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 Modern 
 Engineering Practice 
 
 Sc&oat. a-L 
 
 d 
 
 A Reference Library 
 
 ON ELECTRICITY, STEAM, GAS ENGINES AND PRODUCERS, AUTOMOBILES, 
 
 MARINE AND LOCOMOTIVE WORK, REFRIGERATION, PATTERN 
 
 MAKING, FOUNDRY WORK, SHOP PRACTICE, TOOL MAKING, 
 
 FORGING, MECHANICAL DRAWING, MACHINE DESIGN, 
 
 HEATING, VENTILATION, STEAM FITTING, 
 
 PLUMBING, ELEVATORS, ETC. 
 
 Editor-in- Chief 
 FRANK W. GUNSAULUS 
 
 PRESIDENT, ARMOUR INSTITUTE OF TECHNOLOGY 
 
 Assisted by a Corps of 
 DISTINGUISHED ENGINEERS AND TECHNICAL EXPERTS 
 
 Illustrated with ever Five Thousand Engravings 
 
 TWELVE VOLUMES 
 
 CHICAGO 
 AMERICAN SCHOOL OF CORRESPONDENCE 
 
 1908
 
 COPYRIGHT 1902, 1903, 1905, 1906, 1908 BY 
 AMERICAN SCHOOL OF CORRESPONDENCE 
 
 Entered at Stationers' Hall, London 
 All Rights Reserved
 
 Editor-in-Chief 
 FRANK W. GUNSAULUS 
 
 President, Armour Institute of Technology 
 
 Authors and Collaborators 
 
 F. B. CROCKER, M. E., Ph. D. 
 
 Head of Department of Electrical Engineering, Columbia University. 
 Past President, American Institute of Electrical Engineers. 
 
 WILLIAM T. McCLEMENT, A. M. 
 
 Formerly Professor of Chemical Engineering, Armour Institute of Technology. 
 
 WILLIAM ESTY, S. B., M. A. 
 
 Head of Department of Electrical Engineering, Lehigh University. 
 Joint Author of "The Elements of Electrical Engineering." 
 
 VICTOR C. ALDERSON, D. Sc. 
 
 President, Colorado School of Mines. 
 
 DUGALD C. JACKSON, B. S., C. E. 
 
 Head of Department of Electrical Engineering, Massachusetts Institute of 
 Technology. 
 
 LOUIS DERR, S. B., A. M. 
 
 Associate Professor of Physics, Massachusetts Institute of Technology. 
 
 HOWARD M. RAYMOND, S. B. 
 
 Dean of Engineering Studies, Armour Institute of Technology.
 
 Authors and Collaborators Continued 
 
 KEMPSTER B. MILLER, M. E. 
 
 Telephone Expert and Consulting Engineer. Author of "American Telephone 
 Practice." 
 
 WALTER S. LELAND, S. B. 
 
 Assistant Professor of Naval Architecture, Massachusetts Institute of Technology. 
 American Society of Naval Architects and Marine Engineers. 
 
 GEORGE C. SHAAD, S. B., E. E. 
 
 Associate Professor of Electrical Engineering, Massachusetts Institute of Tech- 
 nology. 
 
 CHARLES DICKERMAN 
 
 Refrigerating Engineer, Pennsylvania Iron Works Co. 
 
 FRITZ LUBBERGER, E. E. 
 
 Chief Engineer, Automatic Electric Co. 
 Western Society of Engineers. 
 
 ALBERT F. HALL, S. B. 
 
 American Society of Mechanical Engineers. 
 
 American Society of Naval Architects and Marine Engineers. 
 
 Institute of Mechanical Engineers of England. 
 
 German Society of Engineers. 
 
 Associate Member, Institute of Civil Engineers of England. 
 
 ALFRED E. PHILLIPS, C. E., Ph. D. 
 
 Professor of Civil Engineering, Armour Institute of Technology. 
 *r* 
 
 CHARLES THOM 
 
 Chief, Quadruplex Department. Western Union Telegraph Co. 
 
 ARTHUR L. RICE, M. M. E. 
 
 Editor of "The Engineer," Chicago. 
 
 !r 
 
 CHARLES E. DURYEA 
 
 First Vice-President, American Motor League. 
 Author of "Roadside Troubles."
 
 Authors and Collaborators Continued 
 
 FRANCIS H. BOYER 
 
 Constructing Engineer. 
 
 American Society of Mechanical Engineers. 
 
 LIONEL S. MARKS, S. B., M. M. E. 
 
 Assistant Professor of Mechanical Engineering, Harvard University. 
 American Society of Mechanical Engineers. 
 
 SAMUEL S. WYER 
 
 Mechanical Engineer. 
 
 American Society of Mechanical Engineers. 
 
 WALTER B. SNOW, S. B. 
 
 Formerly Mechanical Engineer, B. F. Sturtevant Co. 
 American Society of Mechanical Engineers. 
 
 SAMUEL G. McMEEN 
 
 Telephone Expert and Consulting Engineer. 
 
 GEORGE L. FOWLER, A. B., M. E. 
 
 Consulting Engineer. 
 
 American Society of Mechanical Engineers. 
 
 American Railway Master Mechanics' Association. 
 
 LAWRENCE K..SAGER, S. B., M. P. L. 
 
 Patent Attorney and Electrical Expert 
 Formerly Assistant Examiner, U. S. Patent Office. 
 
 WILLIAM C. BOYRER, M. E., M. M. E. 
 
 Formerly Division Engineer, N. Y. and N. J. Telephone Co. 
 
 WILLIAM S. NEWELL, S. B. 
 
 With Bath Iron Works, Bath, Me. 
 
 Formerly Instructor, Massachusetts Institute of Technology. 
 
 ROBERT V. PERRY, S. B., M. E. 
 
 Associate Professor of Machine Design, Armour Institute of Technology.
 
 Authors and Collaborators Continued 
 
 NATHAN HASKELL DOLE 
 
 Editor, "American Dictionary and Cyclopedia," "The Library of the World's Best 
 ' Literature," "The Literature of All Nations," "The International Library 
 of Literature," etc. 
 
 ALFRED E. ZAPF, S. B. 
 
 Secretary, American School of Correspondence. 
 
 WILLIAM G. SNOW, S. B. 
 
 Steam Heating Specialist. 
 
 American Society of Mechanical Engineers. 
 
 Author of "Furnace Heating," etc. 
 
 MAURICE LEBOSQUET, s. B. 
 
 British Society of Chemical Industry. 
 American Chemical Society. 
 
 FREDERICK W. TURNER 
 
 Instructor in Machine Shop Work, Mechanic Arts High School, Boston. 
 
 JAMES RITCHEY 
 
 Formerly Instructor in Wood Working, Armour Institute of Technology. 
 
 JAMES R. CRAVATH 
 
 Western Editor, "Street Railway Journal," Chicago. 
 
 JOHN C. SHERMAN, S. B. 
 
 Formerly with the Westinghouse Companies. 
 
 MELVILLE B. WELLS, C. E. 
 
 Associate Professor of Bridge and Structural Engineering, Armour Institute 
 of Technology. 
 
 CHARLES L. HUBBARD, S. B., M. E. 
 
 Consulting Engineer on Heating, Ventilating, Lighting and Power.
 
 Authors and Collaborators Continued 
 
 R. F. SCHUCIIARDT, B. S. 
 
 Testing Engineer, Chicago Edison Company. 
 ^ 
 
 EDWARD R. MARKHAM 
 
 Consulting Mechanical Engineer. 
 
 Instructor in Machine Shop Work, Harvard University and Rindge Manual 
 
 Training School. 
 
 Formerly Superintendent, Waltham Watch Tool Co. 
 American Society of Mechanical Engineers. 
 
 GEORGE F. GEBHARDT, M. E., M. A. 
 
 Professor of Mechanical Engineering, Armour Institute of Technology. 
 
 CHARLES E. LORD, S. B. 
 
 Manager of Patent Department, Bullock Electric Mfg. Co. 
 ^ 
 
 A. FREDERICK COLLINS 
 
 Author of "Wireless Telegraphy, Its History, Theory, and Practice." 
 
 WM. C. STIMPSON 
 
 Head Instructor in Foundry Work and Forging, Department of Science and 
 Technology, Pratt Institute. 
 
 EVERETT E. KENT, S. B., LL. B. 
 
 Counselor-at-Law, Attorney, and Expert in Patent Cases. 
 
 HENRI F. CHADWICK, S. B. 
 
 President.. Casino Technical Night School, Pittsburg. 
 
 JOHN LORD BACON 
 
 Instructor in Forge Work, Lewis Institute, Chicago. 
 
 ERVIN KENISON, S. B. 
 
 Department of Mechanical Drawing, Massachusetts Institute of Technology. 
 
 CHARLES L. GRIFFIN, S. B. 
 
 Mechanical Engineer, Semet-Solvay Co. 
 
 Formerly Professor of Machine Design, Pennsylvania State College. 
 
 American Society of Mechanical Engineers.
 
 Authors and Collaborators Continued 
 
 PERCY H. THOMAS, S. B. 
 
 Of Thomas & Neall, Electrical Engineers, New York Cit., . 
 Formerly Chief Electrician, Cooper Hewitt Electric Co. 
 
 RALPH H. SWEETSER, S. B. 
 
 Superintendent Algoma Steel Co., Ltd. 
 
 American Institute of Mining Engineers. 
 
 Formerly Instructor, Massachusetts Institute of Technology. 
 
 ROBERT A. MILLIKAN, Ph. D. 
 
 Associate Professor of Physics, University of Chicago. 
 -* 
 
 JOHN H. JALLINGS 
 
 Mechanical Engineer. 
 
 *r* 
 
 LLEWELLYN V. LUDY, M. E. 
 
 Professor of Mechanical Engineering, Purdue University. 
 American Society of Mechanical Engineers. 
 
 CHARLES E. KNOX, E. E. 
 
 Consulting Electrical Engineer. 
 
 American Institute of Electrical Engineers. 
 
 WALTER H. JAMES, S. B. 
 
 Department of Mechanical Drawing, Massachusetts Institute of Technology. 
 Tr- 
 
 LAWRENCE S. SMITH, S. B. 
 
 Department of Mechanical Engineering, Massachusetts Institute of Technology, 
 
 <y- 
 
 NATHAN R, GEORGE, JR., A. M. 
 
 Department of Mathematics, Massachusetts Institute of Technology. 
 Tr* 
 
 LOUIS A. OLNEY, A. C. 
 
 Head of Department of Textile Chemistry and Dyeing, Lowell Textile School. 
 *x 
 
 HARRIS C. TROW, S. B., Managing Editor 
 
 Editor of Textbook Department, American School of Correspondence. 
 American Institute of Electrical Engineers.
 
 Authorities Consulted 
 
 THE editors have freely consulted the standard technical literature of 
 America and Europe in the preparation of these volumes. They 
 desire to express their indebtedness, particularly, to the following 
 eminent authorities, whose well known treatises should be in the library 
 of every engineer. 
 
 Grateful acknowledgment is here made also for the invaluable co-opera- 
 tion of the foremost engineering firms, in making these volumes thoroughly 
 representative of the best and latest practice in the design and construction 
 of steam and electrical machines and machine tools; also for the valuable 
 drawings and data, suggestions, criticisms, and other courtesies. 
 
 FRANCIS BACON CROCKER, M. E., Ph. D. 
 
 Head of Department of Electrical Engineering, Columbia University; Past President, American 
 
 Institute of Electrical Engineers. 
 Author of "Electric Lighting," "Practical Management of Dynamos and Motors." 
 
 SCHUYLER S. WHEELER, D. Sc. 
 
 Electrical Expert of the Board of Electrical Control, New York City; Member American 
 
 Societies of Civil and Mechanical Engineers. 
 Author of "Practical Management of Dynamos and Motors." 
 
 ^ 
 
 WILLIAM M. BARR 
 
 Member of American Society of Mechanical Engineers. 
 
 Author of "Boilers and Furnaces," "Pumping Machinery," "Chimneys of Brick and Metal,' 
 etc. 
 
 ^- 
 
 SIMPSON BOLLAND 
 
 Author of "The Iron Founder," "The Iron Founder's Supplement." 
 
 HORATIO A. FOSTER 
 
 Member American Institute of Electrical Engineers; American Society of Mechanical 
 
 gineers. Consulting Engineer. 
 Author of "Electrical Engineer's Pocketbook." 
 
 J. FISHER-HINNEN 
 
 Late Chief of the Drawing Department at the Oerlikon Works. 
 Author of "Continuous-Current Dynamos." 
 
 WILLIAM F. DURAND, Ph. D. 
 
 Formerly Professor of Marine Engineering, Cornell University. 
 
 Author of "Resistance and Propulsion of Ships," "Practical Marine Engineering. 
 
 W. H. FORD, M. E. 
 
 Author of "Boiler Making for Boiler Makers."
 
 Authorities Consulted Continued 
 
 ROBERT GRIMSHAW, M. E. 
 
 Author of "Steam Engine Catechism." "Boiler Catechism," "Locomotive Catechism, " "Engine 
 Runner's Catechism," "Shop Kinks." etc. 
 
 ^ 
 
 GARDNER D. HISCOX, M. E. 
 
 Author of "Gas, Gasoline, and Oil Engines." 
 
 V 
 
 GEORGE C. V. HOLMES 
 
 Whitworth Scholar: Secretary of the Institute of Naval Architects, etc. 
 Author of "The Steam Engine." 
 
 r 
 
 ROBERT ANDREWS MILLIKAN, Ph. D. 
 
 Associate Professor of Physics in the University of Chicago. 
 Joint Author of "A First Course in Physics." 
 
 V 
 
 WILLIAM KENT, M. E. 
 
 Consulting Engineer; Member of American Society of Mechanical Engineers, etc. 
 Author of "Strength of Materials," "Mechanical Engineer's Pocketbook," "Steam Boiler 
 Economy," etc. 
 
 rx- 
 
 DUGALD C. JACKSON, B. S., C. E. 
 
 Head of Department of Electrical Engineering, Massachusetts Institute of Technology: Member 
 of American Society of Mechanical Engineers; American Institute of Electrical Engineers. 
 
 Author of "A Textbook on Electromagnetism and the Construction of Dynamos," "Alternating 
 Currents and Alternating-Current Machineiy." 
 
 *r 
 
 JOHN PRICE JACKSON 
 
 Professor of Electrical Engineering, Pennsylvania State College; Member of American Institute 
 
 of Electrical Engineers. 
 Author of "Alternating Currents and Alternating-Current Machinery.' 
 
 V^ 
 
 GAETANO LANZA, S. B., C. E., M. E. 
 
 Prof essor of Theoretical and Applied Mechanics, Massachusetts Institute of Technologv Mem- 
 ber of American Society of Mechanical Engineers, etc. 
 Author of "Applied Mechanics." 
 
 Tr. 
 
 C. W. MACCORD, A. M. 
 
 Prof essor of Mechanical Drawing, Stevens Institute of Technology 
 Author of "Movement of Slide Valves by Eccentrics." 
 
 ^ 
 
 MANSFIELD MERRIMAN, Ph. D. 
 
 Professor of Civil Engineering. Lehigh University; Member of American Society of Civil 
 Author of "Mechanics of Materials," "Treatise on Hydraulics," "Elements of Sanitary 
 
 ^ 
 
 CECIL H. PEABODY, S. B. 
 
 Professor of Marine Engineering and Naval Architecture, Massachusetts Institute of 
 Technology. 
 
 Author of "Thermodynamics of the Steam Engine," "Tables of the Properties of Saturated 
 Bolters' " FS t0 Steam En eines," "Manual of Steam Engine Indicators," "Steam
 
 Authorities Consulted Continued 
 
 EDWARD F. MILLER 
 
 Professor of Steam Engineering, Massachusetts Institute of Technology. 
 Author of "Steam Boilers." 
 
 ^- 
 
 WILLIAM JOHN MACQUORN RANKINE, LL. D., F. R. S. S. 
 
 Civil Engineer; Late Regius Professor of Civil Engineering and Mechanics in the University of 
 
 Glasgow, etc. 
 Author of "Applied Mechanics," "The Steam Engine," "Civil Engineering," "Useful Rules and 
 
 Tables," 'Machinery and Mill Work," "A Mechanical Textbook." 
 * 
 
 KEMPSTER B. MILLER, M. E. 
 
 Consulting Engineer, and Telephone Expert. 
 Author of "American Telephone Practice." 
 
 * 
 
 MAURICE A. OUDIN, M. S. 
 
 Member of American Institute of Electrical Engineers. 
 Author of "Standard Polyphase Apparatus and Systems." 
 
 ** 
 
 IRA REMSEN, M. D., Ph. D., LL. D. 
 
 President of Johns Hopkins University, and Professor of Chemistry, etc. 
 
 Author of "Principles of Theoretical Chemistry," "Introduction to the Study of the Compounds 
 of Carbon," "The Elements of Chemistry," "Inorganic Chemistry," etc. 
 
 ^ 
 
 WILLIAM RIPPER 
 
 Professor of Mechanical Engineering in the Sheffield Technical School; Member of the Institute 
 
 of Mechanical Engineers. 
 \uthor of "Machine Drawing and Design," "Practical Chemistry," "Steam," etc. 
 
 ^* 
 
 JOSHUA ROSE, M. E. 
 
 Author of "Mechanical Drawing Self-Taught," "Modern Steam Engineering," "Steam Boilers," 
 "The Slide Valve," "Pattern Maker's Assistant," "Complete Machinist," etc. 
 * 
 
 LAMAR LYNDON, B. E., M. E. 
 
 Consulting Electrical Engineer; Associate Member of American Institute of Electrical 
 
 Engineers; Member of American Electro-Chemical Society. 
 Author of "Storage Battery Engineering." 
 
 > 
 
 ROBERT H. THURSTON, C. E., Ph. B., A. M., LL. D. 
 
 Late Director of Sibley College of Engineering, Cornell University. 
 
 Author of "Manual of the Steam Engine," "Manual of Steam Boilers," "History of the Steam 
 Engine," etc. 
 
 "*" 
 
 SILVANUS P. THOMPSON, D. Sc., B. A., F. R. S., F. R. A. S. 
 
 Principal and Professor of Physics in the City and Guilds of London Technical College. 
 Author of "Electricity and Magnetism," "Dynamo-Electric Machinery," "Polyphase Electric 
 Currents," "Electromagnet," etc. 
 
 ^ 
 
 W. S. FRANKLIN and R. G. WILLIAMSON 
 
 Joint Authors of "The Elements of Alternating Current."
 
 Authorities Consulted Continued 
 
 EDWARD R. MARKHAM 
 
 Instructor in Machine Shop Work, Harvard University and Rindge Manual Training School; 
 
 Formerly Superintendent Waltham Watch Tool Co. 
 Author of "The American Steel Worker." 
 
 TT 
 
 SAMUEL EDWARD WARREN 
 
 Late Professor of Descriptive Geometry and Drawing, Massachusetts Institute of Technology. 
 
 Author of "General Problems in Shades and Shadows," "Shadows and Perspective," "Higher 
 
 General Problems with Linear Perspective of Form," "Shadow and Reflection," etc. 
 
 THOMAS D. WEST 
 
 Practical Moulder and Foundry Manager; Member, American Society of Mechanical Engineers. 
 Author of "American Foundry Practice." 
 
 ^ 
 
 ROBERT WILSON 
 
 Author of "Treatise on Steam Boilers." "Boiler and Factory Chimneys," etc. 
 
 JAMES J. LAWLER 
 
 Author of "Modern Plumbing, Steam and Hot Water Heating." 
 
 WILLIAM C. UNWIN, F. R. S., M. Inst. C. E. 
 
 Professor of Civil and Mechanical Engineering, Central Technical College, City and Guilds of 
 
 London Institute, etc. 
 Author of "Machine Design," "The Development and Transmission of Power from Central 
 
 Stations," etc. 
 
 r>* 
 
 WILLIAM ESTY, S. B., M. A. 
 
 Head of Department of Electrical Engineering, Lehigh University. 
 Joint Author of "The Elements of Electrical Engineering." 
 
 WILLIAM H. VAN DERVOORT, M. E. 
 
 Author of "Modern Machine Shop Tools." 
 
 V 
 
 J. A. EWING, M. A., B. Sc., F. R. S., M. Inst. C. E. 
 
 Professor of Mechanism and Applied Mechanics in the University of Cambridge. 
 Author of "The Steam Engine and Other Heat Engines." 
 
 A. E. SEATON 
 
 Author of "A Manual of Marine Engineering." 
 
 ROLLA C. CARPENTER, M. S., C. E., M. M. E. 
 
 Professor of Experimental Engineering, Cornell University; Member, American Society of Heat- 
 ing and Ventilating Engineers; Member, American Society of Mechanical Engineers. 
 Author of "Heating and Ventilating Buildings."
 
 Table of Contents 
 
 VOLUME XI 
 MACHINE DESIGN . . . . . By C. L. Griffin^ Page *11 
 
 Principles and Methods Mechanical Thought Invention Use of Handbooks 
 
 Calculations and Notes Sketches Theoretical Design Practical Modifica- 
 tion Delineation and Specification Constructive Mechanics Forces and 
 Moments Tension, Compression, Torsion Friction and Lubrication Work- 
 ing Stresses and Strains Designing an Elevator Wire-Rope Drive Reversed 
 Machine Design Classification of Machinery Machine Tools (Lathe, Planer, 
 Milling Machine, etc.) Motive- Power Machinery (Steam Engine, Air-Compres- 
 sor, etc.) Structural Machinery (Cranes, Elevators, Cars, etc.) Mill and 
 Plant Machinery (Rolls, Crushers, Drills, etc.) Cast and Wrought Iron and 
 Steel Original Design Design of Component Parts of Machinery 
 
 HEATING AND VENTILATION . . By C. L. Hubbard Page 197 
 
 Systems of Warming Hot- Air Furnaces Direct and Indirect Steam and Hot- 
 Water Heating Radiators Exhaust Steam Heating Ventilation Heat 
 Losses Direct- and Indirect-Draft Furnaces Furnace Details Smoke-Pipes 
 
 Flues Cold-Air Box Warm- Air Pipes Registers Circulation Coils 
 Systems of Piping Air- Valves Vacuum Systems Fans and Blowers 
 Factory Heating Electric Heating Automatic Regulators Air-Filters and 
 Washers Heating and Ventilating Schools, Churches, etc. 
 
 PLUMBING . . . . . . By C. L. Hubbard Page 411 
 
 Fixtures Bathtubs Water-Closets Urinals Lavatories Sinks Traps 
 Tanks Faucets Soil and Waste Pipes Tile Pipes Cesspools Traps and 
 Vents Siphonage Back and Local Venting Fresh- Air Inlets Foul- Air 
 Outlets Sewage Disposal Pipe Connections (Bathroom, Kitchen Sink) Pipe 
 Sizes Plumbing for Dwelling Houses ; for Apartment Houses; for Hotels; for 
 Railroad Stations; for Schoolhouses ; for Shops and Factories Testing and 
 Inspection Sewerage Systems (Separate, Combined) Manholes Flushing 
 Devices Ventilation of Sewers Catch-Basins Storm Overflows Pumping 
 Stations Tidal Chambers Sewage Purification Sedimentation Mechan- 
 ical Straining Chemical Precipitation Irrigation Intermittent Filtration 
 
 Domestic Water Supply Pumps Storage Tanks Water-Backs Circula- 
 tion Pipes Temperature Regulators Gas Fitting Testing Installation 
 Gas Fixtures Gas Heating and Cooking Gas Meters Gas Machines 
 
 REVIEW QUESTIONS Page 525 
 
 INDEX . Page 539 
 
 *For page numbers, see foot of pages. 
 
 tFor professional standing of authors, see list of Authors and Collaborators at 
 front of volume.
 
 PRINCIPLE OF HOT WATER HEATING ILLUSTRATED BY TRANSVERSE SECTIONAL 
 VIEW SHOWING BOILER, RADIATOR AND EXPANSION TANK, 
 
 American Radiator Company.
 
 it 111 
 
 MACHINE DESIGN, 
 
 PART I. 
 
 Definition. Machine Design is the art of mechanical thought 
 development, and specification. 
 
 It is an art, in that its routine processes can be analyzed and 
 systematically applied. Proficiency in the art positively cannot 
 be attained by any " short cut " method. There is nothing of a 
 spectacular nature in the methods of Machine Design. Large 
 results cannot be accomplished at a single bound, and success is 
 possible only by a patient, step-by-step advance in accordance 
 with well-established principles. 
 
 " Mechanical thought " means the thinking of things strictly 
 from their mechanical side; a study of their mechanical theory, 
 structure, production, and use; a consideration of their mechanical 
 fitness as parts of a machine. 
 
 " Mechanical development " signifies the taking of an idea in 
 the rough, in the crude form, for example, in which it comes from 
 the inventor, working it out in detail, and refining and fixing it in 
 shape by the designing process. Ideas in this way may become 
 commercially practicable designs. 
 
 "Mechanical specification" implies the detailed description 
 of designs, in such exact form that the shop workmen are enabled 
 to construct completely and put in operation the machines repre- 
 sented in the designs. 
 
 The object of Machine Design is the creation of machinery 
 for specific purposes. Every department of a manufacturing 
 plant is a controlling factor in the design and production of the 
 machines built there. A successful desio-n cannot be out of 
 
 O 
 
 harmony with the organized methods . of production. Hence in 
 the high development of the art of Machine Design is involved a 
 knowledge of the operations in all the departments of a manu- 
 facturing plant. The student is therefore urged not only to 
 familiarize himself with the direct production of machinery, but to 
 study the relatiou thereto of the allied commercial departments 
 
 11
 
 MACHINE DESIGN 
 
 IK- should get into the spirit of business at the start, get into the 
 shop atmosphere, execute his work just as though the resulting 
 design were to be built and sold in competition. He should visit 
 shops, work in them if possible, and observe details of design and 
 methods of finishing machine parts. In this way he will begin 
 to store up bits of information, practical and commercial, which 
 will have valuable bearing on his engineering study. 
 
 The labor involved in the design of a complicated automatic 
 machine is evidenced by the designer's wonderful familiarity with 
 : is every detail as he stands before the complete* 1 machine in 
 operation and explains its movements to an observer. The intri- 
 cate mass of levers, shafts, pulleys, gears, cams, clutches, etc., etc., 
 packed into a small space, and confusing even to a mechanical 
 mind, seems like a printed book to the designer of them. 
 
 This is so because it is a familiar journey for the designer's 
 mind to run over a path which it has already traversed so many 
 times that he can see every inch of it with his eyes shut. Every 
 detail of that machine has been picked from a score or more of 
 possible ideas. One by one, ideas have been worked out, laid 
 aside, and others taken up. Little by little, the special fitness of 
 certain devices has become established, but only by patient, care- 
 ful consideration of others, which at first seemed equally good. 
 
 Every line, and corner, and surface of each piece, however 
 small that piece may be, has been through the refining process of 
 theoretical, practical, and commercial design. Every piece has 
 been followed in the mind's eye of its designer from the crude 
 material of which it is made, through the various processes of fin- 
 \shing, to its final location in the completed machine; thus its 
 bodily existence there is but the realization of an old and familiar 
 picture. 
 
 AVhat wonder that the machine seems simple to the designer 
 of it! As he looks back to the multitude of ideas invented, 
 worked out, considered and discarded, the machine in its final 
 form is but a trifle. It merely represents a survival of the fittest. 
 
 No successful machine, however simple, was ever designed 
 that did not go through this slow process of evolution. No 
 machine ever just simply happened by accident to do the work 
 for which it is valued. No other principle upon which the suc- 
 
 12
 
 MACHINE DESIGN 5 
 
 cessful design of machinery depends is so important as this careful, 
 patient consideration of detail. A machine is seldom unsuccessful 
 because some main point of construction is wrong. . The principal 
 features of a machine are usually the easiest to determine. It is 
 a failure because some little detail was overlooked, or hastily con- 
 sidered, or allowed to be neglected, because of the irksome labor 
 necessary to work it out properly. 
 
 There is no task so tedious, for example, as the devising of 
 the method of lubricating the parts of a complicated machine. 
 Yet there is no point of design so vital to its life and operation as 
 an absolute assurance of an adequate supply of oil for the moving 
 parts at all times and under all circumstances. Suitable means 
 often cannot be found, after the parts are together, hence the 
 machine goes into service on a risky basis, with the result, per- 
 haps, of early failure, due to "running dry." Good designers 
 will not permit a design to leave their hands which does not pro- 
 vide practically automatic oiling, or at least such means of lubri- 
 cation that the operator can offer no excuse for neglecting to oil 
 his machine. This is but a single illustration of many which 
 might be presented to impress the definite and detail character 
 necessary in work in Machine Design. 
 
 Relation. The relation which Machine Design should cor- 
 rectly bear to the problems that it seeks to solve, is twofold; and 
 there are, likewise, two points of view corresponding to this two- 
 fold relation, from which a study of the subject should be traced. 
 Neither of these can be discarded and an efficient mastery of the 
 art attained. These points are 
 I. Theory. 
 
 II. Production. 
 
 I. Theory. From this point of view, Machine Design is 
 merely a skeleton or framework process, resulting in a repre- 
 sentation of ideas of pure motion, fundamental shape, and ideal 
 proportion. It implies a working knowledge of physical and 
 mathematical laws. It is a strictly scientific solution of the 
 problem at hand, and may be based purely on theory which has 
 been reasoned out by calculation or deduced from experiment. 
 This is the only sure foundation for intelligent design of any sort. 
 
 But it is not enough to view the subject from the standpoint
 
 MACHINE DESIGN 
 
 of theory alone. If we stopped here we should have nothing but 
 mechanisms, mere laboratory machines, simply structures of 
 itiovnuit v ami examples of line mechanical skill. A machine may 
 lu; correct in the theory of its motions; it may be correct in the 
 theoretical proportions of its parts; it may even be correct in its 
 operation for the time being; and yet its complication, its mis- 
 directed and wasteful effort, its lack of adjustment, its expensive 
 and irregular construction, its lack of compactness, its difficulty 
 of ivudv repair, its inability to hold its own in competition any 
 of these may thro\v the balance to the side of failure. Such a 
 machine, commercially considered, is of little value. No shop 
 will build it, no machinery house will sell it, nobody will buy it 
 if it is put on the market. 
 
 Thus we see that, aside from the theoretical correctness oi 
 principle, the design of a machine must satisfy certain other 
 exacting requirements of a distinctly business nature. 
 
 IT. Production, From this point of view, Machine Design 
 is the practical, marketable development of mechanical ideas. 
 v iewed thus, the theoretical, skeleton design must be so clothed 
 and shaped that its production may be cheap, involving simple 
 and efficient processes of manufacture. It must be judged by the 
 latest shop methods for exact, and maximum output. It must 
 possess all the good points of its competitor, and, withal, some 
 novel and valuable ones of its own. In these days of keen com- 
 petition it is only by carefully studied, well-directed effort toward 
 raj id, efficient, and, therefore, cheap production that any machine 
 can be brought to a commercial basis, no matter what its other 
 merits may be. All this must be thought of and planned for in 
 the design, and the final shapes arrived at are quite as much a 
 result of this second point of view as of the first. 
 
 As a good illustration of this, may be cited the effect of the 
 present somewhat remarkable development of the so-called '-high 
 sj)eed '' steels. The speeds and feeds possible with tools made of 
 these steels are such that the driving power, gearing' and feed 
 mechanism of the ordinary lathe are wholly inadequate to the 
 demands made upon tliem when working the tool to its limit. 
 This means that the basis of design as used for the ordinary tool 
 steel will not do, if the machine is expected to stand up to the 
 
 i i
 
 MACHINE DESIGN 
 
 cuts possible with the new steels. Hence, while the old designs 
 were right for the old standard, a new one has been set, and a 
 thorough revision on a high-speed basis is imminent, else the 
 market for them as machines of maximum; output will' be lost. 
 
 From these definitions it is evident that the designer must 
 not only use all the theory at his command, but must continually 
 inform himself on all processes and conditions of manufacture, 
 and keep an eye on the tende~"y of the sales markets, both 
 of raw material and the finished machinery product. This is 
 what in the broadest sense is meant by the term " Mechanical 
 Thought," thought which is directed and controlled, not only by 
 theoretical principle but by closely observed practice. From the 
 feeblest pretenders of design to those. engineers who consummate 
 the boldest feats and control the largest enterprises, the process 
 which produces results is always the same. Although experience 
 is necessary for the best mechanical judgment, yet the studen.t 
 must at least begin to cultivate good mechanical sense very early 
 in his study of design. 
 
 Invention. Invention is closely related to Machine Design, 
 but is not design itself. Whatever is invented has yet to be 
 designed. An invention is of little value until it has been refined 
 by the process of design. 
 
 Original design is of an inventive nature, but is not strictly 
 invention. Invention is usually considered as the result of genius, 
 and is announced in a flash of brilliancy. We see only the flash, 
 but behind the flash is a long course of the mosl concentrated 
 brain effort. Inventions are not spontaneous, are not thrown off 
 like sparks from the blacksmith's anvil, but are the result of hard 
 and applied thinking. This is worth noting carefully, for the 
 same effort which produces original design may develop a valuable 
 invention. But there is little possibility of inventing anything 
 except through exhaustive analysis and a clear interpretation of 
 such analysis. 
 
 Handbooks and Empirical Data. The subject matter in 
 these is often contradictory in its nature, but valuable nevertheless. 
 Empirical data are data for certain fixed conditions and are not 
 general. Hence, when handbook data are applied to some specific 
 case of design, while the information should be used in the freest
 
 8 MACHINE DESIGN 
 
 manner, yet it must not be forgotten that the case at hand is prob- 
 ably different, in some degree, from that upon which the data were 
 based, and unlike any other case which ever existed or will ever 
 afain exist. Therefore the data should be applied with the greatest 
 discretion, and when so applied will contribute to the success of 
 the design at least as a check, if not as a positive factor. 
 
 The student should at the outset purchase one good handbook, 
 and acquire the habit of consulting it on all occasions, checking 
 and comparing his own calculations and designs therefrom. Care 
 must be taken not to become tied to a handbook to such an extent 
 that one's own lesults are wholly subordinated to it. Independence 
 in design must be cultivated, and the student should not sacrifice 
 his calculated results until they can be shown to be false or based 
 on false as>umption. Originality and confidence in design will be 
 the result if this course be honestly pursued. 
 
 Calculations, Notes, and Records. Accurate calculations are 
 the basis of correct proportions of machine parts. There is aright 
 way to make calculations and a wrong way, and the student will 
 usually take the wrong way unless he is cautioned at the start. 
 
 The wrong way of making calculations is the loose and shift- 
 less fashion of scratching upon a scrap of detached paper marks 
 aiid figures, arranged in haphazard form, and disconnected and 
 incomplete. These calculations are in a few moments' time totally 
 meaningless, even to the author of them himself, and are so easily 
 lost or mislaid that when wanted they usually cannot be found. 
 
 Engineering calculations should always be made systemati- 
 cally, neatly, and in perfectly legible form, in some permanently 
 bound blank book, so that reference may always be had to them at 
 any future time for the purpose of checking or reviewing. Put 
 all the data down. Do not leave in doubt the exact conditions 
 under which the calculations were made. Note the date of calcu- 
 lation. 
 
 Jf a mistake in figures is made, or a change is found neces- 
 sary, never rub out the figures or tear out the leaf, or in any way 
 obliterate the figures. Simply draw a bold cross through the wrong 
 part and begin again. Often a calculation which is supposed to 
 be wrong is later shown to be right, or the facts which caused the 
 error ID ay be needed for investigatior and comparison. Time which 

 
 MACHINE DESIGN 9 
 
 is spent in making figures is always valuable time, time too pre- 
 cious to be thrown away by destroying the record. 
 
 The recording of calculations in a permanent form, as just 
 described, is the general practice in all modern engineering offices. 
 This plan has been established purely as a business policy. In 
 case of error it locates responsibility and settles dispute. Con- 
 sistent designing is made possible through the records of past 
 designs. Proposals, estimates, and bids may often be made 
 instantly, on the basis of what these record books show of sizes 
 and weights. This bookkeeping of calculations is as important a 
 factor of systematic engineering as bookkeeping of business 
 accounts is of financial success. 
 
 The student should procure for this purpose a good blank book 
 with a firm binding, size of page not smaller than 6 by 8 inches 
 (perhaps 8 by 11 inches may be better), and every calculation, how- 
 ever small and apparently unimportant, should be made in it. 
 
 Sample pages of engineering calculations are reproduced in 
 Eigs. 3 to 9. Note the sketch showing the forces. Note the clear 
 statement of data. Note the systematic writing of the equations, 
 and the definite substitutions therein. Note the heavy double 
 underscoring of the result, when obtained. There is nothing in 
 the whole process of the calculation that cannot be reviewed at 
 any moment by anybody, and in the briefest time. 
 
 The development of a personal note-book is of great value to 
 the designer of machinery. The facts of observation and experi- 
 ence recorded in proper form, bearing the imprint of intimate 
 personal contact with the points recorded, cannot be equalled 
 in value by those of any hand or reference book made by another. 
 There is always a flavor about a personal note-book, a sort of 
 guarantee, which makes the use of it by its author definite and 
 sure. 
 
 The habit of taking and recording notes, or even knowing 
 what notes to take, is an art in itself, and the student should 
 begin early to make his note-book. Aside from the value of the 
 notes themselves as a part of his personal equipment, the facility 
 ,v:.iii which his eye will be trained to see and record mechanical 
 things will be of great value in all of his study and work. How 
 many men go through a shop and really see nothing of the opera- 
 
 17
 
 10 MACHINE DESIGN 
 
 tions going on therein, or, seeing them, remember nothing ! "An 
 engineer, trained in this respect, will to a surprising degree be 
 able to retain and sketch little details which fall under his eye for 
 a brief moment only, while he is passing through a crowded shop. 
 
 Some draftsmen have the habit of copying all the standard 
 tables of the various offices in which they work. "While these are 
 of some value in a few cases, yet this is not what is meant by a 
 good note-book in the best sense. Ideas make a good note-book, 
 not a mere tabulation of figures. If the basis upon which stan- 
 dards are founded can be transferred to permanent personal record, 
 or novel methods of calculation, or' simple features of construc- 
 tion, or data of mechanical tests, or efficient arrangement of 
 machinery if tlu*c can be preserved for reference, the note-book 
 will be of greatest value. 
 
 Whatever is noted down, make clear and intelligible, illus- 
 trating by a sketch if possible. Make the cote so clear that 
 reference to it after a long space of years would bring the whole 
 subject before the mind in an instant. If this is not done the 
 author of the note himself will not have patience to dig out the 
 meaning when it is needed; and the note will be of no value. 
 
 METHOD OF DESIGN. 
 
 The fundamental lines of thought and action which every 
 designer follows in the solution of any problem in any class of 
 work whatsoever, are four in number. The expert may carry all 
 these in mind at the same time, without definite separation into a 
 a step- by-step process; but the student must master them in their 
 proper sequence, and thoroughly understand their application. 
 In these four are concentrated the entire art of Machine Design. 
 When they have become so familiar as to be instinctively applied 
 on any and all occasions, good design is the result. The only 
 other quality which will facilitate still further the design of good 
 machinery is experience; and that cannot be taught, it must be 
 acquired by actual work. 
 
 i. Analysis of Conditions and Forces. First, take a good 
 square look at the problem to be solved. Study it from all sides, 
 view it in all lights, note the worst conditions which can possibly 
 exist, note the average conditions of service, note any special or 
 irregular service likely to be called for. 
 
 : -
 
 MACHINE DESIGN 11 
 
 "With these conditions well in mind, make a careful analysis 
 of all the forces, maximum as well as average, which may be 
 brought into play. Make a rough sketch of the piece under con- 
 sideration, and put in these forces. Be sure that these forces are 
 at least approximately right. Go over the analysis carefully 
 again and again. Remember that time saved at the beginning 
 by hasty and poor analysis will actually be time lost at the end; 
 and if the machine actually fails from this reason, heavy financial 
 loss in material and labor will occur. Any haste toward com- 
 pletion of the structure beyond the roughest outline, without this 
 careful study of forces, is a blind leap in the dark, entirely un- 
 scientific, and almost certain to result in ultimate failure. 
 
 On the other hand this principle may be carried too far. In 
 trying to make the analysis thorough and the forces accurate, it is 
 quite possible to consume more than a reasonable amount of time. 
 Again, it is not always easy, and frequently impossible, to deter- 
 mine exactly the forces acting on a given piece. But their nature, 
 whether sudden or slowly applied, rapid in action or only oc- 
 curring at intervals, and their approximate direction and magni- 
 tude at least, are always capable of analysis. There are few, if 
 any, cases where close assumptions cannot be made on the &bove 
 basis and the design proceeded with accordingly. Hence the 
 danger of too great refinement of analysis is simply to be avoided 
 by the designer's plain business sense. 
 
 The first tendency of the student is to pass over the study of 
 the forces as dull and dry, and attempt the design at once. He 
 soon finds himself facing problems oi which he sees no possible 
 solution, and he bases his design on pure guess-work. This is 
 the only solution possible from such a point of view, and is really 
 no solution at all. A guer.s which has some rational backing is 
 often successful; but in that case some analysis is required, and it 
 is not a pure guess, but falls under the very principle we are 
 considering. 
 
 There is no short cut to the design of machine parts which 
 avoids this full understanding of the forces that they must 
 sustain. The size of a belt depends upon the maximum pull 
 upon it, and the designing of belts is nothing but providing 
 sufficient cross-section of leather to prevent the belt tearing under 
 
 19
 
 12 MACHINE 
 
 the pull. Again, if pulley arms are not to break, or shafts twist 
 oil", or bolts be torn apart, or the teeth of gears fail, or keys and 
 pins shear ofr, we must first, of course, iind out what .forces exist 
 which are likely to produce stress that may lead to such 
 breakage. "We should not guess at the sizes, and then run the 
 machine to see if breakage results, and then guess again. Ma- 
 chines are sometimes built in this way, but it is an unreasonable 
 and uncertain method. We must use every effort to foresee the 
 stress which a piece ia liable to receive, before we decide its size, 
 "We must know all the forces approximately, if not positively. 
 The analysis must be thorough enough to permit of reasonable 
 assumption, if not positive assertion, it ia manifestly impossible 
 to solve any problem until we know exactly what the problem is; 
 and a full analysis is the statement of the problem. 
 
 2. Theoretical Design. After we know by careful analysis 
 what stress the machine part has to sustain, the next step is so to 
 design it that it will theoretically resist the applied forces with 
 the least expenditure of material. 
 
 "We often see machinery with the metal of which it is made 
 distributed in the worst possible manner. In places where the 
 stress is heavy and a rigid member is needed, we find a weak, 
 springy part; wrile in other parts, where there are no forces to be 
 resisted, or vibration to be absorbed, there seems to be a waste of 
 good material. Whether in such case the analysis of the forces 
 was poor, or perhaps not made at all, or whether a knowledge of 
 how to design so as to resist the given forces was wholly absent, 
 cannot be told. At any rate, lack of either or both is clearly 
 shown in the result. 
 
 Any member of a machine may vary in form from a solid 
 block or chunk of material to an open ribbed structure. The solid 
 chunk fills the requirement as-faras strength is concerned, unless 
 it is so heavy as to fail from its own weight. But such construe- 
 tion is poor design, except in cases where the concentration of 
 heavy mass <s necessary to absorb repeated blows like those of a 
 hammer. The possibility of these blows should, however, have 
 been determined in the analysis; and the solid, anvil construction 
 then becomes theoretical design for that analysis. 
 
 For steadily applied loads an open, ribbed, or hollow box 
 
 .
 
 MACHINE DESIGN 13 
 
 structure can be made which will distribute the metal where it is 
 theoretically needed, and each fiber will then sustain its proper 
 share of the load. In this way weight, cost, and appearance are 
 heeded; and the service of the piece is as good as, and probably 
 better than, it would be with the clumsy, solid form. 
 
 There is no such thing as putting too much theory into the 
 design of machinery. The strongest trait which an engineer can 
 have is absolute faith in his analyses and calculations, and their 
 reproduction in hia theoretical design. Theoretical design is an 
 indication of scientific advance in the art, and some of the greatest 
 steps of progress which have been made in recent years have been 
 accomplished through a purely theoretical study of machine 
 structure. 
 
 It will never do, however, to be satisfied with theoretical 
 design when it is not in accord with modern commercial and manu- 
 facturing considerations. Hence the next step after the determina- 
 tion of the theoretical design is the study of it from the producing 
 standpoint. 
 
 3. Practical Modification. All theoretical design viewed from 
 the business standpoint is worthless, unless it has been subjected 
 to the test of cheap and efficient production. Each machine detail, 
 though correct in theory, may yet be improperly shaped and unfit 
 for the part it is to play in the general scheme of manufacture. 
 
 The conditions here involved are changeable. What is good 
 design in this decade may be bad in the next. In this light the 
 designer must be a close student of the signs of the times ; he must 
 follow the march of progress, closely applying existing resources, 
 conditions, and facilities, otherwise he cannot produce up-to-date 
 designs. The introduction of new raw materials, the cheapening 
 of production of others, the changing of shop methods, tha use of 
 special machinery, the opening of new markets, the development 
 of new motive agents, all these and many others are constantly 
 demanding some modification in design to meet competition. 
 
 Illustrative of this, note the change which has been wrought 
 by the development of electric power, the rise and decline of the 
 bicycle business, the present manufacture of automobiles, the last 
 named especially with reference to the development of the small 
 motive unit, the gasolene engine, the steam engine, etc. The
 
 It MACHINE DESIGN 
 
 design of much machinery has been materially changed to meet 
 the exacting demands of these new enterprises. 
 
 Practical modifications of design necessary to meet the limi. 
 tations of construction in the pattern shop,, foundry, and machine 
 shop :;re of daily application in the designer's work. He must 
 keep i!, his mind's eye at all times the workmen and the processes 
 tK-y use to create his designs in metal in the shop. 
 
 "How can this be made?" "Can it be made at all?" 
 "Can it be made cheaply?" ""Will it be simple in operation 
 after it is made""" "Can it be readily removed for repair?" 
 " Can it be lubricated ? " " How can it be put in place ? " " How 
 can it be gotten out?" "Will it be made in small quantities 
 qr laro-e?" "Will it sell as a special or standard machine?" 
 etc., etc. 
 
 The consideration of such questions as these is a practical 
 necessity as a business matter. Xo other feature affects the 
 design of machinery more, perhaps; for designs which cannot be 
 built as business propositions are no designs at all. 
 
 The student, it is true, may not have the extended shop 
 knowledge which is essential to this; but he cuu do much for 
 himselt by visiting shops whenever possible, getting hold of shop 
 ways of doing things, and invariably treating his work as a 
 business matter. Though a man may not be a pattern maker, 
 molder, blacksmith, or machinist, yet he can soon gain ideas o* the 
 processes in each of these branches which \vill be of immense 
 advantage to him in his designing work. 
 
 4. Delineation and Specification. This means the clear and 
 concise representation of the design by mechanical drawings. 
 
 This is as much a part of the routine method of Machine De- 
 sign 'as the other three points which have been discussed. The 
 mere act of putting the results of mechanical thinkino- on paper is 
 one of the greatest helps to force thinking machinery to system- 
 atic and definite action. A designer never thinks very long 
 without drawing something, and the student must bring himself to 
 feel that a drawing in its tirst sense is a means of helping hit* owrj 
 thought, and must freely use it as such. 
 
 In its second and final sense, the drawing is an order and 
 specification sheet from the designer to the work: nan. Design 

 
 MACniJSTE DESIGN 15 
 
 which stops short of exact, finished delineation in the form of 
 working shop drawings is only half done. In fact the possibility 
 of a piece being thus exactly drawn is often the crucial test of its 
 feasibility as a part of a machine. It is easy to make general out- 
 lines, but it is not so easy to get down to finished detail. It is 
 safe to say that there is no one thing productive of more trouble, 
 delay and embarrassment, and waste of time and money in the 
 shop, when there need be none from this cause, than a poor detail 
 drawing. The efficiency of the process of design is not fully real- 
 ized, and failures are often recorded where there should be success, 
 merely because the indefiniteness permitted by the designer in the 
 drawings naturally transmitted itself to the workman, and he in 
 turn produced a part indefinite in form and operation. 
 
 The actual process of drawing in the development of a design 
 may be outlined as follows : 
 
 Rough sketches merely representing ideas, not drawn to scale, 
 are first made. These are of use only so far as the choice of me- 
 chanical ideas is concerned, and to carry preliminary dimensions. 
 
 Following these sketches, comes a layout to scale, of the 
 favored sketch, a working out of the relative sizes and location of 
 the parts. This drawing may be of a sketchy nature, carrying a 
 principal dimension here and there to fix and control the detailed 
 design. In this drawing the design is developed and general detail 
 worked out. The minute detail of the individual parts is, however, 
 left to the subsequent working drawing. 
 
 This layout drawing may now be turned over to an expert 
 draftsman or detail designer, who picks out each part, makes an 
 exact drawing of it, studying every little detail of its shape, *nd 
 finally adds complete dimensions and specifications so that the 
 workman is positively informed as to every point of its construction. 
 .. General drawings and cross sections constitute the last step 
 in the process of complete delineation. These show the parts 
 assembled in the complete machine. They also serve a valuable 
 purpose to the draftsman in checking up the dimensions of the 
 detail drawings. Errors which have escaped previous notice are 
 often discovered in this way. The layout, mentioned above, is 
 sometimes finished up into a general drawing; but it is safer to 
 make an entirely new drawing, as changes in detail are often 
 necessary after the layout is made. 
 
 :23
 
 16 MACHINE DESIGN 
 
 The four fundamental lines of thought and action noted 
 above may be summarized thus "analyse and theorize, modify 
 and delineate." This is a maxim easy to remember, applicable 
 to every problem in Machine Design, and always provides the 
 ans\\er to the question "What shall I do, how shall I proceed?" 
 by pointing out the proper sequence in the course to be followed. 
 
 CONSTRUCTIVE MECHANICS. 
 
 Mechanics is a constructive science, its principles lying at the 
 root of the design and operation of all machinery. It is usually 
 taught, however, as an advanced mathematical subject; and the 
 student gets his original conceptions of forces, moments, and 
 beams in the abstract, before he realizes the constructive value of 
 such conceptions. By "Constructive Mechanics" is meant the 
 study of a machine purely from its constructive side, the viewing 
 of the parts with respect to their "mechanics," and satisfying the 
 requirements of the same in form and arrangement. 
 
 The student may cultivate this habit of clear, mechanical per- 
 ception by constantly noting the " mechanics " of the simple 
 structures which he sees in his daily routine of work. Aside 
 from machinery, in which the "mechanics" is often obscure, 
 the world is full of simple examples of natural strength and 
 symmetry, explainable by application of the principles of pure 
 "mechanics." 
 
 Posts and pillars are largest at their bases; overhanging 
 brackets or arms are spread out at the fastening to the wall; 
 heavy swinging gates are counter-balanced bv a ponderous weight; 
 the old-fashioned well sweep carries its tray of stones at the end, 
 adjusting the balance to a nicety; these are examples of things 
 depending for their form and operation upon the principles of 
 'mechanics." The building of them involved "constructive 
 mechanics," and yet their constructor perhaps never heard of the 
 science, using merely his natural sense of mechanical fitness 
 Such simple reasoning is, however, Constructive Mechanics. 
 
 Forces, Moments, and Beams. Machines are nothino- but a, 
 
 O 
 
 collection of (1) parts taking direct stress, or (2) parts acting as 
 loaded beams. Forces actino* iritJiout leverage produce direct 
 stress ou the sustaining part. Forces acting with leverage pro-
 
 MACHINE DESIGN 17 
 
 duce a moment; the sustaining member is a beam, and the stress 
 therein depends on the theory of beams, as explained in " Me- 
 chanics." 
 
 An example of the first fs the load on a rope, the force acting 
 without leverage, and the rope therefore having a direct stress put 
 upon it. 
 
 An example of the second is a push of the hand on the crank 
 of a grindstone. A moment is produced about the hub of tho 
 crank; the arm of the crank is a beam, and the stress at any point 
 of it may be found by the method of theory of beams. 
 
 Tension, Compression, and Torsion. The stress induced in 
 the sustaining part, whether tensile, compressive, or torsional, is 
 caused by the application of forces, either acting directly without 
 leverage, o^ with leverage in the production of moments. 
 
 The forces applied from external sources are at constant war 
 with the resisting forces due to the strength of the fibres of the 
 material composing the machine members. The moments of the 
 external forces are constantly exerted against and balanced by the 
 moments of the internal resistance of the material. Hence, 
 design, from a strength standpoint, is merely a balancing of 
 internal strength against external force. In other words, we may 
 in all cases write a sign of equality, place the applied effort on 
 one side, the effective resistance on the other, and we shall have 
 an equation, which, if capable of solution, will give the proper 
 proportions of the parts considered. 
 
 External Force = Internal Resistance. 
 External Moment = Internal Moment of Resistance. 
 Expressed in terms of the " Mechanics:" 
 P=AS (i) 
 
 BorT=E. (a) 
 
 In these formulas, which are perfectly general, 
 
 P=dircct load in pounds. 
 
 A=area of effective material, in square inches. 
 
 S=working fibre stress of the material (tensile, compressive, or shear- 
 ing), in pounds per square inch. 
 
 8 or T=external moment (bending or torsional), in inch-pounds. 
 
 I=moment of inertia (direct or polar), of the resisting section. 
 
 c= distance of the most remote fibre of the resisting section from the 
 neutral axis.
 
 IS MACHINE DESIGN 
 
 P may produce direct tensile, compressive, or shearing stress. 
 
 B may produce tensile or compressive stress, and requires use of direct 
 moment of inertia in either case. 
 
 T produces shearing stress, and requires use of polar moment of 
 inertia. 
 
 The origin of formula (1) is obvious, the assumption being 
 that the fibre stress is equally distributed to every particle in the 
 area "A." 
 
 The development of formula (2) is given in any text-book in 
 Mechanics. It requires the aid of the Calculus, however. Any 
 good handbook gives values for both the direct moment of inertia 
 and the polar moment of inertia for quite a large variety of sections, 
 so that further reference is an easy matter for the student. These 
 rallies are also obtained through the methods of the Calculus. 
 
 The reason for introducing these formulas at this time is to 
 call the attention of the student especially to the fact of their 
 universal and fundamental use in all problems concerning the 
 strength of machine parts. Nearly every computation may be 
 reduced to or expanded from these two simple equations. .Many 
 complex combinations occur, of course, which will not permit sim- 
 ple and direct application of these formulas, but the student will 
 do well to place himself in perfect command of these two. Assuming 
 that he is able to analyze forces, and compute the simple moment 
 at the point where he wishes to find the strength of section, the 
 rest is the mere insertion of the assumed working fibre stress of 
 the material in the formula (2) above, and solution for the quantity 
 desired. 
 
 When the case is one of combined stress, the relation becomes 
 more complicated and difficult of analysis and solution. The most 
 common case is where bending is combined with torsion, as in the 
 case of a shaft transmitting power, and at the same time loaded 
 transversely between bearings. In fact there are very few cases of 
 shafts in machines, which, at some part of their length, do not 
 hav ;; tliis combined stress. In this case the method of procedure 
 is to find the simple bending moment and the simple torsional 
 moment separately, in the ordinary way. Then the theory of 
 elasticity furnishes us with a formula for an equivalent bending 
 or an equivalent torsional moment which is supposed to produce 
 tee same effect upon the fibres of. the material as the combined 
 
 2 ;
 
 21-INCH SLOTTING MACHINE.
 
 MACHINE DESIGN 
 
 action of the two simple moments acting together. In other 
 words, the separate moments combined in action, being impossible 
 of solution in that form, are reduced to an equivalent simple 
 moment and the solution then becomes the same as for the prev- 
 ious case. 
 
 These equivalent equations are given below, the subscript "e" 
 being added to express separation from the simple moment: 
 
 (3) 
 
 (4) 
 
 B e and T e , found from these equations, are the external mo- 
 ments, and are to be equated to the internal moments of resistance 
 of the section precisely as if they were simple bending or torsional 
 moments. Either may be used. For shafts (4) is generally used, 
 being the simpler of the two in form. 
 
 FRICTION AND LUBRICATION. 
 
 The parts of a machine which have no relative motion with 
 regard to each other are not -dependent upon lubrication of their 
 surfaces for the proper performance of their functions. In cases 
 where relative motion does occur, as between a planer bed and its 
 ways, a shaft and its bearing, or a driving screw and its nut, 
 friction, and consequent resistance to motion, will inevitably 
 occur. Heat will be generated, and cutting or scoring of the 
 surfaces will take place if the surfaces are allowed to run together 
 dry. 
 
 This difficulty, which exists with all materials, cannot be 
 overcome, for it is a result of roughness of surface, characteristic 
 of the material even when highly finished. The problem of the 
 designer, then, is to take conditions as he finds them, and, as he 
 cannot change the physical characteristics of materials, so choose 
 those which are to rub together in the operation of the machine 
 that friction will be reduced to the lowest possible limit. Now it 
 fortunately happens that there are certain agents like oil and 
 graphite, w r hich seem to fill up the hollows in the surface of a 
 solid material, and which themselves have very little friction on 
 other substances. Hence, if a machine permits by its design an 
 automatic supply of these lubricating agents to all surfaces having 
 
 27
 
 MACHINE DESIGX 
 
 motion between them, friction may be reduced to the lowest limit. 
 
 If this full supply of lubricant be secured, and the parts still 
 heat and cut, then the fault may be traced to other causes, such as 
 springy surfaces, localization of pressure, or insufficient radiating 
 surface to carry away the heat of friction as fast as it is generated. 
 
 Lubricating agents are of a nature running from the solid 
 graphite form to a thick grease, then to a heavy dark oil, and 
 finally to a thin, fluid oil flowing as freely as water. The solid and 
 heavy lubricants are applicable to heavily loaded places where the 
 pressure would squeeze out the lighter oils. Grease, forced be- 
 tween the surfaces by compression grease cups, is an admirable 
 lubricator for heavy machinery under severe service. High-speed 
 and accurate machinery, lightly loaded, requires a thin oil, as the 
 fits would not allow room for the heavier lubricants to find their 
 way to the desired spot. The ideal condition in any case is to 
 have a film of lubricant always between the surfaces in contact, 
 and it is this condition at which the designer is always aiming in 
 his lubricating devices. 
 
 Oil ways and channels should be direct, ample in size. 
 readily accessible for cleaning, and distributing the oil by natural 
 ilo\v r over the full extent of the surface. Hidden and remote 
 bearings must be reached by pipes, the mouths of which should 
 bo clearly indicated and accessible to the operator of the machine. 
 Such pipes must be straight, if possible, and readily cleaned. 
 
 There is one practical principle affecting the design of 
 methods of lubrication of a machine which should be borne in 
 mind. This is, "Neglect and carelessness by the operator ynmst 
 be provided for." It is of no use to say that the ruination of a 
 surface or hidden bearing is due to neglect by the operator, if the 
 means for such -lubrication are not perfectly obvious. This is 
 " locking the door after the horse is stolen." The designer has 
 not done his duty until he has made the scheme of lubrication so 
 plain that every part 'must receive its proper supply of oil, except 
 by gross and willful negligence, for which there can be no 
 possible just excuse. 
 
 WORKING STRESSES AND STRAINS. 
 
 Some persons object to the use of these terms, as one is 
 f raquently used for the other, and misunderstanding results. Tins 
 
 28
 
 MACHINE DESIGN 21 
 
 is doubtless true; but the student may as well learn the true 
 relation of the terms once for all, because he will frequently run 
 across them in his reading and reference work, and should inter- 
 pret them rightly. The strict relation of the two is as follows: 
 
 Stress is the internal force in a piece resisting the external 
 force applied to it. A weight of ten pounds hanging on a rope 
 produces a stress of ten pounds in the rope. 
 
 Strain is the change of shape, or deformation, in a piece 
 resisting an external force applied to it. If the above weight of 
 ten pounds stretches the rope J inch, the strain is J inch. 
 
 Unit stress is stress per unit area, e. g., per square inch. 
 
 Unit strain is strain per unit length, e. g,, per inch length. 
 
 In the above case, if the rope were -| square inch in area 
 and 30 inches long, the unit stress, or intensity of stress, is 
 10-7-1 1=20 pounds per square inch; the unit strain is J-=-80= T | ir 
 inch per inch. 
 
 "When stress is induced in a piece, the strain is practically 
 proportional to the stress for all values of the stress below the 
 elastic limit of the material; and when the external load is re- 
 moved the strain will entirely disappear, or the recovering power 
 of the material will restore the piece to the original length. 
 
 Illustrating by the case above, on the supposition that the 
 elastic limit has not been reached by the stress of 20 pounds per 
 square inch, if the load of 10 pounds were taken off, the J-inch 
 strain would disappear and the rope return to its original length; 
 if the load were changed to -| of 10 pounds, or 5 pounds, the 
 strain would be i of J inch, or J inch. 
 
 Now it is found that if we wish a piece to last in service for 
 a long time without danger of breakage, we must not permit it 
 to be stressed anywhere near the elastic limit value. If we do, 
 although it will probably not break at once, it is in a dangerous 
 condition, and not well suited to its requirements as a machine 
 member. The technical name for this weakening effect is " fa. 
 tigue." It is further found that the fatigue due to this repeated 
 stress is reached at a lower limit when the stress is alternating in 
 character than when it is not. In other words, if we first pull on 
 a piece and then push on it, we shall first have the piece in tension 
 and theu in compression; this alternation of stress repeated to
 
 22 MACHINE DESIGN 
 
 near the elastic limit of the material will fatigue it, or wear out 
 the fibres, and it will finally fail. If, however, we first pull on 
 the piece with the same force as before, and then let go, we shall 
 first have the piece in tension and then entirely relieved; such 
 repetition of stress will finally " fatigue " the material, but not so 
 quickly as in the first case. Experiments indicate that it may 
 take twice as many applications in the latter case as in the former. 
 
 The working stress of materials permissible in machines is 
 based on the above facts. The breaking strength divided by a 
 liberal factor of safety will not necessarily give a desirable work- 
 ing stress. The question to be answered is, "^V ill the assumed 
 working fibre stress permit an indefinite number of applications 
 of the load without fatiguing the material ? " 
 
 Hence we see that the same material may be safely used under 
 different assumptions of working stress. For example, a rotating 
 shaft, heavily loaded between bearings, acts as a beam which in 
 each revolution is having its particles btibjected, first to a maxi- 
 mum tensile stress, and then to a maximum compressivo stress. 
 This is obviously a very different stress from that which the same 
 piece would receive if it were a pin in a bridge truss. In the 
 former we have a case where the stress on each particle reverses at 
 each revolution, while in the latter wo have merely the same stress 
 recurring at intervals, but never becoming of the opposite char- 
 acter. For ordinary steel, a value of 8,000 would be reasonable in 
 the former case, while in the latter it may be much higher with 
 safety, perhaps nearly double. 
 
 From the facts stated above, it is evident that exact values for 
 working fibre stress cannot be assumed with certainty and applied 
 broadly in all cases. If the elastic limit of the material is defi- 
 nitely known we can base our working value quite surely on that. 
 
 "With but a general knowledge of the elastic limit, ordinary 
 steel is good for from 12,000 to 15,000 pounds per square inch 
 non -reversing stress, and 8.000 to 10,000 reversing s f ress. Cast 
 iron is such an uncertain metal on account of its variable structure 
 that stresses are always kept low, say from 3,000 to 4,000 for non- 
 reversing stress, and 1,500 to 2,500 for reversing stress. 
 
 "With these values as a guide, and the special conditions con. 
 trolling each case carefully studied, reasonable limits may be 
 
 30
 
 
 
 -*/ 
 
 
 
 $ 
 
 
 i^J 
 
 /Borrow PLATES 
 
 SEMI-CIRCULAR 3'-o"f?/to. 
 
