P; and volume V; to a pressure P, and volume V2. If P; and V; are known as well as Po, the final pressure, V2 may be calculated if the equation of the expansion line is known. ‘This equation will be equation P1V 434% = PoVo! 4 the equation for an adiabatic expansion. P\Vi-—PoV2 0.405 cannot be used for calculating a change of internal energy. In order to obtain the amount of internal energy contained in air it is merely necessary to assume an adiabatic expansion to infinity. The area under such an expansion curve is finite and amounts PiV, If the expansion is not adiabatic, the equation to ate For example, the internal energy contained in 1 ID. of air 405 at atmospheric pressure and 32° F., with a volume of 12.39 cu. ft. is P40; RT, ; eee. OF , which is 0.405 0.405 TBE r 53:2%493 or 64,730 ft.-lb. 0.405 0.405 It is, of course, impossible to obtain this amount of energy from a pound of air, as it is impossible to secure its complete expansion to absolute zero of pressure. CHAPTER IV GRAPHICAL DIAGRAMS Construction of Isothermal Curves.—It is frequently necessary or desirable to construct graphically compression curves represent- ing isothermal and adiabatic changes of air. A method of con- structing the isothermal curve is shown in Fig. 7, in which O rep- ie a 1 4 b Vv Fic. 7.—Graphical construction of equilateral hyperbola. resents the intersection of the coordinates of a pressure-volume plane. If an isothermal line is to be drawn through point a, con- struct horizontal line a—b and vertical line a—c, as shown, then draw any diagonal line as o-1 and complete the rectangle a—1—2-3; 3 isa point on the required curve. In thesame way, other diagonals, as o-4, may be drawn, and the rectangle a—4-5—6 constructed, giving point 6 as another point on the required curve, etc. Another method of constructing this curve is shown in Fig. 8. Assume that it is required to draw the isothermal] line for air through point a. A diagonal line, as 1-2, may be drawn through this point and the distance 2-b made equal to 1~-a; 0 is a point on the required curve. In the same way line 3-4 may be drawn through 0 and the distance 4—c made equal to the distance 3-0, giving another point c on the required curve, etc. In the equation PV”=P,V1"=Po2V.", etc., the value of the exponent may be found, if the values of P and V for any two points 18 GRAPHICAL DIAGRAMS 19 are known, by taking logarithms of both sides of the equation, PiVi"=P2V 2" log PitnXlog Vi=log Pe+n Xlog Ve, and from this _ log Pi—log Pe "log Vo—log V1 Fic. 9.—Graphical construction of exponential curve. Figure 9 represents graphically a curve whose equation is P}V,"= P2V,” in which the numerical value of 7 is 1.405. Curves of this type may be classed as exponential or logarithmic curves. A simple method (Brauer’s) of constructing such curves graphically is given below, together with a development of the equations used. Construction of Exponential Curve.—Brauer’s method of con- structing an exponential curve may be illustrated by assuming any two points, as A and B, Fig. 9, of such a curve and drawing lines through both points perpendicular to both axes. Through C and £ 20 AIR COMPRESSION AND TRANSMISSION draw lines making an angle of 45 degrees the withaxes. D represents the intersection of CD with BH produced, and F the intersection of EF with AL produced. Connecting points D and F with O will give the two angles DOP or 8 and FOV or a. In order to determine the relations between these angles, the following demonstration is given: PPG = Pe GH = eee DH =P, tan B P, =P ,(1+tan P) (1) Vez =s V,ztGB= V,tLE= V,+tiPF ine = Ve4 tan @ Ve =Va(ittan a) Ve=V4(rt-+tan a)” (2) Multiplying equations (1) and (2) PzV%(1+tan a)" =P,V3(1+tan £) but, Puvi Pave (rt+tan a)"=1-+tan 6 tan S=(1-+tan a)"—1 This shows the relation between the angles § and a in terms of the exponent 7. For convenience, it is customary to make tangent of angle a= 0.25. Tan ? has been computed for various values of 7 as follows: n Tang. 2 O.7 0.169 ® 0.8 0.195 0.9 C5223 iO On25 1.0646 0.268 TESS 0. 288 r25 Ou322 I. 333 0.347 T3239 0.358 TAt One7 If, for example, a curve is to be drawn through any point, as A following the equation PiVi17>=P2V_!>, lay off angle VOF, or a, with a tangent equal to 0.25 and angle POD, or , with a tangent of 0.322; then draw AC and AL through A, and construct Jines CD and FH, making angles CDH and FEL equal to 45 degrees, the in- tersection of the horizontal line from D and the vertical line from £ will give point B as one of the required points of the curve. In the same way, other points of the required curve may be obtained. GRAPHICAL DIAGRAMS 21 Heat added or taken away for Isothermal Change.—The funda- mental equation showing the effects of applying heat to air, Q0=S-+ AW, enables a determination of Q, the heat to be applied in the case of expansion, or the heat to be taken away in the case of compression in order to cause the expansion or compression line to follow a certain exponential curve. If this required expansion or compression curve is to be isothermal, S=O and Q=AW, that is, the heat to be applied to secure isothermal expansion must equal the heat equivalent of the 2 . P1Vi loge Vi . work done during the expansion, or — cae * heat units, and in the same way the heat to be taken away, in order to secure isother- mal compression, must equal the heat equivalent of the work done during the compression. Heat Added or taken away for Exponential Change.— Frequently it is desired to secure a compression or expansion curve between the P 0 Fic. 10.—Graphical measurement of change of heat energy. isothermal and adiabatic, following the equation PaVa"=PsVo", as shown in Fig. 10, in which z is less than 1.405. In this case Q= S+AW. It has been pointed out that the mechanical equivalent of the internal energy possessed by air is represented by the area under an adiabatic curve continued to infinity and in Fig. 10 af represents such a curve through point a and be such a curve through point 6. W, or the external work done between a and 8, is repre- sented by the area abcd, or 1+ 2. SX778, or the internal energy for point a by the area 1+4, and SX778 for point b by the area 3+-4. The change of internal energy in going from a to 6 in the case of expansion will be area (3+4) —area (1+4), or 3—1, and as W= 1+2, the mechanical equivalent of Q must equal SX778+W, or 22 AIR COMPRESSION AND TRANSMISSION (3-1) +(1+2), or (3-+2). That is, the mechanical equivalent of the: heat energy to be added during expansion from a to b, or taken away during compression from 6 to a, in order to follow a certain curve on the PV diagram, will be the area bounded by the curve ab and two adiabatics from the ends of the curve to infinity, PuVa—PoV5 Pov P pV, n—I By 0.405 - 0.405 Difference between Isothermal and Adiabatic Compression.— The difference between adiabatic and isothe:mal compression is or, 367.5 3528 333.1 3234 EEE CATR aang ae NSE SN NIN ved a Sl Orme x af COCCI el Ks gms a EOLA NRE BREE SCOUDSENEN: ee gel LECCE eo CELLET ALIS NINE eee TILLELLLELLLL ALAN NINE gree HCL TAIN De NINE ep ALESIS CURSES: breeg CILCCE EEC Net NN e serge HCL CTT TTS SEINE deo F ICCC SSE SSE 3 1323 10 Ps S ; °D em eC LCLLEL LLC NEN o 102.9 o vie PS PRR NS EPS ‘a 2 ore COSC Ge seel: pes Cee TTS ie ESSE 58.8 ears Ss 5 441 4 Hee eee 3 29.4 CREE BEE EE i )4e/ ec Stipes Senses e Haan 0 76 Seah 02 ean niet fen eae eres Fic. 11.—Temperature change due to adiabatic compression. illustrated by the two curves on the PV plane at the left of Fig. 11, which shows that while an isothermal compression of free air to half its original volume will raise its pressure to 2 atmospheres, or 14.7 GRAPHICAL DIAGRAMS 23 lb. gauge at sea-level, the same reduction of volume adiabatically will raise its pressure to 2.82 atmospheres, or 26.75 lb. gage. Jf the re- duction of volume is to 0.2 of the original volume, the pressure for isothermal compression will be 5 atmospheres or 58.8 lb. gage at sea- level, and for adiabatic compression 8.88 atmospheres or 115.83 Ib. gage. Temperatures due to Adiabatic Compression.—Adiabatic com- pression is always accompanied by an increase of temperature fol- 0-405 0-2882 a FZ) . ots Gs). This shows the ratio of the final absolute temperature to the initia! temperature. The right-hand part of Fig. 11 shows the resulting temperature Fahrenheit for adiabatic compression with initial temperatures vary- ing from 0° to 100° F._ From this it is evident that adiabatic com- pression to 0.2, the original volume and consequently 8.8 atmos- pheres, will approximate a final temperature 510° F. if the initial temperature is 60° F. Very high temperatures are to be avoided in compressing air as an explosion may result if the temperature is sufficient to ignite the volatile matter contained in the lubricating oils used. In addition to this, the energy represented by the high temperature will soon be dissipated by radiation. Isothermal compression requires removal of heat energy during compression, and this cannot be accomplished satisfactorily with piston or fan compressors operating at modern speeds. Because of these conditions, high compression is secured in modern compressors by compressing by stages and cooling the air between stages. Compression in single-stage compressols Is usually accompanied by such cooling as can be secured by water-jackets or other means, but with the speeds required the usual effect is to se- cure a compression curve with an exponent m varying between 1.25 ance. 32" | Work done by a Compressor.—The work done in a machine, which draws in air, compresses it, and then discharges the compressed air, can be calculated, it the suction and discharge pressures are known and the character or exponent of the compression curve is given. Exponential Compression.—Let Fig. 12 represent such a series of changes for any compressor, in which the effect of clearance is dis- regarded. In this diagram, which is somewhat similar to the indi- cator card from a piston compressing cylinder, d—a represents the intake of air at a pressure of p2 Ib. per square inch, a—d represents the compression of this air from p2 to pi Ib. per square inch following lowing the equation 24 AIR COMPRESSION AND TRANSMISSION the compression curve p1V 1" = p2V 2” anb-c represents the discharged of the compressed air at a pressure /; lb. per square inch. The area enclosed by the lines d-a—b-c-d will represent the work done if V represents the volume in cubic feet and if p, representing the pressures in pounds per square inch, be multiplied by 144 to give pressures in pounds per square foot. Pp —— eo Pimper oe Fic. 12.—Work diagram of air compressor. The required area will be area a-b-g-f plus area b-c-e-g minus area a—d-—e-f, boVo—paVa nan alae or 144(poVo—paVa) (+1) ) or —-144(oV>—PaVa) Va is usually known in compressed-air calculations, but Vz is not known directly, but as paVa"=poVo” this equation may be sim- or +144 poVo—144 PiVa n—-1 es plified, for p»Vo=paVa (7) > or poVo= paVa &) m , andethe expression may be written: EDN (ere it | | tees I Suppose, for example, it is desired to ascertain the work required to compress 2,500 cu. ft. of air from a suction of atmospheric pressure or 15 lb. absolute to a gauge pressure of 100 Ib. per square inch, or 115 lb. absolute, following a compression Jine whose exponent is 1.3. 1-3-1 rhe) ‘ I.3 (=) j.2o0e This will require 7S xX 244X 152,500 | me : 0-23 oy 4.33 X144X15 X 2,500 (7.6) — 4 or, 23,375,000 X (1.59—1), Or 13,780,000 ft.-lb. GRAPHICAL DIAGRAMS 25 If the compressor is to have this free-air capacity of 2,500 cu. ft. per minute, the horse-power required will be 13780000 33000 SOL ATO. p), Isothermal Compression.—If the compression line a—b was an isothermal line, following the equation paVa=poV», the expression for the area would be ie Vig 144 ov loge V+ Ve baVal, or 144 poVo loge +, or, 144 paVa loge ae Or 144 X15 X2,500 loge a a Or, 5,400,000 loge 7.66 = 5,400,000 X 2.036 = 11,000,000 ft.-lb. If the compressor is to have this free-air capacity of 2,500 cu. ft. per minute, the horse-power required will be I I000000 33000 Or, 233 hep: These calculations show the advantage of having the exponent of the compression line as low as possible, or in other words keeping the temperature of the air during compression from rising. The advantages and methods of attempting this are discussed later. The effect of valves, clearance and friction on the required horse- power is considered later in discussing piston compressors. CHAPTER V AIR AT PRESSURES BELOW THE ATMOSPHERE A study of the properties of air, and of its applications would not be complete without reference to at least a few of the uses of air at pressures below the atmosphere. For purposes of experiment and for laboratory uses, these low pressures are usually obtained by means of the familiar air pump. Venturi Vacuum Pump.—Another method of securing these low pressures is by means of a very simple hydraulic air ejector or ‘“‘venturl vacuum pump”’ as it is sometimes called. This convenient instrument for quickly obtaining an approximate vacuum depends on the principle that a fluid passing at a high veloc- ity through a converging and diverging nozzle in which the curves conform to the shape of the “vena contracta”’ of a jet from an orifice, will produce an approximate vacuum at a point nearest its greatest con- traction and if an air chamber is connected through an orifice at this point the air will be drawn into the jet and a very good vacuum formed in the chamber. In the sketch shown in Fig. 13, tube A may be connected by a rubber hose to a faucet. The con- verging-diverging tube through which the water is forced is shown at D. Tube C, which is connected with the chamber from which the air is to be exhausted, has a check valve E and is connected to the smallest diameter of the nozzle. It has been found that better results are secured when a baffle F is introduced into the dis- charge pipe B, as shown. Sprengle Air Pump.—For a more perfect vacuum than the air pump or the hydraulic air ejector the Sprengle mercurial air pump is used. This pump depends on the fact that if mercury is forced through an inverted U tube the mercury going over the bend will 26 Fic. 13.—Hydraulic air pumps. AIR AT PRESSURES BELOW THE ATMOSPHERE 27 exhaust the air from any chamber that is connected to the U tube at the top of the bend. This pump is used for exhausting the air from incandescent lamp globes and remarkably low pressures are secured with it. Measuring Vacuums.—Although the normal pressure of the atmosphere at sea-level is 14.7 lb. per square inch and pressures above that are designated in the same units, pressures below the atmosphere are not usually so designated but instead are expressed in inches of mercury. If a U tube at the sea-level is filled with mercury and one end connected with a perfect vacuum while the other is in contact with the atmosphere, the mercury will rise to a height of 29.92 in. above the level of the mercury in the leg that is exposed to the atmosphere (1 in. of mercury=o.49 lb. per square inch). Consequently a vacuum gage indicating 20 would represent two-thirds of a perfect vacuum or a pressure of about 10 lb. below the atmosphere, that is, approximately 5 lb. absolute. One of the most familiar uses of pressures below the atmosphere is in a condenser for steam engines in which the back pressure of the engine is reduced considerably below that of the atmosphere, thereby increasing the power of the engine. Condenser Pumps.—Condenser pumps! are of two kinds: cir- culating pumps and air pumps, the circulating pumps being used to force the condensing water through the condenser and the air pumps for removing the condensed steam and air. In some types of condensers, the condensed steam is removed by gravity, as in the barometric type, and the air pump removes but air alone, being in this case called a ‘‘dry-air”’ pump to distinguish from the “‘wet- air’? pump, which removes condensed steam as well as air. Wheeler Combined Pump.—As a circulating pump _ usually lifts the water but a short distance, it is built as a tank pump, but should it be required to lift water through a long line of pipe, as a line to the top of a cooling tower, it must be made of heavier con- struction. Because of the large quantities of water which it handles, it is very frequently built of the centrifugal type. Fig. 14 shows a combined air and circulating pump of the Wheeler Condenser and Engineering Company. The steam cylinder is in the center, the air-pump cylinder at the left and the circulating-pump cylinder at the right. | The circulating pump forms one end support for the condenser. The water is discharged through A into one set of tubes and then 1 Pumping Machinery, Greene. 28 AIR COMPRESSION AND TRANSMISSION it returns through B and the upper set of tubes to C, where it dis- charges. The air pump forms the other support for the shell. It takes the air and water from the condenser and discharges it through D. The suction space F is connected to G. et SSSSSPSSSSUAY 4 Vee pies PN S SASS SSS Sixes an YN N G, rss) SS jp PIE GELS z Ve EA suk NOSE seal ISspsmsssssJ =} NS GLLLLEL peer Zz Air and Condensed Steam Stearn Cylinder Circulating Pump is) LELLLN NN CiLLL/ LLL, WA TSS N Fic. 14.—Wheeler condenser pump. Size of Water and Air Pumps.—To find the size of the water and air ends of the pump, suppose that W pounds of steam per hour at a pressure p are to be condensed. If 7 is heat of vaporization of the steam, x its quality, ¢.° the temperature of the condensed steam, and g the heat of the liquid, and if G pounds of water entering at ti° F. and leaving at ¢.° F. are to be used, G is given by the equation: 5 W (q+%.r— ic) dto—Qti in which the subscripts of g indicate the temperature for which the heat of the liquid is obtained. If the number of revolutions or double strokes N are assumed, the displacement of the water end will be G Ibs. per hr. D3 = oN cubic feet. The air end of the pump is made in many cases of empirical design. Some authors give ratios of volume displaced by the pump per minute to the volume of the condensed steam or to the volume of the low-pressure cylinder of the engine which is dis- charging into the condenser. Several of these are mentioned. AIR AT PRESSURES BELOW THE ATMOSPHERE 29 RATIO OF AIR CYLINDER DISPLACMENT TO LOW-PRESSURE CYLINDER Single-acting vertical pump surface condenser........ Ios 13 single-acting ‘vertical pump jet condenser.:..-....-... 1: 9 Double-acting horizontal pump surface condenser..... ae a Double-acting horizontal pump jet condenser......... be aes Double-acting horizontal pump-compound engine sur- PAGEECMTICLCLLSCLa writ Mer ase nak tag ao Tt 26 Single-acting horizontal pump-compound engine sur- POE SECON COSCL etme Ee kaie (in adn Mee. hehe oe Read STO RATIO OF AIR CYLINDER De ee TO VOLUME OF CONDENSED SIIRIACOPCOLICL CHISEL Me Mine ret eee pe, tie ne Sn ee ee Te OG Net COD CDsct me a Ete Pac ok a heehee Mee oe Ee SAO This may be a satisfactory way, but it is better to estimate the volume from the air probably present. Water usually contains air to about one-fifteenth of its volume. This amount of air is at atmospheric pressure fa. and it must be cared for by the air pump at a reduced pressure. In addition to this there are small leaks in the pipe line which.allow more air to enter. A small hole will destroy the vacuum of the air pump. To find the volume of air per minute the following formula will be used, allowing 100 per cent. for leakage. = Ins I iy thy : : V=(@X2.Xg) (<-) (bps) T, cubic feet per min. p = absolute pressure in the condenser, pounds per square inch. ps = vapor tension or absolute steam pressure corresponding to 7¢.! T. = absolute temperature in condenser. Ta = absolute temperature of atmosphere. This equation shows the importance of making ps as much less than p as possible. The terms p and ps; do not differ much, and by taking the mixture of air and vapor on its way to the air pump, through as cold a passage as possible, the term ps; is made smaller and the denominator is increased, making V small. This is the reason for the great advantage in a counter current for condensers, and even in the condenser, shown in Fig. 14, the coldest water should enter directly over the air-pump inlet so as to cool the mixture going to the pump. From the volume thus computed the displacement of the air pump is given by: Dar=sy cubic feet. 1 See discussion on Partial Pressures Appendix C. 30 AIR COMPRESSION AND TRANSMISSION Knowing the displacements of these pumps a stroke may be assumed, and from it the area determined. A es sq. ft. for the water pump. Aer=—¢ sq. ft. for the air pump. Steam Cylinder Size.—The cards from the water end are shown in the lower part of Fig. 15, while those for the air end are shown above. The combination of these or the addition of them when ¢ Atrnosphere ‘N n N N N N N N N N N N N N Ne N N N a 7 S fe Atmosphere ‘ ie Ure Fic. 15.—Indicator cards of Fic. 16.—U. S. Navy pump condenser pump. cylinder. reduced to the proper scale, on account of the difference in piston area, will give the total work, and from this the area of the steam cylinder may be calculated, if the mean effective pressure (M.E'P.); be found fora given boiler pressure. Allowing 33 per cent. for friction, which is made large to give certain driving power, the following results: : 4 LEP. )arAap+(M-EP.)pA p a iT.0O— 0.23) LUGE ta). Smit. U.S. Navy Air Pumps.—Separate air pumps are often used. Fig. 16 shows the air cylinder of a stream-driven pump used in the U. S. Navy. This air pump is made with two air cylinders driven through gears from a steam cylinder placed on one side of a pump barrel. AIR AT PRESSURES BELOW THE ATMOSPHERE 31 The pump is of the bucket type with foot valves AA and head valves at B. These with the valves in the bucket at C are all spring-con- trolled metal valves. The foot valves aie placed on an inclined partition for the purpose of making it easier to discharge the air when the piston rises and forms a vacuum. The lip around the discharge valve makes a dam and covers the valve with water. This makes them air tight. The other valves are also flooded, since all of the water on the bucket or that over the foot valves cannot be driven out, as the valves limit the motion of the bucket. On thedown stroke of the bucket the pressure in the space above it soon falls to a low vacuum because it had been completely filled with water; this, then, causes the valves to open and take air from the lower portion of the cylinder. ‘The air in the water also separates and rises to the top of the cylinder. Finally the bucket reaches the water below, and this is driven through the valve openings which are uncovered. It is seen that the air leaves first in this case. The water is struck by the bucket surface and will cause considerable shock if the pump is run- ning too rapidly. | Edwards Air Pump.—To do away with shock and to decrease valve resistance, the Edwards air pump, Fig. 17, was introduced. In this air pump water and air enter the space A at the bottom of the pump which is made conical in form. The piston B, which is driven from the steam piston by two rods CC extending — over the shaft and crank, is provided with a conical bottom. As this piston descends there is a vacuum produced, so that when the top of the piston uncovers the openings #, air enters {from the space A around the cylinder barrel, and as the conical bottom enters the water in the bottom of A, this is forced around the curved passage and discharged into the openings at HF. This continues even after the piston starts up, as the momentum causes the water to continue its motion. This discharge of water into the openings as the piston is moving upward acts as a valve to keep the air from coming out as the piston ascends. In a short time, however, the piston covers the ports or openings E and then the air and water are compressed until the pressure is sufficient to overcome the atmospheric pressure on the head valves at H, which are flooded by means of a lip around rN G NOS l NS <<) a Fic. 17.—Edwards air pump cylinder. O2 AIR COMPRESSION AND TRANSMISSION the valve deck. The piston rods CC are carried through long-sleeve stuffing-boxes so arranged that the point H, at which leakage could occur, is water sealed, leaving only one stuffing-box at the plate K to carefor. Thisis a simple matter. Industrial Uses of Vacuums.—One of the earliest applications of air pressure below the atmosphere is shown in a patent dated 1833, for the preparation of leather by the evaporation of certain substances in a partial vacuum, the object being to avoid intense heat. Water at atmospheric pressure boils at 212° F. If the pressure is increased above the atmosphere as in the ordinary boiler, the boiling-point of the water is raised, and for the same reason when it is desired to evaporate any substance at a temperature below its boiling-point for atmospheric pressure it is merely necessary to put the substances in a partial vacuum and its boiling-point is accordingly lowered. This results in evaporation at very low temperatures, a most desir- able feature especially in the drying of fruits, etc. Air at pressures below the at- mosphere is used for drying all kinds of food materials such as meat, fish, fruits, etc. Frequently a solution of a gelatin sugar or gum is used as a coating. Vacuum processes are employed for pickling and salting meats and vegetables, evaporating fruits, re- fining sugar and condensing milk. Wood may be artificially colored and railway timbers impregnated with preserving substances by means of a vacuum. Salt Evaporating Effects.—Probably one of the most interesting applications of the partial vacuum is found in the manufacture of salt, the refining of sugar and the concentration of syrups, liquors, etc., by what is known as the triple effect apparatus. The apparatus in which this is done usually consists of two or three ‘‘effects,’’ as they are called, almost identical in construction. One of these is shown by Fig. 18 and represents one of a “‘train”’ of effects for extracting salt from brine by heating the brine solution, thereby evaporating the water and leaving the salt as a solid deposit. B is the heating chamber or section consisting of a series of vertical flues, conical in section, in which the brine circulates and around Ei Fic. 18.—Vacuum manufacture of salt. ALK AIP PRESSURES BELOW THE ATMOSPHERE 33 which the steam flows. This part is very similar in construction to a vertical flue boiler, with the exception that the flues are conical instead of cylindrical, to prevent deposits on the tubes. Steam js furnished to B through pipe £ either from a boiler or the exhaust of a steam engine, and after giving heat to the brine, which fills the apparatus as shown, the steam is condensed and drawn off. ‘The vapor from the brine in the first effect passes through pipe / into the heating section of the second effect, gives heat to brine in the second effect and in doing so is condensed. This con- densation of the vapor produces a partial vacuum in the first effect, thus lowering the boiling point of the brine in that effect and hence aiding evaporation. The vapor of the brine of the second effect is conducted to the heating chamber of the third effect, imparts heat to the brine in that effect, producing a partial vacuum as in the first instance. The vapor from the third effect passes to an air pump. ‘This air pump maintains a good vacuum in the third effect and in consequence the boiling-point of the brine in that effect is very low indeed. The vacuum in the second effect is not good as in the third, and the boiling-point of the brine in that effect is a little higher. In the first effect the poorest vacuum exists and in consequence the brine here has the highest boiling-point of all and therefore requires the most heat, which is supplied to it from the boiler or the exhaust of the engine operating the air pump. It is because of the different boiling-points of the brine in three effects that the heat of the vapor of brine in the first effect is enabled to evaporate the brine in the second effect and the vapor of brine in the second effect is able to evaporate the brine in the third effect. In each one of the three effects of this apparatus salt is being extracted, the solid matter settling to the bottom of the chamber C from which it can be with- drawn by means of the two valves without disturbing the operation. The salt and some brine with it are deposited on a filter in the cham- ber D. The salt is here washed and the brine below the filter is returned to the evaporating chamber through H. The salt is then removed and a new supply of brine introduced through G. In this way the operations can be made practically continuous and in many plants automatic. In some of the salt machines, instead of having two valves for withdrawing the salt without disturbing the partial vacuum, the lower part of the apparatus consists of a pipe running down such a distance that the partial vacuum will equal the hydrostatic head 3 o4 AIR COMPRESSION AND TRANSMISSION and consequently the salt may be removed without the use of any valves whatever. Concentration of Liquors.—In the concentration of syrups and of many liquors, it is highly important that the liquors should not be heated too highly or they will be scorched. To avoid this, the liquor is moved through pipes at a velocity so great that there is no oppor- tunity for the syrup to become scorched. In the concentration of liquors, a partial evaporation is secured in one effect and the vapor of the liquor separated from the liquor | itself. Both vapor and liquor are then introduced into a second effect which has a lower pressure, and here the vapor from the first o—> < aELer =a) ze 2) 2 F| | = Fic. 19.—Vacuum concentration of liquors. effect gives heat to its own liquor and the liquor is still further concentrated; the resulting liquor and vapor of this second effect are separated as in the first instance and introduced into a third effect where the concentration is carried still further. In some evaporators this is continued in a fourth effect and a still further concentration of the liquor secured. Figure 19 shows an evaporator of the type just explained. The operation is as follows: The steam which may be either the exhaust from an engine or live steam from a boiler is led into the cylindrical chamber through A. The liquid to be concentrated is fed in through the tubes B and enters the evaporator in a small but continuous stream and immediately begins to boil violently, becoming a mass of spray containing, as it rushes along the heated tube, an increasing proportion of steam. The outlet of the tube C being at a lower pressure than B, the contents are propelled through the tubes at a high velocity, finally escaping into the separator D. Here the steam or vapor with its entrained liquid is discharged with considerable force against the baffle plates H, causing the liquid to be separated from the vapor, the concentrated liquor being drawn AIR AT PRESSURES BELOW THE ATMOSPHERE 35 off through a trap F, while the vapor escapes through G to enter the second effect where its heat still further concentrates the liquid, which is conducted from F of the first effect to the second effect, entering through pipes similar to B. The liquid is led from the bot- tom of the separator of the first effect into the coils of the second effect and is further concentrated, passing in this way through the entire system or “train.” The volume of the liquid is being continually reduced as it passes through these effects, and as the pressure falls in passing from one effect to the next the boiling-point is lowered. That in the last effect being the lowest of all, the required low pressure for this effect is secured by a vacuum pump. This relative reduction in pressure and consequently of the boiling temperature automatically adjusts itself, no matter how many effects are used, thus effecting the boiling of the liquid by the steam produced from the same liquid when in the preceding ‘‘effect.”’ One of the advantages claimed for this system of evaporation of a liquid in the form of a spray subjected 1 to heat under a vacuum is that it receives the heat quickly and is concentrated slightly at one temperature, then still more at the lower temperature of ~ the: next effect, and so on, thus re- ducing the danger of over- heating. The rapid move- ment of the liquid aided by =, ; the vapor which is moving a in the same direction keeps ) the liquid in the form of a spray, thus taking up very quickly the heat given to it. i OTT, Evaporation of Cane Juice. pre. 2o,—Vacuum concentration of liquors. —The cross-section of a still different type of evaporator is shown in Fig. 20. The liquid or cane juice is introduced through A and is sprayed from holes in pipe B over a series of steam-pipes. The partially concentrated liquor falls into chamber C and is drawn from there by a centrifugal pump D and forced into the next effect through a pipe similar to A and B of the first effect. Steam for heating the first effect is introduced through pipe E and, after imparting heat to the liquor, is condensed. The 36 AIR COMPRESSION AND TRANSMISSION water falling to the bottom, as shown, is drawn off through F. The vapor from the liquor that has been partially concentrated escapes through G and is introduced to the heating chamber of the second effect through a pipe corresponding to £ of the first effect. As the pressure of the second effect is lower than the pressure of the first effect, the condensed steam from this effect is also introduced into the second effect, and, being at a temperature above that of boiling- point of water at this lower temperature, it gives heat to this effect and helps to evaporate the liquor in it. Vacuum Cleaners.—One of the most recent applications of air at pressure below the atmosphere consists of vacuum cleaners of various types for removing dust and dirt fiom floors and walls, furniture, etc., in buildings. Although many types of machines for producing the 1equired vacuum are on the market, they may be grouped under two heads, namely, portable and stationary types. In the former type of vacuum cleaner, the machine is moved about the room, drawing dust and air through a pump and discharging Fic. 21.—Syphon. into a cloth receptacle, from which the air can escape and in which the dust is trapped. This type of cleaner has the advantage that it is comparatively cheap, but has a disadvantage in that germs are discharged with the air into the room, and from the hygienic point of view this is considered objectionable. The objection mentioned is removed in the second type of cleaner, in which the machine is permanently located in the basement of the building and vacuum pipes lead to the various rooms and floors, to which the hose and cleaning tools are attached. This type of machine is naturally more expensive, but finds considerable favor in large office and hotel buildings. The piston type of air pump is used as well as fans, bellows, and AIR AT PRESSURES BELOW THE ATMOSPHERE 37 rotary blowers. This field of usefulness for air at low pressures has increased to a remarkable extent, but the industry cannot yet be said to be on a fixed basis; that is, there is still considerable informa- tion needed regarding the proper suction pressures to secure the req- uisite cleanliness without injuring the fabric of rugs: and hangings. Syphon.—A discussion of the uses of air at pressures below the at- mosphere would not be complete without some reference to the syphon (Fig. 21). Bis an air chamber, C a water seal for the valve F, D a funnel for filling the syphon and also for sealing valve K against air leakage. After the syphon has been filled, valve K is closed and G and H opened. This starts the syphon in operation. The air that comes in with the water and through the joints of the pipe collects in chamber B and may be discharged by closing valve F, opening valve K, and filling chamber B with water. Then close valve K and open valve F and any air below C will rise into chamber B and the water will take its place without stopping the running of the syphon. CHAPTER VI AIR AT LOW PRESSURES Uses of Air at Low Pressures.—Probably the principal uses made of air at low pressure are for cupolas, furnaces, blacksmith fires, for conveying light materials, as shavings, etc. Avery large field for air at low pressure is for purposes of ventilation for school buildings churches, theaters, assembly halls, factories, mines and tunnels, etc. Its use in this field dates back to the sixteenth century, and while for many years very little thought was paid to it, to-day considerable attention is paid to the subject of ventilation. In fact, no heating system for home, school-house, factory or office building is complete without some system for removing the foul air and replacing it with fresh air. To secure the necessary movement of air in buildings where the number of cubic feet of room per person is a limited quantity, a positive circulation is secured by introducing the fresh air at a pres- sure a few ounces above the atmosphere into the room, or by drawing the foul air from the room by means of an exhaust fan. Compressors for Low Pressures.—The principal machines used for moving air for ventilation and other purposes, either by pressure or suction, are: the centrifugal fans or blowers, the positive blower of the piston or rotary type, and the jet pumps from which are dis- charged jets of steam or compressed air. The requirements for good ventilation demand that large volumes of air must be moved at com- paratively low velocity and pressure, which is not a favorable con- dition for high efficiency and can in general be better satisfied by a centrifugal fan or blower than by any other machine; it may also be stated that the fan is comparatively cheap to install, is simple in construction and possesses a fair efficiency. Tables giving requisite information regarding fans for various purposes can be secured from any of the fan manufacturers, and engineering handbooks usually contain considerable data taken largely from these catalogs. 38 AIR AT LOW PRESSURES 39 It is well to remember, however, that these tables are apt to over- rate the capacity and under-rate the required power for operation. Centrifugal fans are in use furnishing air at pressures varying from 1/4 0z. to 20 oz., and are constructed in all sizes, the largest, of course, being used where large volumes of air are to be moved at very low velocity. . Air for Forges.—An article by William Sangster in the Transac- tions of the American Society of Mechanical Engineers, in Volume 22, page 354, gives the following approximate rules of the air required for forges and cupolas. The maximum pressure required for forges is about 4 oz. per square inch, the ordinary pressure about 2 0z.; 140 cu. ft. of free air per minute is ample and it is estimated that it requires about 1/4 h.p. to furnish air for an ordinary forge. It is customary to estimate that an exhaust fan for a blacksmith-shop must remove four times the amount of air delivered at a pressure of 3/4 0z., and that to do this will require about 1/5 h.p. per forge. Roughly speaking, if the number of forges is divided by 4, the horse- power required to furnish the blast can be found, and if the number of forges is divided by 5, the horse-power required to exhaust the smoke can be found. These exhaust fans run at a much slower speed than the pressure fans and as the pressure of the exhaust air is much lower than the blast the power required for their operation is less, although they move four times the volume that the pressure fans do. In some installations one fan does the work of forcing the blast and ex- hausting the smoke, but as the requirements of a blast fan are so different from those of an exhaust fan, such a combination is not economical. Air for Cupolas.—The air required to melt iron in cupolas may be taken as 40,000 cu. ft. per ton of iron melted, and the horse-power required as three-tenths of the number of tons to be melted per hour, multiplied by pressure of the blast in ounces per square inch. It is well to remember that these figures do not take account of losses in the piping system. These results will, no doubt, fall far short if the pipe system is poorly designed with sharp elbows, small diame- LErsy tc: Air for Ventilation.—In estimating air required for ventilation, the data in Table IV is frequently used: 40 AIR COMPRESSION AND TRANSMISSION TABLE IV.—AMOUNT OF AIR REQUIRED FOR VENTILATION Allowable parts of carbonic Cubic feet of air required per person acid in 10,000 of air Gr COR Per minute | Per hour 5 100 6,000 6 50° 3,000 7 33 2,000 8 25 1,500 9 20 1,200 IO 16 1,000 TABLE V.—AIR SUPPLY FOR VARIOUS BUILDINGS Cubic feet | Cubic feet Air supply per occupant for Pe Aras Heche Hospitals.2.toy chess Get oo ae le he ae ONTO TLOD. 4,800 to 6,000 High schools. . Le ee ate Oe Brae 50 3,000 Grtcrcaccis® te erty, hc BS en ln ce 40 2,400 Theaters and aesenibly nail eae Wears: De 1,500 Ghrarchee an eee ak a ae 20 1,200 TABLE VI.—AIR SUPPLY FOR VARIOUS ROOMS Use choos Changes of air per hour Public.,waiting-room /.. 1.621, dee ol eee ee 4 to 5 Publicstoilets (ces 85h el eee 5 to 6 Coatvand Hocker-rooms.”.. 2... 4. ee eee ee 4-to 5 MMIUSOUIIS BS ence cite «Sch plc athe EEA oe eee rena 3to4 Offices;*piubltes: his iol a, see 4 to 5 Offices private < asl. cst. c Se ee ee ee ee 3 to 4 Public: dining-rooms, 5395 eee ee 4to5 Living-ToOMS WR eee cn Sao een eee pnd Ne eee 3 to 4 Libraries, public. . 5 safle: Bieta d seiaced, ewe TERee ee tues aa eee mT 4 to 5 Libraries, is ae ch SS ee ince Ee cae 3to4 Fuming cabinets fe eivctaica jaboratorres Lo a AOL eh one we ee ree 30 to 60 The following material on fans and blowers is taken from a lecture by Mr. H. de B. Parsons, Consulting Engineer, delivered before the Junior Class of Columbia University: LECTURE BY MR. H. DE B. PARSONS 4] FANS OR BLOWERS ‘A fan or blower is a machine for impelling gas, z.e., for producing a current of gas. In the majority of cases the gas impelled is air. “There are many purposes for which a fan is used, such as for heating, cooling and ventilating buildings, either by exhausting air from, or forcing air into, the apartments; for blowing the fire of a forge or cupola; for creating artificial draft for fuel combustion; for work pertaining to drying; for carrying away obnoxious gases and discharging them at a point where they will not create a nuisance; for carrying away grindings and waste products so that they may not affect the workmen; for conveying light materials, such as saw- dust and small particles, and permitting them to settle in dust chambers; and for the circulation of air in mines and places where explosive gases may collect. “When fans are properly selected for their work they will give satisfactory and economic results, and will require little attention for maintenance. “The conditions of pressure and density of the gas and of speed and capacity of the fan govern the size, type and proportion of the fan and its housing. These conditions are closely related, and all affect the design that should be selected. Even moderate differ- ences in the conditions of operation will have considerable effect upon the power necessary to drive the fan. It therefore follows that a fan should be designed for the conditions under which it is to operate, and conversely, that a fan should be operated under the conditions for which it was designed. ‘Fans are not economical machines to operate against high pres- sures. In such cases a blowing engine or compressor will be the Detter Classification “There are a number of types in use, but nearly all blowers and fans can be classified under one of the follcwing heads: (1) Rotary blowing machine. (2) Disc, axial or propeller wheel fan. (3) Centrifugal fan, either a fan blast or cone wheel. (4) Turbine blast or high-speed centrifugal fan. “Type (1) is a positive or displacement discharge machine, and is a blower or exhauster. “Type (2) is an axial discharge fan. “Type (3) and (4) are peripheral fans. ‘All of the types can be used for exhausting or for blowing, although some are less suitable for exhausting than others. There is a material difference in the selection of a type for an exhaust 42 AIR COMPRESSION AND TRANSMISSION machine, when pressures above the atmosphere on the discharge side of the fan are considered. The disc fan makes a gcod exhauster when a pressure above that of the atmosphere does not have to be maintained on the discharge side, but when such a positive pressure has to be maintained a centrifugal machine is the more suitable. Definitions “There are certain terms used in fan work which are recognized as having specific meanings. ‘Fan Pressure or Draft——Fan pressure or draft means the difference between the pressures on the suction side and on the discharge side of a fan. The difference in pressure is expressed either in ounces per square inch or inches of water. “When a fan is used as an exhauster discharging into the atmos- phere, there will be a partial vacuum on the suction side and slight pressure on the discharge side. In this case the vacuum is expressed as the number of ounces or inches of water below the atmosphete, and the fan pressure or draft is measured by the difference. It is just the same as if the suction were at atmospheric pressure and the discharge at the same number of ounces above the atmosphere. ‘Fan Capacity.—Capacity means the maximum discharge of free air froma fanin cubic feet per minute against a pressure cor- responding to the speed of the tips of the blades. This condition is satisfied in the case of a centrifugal machine when the velocity of the gas entering the inlet is equal to the velocity of the inner edge of the floats at inlet. ‘““Housing.—The casing in which a fan operates is called the ‘housing.’ It is made of metal, of brick, or of wood. Frequently the fan is so set as to project into its foundation, and in such cases the casing only covers the portion which projects above the founda- tion. ‘The fan is then said to have a three-quarter housing. Of course the inlet must be above the foundation or a free passage must be provided to it. “Free Discharge.—A fan is said to have free discharge when the blast is free or unrestricted. This condition is maintained when the total head is practically equivalent to the velocity head. The total head is equal to the velocity head plus the friction head, and with a free discharge head the friction head is practically zero. “Restricted Discharge.—A fan is said to have a restricted dis- charge when the blast is restricted by ducts or by pressure reservoirs. “Free and Restricted Suction.—Similarly to free and restricted discharge, a fan may have either a free or a restricted suction, whereby the gas has either a free or unrestricted entrance into the fan, or a restricted entrance caused by ducts or a reduction in the pres- sure on the suction side. LECTURE BY MR. H. DE B. PARSONS 43 “Coefficient of Contraction.—The ratio of the area of the vena contracta to the area of the orifice is called the ‘coefficient of con- traction.’ ‘Coefficient of Velocity.—As the stream of gas passes the vena contracta its velocity is somewhat increased, and the ratio of the actual velocity to the theoretical velocity is called the ‘coefficient of velocity.’ In a well-shaped delivery orifice this coefficient of -velocity is not far from unity. “Coefficient of Efflux.—The ‘coefficient of efflux’ is the product of the coefficient of contraction and the coefficient of velocity. “Volume of Discharge.—The volume of gas discharged by a fan is a function of the product of the velocity of the gas times the area of the outlet, times the coefficient of efflux. “Blast Area.—The blast area of a fan is the theoretical area of outlet whose coefficient of efflux is unity. The volume of discharge is equal to the blast area times the velocity of discharge. Therefore, the blast area equals the capacity divided by the velocity due to the velocity head. The stream of gas issuing through an outlet is re- duced in area, depending on the shape and character of the orifice. This reduced area is called the ‘vena contracta’ and is usually at a distance from the opening of about half its diameter. This vena contracta is caused by the change in direction of the flow of the mole- cules of the gas as they pass the opening.”’ Measurement of Draft ‘The measurement of draft, either static or both static and veloc- ity pressures is obtained by noting the difference in level of a liquid in the arms of a tube bent on the form of a U, of which one end is connected with a proper tube to the space in which the draft is to be measured. The liquid is generally water although for heavy pressures mercury is sometimes used. “There are different forms of gages which can be bought in the market but for ordinary work the simplest forms are the best. Some of these instruments are so made that they will give a con- tinuous record, and for certain kinds of work these continuous records are of considerable value. ‘““Anemometers are used for measuring the velocity of the gas. Readings should be taken at many points in the cross-section of the current, and even at the same points consecutive readings will not agree. Multiple readings therefore should be made in order to aver- age up these irregularities. “Fan draft is always expressed in ounces per square inch or in inches of a water column whose weight is equal to the ounces per square inch. The velocity corresponds to this pressure, when the friction head is zero. 44 AIR COMPRESSION AND TRANSMISSION ‘When the pressure exceeds two or three pounds per square inch as is the case with many positive blowers, the pressure is then generally expressed in ‘pounds per square inch.’ Corresponding to Various Heads of Water in Inches TABLE VII.—PRESSURES IN OUNCES PER SQUARE INCH Decimal parts of an inch Head in inches 0.00) 0.8 ome O28 0.4 On5 0.6 OF 0.8 0.9 Osmaioe ae 0.00510, 12] O78 7 0,23 OF 209) Ones alo. 10 sO ntOm Oma I 0.58 |)0703° 190.00 | Oa7s 470 Siw Ous7 IFO..03 4207 O0om tie O4mmimoG 2 EALO WAL Rea bay a Fee eT ee) MAT aTR COM Tec Op) at Ot ee 3 Te73UESFO |) Te BS |ATOL | 1.06) 2.02 1e2. OS 2b TA hee Om meee 4 2SAT VW 2e27 N24 2 I 2048 PO RAT eaAOO NO Oe OO aD. 72 mire ae james 5 2280 1-2.04 11-3500) | 3200) - 297 2elee rio 47 24 mg 20m) ec ns 5 amr ey 6 P3247 13-521 3258 |, 3404 53 FOS <7 6 Woh Olas ee 7a) ns cOe mt ReaD 7 AVOAY 4.10 144.10 4322 WAI 28 CA ea AO ed Calafate ee 89) 4024 4007 A273 104.90 W485 des Ot 4.07 15.03 195 Om es ae 9 5.20) 6:26 | 8.35 | a7 te Ae US lace sd ee se O081 SOO mms age TABLE VIII.—HEIGHT OF WATER COLUMN IN INCHES Corresponding to Various Pressures in Ounces perc Square Inch Eres: Decimal parts of an ounce sure in oz per : ‘ : : ; é .6 : 8 O: rae 0.0 Cut One 0.3 0.4 O25 fe) On ° 9 fe) Sf) OnE 1) O35.) -Ol'5 2 a2 0G LOT IAA OAM Walwo2 Taler sot ate et I £272) (1.00) -2.08:) 92, 00 12. Al) 22800 aan 7 7 Od abet ke 2 3. AON 935631053. 81 }) 3.08 ATS (ASS etn5O eed. OF sd O4 sees mon 3 ST LOW eS Se Gal ee a7 EMS oe 106.1. 6503 1 Gi40 8102571 Oars 4 6.02) IvOON 727") 72 AA FROEN Aeon E00 sO aes terol sO MO wAS 5 8.65]. 8782 |G. 00," 0.17) 02344 0.5218 On00 sO. 004510503) Ione. 6 10.38 | 10. $5 (10.73 [TO-DO MIT O7 UT En20 hin A set COG tis 7 Fer reo 7 12.1} 12,28) @o. 40142 363 12, SON Os Lowel os 2 el oi Ou Toe 8 13.844 TA, 00 | T4479. 014. 260 14a Sa 14s 71 ae Sow 5 Obe LS. Sea Oh 18.871 15 574 hFS) 02) 16-00 i1G220 10 48 nOuOe W 10. 70) 20.00) fy DCECTORE BY MR. H. DE BY PARSONS 45 Fan Efficiency “In the operation of a fan or blower there are certain losses utes must exist, the principal losses being: ‘rt. Fluid friction and eddies caused by the movement of the gases. ‘““9, Leakage of the gases backward through the fan or blower. This is sometimes called the ‘slip.’ “2. Mechanical friction of the moving parts of the apparatus. ‘“‘ Generally speaking, these losses increase with the speed of revolu- tion of the fan and also as the difference in pressure between the suction and discharge sides increases. haiine efficiency of a fan or blower is the ratio of the useful work done on the air divided by the work required to drive the fan. Fans are generally driven by steam engines or by motors, and frequently the denominator of the efficiency ratio includes the work of driving the engine or motor. Such an efficiency is really the combined effi- ciency of the prime mover and fan. “The efficiency of a fan wheel with a housing varies with the ratio of diameter of inlet to diameter of wheel. The smaller this ratio the greater will be the theoretical efficiency so long as the area of outlet times the coefficient of efflux is not less than the blast area. ‘““When a centrifugal fan has to work against high pressures, it is desirable, therefore, that the ratio of inlet to wheel diameter be small in order to get the benefit of this increase in efficiency.”’ Flow of Gas Through an Orifice ‘““Gas flowing through an orifice does not obey the same law as the flow of fluids. The reason of this is that gas expands from the higher pressure to the lower pressure as it issues through the orifice. ‘“‘Tmagine the gas in a reservoir R (Fig. 22) flowing from the short cylindrical orifice of section a. Imagine that the reservoir is kept supplied with gas so that its pressure remains constant. Suppose that the division S represents a pound of gas. ‘““As the gas escapes through the orifice a, the pressure is kept constant, and the work OA EQ has been done upon the gas. The gas in expanding develops the expansive work EIMQ, EI being an adiabatic curve. “The outer pressure P, absorbs the work JVOM, and the balance, AEIN, is devoted to accelerating the particles of the pound of gas to a velocity v. 46 AIR COMPRESSION AND TRANSMISSION “Hence the work AEIJN equals the actual energy of 1 lb. of gas moving with a velocity of v ft. per second or a AEIN =(t lb.) X — 2g Therefore v=/2g (AEIN) ft. per second Taking the law of the curve FI as p101)"=fov2"=constant we have: fi nN pe a AEIN=""_ xX 144 piS ae (2) | 1 Fic. 22.—Flow of gas through an orifice. “Letting m =1.405 the ratio of the specific heats and the exponent in adiabatic changes of air ‘ihe a [28x25 X 144 p:S|1— @) be v= 1794 | P15 E —~ C) oe) ft. per second “Tt is found by taking the pressure at the orifice by a gauge G that if the gas flows into another reservoir kept at the back pressure py» the orifice pressure is identical with 2 if the latter is more than about 0.581. That is, if p1 is r00 lb. per square inch absolute, any value of the back pressure greater than about 58 lb. gives this pressure to the orifice, but if the back pressure is the atmosphere the orifice pressure remains 58 lb. “Tt therefore follows that for ao 58 the velocity given by the 1 above formula exists at some point of the jet beyond the orifice at LECTURE BY MR. H. DE B. PARSONS 47 a section a,> a due to the natural spread of the jet, while the velocity at the orifice or throat of the jet is that given by the formula for Loss of Head Due to Friction in Ducts “The frictional resistance to the movement of a gas in a duct is proportional to the surface of the duct. It is, therefore, directly proportional to length and inversely proportional to diameter. It also varies as the square of the velocity. “Therefore, the ducts should be of ample area, or the power lost in friction will be very great. Small pipes and high velocities should be avoided. “Tt is evident that after a certain size of duct is reached, any further change in size or velocity of movement will only have a rel- atively small effect upon friction loss. The limit, therefore, is reached when the increase in space required and the cost will turn the saving in friction into a loss from a commercial standpoint. “Usual Velocity in Ducts.—In heating and ventilating work for theaters, hospitals, churches and large buildings, the limiting velocities usually selected are: (a) In ducts leading from force fans— In borizontalimaineducts 27 427. 2-1 ,000 It, per minute imshorizontalimatnibranches #42. 72.428... a: 1,300 ft, per minute In horizontal branches to risers............. 650 ft. per minute tie WerticalsTisers eau woe es Sin ison Sa bes Ae 800 ft. per minute (b) In ducts leading to exhaust fans— EWevertical riscrs ea erty or aan Goo 1b per minute Tnehorizonraduets tolans 2 sane tears £000 ttn per minute ‘“The frictional loss in ducts can be calculated from the formule for the movement of fluids. In addition to the friction loss of head caused by the passage of a gas through a straight duct, there is a loss at each bend or change of section. “In order to overcome these friction losses, it is necessary that the pressure at the fan end of the duct should equal the sum of the pressure desired at the open end of the duct, and the pressure necessary to overcome the losses in frictional head. “Tn all the following formule the following notation has been used. Notation of Symbols A denotes the area of the duct in square inches. a denotes the blast area, or the ‘effective area of discharge’ in square inches. 48 AIR COMPRESSION AND TRANSMISSION denotes the diameter of duct in inches. denotes the perimeter of duct in inches. denotes a constant. denotes the diameter of the fan wheel in inches. denotes the density of the gas, 7.e., its weight in pounds DerecuLaLe. E denotes the combined efficiency of fan and its prime mover. e denotes fan efficiency, or ratio of useful work to work of driving fan. g denotes the acceleration due to gravity in feet at the end of one second, 32.16 ft. h_ denotes the equivalent head, 7.e., the height of a column of gas in feet having a density d, Sihaee mene will produce the velocity pressure p ounces per square inch. K denotes the capacity of a fan in cubic feet per minute. 1 denotes the length of duct in feet. nm denotes the number of revolutions per minute of fan wheel. Ie Pp Stef ope. denotes the total pressure against which a fan is working.! denotes the velocity pressure in ounces per square inch (or inch of water) against which a fan is working. t denotes the absolute temperature, or 460°+ F. Q denotes the volume of gas discharged by a fan in cubic feet per second. V_ denotes the peripheral velocity of fan wheel in feet per second. vy denotes the velocity of gases in feet per second due to pressure p. W denotes the width of fan wheel in inches. w denotes the width of blades of fan wheel at periphery in inches. ‘Pipe Losses.—Frictional losses are very hard to calculate, as so much depends on the smoothness of the surface and the material of which the ducts are made. “The loss due to surface friction can be estimated from the formule: “For circular ducts of galvanized iron, carefully made, “For rectangular ducts of galvanized iron, carefully made, ly?C 100,000 A in which p denotes the loss of pressure in ounces per square inch. This is an empirical formula based on Weisbach’s general formula for the flow of fluids. 1 The total pressure against which the fan is working is +s, in which ps is the static pressure. LECTURE BY MR. H. DE B. PARSONS 49 ‘“‘Bends create an additional loss which are hard to estimate. For all practical purposes the frictional loss due to bends can be estimated sufficiently accurately as follows, when the ducts are of galvanized iron, carefully made and of fairly smooth surface: (a) For right-angle bends with the radius at the root of the bend equal to one duct diameter, allow an equivalent length of straight pipe equal to 11.1 times the diameter Of the. duct.. [hus in Pig2923, 11 B =20-1n., allow for the bend 11.1 X20 0r 222 in. or roft. of N pipe: : (b) For right-angle bends with a radius at the root of the bend equal to one- half the duct diameter, allow an equivalent length of straight duct equal to 29.5 times the diameter of the duct. (c) For 45-degree bends allow one-third of the loss for right- angle bends.” Fic. 23.—Right angle bend resistance. Rotary Blowing Machines ‘“‘A rotary blower is a positive pressure blower or exhauster, and is not a fan, although it is used for similar purposes. It is positive in its action and it operates by displacement. ‘A rotary blower costs more than a fan of equal capacity, but it is more economical than a fan when operating against high pressures, that is 8 oz. per square inch or more. Turbine blowers, however, are now being built giving efficiencies fully equal to that of rotary blowers. (See Chapter XI). ‘A rotary blower is more economical than a compressor when operating against pressures less than 7 lb. per square inch. Gener ally speaking, the compressor is more economical at pressures In ex- cess of 7 lb. bn Lie ‘‘Rotary blowers can be arranged to give constant pressures or constant volumes. They can also handle liquids as well as gases. ‘““A rotary blower (Fig. 24) consists of a casing in which two impellers revolve in. opposite directions. Each impeller is of a double-lobe section symmetrical with its shaft. The impellers are set so that the lobe of one impeller fits into the recess of the other. The impellers do not touch each other, nor do they touch'the casing, 4 50 AIR COMPRESSION AND TRANSMISSION although they should work as close as is possible without touching so as to prevent loss through leakage. ‘The air is drawn in through the inlet, is caught between the lobe of an impeller and the casing and forced around as the impeller revolves, and discharged through an opening situated in the casing diametrically opposite to the inlet. In order to keep the impellers at their proper relative speeds, one shaft is driven by the other shaft through a pair of gears. + aa e+ CEPUCH DG a rn Tere I I< - Pitch Diameter. >| ¢--~-- pitch Dia, -—---—-9| Fic. 24.—Cross-section through standard blower. “The pitch diameter of these gears controls the size and capacity of the machine. The radius of an impeller, or its half length, is made three-quarters of the pitch diameter of the gears. The casing consists of two semi-cylinders separated by a parallel section. The radius of the cylinders is equal to that of the impellers plus clearance. The width of the parallel section is equal to the pitch diameter of the gears plus the clearance. The speed of revolution is regulated by the safe speed at which the gears can be operated. ‘“‘Blower Pressures and Capacities.—The limit of the gas pressure, in commercial sizes, is about 12 lb. per square inch. The standard commercial sizes have capacities varying from one-quarter of a cubic foot to 400 cu. ft. per revolution. | “Two of the types of rotary blowers in use, are described by the shapes of the ends of the impellers, as cycloidal or involute. When the impeller ends are cycloidal they fit close to each other and leave no waste spaces or pockets. Such machines are adapted to handle wet gases and liquids as well as dry gases. When the impellers are cycloidal, the capacity per each revolution is equal to LBC LU REeDYe Vik He DEO APARKSON S ol the area of the pitch circle of the gears times the length of the cylinder. ‘When the impellers are involute, the capacity is somewhat greater than the cycloidal and depends on the diameter of the generating circle for the involute. This diameter is variable to suit the duty of the blower. “The slip is largest in small machines, and least in large ones. Thus for machines displacing three-quarters of a cubic foot per revo- lution at 1-lb. pressure the slip is about 60 to 70 revolutions, 7.e., the machine has to make that number of revolutions to hold the pressure against leakage. For machines displacing 300 cu. ft. per revolution at 1-lb. pressure, the slip is from 3 to 5 revolutions. The slip for intermediate sizes is about proportional and for pressures other than 1 lb. the slip will vary closely as the square root of the pressures. “For cycloidal types, the casing is 1 1/2-pitch diameters high by 2 1/2-pitch diameters wide. For involute types, the casing section is nearly the same, but depends on the circle on which the involute is rolled, and this depends on the duty for which the machine is designed. “The efficiency is variable, and for the larger sizes is between 80 and 86 per cent. falling off gradually as the pressures exceed 3 lb. per square inch. For smaller sizes the efficiency is less. ‘‘Power for Rotary Blowers.—The horse-power required at the shaft or pulley to drive a rotary positive blower is proportional to the volume and pressure of the air discharged. It is safe to assume that for each 1,000 cu. ft. of free air discharged per minute at 1-lb. pressure, 5 h.p. is required. The following formule are sometimes used in calculating the horse-power. The first two formule give the theoretical horse-power required; and in order to determine the horse-power necessary to drive the rotary positive blower it is necessary to divide the results obtained by the efficiency of the ma- chine. The usual efficiency is between 80 and go per cent. er ee | 11,000 (Cr) a, “This formula is used when it may be assumed that the air is compressed so quickly that it does not have time to cool to atmos- pheric temperature, as in nearly all blower work. Oa = bs) 33,000 (2) hp. = 52 AIR COMPRESSION AND TRANSMISSION “This formula is the ordinary “hydraulic formula” and is ordi- narily used for pressures up to 5 oz. lb. per Sa. ins x GQ) hpi v 200 “This formula is frequently used by makers of positive or rotary blowers for determining the horse-power required to operate the machine. In this formula Q represents the volume of air in cubic feet per minute displaced by the impellers, no allowance being made for slippage. In the above formule P, represents the pressure of = < ‘5 0.06 = Horse Power Curves. 3 Machines of 1500 cv. ff. per ra min. capacity operating the 20: samme tubes in the New York SS Postal Service, March 1909. +) c0) 5. Ee 0. Le} oO AZ, ce) © 0. qui Horse Power Re afr Sees in ee Saves per square [heh Fic. 25.—Power consumed by rotary and piston compressor. the atmosphere or the suction pressure absolute in pounds per square foot and P the compression or discharge pressure in the same units. (See Fig..25.)” Mechanics of the Fan “The laws that govern the flow of gases are the same as those for the movement of liquids. If p, the pressure in ounces per square inch, is divided by 16 and this result multiplied by 144, the pres- sure will be expressed in pounds per square foot. This may also be done by multiplying d or the weight in pounds of one cubic foot of the gas by its height or head /# expressed in feet. That is: Ate = _ 9? and as the fundamental formula for velocity is v?