 ^ RECfD 
 
 12 "X 96 " ACCUMUL A TOR 
 SCALE:-I"J ",3'=lFT 
 
 HYDRAULIC ACCUMULATOR 
 Detail Drawing, to be used with Figure on Opposite PAg
 
 HYDRAULIC ACCUMULATOR 
 
 Assenjblea Drawing with Petals op the vme Sbft
 
 MACHINE DESIGN 23 
 
 assigned for working stress, not only of steels, various grades of 
 cast iron, and mixtures of the same, but of other alloys, brass, 
 bronze, etc. Gun metal, semi-steel, and bronze are intermediate 
 in strength between cast iron and steel. Data on the strength of 
 materials are available in any of the handbooks, and should be con- 
 sulted freely by the student. They will be found somewhat con- 
 flicting, but will assist the judgment in coming to a conclusion. 
 
 Application to Practical Case. In actual practice the only 
 information which the designer has, upon which to base his design, 
 is the object to be accomplished.. He must choose or originate 
 suitable devices, develop the arrangement of the parts, make his 
 own assumptions regarding the operation of the machine, then 
 Analyse and Theorize, Modify and Delineate each detail as 
 he meets it. 
 
 This, it Will be found, is a very different matter from taking 
 some familiar piece of machinery, such as a pulley, or a shaft, or 
 a gear, as an isolated case, the load being definitely given, and 
 proceeding with the design. This is easily done, but is only half 
 the problem, for machine parts, such as pulleys, gears, and shafts, 
 do not confront the designer tagged or labeled with the conditions 
 they are to meet. He is to provide parts to meet the specific, con- 
 ditions, and it is as much a part of his designing method to know 
 how to attack the design of a machine as it is to know how to 
 design the parts in detail after the attack has reduced the members 
 to definitely loaded structures. The whole process must be gone 
 through, the preliminary sketches, calculations, and layout, all of 
 which precede the detail design and working drawings; and no step 
 of the process can be omitted. 
 
 It is for this reason that the present case used for illustration 
 is carried out quite thoroughly. The student should make himself 
 familiar with every step of the designing method as applied to this 
 simple case of design. More complex problems, handled in the 
 same way, will simplify themselves; and when the point is reached 
 where confidence exists to take hold of the design of any machine, 
 however unfamiliar its object may be, or however involved its 
 probable detail appears, the student has become the true designer. 
 It ia the knowing how to attack a problem, to start definite work 
 on it, to go ahead boldly, confident that the method applied will
 
 MACHINE DESIGN 
 
 produce results, that giv3 command of the design of machinery 
 and wins engineering success. 
 
 The special case which has been chosen to illustrate the 
 application of the principles stated in the foregoing pages is ideal, 

 
 MACHINE DESIGN 
 
 in that it does not represent any actual machine at present in 
 operation. Probably builders of hoisting machinery have devices 
 which would improve the machine as shown. In detail, as well 
 as arrangement, they could doubtless make criticism as manufac- 
 turers. The arrangement as shown is merely intended to bring 
 out in simplest form the common elements of transmission ma- 
 chinery as parts of some definite machine, instead of as isolated 
 details. The design is one entirely possible, practical, and me- 
 chanical, but special attention has been paid to simplicity in order 
 to enable the student to follow the method closely, for the method 
 is the chief thing for him to acquire. 
 
 The student is expected to refer constantly to Part II for a 
 more formal and general discussion of the simple machine ele- 
 ments involved in the case considered. Part II is intended to be 
 a simplified and condensed reference book, carried out in accord- 
 ance with the method of machine design as specified in Part I. 
 The student should not wait until he has completed the study of 
 this part before taking up Part II, for the latter is intended for 
 use with the former in the solution of the problems. 
 
 In the case of power transmission about to be studied, the 
 running, conversational method employed assumes that the student 
 is in possession of the matter in Part II on the subject considered. 
 Thus, in the design of the pulley, reference to the subject of 
 " Pulleys " in Part II is necessary to follow the train of calcula- 
 tion; in designing the gear, consult "Gears;" in calculating size 
 of shafts, see Shafts," etc., etc. 
 
 Problem. A machine is to be designed to be set on the floor 
 of a building to drive a wire rope falling from the overhead 
 sheaves of an elevator or hoist. Without regard to details of this 
 overhead arrangement, for its design would be a separate problem, 
 suppose that the data for the rope are as follows: 
 
 Load on rope. . . ............... ---- 5,000 pounds. 
 
 Speed of rope ..................... 150 feet per minute. 
 
 Length of rope to be reeled in ...... 200 feet. 
 
 We shall further assume that the driving power is to be an 
 electric motor belted to the machino, that the required speed 
 reduction can be satisfactorily obtained by a single pair of pulleys 
 and one pair of gears, and that a plain band brake is to be applied 
 to the drum. 
 
 37
 
 MACHINE DESIGN 
 
 TVith this data we shall proceed to work out the detail design 
 of the machine. 
 
 Preliminary Sketch. The first thing to do is to sketch 
 roughly the proposed arrangement of the machine. 
 
 This might appear like Fig. 1 except that it would have no 
 dimensions in addition to the data given above. If the scheme 
 seems suitable, the next step is to make such preliminary calcula- 
 tions as will give further data, exact or closely approximate sizes, 
 to be put at once on the sketch, to outline the future design. 
 
 Rope and Drum. Referring to tables of strength of wire rope 
 (Kent's Pocket Book gives the manufacturers' list), we find that 
 a -inch cast-steel rope will carry 5,000 pounds safely, and that the 
 proper si/e of drum to avoid 
 excessive bending of the rope 
 around it is 27 inches diameter. 
 Allowing J- inch between the 
 coils is the rope winds on the 
 drum, the pitch of coil will be 
 : [ inch as shown in SKetch, Fig. 
 3. The length of one complete 
 
 27 X 3.1410 
 coil is, practically, 17; 
 
 Fig. 2. 
 200 
 
 7.07 feet. To provide for 200 feet will require ,rr7rr=28-f- coils. 
 
 To be safe, let us provide for 00 coils, for which a length of drum 
 (MX : J') + : i~3|. inches is required. 
 
 The space for brake strap may be assumed at 5 inches, and the 
 thickness to provide necessary strength determined later in the 
 design. The frictional surface of the strap may be of basswood 
 blocks, say 1|- inches thick, screwed to the metal band. The 
 diameter of brake surface may be 2s inches. 
 
 Driving Gears. The size of drum gear evidently depends 
 upon the method of fastening to the drum, and, other things being 
 equal, should be kept as small as possible. One way would be to 
 key the gear on the outside of the drum, another to bolt the gear 
 to the end ot the drum. The latter has the advantage that a 
 standard gear pattern can be used with the slight change of 
 
 38
 
 MACHINE DESIGN 
 
 27 
 
 addition of bolt flange on the arms. This makes ( a simple, direct, 
 and strong drive, the bolts being in shear. 
 
 Sketching this arrangement as the preferred one (Fig. 2A), it 
 is evident that the diameter of the gear should be at least as large 
 as the drum in order to keep the tooth load down to a reasonable 
 figure. On the other hand, if made too large, it spreads out the 
 machine and destroys its compactness. As a diameter of 36 
 inches is not excessive, let us assume this, and see if a desirable 
 proportion of gear tooth can be found to carry the load. 
 
 For a pitch diameter of 36 inches there will be a theoretical 
 
 load of ^ )OQx27 =3,750 pounds at the pitch line. But the load 
 
 Fig. 2A. 
 
 on the tooth must not only impart a pull of 5,000 pounds to th? 
 rope, but must -overcome friction between the gear teeth in action, 
 also between the drum shaft and its bearings. Assuming the 
 efficiency between the rope and tooth load to be 95 per cent, the 
 
 net load, therefore, which the tooth must take is ^-55 3,947, sav 
 
 .95 
 
 4,000 pounds. 
 
 39
 
 28 MACHINE DESIGN 
 
 Assuming involute teeth, and applying the "Lewis" formula, 
 (Part II, "GearsVj: 
 
 W = s Xp X f X y W=4,000 
 
 =6ioOO 
 
 4,000=6,000 X p X/ X .116 #=.116 (number of teeth 
 
 assumed at 75) 
 
 p x /= ^ OOQ =5.7 inches j)=circular pitch 
 
 /=face of gear 
 
 Let/=3j3 (a reasonable proportion for machine-cut teeth). 
 Then3xp 2 =5.7 
 
 p =1/^9=1-378 inches 
 The diametral pitch corresponding to this is 
 
 . 
 
 1.378 
 
 which is just between the regular standard pitches, 2 and 2J, for 
 which stock cutters are made. To be safe, let us take the coarser 
 pitch, which is 2. The circular pitch corresponding to this is 
 
 ' t > = 1.57, and making the face about three times the circular 
 
 pitch gives 
 
 3 X 1.57 = 4.71, say 4 J inches. 
 
 The number of teeth in the gear is then 36 X 2 = 72. 
 Referring to the value assumed for the tooth factor in calculation 
 above, it is seen that y was based on 75 as the number of teeth, 
 which is near enough to 72 to avoid the necessity of further check- 
 ing the result. 
 
 The pinion to mesh with this gear should be as small as possi- 
 ble in order to get a high-speed ratio between pinion shaft and 
 drum, otherwise an excessive ratio will be required in the pulleys, 
 making the large one of inconvenient size. Small pinions have 
 the teeth badly undercut and therefore weak, 13 teeth being the 
 lowest limit usually considered desirable, for that reason. Choos- 
 
 13 
 ing that number, we have a pitch diameter of ~^-= 6-5 in., which 
 
 is probably ample to take the shaft and key, and still leave suf- 
 ficient stock under the tooth for strength. If made of cast iron, 
 
 O 
 
 however, the pinion teeth, on account of the low number, will be 
 narrower at the root than those of the gear of 72 teeth. Yet it 
 
 40
 
 MACHINE DESIGN 
 
 was upon the basis of the latter that the pitch was chosen, for it 
 will be remembered that the value of y in the formula was 
 taken at .116. Hence the pinion will be weaker than the gear 
 unless we make it of stronger material than cast iron, of which 
 the large gear is supposed to be made. Steel lends itself very 
 readily to this requirement; and in practice, pinions of less than 20 
 teeth are usually made of this material, hence we shall specify the 
 pinion to be of steel. 
 
 Pulleys. The question now is whether or not we can get a 
 suitable ratio in the pulleys without making the large one of incon- 
 venient size, or giving the motor too slow speed for an economical 
 proportion. 
 
 Suppose we limit ourselves to a diameter of 42 inches for the 
 large pulley, and try a ratio of 4 to 1 ; this will give a diameter 
 for the small pulley of - 4 ^=10J inches. "We shall then have 
 
 Total ratio between drum and motor ........ X. 4=^=22.2 
 
 Rev. per min. of drum to give 150 f. p. m. of 
 
 Eev. per min. of motor ............ . ......... 22.2 X 21.2=470 
 
 Horse-power of motor at 80 per cent efficiency V*V X 5 ' (X ^ ) =30 
 
 33 } (XX) X 80 
 
 A 30 H. P. motor running 470 r. p. m. would be classed as a 
 slow speed motor and would be a heavier machine and cost mora 
 than one of higher speed. It will be noticed, however, that the 
 diameter of the small pulley is already quite reduced, and it is 
 hardly desirable to decrease it still further. Neither can we 
 increase the large pulley, as we have already set the limit at 42 
 inches. Hence, for our present problem we cannot improve mat- 
 ters much without increasing the size of the large gear, which is 
 undesirable, or putting in another pair of gears, which is contrary 
 to the conditions of the problem. As such a motor is perfectly 
 reasonable, we shall assume it to be chosen for the purpose. 
 
 In commercial practice it would be well to pick out some 
 standard make of motor of the required horse-power, note the speed 
 as specified by the makers, and then, if possible, suit the ratio in 
 the machine to this speed. It is always best to use standard ma. 
 chinery, if possible, both from the standpoint of first cost, as well 
 
 11
 
 30 MACHINE DESIGN 
 
 7^. 
 -7;= 7^ 
 
 ^ = 4-oo^6-<s. 
 
 -] r __ 'ty/O'* <=>/*+'''& x/ ^-_ /? 4^ ^. 
 
 / -^- ~\ / sj 
 
 -.o/S~ 
 
 so 
 
 r, 
 
 T^-T -- &^- 
 
 T ~-r^ &-'** 
 
 ' T - ^^'5' " ^ 5~<^ 
 """ /-^ 
 
 
 
 42
 
 MACHINE DESIGN 
 
 31 
 
 as ease of replacing worn parts. Machinery ordered special is 
 expensive in first cost of designing, patterns, and tools, and extra 
 spare parts for emergency orders are not often kept on hand. 
 
 Tabulation of Torsional Moments. For future reference, it is 
 desirable at this point to tabulate the torsional moment, or torque, 
 about each of the three shaft axes, assuming reasonable efficiencies 
 for the various parts, as follows: 
 
 Efficiency between drum and gear tooth 95 per cent 
 
 Efficiency between drum and pinion shaft 90 per cent 
 
 Efficiency between drum and motor shaft 80 per cent 
 
 TABLE OF TORSIONAL MOMENTS. 
 
 Axis. 
 
 Inch Lbs. Torque 
 at 100 Per Cent Efficiency. 
 
 Inch Lbs. Torque, 
 Efficiency as Above. 
 
 Drum 
 
 Pinion 
 
 Motor 
 
 5,OOOX^ 
 
 27 
 
 '67,500 
 
 
 6,000XX ...... =12,187 
 
 XX= 3,047 
 
 This means that the motor develops a torque of 3,809 inch. 
 pounds delivering to pinion shaft 13,541 inch-pounds, and to drum 
 71,052 inch-pounds. 
 
 Width of Belt. The page of calculation for belt width is repro. 
 duced in Fig. 3. 
 
 The calculation as given is strictly scientific, based on the 
 working strength of a cemented joint (#=400 Ibs. per square inch). 
 This is a favorable situation for the use of a cemented joint, be- 
 cause it is easy to provide means of adjusting the belt tension by 
 placing the motor on a sliding base. Otherwise a laced joint could 
 be used, requiring relacing when the belt slackens through its 
 stretch in service. Under the assumption that a double laced belt 
 is used, the empirical formula below is one often applied: 
 
 __ ,300 
 ~~540~- "540" 
 
 Thia gives w -y-^r- 12-4 inches (say 12 inches). 
 
 It should be remembered that this value is purely empirical; 
 it applies to a laced joint, and could not be expected to check the 
 
 43
 
 32 MACHINE DESIGN 
 
 value of 9 inches obtained by the first computation for a cemented 
 joint. It is fairly in proportion. For the quite definite service 
 req aired of the belt in the present case, the width of 9 inches is 
 doubtless sufficient, considering the cemented joint. , 
 
 Length of Bearings. Considerable latitude in choice of length 
 of bearings is permissible, especially in such slow-speed machinery. 
 There is probably little danger from heating, and the question then 
 becomes one of wear. It is better in such cases as the one in ques- 
 tion, to choose boldly a length which seems to be reasonable and 
 proceed with the design on that basis, even if the length be later 
 found out of proportion to the shaft diameter, than to waste too 
 much time in the preliminary calculation over the exact determina- 
 tion of this question. Probably in most cases of commercial prac- 
 tice the existence of patterns, or some other practical consideration, 
 will decide the limits of length. 
 
 In the present instance it seems reasonable that a length of 
 6 inches would fill the requirement for the worst case, that of the 
 drum shaft, and it is obvious that the bearings for the pinion shaft 
 would naturally be of the same length on account of being cast on 
 the same bracket, and faced at the same setting of the planer tool. 
 
 Height of Centers. The large pulley should naturally swing 
 clear of the floor. This will require, say, a total height of 23 
 inches, out which we may take 4 inches for the base, leavino- 19 
 inches as the height, center of bearing to base of bracket. 
 
 Data on Sketch. The data as found above should now be put 
 on the sketch previously made; it will then have the appearance 
 shown in Fig. 1. 
 
 This sketch is now in form to control all the subsequent detail 
 design, and it is expected that the figured dimensions as shown can 
 be maintained. It is impossible to predict this with positiveness, 
 however, as in the working out of the minor details certain 
 may be found desirable, when, of course, they should be made/ 
 
 The shaft sizes do not appear on this sketch, hence before 
 proceeding further the several shaft diameters must be calculated. 
 
 Sizes of Shafts. The calculations of the shaft diameters are 
 good instances of systematic engineering computations, hence thej 
 are reproduced in the exact form in which they were made. The 
 student should learn a valuable lesson in making and recording
 
 MACHINE DESIGN 
 
 calculations by following these carefully. Note that each set of 
 figures is independent, both in the statement of given data, as well 
 as in the actual computation. Observe how easy it would be for 
 the author of these figures or anyone else to check them even after 
 
 105<? 
 
 Fig. 4. 
 
 a long lapse of time. If the machine should unexpectedly fail in 
 service the figures are always available to prove or disprove theor- 
 etical weakness. The right triangles merely indicate that the 
 value of v/BHT 2 was found by the graphical method suggested in
 
 MACHINE DESIGN 
 
 Part II, " Shafts," the figures being put on the triangle as a sim- 
 ple and direct way of recording both process and result. 
 
 Attention is especially called to the fact that in the pinion 
 shaft the size is changed for each piece upon the shaft. This is 
 
 <-/ 'o 3 
 
 1051 
 
 7565 
 
 s. / 
 
 = JZ 
 
 done partly because it is desired to show tl 3 student that the shaft 
 at each of these points should be theorel ically of different size. 
 It is also done because as a practical feature of construction it is a 
 good plan to change the size when the fit changes, partly for rea. 
 sons of production in the shop, partly for ease in slipping pieces
 
 MACHINE DESIGN 
 
 35 
 
 freely endwise on the shaft until they reach their proper fit and 
 location in the assembling of the machine. 
 
 This should not be taken as an absolute requirement in any 
 sense. A straight shaft would be satisfactory in the present case; 
 but the shouldered shaft is a little better construction, in a mechan- 
 ical sense, and does not cost much more. Hence it is used. For 
 the drum the straight shaft seems to answer the requirement well 
 enough. 
 
 62./-03 
 
 <*, 
 
 Fig. ft 
 
 Small Pulley Bore. Fig 4. 
 
 Large Pulley Bore. Fig. 5. 
 
 Bearing Next to Large Pulley. Fig. 6. 
 
 The diameter, 2J-J, as calculated, is based on the supposition 
 that the greatest bending moment is caused by the belt pull on the 
 overhanging pulley, that is, by the forces existing at the left-hand 
 side of the center of the bearing. 
 
 47
 
 MACHINE DESIGN 
 
 But the pinion tooth load produces a heaVy bending on the 
 shaft in the bearing, the shaft in this case acting as a beam sup- 
 
 t&zrrts 
 
 Fig. 7. 
 
 ported at the two bearings and living the tooth load applied as 
 shown. If this latter effect be greater than the former, that is, if 
 
 48
 
 MACHINE DESIGN 87 
 
 the bending moment produced by the pinion tooth load be greater 
 than the bending moment produced by the belt pull, then the diam- 
 eter must be increased to satisfy the latter case. As is seen by 
 the second calculation of Fig. 6, this is not the case, and the diam- 
 eter stands at 2|J as made. 
 
 Pinion Bore. Fig. 7. The pinion being a driving fit upon 
 the shaft, reinforces the shaft to such an extent that it is hardly 
 possible for the shaft to break off very far inside the face of the 
 pinion; but it is quite possible that the metal of the pinion may 
 give enough, or be a little free at the ends of the hole, so that the 
 shaft may be broken off, say -| inch inside the face. In this case, 
 it may fail from the moment of the force at the left-hand bearing 
 or of that at the right. It may fail then at (a) or (b), depending 
 on which section has the greater bending moment. Trying both, 
 it is seen by the calculation that the right-hand moment is the 
 controlling one, and it, therefore, is used. 
 
 Shaft Outside of Pinion. Fig. 8. As there is no power 
 transmitted through this portion of the shaft, there is no torsional 
 moment in it, and the bending moment remains practically the 
 same as inside the pinion. 
 
 The size figures about 2j|, but since there is no use in turn- 
 ing off material just to reduce the size to this, it is well to make 
 it 2|, or just smaller than the fit in the pinion. 
 
 Pinion Shaft Outer Bearing. Fig. 8. This diameter, of 
 course, figures small, as there is no torsion in it, and" the bending 
 moment is not heavy. The practical question comes in, however, 
 whether it is advisable, to make the outer bracket different from 
 the inner one just on account of this bearing. The commercial 
 answer to this would probably be "No," hence the size as figured 
 next to the pinion will be maintained (2j-|). 
 
 Drum Shaft. Fig. 9. In this case, as previously inferred, 
 the simplest thing to do is to use a piece of straight cold-rolled 
 steel, and make both bearings alike, the size being determined 
 according to the worst case of loading which can occur as the 
 rope travels from end to end of the uiim. This case ia evi- 
 dently when the rope is at the end of its travel close to the brake, 
 for at that time both the load on the rope and the load on the pinion 
 tooth which is driving it are exerted upward, and produce the 
 
 49
 
 MACHINE DESIGN 
 
 cn-eatest reaction at the bearing next to the gear. The analysis of 
 the forces for this condition is shown in Fig. 9. 
 
 Other conditions of loading would be when the brake is on 
 and the tooth load relieved, but then the resultant of the brake 
 strap tensions would be diagonally downward and would reduce 
 
 .2.2' '03 
 
 2 Z - 
 
 rather than add to the rope load. Again, when the rope is at 
 the end of the drum farthest from the gear, the load on it and 
 the load on the pinion tooth are both exerted upward as before, but 
 the reaction cannot be ab jreat as in the case of Fig. 9, because the 
 tooth load is still concentrated at the other end of the shaft and 
 produces a relatively small reaction at the rope end 

 
 MACHINE DESIGN 
 
 39 
 
 Preliminary Layout. Fig. 10. Proceeding now with the lay- 
 out to scale, the detail of the parts may be worked out as com- 
 pletely as the scale of the drawing will permit. The work on this 
 drawing may be of an unfinished, sketchy nature, but the measure- 
 ments must be exact as far as they go, for this drawing is to serve 
 as the reference sheet, from which all future detail is to be worked up. 
 
 In this layout may be worked out the sizes of the arms and 
 hubs of pulleys and gears, the proportions of the drum and brake 
 
 T 
 
 
 ^f 
 
 i 
 
 OOO& 
 
 *S. o>v O0>v"T0/K 
 
 ,50 o o 'oS . <MV AXX|^ 
 
 < 
 
 ^ 
 
 
 
 J 
 
 
 
 3/4: 
 
 
 
 
 
 
 
 
 
 
 
 
 t r^ 
 
 2 
 
 
 
 
 "~\\ 
 
 1/^1 
 
 
 a P- 3 
 
 
 
 
 
 x^ 
 
 \ 
 
 
 * (* 
 
 -^ 
 
 r< 
 
 
 
 
 / > 
 
 
 per 
 
 
 t 
 
 < , > 
 
 J2^" 
 
 
 
 
 
 ^4 
 
 i. 
 
 ~t 
 
 -* 
 
 
 
 
 
 "Px 3^.75 
 T - 
 
 "^ -f- -4-OOO 
 
 Fig. 9. 
 
 strap, and the general dimensions of the side brackets and the 
 base. When the detail becomes too fine to work out to advan- 
 tage on this drawing it may be worked out full size by a separate 
 sketch, or left to be finished when it is regularly detailed. The 
 preliminary layout, it should be remembered, is a service sheet 
 only, a means of carrying along the design, and not intended for 
 
 51
 
 Fig. 10.
 
 MACHINE DESIGN 41 
 
 a finished drawing. The moment that the free use of the layout 
 is impaired by trying to make too much of a drawing of it, ita 
 value is largely lost. A designer must have some place to try out 
 his schemes and devices, and the layout drawing is the place to do 
 it. This drawing may be recurred to at intervals in the progress 
 of the design, details being filled in as they are worked out, as 
 they may control the design of adjacent parts. 
 
 As the discussion of the design of each of the members 
 involved in the present problem can be better taken up in con- 
 nection with the detail drawing of each, it will be given there, 
 rather than in connection with the layout, although many of the 
 proportions thus discussed could be worked out directly from the 
 latter. 
 
 Pulleys. Fig. 11. The analysis of the forces in the belt 
 gives, according to the calculation of Fig. 3, a tension in the tight 
 side of 1,059 pounds, and in the slack side 414 pounds. The 
 difference of these, or 1,059 414=645 pounds, is transmitted to 
 the pulley and produces the torque in the shaft. Of course in 
 the small pulley the torque is transmitted from the motor through 
 the pulley to the belt, but both cases are the same as far as the 
 loading of the pulleys is concerned. 
 
 The only other force theoretically acting is the centrifugal 
 force due to the speed of the pulley. This produces tension in 
 the rim and arms, but for the low value of 1,300 feet per minute 
 peripheral velocity in this case may be disregarded. 
 
 Considering the arms as beams loaded at the ends, and that 
 one-half the whole number of arms take the load, and for con. 
 venience, figuring the size of the arms at the center of the pulley 
 gives the following calculation for the large pulley: 
 
 6 1X21=^I=.0393X2,500X& 8 Let 8=2,500 
 
 A=rbreadthofoval 
 
 h*= *' 5 ^ =46 . - .47i= thickness of oval 
 
 vo.ZD 
 
 (say 3.5) 
 
 .4fc=.4x3 5=1.4 (say 1 7-16) 
 
 This is about all the theoretical figuring nece3sary on thia 
 pulley. The rim is made as thin as experience judges it capable 
 of being cast; the arms are tapered to suit the eye, thus giving 
 ample fastening to the rim to provide against shearing off the rim 
 
 5:5
 
 MACHINE DESIGN 43 
 
 from the arms; generous fillets join the arms to both rim and hub; 
 and the hub is given thickness to carry the key, and length 
 enough to prevent tendency to rock on the shaft. Uncertain 
 strains due to unequal cooling in the foundry mold may be set up 
 in the arms and rim, but with careful pouring of the metal they 
 should not be serious, and the low value chosen for the fibre stress 
 allows considerable, margin for strength. 
 
 The small pulley has the same forces to withstand as the 
 large pulley, but on account of its small diameter there is not 
 room enough for arms between the rim and the hub, hence it is 
 made with a web. The web cannot be given any bending by the 
 belt pull, the only tendency which exists in this case being a 
 shearing where the web joins the hub. This shearing also exists 
 throughout the web as well, but at other points farther from the 
 center it is of less magnitude, and moreover, there is more area of 
 metal to take it. The natural way to proportion the thickness of 
 the web is to give it an intermediate thickness between that of the 
 hub and rim, thus securing uniform cooling, and then figure the 
 stress as a check. Making this value ^ inch gives a shearing area 
 of g- multiplied by the circumference of the hub, which is 3.1416 
 
 X 4 = 12.56. The shearing force at the hub is - =1,693 
 
 pounds. Equating the external force to the internal resistance 
 1,693 =^JX 12.56X8 
 
 S ~ jy 10 5C = "^ P oun( * s P er S( l uare i ncn (approx.). 
 
 This is a very low figure, even for cast iron, hence the web is 
 amply strong. The rim and hub are proportioned as for the large 
 pulley. 
 
 The keys are taken from the standard list. They may be 
 checked for shear, crushing in the hub, and crushing in the shaft, 
 but the hubs are so long that it is at once evident without figuring 
 that the stress would run very low in both cases. 
 
 Gears. Fig. 12. The analysis of the forces acting on the 
 gears has been given on page 28, 4,000 pounds being taken at the 
 pitch line. Using this same value, and choosing a T-shaped 
 arm as a good form for a heavily loaded gear like the present one, 
 let us consider that the rim is stiff enough to distribute the load
 
 J 
 
 v 
 
 Fig. 12.
 
 MACHINE DESIGN 45 
 
 equally between all the arms, and that each acts as a beam loaded 
 at the end with its proportion of the tooth load. Before we can 
 determine the length of these arms, however, we must fix upon the 
 size of the flange which is to carry the driving bolts. This is taken 
 at 13 inches. It could be smaller if desired, but drawing the bolts 
 in toward the center increases the load on them, and 13 inches 
 seems reasonable until it is proved otherwise. This makes the 
 
 maximum moment which can come on an arm = 7,666 
 
 6 
 
 inch-pounds. 
 
 Now it is evident that the base of the T arm section, which 
 lies in the plane of rotation, is most effective for driving, and 
 that the center leg of the T does not add much to the driving 
 capacity of the arm, although it increases the lateral stiffness of 
 the arm, as well as providing in casting a free flow of metal between 
 the rim and the hub. Hence the simplest way of treating the sec- 
 tion of the arm for strength is to consider the base of the T 
 only, of rectangular section, breadth J, and depth /*, for which 
 
 . SX^XA 2 . 
 
 the internal moment of resistance is ~ 
 
 o 
 
 Also, it is simplest to assume one dimension, say the breadth, 
 and the allowable fibre stress, and figure for the depth. Taking 
 the breadth at 1J inches, which looks about right, and the fibre 
 stress at 2,500, and equating the external moment to the internal, 
 we have 
 
 3,500X1.125X7,* 
 
 6X7,666 
 
 ~- 2,500X1.125" 
 h =.j/IO = 4.05 (say 4J) 
 
 Drawing in this size, and tapering the arm to the rim as in 
 the case of the pulleys, making -the depth of the rim according to 
 the suggested proportions given in Part II, " Gears," giving the 
 center leg of the T a thickness of ^ inch tapering to 1 inch, and 
 heavily filleting the arms to the rim and center flange, we have a 
 fairly well proportioned gear. 
 
 The next thing to determine is the size of the driving bolts. 
 The circle upon which their centers lie may be 11 inches in diam- 
 
 57
 
 Fig. 13.
 
 MACHINE DESIGN 47 
 
 eter, and there will naturally be six bolts, one between each arm. 
 These bolts are in pure shear, and the material of which thoy are 
 to be made ought to b3 good for at least 8,000 pounds per square 
 inch fibre stress. The force acting at the circumference of an 
 
 11-inch circle would be =-= -==13,091 pounds. 
 
 Equating the load on each bolt to the resisting shear gives 
 
 13.091 . 8,OOOX3.U16X<22 Let A = area resisting shear. 
 
 -"j-=8 t OOOX A=- Let rf=dia> of bolt 
 
 Then A=^ 
 
 4X13,091 
 
 "~6X8,OOOX3.1416~" 
 d= 1/135" (say ,6) %-mch bolts would do. 
 
 But f -inch bolts are pretty small to use in connection with such 
 heavy machinery. They look out of proportion to the adjacent 
 parts. Hence -|-ineh bolts have been substituted as being better 
 suited to the place in spite of the fact that theoretically they are 
 larger than necessary. The extra cost is a small matter. These 
 bolts may crush in the flange as well as shear off, but as there is 
 
 13 091 
 an area of |xlf = 1.422 square inches to take ^ =2,182 
 
 pounds, the pressure per square inch of projected area is only 
 
 2,182 
 
 .' 9 =1,534 pounds, which is very low. 
 
 This gear needs no key to the shaft because all the power 
 comes down the arms and passes off to the drum through the bolts, 
 thus putting no torsional stress in the shaft. The face of the 
 flange is counterbored so as to center the gear upon the drum, 
 without relying upon the fit of the gear upon the shaft to do this. 
 
 The pinion is solid and needs no discussion for its design. 
 
 Brackets and Caps. Fig. 13. As the size of the drum shaft 
 was determined by considering the rope wound close up to the 
 brake, thus giving in combination with the load on the gear tooth 
 the maximum reaction at the bearing as 6,748 pounds, the cap and 
 bolts should be designed to carry the same load. 
 
 For a bearing but 6 inches long, two bolts are sufficient under 
 ordinary conditions and might perhaps do for this case. . The load 
 is pretty heavy, however, and it is deemed wise to provide four 
 bolts, thus securing extra rigidity, and permitting the use of bolts 
 
 59
 
 43 MACHINE DESIGN 
 
 of comparatively small si/e. If the load were distributed equally 
 over all the bolts each would take one-fourth of the whole load, 
 but it is not usually safe to figure them on this basis, because it 
 is difficult to guarantee that each bolt will receive its exact share 
 of stress. Assuming that the two bolts on one side take J the 
 whole load instead of .',, which provides for this uncertain extra 
 stress, each bolt must take care of -*- of 0,74-S, or 2.240, pounds. 
 Allowing 8,000 pounds per square inch fibre stress calls for an 
 
 2,24 ( .) 
 area at the root of the thread of , , T .281 square inch. Con- 
 
 sulting a table of bolts we find that the next -standard size of bolt 
 greater than this is -^, which gives an area of .302- square inch. 
 
 Choosing this size as satisfactory, the bolts should be located 
 as close to the shaft as will permit the hole to be drilled and tapped 
 wituout breaking out. A center distance of 5. 1 , inches accomplishes 
 this result. The distance between centers in the other direction 
 is somewhat arbitrary, although the theoretical distance between 
 the bolt and the end of the bearing to give equal bending moment 
 at the center of the cap and at the line of the bolts is about -/ f of 
 the length, or - 2 5 4 - of (>--!_]- inches. This proportion answers 
 well for the present case, although for long caps it brings the 
 bolts too far in to look well. 
 
 The thickness of the cap may be determined by assuming it 
 to be a beam supported at the bolts and loaded at the middle. 
 This is not strictly true, for the load is distributed over at least a 
 portion of the shaft diameter; moreover, the bolts to some extent 
 make the beam fixed at the ends. It Ix-ing impossible to determine 
 the exact nature of the loading, we may take it as stated, supported 
 at the ends and loaded in the middle, and allow a higher fibre 
 stress than usual, say 8,500. The longitudinal section at the 
 middle of the cap is rectangular, of breadth i\ inches, and der>th 
 unknown, say //. The equation of moments is 
 
 ^Y ZSI S.l>,' 
 
 - < 6 
 
 (y 48 X 5.5 3,500 x fi x 7, 2 
 
 4X3,500X0- 
 h = 1/2JB5=1.G2 (1 j will probably answer) 
 
 60
 
 MACHINE DESIGN 49 
 
 For the other bearing next to the pinion, the load on the tooth 
 acts downward, and the resultant pull of the belt is nearly hori- 
 zontal, hence the cap and bolts must stand but little load, and 
 calculation would give minute values. In a case like this it is 
 well to make the size the same as for the larger bearing, unless 
 the contraction becomes very clumsy thereby. This saves chang- 
 ing drills and taps in making the holes, and preserves the symmetry 
 of the bracket. The |-inch bolts are good proportion for the 
 smaller bearing, hence that size will be maintained throughout. 
 
 The body of the bracket is conveniently made with the web at 
 the side and horizontal ribs extending to the outside. The lotid due 
 to the rope is carried directly down the side ribs and web into 
 the bottom flanges and to the bolts. The analysis of the forces 
 on these bolts is shown in Fig. 14. It is evident from the figure 
 that the resultant belt pull tends to hold the bracket down, while 
 the load on the rope tends to pull it -up, the point about which it 
 tends to rotate being the corner furthest from the drum. It is also 
 evident thac the bolts nearest this corner can have little effect on 
 the holding down, because their leverage is so small about the cor- 
 ner, hence we shall assume that the pair of bolts at the right-hand 
 end of the bracket takes all the load. The belt pull, being hori- 
 zontal. tends to slide the bracket along the base, but this tendency 
 is email, and at any rate is easily taken care of by the two dowel 
 pins, which are thus put in shear. 
 
 The load on the bolts being 4,954 pounds, a heavy bending 
 moment is thrown on the flange of the bracket, tending to break 
 it off at the root of the fillet. The distance to the root of the fillet 
 is 2 inch; the section tending to break is rectangular, of breadth 
 5 1 , inches, and unknown depth //. The equation of moments ia 
 
 6 
 6x4,954x3 
 
 = 1.3 ( say 1J). 
 
 The thickness of the web and ribs of this bracket is hardly 
 capable of calculation. The figure | inch has been chosen in pro- 
 
 Gl
 
 50 
 
 MACIIIXE DESIGN 
 
 portion to tlio size of the largo drum bearing, givino- ample stiff- 
 ness and rigidity, and permitting uniform flow and cooling of the 
 metal in the mold. The opening in the center is made merely to 
 save material, as in that part little stress would exist, the two sides 
 
 5000 
 
 Sgj 
 
 / ^ Inh, 
 
 
 
 I 
 
 T ~ I r> ^ft 
 
 < 3~ '' " 
 
 
 
 W = 
 
 ;w 
 
 + IfT'ixl 
 
 m-7 2> x 
 
 2> 7, & 7 
 
 O / y *y -y 
 
 WUJjJl 
 
 ft 
 
 Carrying tlio load down to the base bolts, and the top serving as a 
 tie between the bearings. 
 
 This bracket might be made with the \veb in the center of the 
 tarings instead of at the side, in which case the expense of the
 
 MACHINE DESIGN 51 
 
 pattern would be slightly greater. It could also be made of closed 
 box form, but would in that case probably weigh more than as 
 shown. 
 
 Drum and Brake. Fig. 15. The analysis of the forces acting 
 on the drum is simple, but its theoretical design is more compli- 
 cated. It is evident that the drum acts as a beam of hollow circular 
 cross section, and that its worst case of loading is when the rope is 
 at or near the middle of the drum length. At the same time the 
 metal of this circular cross section is in a state of torsion between 
 the free end of the rope and the driving gear, due to the load on 
 the gear tooth and the reaction of the rope. Also the wrapping of 
 the rope around the drum tends to crush the metal of the 
 section beneath it, the maximum effect of this action being near 
 the free end of the rope where its tension has not been reduced by 
 friction on the drum surface. 
 
 Now the " mechanics " to solve the problem of these three 
 combined actions is rather complicated. It can JDO at least approx- 
 imately solved, however, for it _ satisfies fairly well the case of 
 combined compression and shear. But on a further study of this 
 particular case, it is seen at once that the diameter of the drum is 
 relatively large with respect to its length, which means that the 
 thickness of the metal may be very small and yet give a large 
 resisting area, or value of "I," both in direct bonding as well as 
 torsion; also it is so- short that the external bending moment will 
 be small. The practical condition now comes in, that the drum 
 can be safely cast only when the thickness of the metal is at a 
 minimum limit, for the core may be out of round, not set centrally, 
 or by some other variation produce thin spots or even develop holes 
 reaching out into the rope groove, discovered only when the latter 
 is turned in the lathe. 
 
 Hence it seems reasonable and safe in this case to make the 
 thickness of the drum depend simply upon the crushing caused by 
 the wrapping of "the rope around it, and we shall take the coil 
 nearest the free end of the rope, assuming that it carries the full 
 load of 5,000 pounds throughout one complete wrap around the 
 drum. 
 
 The area resisting the crushing action may be considered to 
 be that of the cross section of a ring, of width equal to the pitch 
 
 63
 
 Fig. 15,
 
 MACHINE DESIGN 53 
 
 of the groove. Assuming that | inch is the least thickness which 
 can be safely allowed under the groove for casting purposes, let 
 us figure the crushing fibre stress to see if this is sufficiently 
 strong. Disregarding the small amount of metal existing above 
 the bottom of the groove, this gives the area to resist the crushing 
 |X|= ?r|, or .47 inch. Since there are two of these sections ana 
 the rope acts on both sides, the equation of forces is: 
 5,000X2 = Sx.47x2 
 
 5 00() X 2 
 S = \^ ~ = 10620 pounds per square inch. 
 
 "This, for cast iron, in pure crushing, allows plenty of margin 
 for the extra bending and torsional stress, which for such a con- 
 siderable thickness would bs slight. 
 
 The above case indicates a method of reasoning much used in 
 designing machinery, which while following out the specified 
 routine of thought as previously given in these pages, stops short 
 of elaborate and minute theoretical calculation when such is obvi- 
 ously unnecessary. If a drum of great length were to be designed, 
 and of small diameter, the same method of reasoning would deduce 
 the fact that the design should be based on the bending and the 
 torsional moments, the thickness in such a case b^ing so great to 
 withstand these that the intensity of the crushing due to wrap of 
 the rope becomes of inappreciable value. 
 
 The remaining points of design of the drum are determined 
 from practical considerations and judgment of appearance. The 
 ribs behind the arms are put in to give lateral stiffness and guard 
 against endwise collapse. The arms are subject to the same bend- 
 ing as those of the gear, but as they are equally heavy it is not 
 necessary to calculate them. The flange at the driving end is of 
 course matched to that already designed for the gear. The rope 
 is intended to be brought through the right-hand end with an 
 easy bend and the standard form of button wedged on to prevent 
 its pulling through. 
 
 This drum would probably be cast with its axis vertical, and 
 the driving flange down to secure sound metal at that point. 
 Heavy risers would be left at the other end to secure soundness 
 where the rope is fastened. Drums are often cast with the axis 
 horizontal, but the vertical method is more certain to produce 
 a sound casting. The grooves should be turned from th^ 
 
 65
 
 54 MACHINE DESIGN 
 
 solid metal, partly because it is a difficult matter to cast them, but 
 principally because the rope should run on as smooth surface as 
 possible to avoid undue wear. On drums which carry chain instead 
 of \vire rope the grooves are sometimes cast with success, although 
 even in this case the turned groove is generally preferable. 
 
 The brake consists of a wrought- iron band to which are fast- 
 ened wooden blocks, the iron band giving the requisite strength 
 while the blocks give frictional grip on the drum surface and can 
 be easily replaced when worn. As in the designing of a belt the 
 object in view is the grip on the pulley surface by the leather to 
 enable power to be transmitted from the belt to the pulley, so in 
 the case of the brake if we put the proper tension in the strap it 
 can be made to grip the brake drum so tightly that motion between 
 it and the drum cannot occur. The latter case is really the reverse 
 of the first, if the driven pulley be considered, but is identical with 
 the case of the driving pulley, in which the power is transmitted 
 from the pulley to the belt. Of course in the case of the brake 
 uo power is transmitted, as when the brake holds no motion occurs, 
 but the principle of the relative tensions in the strap is the same 
 as for the belt. 
 
 Since the brake drum surface is 28 inches in diameter, the load 
 at that surface which the- brake must hold is 
 
 P = = 4,821 pounds. 
 
 JUT: /\ ~- 
 
 We have then the following calculation corresponding exactly 
 to that of the belt given in Fig. )>. 
 
 T n T =P = 4,821 
 
 log. ^ = 2.720 X .25 X .75 = 0.512 ( for which ^^^ DUmbef 
 
 T T 
 
 Then 2- =3.25 T =^;'= 
 i ..,.,0 
 
 T n -T = 4,S21 T D -i = ^^5 = 4 . 821 
 
 4 81 y 3 ^5 
 
 T n = "" 2 * '" - = 6,963 pounds (say 7,000) 
 
 T = 6,9634,821 = 2.142 pounds (say 2,200)
 
 MACHINE DESIGN 55 
 
 The tight end of the strap must then be capable of carrying a 
 load of 7,000 pounds, and since the width has already been taken at 
 4i inches, the problem is to find the necessary thickness. Equating 
 the external load to the internal resistance we have 
 7,000 A X S Let t = thickness 
 
 " S = fibre stress = 12,000 
 7,000 = 4.5X^X12,000 
 
 _ 
 
 This, however, can be but a preliminary figure, for the riveting 
 of the strap will take out some of the effective area, and the thick- 
 ness will have to be increased to allow for this. Suppose on the 
 basis of this figure we assume the thickness at a slightly increased 
 value, say ^ inch, and proceed to calculate the rivets. 
 
 A group of five rivets will work in well for this case, which 
 
 gives '-= = 1,400 pounds per rivet. A safe shearing fibre stress 
 
 1 400 
 is 6,000, hence the area necessary per rivet is /*QQQ = -23 square 
 
 inch. This comes nearest to the area T 9 5 diameter, but for the 
 sake of using the more general size of rivet (| inch) the latter is 
 chosen, for which the area is .30. 
 
 We must DOW try these rivets in a -^-inch plate for their safe 
 bearing value. The projected area of a |-inch hole in a -^ ff -inch plate 
 
 is | X-& =.117 square inch. -^- = 11,965 (15,000 would be safe) 
 Taking out two ft-inch rivets from the full width of 4i inches 
 
 O o & 
 
 leaves 4J (2 X g) 3.25, and makes the net area of strap to take 
 stress 8.25 Xi\=.61 square inches. Re-calculating the fibre stress 
 for this area gives 
 7,000 = . 61 XS 
 
 ~ _ 7,000 = 11,475 (which approximates the previous value 
 
 = ~M~ of 12,000). 
 
 The slack end of the strap has to take but 2,200 pounds, hence 
 a different calculation might be made for this end giving smaller 
 rivets; but as it is impractical to change the thickness of the strap 
 to meet this reduced load, it is well to maintain the same propor- 
 tion of joint as at the tight end. The spacing of the rivets in both 
 
 67
 
 11 
 
 75.- 
 
 n 
 
 * * 
 
 Fig. 16.
 
 MACHINE DESIGN 5? 
 
 cases follows the ordinary rule allowing at least three times the 
 diameter of the rivet as center distance, and one-half this value to 
 the edge of the plate. 
 
 c5 J 
 
 The threaded end of the forging on the strap also has to carry 
 the load of 2,200 pounds, for which a size smaller than 1 inch 
 would suffice. It is natural, however, for the sake of general pro- 
 portion to make the bolt as strong as the strap, and a 1-inch bolt 
 gives an area of .52 square inch, nearly equalling the value of 
 .61 net area of strap noted above. 
 
 Base, Brake=Strap Bracket and Foot Lever. Fig 16. The 
 base cannot be definitely calculated, and can best be proportioned 
 by judgment. It must not distort, twist, or spring in any way to 
 throw the shafts out of line. The area in contact with the founda- 
 tion upon which it rests must be ample to carry the weight of the 
 whole machine with a low unit pressure. Although the form 
 shown is perfectly practicable to cast and machine, and is simple 
 ard rigid, yet it is questionable if a bolted-up construction, say of 
 four pieces, might not be equally rigid and yet involve greater 
 facility of production in both the foundry and machine shop on 
 account of the reduced sizes of parts to be handled. This is a 
 question which depends on the equipment and methods of the 
 individual shop, and is an illustration of the practical control of 
 design by manufacturing conditions. 
 
 The brake-strap bracket and foot lever, also shown in this 
 figure, are examples of machine parts which are quite definitely 
 loaded, and the designing of which is a simple matter. Further 
 discussion of their design is not made, the student being given 
 opportunity for some original thought in determining the forces 
 and moments that control their design. 
 
 Gear Guard and Brake=Relief Spring. In exposed machin- 
 ery of this character it is desirable to cover over the gears with a 
 guard to prevent anything accidentally dropping between the 
 teeth and perhaps wrecking the whole machine. This guard is not 
 shown, as it involves little of an engineering nature to interest 
 the student. It could readily be made of sheet metal or light 
 boiler plate, bent to follow the contour of the gears and fastened 
 to the top flange of the main bracket. 
 
 If the brake be not automatically supported at its top it will 
 
 69
 
 MACHINE DESIGN 
 
 lie with considerable pressure, due to its own weight, on the brake 
 surface when it is supposed to be free fron, :'t, and by the friction 
 thereby created will produce a heavy drag and waste of power. 
 A spring connection fastened to an overhead beam is a simple way 
 of accomplishing the desired result. A flat supporting strap car- 
 ried out from the gear guard, having some degree of spring in it, 
 is a neater method of solving the problem. The spring should 
 be just strong enough to counterbalance the weight of the strap 
 and yet not resist to an appreciable degree the force applied to 
 throw the brake on. 
 
 GENERAL DRAWING. 
 
 The last step in the process of design of a machine is the 
 making of the assembled or general drawing. This should be 
 built up piece by piece from the detail drawings, thereby serving 
 as a last check on the parts going together. This drawing may 
 be a cross section or an outside view. In any case it is not wise 
 to try to show too much of the inside construction by dotted lines. 
 for if this be attempted, the drawing soon loses its character of 
 clearness, and becomes practically useless. A general drawing 
 should clearly hint at, but not specify, detailed design. It is 
 just as valuable a part of the design as the detail drawing, but 
 it cannot be made to answer for both with any degree of success. 
 A good general drawing has plenty of views, and an abundance of 
 Cross sections, but few dotted lines. 
 
 The general drawing of the machine under consideration is 
 left for the student to work up from the complete details shown. 
 It would look something like the preliminary layout of Fig. 10, if 
 the same were carefully carried out to finished form. A plain out- 
 side view would probably be more satisfactory in this case than a 
 cross section, as the latter would show little more of value than the 
 former. The functions which the general drawing may serve are 
 many and varied. Its principal usefulness is, perhaps, in showing 
 to the workman how the various parts go together, enabling him to 
 sort out readily the finished detail parts and assemble them, finally 
 producing the complete structure. Otherwise the making of a 
 machine, even with the parts all at hand, would be like the putting 
 together of the many parts of an intricate puzzle, and much time 
 
 i o
 
 MACHINE DESIGN 59 
 
 would be wasted in trying to make the several parts fit, with per- 
 haps never complete success in giving each its absolutely correct 
 location. 
 
 The general drawing also gives valuable information as to the 
 total space occupied by the completed machine, enabling its loca- 
 tion in a crowded manufacturing plant to be planned for, its con- 
 nection to the main driving element arranged, and its convenience 
 of operation studied. 
 
 In some classes of work it is a convenient practice to letter 
 each part on the general drawing, and to note the same letters on 
 the specification or order sheet, thus enabling the whole machine 
 to be ordered from, the general drawings. This is a very excel- 
 lent service performed by the general drawing in certain lines of 
 work, but for such a purpose the drawing is quite inapplicable 
 in others. 
 
 Merely as a basis for judgment of design, the general drawing 
 fulfils an important function in any class of work, for it approaches 
 the nearest possible to the actual appearance that the machine will 
 have when finished. A good general drawing is, for critical pur- 
 poses, of as much value to the expert eye of the mechanical 
 engineer as the elaborate and colored sketch of the architect is to 
 the house builder or landscape designer. 
 
 1 O 
 
 From the above it is readily understood that the general 
 drawing, although a mere putting together of parts in illustration, 
 is yet of great assistance in producing finished and exact machine 
 design. 
 
 GENERAL COMMENTS ON PRECEDING PROBLEM. 
 
 After following through the detail of work as given in the 
 preceding pages, it is worth while to stop for a moment and 
 take a brief survey or review of the subject as illustrated therein. 
 
 If the text be carefully studied it will be seen that in every 
 part to be designed the same routine method has been followed, 
 regardless of the final outcome. In some cases it may seem a 
 roundabout procedure to follow a train of thought that finally 
 ends in a design apparently based on purely practical judgment, 
 the theory having had but very little if any influence. The ques- 
 tion at once arises Why not use the empirical rule or formula in 
 
 71
 
 60 MACHINE DESIGN 
 
 the first place ? Why not make a good guess at once ? Why not 
 save all the time and energy devoted to a careful analysis and 
 theory, if we are finally to throw them away and not base our 
 design on them '( 
 
 The principle to be noted in this connection is. that it is just 
 as fatal to good design to rely upon bare experience and upon 
 judgment alone, as it is to construct solely according to what pure 
 theory tells us. There are many things in the operation of 
 machinery that are totally inexplicable from the purely practical 
 point of view, and will forever remain so until we analyze them 
 and theorize on them. Many good things in machinery have 
 been the result of what might be called "reversed-' machine 
 design. When a new machine is started, it frequently, or we 
 might almost say always, fails to do its work just as it is expected 
 to do it. This is because some little point of design is bad. owing 
 to the inability of drawings, however good they may be. to show 
 all that the machine itself in bodily form and in motion shows. 
 
 Now. if our analysis and theory have been good in the 
 designing process, it is almost sure that we can very readily 
 analyze and theorize on the trouble that exists when the machine 
 is finished, can detect the weakness, and can correct it with coin- 
 paratively small change in the general design. This is reversed'' 
 machine design. 
 
 Jf. on the contrary, we have based our design purely on guess- 
 work, allowing our fancy full and free plav to work out the details 
 without further basis, we may consider ourselves lucky if the 
 machine runs at all. This, however, is not the worst of the 
 situation. If the machine does actually operate, even as well as 
 it might reasonably be expected to. but still has the usual diffi- 
 culty of some little kink or hitch that was not expected, then, as a 
 result of the method upon which the whole thing has been con- 
 structed, we have no definite plan of action to proceed upon. We 
 must try first this, then that scheme to obviate the trouble. We 
 may be fortunate enough to " strike it "' the first time ; we may 
 never strike it. It is doubtful if the machine ever can be made to 
 work at highest efficiency ; and if fairly good residts be finally 
 obtained we never know the reason why. and have nothino- on 
 ' which to base any future action or design. 
 
 72
 
 MACHINE DESIGN 61 
 
 This haphazard process is not machine design at all, either 
 in name or in result. 
 
 As has previously been stated in these pages, there is no 
 such thing as too much analysis or theory in the designing of 
 machinery. Even if we carefully analyze, theorize with rigorous 
 exactness, and then practically modify our construction to such a 
 point -that the original theoretical shape is almost or entirely lost, 
 the apparently roundabout process is not in vain, for we are in per- 
 fect control of our design. We know exactly what it has to take in 
 the way of forces, blows and vibrations. We know what its ideal 
 shape should be. We know where we can practically modify its 
 form without weakening it excessively or adding excess of material. 
 In other words we know all about it, and therefore know exactly 
 what we can do with it ; and whether it follows in its shape the 
 outline that pure theory gives it or some other outline, it is never- 
 theless well designed. 
 
 O 
 
 "Reversed" machine design, as described above, based on 
 observation and experiment with regard to machines already in 
 operation, is just as impossible without exact analysis and theory 
 as is original design based merely on mechanical ideas in the 
 abstract. The method once learned and made a habit of mind 
 will produce results with equal facility in either case, and results 
 are what the mechanical world is seeking. 
 
 Another point worth noting in the progress of the problem 
 as given is the absolute necessity of possessing some knowlege of 
 Mechanics. The more of this subject the designer can have at 
 his finger ends, the more ready and successful will he be in all 
 problems of Machine Design. However, the principles of forces 
 and moments clearly understood, and the application of the same 
 in the all-important subject, "Strength of Beams," constitute a 
 fund of information that will give a splendid start and a good 
 working basis for simple designs. It should always be remem- 
 bered that a complicated design is little more than a combination 
 of simple designs, and if one has the ability to dissect and analyze 
 what seems at first like a bewildering maze of parts, complication 
 is speedily changed to simplicity. 
 
 Common sense goes a long way in good designing. There is 
 QOthing mysterious about the process If the beginner will only 
 
 73
 
 62 MACHINE DESIGN 
 
 avoid doing things that are foolish and ridiculous on their very 
 face, if he will exercise the same judgment that he uses in the 
 daily affairs of his life and will mix in something of mechanics and 
 mechanical method, he will be on the direct road to success in the 
 art. 
 
 Good drawing is an essential element of good design, and it 
 is especially urged that the sketches and drawings as reproduced 
 in the preceding text be studied with this in mind. By a good 
 drawing is meant not a showy piece of work, finely shaded or 
 artistically lettered, but an exact layout, definite and measurable, 
 L'orrectly dimensioned if in detail, and meaning exactly what it 
 says. Machine design is an exact science, and the designer can- 
 not shirk responsibility by permitting his work to be shiftless and 
 loose. If he cannot delineate clearly and in definite form what he 
 determines in his mind the structure should be, then it is purely 
 good luck if he achieves success, and it may safely be asserted that 
 the success is due to some subsequent care and finished design 
 added to his feeble effort, rather than to any expertness of his own. 
 Such success is of a very doubtful nature, and if not bordering on 
 financial loss it is at least secured only at a low working efficiency. 
 
 As examples of good drawings the plates shown are not 
 claimed to be anything extraordinary, but it will be noted that they 
 are clean-cut and definite, and that even the sketches are unmis- 
 takable as to that which they are intended to illustrate. The 
 information as to the design is all there; nothing is left to the 
 imagination. 
 
 Classification of Machinery. It is intended to be made clear 
 in all that has preceded, that the same method of attack and pro- 
 cedure may be applied to the designing of machinery, whatever 
 may be the class or kind. This is a fundamental principle. 
 \\ hen it is logically carried cut, however, it produces very differ- 
 ent results, as is evidenced by the characteristics of style peculiar 
 to each of the classes of machinery to one or another of which 
 all machines belong. 
 
 For example, an engine lathe has a style similar to a di ill 
 press, or a boring mill, or a screw machine, or a milling machine. 
 It is very different, however, from the style of a steam engine, or 
 a pump, or an air compressor, or a locomotive; it is still more dif- 
 
 74
 
 MACHINE DESIGN 63 
 
 ferent from the style of a rolling mill, or a link belt conveyor, or 
 a coal crusher, or a stamp mill. 
 
 These classes of machinery are so distinctly marked that the 
 novice is easily able to perceive that there is some controlling 
 influence in each which marks its peculiar style. He should at 
 the same time see that the very analysis that has been so strongly 
 insisted upon in these pages is the direct cause of the marked 
 characteristic in design. Each class of machinery must satisfy 
 certain exacting conditions different from those of any other, and 
 it is the careful study of these conditions, as fundamentally 
 enforced, which leads to the strictly logical design. 
 
 A few of the most common classes are enumerated below, 
 and their prominent features noted. It is hoped that a study of 
 them will familiarize the student in a general way with the 
 requirements of each, and serve as a guide to a more comprehen- 
 sive study of their detail design than is possible in these pages. 
 
 Machine Tools. Examples: lathe, planer, milling machine, 
 drill press, screw machine, boring mill, grinding machine, etc., etc. 
 
 The machines of this class are all utilized for the finishing of 
 metal surfaces. They are really at the root of the production of 
 machinery of all other classes. Accuracy is their prime character- 
 istic accuracy of construction, accuracy of operation, accuracy of 
 adjustment. Any inaccuracy that exists primarily in a machine 
 tool is reproduced in every piece upon which it produces a finished 
 surface ; and since the mere act of finishing a surface upon any- 
 thing implies that a rough and inaccurate surface will not answer, 
 the tool then fails of its purpose if it cannot produce a true sur- 
 face: it does not accomplish that for which it was designed. 
 
 The effect that this element of accuracy has upon the design 
 of a machine tool is to require long bearings, convenient and exact 
 methods of adjustment, stiffness, excess of material to absorb 
 vibration, special shapes to facilitate application of jigs, fixtures, 
 and exact manufacturing devices insuring interchangeabilit^ of 
 parts, dust guards, and automatic lubrication. 
 
 Machine tools are essentially machines of maximum output, 
 and depend for their success, not only upon their accuracy as 
 noted, but also upon their ability to do the greatest amount of work 
 per square foot of space occupied, with the least amount of manual 
 
 75
 
 64 MACHINE DESIGN 
 
 labor and attention on the part of the operator. This is especially 
 true of automatic machinery, which perhaps might be classed by 
 itself in this respect, but which is nevertheless included under the 
 broad term of a machine for producing finished surfaces, being 
 merely the highest and most refined form of same. For machines 
 of this class the designer has to study every detail with the most 
 minute attention, packing away the operating parts into the 
 smallest space and yet providing ready means for access, removal, 
 and repair. Clearances that would be too little for other kinds of 
 machinery are permitted and provided for; material of high grade, 
 strength, and wearing quality, though expensive in first cost, and 
 requiring the most expert skill to finish and to fit into place, must 
 be used in order to keep the machine compact and yet of large 
 capacity, to make it reasonably light in weight and yet amply 
 strong. 
 
 Another point which has a great influence on the design of a 
 machine tool is that we can never tell in advance just what it will 
 have to stand in work, for the variation in the material that it fin- 
 ishes, the uncertain skill of the operator who runs it, the crowding 
 to its limit of capacity and even beyond in times of press of business, 
 and the many other stresses that may suddenly and without warn- 
 ing be thrown upon it. must all be thought of and provided for. 
 
 The points above mentioned are but a few of those which the 
 designer of machine tools has to meet, and are presented merely 
 as illustrations to show the special skill required in this class of 
 machinery. It is readily seen that while the machine tool 
 designer has great latitude in choice of material and in expendi- 
 ture of money for refinement of structure perhaps greater lati- 
 tude than in any other class, yet he is held down as in no other 
 to the. final productive results, a small percentage of failure entirely 
 throwing out the machine as a marketable product. 
 
 The style and external appearance of machine tools have a 
 character of their own resulting from this extreme detailed care in 
 design. Corners and fillets are carefully rounded; surfaces and 
 intersections are definitely made; in short, the mechanical beauty 
 of a machine tool is seen only from a near view and close inspec- 
 tion, and it is to this end that the design is constantly directed 
 Appearance is a large factor in the sale of a fine tool, and the 
 
 76
 
 MACHINE DESIGN 65 
 
 prestige of the American trade abroad in this respect is very 
 noticeable. 
 
 Motive=Power flachinery. Examples: Steam engine, gas 
 engine, air compressor, steam pump, hydraulic machinery, etc., etc. 
 
 The element of heat enters into the design of all machinery 
 in this class. The natural agents, air, gas, and water, in their 
 various forms, are taken into the machine in the most efficient 
 form in which it is possible to obtain them, are robbed of their 
 energy to provide power, and are discharged in a form as weak 
 and inert as the efficiency of the machine will determine. 
 
 In contrast to the class of machinery just studied, it should 
 be noted that these machines do not produce any material thing; 
 that is, they do not produce finished surfaces on metals, make 
 screws or bolts, bore holes in castings, or turn line shafting. 
 They merely take the energy of the natural agent, which is not in 
 a form available for use, and transform it into motive power for 
 general use. 
 
 Hence the element of accuracy as entering into the design of 
 these machines is necessary only for their own efficient operation, 
 and not for the quality of the thing which they produce, as in the 
 case of machine tools. For example, the power furnished by one 
 steam engine to drive a line shaft is as good as that of another as 
 far as the rotating of the shaft is concerned, provided, of course, 
 that both are equipped with the same quality of governing mechan- 
 ism. The fact that one of the engines has a good adjusting device 
 on the main bearing while the other has not is of no consequence 
 from the standpoint of the- line shaft, but it is, of course, of con- 
 sequence respecting the efficient operation of the engines. 
 
 The design of steam engines and similar machines is of a 
 rough nature compared with that of machine tools, as far as the 
 detail of surface is concerned. General accuracy is nevertheless 
 essential for the machine's own sake, but while in the machine 
 tool we deal with thousandths of an inch, in the steam engine 
 hundredths of an inch indicates fine work. 
 
 These machines are subject to extremes of temperature that 
 have to be provided for in the design and arrangement of the parts. 
 Being prime movers, controlling the operation of many machines, 
 they must be certain to run during their period of work; hence 
 
 77
 
 66 MACHINE DESIGN 
 
 design and adjustment must be positive, and when the latter can- 
 not be made while running, it must be quickly and definitely accom- 
 plished when a stop is made. Simplicity of construction is essential, 
 facilitating cheap and quick repairs. The design should be such 
 that constant attention while running is avoided, the usual atten- 
 tion of the engineer being a safeguard rather than an implied fac- 
 tor of the original design. General rigidity and stiffness are 
 important, also good balancing of the moving parts, and weight for 
 absorption of vibration; otherwise under the constant daily run the 
 machines will tear to pieces not only themselves but their founda- 
 tions. 
 
 As far as external appearance goes in -this and subsequent 
 classes to be mentioned we are on a very different basis from that 
 of machine tools. General mechanical symmetry of form is aimed 
 at in the design, and the several smaller parts depend for their out- 
 line (aside from considerations of strength, which are, of course, 
 always in order) upon the harmonious relation which they bear to 
 the main and fundamental elements of the machine. Such 
 machinery as air compressors, steam encrines. pumps, and the like 
 are viewed as a whole, and criticised, not detail by detail, as is the 
 machine tool, but as to general effect of outline observed from 
 some distance. To convey the desired effect to the eye the desio-n 
 
 . *. C 1 
 
 must be bold and massive, connections simple and direct, and the 
 smaller parts must not be so dwarfed in size as to appear like deli- 
 cate ornaments instead of integral parts of the machine. The lines 
 of connected parts must be continuous from one part to the other; 
 and when interrupted by flanges, bosses, or lugs, the latter, which 
 are merely incidental to the former must not be allowed to obscure 
 wholly the main lines of the fundamental pieces. 
 
 It is attention to such points as thes that marks the difference 
 between well-designed motive-power n.cu.hinery and that of the 
 opposite character. Even though the little details of fillets and 
 corners and surfaces may have their effect from a close point of 
 view, the design will stand or fall in excellence on its bolder 
 features, as noted above. 
 
 Structural Machinery. Examples: Hoists, cranes, elevators, 
 transfer tables, locomotives, cars, conveyors, cable-ways, etc., etc. 
 
 In the two preceding classes that have been noted, cast iron 
 
 78
 
 MACHINE DESIGN 67 
 
 in the form of foundry castings enters as the principal material. 
 Steel is utilized for shafts, studs, pins, and keys. Also special 
 forgings, malleable iron and steel castings enter as factors in the 
 production of the machinery discussed. Foundry castings, how- 
 -ever, compose the great body of the material used, and the chief 
 problems involved are those of the expert moulding of cast iron, 
 and the handling and finishing of the same. For the operating 
 parts, steel of fine grade is used in highly finished form, expens- 
 ive because of its fineness, and yet a necessity to the extent it is 
 used. Brass and bronze are used in the same way, generally in 
 connection with the bearings for the shafts. 
 
 O 
 
 Structural machinery, on the contrary, uses steel as the basis 
 of its construction. The fundamental structure is built up of 
 plates, channels, beams, and angles; castings, though numerous, 
 are relatively small, being riveted or bolted to the main structure 
 and controlled in their design by its requirements. 
 
 Steel is used in this manner partly because the exclusive use 
 of castings is prohibited on account of the excessive weight, and 
 therefore expense, and partly because castings could not be made 
 which would possess the necessary toughness and strength. In 
 many cases the size of the machinery is such that castings, even 
 if they could be made, would not support their own weight. 
 Moreover, machinery of this class is subjected to rough service, 
 and yet must be practically infallible under all conditions, neither 
 being uncertain in operation at critical moments nor entirely fail- 
 ing under an extraordinary load. 
 
 The design of structural machinery is tied up to con- 
 ditions existing largely outside of, the locality in which the ma- 
 chinery is built. The steel plates and structural shapes required, 
 being products of the rolling mill, have to conform to the latter's 
 standards. The rivets, bolts and other fastenings have to be in 
 accordance with the established practice of the structural iron 
 worker, in order to. permit punching, shearing and bending ma- 
 chinery of regular form to be utilized. Shipment on standard 
 railway cars has to be considered, the design often requiring to be 
 modified to permit this and nevertheless insure positive and 
 accurate assembling in the field. 
 
 Steel castings, both large and small, find ready application in
 
 68 MACHINE DESIGN 
 
 this class of work; also steel forcings, requiring to be worked 
 under a heavy hammer and in many cases by specially devised 
 processes. 
 
 In structural design less of the actual process of manufacture 
 is under the eye of the designer than in the former class3S of 
 machinery which have been considered, and hence more allowance 
 has to be made for things not coming exactly right to the fraction 
 of an inch. It would be bad design to plan any structural piece 
 of work with the same closeness of detail permitted, and in fact 
 required, in the case of machine tools, or even in the case of motive- 
 power machinery. In planning structural work the idea must be 
 carried out, of certainty of operation in spite of roughness of detail 
 and variations of construction. This does not necessarily imply 
 inaccuracy, or shiftless, loosely constructed machinery; on the con- 
 trary, quite the reverse. The locomotive, for example, is one of 
 the most refined pieces of mechanism that exists today; and yet 
 the methods applied to the construction of machine tools would 
 prove a failure on the locomotive. The design of a car axle box 
 has to be just right else it will heat and destroy itself; the same is 
 true of the spindle of a fine engine lathe; and yet how rough the 
 former is compared with the latter, and how unsuited either would 
 be for use on the service of the other. 
 
 As a general rule structural machinery can be more closely 
 proportioned to theoretically calculated size than can the preceding 
 types. The rolled material of which it is made is of a uniform 
 and homogeneous nature owing to its process of manufacture, 
 hence its every fibre may be counted on to sustain its share of the 
 total load imposed upon it. This is in sharp contrast to the case 
 of cast iron, which is of such a porous and irregular structure that 
 we have to use a large factor of safety to cover this inherent 
 defect. 
 
 Steel castings of both small and large size (which are quite 
 apt to be utilized in this class of machinery for parts that can with 
 difficulty be made out of rolled material), if properly designed of 
 uniform thickness, with all corners well filleted and with the 
 channels for the flow of the molten metal direct and ample, are 
 nearly as reliable as rolled steel. In parts subject to excessive 
 vibration, shocks, and sudden wrenchings, as, for example, the 
 
 80
 
 MACHINE DESIGN 69 
 
 side frames or the connecting rod of a locomotive, the forged and 
 hammered material is practically a necessity. This is especially 
 the case when the possible breakage of the part would cause 
 serious consequences involving heavy loss of life and property. 
 
 From the several points of view as above considered, it can 
 be readily appreciated that, while structural work is in one sense 
 rough and unpolished, yet it requires, from an engineering stand- 
 point, quite as much breadth of experience and judgment as any 
 of the other types. The fine-tool designer, least of all, perhaps, 
 requires book theory, but does require an extended machine-shop 
 experience. The designer of motive-power machinery needs pure 
 physical theory and shop experience of a large and broad scope. 
 The structural designer is least of all concerned with refined and 
 minute finishing processes, but utilizes his theory absolutely, even 
 though roughly. 
 
 Mill and Plant Machinery. Examples : Rolling mills, 
 mining machinery, crushers, stamps, rock drills, coal cutters, the 
 machinery of blast furnaces and steel mills, tube mills, etc*., etc. 
 
 This machinery constitutes a class which in the roughness 
 of its operation exceeds all others. Moreover, it is machinery 
 which for the most part is in continuous operation 24 hours per 
 day and 365 days in the year. Hence refinement, even such as 
 might be permitted in the preceding class of Structural Machinery, 
 would be fatal here. The conditions that surround plant machinery 
 are unfavorable in the extreme to the life of any material or metal, 
 and it is not possible to change these conditions or give more 
 than partial protection to the operating parts. Hence the design 
 of such machinery must proceed primarily on the assumption 
 that abuse and neglect, grinding away of surfaces, chemical eating 
 away of metal, flooding of parts with water gritty "and corrosive, 
 subjection to sudden bursts of flame and intense heat, etc., will 
 in a relatively short time totally destroy, perhaps, the entire 
 structure. 
 
 In view of the continuous nature of the working process, 
 which must be kept up in spite of these almost insurmountable 
 conditions, the problem in each case becomes one of expediency; 
 and the designs and arrangement of machinery must be so worked 
 out that operation, repair, construction, and installation can all go 
 
 81
 
 70 MACHINE DESIGN 
 
 on simultaneously without stopping the continuous process, and 
 with but a small degree of inconvenience to the operation of the 
 plant. 
 
 This problem, difficult though it may seem, can be worked 
 out successfully, as is evidenced by the great number of plants of 
 the continuous character operating at high efficiency throughout 
 the world. The engineering and designing skill required to ac- 
 complish this, is perhaps of the highest degree met with in mod- 
 ern practice, for in it is involved a working knowledge of the 
 possibilities, if not the detailed designs of machinery included in 
 all classes. And yet, as in the most elementary case of simple 
 design that can be conceived, the result is accomplished in the 
 same way, namely, by studying the conditions (analysis), devel- 
 oping an ideal application to those conditions (theory), and then 
 reducing the ideal design to a practical basis (modification). 
 
 A Few Pointed Suggestions on Original Design. Original 
 design deals with the development of original mechanical ideas. 
 The JO'S me requisite for the development of an idea is to under- 
 stand thoroughly the idea in the rough. See distinctly the mark 
 aimed at, and never lose sight of it. If a method of reaching it 
 is already outlined, understand that also thoroughly and the prin- 
 ciples involved. It is impossible to go ahead blindly and hope to 
 come out right. No good machine was ever built that does not 
 stand for hours of concentrated thought on the part of its designer. 
 Good machines never lift.pper,, they always yrow. 
 
 Just as soon as the object to be accomplished is clearly under- 
 stood, begin to produce some visible work on the problem. Sketch 
 something. Get some ideas on paper. Ideas on paper suggest 
 other ideas. If the problem, for example, is one of lathe 
 design, sketch a rectangle, and call it the headstock; another rec- 
 tangle, and call it the footstock; a couple of scratches for the 
 centers; some steps for the cone pulley; three or four lines: for the 
 bed'; and as many more for the supports. There is now something 
 on paper to look at; the design is begun. 
 
 It is much better to stare at this sketch, than into blank 
 space trying to imagine the finished design. No matter how rough 
 the sketch may be, a short study of it will develop some limitino- 
 conditions that before were not apparent. Guess at a few rough 
 
 82
 
 MACHINE DESIGN 71 
 
 dimensions; put them on the sketch; develop another view a plan 
 or a side elevation all still in the roughest style, without any 
 regard to finished detail. Information will be growing all the 
 while, and the problem will be opening up. At this stage it is 
 probable that the sketch can easily be seen to be wrong in many 
 respects. Perhaps the arrangement will not do at all. 
 
 This is a good sign.. It show r s that the design is progressing. 
 It is a valuable thing to know that certain plans cannot be fol- 
 lowed. Do Dot rub out part of the sketch already made and try 
 to remedy it. Begin again. Make another sketch. Sketch paper 
 is cheap. By and by it may prove to be very desirable to have 
 that first rough outline available for comparison; or it may be that 
 some of its ideas can be applied on other sketches. The second 
 sketch may "show up" little or no better than the first. Make 
 another, and another, and another, until the subject is thoroughly 
 digested. It is wonderful how helpful it is to have some marks 
 on paper relative to a design, even though they be of the utmost 
 crudeness. They save imaginative power tremendously;. and, even 
 with them, all available powers of imagination will be needed 
 before the design is perfected. 
 
 A careful comparison of one's sketches, rejecting here, and 
 approving there, will, little by little, bring about a definite opinion, 
 and the scale drawing can be begun. 
 
 As in the case of the first sketch, so in the case of the first 
 scale drawing, get some lines on paper as quickly as possible. 
 Draw something, even if it is nothing more than a straight hori- 
 zontal line. Do not stare at blank paper for an hour trying to 
 imagine how the tenth or eleventh line is going to be drawn in 
 relation to the first line. .Do not worry about the later lines 
 until it is time for them Draw the first line at once; and, when 
 the second line is drawn, if the first line proves to be wrong, 
 make it right. As in the rough sketch, that first horizontal line 
 is an immense relief from the great waste of blank paper of a 
 fresh sheet. It is something to look at. It is the beginning of a 
 detailed design. If it happens not to be the absolutely correct 
 foundation to build upon, it at least is something to tear down. 
 The main purpose of these preliminary drawings is to keep the 
 mind active on the problem; and advance toward the final accom- 
 
 83
 
 MACHINE DESIGN 
 
 plisbment of the design is often made quite as rapidly by discover- 
 ing what to tear down as by consistently building up. 
 
 . AVhen a detail draftsman who has been used to having all his 
 work laid out for him by an expert designer attempts to take up 
 original work for himself, he encounters the drawing of that first 
 line in a way he never did before. He is apt to worry for some 
 time over the possible or impossible results of drawing that first 
 line. If he continue this, he will be sure to fail. The second line 
 is much easier to draw than the first, and the third than the second; 
 and the next hundred will follow on in comparatively smooth 
 sequence, all because of bold action on the first few lines. 
 
 And yet. just as the design appears to be progressing smoothly, 
 and the advanced progress of the drawing seems cause for congratu- 
 lation, careful consideration may disclose a "-snag" not previously 
 known to exist in the problem. Further study pursued along 
 the line of this new discovery may show that the whole layout 
 thus far has been radically wrong, and that a fresh start will have 
 to be made. At such a time the young designer is apt to feel 
 that his labor has all been thrown away, and he becomes discour- 
 aged. There is, however, no cause for discouragement. Machine 
 Design might almost be defined to be the successful elimination 
 of snags." It takes some ability to discover an obstacle of this 
 sort; to know a snag"' when an opportunity to see it is given. 
 It takes a good designer to eliminate such a difficulty after it has 
 been found. If there were no snags"'' it would not require great 
 ability to design machines. M-any machines fail because in them 
 there are a lot of undiscovered -snags." . Others fail because the 
 'snags." although discovered, were not eliminated by careful design. 
 Do not be afraid to make a lot of "first" drawings. It is 
 just as important to digest the design thoroughly by means of 
 scale drawings, as it was to digest it originally by means of 
 the rough sketches. An attempt to make the first drawing of an 
 original design absolutely right would, it is safe to say, produce a 
 poor design, one that could be much improved by further trial. 
 Let the drawings multiply, one after another, until the final one 
 is reached, in which the perfection of detail will eliminate all the 
 bad points of the preceding drafts and incorporate good ones of its 
 own based on the study of the others. 
 
 84
 
 MACHINE DESIGN 73 , 
 
 And yet it is often true that the first design laid out, even 
 after many others have been developed, may be found to possess 
 features that render a return to it desirable. This is why it is 
 always better to produce a collection of designs than to attempt 
 to rub out and work over the first one. The best designers usually 
 have a great number of sketches showing how to accomplish a 
 single result. Likewise, they also have a series of layouts to scale s 
 showing in detailed form the development of their various ideas. 
 This is because, without a careful consideration of many methods^ 
 they themselves feel incompetent to judge of the best design pos- 
 sible for accomplishing a given result. 
 
 Sketches and original designs should always be dated and 
 signed. Different designers may be working on the same prob- 
 lem, and priority of design will never be allowed except upon 
 signed and witnessed papers. It is embarrassing to find, after 
 months and perhaps years have passed since an original drawing 
 was made, that one's rights have been preempted merely because 
 there was no date or signature to define them. 
 
 In redesigning or modifying an existing machine, never make 
 a change merely for the sake of doing so. Give the good points of 
 the machine a, chance, and devote attention in the new design to 
 correcting the bad points. It is in bad taste, if it be not actually 
 childish, to "look wise and suggest a change" in details which 
 happen to have been designed by another party, but which, never- 
 theless, are by common engineering judgment pronounced good 
 for the special work intended. This element of unfair and selfish 
 criticism has more than a moral bearing. When it is carried into 
 the superintendence of designing work, it extinguishes the person- 
 ality of the subordinate draftsman; his efficiency as an original 
 thinker is lowered; and narrow designs are produced. 
 
 "The best way for a subordinate to dispose of what 
 appears to be a poor suggestion from a superior, is to work it out 
 to the best degree possible." If it turns out to be good the 
 credit of working it out belongs to the man who did it. If it is 
 actually bad, a careful working out will usually develop the fact 
 beyond dispute, and save unprofitable argument. For the success 
 or failure of- a machine there is only one argument better than 
 the detail drawings, and that is the machine itself in operation. 
 
 85
 
 74 MACHINE DESIGN 
 
 Detail drawings, however, are infinitely better prosecutors or 
 defendants than u multitude of wordy counsel. 
 
 Summary. The above classification of machinery might be 
 subdivided and extended indefinitely, and on the broad basis on 
 which it is given it doubtless does not cover the entire field. As 
 an illustration, however, not only of types of machinery, but of 
 methdlls of design and study, it is hoped that it may be of assist- 
 ance in giving a start to the student of machine design, in what- 
 ever class his interests may happen to lie. 
 
 It is the general principles of the art which it is important to 
 master. It is not the designing of a locomotive, or a stationary 
 steam engine, or a crane, or an engine lathe, or a rolling mill, 
 which should be sought to be learned, but the designing of any- 
 tliiittj that may confront us. Specializing is sure to come to the 
 designer in the course of his experience, and when it does he merely 
 fits to the particular specialty the principles he knows for all, and 
 practically develops them along that individual line. 
 
 86
 
 MACHINE DESIGN, 
 
 PART II. 
 
 Introduction. In Part I is illustrated a definite and systematic method 
 of attacking the design of a machine as a whole. In Part II the same plan is 
 followed with regard to the detail of its component parts, the machine ele- 
 ments which are chosen as illustrations of the method, being the simplest and 
 most familiar forms in common use. - 
 
 As before, the student must strive to grasp and absorb the method of design 
 rather than any specific and established form of a machine part. Part II is 
 not a compendium of design, does not attempt to be complete or exhaustive in 
 any of its chapters, but is condensed and simplified in order to lead the 
 student into systematic mechanical thinking and logical and definite action. 
 Each chapter is intended to stimulate to further and more exhaustive study 
 along lines broader than, and under conditions different from those that can 
 be specified in a general discussion. But no matter how deeply investigation 
 may be carried, or how specialized the study may become, the student must 
 real : ze that his path of action in any case whatsoever must lie along the 
 lines of Analysis, Theory, and Practical Modification systematically applied. 
 
 BELTS. 
 
 NOTATION The following notation is used throughout the chapter on Belts : 
 
 A= Sectional area of belt (square inches) R = Radius of pulley (feet). 
 
 = bh. r = Radius of pulley (inches). 
 
 6= Width of belt (inches). ' T = Initial tension (Ibs.). 
 
 F=Force of friction at pulley rim (Ibs.). T n =Total tension on tight side (Ibs.). 
 
 h =Thickness of belt (inches) T =Total tension on slack side (Ibs.). 
 
 ^-Coefficient of friction. t - Working tension of belt (Ibs. per 
 N=Number of revolutions of pulley per square inch). 
 
 minute. V = Velocity of belt (feet per minute). 
 
 71 =Fractionof circumference of pulley w -Weight of belt per cubic inch (Ibs.). 
 
 embraced by belt. z = Factor due to centrifugal force. 
 P=Driving force at pulley rim (lbs.)=F. 
 
 ANALYSIS. When a belt is stretched over a pair of pulleys, 
 is cut off at the proper length, and is laced together into an end- 
 less band, it is evident that as long as the belt is at rest there is a 
 nearly uniform tension in it throughout its length, due to the tight- 
 ness with which the lacing is drawn up. If the distance between 
 the pulleys is considerable, the weight of the belt itself as it hangs 
 between the pullftvs will produce a slightly greater tension next to
 
 76 MACHINE DESIGN 
 
 the pulleys than exists in the middle of the span. This increase 
 of tension due to the weight of the belt would make but little dif- 
 ference in the unit-stress in the material of which the belt is made; 
 hence it may safely be assumed that the tension in the belt when 
 at rest is uniform throughout its entire length. 
 
 When we start to transmit power through the belt by turning 
 one of the pulleys, thereby driving the other pulley the condition 
 of stress in the belt is at once materially changed. As the belt is 
 a flexible member, we can transmit only a pull to the other pulley, 
 thereby turning it around, the push which is at the same time 
 given to the other side of the belt merely acting to make the belt 
 sag or become slack. Hence the immediate effect of starting mo- 
 tion in a belt is to change the condition of equal tension through- 
 out its length, to that of unequal tension in the two sides. The 
 driving side is tight, while the other is loose, the former having 
 gained as much tension as the latter has lost, and the sum of the 
 two being practically equal to the sum of the tensions in the two 
 sides of the belt when at rest. This is not strictly true, as will be 
 shown later; but it is sufficiently accurate to form a good basis 
 for the practical design, at least of slow-speed belts. 
 
 This condition of tight and slack sides is made possible by 
 the fact that the belt, in being wrapped around the pulleys under 
 tension, has friction on their surfaces. Thus, we can pull hard on 
 one side without slipping the belt around the pulleys, but could 
 not do this if the pulleys were perfectly smooth or frictionless, for 
 in that case the slightest pull on one side would slip the belt 
 around the pulleys. In fact, it would be impossible to produce 
 any pull by means of the driving pulley, for the pulley would 
 merely slip around inside the belt. 
 
 The amount of pull we can apply to the belt is therefore lim- 
 ited by the tension at which the belt slips around the pulley. 
 Moreover, since the force of friction between the belt and pulley 
 is dependent upon the normal force with which the belt is pressed 
 against the pulley, and the coefficient of friction between the two, 
 it is evident that the tighter the belt is laced up, and the rougher 
 the surfaces of the pulley and belt, the greater is the force that 
 can be transmitted through the belt. This leads to the conclusion 
 that it would be possible to transmit any amount of power through 
 
 90
 
 RACK CUTTING PLANER.
 
 MACHINE DESIGN 77 
 
 any belt however small, if the belt were only laced ap tight 
 enough. 
 
 This conclusion is literally true; but the important fact now 
 comes in, that the strength of the material of which the belt is 
 made is limited, and while theoretically we might be able to ac- 
 complish the above, it would be impossible to do so in practice, 
 for at a certain point the belt would break under the strain. Other 
 practical considerations also come in, which fix this limit of power 
 transmission at a point far below the breaking strength of the ma- 
 terial. 
 
 The complete analysis is not quite as simple as the above, es- 
 pecially for high-speed belts. When the driving side of the belt 
 becomes tight, it stretches and grows longer; and at the same 
 time the other side of the belt becomes slack and grows shorter. 
 But it is not true that the increase in the one side is the same as 
 the decrease in the other, and this fact produces the condition that 
 the sum of the tensions in motion is not quite the same as the sum 
 of the tensions at rest. 
 
 Again, when the belt, as it passes around the pulley, changes 
 its straight-line direction to circular motion, each particle of the 
 belt like a body whirling at the end of a cord about a center of 
 rotation tends by centrifugal force to fly away from the surface 
 of the pulley, thereby decreasing the normal pressure, and hence 
 the friction. This centrifugal force also changes somewhat the 
 tensions in the belt'between the pulleys. As the centrifugal force 
 increases in proportion to the square of the linear velocity, it is 
 evident that the effect is greater at high speeds than at moderate 
 or low speeds. 
 
 A further circumstance that affects the driving power of a 
 belt is the stiffness of the leather or other material of which the 
 belt is made. As it passes around the pulley, the belt is bent to 
 conform to the circumference of the pulley, and is. again straight- 
 ened out as it leaves the pulley. Hence the theoretically perfect 
 action is modified somewhat according to the sharpness of the 
 bending and the thickness or flexibility of the belt; in other words, 
 a small pulley carrying a thick belt would be the worst case for 
 successful calculation on a theoretical basis. 
 
 THEORY. The condition of the tight and loose sides of a 
 
 91
 
 78 
 
 MACHINE DESIGN 
 
 belt transmitting power, is similar to that of the weighted strap 
 and fixed pulley shewn in Fig. 17. If motion is desired of the 
 strap around the pulley, it is necessary to make the weight W 2 of 
 such a magnitude that it will overcome not only the weight W,. 
 but also the friction between the strap and the pulley. The strap 
 tension T r is. of course, equal to ~\V. . and T to "W,. The equation 
 showinn- the balance of forces for the condition when motion is 
 about to occur, is: 
 
 T n - To = F = P ( driving force). (5) 
 
 If the pulley be free to turn on its axis, instead cf beingfixed 
 
 as in Fig. 17, the strap by its 
 friction on the pulley will turn 
 the pulley, and the force of 
 friction F becomes the driving 
 force for the pulley as noted 
 in equation 5 above. 
 
 In Fig. 18, let us sup- 
 pose that "W is a weight repre- 
 senting the resistance to be 
 overcome. The tensions T n 
 and T , equal at first owing to 
 stretching the belt tightly 
 over the pulleys at rest, change 
 when an attempt is made to 
 raise the weight by turning 
 thelarger pulley; and just as 
 the weight leaves the floor, the 
 equality of moments about 
 the axis of the driven pulley 
 gives the following equation: 
 
 ( T U '- T ) r = F Xr = Pxr = W X r,. (6) 
 
 This equality of moments remains as long as the motion of 
 the weight is uniform, and represents closely the conditions under 
 which belt pulleys work. 
 
 Although we know from the above what the difference of the 
 belt tensions is, and what this difference will do when applied to 
 
 Fig. 17.
 
 MACHINE DESIGN 
 
 79 
 
 the surface of a given pulley, we do not yet know what either 
 T n or T actually is; and until we do know, we cannot correctly 
 proportion the belt. Hence we must find another relation between 
 T n and T which we can combine with equations 5 and 6. This 
 relation is deduced by a process of higher mathematics, which re- 
 sults as follows: 
 
 T 
 
 Common logarithm r p2- = 2.729 p (1 - s)n. (7) 
 
 Treating equations 5 and 7 as simultaneous, values of both 
 T n and T can be found by the regular algebraic solution. As T n 
 is the larger, the actual area of belt to provide the necessary strength 
 must be made to depend upon it. 
 
 The factors in equation 7 depends upon the centrifugal force 
 
 Fig. 18. 
 
 developed by the weight of the belt passing around the pulley. Its 
 value, found from mechanics, is: 
 
 w X V 2 
 = 9,660 X f" 
 
 Having found the maximum pull on the belt, it now remains 
 to write the equation: 
 
 External force = Internal resistance; 
 or, T n = I X h X t. (8) 
 
 Usually the most convenient way to handle this equation is 
 to assume k and t, and then solve for b.
 
 80 MACHINE DESIGN 
 
 Summing up the theoretical treatment of belt design, we 
 simply combine equations 5, 0, 7. and S, and solve for the quantity 
 desired. Discussion of the constants involved in these equations, 
 and of the practical factors controlling them, is given in the fol- 
 lowing : 
 
 PRACTICAL MODIFICATION. The force of friction F. which 
 is the same as driving force P. depends on: 
 
 Coefficient of friction (/zi between belt and pulley; 
 
 Tightness of the belt; 
 
 Centrifugal force of the belt; 
 
 Angle of contact of belt with pulley. 
 
 The coefficient of friction (^), according to experiments and 
 observed operation of belts transmitting power, varies from .15 to 
 .51) for leather on cast iron. An average value consistent with a 
 reasonable amount of slip, the belt being in good running order, 
 is .30. If the belt is oily, or likely to become so in use, a lower 
 value should be taken. 
 
 The tighter the belt is drawn up, the greater is the pressure 
 against the pulley, and hence the greater is the force of friction. 
 But if we pull the belt up too tightly, when we begin to drive, 
 T n becomes too great, and the belt breaks or is under such stress 
 that k wears out quickly. Moreover, the great side pressure on 
 the bearings carrying the shaft produces excessive friction, and the 
 drive is inefficient. This is why a narrow belt driven at hio-h 
 
 */ O 
 
 speed is more efficient than a wide belt at slow speed, for we can- 
 not pull up the former as tightly as the latter without overstraining 
 it. and yet it is possible to get the required power out of the nar- 
 row belt by running it at high speed. 
 
 The centrifugal force is of small importance for low speeds, 
 say of 3.000 feet per minute and less; and it therefore may usu- 
 ally be neglected. The factor z then becomes zero in the expres- 
 sion 1-2 in equation 7, and the second member of the equation 
 stands simply 2.729 X /u, X />. 
 
 The angle of contact of belt with pulley is important, as a 
 large value gives a great difference between T u and T ; and it is 
 desirable to make this difference as great as possible, because there- 
 by the driving force is increased. The loose side of a horizontal 
 belt should always be above, as then the natural sag of the loose 
 
 94
 
 MACHINE DESIGN 81 
 
 side due to its slackness tends to increase the angle of contact with 
 the pulley, -while the tightening up of the lower side acts against 
 its sag to make the loss of wrap as little as possible. Vertical belts 
 which have the driving pulley uppermost, utilize the weight of the 
 belt to increase the pressure against the surface of the pulley, slightly 
 increasing its capacity for driving. The angle of contact may 
 be artificially increased by a tightening pulley which presses the 
 belt -further around the pulley than it would naturally lie. It 
 adds however, the friction of its own bearing, and impairs the effi- 
 ciency of the drive. For ordinary horizontal belts, the angle of 
 contact is but little more than 180, and the value of n in equation 
 7 may be safely assumed at ^ unless the pulleys are of relatively 
 great difference of diameter and very close together. 
 
 Strength of Leather Belting. The breaking tensile strength 
 of leather belting varies from 3,000 to 5,000 pounds per square 
 inch. Joints are made by lacing, by metal fasteners, or by cement- 
 ing. The strength of a laced joint may be about T 7 T , of a metal- 
 fastened joint, about |, and of a cemented joint, about equal to 
 the full strength of the belt cross-sectional area. The proper 
 working strength of belting depends on the use to which the belt 
 is put. A continuously running belt should have a low tension 
 in order to have long life and a minimum loss of time for repairs. 
 For double leather belting it has been shown that a working ten- 
 sion of 240 pounds per square inch of sectional area gives an an- 
 nual cost for repairs, maintenance, and renewals of 14 per 
 cent of first cost. At 400 pounds working tension, the annual ex- 
 pense becomes 37 per cent of first cost. These results apply to 
 belts running continuously; larger values may be used where the 
 full load comes on but a short time, as in the case of dynamos. 
 
 Good average values for working tensions of leather belts are: 
 
 Cemented joints, 400 pounds per square inch. 
 Laced joints, 300 " " " " 
 
 Metal joints, 250 " " " " 
 
 Horse=Power Transmitted by Belting. If P is the driving 
 force in pounds at the rim of the pulley, and V is the velocity of 
 the belt in feet per minute, the theoretical horse-power transmitted 
 is evidently : 
 
 05
 
 82 MACHINE DESIGN 
 
 
 It is evident from the above that the horse-power of a belt .de- 
 pends upon two things, the driving force Pand the velocity V. If 
 either of these factors is increased, the horse-power is increased. 
 Increasing P means a ticrkt belt. Hence a tifht belt and hio-h 
 
 O & ^5 O 
 
 speed together give maximum horse-power. But a tight belt 
 means more side strain on shaft and journal. Therefore, from the 
 standpoint of efficiency, -use a narrow belt under low tension at as 
 hiyh a speed as possible. 
 
 Empirical rules for horse-power of belting, if used with judg- 
 ment, give safe results when applied to very general cases. A 
 common rule used by American engineers is: 
 
 For a double belt, assuming double strength, this becomes: 
 
 With large pulleys and moderate velocities, this may hold 
 good. AVith small pulleys and high velocities, however, the un- 
 certain stresses induced by the bending of the libers of the belt 
 around the pulley, and the relatively great loss due to centrifugal 
 force, modify this relation 1 and a safer value for a double belt of 
 the ordinary kind is: 
 
 or. still safer. II. P. = -jffi- (13) 
 
 If we compare the theoretical value of equation 9 with the 
 empirical value of equation 10 by putting them equal -to each 
 other, thus: 
 
 11 P - P X Y =' J XV 
 83.000 ~~ 1,000 ' 
 
 and solve for P, we get : 
 
 D6
 
 MACHINE DESIGN 83 
 
 P = 33. 
 
 (14) 
 
 This develops ^the fact that the empirical rule of equation ]0 as- 
 sumes a driving force of 33 pounds per inch of width of single 
 belt. 
 
 Another way of expressing equation 10 is: A single belt 
 will transmit one horse-power for every inch of width at a belt 
 speed of 1,000 feet per minute. 
 
 Speed of Belting. The most economical speed is somewhere 
 between 4,000 and 5,000 feet per minute. Above these values 
 the life of the belt is shortened; also "flapping," "chasing," and 
 centrifugal force cause considerable loss of power. The limit of 
 speed with cast-iron pulleys is fixed at the safe limit for bursting 
 of the rim, which may be taken at one mile per minute. 
 
 Material of Belting. Oak-tanned leather, made from the 
 part of the hide which covers the back of the ox, gives the best re- 
 sults for leather belting. The thickness of the leather varies 
 from .18 to .25 inch. It weighs from .03 to .04 pound per cubic 
 inch. The average thickness of double leather belts may be taken 
 as .33 inch, although a variation in thickness from \ inch to T 7 T 
 inch is not uncommon. Double leather belts may be ordered 
 light, medium, or heavy. 
 
 In a single- thickness belt the grain or hair side should be 
 next to the pulley, for the flesh side is the stronger and is there- 
 fore better able to resist the tensile stress due to bending set up 
 where the belt makes and leaves contact with the pulley face. 
 Double leather belts are made by cementing the flesh sides of 
 two thicknesses of belt together, leaving the grain side exposed 
 to surface wear. 
 
 Raw hide and semi-raw hide belts have a slightly higher co- 
 efficient of friction than ordinary tanned belts. They are useful in 
 damp places. The strength of these belts is about one and one- 
 half times that of tanned leather. 
 
 Cotton, cotton -leather, rubber, and leather link belting are 
 some of the forms on the market, each of which is especially 
 adapted to certain uses. For their weights and their tensile and 
 working strengths consult the manufacturers' catalogues. 
 
 A prominent manufacturer's practice in regard to the sizes of 
 
 97
 
 MACHINE DESIGN 
 
 leather belting will he found useful for comparison, and is indicated 
 in the table on page 12. 
 
 Initial Tension in Belt. On the assumption that the sum of 
 the tensions is unchanged, whether the belt be at rest or driving, 
 we should have the following relation : 
 
 whence. 
 
 T = 
 
 1V4-T 
 
 (IS) 
 
 This is not strictly true, however, as is stated in the i% Analysis' 
 of '- Belts. '' It has been found that in a horizontal belt working at 
 about 400 Ibs. tension per square inch on the tight side, and hav- 
 ing 2 per cent slip on cast-iron pulleys ( i. e., the surface of the 
 
 Sizes of Leather Belting. 
 
 WIDTH. 
 
 THICKNESS. 
 
 Single. 
 
 Double. 
 
 1 inch. 
 
 yV inch. 
 
 f'u inch. 
 
 2 " 
 
 
 T 5 , " 
 
 3 " 
 
 7 u 
 2" 
 
 3 u 
 
 ' "ff 
 
 4 " 
 
 *V " 
 
 1 "' 
 
 5 " 
 
 sV " 
 
 f " 
 
 6 " 
 
 sV " 
 
 f " 
 
 10 " 
 
 5 u 
 T6" 
 
 3. <; 
 
 12 " 
 
 
 f " 
 
 14 " 
 
 
 M " 
 
 20 " 
 
 TV " 
 
 driven pulley moving 2 per cent slower than that of the driver), 
 the increase of the sum of the tensions when in motion over the 
 sum of the tensions at rest, may be taken at about ^ the value of 
 the tensions at rest. Expressing this in the form of an equation 
 
 Tn + T.^^T)^ 8 -^. 
 
 _ fT _|_ T \ 
 -cT k A n ' A oj- 
 
 (16)
 
 MACHINE DESIGN 85 
 
 The value of T thus found would be the pounds initial tension to 
 which the belt should be pulled up when being laced, in order to 
 produce T n and T when driving. 
 
 This value is not of very great practical importance, as the 
 proper tightness of belt is usually secured by trial, by tightening 
 pulleys, by pulley adjustment (as in motor drives), or by shorten- 
 ing the belt from time to time as needed. It is worth noting, 
 however, that for the most economical life of the belt it would be 
 very desirable in every case to weigh the tension by a spring bal- 
 ance when giving the belt its initial tension. This, however, is 
 not always easy or even feasible; hence it is a refinement with 
 which good practice~usually dispenses, except in the case of large 
 and heavy belts. 
 
 PROBLEMS ON BELTS. 
 
 1. Determine the belt tensions in a laced belt transmitting 50 
 horse-power at a velocity of 3,500 feet per minute. Suppose that 
 the arc of contact is 180; weight of belt = .035 pound per cub. 
 In.; and coefficient of friction 25 per cent. 
 
 2. What is the width of above belt if it is T 3 inch in thick- 
 ness ? 
 
 3. What initial tension must be placed on above belt ? 
 
 4. The main drive pulley of a 120-horse-power water wheel 
 is 6 feet in diameter. A cemented leather belt is to connect the 
 main pulley to a 3-foot pulley on the line shafting in a mill. The 
 horizontal distance between centers of shafting is 24 feet; coeffi- 
 cient of friction, 30 per cent; revolutions per minute of line shaft- 
 ing, 180. DesJgn the belt for this drive. 
 
 5. An 8-.inch double belt ^ inch thick connects 2 pulleys of 
 30-inch and 20-inch diameter respectively. The horizontal dis- 
 tance between the centers is 12.5 feet. The coefficient of friction 
 is 0.3, and the weight of belt per cubic inch is 0.035 pound. 
 Working tension, 300 pounds per square inch. Speed of belt 
 5,000 feet per minute. Lower face of 30-inch pulley is the driv- 
 ing face. Required the H. P. which may be transmitted (theo- 
 retically). 
 
 6. Compare the theoretical horse-power in problem 5 with 
 that obtained by the use of empirical formula. 
 
 09
 
 86 MACHINE DESIGN 
 
 PULLEYS. 
 
 NOTATION The following notation is used throughout the chapter on Pulleys: 
 
 A = Area of rim (sq. in.). I = Length of hub (inches). 
 
 a " " arm ( ' ' ). N = Number of arms. 
 
 b =Center of pulley to center of belt n = " " rim bolts, each side. 
 
 (inches; practically equal to R). P ^Driving force of belt (Ibs.). 
 
 C'i = Total centrifugal force of rim (Ibs.). Pi = Forcc at circumference of shaft 
 c = Distance from neutral axis to outer (Ibs.). 
 
 fiber (inches). Pi= Force at circumference of hub (Ibs.). 
 
 D = Diameter of pulley (inches). p Stress in rim due to centrifugal force 
 DI- " "hub ( " ). (Ibs. per sq. in.). 
 
 (/! = ' "bolt at root of thread R =Raclius of pulley (inches). 
 
 (inche.-). S -Fiber stress (Ibs. per sq. in.). 
 
 (/ --Diameter of bolt holes (inches). s -Fiber stress in flange (Ibs. persq. in.). 
 
 H = Acceleration due to gravity (ft. T = Thickness of web (inches). 
 
 per sec.). t " '' rim ( " ). 
 
 /i = Width of arm at any section (inche.-). /2 - " " " bolt flange (inches). 
 
 I = Moment of inertia- T u = Tension of belt on tight side (Ibs.). 
 
 L = Length of arm, center of belt to hub T = " " " "loose " ( " ). 
 
 (inches). v = Velocity of rim (ft. per sec.). 
 
 Li=Length of rim flange of split pulley / =Weightof material (Ibs. per cub. in.). 
 
 (inches). 
 
 ANALYSIS. If a flexible band be wrapped completely about 
 
 a pulley, and a heavy stress be put upon each end of the band, the 
 rim of the pulley will tend to collapse just like a boiler tube with 
 steam pressure on the outside of it. A compressive stress is in- 
 duced which is very nearly evenly distributed over the cross-sec- 
 tion of the rim, except at points where the arms are connected 
 thereto. At these points the arms, acting like rigid posts, take 
 this cornpressive stre'ss. Now, a pulley never has a belt wrapped 
 completely round it, the fraction of the circumference embraced by 
 the belt being usually about A, and seldom, even with a tightener 
 pulley, reaching |. Assuming the wrap to be 4- the circumference, 
 and that all the side pull of the belt comes on the rim. none being 
 transmitted through the arms to the hub, we then have one-half of 
 the rim pressed hard against the other half by a force equal to the 
 resultant of the belt tensions, which, in this case, would be the 
 sum of them. Dividing the pulley by a plane through its center 
 and perpendicular to the belt, the cross-section of the rim cut by 
 this plane has to take this compressive stress- 
 
 This analysis is satisfactory from an ideal standpoint only, for 
 the intensity of stress due to the direct pull of the belt, with the 
 usual practical proportions of rim, would be very small. More- 
 over, the element of speed has not been considered. 
 
 When the pulley is under speed, a set of conditions which 
 
 100
 
 MACHINE DESIGN 87 
 
 complicates matters is introduced. The centrifugal force due to 
 the weight of the rim and arms is no longer negligible, but has 
 an important influence upon the design and material used. This 
 centrifugal force acts against the effect of the belt wrap, tending 
 to reduce the compressive stress, or, overcoming the latter entirely, 
 sets up a tensional stress both in the rim and in the arms. It also 
 tends to distort the rim from a true circle by bowing out the rim 
 between the arms, thus producing a bending moment in the rim, 
 maximum at the points where the rim joins each arm. 
 
 It can readily be imagined that the analysis in detail of these 
 various stresses in the rim acting in conjunction with each other 
 is quite complicated far too much so in fact, to be introduced 
 here. As in most cases of such design, however, one controll- 
 ing influence can be separated out from the others, and the de- 
 sign based thereon with sufficient margin of strength to satisfy 
 the more obscure conditions. This is rational treatment, and the 
 " theory " will be studied accordingly. 
 
 The rim, being fastened to the ends of the arms, tends, when 
 driving, to be sheared off, the resisting area being the areas of the 
 cross-sections of the arms at their point of joining the rim. The 
 force that produces this shearing tendency is the driving force of 
 the belt, or the difference between the tensions of the tight and 
 loose sides. 
 
 Again, at the point of connection of the arms to th hub, s 
 shearing action takes place, so that, if this shearing tendency were 
 carried to rupture, the hub would literally be torn out of the arms. 
 Now, viewing the arms as beams loaded at the end with the driv- 
 ing force of the belt, and fixed at the hub, a heavy bending stress 
 is set up, which is maximum at the point of connection to the 
 hub. If the rim were stiff enough to distribute this driving force 
 equally between the arms, each arm would take its proportional 
 share of the load. The rim, however, is quite thin and flexible; 
 and it is not safe to assume this perfect distribution. It is usual 
 to consider that one-half the whole number of arms take the full 
 driving force. 
 
 THEORY Pulley Rim. Evidently it is practically impossible 
 to make so thin a rim that it will collapse under the pull of a belt. 
 As far as the theory of the rim is concerned, its proportion prob- 
 
 101
 
 MACHINE DESIGN 
 
 ably depends more upon the calculation for centrifugal force than 
 upon anything else. 
 
 In order to separate- this action from that of any other forces, 
 let us suppose that the rim is entirely free from the arms and hub. 
 and is rotating about its center. Every particle, by centrifugal 
 force, tends to liy radially outward from the center. This condi- 
 tion is represented in Fig. 1'-). The tendency with which one-half 
 of the rim tends to tiy apart from the other is indicated by the 
 force C,; and the relation between C, and the small radial force c 
 for each unit-length of rim can readily be found from the prin- 
 ciples of mechanics. The case is exactly, like that of a boiler or a 
 thin pipe subjected to uniform internal pressure, which, if carried 
 to rupture, would split the rim along a longitudinal seam. 
 
 Fig. 19. 
 
 The tensile stress thus induced per square inch can be found 
 by simple mechanics to be: 
 
 or, since ?/ -- 0.2> pound, and y =- 3'2.2 feet per second. 
 
 Jt = 0.01)7 -e* ( say-^j) 5 (l8) 
 
 and. ify/ be taken equal to 1,000 pounds per square inch, which is 
 as high as it is safe to work cast iron in this place, 
 
 v = 100 feet per second. (i9) 
 
 This shows the curious fact that the intensity of stress in the rim 
 
 102
 
 MACHINE DESIGN 
 
 89 
 
 is directly proportional to the square of the linear velocity, and 
 wholly independent of the area of cross -section. It is also to be 
 noted that 100 feet per second is about the limit of speed for cast- 
 iron pulleys to be safe against bursting. 
 
 If we wish to consider theoretically the rim together with the 
 arms as actually connected to it, we get a much more complicated 
 relation. This condition is shown in Fig. 20, where the rim, ex- 
 panding more than the arms, bulges out between them. This 
 makes the rim act something like a continuous beam uniformly 
 loaded; but even then the resulting stress is not clearly defined on 
 account of the variable stretch in the arms. Investigation on this 
 basis is not needed further than to note that it is theoretically 
 better, in the case of a split pulley, to make the joint close to the 
 arms, rather than in the middle of a span. 
 
 Pulley Arms. The centrifugal force developed by the rim 
 and arms tends to piill the arms from the hub. On the belt side, 
 this is balanced to some extent by the belt wrap, which tends to 
 compress the arm and relieve the tension. On the side away 
 from the belt, the centrifugal action has 
 full play, but the arm is usually of such 
 cross-section that the intensity of this stress 
 is very low. It may safely be neglected. 
 
 The rim being very thin in most cases, 
 its distributing effect cannot be depended 
 on, hence the driving force of the belt may 
 be taken entirely by the arms immediately 
 under the portion of the belt in contact with 
 the pulley face. For a wrap of 180 this 
 
 Fig. 21. 
 
 means that only one-half of the pulley arms can be considered as 
 effective in transmitting the turning effort to the hub. Each of 
 these arms is a lever fixed at one end to the hub and loaded at the 
 pther. A lever of this description is called a " cantilever " beam, 
 its maximum moment existing at its fixed end. The load that each 
 
 p 
 of these beams may be subjected to is-^-, and therefore the maxi- 
 
 imnrn external moment at the Irob is 
 
 2PL 
 
 From mechanics we 
 
 103
 
 90 MACHINE DESIGN 
 
 know that the internal moment of resistance of any beam section 
 is , and that equilibrium of the beam can be satisfied only 
 
 when the external moment is equal to the internal moment of re- 
 sistance of the beam section. Equating these two, we have: 
 
 2PL SI 
 
 The arms of a pulley are usually of the elliptical or segmental 
 cross-section, and may be of the proportions shown in Fig. 21. 
 
 For either of these sections the fraction is approximately equal 
 
 to 0.0393/> 3 . For convenience (the error caused being on the safe 
 side). L may be taken as equal to the full radius of the pulley R, 
 whence 
 
 >PR 9,T __ T ,P 
 
 4^ (1 " N > )K = 0.0393S/,', (21) 
 
 in which S may be from 2.000 to 2,250 for cast iron 
 
 Taking moments about the center of the pulley, and solving 
 for P,. the force acting at the circumference of the hub, we have : 
 
 2PE P D, 
 
 
 P 2 = ~ (22) 
 
 The area of an elliptical section is IT times the product of the 
 half axes. AVith the proportions of Fig. 21. this becomes: 
 
 <> = 77 X 0.27, X 0.5/< = ~ (23) 
 
 Equating the external force to the internal shearing resistance, we 
 have : 
 
 4PR _ 7r/rS s 
 ND, - TIT 
 
 S a = = 4^^ 
 
 104
 
 MACHINE DESIGN 
 
 91 
 
 in which the shearing stress S s may ran from 1,500 to 1,800 for 
 cast iron. 
 
 Although -both bending and shearing stresses as calculated 
 above exist at the base of the arms, the bending is, in practically 
 every case, the controlling factor in the design of the arms. An 
 arm-section large enough to resist bending would have a very low 
 intensity of shear. 
 
 If the number of arms be increased indefinitely, we come to 
 a continuous arm or web, in which the bending action is elimi- 
 nated. It may still shear off at the hub, where the area of metal 
 is the least, at minimum circumference. In this case the area 
 under shearing stress is ^DjT; and the 'force at the circumference 
 of the hub, is 
 
 PR 2PR 
 
 D, 
 
 Equating external force to in- 
 ternal shearing resistance, we 
 have : 
 
 (25) 
 
 or, ,= 
 
 Fig. 22. 
 
 Pulley Hub. As in the 
 
 case of the arms, centrifugal 
 force does not play much part in the design of the hub of a pulley. 
 The hub is designed principally to carry the key, and through it 
 transmit the turning moment to the shaft. Considered thus, the 
 hub may tear along the line of the key or crush in front of the key. 
 For example, in Fig. 22, if the connection with the lower 
 arms be neglected, and the upper arms be held fast while a turning 
 force P,, at the surface of the shaft, is transmitted to the hub 
 through the key, then the metal of the hub directly in front of the 
 key is under crushing stress; and the metal along the line eb, from 
 the corner to the outside, is under tensile stress. This condition is 
 the worst that could possibly happen, because the bracing effect of 
 the lower arms has been neglected, and the key is located between 
 the arms. 
 
 105
 
 02 MACHINE DESIGN 
 
 Takino- moments about the center of the shaft, the value of the 
 force at the shaft circumference, or the '-key pull," is: 
 
 p.=: (26) 
 
 P /' 
 
 Xow-n . k being the distance from the center of shaft to 
 P, i- 
 
 center of cb. and the area of metal which is subjected to the tearing 
 action P.^ is / /; <:b. Equating the external force to the internal 
 resistance, and assuming that the stress is equally distributed over 
 the area / '/. cb, we have: 
 
 3 / ! /,' ^ i' ' 
 
 The intensity of crushing on the metal in front of the key, due 
 to force P,. depends upon the thickness of the key, and is properly 
 discussed later under "Keys." 
 
 PRACTICAL MODIFICATION Pulley Rim. The theoretical 
 calculation for the thickness of the rim may give a thickness that 
 could not be cast in the foundry, and the section in that case will 
 have to be increased. As light a section as can be readily cast will 
 usually be found abundantly strong for the forces it has to resist. 
 A minimum thickness at the edge of the rim is about T 3 (} inch; 
 and as the pulleys increase in size, the rim also must be made 
 thicker; otherwise the rim will cool so much more quickly than 
 the arms, that the latter, on cooling, will develop shrinkage cracks 
 at the point of junction. 
 
 For a velocity of 0.000 feet per minute, we find from equation 
 1"5 that the tension in pounds per square inch, in the rim, due to 
 centrifugal force, is 970. Though this in itself is a low value, yet 
 the uncertain nature of cast iron, its condition of internal stress, 
 due to casting, and the likely existence of hidden flaws and pockets, 
 have established the usage of this figure as the highest safe limit 
 for the peripheral speed of cast-iron pulleys. It is easily remem- 
 bered that riixt-iroii }>till<:ij* ar<- znf<> for a l>n<*'ir velocity of about 
 out mi If in: r in 'm iitc. 
 
 106
 
 MACHINE DESIGN 
 
 To prevent the belt from running off the pulley, a "crown" 
 or rounding surface is given the rim. A tapered face, which is 
 more easily produced in the ordinary shop, may be used instead. 
 This taper should be as little as possible, consistent with the belt 
 staying on the pulley; ^ inch per foot each way from the center 
 is not too much for faces 4 inches wide and less; while above this 
 width ^ inch per foot is enough. As little as J inch total crown 
 has been found to be sufficient on a 24-inch face, but this is 
 probably too little for general service. 
 
 Instead of being "crowned," the pulley may be flanged at the 
 edges; but flanged pulley rims chafe and wear the edge of the belt. 
 
 The inside of the rim of a cast-iron pulley should have a taper 
 of 4 inch per foot to permit easy withdrawal from the foundry 
 
 Fig. 23. 
 
 mould. This is known as "draft." If the pattern be of metal, or 
 if the pulley be machine-moulded, the greater truth of the casting 
 does not require that the inside of the rim be turned, as the pulley, 
 at low speeds, will be in sufficiently good balance to run smoothly.- 
 For roughly moulded pulleys, and for use at high speeds, however, 
 it is necessary that the rim be turned on the inside to give the 
 pulley a running balance. 
 
 Fig. 23 shows a plain rim a also one stiffened by a rib b. 
 Where heavy arms are used this rib is essential so that there will 
 not be too sudden change of section at the junction of rim and arm. 
 and consequent cracks or spongy metal. 
 
 Pulley Arms. The arms should be well filletted at both "rim 
 and hub, to render the flow of metal free and uniform in the mould. 
 The general proportions of arms and connections to both hub and 
 rim may perhaps be best developed by trial to scale on the draw- 
 ing board. The base of the arm being determined, it may gradu- 
 
 107
 
 94 MACHINE DESIGN 
 
 ally taper to the rim, where it takes about the relation of to | 
 the dimensions chosen at the hub. The taper may be modified 
 until it looks right, and then the sizes checked for strength. 
 
 Six arms are used in the great majority of pulleys. This 
 number not only looks well, but is adapted to the standard three- 
 jawed chucks and common clamping devices found in most shops. 
 Elliptical arms look better than the segmental style. The flat, 
 rectangular arm gives a very clumsy and heavy appearance, and is 
 seldom found except on the very cheapest work. 
 
 A double set of arms may be used on an excessively wide 
 face, but it complicates the casting to some extent. 
 
 Although a web pulley may be calculated for shear at the 
 hub. yet it will usually be found that with a thickness of web in- 
 termediate between the thickness of the rim and that of the hub. 
 which will satisfy the casting requirements, the requirements as to 
 strength will by fully met. 
 
 Pulley Hub. The hub should have a taper of i inch per foot 
 draft, similar to that of the inside of the rim. The length of the 
 hub is arbitrary, but should be ample to prevent rocking on the 
 shaft. A common rule is to make it about | the face width of 
 the pulley. 
 
 The diameter of the hub, aside from the theoretical consider, 
 ation given above, must be sufficient to take the wedging action of a 
 taper key without splitting. This relation cannot well be calcu- 
 lated. Probably the best rule that exists is the familiar one that 
 the hub should be twice the diameter of the shaft. This rule, 
 however, cannot be literally adhered to. as it gives too small hubs 
 
 for small shafts and too laro-e ones for laro-e shafts. It is always 
 
 G / 
 
 well to locate the key, if possible, underneath an arm instead of 
 between the arms, thus gaining the additional strength due to the 
 backing of the arm. 
 
 SPLIT PULLEYS. 
 
 ANALYSIS and THEORY. The split pulley is made in 
 halves and provided with bolts through flanges arid bosses on the 
 hub for holding the two halves together. When the pulley is in 
 place on the shaft, bolted up as one piece, it is subjected to the 
 same forces as the simple pulley. Hence its general design fol- 
 
 108
 
 MACHINE DESIGN 
 
 lows the same principles, and we need only study the fastening of 
 the two halves, and the effect of this fastening on the detail of rim 
 and hub. 
 
 The simplest stress we have to consider on the rim bolts is 
 one of pure tension, due to the centrifugal force of the halves 
 of the pulley, A safe assumption to make is that the rim is free 
 
 Fig. 24. 
 
 from the arms and hub, as in the simple pulley, and that the cen- 
 trifugal force developed by it has to be taken by the rim bolts 
 alone. In other words, consider the rim bolts as belonging en- 
 tirely to the rim, and make them as strong as the rim, leaving the 
 hub bolts to take the centrifugal force of the arms and hub, and 
 the spreading tendency due to the key. 
 
 Another tensile stress is induced in the rim bolts by the fact, 
 that, having made an open joint in the rim, and in addition placed 
 the extra weight of lugs there, the centrifugal action at this point 
 is increased, and at the same time a point of weakness 'in the rim 
 
 109
 
 9G 
 
 MACHINE DESIGN 
 
 introduced. Referring to Fig. 24, the rim flanges EJ tend to fly 
 out due to the centrifugal force C F . This tends to open the joint 
 J at the outside of the rim ; to throw a bending stress on the rim, 
 maximum at the point F ; and to "heel" the rim flanges about 
 the point E. The rim bolts acting on the leverage c about the 
 point E must resist these tendencies, and are thereby put in 
 tension. 
 
 Referring to equation 18, we find the intensity of stress due to 
 the centrifugal force of the rim in Ibs. per square inch to be : 
 
 If A is the sectional area of the rim in square inches, this means 
 that the total strength of 
 the rim is represented by 
 
 - The strength of a 
 bolt is represented by the 
 
 expression - If. now, 
 
 there are // bolts in the 
 iiange. the total resisting 
 
 forceof the bolts is -; 
 
 and the equation represent- 
 ing equality of strength be- 
 tween rim and bolts is : 
 
 AV* __ //sw; 2 
 To"" ^T^ 
 
 from which, by a proper 
 assumption of the fiber 
 stress S, which should be Fi ^' ^ 
 
 low. the opening-up tendency of the joint being neglected, the diam- 
 eter at the root of the thread <7, may be calculated, and the nom- 
 inal bolt diameter chosen. Reference to the table for strength 
 of bolts, given in the chapter on Bolts, Studs, etc., will be found 
 convenient. 
 
 110
 
 MACHINE DESIGN 97 
 
 It is very doubtful if the tension on the flange bolts, due to 
 the " heeling" about E can be calculated with sufficient accuracy to 
 be of much value. It is probably better to assume S at a low value, 
 say 4,000, and, in addition, for large and high-speed pulleys, stif- 
 fen the rim by running a rib between the flange and the adjacent 
 arm. It is evident that if we make the rim so stiff that it cannot 
 deflect, there will be no " heeling " about E ; and the bolts will 
 be well proportioned by the preceding calculation, giving them 
 equal strength to that of the rim section. 
 
 For the bolt flange itself, any tendency to open at the joint J 
 would cause it to act like a beam loaded at some point near its 
 middle with the bolt load, and supported at J and E. This 
 condition is shown in Fig. 25. Probably the weakest section 
 would be along the line of the bolt centers. We have just noted 
 
 that the carrying capacity of the bolts is . ' . Hence, assum- 
 ing that e = \f, which is about the worst case which could hap- 
 pen, we have a beam of lengthy loaded at the middle with 
 
 and supported at the ends. Equating the external moment to 
 the internal moment, we have : 
 
 from which the fiber stress * in the flange may be calculated and 
 judged for its allowable value. 
 
 L, maybe assumed a little narrower than the pulley face; and 
 t 2 from 1 inch to 2 inches or more, depending on the thickness of 
 the rim. 
 
 The hub bolts doubtless assist the rim bolts in preventing 
 the halves of the pulley from flying apart. They also clamp the 
 hub tightly to the shaft, preventing any looseness on the key. 
 Their function is a rather general one; and the specific stress 
 which they receive is practically impossible to calculate. As a 
 matter of fact, if the hub bolts were left out entirely, the pulley 
 would still drive fairly well, but general rigidity and steadiness 
 would be impaired. Hence the size of the hub- bolts is more a 
 practical question than one involving calculation. The rim bolts 
 
 111
 
 OS MACHINE DESIGX 
 
 should be figured first, and their size determined on; then the hub 
 bolts CMII be judged in proportion to the rim bolts, the diameter of 
 shaft, the thickness and length of the hub, and the general form 
 of the pulley. Often appearance is the deciding factor, it being 
 manifestly inconsistent to associate small fastenings with large 
 shafts or hubs, even though the load be actually small. 
 
 PRACTICAL MODIFICATION. Practical considerations are 
 chiefly responsible for the locution of the joint in a split pulley 
 between the anus instead of directly at the end of an arm. where 
 theoretically it would seem to be required. It is usually more 
 convenient in the foundry and machine shop to have the joint be- 
 tween the arms; so we generally find it placed there, and strength 
 provided to permit this. It is possible, however, to provide a 
 double arm, or a single split arm, in which case the joint of the 
 pulley comes at the arm, and the "heeling" action of the rim 
 flanges is prevented. 
 
 The rim bolts should be crowde I as close as possible t> the 
 rim in order to reduce the stress on them, and also the stress in 
 the flange itself. The practical point must not be forgotten, how- 
 ever that the bolts must have sufficient clearance to be put into 
 place beneath the rim. 
 
 While it is evident that the rim bolts are most effective in 
 taking care of the centrifugal action of the halves, yet in small 
 split pulleys it is quite common to omit the rim bolts and to 
 use the jub bolts for the double purpose of clamping the shaft 
 and holding the two halves together. The pulley is cast with its 
 rim continuous throughout the full circle, and it is machined in 
 this form. It is then cracked in two by a well-directed blow of a 
 cold chisel, the casting being especially arranged for this along the 
 division line by cores so set that but a narrow fin of metal holds 
 the two parts together. This provides sufficient strength for cast- 
 ing and turning, but permits the cold chisel to break the connec- 
 tion easily. 
 
 SPECIAL FORflS OF PULLEYS. 
 
 The plain cast-iron pulley has been used in the foregoing 
 discussion as a basis of design. A pulley is, however, such a 
 common commercial article, and finds such universal use, that
 
 MACHINE DESIGN 99 
 
 special forms> which can be bought in the open market, are not 
 only cheaper but better than the plain cast-iron pulley, at least for 
 regular line-shaft work. 
 
 Cast iron is a treacherous and uncertain material for rims of 
 pulleys. It is not wells.uited to high fiber stresses; hence the range 
 of speed permissible for pulley rims of cast iron is limited. Steel 
 and wrought iron, having several times the tensional strength of 
 cast iron, and being, moreover, much more nearly homogeneous 
 in texture, are well suited for this work; one of the best pulleys on 
 the market consists of a steel rim riveted to a cast-iron spider. 
 Such an arrangement combines strength and lightness, without 
 increasing complication or expense. 
 
 The all-steel pulley is a step further in 'this direction. Here 
 the rim, arms, and hub are each pressed into shape by specially 
 devised machinery, then riveted and bolted together. This pulley 
 is strictly a manufactured article, which could not compete with the 
 simpler forms unless built in large quantities, enabling automatic 
 machinery to be used. Large numbers of pulleys are built in this 
 way, and are put on the market at reasonable prices. 
 
 Wood-rim pulleys have been made for many years, and, 
 except for their clumsy appearance,, are excellent in many respects. 
 The rim is built up of segments in much the same way, as an ordi- 
 nary pattern is made, the segments being so arranged that they 
 will not shrink- or twist out of shape from moisture. The hubs 
 may be of cast iron, bolted to wooden webs, and carrying hard- 
 wood split bushings, which may be varied in bore within certain 
 limits so as to fit different sizes of shafting. The wooden pulley 
 is readily and most often used in the split form, thus enabling it 
 to be put in position easily at any point of a crowded shaft. It is 
 often merely clamped in place, thus avoiding the use of keys or 
 set screws, and not burring or roughening the shaft in any way. 
 
 PROBLEMS ON PULLEYS. 
 
 1. Calculate the tensile stress due to centrifugal force in 
 the rim of a cast-iron pulley 30 inches in diameter, at 500 revolu- 
 tions per minute. 
 
 2. The driving force of a belt on a 36-inch pulley is 800 
 Jbs., and the belt wrap about 180. Calculate proportions of el-
 
 100 MACHINE DESIGN 
 
 liptical arms to resist bending, the allowable fiber stress being 
 2,000. 
 
 3. A pulley 12 inches in diameter. j>-inch web, 4- inch diam- 
 eter hub, transmits 25 horse-power at a belt speed of 3,000 ft. 
 per minute. Calculate the maximum shearing stress in the web. 
 
 4. In Ficr. 24 assume the followino- data: L, - 1 inches: 
 
 O O ! 
 
 t.,=^\ inch; e="L^ inches; y= 3 inches; area of rim = 3 sq. 
 in.; allowable tensile stress in rim 1,000 Ibs. per sq. in. Calculate 
 the diameter of the rim bolts. 
 
 o. Calculate the fiber stress in the rim bolt flange along the 
 line of the bolts. 
 
 SHAFTS. 
 
 NOTATION The following notation is used throughout the chapter ou Shafts : 
 
 A,, = Angular deflection (degrees). L = Length along shaft (inches). 
 
 H = Simple bending moment (inch-lbs.). LI, L '^Length of bearings (inches.) 
 
 Be= Equivalent bending moment (inch- M =Distance betwe en bearings (feet.) 
 
 N =Number of revolutions per minute. 
 
 c ^Distance from neutral axis to outer 
 
 fiber (toches). =Driving force of belt (Ibs.). 
 
 d. do, do, da, d4=Diameters of shaft Pl=Load applied as stated (Ibs.). 
 
 (inches). R =Radius at which load as stated acts 
 
 di = Internal diameter of shaft (inches). (inches). 
 
 E= Direct modulus of elasticity (a S =Fiber stress, tension, compression, 
 ratio). or shearing (Ibs. per-sq. in.). 
 
 c =Transverse deflection (inches). T =Simple twisting moment (inch-lbs.). 
 
 G=Transverse modulus of elasticity (a T e = Equivalent twisting moment (inch- 
 ratio). lbs ->- 
 
 H=Horse-power (33,000 ft.-lbs. per min- T n =Tension in tight side of belt (Ibs.). 
 
 ute). T,,=Tension in loose side of belt (Ibs.). 
 
 I = Moment of inertia. \V = Load applied as stated (Ibs.). 
 
 K = Distance between bearings (inches). 
 