= gh. v=V2 gh= 4/18 9 PEGCOURPepyeV RSA DEI BYPARSONS 53 “When # is given in inches of water: 62.4 p=hd; na SP I2 V=4/10.4 gt “The theoretical velocity obtained by using this last formula is greater than the actual velocity produced by the fan, because friction and eddies will restrict the freedom of flow. The formula, however, shows that the flow of gases through an orifice increases as the square root of the pressure and inversely as the square root of the density. “The head is made up of two parts—that necessary to overcome the friction and eddy losses and that necessary to produce the veloc- ity obtained. ‘““The pressure produced by afan may be considered as equal to the weight of a column of gas one square foot in area which the fan is supporting. This weight is equal to the height of the column times the density of the gas. The “equivalent head’ is the height of this column of gas. Therefore, for any given pressure, the greater the head the less will be the density, and vice versa. Also, the greater the head required to produce a given pressure the greater will be the velocity. ‘““As liquids have greater densities than gases, their equivalent heads for equal pressures will be less than the equivalent heads for gases. As velocities vary as the square roots of the head, the veloc- ity of gases will be greater than those of liquids under the same conditions of pressure. That is the reason why gases issue through orifices at greater velocity than liquids under the same pressure conditions. ‘“‘As gases are compressible, their density will vary with the pres- sure. Their density also varies with the temperature and with the humidity contained. Since the velocity varies as the square root of the head, and as the head varies inversely as the density, any in- crease in density due to increase in pressure will reduce the head and consequently the velocity. “Conversely any increase in temperature reduces the density and consequently increases the head and also the velocity. The velocity is entirely dependent upon the head. Therefore, in mak- ing calculations for fan operations the effect of both temperature and density must be considered. For fan operation the standards generally adopted are: for temperature 60° F. and for density the weight of a cubic foot in pounds at atmospheric pressure or 14.7 lb. Therefore 54 AIR COMPRESSION AND TRANSMISSION per square inch absolute. When the density of the gas is given for any pressure and temperature its density at any other pressure or temperature can be found with sufficient accuracy for all ordinary fan operations, by assuming that the density will vary inversely as the absolute temperatures, and directly as the absolute pressures. ‘Thus d) = Z by “Tf a cubic foot of dry air weighs 0.077884 Ib. at 50° F. its weight uy (50-++460) X0.077884 at 600° would be dy Ie es = 0.03751 lb. ‘Also, as the density varies directly as the absolute pressure jab Pp “The pressure per square inch at atmospheric pressure is 14.7 lb. absolute or 235 0z. Therefore, the density at 3 oz. gauge pressure would be: _ (235+3) X0.077884 dy 235 =0.0788 “The head can be expressed for 50° F. when # is given in ounces per square inch thus: jp TAA ANP KP ROSS ee MPs 6XdK 23ST IX(235+P) (235d-+dp) 235 | ‘“When # is expressed in inches of water as 62.4 vie 5-2 PK 400; a ae Ss eee ene PSEA) SE 400.7 “Since 62.4 lb. the weight of a cubic foot of water at 50° F. divided by 12 is the weight of a column of water 12 in. square and 1 in. high, and since the pressure at one atmosphere (14.7) would sustain a column of water 33.9 ft. or 406.7 in. high; “Substituting these values in the formula for velocity and ex- pressing p as the velocity pressure in ounces per square inch 04 |26X ALLS Pi. HOA 32K 21 US pee [136036.8p 235d+dp (235+p)d (235+p)d EECTURE BY MR. H. DE B. PARSONS 55 When # is expressed in inches of water 0=4)28X 2115p = (RE CEO | ee | 406.7d+dp N (406.7+p)d (406.7-+p)d For dry air at 50° F. d=0.077884. “These two formule are those used to calculate tables giving the theoretical velocities expected at different pressures. If the gas is not dry, but contains some vapor or moisture, its density will vary es Fahrenheit ie a Pe ee Fala a a Temperature of Air, Degre 0 10 foe 30 40 50 60 70 80 Vapor Content, Grains per Cu. Ft. (7000 Grains = | Pound) Fic. 26.—Humidity of air. by the quantity of mcisture which it contains, Fig. 26. (See Appen- dix C and chart.) “Tf the gas is at any other temperature than so” F. its density will decrease as the temperature rises, and conversely will increase as the temperature falls. As the temperature varies so will the veloc- ity. As the gas becomes lighter from increases of temperature, the velocity will increase as the square root of the ratio of the abso- lute temperature considered to the absolute temperature of 50° F. The converse is also true, as the gas becomes heavier from decreases of temperature, the velocity will decrease in the same ratio.” Effect of Outlet on Capacity ‘The shape of the opening through which the gas is discharged from a fan affects the volume discharged in a given time. The 56 AIR COMPRESSION AND TRANSMISSION shape of the orifice and the form of the duct affect the size of the vena contracta and therefore the blast area of the fan and the volume of the gas discharged. ‘““As stated, the volume of discharge is a function of the product of the blast area times the velocity and the blast area is determined by multiplying the area of the orifice by the coefficient of efflux. The coefficients of efflux commonly used in practice for different types of orifices are: Orifice-in-a ‘thin plates... sn nraein ee a ee SSO Short cylindrcalspipessies cane eee eee ee eee ee O75 Rounded ot-conicalmouth pieccss seat t eee 0.98 Conical pipe, angle of convergence about 6 degrees..... 0.92 ‘With peripheral discharge fans, when the area of the outlet of a fan multiplied by the proper coefficient of discharge is less than the blast area of the fan, the pressure in the housing will equal that corresponding to the velocity of the tips of the blades, and the vol- ume of discharge will be less than the capacity of the fan. ‘When the area of the outlet multiplied by its coefficient of dis- charge is greater than the blast area, the volume of discharge will be greater than the capacity of the fan, and the velocity of the gas as it enters the inlet must be greater than the speed of the inner edges of the blades. Consequently, the pressure in the housing will be less than that corresponding to the speed of the tips of the blades.” Work Required to Move a Volume of Gas ‘A fan operating against 1 oz. of pressure per square inch and dis- charging the gas through an orifice having too sq. in. performs work which may be calculated in the following manner: “The total pressure against the fan is 100 sq. in. times the coeff- cient of efflux (say 0.75) times 1 0z., or 75 oz. or 4.7 lb. ‘“‘ Assuming that the gas is air, then from the formula for velocity of dry air at 50° F. the air will have a theoretical discharge velocity through the blast area of 5,162 ft. per minute. ‘The effective work is, therefore, 5,162 4.7 or 24,250 ft.-lb. per minute or 0.735 h.p. The actual work of driving the fan is greater than this result by the amount of power required to over- come the mechanical resistance and losses in the fan. This resist- ance is made up of the losses due to friction, windage and leakage. If these losses aggregate as much as the network then the power to drive the fan would be twice the network, 7.e., the efficiency of the fan as a machine would be 50 per cent. The actual power required to drive the fan would be Be 1.47 hip, EEUGLUKE BY VMK.Hs DEB, PARSONS 57 “Placing the above in form of formule and taking f in ounces per square inch, Useful work =Py=—2 Hits 0S Fel See, Since jee 16 p _ dv De 18g From previous formula v?= 18 g adv Therefore useful work =—.— ft. lbs. per sec. 2882 ‘““When # is given in inches of water Useful work =Py= 52” {t. lbs. per sec. 144 Since pete cee ued 144°* 12 144 p dv? From orevious formula v2 =10.4 ¢*, or p= : 4§ @ p 10.42 5.2adv° ~—_—adv® I44X10.4g 288¢ Therefore useful work = ft. lbs. per sec. “In these formule, av is proportional to the volume of gas dis- charged by the fan. Since a is in square inches, the volume of cubic feet per second will be | av aaerr “Representing the efficiency by E the work to drive the fan may be fag eee es ah expressed as 238g Pols. Del sec, ‘From these formule it will be seen that the power varies as the cube of the gas velocity, while the pressure varies as the square of the velocity and the volume directly as the velocity. ‘From a consideration of these factors it is evident that fans are more economical when used to move large volumes of gas at low pressure than small volumes at high pressure. For this reason fans are not economical machines for compressing gases. In addition to the above, fans always have a clearance space between the revolving wheel and its housing, through which space the gases have a tendency when under pressure to leak backward, which tendency we have seen increases as the square root of the pressure. Fans are seldom used for pressures exceeding about ro oz., when higher pres- sures are desired the positive blowers are more efficient and are used 58 AIR COMPRESSION AND TRANSMISSION for pressures as high as 8 lb. When still higher pressures are desired, compressors or blowing engines, such as described later should fa used. “Tn the formula above the value of v is that due to velocity head. When the dynamic head is known, that is the velocity head plus the friction or static head, a simple formula for brake horse-power to drive the fan is: ‘““When ? is given in ounces per square inch ee brake h.p.= Bese “When # is given in inches of water OX5.2 p brake h.p.= ssoKE Design of Fans “Tt must be evident that unless a fan is properly designed for the work which it has to perform, there wil! be considerable loss in power required to drive it. “The peripheral speed of a fan must be such as to create the - desired pressure. The pressure against which the fan has to oper- ate is first determined, and having settled on the pressure the peripheral speed is made to conform with it. ‘Furthermore, if the fan be direct connected either to an engine or to a motor, dhe speed of the fan will have to conform to that of the prime mover. “The work formule given above are all based on the blast area of the fan. The way in which these formule will apply to the differ- ent types of fans will be made clearer under ‘ Description of Fans.’ ‘‘For any size of centrifugal fan there exists a certain maximum area over which a given pressure may be maintained, depending upon and proportional to the speed at which the fan is operated. If this area, sometimes called the ‘capacity area,’ ‘blast area’ or ‘effective area of discharge’ be increased, the pressure is lower while’ _ the volume is increased. Contrariwise, if this area be decreased, the pressure remains constant while the volume is increased. In practice the outlet of a fan rarely exceeds the ‘blast area.’’’ - Description of Fans ‘A disc, radial or propeller wheel fan consists of a machine having blades so mounted on an axle or shaft that when the shaft revolves these blades operate like a screw, and the gas is impelled ee in the direction of the axis. ‘The blades may be straight and flat or curved. The blades may be curved in different ways so as to increase the screw effect and LECTURE BY MK. Ae DE B..PAKSONS 59 diminish the centrifugal effect. Disc fans with curved blades will operate against slightly higher pressures and deliver more gas than those with straight blades. ‘“‘As the gas enters the fan it will be forced forward with some centrifugal effect; and this centrifugal effect can be somewhat reduced by having the blades revolve inside of a tube so as to pre- vent the gas from escaping over the outer edges of the blades. ‘“‘Disc fans will not operate economically against a pressure, as the pressure will increase the slip and the leakage of the air from the blades at the tip. If the pressure is at all high the gas will be drawn backward near the axis and will be blown forward near the outer tips of the blades, or in other words, the fan disc will simply circulate the air without making any delivery. ‘Disc fans operate best when drawing gas from a practically free suction and discharging it at no pressure. When these fans are set up care must be taken that they do not operate against the wind, as the wind pressure will vitiate the operation of delivery. “The number of blades appear to have a small effect upon the discharge, provided, of course, that the number is neither too large nor too small. Too many blades will simply churn the air and produce the effect of cavitation. Too few blades will not give a sufficient grip on the air to force it forward with the proper delivery. ‘The gas delivered by a disc fan is very irregular in velocity. If anemometer readings are taken at different points in front of the disc, the recorded velocities will be found to vary without apparent reason, and the variation will not remain constant. It is, therefore, very hard to determine the mean velocity of discharge of the gas. “The number of revolutions is limited by the strength of the fan and by the fact that a high velocity will cause the fan to hum and be noisy. The revolutions are usually limited so that the velocity at the tips of the blades shall not exceed 8,500 ft. per minute. (For noiseless operation, 4,000. Usual maximum 7,000). On this as- sumption, if D denotes the diameter of a fan in inches and nm denotes the number of revolutions per minute. zDn es see sures and Dn=32,000 (nearly). “This last equation may be used to determine the limiting revo- lutions or diameter by assuming one or the other. “The volume of gases discharged by a disc fan with a free suction and discharge can be estimated from the formula: D? : =1/4 2—v in which v=0.20V Q=1/4 a 39 60 AIR COMPRESSION AND TRANSMISSION “The brake horse-power for the fan with the above value of Q can be estimated from the formula: _OXxdXv3/? ( 13.5 is a constant RLS OED 550X 28 ‘S \found from experience ‘When a disc fan operates against a pressure, 7.e., not with a free suction and discharge the above formule must be changed as Q becomes less because the slip becomes greater. 2 ‘‘ Approximately 0 = 1/47 (=) vy in which v! equals 1.25v less 45 per cent. of the theoretical velocity due to the pressure against which the fan is working. “The brake horse-power will be the same as if the fan were work- ing without restriction, although the volume of discharge Q will be less. “Example: Free suction and discharge. Fan wheel 48 in. in diameter running at 450 revolutions per minute. Find Q and brake horse-power. Dry air at 50° F. a Se ee ee V=0.39X3.14X— Xoo 36.8 8 2, Q=1/4X3.14Xx (E) X36.8=462 462 X0.077884 X 36.83/2 X 13-5 550 X 64.32 Brake horse-power = 3:07 ‘‘Also restricted discharge. Find Q and brake horse-power for the same fan and conditions when operating at 5/8 in. of water pressure. “The velocity due to 5/8-in. water pressure is 51.8 ft. per second. vi=1,.25 X36.8—0.45 X51.8= 22.8 Q\ 2 Q=1/4X3.14X (~) X22 9 = 250 “The brake horse-power would be 3.07 because it is approximately the same as if the fan were working unrestricted. It is found by substituting the unrestricted value of Q instead of the actual re- stricted value. “Centrifugal Fans.—Centrifugal fans operate on the principle of the vortex. They suck the gas in and discharge it off the periphery of the wheel by centrifugal action. ‘Fan Blast or Steel Plate Machine.—The fan wheel consists of an axle or shaft on which are mounted radial arms carrying floats or blades. Each blade is narrower across the tip than it is across the LECTURE BY MR. H. DE B. PARSONS 61 body. The blades are mounted inside of side plates, so that the gas is confined in the spaces between the blades, which thus form passages from the suction to the discharge side of the fan. Thése side plates also prevent the loss of friction between the revolving air and the sides of the housing. ‘“‘Sometimes the blades are curved backward at the tips so as to make the fan run more quietly, and sometimes the blades are curved backward for their whole depth so that the gas may enter the wheel and pass through it without shock. ‘““When fan wheels have flat blades, they can be run equally well in either direction, but when the blades are curved, the wheels should revolve with the convex sides of the blades in advance. ‘““When these fans are used for blowers, there is usually an inlet on both sides of the housing; and when used as exhausters, usually an inlet on one side only, as it facilitates the connection with the suction duct. w+ 04D es 4 ‘ ‘ J “The diameter of inlet is gener- wid ae 9 _ 1 ally 0.6 or 0.7 of the diameter of 4-4 /east ia, but beection Ahad heal actually from ' of Fan e Ian wheel. 2a to $a. : Wheel “For high efficiency the area of Lv inlet should not exceed 4o per cent. Ol athe dise, areayo! they wheel. The full width of the blades is generally made either one-half or three-eights of the diameter of the “wheel. The blades are generally cut off at the upper outer corners so as to taper at the tips at an angle of about 20 degrees with the side edges, but their width at the periphery should be not less than 0.6 to 0.7 of the width at the root, 7.e., not less than their maximum width times the same ratio as was chosen with the ratio of inlet to wheel diameter. Usually w=o0.4 D and w=o.5 D (see Fig. 27). | ‘The width of the fan is made such as to provide the proper area for the flow of the gases through it so as to discharge the required volume. If the diameter of the fan wheel is made too small, it may not be possible to give the wheel sufficient width to permit the necessary discharge of volume, unless the fan is run at a very high rate of speed. This increased speed will result in raising the pres- sure above that required, and will, therefore, increase the power Fic. 27.—Steel plate fans. 62 AIR COMPRESSION AND TRANSMISSION necessary to drive the fan. Contrariwise, if the wheel be given a large diameter it may have to be made so narrow, in order to dis- charge the required volume, as to become impracticable. It will, therefore, be seen that under any given conditions there will prob- ably be one diameter and width which will be best suited for the work. “The blades of this type of fan are given sufficient depth so as to project inside of the circle of the inlet in order that they may better grip the incoming gas and force it through the wheel. ‘With a peripheral discharge fan enclosed in a housing, the limit of its capacity to maintain a given pressure is measured by its blast area. In other words the velocity of discharge will be approxi- mately equal to the peripheral speed of the fan, and the volume will be measured by this velocity times the blast area. ‘“‘Tf the blast area be increased the pressure will be less, and if the blast area be decreased the pressure will remain the same. For a peripheral discharge fan with a housing the blast area can be cal- culated as follows: Let D denote diameter of fan wheel in inches; w denote width of fan wheel at periphery in inches; c denote a constant, depending upon the design of the fan and its housing, but which has a value not far from 2 1/2 to ? a denote the blast area in square inches. D D Blastrarea—o — es = = g(nearly) “Tf the shape of the discharge orifice and duct be known, and the coefficient of contraction determined, the area of the discharge orifice would be the blast area, as determined from the above formula multiplied by the reciprocal of the coefficient of contraction. “The usual maximum peripheral velocity for standard fans is 6,600 (for noiseless operation about 4,200) ft. per minute, but should not exceed 8,000 ft. per minute. This latter figure limits the pres- sure to 1 3/4 oz. per square inch but special fans may be designed to maintain a pressure as high as about 12 oz. “The volume past the blast area is about 86 per cent. of the peripheral speed. In other words, the peripheral speed must be 1.16 times the velocity due to the pressure of V =1.16 2. V wheel circumference Therefore n “The efficiencies without prime movers vary from 45 to 50 per cent. for commercial sizes when using dynamic head, or from 30 to 35 EPEGCLOREOBY MRA Ho DE B- PARSONS 63 per cent. when using velocity lead. The outlet is generally made square, and its area is usually about two and one-half times the blast area, or A =2 1/2 a, but never less than 1 1/2 a. - “This proportioning will make the bottom of the outlet below the - periphery of the wheel. The efficiency of commercial sizes is about 45 to 50 per cent. without a prime mover. If the prime mover efficiency is taken at 85 to 90 per cent. then the total efficiency of the fan and prime mover would be between 38 and 45 per cent. Example: ‘“‘Given the quantity of air per minute, 65,000 cu. ft., the temper- ature of dry air 70° F. and the pressure 1 3/4 in. of water. Deter- mine the diameter of fan, revolutions and brake horse-power. Under these conditions the density of the gas or its weight per cubic foot may be taken as 0.0754 lbs. a] 136036.8 X1.75 e v= = 88.0 (406.7-+1.75) X0.0754 65000 «X88.0 _ 65000X144 _ eee: Therefore a= 60% 88.0 =1,770 Making w=0.4D dak 1 7O= 91 D*=11,500,, D=107 ez", 10 6 00.0 == 102 Wheel circumference x14 = 27.0 it. ESE 27-9 With E as 45 per cent. the power to drive the fan is Therefore nN 220 1770 X0.0754 X 88 By 550X288 X 32.16 X0.45 “‘Ffousing.—The housing is placed around the wheel in an eccen- tric position and has a form approaching the spiral. This arrange- ment facilitates the gas delivery from the wheel. The openings for discharge of the gas are tangential to the wheel. There may be one or more openings as circumstances demand but their combined area of discharge should not exceed the fan capacity. It makes no difference whether these discharge outlets are placed horizontally or vertically. “The arrangement of discharge outlet, however, gives a name to the fan—as a horizontal top discharge, a vertical discharge, a hori- Brake horse-power 64 AIR COMPRESSION AND TRANSMISSION SS SS S wf ——— SS Ss SSS Ss =" = SSeS See Se SSeS sss Ss Sse SS == 35553 [22SS = = SSS ee Fic. 28.—Full housed steel plate Fic. 29.—Full housed steel plate fan. fan. Left-hand bottom horizontal Right-hand top horizontal discharge. discharge. Fic. 30.—Three-quarter housed steel Fic. 31.—Three-quarter housed plate fan. Right-hand bottom horizon- steel plate fan. Left-hand top tal discharge. horizontal discharge. LECTURE BY MR. H. DE B. PARSONS 65 zontal bottom discharge, a double discharge, etc. (Figs. 28, 29, 30, 2randes 2.) “The spiral or scroll form of the casing should be such as to let the gas escape with freedom from all parts of the periphery. The smaller diameter of the scroll should not be less than Di and the re ence D denotes the diameter of the wheel in inches; a denotes the blast area in square inches; W denotes the maximum width of blades in inches. larger diameter not less than D+ de fae O oy” A! qu Fic. 32.—Allis Chalmers steel ventilating fan. ‘Cone Wheel Fans.—The cone wheel fan is a single inlet pe- ripheral discharge fan. It is used both with and without a housing. Cone wheel fans are not efficient for use against pressures in excess of 1 oz. per square inch and are seldom used against pressures as high as this limit. Generally speaking, they are not as economical in the handling of gases as centrifugal fan-blast machinery properly encased in a well-designed close-fitting housing. ‘““Cone wheels should have a perfectly free inlet and be arranged to have a free discharge of air from all points of the periphery. When cone wheels are encased in a housing the housing is usually much larger than the fan wheel to permit a perfectly free and un- restricted discharge. As ordinarily arranged, the inlet to a cone wheel is a hole in a wall of the apartment from which the gas is to be sucked-(Figs. 33 and 34). “On the axle or shaft of the fan there is mounted a cone with its apex turned toward the inlet. Between the cone and the periphery of the wheel there are blades or floats, and these blades are encased 5 66 AIR COMPRESSION AND TRANSMISSION inside of side plates. As the air enters the inlet it is deflected by the cone to the floats, which together with the side plates, continue to change the direction of the air so that it is discharged off the pe- riphery in a plane at right angles to the shaft or line of entrance. The width of cone wheels is generally one-quarter the diameter of the wheel, and the inlet opening is generally three-quarters of the diameter of the wheel. The floats are curved backward and tapered WE Fic. 46.—Cylinder efficiency. compress isothermally a volume of air at atmospheric pressure equal to the intake piston displacement divided by the actual work done in the air cylinder. This would be Fig. 46, the area AKCG divided by the shaded area, or the actual work done in the air cylinder. Efficiency of Compression.—The efficiency of compression may be defined as the product of the cylinder efficiency and the true volumet- ric efficiency, or it is the work done in a complete cycle to compress isothermally, without clearance, a given volume of free air divided by the work actually expended in compressing the same volume of free air. EFFICIENCIES AND ENERGY COMPENSATION 81 Mechanical Efficiency.—The mechanical efficiency of an air com- pressor is the work done in the air cylinders divided by the work done in the steam cylinders, if driven direct by steam, or in the gas-engine cylinders, if gas engines are used, or the work delivered at the belt if the compressor is belt driven. Net Efficiency.—The net efficiency of a compressor unit driven by a steam engine or turbine direct is the ratio of the internal energy available in the compressed air at room temperature to the heat energy available in the steam supplied; or it is the energy available by adiabatic expansion of the compressed air at room temperature to atmospheric pressure divided by the energy available in the steam supplied, if expanded adiabatically in a Rankine cycle. In considering efficiencies of air compressors, it is important to distinguish between a machine used for compressing air as a means of storing and transmitting mechanical energy, in which the ideal compression is isothermal, and a machine used for supplying air under pressure for purposes of combustion, as in forges, cupolas and blast furnaces. In these last cases the pressures are comparatively low and the resulting increase of temperature due to adiabatic com- pression is not objectionable. In fact there is ample justification for taking, in these cases, adiabatic compression as the standard. Blower Efficiency.—Henry F. Schmidt in an article in the Journal A. S. M. E. of Nov., 1912, on “‘Centrifugal Blowers” indicates a “blower efficiency’? for any blower not water-jacketed, by dividing the rise of temperature, as calculated from adiabatic compression from the suction to the discharge pressure, by the actual rise of temperature taking place during the compression in the blower. The losses in a blower are principally friction, eddies and leakage. All energy losses reappear as heat and bring the temperature after compression higher than that due to adiabatic compression, and in the article the author proves that this ratio will reduce to the form 11—T2. ; ae ; ToT, in which Tis the initial temperature of the air, 71’ its actual final temperature, and 7, the final temperature if the compression had been adiabatic. This formula is open to the criticism that the radiation is disregarded, but as its value is comparatively small the ‘blower efficiency” expression has the decided advantage of sim- plicity and ease of determination. Economic Efficiency.—Franz zur Nedden in his articles on Turbo- blowers and Compressors in the Engineering Magazine for Nov., 1912, states that the thermic losses of a compressed gas may be 6 82 AIR COMPRESSION AND TRANSMISSION expressed by the contraction which it undergoes in cooling. In place of the larger volume of power medium which leaves the com- pressor, a diminished volume only at the same pressure reaches the destination. As in perfect gases contraction due to cooling is in direct proportion to the absolute temperature, the fraction formed by taking the absolute temperature of the atmosphere as the numera- tor and the absolute temperature of the air or gas leaving the compressor as the denominator, might be taken as a fair expression of the losses caused by the unutilized heating of the gas or air in the compressor. As this loss would not occur if the gases were compressed isother- mally it is debited entirely to the compressor. He cites in illustra- tion a compressor of the piston type of 140,000 cu. ft. per hour capacity working against 115 lb. per square inch at go r.p.m., in which the temperature leaving the compressor was 197° F. and the temperature of the atmosphere 41° F., this gives an ‘‘economic f 460+41 __ 501 400197 657 Energy Compensation.—If an air compressor is driven direct by a steam engine with the steam and air cylinders tandem and one efficiency”’ o = 76.1 per cent. V (LLL LLL] VE LLIILZLIL LLL) y | y Z == Z BL Ae y ey (= Steam ‘Air Fic. 47.—Direct acting steam compressor. common piston-rod as shown in Fig. 47, with the valves arranged to give a steam and air card as shown, the greatest force is exerted on the piston-rod at the time when the least is required in the air cylin- der and when the air cylinder needs the greatest force applied to expel the compressed air, the least is being applied in the steam cylinder. Many ingenious contrivances have been devised for storing the excess energy developed in the steam cylinder during the beginning of the stroke and drawing on this excess during the last part of the stroke. EFFICIENCIES AND ENERGY COMPENSATION _ .88 When a fly-wheel is used it must of necessity be very large in order to do this, as the amount of energy that can be stored in the fly- wheel will depend upon its weight and speed. Hydraulic Compensator.—One form of energy compensator is shown in Fig. 48, which represents a sketch of a D’Auria non- rotative air compressor. The desired result is obtained by using a ‘“‘ hydraulic compensator,” which consists of a cylinder A fitted with a plunger B carried by the same piston-rod that connects the steam and air piston. The ends of the compensator cylinder communicate with each other by Seomcesas A Comm nant Y au, é H gf D SESE Fic. 48.—D’Auria System of energy compensation. means of a loop of pipe c-c—c so constructed as to form a very rigid bed-plate for the machine, a very desirable feature, as it helps to keep the machine in alignment. The cylinder and pipe are filled with water, or any other liquid, leakage being made up through a pipe. When the compensator is in action, the liquid column contained in the compensator is moved reciprocally and as it requires energy to start a mass moving and also to stop it after it gets in motion, the excess energy of the steam cylinder is used up or rather stored in starting the liquid in motion during the first part of the stroke, and this excess energy is given back during the last part of the stroke as the pistons near the end of their stroke. Lever Compensation.—Sometimes two steam air compressors are placed side by side and the piston-rods connected by a system of levers as shown in Fig. 49, so that the excess energy that is not needed in one air cylinder is conveyed by the system of levers to the other air compressor and aids that near the end of its stroke. By this ~ arrangement one compressor supplements the other. Weight Compensation.—A method adopted by the Norwalk Iron Works is best shown in their two-stage compressor, driven by a tandem compound steam engine, as shown in Fig. 50. 84 AIR COMPRESSION AND TRANSMISSION By arranging air and steam cylinders, as shown, with a common piston-rod, an excessively heavy moving piece is secured, which requires considerable energy to start in motion and also to bring to rest near the end of the stroke. That is, a large share of the energy Gx ZZ i ae SAAS Fic. 49.—Lever system of energy compensation. developed in the steam cylinder during the beginning of the stroke is used in starting this heavy piece in motion and the extra energy required in the air cylinders during the last part of the stroke is taken from this moving mass in bringing it to rest. gure “ur by SSS OSS has yp Ee 2 el ae} Ne ve S =a fe Ml S| ae = as E er “ Pipl ie : SS Life i= = = == 9_ ira ey | a aes Fic. 50.—Norwalk compressor. Straight-line Compressor.—The balance is aided still further by a fly-wheel which with shaft and eccentrics is used to operate the valves. It is evident that an air compressor which has the steam cylinder and the air cylinder on the same piston-rod will apply the power in the most direct manner and will involve the simplest mechanism in construction. This type of compressor (Fig. 51) is usually referred to as a straight-line air compressor and is usually equipped with one or EFFICIENCIES AND ENERGY COMPENSATION 85 two fly-wheels to act as energy compensators. Even then it is difficult to secure a very good economy, especially with light fly- wheels. In order to secure maximum economy of steam an early cut-off is desirable, but if no fly-wheels are used this cannot be obtained, and it is necessary to admit boiler steam for almost the entire stroke. The air compressor used by the Westinghouse Air Brake Company in their familiar system of train brakes is of this type. It is admira- bly suited for this purpose because of its simplicity and the fact Fic. 51.—Straight-line air compressor. that it does the most work when the engine is at rest or using only a portion of its steam, and for this reason it utilizes steam that might otherwise escape out of the safety valve. Many efforts have been made to equalize the steam power and air resistance by using a crank shaft and placing the crank pins of the steam and air-connecting rods at an angle with each other so that the greatest force would be exerted in the steam cylinder at the time the greatest resistance was being encountered in the air cylinder. The same thing may also be accomplished by placing the cylinders at an angle with each other. Various compressors have been built on this principle, the angle between the cylinders varying in different designs, being in some 45 degrees, in others go degrees, and in still others 135 degrees. The best results, how- ever, have been secured with an angle of go degrees. This arrangement has been adopted by some manufacturers of compressors for refrigerating plants, but has not been used by manufacturers of air compressors to any extent. Fig. 52 may make 86 AIR COMPRESSION AND TRANSMISSION this clearer, with the horizontal cylinder for steam and the vertical one for the ammonia compressor. When the steam piston is at dead center the air piston has completed about half its stroke, and the high steam pressure admitted to the steam cylinder during the first part of the stroke will be available for moving the compressor piston through the last half of its stroke when the greatest resistance is encountered. As the steam piston is completing the last half of its stroke, the compressor piston starts down compressing a new supply of free air on its lower side if of the double acting type, and as the work of the first half of the stroke of the air piston is com- CHEAT TEC EOL CUCE CAE COLEEOEEGy Fic. 52.—Horizontal-vertical arrangement of cylinders. paratively slight, the pressure in the steam cylinder can be reduced for the last half of its stroke, giving both economy of steam and uniformity of speed. Duplex Compressor.— More frequently this result is accomplished by placing the two cylinders in a horizontal plane with the crank pins at an angle of 90 degrees as shown by Fig. 53. This arrange- ment is frequently adopted when air compressors are driven by gas engines and if an air compressor is driven by a belt the compressor will operate much more evenly and hence with a more uniform pull on the belt if two or more cylinders are used with the crank pins of each placed at an angle with each other. The “duplex air compressor” is designed on this plan with two cylinders side by side, the crank pins for the two compressors being at an angle of 90 degrees with each other. The motive EFFICIENCIES AND ENERGY COMPENSATION 87 power may be either belt, electric motor or steam engine. If the latter, it is not uncommon to place the steam cylinders tandem with the air cylinders, using a common piston rod, as shown in Fig, 54. NST SY NL__ift eS TM Vy —Z J a} N = sl | Dy Fic. 54.