 ANALYSIS. The simplest case of shaft loading is shown in 
 Fig. 26. The equal forces W, similarly applied to the disc at the 
 distance R from its center, tend to twist the shaft off, the tendency 
 being equal at all points of the length L between the disc and the 
 post,' to which the shaft is rigidly fastened. The fastening to the 
 post, of course, in this ideal case, takes the place of a resisting 
 member of a machine. A state of pure torsion is induced in the 
 shaft; and any element, such as ca, is distorted to the position c-J, 
 aob being the angular deflection for the distance L. 
 
 The case of Fig. 27 is illustrative of what occurs when a belt 
 pulley is substituted for the simple disc. Here the twisting action 
 is caused by the driving force of the belt, which is T D - T = P.
 
 MACHINE DESIGN 
 
 101 
 
 acting at the radius R. Torsion and angular deflection exist in 
 the shaft, as in Fig. 26. In addition, however, another stress of 
 a different kind has been introduced; for not only does the shaft 
 tend to be twisted off, but the forces T n and T , acting together, 
 tend to bend the shaft, the bending moment varying with every 
 section of the shaft, being nothing at the point <?, and maximum 
 at the point c. This combined action is the most common of any 
 that we find in ordinary machinery, occurring in nearly every case 
 with which we have to deal. 
 
 In Fig. 27, if the forces T n and T be made equal, there will 
 be no tendency at all to twist off the shaft, but the bending will 
 remain, being maximum at the point c. This condition is illustra- 
 tive of the case of all ordinary pins and studs in machines. In 
 
 this sense, a pin or a stud is sim- 
 ply a shaft which is fixed to the 
 frame of the machine, there be- 
 ing no tendency to turning of the 
 pin or stud itself. The same 
 condition would be realized if 
 the disc in Fig. 27 were loose 
 upon the shaft. In that case, 
 the bending moment would be 
 caused by T n + T acting with 
 the leverage L. Of course there 
 would have to be some resistance 
 for T n -T to work against, in 
 order that torsion should not be 
 transmitted through the shaft. 
 
 O 
 
 This condition might be intro- 
 Fig. 26. duced by having a similar disc 
 
 lock with the first one by means 
 of lugs on its face, thus receiving and transmitting the torsion. 
 
 If the distance L becomes very great, both the angular deflec- 
 tion due to twisting, and the sidewise deflection due to bending, 
 become excessive, and not permissible in good design. This 
 trouble is remedied by placing a bearing at some point closer to 
 the disc, which, as it decreases L, of course, decreases the bending 
 moment and therefore the transverse deflection. The angular de- 
 
 115
 
 102 
 
 MACHINE DESIGN 
 
 flection can be decreased only by bringing the resistance and load 
 nearer together. 
 
 The above implies, of course, that the diameter of the shaft is not 
 changed, it being obvious that increase of diameter means increase of strength 
 and corresponding decrease of both angular and transverse deflection. 
 
 If the speed of the shaft be very hifh, and the distance be- 
 
 1 */ O 
 
 tween bearings, represented byL, be very great, the shaft will take 
 a shape like a bo\v string \vhen it is vibrated., and smooth action 
 cannot be maintained. 
 
 It is necessary to carry the cases of Figs. 2*> and 27 but a 
 
 Fig. 27. 
 
 single step farther to illustrate the actual working conditions of 
 shafting in machines. Suppose the rigid post to have the shaft 
 passing clear through it. and to act as a bearing, so that the shaft 
 can freely rotate in it, the resistance being exerted somewhere be- 
 yond. The twisting moment will be unchanged, also the bending 
 moment; but the effect of the bendino- moment will be on each 
 
 O 
 
 particle of the shaft in succession, now putting compression on a 
 given particle, and then tension, then compression again, and so 
 on. a complete cycle being performed for each revohitiou. This
 
 MACHINE DESIGN 103 
 
 brings out a very important difference between the bending stress 
 in pins and the bending stress in rotating shafts. In the one case 
 the bending stress is non -re versing; in the other, reversing; and 
 a much higher fiber stress is permissible in the former than in the 
 latter. 
 
 THEORY Simple Torsion. In the case of simple torsion 
 the stress induced in the shaft is a shearing one. The external 
 moment acts about the axis of the shaft, or is a polar moment; 
 hence in the expression for the moment of the internal forces, the 
 polar moment of inertia must be used. Now, from mechanics we 
 have: 
 
 T SI ' 
 i- T' 
 
 I d 3 
 and = -=-y- (for circular section of diameter d)\ 
 
 g^3 
 
 therefore, T = -g-p (3) 
 
 from which the diameter for any given twisting moment and fiber 
 stress can readily be found. 
 
 For a hollow shaft this expression becomes: 
 
 T 
 
 Simple Bending. The stresses induced in a pin or shaft under 
 simple bending are compression and tension. The external moment 
 in this case is transverse, or about an axis across the shaft; hence 
 the direct moment of inertia is applicable to the equation of forces. 
 
 B SI - 
 
 -D = - > 
 
 C 
 
 I d 3 
 and = jjy-jj (for circular section of diameter d) ; 
 
 therefore, B = 1O2' ( 32 ) 
 
 For a hollow shaft or pin this expression becomes: 
 
 (33) 
 
 Combined Stresses. In the greater number of cases met with
 
 104 
 
 MACHINE DESIGN 
 
 in practice, we find two or more simple stresses acting at the same 
 time, and, although the shaft may be strong enough for any one of 
 them alone, it may fail under their combined action. The most 
 common cases are discussed below. 
 
 Tension or Pressure Combined with Bending. In Fig. 28, 
 the load AV produces a tension acting over the whole area of d, due 
 to its direct pull. It also produces a bending action due to the 
 leverage II, which puts the fibers at B in tension and those at the 
 opposite side in compression. It is evident, therefore, that by 
 taking the algebraic sum of the stresses at either side we shall 
 obtain the net stress. It is also evident that the greatest and 
 
 w 
 
 Fig. 28. Fig. 29 
 
 controlling stress will occur on the side where the stresses add, or 
 on the tension side. Hence, from mechanics, 
 
 or, 
 Also, 
 
 Y (due to direct tension). (34) 
 
 WE = 
 
 10.2' 
 
 10.2 WR , 
 or ? TJ (due to bending). (35) 
 
 T ience the combined tensional stress acting at the point B, or, in 
 
 118
 
 MACHINE DESIGN 
 
 105 
 
 fact, at any point on the extreme outside of the vertical shaft to- 
 ward the force W, is : 
 
 c _ 4W _j_ 10 ' 2 WR 
 ~ ird 2 
 
 (36) 
 
 If W acted in the opposite direction, the greatest stress would 
 still be at the side B, but would be a compression instead of a ten- 
 sion, of the same magnitude as before. 
 
 Tension or Compression Combined with Torsion. In Fig. 29, 
 Y might be the end load on a vertical shaft; and the two forces W 
 might act in conjunction with it as in the case of Fig. 26, at the 
 radius R. This case is not very often met with. It is usually 
 possible to combine the moments, find an equivalent moment of a 
 simple kind, and use the corresponding simple fiber stress. In the 
 case in question we have a direct stress to be combined with a 
 shearing stress, and mechanics gives us the following solution: 
 
 Fig. 30. 
 
 Let S s = simple shearing stress (Ibs. per sq in.). 
 Let S c = simple compressive stress (Ibs. per sq. in.). 
 Let S rs = resultant shearing stress (Ibs. per sq. in.). 
 Let S rc =resultant compressive stress (Ibs. per sq. in.). 
 
 We then have : 
 
 ' 5.1 ' 
 
 _ 5.1(2WR) 
 d 3 
 
 (37) 
 
 Also, 
 
 v 
 
 V = 
 
 119
 
 100 MACHINE DESIGN 
 
 Sc = rV. (38) 
 
 Xow, from a solution given in simplest form in " Merriman's 
 Mechanics"- which the student may consult, if desired values 
 for the resultant stresses can be found. Whichever of these is 
 the critical one for the material used, should form the basis for its 
 diameter: 
 
 (39) 
 
 Also, 6^= -5 + ^8.'+. (40) 
 
 Bending Combined with Torsion. In Fig. 30, the load W 
 acts not only to twist the shaft off. . but also presses it sidewise 
 against the bearing. As it is usually customary to figure the 
 maximum moment as taking place at the center of the bearing, 
 the length L. which determines the bending moment, is taken -to 
 that point. The theory of the stress induced in this case is com- 
 plicated. In order to make the magnitude of the moments clearer, 
 let us introduce the two equal and opposite forces F and F 1 , each 
 equal to W. at the point ('. We can evidently do this without 
 changing the equilibrium of the shaft in any way. We now see 
 that W and F 1 act as a couple giving a twisting moment WR ; 
 and that F acts with a leverage L, producing a bending moment 
 FL = WL, at the middle of the bearing. 
 
 If. now, we find an equivalent twisting moment, or an equiv- 
 alent bending moment, which would produce the same effect on 
 the fibers of the shaft as the two combined, we can treat the cal- 
 culation of the diameter as a simple case, and proceed as in the 
 cases of simple torsion and simple bending considered above. This 
 relation is given us in mechanics: 
 
 
 (42) 
 
 These expressions are true in relation to each other, on the assump- 
 tion that the allowable fiber stress S is the same for tension, com- 
 
 120
 
 MACHINE DESIGN 107 
 
 pression, and shearing. For the material of which shafts are usu- 
 ally made, this is near enough to the truth to give safe and practi- 
 cal results. Using the expressions for internal moments of resist- 
 ance as previously noted for circular sections, we then have : 
 
 jz 
 
 (43) 
 
 Also, T.= (44) 
 
 Either equation may be used ; the diameter d will result the same 
 whichever equation is taken. For the sake of simplicity, equation 
 42 is generally preferred, equation 44 being taken in conjunction 
 with it. 
 
 The expression 1/B 2 + T 2 is one that would be a long and 
 tedious task to calculate. By inspection it is readily seen that 
 this quantity can be graphically represented by means of a right- 
 angled triangle having B and T as the sides. We may then lay 
 down on a piece of paper, to some convenient scale, the moments 
 B and T as the sides of a right-angled triangle, when, upon 
 measuring the hypothenuse, we can easily read off to the same 
 scale 1/B 2 + I" 2 . Even if the drawing is made to a small scale, 
 the accuracy of the reading will be sufficient to enable the value 
 for d to be solved very closely. This graphical method is illus- 
 trated in Part I. 
 
 Deflection. For a shaft subjected to pure torsion, as in Fig. 
 26, the angular deflection due to the load may be carried to a cer- 
 tain point before the limit of working fiber stress is exceeded. 
 The equation worked out from mechanics for this condition, is: 
 
 584 TL 
 A = --> (45) 
 
 which at once gives the number of degrees of angular deflection 
 for a shaft whose modulus of elasticity, torsional moment, and 
 length are known. 
 
 The shearing modulus of elasticity of ordinary shaft steel runs from 
 10,000,000 to 13,000,000, giving as an average about 12,000,000. 
 
 By the welLknown relation of " Hooke's law " (stresses pro- 
 portional to strains within the elastic limit of the material), we have: 
 
 121
 
 10S MACHINE DESIGN 
 
 A SL . 
 300 r ~ TrG^' 
 
 A?rG^ 
 "WIT ( 46 ) 
 
 A twist of one degree in a length of twenty diameters is a 
 usual allowance. Substituting A = 1, L = 20d, and G = 12,000, 
 000. we have: 
 
 S = 5,240 (nearly). (47) 
 
 This is a safe value for shearing fiber stress in steel. In fact, in 
 calculations for strength, even for reversing stresses, the usual 
 figure is 8.000 (Ibs. per square inch), thus indicating that the re- 
 lation of one degree to twenty diameters is well within the limit 
 of strength. 
 
 for a hollow shaft the above formula becomes : 
 
 584 TL 
 
 A -a,vz* ./n- (48) 
 
 Transverse deflection occurs when the shaft is subjected to a 
 bending moment. It may therefore exist alone or in conjunction 
 with angular deflection. Transverse deflection of shafts, however, 
 rarely exists u]> to the point of limiting fiber stress, because before 
 that point is reached the alignment of the shaft is so disturbed 
 that it is not practicable as a device for transmitting power. A 
 transverse deflection of .01 inch per foot of length is a common 
 allowance ; but it is impossible to fix any general limit, as in many 
 cas' j s this figure, Jf exceeded, would do no harm, while in others 
 such as heavily loaded or high-speed bearings even the figure 
 given might be fatal to good operation. 
 
 The formula for transverse deflection, deduced from mechan- 
 ics, varies with the system of loading. The three 'most common 
 conditions only are given below, reference to the handbook being 
 necessary if other conditions must be satisfied: 
 
 Fixed at one end, loaded at ttie other, 
 
 " 
 
 (49) - 
 
 122
 
 GENERAL ARRANGEMENT OF JONVAL TURBINE. 
 
 Central Engineering Works, Oldham, Eng.
 
 MACHINE DESIGN 109 
 
 Supported at ends, loaded in middle, 
 
 WL 3 
 
 * = 48ET (50) 
 
 Supported at ends, loaded uniformly, 
 
 _5WL 
 
 ~ 384 El" ^^ 
 
 For transverse deflection the direct modulus of elasticity must 
 be used, for the fibers are stretched or compressed, instead of being 
 subjected to a shearing action. The most usual value of the di- 
 rect modulus of elasticity for ordinary steel is 30,000,000, and is 
 denoted in most books by the symbol E. Both the shearing and 
 direct moduli of elasticity are really nothing but the ratio of the 
 stress to the strain produced by that stress, it being assumed that 
 the given material is perfectly elastic. A material is supposed to 
 be perfectly elastic up to a certain limit of stress, and it is within 
 this limit that the relation as above holds good. 
 
 Expressed in the form of an equation this would be : 
 
 Centrifugal Whirling. If a line shaft deflect but slightly, 
 due to its own weight, or the weight or pressure of other bodies 
 upon it, and then be run at a high speed, the centrifugal force set 
 up increases the deflection, and the shaft whirls about the geomet- 
 rical line through the centers of the bearings, causing vibration 
 and wear in the adjoining members. It is evident that the prac- 
 tical remedy for this tendency in a shaft of given diameter and 
 speed is to locate the bearings sufficiently close to render the action 
 of small effect. 
 
 Many formulae might be given for this relation, each being 
 based on different assumptions. Perhaps as widely applied and 
 as simple as any, is the " Rankine " formula, which sets the limit 
 of length between bearings for shafts not greatly loaded by inter- 
 mediate pulleys or side strains : 
 
 M -175 J^-- (53) 
 
 123
 
 110 
 
 MACHINE DESIGN 
 
 Horse=Power of Shafting. Horse-power is a certain specific 
 rate of doing work, ?;/.?., 33,000 foot-pounds per minute. Hence, 
 to find the horse-power that a shaft will transmit, we must first 
 find the work done, and then relate it to the speed. Take, for ex- 
 ample, the case of a pulley, the symbols being the same as before 
 
 namely, P-- driving force at rim of pulley (Ibs.); R radius 
 
 of pulley (inches) ; N = number of revolutions per minute; and 
 II horse-power. Then. 
 
 Work force X distance = P X (2 IT RX) = II X 33,000 X 12; 
 
 63,02511 
 
 PR- -^ (54) 
 
 This is one of the most useful equations for calculations involving 
 horse -power. P>y it the number of inch-pounds torsion for any 
 horse-power can be at once ascertained. 
 
 It should be clearly noted, however, that in. this equation the 
 bending moment does not enter at all. Hence any shaft based in 
 size on JioTse-power alone, is based on torsional -moment alon-e, 
 bending moment being entirely neglected. In many cases the 
 bending moment is the controlling one as to limiting fiber stress. 
 Hence empirical shafting formulae depending upon the horse- 
 power relation are unsafe, unless it is definitely known just what 
 torsional and bending moments have been assumed. 
 
 The only safe way to figure the size of a shaft is to find 
 accurately what torsional moment and bending moment it has to 
 sustain, and then combine them according to equation 41 or 42 
 
 124
 
 MACHINE DESIGK 111 
 
 introducing the element of speed as basis for assumption of a high 
 or .low working fiber stress. 
 
 PRACTICAL MODIFICATION. The practical methods of 
 handling the theoretical shaft equations have reference to the fit of 
 the shaft within the several pieces upon it. The running fit of a 
 shaft in a bearing is usually considered to be so loose that the shaft 
 could freely deflect to the center of the bearing. 'This is doubtless 
 an extreme view of the case, but it is the only safe assumption. 
 Hence a shaft running in bearings (see Fig. 31) is supposed to be 
 supported at the centers of those bearings, and its theoretical 
 strength is based on this supposition. 
 
 For a tight or driving fit upon the shaft, a safe assumption to 
 make is that there is looseness enough at the ends of the fit to per- 
 mit the shaft to be stressed by the load a short distance within the 
 faces of the hub, say from ^ inch to 1 inch. For example, refer- 
 ring to Fig. 31, suppose P> to be the transverse load, exerted 
 through a hub fast upon the part of the shaft d 3 . Taking mo- 
 ments about the center of one bearing, and solving for the reaction 
 at the center of the other, we have : 
 
 (55) 
 
 Also, P, t = R 2 K; 
 
 K^TT 
 
 Now, as far as the part of shaft d 3 is concerned, it may depend for 
 It: size on the bending moment R 2 J, or on Rj a. The reason the 
 lever arm is not taken to the point directly under the load P,, is 
 because it is not practically possible to break the shaft at that 
 point, on account of the reinforcement of the hub, which is tightly 
 fitted upon it. Trying these moments to see which is the greater,' 
 we shall find that the greater moment always occurs in connection 
 with the longer lever arm. Hence R 2 I will be greater than R t a. 
 We then write the equation of external moment = internal mo- 
 ment: 
 
 Sd 3 3 
 R ' 6 ~ : T02"' 
 
 125
 
 112 MACHINE DESIGN 
 
 4 = N I^- (57) 
 
 For the size of bearing A we have the maximum bending HID- 
 ment: 
 
 , L I Sd* 
 
 i 
 
 or, d t =^ g-gi- (58) 
 
 For the size of bearin B we have the maximum moment: 
 
 10.2 ' 
 
 4^ ' < 59) 
 
 The above calculations are, of course, on the assumption that no torsion 
 is transmitted either way through this axle. We should in that case have 
 combined torsion and bending. This has been made sufficiently clear, in pre- 
 ceding paragraphs and in Part I, to require no further illustration. 
 
 The dotted line in Fig. 81 shows the theoretical shape the 
 axle should take under the assumed conditions. The practical 
 modification of this shape is obvious. At the shoulders of the 
 shaft the corners should not be sharp, but carefully filleted, to 
 avoid the possible starting of a crack at those points. 
 
 Often the diameter of certain parts of a shaft may be larger 
 than strength actually calls for. For example, in Fig. 81, the 
 part c7 :i need only be as large as the dotted line; but it is obvious 
 that unless the key is sunk in the body of the shaft, the hub could 
 not be slipped into place over the part </ 4 . If, however, the diam- 
 eter r/ 3 be made large enough so that the bottom of the key will 
 clear r7 4 , the rotary cutter which forms the key way in r7 3 will also 
 clear *7 4 , and the key way can be more easily produced. 
 
 In cases where fits are not required to be snug, a straight 
 shaft of cold-rolled steel is commonly used. Here any parts fast- 
 ened on the middle of the shaft have to be driven over a consider- 
 able length of the shaft before they reach their final position. 
 Moreover, there is no definite shoulder to stop against, and meas- 
 urement has to be resorted to in locating them. 
 
 126
 
 MACHINE DESIGN 113 
 
 It does not pay to turn any portion of a cold-rolled shaft, un- 
 less it be the very ends, for relieving the " skin tension " in such 
 material is sure to throw the shaft out of line and necessitate 
 subsequent straightening. 
 
 Turned-steel shafts for machines may with advantage be 
 slightly varied in diameter wherever the fit changes; and although 
 the production of shoulders costs something, yet it assists greatly 
 in bringing the parts to their exact location, and enables the work- 
 man to concentrate his best skill on the fine bearing fits, and to 
 save time by rough -turn ing the parts that have no fits. 
 
 Hollow shafts are practicable only for large sizes. The advan- 
 tages of removing the inner core of metal, aside from some specific 
 requirement of the machine, are that it eliminates all possibility of 
 cracks starting from the checks that may exist at the center, per- 
 mits inspection of the material of a shaft, and, in case of hollow- 
 forged shafts, gives an opening for the forging mandrel. In the 
 last case, the material is improved by a rolling process. 
 
 The material most common for use in machine shafting is the 
 ordinary " Machinery Steel," made by the Bessemer process. This 
 steel is apt to be "seamy," and often contains checks and flaws 
 that are detected only upon sudden and unexpected breakage of a 
 part apparently sound. This characteristic is a result of the proc- 
 ess employed in the manufacture of the steel, and thus far has 
 never been Wholly eliminated. Bessemer steel is, nevertheless, a 
 very useful material, and the above weakness is not so serious but 
 that this kind of steel can be used with success in the great majority 
 of cases. 
 
 When a more homogeneous shaft is desired, open=hearth steel 
 is available. This is a more reliable material to use than the Bes- 
 semer, and costs somewhat more. It makes a stiff, true, fine-sur- 
 faced shaft, high-grade in every respect. It is usually specified 
 for armature shafts of dynamos and motors. 
 
 Steels of special strength, toughness, and elasticity are made 
 under numerous processes. Nickel steel is perhaps the most con- 
 spicuous example. While for this steel a high price has to be 
 paid, yet its great strength, in connection with other valuable qual- 
 ities, makes it a material extremely valuable for service where light 
 weight is essential, or where contracted space demands small size. 
 
 127
 
 114 MACHINE DESIGN 
 
 The range of strength of these various steels is so great that it is well- 
 nigh iseless to go into a discussion of it here. "Reference should be had to 
 the t tended discussions of the handbooks, and to special trade pamphlets. 
 A st ly of the possibilities of steel in its various forms for use in shafting, 
 is vc - valuable as a basis for design, as it can almost be said that a machine 
 consi ts chiefly of a "collection of shafts with a structure built round them." 
 The lafts are like a core, and evidently the size of the core determines the 
 shell about it. 
 
 PROBLEHS ON SHAFTS. 
 
 1. Required the twisting moment on a shaft that transmits 
 30 horse-power at 120 revolutions per minute. 
 
 2. Find the diameter of a steel shaft designed to transmit 50 
 horse-power at 150 revolutions per minute. 
 
 3. Assuming same data as in Problem 1, find the diameters 
 of a hollow shaft for a value of S 8,000. 
 
 4. A belt on an idler pulley embraces an angle of 120 
 degrees. Assuming tension of belt 1,000 pounds on each side, 
 and pulley located midway between bearings, which are 30 inches 
 from center to center, what is the diameter of shaft required '. 
 
 5. ( 'alculate the diameter of a steel shaft designed to transmit 
 a twisting moment of 400.000 inch-pounds and also to take a 
 bending moment of 300,000 inch-pounds. 
 
 G. Find the angular deflection in a 4-inch shaft 20 feet long 
 when subjected to a load of 5,500 pounds applied to an arm of 
 30-inch radius. Assume transverse modulus of elasticity equal to 
 12,000.000. 
 
 7. The overhung crank of a steam engine has a force of 
 32,000 Ibs. at the center of the crank pin. which is 12 inches from 
 the center of the shaft bear in tr, measured parallel to the shaft. 
 The radius of crank arm is 10 inches. Assume S equal to 10,000. 
 Calculate the diameter of the crank shaft. 
 
 S. On 'a short, vertical steel shaft the load is 5,000 pounds. 
 A gear, 36 teeth, 1^ diametral pitch, at top of shaft, transmits a 
 load of 4,000 pounds at the pitch line. Safe shear 7,500. What 
 is the diameter of the shaft ? 
 
 SPUR GEARS. 
 
 NOTATION The following notation is used throughout the chapter on Spur Gears: 
 
 6 =Breaclth of -rectangular section of M. Mi-Revolutions per minute. 
 
 arm (inches). jU,= Coefficient of friction between teeth. 
 
 128
 
 MACHINE DESIGN 115 
 
 C = Width of arm extended to pitch . N=Number of teeth, 
 
 line (inches). M = Number of arms. 
 
 c =Distancefrom neutral axis to outer P=Diametral pitch (teeth per inch of . 
 
 fiber (inches). diameter). 
 
 D=Pitch diameter of gear (inches). P'=Circular pitch (inches). 
 
 F=Face of gear (inches). Q, Qi=Normal pressure between teeth 
 f =Clearance of tooth at bottom (Ibs.). 
 
 (inches). R,Ri=Resultant, pressure between 
 G=Thickness of arm extended to pitch teeth (Ibs.). 
 
 line (inches). ,-, n = Radius of pitch circles (inches). 
 
 H=Thickness of tooth at any section s = Fiber stress of material (Ibs. per 
 
 (inches). sq. in.). 
 
 7i = Depth of rectangular section of arm s = Addendum of tooth (inches) =De- 
 
 (inches). dendum of tooth. 
 
 I =Moment of inertia. t ^Thickness of tooth at pitch line 
 'K= Thickness of rim (inches). (inches). 
 
 L= Distance from top of tooth to any w=Load at pitch line (Ibs.). 
 
 section (inches). y ^Coefficient for " Lewis " formula. 
 
 ANALYSIS. If a cylinder be placed on a plane surface, with 
 its axis parallel to the plane, an attempt to rotate the cylinder 
 about its axis would cause it to roll on the plane. 
 
 Again, if two cylinders be provided with axial bearings, and 
 be slightly pressed together, motion of one about its axis will 
 cause a similar motion of the other, the two surfaces rolling one 
 on the other at their common tangent line. If moved with care, 
 there will be no slipping in either of the above cases which is 
 explained by the fact that no matter how smooth the surfaces may 
 appear to be, there is still sufficient roughness to make the little 
 irregularities interlock and act like minute teeth. 
 
 The magnitude of the force possible to be transmitted de- 
 pends not only on the roughness of the surfaces, but on the 
 amount of pressure between them. Suppose that one cylinder is 
 a part of a hoisting drum, on which is wound a rope with a weight 
 attached. We can readily make the weight so great that, no mat- 
 ter how hard we press the two cylinders together, the driving 
 cylinder will not turn the hoisting cylinder, but will slip past it. 
 If now, instead of increasing the pressure, which is detrimental 
 both to cylinders and bearings of same, we increase the coarseness 
 of the surfaces, or, in other words, put teeth of appreciable size 
 on these surfaces, we attain the desired result of positively driving 
 without excessive side pressure. 
 
 These artificial projections, or teeth, must fit into one another; 
 hence the surfaces of the original cylinders, having been broken 
 up into alternate projections and hollows, have entirely disap- 
 
 129
 
 110 
 
 MACHINE DESIGN 
 
 peared to the eye; they nevertheless exist as ideal or imaginary 
 surfaces, which roll together with the same surface velocities as if 
 in bodily form, provided that the curves of the teeth are correctly 
 formed. Several mathematical curves are available for use as 
 tooth outlines, but in practice the involute and cycloidal curves 
 are the only ones used for this purpose. 
 
 The ideal surfaces are known as pitch cylinders or pitch 
 circles. In Fig. 32 is shown an end view of such a pair of cylin- 
 ders in contact at their pitch point P. In gear calculations we 
 assume that there is no slip, between the pitch circles, acting as 
 driving cylinders; hence the speeds of the two pitch circles at the 
 
 pitch point are equal. If M and M t he the revolutions per minute 
 of the cylinders respectively, /' and i\ their radii, then 
 
 
 M 
 
 That is, the number of revolutions varies inversely as the radii. 
 
 The simple calculation as above is the key to all calculations 
 involving gear trains in reference to their speed ratio. 
 
 Fig. 33 represents cycloidal teeth in the two extreme positions 
 of beginning and ending contact. The normal pressure Q or Q x 
 between the teeth in each position acts through the pitch point O, 
 as it must always do in order to insure the condition of ideal roll- 
 
 ISO
 
 MACHINE DESIGN 
 
 117 
 
 ing of the pitch circles, and the velocity ratio proportional to 
 
 As the surfaces of the teeth slide together, frictional resistance is 
 produced at their point of contact. This force is widely variable, 
 depending on the material and condition of the tooth surfaces, 
 whether smooth and well lubricated, or rough and gritty. As this 
 resistance acts in conjunction with the normal force between the 
 teeth, we may construct a parallelogram of forces on these two as 
 a base, the resultant pressure between the teeth being slightly 
 changed thereby, as shown in Fig 33. 
 
 Assuming a coefficient of friction fJ,, the force of friction is /A Q or p Qi 
 and the resultant pressure R or Ri. 
 
 Tooth B of the FOLLOWER is therefore under a heavy bending moment 
 measured by the product RL, L 
 being the perpendicular distance 
 from the center of the tooth at 
 its base to the line of the force. 
 This tooth also has a relatively 
 small compressive stress due to 
 the resolved part of R along the 
 radius, and a relatively small 
 shearing stress due to the re- 
 solved part of R along a tangent 
 to the pitch circle. 
 
 Tooth D of the driven wheel 
 or FOLLOWER has a relatively 
 large shearing stress, a small 
 bending . moment, and practi- 
 cally no direct compressive 
 
 Tooth A of the driving wheel 
 or DRIVER has a relatively large 
 shearing stress, a small bending moment, and small compressive stress. 
 
 Tooth C of the DRIVER has a large bending moment, but small com 
 pressive and shearing stresses. 
 
 The conditions as noted above are not those of every pair of 
 gears, in fact they vary with every difference of pitch circle, or of 
 detail and position of tooth. It is true, however, that in nearly 
 all cases in practice the bending stress is the controlling one from 
 a theoretical standpoint. Moreover, the designer must consider 
 the form and strength of the tooth when it is under the condition 
 of maximum moment. This evidently, from the above, occurs at 
 the beginning of contact, for the follower teeth; and at the end of 
 contact, for the driver teeth. In the particular case illustrated in 
 
 131
 
 us 
 
 MACHINE DESIGN 
 
 Fig. 8-5, if the material in both gears were the same, tooth C, 
 being the weaker at the root, would probably break before B; but 
 if C were of steel, and B of cast iron, B might break first. 
 
 It will be noticed that E, is nearly parallel to the top of the 
 tooth; and it may easily happen that the friction may become of 
 such a value that it will turn the direction of R until it lies along 
 the top of the tooth exactly, which is the condition for maximum 
 moment. For strength calculations it is usual to consider this 
 condition as existing in all cases. 
 
 At the beginning of contact there is more or less shock when 
 the teeth strike together, and this effect is much more evident at 
 hio'h speeds. There is also at the beginning of contact a sort of 
 
 C i o o 
 
 chattering action as the driving tooth rubs along the driven tooth. 
 
 Uniform distribution of pressure along the face of the tooth is 
 often impaired by uneven wear of the bearings supporting the gear 
 shafts, the pressure being localized on one corner of the tooth. The 
 same effect is caused by the accidental presence of foreign material 
 between the teeth. Again, in cast gearing, the spacing may be 
 irregular, or. on account of draft on the pattern, the teeth may bear 
 at the high points only. "While it is 
 usual to consider that the load is evenly 
 distributed along the face of the tooth, 
 yet the above considerations show that 
 mi ample margin of strength must al- 
 ways !>' all meed on account of these 
 uncertainties. 
 
 "When the number of teeth in the 
 mating gears is high, the load will be 
 distributed between several teeth ; but, 
 as it is almost certain that at some time 
 the proper distribution of load will not 
 
 exist, and that one tooth will receive the full load, it is considered 
 that practically the only safe method is so to design the teeth that 
 a single tooth may be relied upon to withstand the full load without 
 failure. 
 
 THEORY. Based on the Analysis as given, the theory of gear 
 teeth assumes that one tooth takes the whole load, and that this load 
 is evenly distributed along the top of the tooth and acts parallel with 
 
 Fig. 34. 
 
 132
 
 MACHINE DESIGN 119 
 
 ?ts base, thus reducing the condition of the tooth to that of a 
 cantilever beam. The magnitude of this load at the top of the 
 tooth is taken for convenience the same as the force transmitted at 
 the pitch circle. This condition is shown in Fig. 34. Equating 
 the external moment to the internal moment, we then have, from 
 mechanics: 
 
 The thickness II is usually taken either at the pitch line or at 
 the root of the tooth just before the fillet begins; and L, of 
 course, is dependent on the tooth dimensions. The formula is 
 most readily used when the outline of the tooth is either assumed 
 or known, a trial calculation being made to see if it will stand the 
 load, and a series of subsequent calculations followed out in the 
 same way until a suitable tooth is found. This method is pursued 
 because there are certain even pitches which it is desirable to use; 
 and it is safe tc say that any calculation figured the reverse way 
 would result in fractional pitches. The latter course may be used, 
 however, and the nearest even pitch chosen as the proper one. 
 
 As stated under "Analysis," there are a great many circum- 
 stances attending the operation of gears which make impossible 
 the purely theoretical application of the beam formulae. For this 
 reason there is no one element of machinery which depends so 
 much on experience and judgment for correct proportion as the 
 tooth of a gear. Hence it is true that a rational formula based on 
 the theoretical one is really of the greater practical value in tooth 
 design. 
 
 If we examine formula 61, we find that in a form solved for 
 W, we have: 
 
 W=. (6,)-'. 
 
 Of these quantities, H and L are the only variables, for we can 
 make the others what we choose. II and L depend upon the 
 circular pitch P 1 and the curvature and outline of the tooth. If 
 now we could settle or> a standard system of teeth, we could estab- 
 lish a coefficient to ba used to take the place of the variable part 
 
 133
 
 120 MACHINE DESIGN 
 
 of II and L, which depends on the outline of tooth, and we should 
 thus have an empirical formula which would be on a theoretical 
 basis. 
 
 This, 3Ir. "Wilfred Lewis has done; and it is safe to say 
 that this formula is more universally used and with more satis- 
 
 factory practical results than any other formula, theoretical or 
 practical, that has ever been devised. His coefficient is known as 
 //, and was determined from many actual drawings of different 
 forms of teeth showing the weakest section. This coefficient is 
 worked out for the three most common systems as follows: 
 
 01 
 For 2CP involute, y = 0.154 - -T^ 
 
 For 1-V involute 0.684 
 
 and ccloidal ^' = - m ' 
 
 For radial flanks, // = 0.075 - -1= (65) 
 
 The tooth upon which the above is based is the American standard or 
 Brown & Sharpe tooth, for which the proportions are shown in Fig. 35. 
 
 The ''Lewis " formula* is: 
 
 W = SF Fy. (66) 
 
 A table indicating the value of S for different speeds follows: 
 
 Safe Working Stresses for Different Speeds. 
 
 Spood of tooth, 100 i 200 ; 300 I 600 i 900 I 1200 1800 i 2400 
 
 ft. per mm. 
 
 Castirou , 8000! 6000 I 4800 j 4000 i 3003 i 2400 i 2000 : 1700 
 
 Steel 20000 ; 15000 I 12000 10000 i 7500 I 6000 5000 4300 
 
 *XOTE. A full and convenient statement of the Lewis formula will 
 be found 'in "Kent 's Pocket Book. " 
 
 134
 
 MACHINE DESIGN 
 
 121 
 
 A usual relation of F to P 1 is: 
 
 For cast teeth, F = 2P 1 to 3P 1 . 
 For cut teeth, F = 3P 1 to 4P 1 . 
 
 (66) 
 (67) 
 
 The usual method of handling these formulae is as follows: 
 
 The pitch circles of the proposed gears are known or can be assumed; 
 hence W can readily be figured, also the speed of tho teeth, whence S can 
 be read from the table. The desired relation of F to P 1 can be arbitrarily 
 chosen, when P 1 and y become the only unknown quantities in the equation. 
 A shrewd guess can be made for the number of teeth, and y calculated there- 
 from. Then solve the equation for P A which will undoubtedly be fractional. 
 Choose the nearest even pitch, or, if it is desired to keep an even diametraj 
 pitch, the fractional pitch that will bring an even diametral pitch. Now, 
 from this final and corrected pitch, and the diameter of the pitch circle, 
 calculate the number of teeth N in the gear. Check the assumed value of y 
 by this positive value of N. 
 
 Another good way of using this formula is to start with the 
 pitch and face desired, and the diameter of the pitch circle. In 
 
 Fig. 37. 
 
 this case W is the only unknown quantity, and when found can be 
 compared with the load required to be carried. If too small, 
 make another and successive calculations until the result approxi- 
 mates the required load. 
 
 SPUR GEAR Rin, ARHS, AND HUB. 
 
 ANALYSIS and THEORY. The rim of a gear has to transmit 
 the load on the teeth to the arms. It is thus in tension on one side 
 of the teeth in action, and in compression on the other. The sec- 
 tion of the rim, however, is so dependent on other practical con- 
 siderations which call for an excess of strength in this respect, that 
 
 135
 
 122 
 
 MACHINE DESIGN 
 
 it is not considered worth \vhile to attempt a calculation on ih\$ 
 basis. 
 
 Gears seldom run fast enough to make necessary a calculation 
 for centrifugal force ; and in general it can be said that the design 
 of the rim is entirely dependent on practical considerations. These 
 will appear later under k< Practical Modification. " 
 
 The arms of a gear are stressed the same as pulley arms, the 
 same theory answering for both, except that a gear rim always be- 
 ing much heavier than a pulley rim, the distribution of load 
 amongst the arms is better in the case of a gear than of a pulley, 
 and it is usually safe to assume that each arm of a gear takes its full 
 proportion of load ; or. for an oval section, equating the external 
 moment to the internal moment as in the case of pulleys, we have : 
 
 -^5- = 0.0393 SA 3 . (68) 
 
 Heavy spur gears have the arms of a cross or T section (Fig. 
 
 i 
 
 Fig. 33. 
 
 37i, the latter being especially applicable to the case of bevel gears 
 where there is considerable side thrust. The simplest way of 
 treating such sections is to consider that the whole bending moment 
 is taken by the rectangular section whose greater dimension is in 
 the direction of the load. The rest of the section, being close to 
 the neutral axis of the section, is of little value in resisting the 
 direct load, its function being to give sidewise stiffness. The 
 equation for the cross or T style of arm, then is : 
 
 W I) 
 
 X ~77~ 
 
 (69) 
 
 136
 
 MACHINE DESIGN 123 
 
 Either b or h may be assumed, and the other determined. As a 
 guide to the section, b may be taken at about the thickness of the 
 tooth. 
 
 Gear hubs are in no wise different from the hubs of pulleys or 
 other rotating pieces. The depth necessary for providing suffi- 
 cient strength over the key to avoid splitting is the guiding ele- 
 ment, and can usually be best determined by careful judgment. 
 
 PRACTICAL MODIFICATION. The practical requirements, 
 which no theory will satisfy, are many and varied. Sudden and 
 severe shock, excessive wear due to an atmosphere of grit and corros- 
 ive elements, abrupt reversal of the mechanism, the throwing-in of 
 clutches and pawls, the action of brakes these and many other 
 influences have an important bearing on gear design, but not one 
 that can be calculated. The only method of procedure in such 
 cases is to base the design on analysis and theory as previously 
 given, antf then add to the face of gear, thickness of tooth, or pitch 
 an amount which judgment and experience dictate as sufficient. 
 
 Excessive noise and vibration are difficult to prevent at high 
 speeds. At 1,000 feet per minute, gears are apt to run with an 
 unpleasant amount of noise. At speeds beyond this, it is often 
 necessary to provide mortise teeth, or teeth of hard wood set into 
 a cast-iron rim (see Fig. 38). Rawhide pinions are useful in this 
 regard. Fine pitches with a long face of tooth run much more 
 smoothly at high speeds than a coarse pitch and narrow-faced tooth 
 of equal strength. Greater care in alignment of shafts, however, 
 is necessary, also stiffer supports. 
 
 Should it be impracticable to use a standard tooth of sufficient 
 strength, there are several ways in .which we can increase the 
 carrying capacity without increasing the pitch. These are: 
 
 1. Use a stronger material, such as steel. 
 
 2. Shroud the teeth. 
 
 3. Use a hook tooth. 
 
 4. Use a stub tooth. 
 
 Shrouding a tooth consists in connecting the ends of the teeth 
 with a rim of metal. When this rim is extended to the top of -the 
 tooth, the process is called " full- shrouding" (Fig. 39);' and when 
 carried only to the pitch line, it is termed "half-shrouding" 
 (Fig. 40). The theoretical effect of shrouding is to make the tooth 
 
 137
 
 124 
 
 MACHINE DESIGN 
 
 act like a short beam built in at the sides; and the tootli will 
 practically have to be sheared out in order to fail. This modifica- 
 tion of gear design requires the teeth to be cast, as the cutter 
 cannot pass through the shrouding. The strength of the shrouded 
 gear is estimated to be from 25 to 50 per cent above that of the- 
 plain-tooth type. 
 
 Fig. 39. 
 
 Fig. 40, 
 
 The hook-tooth gear (Fig- 41) is applicable only to cases 
 where the load on tho tooth does not reverse. The working side 
 of the tooth is made of the usual standard curve, while the back is 
 made of a curve of greater obliquity, resulting in a considerable 
 increase of thickness at the root of the tooth. A comparison of 
 strength between this form and the standard may be made by 
 drawing the two teeth for a given pitch, measuring their thickness 
 just at top of the fillet, and finding the relation of the squares 
 of these dimensions. The truth of this relation is readily seen from 
 an inspection of formula Gl. 
 
 The stub tooth merely involves the shortening of the height 
 
 138
 
 MACHINE DESIGK 12o 
 
 of the tooth in order to reduce the lever arm on which the load 
 aqts, thus reducing the moment, and thereby permitting a greater 
 load to be carried for the same stress. 
 
 The rim of a gear is dependent for its proportions chiefly on 
 questions of practical moulding and machining. It must bear a 
 certain relation to the teeth and arms, so that, when it is cooling in 
 the mould, serious shrinkage stresses will not be set up, forming 
 pockets and cracks. Moreover, when under pressure of the cutter 
 in the producing of the teeth, it must not chatter or spring. This 
 condition is quite well attained in ordinary gears when the thick- 
 ness of the rim below the base of the tooth is made about the same 
 as the thickness of the tooth. 
 
 LIGHT PRESSURE 
 ON BACK OF TOOTH. 
 35 e ll> 
 
 LOADED SIDE 
 5" INVOLUTE. 
 
 Fig. 41. 
 
 The stiffening ribs and arms must all be joined to the rim by 
 ample fillets, and the cross-section must be as uniform as possible, 
 to prevent unequal cooling and consequent pulling-away of the 
 arms from the rim or hub. Often the calculated size of the arms 
 at both rim and hub has to be modified considerably to meet this 
 requirement. 
 
 The arms are usually tapered to suit the designer's eye, a 
 small gear requiring more taper per foot than a large one. Both 
 rim and hub should be tapered ^ inch per foot to permit easy 
 drawing-out from the mould. 
 
 The proportions given in the following table have been used 
 with success as a basis of gear design in manufacturing practice. 
 The table will serve as an excellent guide in laying out, and can be 
 closely followed, in most cases with but slight modification. 
 Web gears are introduced for small diameters where the arms begin 
 to look awkward and clumsy. 
 
 139
 
 120 
 
 MACHINE DESIGN 
 
 Gear Design Data. 
 
 Measurements given in inches. Letters refer to Fig. 42 
 
 Diametral pitch . . 
 
 P 
 
 1* 
 
 
 
 2 
 
 2i 
 
 3 
 
 Si 
 
 4 
 
 5 
 
 6 
 
 8 
 
 Face 
 
 F 
 
 
 51 
 
 
 3| 
 
 3V 
 
 2| 
 
 91 
 
 91 
 
 I? 
 
 U 
 
 
 
 
 
 
 
 
 
 
 
 d 
 
 a 
 
 Thickness of arm 
 \v h e n extended 
 to pitch line. . . . 
 
 G 
 
 If 
 
 u 
 
 
 1 
 
 7 
 
 u 
 
 s , 
 
 H 
 
 JS 
 
 8 
 
 A 
 
 Width of arm when 
 extended to 
 pitch line 
 
 c 
 
 4 
 
 ^ 
 
 3 
 
 2J 
 
 2J 
 
 2 
 
 li 
 
 1A 
 
 I 3 
 
 
 Thickness of rim . . 
 
 K 
 
 2| 
 
 2| 
 
 2J 
 
 11 
 
 H 
 
 If 
 
 H 
 
 1 
 
 3 
 
 1 
 
 Depth of rib 
 
 E 
 
 2 
 
 It 
 
 H 
 
 H 
 
 1 
 
 1 
 
 5 
 
 1 
 
 i 
 
 8 
 
 Thickness of web. 
 
 T 
 
 H 
 
 1 
 
 8 
 
 1 
 
 s 
 
 9 
 
 1 (J 
 
 4 
 
 A 
 
 8 
 
 "1 
 
 Number of arms, 6. 
 
 Give inside of rims and hub a draft of i inch per foot. 
 
 BEVEL GEARS. 
 
 NOTATION -The following notation is used throughout the chapter on Bevel Gears : 
 
 A = Apex distance at pitch element of 
 
 cone (inches). 
 A' = Apex distance at bottom element 
 
 of tooth (inches). 
 
 ]> = Angle of bottom of tooth (degrees). 
 C = Pitch angle (degrees). 
 D = Pitch diameter (inches). 
 E = Radius increment of gear (inches). 
 F =Face of gear (inches). 
 / ^Clearance at bottom (inches). 
 O = Angle of face (degrees). 
 H =Cutting angle (degrees). 
 K =Radius increment of pinion 
 
 (inches). 
 
 N = Number of teeth. 
 I^ 1 Formative number of teeth, or 
 
 the number corresponding to the 
 
 spur gear on which the outline of 
 
 toot h is made. 
 
 ANALYSIS. It is possible to consider bevel gears as the 
 general case of which spur gears are a special form. The pitch 
 
 O D=Outside diameter (inches). 
 
 P =Diamctral pitch related to pitch 
 
 diameter (teeth per inch). 
 Pi =Circular pitch measured on the 
 
 circumference of D (inches). 
 S = Working strength of material (Ibs. 
 
 per sq. in.). 
 s =Addendum, or height of tooth 
 
 above pitch line (inches). 
 +/= Depth of tooth below pitch line 
 
 (inches). 
 
 T =Anglo of top of tooth (degrees). 
 t =Thickness of tooth at pitch line 
 
 (inches). 
 
 W = Working load at pitch line (Ibs.). 
 y =Factor in "Lewis" formula. 
 
 140
 
 MACHINE DESIGN 
 
 127 
 
 surfaces of spur gears described above as cylinders, mathematically 
 considered, are cones whose vertices are infinitely distant, while 
 bevel gears likewise are based on pitch cones, but with a vertex at 
 some finite point, common to the mating pair. Hence, as we 
 might expect, the laws of tooth action are similar in bevel gears 
 to those in the case of spur gears. The profile of the tooth in the 
 former case, however, is based, not on the real radius of the pitch 
 cone, but on the radius of the normal cone ; and in the develop- 
 ment of the outline the latter is treated just as though it were the 
 radius of a spur gear. The tooth thus formed is wrapped back up- 
 on the normal cone face, and becomes the large end of the taper- 
 ing bevel-gear tooth (see Fig. 44). 
 
 Fig. 42. 
 
 The teeth of bevel gears, being simply projections with bases on 
 the pitch cones, have a varying cross-section decreasing toward the 
 vertex ; also a trapezoidal section of root, the latter section acting 
 as a beam section to resist the cantilever moment due to the tooth 
 load. 
 
 The arms inust, as in the case of spur gears, transmit the load 
 from the tooth to the shaft; in addition, the arms of a bevel gear 
 are subjected to a side thrust due to the wedging action of the 
 cones. Hence sidewise stiffness of the arms is more essential in 
 this type of gear than in the case of the spur gear. 
 
 THEORY. It is evident that the calculation of tooth strength 
 based on a trapezoidal section of root would be somewhat compli- 
 
 141
 
 128 
 
 MACHINE DESIGN 
 
 cated ; also that the trapezoid in most cases would be but little 
 different from a true rectangle. Hence the error will be but 
 slight if the average cross-section of the tooth be taken to repre- 
 sent its strength, and the calculation made accordingly. 
 
 142
 
 130 
 
 MACHINE DESIGN 
 
 Fitr. 45 shows a bevel-gear tooth with the averao-e cross-sec- 
 tion in dotted lines. For the purpose of calculation, the assump- 
 tion is made that the section A is carried the full length of the 
 face of the gear, and that the load which this average tooth must 
 carry is the calculated load at the pitch line of section A. This 
 is equivalent to saying that the strength of a bevel-gear tooth is 
 equal to that of a spur-gear tooth which has the same face, and a 
 section identical with that cut out by a plane at the middle of the 
 bevel tooth. The load, as in the case of the spur gear, should be 
 taken at the top of the tooth; and its magnitude can be con- 
 veniently calculated at tlie mean pitch radius of the bevel face, 
 without appreciable error. 
 
 This similarity to spur gears being borne 
 in mind, the calculation for strength needs no 
 further treatment. Once the average tooth is 
 assumed or found by layout, a strict following- 
 out of the methods pursued for spur-gear 
 teeth will bring consistent results. 
 
 The detail design of a pair of bevel gears 
 involves some trigonometrical computations 
 in order properly to dimension the drawing 
 for use in finishing the blanks and subse- 
 quently in cutting the teeth, or. in the case 
 of cast gears, in making the pattern. These 
 
 calculations, although simple, are yet apt to be tedious; and inac- 
 curacies are likely to creep in if a definite system of relations 
 be- not maintained. Hence the results of these calculations are 
 given below in condensed and reduced form. The deduction of 
 these formulae is a simple and interestincr exercise in trigonometry; 
 and it is urged that they be worked out by the student from the 
 figure, in which case he will feel greater confidence in their use. 
 
 Axes of Gears at 90 Degrees. 
 
 Use subscript 1 for gear; P for pinion. Letters refer to Fig. 44. 
 
 p-2L_ ? 
 
 - ]> - pi' 
 
 1 P' 
 
 - p ~ 77 ' 
 
 P' 7T 
 
 (70) 
 (71) 
 (72) 
 
 144
 
 MACHINE DESIGN 131 
 
 t P 1 TT 
 
 f - 10 ~ 20 ~ 20P' 
 tan C p = j^-; tan Ci = ^-- 
 
 (73) 
 (74) 
 
 tanT =-= N 
 
 (75) 
 
 tan B = jL+/ = 2.31^sm C 
 
 (76) 
 
 s +/ = A tan B = ^^ = (X3G8F'. 
 N 1 1 
 
 (77) 
 
 A = 2P sin C = 2P 1/Nl2 + N P 2 = ~2~ I 7 I>i 2 - 
 
 f D P 2. ( 78 ) 
 (79) 
 
 (80) 
 (81) 
 (82) 
 
 A cos B 2P cos B sin C ' 
 Gi = 90 - (Ci + T ) ; G P = 90 - (C p + T). 
 E = S cos Ci = S sin C P . 
 K = S cos Cp = S sin Ci. 
 
 PRACTICAL MODIFICATION. The practical requirements 
 to be met in transmission of power by bevel gears are the same as 
 for spur gears; but in the case of bevel gears even greater care is 
 necessary to provide stiffness, strength, true alignment, and rigid 
 supports. As far as the gears themselves are concerned, a long 
 face is desirable; but it is much more difficult to gain the ad- 
 vantage of its strength than in the case of spur gears, because full 
 bearing along the length of the tooth is hard to guarantee. 
 
 The rim usually requires a series of ribs running to the hub 
 to give required stiffness and strength against the side thrust which 
 is always present in a pair of bevel gears. Instead of arms, the 
 tendency of bevel -gear design, except for very large gears, is toward 
 a web on . account of the bette^ and more uniform connection 
 thereby secured between rim and hub. This web may be lightened 
 by a number of holes, so that the resultant effect is that of a num- 
 ber of wide and flat arms. 
 
 The hubs naturally have to be fully as long as those of spur 
 gears, because there is greater tendency to rock on the shaft, due 
 to the side thrust from the teeth, mentioned above. 
 
 The teeth on small gears are cut with rotary cutters, at least 
 two finishing cuts being necessary, one for each side of the taper- 
 ing tooth. The more accurate method is to plane the teeth on a 
 special gear planer, and this method is followed on all gears of 
 any considerable size. The practical requirement here is that no 
 portion of the hub shall project so as to interfere with the stroke 
 
 145
 
 i:!2 MACHINE DESIGN 
 
 of the planer tool. The requirements of gear planers vary some- 
 what in this regard. 
 
 Finally, after all that is possible has been done in the design 
 of the gear itself to render it suitable to withstand the varied 
 stresses, especial attention must be paid to the rigidity of the 
 supporting shafts and bearings. Bearings should always be close 
 up to the hubs of the gears, and, if possible the bearing for both 
 pinion and gear should be cast in the same piece. If this is not 
 done, the tendency of the separate bearings to get out of line and 
 destroy the full bearing of the teeth is difficult to control. Thrust 
 washers are desirable against the hubs of both pinion and gear; 
 also proper means of well lubricating the same. 
 
 "With these considerations carefully met, bevel gears are not 
 the bugbear of machine design that they are sometimes claimed 
 to be. The common reason why bevel gears cut and fail to work 
 smoothly, is that the gears and supports are not designed carefully 
 enough in relation to each other. This is also true of spur gears, 
 but the bevel gear will reveal imperfections in its design far the 
 more quickly of the two. 
 
 WORM AND WORM GEAR. 
 
 NOTATION The following notation is used throughout the chapter on Worm and 
 W^rni Gear: 
 
 I) Pitch diameter of gear (inches). I J 1 =Circular pitch = Pitch (if worm 
 
 K = Efficiency between worm shaft and thread (inches). 
 
 gear shaft (per cent). R = Radius of pitch circle of worm gear 
 
 f =Clearauce of tooth at bottom .^ (inches). 
 
 (inches). s = Addendum of tooth (inches). 
 
 / = Index of worm thread (1 for single' T = Twisting moment on gear shaft 
 
 2 for double, etc.). (inch-lbs.). 
 
 }j = Load of worm thread (inches). T xv =T\visting moment qn worm shaft 
 
 M = Revolutions of gear shaft per (inch-lbs.). 
 
 minute. t = Thickness of to'oth at pitch line 
 
 Mw = Revolutions of worm shaft per (inches). 
 
 minute. W =Load at pitch line (Ibs.). 
 X = Number of teeth i:i gear. 
 
 ANALYSIS. The simplest way of analyzing the case of the 
 worm and worm gear is to base it upon an ordinary screw 
 and nut. Take, for example, the lead screw of a common lathe. 
 The carriage carries a nut, through which the lead screw passes. 
 BV the rotation of the screw, the carriage, being constrained by the 
 guides to travel lengthwise of the ways, is moved. This motion 
 
 143
 
 MACHINE DESIGN 133 
 
 is, for a single -threaded screw, a distance per revolution equal to 
 the lead of the screw. 
 
 Now, suppose that the carriage, instead of sliding along the 
 ways, is compelled to turn about an axis at some point below the 
 ways. Also, suppose the top of the nut to be cut off, and its length 
 made endless by wrapping it around a circle struck from the center 
 about which the carriage rotates. This reduces the nut to a 
 peculiar kind of spur gear, the partial threads of the nut now 
 having the appearance of twisted teeth. 
 
 This special form of spur gear, based on tne idea of a threaded 
 nut, is known as a worm gear, and the screw is termed a worm. 
 The teeth are loaded similarly to those of a spur gear, but with the 
 additional feature of a large amount of sliding along the tooth 
 surfaces. This, of course, means considerable friction; and it is in 
 fact possible to utilize the worm and worm gear as an efficient 
 device, only by running the teeth constantly in a bath of oil. 
 Even then the pressures have to be kept well down to insure the 
 required term of life of the tooth surfaces. 
 
 It is evident that for one revolution of a single-threaded worm, 
 one tooth of the gear will be passed. The speed ratio between the 
 worm gear and worm shaft will then be equal to the number of 
 teeth in the gear, which is relatively great. Hence the worm and 
 worm gear are principally useful in giving large speed reduction 
 in a small amount of space. 
 
 THEORY. The theory of worm-wheel teeth is complicated 
 and obscure. The production of the teeth is simple, a dummy worm 
 with cutting edges, called a "hob," being allowed to carve its way 
 into the worm-gear blank, thus producing the teeth and at the 
 same time driving the worm gear about its axis. 
 
 It is clear that if we know the torsional moment on the worm- 
 gear shaft, and the pitch radius of the worm gear, we can find the 
 load on the teeth at the pitch line by dividing the former by the 
 latter. Expressed as an equation: 
 
 WR = T;orW=^-. (83) 
 
 How we shall consider this value of W as distributed on the 
 teeth, is a question difficult to answer. The teeth not only are 
 
 147
 
 184 MACHINE DESIGN 
 
 Curved to embrace the worm, but are twisted across the face of the 
 gear, so that it would be practically impossible to devise a purely 
 theoretical method of exact calculation. The most reasonable thing 
 to do is to assume the teeth as being equally as strong as spur-gear 
 teeth of the same circular pitch, and to figure them accordingly. 
 It is probably true, however, that the load is carried by more than 
 one tooth, especially in a hobbed wheel; so we shall be safe in 
 assuming that two and, in case of large wheels, three teeth 
 divide the load between them. "With these considerations borne 
 in mind, the case reduces itself to that of a simple spur-gear 
 tooth calculation, which has already been explained under the 
 heading "Spur Gears." 
 
 The worm teeth, or threads, are probably always stronger than 
 the worm-gear teeth; so no calculation for their strength need be 
 made. 
 
 The twisting moment on the worm shaft is not determined so 
 directly as in the case of spur gears. The relative number of 
 revolutions of the two shafts depends upon the " lead " of the 
 worm thread and the number of teeth in the gear. 
 
 Lead ( L ) is the distance parallel to the axis of the worm which 
 any point in the thread advances in one revolution of the worm. 
 Pitch (P 1 ) is the distance parallel to the axis of the worm between 
 corresponding points on adjacent threads. The distinction between 
 lead and pitch should be carefully observed, as the two are often 
 confounded, one with the other. 
 
 The thread may be single, double, triple, etc., the index of the 
 thread /', being 1, 2, 3, etc., in accordance therewith. The relation 
 between lead and pitch may then be expressed by an equation, thus: 
 
 L = I P. (84) 
 
 "When the index of the thread is changed the speed ratio is 
 changed, the relation being shown by the equation: 
 
 - <*> 
 
 If the efficiency were 100 per cent- between the two shafts, 
 the twisting moments would be inversely as the ratio of the speeds 
 thus: 
 
 148
 
 MACHINE DESIGN 135 
 
 M 
 
 T w = ; (86) 
 
 but for an efficiency E the equation would be: 
 T i 
 
 T - 
 
 The diameter of the worm is arbitrary. Change of thie 
 diameter has no effect on the speed ratio. It has a slight effect OL 
 the efficiency, the smaller worm giving a little higher efficiency. 
 The diameter of the worm runs ordinarily from 3 to 10 times the 
 circular pitch, an average value being 4P 1 or 5P 1 . 
 
 A longitudinal cross-section through the axis of the worm 
 cuts out a rack tooth, and this tooth section is usually made of the 
 standard 14^ involute form shown in Fig. 46 for a rack. 
 
 The end thrust, of a mag- 
 nitude practically equal to the 
 pressure between the teeth, 
 has to be taken by the hub of 
 the worm against the face of 
 'the shaft bearing. A serious 
 loss of efficiency from friction Fig. 46. 
 
 is likely to occur here. This 
 
 is often reduced, however, by roller or ball bearings. With two 
 worms on the same shaft, each driving into a separate worm gear, 
 it is possible to make one of the worms right-hand thread, and 
 the other left-hand, in which case the thrust is self-contained in 
 the shaft itself, and there is absolutely no end thrust against the 
 face of the bearing. This involves a double outfit throughout, and 
 is not always practicable. 
 
 There are few mathematical equations necessary for the dimen- 
 sioning of a worm and worm gear. The formulae for the tooth 
 parts as given on page 120 apply equally well in this case. 
 
 PRACTICAL MODIFICATION. The discussion of the effi- 
 ciency E of the worm and worm gear is more of a practical than 
 
 149
 
 130 MACHINE DESIGN 
 
 of a theoretical nature. It seems to be true from actual operation, 
 as well as theory, that the steeper the threads the higher the effi- 
 ciency. In actual practice we seldom have opportunity to change 
 the slope of the thread to get increased efficiency. The slope 
 is usually settled from considerations of speed ratio, or available 
 space, or some other condition. The usual practical problem is to 
 take a given worm and worm gear, and to make out of it as efficient 
 a device as possible. With hobbed gears running in oil baths, and 
 with moderate pressures and speeds, the efficiency will range between 
 40 per cent and 70 per cent. The latter figure is higher than is 
 usually attained. 
 
 To avoid cutting and to secure high efficiency, it seems es- 
 sential to make the worm and the gear of different materials. 
 The worm-thread surfaces being in contact a greater number of 
 times than the gear teeth, should evidently be of the harder material. 
 Hence we usually find the worm of steel, and the gear of cast iron, 
 brass, or bronze. To save the expense of a large and heavy bronze 
 gear, it is common to make a cast-iron center and bolt a bronze 
 rim to it. 
 
 The worm, being the most liable to replacement from wear, 
 it is desirable so to arrange its shaft fastening and general acces- 
 sibility that it may be readily removed without disturbing the 
 worm gear. 
 
 The circular pitch of the gear and the pitch of the worm 
 thread must be the same, and the practical question comes in as to 
 the threads per inch possible to be cut in the lathe in the pro- 
 duction of the worm thread. The pitch must satisfy this require- 
 ment; hence the pitch will usually be fractional, and the diameter 
 of the worm gear, to give the necessary number of teeth, must be 
 brought to it. While it would perhaps be desirable to keep an 
 even diametral pitch for the worm gear, yet it would be poor de- 
 sign to specify a worm thread which could not be cut in a lathe. 
 
 The standard involute of 1-44, and the standard proportions 
 of teeth as given on page 120 are usually used for worm threads. 
 This system requires the gear to have at least 30 teeth, for if fewer 
 teeth are used the thread of the worm will interfere with the 
 flanks of the gear teeth. This is a mathematical relation, and 
 there are methods of preventing it by change of tooth proportions 
 
 150
 
 MACHINE DESIGN 137 
 
 
 
 or of angle of worm thread ; but there are few instances in which 
 less than 30 teeth are required, and it is not deemed worth while 
 to go into a lengthy discussion of this point. 
 
 The angle of the worm embraced by the worm-gear teeth 
 varies from 60 to 90, and the general dimensions of rim are made 
 about the same as for spur gears. The arms, or the web, have the 
 same reasons for their size and shape. Probably web gears and 
 cross-shaped arms are more common than oval or elliptical sections. 
 
 Worm gears sometimes have cast teeth, but they are for the 
 roughest service only, and give but a point bearing at the middle 
 of the tooth. An accurately hobbed worm gear will give a bearing 
 clear across the face of the tooth, and, if properly set up and cared 
 for, makes a good mechanical device although admittedly of some- 
 what low efficiency. 
 
 Fig. 47 shows a detail drawing of a standard worm and worm 
 gear. It should serve as a suggestion in design, and an illustration 
 of the shop dimensions required for its production. 
 
 PROBLEMS ON SPUR, BEVEL, AND WORM GEARS. 
 
 1. Calculate proportions of a standard Brown & Sharpe 
 gear tooth of 1^ diametral pitch, making a rough sketch and put- 
 ting the dimensions on it. 
 
 2. Suppose the above tooth to be loaded at the top with 
 5,000 Ibs. If the face be 6 inches, calculate the fiber stress at the 
 pitch line, due to bending. 
 
 3. A tooth load of 1,200 Ibs. is transmitted between two 
 spur gears of 12-inch and 30-inch diameter, the latter gear making 
 100 revolutions per minute. Calculate a suitable pitch and face 
 of tooth by the " Lewis " formula. 
 