—Duplex steam-driven compressor. The steam cylinders may be either cylinders of a cross-compound engine, or two separate simple steam engines. Similarly, the two air cylinders may be cylinders of two separate air compressors or 88 AIR COMPRESSION AND TRANSMISSION cylinders of a two-stage compressor. The name ‘“Duplex”’ is applied to any of these designs. Figure 55 shows a sketch of the arrangement of cylinders for a two-stage duplex compressor driven by a cross-compound steam engine. A little study of these sketches will make it clear that with such a duplex arrangement when the greatest power is developed in one steam cylinder, this excess power can be utilized by means of the common crank shaft in overcoming the maximum resistance that is being encountered in the other air cylinder. With the cranks ap Fic. 55.—Duplex cross compound steam, two-stage air compressor. go degrees apart there is little difficulty in starting, even if compound steam cylinders are used, for if the compressor would stop with the high-pressure cylinder at dead center, live steam may be admitted to the low-pressure cylinder by means of a by-pass. Commercially, the duplex compressor appeals to the trade in that one side or half of the machine may be furnished with fly- wheel and out-board bearing designed for a complete machine, and as the demand for compressed air increases, the output may be increased by installing the remaining side of the machine. The belt compressor is probably the best type for small capacities when it can be used conveniently, as is the case in a great many factories, for the losses in a steam cylinder, especially of small power, are excessive as compared with the loss of power due to belt transmission. Cit’ ili Re EX MULTI-STAGE COMPRESSION It was pointed out in Chapter VII that it was not advisable to attempt compression above 80 lb. per square inch in a single cylinder because of the loss of energy and danger of explosion due to the re- sulting high temperatures. 7 It frequently happens, however, that pressures much higher than this are demanded for commercial purposes, and in order to satisfy this demand, avoid the danger just referred to, and reduce the losses MEREBEU AS ses SSS SSS b f q i f es je OPO La =e SESE EELS ERASE LUE UNEENANUNENENENESSND e Fic. 56.—Saving due to multi-stage compression. due to adiabatic compression, engineers have adopted a multi-stage system of compression; compressing the air partly in one cylinder, passing it through an intercooler where its temperature and volume are reduced, then compressing it still further in a second cylinder, and, if the pressures required are high, this compressed air is passed to a second intercooler, thence to a third cylinder and in some cases a 89 90 AIR COMPRESSION AND TRANSMISSION third intercooler and a fourth cylinder are required to secure the desired compression pressure economically. Advantage of Multi-stage Compression.—The advantages of this system of compression more than offset the extra expense in constructing the compressor. The saving in power required may be illustrated by Fig. 56, where a—d represents the adiabatic line from atmospheric pressure to the required receiver pressure, a—c an iso- thermal line between the same pressures. The shaded area repre- sents the total work of compression in the four cylinders, the differ- ence between this area and the area abde representing the saving in power due to the multi-stage system of compression. afne repre- sents the work done in the first cylinder, fn the volume occupied by the air as it leaves this cylinder. In the intercooler the temperature of the air, if this part of the apparatus is properly designed, will be reduced to the inlet temperature, and in consequence the volume will be reduced from fx to on. Compression in the second cylinder will raise the pressure to g and reduce the volume of the compressed air to gm. In the second intercooler the volume will be reduced as the temperature is reduced to the inlet temperature from gm to pm, and so.on. ‘This secures a compression that requires a smaller expendi- ture of energy than adiabatic compression, giving results that com- pare very favorably with the ideal isothermal compression without serious difficulty. Pressures Used for Various Stages.—Of course this arrangement increases the first cost of the compressor and for that reason the ad- visability of installing multi-stage compression will depend upon the pressure required. Some authorities recommend two-stage com- pression for pressures as low as 50 lb., but this practice is unusual. It is certain, however, that for pressures from 80 to 500 lb. the two- stage compressor should be used; for pressures from 500 to 1,000 lb. the three-stage, and for pressure between 1,000 and 3,000 lb. the four- stage compressor. Intercoolers.—To secure best results care should be taken to see that the intercooler between the different cylinders reduces the temperature of the air as nearly as possible to that of the air at the compressor inlet. As it is important that the flow of air through the intercooler should be as low as possible, it is desirable to reduce the pulsating effect of the discharge of partially compressed air to the intercooler. This is usually accomplished by using large ports and passages. The larger the volume of the intercooler, the more time for the MULTI-STAGE COMPRESSION Fic. 57.—Intercooler for duplex two-stage compressor. Wa ter Outlet > KS as See SS | See Uy N= UJ 4 U a . eet oe ak id Site esses SY eee sf (e ~] LO: meas ee ‘Of $22 Yor Ogee Ss (| wz J cc OL Ne (a hig a\'=| YTZZALLIP OTP LIZZ ne s ZZA Rae. ML T | y i Cima waa waar ar ae Re RS ll Robeech ZA U — if N MY] eS fe = S 20 Curve showing intercooler surtace| 4 10 100 |b. discharge pressure at sea c- ae level to obtain pertect intercooling. ee eae 22) a= |b z SCS et eee £ ad = [so one ase ae = Tee eee a Z, Bae eee Bere ‘ a [ES ete hit] | a t ea [9 5] a a a 8°9 5 45 50 35 Dereace ieniperarre pee Air Peand and Water enone Fic. 61.—Intercooler surface required. IS cS BS i Se | D ro Gallons of Water per Hour Volume of water Sanilgd for perfect intercoo 100 Ib. disch. pressure sea level operation Wath and without cylinder Jacket water. ay, on Fala ELE 280 Siew =o an ea v 260 77 a (allel a NR ESE sca) tp Coy ye lay Ae sae z VA ie a Es BOP ROES eee ine | SSE 120 VALS PAV BBVA 90 ewetee rCiaiestern beneee Fahrenert Fic. 62.—Water required for intercooling. MULTI-STAGE COMPRESSION 95 This expression will be a minimum when the part within the brackets is a minimum. As fa, or the inlet pressure, and pa, the discharge from the high-pressure cylinder, are fixed, the only variable is the intercooler pressure, or po. (jak n—1 Differentiating eo) Oe ian cp ies | with respect to pp and equating to zero will give the requisite condition of proper inter- cooler pressure for minimum expenditure of energy. n—1 in n—1 1h el fh —1 I Aba AP === == 1 Pay 3 ee + Se, Ci =o Raa Laas’ a =— in I TNS = : Did ae Doak ee Ts - py HES ny pe n b—n 1—n Pe = a5 a aSpE De wD ee po=NV Paba That is, for two-stage compression the most economical expendi- ture of energy is secured when the intercooler pressure is the square root of the product of the given suction and discharge pressure of the machine. As perfect intercooling is assumed, paVa=poVo and the areas of the two cards must be equal, that is, the most economical results are secured when the work of compression is divided equally between the two cylinders. Let Fig. 63 represent an ideal card of a three-stage air compressor without clearance, in which p3 represents the pressure in the first intercooler, and 4 the pressure in the second intercooler. These first two stages may be considered as two-stage compressors between bp; and p,4 in which, for the most economical results, b3s=WV pips and in the same way and for the same reason, pi=V Papo from which p3= V obo and pa=V pips? The effect of clearance on the above discussion can be shown by referring to Fig. 64, showing cards for a two-stage compressor 96 AIR COMPRESSION AND TRANSMISSION with clearance. The area showing the work done is AJKLSTZ, which may be considered as AJNF+KLEN—ZSEF, This will evidently be a minimum when the expressions for these areas are a minimum, but as the expression for ZSEF does not contain the Pon a gs eae me--—---——-—— — --— -— - -— - | Lo o NY, Se ee ee eee 0 Fic. 63.—Proper receiver pressure for multi-stage compression. variable pz, this term will drop out in differentiating and, as a result, it will follow that the intercooler pressure giving the most economical result will be with clearance as without clearance. Px = iy V Fic. 64.—Effect of clearance on receiver pressure. The same method will show that most economical receiver pres- sures for a three-stage compressor are: p3= V pbs and p4= V pipe? MULTI-STAGE COMPRESSION 97 when clearance is considered as when clearance is omitted in the discussion. Effect of Clearance on Volumetric Efficiency.—It was pointed out in Chapter VIII that the real volumetric efficiency of an air compressor could be expressed as re helmet] Figure 64 has assumed the clearance in the various cylinders to be proportional, that is, the ratio of clearance volume to piston displacement in each cylinder was such that clearance lines of each cylinder unite to form a continuous expansion line. If C represent the clearance of the low pressure cylinder and po represent the intercooler pressure, pa the suction pressure and pe the discharge pressure from the high-pressure cylinder, then the real volumetric efficiency of a two-stage air compressor may be ex- pressed I Bpe 4 pi oe Po a | re Batee| eI] but as Po=N Pabey this may be written Tam pi'| | (Patbe?\ > |) Tr fe: el ( Pa. es Tom Pr}, _¢| (Pe) on— || arena aa} In the same way, the true volumetric efficiency of a three-stage air compressor may be expressed as or Tam Ps is| (2 nor] 16s Pam | - Pa J in which fe is the discharge pressure from the last cylinder and pa the suction pressure of the low-pressure cylinder. Figure 45 shows graphically the effect on volumetric efficiency of compressing by stages and the resulting advantage in capacity. CHAPTER X DETAILS OF PISTON AIR COMPRESSORS Classification of Valves.—Most of the various types of inlet valves for piston air compressors may be divided into two general classes: first, those which are automatically opened by atmospheric pressure and closed by means of their own inertia or weight, by springs, or by air pressure; and second, those which are opened and closed by direct and positive mechanical connection with the crank-shaft or some other moving part of the machine. Each of these classes include many forms of valve design. Valves of the first class are entirely automatic in their action, their opening and closing points depending entirely upon the con- ditions of pressure within the cylinder. However, they have certain advantages which will be considered later. Valves of the second class, with one or two exceptions, have their points of opening and closing fixed without regard to changes in operating conditions, and the present tendency among designers and manufacturers seems to be toward valves of this class. Mechanical Valves.—Nothing can be superior to mechanically operated valves when properly adjusted to operating conditions, as by their aid several of the losses of air compression have been reduced to a minimum. On the other hand, faulty adjustment of valves, sometimes combined with improper design, renders them extremely low in both efficiency and capacity. Inlet Valve Setting.—If inlet valves are so set that they open almost exactly when the piston is at the end of its stroke, the card will indicate absolutely no clearance at either end of the cylinder, the clearance air being exhausted into the intake. If the inlet valve closes slightly before the piston reaches the end of its suction stroke, the volumetric efficiency is also reduced. In case the inlet valves are so constructed that they cannot open until the clearance air has been expanded to atmospheric pressure, the only loss due to this clearance is one of capacity, which may be Overcome by an increase in size or speed of piston. If, however, 98 Pt yer DETAILS OF PISTON AIR COMPRESSORS wh the inlet valve opens when the piston is in its extreme position, the clearance air is exhausted through the intake, making a direct loss of power as well as of capacity. Figure 65 is reproduced from a card taken from a machine in which the inlet valves were set to open when the piston was exactly at the end of its stroke. In most of these cases the exhaust through the intake is sufficient to cause considerable noise. Figure 66 shows a card from the same machine with the valves set properly for their particular pressure. This change in the time of opening the inlet pm. Fic. 65.—Mechanically Fic. 66.—Mechanically oper- operated inlet valve opened at ated inlet valve properly set. end of stroke. valve has not effected the volume of air discharged, but the power required to operate the compressor has been considerably reduced and the machine will run more smoothly with less shock to the moving parts at the end of the stroke. Effect of Changing Discharge Pressure.—lIf the pressure of dis- charge is now increased, the former troubles appear again, resulting in a card shown by Fig. 67. If this pressure is to be maintained con- Z)_4 Fic. 67.—Effect of increasing Fic. 68.—Effect of decreas- discharge pressure. ing discharge pressure. tinuously, the inlet valve will have to be adjusted to open a little later in order to give the best results. In the same way, if for any reason the discharge pressure should be reduced after the valves have been set correctly, the indicator card will resemble Fig. 68, and if the compressor is to operate con- ” 100 AIR COMPRESSION AND TRANSMISSION tinuously at this lower pressure the inlet valve will have to be ad- justed to open a little earlier. Figures 69 and 7o show indicator cards from improperly set mechanically operated discharge valves with the defect indicated under each. Every machine with mechanically operated valves should be carefully examined to determine whether they operate at the correct Fic. 69.—Mechanically Fic. 70.—Mechanically operated discharge valve operated discharge valve opening too early. opening too late. time, andif not, should be so adjusted in order to raise the efficiency of operation. The principal disadvantages of the mechancally operated valves are the increased cost and the extra attention required to keep the valves set properly. Automatic Valves.—In compressors using automatic valves, how- ever, there is no necessity of timing the valves to suit changes of pressure, as the operation of the valves is controlled entirely by the conditions or pressure within and without the cylinder. It must be remembered that the majority of air compressors operate at a fixed pressure of discharge and after the valve is once set for this discharge, there is no further need of changing it. Both types of valves have advantages and disadvantages peculiar to each and a choice of valves should not be made in any important instance without a thorough investigation of all the variable factors. involved. Valve Area.—A very important matter to be considered is the inlet valve area or port opening required for the proper action of a machine. Asin other points of design, it is necessary to compromise the desired ends, for the larger the inlet valve the less will be the water-jacketed cylinder surface, and as both are desirable it is im- possible to give absolute ratios of inlet areas to cylinder sizes. Some designers make inlet areas 5 per cent. of the piston area, and other DETAILS OF PISTON AIR COMPRESSORS 101 designers use as high as 14 per cent. asthe ratio. The design of the valve, the cylinder proportions, and the speed of the machine, all have an influence in determining this point. The following data is given by the chief draftsman of a large com- pressor company as the practice of that company resulting from an experience of many years: “Roughly speaking,” 5,000 ft. per minute for the velocity of the air through the valve gives good results. This being the case, a slow-running machine would require a smaller valve than a high- speed compressor with a ‘piston-inlet’ valve, having a piston speed of from 300 to 350 ft. per minute, the inlet area is from 5 to 6 per cent. of the piston area. On large compressors with a piston speed of from 500 to 600 ft. per minute, the valve area ranges from 6 1/2 to 7 per cent: of the piston area. The discharge valves which are of the poppet type are from ro to 12 per cent. of the piston area. On machines having both inlet and discharge valves of the poppet type, the ratio should be about 12 per cent. for machines of that speed. For piston speeds not exceeding 4oo ft. per minute it is probable that ro per cent. is enough. The area of the discharge valve should not be less than that of the inlet, for although the volume of discharge is less than the volume of admission, this discharge must take place in a considerably shorter space of time. Forms of Poppet Valves.—Probably the automatic poppet valve is the most common form of valve in use. A few designs are shown in Figs. 71 and 72. Fic. 71.—Air inlet valve. The principal difficulty to guard against in the design of an auto- matic valve is to avoid the possibility of the valve itself being drawn into the cylinder with the in-rushing air. This may happen through the breaking of the spring and disastrous results frequently happen, for on the return stroke of the piston, the cylinder head, or the piston, or some other part of the apparatus is sure to suffer. Figure 73 illustrates a peculiar valve designed for a single-acting compressor, 7.¢., a type of piston compressor in which the air com- 102 AIR COMPRESSION AND TRANSMISSION pression takes place on only one side of the piston instead of both as is usually the case. JB is the inlet valve which is located in the center Fic. 72.—Air discharge valve. of the piston and is held on its seat by the spring D. The discharge valve A is a radical departure from the older designs of compressor Fic. 73.—Valve in cylinder fee valves, being a flat disc covering the entire area of the cylinder and held in its seat by a guide and spring. AS AA rz raedsaiteg ae Ee a = ——ews AL OH a A fa om | zee ‘* 4 is Ae Se iA eek ay S Le ed N Vy GPR iN yee LL Fic. 74.—Piston inlet valve. Its face and the face of the piston are perfectly flat, so that the piston may strike the valve and deliver all the air with no clearance DETAILS OF PISTON AIR COMPRESSORS 103 space to reduce its capacity. A large area of discharge is obtained by a very small movement of the valve and no pounding is made by its action, for the compressor is of the straight-line type and the compression in the steam cylinder acts as a cushion to relieve the pounding that might otherwise occur with no clearance. Piston-inlet Valves.—One of the most interesting forms of inlet valve is the piston-inlet valve, as manufactured by the Ingersoll- Rand Company, a sketch of which is shown in Fig. 74. By this arrangement the entering air comes in through the tube 4, which projects through the head end of the cylinder. The air passes through this to the center of the piston which is hollow. Communication is obtained from this hollow piston to the cylinder through the ring-shaped valves B, which are made of open-hearth steel in one piece without a weld. These valves have a movement of about 1/4 in., and are held in place by pins which are set in slots in the valve. The two inlet valves B and the tube A are carried back and forth with the piston. The valve on that face of the piston which is towaid the right is closed as the piston moves to the right, while that on the left side is open to admit a fresh supply of air to the left side of the piston while air is being compressed on the right side. - When the piston reaches the end of its stroke, the inlet valve closes because of its own inertia and as the piston starts on the return stroke the valve that was formerly closed is now left behind for about 1/4 in. of the piston travel and remains open during the entire stroke. When the valves are closed, their face is almost flush with the piston face, thus reducing the clearance space to minimum. There are no springs in the construction of this valve, and it has been found to work equally well with slow or high speed. These valves are guaranteed by the company for five years. Discharge valves are shown at H. These conduct the com- pressed air to the discharge pipe F. All these types of automatically operated valves have the ad- vantage that they adjust themselves to meet varying changes in air pressure automatically. Semi-mechanical Valves.—There are several types of semi- mechanically operated valves on the market. Some of these con- sist essentially of an arrangement of levers to remove the action of the spring on the inlet valves during admission, permitting the valve to open instantly and freely and remain open without any clattering 104 AIR COMPRESSION AND TRANSMISSION until the end of the stroke, when the spring tension is permitted to act on the valve and close it. Attention has already been called to the fact that many auto- matic valves close before the end of the stroke, due to the fact that the piston is rapidly reducing its speed at that time. If the inlet valve Fic. 75.—Mechanical valve of Corliss type. closes before the end of the stroke, the volumetric efficiency is natur- ally reduced, and on this account the mechanically operated inlet valve is preferred by many engineers. In addition to the mechanical operation of poppet spring valves just mentioned, some air compressors are equipped with valves VY _Y w/N —A MVS mi) $e WV 3 ES Z i md = . = Z a= eee est iain = 1 = mai va $ r— ‘S ry G ae 4 7 4 s NY: ms Zi 4 oe Aa SSSSSS XM eal / LAN hy c . IN w\ aS ia — rent MY a %, —_ 7A Vor on ee? = y} f, Bhsessacach, fr, 45 Y D h oacaracea fi 52 t=) 4 ere rd B Se FN N SSSSSSSSSSsog Sy] Ss VE Ssoxesssssd Fic. 76.—Southwork blowing engine valve. which resemble in action and appearance Corliss steam valves. Fig. 75 gives an illustration of this form of valve, which is opened and closed by a rotating motion, given to them by levers from a wrist plate or eccentric. This type of valve is sometimes used for the discharge valve on compressors, but cannot be operated successfully for very high DETAILS OF PISTON AIR COMPRESSORS 105 pressures because the clearance is made excessive. Mechanically operated valves are usually used on large blowing engines for blast furnaces. One type is shown in Figs. 76 and 77. In this type of compressor, it is desirable to secure large, free opening for suction, and one of the latest designs consists of a large cylinder on the out- side of the compressing cylinder which reciprocates back and forth, and in so doing opens large slots at the end of the cylinder, giving very free opening for inlet. a Uf aMlllbilttithy \ SS vi ~ =y Ce) Seay Ss WZ SS AANA AAA RAAARAARARESASRARA RASA BS ERESERESENS Fic. 77.—Kennedy blowing engine valve. Regulators, Unloading Devices, Etc. It is often essential that the pressure of air in an air receiver be kept constantly at a fixed point and as the number of tools using air at the same time will vary in any installation, some automatic device must be used so that the_compressor will be furnishing air when needed and when no air is needed this device must prevent any unnecessary work being done at the compressor. There will be times when every tool that is taking air from the receiver will be in operation and the compressor must have a capacity sufficient for such occasions; and again there will be times when none of the tools are in operation and the work at the time being done at the com- pressor would be in excess of the needs if some automatic system of regulation is not used. Belt Regulator.—Probably the simplest form of regulator is the one that is often used on belt-driven air compressors. ‘This consists of a belt-shifting device so arranged that when the pressure gets above the desired point the belt is shifted off the compressor wheel and onto a loose pulley. When the pressure falls below this fixed point the belt is shifted back again, and the compressor is thus 106 AIR COMPRESSION AND TRANSMISSION automatically started and stopped to suit the changing amount of compressed air that is needed. Westinghouse Governor.—Fig. 78 shows a sketch of the governor used on the Westinghouse air brake. It consists of a piston A moving in a cylinder and directly connected to the steam valve C which supplies steam to the air compressor, or air pump as it is more commonly called. A spring, D, helps to hold this up and hence keep the steam valve open. Pipe £ leads from the air reser- %, D> TAT TTD ay praia asst Y WH: ‘t su w/ | : Kok Lad Uy \ ih MT \ Be, hdl K Vlsse WN NU Yi rms Ne VAL ey) Zbl NS 2 ry Z % Fic. 78.—Westinghouse governor. voir to the governor. Communication between E and the cylinder above A is closed by a needle valve Ff, which is held on its seat by the governor spring K. When the air pressure in the main reservoir gets up to its maximum, the pressure in £ is sufficient to raise the small piston H against the governor spring K, lift Ff from its seat and allow the air to press on A and thus close the steam valve and stop the air pump. A small opening, L, allows the air above A to escape gradually into the atmosphere. As air is used in releasing DETAILS OF PISTON AIR COMPRESSORS 107 the brakes, the pressure in the reservoir will be reduced, and when this happens, spring K can overcome the air pressure and seat F and spring D will then raise piston A, open the steam valve C and start the pump. The governor used for controlling the compressor for electric- driven air-brake systems consists of an ordinary Bourbon pressure gage with a special needle or hand, which upon coming in contact with a stud at the position of minimum pressure causes an electric current to flow through a magnet coil. This coil operates a plunger to which the contact pieces for the motor circuit are attached and MeL Fic. 79.—Belt regulator. in this way the circuit is closed and the motor started. As soon as the air pressure reaches the desired maximum the gage hand strikes another stud, causing current to pass through a second solenoid magnet which pulls the plunger referred to in the opposite direction and stops the compressor motor. By this mechanism it is possible to get a close margin between the maximum and minimum pressure. This margin can be changed by moving the studs. Figure 79 shows a form of regulator for belt-driven compressors ~which stops the compressor when the desired maximum pressure 108 AIR COMPRESSION AND TRANSMISSION is reached. When the desired upper limit is reached the belt is shifted from the tight to the loose pulley. Norwalk Regulator.—One of the simplest forms of regulators for steam-driven air compressors is the one made by the Norwalk Iron Works shown in Fig. 80. It consists of a balanced steam valve A placed in the steam-pipe near the steam cylinder and con- trolled by the air pressure in the receiver. A small cylinder B contains a piston connected with the opp balanced valve A by the stem C. Above s this small piston is a stop screw D pro- jecting above the cylinder head for regulat- ing the lift of the piston. The air from the receiver is led through a small safety valve E which regulates the pressure at which air can escape into the cylinder B to move the piston. Above the disc of the small safety y valve is a spring whose tension is regulated i by ascrew F allowing the pressure at which air is permitted to enter cylinder B to be changed at will. The air passes into cylin- der B below the piston and if no escape were provided would drive the piston to the top of B. To regulate this a very fine slot is cut in the side of the small cylinder. When the piston rises it uncovers this slot and thus furnishes an escape for the air which is passing the safety valve. If only a little air enters then a small part of the slot will accommodate it and the piston will take a low position. With more air escaping the piston will rise higher and uncover more of the slot, thus providing a larger opening for its exit. As the slot is very fine, a very little difference in the quantity of air will cause the piston to assume a high or low position. After the small safety valve begins to blow an almost insensible increase of pressure in the reservoir will furnish enough more air to carry the piston to the top of the cylinder. Thus any degree of regulation is obtained by a very little difference of pressure, as the air which works on the piston in the small cylinder has only to perform the work of lifting the piston and valve suff- ciently to uncover enough of the slot so that it can escape; its pressure is very slight. The piston is fitted loosely and the whole apparatus moves as nearly without friction as can be imagined. aaear Hy sere Hj TI tis Fic. 80.—Norwalk governor. DETAILS OF PISTON AIR COMPRESSORS 109 When this regulator is applied to compressors having a single steam cylinder, it is possible for the valve to be carried so high as to cut off all steam and to stop the engine on the center. This would be objectionable. To obviate this, there is placed on the top of the small cylinder a screw stop which can be set to prevent the closing of the steam valve more than is sufficient to run the engine at the slowest possible speed. Combined Governor and Regulator.—Another combined speed and air-pressure governor is shown in Fig. 81. This not only Breas : arate sean LN aN Nalalol ahaha # ca ae en aN | ae De PE LP PT A wr oe LZ <2 eS eget 0 | 0 Cher ps Full Load Full Load LHP 2425, H.P Input 325 2s a Vol A%, PREIS pons ye ser ae (RAN Ws oe Hees Sg ee M -P 429 \ nee Ui O54 aes heres as SP phe eet = Lees 7, : 0 First Step First Step LHP 1812, HP Input 221 Voluime 46%, PE 96. etal wh fr PAS UM EP oe Ey, RIE Pi ae me eee a A a ra BRIS Veen (eons Sn ge ee as oe eet, r. : see TR aa A ae eB ceria eae te ee ma 0 Second Step Second Step LHP 104.2, H.R input !5é Volurne 27%, PF, 95 3 Sparen MEP 66--> WN (SEH Ma. et oe eee Bd eee LMEP SEG ee aso a Be HONS ~< ie ee ee ee bee ce LE nia Ae. 0 ——— 0 Third Step Third Step LHP 31.3, H.P Input 97 Volume 8%, PF 94 % ~~. MEP 586 MEP 556_-- ~ M.E.PL84 -7 oe ne To P A 14 Bee a = a == ae - wa Ni ee perc St as ea ee Fourth Step Fourth Step Fic. 85.—Cards showing clearance unloader. CHAPTER XI TURBO-COMPRESSORS The Engineering Magazine in recent issues has given a series of five articles on turbo-blowers and compressors by Franz zur Nedden, Superintending Engineer of Weise and Monski, Halle-Saale, Ger- many, from which the following material and illustrations have been gathered. The introduction of the steam turbine as a competitor of the reciprocating engine has necessitated a similar change in the design and construction of pumps, blowers, and compressors and has natu- rally led to the production of turbine machines built for compress- ing air or gases. The advantages of turbo-compressors, however, are not so apparent in small as in large size units, and the high cost of such units in the experimental development of this machine has made its introduction rather slow. The recent development, however, of exhaust steam turbines has stimulated the use of turbo-blowers. ‘“‘Tt is well known that the economy of the steam turbine increases directly with its rotative speed, and even electric generators of the highest speeds are slow-running machines when compared with the steam turbine operating at the number of revolutions required to secure the best economy. The turbo-compressor, like the steam turbine, becomes more and more economical the faster it runs, and is therefore a proper companion of the steam turbine. Speeds of 4,000 revolutions per minute and even more are not unusual to the design of turbo-compressors. “Tf large volumes of compressed air are wanted in plants where considerable quantities of exhaust steam are available at the same time, the coupling of an exhaust-steam turbine with a centrifugal compressor becomes an ideal arrangement, and the combination is far superior in economy to the piston compressor driven by an electric motor or a high-pressure steam engine.”’ Design of Turbo-compressors “In studying the development of turbo-compressors it is most interesting to observe that Rateau and Parsons dealt with the prob- lems of design quite differently. 8 113 114 AIR COMPRESSION AND TRANSMISSION ‘“‘Rateau Blower.—Prof. Rateau did not take the structural features of his new machine from his steam turbine, but from his high-lift turbine pump. His turbo-compressor and turbo-pump are so similar that a superficial inspection of the drawing of the two ~ machines might not reveal the difference (Fig 86). Za pe OO OL OO LOE ys Soo SWS yo” NN =o Soy Tires hx Soy Awa AY SS SSsoeN FAQS SN a) < Vr) 4 Bf i \e Y j PST RBZ ZK Dee 2ZALZZ) ! on i 7A 7S ( ees EE EE Bd Raleeaten ‘Co A || | ie uy e7 SAS aot Toy Sele gaan \ SSS ake RS lf orn f} \ Fic. 86.—Original Rateau turbine blower. “The air upon entering the impeller near its nave is seized by the impeller blades and thrown outward radially. Its kinetic energy due to velocity upon leaving the periphery is changed into pressure in the fixed diffusor channel, and being led back toward the center the air enters the second impeller to undergo the same process in a second stage and so on. Some essential differences in the design of details will be taken up later on. “The Parsons Blower.—Mr. Parsons, on the other hand, made the turbo-blower merely an inversion of his steam turbine. Fig. 87 shows a unit consisting of a standard Parsons steam turbine (on © anne a eae: : \\ wv ie z My \ Rspstissssscy SE) AAO oti | \ “ft vi i eth = fal ONIN Ne ANE Ar UMA | jet EY, NAY SLOAN SS UN u Me eee SSS Se hb laisipeseas oa d ‘ices niE es) NI U a £6 A 2 Ea TS | SS ay | KOS ASES SE SSS iS Ss CS NAN NEZZ ANGE L244 rat Ua | LL d Fic. 87.