 4. Assuming a ^-inch web on the 12-inch gear, calculate the 
 shearing fiber stress at the outside of a hub 4 inches in diameter 
 
 5. Design elliptical arms for the 30-inch gear, allowing 
 S = 2,200. 
 
 6. Design cross-shaped arms for 30-inch gear. 
 
 7. Calculate the dimensions shown in formulae 70 to 82 in- 
 clusive for a pair of bevel gears of 20 and 60 teeth respectively, 2 
 diametral pitch, and 4-inch face. (The use of logarithmic tables 
 makes the calculation much easier than with the natural functions.) 
 
 151
 
 MACHINE DESIGN 
 
 139 
 
 8. A worm wheel has 40 teeth, 3 diametral pitch, and double 
 thread. Calculate (#) its lead; () its pitch diameter. 
 
 FRICTION CLUTCHES. 
 
 DOTATION The following notation is used throughout the chapter on Friction Clutches : . 
 
 a = Angle between clutch face 
 and axis of shaft (degrees) 
 
 H =Horse-power (33jOOO ft.-lbs. 
 per minute). 
 
 ]JL = Coefficient of friction (per 
 cent). 
 
 N ^Number of revolutions per 
 minute. 
 
 P = Force to hold clutch in gear 
 to produce W (Ibs.). 
 
 R =Mean radius of friction sur- 
 face (inches). 
 
 T =Twisting moment about 
 shaft axis (inch-lbs.). 
 
 V = Force normal to clutch face 
 (Ibs.). 
 
 W=Load at mean radius of 
 friction surface (Ibs.). 
 
 ANALYSIS. The 
 
 friction clutch is a de- 
 vice for connecting at 
 oo will two separate pieces 
 of shaft, transmitting an 
 amount of power be- 
 tween them to the capac- 
 ity of the clutch. The 
 connection is usually ac- 
 complished while the 
 driving shaft is under 
 full speed, the slipping 
 bet /een the surfaces 
 which occurs during the 
 throwing-in of the 
 clutch, permitting the 
 driven shaft to pick up 
 the speed of the other 
 gradually, without ap- 
 preciable shock. The 
 disconnection is made in 
 the same manner, the 
 
 153
 
 140 
 
 MACHINE DESIGN 
 
 amount of slipping which occurs depending on the suddenness with 
 which the clutch is thrown out. 
 
 The force of friction is the sole driving element, hence the 
 
 problem is to secure as 
 large a force of friction 
 as possible. But friction 
 cannot be secured with- 
 out a heavy normal pres- 
 sure between surfaces 
 having a high coefficient 
 of friction between them. 
 The many varieties of 
 friction clutches which 
 are on the market or de- 
 signed for some special 
 purpose, are all devices 
 for accomplishing one 
 and the same effect, vis., 
 the production of a heavy 
 normal force or pressure 
 between surfaces at such 
 a radius from the driven 
 axis, that the product of 
 the force of friction 
 thereby created and the 
 radius shall equal the 
 desired twisting moment 
 about that axis. 
 
 Three typical meth- 
 odsof accomplishing this 
 are shown in Figs. 48, 
 49, and 50. None of 
 these drawings is worked 
 out in operative detail. 
 They are merely illus- 
 trations of principle, and are drawn in the simplest form for that 
 purpose. 
 
 In Eig. 48 the normal pressure is created in the simplest pos- 
 
 154
 
 MACHINE DESIGN 
 
 141 
 
 sible way, an absolutely direct push being exerted between the 
 discs, due to the thrust P of the clutch fork. 
 
 In Fig. 49 advantage is taken of the wedge action of the in- 
 clined faces, the result be- 
 ing that it takes less thrust 
 P to produce the required 
 normal pressure at the ra- 
 dius II. 
 
 In Fig. 50 the inclin- 
 ation of the faces is carried 
 so far that the angle a of 
 Fig. 49 has become zero; 
 and by the toggle-joint ac- 
 tion of the link pivoted to 
 the clutch collar, the nor- 
 mal force produced may .be 
 very great for a slight thrust 
 P. By careful adjustment 
 of the length of the link so 
 that the jaw. takes hold of 
 the clutch surface, when 
 the link stands nearly ver- 
 tical, a very easy operating 
 device is secured, and the 
 thrust P is made a mini- 
 mum. 
 
 THEORY. Referring 
 to Fig. 48 in order to cal- 
 culate the twisting mo- 
 ment, we must remember 
 that the force of friction 
 between two surfaces is 
 equal to the normal pres- 
 sure times the coefficient of 
 friction. This, in the form 
 of an equation, using the symbols of the figure, is : 
 
 W = p P. (88) 
 
 155
 
 142 MACHINE DESIGN 
 
 Hence we may consider that we have a force of magnitude ftP 
 acting at the mean radius II of the clutch surface. The twisting 
 moment will then be : 
 
 T = AVR = /xPR. (89) 
 
 Referring to equation 54, which gives twisting moment in terms 
 of horse-power, and putting the two expressions equal to each other, 
 we have : 
 
 This expression gives at once the horse-power that the clutch will 
 transmit with a given end thrust P. 
 
 In Fig. 49 the equilibrium of the forces is shown in the little 
 sketch at the left of the figure. The clutch faces are supposed 
 to be in gear, and the extra force necessary to slide the two to- 
 gether is not considered, as it is of small importance. The static 
 equations then are : 
 
 P = 2 sin a ; 
 
 or, Y P cosec a. (90 
 
 TV = /jiV = pP cosec a. (92) 
 
 T = TVR = ^PR cosec a. (93) 
 
 H = (94) 
 
 In Fig. 50, P would of course be variable, depending on the 
 inclination of the little link. The amount of horse-power which 
 this clutch would transmit would be the same as in the case of the 
 device illustrated in Fig. 49, for an equal normal force Y produced. 
 
 The further theoretical design of such clutches should be in 
 
 O 
 
 accordance with the same principles as for arms and webs of 
 pulleys, gears, etc. The length of the hubs must be liberal in 
 
 156
 
 MACHINE DESIGK U3 
 
 order to prevent tipping on tlie shaft as a result of uneven wear. 
 The end thrust is apt to be considerable; and extra side stiffness 
 must be provided, as well as a rim that will not spring under the 
 radial pressure. 
 
 PRACTICAL HODIFICATION. It is desirable to make the 
 most complicated part of a friction clutch the driven part, for then 
 the mechanism requiring the closest attention and adjustment may 
 be brought to and kept at rest when no transmission of power is 
 desired. 
 
 Simplicity is an important practical requirement in clutches. 
 The wearing, surfaces are subjected to severe usage; and it is 
 essential that they be made not only strong in the first place, but 
 also capable of being readily replaced when worn out, as they are 
 sure to be after some service. 
 
 The form of clutch shown in Fig. 50 is the most efficient 
 form of the three shown, although its commercial design is consid- 
 erably different from that indicated. Usually the jaws grip both 
 sides of the rim, pinching it between them. This relieves the 
 clutch rim of the radial unbalanced thrust. 
 
 Adjusting screws must be provided for taking up the wear, 
 and lock nuts for maintaining their position. 
 
 Theoretically, the rubbing surfaces should be of those materials 
 whose coefficient of friction is the highest; but the practical ques- 
 tion of wear comes in, and hence we usually find both surfaces of 
 metal, cast iron being most common. For metal on metal the 
 coefficient of friction JJL cannot be safely assumed at more than 15 
 per cent, because the surfaces are sure to get oily. 
 
 A leather facing on one of the surfaces gives good results as 
 to coefficient of friction, p. having a value, even for oily leather, of 
 20 per cent. Much slipping, however, is apt to burn the leather; 
 and this is most likely to occur at high speeds. 
 
 Wood on cast iron gives a little higher coefficient of friction 
 for an oily surface than metal on metal. Wood blocks can be so 
 set into the face of the jaws as to be readily replaced when worn, 
 and in such case make an excellent facing. 
 
 The angle a of a cone friction clutch of the type shown in 
 Fig. 49, may evidently be made so small that the two parts will 
 wedge together tightly with a very slight pressure P; or it may 
 
 157
 
 144 
 
 MACHINE DESIGN 
 
 158
 
 MACHINE DESIGN 145 
 
 be so large as to have little wedging action, and approach the con- 
 dition illustrated in Fig. 48. Between these limits there is a 
 practical value which neither gives a wedging action so great as to 
 make the surfaces difficult to pull apart, nor, on the other hand, 
 requires an objectionable end thrust along the shaft in order to 
 make the clutch drive properly. 
 
 For a = about 15, the surfaces will free themselves whenP is relieved. 
 " a = " 12, " " require slight pull to be freed. 
 " a = " 10, " " cannot be freed by direct pull of the 
 hand, but require some leverage to produce the necessary force P. 
 
 PROBLEMS ON FRICTION CLUTCHES. 
 
 1. With what force must we hold a friction clutch in to 
 transmit 30 horse-power at 200 revolutions per minute, assuming 
 working radius of clutch to be 12 inches; coefficient of friction 15 
 per cent; angle a =10 ? 
 
 2. How much horse-power could be transmitted, other con- 
 ditions remaining the same, if the working radius were increased 
 to 18 inches ? 
 
 3. What force would be necessary in problem 1, if the angle 
 a were 15, other conditions remaining the same ? 
 
 COUPLINGS. 
 
 DOTATION. The following notation is used throughout the chapter on Couplings: 
 
 D = Diameter of shaft (inches). Sc =Safe crushing fiber stress (Ibs. per 
 d =Diameter of bolt body (inches). sq. in.). 
 
 n = Number of bolts. T =Twisting moment (inch-lbs.). 
 R = Radius of bolt circle (inches). <=Thickness of flange (inches). 
 
 S =Safe shearing fiber stress (Ibs. per W =Load on bolts (Ibs.). 
 sq. in.). 
 
 ANALYSIS. Kigid couplings, are intended to make the 
 shafts which they connect act as a solid, continuous shaft. In 
 order that the shaft may be worked up to its full strength capac- 
 ity, the coupling must be as strong in all respects as the shaft, 
 or, in other words, it must transmit the same torsional moment. 
 In the analysis of the forces which come upon these couplings, it 
 is not considered that they are to take any side load, but thr.t they 
 are to act purely as torsional elements. It is doubtless true that in 
 many cases they do have to provide some side strength and stiff- 
 ness, but this is not their natural function, nor the one upon which 
 their design is based. 
 
 159
 
 146 MACHINE DESIGN 
 
 Referring to Fig. 51, which is the type most convenient for 
 analysis, we have an example of the simplest form of flange coup- 
 ling. It consists merely of hubs keyed to the two portions, with 
 flanges driving through shear on a series of bolts arranged con- 
 centrically about the shaft. The hubs, keys, and tlanges are sub- 
 ]ect- to the same conditions of design as the hubs, keys, and web of 
 a gear or pulley, the key tending to shear and be crushed in the 
 hub and shaft, and the hub tending to be torn or sheared from the 
 flange. The driving bolts, which must be carefully fitted in 
 reamed holes, are subject to a purely shearing stress over their full 
 area at the joint, and at the same time tend to crush the metal in 
 the flange, against which they bear, over their projected area. 
 This latter stress is seldom of importance, the thickness of the 
 flange, for practical reasons, being sufficient to make the crushing 
 stress very low. 
 
 THEORY. The theory of hubs, keys, and flanges, being like 
 that already given for pulleys and gears, need not be repeated for 
 couplings. The shearing stress on the bolts is the only new point 
 to be studied. 
 
 In Fig. 51, for a twisting moment on the shaft of T, the load 
 
 T 
 
 at the bolt circle is ~\Y = - r . If the number of bolts be;/. 
 it 
 
 equating the external force to the internal strength, we have: 
 
 T S77Y/ 2 
 
 Although the crushing will seldom be of importance, yet for 
 the sake of completeness its equation is given, thus: 
 
 W= ^- =Sc(?tn. (96) 
 
 The internal moment of resistance of the shaft is ^- ; 
 
 0.1 
 
 hence the equation representing full equality of strength between 
 the shaft and the coupling, depending upon the shearing strength 
 cf the bolts, is: 
 
 SD 3 fern/ 2 
 
 160
 
 MACHINE DESIGN 
 
 147 
 
 The theory of the other types of couplings is obscure, except 
 as regards the proportions of the key, which are the same in all 
 cases. The shell of the clamp coupling, Fig. 52, should be thick 
 enough to give equal torsional strength with the shaft; but the 
 exact function which the bolts perform is difficult to determine. 
 In general the bolts clamp the coupling tightly on the shaft and 
 provide rigidity, but the key does the principal amount of the 
 driving. The bolt sizes, in these couplings, are based on judgment 
 and relation to surrounding parts, rather than on theory. 
 
 PRACTICAL HODIFICATION. All couplings must be made 
 with care and nicely fitted, for their tendency, otherwise, is to 
 
 Fig. 52. 
 
 spring the shafts out of line. In the case of the flange coupling, 
 the two halves may be keyed in place on the shafts, the latter then 
 swung on centers in the lathe, and the joint faced off. Thus the 
 joint will be true to the axis of the shaft; and, when it is clamped 
 in position by the bolts, no springing out of line can take place. 
 
 A flange F (see Fig. 51) is sometimes made on this form of 
 coupling, in order to guard the bolts. It may be used, also, to take 
 a light belt for driving machinery; but a side load is thereby thrown 
 on the shaft at the joint, which is at the very point where it is desir- 
 able to avoid it. 
 
 The simplest form of rigid coupling consists of a plain sleeve 
 slipped over from one shaft to the other, when the second is butted 
 up against the first. This is known as a muff coupling. When 
 'once in place, this is a very excellent coupling, as it is perfectly 
 smooth on the outside, and consists of the fewest possible parts, 
 merely a sleeve and a key. It is, however, expensive to fi, 
 
 161
 
 148 
 
 MACHINE DESIGN 
 
 difficult to remove, and requires an extra space of half its length 
 on the shaft over which to be slipped back. 
 
 The clamp coupling is a good coupling for moderate- sized 
 shafts, where the flange type of Fig. 51 would be unnecessarily 
 expensive. The clam p coupling, Fig. 52, is simply a muff coupling 
 split in halves, and recessed for bolts. It is cheap and is easily 
 applied and removed, even with a crowded shaft. If bored with a 
 piece of paper in the joint, when it is clamped in position it will 
 
 iiinch the shaft tiditly and make a rkml connection. It is desir- 
 
 i o J f-> 
 
 able to have the bolt-heads protected as much as possible, and this 
 mav be accomplished by making the outside diameter lame enough 
 
 I J O 7"^ O 
 
 so that the bolts will not project. Often an additional shell is 
 provided to encase the coupling completely after it is located. 
 
 n 
 
 Fig. 53. 
 
 There are many other special forms of couplings, some of 
 them adjustable. Most of them depend upon a wedging action 
 -xerte^d by taper cones, screws, or keys. Trade catalogues are to 
 be sought for their description. 
 
 The claw coupling, Fig. 53, is nothing but a heavy flange 
 coupling with interlocking claws or jaws on the faces of the flano-es, 
 to take the place of the driving bolts. This coupling can be thrown 
 in or out as desired, although it usually performs the service of a 
 rigid coupling, as it is not suited toclutching-in during rapid mo- 
 tion, like a friction clutch. 
 
 Flexible couplings, which allow slight lack of alignment, are 
 made by introducing between the flanges of a coupling a flexible 
 disc, the one flange being fastened to the inner circle of the disc, 
 the other to the outer circle. This is also accomplished by pro- 
 viding the faces of the flange coupling with pins that drive by 
 
 162
 
 MACHINE DESIGN 
 
 149 
 
 pressure together or through leather straps wrapped round the 
 pins. These devices are mostly of a special and often uncertain 
 nature, lacking the positiveness which is one essential feature 
 of a good coupling. 
 
 PROBLEMS ON COUPLINGS. 
 
 1. A flange coupling of the type of Fig. 51 is used on a shaft 
 2 inches is diameter. The hub is 3 inches long, and carries a 
 standard key, of proportions indicated below in the table of "Pro- 
 portions for Gib Keys" (page 106). The bolt circle is 7 inches 
 in diameter, and it is desired to use |-inch bolts. How many 
 bolts are needed to transmit 60,000 inch-lbs., for a fiber stress in 
 the bolt of 6,000 ? 
 
 2. Using 6 bolts, what diameter of bolt would be required ? 
 
 3. If four |-inch bolts were used on a circle of 8 inches di- 
 ameter, what diameter of shaft would be used in the coupling to 
 give equal strength with the bolts ? 
 
 BOLTS, STUDS, NUTS, AND SCREWS. 
 
 NOTATION The following notation is used throughout the chapter on Bolts, Studs, 
 Nuts, and Screws: 
 
 d = Diameter of bolt (inches). 
 
 di = Diameter at root of thread (in- 
 ches). 
 
 H = Height of nut (inches). 
 
 I = Initial axial tension (Ibs.). 
 
 k = Allowable bearing pressure on sur- 
 face of thread (Ibs, per sq. in.). 
 
 L = Lead, or distance nut advances 
 along axis in one revolution 
 (inches). 
 
 I = Length of wrench handle (inches) 
 
 B 
 n = Number of threads in nut= -. 
 
 P = Axial load (Ibs.). 
 
 ;; = Pitch of thread, or distance be- 
 tween similar points on adjacent 
 threads, measured parallel to 
 axis (inches). 
 
 S = Fiber stress (Ibs. per sq. in.). 
 
 W = Load on bolt (Ibs.). 
 
 Fig. 54. 
 
 ANALYSIS. A bolt is simply a cylindrical bar of metal 
 upset at one end to form a head, and having a thread at the other 
 end, Fig. 54. A stud is a bolt in which the head is replaced by 
 a thread; or it is a cylindrical bar threaded at both ends, usually 
 
 163
 
 150 
 
 MACHINE DESIGN 
 
 having a small plain portion in the middle, Fig. 55. The object 
 of bolts and studs is to clamp machine parts together, and yet 
 permit these same parts to be readily disconnected. The bolt 
 passes through the pieces to be connected, and, when tightened, 
 causes surface compression between the parts, while the reactions 
 on the head and nut produce tension in the bolt. Studs and tap 
 bolts pass through one of the connected parts and are screwed 
 into the other, the stud remaining in position when the parts are 
 disconnected. 
 
 As all materials are elastic within certain limits, the action of 
 
 Fie. 55. 
 
 Fig. 55. 
 
 a bolt in clamping two machine parts together, more especially if 
 there is an elastic packing between them, may be represented 
 diagrammatically by Fig. 50, in which a spring has been introduced 
 to take the compression due to screwing up the nut. Evidently 
 the tension in the bolt is equal to the force necessary to compress 
 the spring. Now, suppose that two weights, each equal to i W, 
 are placed symmetrically on either side of the bolt, then the tension 
 in the bolt will be increased by the added weights if the bolt is 
 perfectly rigid. The bolt, however, stretches; hence some of the 
 compression on the spring is relieved and the total tension in the 
 
 164
 
 MACHINE DESIGN 
 
 151 
 
 bolt is less than W + I, by an amount depending on the relative 
 elasticity of the bolt and spring. 
 
 Suppose that the stud in Fig. 55 is one of the studs connect- 
 ing the cover to the cylinder of a steam engine, and that the studs 
 have a small initial tension; then the pressure of the steam loads 
 each stud, and, if the studs stretch enough to relieve the initial 
 pressure between the two surfaces, then their stress is due to the 
 steam pressure only; or, from Fig. 56, when I = W ; the initial 
 pressure due to the elasticity of the joint is entirely relieved by the 
 assumed stretch of the studs. Except to prevent leakage, it is 
 seldom necessary to consider the initial tension, for the stretch 
 of the bolt may be counted on to relieve 
 this force, and the working tension on the 
 bolt is simply the load applied. 
 
 For shocks or blows, as in the case 
 of the bolts found on the marine type of 
 connecting-rod end, the stretch of the 
 bolts acts like a spring to reduce the re- 
 sulting tensions. So important is this 
 feature that the body of the bolt is fre- 
 quently turned down to the diameter of 
 the bottom of the thread, thus uniformly 
 distributing the stretch through the full 
 length of the bolt, instead of localizing it 
 at the threaded parts. 
 
 In tightening up a bolt, the friction 
 at the surface of the thread produces a twisting moment, which 
 increases the stress in the bolts, just as in the case of shafting 
 under combined tension and torsion; but the increase is small in 
 amount, and may readily be taken care of by permitting low values 
 only for the fiber stress. 
 
 In a flange coupling, bolts are acted upon by forces perpen- 
 dicular to the axis, and hence are under pure shearing stress. If 
 the torque on the shaft becomes too great, failure will occur by 
 the bolts shearing off at the joint of the coupling. 
 
 A bolt under tension communicates its load to the nut through 
 the locking of the threads together. If the nut is thin, and the 
 number of threads to take the load few, the threads may break or 
 
 Fig. 56. 
 
 165
 
 ID 2 MACHINE DESIGN 
 
 shear off at the root. "With a V thread there is produced a com- 
 ponent force, perpendicular to the axis of the bolt, which tends to 
 split the nut. 
 
 In screws for continuous transmission of motion and power. 
 the thread may be compared to a rough inclined plane, on which a 
 small block, the nut, is being pushed upward by a force parallel to 
 the base of the plane. The angle at the bottom of the plane is the 
 angle of the helix, or an angle whose tangent is the lead divided 
 by the circumference of the screw. The horizontal force corre- 
 sponds to the tangential force on the screw. The friction at the 
 surface of the thread produces a twisting moment about the axis of 
 the screw, which, combined with the axial load, subjects the screw 
 to combined tension and torsion. Screws with square threads are 
 generally used for this service, the sides of the thread exerting no 
 bursting pressure on the nut. The proportions of screw thread 
 for transmission of power depend more on the bearing pressure 
 than on strength. If the bearing surface be too small and lubrica- 
 tion poor, the screw will cut and wear rapidly. 
 
 THEORY. A direct tensile stress is induced in a bolt when 
 it carries a load exerted along its axis. This load must be taken 
 by the section of the bolt at the bottom of the thread. If the area 
 
 at the root of the thread is - , and if S is the allowable stress 
 
 per square inch, then the internal resistance of the bolt is 
 
 T ' ' . Equating the external load to the internal strength we have: 
 
 . (98) 
 
 For bolts which are used to clamp two machine parts together 
 so that they will not separate under the action of an applied load, 
 the initial tension of the bolt must be at least equal to the applied 
 load. If the applied load is "W, then the parts are just about to 
 separate when I = "W. Therefore the above relation for strength 
 is applicable. As the initial tension to prevent separation should 
 be a little greater than "W, a value of S should be chosen so that. 
 there will be a margin of safety. For ordinary wrought iron and 
 steel, S may be taken at 6,000 to 8,000. 
 
 166
 
 MACHINE DESIGN 
 
 153 
 
 If, however, the joints must be such that there is no leakage 
 between the surfaces, as in the case of a steam cylinder head, and 
 supposing that elastic packings are placed in the joints, then a 
 much larger margin should be made, for the maximum load which 
 may come on the bolt is I -f- W, where "YV is the proportional 
 share of the internal pressure carried by the bolt. In such cases 
 S = 3,000 to 5,000, using the lower value for bolts of less than 
 |-inch diameter,. - 
 
 The table given on page 154 will be found very useful in pro- 
 portioning bolts with U. S. standard thread for any desired fiber 
 stress. 
 
 To find the initial tension due to screwing up the nut, we 
 
 Fig. 56a. 
 
 may assume the length of the handle of an ordinary wrench, meas- 
 ured from the center of ths bolt, as about 16 times the diameter 
 of the bolt. For one turn of the wrench a force F at the handle 
 would pass over a distance 2irl, and the work done is equal to the 
 product of the force and space, or F X %Trl. At the same time 
 the axial load P would be moved a distance p along the axis. 
 Assuming that there is no friction, the equation for the equality 
 of the work at the handle and at the screw is: 
 
 F27T/ = 
 
 (99) 
 
 Friction, however, is always present; hence the ratio of the useful 
 work (Pp) to the work applied (F2irl) is not unity as above re- 
 
 167
 
 nt -bs and j 
 *ai ooo'i 
 
 IV 
 
 a -tit -bs .tod ! g g -2 S 3 
 
 C ! qy oor-.-i.-r.r.*t;: 
 
 -' ~ '' '* - - - ?; s s s s rt x = r> J 2 if z- '^ '? H '^ z .V & - '^ 1 1- i r 
 
 ; 
 
 u\ -bs .tod S 3 ?5 Sc S S 
 
 IV "" "" u 
 
 
 tit -bs uod , g,~SSe 
 
 la? 
 
 ut 'Tjs .tod x i-Si^S 
 
 H S ^ 
 
 s<i i ooo'i ---* r r: r, ?; 5 = ;;-: t -2 g s --, ^ -- i r-- 4! x -^ f, s' g -. | g = g |r 
 IV 
 
 Isl 
 
 tn -bs .tod S <"' = S S -2 3 
 
 |l| 
 
 tit -bs .tad VlS So 2 3 
 
 K 
 
 sai ooo'S ; ~ - 1 K - x - - o s K = 5 = '- .7! x ^ _- :- : g :-. ' -r :t p- i: -; .--: 
 IV ' ""- 
 
 < 
 
 t,t-bsaod SSrrSiiHs 
 
 
 5V 
 
 
 PIX 
 
 .y 
 
 jo uionofl _-"_-: ri^i re ---'.-'^i-x^-'ri-^^rt 
 
 < 
 
 
 < 
 
 r- ^-^-^^rKKSiiSSSSKSsHK 
 
 
 */-* VAV^VA'^M 
 
 qout .tsd 
 
 ^ CI vsi ~: xct 
 
 168
 
 MACHINE DESIGN 
 
 155 
 
 lations assume. From numerous experiments on the frict'on of 
 screws and nuts, it has been found that the efficiency may be as 
 low as 10 per cent. Introducing the efficiency in above equation, 
 it may be written: 
 
 ?p 1 
 
 TO HF (IOO) 
 
 Assuming that 50- pounds is exerted by a workman in 
 
 Fig. 58. 
 
 tightening up the nut on a 1-inch bolt, the equation above shows 
 that P = 4,021 pounds; or the initial tension is somewhat less 
 than the tabular safe load shown for a 1-inch bolt, with S assumed 
 at 10,000 pounds per sq. inch. 
 
 For shearing stresses the bolt should be fitted so that the body 
 of the bolt, not the threads, resists the force tending to shear off 
 the bolt perpendicular to its axis. The internal strength of the 
 bolt to resist shear is the allowable stress S times the area of the 
 
 bolt in shear, or - If W represents the external force tending 
 
 to shear the bolt the equality of the external force to the internal 
 strength is : 
 
 w=*5. (,oi) 
 
 169
 
 150 MACHINE DESIGN 
 
 Reference to the table on page 154 for the shearing strength of 
 holts, may be made to save the labor of calculations. 
 
 Let Fig. 58 represent a square thread screw for the transmis- 
 sion of motion. The surface on which the axial pressure bears, if 
 
 // is the number of threads in a nut, is (<7 2 <l\\ it. Suppose 
 
 that a pressure of /' pounds per square inch is allowed on the 
 surface of the thread. Then the greatest permissible axial load 1* 
 must not exceed the allowable pressure; or, equating, 
 
 P = I- _ (<P - ^) n (102) 
 
 The value of 1\' varies with the service required. If the motion be 
 slow and the lubrication very good, k may be as high as 900. For 
 rapid motion and doubtful lubrication, k may not be over 200. 
 Between these extremes the designer must use his judgment, 
 remembering that the higher the speed the lower is the allowable 
 bearing pressure. 
 
 PRACTICAL MODIFICATION. It will be noted in the 
 formula' for holt strengths that different values for S are assumed. 
 This is necessary on account of the uncertain initial stresses which 
 are produced is setting up the nuts. For cases of mere fastening, 
 the safe tension is high, as just before the joint opens the tension 
 is about equal to the load and yet the fastening is secure. On 
 the other- hand, bolts or studs fastening joints subjected to internal 
 fluid pressure must be stressed initially to a greater amount than 
 the working pressure which is to come on the bolt. As this initial 
 stress is a matter of judgment on the part of the workman, the 
 designer, in order to be on the safe side, should specify not less 
 than -inch or : ]-inch bolts for ordinary work, so that the bolts 
 may not be broken off by a careless workman accidentally putting 
 a greater force than necessary on the wrench handle. In making 
 a steam-tight joint, the spacing of the bolts will generally deter- 
 mine their number; hence we often rind an excess of bolt strength 
 in joints of this character. 
 
 Through bolts are preferred to studs, and studs to tap. bolts 
 or cap screws. I f possible, the design should be such that through 
 bolts may be used. They are cheapest, are always in standard 
 
 170
 
 MACHINE DESIGN 157 
 
 stockj and well resist rough usage in connecting and disconnecting. 
 The threads in cast iron are weak and have a tendency to crumble; 
 and if a through bolt cannot be used in such a case, a stud, which 
 can be placed in position once for all, should be employed not a 
 tap bolt, which injures the thread in the casting every time it is 
 removed. 
 
 The plain portion of a stud should be screwed up tight 
 against the shoulder, and the tapped hole should be deep enough 
 to prevent bottoming. To avoid breaking off the stud at the 
 shoulder, a neck, or groove, may be made at the lower end of the 
 thread entering the nut. 
 
 To withstand shearing forces the bolts must be fitted so that 
 no lost motion may occur, otherwise pure shearing will not be 
 secured. 
 
 Nuts are generally made hexagonal, but for rough work are 
 often made square. The hexagonal nut allows the wrench to turn 
 through a smaller angle in tightening up, and is preferred to the 
 square nut. Experiments and calculations show that the height 
 of the nut with standard threads may be about |? the diameter of 
 the bolt and still have the shearing strength of the thread equal to 
 the tensile strength of the bolt at the root of the thread. Practi- 
 
 O 
 
 cally, however, it is difficult to apply such a thin wrench as this 
 proportion would call for on ordinary bolts. More commonly the 
 height of the nut is made equal to the diameter of the bolt so that 
 the length of thread will guide the nut on the bolt, give a low 
 bearing pressure on the threads, and enable a suitable wrench to 
 be easily applied. The standard proportions for bolts and nuts 
 may be found in any handbook. Not all manufacturers conform 
 to the United States standard; nor do manufacturers in all cases 
 conform to one another in practice. 
 
 If the bolt is subject to vibration, the nuts have a tendency to 
 loosen. A common method of preventing this is to use double 
 nuts, or lock nuts, as they are called (see Fig. 55 A). The under 
 nut is screwed tightly against the surface, and held by a wrench 
 while the second nut is screwed down tightly against the first. 
 The effect is to cause the threads of the upper nut to bear against 
 the under sides of the threads of the bolt. The load on the bolt is 
 sustained therefore by the upper nut, which should be the thicker 
 
 171
 
 158 
 
 MACHINE DESIGN 
 
 of the two ; but for convenience in applying wrenches the position 
 of the nuts is often reversed. 
 
 The form of thread adapted to transmitting power is the 
 square thread, which, although giving less bursting pressure 
 on the nut, is not as strong as the Y thread for a given length, 
 since the total section of thread at the bottom is only ^ as great. 
 If the pressure is to be transmitted in but one direction, the two 
 
 Fig. 59. 
 
 types may be combined advantageously to form tne buttress thread 
 of the proportions shown in Fig. 59. Often, as in the carriage of 
 a lathe, to allow the split nut to be opened and closed over the lead 
 screw, the sides of the thread are placed at a small angle, say 15", 
 to each other, as illustrated in Fig. 60. 
 
 The practical commercial forms in which wo find screwed 
 fastenings are included in five classes, as follows: 
 
 | P'TCH 
 
 1. Through bolts (Fig. 61), usually rough stock, with square 
 upset heads, and square or hexagonal nuts. 
 
 2. Tap bolts (Fig. 62), also called cap screws. These usu- 
 ally have hexagonal heads, and are found both in the rough form, 
 and finished from the rolled hexagonal bar in the screw machine. 
 
 3. Studs (Fig. 63), rough or finished stock, threaded in the 
 screw machine. 
 
 4. Set screws (Fig. 64), usually with square heads, and 
 case-hardened points. Many varieties of set screws are made, the 
 
 172
 
 MACHINE DESIGN 
 
 159 
 
 principal distinguishing feature of each being in the shape of the 
 point. Thus, in addition to the plain beveled point, we find 
 the " cupped," rounded, conical, and " teat " points. 
 
 Fig. 61. Fig. 62. Fig. 63. 
 
 5. Machine screws (Fig. 64), usually round, " button," 
 or countersunk head. Common proportions are indicated relative 
 to diameter of body of screw. 
 
 Fig. 64. 
 
 PROBLEflS ON BOLTS, STUDS, NUTS, AND SCREWS. 
 
 1. Calculate the diameter of a bolt to sustain a load of 
 5,000 Ibs. 
 
 173
 
 1(50 
 
 MACHINE DESIGN 
 
 2. The shearing force to be resisted by each of the bolts of a 
 flange coupling is 1,200 Ibs. What commercial size of bolt is 
 required ? 
 
 3. With a wrench It) times the diameter of the bolt and an 
 efficiency of 10 per cent, what axial load can a man exert on a' 
 standard |-inch bolt, if he pulls 40 Ibs. at the end of the wrench 
 handle? 
 
 4. A single, square- threaded screw of diameter 2 inches, 
 lead j inch, depth of thread inch, length of nut ;] inches, is to 
 be allowed a bearing pressure of HOO Ibs. per square inch. What 
 axial load can be carried ( 
 
 o. Calculate the shearing stress at the root of the thread in 
 problem 4. 
 
 Fig. 64a. 
 
 KEYS, PINS, AND COTTERS. 
 
 NOTATION The following notation is used throughout the chapter on Keys, Pins, and 
 
 Cotters: 
 
 = Average diameter of rod (inches). 
 = Outside diameter of socket (in- 
 cies). 
 
 of shaft (inches). 
 
 r = Urivi 
 
 PI = Axia 
 
 S c = Saf 
 
 g force (Ibs.). 
 oad on rod (IDs.). 
 s at which I' acts (inches), 
 rushing fiber stress (Ibs. 
 
 per sq. in.). 
 
 SiT = Safe shearing liber stress (Ibs. 
 per sq. in.). 
 
 St =Safe tensile fiber stress (Ibs. per 
 sq. in.). 
 
 T = Thickness of key (inches). 
 
 W = Width of key (inches). 
 
 w = Average width of cotter (inches). 
 
 v"i = End of slot to end of rod (inches). 
 
 ir-2 = End of slot to end of socket (in- 
 ches). 
 
 KEYS AND PINS. 
 ANALYSIS. Keys and pins are used to prevent relative 
 
 174
 
 MACHINE DESIGN 161 
 
 rotary motion between machine parts intended to act together as 
 one piece. If we drill completely through a hub and across the 
 shaft, and insert a tightly fitted pin, any rotary motion of the one 
 will be transmitted to the other, provided the pin does not fail by 
 shearing off at the joint between the shaft and the hub. The 
 shearing area is the sum of the cross -sections of the pin at the 
 joint. 
 
 We may drill a hole in the joint, the axis of the hole being 
 parallel to the axis of the shaft, and drive in a pin, in which case 
 we introduce a shearing area as before, but the area is now equal 
 to the diameter of the pin multiplied by its length, and the pin is 
 stressed sidewise, instead of across. It is evident in the sidewise 
 case that we may increase the shearing area to anything we please, 
 without changing the diameter of the pin, merely by increasing 
 the length of the pin. 
 
 As there are some manufacturing reasons why a round pin 
 placed lengthwise in the joint is not always applicable, we may 
 make the pin a rectangular one, in which case it is called a key. 
 
 When pins are driven across the shaft as in the first instance, 
 they are usually made taper. This is because it is easier to ream 
 a taper hole to size than a straight hole, and a taper pin will drive 
 more easily than a straight pin, it not being necessary to match the 
 hole in hub and shaft so exactly in order that the pin may enter. 
 The taper pin will draw the holes into line as it is driven, and can 
 be backed out readily in removal. 
 
 Keys of the rectangular form are either straight or tapered, 
 but for different reasons from those just stated for pins. Straight 
 keys have working bearing only at the sides, driving purely by 
 shear, crushing being exerted by the side of the key in both shaft 
 and hub, over the area against the key. The key itself does not 
 prevent end motion along the shaft; and if end motion is not 
 desired, auxiliary means of some sort must be resorted to, as, for 
 example, set screws through the hub jamming hard against the top 
 of the key. 
 
 If end motion along the shaft is desired, the key is called a 
 spline, and, while not jammed against the shaft, is yet prevented 
 from changing its relation to the hub by some means such as 
 illustrated in Fig. 65. 
 
 175
 
 MACHINE DESIGN 
 
 Taper. keys not only drive through sidewise shearing strength, 
 but prevent endwise motion by the wedging action exerted between 
 the shaft and hub. These keys drive more like a strut from corner to 
 corner; but this action is incidental rather than intentional, and the 
 proportions of a taper key should be such that it will give its full 
 resisting area in shearing and crushing, the same as a straight* key. 
 
 Fig. 65. 
 
 THEORY. Suppose that the pin illustrated in Fig. 66 passes 
 through hub and shaft, and the driving force P acts at the radius 
 R; then the force which is exerted at the surface of the shaft to 
 
 2 PR 
 
 shear off the pin at the points A and B is ^ . If D : is the 
 
 average diameter of the pin, its shearing strength is - - 1_. 
 
 Equating the external force to the internal strength, we have : 
 2PR 277-D, 2 S s 
 
 4 ' 
 |4PIT~ 
 
 \ WST' 
 
 (103) 
 
 In Fig. 67 a rectangular key is sunk half way in hub and 
 shaft according to usual practice. Here the force at the surface 
 
 176
 
 MACHINE DESIGN 
 
 163 
 
 of the shaft, calculated the same as before, not only tends to shear 
 off the key along the line AB, but tends to crush both the por- 
 tion in the shaft and in the hub. The shearing strength along the 
 
 Fig. 66. 
 
 Fig. 67. 
 
 line AB is LWS S . Equating external force to internal strength, 
 we have: 
 
 2PR 
 
 (.04) 
 
 The crushing strength is, of course, that due to the weaker 
 metal, whether in shaft or hub. Let S c be tnis least safe crushing 
 
 LT 
 
 fiber stress. The crushing strength then is ^- S c , and, equating 
 
 external force to internal strength, we have: 
 2PR LT 
 
 or, 
 
 4PR 
 
 (105) 
 
 The proportions of the key must be such that the equations as 
 above, both for shearing and for crushing, shall be satisfied. 
 
 PRACTICAL MODIFICATION. Pins across the shaft can be 
 used to drive light work only, for the shearing area cannot be very 
 large. A large pin cuts away too much area of the shaft, decreas- 
 ing the latter's strength, Pins are useful in preventing end motion, 
 but in this case are expected to take no shear, and may be of small 
 
 177
 
 104 MACHINE DESIGN 
 
 diameter. The common split pin is especially adapted to this 
 service, and is a standard commercial article. 
 
 Taper pins are usually listed according to the Morse standard 
 taper, proportions of which may be found in any handbook. It 
 is desirable to use standardise? pins in machine construction, as 
 the reamers are a commercial article of accepted value, and readily 
 obtainable in the machine-tool market. 
 
 AVith properly fitted keys, the shearing strength is usually 
 the controlling element. For shafts of ordinary size, the standard 
 proportions as given in tables like that below are safe enough 
 without calculation, up to the limit of torsional strength of the 
 shaft. For special cases of short hubs or heavy loads, a calcula- 
 tion is needed to check the size, and perhaps modify it. 
 
 Splines, also known as ' feather k^ys." require thickness 
 greater than regular keys, on account of the 
 slidincr at the sides. A table suggesting 
 proportions for splines is given on page lo'l>. 
 
 Though the spline may be either in th;- 
 shaft or hub, it is the more usual thing to 
 lind the spline dovetailed (Fig. G7'>), 
 "gibbed." or otherwise fastened in the 
 hub; and a long spline way made in the 
 shaft, in which it slides. 
 
 The straight key, accurately fitted, is l^s- ^~ ul - 
 
 the most desirable fastening device for ac- 
 curate machines, such as machine tools, on account of the fact that 
 there is absolutely no radial force exerted to throw the parts out of 
 true. It, however, requires a tight lit of hub to shaft, as the key 
 cannot be relied upon to take up any looseness. 
 
 The taper key (Fig. (">S), by its wedging action, will 'take up 
 some looseness, but in so doing throws the parts out slightly. 
 Or, even If the bored fit be good, if the taper key be not driven 
 home with care, it will spring the hub, and make the parts run 
 untrue. The great advantage, however, that the taper key has of 
 holding the hub from endwise motion, renders it a very useful 
 and practical article. It is usually provided with ahead, or " gib." 
 which permits a draw hook to be used to wedge between the face 
 of the hub and the key to facilitate starting the key from its seat. 
 
 178
 
 MACHINE DESIGN 
 
 165 
 
 Two keys at 90 from each other may be used in cases where 
 one key will not suffice. The fine workmanship involved in 
 spacing these keys so that they will drive equally makes this plan 
 inadvisable except in case of positive and unavoidable necessity. 
 
 The " Woodruff " key (Fig. 69) is a useful patented article 
 for certain locations. This key is a half-disc, sunk in the shaft 
 
 _L 
 
 H , TAPER 
 
 PER FT. 
 
 1 
 
 Fig. 68. 
 
 and the hub is slipped over it. A simple rotary cutter is dropped 
 into the shaft to produce the key seat; and on account of the 
 depth in the shaft, the tendency to rock sidewise is eliminated, 
 and the drive is purely by shear. 
 
 Keys may be milled out of solid stock, or drop-forged to 
 within a small fraction of finished size. The drop-forged key is 
 an excellent modern production and requires but a minimum 
 
 Fig. 69. 
 
 amount of fitting. Any key, no matter how produced, requires 
 some hand fitting and draw filing to bring it properly to its seat 
 and give it full bearing. 
 
 It is good mechanical policy to avoid keyed fastenings 
 whenever possible. This does not mean that keys may never be 
 used, but that a key is not an ideal way to produce an absolutely 
 positive drive, partly because it is an expensive device, and partly 
 because the tendency of any key is to work itself loose, even if 
 carefully fitted. 
 
 The following tables are suggested as a guide to proportions 
 
 179
 
 100 
 
 MACHINE DESIGN 
 
 of <nb keys and feather key?, and will be found useful in the 
 absence of any manufacturer's standard list: 
 
 Fit-. 70. PROPORTIONS FOR GIB KEYS. 
 
 Diameter of shaft (rf), inches. 
 
 t! 1 ! 1 * 
 
 If 
 
 2 2J;3i 
 
 4 
 
 5 
 
 6J 
 
 Width (W), inches. 
 
 T 5 Jf T\ 
 
 1 
 
 T 9 ff 
 
 I 
 
 1 T V 
 
 ! T 5 o 
 
 If 
 
 Thickness (T). inches. 
 
 1 1 9 ' r> 13 7 1721 
 4 '3 f\ T6 '$2 T"B j "ST 1 32" 
 
 If 
 
 1 
 
 ^ 
 
 Via. 11. PROPORTIONS FOR FEATHER KEYS. 
 
 I 
 
 
 
 
 
 
 
 
 Diameter of Shaft (d), inches, I !| 
 
 1 
 
 r, 
 
 H 
 
 2 
 
 2 i 
 
 2} 3 
 
 81 
 
 4 4* 
 
 Width CWi. inches. T \ 
 
 A 
 
 i 
 
 i 
 
 A 1 
 
 
 i 
 
 T 9 
 
 A i 
 
 Thickness (T), inches. 1 J 
 
 5 
 
 T'i 
 
 3 
 
 8 
 
 3 
 8 
 
 7 
 T6 
 
 i 
 
 i 
 
 1 
 
 * t_|l 
 
 COTTERS. 
 
 ANALYSIS. (Jotters are used to fasten hubs to rods rather 
 than shafts, the distinction between a rod and a shaft being that 
 a rod takes its load in the direction of its length, and does not 
 drive by rotation. A cotter, therefore, is nothing but a cross-pin 
 of modified form, to take shearing and crushing stress in the 
 direction of the axis of the rod. instead of perpendicular to it. 
 
 Referring to Fig. 72, one will see that the cotter is made 
 long and thin long, in order to get sufficient shearing area to resist 
 shearing along lines A and B; thin, in order to cut as little cross- 
 sectional area out of the body of the shaft as possible. The cotter 
 itself tends to shear along the lines A and B, and crush along the 
 surfaces K. G, and .1. The socket tends to crush alono- the surfaces 
 
 O 
 
 K and G. The rod end D tends to be sheared out along the lines 
 II and Q E. and also to be crushed along the surface J. The 
 socket tends to be sheared aloncr the lines V U and X. Y. 
 
 o 
 
 The cotter is made taper on one side, thus enabling it to draw 
 up the flange of the rod tiVhtly against the head of the socket. 
 
 O J O 
 
 This taper must not be great enough to permit easy "backing out" 
 ;md loosening of the cotter under load or vibration in the rod. In 
 responsible situations this cannot be safely guarded against except 
 through some auxiliary locking device, such as lock nuts on the 
 end of the cotter (Fig. 73). 
 
 THEORY. Referring to Fig. 72, assume an axial load of P t , 
 as shown. The successive equations of external force to internal 
 
 180
 
 MACHINE DESIGN 
 
 167 
 
 strength are enumerated below, for the different actions that take 
 place : 
 
 For shearing along lines A and B, w being the average 
 width of cotter, and S s safe shearing stress of cotter, 
 
 j = 2TwS s . 
 
 (106) 
 
 Fig. 72. 
 For crushing along surfaces K and G, S being least safe 
 
 O O <H 
 
 crushing stress, whether of cotter or socket, 
 
 (I0 7 ) 
 fe erne. 
 
 \=.iyrs . (108) 
 
 For crushing along surface J, S c being least safe crushing 
 stress, whether of cotter or socket, 
 
 181
 
 MACHINE DESIGN 
 
 For shearing along surfaces CII and QE, S s being safe shear 
 in" 1 stress of rod end, and v, end of slot to end of rod, 
 
 l'i = ^DS, ( I09 ) 
 
 For tension in rod end at section across slot, S t being safe 
 tensile stress in rod end, 
 
 (no) 
 
 For tension in socket at section across slot, JS t being safe ten- 
 sile stress in socket, 
 
 (Hi) 
 
 For shearing in socket along the lines YU and XY, S 6 being 
 safe 1 shearing stress in the socket, and u\ 2 end of slot to end of 
 socket, 
 
 P 1 = 2w,(V 1 -T>)$ s . (112) 
 
 The ])roportions of cotter and socket may be fixed to some 
 
 extent by practical or as 
 suraed conditions. The di- 
 mensions may then be tested 
 by the above equations, that 
 the safe working stresses may 
 not be exceeded, the dimen- 
 sions being then modified ac- 
 cordingly. 
 
 The steel of which both 
 cotter and rod would ordina- 
 rily be made 1 has range of 
 working iiber stress as 
 follows : 
 Tension, 8,(XX) to 1*2,(XX) (Ibs. pel 
 
 sq. in.) 
 Compression, 10,000 to 10,000 (Ibs 
 
 per sq. in.) 
 Shear, 6,000 to 10,000 (Ibs. per 
 
 sq. in.) 
 
 The socket, if made of 
 iron, will be weak as regards tension, tendency to shear out at 
 
 cast 
 
 182
 
 MACHINE DESIGN 
 
 169 
 
 the end. and tendency to split. The uncertainty of cast iron to 
 resist these is so great that the hub or socket must be very clumsy 
 in order to have enough surplus strength. This is always a notice- 
 able feature of the cotter type of fastening, and cannot well be 
 avoided. 
 
 PRACTICAL MODIFICATION. The driving faces of the cot- 
 ter are often made semicircular. This not only gives more shear- 
 ing area at the sides of the slots, but makes the production of the 
 slots easier in the shop. It also avoids the general objection to 
 sharp corners namely, a tendency to start cracks. 
 
 A practicable taper for 
 cotters is ^ inch per foot. 
 This will under ordinary 
 circumstances prevent the 
 cotter from backing out 
 under the action of the load. 
 When set screws against 
 the side of the cotter, or 
 
 lock nuts are used, as in 
 Fig. 73, the taper may be 
 greater than this, perhaps 
 as much as li inches per 
 foot. 
 
 In the common use of 
 the cotter for holding the Fig. 74. 
 
 strap at the ends of con- 
 necting rods, the strap acts like a modified form of socket. This is 
 shown in Figs. 73 and 74. Here, in addition to holding the strap 
 and rod together lengthwise, it may be necessary to prevent their 
 spreading, and for this purpose an auxiliary piece G with gib ends 
 is used. The tendency without this extra piece is shown by the 
 dotted lines in Fig. 74. 
 
 The general mechanical fault with cottered joints is that the 
 action of the load, especially \vhen it constantly reverses, as in 
 pump piston rods, always tends to work the cotter loose. Vibra- 
 tion also tends to produce the same effect. Once this looseness is 
 started in the joint, the cotter loses its pure crushing and shearing 
 action, and begins to partake of the nature of a hammer, and 
 
 183
 
 170 MACHINE DESIGN 
 
 pounds itself and its bearing surfaces out of their true shape. 
 Instead of a collar on the rod, we often find a taper fit of the rod 
 in the socket; and any looseness in this case is still worse, for the 
 rod then has end play in the socket, and by its " shucking" back 
 and forth tends to split open the socket. 
 
 The only answer to these objections is to provide a positive 
 locking device, and take up any looseness the instant it appears. 
 
 PROBLEMS ON KEYS, PINS, AND COTTERS. 
 
 1. Calculate the safe load in shear which can be carried on a key 
 -A inch wide, ^ inch thick, and 5 inches long. Assume S s = 6,000. 
 
 2. Assuming the above key to be -j 3 fl inch in hub and-j 3 (] inch 
 in shaft, test its proportions for crushing, at S c = 16,000. 
 
 3. A gear 60 inches in diameter has a load of 3,000 Ibs. at 
 the pitch line. The shaft is -i inches in diameter, in a hub, 
 5 inches long; and the key is a standard gib key as given in the 
 table. Test its proportions for shearing. 
 
 4-. A piston rod 2 inches in diameter carries a cotter inch 
 
 J O 
 
 thick, and has an axial load of 20,000 Ibs. Calculate the average 
 width of the cotter. S s = 0,000. 
 
 3. Calculate fiber stress in rod in preceding problem at 
 section through slot. 
 
 6. How far from the end of rod must the end of slot be ? 
 
 7. Calculate the crushing fiber stresses on cotter, rod, and 
 socket. 
 
 <S. How far from the end of socket must the end of slot be, 
 assuming the socket to be of steel ? 
 
 BEARINGS, BRACKETS, AND STANDS. 
 
 NOTATION The following notation is used throughout the chapters on Bearings 
 Brackets, and Stands. 
 
 A = Area (square inches). Iv = Number of revolutions per minute. 
 
 n = Distance between bolt centers n = Number of bolts in cap. 
 
 (inches). >n Number of bolts in bracket base. 
 
 = Width of bracket base (inches). P = Total pressure on bearing (Ibs.). 
 
 Distance of neutral axis from outer p = Pressure per square inch of pro- 
 
 liber (inches). jected area (Ibs). 
 
 n = Diameter of shaft (inches). S = Safe tensile fiber stress (Ibs.). 
 
 '/= Diameter of bolt body (inches). S s = " shearing " (Ibs.). 
 
 <l\= Diameter at root of thread (inches). T = 'Total load on bolts at top of 
 II = Horse-power. bracket (Ibs.), 
 
 = Thickness of cap at center (inches). t = Thickness of bracket base (inches). 
 
 I = Moment of inertia. x = Distance from line of action of load 
 I, = Length of bearing (inches). to any section of bracket(inches). 
 
 A= Coefficient of friction (per cent). 
 
 184
 
 MACHINE DESIGN 171 
 
 ANALYSIS. Machine surfaces taking weight and pressure 
 of other parts in motion upon them are, in general, known as 
 bearings. If the motion is rectilinear, the bearing is termed a 
 slide, guide, or way, such as the cross slide of a lathe, the cross- 
 head guide of a steam engine, or the ways of a lathe bed. 
 
 If the motion is a rotary one, like that of the spindle of a lathe, 
 the simple word " bearing " is generally used. 
 
 In any bearing, sliding or rotary, there must be strength to 
 carry the load, stiffness to distribute the pressure evenly over the 
 full bearing surface, low intensity of such pressure to prevent the 
 lubricant from being squeezed out and to minimize the wear, and 
 sufficient radiating surface to carry away the heat generated by 
 friction of the surfaces as fast as it is generated. Sliding bearings 
 are of such varied nature, and exist under conditions so peculiar 
 to each case, that a general analysis is practically impossible 
 beyond that given in the sentence above. 
 
 Rotary bearings can be more definitely studied, as 'there are 
 but two variable dimensions, diameter and length, and it is the 
 proper relation between these two that determines a good bearing. 
 The size of the shaft, ^as noted under "Shafts," is calculated by 
 taking the bending moment at the center of the bearing, combin- 
 ing it with the twisting moment, and solving for the diameter 
 consistent with the assumed fiber stress. But this size must then 
 be tried for deflection due to the bending load, in order that the 
 requirement for stiffness may be fulfilled. When this is accom- 
 plished, the friction at the bearing surface may still generate so 
 much heat that the exposed surface of the bearing win not radiate 
 it as fast as generated, in which case the bearing gets hotter and 
 hotter, until it finally burns out the lubricant and melts the lining 
 of the bearing, and ruin results. 
 
 The heat condition is usually the critical one, as it is very 
 easy to make a short bearing which is strong enough and amply 
 stiff for the load it carries, but which nevertheless is a failure as 
 a bearing, because it has so small a radiating surface that it can- 
 not run cool. 
 
 The side load which causes the friction and the consequent 
 development of heat, is due to the pull of the belt in the case of 
 pulleys, the load on the teeth or gears, the puil on cranks and 
 
 185
 
 172 MACHINE DESIGN 
 
 levers, the weight of parts, etc. If we could exert pure torsion on 
 shafts without any side pressure, and counteract all the weight 
 that comes on the shaft, we should not have any trouble with the 
 development of heat in bearings; in fact, there would theoretically 
 be no need of bearings, as the shafts would naturally spin about 
 their axes, and would not need support. 
 
 It can be shown., theoretically, that the radiating surface of a 
 bearing increases relatively to the heat generated by a given side 
 load, milij 'ii'Jicii tJie length of tit e heaving v'.v 'tm-rc<ixt'il. In other 
 words, increasing the diameter and not the length, theoretically 
 increases the heat generated per unit of time just as much as it 
 increases the radiating surface; hence nothing is gained, and heat 
 accumulates in the bearing as before. This important fact is veri- 
 fied by the design of high-speed bearings, which, it is always 
 noted, are very long in proportion to their diameter, thus giving 
 relatively high radiating power. 
 
 Bearings must be rigidly fastened to the body of the machine 
 in some way, and the immediate support is termed a bracket, 
 frame, or housing. "Bracket" is a very general term, and ap- 
 plfes to the supports of other machine parts besides ''bearings/' 
 It is especially applicable to the more familiar types of bearing 
 supports, and is here introduced to make the analysis complete. 
 
 The bracket must be strong enough as a beam to take the 
 side load, the bending moment being figured at such points as are 
 necessary to determine its outline. It may be of solid, box, or 
 ribbed form, the latter beino 1 the most economical of material, and 
 
 o 
 
 usually permitting the simplest pattern. The fastening of the 
 bracket to the main body of the machine must be broad to give 
 stability; the bolts act partly in shear to keep the bracket from 
 sliding along its base, and partly in tension to resist its tendency 
 to rotate about some one of its edges, due to the side pull of the 
 belt, gear tooth, or lever load, as the case may be. The weight of 
 the bracket itself and of the parts it sustains through the bearing, 
 has likewise to be considered; and this acts, in conjunction with 
 the working load on the bearing, to modify the direction and 
 magnitude of the resultant load on the bracket and its fastening. 
 Stands are forms of brackets, and are subject to the same 
 analysis. The distinction is by no means well defined, although 
 
 186
 
 MACHINE DESIGN 
 
 173 
 
 we usually think moie readily of a stand as having an upright or 
 inverted position with reference to the ground. The ordinary 
 " hanger " is a good example of an inverted stand; and the regular 
 " floor stand," found on jack shafts in some power houses, is an 
 example of the general class. 
 
 THEORY. As the method of calculation of the diameter of 
 the shaft, as well as its deflection, has been considered under 
 " Shafts," we may assume that the theoretical study of bearings 
 starts on a given basis of shaft diameter D. The main problem 
 then being one of heat control, let us first calculate the amount of 
 heat developed in a bearing by a given side load. The force of 
 friction acts at the circumference of the shaft, and is equal to the 
 coefficient of friction times the normal force; or, for a given side load 
 P, Fig. 75, the force of friction 
 would be jjiP. The peripheral 
 speed of the shaft for rN revolu- 
 
 7TDN 
 
 .tions per minute is ^- feet 
 
 per minute. As work is " force 
 times distance," the work wasted 
 
 in friction is then 
 
 foot- 
 
 pounds per minute. One horse- 
 power being equal to 33,000 foot- 
 pounds per minute, we have the 
 equation, 
 
 Fig. 75. 
 
 ~ 12 X 33,000 
 
 The value of jLt for ordinary, well -lubricated bearings, may run as 
 low as 5 per cent; but as the lubrication is often impaired, it 
 quite commonly rises to 10 or 12 per cent. A value of 8 per cent 
 is a fair average. This amount of horse-power is dissipated 
 through the bearing in the form of heat. If we could exactly 
 determine the ability that each particle of the metal around the 
 shaft had to transmit the heat, or to pass it along to the outside 
 of the casting, and if we could then determine the ability of the 
 particles of air surrounding the casting to receive and carry away 
 
 187
 
 174 MACHINE DESIGN 
 
 this heat, we could calculate just such proportions of the bearing 
 and its casing as would never choke or retard this free transfer of 
 heat away from the running surface. 
 
 Such refined theory is not practical, owing to the complicated 
 shapes and conditions surrounding the bearing. The best that we 
 can do is to say that for the usual proportions of bearings the side 
 load may exist up to a certain intensity of " pressure per square 
 inch of projected area " of bearing, or, in form of an equation, 
 
 P=pLD. (n 4 ) 
 
 The constant j9 is of a variable nature, depending on lubrication, 
 speed, air contact, and other special conditions. For ordinary 
 bearings having continuous pressure in one direction, and only 
 fair lubrication, 400 to 500 is an average value. When the pres- 
 sure changes direction at every'half-revolution, the lubricant has 
 a better chance to work fully over the bearing surface, and a 
 higher value is permissible, say, 500 to 800. In locations where 
 mere oscillation takes place, not continuous rotation, and reversal- 
 of pressure occurs, as on the cross-head pin of a steam engine, p 
 may run as high as 900 to 1,200. On the crank pins of locomo- 
 tives, which have the reversal of pressure, and the benefit of high 
 velocity through the air to facilitate cooling, the pressures may run 
 equally high. On the eccentric crank pins of punching and shear- 
 ing machines, where the pressure acts only for a brief instant and 
 at intervals, the pressure ranges still higher without any dangerous 
 heating action. 
 
 When a bearing, for practical reasons, is provided with a cap 
 held in place by bolts or studs, the tlieory of the cap and bolts is 
 of little importance, unless the load comes directly against the rap 
 and bolts. Except in the latter case, the proportions of the cap and 
 the size of the bolts are dependent upon general appearance 
 and utility, it being manifestly desirable to provide a substantial 
 design, even though some excess of strength is thereby introduced. 
 
 For the worst case of loading, however, which is when the 
 cap is acted upon by the direct load, such as P in Fig. 71), we have 
 the condition of a centrally loaded beam supported at the bolts. 
 It is probable that the beam is partially fixed at the ends by the 
 clamping of the nut; also that the load P, instead of being con- 
 
 188
 
 MACHINE DESIGN 
 
 175 
 
 centrated at the center, is to some extent distributed. It is hardly 
 
 Pa Pa , 
 
 fair to assume the external moment equal to -~- or j , the one 
 
 being too small, perhaps, and the other too large. It will be rea- 
 sonable to take the external moment at p , in which case, equat- 
 
 X 
 
 Fig. 76. 
 ing tie external moment to the internal moment of resistance, 
 
 Pa 
 T 
 
 SI 
 
 6' 
 
 SLA 2 
 
 from which, the length of bearing being known, we may calculate 
 the thickness h. 
 
 One bolt on each side is sufficient for bearings not more 
 than inches long, but for longer bearings we usually find two 
 bolts 'on a side. The theoretical location for two bolts on a side, 
 in order that the bearing may be equally strong at the bolts and 
 at the center of the length, may be shown by the principles of 
 
 mechanics to be -^r L from each end, as indicated in Fig. 76. 
 The bolts are evidently in direct tension, and if equally loaded 
 
 189
 
 17(5 MACHINE DESIGN 
 
 would each take their fractional share of the whole load P. This 
 
 2 
 
 is difficult to <marantee, and it is safer to consider that -;r~ P may 
 
 o 
 
 he taken by the holts on one side. On this hasis, for total number 
 of bolts //, equating the external force to the internal resistance of 
 the holts, we have : 
 
 from which the proper commercial diameter may be readily found. 
 The bracket may have the shape shown in Fig. 77. The 
 portion at B is under direct shearing stress; and if A be the area 
 at this point, and S s the safe shearing stress, then, equating the 
 external force to the internal shearing resistance, 
 
 P=AS S . (117) 
 
 The same shear comes on all parts of the bracket to the left of the 
 load, but there is an excess of shearing strength at these points. 
 
 At the point of fastening, the bolts are in shear, due to the 
 same load, for which the equation is 
 
 P = -^x,S, (118) 
 
 For the upper bolts, the case is that of direct tension, assum- 
 ing that the whole bracket tends to rotate about the lower edge E. 
 To iind the load T on these bolts, we should take moments about 
 the point E, as follows: 
 
 PL 1 =T/;orT= ^ (119) 
 
 Then, equating the external force to the internal resistance, 
 T = ^ = ^ X fs. (.30) 
 
 The upper flange is loaded with the bolt load T, and tends to 
 break off at the point of connection to the main body of the 
 bracket, the external moment, therefore, being T/'. The section 
 of the flange is rectangular; hence the equation of external and in- 
 ternal moments is: 
 
 190
 
 MACHINE DESIGN 
 
 177 
 
 = -B- ( I2I > 
 
 It may De noted that the lower bolts act on such a small leverage 
 about E, that they would stretch and thus permit all the load to 
 be thrown on the upper bolts; this is the reason why they are not 
 subject to calculation for tension. 
 
 . b . 
 
 
 
 $ 
 
 j 
 
 $- 
 
 Fig. 77. 
 
 The section of the bracket to the left of the load P is depend- 
 ent upon the bending moment, for, if this section is large enough 
 to take the bending moment properly, the shear may be disregard- 
 ed. It should be calculated at several points, to make sure that 
 the fiber stress is within allowable limits. The general expression 
 for the equation of moments is, for any section at leverage x, 
 
 p*= (IM) 
 
 from which, by the proper substitution of the moment of in- 
 
 191
 
 178 
 
 MACHINE DESIGN 
 
 ertia of the section, the fiber stress can be calculated. The mo- 
 ment of inertia for simple ribbed sections can be found in most 
 handbooks. The process of solution of the above equation, though 
 
 simple, is apt to be tedious, 
 and is not considered neces- 
 sary to illustrate here. 
 
 PRACTICAL MODIFI = 
 CATION. Adjustment is an 
 important practical feature of 
 bearings. Unless the propor- 
 tions are so ample that wear 
 is inappreciable, simple and 
 ready adjustment must be 
 provided. The taper bush- 
 ing. Fig. 79, is neat and sat- 
 isfactory for machinery in 
 which expense and refinement 
 are permissible. This is true 
 of some machine tools, but is 
 not true of the general ' run " of bearings. The most common 
 form of adjustment is secured by the plain cap (which mayor may 
 
 Fig. 79. 
 
 not be tongued into the bracket), with liners placed in -the joint 
 when new, which may subsequently be removed or reduced so as 
 to allow the cap to close down upon the shaft. Several forms of 
 cap bearings are illustrated in Figs. 80, 81, and 82. 
 
 192
 
 MACHINE DESIGN 
 
 179 
 
 Large engine shaft bearings have special forms of adjustment 
 by means of wedges and screws, which take up the wear in all 
 directions, at the same time accurately preserving the alignment 
 of the shafts; but this refinement is seldom required for shafts of 
 ordinary machinery. 
 
 In cases where the cap bearing is not applicable, a simple 
 bushing may be used. This may be removed when worn, and a 
 
 Fig. 80. Fig. 81. 
 
 new one inserted, the exact alignment being maintained, as the 
 outside will be concentric with the original axis of shaft, regard- 
 less of the wear which has taken place in the bore. 
 
 The lubrication of bearings is a part of the design, in that 
 the lubricant should be intro- 
 duced at the proper point, and 
 pains taken to guarantee its dis- 
 tribution to all points of the run- 
 ning surface. The method of 
 lubrication should be so certain 
 that no excuse for its failure 
 would be possible. Grease is a 
 successful lubricator for heavy 
 loads and slow speeds, oil for 
 light loads and high speeds. 
 
 In order to insure the lubri- Fig. 82. 
 
 cant reaching the sliding sur- 
 faces and entering between them, it must be introduced at a point 
 
 193
 
 ISO MACHINE DESIGN 
 
 where the pressure is moderate, and where the motion of the j tarts 
 will naturally lead it to all points of the bearing. Grooves and 
 channels of ample size assist in this regard. A special form of 
 bearing uses a ring riding on the shaft to carry the oil constantly 
 from a small reservoir beneath the shaft up to the top, when- it is 
 distributed along the bearing and finally Hows back to the reser- 
 voir and is used again. 
 
 Tlu> materials of which bearings are made vary with the 
 service required and with the refinement of the bearing. ( 'ast iron 
 makes an excellent bearing for light loads and slow speeds, but 
 it is very apt to "seize*' the shaft in case the lubrication is in the 
 least degree impaired. Bronze, in its many forms. of density and 
 hardness, is extensively used for high-grade bearings, but it also 
 has little natural lubricating power, and requires careful attention 
 to keep it in good condition. 
 
 Babbitt, a composition metal, of varying degrees of hardness, 
 is the most universal and satisfactory material for ordinary bear- 
 ings. It affords a cheap method of production, being poured in 
 molten form around a mandrel, and firmly retained in its casing or 
 shell through dovetailed pockets into which the metal flows and 
 hardens. It requires no boring or extensive fitting. Some 
 scraping to uniform bearing is necessary in most cases, but this is 
 easily and cheaply done. Babbitt is a durable material, and has 
 some natural lubricating power, so that it has less tendency to 
 heat with scanty lubrication than any of the materials previously 
 mentioned. Almost any grade of bearing may be produced w r ith 
 babbitt. In its finest form the babbitt is hammered, or pened, 
 into the shell of the bearing, and then bored out nearly to size, a 
 slightly tapered mandrel being subsequently drawn through, com- 
 pressing the babbitt and giving a polished surface. 
 
 A combination bearing of babbitt and bronze is sometimes 
 used. In this the bronze lies in strips from end to end of the 
 bearing, and the babbitt fills in between the strips. The shell, 
 Deing of bronze, gives the required stiffness, and the babbitt the 
 favorable running quality. 
 
 PROBLEMS ON BEARINGS, BRACKETS, AND STANDS. 
 
 1. Tiie allowable pressure on a bearing is 300 pounds per 
 
 194
 
 MACHINE DESIGN 181 
 
 square inch of projected area. What is the required length of 
 the bearing if the total load is 4,500 pounds and the diameter is 
 3 inches ? 
 
 2. The cross-head pin of a steam engine must be 2.5 inches 
 in diameter to withstand the shearing strain. If the maximum 
 pressure is 10,000 pounds, what length should be given to the pin ? 
 
 3. The journals on the tender of a locomotive are 8^ X 7 
 inches. The total weight of the tender and load is 60,000 pounds. 
 If there are 8 journals, what is the pressure per square inch of 
 projected area ? 
 
 4. What horse-power is lost in friction at the circumference 
 of a 3-inch bearing carry ing a load of 6,000 pounds, if the number 
 of revolutions per minute is 150 and the coefficient of friction is 
 assumed to be 5 per cent ? 
 
 5. The cast-iron bracket in Fig. 77 has a load P of 1,000 
 pounds. Determine the fiber stress in the web section at the base 
 of the bracket if the thickness is taken at ^ inch, and L x = 12 
 inches; I = 20 inches; k = 11 inches; t = 1 inch. 
 
 6. Calculate the diameter of the bolts at the top of the 
 bracket. 
 
 7. Assuming r equal to 6 inches, what is the fiber stress at 
 the root of flange ? 
 
 195
 
 HOT WATER HEATER AND CONNECTIONS.
 
 HEATING AND VENTILATION 
 
 PART I 
 
 SYSTEMS OF WARMING 
 
 Any system of warming must include, first, the combustion 
 of fuel, which may take place in a fireplace, stove, or furnace, or a 
 steam, or hot-water boiler; second, a system of transmission, by means 
 of which the heat may be carried, with as little loss as possible, to the 
 place where it is to be used for warming; and third, a system of dif- 
 fusion, which will convey the heat to the air in a room, and to its 
 walls, floors, etc., in the most economical way. 
 
 Stoves. The simplest and cheapest form of heating is the stove. 
 The heat is diffused by radiation and convection directly to the objects 
 and air in the room, and no special system of transmission is'required. 
 The stove is used largely in the country, and is especially adapted 
 to the warming of small dwelling-houses and isolated rooms. 
 
 Furnaces. Next in cost of installation and in simplicity of 
 operation, is the hot-air furnace. In this method, the air is drawn 
 over heated surfaces and then transmitted through pipes, while at 
 a high temperature, to the rooms where heat is required. 'Furnaces 
 are used largely for warming dwelling-houses, also churches, halls, 
 and schoolhouses of small size. They are more costly than stoves, 
 but have certain advantages over that form of heating. They require 
 less care, as several rooms may be warmed from a single furnace; 
 and, being placed in the basement, more space is available in the 
 rooms above, and the dirt and litter connected with the care of a stove 
 are largely done away with. . They require less care, as only one fire 
 is necessary to warm all the rooms in a house of ordinary size. One 
 great advantage in the furnace method of warming comes from the 
 constant supply of fresh air which is required to bring the heat into 
 the rooms. While this is greatly to be desired from a sanitary stand- 
 point, it calls for the consumption of a larger amount of fuel than 
 would otherwise be necessary. This is true because heat is required 
 to warm the fresh air from out of doors up to the temperature of the 
 
 197
 
 HEATING AND VENTILATION 
 
 rooms, in addition to replacing the heat lost by leakage and conduction 
 through walls and windows. 
 
 A more even temperature may be maintained with a furnace 
 than by the use of stoves, owing to the greater depth and size of the 
 fire, which allows it to be more easily controlled. 
 
 ^ hen a building is placed in an exposed location, there is often 
 difficulty in warming rooms on the north and west sides, or on that 
 side toward the prevailing winds. This may be overcome to some ex- 
 tent by a proper location of the furnace and by the use of extra large 
 pipes for conveying the hot air to those rooms requiring special at- 
 tention. 
 
 Direct Steam. Direct steam, so called, is widely used in all 
 classes of buildings, both by itself and in combination with other 
 systems. The first cost of installation is greater than for a furnace; 
 but the amount of fuel required is less, as no outside air supply is 
 necessary. If used for warming hospitals, schoolhouses, or other 
 buildings where a generous supply of fresh air is desired, this method 
 must be supplemented by some form of ventilating system. 
 
 One of the principal advantages of direct steam is the ability 
 to heat all rooms alike, regardless of their location or of the action 
 of winds. 
 
 When compared with hot-water heating, it has still another 
 desirable feature which is its freedom from damage by the freezing 
 of water in the radiators when closed, which is likely to happen in 
 unused rooms during very cold weather in the case of the former 
 system. 
 
 On the other hand, the sizes of the radiators must be proportioned 
 for warming the rooms in the coldest weather, and unfortunately 
 there is no satisfactory method of regulating the amount of heat in 
 mild weather, except by shutting off or turning on steam in the radia- 
 ators at more or less frequent intervals as may be required, unless one 
 of the expensive systems of automatic control is employed. In large 
 rooms, a certain amount of regulation can be secured by dividing 
 the radiation into two or more parts, so that different combinations 
 may be used under varying conditions of outside temperature. If 
 two radiators are used, their surface should be proportioned, when 
 convenient, in the ratio of 1 to 2, in which case one-third, two-thirds, 
 or the whole power of the radiation can be used as desired. 
 
 198
 
 HEATING AND VENTILATION 
 
 Indirect Steam. This system of heating combines some of the 
 advantages of both the furnace and direct steam, but is more costly 
 to install than either of these. The amount of fuel required is about 
 the same as for furnace heating, because in each case the cool fresh 
 air must be warmed up to the temperature of the room, before it can 
 become a medium for conveying heat to oifset that lost by leakage 
 and conduction through walls and windows. 
 
 A system for indirect steam may be so designed that it will supply 
 a greater quantity of fresh air than the ordinary form of furnace, in 
 which case the cost of fuel will of course be increased in proportion to 
 the volume of air supplied. Instead of placing the radiators in the 
 rooms, a special form of heater is supported near the basement ceiling 
 and encased in either galvanized iron or brick. A cold-air- supply 
 duct is connected with the space below the heater, and warm air pipes 
 are taken from the top and connected with registers in the rooms to 
 be heated the same as in the case of furnace heating. 
 
 A separate stack or heater may be provided for each register if 
 the rooms are large; but, if small and so located that they may be 
 reached by short runs of horizontal pipe, a single heater may serve 
 for two or more rooms. 
 
 The advantage of indirect steam over furnace heating comes from 
 the fact that the stacks may be placed at or near the bases of the flues 
 leading to the different rooms, thus doing away with long, horizontal 
 runs of pipe, and counteracting to a considerable extent the effect of 
 wind pressure upon exposed rooms. Indirect and direct heating are 
 often combined to advantage by using the former for the more import- 
 ant rooms, where ventilation is desired, and the latter for rooms more 
 remote or where heat only is required. 
 
 Another advantage is the large ratio between the radiating sur- 
 face and grate-area, as compared with a furnace ; this results in a large 
 volume of air being warmed to a moderate temperature instead of a 
 smaller quantity being heated to a much higher temperature, thus 
 giving a more agreeable quality to the air and rendering it less dry. 
 
 Indirect steam is adapted to all the buildings mentioned in con- 
 nection with furnace heating, and may be used to much better advan- 
 tage in those of large size. This applies especially to cases where 
 more than one furnace is necessary; for, with steam heat, a single 
 boiler, or a battery of boilers, may be marie to supply heat for a build- 
 
 199
 
 HEATING AND VENTILATION 
 
 ing of any she, or for a group of several buildings, if desired, and is 
 much easier to care for than several furnaces widely scattered. 
 
 Direct-Indirect Radiators. These radiators are placed in the 
 room the same as the ordinary direct type. The construction is such 
 that when the sections are in place, small flues are formed between 
 them; and air, beirfg admitted through an opening in the outside wall, 
 passes upward through them and becomes heated before entering the 
 room. A switch damper is placed in the casing at the base of the 
 radiator, so that air may be taken from the room itself instead of 
 from out of doors, if so desired. Radiators of this kind are not used 
 to any great extent, as there is likely to be more or less leakage of cold 
 air into the room around the base. If ventilation is required, it is 
 better to use the regular form of indirect heater with flue and register, 
 if possible. It is sometimes desirable to partially ventilate an isolated 
 room where it would be impossible to run a flue, and in cases of this 
 kind the direct-indirect form is often useful. 
 
 Direct Hot Water. Hot water is especially adapted to the warm- 
 ing of dwellings and greenhouses, owing to the ease with which the 
 temperature can be regulated. ^Yhen steam is used, the radiators are 
 always at practically the same temperature, while with hot water the 
 temperature can be varied at will. A system for hot-water heating 
 costs more to install than one for steam, as the radiators must be larger 
 and the pipes .more carefully run. On the other hand, the cost of 
 operating is somewhat less, because the water need be carried only at 
 a temperature suflicientlv high to warm the rooms properly in mild 
 weather, while with steam the building is likely to become overheated, 
 and more or less heat wasted through open doors and windows. 
 
 A comparison of the relative costs of installing and operating hot- 
 air, steam, and hot-water systems, is given in Table I. 
 
 TABLE I 
 Relative Cost of Heating Systems 
 
 HOT Am 
 
 STEAM 
 
 HOT WATER 
 
 Relative cost of apparatus 9 
 
 13 
 
 15 
 
 Relative cost, adding repairs and fuel 
 
 
 
 for five years 29* 
 
 29? 
 
 27 
 
 Relative cost, adding repairs and fuel for 
 
 
 
 fifteen years SI 
 
 63 
 
 52^ 
 
 200
 
 HEATING AND VENTILATION 
 
 One disadvantage in the use of hot water is the danger from 
 freezing when radiators are shut off in unused rooms. This makes 
 it necessary in very cold weather to have all parts of the system turned 
 on sufficiently to produce a circulation, even if very slow. This is 
 sometimes accomplished by drilling a very small hole (about | inch) 
 in the valve-seat, to that when closed there will still be a very slow 
 circulation through the radiator, thus preventing the temperature of 
 the water from reaching the freezing point. 
 
 Indirect Hot Water. This is used under the same conditions as 
 indirect steam, but more especially in the case of dwellings and hospi- 
 tals. When applied to other and larger buildings, it is customary to 
 force the water through the mains by means of a pump. Larger 
 heating stacks and supply pipes are required than for steam; but the 
 arrangement and size of air-flues and registers are practically the 
 same, although they are sometimes made slightly larger in special cases, 
 
 Exhaust Steam. Exhaust steam is used for heating in connection 
 with power plants, as in shops and factories, or in office buildings 
 which have their own lighting plants. There are two methods of 
 using exhaust steam for heating purposes. One is to carry a back 
 pressure of 2 to 5 pounds on the engines, depending upon the length 
 and size of the pipe mains ; and the other is to use some form of vacuum 
 system attached to the returns or air-valves, which tends to reduce 
 the back pressure rather than to increase it. 
 
 Where the first method is used and a back pressure carried, either 
 the boiler pressure or the cut-off of the engines must be increased, to 
 keep the mean effective pressure the same and not reduce the horse- 
 power delivered. In general it is more economical to utilize the ex- 
 haust steam for heating. There are instances, however, where the 
 relation between the quantities of steam required for heating and for 
 power are such especially if the engines are run condensing that 
 it is better to throw the exhaust away and heat with live steam. 
 Where the vacuum method is used, these difficulties are avoided ; and 
 for this reason that method is coming into quite common use. 
 If the condensation from the exhaust steam is returned to the 
 boilers, the oil must first be removed ; this is usually accomplished by 
 passing the steam through some form of grease extractor as it leaves 
 the engine. The water of condensation is often passed through a 
 separating tank in addition to this, before it is delivered to the return 
 
 201
 
 fl HEATING AND VENTILATION 
 
 pumps. It is bettor, however, to remove a portion of the oil before 
 the steam enters the heating system ; otherwise a coating will be formed 
 upon the inner surfaces of the radiators, which will reduce their 
 efficiency to some extent. 
 
 Forced Blast. This method of heating, in different forms, is 
 used for the warming of factories, schools, churches, theaters, halls 
 in <fact, any large building where good ventilation is desired. The 
 air for warming is drawn or forced through a heater of special design, 
 and discharged by a fan or blower into ducts .which lead to registers 
 placed in the rooms to be warmed. The heater is usually made up in 
 sections, so that steam may be admitted to or shut off from any section 
 independently of the others, and the temperature of the air regulated 
 in this manner. Sometimes a by-pass damper is attached, so that 
 part of the air will pass through the heater and part around or over it; 
 in this way the proportions of cold and heated air may be so adjusted 
 as to give the desired temperature to the air entering the rooms. These 
 forms of regulation are common where a blower is used for warming 
 a single room, as in the case of a church or hall; but where several 
 rooms are warmed, as in a schoolhouse. it is customary to use the 
 main or primary heater at the blower for warming the air to a given 
 temperature (somewhat below that which is actually required), and 
 to supplement this by placing secondary coils or heaters at the bottoms 
 of the flues leading to the different rooms. By means of this arrange- 
 ment, the temperature of each room can be regulated independently 
 of the others. The so-called double-duct system is sometimes employed. 
 In this case, two ducts are carried to each register, one supplying hot 
 air and the other cold or tempered air; and a damper for mixing these 
 in the right proportions is placed in the flue, below the register. 
 
 Electric Heating. Unless electricity can be produced at a very 
 low cost, it is not practicable for heating residences or large buildings. 
 The electric heater, however, has quite a wide field of application in- 
 heating small offices, bathrooms, electric cars, etc. It is a convenient 
 method of warming isolated rooms on cold mornings, in late spring and 
 earlv fall, when the regular heating apparatus of the building is not in 
 operation. It has the advantage of being instantly available, and the 
 amount of heat can be regulated at will. Electric heaters are clean, 
 do not vitiate the air, and are easily moved from place to place. 
 
 202
 
 HEATING AND VENTILATION f 
 
 PRINCIPLES OF VENTILATION 
 
 Closely connected with the subject of heating is the problem of 
 maintaining air of a certain standard of purity in the various buildings 
 occupied. 
 
 The introduction of pure air can be done properly only in con- 
 nection with some system of heating; and no system of heating is 
 complete without a supply of pure air, depending in amount upon the 
 kind of building and the purpose for which it is used. 
 
 Composition of the Atmosphere. Atmospheric air is not a simple 
 substance but a mechanical mixture. Oxygen and nitrogen, the 
 principal constituents, are present in very nearly the proportion of one 
 part of oxygen to four parts of nitrogen by weight. Carbonic acid gas, 
 the product of all combustion, exists in the proportion of 3 to 5 parts 
 in 10,000 in the open country. Water in the form of vapor, varies 
 greatly with the temperature and with the exposure of the air to open 
 bodies of water. In addition to the above, there are generally present, 
 in variable but exceedingly small quantities, ammonia, sulphuretted 
 hydrogen, sulphuric, sulphurous, nitric, and nitrous acids, floating 
 organic and inorganic matter, and local impurities. Air also contains 
 ozone, which is a peculiarly active form of oxygen ; and lately another 
 constituent called argon has been discovered. 
 
 Oxygen is the most important element of the air, so far as both 
 heating and ventilation are concerned. It is the active element in the 
 chemical process of combustion and also in the somewhat similar 
 process which takes place in the respiration of human beings. Taken 
 into the lungs, it acts upon the excess of carbon in the blood, and pos- 
 sibly upon other ingredients, forming chemical compounds which are 
 thrown off in the act of respiration or breathing. 
 
 Nitrogen. The principal bulk of the atmosphere is nitrogen, 
 which exists uniformly diffused with oxygen and carbonic acid gas. 
 This element is practically inert in all processes of combustion or 
 respiration. It is not affected in composition, either bypassing through 
 a furnace during combustion or through the lungs in the process of 
 respiration. Its action is to render the oxygen less active, and to 
 absorb some part of the heat produced by the process of oxidation. 
 
 Carbonic acid gas is of itself only a neutral constituent of the 
 atmosphere, like nitrogen ; and contrary to the general impression 
 its presence in moderately large quantities (if uncombined with other 
 
 203
 
 HEATING AND VENTILATION 
 
 substances) is neither disagreeable nor especially harmful. Its 
 presence, however, in air provided for respiration, decreases the readi- 
 ness with which the carbon of the blood unites with the oxygen of the 
 air; and therefore, when present in sufficient quantity, it may cause 
 indirectly, not only serious, but fatal results. The real harm of a 
 vitiated atmosphere, however, is caused by the other constituent 
 gases and by the minute organisms which are produced in the process 
 of respiration. It is known that these other impurities exist in fixed 
 proportion to the amount of carbonic acid present in an atmosphere 
 vitiated by respiration. Therefore, as the relative proportion of 
 carbonic acid can easily be determined by experiment, the fixing of a 
 standard limit of the amount in which it may be allowed, also limits the 
 amounts of other impurities which are found in combination with it. 
 
 When carbonic acid is present in excess of 10 parts in 10,000 
 parts of air, a feeling of weariness and stuffiness, generally accompanied 
 by a headache, will be experienced; \vhile with even 8 parts in 10,000 
 parts a room would be considered close. For general considerations 
 of ventilation, the limit should be placed at to 7 parts in 10,000, thus 
 allowing an increase of 2 to 3 parts over that present in, outdoor air, 
 which may be considered to contain four parts in 10,000 under ordi- 
 nary conditions. 
 
 Analysis of Air. An accurate qualitative and quantitative 
 analysis of air samples can be made only by an experienced chemist. 
 There are, however, several approximate methods for determining 
 the amount of carbonic acid present, which are sufficiently exact for 
 practical purposes. Among these the following is one of the simplest : 
 
 The necessary apparatus consists of six clean, dry, and tightly 
 corked bottles, containing respectively 100, 200, 250, 300, 350, and 400 
 cubic centimeters, a glass tube containing exactly 15 cubic centimeters 
 to a given mark, and a bottle of perfectly clear, fresh limewater. The 
 bottles should be filled with the air to be examined by means of a hand- 
 ball syringe. Add to the smallest bottle 15 cubic centimeters of the 
 limewater, put in the cork, and shake well. If the limewater has a 
 milky appearance, the amount of carbonic acid will be at least 16 
 parts in 10,000. If the contents of the bottle remain clear, treat the 
 bottle of 200 cubic centimeters in the same manner; a milky appear- 
 ance or turbidity in this would indicate 12 parts in 10,000. In a 
 similar manner, turbidity in the 250 cubic centimeter bottle indicates 
 
 204
 
 HEATING AND VENTILATION 9 
 
 10 parts in 10,000; in the 300, 8 parts; in the 350, 7 parts; and in the 
 400, less than 6 parts. The ability to conduct more accurate analyses 
 can be attained only by special study and a knowledge of chemical 
 properties and of methods of investigation. 
 
 Another method similar to the above, makes use of a glass 
 cylinder containing a given quantity of limewater and provided with a 
 piston. A sample of the air to be tested is drawn into the cylinder by 
 an upward movement of the piston. The cylinder is then thoroughly 
 shaken, and if the limewater shows a milky appearance, it indicates 
 a certain proportion of carbonic acid in the air. If the limewater 
 remains clear, the air is forced out, and another cylinder full drawn in, 
 the operation being repeated until the limewater becomes milky. 
 The size of the cylinder and the quantity of limewater are so propor- 
 tioned that a change in color at the first, second, third, etc., cylinder 
 full of air indicates different proportions of carbonic acid. This test 
 is really the same in principle as the one previously described; but the 
 apparatus used is in more convenient form. 
 
 Air Required for Ventilation. The amount of air required to 
 maintain any given standard of purity can very easily be determined, 
 provided we know the amount of carbonic acid given off in the process 
 of respiration. It has been found by experiment that the average 
 production of carbonic acid by an adult at rest is about .6 cubic foot 
 per hour. If we assume the proportion of this gas as 4 parts in 10,000 
 in the external air, and are to allow 6 parts in 10,000 in an occupied 
 room, the gain will be 2 parts in 10,000; or, in other words, there will 
 
 2 
 be = .0002 cubic foot of carbonic acid mixed with each cubic 
 
 foot of fresrf air entering the room. Therefore, if one person gives 
 off .6 cubic foot of carbonic acid per hour, it will require .6 -r- .0002 
 =* 3,000 cubic feet of air per hour per person to keep the air in the 
 room at the standard of purity assumed that is, 6 parts of carbonic 
 acid in 10,000 of air. 
 
 Table II has been computed in this manner, and shows the 
 amount of air which must be introduced for each person in order to 
 maintain various standards of purity. 
 
 While this table gives the theoretical quantities of air required 
 for different standards of purity, and may be used as a guide, it will be 
 better in actual practice to use quantities which experience has shown 
 
 205
 
 10 
 
 HEATING AND VENTILATION 
 
 to give good results in different types of buildings. In auditoriums 
 where the cubic space per individual is large, and in which the atmos- 
 phere is thoroughly fresh before the rooms are occupied, and the 
 occupancy is of only two or three hours' duration, the air-supply may 
 be reduced somewhat from the figures given below. 
 
 TABLE II 
 Quantity of Air Required per Person 
 
 STANDARD PARTS OF CARBONIC 
 ACID IN 10,000 OF AIR 
 
 CUBIC FEET OF AIR REQUIRED PER PERSON 
 
 INR OM Per Minute 
 
 Per Hour 
 
 5 
 
 100 
 
 6,000 
 
 G 
 
 50 
 
 3,000 
 
 7 
 
 33 
 
 2,000 
 
 8 
 
 25 
 
 1,500 
 
 9 
 
 20 
 
 1,200 
 
 10 
 
 16 
 
 1,000 
 
 Table III represents good modern practice and may be used 
 with satisfactory results : 
 
 TABLE III 
 Air Required for Ventilation of Various Classes of Buildings 
 
 CUBIC FEET PER 
 
 AIR-SUPPLY PER OCCUPANT FOR 
 
 MlNUlE 
 
 HOUR 
 
 Hospitals 
 
 80 to 100 
 
 4, 800 to 6, 000 
 
 High Schools 
 
 50 
 
 3, 000 
 
 Grammar Schools 
 
 40 
 
 2, 400 
 
 Theaters and Assembly Halls 
 
 25 
 
 1 , 500 
 
 Churches 
 
 20 
 
 1,200 
 
 CUBIC FEET PER 
 
 When possible, the air-supply to any given room should be based 
 upon the number of occupants. It sometimes happens, however, 
 that this information is not available, or the character of the room is 
 such that the number of persons occupying it may vary, as in the case 
 of public waiting rooms, toilet rooms, etc. In instances of this kind, 
 the required air-volume may be based upon the number of changes 
 per hour. In using this method, various considerations must be taken 
 into account, such as the use of the room and its condition as to crowd- 
 ing, character of occupants, etc. In general, the following will be 
 found satisfactory for average conditions : 
 
 206
 
 HEATING AND VENTILATION 
 
 11 
 
 TABLE IV 
 Number of Changes of Air Required in Various Rooms 
 
 USE or ROOM 
 
 CHANGES OF AIR PER HOUR 
 
 Public Waiting Room 
 
 4 to 5 
 
 Public Toilets 
 
 5 
 
 6 
 
 Coat and Locker Rooms 
 
 4 
 
 5 
 
 Museums 
 
 3 
 
 4 
 
 Offices, Public 
 
 4 
 
 5 
 
 Offices, Private 
 
 3 
 
 4 
 
 Public Dining Rooms 
 
 4 
 
 5 
 
 Living Rooms 
 
 3 
 
 4 
 
 Libraries, Public 
 
 4 
 
 5 
 
 Libraries, Private 
 
 3 
 
 4 
 
 Force for Moving Air. Air is moved for ventilating purposes in 
 two ways: (1) by expansion due to heating; (2) by mechanical means. 
 The effect of heat on the air is to increase its volume and therefore 
 lessen its density or weight, so that it tends to rise and is replaced by 
 the colder air below. The available force for moving air obtained in 
 this way is very small, and is quite likely to be overcome by wind or 
 external causes. It will be found in general that the heat used for 
 producing velocity in this manner, when transformed into work in 
 the steam engine, is greatly in 
 excess of that required to pro- 
 duce the same effect by the use of 
 a fan. 
 
 Ventilation by mechanical 
 means is performed either 'by 
 pressure or by suction. The for- 
 mer is used for delivering fresh air 
 into a building, and the latter for 
 removing the foul air from it. 
 By both processes the air is moved 
 without change in temperature, 
 and the force for moving must be sufficient to overcome the effects 
 of wind or changes in outside temperature. Some form of fan is used 
 for this purpose. 
 
 Measurements of Velocity. The velocity of air in ventilating 
 ducts and flues is measured directly by an instrument called an ane- 
 mometer. A common form of this instrument is shown in Fig. 1. It 
 consists of a series of flat vanes attached to an axis, and a series of dials. 
 
 Fig. 1. Common Form of Anemometer, for 
 Measuring Velocity of Air-Currents. 
 
 207
 
 12 HEATING AND VENTILATION 
 
 The revolution of the axis causes motion of the hands in proportion to 
 the velocity of the air, and the result can he read directly from the dials 
 for any given period. 
 
 For approximate results the anemometer may be slowly moved 
 across the opening in either vertical or horizontal parallel lines, so 
 that the readings will be made up of velocities taken from all parts of 
 the opening. For more accurate work, the opening should be divided 
 into a number of squares by means of small twine, and readings taken 
 at the center of each. The mean of these readings will give the 
 average velocity of the air through the entire opening. 
 
 AIR DISTRIBUTION 
 
 The location of the air inlet to a room depends upon the size of 
 the room and the purpose for which it is used. In the case of living 
 rooms in dwelling-houses, the registers are placed either in the floor 
 or in the wall near the floor; this brings the warm air in at the coldest 
 part of the room and gives an opportunity for warming or drying the 
 feet if desired. In the case of schoolrooms, where large volumes of 
 warm air at moderate temperatures are required, it is best to discharge 
 it through openings in the wall at a height of 7 or 3 feet from the floor; 
 this gives a more even distribution, as the warmer air tends to rise and 
 hence spreads uniformly under the ceiling; it then gradually displaces 
 other air, and the room becomes filled with pure air without sensible 
 currents or drafts. The cooler air sinks to the bottom of the room, and 
 can be taken off through ventilating registers placed near the floor. 
 The relative positions of the inlet and outlet are often governed to 
 some extent by the building construction; but, if possible, they should 
 both l>e located in the same side of the room. Figs. 2, 3, and 4 show 
 common arrangements. 
 
 The vent outlet should always, if possible, be placed in an inside 
 wall ; otherwise it will become chilled and the air-flow through it will 
 become sluggish. In theaters and churches which are closely packed, 
 the air should enter at or near the floor, in finely-divided streams; and 
 the discharge ventilation should be through openings in the ceiling. 
 The reason for this is the large amount of animal heat given off from 
 the bodies of the audience; this causes the air to become still further 
 heated after entering the room, and the tendency is to rise continuously 
 
 ROh
 
 HEATING AND VENTILATION 
 
 13 
 
 from floor to ceiling, thus carrying away all impurities from respiration 
 as fast as they are given off. 
 
 All audience halls in which the occupants are closely seated should 
 be treated in the same manner, when possible. This, however, can- 
 not always be done, as the seats are often made removable so that the 
 
 ours/oe WALL 
 
 OUTSIDE \MALL 
 
 OUTSIDE V&UJ. 
 
 Fig. 3. Fig. 3. Fig. 4. 
 
 Diagrams Showing Relative Positions of Air Inlets and Outlets as Commonly. Arranged. 
 
 floor can be used for other purposes. In cases of this kind, part of 
 the air may be introduced through floor registers placed along the outer 
 aisles, and the remainder by means of wall inlets the same as for school- 
 rooms. The discharge ventilation should be partly through registers 
 near the floor, supplemented by ample ceiling vents for use when the 
 hall is crowded or the outside temperature high. 
 
 The matter of air-velocities, size of flues, etc., will be taken up 
 under the head of "Indirect Heating." 
 
 HEAT LOSS FROM BUILDINGS 
 
 A British Thermal Unit, or B. T. U., has been defined as the 
 amount of heat required to raise the temperature of one pound of 
 water one degree F. This measure of heat enters into many of the 
 calculations involved in the solving of problems in heating and ventila- 
 tion, and one should familiarize himself with the exact meaning of 
 the term. 
 
 Causes of Heat Loss. The heat loss from a building is due to 
 the following causes: (1) radiation and conduction of heat through 
 walls and windows; (2) leakage of warm air around doors and win- 
 dows and through the walls themselves; and (3) heat required to warm 
 the air for ventilation. 
 
 Loss through Walls and Windows. The loss of heat through 
 the walls of a building depends upon the material used in construction
 
 1 1 
 
 HEATING AND VENTILATION 
 
 TABLE V 
 
 Heat Losses in B. T. U. per Square Foot of Surface per Hour- 
 Southern Exposure 
 
 
 
 IDE 
 
 AND 
 
 OUT- 
 
 
 
 
 10 
 
 20 
 
 30 
 
 40 
 
 50 60 
 
 70 
 
 80 
 
 90 
 
 100 
 
 8-in. Br ck Wall 
 
 5 
 
 9 
 
 13 
 
 18 
 
 22 27 31 
 
 36 40 
 
 45 
 
 12-in. Br ck Wall 
 
 4 
 
 7 
 
 10 13 
 
 ie; 20 23 
 
 26 
 
 30 33 
 
 16-in. Br ck Wall 
 
 3 
 
 5 
 
 8 ; 10 
 
 13 16 
 
 19 
 
 22 
 
 24 
 
 27 
 
 20-in. Br ck Wall 
 
 2.8 
 
 4.5 
 
 7 9 
 
 11 14 
 
 16 
 
 18 
 
 20 
 
 23 
 
 24-in. Br ck Wall 
 
 2.5 
 
 4 
 
 6 
 
 8 
 
 10 12 
 
 14 
 
 1(1 
 
 18 
 
 20 
 
 2S-in. Brick Wall 
 
 2 
 
 3.5 
 
 5 
 
 7 
 
 9 11 
 
 13 
 
 14 
 
 16 
 
 18 
 
 32-in. Brick Wall 
 
 1 5 
 
 3 
 
 4 5 
 
 fi 
 
 8 10 
 
 11 
 
 13 
 
 15 
 
 16 
 
 Single Window 
 
 12 
 
 24 
 
 36 
 
 lit 
 
 60 73 
 
 85 
 
 93110122 
 
 Double Window 
 
 8 
 
 16 
 
 24 
 
 32 
 
 40 48 
 
 56 
 
 62 
 
 7D 
 
 78 
 
 Single Skylight 
 
 11 
 
 21 
 
 31 
 
 42 52 63 
 
 73 
 
 84 
 
 94 
 
 104 
 
 Double Skylight 
 
 7 
 
 14 
 
 90 
 
 28 35 
 
 1" 
 
 48 
 
 56 
 
 62 
 
 70 
 
 
 
 12 
 
 16 20 
 
 94 
 
 98 
 
 
 
 Ofi 
 
 
 
 3 
 
 K 
 
 Q 
 
 
 i - 
 
 90 
 
 ')-> 
 
 
 
 2-in. Solid Plaster Partition 
 
 6 
 
 12 
 
 18 
 
 24 30 
 
 36 
 
 4? 
 
 48 
 
 54 
 
 60 
 
 3-in. Solid Plaster Partition 5 
 
 10 
 
 15 
 
 20! 25 
 
 30s 35 
 
 41 
 
 45 
 
 50 
 
 Concrete Floor on Brick Arch. ... 9 4 
 
 6.5 
 
 9| 11 
 
 13) 15 
 
 18 
 
 20 22 
 
 Wood Floor on Brick Arch 
 
 1.5 3 
 
 4 5 
 
 6: 7 
 
 9 10 
 
 12 13 15 
 
 Double Wood Floor 
 
 1 
 
 2 
 
 3 
 
 4 5 
 
 6 
 
 7 
 
 8 9 10 
 
 Walls of Ordinary Wooden 
 
 
 
 
 
 
 
 
 
 
 
 Dwellings 
 
 3 5 
 
 8 
 
 10, 13 
 
 16 19 
 
 22 24 27 
 
 1 ; i 
 
 For solid stone walls, multiply the figures for brick of the same thickness 
 by 1.7. Where rooms have a cold attic above or cellar beneath, multiply the 
 heat loss through walls and windows by 1.1. 
 
 Correction for Leakage. The figures given in the above table apply only 
 to the most thorough construction. For the average well-built house, the 
 results should be increased about 10 per cent; for fairly good construction, 
 20 per cent; and for poor construction, 30 per cent. 
 
 Table V applies only to a southern exposure; for other exposures multi- 
 ply the heat loss given in Table V by the factors given in Table VI. 
 
 of the wall, the thickness, the number of layers, and the difference 
 between the inside and outside temperatures. The exact amount of 
 heat lost in this way is very difficult to determine theoretically, hence 
 we depend principally on the results of experiments. 
 
 Loss by Air-Leakage. The leakage of air from a room varies 
 from one to two or more changes of the entire contents per hour, 
 depending upon the construction, opening of doors, etc. It is com- 
 mon practice to allow for one change per hour in well-constructed 
 buildings where two walls of the room have an outside exposure. As 
 the amount of leakage depends upon the extent of exposed wall and 
 window surface, the simplest way of providing for this is to increase 
 
 310
 
 HEATING AND VENTILATION 15 
 
 TABLE VI 
 Factors for Calculating Heat Loss for Other than Southern Exposures 
 
 EXPOSURE 
 
 FACTOR 
 
 N. 
 
 1.32 
 
 E. 
 
 1.12 
 
 S. 
 
 1.0 
 
 w. 
 
 1.20 
 
 N.E. 
 
 1.22 
 
 N.W. 
 
 1.26 
 
 S.E. 
 
 1.06 
 
 s.w. 
 
 1.10 
 
 N., E., S., and W., or total exposure 
 
 1.16 
 
 the total loss through walls and windows by a factor depending upon 
 the tightness of the building construction. Authorities differ con- 
 siderably in the factors given for heat losses, and there are various 
 methods for computing the same. The figures given in Table V have 
 been used extensively in actual practice, and have been found to give 
 good results when used with judgment. The table gives the heat losses 
 through different thicknesses of walls, doors, windows, etc., in B. T. 
 IL, per square foot of surface per hour, for varying differences in inside 
 and outside temperatures. 
 
 In computing the heat loss through walls, only those exposed to 
 the outside air are considered. 
 
 In order to make the use of the table clear, we shall give a num- 
 ber of examples illustrating its use: 
 
 Example 1. Assuming an inside temperature of 70, what will be the 
 heat loss from a room having an exposed wall surface of 200 square feet and a 
 gclass surface of 50 square feet, when the outside temperature is zero? The 
 wall is of brick, 16 inches in thickness, and has a southern exposure; the win- 
 dows are single; and the construction is of the best, so that no account need 
 be taken of leakage 
 
 We find from Table V, that the factor for a 16-inch brick wall 
 with a difference in temperature of 70 is 19, and that for glass (single 
 window) under the same condition is 85; therefore, 
 
 Loss through walls = 200 X 19 = 3,800 
 Loss through windows = . 50 X 85 = 4,250 
 
 Total loss per hour = 8,050 B.T.U. 
 
 Example 2. A room 15 ft. square and 10 ft. high has two exposed walls, 
 one toward the north, and the other toward the west. There are 4 windows, 
 each 3 feet by 6 feet in size. The two in the north wall are double, while the 
 
 311
 
 16 HEATING AND VENTILATION 
 
 other two are single. The walls are of brick, 20 inches in thickness. With an 
 inside temperature of 70. what will be the heat loss per hour when it is 10 
 below zero? 
 
 Total exposed surfaee = 15 X 10 X 2 - 300 
 Glass surface = 3 X C X 4 = 72 
 
 Net wall surface 228 
 
 Difference between inside and outside temperature SO . 
 Factor for 20-inch brick wall is 18. 
 Factor for single window is 93. 
 Factor for double window is 62. 
 The heat losses are as follows: 
 
 Wall, 228 X 18 - 4,104 
 
 Single windows, 36 X 93 = 3,348 
 
 Double windows, 36 X 62 = 2,232 
 
 9,684 B.T.U. 
 
 As one side is toward the north, and the other toward the west, the 
 actual exposure is N. W. Looking in Table VI, we find the correction 
 factor for this exposure to be 1.26; therefore the total heat loss is 
 9,684 X 1.26 = 12,201.84 B.T.U. 
 
 1'lxnmple 3. A dwelling-house of fair wooden construction measures 
 160 ft. around the outside; it has 2 stories, each 8 ft. in height; the windows 
 are single, and the glass surface amounts to one-fifth the total exposure; the 
 attic and cellar are umvarmed. If 8,000 B. T. I*, are utilized from each pound 
 of coal burned in the furnace, how many pounds will be required per hour to 
 maintain a temperature of 70 when it is 20 above zero outside? 
 
 Total exposure = 160 X 1 
 Glass surface = 2,560 -H 
 
 Net wall 
 
 Temperature difference = 70 20 = 50 
 Wall 2,048 X 13 = 26,624 
 
 Glass 512 X 60 = 30,720 
 
 57,344 B.T.U. 
 
 As the building is exposed on all sides, the factor for exposure will be 
 the average of those for N., E., S., and W., or 
 
 (1.32 + 1.12 + 1.0 + 1.20) -f- 4 = 1 16 
 The house has a cold cellar and attic, so we must increase the heat loss 
 
 318
 
 HEATING AND VENTILATION 17 
 
 10 per cent for each of the first two conditions, and 20 per cent for the 
 last. Making these corrections we have: 
 
 57,344 X 1.16 X 1.10 X 1.10 X 1.20 = 96,338 B.T.U. 
 If one pound of coal furnishes 8,000 B. T. IL, then 96,338 -f- 8,000 = 
 12 pounds of coal per hour required to warm the building to 70 
 under the conditions stated. 
 
 Approximate Method. For dwelling-houses of the average con- 
 struction, the following simple method for calculating the heat loss 
 may be used. Multiply the total exposed surface by 45, which will 
 give the heat loss in B. T. U. per hour for an inside temperature of 70 
 in zero weather. 
 
 This factor is obtained in the following manner : Assume the glass 
 surface to be one-sixth the total exposure, which is an average propor- 
 tion. Then each square foot of exposed surface consists one-sixth 
 of glass and five-sixths of wall, and the heat loss for 70 difference in 
 temperature would be as follows : 
 
 Wall X 19 = 15.8 
 
 Glass X 85 = 14.1 
 8 
 
 29.9 
 
 Increasing this 20 per cent for leakage, 16 per cent for exposure, and 
 10 per cent for cold ceilings, we have : 
 
 29.9 X 1.20 X 1.16 X 1.10 = 45. 
 
 The loss through floors is considered as being offset by including 
 the kitchen walls of a dwelling-house, which are warmed by the range, 
 and which would .not otherwise be included if computing the size of a 
 furnace or boiler for heating. . 
 
 If the heat loss is required for outside temperatures other than 
 zero, multiply by 50 for 10 degrees below, and by 40 for 10 degrees 
 above zero. 
 
 This method is convenient for approximations in the case of 
 dwelling-houses; but the more exact method should be used for other 
 types of buildings, and in all cases for computing the heating surface 
 for separate rooms. When calculating the heat loss from isolated 
 rooms, the cold inside walls as well as the outside must be considered. 
 
 The loss through a wall next to a cold attic or other un warmed space 
 may in general be taken as about two-thirds that of an outside wall.
 
 18 HEATING AND VENTILATION 
 
 Heat Loss by Ventilation. One B. T. U. will raise the tempera- 
 ture of 1 cubic- foot of air 55 degrees at average temperatures and 
 pressures, or will raise 55 cubic feet 1 degree, so that the heat required 
 for the ventilation of any room can be found by the following formula : 
 
 Cu. ft. of air per hour X Number of degrees rise 
 
 ^ = B. 1 . I . required. 
 
 To compute the heat loss for any given room which is to be 
 ventilated, first find the loss through walls and windows, and correct 
 for exposure and leakage; then compute the amount required for 
 ventilation as above, and take the sum of the two. An inside tem- 
 perature of 70 is always assumed unless otherwise stated. 
 
 Examples. What quantity of heat will be required to warm 100,000 
 cubic feet of air to 70 for ventilating purposes when the outside temperature 
 is 10 below zero? 
 
 100,000 X 80 -r- 55 = 145,454 B. T. U. 
 
 How many B. T. T . will be required per hour for the ventilation of a 
 church seating 500 people, in zero weather? 
 
 Referring to Table III, we find that the total air required per 
 hour is 1,200 X 500 - 600,000 cu. ft.; therefore 600,000 X 70 -T- 55 
 - 763,636 B. T. U. 
 
 Rise in Temperature . 
 The factor - is approximately 1.1 for 60 , 
 
 1.3 for 70, and 1.5 for 80. Assuming a temperature of 70 for the 
 entering air, we may multiply the air-volume supplied for ventilation 
 by 1.1 for an outside temperature of 10 above 0, by 1.3 for zero, and 
 by 1 .5 for 10 below zero which covers the conditions most commonly 
 met with in practice. 
 
 EXAMPLES FOR PRACTICE 
 
 1. A room in a grammar school 28 ft. by 32 ft. and 12 feet high is 
 to accommodate 50 pupils. The walls are of brick 16 inches in thick- 
 ness; and there are 6 single windows in the room, each 3 ft. by 6 ft.; 
 there are warm rooms above and below; the exposure is S. E. How 
 many B. T. U. will be required per hour for warming the room, and 
 how many for ventilation, in zero weather, assuming the building to 
 be of average construction? 
 
 Axs. 24,261 + for warming; 152,727 + for ventilation. 
 
 2. A stone church seating 400 people has walls 20 inches in 
 thickness. It has a wall exposure of 5,000 square feet, a glass expos- 
 
 814
 
 HEATING AND VENTILATION 19 
 
 tire (single windows) of 600 square feet, and a roof exposure of 7,000 
 square feet; the roof is of 2-inch pine plank, and the factor for heat 
 loss may be taken the same as for a 2-inch wooden door. The floor 
 is of wood on brick arches, and has a.n area of 4,000 square feet. The 
 building is exposed on all sides, and is of first-class construction. 
 What will be the heat required per hour for both warming and ventila- 
 tion when the outside temperature is 20 above zero? 
 
 ANS. 296,380 for warming; 436,363 + for ventilation. 
 3. A dwelling-house of average wooden construction measures 
 200 feet around the outside, and has 3 stories, each 9 feet high. 
 Compute the heat loss by the approximate method when the tem- 
 perature is 10 below zero. 
 
 ANS. 270,000 B. T. U. per hour. 
 
 FURNACE HEATING 
 
 In construction, a furnace is a large stove with a combustion 
 chamber of ample size over the fire, the whole being inclosed in a 
 casing of sheet iron or brick. The bottom of the casing is provided 
 with a cold-air inlet, and at the top are pipes which connect with 
 registers placed in the various rooms to be heated. Cold, fresh air 
 is brought from out of doors through a pipe or duct called the cold-air 
 box; this air enters the space between the casing and the furnace near 
 the bottom, and, in passing over the hot surfaces of the fire-pot and 
 combustion chamber, becomes heated. It then rises through the 
 warm-air pipes at the top of the casing, and is discharged through the 
 .registers into the rooms above. / 
 
 As the warm air is taken from the top of the furnace, cold air 
 flows in through the cold-air box to take its place. The air for heating 
 the rooms does not enter the combustion chamber. 
 
 Fig. 5 shows the general arrangement of a furnace with its con- 
 necting pipes. The cold-air inlet is seen at the bottom, and the hot-air 
 pipes at the top; these are all provided with dampers for shutting off or 
 regulating the amount of air flowing through them. The feed or fire 
 door is shown at the front, and the ash door beneath it; a water-pan is 
 placed inside the casing, and furnishes moisture to the warm air before 
 passing into the rooms; water is either poured into the pan through an 
 opening in the front, provided for this purpose, or is supplied auto- 
 matically through a pipe. 
 
 215
 
 20 
 
 HEATING AND VENTILATION 
 
 The fire 1 is regulated by means of a draft slide in the ash door, and 
 a cold-air or regulating damper placed in the smoke-pipe. Clean-out 
 doors are placed at different points in the casing for the removal of 
 
 ashes and soot. Furnaces* are made either of cast iron, or of wrought- 
 iron plates riveted together and provided with brick-lined firepots. 
 
 Types of Furnaces. Furnaces may be divided into two general 
 
 216
 
 HEATING AND VENTILATION 
 
 21 
 
 types known as direct-draft and indirect-draft. Fig. 6 shows a com- 
 mon form of direct-draft furnace with a brick setting; the better class 
 have a radiator, generally placed at the top, through which the gases 
 pass before reaching the smoke-pipe. They have but one damper, 
 usually combined with a cold-air check. Many of the cheaper direct- 
 
 Fig. 6. A Common Type of Direct-Draft Furnace in Brick Setting. 
 'Cast-Iron Radiator at Top. 
 
 draft furnaces have no radiator at all, the gases passing directly into 
 the smoke-pipe and carrying away much heat that should be utilized. 
 
 The furnace shown in Fig. 6 is made of cast iron and has a large 
 radiator at the top; the smoke connection is shown at the rear. 
 
 Fig. 7 represents another form of direct-draft furnace. In this 
 case the radiator is made of sheet-steel plates riveted together, and the 
 outer casing is of heavy galvanized iron instead of brick. 
 
 In the ordinary indirect-draft type of furnace (see Fig. 8), the 
 gases pass downward through flues to a radiator located near the base, 
 
 217
 
 >> 
 
 HEATING AND VENTILATION 
 
 thence upward through another flue to the smoke-pipe. In addition 
 to the damper in the smoke-pipe, a direct-draft damper is required 
 to give direct connection with the funnel when coal is first put on, to 
 facilitate the escape of gas to the chimney. When the chimney draft 
 
 r. 7. Direct-Draft Furnace with Galvanized-Iron Casing. Radiator (at top) 
 Made of Riveted Steel Plates. 
 
 is weak, trouble from gas is more likely to be experienced with fur- 
 naces of this type than with those having a direct draft. 
 
 Grates. No part of a furnace is of more importance than the 
 grates. The plain grate rotating about a center pin was for a long 
 time the one most commonly used. These grates were usually pro- 
 vided with a clinker door for removing any refuse too large to pass 
 between the grate bars. The action of such grates tends to leave a 
 
 21S
 
 CONE EXHAUST FAN, INLET SIDE. 
 
 American Blower Co.
 
 HEATING AND VENTILATION 
 
 23 
 
 cone of ashes in the center of the fire causing it to burn more freely 
 around the edges. A better form of grate is the revolving triangular 
 pattern, which is now used in many of the leading furnaces. It con- 
 sists of a series of triangular bars having teeth. The bars are con- 
 nected by gears, and are turned by means of a detachable lever. If 
 
 Fig. 8. Indirect-Draft Tj 
 
 >e of Furnace. Gases Pass Downward to Kadiator at Bottom, 
 Thence Upward to Smoke-Pipe. 
 
 properly used, this grate will cut a slice of ashes and clinkers from 
 under the entire fire with little, if any loss of uncr nsumed coal. 
 
 The Firepot. Firepots are generally made of cast iron or of steel 
 plate lined with firebrick. The depth ranges from about 12 to 18 
 inches. In cast-iron furnaces of the better class, the firepot is made 
 very heavy, to insure durability and to render it less likely to become 
 red-hot. The firepot is sometimes made in two pieces, to reduce the 
 
 219
 
 HEATING AXD VENTILATION 
 
 liability to cracking. The heating surface is sometimes increased by 
 corrugations, pins, or ribs. 
 
 A tirebrick lining is necessary in a wrought-iron or steel furnace 
 to protect the thin shell from the intense heat of the fire. Since brick- 
 lined rirepots are much less effective than cast-iron in transmitting 
 heat, such furnaces depend to a great extent for their efficiency on the 
 heating surface in the dora: and radiator: and this, as a rule, is much 
 greater than in those of cast iron. 
 
 Cast-iron furnaces have the advantage when coal is first put on 
 ami the drop flues and radiator are cut out by the direct dampen of 
 still giving off heat 'rom the fi repot, while in the case of brick linings 
 very little heat is given off 5:. this way. and the rooms are likely tc 
 :.-"ine somewhat cooled before the fresh coal becomes thoroughly 
 united. 
 
 Combustion Chamber. The body of the furnace alx>ve the fire- 
 ixit. commonly called the dome or feed section, provides a combustion 
 chamlier. This chaml>er should be of sufficient size to permit the 
 i-ases to become thoroughly mixed with the air passing up through the 
 rire or entering through openings provided for the purpose in the feed 
 door. In a well-designed furnace, this space should be somewhat 
 larger than the firepot. 
 
 Radiator. The radiator, so called, with which all furnaces of 
 the better class are provided, acts as a sort of reservoir in which the 
 u'ases are kept in contact with the air passing over the furnace until 
 they have parted with a considerable portion of their heat. Radiators 
 an- built of ca-t iron, of steel plate, or of a combination of the two. 
 The former is more durable and can l>e marie with fewer joints, but 
 owing to the difficulty of casting radiators of large size, steel plate is 
 commonly used for the sides. 
 
 The effectiveness of a radiator depends on its form, its heating 
 surface, and the difference between the temperature of the gases and 
 the surrounding air. Owing to the accumulation of soot, the bottom 
 surface becomes practically worthless after the furnace has been in 
 :>e a short time: surfaces, to be effective, must therefore be self- 
 cleaning. 
 
 If the radiator is placed near the bottom of the furnace the gases 
 are surrounded by air at the lowest temperature, which renders the 
 radiator more effective for a given size than if placed near the top and 
 
 220
 
 HEATIXG AXD VENTILATIOK 2-5 
 
 surrounded by warm air. On the other hand, the cold air has a ten- 
 dency to condense the gases, and the acids thus formed are likely to 
 corrode the iron. 
 
 Heating Surface. The different heating surfaces may be de- 
 scribed as follows: Firepot surface; surfaces acted upon by direct 
 rays of heat from the fire, such as the dome or combustion chamber; 
 gas- or smoke-heated surfaces, such as flues or radiators; and ex- 
 tended surfaces, such as pins or ribs. Surfaces unlike in character 
 and location, vary greatly in heating power, so that, in making com- 
 parisons of different furnaces, we must know the kind, form, and 
 location of the heating surfaces, as well as the area. 
 
 In some furnaces having an unusually large amount of surface, 
 it will be -found on inspection that a large part would soon become 
 practically useless from the accumulation cf soot. In others a large 
 portion of the surface is lined with firebrick, or is so situated that the 
 air-currents are not likely to strike it. 
 
 The ratio of grate to heating surface varies somewhat according 
 to the size of furnace. It may be taken as 1 to 25 in the smaller sizes, 
 and 1 to 15 in the larger. 
 
 Efficiency. One of the first items to be determined in esti- 
 mating the heating capacity of a furnace, is its efficiency that is, 
 the proportion of the heat in the coal that may be utilized for warming. 
 The efficiency depends chiefly on the area of the heating surface as 
 compared with the grate, on its character and arrangement, and on 
 the rate of combustion. The usual proportions between grate and 
 heating surface have been stated. The rate of combustion required 
 to maintain a temperature of 70 in the house, depends, of course, 
 on the outside temperature. In very cold weather a rate of 4 to 5 
 pounds of coal per square foot of grate per hour must be main- 
 tained. 
 
 One pound of good anthracite coal will give off about 13,000 
 B. T. U., and a good furnace should utilize 70 per cent of this heat. 
 The efficiency of an ordinary furnace is often much less, sometimes 
 as low as 50 per cent. 
 
 In estimating the required size of a first-class furnace with good 
 chimney draft, we may safely count upon a maximum combustion 
 of 5 pounds of coal per square foot of grate per hour, and may assume 
 that 8,000 B. T. U. will be utilized for warming purposes from each 
 
 221
 
 20 HEATING AND VENTILATION 
 
 pound burned. This quantity corresponds to an efficiency of GO 
 
 per cent. 
 
 Heating Capacity. Having determined the heat loss from a 
 building by the methods previously given, it is a simple matter to 
 compute the size of grate necessary to burn a sufficient quantity of 
 coal to furnish the amount of heat required for warming. 
 
 In computing the size of furnace, it is customary to consider the 
 whole house as a single room, with four outside walls and a cold attic. 
 The heat losses by conduction and leakage are computed, and in- 
 creased 10 per cent for the cold attic, and 16 per cent for exposure. 
 The heat delivered to the various rooms may be considered as being 
 made up of two parts first, that required to warm the outside air 
 up to 70 (the temperature of the rooms); and second, the quantity 
 which must be added to this to offset the loss by conduction and leak- 
 age. Air is usually delivered through the registers at a temperature 
 of 120, with zero conditions outside, in the best class of residence 
 
 work; so that of the heat given to the entering air may be con- 
 
 50 
 sidered as making. up the first part, mentioned above, leaving 
 
 available for purely heating purposes. From ihis it is evident that 
 
 50 
 the heat supplied to the entering air must be equal to 1 -f- - = 2.4 
 
 times that required to offset the loss by conduction and leakage. 
 
 Example. The loss through the walls and windows of a building is 
 found to be 80,000 B. T. U. per hour in zero weather. What will be the size 
 of furnace required to maintain an inside temperature of 70 degrees? 
 
 From the above, we have the total heat required, equal to 80,000 
 X 2.4 = 192,000 B. T. U. per hour. If we assume that 8,000 B. T. 
 U. are utilized per pound of coal, then 192,000 * 8,000 - 24 pounds 
 of coal required per hour; and if o pounds can be burned on each 
 
 24 
 square foot of grate per hour, then-^- == 4.8 square feet required. 
 
 A grate 30 inches in diameter has an area of 4.9 square feet, and is the 
 size we should use. 
 
 When the outside temperature is taken as 10 below zero, multi- 
 ply by 2.6 instead of 2.4; and multiply by 2.8 for 20 below. 
 
 Table VII will be found useful in determining the diameter of 
 fi repot required.
 
 HEATING AND VENTILATION" 27 
 
 TABLE VII 
 
 Firepot Dimensions 
 
 AVERAGE DIAMETER OF GRATE, IN INCHES 
 
 AREA IN SQUARE FEET 
 
 18 
 
 1.77 
 
 20 
 
 2.18 
 
 22 
 
 2.64 
 
 24 
 
 3.14 
 
 26 
 
 3.69 
 
 28 
 
 4.27 
 
 30 
 
 4.91 
 
 32 
 
 5.58 
 
 EXAMPLES FOR PRACTICE 
 
 1. A brick apartment house is 20 feet wide, and has 4 stories, 
 each being 10 feet in height. The house is one of a block, and is 
 exposed only at the front and rear. The walls are 16 inches thick, 
 and the block is so sheltered that no correction need be made for 
 exposure. Single windows make up ^ the total exposed surface. 
 Figure for cold attic but warm basement. What area of grate surface 
 will be required for a furnace to keep the house at a temperature of 
 70 when it is 10 below zero outside? ANS. 3.5 square feet. 
 
 2. A house having a furnace with a firepot 30 inches in diameter, 
 is not sufficiently warmed, and it is decided to add a second furnace 
 to be used in connection with the one already in. The heat loss from 
 the building is found by computation to be 133,600 B. T. U. per hour, 
 in zero weather. What diameter of firepot will be required for the 
 extra furnace? ANS. 24 inches. 
 
 Location of Furnace. A furnace should be so placed that the 
 warm-air pipes will be of nearly the same length. The air travels 
 most readily through pipes leading toward the sheltered side of the 
 house and to the upper rooms. Therefore pipes leading tow r ard the 
 north or west, or to rooms on the first floor, should be favored in 
 regard to length and size. The furnace should be placed somewhat 
 to the north or west of the center of the house, or toward the points 
 of compass from which the prevailing winds blow. 
 
 Smoke=Pipes. Furnace smoke-pipes range in size from about 
 6 inches in the smaller sizes to 8 or 9 inches in the larger ones. They 
 are generally made of galvanized iron of No. 24 gauge or heavier. 
 The pipe should be carried to the chimney as directly as possible, 
 
 323
 
 28 HEATING AND VENTILATION 
 
 avoiding bends which increase the resistance and diminish the draft. 
 Where a smoke-pipe passes through a partition, it should be pro- 
 tected by a soapstone or double-perforated metal collar having a 
 diameter at least 8 inches greater than that of the pipe. The top of 
 the smoke-pipe should not be placed within 8 inches of unprotected 
 beams, nor less than inches under beams protected by asbestos or 
 plaster with a metal shield beneath. A collar to make tight con- 
 nection with the chimney should be riveted to the pipe about 5 inches 
 from the end, to prevent the pipe being pushed too far into the flue. 
 Where the pipe is of unusual length, it is well to cover it to prevent 
 loss of heat and the condensation of smoke. 
 
 Chimney Flues. Chimney flues, if built of brick, should have 
 walls 8 inches in thickness, unless terra-cotta linings are used, when 
 only 4 inches of brickwork is required. Except in small houses 
 where an 8 by 8-inch flue may be used, the nominal size of the smoke 
 flue should be at least 8 by 12-inches;to allow for contractions or off- 
 sets. A clean-out door should be placed at the bottom of the flue, 
 for removing ashes and soot. A square flue cannot be reckoned at 
 its full area, as the corners are of little value. To avoid down drafts, 
 the top of the chimney must be carried above the highest point of the 
 roof unless provided with a suitable hood or top. 
 
 Cold=Air Box. The cold-air box should be large enough to 
 supply a volume of air sufficient to fill all the hot-air pipes at the same 
 time. If the supply is too small, the distribution is sure to be unequal, 
 and the cellar will become overheated from lack of air to carry away 
 the heat generated. 
 
 If a box is made too small, or is throttled down so that the volume 
 of air entering the furnace is not large enough to fill all the pipes, 
 it will be found that those leading to the less exposed side of the 
 house or to the upper rooms will take the entire supply, and that 
 additional air to supply the deficiency will be drawn down through 
 registers in rooms less favorably situated. It is common practice 
 to make the area of the cold-air box three-fourths the combined 
 area of the hot-air pipes. The inlet should be placed where the 
 prevailing cold winds will blow into it; this is commonly on the north 
 or west side of the house. If it is placed on the side awav from the 
 wind, warm air from the furnace is likely to be drawn out through 
 the cold -air box. 
 
 224
 
 HEATING AND VENTILATION 
 
 2!) 
 
 Whatever may be the location of the entrance to the cold-air 
 box, changes in the direction of the wind may take place which will 
 bring the inlet on the wrong side of the house. To prevent the 
 possibility of such changes affecting the action of the furnace, the 
 cold-air box is sometimes extended through the house and left open 
 at both ends, with check-dampers arranged to prevent back-drafts. 
 These checks should be placed some distance from the entrance, to 
 prevent their becoming clogged with snow or sleet. 
 
 The cold-air box is generally made of matched boards; but 
 galvanized iron is much better; it costs more than wood, but is well 
 worth the extra expense on account of tightness, which keeps the dust 
 and ashes from being drawn into the furnace casing to be discharged 
 through the registers into the rooms above. 
 
 The cold-air inlet should be covered with galvanized wire netting 
 with a mesh of at least three-eighths of an inch. The frame to which 
 it is attached should not 
 
 ^ FOFI RETURNING 
 
 be smaller than the in- |'| { AIR mow ABOVE 
 
 side dimensions of the 
 
 cold-air box. A door to 
 
 admit air from the cellar 
 
 to the cold-air box is 
 
 generally provided. As 
 
 a rule, air should be 
 
 taken from this source, 
 
 only when the house is 
 
 temporarily unoccupied 
 
 or during high winds. 
 
 Return Duct. In 
 some cases it is desirable 
 to return air to the fur- 
 nace from the rooms 
 above, to be reheated. Ducts for this purpose are common in places 
 where the winter temperature is frequently below zero. Return 
 ducts when used, should be in addition to the regular cold-air box. 
 Fig. 9 shows a common method of making the connection between 
 the two. By proper adjustment of the swinging damper, the air can 
 be taken either from out of doors or through the register from the 
 room above. The return register is often placed in the hallway of 
 
 Fig 9. Common Method of Connecting Return Duct to 
 Cold- Air Box.
 
 30 
 
 HEATING AND VENTILATION 
 
 a house, so that it will take the cold air which rushes in when the 
 door is opened and also that which may leak in around it while 
 closed. Check-valves or flaps of light gossamer or woolen cloth 
 should be placed between the cold-air box and the registers to pre- 
 vent back-drafts during winds. 
 