—Parsons turbine blower with steam turbine. the left-hand side) coupled direct with a turbo-blower of the usual Parsons type, and delivering 1,600 cu. ft. per minute against a pres- sure of 6 to 20 in. of mercury at speeds varying from 2,400 to 3,400 revolutions. “The air is drawn into the chamber B, and conducted into the periphery blades of the runner A by fixed guide blades D. The following blades are not shown in the section merely for simplicity of outline. TURBO-COMPRESSORS 115 “The principal divergence from the Rateau design is that the impellers of the Parsons turbo-blower throw the air in an axial direc- tion to the next guide apparatus. Parsons undertook to transform the kinetic energy of the air as it leaves the impeller blades into pressure by simply opposing plain straight blades against its flow. The second guide-wheel transmits the air axially to the second impeller, which again throws it axially into the third guide-wheel, and soon. Fig. 88 shows a developed section through several rows of blades. | “The excellent reputation of the Parsons machines helped the introduction of his turbo-blower, which was rapidly accepted and PVE be | ~e | | | Guide Me POON oe Fic.” 88.—Developed section of Parson’s blades. put into practical operation. At a time when more than a dozen Parsons blowers were in operation or under construction, Rateau was still experimenting with his first turbo-blower. Nevertheless, Prof. Rateau succeeded in making up this delay and soon advanced to the point of combining several of his blowers in series, thus pro- ceeding to obtain final pressures of 100 to 150 lb. per square inch. The excellent results which he and his assistant, Piof. Armengaud, obtained from their high-pressure machines induced even the licensees of Parsons steam-turbine patents to secure rights for the Rateau turbo-compressors. A careful comparison of both systems will disclose seme reasons for the rapid adoption of the Rateau system. “Cooling Turbo-compressors.—Increase of temperature makes special cooling arrangements indispensable, especially with turbo- compressors, 7.¢., with machines compressing air to more than 20 lb. per square inch absolute pressure. Economical cooling becomes 116 AIR COMPRESSION AND TRANSMISSION a vital question in the thermal efficiency of the compressor. On this point it decidedly excels the piston compressor, as it is impos- sible to cool the air continuously when it is compressed in cylinders. (See Figs. 89 and 90.) Here jacket cooling is the most important part of the whole cooling system, and the special intermediate coolers used between the separate cylinders of compound piston Quant. ell qiry xO LN SS letotoneteronentansioes Aa a FRB ae £277 LLL Lace —— SOnerIC AIP. a AT A A a Lid Atmospheric Alt ———— per yee is 5 10 Yolume, Cubic Feet per Haur Fic. 89.—Diagram three-stage piston compression. compressors are generally considered wholly unnecessary in the turbo- compressor. In the turbo-machine compression of the air proceeds much more gradually, the distance traveled by every particle of air is consequently much greater than with piston compressors, and the entire area available for the cooling influence of the water is BUS Va KK Vili eee SSS Coble Feet wee 0 500 ; 1000 1500 Volume, Cubic Feet per Hour” Fic. 90.—Diagram of tubo compression. many times as large as that in the piston compressor of equal capac- ity; therefore, the air pumped by the tucbo-compressor can be kept at nearly constant temperature throughout the operation. Cooling arrangements of the counter-current type can easily be used to give maximum effectiveness, a condition not readily attained in com- pressors of piston type. TURBO-COMPRESSORS isles COOLING DEVICES “The principal differences noticeable between various turbo- compressor systems are in their cooling arrangements. The various licensees of Prof. Rateau do not use a uniform cooling device. Fig. g1 shows one of the first water-cooled Rateau compressors which has been successful in practical operation. Fig. 92 shows its internal features. Each of the three groups coupled in series contains seven oY Ni Nees iN MMos A) Yi YA ae : Al aime 4 —— ns | if = zm 7 ain iff i Ue il, — LH Wii i Fic. 91.—Water-cooled turbo compressor. or eight stages. Each casing is separable horizontally into two parts, a form which seems to have become standard for turbo-compressors as it has for steam turbines. The cooling water enters the casing from below at the highest pressure stage of the group. It passes thence to the upper part through copper tubes, shown in Fig. 91, goes through a core-hole at the top of the highest stage into the upper half of the highest ons but one, and again through copper “ HT bn ' ae _—————Sa i oy WT, ———— LLLLLLLLLLLLL LLL Ae ee ecg er cnemene es teen ce: PAs0-a=> : Fic. 92.—Turbo compressor built by Brown, Boveri and Co. tubes into the lower half, whence it goes through a core-hole into the lower half of the next lower stage, and soon. Later, the copper pipes were replaced by small bored holes passing through the horizontal joints. (See Fig. 92.) This system has the disadvantage that there is no assurance that the water shall completely fill up the cooling chamber, as the core-holes are not always at the very highest points of the chambers. ‘““Messrs. Brown, Boveri & Co. avoided this difficulty, and, more- 118 AIR COMPRESSION AND TRANSMISSION over, greatly enlarged the cooling area by casting the vanes hollow, thus leading the air back to the center and creating a separate inte- rior cooling chamber B, Fig. 93. The water, after filling chamber A, flows through the hollow guide vane into chamber B, and thence by Pas ek pipe D (which is screwed into highest point of chamber A of the next stage. Though the excellence of this system cannot be denied, it is, on the other hand, very expensive, for the castings become highly complicated, and the foundry work, moreover, must be such as to guarantee that all sur- faces are absolutely smooth, as the elle frictional resistance of air is dependent on the roughness of the surface over which it passes. The cost of casting these casings was about 5 1/4 cents a pound in place of 3 1/2 for average casings, and even then this famous foundry could not avoid 15 to 20 per cent. waste. E “‘C. H. Jaeger of Leipzig wisely separates the casing of his turbo- compressors into as many chambers as there are stages, and screws these together as shown in Fig. 94. Furthermore, he separates each SSSSOQq Y A Y WV, y y V) mY, j bod) Fic. 93.—Ipmroved cooling sys- tem for turbo compression. Sen wal NS avtall uu Winch aaa wee Ne i ee a a= i ed, META iy LLL LL LULL i! UML AA As ze ‘ oa = ee IN = W\ ill NS WA WA Fic. 94.—Water-cooled Jaeger turbo compressor. stage into an upper and lower half. Though this system increases considerably the number of machined surfaces, it nevertheless insures small casings and enables the maker to manufacture the single stages on a large scale and to combine out of stock as many as are needed for any special requirement. “Expansion of Casing.—Another effect of temperature rise, and one which acts on the machine, is the expansion of the casing by heat. Special preventive measures must therefore be taken to avoid TURBO-COMPRESSORS 119 any alteration in the relative position of the casing and the runners. As the casing rests by lateral supports.on the bed-plate, the absolute height of its center above that bed-plate will change as soon as the casing becomes heated and expands. If the shaft, revolving within this casing with a clearance as small as 1/1000 of an inch, is supported by bearings which remain practically cool, the distance between the center of the shaft and the bed-plate will remain unchanged. Therefore, the centers of the casing and of the shaft, which may coincide when both are cold, must differ as soon as the blower comes into operation and the temperature of the casing rises. The clearances will then not only become eccen- tric, but very probably the shaft and the vanes of the im- pellers will come into close contact with the fixed parts, causing heavy friction, and because of the absence of any lubricating medium they would very likely seize. “Designers of turbo-compressors have overcome the difficulty of axial expansion by means already well known in the steam engine and the piston compressor. These difficulties are, of course, larger with long-extended turbo-compressors than with single-casing turbo- blowers. The blower illustrated in Fig. 95 rests with one end only on the bed-plate, the other end being free to move or expand. When additional stages are required, the design must be altered tc a form now quite generally adopted by the licensees both of Prof. Rateau and Messrs. C. H. Jaeger & Co. The body is supported only by the two terminal covers which carry the bearings. One of the bearings is fixed rigidly to the bed-plate, while the other is allowed to slide to some extent on the machine rest. (See Fig. 94.) With very long blowers, it might perhaps be advisable to support the body by lateral feet, the machined surfaces of which might move freely on the bed-plate on exactly the same horizontal plane as the axis of the blower. In this way radial expansion would not alter the height of the geometric center of the casing above the bed-plate. ‘“fRunners.— Many of the problems that had been solved in design- ing steam turbines assisted in the solution of the design of turbo- blowers, but although Parsons was able to adapt his steam-turbine S Wsr¥% N TA N= ‘=e Neth =e 42 Is Wy dd / Wi Fic. 95.—Jaeger’s turbo-blower. 120 AIR COMPRESSION AND TRANSMISSION runners to his blower, the original designs of Rateau and Jaeger had unsymmetrical runners, which had a tendency to become deformed under high speed. This difficulty was finally overcome by the use - of impellers made with a solid hub with blades and lateral flanks of pressed sheet-nickel steel, as shown in Fig. 96. “It is not very difficult to insure tightness between the single stages of turbo-blowers and turbo-compressors. The pressure Fic. 96.—Jaeger’s patent impeller. differences against which the clearances have to be kept tight are comparatively small, as the delivery pressure is distributed over many stages; and, on the other hand, long clearances are secured almost automatically as the stages are placed one after another in the casing. With air, as with water, the leakage resistance of a clearance is greater the longer and narrower it is, but the problem Z ) iMlalal: Fic. 97.—Labyrinth bushing. of maintaining tightness against leakage with gaseous media is facilitated by the labyrinth effect which is utilized on a large scale in the manufacture of steam turbines. ‘“‘Figure 97 shows such a labyrinth as used by Brown, Boveri & Co., the action being briefly described thus: “The air passing through the small clearance A expands as it enters the following chamber B. By this expansion its pressure is greatly decreased, and it traverses the second clearance C at a con- TURBO-COMPRESSORS a siderably lower pressure than that at which it passed through 4; owing to the expansion in the second chamber D, still less pressure is left for forcing the air through the third clearance F, and so on, and it is therefore impossible for any considerable quantity of air to pass the labyrinth. “Balancing Axial Thrust.—The only point at which any great loss of air occurs is in connection with the usual methods for balancing the axial thrust. Special arrangements for this balancing become necessary, for, as with centrifugal pumps, the annular area opposite the entrance to each impeller is subject to a heavier pressure than the entrance itself. And, as with centrifugal pumps, there are sev- eral ways of obtaining perfect balance, perhaps the best being that illustrated in Fig. 98. [ f-—<—<———aaa) EG) SSN Lees) = Sy SS > Seer SN Se Lara S Sag) Px g la a Sa eo oi (Z Uy 4s ag | A NA ah N SD aos... (Dara Ss= on 4 J \ 7 A, mA TN ‘ oy 2i—j} SS ey = | Mea ar AF 1 SSS — => J ae LZ e ~ b = 2 K ae C N SS el A? a ———S == ie « eh ae, ‘ Tae SY Mle Y 7 ey C11 y Uo Fic. 98.—Turbo blower of 25,000 cu. ft. capacity. “Balance by Counter-position.—Here the blower draws the air from both sides, and delivers it after both halves of the entire quan- tity have been compressed separately in wheels of the same dimen- sions through which they pass in opposite directions. Thus, any axial thrust arising in a wheel on one side is balanced by an equal thrust exerted by a corresponding wheel on the other side. This advantage of balancing axial thrust most perfectly, and practically without any leakage losses, is paid for, however, in this instance by a cumbersome arrangement and poor efficiency. It is obvious that the use of double the number of rotating sheaves for compressing the same quantity of air doubles also the amount of energy lost by frictional resistance. In other words, a blower like that shown in Fig. 98 is simply two blowers, each for half the delivery, coupled in parallel; and, as the efficiency of all rotating machines drops with 122 AIR COMPRESSION AND TRANSMISSION decreasing delivery, it is clear that the efficiency of these two blowers must be lower than if the whole quantity were dealt with in one single machine. . ‘Balancing by Diminishing Back Area.—Another design which is standard in the blowers of some of Prof. Rateau’s licensees, for Ph Dar Ri OLR AL AS Ay wou | ih: 2a | aay Nw wr Ne ae 7 LL, AZ ISS : q EN \ SJ ISS a t: ) s =S5 ae t q Ne-i © aA = ew an “ee \ =< * Zpezg Giee| J — 7 RSS ZZZLZAS ay tN ISSSSSNW7ZZL77ASSSSNSNVZZ nay, 4 , S Wa Fic. 100.—Piston-balanced turbo compressor. example the Skoda-Werke at Pilsen, and Messrs. Kuehnle, Kopp & Kausch, at Frankenthal, is adopted from the well-known Rateau turbine pumps. ‘The excess pressure acting on the back of each TURBO-COMPRESSORS 123 impeller can be cancelled by simply diminishing this back area pro rata with the increase in pressure. This is done by leaving free an annular margin at the periphery of the back of each impeller as shown by Fig. 99. The disadvantage of heavy wear and tear, which appears when this system is used in turbine pumps, is certainly very much less serious when atmospheric air is dealt with. Never- theless, there is a certain loss due to the formation of vortices in the cells of the impeller where the air is confined by a rotating disc on one side and an immovable casing on the other side, and this defect is unavoidable in this otherwise excellent balancing system. ‘“‘Balancing by Balancing Piston.—The design which is now prac- tically standard, Fig. 100, is characterized by a continuous flow of air through the impellers on one direction, while the consequent axial thrust is reduced by other means. ‘“‘Beyond the last stage there is fixed on the shaft a piston which is of the same diameter as the entrance of the impellers and extends as far as possible axially. It revolves with a very small clearance in a box containing a labyrinth, such as that described above. “‘One side of this piston is under the full pressure of the last stage, the other side being connected by a large pipe to the entrance cham- ber. The effort which the pressures of all the stages exert on the piston area is thus equal to the effort which the pressures of the single stages altogether exert on the single impellers, and as the two forces act in» opposite directions the balance is perfect. Here again is another reason for limiting the number of stages that may be coupled together in a single casing, for although it is possible normally to keep the losses caused by the balancing piston of a blower within limits of 1 per cent., this would not be possible if the pressure differences were as great as 50 lb. or perhaps 100 lb. per square inch. “‘Stuffing-boxes.—The problem of a reliable, tight stuffing-box, which is so difficult in the design of turbo-pumps, can be most per- fectly and easily solved in the turbo-compressor. The first group of a compressor, or the whole of any blower which is of the piston- balance type just described, needs, we might say, no stuffing-box at all, as both free ends of the machine are under atmospheric pres- sure, and if air should be sucked in around the shafts, no harm would be done, as air is just what the blower requires; only in cases where the blower has to deal with very poisonous or valuable gases would it be necessary to provide a special packing. In all the following casings (that is, in casings containing the high-pressure groups), stuffing-boxes may be wholly dispensed with by using a fully capped bearing, as in Fig. 92. The probability of water mixing with the oil would, of course, forbid this design with any good centrifugal pump or water turbine.” 124 AIR COMPRESSION AND TRANSMISSION “Figure ror shows test curves taken during the practical operation of one of the latest turbine blowers supplied by C. H. Jaeger & Co. to the Grillo Zinc Works, Ltd., Hamborn on the Rhine. The curves show the relation between pressure, power absorbed by the blower spindle, efficiency, and duty at constant running speed. The pressure, horse-power, and efficiency, are ordinates over the respective duties as abscisse, in like manner to that followed in making these curves for turbine pumps. It is easily seen that over a fairly wide range the pressure and efficiency remain nearly constant, and the regulation of the capacity can therefore be made by simply throttling down the surplus quantity. The speed of revolution need not be altered, and alternating-current motors oran exhaust-steam turbine may readily be used for driving these blowers in their simplest form. m.m. Water Column B.H.P. os +H | Ane ae a ee ES ho 100 2800 / pressuce eae as l eee ste Hee 52000 i Sar | | TT 10 a: pee -T IA Alea ae 1600 80 A ae aS Y 5 [Le A ipameceae || 508 200 60 ae" ! Lap. S | (S) [ame SU 400 dear BLL N Md g00 “i4q} Lo es = eae ne ST | | Nie 2 400 520 | EA ree 5 yre behing the Blower a ee 10 5 eZ Laessure penis MTT Uh 0 10 2 30 40 50 6 7 8&8 9% 100 {10 (20 120 40 -Quantity Sucked Fic. to1.—Test curves, Jaeger’s turbo-blower. ‘Coupling Compressors.—In some cases, as, for instance, in blast furnaces, it may be necessary to generate an extra high pres- sure for short periods. Such necessities may arise, for example, if the resistance of the air nozzles or of the column of melting ore is increased. The centrifugal blower running at constant speed would not be able to drive the air through the mains at a pressure much higher than normal. If, therefore, no means for regulating the run- ning speed are available, some airangement must be supplied such as that furnished by Sautter, Harle and Cie, to the iron works at Chasse. Fig. 102 shows how coupling either in parallel or in series is combined with perfect balancing of the impellers. ‘Although coupling the stages alternately either in parallel or in series permits us either to deliver a la1ge quantity at normal pressure or a reduced quantity at double that pressure, this mode of regula- TURBO-COMPRESSORS 125 tion is unsuited to a great many cases. For instance, in the majority of chemical processes, the delivery of constant volumes of gas is necessary for the economical working of the process and the uniform quality of the product. One of the best known of these processes is the melting of pig iron in the cupola. The problem of delivering Fic. 102.—Arrangements for coupling turbo blowers. the constant volume against varying head can be solved only by using varying speeds, but under this condition it can be solved by the turbo-blower with almost unexcelled exactness. The means by which this is effected is an apparatus which has been called by its inventor, Prof. Rateau, the ‘Multiplicator.’ “Rateau Multiplicator—tFig. 103 shows a cross-section of the Multiplicator as applied in the well-known turbo-blower plant at ‘Fic. 103.—Rateau multiplicator. Rothe Erde. The principle is the same as that of the Venturi water meter; that is, by tapering a pipe the velocity with which the gas passes through it is increased as the diameter is narrowed. As no addition or subtraction of energy is made during the passage of gas through the pipe, any increase of velocity must be accompanied by a decrease of static pressure. Ifthe air be tapped from the narrow- est and widest points of the tapered pipe, and the tapping pipes be led to opposite sides of a movable piston, it is clear that the difference in static pressure on the two sides of the piston will either move that piston or exert a certain effort on the piston-rod. 126 AIR COMPRESSION AND TRANSMISSION “The greater the reduction of cross-section in the tapered pipe is made, the greater becomes the effect exerted through the piston- rod, and the greater also becomes the variation in that effort caused by any increase or reduction of velocity in the main; that is, of the quantity passing through this main per second. ‘Therefore, to obtain a very sensitive piece of apparatus powerful enough to move a governor gearing when the variation in the delivery is © but 1 or 2 per cent., it would be necessary to make such a great difference of cross-sectional area that the resistance of the mains would be considerably increased by the throttling effect of the taper. == x : ead £ = S 8 Et Ny S C= ry ce 3 & Regulating _% Throttle Valve. 7 a) N , TZLILL ¢ Ngo oe Fic. 104.—Piston controlled by Fic. tos.—Connection between piston multiplicator. and regulators. “Here the ingenuity of Prof. Rateau’s method appears. He tapers the main but very slightly and inserts at the narrowest end a system of pipes as shown in Fig. 103. At the point a the static pressure is already reduced somewhat below that in the normal pressure main. At the point 6 the pressuie of the small quantity tapped off at a is again decreased. Finally, the static pressure at c is in turn much lower than at 6. The effect of this arrangement is so great that with a velocity of 60 ft. per second in the mains, the difference of static pressure between a and c was about 6 in. of mercury, while the loss occasioned by the whole installation was at the same moment not mote than 3/8 in. of water column. By put- ting the two ends of the cylinder A, Fig. 104, in connection with the narrowest and widest points of the tapered piping system, a consid- TURBO-COMPRESSORS | 127 erable force can be exerted on the spring B. It can easily be cal- culated that a difference of 2 1/2 lb. in total pressure is generated by a variation of about 1 per cent. in the velocity of the air current passing through the mains; that is, when the quantity delivered by the blower varies by about 1 per cent., a force of about 2 1/2 Ib. becomes available for moving the regulator. “Figure 105 gives an idea of the manner in which the gearing was arranged in a special case. The speed regulator and regulating throttle valve of a Parsons steam turbine were influenced simulta- neously. In like manner the regulating lever of any driving electric motor can be moved in exact proportion to the momentum of the air piston, as shown in Fig. 103. ‘It is very interesting to see how this achievement enabled turbo- blowers of the Rateau system to create an entirely new field for them- selves. One of the licensees of Prof. Rateau, the machine-manu- facturing establishment of Kuehnle, Kopp & Kauschat Frankenthal, delivered some turbo-blowers for the Anilin and Soda Factory at Baden for the purpose of blowing air through the electric arc in the newly invented process of obtaining nitric acid directly from the at- mosphere. These turbo-blowels were to replace reciprocating blow- ers, which had caused great trouble and expense. It was necessary to connect them with a very large air-tank in order to produce reason- able steadiness of the air current, and when inspection of the recipro- cating blowers was necessary, it was impossible except by the skill of very experienced mechanics, and even then only with the greatest risk, to take one of the blowers out of service and at the same time start ancther without interfering with the continuous current of air. The turbine-blower not only gave an absolutely continuous air current, but proved so safe in operation that no change of blowers was needed during the entire process, which generally lasts uninter- ruptedly for several months. “Mixing Blower.—This extraordinary success of the turbo- blower impelled the Badische Anilin and Soda Fabiik to order fiom Kuehnle, Kopp & Kausch another kind of turbo-machine— that is, a mixing blower, which is shown in Fig. 106. Two different gases ale drawn by different sets of impellers, keyed on the same shaft, and are delivered to two different delivery pipes. This alrangement has the advantage that owing to the compulsory equality of speed of both impeller groups, the relation between the quantities of the gases continuously delivered is absolutely the same (that is, it is proportionate to the cross-sections of the impellers) providing the resistance remains equal in both delivery pipes. As this last con- dition cannot be kept uniform during the chemical process, auxili- ary throttle valves are inserted in the delivery pipes and worked by two Multiplicators. These latter, after careful adjustment, 128 AIR COMPRESSION AND TRANSMISSION insure the maintenance of absolutely constant mixing rates between the two deliveries under all conditions. The makers were required to guarantee that the mixing ratio should be kept constant within a margin of 1 per cent., and their machines wete so perfectly designed iM an Ss Q Ly LY N K) k) y N) H N 4 NS el GPG Sa cS a Sy ‘ G a aT LF a 48 } J oS 5 cS vw ZZZZ csSh yy oavenh Be Cy ise i eee Fic. 107.—Rateau turbo-compressor, 140,000 cu. ft. per hour. that the Badische Anilin and Soda Fabrik at once began to develop new processes for the electric synthesis of gases, which were made possible only by the new mixing turbo-blower.” The cross-section of a Rateau Turbo-compressor of 140,000 cu. ft. per hour running at 4,600 r.p.m. is shown as Fig. 107. CHAPTER XII HYDRAULIC COMPRESSION OF AIR The method of compressing air by means of falling water, without the use of any other moving part whatever, forms one of the most interesting topics in the subject of air compression. The large installations in northern Michigan, together with the large compressors of the same type in British Columbia, Quebec and Connecticut, give some idea of the extent to which this very simple method of utilizing the energy of falling water is being ap- plied. All of these installations have been completed within very Fic. 108.—The trompe. Fic. tog.—Frizell’s hydraulic compressor. SNe recent years and their success gives promise of many more such plants being planned. Trompe.—One of the oldest forms of compressing air is by means of a trompe or water bellows, a device of historic interest, in which water was lead from a higher to a lower level through a pipe or bam- boo pole with openings in the side through which air entered and mingled with the descending water and was later trapped from it, as shown in Fig. 108, for use in forges. A great many impovements have been made on this aan ap- paratus and quite distinct types developed from it. Frizell’s Compressor.—One of these is shown in Fig. 109, the invention of J. P. Frizell of Boston, Massachusetts. This device utilizes an inverted syphon having a horizontal passage C between 9 129 130 AIR COMPRESSION AND TRANSMISSION the two legs, Band. A stream of water is led into the upper end of the longer leg B and at the top of the horizontal passage C’ be- tween the two legs of the syphon, an enlarged chamber, D, is con- structed in which the air separates from the water. The water freed from the air passes up the shorter leg, F, of the syphon to the tail race. The pressure of air accumulating in the chamber is determined by the height of water in the shorter leg. This application of carrying upward the water after the air is separated from it seems to have been original with Mr. Frizell, and in this respect his device differs from the old trompe. Mr. Frizell made two working models of this type of apparatus. In the first one, the legs of the syphon were 3 in. in diameter, the head of water being 25 in. and an efficiency of 26 1/2 per cent. was obtained. A larger apparatus was then constructed at the Falls of St. Anthony on the Mississippi River a few miles above St. Paul; the longer leg of the syphon in this plant was 15 X30 in. and the shorter leg of the syphon 24X48 in. in section; the height of water above the air chamber was 29 ft. The head in feet varied from 0.98 to 5.02; the first head being just sufficient to cause a flow through the pipes. With the working head changed from 2.54 ft. to 5.02 ft., the efficiency varied from 40.4 per-cent. to 50.7 per cent., the quantity of water in these cases varying from 5.92 to 11.89 cu. ft. per second. Mr. Frizell estimates from the experiments he has made that with a shaft ro ft. in diameter, a depth of 120 ft. and a fall of 15 ft., the efficiency would be 76 per cent.; and with a head of 30 ft. and a fall of 230 ft. the efficiency would be 81 per cent. Mr. Frizell’s first experiments involved a large outlay in cost of plant and were not entirely satisfactory; but where there is a mod- erate water fall and plenty of water, this is no doubt a very simple method of compressing air. This system is applicable to either high or low falls and although no installations of this type of air compressors were made until a number of years after Mr. Frizell’s patents were obtained, the fact that he is the pioneer in this line entitles him to a great deal of credit. | The following explanation of this system is taken from The Railway and Engineering Review, Sept. 17, 1898. “The general principles underlying this method of compression is familiar to most in one form or another. For instance, it is well known how readily water breaks into foam, which is due to its being HYDRAULIC COMPRESSION OF AIR 131 impregnated with airin minute bubbles. Since bubbles rise in water at a velocity depending on the size of the bubble, it is obvious that air drawn into a current of water moving downward with a velocity in excess of that at which the bubbles rise will be carried down and subjected to a pressure corresponding to the depth attained, and moreover the compression will take place isothermally, a process which is not accomplished by any method of piston compression. If the direction of the water be then altered to a horizontal one, the air will rise in a few seconds to the top of the passage and accumulate in a suitable chamber under the desired pressure. The length of the horizontal tunnel will be controlled by the necessity of placing the entrance to the air chamber far enough from the descending branch to admit of the complete escape of the air bubbles. ‘‘A method of introducing air into the descending column of water is to surround the shaft with a bulkhead of masonry, over which Fic. t10.—Syphon bulkhead. the water is led in a covered channel, the bottom of which rises a little above the highest level of the water. This forms a syphon as shown in Fig. r1o. ‘“‘At the point A the pressure within the syphon is less than that of the external air, and the latter will flow in through any opening. This is evident, because the flow of water depends upon the syphon principle. This space A extends around the masonry bulkhead and is in communication with the atmosphere. It is also connected with a pump for the purpose of removing any water that may collect in it, the amount of air being regulated by opening or closing holes in chamber A.” Baloche and Krahnass Compressor.—Another device, shown in Fig. rrr, differs somewhat from that of Mr. Frizell. It was invented by A. Baloche and A. Krahnass in 1885 and consisted of a syphon, B, carrying water from an upper to a lower reservoir, the lower end of the syphon being projected through an inverted vessel, R, placed nearly at the bottom of the second reservoir. Just beyond the bend 132 AIR COMPRESSION AND TRANSMISSION in the syphon and in line with the axis of its longer leg, an air pipe, T, projected into the descending leg of the syphon. This entrained the air with the descending column and carried it down into the in- verted chamber, R, from which the air escaped at the top, while the water passed out from the bottom into the lower reservoir. This apparatus produced pressure on the air in the top of the inverted chamber due to the height of the water column upon it. Arthur Compressor.—Another device, shown in Fig. 112, patented by Thomas Arthur in 1888, differs from the last in having a stream Fic. 111.—Baloche and Krah- Fic. 112.—Arthur’s hydraulic com- nass’s hydraulic compressor. pressor. of water led directly into the top of the vertical pipe A. Inserted into the mouth of this pipe is a double cylindrical cone, C, forming an annular air passage between it and the walls of the pipe A. Owing to the increase in the velocity of the water passing through the nar- row throat of the double cone, air is inhaled through the pipe D, through the annular space mentioned and through perforations in the lower cone and is entrained with the falling water. Through the down-flow pipe A rises a vertical delivery pipe, Z, for the compressed air, having its lower end, H, enlarged and open at the bottom. Projecting upward into this enlarged air-delivery pipe is a water escape pipe, /, through which the water passes after parting with the air. The escape pipe is in the form of an inverted syphon and maintains on the air in the delivery pipe Z a pressure due to the elevation of the water at the discharge point above the air line in the large end of the delivery pipe. HYDRAULIC COMPRESSION OF AIR 133 Taylor Compressor.—The hydraulic compressor system of Mr. Taylor is shown by Fig. 113. The large recent installations referred to are principally based upon his patents. With Taylor’s system a series of small air pipes placed vertically in the upper end of the falling column of water introduce the air into the water. The compressed air and water are separated at the bottom of the shaft. Mr. Taylor seems to have been the first to introduce the plan of dividing the air inlets into a great number of small openings evenly distributed over the area of the water inlet. Fic. 113.—Taylor’s hydraulic compressor. In the figure shown, these air tubes are represented at C, all terminating at the conical entrance B to the down-flow pipe H. The water supply is furnished to this down-flow pipe through a flume D. As the water falls it draws air through the small tubes, carrying it down to the separating tank G, where it is liberated at a pressure depending on the weight of the water in the vertical pipe Z. The compressed air is then conducted through the pipe K to the place to be used. The distance from M to the tail race L represents the height or fall of water that is available. Taylor at first seems to have attempted to utilize centrifugal action in causing the separation of the air and water in the large chamber at the bottom, but afterward abandoned this scheme and ‘used instead forms of deflector plates in combination with a gradu- ally enlarging section of the lower end of the down-flow column in 134 AIR COMPRESSION AND TRANSMISSION order to decrease the velocity of the air and water and cause the water to part more readily from the air. The position of the hopper or frame carrying the air inlet tubes regulates the amount of water that is admitted to the vertical pipe. The quantity of air regulates itself and is neither more nor less than the given quantity of water can carry. If the descending column is so loaded with air that it does not preponderate sufficiently over the ascending column, the water in the former will rise, the commotion will diminish and less water will enter. In the contrary case the water falls, commotion increases and more air is taken in. ; Taylor Compressor at Magog, Quebec.—The first one of these com- pressors on the Taylor principle was installed at Magog, Quebec, to furnish power for the print works of the Dominion Cotton Mills Company. The head of water is 22 ft., the down-flow pipe is 44 in. in diameter and extends downward through a vertical shaft ro ft. in section and 128 ft. deep. At the bottom of the shaft the com- pressor pipe enters a large tank 17 ft. in diameter and tro ft. high, which is known as the air chamber and separator. A series of very careful experiments have been conducted at the Magog plant by Professor Kennedy and others; and it has been demonstrated that with a head of 19 1/2 ft. of water using 4,292 cu. ft. of water per minute, the equivalent of 1,148 cu. ft. of free air per minute was recovered at a pressure of 53.3 lb. showing that of a gross horse-power of 158.1, 117.7 h.p. of effective work was used in compressing air, giving an efficiency of 71 per cent. which is very satisfactory. _This compressed air was then used in an old Corliss engine, with- out changing the valve gear in any way from what it was when adjusted for steam, and 81 h.p. was recovered, showing a total of work recovered from the falling water of 51.2 per cent. When the compressed air was heated to 276° before being used in the engine, 11m h.p. was recovered. The heating required 115 lb. of coke per hour, equal to about 23 h.p. The efficiency, therefore, including the falling water and the fuel consumed, was 61 1/2 per cent. It has been calculated from other experiments that if the compressed air had been heated to 300° the total efficiency secured would have been 87 1/2 per cent. When it is considered that a good water turbine will give an eff- ciency of 85 per cent. and that part of the power developed in , the turbine will be lost through transmission before the power is available, it is evident that this system is a very efficient method HVDRAULIC COMPRESSION OF AIR 135 of generating and transmitting power. For if the efficiency of the turbine is 85 per cent. and that of the system that is used for con- verting the power in the turbine into a more.available form 80 per cent., the total efficiency of the system will be 0.80X0.85 or 68 per cent. This shows the immense importance of this device. Its field of usefulness is certainly a large one. Taylor Compressor at Ainsworth, B. C.—Figure 114 illustrates a sketch of the upper part of the Taylor Hydraulic compressing plant at Ainsworth, B. C., which is < A é 6 q ——oF quite unique in that it did not re- ) AT quire the sinking of a very deep B i B shaft. Theapparatusis constructed aAadianng against the vertical wall of the canyon in the rugged mountain dis- trict in which it was built. The plant is located on Coffee Creek to the south of Ainsworth and about 2 1/2 miles from the principal mines to which it supplies compressed air. ‘The creek has a flow varying from 2,500 cu. ft. per minute to several thousand, and the flume used is stave barrel construction, round steel bands being bolted around it every at... Phe wtilume? is 17250711, in length, 5 ft. in diameter in the clear, the available head at the compressor being 107 1/2 ft. The water at the compressor tower is received in a wooden tank 12 ft. in diameter and 20 ft. in height. A down-flow pipe passes from the water level through the bottom of this tank down perpendic- ularly and at the creek level a shaft extends to a depth of 210 ft., making a total vertical height to the shaft of over 300 ft. This down-flow pipe, which is 2 ft. 9 in. in diameter outside, is also of stave construction throughout, the bands being placed from 6 in. to 3 ft. apart, depending on the pressure to which a particular section is subjected. This terminates in a great bell-shaped chamber at the bottom of the shaft 17 ft. in diameter and 17 ft. high, the bottom of this chamber being about 2 ft. above the bottom of the shaft, thus allow- Fic. 114.—Taylor’s compressor at Ainsworth, B. C. 136 AIR COMPRESSION AND TRANSMISSION ing the water to pass out and up the shaft to the tail race. A deep circular groove was dug in the bottom of the shaft to aid in separating the air from the water. As the distance from the water level of the air chamber to the tail race is about 200 ft., the pressure on the air is about 87 lb. per square inch. The air is conducted from-the compressor through a g-in. pipe which supplies compressed air through several branches to over I5 mining properties. The total length of pipe is over 2 miles. A pipe reaches from the surface of the creek level—that is, the tail race—to the dividing line between the air and water of the large chamber at the bottom; so that if more air is being compressed than is being used, the water line in this chamber will be lowered and the surplus air escape, while if the pressure of air falls, the escape pipe will be closed. The actual effective head of water in the apparatus is 107 1/2 ft. and if a turbine had been used, with an efficiency of 75 per cent. the available horse-power generated would amount to 620. This installation has cost in the neighborhood of $60,000, including incorporation, water-power, development and pipe line. Of this investment, $20,000 will cover the pipe-line cost, $10,000 the water- power improvements, and $30,000 the compressor cost. This last item was unusually high because. of the extremely hard founda- tion through which the shaft was sunk. Taylor Compressor at Victoria Mine, Mich.—In 1906 a large plant of this type was installed at Victoria Copper Mine near Rock- land, Ontonagon County, Michigan, which consisted of three com- pressing units with a total capacity of from 34,000 to 36,000 cu. ft. of free air per minute. A series of tests made on a single intake head by Prof. F. W. Sperr, gave the following results: TABLE X.—AIR MEASUREMENTS : , Absolute pressures Velocity | Cubic feet |_ Square feet feet per per area 3 Free air, | Compressed second minute : pounds | air, pounds Horse-power 4 44.09 10,580 14 128 1,430 49.74 11,930 14 128 T,627 4 38.50 9,238 14 128 1,248 aN HYDRAULIC COMPRESSION OF AIR 137 TABLE XI.—WATER MEASUREMENTS Mune Velocity | Cubic feet Bibcen cr: feet per per Head, feet | Horse-power area : per cent. second minute 71.75 3-933 13,057 79.5 1,741 82.17 67.03 3.684 14,820 70.0 1,961 82.27 7210 2.936 12,710 70.6 1,700 7350 Phenomena of Hydraulic Air Compression.—There are several phenomena in connection with this method of compressing air that at first thought seem paradoxial. In compressing air by hydraulic means, the air becomes drier during the compression, but no matter what may be its initial condition as to humidity at the end of compression it will, in all probability, be saturated with moisture. Air almost always contains moisture. Its capacity for moisture is determined by the combined conditions of pressure and tempera- ture to which it is at the time subjected. Changes, either of pressure or of temperature, immediately change the capacity of air for water, and if the free air is saturated with moisture its capacity for water will be reduced whenever the pres- sure is increased or the temperature decreased, and in consequence water will be precipitated. When air is compressed by hydraulic means, isothermal com- pression is secured and, generally speaking, at uniform temperature a given volume of air implies a capacity for a certain weight of water whether the air is at a pressure of one or one hundred at- mospheres, but if the air is compressed through a range from 1 to too atmospheres, its volume will be reduced, if the compression is isothermal, to 1/100 the original volume, and in consequence 99/toc of the weight of moisture it originally held will be precipi- tated. The air is still saturated, but the total weight of water held in suspension has been reduced. That is, this method of com- pression has reduced the weight of moisture present in the air and hence dried it, but at the end of compression the air is saturated with moisture. Another interesting phenomenon in connection with this type of compressor has recently been brought to light. It has been found that air compressed by this method contains less oxygen than free 138 AIR COMPRESSION AND TRANSMISSION air of the atmosphere and in consequence its use in mines is not as beneficial as air from other types of compressors. It will be observed that, with this construction, the material used for the down-flow pipe need only be of sufficient strength to carry the weight of water and pressure generated in the working head of the water-power, as once it reaches the tail race level the internal pressure is gradually neutralized from that point down by the pres- sure in the return water surrounding the down-flow pipe; so that any pressure almost may be reached without increasing the strength of the down-flow pipe. The material for the down-flow pipe may be iron or wood hooped with iron, and the shaft may be constructed of inexpensive timber as it is preserved by being constantly in the water. By this method, low falls, otherwise useless, are made available and the same pressures can be obtained as from high falls, the horse- power being determined by the diameter of the down-flow pipe, and the height and volume of water in fall, while the pressure depends solely upon the depth of the well or shaft; therefore, any desired pressure can be obtained. Briefly stated, the air is compressed by the direct pressure of falling water without the aid of any moving mechanism and prac- tically without expense for maintenance or attendance after instal- lation. By this system any fall of water varying in working head may be utilized, any pressure required can be produced and uniformly maintained up to the capacity of the water-power, delivering the compressed air at the temperature of the water. This drying of the air and the fact that practically isothermal compression is secured, form the great advantages of this system of air compression. ‘The initial cost need not be excessive, and as the cost of attendance is slight, for certain purposes the method is ideal. Its field of operation is quite broad, as a high fall of water is not essential, for any desired pressure can be obtained from any fall, the capacity being determined by the power available in the water fall. Losses of Hydraulic Compression.—The losses inherent in this method of compression are: (1) The head expended in impregnating the water with air. This usually amounts to about 1 ft. (2) A loss which may be called the slip due to the velocity with which the bubbles tend to rise. It is obvious that the rise of bubbles during the decent of the water is a lost motion which deducts from HYDRAULIC COMPRESSION OF AIR 139 the efficiency of the system and in addition there is a head con- sumed in friction. (3) A loss due to the increasing solution of the air in the water with the increasing pressure as the water and air descend. This air does not separate from the water in the lower chamber but is eliminated in the ascending shaft in the same order that it is dissolved in the descending shaft. The escaping air in the ascending shaft aids the movement of the water and this partly balances the loss in the descending column. There are on the market to-day small hydraulic air compressors for furnishing compressed air in small quantities for dental and other purposes. They can be operated by water pressure from any water- works supply and on this account are particularly adapted for such purposes. CHAPTER XIII EFFECT OF ALTITUDE AND COMPRESSOR TESTS! As the density of the atmosphere decreases with the altitude, a compressor located at a high altitude will take in a smaller weight of air at each stroke, that is, if the compressor is located at a high altitude, the air is taken in at a lower pressure and in consequence the early part of the compression stroke is occupied in compressing the air from this lower density up to a standard atmospheric pressure at the sea-level. The reduction of pressure at the inlet would, of course, affect the power expended in compressing the air, but the decrease in power required does not vary in the same ratio as the decrease in capacity. For this reason compressors to be used at high altitudes should have the steam and air cylinders properly . proportioned to meet the varying conditions at different levels. Effect of Altitude on Capacity.—This matter is of special im- portance in connection with mining operations, because of the large number of mines situated in elevated mountain regions. The rated capacities of compressors, in cubic feet of air, as given in the makers’ catalogues, are for work at normal atmospheric pressure, and due allowance must be made for decreased output at elevations above sea-level. This reduction in output, which is usually also tabulated in handbooks and catalogues, should receive due consideration in order to avoid serious errors. For example, the volume of compressed air delivered at 60-lb. pressure, at 10,000 ft. elevation is only 72.7 per cent. of the volume delivered at the same pressure by the same compressor at sea-level. In other words, a compressor which at sea-level will supply power for 1o rock-drills, will at an elevation of 10,000 ft. furnish air for only 7 drills. Effect of Altitude on Power.—The foregoing statement relates only to the volumetric capacity of the compressor. It must be re- membered that the heat of compression increases with the ratio of the final absolute pressure to the initial absolute pressure. As this ratio increases with the altitude, more heat will be generated by compres- sion to a given pressure at high altitudes than at sea-level. This additional heat temporarily increases the pressure of the air in the cylinder while under compression, and more power is therefore re- 1Peele, Compressed Air Plant. 140 HHPECIOCOFr ALTITUDE AND. COMPRESSOR TESTS ~ 141 quired to compress and deliver a given quantity of air. The cor- responding loss of work, due to the subsequent cooling of the air in receiver and piping, also increases with the altitude. Relation between Altitude and Volume.—Contrary to a common impression, the volume of air delivered by a given compressor does not bear a constant ratio to the barometric pressure, but at different altitudes this volume decreases slower than the barometric pressure. This relation may be shown as follows: Two ideal indicator cards are represented in Fig. 115, one of a compressor working at sea-level with = _ -—- =<- “= oa” 4 Ce P. P. —----—— eth eet be as ee 1 ' | { t t 1 f < 4 re , | | 1 Fic. 115.—Effect of altitude. an initial pressure Py, the other at an altitude with a lower initial pressure P2. The initial volume V and the final gage pressure P are the same for both compressors, P3 and P, being the respective final absolute pressures. V1 and Ve are the final volumes, corre- sponding to the dotted isothermal curves, these volumes being taken as the basis because they are those to which the compressed air will eventually shrink on losing the heat of compression. From the theory of air compression, VAeP VP\—= Vik; or Wire, (1) Vee: and VPo=VoPa, or V7, (2) But since P3=P,+P, and Ps=P2+P, equations (1) and (2) may be written: ary Cae if je (3) and is ena. i (4) 142 AIR COMPRESSION AND TRANSMISSION Dividing equation (3) by equation (4) li i+ Vogue 1 F Bae i : ge ae po Vie Vee ioe pease (5) ari This gives an expression for the ratio between pressure and volume at sea-level and for any altitude above sea-level, of which the corre- sponding barometric pressure isP2. Thus, let Pps=10lb.,P=golb., and V;=0.1404 cu. ft. By substituting these quantities in equa- tion (5), V2 is found to be 0.0999, or approximately o.1 cu. ft. In Table XII, columns 4 and 5, are given the relative volumetric © outputs, at gage pressures of 70 and go lb. of a compressor working at different altitudes, the figures being percentages of the normal output at sea-level. These percentages have been derived by Mr. F. A. Halsey from equation (5), a constant loss of initial pressure of c.75 lb. being assumed to allow for the resistance presented by the inlet valves, to which reference has been made in another chapter. That is, for practical purposes the sea-level atmospheric pressure is taken as 14, instead of 14.7 lb. The other columns show the mean effective pressures and indicated horse-powers, corresponding to different altitudes, up to 15,000 ft., which will be found convenient for reference. It should be noted from the figures in columns 4 and 5, which are for the ordinary range of pressure employed in mining, that, though there is a difference of 20 lb. between the two gage pressures, yet the outputs at different altitudes vary only by a few thousandths and may often be neglected.! Wide differences, however, occur in the columns of mean effective pressures and horse-powers. Owing to the increase of piston displacement per indicated horse-power, as shown in columns 8 and 9 of the table, some builders make the air cylinders of compressors for mountain work of larger diameter for the same size of steam cylinder than those for sea-level service. As against the losses of the air end of the compressor at high altitudes, there is some gain in mean effective pressure of the steam cylinders, because the exhaust takes place against lower atmospheric pressure. The same is true in part of the air exhaust of machines using the compressed air. But the 1 Attention may be called to the fact that for this reason, in compressor- builders’ catalogues, no account is taken of the gage pressures in tables of compressor capacities at altitudes. EFFECT OF ALTITUDE AND COMPRESSOR TESTS 148 resultant of these gains is small and cannot be given much weight in offsetting the losses. TABLE XII . ‘ f , Barometric poke eee Cubic feet Pressure pistons compressed .7 Relative out-| M.E.P. for placement : ene : ce. oi air per indicated put for gage gage pres- per indicated horse-power Altitude, pressure sure horse-power foreraze feet Pounds for gage Taches ve préséitre pressure mer- square cury ach : 7.OnlDeiLOOm Delle Onl Den OO; bs 1770: 1bn00) Lbs 1.70 1b. | 90 1b. I 2 3 4 5 6 i. 8 9 Io II fo) 30.00 17 5S OOO LE NOOOU Sale So Neal OOS 5,00 et. LAAN On sor I,000 28.88 Te? ONO TOO 7aLOR OOO IES 2e Ollme 37> Olle yn O3 ale O,. 00m i. k23 nl cOm7 a7 2,000 27.80 TA OVMMOMOS Su LOTOS ses 2a. MesOnOM) 7S Os2On) ele Toss OL773 3,000 26.76 U3 eLOe | OFOOA LO ROOOH EST a Sle 3053) I) Feo 71, Oc ZT Hl T.O84) 190.7750 4,000) 25.76 T22O7MOnS (nO eCOON, GEeO leas eOmle7 43004) Oo4 30 2. O05 a) 0.740 5,000 24.79 P22 OMNLOMGAG HOSS Ones On5 ues 5 Omiya 5 Loos 55 aie BOAO) Pron 733 6,000 23.86 Tey Ga ROMO Css LOMmOO Olle OOM s Aisin OS) al. Or. Oil ate O26) \kOe 720 7,000 22.97 Dees On One Sun Ole OON ee Oud aime 37 lee 1S Onl O47 ON ie ON Le sOn 70'S 8,000 PAP) Su TOMS 7 OMT SOULOM 7S Lm2o Oma sa ale 704 O02 OL OOd i) On005 9,000 PA PAO, LOMAOM MOR 72 TMPOM 7232 Seow S2n Silo 5OOMs 7: OONl O1O76 ale 0.083 I0,000 20.49 TORO 7a OMT OSL OnOOO! E276 5. lest Sil (Oo 224 071.204) OLOSOMI T0070 II,000 Lon 72 On OmmFOF OSOML ORO Mae 2 7 Amie Gl so 3O ls 7134 aOLOAZE I O2058 I2,000 18.98 Onset LO sO5010 50473 |620,.0)1 30.0.9) 8554 107240, 1) 0.025 5) 0.046 13,000 Qua] SAOSMLOVOS2IOmO 232003 sO MOMS. 7k wn OAM OOO Ga 1041035 I4,000 D750 865 04008) 02.000)) 25q8 e204 oe S58) 7.800) On8Org 02624 15,000 16.93 SES 2 MOMS osNLOM S57 OlmMe Se sale COOL OOM: 7 (OO O.o 75 moe OLS The relation between compressor output and barometric pressure may be expressed simply in another way. Take the case of two compressors of the same size, one operating under an atmospheric pressure of, say, 14 Ib. and the othe at 10 lb. (corresponding approxi- mately to an altitude of 10,000 ft.). If the first compressor is producing 6 compressions, the final absolute pressure will be 146 = 84 lb. or about 70 lb. gage pressure. To produce the same gage pressure, the other compressor must work to an absolute pressure of 7o+10=80 lb., the number of compressions corresponding to ep ibe 2 which is ert From each cubic foot of free air the compressor will produce 1/6 of a cu. ft. of compressed air, and the second complessor, 1/8 cu. ft. Hence, the ratio of the respective outputs of the two compressors will be 1/8+1/6=3/4 or 0.750. As com- 144 AIR COMPRESSION AND TRANSMISSION pared with this, the ratio of the respective barometric pressures 5 10 iS ade COMPRESSOR TESTS To indicate the observations required to secure the data for the complete test of a compressor, together with the deductions from the observed data, the following record of the test of a com- pound, two-stage Nordberg compressor, at the mines of the Tennes- see Copper Co., will be found useful.’ It will be noted that items 28, 29 and 32 to 35 are necessary in this case, because the boiler plant supplied steam for the hoisting engine and an independent condenser, as well as for the compressor. Though the hoist was not running, steam was passing continuously to the jackets of the cylinders. The same conditions would often be met in other tests. The boiler-feed water was taken from a wooden tank, and during the run this water was supplied from two barrels on scales set temporarily over the tank. The water of condensation from steam jackets and reheater was drawn off continuously and also weighed. The calorimeter tests were made with a Peabody throttling calori- meter. Eight sets of indicator cards were taken during the 8-hour test, at hourly intervals. ITEMS OF COMPRESSOR TEST Altitude, 1,800 feet 1. Date of test, February 16, 1902. 2. Dutation of.test. hours<,6) a 8 3. Diameter of high-pressure Sank (aindee (steam jacketed); inches im wen ee eee 14 4. Diameter of low-pressure steam cylinder (steam, jacketed), inches.) v)j.s.42 4am. 28 5. Diameter of low-pressure air cylinder, inches... 24 1/2 6. Diameter of high-pressure air cylinder, inches. 15 3/8 7estroke ol allpistons, Inehesa 4. ase eae ee 42 8, Diameteriol piston-rods mechanical efficiency to have been 76.5 per cent. ‘The theoretical horse-power required to compress isothermally 1 cu. ft. of free air per minute to 96 lb. (the average pressure) isc.129. The theoretical HEP ECT OF ALTITUDE AND COMPRESSOR TESTS 151 useful work done by the compressor is, therefore, 758 X0.129 or 97.8, and the net total efficiency of the compressor is 97.8-+161 or 60.8 per cent. The cost data were furnished by the owner and are based on one year’s operation. In Fig. 118 these costs are plotted, showing how the cost per steam horse-power, per year is affected by the $0 i plea ep Nea SNCS Goooeeeeee EN Saale beets tas pam melanie taal eal Magee menienal ik ied eesti ri elie roa ees estan Poe | Sh ele FUG a ait Smo e les iaia ue SS CEA ee a on Se eeeeee res mises 1a a Stl Recieve: ac ela RRA REM 2 ail Mieisiehs elalelshlal Se lise: Remmi alsin SHER Ft eu ia Baer DEL Beaeld seroeiile lab ieee ia ies Melosh | abd Song Taam i Hloe a oP ST iia is ce Pe InP JN fafa a eae a ae IT esa Lo | R. pM. > Fic. 119.—Test results of compressor plant No. 1. average running speed of the compressor. The curve of Fig. 119 shows the operating costs in another way. ‘These costs may be read in terms of 1,000 cu. ft. of free air compressed to too |b. or 1,000 cu. ft. of compressed air at too lb. gage pressure. Test of Plant Number Two.—The plant consisted of three 150 h.p. return tubular boilers, supplying steam for a Corliss engine, 152 AIR COMPRESSION AND TRANSMISSION the air compressor, and steam heating. To determine the boiler horse-power, a meter was placed on the steam-pipe to the compressor during the test run, so that only the portion of steam actually used by the compressor was charged to the same. The compressor was duplex, with Meyer valve gear, simple steam cylinders 14X22 in. real ats ee | | a pe of TT A a ce a A STA an ie a] ee | ea BB 02 oo wo EEA g A 5 0g TSE 4 caer: A A A 81s le 1 a lays relies oe in EE AAD, ail 2 BURN a bales i MPV per x 5 x - 4 fe 70 e a HEME BAVOGGn ears BG MOO Anime. i.e RIGA SIRE, a HOPE He tat h/ 3 IM WAU/ ApS Cle E ee). in Bar 30 100 20 0 0 20 40 60 80 100 ~=3=—-:120 R. p.M. Fic. 120.—Test results of compressor plant No. 2. and two-stage air end, 14 and 22 X22-in. stroke, rated by the manu- facturer at 1,050 cu. ft. of free air per minute at 105 revolutions. At this plant the test lasted over a month, with the following results: EFFECT OF ALTITUDE AND COMPRESSOR TESTS 153 otal coal consumed apounds.. NIC e ANG eee ee : ACO Ce ao ae E aaah e GRanee cnn dea > ena | pel a eilghel Serta iat) adit a bess Chad OE ia) Be Wa S2S0RR an eo Les Siete = LS De aes es : Cease 5 aba Ca a el ae a a ex eesti ee Ves ees = 100 a 0 10 20 30 40 50 60 70 80 90 100. R. p. M. Fic. 121.—Test results of compressor plant No. 2. Hourly readings of the revolution counter were taken, showing an average speed of 36.05 revolutions. At this speed the steam consumption was 51 lb. per indicated horse-power hour, as measured at the throttle, the air meter showing a delivery of 275 cu. ft. of free air per minute. The total efficiency was 67 per cent. Taking the ordinary method of computing the mechanical efficiency only at the same speed, there would be 48 air h.p., divided by 54 steam h.p., giving an efficiency of 89 per cent. 154 AIR COMPRESSION AND TRANSMISSION The coal consumption per indicated horse-power per year, as shown by the books of the company, amounted at the average speed to about 56 tons. Figs. 119, 120, 121, and 122 present details of the test on this plant, which was conducted similar to that on plant No. I. —152 [eg a sale 4 Ra Be KI de vali) ai PEELE EEE} VP) o i So S 7 Se S El aN IS ICS 7, SRR RA GR BRAS EAS maee Qo. = eh EERE EERE 3 rd UE EMI ASE lL 2 SSCS ese eee oO SII F i ae Sa ies eee We #2) ea aw Reo lalae ea ea BAG elaciealees alla 5 [aa ae aa | elo seein 2 oa eae BS WMEIDILI Le EE Se AY) Fic. 122.—Test results of compressor plant No. 2. Test of Plant Number Three.—This plant consisted of two 125 h.p. return tubular boilers, supplying steam for a non-condensing cross-compound air compressor of standard make; steam cylinders 18 and 35 X24 in., air cylinders 14 and 28X24 in. A two weeks’ run gave the following results: | Total-coalbutned, pounds j-\..) eee 221,190 Total fced-water, cubic feetiay a. sue nas fae 7a Total feed-waters pounds .f20.7) eee 2,094,057 Average temperature feed-water, degrees Fah- Tenhel tie. chaos cue OM Pe wih ee ar 154 EFFECT OF ALTITUDE AND COMPRESSOR TESTS 155 Average evaporation per pound coal con- SUMMER SOU Ge wager net yc ents ira ster at. wis 9.48 Avetage boiler horse-power.. 0...’ s05 fag ees 208 Average revolutions per minute: ..55 2.0. 06 cc. 66 Average indicated horse-power of steam end, at OUT DAMM aloe Cury Gy maa ons teat ok avg es 210 _ Average indicated horse-power of air end (from CULEVG) RANE eRe Ie, ore haan Naa T2005 Ayeracersteam preseureayasue nadine 22s ee eos oon 97 Average Gi Pressure sje. wet seta tae yas plas ee 07 Average outside temperature, degrees Fahren- eT teat ete Cee emer nr AE cred SM cee Lig 3 . 23 Average air piston displacement at normal SPecd cubic resteati goa Hea: af ects Wes Tey Metered output in cubic feet corrected to 70° F. 734 4 CHES EE : ae { Fig eas OE 128 8 RCT Na a Sig AN alee tl el he a 8 Baca 2 Sie %6 3 : ia : 5 0 80 me eB 2 8 — ene [as ae aSs = 5 AGES Shae ee vas Hae 32 100 Bt ES Goer 10 20 30 40 R Oe 60 10 80 90 Fic. 125.—Test results of compressor plant No. 3. mining and other work in which machine drills play an important part. These losses are always recognized as existing by compressor builders and by intelligent users, and it is clearly desirable that properly conducted tests should be made more frequently. Again, compressor plants generally develop less power than their full rated capacity. It should be remembered that an air compressor is essentially a variable speed machine, its speed being regulated by some form of throttling governor, connected with the air-pressure regulator. The machine is therefore called on to run only as fast 158 AIR COMPRESSION AND TRANSMISSION as the demand for air may require. It may be suggested that it would be well for compressor builders to give in their catalogues the actual horse-power rating at different speeds, with a table of ol RADSRGE Ea mE me SB laaaeimiee ieee aera ma a Bo A 1600 S oS Oo > oOo @o c=) o o 35 © 4 600 0 “10 pave 80 30 i000 Fic. 126.—Test results of compressor plant No. 4. efficiencies at different loads and speeds, just as is done by some of the manufacturers of electrical machinery. Catalogues might also include some definite data respecting the cost per horse-power delivered by the air end of the compressor at different working speeds. CHAPTER XIV RECEIVERS. MEASUREMENT AND TRANSMISSION OF COMPRESSED AIR RECEIVERS The purpose of installing a receiver is four-fold: First, to equalize the pulsations in the air coming from the compressor; second, to collect the water and grease held in suspension by the compressed air as it leaves the compressor; third, to reduce the friction of air in the pipe system; and fourth, to cool the air as thoroughly as possible before entering the transmission system. It does not act primaiily as a reservoir of power, for in order to accomplish this its size would become impractical. However, in 8 ‘ For 4'Satety =3 = ff Lhe | Valve ~, 8 5 Lg) _ foe ». . TZ ‘| WTAE 4 i] | AWN AH HI Ht Hk Hl ie ay Hua H ' fa, pest SISISISESIS SISESISESISLSS 3 ptt V9 its ghee at pS eR N a, eH LZZ ae, 4 Lary) p~ Fic. 127.—Receiver aftercooler. compensating for the air pulsations it maintains constant pressure in the pipe line and in that way reduces friction. In order to facilitate the removal of water from the compressed air, it is frequently equipped with a coil of pipes (Fig. 127) filled with cooling water, in this way serving as an “after-cooler,” as it is called. When so equipped the difficulty with water in the trans- mission line and frost at the exhaust pipe of a compressed-air motor is reduced. When the pipe line is very long, receivers are placed at both ends of the pipe; this increases the effectiveness of the receiver and reduces materially the pipe friction. 159 160 AIR COMPRESSION AND TRANSMISSION As manufactured, these 1eceivers are usually supplied with a pressure-gage, safety-valve, blow-off cock and frequently a man-hole. They are made either horizontal or vertical and of cubical contents varying usually from 30 to 400 cu. ft. For exceptional cases as for compressed air-pressure water systems, they are frequently made much larger. THE MEASUREMENT OF AIR AND GASES ‘The measurement of compressed air and gas in the commercial distribution and sale of these commodities and in testing com- F pressors has attracted a great deal of Seen te attention in recent times and excel- Re m ten pane Fe ul lent articles’ are to be found in the aa ci technical press. The material here given has been gathered from these sources and includes some interest- ing results of tests made in the Steam and Gas Engineering Labora- tory of the University of Wisconsin. “Standards of Measurement.— In making measurements it is usually necessary to ascertain the number of ‘standard cubic feet’ passing in a given time. The contents of a stan- dard cubic foot are determined by the assumed standards of tempera- ture and pressure used in defining the unit of measurement. Scientific data on gases are usually referred to the freezing temperature of water : and to the mean barometric pressure. Fic. 128.—Wet displacement Common commercial standards of meter. temperature and pressure in gas measurement are 60° F. and 30 in. jini a uideaidtidtin nn : y it i ce Md Wt of mercury, respectively. ‘““A quite general classification of meters includes two main types: volumetric meters and velocity meters. ‘Volumetric Meters.—Volumetric meters include what are known as “dry meters,’ operating on the general principle of a bellows, and ‘wet meters.’ The latter are built in large sizes for use at gas works 1The Measurement of Gases, Prof. Carl C. Thomas, Jour. Franklin Inst., Nov., 1911. Measurement of Nat. Gas, Thos. R. Weymouth, Jour. A. S. M. E.., Nov., 1912. Flow of Gas through Lines of Pipe, Forrest M. Towl, Lecture Columbia Univ., rort. MEASUREMENT OF COMPRESSED AIR 161 in measuring the gas, as made, before being passed for storage to the holders (Fig. 128). These meters are known as station meters, their construction is, in general, that of a drum revolving within a cylinder or tank which is more than half filled with water. The revolving drum consists of a shaft carrying three or four partitions arranged in a spiral form. These partitions emerge in turn from the water as the shaft revolves, and each forms with the water a water- sealed compartment, which alternately receives and delivers gas. The drum receives its motion from the pressure of the gas itself and the number of revolutions of the shaft when properly calibrated give an index of the quantity of gas passing through the meter. In testing air compressors, volumetric methods of measuring the air compressed are sometimes used by installing three tanks. The compressor is arranged to discharge constantly into one of these at a constant pressure. This tank in turn discharges alternately into either of the other two. It fills one tank while the other is being discharged to the atmosphere and when the pressure approaches that of the compressor the discharge is turned into the empty tank. By noting the temperature and pressure and having the volume of the two tanks it is possible to calculate the volume of air which each has received from the compressor. “Velocity Meters.—Volumetric methods of measurement, how- ever, are not always feasible nor very satisfactory, and other methods of measurement depending on the velo- city of flow of the air or gas have been developed and made use of in commercial work. These methods may be separated into three types: the orifice or Pitot-tube type, which depends for its operation upon fundamental principles of hydraulics; the Venturi meter, which depends upon thermo-dynamic principles involved in the adiabatic expansion of the gas or air as it flows through the reduced cross-sectional area of the Venturi tube; and the heat meter, of which the Thomas electric meter, manufactured by the Cutler-Hammer Co., fy¢. 129.—Simple form of Milwaukee, Wis., is the best example, in Pitot tube. which the temperature of the gas or air is increased through a known range by a measurable amount of heat. From a knowledge of the specific heat of the gas and air, the weight of gas or air flowing through the meter is automatically determined and recorded. “Ditot Tube.—The Pitot tube (Fig. 129) affords a means of 11 . 162 AIR COMPRESSION AND TRANSMISSION measuling the velocity of air or gas through a pipe at any given point in the pipe section. In its simplest form it consists of two small tubes inserted in the pipe line—one having an opening pointed up-stream and communicating to one end of a U-tube the pressure due to velocity head in addition to the static pressure in the pipe; the other having an opening at right angles to the direction of flow and communicating to the opposite end of the U-tube the static pressure only. The difference between these two pressures is the pressure due to velocity alone, and from this, velocity of the gas or air in the pipe can be computed by means of the formula v?=2¢h where h is the static head necessary to give to the air or gas a veloc- ity of vft. persecond. From a knowledge of the cross-sectional area as Slots in Sides or Outer tke wane Z ‘ ‘ LY Fic. 130.—Modern form of Pitot tube. of the pipe and the density of gas at observed pressure and tempera- ture, the quantity passing per unit of time can be computed. Fig. 130 shows a modern type of Pitot tube. “The velocity of gas flowing through a pipe is not the same at all points in the section. It falls off gradually from the center out- ward and very rapidly near the inner skin of the pipe. In order to obtain accurate results with Pitot tubes, without exploring the pipe at several different depths, it is necessary to ‘standardize’ the tube and pipe together and find the depth at which the tube will indicate the mean velocity; that is, a Pitot tube will not necessarily give consistent readings if placed in a given position in pipes of different sizes, different conditions of surface, etc. The tube must be located with special reference to the size, shape, and condition of pipe with which it is used. Great care must be taken that the openings MEASUREMENT OF COMPRESSED AIR 163 through which the pressures are communicated to the U-tube are properly placed with respect to the direction of flow, and they must be kept free from deposits. “The general formula for the Pitot tube and the orifice is derived from the law of falling bodies. Let T = absolute temperature of flowing gas, degrees Fahrenheit. P = absolute pressure of flowing gas, pounds per square inch. w = weight per cubic foot of flowing gas, at P and T. G = specific gravity of flowing gas, (air 1.0). v = actual velocity of flowing gas, feet per second. h; = height in feet of homogeneous column of gas at P and T producing 2. 3 h = corresponding height of water column in inches. W. = weight per cubic foot of water, 62.37 lb. at 60° F. P, = absolute storage pressure base, pounds per square inch. [, = absolute storage temperature base, degrees Fahrenheit. Wa = weight per cubic feet air at 32° F. and 14.7lb.=0.08073 lb. d = actual inside diameter of pipe or orifice in inches. E = efficiency of Pitot tube or orifice. Q = flow in cubic feet per hour at P, and T,. Then V=A/2gh; =|2 8 a ie W=WaG aT vy ae pez OES ita Pal O= 218.44 ka? a “Prof. S. W. Robinson who was probably the first to use the Pitot tube in connection with the flow of natural gas has developed the following formula which has heen used by natural gas men for a number of years: | OQ =1,462,250 d? es) 0.29 os de This was derived from the formula for adiabatic flow n—1 oo 2g X44 Po hf Pi\ on ie in which G1) w |G) geal 164 AIR COMPRESSION AND TRANSMISSION v = velocity of flowing gas, feet per second. Py) = absolute pressure of the atmosphere, pounds per square inch. n = ratio of the specific heats. w = weight per cubic foot of gas at pressure P,. G = specific gravity of gas, air I. P, = absolute pressure shown by Pitot tube, pounds per square inch. d = internal diameter of well mouth, inches. = open-flow capacity of well, cubic feet per 24 hours. “Prof. Robinson has computed tables from the above formula which have been used for years. The computations are based on the following: nm =I1.408 2g =04.3 Ps =14.6 Gir=0:0 IE i i Se Rito Ne. To = absolute temperature of melting ice. T = absolute temperature of flowing gas. I’, = absolute temperature of storage. “Thos. R. Weymouth in his article in the Journ. A. S. M. E. points out that for natural gas the ratio of the specific heats is more nearly equal to 1.266 and by using Le OO nel. (le ree NE Vt ae ay) P, = storage pressure 14.65 the formula becomes: if 0-21 a O=1,758,560 ay (44) Sh }* el AA “In order to obtain a mean value of / for the use in Pitot tube measurements Prof. G. J. Davis of the University of Wisconsin devised the following method which is illustrated in Figs. 131 and 132 showing results of an actual test of a Pitot tube placed tandem with a Venturi meter and a Thomas electric meter. ‘The horizontal represents distances from the center of the pipe at which readings of # were observed. On the vertical a suitable scale of values of \/h is laid off. Readings of ~/h are then plotted and joined by radial lines to the point representing the center of the pipe. The intersections of the slanting lines with the perpendiculars MEASUREMENT OF COMPRESSED AIR 165 representing the positions at which the corresponding values of Vh were read are points through which a smooth curve can be drawn. The area under the curve may now be determined and from this the altitude of a triangle having the same area and base as the irregular figure will give the mean / to be used in computing the mean velocity. ‘““The mean velocity V is determined from the formula V? =2¢h after reducing the # determined to equivalent feet of air. The pounds per hour will then equal 3,600 AVG where A is the area of the pipe in square feet. eee Gee A NAG \ EN LAREN GE aces ae rey : ! Val a aa BA I gt LA = ieee AA Sa VAC SSR Zasi ap aaa 3 0.1 FAR =e 5 07 - Puta A oe. [eal nla Te ‘CCEA : FA “OOO sA } LG 04 J Zt ott wis =o L EL 02 Eee 2a ae 02 Kt ale area ae eine it KAZ ie premanee Sent Center of bier eine Distance from Center oF Pipe, mohes, Fic. 131.—Graphical method of Fic. 132.—Graphical method of determining mean head. determining mean head. V is the velocity in feet per second. G is the weight of a cubic foot of air as it passed through the pipe. “‘In measuring air by means of a Pitot tube it is necessary to take into account the humidity of the atmosphere and make corrections as indicated in the discussion on Humidity given in Appendix C. ‘‘In measuring large quantities of air in testing air compressors it is quite a common practice to have the air escape through a suitable orifice to the atmosphere. An apparatus of this kind is shown in Fig. 22 and one for large installations in Fig. 133. “The formula usually used for measuring air under these condi- tions is 166 AIR COMPRESSION AND TRANSMISSION ie W =0.53A Tz where P; is greater than twice atmospheric pressure. 7 TT, Tt UM, iets Ui ; / “frien, "| ; rT 7 ia ili > 7 i 3 : eit ti! (Uy \ LT. TV. Ahi batons, Hil! (iil AR aig i ; \ NTR NNN aii AA |i NN a : a in i ' al gu a + Ge wy gulls ei Fic. 133.—Apparatus for measuring large quantities of air. \ When P, is less than twice atmospheric pressure the formula usually used is W =1.060A A eeieee 163 “This last formula, however, is A not entirely reliable (see ‘Air Flowing into Atmosphere through Circular Orifices’ by R. J. Durley, Trans, ASS. MAES Y ol27 In the above formule W = weight of air escaping in pounds per second. P. = pressure of atmosphere in pounds per square inch. P, = pressure before the nozzle in pounds per square inch absolute. (NNhhawm vrssr aa seees. 4 T, = absolute temperature of SI] Ss . ° NIN air entering the nozzle. A = area of nozzle in square foc “Tn using a nozzle or orifice it is also necessary to consider the humidity of the atmosphere in measuring air. “St, Johns Meter.—A number of meters have been made making use of an orifice for measuring the flow of air. Such meters are usu- PRaveeaaaarvees Fic. 134.—St. John meter. MEASUREMENT OF COMPRESSED AIR 167 ally calibrated by means of a gasometer. The St. Johns meter, Fig. 134, is in effect a variable orifice meter. The position of the plug S determines the size of the orifice through which the air passes and a graphical record is kept of the position of this plug on a drum moved by clock work and by planimetering this chart the average position can be determined and the consumption be calculated. ‘Venturi Meter.—The Venturi meter, Fig. 135, consists of a throat or gradually contracted portion of the passage, which causes a de- ik {AU IOOU MOOI Fic. 135.—Venturi tube. crease in pressure and increase in velocity of the gas flowing through it. area of the up-stream section in square feet. Az = area of throat in square feet. P, = pressure at up-stream side, pounds per square inch. P., = pressure at throat, pounds per square inch. G, = weight of gas at up-stream section, pounds per second. n = ratio of specific heats, constant pressure to constant volume. V2 = velocity of gas at throat, feet per second. te O o aN I “By equating the loss in potential energy to the increase in kinetic energy it is found that N bo | Pgs a Saas ty] Pt aa to oR S eer 2 NH = | ST ee | a | 3 | Lon] dole pe 4a \7(£2)\2 ae AyIEN Ps 1 ce . ° ie ee ° The quantity flowing O=A2V.G1 (3) ” in cubic feet per second. 1 “Tt is frequently necessary to take small readings of pressures with both the Pitot tube and Venturi meter, and in order to do this 168 AIR COMPRESSION AND TRANSMISSION accurately the water columns should be read with a micrometer gage or differential (inclined) water column. ‘“‘A similar formula for the flow expressed in cubic feet per hour would be Po ned Ts n Jey ‘poe ; Gal = O40 Ag) ee eee 2\ in Cee PNG JT; (>,) “Terms in this formula not appearing in the other are Q1 = flow in cubic feet per hour. T, = absolute temperature of gas at entrance. I, = absolute temperature of storage base pounds per square inch. P, = absolute pressure of storage base pounds, per square inch. G = specific gravity of gas, air=1. “Thomas Meter.—The Thomas electric meter is based upon the principle of heating the air or gas through a known range of temper- y L

3 \. iS | Fic. 137.—Diagrammatic sketch of Thomas electric meter. resistance of the exit thermometer for a rise in temperature of prac- tically 2° F. The meter in the laboratory of the University of Wisconsin is for 2.0152° F. ‘The operation of the meter is as follows: With gas flowing through the meter but with no energy in the heater, and with R; out of cir- cuit, the two thermometers are brought to the same balance by means of the balancing rheostat and the galvanometer. Then the resistance R: is put in circuit and sufficient electrical energy is supplied to the heater to bring the galvanometer to balance again, by bringing the exit gas to a temperature 2.0152°, with the meter mentioned, higher than that of the entering gas. The measuring instruments in the heater circuit then indicate the energy required 170 AIR COMPRESSION AND TRANSMISSION to raise the temperature of the air or gas through a known range. The quantity of gas flowing can be found by the equation Ww a 3412k ts where W is the number of pounds of gas or air per hour, # the amount of energy supplied in watts per hour, ¢ the rise of temperature in degrees Fahrenheit, and s the specific heat at constant pressure of the gas or air. “With the laboratory meter the air flowing through the meter per minute is given by the formula 0.028218 E;. “In applying this meter to gases it is necessary to ascertain the composition of the gases in order to obtain the mean specific heat for use with the meter. “The meter in commercial form is equipped with automatic devices to regulate the flow of current through the heater so as to maintain a constant difference of temperature between the resistance ° thermometers of 2°. The electrical instruments for measuring the consumption of current in the heater are then calibrated to read either weight or quantity of gas flowing and this reading is recorded graphically. “Meter Comparisons.—At the University of Wisconsin tests were run by placing a Venturi meter, Pitot tube and Thomas meter SAG To ‘ Sweet Pitot TORE fom Atte 0 Driven Fan Fic. 138.—Sketch of meters placed tandem for testing. in tandem, as shown by Fig. 138. The results of these tests are shown as Fig. 139. A remarkable similar set of readings were secured. “In April, 1911, a Thomas meter was tested on a natural-gas line by comparison with Pitot-tube measurements giving practically iden- tical results. This meter had a maximum capacity of 750,000 cu. ft. of free gas per hour and an accurate minimum capacity of 12,500 cu. MEASUREMENT OF COMPRESSED AIR 171 ft. It gave a continuous graphical record and integrated values of the gas directly in standard cubic feet at 15.025 lb. absolute pressure and 60° F., although the pressure of the gas varies from 50 to 200 |b. gage and the temperature varies with weather conditions. The specific heat was calculated from an average analysis of the gas for the standard conditions given above. This particular meter was placed in a ro-in. line and located about a mile and a half from a very ena, co + Scere ts Gas Engineering ee University of Wisconsin, June 2-/9/1 Electric Meter « Venturi Meter x ——— Pitot Tube o—---- 0 0 100 200 300 400 500 600 700 800 900 1000 1100 R.p.M. of Fan Fic. 139.—Result of test. complete Pitot-tube meter station. A 22-hour comparative test showed a difference of 0.2 per cent. between the two meters and a similar comparative test from April 17 to June 3, 1911, showed the same difference.”’ _ PIPE LINES! “The transporting of gas or air requires a line which shall be “air tight.” It is much more difficult to make a line to hold gas or air under pressure than it is to hold a liquid. Trouble has been expe- rienced in almost all lines built for high pressure on account of the leaking of the gas at the couplings. The first high-pressure lines were laid with bell and spigot joints, caulked with lead. The lines 1 Forrest M. Towl, Lecture Columbia University, 1o1t1. siz AIR COMPRESSION AND TRANSMISSION might be tight when they were first laid but the movement in expand- ing and contracting soon caused them to leak in large amounts. ‘The next lines used were of wrought iron or steel pipe with screw joints. While these held much better than the bell and spigot type, there was still enough leakage to make it desirable to have a more perfect joint. The leakage on some of the earlier screw-joint gas lines was such that by putting a rubber bag over the coupling, gas could often be collected at the rate of from 20 to 50 cu. ft. per hour, or enough to run a good-sized torch. This was true of lines up to 8 or ro in. in diameter. When the lines became larger, the leakage increased so much that it was practically impossible to use large size lines and get a large percentage of the product at the market. ‘‘As the demand for natural gas increased, it became necessary to use larger lines, and a rubber packed stuffing-box was developed. The first successful joint of this kind in the market was the Dresser coupler, and it is due largely to this and other couplings that the natural-gas industry has become so great. | ‘Dresser Coupler.—The Dresser coupler consists of a sleeve into which the ends of the pipe are placed. There is a projection at the center of the sleeve so that the ends of the pipe will be each inserted into the sleeve the same distance. This sleeve acts as a follower to compress rubber in an annular space into the end rings which are drawn together by bolts. The rubber is surrounded on one side by the pipe, on another by the body of the coupling, and Fic. 140.—Dresser On the remaining side by the end rings so that pipe coupler. there is very little of the surface of the rubber exposed either to the gas on the inside or the air on the outside of the line. It is found that these joints will last for years. (Fig. 140 shows a cross-section of the Dresser coupler.) ‘‘“Hammon Coupler.—The Hammon coupler is a modification of the Dresser, one of the principal features of which is that the pro- jection at the center of the sleeve is made by lugs welded onto the sleeve. When it becomes necessary to take apart one of these couplers, the lugs can be broken off and the coupler slipped back so as to allow the pipe to be easily removed. (Fig. 141 shows the Ham- mon coupler.) ‘Lines of pipe can be built in almost any kind of country, but it is necessary in some places to arrange to keep the lines from acting as a Bourbon tube and expanding in one direction until the ends of the pipe may be pulled out of the coupling. To avoid this trouble it is customary in such places as river crossings to use screw pipe, and to place over the collar a clamp which is constructed to make a rubber joint between the ends of the collar and the pipe. \ ) } tt iain PS SS SSS SB RS ca ereveereeenrrnrnrernrrrrrr rr MEASUREMENT OF COMPRESSED AIR 173 “For power-transmission lines or for temporary gas lines, where the distances are short or the service temporary, it is not considered necessary to bury the pipe, it will be found that the screw-joint pipe is satisfactory, but for other natural-gas or air service, the rubber coupling has many things to recommend it, and when the capacity requires large pipe, it is almost absolutely necessary to use this type of coupling. These coupling have been used for manu- factured gas, but it is found that the condensation from the gas collects in the coupling and soon causes a leak in the rubber joint. Work is now in progress to per- fect a material which will not be acted upon by the condensation in the gas and which will make a . gas-tight joint. Fic. 141.—Hammon pipe coupler. In using screwed joints for air it is necessary that the lead, litharge, or other material used at the joint should be applied on the ends of the pipe and not in the coup- lings, so that the surplus is brought outside instead of within the pipe where it may cause a more or less serious obstruction.” Pipe-line Formulz.—A very simple formula is often used for calculating pipe lines for compressed air. Deo a) or pee pi~ bs Wy V/] Wi in which D =the volume of compressed air in cubic feet per minute dis- charged at the final pressure. ¢ =a coefficient varying with the diameter of tke pipe, as determined by experiment, d =diameter of pipe in inches, 1 =length of pipe in feet, pi =initial gage pressure in pounds per square inch, p2 =final gage pressure in pounds per square inch, 1 The actual diameters of wrought-iron pipe are not the same as the nomina- diameters for all sizes. This difference is small, however, except in the 1 1/4 in. and 1 1/2 in. sizes, the actual diameters of which are 1.38 in. and 1.61 in. respectively. 174 AIR COMPRESSION AND TRANSMISSION w, =the density of the air, or its weight in pounds per cubic foot at the initial pressure #1. The second form of the formula, as given above, will be found convenient for most calculations, as the facto1s can be considered in groups. In Tables XIII and XIV are given the values of c, d°, and c\/d5, The values of c show some apparent discrepancy for sizes of pipe larger than 9 in. but there would be no very material dif- ferences in the results. » TABLE XIII Diameter of pipe, Values of Fifth powers of Values of inches C d c\/ds I 45-3 i 45-3 2 5200 a2 207 3 56.5 243 876 4 58.0 1,024 1,856 5 59.0 3,125 3,298 6 59.8 7,776 5,273 7 60.3 16,807 7,317 8 60.7 32,768 10,988 9 61.0 59,049 14,812 IO 61/32 100,000 19,480 i 61.8 161,051 24,800 12 62.0 248,832 30,926 TABLE XIV.—VALUES OF Wi FOR ET ACE EGS pene UP 100 LBS.PER SQUARE Gage pressure, : | — Gage pressure, = ap a Vw | pounds - Vw ° 0.0761 0.276 “is 0.3607 0.600 5 0.1020 0.319 60 0. 3866 0.622 ite) 0.1278 0.358 65 eg As 0.642 cf On 527 0.302 70 0.4383 0.662 20 0.1796 0.424 7 o.4042 0.681 25 0.2055 0.453 80 0.4901 0.700 30 O. 2313 0.481 85 0.5160 0.718 25 O.2572 0,507 go 0.5418 Of736 40 0. 2831 0.532 95 0.5677 0.753 A5 ‘0.3090 0.556 Too 0.5936 0.770 50 0.3348 O. 578.2 eva 2 yan a he he al cea OR te ee MEASUREMENT OF COMPRESSED AIR 175 Mr. Frank Richards gives the following formula for determin- ing the loss of pressure in pipes: 2h 10,000D°a from which 10,000D*a L V= In these equations D=diameter of pipe in inches. L =\length of pipe in feet. V =volume of compressed air delivered in cubic feet per min. H =head of difference of pressure required to overcome friction and maintain the flow. | a =constant depending on the diameter of the pipe. TABLE XV.—VALUES OF a, D' AND Dia FOR WROUGHT-IRON PIPE. Gane ; Ds Dia pipe diameter I in. 0135 I 023% 1% in fans RES Ta52s Tz in 0.662 7.59 5,03 ain, 0.565 ex 18.08 anit 0.65 97.65 63.47 3 in 0.73 243. ETA 33 in O87 525. 413.2 4 in 0.84 1024. 860.2 5 in 0.934 2125. 2010075 6 in I .000 vie by doe Os 8 in Te ks 32768. 36864. ro in pane 100000. 120000. 2-10 T20 248832. 213525. 16 in N34 1048575. I4O5001. 20 in 1.4 3200000. 4480000. 24 in I.45 7962624. 11545805. For example, suppose it is desired to determine the loss in pressure in transmitting 300 cu. ft. of compressed air per min. through a 6-in. pipe one mile in length. L =5280, D*a for a 6-in. pipe=7776 2 Nehey vind eb EBON Ne) 10000 X 7776 6.11 lb. That is, the pressure drop will be 176 AIR COMPRESSION AND TRANSMISSION As another example, suppose it is desired to ascertain the proper size of wrought-iron pipe for transmitting compressed air from a compressor of 1500 cu. ft. free air capacity per min. at 80 lb. gauge a distance of 2000 ft., with an allowable loss of pressure of 5 lb. The pressure at delivery will be 75 lb. gauge or. practically 6 atmospheres. ‘The volume of compressed air delivered per minute will be: 1500+6=250 cu. ft. per min. =V As H=5 the formula Paes tooo0oH 250” X 2000 10000 X 5 ere From Table XV it is seen that D*a for a 5-in. pipe is 2918.75 and for a 6-in. pipe 7776. This would indicate the advisability of selecting 5-in. pipe for the conditions of this problem. The friction in pipe elbows may be expressed in terms of equivalent lengths of straight pipe. Elbows having the largest radius will naturally give the least friction and the accompanying table as given by the Norwalk Compressor Co. gives the friction effect of elbows in terms of the radius. may be used with proper substitutions, from which 5 TABLE XVI.—FRICTION EFFECT OF ELBOWS IN TERMS OF PIPE LENGTHS Radius of elbow in pipe diameters On Ww bo eS dle eS | vol ated [ OH HD 4048) 4065/4082 4216)4232|4249 4378/4393|4409 4533/4548) 4564 | 4683)4698/4713 4857 4997 5119/5132 5250/5263 5366!5378/5391 4116 4281 4440 4594 4742 4886 5024 5159 5289 5416 3997/4014 41664183 4330/4346 4487/4502 4639) 4654 m bo bo bO bO bo bo bo bo bo wwwwo PRP PA He Or Or Or Or 4786/4800|4814 4928) 4942/4955 5065/5079] 5092 5198}5211/5224 5328/5340) 5353 ee Oona “I CO 00 CO © CO 00 00 00 CO bo bo BO bO bo Co WO OO 5490|5502/5514 5611}5623/5635 5729 5740|5752 5843/5855|5866 5955/5966)5977 6064) 6075) 6085 6170/6180/6191 6274/ 6284/6294 6375)/6385|6395 6474/ 6484/6493 5539 5658 5775 5888 5999 6107 6212 6314 6415 6513 5453/5465|5478 5575/5587|5599 5694|5705|5717 5809| 5821/5832 5922/5933|/5944 Www, > eee PP See et CLD DAN NIT I 6031)|6042|6053 6138/6149/6160 6243/6253/6263 6345) 6355/6365 6444/6454) 6464 a Co 0) 09 09 OO 6609 6702 6794 6884 6972 7059 7143 6580)6590 6675/6684 6767|6776 6857|6866 6946/6955 7033|7042 7118|7126 6542|6551/6561 6637| 6646/6656 6730|6739|6749 6821/6830|/6839 6911/6920/6928 6998) 7007/7016 7084/7093'7101 ee Drrwryrmp nwwnwpnywrn 09 09 Oo Oo 09 RNS No, Mon Moy Mo ea eg en AMARA ARMRAO AOMINTN NIWA 00 00 00 00 © | | 7168/7177 7251/7259 7332/7340 7185 7267 7348 7202 7284 7364 7210 7292 7372 7226 7308 7388 | bo bo bo bo bo bo bo bo © CO Re ee Or Or Or Or Or C2 2 2 > AOon4nna “I ~I ~I “100 00 CO 00 CO © ~I ~I ~1 00 00 186 AIR COMPRESSION AND TRANSMISSION 1 2 7419 7497 7574 7649 7723 7796 7868 7938 8000/8007 8069) 8075 8136/8142 8202/8209 8267|8274 8331)8338 8395)/8401 7412 7490 7566 7642 7716 1789 7860 7931 8463 8525 8585 8639/8645 8698/8704 8756/8762 8814/8820 8871'8876 8927/8932 8982/8987 8457 8519 8579 9042 9096 9036 9090 9143/9149 9196/9201 9248/9253 9299/9304 9350/9355 9400/9405 9450/9455 9499/9504 9552 9600 9647 9547 9595 9643 9689/9694 9736/9741 9782)9786 9827/9832 9872/9877 9917/9921 9961/9965 3 7427 7505 7582 7657 7731 4, 7435 7513 7589 7664 7738 7810 7882 7952 8021 8089 8156 8222 8287 8351 8414 8476 8537 8597 8657 8716 8774 8831 8887 8943 8998 9053 9106 9159 9212 9263 9315 9365 9415 9465 9513 9562 9609 9657 9703 9750 9795 9841 9886 9930 9974 LOGARITHMS. 5 6 7 8 9 7443)7451 || 7459|7466)7474 7520|7528 || 7536|7543|7551 7597|7604 || 7612/7619)7627 7672)|7679 || 7686/7694|7701 7745)7752 || 7760|7767|7774 7818|7825 || 7832|7839)7846 7889|7896 || 7903/7910)\7917 7959|}7966 || 7973/7980) 7987 8028/8035 || 8041/8048/8055 8096/8102 || 8109)8116)8122 8162/8169 || 8176)8182)8189 8228/8235 || 8241/8248|/8254 8293/8299 || 8306/8312/8319 8357/8363 || 8370/8376|8382 8420/8426 || 8432)8439)8445 8482/8488 |) 8494/8500/8506 8543/8549 || 8555/8561/8567 8603/8609 || 8615)8621|8627 8663/8669 || 8675/8681/86386 8722/8727 || 8733/8739|8745 8779/8785 || 8791/8797/8802 8837/8842 || 8848/8854/8859 8893 8899 || 8904/8910)8915 8949/8954 || 8960/8965/8971 9004)9009 || 9015)9020)9025 9058/9063 || 9069/9074/9079 9112/9117 || 9122)9128/9133 9165)9170 || 9175)9180/9186 9217/9222 || 9227/9232/9238 9269/9274 || 9279)9284/9289 9320/9325 || 9330/9335/9340 9370/9375 || 9380/9385/9390 9420/9425 || 9430)9435/9440 9469/9474 || 9479)/9484/9489 9518/9523 |) 9528/9533/9538 9566/9571 || 9576|9581/9586 9614/9619 || 9624)/9628)9633 9661/9666 || 9671}9675|9680 9708/9713 || 9717|/9722/9727 9754/9759 || 9763|9768/9773 9800)9805 || 9809/9814/9818 9845/9850 || 9854)9859)/9863 9890/9894 || 9899}/9903)9908 9934/9939 || 9943)/9948)/9952 9978/9983 || 9987/9991/9996 1 2534) 4. 6 (Gave Ss et et — bo bo bO bo bo bo bo bo bo bo bo bo bo — a et ee pt et ot ee ee ee wmnodnhynwlrynmynnmnyn NWwwwwl wowwwow wowweo — at pt et — a pe pp pe SSS oCcoorrF co eo CO CO a aoe ' tt pt pt mer bo bo See ep See et tt et ht tt ee bo bo bo bo bo bo bo bO bO bo bo bo bo bo bo bo bo bo bo bo Oe ee a eG Proportional Parts. ee’ ee ee bo bo bo bo bo bo bo bo bo bo bo bo bo bo bo bo bo bo bo bo ww We PP PP Cow WO 0 Co Go GO GO ww 0 0 Qo Oo OO GO OO bo bo bo Go CO bo bo bo bb bo bo bo bo bd bo [antl alls lls ls EPP PP PRR RR oon Oo GO GOD wwwww ew O93 0) OO WwWwwww eo) 09 Co WO Ww a WwWwwe He ee He ee He ee Ree eR PR OL OT or Ovr9or1ror1 or or Or Orv or or or Or Or Or Or Or Or Ot Ot Or Od Co tg cl a ls ll Leal als eels oll sd PPP LP Pp He He HR OT Or Or Or Or Or Or Or Or Ot Or Or Or Otic & DD 2 2 PORWOMOD Wsaivwsy OD DD OD eee PP He Ee BR Or Or Or Ot Or Or Or CO ee PP PP LP ee APPENDIX A 187 The log of 0.483°°*? is found by multiplying the log by the exponent or 0.42 (9.6839—10) which is 4.067238—4.2. It is difficult to get the antilog of this directly, but the value of the logarithm is not changed if a number be added to the first part and subtracted from the second part to make this —1o. In this case add 5.8 to the first and substract 5.8 from the second, making the log of 0.4839” 9.8672 —TIo. The antilog of this is 0.736 plus 0.0004 or 0.7364. That is, 0.483°°4? is equal to 0.7364. APPENDIX B Naperian Logarithms.—The natural, hyperbolic or naperian logarithm of a number can be found by multiplying the common log- arithm of the number by 2.3026 but the solution of problems involv- ing this log or the loge as it is written will be facilitated by the use of the following tables which read from 1 to 10 by increments of hundredths. For example, the loge of 4.36 is given directly as 1.4725. Characteristics and mantissas are not handled in this table in the same way as the common logs. But as the log of 43.6 is the same as the log. of 4.36 X10 this may be found by adding the logse of 4.36 and to. In this case this is the sum of 1.4725 and 2.3026 or 3.7151. That is, the loge of 43.6 is 3.7151. . In the same way the loge of .436 is the same as the loge of (4.36 divided by 10) or the loge of 4.36 minus the loge of 10. In this case it 1S 1.4725—2.3026 or —o.8301. That is the loge of 0.436 is —0.8301, a negative number. } 188 PEAY DIX, B ; 189 € = 2.7182818 log e = 0.4342945 = M 0 1 2 3 4 5 6 7 8 9 1.0 {0.0000 |0.00995/0.01980,0. 02956/0. 03922\0. 04879|0. 05827/0. 06766|0. 07696/0. 08618 1.1 /0.09531)0.1044 )0.1133 |0.1222 |0.1310 |0.1398 |0.1484 |0.1570 |0.1655 |0.1739 1.2 |0.1823 |0.1906 |0.1988 |0.2070 |0.2151 |0.2231 |0.2311 |0. 2390 |0.2469 |0. 2546 1.3 |0.2624 |0.2700 |0.2776 /0.2852 |0.2927 |0.3001 |0.3075 |0.3148 |0.3221 |0.3293 1.4 |0.3365 |0.3436 |0.3507 |0.3577 {0.3646 |0.3716 |0.3784 |0.3853 » 720 |0.3988 1.5 0.4055 |0.4121 |0.4187 |0.4253 |0.4318 |0.4382 |0.4447 |0.4511 {0.4574 |0.4637 1.6 |0.4700 |0.4762 |0.4824 |0.4886 |0.4947 /0.5008 {0.5068 [0.5128 |0.5188 |0.5247 1.7 |0.5306 |0.5365 |0.5423 |0.5481 /0.5539 /0.5596 |0.5653 |0.5710 |0.5766 |0.5822 1.8 |0.5878 |0.5933 |0.5988 |0.6043 |0.6098 |0.6152 /0.6206 /0.6259 |0.6313 |0. 6366 1.9 |0.6418 |0.6471 |0.6523 [0.6575 |0.6627 |0.6678 /0.6729 |0.6780 |0.6831 |0.6881 2.0 |0.6931 |0.6981 |0.7031 |0.7080 |0.7129 |0.7178 |0.7227 |0.7275 |0.7324 |0.7372 2.1 (0.7419 |0.7467 |0.7514 |0.7561 |0.7608 |0.7655 |0.7701 |0.7747 |0.7793 |0. 7839 2.2 (0.7884 |0.7930 |0.7975 |0.8020 |0.8065 |0.8109 |0.8154 |0.8198 /0.8242 |0.8286 2.3 |0.8329 |0.8372 |0.8416 |0.8459 |0.8502 |0.8544 |0.8587 |0.8629 /0.8671 |0.8713 2.4 |0.8755 |0.8796 |0.8838 |0.8879 /0.8920 |0.8961 /0.9002 |0.9042 |0.9083 |0.9123 2.5 |0.9163 |0.9203 |0.9243 |0.9282 |0.9322 |0.9361 |0.9400 |0.9439 |0.9478 |0.9517 2.6 |0.9555 |0.9594 |0.9632 0.9670 |0.9708 |0.9746 |0.9783 |0.9821 |0.9858 |0.9895 2.7 |0.9933 |0.9969 |1.0006 /1.0043 |1.0080 {1.0116 |1.0152 |1.0188 /1.0225 |1.0260 2.8 |1.0296 {1.0332 |1.0367 |1.0403 |1.0438 |1.0473 |1.0508 [1.0543 |1.0578 |1.0613 2.9 {1.0647 |1.0682 |1.0716 {1.0750 |1.0784 |1.0818 |1.0852 |1.0886 |1.0919 [1.0953 3.0 {1.0986 |1.1019 (1.1053 |1.1086 )1.1119 |1.1151 {1.1184 |1.1217 {1.1249 /1.1282 13.1 (1.1314 |1.1346 )1.1378 |1.1410 |1.1442 |1.1474 )1.1506 1.1537 |1.1569 /1.1600 3.2 /1.1632 /1.1663 |1.1694 |1.1725 |1.1756 {1.1787 |1.1817 |1.1848 |1.1878 |1.1909 3.3 {1.1939 |1.1969 |1.2000 {1.2030 |1.2060 {1.2090 [1.2119 |1.2149 {1.2179 |1.2208 3.4 {1.2238 |1.2267 |1.2296 |1.2326 {1.2355 |1.2384 [1.2413 |1.2442 (1.2470 |1. 2499 3.5 /1.2528 |1.2556 |1.2585 |1.2613 |1.2641 {1.2669 |1.2698 |1.2726 |1.2754 |1.2782 3.6 [1.2809 |1.2837 |1.2865 |1.2892 |1.2920 {1.2947 |1.2975 |1.3002 {1.3029 /1.3056 3.7 {1.3083 |1.3110 |1.3137 [1.3164 |1.3191 {1.3218 |1.3244 |1.3271 |1.3297 |1.3324 3.8 {1.3350 |1.3376 |1.3403 |1.3429 |1.3455 |1.3481 |1.3507 |1.3533 |1.3558 |1.3584 3.9 {1.3610 /1.3635 |1.3661 |1.3686 |1.3712 |1.3737 |1.3762 |1.3788 |1.3813 |1. 3838 4.0 {1.3863 |1.3888 {1.3913 |1.3938 /1.3962 |1.3987 |1.4012 |1.4036 |1.4061 |1. 4085 4.1 {1.4110 |1.4134 |1.4159 |1.4183 |1.4207 |1.4231 |1.4255 |1.4279 |1. 4303 |1.4327 4.2 |1.4351 |1.4375 |1.4398 |1.4422 |1.4446 |1.4469 [1.4493 |1.4516 /1. 4540 |1.4563 4.3 |1.4586 |1.4609 |1.4633 |1.4656 |1.4679 /1.4702 |1.4725 |1.4748 |1.4770 |1.4793 4.4 |1.4816 |1.4839 |1.4861 |1.4884 |1.4907 |1.4929 |1.4951 |1.4974 |1.4996 |1.5019 4.5 |1.5041 |1.5063 |1.5085 |1.5107 {1.5129 |1.5151 |1.5173 [1.5195 [1.5217 [1.5239 4.6 |1.5261 |1.5282 |1.5304 |1.5326 |1.5347 |1.5369 |1.5390 |1.5412 |1.5433 |1.5454 4,7 |1.5476 |1.5497 |1.5518 |1.5539 |1.5560 /1.5581 |1.5602 |1.5623 |1.5644 /1.5665 4.8 |1.5686 |1.5707 |1.5728 |1.5748 |1.5769 {1.5790 {1.5810 1.5831 (1.5851 |1.5872 4.9 1.5892 |1.5913 |1.5933 |1.5953 {1.5974 |1.5994 {1.6014 |1.6034 |1.6054 |1.6074 5.0 {1.6094 [1.6114 |1.6134 |1.6154 |1.6174 {1.6194 |1.6214 |1.6233 (1.6253 |1.6273 5.1 |1.6292 |1.6312 |1.6332 |1.6351 |1.6371 |1.6390 |1.6409 |1.6429 |1.6448 |1. 6467 5.2 |1.6487 |1.6506 |1.6525 |1.6544 |1.6563 /1.6582 |1.6601 |1.6620 {1.6639 |1.6658 5.3 |1.6677 |1.6696 |1.6715 |1.6734 |1.6752 |1.6771 |1.6790 |1.6808 |1.6827 {1.6845 5.4 |1.6864 |1.6882 |1.6901 |1.6919 |1.6938 |1.6956 |1.6974 |1.6993 |1. 7011 |1.7029 5.5 |1.7047 |1.7066 |1.7884 |1.7102 |1.7120 /1.7138 [1.7156 {1.7174 |1.7192 |1.7210 5.6 (1.7228 |1.7246 |1.7263 |1.7281 |1.7299 |1.7317 [1.7334 [1.7352 |1.7370 |1. 