 The return duct should not be used too freely at the expense of 
 outdoor air, and its use is not recommended except during the night 
 when air is admitted to the sleeping rooms through open windows. 
 
 Warm=Air Pipes. The required size of the warm-air pipe to 
 any given room, depends on the heat loss from the room and on the 
 volume of warm air required -to offset this loss. Each cubic foot of 
 air warmed from zero to 120 degrees brings into a room 2.2 B. T. U. 
 \Ve have already seen that in zero weather, with the air entering the 
 
 50 
 
 registers at 120 degrees, only - - of the heat contained in the air is 
 
 available for offsetting the losses by radiation and conduction, so that 
 
 50 
 
 only 2.2 X == .OB. T. U. in each cubic foot of entering air can 
 
 be utilized for warming purposes. Therefore, if we divide the com- 
 puted heat loss in B. T. U. from a room, by .9, it will give the number 
 of cubic feet of air at 120 degrees necessary to warm the room in zero 
 weather. 
 
 As the outside temperature becomes colder, the quantity of heat 
 brought in per cubic foot of air increases; but the proportion avail- 
 able for warming purposes becomes less at nearly the same rate, so 
 
 TABLE VIII 
 Warm=Air Pipe Dimensions 
 
 DIAMETER OF PIPE, 
 IN INCHES 
 
 AREA AREA 
 IN SQUARE INCHES IN SQUARE FEET 
 
 6 
 
 28 .196 
 
 7 
 
 38 
 
 .267 
 
 8 
 
 50 
 
 .349 
 
 9 64 
 
 .442 
 
 10 
 
 79 
 
 .545 
 
 11 
 
 95 
 
 .660 
 
 12 
 
 113 
 
 .785 
 
 13 
 
 133 
 
 .922 
 
 14 
 
 154 
 
 1.07 
 
 15 
 
 177 
 
 1.23 
 
 16 
 
 201 
 
 1.40
 
 HEATING AND VENTILATION 31 
 
 that for all practical purposes we may use the figure .9 for all usual 
 conditions. In calculating the size of pipe required, we may assume 
 maximum velocities of 260 and 380 feet per minute for rooms on the 
 first and second floors respectively. Knowing the number of cubic 
 feet of air per minute to be delivered, we can divide it by the velocity, 
 which will give us the required area of the pipe in square feet. 
 
 Round pipes of tin or galvanized iron are used for this purpose. 
 Table VIII will be found useful in determining the required diameters 
 of pipe in inches. 
 
 Example. The heat loss from a room on the second floor is 18,000 B. 
 T. U. per hour. What diameter of warm -air pipe will be required? 
 
 18,000 -^ .9 = 20,000 = cubic feet of air required per hour. 
 20,000 -^ 60 = 333 per minute. Assuming a velocity of 380 feet 
 per minute, we have 333 -=- 380 = .87 square foot, which is the 
 area of pipe required. Referring to Table VIII, we find this comes 
 between a 12-inch and a 13-inch pipe, and the larger size would 
 probably be chosen. 
 
 EXAMPLES FOR PRACTICE 
 
 1. A first-floor room has a computed loss of 27,000 B. T. U. 
 per hour when it is 10 below zero. The air for warming is to enter 
 through two pipes of equal size, and at a temperature of 120 degrees. 
 What will be the required diameter of the pipes? 
 
 ANS. 14 inches. 
 
 2. If in the above example the room had been on the second 
 floor, and the air was to be delivered through a single pipe, what 
 diameter would be required? 
 
 ANS. 16 inches. 
 
 Since long horizontal runs of pipe increase the resistance and 
 loss of heat, they should not in general be over 12 or 14 feet in length. 
 This applies especially to pipes leading to rooms on the first floor, 
 or to those on the cold side of the house. Pipes of excessive length 
 should be increased in size because of the added resistance. 
 
 Figs. 10 and 11 show common methods of running the pipes in 
 the basement. The first gives the best results, and should be used 
 where the basement is of sufficient height to allow it. A damper 
 should be placed in each pipe near the furnace, for regulating the flow 
 of air to the different rooms, or for shutting it off entirely when desired. 
 
 327
 
 HEATING AND VENTILATION 
 
 While round pipe risers give the best results, it is not always 
 possible to provide a sufficient space for them, and flat or oval pipes 
 are substituted. When vertical pipes must be placed in single par- 
 titions, much better results will be obtained if the studding can be 
 
 Fig. 10. Fig. 11. 
 
 Common Methods of Running Hot-Air Pipes in Basement. Method Shown in Fig. 10 
 is Preferable where Feasible. 
 
 made 5 or 6 inches deep instead of 4 as is usually done. Flues should 
 never in any case be made less than 3i inches in depth. Each room 
 should be heated by a separate pipe. In some cases, however, it is 
 allowable to run a single riser to heat two unimportant rooms on an 
 upper floor. A clear space of at least >- inch should be left between 
 the risers and studs, and the latter should be carefully tinned, and the 
 
 TABLE IX 
 Dimensions of Oval Pipes 
 
 DIMENSION- OF PIP 
 
 E AREA IN SQUARE INCHES 
 
 6 ovalocl to 5 i 
 
 27 
 
 7 " "4 
 
 31 
 
 7 " " 31 
 
 29 
 
 7 " " 6" 
 
 38 
 
 S " ' 5 
 
 43 
 
 '4 
 
 4.5 
 
 9 " r> 
 
 57 
 
 " ' o 
 
 51 
 
 10 " ' 3.V 
 
 46 
 
 11 " '4 
 
 58 
 
 12 " ' 3* 
 
 55 
 
 10 " " 6 
 
 67 
 
 11 "' " 5 
 
 67 
 
 14 ' " 4 
 
 76 
 
 1 " " 3V 
 
 73 
 
 1 " " 6" 
 
 So 
 
 1 " " ;'j 
 
 75 
 
 ,, .. .. 4 
 
 96 
 
 2, " :u 
 
 100 
 
 228
 
 HEATING AN.D VENTILATION 
 
 33 
 
 space between them on both sides covered with tin, asbestos, or wire 
 lath. 
 
 Table IX gives the capacity of oval pipes. A 6-inch pipe ovaled 
 to 5 means that a 6-inch pipe has been flattened out to a thickness of 
 5 inches, and column 2 gives the resulting area. 
 
 Having determined the size of round pipe required, an equiva- 
 lent oval pipe can be selected from the table to suit the space available. 
 
 Registers. The registers which control the supply of warm 
 air to the rooms, generally have a net area equal to two-thirds of their 
 gross area. The net area should be from 10 to 20 per cent greater 
 than the area of the pipe connected with it. It is common practice 
 to use registers having the short dimensions equal to, and the long 
 dimensions about one-half greater than, the diameter of the pipe. 
 This would give standard sizes for different diameters of pipe, as 
 listed in Table X. 
 
 TABLE X 
 Sizes of Registers for Different Sizes of Pipes 
 
 DIAMETER OF PIPE 
 
 SIZE OF REGISTER 
 
 6 i 
 
 n. 
 
 6 X 10 i 
 
 n. 
 
 7 
 
 ' 
 
 7 X 10 ' 
 
 
 8 
 
 ' 
 
 8 X 12 
 
 
 9 
 
 < 
 
 9 X 14 
 
 
 10 
 
 ' 
 
 10 X 15 
 
 
 11 
 
 ' 
 
 11 X 16 
 
 
 12 
 
 1 
 
 12 X 17 
 
 
 13 
 
 ' 
 
 14 X 20 
 
 
 14 
 
 ' 
 
 14 X 22 
 
 
 15 
 
 1 
 
 15 X 22 
 
 
 16 
 
 
 16 X 24 
 
 
 Combination Systems. A combination system for heating by 
 hot air and hot water consists of an ordinary furnace with some form 
 of surface for heating water, placed either in contact with the fire or 
 suspended above it. Fig. 12 shows a common arrangement where 
 part of the heating surface forms a portion of the lining to the firepot 
 and the remainder is above the fire. 
 
 Care must be taken to proportion properly the work to be done 
 by the air and the water; else one will operate at the expense of the 
 other. One square foot of heating surface in contact with the fire is 
 capable of supplying from 40 to 50 square feet of radiating surface, 
 
 129
 
 HEATING AND VENTILATION 
 
 and one square foot suspended over the fire will supply from 15 to 25 
 square feet of radiation. 
 
 The value or efficiency of the heating surface varies so widely in 
 different makes that it is best to state the required conditions to the 
 
 Fig. 12. Combination Furnace, for Heating by Both Hot Air and Hot Water. 
 
 manufacturers and have them proportion the surfaces as their experi- 
 ence has found best for their particular type of furnace. 
 
 Care and Management of Furnaces. The following general 
 rules apply to the management of all hard coal furnaces. 
 
 The fire should be thoroughly shaken once or twice daily in cold 
 weather. It is well to keep the firepot heaping full at all tiroes. In 
 
 230
 
 HEATING AND VENTILATION 35 
 
 this way a more even temperature may be maintained, less attention is 
 required, and no more coal is burned than when the pot is only partly 
 filled. In mild weather the mistake is frequently made of carrying a 
 thin fire, which requires frequent attention and is likely to die out. 
 Instead, to diminish the temperature in the house, keep the firepot 
 full and allow ashes to accumulate on the grate (not under it) by shak- 
 ing less frequently or less vigorously. The ashes will hold the heat 
 and render it an easy matter to maintain and control the fire. When 
 feeding coal on a low fire, open the drafts and neither rake nor shake 
 the fire till the fresh coal becomes ignited. The air supply to the fire 
 is of the greatest importance. An insufficient amount results in incom- 
 plete combustion and a great loss of heat. To secure proper combus- 
 tion, the fire should be controlled principally by means of the ash-pit 
 through the ash-pit door or slide. 
 
 The smoke-pipe damper should be opened only enough to carry 
 off the gas or smoke and to give the necessary draft. The openings 
 in the feed door act as a check on the fire, and should be kept closed 
 during cold weather, except just after firing, when with a good draft 
 they may be partly opened to increase the air-supply and promote the 
 proper combustion of the gases. 
 
 Keep the ash-pit clear to avoid warping or melting the grate. 
 The cold-air box should be kept wide open except during winds or 
 when the fire is low. At such times it may be partly, but never com- 
 pletely closed. Too much stress cannot be laid on the importance 
 of a sufficient air-supply to the furnace. It costs little if any more 
 to maintain a comfortable temperature in the house night and day 
 than to allow the rooms to become so cold during the night that the 
 fire must be forced in the morning to warm them up to a comfortable 
 temperature. 
 
 In case the warm air fails at times to reach certain rooms, it 
 may be forced into them by temporarily closing the registers in other 
 rooms. The current once established will generally continue after 
 the other registers have been opened. 
 
 It is best to burn as hard coal as the draft will warrant. Egg 
 size is better than larger coal, since for a given weight small lumps 
 expose more surface and ignite more quickly than larger ones. The 
 furnace and smoke-pipe should be thoroughly cleaned once a year.
 
 36 HEATING AND VENTILATION 
 
 This should he done just after the fire has been allowed to go out in 
 the spring. 
 
 STEAM BOILERS 
 
 Types. The boilers used for heating are the same as have already 
 been described for power work. In addition there is the oast-iron 
 sectional boiler, used almost exclusively for dwelling-houses. 
 
 Tubular Boilers. Tubular boilers are largely used for heating 
 purposes, and are adapted to all classes of buildings except dwelling- 
 houses and the special cases mentioned later, for which sectional 
 boilers are preferable. A boiler horse-pou-cr has been defined as the 
 evaporation of 34? pounds of water from and at a temperature of 212 
 degrees, and in doing this 33,317 B. T. U. are absorbed, which are 
 again given out when the steam is condensed in the radiators. Hence 
 to find the boiler H. P. required for warming any given building, we 
 have only to compute the heat loss per hour by the methods already 
 given, and divide the result by 33,330. It is more common to divide 
 by the number 33,000, which gives a slightly larger boiler and is on 
 the side of safety. 
 
 The commercial horse-power of a well-designed boiler is based 
 upon its heating surface; and for the best economy in heating work, 
 it should be so proportioned as to have about 1 square foot heating of 
 surface for each 2 pounds of water to be evaporated from and at 212 
 degrees F. This gives 34.5 -=- 2 = 17.2 square feet of heating surface 
 per horse-power, which is geNerally taken as 1 5 in practice. Makers of 
 tubular boilers commonly rate them on a basis of 12 square feet of heat- 
 ing surface per horse-power. This is a safe figure under the conditions 
 of power work, where skilled firemen are employed and where more 
 care is taken to keep the heating surfaces free from soot and ashes. 
 For heating plants, however, it is better to rate the boilers upon 15 
 square feet per horse-power as stated above. 
 
 There is some difference of opinion as to the proper method of 
 computing the heating surface of tubular boilers. In general, all 
 surface is taken which is exposed to the hot gases on one side and to 
 the water on the other. A safe rule, and the one by which Table 
 XII is computed, is to take J the area of the shell, f of the rear head, 
 less the tube area, and the interior surface of all the tubes. 
 
 The required amount of grate area, and the proper ratio of heat- 
 
 232
 
 HEATING AND VENTILATION 
 
 ing surface to grate area, vary a good deal, depending on the character 
 of the fuel and on the chimney draft. By assuming the probable 
 rates of combustion and evaporation, we may compute the required 
 grate area for any boiler from the formula : 
 
 H.P. x 34.5 
 
 E XC > 
 in which 
 
 S = Total grate area, in square feet; 
 
 E = Pounds of water evaporated per pound of coal ; 
 
 C = Pounds of coal burned per square foot of grate per hour. 
 
 Table XI gives the approximate grate area per H. P. for different 
 rates of evaporation and combustion as computed by the above 
 equation. 
 
 TABLE XI 
 
 Grate Area per Horse-Power for Different Rates of Evaporation and 
 Combustion 
 
 i 
 
 POUNDS OF COAL BURNED PER SQUARE FOOT OF GRATE PER HOUR 
 
 POUNDS OP STEAM PER 
 POUND OF COAL 
 
 8 Ibs. 
 
 10 Ibs. 12 Ibs. 
 
 Square Feet of Grate Surface per Horse- Power 
 
 10 
 
 .43 
 
 .35 
 
 .28 
 
 9 
 
 .48 
 
 .38 
 
 . 32 
 
 8 
 
 .54 
 
 .43 
 
 .36 
 
 7 
 
 .62 
 
 .49 
 
 .41 
 
 6 
 
 .72 
 
 .58 
 
 .48 
 
 For example, with an evaporation of 8 pounds of steam per pound of 
 coal, and a combustion of 10 pounds of coal per square foot of grate, .43 of a 
 square foot of grate surface per H. P. would be called for. 
 
 The ratio of heating to grate surface in this type of boiler ranges 
 from 30 to 40, and therefore allows under ordinary conditions a com- 
 bustion of from 8 to 10 pounds of coal per square foot of grate. This 
 is easily obtained with a good chimney draft and careful firing. The 
 larger the boiler, the more important the plant usually, and the greater 
 the care bestowed upon it, so that we may generally count on a higher 
 rate of combustion and a greater efficiency as the size of the boiler 
 increases. Table XII will be found very useful in determining 
 the size of boiler required under different conditions. The grate 
 area is computed for an evaporation of 8 pounds of water per pound 
 
 233
 
 38 
 
 HEATING AND VENTILATION 
 
 TABLE XII 
 
 DlWKTFK 
 
 
 
 
 
 SIZE OF 
 
 SIZE OF 
 
 OF SHELL 
 IN INCHES 
 
 OF TUBES QFTi-HKs 
 IN INCHES 
 
 OF TUBES 
 IN FEET 
 
 POWER 
 
 GRATE IN 
 , INCHES 
 
 UPTAKE 
 IN INCHES 
 
 SMOKE- 
 PIPE IN 
 SQ. IN 
 
 
 
 
 
 
 
 
 30 
 
 28 -2y 2 
 
 6 
 
 8.5 
 
 24 x 36 
 
 10x14 
 
 140 
 
 
 
 7 
 
 9.9 
 
 . 24 x 36 
 
 10x14 
 
 140 
 
 
 
 8 
 
 11.2 
 
 24 x 36 
 
 10x14 
 
 140 
 
 
 
 9 
 
 12.6 
 
 24 x 42 
 
 10x14 
 
 140 
 
 
 
 10 
 
 14.0 
 
 24 x 42 
 
 10x14 
 
 140 
 
 86 
 
 34 iy, 
 
 8 
 
 13.6 
 
 i 30 x 36 
 
 10x16 
 
 160 
 
 
 
 9 
 
 15.3 
 
 30 x 42 
 
 10x18 
 
 180 
 
 
 
 10 
 
 16.9 
 
 30 x 42 
 
 10x18 
 
 180 
 
 
 
 11 
 
 18.6 
 
 30 x 48 
 
 10 x 20 
 
 200 
 
 
 
 12 
 
 20.9 
 
 30 x 48 
 
 10 x 20 
 
 200 
 
 42 
 
 :>4 3 
 
 9 
 
 18.5 
 
 86 x 42 
 
 10x20 
 
 200 
 
 
 
 10 
 
 20.5 
 
 86 x 42 
 
 10 x 20 
 
 200 
 
 
 
 11 
 
 22.5 
 
 36 x 48 
 
 10 x 25 
 
 250 
 
 
 
 12 
 
 24.5 
 
 36 x 48 
 
 10 x 25 
 
 250 
 
 
 
 13 
 
 26.5 
 
 36 x 48 
 
 10x28 
 
 280 
 
 
 
 14 
 
 ' 28.5 
 
 36 x 54 
 
 10x28 
 
 280 
 
 48 
 
 44 3 
 
 10 
 
 30.4 
 
 42x48 
 
 10x28 
 
 280 
 
 
 
 11 
 
 33 2 
 
 42 x 48 
 
 10 x 28 
 
 280 
 
 
 
 12 
 
 85.7 
 
 42 x 54 
 
 10 x 32 
 
 320 
 
 
 
 13 
 
 38.3 
 
 42 x 54 
 
 10x32 
 
 320 
 
 
 
 14 
 
 40.8 
 
 42x60 
 
 10x36 
 
 360 
 
 
 
 15 
 
 43.4 
 
 42 x 60 
 
 10 x 36 
 
 360 
 
 
 
 16 
 
 45.9 
 
 42 x 60 
 
 10x36 
 
 360 
 
 54 
 
 54 3 
 
 11 
 
 34.6 
 
 48 x 54 
 
 10 x 38 
 
 3SO 
 
 
 
 12 
 
 87 . 7 
 
 48 x 54 
 
 10 x 38 
 
 380 
 
 
 
 13 
 
 40.8 
 
 48 x 54 
 
 10 x 38 
 
 380 
 
 
 
 14 
 
 43.9 
 
 48 x 54 
 
 10x38 
 
 380 
 
 
 
 15 
 
 47.0 
 
 48 x 60 
 
 10 x 40 
 
 400 
 
 
 
 16 
 
 50.1 
 
 48x60 
 
 10x40 
 
 400 
 
 
 46 \\y. 
 
 ' 17 
 
 53.0 
 
 48x60 
 
 10x40 
 
 400 
 
 60 
 
 72 8 
 
 12 
 
 48.4 
 
 54 x 60 
 
 12x40 
 
 460 
 
 
 
 13 
 
 52.4 
 
 54 x 60 
 
 12x40 
 
 460 
 
 
 
 14 
 
 56.4 
 
 54 x60 
 
 12x40 
 
 460 
 
 
 
 15 
 
 60.4 
 
 54 x 66 
 
 12x42 
 
 500 
 
 
 
 16 
 
 64.4 
 
 54 x 66 
 
 12 x 42 
 
 500 
 
 
 64 31^ 
 
 17 
 
 71.4 
 
 54 x 72 
 
 12x48 
 
 550 
 
 
 
 18 
 
 75 . 6 
 
 54 x 72 
 
 12x48 
 
 550 
 
 66 
 
 90 3 
 
 14 
 
 70.1 
 
 60x66 
 
 12x48 
 
 500 
 
 
 
 15 
 
 75.0 
 
 60 x 72 
 
 12x52 
 
 620 
 
 
 
 16 
 
 80.0 
 
 60 x 72 
 
 12x52 
 
 620 
 
 
 78 3y 2 
 
 17 
 
 86.0 
 
 60x78 
 
 12 x 56 
 
 670 
 
 
 
 18 
 
 91.1 
 
 60x78 
 
 12x56 
 
 670 
 
 
 
 19 
 
 96.2 
 
 60 x 78 
 
 12x56 
 
 670 
 
 
 62 4 
 
 20 
 
 93.1 
 
 60x78 
 
 12x56 
 
 670 
 
 72 
 
 ' 114 3 
 
 14 
 
 87.4 
 
 66 x 72 
 
 12 x 56 
 
 670 
 
 
 
 15 
 
 93.6 
 
 66 x 72 
 
 12x56 
 
 670 
 
 
 
 16 
 
 99.7 
 
 66 x78 
 
 12 x62 
 
 740 
 
 
 98 3i^ 
 
 17 
 
 106.4 
 
 66 x 78 
 
 12x62 
 
 740 
 
 
 
 18 
 
 112.6 
 
 66 x 84 
 
 12x66 
 
 790 
 
 
 
 19 
 
 118.8 
 
 66 x 84 
 
 12 x 66 
 
 790 
 
 
 72 4 
 
 20 
 
 107.3 
 
 66x84 
 
 12x66 
 
 790 
 
 234
 
 DIRECT-INDIRECT SYSTEM OF WARMING, SHOWING ADJUSTABLE DAMPER. 
 American Radiator Company.
 
 MEATING AND VENTILATION 39 
 
 of coal, which corresponds to an efficiency of about 60 per cent, and 
 is about the average obtained in practice for heating boilers. 
 
 The areas of uptake and smoke-pipe are figured on a basis of 
 1 square foot to 7 square feet of grate surface, and the results given 
 in round numbers. In the smaller sizes the xelative size of smoke- 
 pipe is greater. The rate of combustion runs from 6 pounds in the 
 smaller sizes to 11 in the larger. Boilers of the proportions given 
 in the table, correspond well with those used in actual practice, and 
 may be relied upon to give good results under all ordinary conditions. 
 
 Water-tube boilers are often used for heating purposes, but more 
 especially in connection with power plants. The method of com- 
 puting the required H. P. is the same as for tubular boilers. 
 
 Sectional Boilers. Fig. 13 shows a common form of cast-iron 
 boiler. It is made up of slabs or sections, each one of which is con- 
 nected by nipples with headers at the sides and top. The top header 
 acts as a steam drum, and the lower ones act as mud drums; they also 
 receive the water of condensation from the radiators. The gases 
 from the fire pass backward and forward through flues and are finally 
 taken off at the rear of the boiler. 
 
 Another common form of sectional boiler is shown in Fig. 14. 
 It is made up of sections which increase the length like the one just 
 described. These boilers have no drum connecting with the sections; 
 but instead, each section connects with the adjacent one through 
 openings at the top and bottom, as shown. 
 
 The ratio of heating to grate surface in boilers of this type ranges 
 from 15 to 25 in the best makes. They are provided with the usual 
 attachments, such as pressure-gauge, water-glass, gauge-cocks, and 
 safety-valve; a low-pressure damper regulator is furnished for operat- 
 ing the draft doors, thus keeping the steam pressure practically con- 
 stant. A pressure of from 1 to 5 pounds is usually carried on these 
 boilers, depending upon the outside temperature. The usual setting 
 is simply a covering of some kind of non-conducting material like 
 plastic magnesia or asbestos, although some forms are enclosed in 
 light brickwork. 
 
 In computing the required size, we may proceed in the same 
 manner as in the case of a furnace. For the best types of house- 
 heating boilers, we may assume & combustion of 5 pounds of coal per 
 square foot of grate per hour, and an average efficiency of GO per cent, 
 
 235
 
 HEATING AND VENTILATION 
 
 which corresponds to S,000 B. T. U. per pound of coal, available for 
 useful work. 
 
 In the case of direct-steam heating, we have only to supply heat 
 to offset that lost by radiation and conduction ; so that the grate area 
 may be found by dividing the computed heat loss per hour by 8,000, 
 which gives the number of pounds of coal; and this in turn, divided 
 by 5, will give the area of grate required. The most efficient rate of 
 
 Fig. 13. Commo 
 
 Headers at Sides and Top 
 
 combustion will depend somewhat upon the ratio between the grate 
 and heating surface. It has been found by experience that about 4 
 of a pound of coal per hour for each square foot of heating surface 
 gives the best results; so that, by knowing the ratio of heating surface 
 to grate area for any make of heater, we can easily compute the most 
 efficient rate of combustion, and from it determine the necessar rate
 
 HEATING AND VENTILATION 
 
 11 
 
 For example, suppose the heat loss from a building to be 480,000 
 B. T. U. per hour, and that we wish to use a heater in which the ratio 
 of heating surface to grate area is 24. What will be the most efficient 
 rate of combustion and the required 
 grate area? 480,000 -5- 8,000 - 60 
 pounds of coal per hour, and 24 -T- 4 
 = 6, which is the best rate of com- 
 bustion to employ; therefore 60 -f- 6 
 = 10, the grate area required. 
 
 There are many different designs 
 of cast-iron boilers for low-pressure 
 steam and hot-water heating. In gen- 
 eral, boilers having a drum connected 
 by nipples with each section give 
 dryer steam and hold a steadier water- 
 line than the second form, especially 
 when forced above their normal ca- 
 pacity. The steam, in passing through 
 the openings between successive sec- 
 tions in order to reach the outlet, 
 
 is apt to carry with it more or less water, and to choke the openings, 
 thus producing an uneven pressure in different parts of the boiler. 
 
 In the case of hot-water boilers this objection disappears. 
 
 In order to adapt this type of boiler to steam work, the opening 
 between the sections should be of good size, with an ample steam 
 space above the water-line; and the nozzles for the discharge of steam 
 should be located at frequent intervals. 
 
 Fig. 14. Another. Type of Sectional 
 Boiler. Here there are no drums, 
 the sections being directly 
 connected through open- 
 ings at top and bottom. 
 Courtesy of American Radiator Co. 
 
 EXAMPLES FOR PRACTICE 
 
 1. The heat loss from a building is 240,000 B. T. U. per hour, 
 and the ratio of heating to grate area in the heater to be used is 20. 
 What will be the required grate area? ANS. 6 sq. ft. 
 
 2. The heat loss from a building is 168,000 B. T. U. per hour, and 
 the chimney draft is such that not over 3 pounds of coal per hour can 
 be burned per square foot of grate. What ratio of heating to grate 
 area will be necessary, and what will be the required grate area? 
 
 ANS. Ratio, 12. Grate area, 7 sq. ft.
 
 42 HEATING AND VENTILATION 
 
 Cast-iron sectional boilers are used for dwelling-houses, small 
 schoolhouses, churches, etc., where low pressures are carried. They 
 are increased in size by adding more slabs or sections. After a certain 
 length is reached, the rear sections become less and less efficient, thus 
 limiting the size and power. 
 
 Horse=Po\ver for Ventilation. We already know that one 
 B. T. U. will raise the temperature of 1 cubic foot of air 55 degrees, 
 or it will raise 100 cubic feet T -J- T of 55 degrees, or ^/V of 1 degree; 
 therefore, to raise 100 cubic feet 1 degree, it will take 1 -r- -**$, or y 1 / 
 B. T. U.; and to raise 100 cubic feet through 100 degrees, it will take 
 yy x 100 B. T. U. In other words, the B. T. U. required to raise 
 any given volume of air through any number of degrees in tempera- 
 ture, is equal to 
 
 Volume of air in cubic ft. X Degrees raised 
 55 
 
 Example. How many B. T. V. are required to raise 100,000 
 cubic feet of air 70 degrees? 
 
 100,000 X 70 _ 127272 _ { 
 55 
 
 To compute the H. P. required for the ventilation of a building, 
 we multiply the total air-supply, in cubic feet per hour, by the number 
 of degrees through which it is to be raised, and divide the result by 55. 
 This gives the B. T. U. per hour, which, divided by 33,000, will give 
 the II. P. required. In using this rule, always take the air-supply in 
 cubic feet per hour. 
 
 EXAMPLES FOR PRACTICE 
 
 1. The heat loss from a building is 1,050,000 B. T. U. per hour. 
 There is to be an air-supply of 1,500,000 cubic feet per hour, raised 
 through 70 degrees. What is the total boiler H. P. required? 
 
 Axs. 10S. 
 
 2. A high school has 10 classrooms, each occupied by 50 pupils. 
 Air is to be delivered to the rooms at a temperature of 70 degrees. 
 What will be the total H. P. required to heat and ventilate the building 
 when it is 10 degrees below zero, if the heat loss through walls and 
 windows is 1,320,000 B. T. U. per hour? Axs. 100-f-. 
 
 DIRECT=STEAM HEATING 
 
 A system of direct-steam heating consists (1) of a furnace and
 
 HEATING AND VENTILATION 
 
 boiler for the combustion of fuel and the generation of steam; (2) a 
 system of pipes for conveying the steam to the radiators and for 
 returning the water of condensation to the boiler; and (3) radiators 
 or coils placed in the rooms for diffusing the heat. 
 
 Various types of boilers are used, depending upon the size and 
 kind of building to be warmed. Some form of cast-iron sectional 
 boiler is commonly used for dwelling-houses, while the tubular or 
 water-tube boiler is more usually employed in larger buildings. 
 Where the boiler is used for heating purposes only, a low steam-pres- 
 sure of from 2 to 10 pounds is carried, and the condensation flows 
 back by gravity to the boiler, which is placed below the lowest radiator. 
 When, for any reason, a higher 
 pressure is required, the steam for 
 the heating system is made to 
 pass through a reducing valve, 
 and the condensation is returned 
 to the boiler by means of a pump 
 or return trap. 
 
 Types of Radiating Surface. 
 The radiation used indirect-steam 
 heating is made up of cast-iron 
 radiators of various forms, pipe 
 radiators, and circulation coils. 
 
 Cast=Iron Radiators. The 
 general form of a cast-iron sec- 
 tional radiator is shown in Fig. 
 15. Radiators of this type are 
 made up of sections, the number 
 
 depending upon the amount of heating surface required. Fig. 16 
 shows an intermediate section of a radiator of this type. 
 It is simply a loop with inlet and outlet at the bottom^ The 
 end sections are the same, except that they have legs, as shown in 
 Fig. 17. These sections are connected at the bottom by special 
 nipples, so that steam entering at the end. fills the bottom of the 
 radiator, and, being lighter than the air, rises through the loops and 
 forces the air downward and toward the farther end, where it is dis-* 
 charged through an air-valve placed about midway of the last section. 
 There are many different designs varying in height and width, te 
 
 Fig. 15. Common Type of Cast-Iron 
 Sectional Radiator. 
 
 839
 
 44 
 
 HEATING AND VENTILATION 
 
 suit all conditions. The wall pattern shown in Fig. 18 is very con- 
 venient when it is desired to place the radiator above the floor, as in 
 
 bathrooms, etc.; it is also a con- 
 venient form to place under the 
 window's of halls and churches 
 to counteract the effect of cold 
 down drafts. It is adapted to 
 nearly every place where the or- 
 dinary direct radiator can be 
 used, and may be connected up 
 in different ways to meet the va- 
 rious requirements. 
 
 A low and moderately shallow 
 radiator, with ample space for the 
 circulation of air between the 
 sections, is more efficient than a 
 deep radiator w r ith the sections 
 closely packed together. One- 
 and two-column radiators, so 
 called, are preferable to three- 
 sufficient space to use them. 
 
 o 
 
 ^ 
 
 Fig. 16. 
 
 rig. IT 
 
 Intermediate and End Sections of Kadi; 
 Shown in Fig. 15. The end sections 
 (at right) have legs. 
 
 and four-column, when there 
 
 f 
 
 Fig. 18. Cast-iron Sectional Radiator of Wall Pattern. 
 
 The standard height of a radiator is 36 or 38 inches, and, if 
 possible, it is better not to exceed this. 
 
 240
 
 HEATING AND VENTILATION 
 
 For small radiators, it is better practice to use lower sections and 
 increase the length; this makes the radiator slightly more efficient 
 and gives a much better appearance. 
 
 To get the best results from wall radiators, they should be set 
 out at least H inches from the wall to allow a free circulation of air 
 back of them. Patterns having cross-bars should be placed, if 
 possible, with the bars in a vertical position, as their efficiency is 
 impaired somewhat when placed horizontally. 
 
 Pipe Radiators. This type of radiator (see Fig. 19) is made up of 
 wrought-iron pipes 
 screwed into a cast- 
 iron base. The 
 pipes are either con- 
 nected in pairs at 
 the top by return 
 bends, or each sep- 
 arate tube has a 
 thin metal dia- 
 phragm passing up 
 the center nearly to 
 the top. It is nec- 
 essary that a loop 
 be formed, else a 
 "dead end" would 
 occur. This would 
 become filled with 
 air a n d prevent 
 steam from enter- 
 ing, thus causing portions of the radiator to remain cold. 
 
 Circulation Coils. These are usually made up of 1 or lj-inch 
 wrought-iron pipe, and may be hung on the walls of a room by means 
 of hook plates, or suspended overhead on hangers and rolls. 
 
 Fig. 20 shows a common form for schoolhouse and similar work; 
 this coil is usually made of lj-inch pipe screwed into headers or 
 branch tees at the ends, and is hung on the wall just below the windows. 
 This is known as a branch coil. Fig. 21 shows a trombone coil, which 
 is commonly used when the pipes cannot turn a corner, and where 
 the entire coil must be placed upon one side of the room. Fig. 22 
 
 Fig. 1K Wrought-iron Pipe Radiator. 
 
 341
 
 HEATING AND VENTILATION 
 
 is called a miter coil, and is used under the same conditions as a trom- 
 bone coil if there is room for the vertical portion. This form is not 
 so pleasing in appearance as either of the other two, and is found only 
 in factories or shops, where looks are of minor importance. 
 
 Fig. 20. Common Form of ' Branch' ' Coil for Circulation of Direct Steam. 
 
 Overhead coils are usuallv of the miter form, laid on the side and 
 suspended about a foot from the ceiling; they are less efficient than 
 when placed nearer the floor, as the warm air stays at the ceiling and 
 the lower part of the room is likely to remain cold. They are used 
 
 Fig. 21. "Trombone'' Coil. Used where Entire Coil must be Placed on One Side < f Room 
 
 only when wall coils or radiators would be in the way of fixtures, or 
 when they would come below the water-line of the boiler if placed 
 near the floor. 
 
 When steam is first turned on a coil, it usually passes through a 
 
 Fig. 22. "Miter" Coil. Adapted, like the "Trombone." Only to a Single Wall. 
 Frequently Used in Factories and Shops. 
 
 portion of the pipes first and heats them while the others remain cold 
 and full of air. Therefore the coil must always be made up in such 
 a way that each pipe shall have a certain amount of spring and may 
 expand independently without bringing undue strains upon the others. 
 Circulation coils should incline about 1 inch in 20 feet toward the 
 
 242
 
 HEATING AND VENTILATION 47 
 
 return end in order to secure proper drainage and quietness of opera- 
 tion. 
 
 Efficiency of Radiators. The efficiency of a radiator that is, 
 the B. T. U. which it gives off per square foot of surface per hour 
 depends upon the difference in temperature between the steam in the 
 radiator and the surrounding air, the velocity of the air over the 
 radiator, and the quality of the surface, whether smooth or rough. 
 In ordinary low-pressure heating, the first condition is practically 
 constant; but the second varies somewhat with the pattern of the 
 radiator. An open design which allows the air to circulate freely 
 over the radiating surfaces, is more efficient than a closed pattern, 
 and for this reason a pipe coil is more efficient than a radiator. 
 
 In a large number of tests of cast-iron and pipe radiators, working 
 under usual conditions, the heat given off per square foot of surface 
 per hour for each degree difference in temperature between the steam 
 and surrounding air was found to average about 1 . 7 B. T. U. The 
 temperature of steam at 3 pounds' pressure is 220 degrees, and 220 70 
 = 150, which may be taken as the average difference between the 
 temperature of the steam and the air of the room, in ordinary low- 
 pressure work. Taking the above results, we have 150 X 1 .7 = 255 
 B. T. U. as the efficiency of an average cast-iron or pipe radiator. 
 This, for convenient use, may be taken as 250. A circulation coil 
 made up of pipes from 1 to 2 inches in diameter, will easily give off 
 300 B. T. U. under the same conditions; and a cast-iron wall radiator 
 with ample space back of it should have an efficiency equal to that 
 of a wall coil. While overhead coils have a higher efficiency than 
 cast-iron radiators, their position near the ceiling reduces their effec- 
 tiveness, so that in practice the efficiency should not be taken over 
 250 B. T. U. per hour at the most. Tabulating the above we have: 
 
 TABLE XIII 
 Efficiency of Radiators, Coils, etc. 
 
 TYPE OF RADIATING SURFACE RADIATION PER SQUARE FOOT OF SURFACE 
 
 PER HOUR 
 
 Cast-Iron Sectional and Pipe Radiators 
 \Yall Radiators 
 Ceiling Coils 
 Wall Coils 
 
 250 B. T. U. 
 
 300 
 
 200 to 250 " 
 
 300 
 
 243
 
 48 HEATING AND VENTILATION 
 
 If the radiator is for warming a room which is to be kept at a 
 temperature above or below 70 degrees, or if the steam pressure is 
 greater than 3 pounds, the radiating surface may be changed in the 
 same proportion as the difference in temperature between the steam 
 and the air. 
 
 For example, if a room is to be kept at a temperature of 00, the 
 efficiency of the radiator becomes -j^- X 250 = 268; that is, the 
 efficiency varies directly as the difference in temperature between the 
 steam and the air of the room. It is not customary to consider this 
 unless the steam pressure should be raised to 10 or 15 pounds or the 
 temperature of the rooms changed 15 or 20 degrees from the normal. 
 
 From the above it is easy to compute the size of radiator for any 
 given room. First compute the heat loss per hour by conduction and 
 leakage in the coldest weather; then divide the result by the effi- 
 ciency of the type of radiator to be used. It is customary to make the 
 radiators of such size that they will warm the rooms to 70 degrees in 
 the coldest weather. As the low-temperature limit varies a good deal 
 in different localities, even in the same State, the lowest temperature 
 for which we wish to provide must be settled upon before any calcu- 
 lations are made. In Xew England and through the Middle and 
 Western States, it is usual to figure on warming a building to 70 
 degrees when the outside temperature is from zero to 10 degrees 
 below. 
 
 The different makers of radiators publish in their catalogues, 
 tables giving the square feet of heating surface for different styles and 
 heights, and these can be used in determining the number of sections 
 required for all special cases. 
 
 If pipe coils are to be used, it becomes necessary to reduce square 
 feet of heating surface to linear feet of pipe; this can be done by means 
 of the factors o-iven below. 
 
 = linear ft. of 1 -in. pipe 
 Square feet of heating surf ice X -{ ~" t( 
 
 " 2 -in. " 
 
 The size of radiator is made only sufficient to keep the room 
 warm after it is once heated ; and no allowance is made for warming 
 up; that is, the heat given off by the radiator is just equal to that lost 
 through walls and. windows. This condition is offset in two ways 
 
 244
 
 HEATING AND VENTILATION 49 
 
 first, when the room is cold, the difference in temperature between 
 the steam and the air of the room is greater, and the radiator is more 
 efficient; and second, the radiator is proportioned for the coldest 
 weather, so that for a greater part of the time it is larger than neces- 
 sary. 
 
 EXAMPLES FOR PRACTICE 
 
 1 . The heat loss from a room is 25,000 B. T. U. per hour in 
 the coldest weather. What size of direct radiator will be required? 
 
 ANS. 100 square feet. 
 
 2. A schoolroom is to be warmed with circulation coils of 1|- 
 inch pipe. The heat loss is 30,000 B. T. U. per hour. What length 
 of pipe will be required? ANS. 230 linear feet. 
 
 Location of Radiators. Radiators should, if possible, be placed 
 in the coldest part of the room, as under windows or near outside 
 doors. In living rooms it is often desirable to keep the windows free, 
 in which case the radiators may be placed at one side. Circulation 
 coils are run along the outside walls of a room under the windows, 
 Sometimes the position of the radiators is decided by the necessary 
 location of the pipe risers, so that a certain amount of judgment must 
 be used in each special case as to the best arrangement to suit all 
 requirements. 
 
 Systems of Piping. There are three distinct systems of piping, 
 know r n as the two-pipe system, the one-pipe relief system, and the one- 
 pipe circuit system, with various modifications of each and combina- 
 tions of the different systems. 
 
 Fig. 23 shows the arrangement of piping and radiators in the 
 two-pipe system. The steam main leads from the top of the boiler, 
 and the branches are carried along near the basement ceiling. Risers 
 are taken from the supply branches, and carried up to the radiators 
 on the different floors; and return pipes are brought down to the 
 return mains, which should be placed near the basement floor below 
 the water-line of the boiler. Where the building is more than two 
 stories high, radiators in similar positions on different floors are con- 
 nected with the same riser, which may run to the highest floor; and a 
 corresponding return drop connecting with each radiator is carried 
 down beside the riser to the basement. A system in which the main 
 horizontal returns are below the water-line of the boiler is said to 
 
 245
 
 HEATING AND VENTILATION 
 
 have a wet or sealed return. If the returns are overhead and above the 
 water-line, it is called a dry return. Where the steam is exposed to 
 extended surfaces of water, as in overhead returns, where the con- 
 densation partially fills the pipes, there is likely to be cracking or 
 water-hammer, due to the sudden condensation of the steam as it 
 comes in contact with the cooler water. This is especially noticeable 
 when steam is first turned into cold pipes and radiators, and the con- 
 densation is excessive. When dry returns are used, the pipes should 
 be large and have a good pitch toward the boiler. 
 
 In the case of sealed returns, the onlv contact between the steam 
 
 Fig. 23. Arrangement of Piping and Radiators in "Two-Pipe" System. 
 
 and standing water is in the vertical returns, where the exposed sur- 
 faces are very small (being equal to the sectional area of the pipes), 
 and trouble from water-hammer is practically done away with. Dry 
 returns should be given an incline of at least 1 inch in 10 feet, while 
 for wet returns 1 inch in 20 or even 40 feet is ample. The ends of all 
 steam mains and branches should be dripped into the returns. If the 
 return is sealed, the drip maybe directly connected as shown in Fig. 
 24 ; but if it is dry, the connection should be provided with a siphon 
 loop as indicated in Fig. 25. The loop becomes filled with water, 
 and prevents steam from flowing directly into the return. As the 
 
 246
 
 HEATING AND VENTILATION 
 
 condensation collects in the loop, it overflows into the return pipe and 
 is carried away. The return pipes in this case are of course filled with 
 steam above the water; but it is steam which has passed through 
 the radiators and their return connections, and is therefore at a 
 slightly lower pressure; steam Marn 
 
 so that, if steam were ad- 
 mitted directly from the 
 main, it would tend to 
 hold back the water in 
 
 Wate- 
 
 more distant returns and 
 
 cause surging and crack- Retxir-n 
 
 ing in the pipes. Some- Fig . 24 . Drip from Steam M ain Connected Directly 
 
 times the boiler is at a to sealed Return. 
 
 lower level than the basement in which the returns are run, and it then 
 becomes necessary to establish a false water-line. This is done by 
 making connections as shown in Fig. 26. 
 
 It is readily seen that the return water, in order to reach the 
 boiler, must flow through the trap, which raises the water-line or 
 seal to the level shown by the dotted line. The balance pipe is to 
 equalize the pressure above and below the water in the trap, and 
 prevent siphonic action, which would tend to drain the water out of 
 the return mains after a flow was once started. 
 
 The balance pipe, when possible, should be 15 or 20 feet in 
 length, with a throttle-valve placed near its connection with the 
 
 main. This valve 
 should be opened just 
 enough to allow the 
 steam-pressure to act 
 upon the air which oc- 
 cupies the space above 
 the water in the trap ; 
 but it should not be 
 
 SipVior* 
 
 Fig. 25. Use of Siphon in Connecting Drip from Steam 
 Main to a "Dry" Return. 
 
 opened sufficiently to 
 allow the steam to 
 enter in large volume and drive the air out. The success of this 
 arrangement depends upon keeping a layer or cushion of cool air 
 next to the surface of the water in the trap, and this is easily done 
 by following the method here described. 
 
 247
 
 52 
 
 HEATING AND VENTILATION 
 
 Water-lirie 
 
 One=Pipe Relief System. In this system of piping, the radiators 
 have but a single connection, the steam flowing in and the condensa- 
 tion draining out through the same pipe. Fig. 27 shows the method 
 of running the pipes for this system. The steam main, as before, 
 leads from the top of the boiler, and is carried to as high a point as the 
 basement ceiling will allow; it then slopes downward with a grade 
 of about 1 inch in 10 feet, and makes a circuit of the building or a 
 portion of it. 
 
 Risers are taken from the top and carried to the radiators above, 
 as in the two-pipe system; but in this case, the condensation flows 
 back through the same pipe, and drains into the return main near the 
 
 floor through 
 drip connections 
 which are made 
 at frequent in- 
 tervals. In a 
 two-story build- 
 ing, the bottom 
 of, each riser to 
 the second floor 
 is dripped; and 
 in larger build- 
 ings, it is cus- 
 tomary to drip 
 each riser that 
 has more than 
 one radiator con- 
 nected with it. If the radiators are large and at a considerable dis- 
 tance from the next riser, it is better to make a drip connection for 
 each radiator. "When the return- main is overhead, the risers should 
 be dripped through siphon loops; but the ends of the branches 
 should make direct connection with the returns. This is the reverse 
 of the two-pipe system. In this case the lowest pressure is at the 
 ends of the mains, so that steam introduced into the returns at these 
 points will cause no trouble in the pipes connecting between these and 
 the boiler. 
 
 If no steam is allowed to enter the returns, a vacuum will be 
 formed, and there will be no pressure to force the water back to the 
 
 Boiler ''" 
 
 f. 
 
 ! 
 
 
 
 i 
 
 Fig. 26. Connections Made to Establish "False" Water-Lim 
 when Boiler is below Basement Level. 
 
 248
 
 HEATING AND VENTILATION 
 
 53 
 
 boiler. A check-valve should always be placed in the main return 
 
 Fig. 27. Arrangement of Piping and Radiators in "One-Pipe Relief" System. 
 
 near the boiler, to prevent the water from flowing out in case of 
 vacuum being formed suddenly in the pipes. 
 
 gementof Piping and Radiators in "One-Pipe Circuit" System. 
 
 There is but little difference in the cost of the two systems, as 
 larger pipes and valves are required for the single-pipe method. 
 
 849
 
 HEATING AND VENTILATION 
 
 \Vith radiators of medium size and properly proportioned connections, 
 the single-pipe system in preferable, there being but one valve to 
 operate and only one-half the number of risers passing through the 
 lower rooms. 
 
 One=Pipe Circuit System. In this case, illustrated in Fig. 28, the 
 steam main rises to the highest point of the basement, as before; and 
 then, with a considerable pitch, makes an entire circuit of the build- 
 ing, and again connects with the boiler below the water-line. Single 
 
 - ___ _ _ risers are taken 
 
 1 ^ l-^ 
 
 f ' M 
 
 from the top; and. 
 
 
 
 the condensa- 
 tion drains back 
 through the 
 
 1 1 
 
 n p 
 
 
 1 Siphon 
 ConrvecUo-n <jj 
 l> in 
 
 CV.ecV Valve 
 Connection^ 
 
 is carried along 
 with the flow of 
 steam to the ex- 
 
 rj tfj 
 
 {_ }_ 
 
 
 *^ Sealed Return 
 
 Sealed Ret ^rn f*^ 
 
 main, where it is 
 returned to the 
 b o i 1 e r. T h e 
 main is made 
 
 - 
 
 
 
 Fig. 29. "One-Pipe Circuit" 
 Bui 
 
 System. Adapted to a Large 
 
 ding. 
 
 large, and of 
 the same size 
 
 throughout its entire length. It must be given a good pitch to insure 
 satisfactory results. 
 
 ( )ne objection to a single-pipe system is that the steam and return 
 water are flowing in opposite directions, and the risers must be made 
 of extra large size to prevent any interference. This is overcome in 
 large buildings by carrying a single riser to the attic, large enough 
 to supply the entire building; then branching and running "drops" 
 to the basement. In this system the flow of steam is downward, as 
 well as that of water. This method of piping may be used with good 
 results in two-pipe systems as well. Care must always be taken that 
 no pockets or low points occur in any of the lines of pipe; but if for 
 any reason they cannot be avoided, they should be carefully drained. 
 
 A modification of this system, adapting it to large buildings, is 
 shown in diagram in Fig. 29. The riser shown in this case is one of 
 
 250
 
 ROCOCO ORNAMENTAL TriREE COLUMN PATTERN RADIATOR FOB 
 WARMING BY HOT WATER. 
 
 American Radiator Company.
 
 HEATING AND VENTILATION 
 
 55 
 
 several, the number depending upon the size of the building; and 
 may be supplied at either bottom or top as most desirable. If steam 
 is supplied at the bottom of the riser, as shown in the cut, all of the 
 drip connections with the return drop, except the upper one, should 
 
 Fig. 30. "Two- Pipe" Connection of Radia- 
 tor to Riser and Return. 
 
 Pig. 31. 
 
 'One-Pipe" Connection of Radia- 
 tor to Basement Main. 
 
 be sealed with either a siphon loop or a check-valve, to prevent the 
 steam from short-circuiting and holding back the condensation in the 
 returns above. If an overhead supply is .used, the arrangement 
 should be the reverse; that is, all return connections should be sealed 
 except the lowest. 
 
 Sometimes a separate drip is carried down from each set of 
 radiators, as shown on the lower story, being connected with the 
 main return below the water-line of the 
 boiler. In case this is done, it is well to 
 provide a check-valve in each drip below 
 the water-line. 
 
 In buildings of any considerable size, 
 it is well fo divide the piping system into 
 sections by means of valves placed in the 
 corresponding supply and return branches. 
 These are for use in case of a break in 
 any part of the system, so that it will be 
 necessary to shut off only a small part of 
 the heating system during repairs. In tall buildings, it is customary 
 to place valves at the top and bottom of each riser, for the same 
 purpose. 
 
 Radiator Connections. Figs. 30, 31, and 32 show the common 
 
 Fig. 32. "One-Pipe" Connection 
 of Radiator to Riser. 
 
 251
 
 56 HEATIXG AND VENTILATION 
 
 methods of making connections between supply pipes and radiators. 
 Fig. 30 shows a two-pipe connection with a riser; the return is carried 
 down to the main below. Fig. 31 shows a smgle-pipe connection 
 with a basement main; and Fig. 32, a single connection with a riser. 
 
 Care must always be taken to make the horizontal part of the 
 piping between the radiator and riser as short as possible, and to give 
 it a good pitch toward the riser. There are various ways of making 
 these connections, especially suited to different conditions; but the 
 examples given serve to show the general principle to be followed. 
 
 Figs. 20, 21, and 22 show the common methods of making steam 
 and return connections with circulation coils. The position of the 
 air-valve is shown in each case. 
 
 Expansion of Pipes. Cold steam pipes expand approximately 
 
 Fig. 33. Elevation and Plan of Swivel-Joint to Counteract Effects of Expansion and 
 Contraction in Pipes. 
 
 1 inch in each 100 feet in length when low-pressure steam is turned 
 into them ; so that, in laying out a system of piping, we must arrange 
 it in such a manner that there will be sufficient "spring" or "give" to 
 the pipes to prevent injurious strains. This is done by means of off- 
 sets and bends. In the case of larger pipes this simple method will 
 not be sufficient, and swivel or slip joints must be used to take up the 
 expansion. 
 
 The method of making up a swivel-joint is shown in Fig. 33. 
 Any lengthening of the pipe A will be taken up by slight turning or 
 swivel movements at the points B and C. A slip-joint is shown in 
 
 252
 
 HEATING AND VENTILATION 
 
 5? 
 
 Fig. 34. The part c slides inside the shell d, and is made steam- 
 tight by a stuffing-box, as shown. The pipes are connected at the 
 flanges A and B. 
 When pipes 
 pass through 
 
 d I C 
 
 Q 
 
 Fig. 34. "Slip-Jotat" Connection to Take Care of Expansion 
 and Contraction of Pipes. 
 
 floors or parti- 
 
 tions, the wood- 
 
 work should be 
 
 protected by gal- 
 
 vanized-iron 
 
 sleeves having a 
 
 diameter from f to 1 inch greater than the pipe. Fig. 35 shows a 
 
 form of adjustable floor-sleeve 
 which may be lengthened or 
 shortened to conform to the 
 thickness of floor or partition. 
 If plain sleeves are used, a 
 plate should be placed around 
 
 L - ""' Fig. 36. Floor-Plate Adjusted to Plain 
 
 Fig. 35. Adjustable Metal Sleeve for Carrying Sleeve for Carrying Pipe through 
 
 Pipe through Floor or Partition. Floor or Partition. 
 
 the pipe where it passes through the floor or partition. These are 
 
 Fig. 37. Angle Valve. 
 
 Fig. 38. Offset Valve. Fig. 39. Corner Valve. 
 
 Valves for Radiator Connections. 
 
 made in two parts so that they may be put in place after the pipe is 
 hung. A plate of this kind is shown in Fig. 36. 
 
 253
 
 HEATING AND VENTILATION 
 
 Valves. The different styles commonly used for radiator con- 
 nections are shown in Figs. 37, 38, and 39, and are known as angle, 
 offset, and corner valves, respectively. The first is used when the 
 radiator is at the top of a riser or when the connections are like those 
 shown in Figs. 30, 31, and 32; the second is used when the connection 
 
 Fit:. 40. Indicating Effect of Using Globe Valve on Horizontal Steam Supply 
 Pipe or Dry Return. 
 
 between the riser and radiator is above the floor; and the third, when 
 the radiator has to be set close in the corner of a room and there is not 
 space for the usual connection. 
 
 A globe valve should never be used in a horizontal steam supply 
 or dry return. The reason for this is plainly 
 shown in Fig. 40. In order for water to flow 
 through the valve, it must rise to a height 
 shown by the dotted line, which would half 
 fill the pipes, and cause serious trouble from 
 water-hammer. The gate valve shown in 
 Fig. 41 does not have this undesirable fea- 
 ture, as the opening is on a level with the 
 bottom of the pipe. 
 
 Fig. 41. Gate Valve. Fig. 42. Simplest Form of Air-Valve. Operated by Hand. 
 
 Air=Valves. Valves of various kinds are used for freeing the 
 radiators from air when steam is turned on. Fig. 42 shows the 
 simplest form, which is operated by hand. Fig. 43 is a type of auto- 
 matic valve, consisting of a shell, which is attached to the radiator. 
 E >s a small opening which may be closed by the spindle C, which 
 
 254
 
 HEATING AND VENTILATION 
 
 is provided with a conical end. D is a strip composed of a layer of 
 iron or steel and one of brass soldered or brazed together. The 
 action of the valve is as follows : 
 when the radiator is cold and filled 
 with air the valve stands as shown 
 in the cut. When steam is turned 
 on, the air is driven out through 
 the opening B. As soon as this 
 is expelled and steam strikes the 
 strip D, the two prongs spring 
 apart owing to the unequal ex- 
 pansion of the two metals due to 
 the heat of the steam. This 
 raises the spindle C, and closes 
 the opening so that no steam can 
 escape. If air should collect in 
 the valve, and the metal strip 
 become cool, it would contract, 
 and the spindle would drop and 
 allow the air to escape through B 
 
 as before. E is an adjusting nut. F is a float attached to the spindle, 
 and is supposed, in case of a sudden rush 
 of water with the air, to rise and close the 
 opening; this action, however, is some- 
 what uncertain, especially if the pressure 
 of water continues for some time. 
 
 There are other types of valves acting 
 on the same principle. The valve shown 
 
 Fig. 43. Radiator Automatic Air- Valve. 
 
 Operated by Metal Strip />, Consisting 
 
 of Two Pieces of Metal of Unequal 
 
 Expansive Power. 
 
 Fig. 44. Automatic Air- Valve. Closed by Expansion 
 of a Piece of Vulcanite. 
 
 j. 45. Automatic Air- Valve, 
 srated by Expansion of 
 rum <7Due to Vaporiza- 
 tion of Alcohol with 
 which It is Partly 
 Filled. 
 
 in Fig. 44 is closed by the expansion of a piece of vulcanite instead 
 of a metal strip, and has no water float. 
 
 255
 
 60 
 
 HEATING AND VENTILATION 
 
 The valve shown in Fig. 45 acts on a somewhat different prin- 
 ciple. The float C is made of thin brass, closed at top and bottom, 
 and is partially filled with wood alcohol. When steam strikes the 
 float, the alcohol is vaporized, and creates a pressure sufficient to 
 bulge out the ends slightly, which raises the spindle and closes the 
 opening B. 
 
 Fig. 4(J shows a form of so-called vacuum valve. It acts in a 
 similar manner to those already described, but has in addition a 
 ball check which prevents the air 'from being 
 drawn into the radiator, should the steam go 
 down and a vacuum be formed. If a partial 
 vacuum exists in the boiler and radiators, the 
 boiling point, and consequently the tempera- 
 ture of the steam, are lowered, and less heal is 
 given off by the radiators. This method of 
 operating a heating plant is sometimes advo- 
 cated for spring and fall, when little heat is re- 
 quired, and when steam under pressure would 
 overheat the rooms. 
 
 Pipe Sizes. The proportioning of the steam 
 pipes in a heating plant is of the greatest im- 
 portance, and should be carefully worked out 
 by methods which experience has proved to be 
 correct. There are several ways of doing this; 
 but for ordinary conditions, Tables XIV, XV, 
 and XVI have given excellent results in actual practice. They 
 have been computed from what is known as D'Arcy's formula, with 
 suitable corrections made for actual working conditions. As the 
 computations are somewhat complicated, only the results will be given 
 here, with full directions for their proper use. 
 
 Table XIV gives the flow of steam in pounds per minute for 
 pipes of different diameters and with varying drops in pressure be- 
 tween the supply and discharge ends of the pipe. These quantities 
 are for pipes 100 feet in length; for other lengths the results must be 
 corrected by the factors given in Table XVI. As the length of pipe 
 increases, friction becomes greater, and the quantity of steam dis- 
 charged in a given time is diminished. 
 
 Table XIV is computed on the assumption that the drop in 
 
 Fig. 46. Vacuum Valve
 
 HEATING AND VENTILATION 
 
 (11 
 
 TABLE XIV 
 
 Flow of Steam in Pipes of Various Sizes, with Various Drops in Pres- 
 sure between Supply and discharge Ends 
 
 Calculated for 100-Foot Lengths of Pipe 
 
 DROP IN PRESSURE (POUNDS) 
 
 ft" 1 
 
 M 
 
 X 
 
 M 
 
 1 
 
 iy 2 
 
 2 
 
 3 
 
 4 
 
 5 
 
 l 
 
 .44 
 
 .63 
 
 .78 
 
 91 
 
 1.13 
 
 1.31 
 
 1.66 
 
 1.97 
 
 2.26 
 
 1/4 
 
 .81 
 
 1.16 
 
 1.43 
 
 1.66 
 
 2.05 
 
 2.39 
 
 3.02 
 
 3.59 
 
 4.12 
 
 iy 2 
 
 1.06 
 
 1.89 
 
 2.34 
 
 2.71 
 
 3.36 
 
 3.92 
 
 4.94 
 
 5.88 
 
 6.75 
 
 2 
 
 2.93 
 
 4.17 
 
 5.16 
 
 5.99 
 
 7.43 
 
 8.65 
 
 10.9 
 
 13.0 
 
 14.9 
 
 2% 
 
 5.29 
 
 7.52 
 
 9.32 
 
 10.8 
 
 13.4 
 
 15.6 
 
 19.7 
 
 23 A 
 
 26.9 
 
 3 
 
 8.61 
 
 12.3 
 
 15.2 
 
 17.6 
 
 21.8 
 
 25.4 
 
 32 
 
 31.8 
 
 43.7 
 
 ; ; i .; 
 
 12.9 
 
 18.3 
 
 22.'6 
 
 26.3 
 
 32.5 
 
 37.9 
 
 47.8 
 
 56.9 
 
 65.3 
 
 4 
 
 18 1 
 
 25.7 
 
 31.8 
 
 36.9 
 
 45.8 
 
 53.3 
 
 67.2 
 
 80.1 
 
 91.9 
 
 5 
 
 32.2 
 
 45.7 
 
 56.6 
 
 65.7 
 
 . 81.3 
 
 94.7 
 
 120 
 
 142 
 
 163 
 
 6 
 
 51.7 
 
 73.3 
 
 90.9 
 
 106 
 
 131 
 
 152 
 
 192 
 
 229 
 
 262 
 
 7 
 
 76.7 
 
 109 
 
 135 
 
 157 
 
 194 
 
 226 
 
 285 
 
 339 
 
 390 
 
 8 
 
 108 
 
 154 
 
 190 
 
 222 
 
 274 
 
 319 
 
 402 
 
 478 
 
 549 
 
 9 
 
 147 
 
 209 
 
 258 
 
 299 
 
 371 
 
 432 
 
 545 
 
 649 
 
 745 
 
 
 
 192 
 
 273 
 
 339 
 
 393 
 
 487 
 
 567 
 
 715 
 
 852 
 
 977 
 
 2 
 
 305 
 
 434 
 
 537 
 
 623 
 
 771 
 
 899 
 
 1,130 
 
 1,350 
 
 1,550 
 
 5 
 
 535 
 
 761 
 
 942 
 
 1,090 
 
 1,350 
 
 1,580 
 
 1,990 
 
 2,370 
 
 2,720 
 
 pressure between the two ends of the pipe equals the initial pressure. 
 If the drop in pressure is less than the initial pressure, the actual 
 discharge will be slightly greater than the quantities given in the table; 
 
 TABLE XV 
 
 Factors for Calculating Flow of Steam in Pipes under Initial Pres- 
 sures above Five Pounds 
 
 To be used in connection with Table XIV 
 
 DROP IN* 
 
 
 I 
 
 NITIAL PRESS 
 
 URE (POUNDS 
 
 ) 
 
 
 N POUNDS 
 
 10 
 
 20 
 
 30 
 
 40 
 
 60 
 
 80 
 
 J 
 
 1.27 
 
 1.49 
 
 1.68 
 
 1.84 
 
 2.13 
 
 2.38 
 
 | 
 
 1.26 
 
 1.48 
 
 1.66 
 
 .83 
 
 2.11 
 
 2.36 
 
 1 
 
 .24 
 
 1.46 
 
 1.64 
 
 .80 
 
 2.08 
 
 2.32 
 
 2 
 
 .21 
 
 1.41 
 
 1.59 
 
 .75 
 
 2.02 
 
 2.26 
 
 3 
 
 .17 
 
 1.37 
 
 1.55 
 
 .70 
 
 1.97 
 
 2.20 
 
 4 
 
 .14 
 
 1.34 
 
 1.51 
 
 .66 
 
 1.92 
 
 2.14 
 
 5 
 
 .12 
 
 1.31 
 
 1.47 
 
 .62 
 
 1.87. 
 