7387 190 AIR COMPRESSION AND TRANSMISSION NAPERIAN LOGARITHMS. eS et pe ——— a =" — pat pe ai hee! ve eee 8. . or ceils bO bO bO bo bo bo bo bo bo bo et _— — eee — eee —oe — aay bo bo bo bO bo bo bo DO bo bo bo bo bo bo bo bo bo eet oe Rt pet ——a— — ee — ee Nowy bobo bo bobo bo bo DNMp MMH MHP WH WH HYD Bee Se Eee Ddb MNMN Whwrp WO HWWHY HWwry COC CON AUR WHR © DON DOA WHH OO DON DOR WHH ©O CON QOR WHHL © SON D OOD WOOD OOO © MMM WMH MMH © NNN NNN NNN N Q2H 2QQ QAM @ aaa APPENDIX C HYGROMETRY'! Hygrometry is the measurement of the amount of water vapor in the atmosphere. There is always more or less water vapor in the atmosphere depending onits temperature and its degree of saturation. The study of hygrometry is of increasing importance. It has been found by experience that the moisture in air has a marked effect on many industrial processes, suchas the spinning of cotton, the smelting of iron in blast furnaces and the ventilation of factories and other buildings. It isalso necessary to know the amount of moisture pres- ent in all measurement of air or gases and in tests of machin- ery for handling the same. According to Dalton’s law, when a mixture of two gases fills a space of, say, 1 cu. ft., the pressure in the space is the sum of the two pres- sures that would be produced by a cubic foot of each of the gases alone at the same temperature. In the same manner a mixture of air and vapor hasa pressure which is the sum of the pressure of an equal vol- ume of dry air, and of vapor alone, each at the given temperature of the mixture. Air and vapor occur in mixtures varying from prac- tically dry air to a state of saturation such that any addition to the mixture of vapor at the same temperature causes a portion to con- dense. To every temperature there corresponds a certain water- vapor pressure or partial pressure which may be found in steam tables such as ‘“‘ Marks and Davis” or ‘‘ Peabody’s.”’ Air in actual practice rarely contains vapor with 1oo per cent. sat- uration and the weight of water vapor present is less than the maxi- mum for that temperature of air. The air is then said to be only partially saturated, and the degree of saturation is expressed by the ratio of the weight of water vapor actually contained in a given space to the maximum weight that the space can contain under the condi- tions of absolute pressures and temperatures existing at that time. This ratio is known as the “Relative Humidity.” Absolute Humidity.—The absolute humidity is the weight of water 1 Christie’s and Kowalke’s Steam and Gas Engineering Laboratory Notes. 191 192 AIR COMPRESSION AND TRANSMISSION vapor that 1 cu. ft. actually contains under the given pressure and temperature conditions. Relative Humidity.—Relative humidity is usually determined by means of psychrometers or wet -and dry-bulb thermometers. These consist of two thermometers fastened to a frame and placed in a current of air. The bulb of one thermometer is kept covered with cotton wick and is kept thoroughly wet with water at room tempera- ture. Ifthe airis not saturated, evaporation will take place from the wet bulb and its temperature will be lowered by the abstraction of the latent heat of the water. This lowering of the temperature has been found to be a measure of the relative humidity. Psychrometers.—Psychrometers are made in two types, stationary and sling. In the sling psychrometer the wick is moistened and the whole frame whirled around by a handle for 15 or 20 seconds. The wet bulb thermometer is read immediately after stopping. By the use of Chart A of the accompanying diagram the relative humidity may be obtained from the readings of the two thermometers. For example, if the dry-bulb thermometer shows a reading of 72° and the wet bulb 61°, or a difference of 11°, the relative humidity is 52.6 per cent., if the atmospheric pressure is 30 in. of mercury.. Ifthe atmos- pheric pressure is 28 in. the chart reading should be increased 2X 1/100 of 52.6 or 1.05, making the corrected relative humidity 53.65 per cent. In making accurate measurements of air it is necessary to deter- mine carefully the weight of moisture present in the atmosphere and the volume occupied by this vapor. In order to do this, reference is made to data regarding the density of vapor at various temperatures and pressures. This information is given in most steam tables and the following figures have been taken from Marks and Davis tables. The density or weight of the vapor per cubic foot isshown graphically in Chart C of the large diagram as the line marked 100 per cent. This same chart also shows weights of the vapor to be used in calcu- lations with air of various humidities, as shown in the example fol- lowing’ the tables. — ee ee “= Le ee SS te — < “4 : ‘ Te Bs we 2 7 = een ae mba \ . > pet aren ~~) es mee 5 ae tf ee a ahd pes myc ge: « ie, i eal: EE WE Sree Rony ons i - we * 4 4 , rp J pS } c « oe a9 ‘ } oes t ‘ shed 1 $ 5, } ‘ , J : ee ri ! i ed?” be th ee r te te ogee She a - nes a Snes eae! batcs 4 1 - Ne wh ert earl , “to” “iS 2 tg eg the : ‘ | mbes wauecs Saaees ta, See eceee eae ng ; ae ep ARs re ee ; Ce BNA Ol oss eS “hd ? “y ronment 4 ee, «=, Pea | AK ¥ ~ - ye be ’ * : - 4 ys 2 , ha . oT a's > S id =e w ts ee iS a- 3. ~*~ Py a * ~ ’ ¥ 5 . ASA, . f . : ? ra . > ; é is sv . rT ae, - Line OF obras! < as +32 § ape IN ie ner ; no eM ie Ut Oh OSes ey Sis se eS a & aes im 2% > ‘ .* a" o> fa: x 4 Er “t-i-* 4 S > ; ' “Fy dee he ee res ~ ¥ a - % - oe a + Anes — ie. waice OL , ‘ ; 4 S . eH ' r ' : i ¥ *% Oe ela She Se PT : _ ee : bigs ek Poe be) ee aK % al i er Os: es CSAP Ly anes Se SRS CRN ete er Cone = = fs . ‘ i , t I oo oer BEN, t en — SOE ee a Sy ere 1 SESS 2 Soto eae a ss = = “ e = \ ~ aa a SSFP a) SIN 1) sear WES COA) SEY SN NNER a Saeco (OOS ESET eS Re Boe a Ee ‘ Temperature of Air or Dry Bulb Thermometer, Degrees Fahrenheit coy o fo} o So 100 F = = = =: = £ 5 | = >! pe = 2 1 ao = 3 mod 2 1 4 = ry 5 S Fe ” = 7 3 E a 5 aS &S = v eer 0 = > § Pe =< xk = 10-5 of = Ee ~v nea oS — ae ~ > 3 Fy es + Dil 5 eze : 88 EES z pee bans = = 4 5 o gt =< 2 +fo = cy © Sts = Ibi ae =. © aS Pte les £ 3g 50 Ss oo? ~ 7 3 eg = = Ss - -o¢ 18 @ PA See A a Les 19 mo] rT) E2555 a: 282" 71 Ps "s rae y~ (er oo = o = 230 ees 1 = al > Ena So ~ 4 8 -—-> - 3 ot 3 = 25 = «3530 = = Ew ~ 75

~F-L17 36 Ea ld e (oa 3 ow 38 =k f S 39 Yo Oo Lo ss 40 ce 4l ov ;’ 42 vo ge Bi -=3 0 CHART A rey re ° 2 is) Ss Ss So So is 105 of, 6 is F : | | TTT y | ourune | | [ Lop ; | OUTLINE OF CALCULATIONS ; Specific Heat of Air ot 14.5 Lb. per Sq. Ih: + Weight of Water Vapor in Pounds} per Cubic!Foot+ = 2 2 ae. ae + i al Teoh Zz P 7B. TU; perPound PSb-oe Ieatcvintea from Valves givenin Marke a Dowie Steam Tables i i : 4 das roe ees ieee al a, hu oO w uw ‘a = : . i e A Bal ae | lies i Ss S S S | S 3 By Sturated vapor pressure in lbs. per sq. in.(Marks &Davis Stearn Tables used) | we 6 lo or AS? ASD Ay AS 40% 0 fo coe or S = B ° = Ss S Ss Ss Ss xP r Cent Hurniality | | | | | hae 00045 100 = f Se] a Ea 1 Pala |RT 5 Wee pei W= gt Worx My pe 2 — S ie 33 ge GED AOA oud) 3 8 0.0035 ++ < 90 F5S5|4596+7 ilies! $ [2 = + =i =\5 ~—t oO a nee 448 14.0) x £ o£. (OB S5\45S9.6 +4) - | a haa a ion ib s 3 L aoa Wo + We) Ser) + Wy Sw) a S + S fe S s = Way? WeFX 3 Ss ie i+ ‘cal at VE PX My, Ss > p + = 0.0030 i 2 £ 85 3 a alae 2 & 3 S ¢ > £ 4 i 5 S = co 4° ae 8 2 4 | o wo oe 2 ey a 1 cS 8 tg = ~ += aH S S. | Ta r Cor re + x r3 = $ a I SSS AOS ee Se c 0.0025 S18 lst! 3 fe, | LT LY ree |S Tr T || oe s+ rt ‘ = AO = E <> OF ue S ie | | =a x | ‘a & | AS esc ty Son a > 8 2 | |_| les we ae i 1 fe af e Ss g = + =H e Fe ii 164 te oe. Re = & Mo & Bas a ee Sat ret = a 7 ao020 "4 ‘$ & : a | : Hts bs Hee EHH Z £ a Sales = 2 Sy rete re = i & + | “ 2 ae jee ee 13 RG #3 : sleet & RG S ~ Rs S| tt Ie Lt + o & a = 5 a {its SLE re mS I &A8 g 70 eS rast i Nes ee 2 cs Heer 1 « AS Lag is Teo S | es | | ae ~Oy eS | 4 : at = Tl Ss 7 hey * rae Se a e S 7 y & %S pee anee fooes Betts HEE ) SEE ee eet Cees . s we S 65 x 8 | - Ly | =e elms} _ & 5S ; x S) aE Ss 4—S ie ey [ : t +. ttt eet { : Ct ae POPE ae a et et 5 ; = = T ir + + Al | as roe | 3 oa < = 2 | ©) = | EEC | aS 7 Tt ; 60 ] leaatssye | ie a CI > = | : L S « < a t * es " = Error in Specific Heat Curves: ; = oe es ee 4100 °F, 100% hurnidity anid pressure of #0 /é or- a at S = e: TI] gs ima iS | /5.0 |b per sg.in. these vizlves are in errorgof orre %. Bil ie Js iS | [ ze ' At 60°F, 00% humidity arid pressure of 140 /b or + ie [ [ | i © H 18.0 Ib. per sg.in. these values are in errorg ofone % = tn : +—|—+ “tt Ve | et | 2 55 S w ne % . CHART B CHART C zg : GHART.D * CHART E 8 CHART F g CHART 6 sg s 3 s Humipiry, WEIGHTS PER CuBIC Foor AND SPECIFIC HEATS oF W,. C. RowsE, Mapison, Wis. 1 TIXTURES OF AIR AND WATER VAPOR = 105 95 90 ao a s erature of Air, Degrees Fahrenhe ~~ Temp 65 60 55 APPENDIX, C 193 Tables showing the temperature, pressure, specific volume and density of steam or water vapor from 32° to 219° F., condensed from Marks’ and Davis’ Steam Tables by permission of the publishers, Longmans, Green & Co. pO Specific vol., Density, Temperature : cea cubic feet pounds per Pounds per Inches per pound cubic foot square inch mercury 32 0.0886 0.1804 3,204 ; O.000304 2 2A Be 0.0922 0.1878 ; pL Om ee 19 OC. 0003T0 34 0.0960 0.1955 3,052 0.000328 35 0.0999 0. 2034 2,938 ©.000340 36 0.1040 Oar rn? 2,829 0.000353 27, 0.1081 - 0.2202 ayn 0.000367 38 O.1T25 O.2290 2,626 0.000381 30 Oni170 0.2382 2,530 0.000395 40 OLT227, OV2477 2,438 0.000410 41 0.1265 0.2575 pe Ke. 0.000425 42 0.1315 0.2677 2,266 0.000441 43 0.1366 On 2782 2,185 0.000458 44 0.1420 0. 2890 2,107 0.000475 45 OfT 47s ©. 3002 2,033 0.000492 46 OLDE 32 0.3118 1,961 ©.000510 47 0.1591 0.3238 1,892 ©.000529 48 0.1051 0.3363 1,826 0.000548 49 0.1715 0.3492 1,763 0.000567 50 0.1780 0.3625 1,702 0.000587 51 0.1848 0.3762 1,643 0.000608 52 O.1Q17 0.3903 1,586 0.000630 53 0.1989 ©. 4049 1,532 0.000653 54 0.2063 0.4201 1,480 0.000676 55 0.2140 0.4357 1,430 2.000700 56 0.2219 0.4518 1,381 0.000724 i) 0.2301 0.4684 335 0.000749 58 0.2385 0.4856 1,291 0.000775 59 Os 2472 0.5034 1,249 0.000801 13 194 AIR COMPRESSION AND TRANSMISSION Pate Specific vol., Density, Temperature : re tometer cubic feet pounds per Pounds per Inches per pound cubic foot square inch mercury 60 0.2562 0.522 1,208 0.000828 61 O2054 0.541 1,168 0.000856 62 0.2749 0.560 1,130 0.000885 63 0.2847 0.580 1,093 ©.O000Q15 64 ©. 29049 0.601 1,058 0.000946 65 0.3054 oO. 022 1,024 0.000977 66 0.3161 0.644 ggI ©.O001009 67 0. 3272 0.667 959 ©.001043 68 0.3386 0.690 928 O.001077 69 0.3504 On7iA 899 O.OO111I2 70 0.3626 0.739 871 0.001148 71 Bgat 0.764 843 0.001186 7 0. 3880 0.790 817 O.001224 Fes O.4012 0.817 792 0.001263 74 0.4148 0.845 767 ©.001304 ws 0.4288 0.873 743 0.001346 76 0.4432 0.903 720 0.001389 ot 0.4581 0.03% 698 0.001433 78 0.4735 0.964 677 0.001477 79 0.4893 0.996 657 0.001523 80 0.505 I.029 636.8 ©.001570 8I O15 22 ip O0s O17 5 0.001619 82 0.539 1.098 598.7 0.001670 83 OL587 TLi134 580.5 O.001723 84 OVS75 ie 7a 562.9 O20017 77 85 0.594 I. 209 545.9 0.001832 86 O01? 1.248 526:.,5 0.001889 87 0.633 1.289 Bay ©.001947 88 0.654 1 B31 498.4 ©.002007 89 C2075 Daas 483.6 0.002068 go 0.696 TgA17 469.3 O.002131 QI °.718 1.462 455-5 0.002195 92 OL7AT 1.508 442.2 0.002261 93 0.765 T2556 429.4 0.002320 04 0.789 1.605 417.0 0.002398 APPENDIX C 195 Pressure . : Specific vol., Density, Temperature 2 Fahrenheit cubic feet pounds per Pounds per Inches per pound cubic foot square inch mercury 95 0.813 1.655 405.0 0.002469 96 0.838 1.706 303-4 0.002542 97 0.864 Le 7S0 20242 0.002617 98 0.891 1,813 27 LMA 0.002693 99 0.918 1.869 360.9 0.002771 100 0.946 1.926 350.8 0.002851 IOI 0.975 1.985 GAO 0.002933 102 1.005 2.045 ZZ 1s 0.003017 103 TROZS Siew B2242 0.003104 104 1.066 py hs Sy iew 0.003192 105 1.098 22230 BO4m 7) 0.003282 106 Pers 26303 2960.4 0.003374 107 1.165 gus72 288.3 0.003469 108 I.199 e443 280.5 0.003565 109 re235 2eSLs 27250 0.003664 IIO Lear 2.589 265.5 0.003766 III 1.308 2.665 2522 0.003871 Lis 1.346 2740 oa Ret) 0.003978 by he 14386 2,822 244.7 0.004087 II4 1.426 2.904 238.2 0.004198 II5 1.467 2.987 2270 0.004312 116 I.509 3.072 22573 0.004429 ray 14552 Be ror 219.9 0.004548 118 1.597 2-252 ZrAe TL 0.004671 I1g 1.642 3.344 208.5 0.004796 120 1.689 3.438 203.1 0.004924 I2E 1.736 aoe 197.9 0.005054 22 e705 3.635 192.8 0.005187 123 1.835 By Ta 187.9. 0.005323 124 1.886 3.841 183.1 0.005462 125 1.938 3.948 178.4 0.005605 126 1.992 4.057 17300 0.005751 127 2.047 4.168 169.6 ©.005900 128 21O 4.282 16553 0.006052 129 2.160 4.399 POT SI 0.006207 196 AIR COMPRESSION AND TRANSMISSION Pena Specific vol., Density, Temperature ; ea Nes cubic feet pounds per Pounds per Inches per pound cubic foot square inch mercury 130 2270 AasZ TS 7% 0.00637 131 221276 4.64 a5 a2 0.00653 132 2.340 4.76 149.4 0.00669 133 2.403 4.89 145.8 0.00686 134 2.467 5.02 142.2 0.00703 135 2.533 5.16 13027 0.00721 136 2.600 5.29 135.4 0.00739 £37 2.669 5-43 Poza 0.00757 138 R740 5.58 128.9 0.00776 139 2.812 ew ke 125.5 0.00795 140 2.885 5.88 122.3 0.00814 141 2.960 6.03 119.9 0.00834 142 Bk027 6.18 fi721 0.00854 143 Seni as 6.34 114.3 0.00875 144 BOs OF 55 IIr.6 0.00896 145 Bee 77 6.67 109.0 0.00918 146 Be ZOT 6.84 106.5 0.00940 147 3.446 702 104.0 0.00962 148 23:3532 7220 101.6 0.00985 149 3,023 7.38 99.2 0.01008 150 3.714 2A57 96.9 O,O1L0s2 I51 3.809 7 270 04.7 0.01056 152 3.902 7.95 92.6 0.01080 153 3-999 8.14 9005 = O.O1I05 154 4.098 8.34 88.4 O;OEI3I 155 4.199 Gas5 86.4 O.OII57 156 4.303 8.76 84.5 0.01184 r57 4.408 8.98 82.6 O.OI2I1 158 4.515 Q.20 80.7 0.01239 159 4.625 Q.42 78.9 0.01267 160 4.737 9.65 7702 0.01296 161 4.851 9.88 7S uS 0.01325 162 4.967 10.12 fc tates O.01355 163 5.086 10. 36 FORD 0.01386 164 5.208 10.61 70.6 O.OI417 Temperature Fahrenheit APPENDIX,C 197 Pressure : ; Specific vol., Density, cubic feet pounds per Pounds per Inches per pound cubic foot square inch mercury 5-333 10.86 69.1 0.01448 5-460 LLere 67.6 0.01480 5-589 T1245 66.1 O.OI1513 cana LI.65 64.7 0.01546 5.855 II.Q2 63.3 0.01580 5.992 12520 62.0 0.01614 OL 135 12.48 60:7 0.01649 09273 iy | 59.4 0.01685 6.417 13.07 58.1 O-On7 21 6.564 E3437 56.9 0.01758 6.714 E3307 Bey 0.017096 6.867 13.98 54.5 0.01834 i; O23 14.30 53-4 0.01873 Teth2 14.62 cos 0.01912 7-344 14.95 51.2 0.01953 fhe wt 15.29 5O. 15 0.01994 7.68 15403 49.12 0.02036 TEs 15.098 48.12 0.02078 8.02 16.34 47.14 O-O2T2T 8.20 £570 46.18 0.02165 8.38 17.07 Aseas 0.02210 8.57 17.45 44.34 0.02255 8.76 L7os 43.45 0.02301 nOE05 10.22 42.59 0.02348 9.14 18.61 ALTA 0.02396 9.34 19.02 40.91 0.02444 9.54 19.43 40.10 0.02493 9.74 19.83 39.31 0.02544 9.95 20.27 38.54 0.02505 TOL 7 20n7t 37.78 0.02647 10.39 Zia Ds 37.04 0.02700 10.61 21.60 3632 0.02753 10.83 22505 acyo? 0.02807 II.06 PUNE FAnOS 0.02863 71.20 22.99 34.26 0.02919 198 AIR COMPRESSION AND TRANSMISSION Eres Specific vol., Density, Temperature ’ Pahreoheit cubic feet pounds per Pounds per Inches per pound cubic foot square inch mercury 200 tT ah 2 225A 7 33.60 0.02976 201 11.76 23.95 32.96 0.03034 202 12.0% 24.45 3 2e a3 0.03093 203 12520 24.96 2272 0.03153 204 12555 25.48 Gratz 0.03214 205 T2477 26.00 20,53 0.03276 206 13203 20.53 29.95 0.03339 207 i3430 27.08 29.39 0.03402 208 Tig 554 2763 28.85 0.03466 209 13505 28.19 Baa 0.03531 210 T4512 28.76 27.80 0.03597 Bit 14.41 20.33 27-20 0.03664 Bee I4.70 29.92 26.79 Of02732 213 14.99 202 26.30 0.03802 214 15.29 ar 1s 25202 0.03873 Partial Pressures.—Suppose, for example, the barometers read 29.214 in. of mercury at a temperature of 78° F. Chart F of the diagram shows that at this temperature 1 in. of mercury corresponds to a pressure of 0.4889 Ib. per square inch. That is, the barometer reading of 29.214 in. of mercury corresponds to an absolute pressure of 14.2827 lb. per square inch. If the air is saturated with moisture at 78° F., the pressure exerted by this vapor is, as shown from the tables of Marks and Davis, 0.4735 lb. persquareinch. The pressure of the dry air present would then be 14.2827—0.4735 or 13.8092 lb. per square inch. Suppose the psychrometer shows a relative humidity of 40 per cent. As the vapor pressures are proportional to the absolute weights, the pressure exerted by the moisture in the air will be 40 per cent. of 0.4735 or 0.1894 lb. per square inch. In this case the pressure due to the dry air present will be 14.2827 —0.1894 or 14.0933 lb. per square inch. If it is necessary to find the weight of a cubic foot of this moist air, this can be found by adding the weight of the cubic foot of dry ALPEN DIX'G VES}) air at its pressure and temperature to the weight of the vapor present. The weight of vapor present is found by multiplying the weight of a cubic foot of vapor at the given temperature by the relative humidity. The tables show that 78° F., the weight of a cubic foot of vapor, is 0.001477. The weight of the vapor present in the example is 40 per cent. X0.001477 or 0.000501 lb. The weight of dry air present is found from the formula BiVa 144 X 14.0933 Sh Sys == - =0.070 53-311 53-3(460+78) Nie The weight per cubic foot of the air and its accompanying vapor is == le 0.000591 +0.070773 =0.071364. This calculation can be made quite simply by referring to the various charts of the large diagram. By referring to Chart D it will be seen that the weight of air at 4o per cent. relative humidity and 78° F. is .o6992 lb. per cubic foot if the pressure of the atmosphere is 14 lb. per square inch. In the example given the pressure is 14.2827 lb. per square inch. By referring to Chart E it will be seen that for the pressure of 14.2827 and temperature of 78° F. a correction of 0.00144 should be added making the weight per cubic foot of this mixture 0.06992-+0.00144 or .07136 lb. per cubic foot. When it is desired to measure air with a Thomas electric meter, the mean specific heat of the mixture of air and water vapor must be known. W. H. Carrier in his paper ‘‘ Rational Psychrometric Formule,” Journal A. S. M. E., Nov., 1911, gives the following values which represent the results of the more recent investigations on the specific heat of air and water vapor. Instantaneous specific heat of air C pa =0.24112-+0.0000001 where ¢ is the temperature in degrees Fahrenheit; and the instan- taneous specific heat of water vapor as approximately C ps =0.4423 +0.0001 8 where ¢ is the temperature in degrees Fahrenheit. Applying these formule to the example given with temperature of 78, C pa IS 0.241822 and C ps 1S 0.45634. 200 AIR COMPRESSION AND TRANSMISSION The mean specific heat can then be found by multiplying the weight of each substance in the mixture by its specific heat, adding the products, and dividing the sum by the weight of the mixture. Thus For the air, 0.070773 X0.241822 =0.017114 For the moisture, 0.000591 X0.45634 =0.000270 0.017384 Mean specific heat is 0.017384 -+0.071364 or 0.2436. The mean specific heat may also be obtained by referring to Chart B of the large diagram. This shows that for the given temp- erature of 78° F. and a relative humidity of 40 per cent. the mean specific heat may be taken as 0.2435. The above principles are applied commercially in testing steam condensers. An accurate thermometer is placed in the suction to the dry air pump and a mercury column attached to the same. In a condenser the conditions are such that the mixture is always saturated. Hence the pressure due to water vapor passing to the air pump will equal that due to its temperature as given in the steam tables. Then the difference between this pressure and that shown by the mercury column will equal the pressure due to the dry air in the mixture. If the volumetric efficiency of the air pump is known, the amount of air pumped can be computed, and this gives a means of readily checking the condensing equipment - for air leakage. The large diagram containing Charts A, B, C, D, E, F and G was prepared by W. C. Rowse, Instructor in the Steam and Gas Engineering Department of the University of Wisconsin. INDEX Absolute humidity, 191 temperature, 5 zero, 6 Action of piston compressor, 70 Actual card of piston compressor, 78 compression, 75 Advantage of isothermal compressor, 25 of multi-stage compressor, 90 AIT UE at low pressures, 38, 68 at pressures below the atmosphere, 26,—68 composition, 1 characteristics, 1-4 and energy equations, 10-17 compressor cards, 75 discharge valve, 102 density at various pressures, 174 dry, 4 for cupolas, 39 for forges, 39 for ventilation, 39, 40 free, 2 humidity, 2-6 internal energy, 6, 7, 16 in water, 29 inlet valve, ror measurement, 160-171 pump, Edwards, 31 U.S. Navy, 30 supply for various buildings and rooms, 40 Allis Chalmers fan, 65 Altitude effect, 140-144 Anemometers, 43 Apparatus for measuring large quan- tities of air, 166 Apparent specific heat, 8 volumetric efficiency, 77 Area of inlet valves, 100 of discharge valves, 1or of fan blast, 43, 62 Arrangements for coupling turbo- blowers, 125 Arthur compressor, 132 Arthur, Thomas, 132 Automatic valves, 100 Available power, 179 Axial discharge fan, 41 thrust, balancing, 121 Balancing axial thrust, 121 Rateau impellers, 122 by balancing piston, 123 by counter position, 121 by diminishing back area, 122 Baloche and Krahnass compressor, eWay Bed Belt regulator, 105, 107 Blast area, fans, 43, 62 Blower capacities, 50 cross section, 50 definitions, 42 efficiency, 81 losses, 81 mixing, 127 Parsons, 114 pressures, 50 Rateau, 114 Blowing engine, 41 Blowers, 41 Boyle’s law, 10 Brake horse-power for fans, 58, 60, 66 Brauer’s method of constructing ex- ponential curves, 19 Brown, Boveri and Co. turbo-com- pressor, 117 British thermal unit, 6 Buildings, air required, 40 Calculated and actual horse-power required for single stage com- pression, 74 Capacity of blowers, 50 of fans, 42 of intercoolers, 93, 94 201 202 Capacity of receivers, 160 Card of piston compressor, actual, 78 ideal, 77 Cards, combined two-stage, 147 clearance unloader, 112 from air compressors, 70, 75 showing adiabatic and isother- mal compression, 73 Carrier, W. H., 199 Centrifugal fans, 38-65 Channing, J. Parke, 144 Characteristic and energy equations fOtedit, 20-87 equation for perfect gas, IO Characteristics of air, 1-4 Christie, A. G., 101 Classification of fans and blowers, 41 of valves, 98 Clayton governor, I09 Cleaning valves, 182 Clearance effect, 70, 71, 96, 97, 990 methods of reducing, 71 unloader, 110, 112 > Cards 142 Coefficient of contraction, 43 of efflux, 43, 56 of velocity, 43 Combined cards, two-stage compressor, 147 governor and regulator, 109 Common logarithms, 184-186 Comparative effect of altitude on out- put, 143 Compensator, hydraulic, 83 lever, 83, 84 weight, 83 Composition of air, 1 Compressed air explosions, 182 Compression, actual, 75 isothermal, 25 line, 73 wet and dry, 74 exponential, 23 Compressor, direct-acting steam, 82 low pressure, 38 tests, 144, 158 Computation of internal or intrinsic energy. 16 INDEX Concentration of liquors, 34 Condenser pumps, 27 Cone wheel fans, 65, 66 Constants for pipe formule, 174,175 Construction of equilateral hyperbola, 18, 19 of exponential curves, 19 of isothermal curves, 18 Contraction, coefficient of, 43 Cooling capacity, 93 devices, 117 surface, 93 turbo-compressors, II5 Cost of Taylor compressor at Ains-_ worth, B. C., 136 Coupling compressors, 124 Cross-section, standard blower, 50 piston compressor, 69 Cupolas, air required, 39 Cutler-Hammer Co., 161 Cylinder efficiency, 80 D’Auria system of energy compensa- tion, 83 Dalton’s law, 191 Davis, G. J., 164 Definitions, fundamental, 5—9 for fans and blowers, 42 Density of air for various pressures, 174 of water vapor, 193-108 Description of fans, 58 Design of fans, 58, 67 of turbo-compressors, 113 Details of piston air compressors, 98- 110 Developed section of Parsons blades,115 Devices, cooling, 117 Diagram, three stage piston compres- sor, 116 turbo-compressor, 116 Diagrammatic sketch of Thomas elec- tric meter, 169 Diagrams, graphical, 18-25 Difference between isothermal and adiabatic compression, 22 Direct acting steam compressor, 82 Disc fan, 58 Discharge from a fan, 57, 59, 66 valve, 102 INDEX Discharge, area, or Draft measurement, 43 Dresser coupler, 172 Dry air, 4 pump, 27 Duplex compressor, 86 cross compound steam, two-stage air compressor, 88 belt driven compressor, 87 steam driven compressor, 87 Durleys Ref. 266 Economic efficiency, 81 Edwards air pump, 31 Effect of altitude, 140-144 of clearance, 70, 71, 96, 97 of changing discharge pressure, 99 of early closing of inlet valve, 73 of pressure on temperature, 4 Effects of heat, 6 of outlet on capacity, 55 Effects of pressure on tempera- ture A Efficiency, apparent volumetric, 77 blower, 81 cylinder, 80 economic, 81 of compression, 80 of fans, 45 of Taylor compressor, 134 Efficiencies, 77-82 true volumetric, 80 Efflux, coefficient of, 43, 56 Electric meter, diagram, 169 Energy, 5 compensation, 82-88 in air, 6 Engineering Magazine, 113 Equalizing steam pressure and air resistance, 82 Equilateral hyperbola, 18, 19 External energy changes, 6 Expansion of casing, 118 Explosions, compressed air, 182 Exponential compression, 23 curve construction, 19 Fan, blast or steel plate, 60 capacity, 42 203 Fan, centrifugal, 38-65 cone wheel, 65-66 definitions, 42 design, 58-67 description, 58 discharge, 58, 59, 66 efficiency, 45 losses, 45 mechanics of, 52 pressure, 42 proportions, 41, 61 radial wheel, 58 speed, 62, 67 Fans, axial, 41 classification of, 41 or blowers, 41 Flow of gas through an orifice, 45, 46 Forges, air required, 39 Forms of poppet valves, ror Free air, 2 discharge, 42 Friction effect of elbows, 61, 176 Frigells |5.P:.120 Frizell’s compressor, 129 Fundamental definitions, 5-9 Gases in air, I Governor and regulator combined, 109 Clayton, 109 for electric driven compressors, 107 Nordberg, 109, 110 Grains, vapor per cu. ft. saturated air, 2 Graphical construction of exponential curve, 18, 19 of isothermal curve, 18, 19 diagrams, 18-25 method of determining head, 165 mean Halsey, F. A., 142 Hammon coupler, 172, 173 Heat. 5 added or taken away for iso- thermal change, 21 for exponential change, 21 etrects.6 taken away during compression, 22 204 Hero’s device for opening temple doors, VII fountain, VII Horse-power, brake for fans, 58, 60, 66 single-stage compression, 74 Horizontal-vertical arrangement of cylinders, 86 Housing for fans, 42-63 Humidity, absolute, ror OL aipmtone 1s & Hydraulic air compression, 129-139 air pump, 26 . compensator, 83° * compression losses, 138 compressor, Arthur’s, 132 Baloche and Krahnass, 131, 132. Taylor’s, 133-137 Hygrometry, 191 Ideal card, piston compressor, 77 Impellers, rotary blowers, 49, 50 Improved cooling, turbo-compressors, 118 Indicator card piston compressor, 70 cards, condenser pumps, 30 Industrial uses vacuum, 32 Ingersoll Rand Co., 103, 111, 112 compressor, 147 Inlet connection, 183 for blowing fan, 61 for exhaust fan, 61 valve, Ior area, 100 setting, Ior Intercoolers, 90 capacity, 93 Nordberg, 92 pressure, 93 surface required, 93 types, 92 tubes, 92 with separator, 92 Internal energy changes, 6 or intrinsic energy of air, 7 computation of, 16 acver. (5 Heerco Jaeger’s turbo-blower, 119 patent impeller, 120 INDEX Kennedy blowing engine valve, 105 Kowalke, O. L., 191 Krahnass, A., 131 Labyrinth bushing, 120 Law, Boyle’s, 10 of Charles, ro Leakage past turbo-stages, 120 Lecture by H. deB. Parsons on fans, 41-68 Lever compensation, 83, 84 Leyner air reheater, 177 Liquors, concentration of, 34 Logarithms, common, 184-186 Naperian, 188-190 Loss of capacity due to clearance, 79 of head due to friction in ducts, 47 Losses of blower, 81 of hydraulic compression, 138 Low pressures, compressors, 38 Lubricating compressors, 182 Marks and Davis condensed steam tables, 193-198 Measurement of compressed air, 160- 171 of draft, 43 of large quantities of air, 166 Measuring vacuums, 27 Mechanical efficiency, 81 valve of Corliss type, 104 valves, 98 Mechanically operated discharge valve, I0o Mechanics of the fan, 52 Mercurial air pump, 26 Meter comparisons, 170 test results, 171 Methods of reducing clearance, 71 Mines and Minerals, 144 Mixing blower, 127 Mode of conducting tests, 147 Modern form of Pitot tube, 162 Moisture precipitated from air, 3 Mt. Cenis tunnel, VIIT Multi-stage compression, 97 advantages, 90 Naperian logarithms, 188-190 INDEX Net efficiency, 81 Nordberg compressor test, 144 governor, 10g—110 intercooler, 92 Mfg. Co., 109 Norwalk compressor, 84 regulator, 108 Notation of symbols for fan formule, 47 Numerical value of R, 10 Orifice, flow of gas in, 45, 46 Oxygen in air, I in hydraulic compressed air, 137 Parsons, H. deB., 41-68 blower, 114 blades, 115 Partial pressures, 198 Peele, Robert, 140 Perfect gas, characteristic equation, IO intercooling, 93 Peripheral speed of fans, 62, 67 Phenomena of hydraulic air compres- sion, 137 Pipe couplers, 172, 173 formule, constants, 174, 175 lines, 171-176 line formule, 173 losses, ducts, 48 Piston, balancing, 123 -balanced turbo-compressor, 122 compression, hydraulic, 72 three-stage diagram, 116 compressor action, 70 cross-section, 69 details, 98-112 compressors, 69-77 controlled by multiplicator, 126 -inlet valve, 102, 108 Pitot tube, 161, 162 Pounds of water precipitated per cu. ft. cooled air, 3 Power, 5 available, 179 consumed by rotary and piston compressors, 52 for rotary blowers, 51 205 Pressures, blower, 50 oz. per sq. in. in water head to inches, 44 used for various stages, 90 water column in inches to oz. per sq. in., 44 Proper receiver pressure for multi- stage compression, 96 Propeller fan, 58 Proportions of fans and housing, 41, 61 of rotary blowers, 50 Psychrometers, 192 Pump, dry air condenser, 26 Pumps, condenser, 26-30 R, numerical value, 10 Radial wheel fan, 58 Railway and Engineering Review, 130 Rand Imperial unloader, 111 Rateau blower, 114 multiplicator, 125 turbo-compressor, 128 Ratio of air cylinder to low-pressure steam cylinder, 29 of air cylinder to volume of con- densed steam, 29 of port to cylinder area, 100 Real specific heat, 8 Receiver aftercoolers, 159 intercoolers, 92 capacity, 160 Receivers, 159 Regulator, belt, 105, 107 and governor combined, 109 Norwalk, 108 Regulators and unloading devices, 105 Relation between altitude and volume, 141 specific heats, 10 Relations between P, v and T for adiabatic and _ exponentia changes, 16 Relative humidity, 192 Restricted discharge, 42 Results of meter tests, 171 of tests, 148 Richards, Frank, 175 Right-angle bend resistance, 49 206 Robinson, S. W., 163 Rotary blowing machines, 49 blowers, proportions, 50 Rooms, air required, 40 Rowse, S. W., 200 Runners, 119 Salt evaporating effects, 32 Sangster, Wm., 39 Schmidt, Henry F., 81 Sectional view of Thomas meter, 168 Selection of air compressors, 179-182 Semi-mechanical valves, 103 Shape of fan blades, 58, 61, 66, 67 Simple form of Pitot tube, 161 Single-stage compression, horse-power required, 74 Sirocco double inlet fan, 68 Size and type of compressor, 181 of water and air pumps, 28 Sketch of meters placed tandem for testing, 170 Sommeiller’s compressor, IX Southwork blowing engine valve, 104 Specific heat, 7 apparent, and real, 8 at constant pressure, 7 at constant volume, 7 at various pressures peratures, 8 volume of water vapor, 193-1098 Speed of fans, 58, 62, 67 of turbo-compressors, 113 Sperr, aa Ws E36 Sprengle air pump, 26 St. John’s meter, 166 Standards of measurement, 160 Steam cylinder size, 30 Steel plate fans, 61, 64 Straight line compressor, 84 Stuffing boxes, 123 Suction line, 73 Surface of intercoolers, 93 Sullivan air reheater, 177 Mch) Cota 153 Summary of tests, 157 Syphon, 37 bulk head, 131 electric and tem- INDEX Taylor, Charles H., 133 compressor, 133 efficiency, 134 at Ainsworth, B. C., 135 at Magog, Quebec, 134 at Victoria mine Michigan, 136 Temperature, 5 absolute, 5 Temperatures due to adiabatic com- pression, 22, 23 Test curves, Jaeger’s turbo-blower, 124 of hydraulic compressor, 136 of plant No. 1, 148-151 of plant No. 2, 151-154 of plant No. 3, 154-156 of plant No. 4, 156-157 Tests, mode of conducting, 147 Thomas, Cy Ci rr60 meter, 168 diagram, 169 Three-quarter housed steel plate fan, 64 Tightness between stages, 120 Towl, Forrest, M., 160, 171 Trompe, 129 True volumetric efficiency, 80 Turbine blast or Sirocco fan, 67 Turbo-blower coupling arrangements, 125 ol2s 000 Cutt. 121 of 140,000 cu. ft. capacity, 128 Turbo-compressor cooling, 115 design, 113 diagram, 116 for mixing air and gas, 128 Jaeger’s, 119 Parson’s, 114 Turbo-compressors, 113-128 Two-stage compressor cards, 147 Types of blading, 68 U. S. Navy pump, 30 Uncovering port to release clearance pressure, 71 Unloader, clearance, 110, 112 Rand Imperial, 111 Unloading devices, 110 Uses of air at low pressures, 38 Usual velocity in ducts, 47 Vacuum cleaners, 36 concentration of liquors, 34, 35 manufacture of salt, 32 measurement, 27 Valve area, 100 of discharge, 101 gear, 179 in cylinder head, 102 mechanical, 98 poppet, Io1 piston-inlet, 102 setting, 101 semi-mechanical, 103 Valves, area of inlet, 100 automatic, 100 classification, 98 cleaning, 182 Vapor in air, 1 Velocity, coefficient of, 43 of air through ports, ror meters, 161 Ventilation, air required, 39, 40 Venturi meter, 167 vacuum pump, 26 Volumetric efficiency, 77 apparent, 77 true, 80 meters, 160 Water, air in, 29 INDEX 207 Water-cooled turbo-compressor, 117, 118 Water measurements, hydraulic com- pressor tests, 137 percipitated from compressed air, 3 present in saturated air, 2, 55 required for intercooler, 94 Webb, Richard, L., 146 Weight compensation, 83 of air, 10 Westinghouse air pump, 85 governor, 106 Wet air pump, 27 displacement meter, 160 and dry compression, 74 Weymouth, Thos. R., 164 Wheeler combined pump, 27 condenser pump, 28 Work, 5 done by a compressor, 23 of adiabatic change, 15 of exponential change, 14 of isothermal change, 12 required to move a volume of gas 56 Zero, absolute, 6 Zur Nedden, Franz, 81, 113 =o oo es pee Sensis sitet . sseesneeiciacocet net mea tenpeat et ‘=< sree: SEHR eorereeere erate : 6 == o terete SM See etree sir: te 4 ee eae ae es ac ese sea nee ae ore cee aanee apres cen ramen tenance rere EE renee cLeteP OER EE SHIH: bs om) SEH eee pepe SESE SSH Hirt: === ay Siena onesie Naa casa sescenensrcesssgeseveeveeescerersererey SSHNGIN Eirias — ies serge tates toss ea ones tosecne aga tegwsoteetenersenensesatesenterereaerraveeseeeet PH EIT a ES coe ret careatnecomrab neem eet ciieaseisseess SHETISIEHE MEST [=o sigdsistecsscevesee oat opaceeteerrocstgedsttise ctebsespistesrsosssraseasatesseeeressestevsieesess b2E LESS OHS 7 wid recee ew rer Tesep eA yee aiyenee aba ead iyapaten atyign PESTON ICSD ION Heit coy oppress ie eee basi desde ebeersiebuseousecerdeatecddecds nee UUToooUDUUD fener 634 SUSSbopupUAusebeicadssameds sie ST. 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