 2.09 
 
 but this difference will be small for pressures up to 5 pounds, and may 
 be neglected, as it is on the side of safety. For higher initial pressures, 
 Table XV has been prepared. This is to be used in connection with 
 Table XIV as follows : First find from Table XIV the quantity of 
 steam which will be discharged through the given diameter of pipe 
 
 257
 
 02 HEATING AND VENTILATION 
 
 TABLE XVI 
 
 Factors for Calculating Flow of Steam in Pipes of Other Lengths 
 than 100 Feet 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 10 
 
 316 
 
 120 
 
 .91 
 
 275 
 
 .60 
 
 600 
 
 .40 
 
 20 
 
 2.24 
 
 130 
 
 .87 
 
 300 
 
 . o/ 
 
 650 
 
 . 39 
 
 30 
 
 1.82 
 
 140 
 
 .84 
 
 325 
 
 . 55 
 
 700 
 
 .37 
 
 40 
 
 1.58 
 
 150 
 
 .81 
 
 350 
 
 .53 
 
 750 
 
 .36 
 
 50 
 
 1.41 
 
 160 
 
 .79 
 
 375 
 
 .51 
 
 800 
 
 . 35 
 
 60 
 
 1.29 
 
 170 
 
 .76 
 
 400 
 
 .50 
 
 850 
 
 .34 
 
 70 
 
 1.20 
 
 180 
 
 .74 
 
 425 
 
 .48 
 
 900 
 
 .33 
 
 80 
 
 1.12 
 
 190 
 
 72 
 
 450 
 
 .47 
 
 950 
 
 .32 
 
 90 
 
 1.05 
 
 200 
 
 .70 
 
 475 
 
 .46 
 
 1,000 
 
 .31 
 
 100 
 
 1 . 00 
 
 225 
 
 .66 
 
 500 
 
 .45 
 
 
 
 110 
 
 .95 
 
 250 
 
 .63 
 
 550 
 
 .42 
 
 
 
 with the assumed drop in pressure; then look in Table XV for the 
 factor corresponding with the assumed drop and the higher initial 
 pressure to be used. The quantity given in Table XIV, multiplied 
 by this factor, will give the actual capacity of the pipe under the given 
 conditions. 
 
 Example What weight of steam will be discharged through a 3-inch 
 pipe 100 feet long, with an initial pressure of 60 pounds and a drop of 2 pounds? 
 
 Looking in Table XIV, we find that a 3-inch pipe will dis- 
 charge 25 . 4 pounds of steam per minute with a 2-pound drop. Then 
 looking in Table XV, we find the factor corresponding to GO pounds 
 initial pressure and a drop of 2 pounds to be 2.02. Then according 
 to the rule given, 25.4 X 2.02 = 51 .3 pounds, which is the capacity 
 of a 3-inch pipe under the assumed conditions. 
 
 Sometimes the problem will be presented in the following way: 
 What size of pipe will be required to deliver SO pounds of steam a 
 distance of 100 feet with an initial pressure of 40 pounds and a drop 
 of 3 pounds? 
 
 We have seen that the higher the initial pressure with a given 
 drop-, the greater will be the quantity of steam discharged; therefore 
 a smaller pipe will be required to deliver 80 pounds of steam at 40 
 pounds than at 3 pounds initial pressure From Table XV, we find 
 that a given pipe will discharge 1 .7 times as much steam per minute 
 with a pressure of 40 pounds and a drop of 3 pounds, as it would with 
 a pressure of 3 pounds, dropping to zero. From this it is evident 
 that if we divide SO by 1 .7 and look in Table XIV under "3 pounds 
 
 358
 
 HEATING AND VENTILATION 63 
 
 drop" for the result thus obtained, the size of pipe corresponding will 
 be that required. Now, 80 -r- 1 .7 = 47. The nearest number in the 
 table marked "3 pounds drop" is 47.8, which corresponds to a 3^- 
 inch pipe, which is the size required. 
 
 These conditions will seldom be met with in low-pressure heating, 
 but apply more particularly to combination power and heating plants, 
 and will be taken up more fully under that head. For lengths of 
 pipe other than 100 feet, multiply the quantities given in Table XIV 
 by the factors found in Table XVI. 
 
 Example What weight of steam will be discharged per minute through 
 a 3-inch pipe 450 feet long, with a pressure of 5 pounds and a drop of pound? 
 
 Table XIV, which may be used for all pressures below 10 pounds, 
 gives for a 3^-inch pipe 100 feet long, a capacity of 18.3 pounds for 
 the above conditions. Looking in Table XVI, we find the correction 
 factor for 450 feet to be .47. Then 18.3 X .47-8.6 pounds, the 
 quantity of steam which will be discharged if the pipe is 450 feet 
 
 long- 
 Examples involving the use of Tables XIV, XV, and XVI in 
 combination, are quite common in practice. The following example 
 will show the method of calculation: 
 
 What size of pipe will be required to deliver 90 pounds of steam per 
 minute a distance of 800 feet, with an initial pressure of 80 pounds and a drop 
 of 5 pounds? 
 
 Table XVI gives the factor for 800 feet as .35, and Table XV, 
 that for 80 'pounds pressure and 5 pounds drop, as 2.09. Then 
 
 90 
 
 - ^-7.7. = 123, which is the equivalent quantity we must look 
 . oo X 2 . 09 
 
 for in Table XIV. We find that a 4-inch pipe will discharge 91.9 
 pounds, and a 5-inch pipe 163 pounds. A 4^-inch pipe is not com- 
 monly carried in stock, and we should probably use a 5-inch in this 
 case, unless it was decided to use a 4-inch and allow a slightly greater 
 drop in pressure. In ordinary heating work, with pressures varying 
 from 2 to 5 pounds, a drop of \ pound in 100 feet has been found to 
 give satisfactory results. 
 
 In computing the pipe sizes for a heating system by the above 
 methods, it would be a long process to work out the size of each 
 branch separately. Accordingly Table XVII has been prepared for 
 ready use in low-pressure work. 
 
 259
 
 (11 
 
 HEATING AND VENTILATION 
 
 As most direct heating systems, and especially those in school- 
 houses, are made up of both radiators and circulation coils, an effi- 
 ciency of 300 B. T. U. has been taken for direct radiation of whatever 
 variety, no distinction being made between the different kinds. This 
 gives a slightly larger pipe than is necessary for cast-iron radiators; 
 but it is probably offset by bends in the pipes, and in any case gives a 
 slight factor of safety. We find from a steam table that the latent 
 heat of steam at 20 pounds above a vacuum (which corresponds to 
 5 pounds' gauge-pressure) is 954 + B. T. U. which means that, for 
 every pound of steam condensed in a radiator, 9o4 B. T. U. are given 
 off for warming the air of the room. If a radiator has an efficiency 
 of 300 B. T. U., then each square foot of surface will condense 300 H- 
 9.">4 = .314 pound of steam per hour; so that we may assume in 
 round numbers a condensation of \ of a pound of steam per hour for 
 each square foot of direct radiation, when computing the sizes of 
 steam pipes in low-pressure heating. Table XVII has been calculated 
 on this assumption, and gives the square feet of heating surface 
 
 TABLE XVI! 
 
 Heating Surface Supplied by Pipes of Various Sizes 
 Length of Pipe, 100 Feet 
 
 SQUARK FKKT OF HKATIXG SURFACE 
 
 \ Pound Drop J Pound Drop 
 
 80 
 
 114 
 
 
 145 
 
 210 
 
 
 190 
 
 340 
 
 
 525 
 
 750 
 
 
 950 
 
 1,350 
 
 
 1.550 
 
 2.210 
 
 
 2,320 
 
 3,290 
 
 
 3,250 
 
 4,620 
 
 
 5,800 
 
 8,220 
 
 
 9.320 
 
 13,200 
 
 13.800 
 
 19.020 
 
 19.440 27.720 
 
 which different sizes of pipe will supply, with drops in pressure of 
 \ and ', pounds in each 100 feet of pipe. The former should be used 
 for pressures from 1 to 5 pounds, and the latter may be used for 
 pressures over 5 pounds, under ordinary conditions. The sizes of 
 long mains and special pipes of large size should be proportioned 
 directlv from Tables XIV, XV, and XVI. 
 
 260
 
 HEATING AND VENTILATION 
 
 Where the two-pipe system is used and the radiators have sepa- 
 rate supply and return pipes, the risers or vertical pipes may be taken 
 from Table XVII; but if the single-pipe system is used, the risers 
 must be increased in size, as the steam and water are flowing in oppo- 
 site directions and must have plenty of room to pass each other. It 
 is customary in this case to base the computation on the velocity of 
 the steam in the pipes, rather than on the drop in pressure. Assum- 
 ing, as before, a condensation of one-third of a pound of steam per 
 hour per square foot of radiation, Tables XVIII and XIX have been 
 prepared for velocities of 10 and 15 feet per second. The sizes given 
 in Table XIX have been found sufficient in most cases ; but the larger 
 sizes, based on a flow of 10 feet per second, give greater safety and 
 should be more generally used. The size of the largest riser should 
 usually be limited to 2^ inches in school and dwelling-house work, 
 unless it is a special pipe carried up in a concealed position. If the 
 length of riser is short between the lowest radiator and the main, a 
 higher velocity of 20 feet or more may be allowed through thjs por- 
 tion, rather than make the pipe excessively large. 
 
 TABLE XVIII TABLE XIX 
 
 Radiating Surface Supplied by Steam Risers 
 
 1 FEET PER SECOND VELOCITY 
 
 15 FEET PER SECOND VELOCITY 
 
 Size of Pipe 
 
 Sq. Feet of Radiation 
 
 Size of Pipe 
 
 Sq. Feet of Radiation 
 
 1 in. 
 
 30 
 
 1 in. 
 
 50 
 
 H ' 
 
 60 
 
 H " 
 
 90 
 
 1? ' 
 
 80 
 
 if" 
 
 120 
 
 2 ' 
 
 130 
 
 2 " 
 
 200 
 
 2J ' 
 
 190 
 
 2J " 
 
 290 
 
 3 ' 
 
 290 
 
 3 " 
 
 340 
 
 3* ' 
 
 390 
 
 3J " 
 
 . 590 
 
 EXAMPLES FOR PRACTICE 
 
 1. How many pounds of steam will be delivered per minute, 
 through a 3^-inch pipe 600 feet long, with an initial pressure of 5 
 pounds and a drop of | pound? ANS. 7.32 pounds. 
 
 2. What size pipe will be required to deliver 25.52 pounds 
 of steam per minute with an initial pressure of 3 pounds and a drop 
 of j pound, the length of the pipe being 50 feet? ANS. 4-inch. 
 
 3. Compute the size of pipe required to supply 10,000 square 
 feet of direct radiation (assume ^ of a pound of steam per square 
 
 261
 
 66 
 
 HEATING AND VENTILATION 
 
 foot per hour) where the distance to the boiler house is 300 feet, and 
 the pressure carried is 10 pounds, allowing a drop in pressure of 
 4 pounds. Axs. 5-inch (this is slightly larger than is required, while 
 a 4-inch is much too small). 
 
 TABLE XX 
 Sizes of Returns for Steam Pipes (in Inches) 
 
 DIAMETER <n- STEAM PIPK DIAMETER OF DRY RETURN DIAMKTER OF SEALED RETURN 
 
 1 1 
 
 1 
 
 U i 
 
 1 - 
 
 H H 
 
 1 
 
 2 
 
 H 
 
 U 
 
 24 
 
 2 
 
 14 
 
 3" 
 
 2* 
 
 2" 
 
 34 
 
 . 24 
 
 2 
 
 4 
 
 3 
 
 24 
 
 o 
 
 3 
 
 2* 
 
 6 
 
 3* 
 
 3 
 
 7 
 
 34 
 
 3 
 
 8 
 
 4 
 
 34 
 
 5 
 
 34 
 
 i n 5 
 
 4" 
 
 12 6 5 
 
 Returns. The size of return pipes is usually a matter of custom 
 and judgment rather than computation. It is a common rule among 
 steamh'tters to make the returns one size smaller than the corre- 
 sponding steam pipes. This is a good rule for the smaller sizes, but 
 gives a larger return than is necessary for the larger sizes of pipe. 
 Table XX gives different sizes of steam pipes with the corresponding 
 diameters for dry and sealed returns. 
 
 TABLE XXI 
 Pipe Sizes for Radiator Connections 
 
 SQUARE FEET c 
 
 E RADIATION 
 
 STEAM RETURN 
 
 Two-Pipe 
 
 10 to 30 
 30 to 48 
 48 to 96 
 96 to 150 
 
 f inch f inch 
 
 1! " i i! : ' 
 
 Single-Pipe 
 
 10 to 24 
 24 to 60 
 60 to 80 
 
 80 to 130 
 
 i 
 
 1 inch 
 i 
 
 i* - 
 
 I 
 
 262
 
 HEATING AND VENTILATION 
 
 67 
 
 The length of run and number of turns in a return pipe should 
 be noted, and any unusual conditions provided for. Where the 
 condensation is discharged through a trap into a lower pressure, the 
 sizes given may be slightly reduced, especially among the larger 
 sizes, depending upon the differences in pressure. 
 
 Radiators are usually tapped for pipe connections as shown in 
 Table XXI, and these sizes may be 
 used for the connections with the 
 mains or risers. 
 
 Boiler Connections. The steam 
 main should be connected to the 
 rear nozzle, if a tubular boiler is 
 used, as the boiling of the water is 
 less violent at this point and dryer 
 steam will be obtained. The shut- 
 off valve should be placed in such a position that pockets for the 
 accumulation of condensation will be avoided. Fig. 47 shows a good 
 position for the valve. 
 
 The size of steam connection may be computed by means of the 
 methods already given, if desired. But for convenience the sizes 
 given in Table XXII may be used with satisfactory results for the 
 short runs between the boilers and main header. 
 
 Fig 47. Good Position for Shut-Off 
 Valve. 
 
 TABLE XXII 
 Pipe Sizes from Boiler to Main Header 
 
 DIAMETER OF BOILER 
 
 SIZE OF STKAM 
 
 36 inches 
 
 3 inches 
 
 42 
 
 
 4 
 
 
 48 
 
 
 4 
 
 
 54 
 
 
 5 
 
 
 60 
 
 
 5 
 
 
 66 
 
 
 6 
 
 
 72 
 
 
 6 
 
 
 The return connection is made through the blow-off pipe, and 
 should be arranged so that the boiler can be blown off without draining 
 the returns. A check- valve should be placed in the main return, and 
 a plug-cock in the blow-off pipe. Fig. 48 shows in plan a good 
 arrangement for these connections.
 
 HEATING AND VEXTILATIOX 
 
 The feed connections, with the exception of that part exposed 
 in the smoke-bonnet, are always made of brass in the best class of 
 work. The small section referred to should be of extra heavv wrought 
 
 Fig. 48. A Good Arran.uemem of Return and Rlow-Off Connections. 
 
 iron. The branch to each boiler should be provided with a gate 
 or globe valve and a check-valve, the former being placed next to the 
 boiler. 
 
 Table XXIII gives suitable sizes for return, blow-off, and feed 
 pipes for boilers of different diameters. 
 
 TABLE XXIII 
 Sizes tor Return, Blow=Off, and Feed Pipes 
 
 DIAMETER OF Hoil 
 
 SIZE OF PIPK SIZE OF BLOW-OFF j 
 
 GRAVITY KKTURN PIPE 
 
 MO i nolle* 
 
 H inches 
 
 1 \ inches 
 
 1 
 
 inch 
 
 j., 
 
 9 ' 
 
 H ' 
 
 1 
 
 
 }s 
 
 2 
 
 H ' 
 
 1 
 
 
 /H 
 
 2i " 
 
 9 " 
 
 H 
 
 
 00 
 
 2i " 
 
 9 " 
 
 M 
 
 " 
 
 tiO 
 
 3 
 
 2t 
 
 
 " 
 
 "2 
 
 3 
 
 2i 
 
 l* 
 
 
 Blow=0ff Tank. Where the blow-off pipe connects with a 
 sewer, some means must be provided for cooling the water, or the 
 expansion and contraction caused by the hot water flowing through 
 the drain-pipes will start the joints and cause leaks. For this reason 
 it is customary to pass the water through a blow-off tank. A form 
 of wrought-iron tank is shown in Fig. 49. It consists of a receiver 
 supported on cast-iron cradles. The tank ordinarily stands nearly 
 full of cold water. 
 
 The pipe from the boiler enters above the water-line, and the 
 sewer connection leads from near the bottom, as shown. A vapor 
 pipe is carried from the top of the tank above the roof of the building. 
 When water from the boiler is blown into the tank, cold water from 
 
 264
 
 HEATING AND VENTILATION 
 
 the bottom flows into the sewer, and the steam is carried off through 
 the vapor pipe. The equalizing pipe is to prevent any siphon action 
 which might draw the water out of the tank after a flow is once started. 
 As only a part of the water is blown out of a boiler at one time, the 
 blow-off tank can be of a comparatively small size. A tank 24 by 48 
 inches should be large enough for boilers up to 48 inches in diameter; 
 
 CQUAL/Z/MG 
 
 PIPE 
 
 FROM BOILER 
 
 WATER LINE 
 
 Fig. 49. Connections of Blow-Off Tank. 
 
 and one 36 by 72 inches should care for a boiler 72 inches in diameter. 
 If smaller quantities of water are blown off at one time, smaller tanks 
 can be used. The sizes given above are sufficient for batteries of 2 or 
 more boilers, as one boiler can be blown off and the water allowed to 
 cool before a second one is blown off. Cast-iron tanks are often 
 used in place of wrought-iron, and these may be sunk in the ground 
 if desired. 
 
 865
 
 Cast Iron Seamless Tubular Steam Heater.
 
 HEATING AND VENTILATION 
 
 PART II 
 
 INDIRECT STEAM HEATING 
 
 As already stated, in the indirect method of steam heating, a 
 special form of heater is placed beneath the floor, and encased in 
 galvanized iron or in brickwork. A cold-air box is connected with 
 the space beneath the heater; and warm-air pipes at the top are 
 connected with registers in the floors or walls as already described for 
 furnaces. A separate heater may be provided for each register if the 
 rooms are large, or two or more registers may be connected with the 
 same heater if the horizontal runs of pipe are short. Fig. 50 shows 
 a section through a heater arranged for introducing hot air into a 
 room through a floor register; and Fig. 51 shows the same type of 
 heater connected with a wall register. The cold-air box is seen at 
 the bottom of the casing; and the air, in passing through the spaces 
 between the sections of the heater, becomes warmed, and rises to the 
 rooms above. 
 
 Different forms of indirect heaters are shown in Figs. 52 and 53. 
 Several sections con- 
 nected in a single group -^ __ ___^^^_ __ ._ = 
 
 are called a stack. Some- 
 times the stacks are en- 
 cased in brickwork built 
 up from the basement 
 floor, instead of in gal- 
 vanized iron as shown in 
 the cuts. This method 
 of heating provides fresh 
 air for ventilation, and for 
 this reason is especially 
 
 adapted for schoolhouses, hospitals, churches, etc. As com- 
 pared with furnace heating, it has the advantage of being less 
 affected by outside wind-pressure, as long runs of horizontal pipe 
 
 Fig. 50. Steam Heater Placed under Floor Register 
 Indirect System. 
 
 267
 
 HEATING AND VENTILATION 
 
 are avoided and the heaters can be placed near the registers. In a 
 large building where several furnaces would be required, a single 
 
 boiler can be used, and the num- 
 ber of stacks increased to suit 
 the existing conditions, thus 
 making it necessary to run but 
 a single fire. Another advan- 
 tage is the large ratio between 
 the heating and grate surface 
 as compared with a furnace; 
 and as a result, a large quan- 
 tity of air is warmed to a mod- 
 erate temperature, in place of 
 a smaller quantity heated to a 
 much higher temperature. 
 This gives a more agreeable 
 quality to the air, and renders 
 it less dry. Direct and indi- 
 rect systems are often com- 
 bined, thus providing the liv- 
 ing rooms with ventilation, while the hallways, corridors, etc., have 
 only .direct radiators for warming. 
 
 Types of Heaters. Various forms of indirect radiators are shown 
 in Figs. 52, 53, 54, and 50. A hot-water radiator may be used for 
 steam; but a steam radiator cannot alwavs be used for hot water, as 
 
 Fig. 51. Steam Heater Conn 
 ister. Indirect S 
 
 .ted to Wall Reg- 
 stem. 
 
 Fig. 52. One Form of Indirect Steam or Hot-Water Heater. 
 
 it must be especially designed to produce a continuous flow of water 
 through it from top to bottom. Figs. 54 and 55 show the outside 
 and the interior construction of a common pattern of indirect radiator
 
 HEATING AND VENTILATION 
 
 73 
 
 designed especially for steam. The arrows in Fig. 55 indicate the 
 path of the steam through the radiator, which is supplied at the right, 
 while the return connection is at the left. The air-valve in this case 
 should he connected in the end of the last section near the return. 
 
 Fig. 53. Another Form of Indirect Steam or Hot- Water Heater. 
 
 A very efficient form of radiator, and one that is especially adapted 
 to the warming of large volumes of air, as in schoolhouse work, is 
 shown in Fig. 56, and is known as the School pin radiator. This can 
 
 Fig. 54. Exterior View of a Common Type of Radiator for Indirect-Steam Heating. 
 
 be used for either steam or hot water, as there is a continuous passage 
 downward from the supply connection at the top to the return at the 
 bottom. These sections or slabs are made up in stacks after the 
 
 Fig. 55. Interior Mechanism of Radiator Shown in Fig. 54. 
 
 manner shown in Fig. 57, which represents an end view of several 
 sections connected together with special nipples. 
 
 A very efficient form of indirect heater may be made up of 
 wrought-iron pipe joined together with branch tees and return bends.
 
 74 
 
 HEATING AND VENTILATION 
 
 A heater like that shown in Fig. 58 is known as a box coil. Its effi- 
 ciency is increased if the pipes are staggered that is, if the pipes in 
 alternate rows are placed over the spaces between those in the row 
 below. 
 
 Efficiency of Heaters. The efficiency of an indirect heater 
 
 Fig. 50. "School Pin" Radiator, Especially Adapted for Warming Large Volumes of 
 Air by Either Steam or Hot Water. 
 
 depends upon its form, the difference in temperature between the 
 steam and the surrounding air, and the velocity with which the air 
 passes over the heater. Under ordinary conditions in dwelling-house 
 work, a good form of indirect radiator will give off about 2 B. T. U. 
 per square foot per hour for 
 each degree difference in tem- 
 perature between the steam 
 and the entering air. Assum- 
 ing a steam pressure of 2 
 pounds and an outside tem- 
 perature of zero, we should 
 have a difference in tempera- 
 ture of about 220 degrees, 
 which, under the conditions 
 stated, would give an efficiency 
 of 220 X 2 = 440 B. T. U. 
 per hour for each square foot 
 of radiation. By making a similar computation for 10 degrees be- 
 low zero, we find the efficiency to be 460. In the same manner we 
 may calculate the efficiency for varying conditions of steam pressure 
 and outside temperature. In the case of schoolhouses and similar 
 buildings where large volumes of air are warmed to a moderate tem- 
 
 Fig. 57. End View of Several "School Pin" 
 Radiator Sections Connected Together. 
 
 270
 
 HEATING AND VENTILATION 
 
 75 
 
 perature, a somewhat higher efficiency is obtained, owing to the in- 
 creased velocity of the air over the heaters. Where efficiencies of 440 
 and 460 are used for dwellings, we may substitute 600 and 620 for 
 schoolhouses. This corresponds approximately to 2.7 B. T. U. per 
 square foot per hour for a difference of 1 degree between the air and 
 steam. 
 
 The principles involved in indirect steam heating are sirhilar 
 to those already described in furnace heating. Part of the heat given 
 off by the radiator must be used in warming up the air-supply to the 
 temperature of the room, and part for offsetting the loss by conduction 
 through walls and windows. The method of computing the heating 
 surface required, depends upon the volume of air to be supplied to the 
 room. In the case of a schoolroom or hall, where the air quantity 
 
 S/I3C l//~H/ 
 
 
 
 1 
 
 
 
 
 
 ! 
 
 
 
 
 
 i r 
 1 CD 
 
 
 
 Fig, 58.. "Box Coil," Built Up of Wrought-Iron Pipe, for Indirect- Steam Heating. 
 
 is large as compared with the exposed wall and window surface, we 
 should proceed as follows: 
 
 First compute the B. T. U. required for loss by conduction 
 through walls and windows; and to this, add the B. T. U. required 
 for the necessary ventilation; and divide the sum by the efficiency 
 of the radiators. An example will make this clear. 
 
 Example. How many square feet of indirect radiation will be required 
 to warm and ventilate a schoolroom in zero weather, where the heat loss by 
 conduction through walls and windows is 36,000 B. T. U., and the air-supplv 
 is 100,000 cubic feet per hour? 
 
 By the methods given under "Heat for Ventilation," we have 
 
 100,000 X 70 x 127,272 = B. T. U. required for ventilation. 
 
 55 
 36,000 + 127,272 - 163,272 B. T. U. = Total heat required. 
 
 This in turn divided by 600 (the efficiency of indirect radiators 
 under these conditions) gives 272 square feet of surface required. 
 
 271
 
 76 HEATING AND VENTILATION 
 
 In the case of a dwelling-house the conditions are somewhat 
 changed, for a room having a comparatively large exposure will have 
 perhaps only 2 or 3 occupants, so that, if the small air-quantity neces- 
 sary in this case were used to convey the required amount of heat 
 to the room, it would have to be raised to an excessively high temper- 
 ature. It has been found by experience that the radiating surface 
 necessary for indirect heating is about 50 per cent greater than that 
 required for direct heating. So for this work we may compute the 
 surface required for direct radiation, and multiply the result by 1.5. 
 
 Buildings like hospitals are in a class between dwellings and 
 schoolhouses. The air-supply is based on the number of occupants, 
 as in schools, but other conditions conform more nearly to dwelling- 
 houses. 
 
 To obtain the radiating surface for buildings of this class, we 
 compute the total heat required for warming and ventilation as in 
 the case of schoolhouses, and divide the sum by the efficiencies given 
 for dwellings that is, 440 for zero weather, and 460 for 10 degrees 
 below. 
 
 Example. A hospital ward requires 50,000 cubic feet of air per hour for 
 ventilation; and the heat loss by conduction through walls, etc., is 100,000 
 B. T. U. per hour. How many square feet of indirect radiation will be required 
 to warm the ward in zero weather? 
 
 50,000 X 70 - 55 = 63,630 B. T. U. for ventilation; then, 
 
 63,636 + 100,000 
 
 = 3/2 + square teet. 
 
 440 
 
 EXAMPLES FOR PRACTICE 
 
 1. A schoolroom having 40 pupils is to be warmed and venti- 
 lated when it is 10 degrees below zero. If the heat loss by conduction 
 is 30,000 B. T. U. per hour, and the air supply is to be 40 cubic feet 
 per minute per pupil, how many -square feet of indirect radiation will 
 be required? Axs. 273. 
 
 2. A contagious ward in a hospital has 10 beds, requiring 6,000 
 cubic feet of air each, per hour. The heat loss by conduction in zero 
 weather is 80,000 B. T. U. How many square feet of indirect radia- 
 tion will be required? Axs. 355. 
 
 3. The heat loss from a sitting room is 11,250 B. T. U. per 
 hour in zero weather. How many square feet of indirect radiation 
 will be required to warm it? Axs. 75. 
 
 272
 
 HEATING AND VENTILATION 
 
 77 
 
 LAG 
 SCREW ' 
 
 Stacks and Casings. It has already been stated that a group of 
 sections connected together is called a stack, and examples of these 
 with their casings are shown in Figs. 50 and 51. The casings are 
 usually made of galvanized iron, and are made up in sections by 
 means of small bolts so that they may be taken apart in case it is 
 necessary to make repairs. Large stacks are often enclosed in brick- 
 work, the sides consisting of 8-inch walls; and the top being covered 
 over with a layer of brick and mortar supported on light wrought-iron 
 tee-bars. Blocks of asbestos are sometimes used for covering, instead 
 of brick, the whole being covered over with plastic material of the 
 same kind. 
 
 Where a single stack supplies several flues or registers, the 
 connections between these and the warm-air chamber are made in 
 the same manner as already described for furnace heating. When 
 galvanized-iron casings are used, the heater is supported by hangers 
 from the floor above. Fig. 
 59 shows the method of 
 hanging a heater from a 
 wooden floor. If the floor 
 is of fireproof construc- 
 tion, the hangers may pass 
 up through the brick- 
 work, and the ends be 
 provided with nuts and large washers or plates ; or they may be clamped 
 to the iron beams which carry the floor. W T here brick casings are 
 used, the heaters are supported upon pieces of pipe or light I-beams 
 built into the walls. 
 
 The warm-air space above the heater should never be less than 
 8 inches, while 12 inches is preferable for heaters of large size. The 
 cold-air space may be an inch or two less; but if there is plenty of 
 room, it is good practice to make it the same as the space above. 
 
 Dampers. The general arrangement of a galvanized-iron casing 
 and mixing damper is shown in Fig. 60. The cold-air duct is brought 
 along the basement ceiling from the inlet window, and connects 
 with the cold-air chamber beneath the heater. The entering air passes 
 up between the sections, and rises through the register above, as shown 
 by the arrows. When the mixing damper is in its lowest position, 
 all air reaching the register must pass through the heater; but if the 
 
 IRON 
 ffOJD 
 
 nnnnnnnn 
 
 WftO'T IRON RIPE 
 
 Fig. 59. Method of Hanging a Heater below a Wooden 
 Floor. 
 
 S73
 
 78 
 
 HEATING AND VENTILATION 
 
 damper is raised to the position shown, part of the air will pass by 
 without going through the heater, and the mixture entering through 
 the register will be at a lower temperature than before. By changing 
 
 FLOOR REG/STEFl 
 
 ,,-JJ 
 
 
 V 
 
 /HEAT, 
 
 r* 
 
 / 
 
 S 
 
 
 > -- 
 
 J 
 
 GALVANIZED IRON SLIDING DOOR 
 CAS/NG 
 
 Fig. (30. General Arrangement of a Galvanizert-Iron Casing and Mixing Damper. 
 Damper between Heater and Register. 
 
 the position of the clamper, the proportions of warm and cold air 
 delivered to the room can be varied, thus regulating the temperatuie 
 without diminishing to any great extent the quantity of air delivered. 
 
 I 
 
 07 
 
 / 
 
 / 
 
 COLD XI //? 
 
 / 
 
 ^ 
 
 / 
 
 ~y>. 
 
 
 Fig. 61. Heater and Mixing Damper with Brick Casing. Damper between 
 Heater and Register. 
 
 The objection to this form of damper is that there is a tendency for 
 the air to enter the room before it is thoroughly mixed; that is, a 
 stream of warm air will rise through one half of the register while 
 
 274
 
 HEATING AND VENTILATION 
 
 7!) 
 
 cold air enters through the other. This is especially true if the con- 
 nection between the damper and register is short. Fig. 61 shows 
 a similar heater and mixing damper, with brick casing. Cold air is 
 admitted to the large chamber below the heater, and rises through 
 the sections to the register as before. The action of the mixing 
 damper is the same as already described. Several flues or registers 
 may be connected with a stack of this form, each connection having, 
 in addition to its mixing damper, an adjusting damper for regulating 
 the flow of air to the different rooms. 
 
 Another way of proportioning the air-flow in cases of this kind 
 is to divide the hot-air chamber above the heater into sections, by 
 means of galvanized-iron partitions, giving to each room its proper 
 share of heating surface. If the cold-air supply is made sufficiently 
 large, this arrangement is preferable to using adjusting dampers as 
 
 i 
 
 - 
 
 1 
 
 
 
 
 I ft 
 
 ^2 -^ --s-r- -=; 
 
 - J~ 
 
 
 LZj 
 
 
 ^ 
 
 
 " -^ 
 
 Fig. 
 
 Another Arrangement of Mixing Damper and Heater in Galvanized-Iron 
 Casing. Heater between Damper and Register. 
 
 described above. The partitions should be carried down the full 
 depth of the heater between the sections, to secure the best results. 
 The arrangement shown in Fig. 62 is somewhat different, and 
 overcomes the objection noted in connection with Fig. 60, by sub- 
 stituting another. The mixing damper in this case is placed at the 
 other end of the heater. When it is in its highest position, all of the 
 air must pass through the heater before reaching the register; but 
 when partially lowered, a part of the air passes over the heater, 
 and the result is a mixture of cold and warm air, in proportions 
 depending upon the position of the damper. As the layer of warm 
 air in this case is below the cold air, it tends to rise through it, and a 
 more thorough mixture is obtained than is possible with the damper 
 shown-in Fig. 60. One quite serious objection, however, to this form 
 of damper, is illustrated in Fig. 63. When the damper is nearly 
 
 875
 
 HEATING AND VENTILATION 
 
 Fig. 63. Showing Difficulty of Regulat 
 
 iiig Temperature with Arrangement 
 
 in Fig. 62. 
 
 closed so that the greater part of the air enters above the heater, it 
 has a tendency to fall between the sections, as shown by the arrows, 
 and, becoming heated, rises again, so that it is impossible to deliver 
 
 air to a room below a certain tem- 
 perature. This peculiar action in- 
 creases as the quantity of air admit- 
 ted below the heater is diminished. 
 When the inlet register is placed in 
 the wall at some distance above 
 the floor, as in schoolhouse work, a thorough mixture of air can be 
 obtained by plac- 
 ing the heater so 
 that the current 
 of warm air will 
 pass up the front 
 of the flue and be 
 discharged into 
 the room through 
 the lower part of 
 the register. This 
 is shown quite 
 clearly in Fig. 64, 
 where the cur- 
 rent of warm air 
 is represented by 
 crooked arrows, 
 and the cold air 
 by straight ar- 
 rows. The two 
 currents pass up 
 the flue separate- 
 ly; but as soon 
 as they are dis- 
 charged through " 
 
 . , Fig. 64. Arrangement of Heater and Damper Causing Warm Air 
 
 the register the to Enter Room through Lower Part of Register, thus 
 
 . Securing Thorough Mixing 
 
 warm air tends 
 
 to rise, and the cold air to fall, with the result of a more or less 
 
 complete mixture, as shown. 
 
 H 
 
 O3 
 
 376
 
 HEATING, AND VENTILATION 
 
 It is often desirable to warm a room at times when ventilation 
 is not necessary, as in the case of living rooms during the night, or 
 for quick warming in the morning. A register and damper for air 
 rotation should be provided i .1 this case. Fig. 65 shows an arrange- 
 ment for this purpose. When the damper is in the position shown, 
 air will be taken from the room above and be warmed over and over; 
 but, by raising the damper, the supply will be taken from outside. 
 Special care should be taken to make all mixing dampers tight against 
 air-leakage, else their advantages will be lost. They should work 
 easily and close tightly against flanges covered with felt. They may 
 be operated from the rooms above by means of chains passing over 
 
 1 
 
 2 
 
 I 
 
 \ 
 
 - 
 
 
 
 
 I 
 
 1 
 
 1 
 
 *OLB A/fl DUCT 
 
 
 ^. : 
 
 v ) 
 
 
 
 
 
 
 1 h 
 
 
 
 
 
 
 
 
 
 
 ] 
 
 Fig. i 
 
 Arrangement for Quick Heating without Ventilation. Damper Shuts off Fresh 
 Air, and Air of Room Heated by Rotating Forth and Back through 
 Register and Heater. 
 
 guide-pulleys; special attachments should be 'provided for holding 
 in any desired position. 
 
 Warm=Air Flues. The required size of the warm-air flue between 
 the heater and the register, depends first upon the difference in tem- 
 perature between the air in the flue and that of the room, and second, 
 upon the height of the flue. In dwelling-houses, where the con- 
 ditions are practically constant, it is customary to allow 2 square 
 inches area for each square foot of radiation when the room is on the 
 first floor, and 1^ square inches for the second and third floors. In 
 the case of hospitals, where a greater volume of air is required, these 
 figures may be increased to 3 square inches for the first floor wards, 
 and 2 square inches for those on the upper floors. 
 
 In schoolhouse work, it is more usual to calculate the size of 
 flue from an assumed velocity of air-flow through it. This will vary 
 greatly according to the outside temperature and the prevailing wind 
 conditions. The following figures may be taken as average velocities 
 
 877
 
 82 HEATING AND VENTILATION 
 
 obtained in practice, and may be used as a basis for calculating the 
 required flue areas for the different stories of a school building: 
 
 1st floor, 280 feet per minute. 
 2nd " , 340 " 
 3rd " , 400 " 
 
 These velocities will be increased somewhat in cold and windy weather 
 arid will be reduced when the atmosphere is mild and damp. 
 
 Having assumed these velocities, and knowing the number of 
 cubic feet of air to be delivered to the room per minute, we have only 
 to divide this quanity by the assumed velocity, to obtain the required 
 'flue area in square feet. 
 
 Example. A schoolroom on the second floor is to have an air-supply of 
 2,000 cubic feet per minute. What will be the required flue area? 
 
 Axs. 2000 -T- 340 = 5.8 + sq. feet. 
 
 The velocities would be higher in the coldest weather, and dampers 
 should be placed in the flues for throttling the air-supply when nec- 
 essary. 
 
 Cold=Air Ducts. The cold-air ducts supplying heaters should 
 be planned in a manner similar to that described for furnace heating. 
 The air-inlet should be on the north or west side of the building; but 
 this of course is not always possible. The method of having a large 
 trunk line or duct with inlets on fwo or more sides of the building, 
 should be carried out when possible. A cold-air room with large 
 inlet windows, and ducts connecting with the heaters, makes a good 
 arrangement for schoolhouse work. The inlet windows in this case 
 should be provided with check-valves to prevent any outward flow of 
 air. A detail of this arrangement is shown in Fig. 66. 
 
 This consists of a boxing around the window, extending from 
 the floor to the ceiling. The front is sloped as shown, and is closed 
 from the ceiling to a point below the bottom of the window. The 
 remainder is open, and covered with a wire netting of about ^-inch 
 mesh; to this are fastened flaps or checks of gossamer cloth about 
 6 inches in width. These are hemmed on both edges and a stout 
 wire is run through the upper hem which is fastened to the netting 
 by means of small copper or soft iron wire. The checks allow the air 
 to flow inward but close when there is any tendency for the current 
 to reverse. 
 
 The area of the cold-air duct for any heater should be about 
 three-fourths the total area of the warm-air ducts leading from it. 
 
 278
 
 HEATING AND VENTILATION 
 
 83 
 
 If the duct is of any considerable length or contains sharp bends, it 
 should be made, the full size of all the warm-air ducts. Adjusting 
 dampers should be placed in the supply duct to each separate stack. 
 If a trunk with two inlets is used, each inlet should be of sufficient 
 size to furnish the full amount of air required, and should be pro- 
 vided with cloth checks for preventing an outward flow of air, as 
 already described. The inlet windows should be provided with 
 some form of damper or slide, outside of which should be placed a 
 wire grating, backed by a netting of about f-inch mesh. 
 
 Vent Flues. In dwelling-houses, vent flues are often omitted, 
 and the frequent opening of doors and leakage are depended upon to 
 carry away the im- 
 pure air. A well- 
 designed system of 
 warming should 
 provide some means 
 for discharge ven- 
 tilation, especially 
 for bathrooms and 
 toilet-rooms, and 
 also for living rooms 
 where lights are 
 burned in the even- 
 ing. Fireplaces are 
 usually provided in 
 the more important 
 rooms of a well- 
 built house, and 
 these are made to 
 
 serve as vent flues. In rooms having no fireplaces, special flues 
 of tin or galvanized iron may be carried up in the partitions in 
 the same manner as the warm-air flues. These should be gathered 
 together in the attic, and connected with a brick flue running up 
 beside the boiler or range chimney. 
 
 Very fair results may be obtained by simply letting the flues open 
 into an unfinished attic, and depending upon leakage through the 
 roof to carry away the foul air. 
 
 Fig. 66. Air-Inlet Provided with Check-Valves to Prevent 
 Outward Flow of Air. 
 
 979
 
 HEATING AND VENTILATION 
 
 The sizes of flues may be made the reverse of the warm-air flues 
 that is, 1-2- square inches area per square foot of indirect radiation 
 for rooms on the first floor, and 2 square inches for those on the 
 second. This is because the velocity of flow will depend upon the 
 height of flue, and will therefore be greater from the first floor. The 
 flow of air through the vents will be slow at best, unless some means 
 is provided for warming the air in the flue to a temperature above 
 that of the room with which it connects. 
 
 The method of carrying up the outboard discharge beside a warm 
 chimney is usually sufficient in dwelling-houses; but when it is 
 
 desired to move larger 
 quantities of air, a loop 
 of steam pipe should be 
 run inside the flue. This 
 should be connected for 
 drainage and air-venting 
 as shown in Fig. 67. 
 When vents are carried 
 through the roof inde- 
 pendently, some form of 
 protecting hood should 
 be provided for keeping 
 out the snow r and rain. 
 A simple form is shown 
 in Fig. 68. Flues carried 
 outboard in this way 
 should always be ex- 
 
 Air 
 Valvt 
 
 Ste<am 
 
 Return 
 
 Fig. 67. Loop of Steam Pip:* to be Run Inside Flue 
 Connected for Drainage and Air- Venting. 
 
 tended well above the ridges of adjacent roofs to prevent down 
 drafts in windy weather. 
 
 For schoolhouse work we may assume average velocities through 
 the vent flues, as follows: 
 
 1st floor, 340 feet per minute. 
 2nd " , 280 " " 
 3rd " , 220 " " 
 
 Where flue sizes are based on these velocities, it is well to guard 
 against down drafts by placing an aspirating coil in the flue. A 
 single row of pipes across the flue as shown in Fig. 69, is usually 
 sufficient for this purpose when the flues are large and straight; 
 
 280
 
 HEATING AND VENTILATION 
 
 otherwise, two rows should be provided. The slant height of the 
 heater should be about twice the depth of the flue, so that the area 
 between the pipes shall equal the 
 free area of the flue. 
 
 Large vent flues of this kind 
 should always be provided with 
 dampers for closing at night, and 
 for regulation during strong winds. 
 
 Sometimes it is desired to move 
 a given quantity of air through a 
 flue which is already in place. 
 Table XXIV shows what velocities 
 may be obtained through flues of 
 different heights, for varying dif- 
 ferences in temperature between the 
 outside air and that in the flue. 
 
 . Example. It is desired to discharge 1,300 cubic feet of air per minute 
 through a flue having an area of 4 square feet and a height of 30 feet. If the 
 efficiency of an aspirating coil is 400 B. T. U., how many square feet of surface 
 will be required to move this amount of air when the temperature of the room 
 is 70 and the outside temperature is 60? 
 
 /^/povr 
 Hfl 
 
 Fig. 68. Section Showing Simple Form 
 of Protecting Hood for Vent Car- 
 ried through Roof. 
 
 Fig. 69. Aspirating Coil Placed in Flue to Prevent Down Drafts. 
 
 1,300 -T- 4 = 325 feet per minute = Velocity through the flue. 
 Looking in Table XXIV, and following along the line opposite a 
 30-foot flue, we find that to obtain this velocity there must be a differ- 
 ence of 30 degrees between the air in the flue and the external air. 
 
 281
 
 HEATING AND VENTILATION 
 
 If the outside temperature is 60 degrees, then the air in the flue must 
 he raised to 60 + 30 = 90 degrees. The air of the room being at 
 70 degrees, a rise of 20 degrees is necessary. So the problem resolves 
 itself into the following: What amount of heating surface having an 
 
 TABLE XXIV 
 
 Air=Flow through Flues of Various Heights under Varying 
 Conditions of Temperature 
 
 (Volumes given in cubic feet per square foot of sectional area of flue) 
 
 HEIGHT OF 
 FLUE 
 IN FEKT 
 
 
 5^ 
 
 10 15 
 
 20 30 = 
 
 50* 
 
 5 
 
 55 
 
 76 
 
 94 
 
 109 
 
 134 
 
 167 
 
 10 
 
 77 
 
 108 
 
 133 
 
 153 
 
 188 
 
 242 
 
 15 
 
 94 
 
 133 
 
 162 
 
 188 
 
 230 
 
 297 
 
 20 
 
 108 
 
 153 
 
 188 
 
 217 
 
 265 
 
 342 
 
 25 
 
 121 
 
 171 
 
 210 
 
 242 
 
 297 
 
 383 
 
 30 
 
 133 
 
 188 
 
 230 
 
 265 
 
 325 
 
 419 
 
 35 
 
 143 
 
 203 
 
 248 286 
 
 351 
 
 453 
 
 40 
 
 1 53 
 
 217 
 
 265 306 
 
 375 
 
 484 
 
 45 
 
 162 
 
 230 
 
 282 
 
 325 
 
 39.8 
 
 514 
 
 50 
 
 . 171 
 
 242 
 
 297 342 
 
 419 
 
 541 
 
 GO 
 
 188 
 
 264 325 
 
 373 
 
 461 
 
 594 
 
 efficiency of 400 B. T. U. is necessary to raise 1,300 cubic feet of air 
 per minute through 20 degrees? 
 
 1,300 cubic feet per minute = 1,300 X 60 = 7S,()()() per hour; 
 and making use of our formula for "heat for ventilation," we have 
 78.000 X 20 = 28j3( . 3BTU . 
 
 55 
 and this divided by 400 = 71 square feet of heating surface required. 
 
 EXAMPLES FOR PRACTICE 
 
 1. A schoolroom on the third floor has 50 pupils, who are 
 to be furnished with 30 cubic feet of air per minute each. What will 
 be the required areas in square feet of the supply and vent flues? 
 
 Axs. Supply, 3.7 +. Vent, 6.8 +. 
 
 2. What size of heater will be required in a vent flue 40 feet 
 high and with an area of 5 square feet, to enable it to discharge 1,530 
 cubic feet per minute, when the outside temperature is 60? (Assume 
 an efficiency of 400 B. T. U. for the heater.) Axs. 41 .7 square feet.
 
 HEATING AND VENTILATION 
 
 87 
 
 Registers. Registers are made of cast iron and bronze, in a 
 great variety of sizes and patterns. The almost universal finish for 
 cast-iron registers is black "Japan;" but they are also finished in 
 colors and electroplated with 
 copper and nickel. Fig. 70 
 shows a section through a 
 floor register, in which A rep- 
 resents the valves, which may 
 be turned in a vertical or hori- 
 zontal position, thus opening 
 
 Fig. 70. Section through a Floor Register. 
 
 or closing the register; B is the 
 iron border; C, the register box 
 of tin or galvanized iron; and D, the warm-air pipe. Floor registers 
 are usually set in cast-iron borders, one of which is shown in Fig. 71 ; 
 while wall registers may be screwed directly to wooden borders or 
 frames to correspond with the finish of the room. Wall registers 
 should be provided with pull-cords for opening and closing from the 
 floor; these are shown in Fig. 72. The plain lattice pattern shown in 
 Fig. 73 is the best for schoolhouse work, as it has a comparatively 
 
 free opening for 
 air-flow and is 
 pleasing and sim- 
 ple in design. 
 More elaborate 
 patterns are used 
 for fine dwelling- 
 house work. 
 Registers with 
 shut-off valves 
 are used for air- 
 inlets, while the 
 plain register 
 faces without the 
 valves are placed 
 in the vent open- 
 ings. The vent flues are usually gathered together in the attic, and 
 a single damper may be used to shut off the whole number at once. 
 Flat or round wire gratings of open pattern are often used in place of 
 
 Cast-Iron Border for a Floor Register.
 
 HEATING AND VENTILATION 
 
 register faces. The grill or solid part of a register face usually takes 
 up about of the area; hence in computing the size, we must allow 
 for this by multiplying the required "net area" by 1 .5, to obtain the 
 "total" or "over-all" area. 
 
 Example. Suppose we have a flue 10 inc-hes in width and wish to use a 
 register bavins: a free area of 200 square inches. What will he the required 
 height of the register? 
 
 200 X 1.5 = 300 square inches, which is the total area required; 
 then 300 -r- 10 = 30, which is the required height, and we should use 
 a 10 by 30-inch register. When a register is spoken of as a 10 by 
 
 ir 
 
 IB 
 
 IVENTILATORJ 
 FOR 
 
 CORDS 
 
 _ 
 
 j 
 
 Fig. 72. Wall Register with Pull 
 
 Cords for Opening and 
 
 Closing. 
 
 Fig. 73. Plain Lattice Pattern Register. Best 
 for Schoolhouse Work. 
 
 30-inch or a 10 by 20-inch, etc., the dimensions of the latticed opening 
 are meant, and not the outside dimensions of the whole register. The 
 free opening should have the same area as the flue with which it con- 
 nects. In designing new work, one should provide himself with a 
 trade catalogue, and use only standard sizes, as special patterns and 
 sizes are costly. Fig. 74 shows the method of placing gossamer 
 check-valves back of the vent register faces to prevent down drafts, 
 the same as described for fresh-air inlets.
 
 HEATING AND VENTILATION 
 
 Inlet registers in dwelling-house and similar work are placed 
 either in the floor or in the baseboard ; sometimes they are located 
 under the windows, just above the baseboard. The object in view 
 is to place them where the currents of air entering the room will not 
 be objectionable to persons sitting near windows. A long, narrow 
 floor-register placed close to the wall in front of a window, sends 
 up a shallow current of warm air, which is not especially noticeable 
 
 COSSAMER 
 CHECKS 
 
 WIRE 
 NETTING 
 
 Wig. 74. Method of Placing Gossamer Check- Valves back of Vent Register Face 
 to Prevent Down Drafts. 
 
 to one sitting near it. Inlet registers are preferably placed near 
 outside walls, especially in large rooms. Vent registers should be 
 placed in inside walls, near the floor. 
 
 Pipe Connections. The two-pipe system with dry or sealed 
 returns is used in indirect heating. The conditions to be met are 
 practically the same as in direct heating, the only difference being 
 that the radiators are at the basement ceiling instead of on the floors 
 above. The exact method of making the pipe connections will 
 depend somewhat upon existing conditions; but the general method 
 shown in Fig. 75 may be used as a guide, with modifications to suit
 
 90 
 
 HEATING AND VENTILATION' 
 
 any special case. The ends of all supply mains should be dripped, 
 and the horizontal returns should be sealed if possible. 
 
 Pipe Sizes. The tables already given for the proportioning of 
 pipe sizes can be used for indirect systems. The following table has 
 been computed for an efficiency of 640 B. T. U. per square foot of 
 surface per hour, which corresponds to a condensation of -, of a pound 
 of steam. This is twice that allowed for direct radiation in Table 
 
 DRfP 
 
 WATER L/Aff 
 
 MAIN RETURN 
 
 Fig. 
 
 iort of Makintr Pipe and Radiator Connections, in Basement, 
 in In lireet Heating. 
 
 XVII; so that we can consider 1 square foot of indirect surface as 
 equal to 2 of direct in computing pipe sizes. 
 
 As the indirect heaters are placed in the basement, care must b.e 
 taken that the bottom of the radiator does not come too near the 
 water-line of the boiler, or the condensation will not flow back prop- 
 erly; this distance, under ordinary conditions, should not be less than 
 2 feet. If much less than this, the pipes should be made extra large, 
 so that there may be little or no drop in pressure between the boiler
 
 HEATING AND VENTILATION 
 
 '.U 
 
 TABLE XXV 
 Indirect Radiating Surface Supplied by Pipes of Various Sizes 
 
 
 SQUARE FEET OF INDIRECT RADIATION WHICH WILL BE SUPPLIED WITH 
 
 SIZK OF PIPE 
 
 
 
 1 Pound Drop in 200 Feet 
 
 1 Pound Drop in 1 00 Feet 
 
 i Pound Drop in 100 Feet 
 
 1 in. 
 
 28 
 
 40 
 
 57 
 
 
 51 
 
 72 
 
 105 
 
 H 
 
 67 
 
 95 
 
 170 
 
 2 
 
 185 
 
 262 
 
 375 
 
 2* 
 
 335 
 
 475 
 
 675 
 
 3 
 
 540 
 
 775 
 
 1, 105 
 
 3| 
 
 812 
 
 1, 160 
 
 1,645 
 
 4 
 
 1, 140 
 
 1,625 
 
 2,310 
 
 5 
 
 2,030 
 
 2,900 
 
 4, 110 
 
 6 
 
 3, 260 
 
 4, 660 
 
 6, 600 
 
 7 
 
 4,830 
 
 .6, 900 
 
 9,810 
 
 8 
 
 6,800 
 
 9,720 
 
 13,860 
 
 and the heater. A drop in pressure of 1 pound would raise the 
 water-lme at the heater 2.4 feet. 
 
 -_ 
 
 Fig. 76. General Form of Direct-Indirect Fig. 
 Radiator. 
 
 Radiator Shown 
 
 Direct=Indirect Radiators. A direct-indirect radiator is similar 
 in form to a direct x radiator, and is placed in a room in the same 
 
 287
 
 92 HEATING AND VENTILATION 
 
 manner. Fig. 76 shows the general form of this type of radiator; 
 and Fig. 77 shows a section through the same. The shape of the 
 sections is such, that when in place, small flues are formed between 
 them. Air is admitted through an opening in the outside wall; and, 
 in passing upward through these flues, becomes heated before enter- 
 ing the room. A switch-damper is placed in the duct at the base of 
 the radiator, so that the air may be taken from the room itself instead 
 1 from out of doors, if so desired. This is shown more particularly 
 in Fig. 7(>. 
 
 Fig. 78 shows the wall box provided with louvre slats and netting, 
 through which the air is drawn. A damper door is placed at either 
 
 end of the radiator base; 
 and, if desired, when the 
 cold-air supply is shut off 
 by means of the register 
 in the air-duct, the radia- 
 tor can be converted into 
 the ordinary type by 
 opening both damp'er 
 doors, thus taking the air 
 
 ? ,1 , 
 
 irom the room instead 
 of from the outside. It is customary to increase the size of a direct- 
 indirect radiator 30 per cent above that called for in the case of 
 direct heating. 
 
 CARE AND MANAGEMENT OF STEAM= 
 HEATING BOILERS 
 
 Special directions are usually supplied by the maker for each 
 kind of boiler, or for those which are to be managed in any peculiar 
 way. The following general directions apply to all makes, and may 
 be used regardless of the type of boiler employed: 
 
 Before starting the fire, see that the boiler contains sufficient 
 water. The water-line should be at about the center of the gauge- 
 glass. 
 
 The smoke-pipe and chimney flue should be clean, and the draft 
 good. 
 
 Build the fire in the usual way, using a quality of coal which is 
 best adapted to the heater. In operating the fire, keep the firepot
 
 HEATING AND VENTILATION 93 
 
 full of coal, and shake down and remove all ashes and cinders as often 
 as the state of the fire requires it. 
 
 Hot ashes or cinders must not be allowed to remain in the ashpit 
 under the grate-bars, but must be removed at regular intervals to 
 prevent burning out the grate. 
 
 To control the fire, see that the damper regulator is properly 
 attached to the draft doors and the damper; then regulate the draft 
 by weighting the automatic lever as may be required to obtain the 
 necessary steam pressure for warming. Should the water in the 
 boiler escape by means of a broken gauge-glass, or from any other 
 cause, the fire should be dumped, and the boiler allowed to cool before 
 adding cold water. 
 
 An empty boiler should never be filled when hot. If the water 
 gets low at any time, but still shows in the gauge-glass, more water 
 should be added by the means provided for this purpose. 
 
 The safety-valve should be lifted occasionally to see that it is 
 in working order. 
 
 If the boiler is used in connection with a gravity system, it should 
 be cleaned each year by filling with pure water and emptying through 
 the blow -off. If it should become foul or dirty, it can be thoroughly 
 cleansed by adding a few pounds of caustic soda, and allowing it to 
 stand for a day, and then emptying and thoroughly rinsing. 
 
 During the summer months, it is recommended that the water 
 be drawn off from the system, and that air-valves and safety-valves 
 be opened to permit the heater to dry out and to remain so. Good 
 results, however, are obtained by filling the heater full of water, 
 driving off the air by boiling slowly, and allowing it to remain in this 
 condition until needed in the fall. The water should then be drawn 
 off and fresh water added. 
 
 The heating surface of the boiler should be kept clean and free from 
 ashes and soot by means of a brush made especially for this purpose. 
 
 Should any of the rooms fail to heat, examine the steam valves 
 in the radiators. If a two-pipe system, both valves at each radiator 
 must be opened or closed at the same time, as required. See that 
 the air-valves are in working condition. 
 
 If the building is to be unoccupied in cold weather, draw all the 
 water out of the system by opening the blow-off pipe at the boiler and 
 all steam valves and air-valves at the radiators.
 
 HEATING AND VENTILATION 
 
 HOT= WATER HEATERS 
 
 Types. Hot-water heaters differ from steam boilers principally 
 in the omission of the reservoir or space for steam above the heating 
 surface. The steam boiler might answer as a heater for hot water; 
 
 but the large capacity 
 left for the steam would 
 tend to make its opera- 
 tion slow and rather 
 unsatisfactory, although 
 the same type of boiler 
 is sometimes used for 
 both steam and hot 
 water. The passages in 
 a hot-water heater need 
 not extend so directly 
 from bottom to top as 
 in a steam boiler, since 
 the problem of provid- 
 ing for the free liberation 
 of the steam bubbles 
 does not have to be con- 
 sidered. In general, the 
 heat from the furnace 
 should strike the sur- 
 faces in such a manner 
 as to increase the natural 
 circulation; this may be 
 accomplished to a cer- 
 tain extent by arranging 
 the heating surface so 
 that a large proportion 
 of the direct heat will 
 be absorbed near the 
 top o f - t'h e heater. 
 
 Practically the boilers for low-pressure steam and for hot water differ 
 from each other very little as to the character of the heating surface, 
 so that the methods already given for computing the size of grate 
 surface, horse-power, etc., under the head of "Steam Boilers," can be 
 
 Richardson Sectional Hot-Water Heater.
 
 HEATING AND VENTILATION 
 
 95 
 
 used with satisfactory results in the case of hot-water heaters. 
 
 It is sometimes stated that, owing to the greater difference in tem- 
 perature between the furnace gases and the .water in a hot-water 
 heater, as compared with steam, the heating surface will be more 
 efficient and a smaller heater can be used. While this is true to a 
 certain extent, different authorities agree that this advantage is so 
 small that no account should betaken of it, and the general propor- 
 tions of the heater should be calculated in the same manner as for 
 steam. Fig. 79 shows a form of hot-water heater made up of slabs 
 or sections similar to the sectional steam boiler shown in Part I. 
 The size can be increased in a similar manner, by adding more 
 sections. In this case, however, the boiler is increased in width in- 
 stead of in length. This has an advantage in the larger sizes, as a 
 second fire door can 
 be added, and all 
 parts of the grate 
 can be reached as 
 well in the large sizes 
 as in the small. 
 
 Fig. 80 shows a 
 different form of sec- 
 tional boiler, in which 
 the sections are 
 placed one above an- 
 other. These boilers 
 are circular in form 
 and well adapted to 
 dwelling-houses and 
 similar work. 
 
 Fig. 81 shows another type of cast-iron heater which is not made 
 in sections. The space between the outer and inner shells surround- 
 ing the furnace is filled with water, and also the cross-pipes directly 
 over the fire and the drum at the top. The supply to the radiators 
 is taken off from the top of the heater, and the return connects at the 
 lowest point. 
 
 The ordinary horizontal and vertical tubular boilers, with various 
 modifications, are used to a considerable extent for hot-water heating, 
 
 Fig. 80, 
 
 Invincible" Boiler, with Sections 
 
 Superposed. 
 Courtesy of American Radiator Co. 
 
 291
 
 96 
 
 HEATING AXD VENTILATION 
 
 and are well adapted to this class of work, especially in the case of 
 large buildings. 
 
 Automatic regulators are often used for the purpose of main- 
 taining a constant temperature of the water. They are constructed 
 in different ways some depend upon the expansion of a metal pipe 
 or rod at different temperatures, and others upon the vaporization 
 
 and consequent pres- 
 sure of certain volatile 
 liquids. These means 
 are usually employed 
 to open small valves 
 which admit water- 
 pressure under rubber 
 diaphragms; and these 
 in turn are connected 
 by means of chains 
 with the draft doors 
 of the furnace, and so 
 regulate the draft as 
 required to maintain 
 an even temperature 
 of the water in the 
 heater. Fig. 82 shows 
 one of the first kind. 
 .1 is a metal rod placed 
 in the flow pipe from 
 the heater, and is so 
 connected with the 
 valve B that when the 
 water reaches a certain 
 
 temperature the expansion of the rod opens the valve and admits 
 water from the street pressure through the pipes C and D into the 
 chamber E. The bottom of E consists of a rubber diaphragm, 
 which is forced down by the water-pressure and carries with it the 
 1-ever which operates the dampers as shown, and checks the fire. 
 When the temperature of the water drops, the rod contracts and 
 valve B closes, shutting off the pressure from the chamber E. A 
 spring is provided to throw the lever back to ita original position, 
 
 Fig. 81 Cast-Iron Heater Not Made in Sections. Water 
 Fills Cross-Pipes and Space between Outer and 
 
 es and Space be 
 Inner Shells. 
 
 293
 
 HEATING AN> VENTILATION 
 
 '.17 
 
 and the water above the diaphragm is forced out through the pet- 
 cock G, which is kept slightly open all the time. 
 
 DIRECT HOT=WATER HEATING 
 
 A hot-water system is similar in construction and operation to 
 one designed for steam, except that hot water flows through the 
 pipes and radiators instead. 
 
 The circulation through the pipes is produced solely by the dif- 
 ference in weight of the 
 water in the supply and 
 return, due to the differ- 
 e n c e in temperature.. 
 When water is heated it 
 expands, and thus a 
 given volume becomes 
 lighter and tends to rise, 
 and the cooler water flows 
 in to take its place; if the 
 application of heat is kept 
 up, the circulation thus 
 produced is continuous. 
 The velocity of flow de- 
 pends upon the difference 
 in temperature between 
 the supply and return, 
 and the height of the 
 radiator above the boiler. 
 The horizontal distance 
 of the radiator from the 
 boiler is also an important factor affecting the velocity of flow. 
 
 This action is best shown by means of a diagram, as in Fig. 83. 
 If a glass tube of the form shown in the figure is filled with water and 
 held in a vertical position, no movement of the water will be noticed, 
 because the two columns A and B are of the same weight, and there- 
 fore in equilibrium. Now, if a lamp flame be held near the tube A, 
 the small bubbles of steam which are formed will show the water 
 to be in motion, with a current flowing in the direction indicated by 
 the arrows. The reason for this is, that, as the water in A is heated, 
 
 Fig. 82. Hot- Water Heater with Automatic Regu- 
 lator Operated through Expansion and Con- 
 traction of Metal Rod in Flow Pipe.
 
 IIKATIXG AND VENTILATION 
 
 Fig. S3. Illustrating 
 How the Heating 
 of Water Causes 
 Circulation. 
 
 it expands and becomes lighter for a given volume, and is forced 
 
 upward by the heavier water in B falling to the bottom of the tube. 
 
 The heated water flows from .1 through the connecting tube at the 
 top, into B, where it takes the plaee of the 
 cooler water which is settling to the bottom. If, 
 now, the lamp be replaced by a furnace, and the 
 columns A and B be connected at the top by 
 inserting a radiator, the illustration will assume 
 the practical form as utilized in hot-water heating 
 (see Fig. 84). 
 
 The heat given off by the radiator always 
 insures a difference in temperature between the 
 columns of water in the supply and return pipes, 
 so fliat as long as heat is supplied by the furnace 
 the flow of water will continue. The greater the 
 
 difference in temperature of the water in the two pipes, the greater 
 
 the difference in weight, and con- 
 sequently the faster the flow. The 
 
 greater the height of the radiator 
 
 above the heater, the more rapid 
 
 will be the circulation, because the 
 
 total difference in weight between 
 
 the water in the supply and return 
 
 risers will vary directly with their 
 
 height. From the above it is evident 
 
 that the rapidity of flow depends 
 
 chiefly upon the temperature differ- 
 ence between the supply and return, 
 
 and upon the height of the radiator 
 
 above the heater. Another factor 
 
 which must be considered in long 
 
 runs of horizontal pipe is the fric- 
 
 iional resistance. 
 
 Systems of Circulation. There 
 
 are two distinct systems of cir- 
 culation employed one depending 
 
 on the difference in temperature 
 
 of the water in the supply and return pipes, called gravity circulation; 
 
 D- 
 
 Fig. 84. Illustrating Simple Circula- 
 tion in a Heating System. 
 
 294
 
 HEATING AND VENTILATION 
 
 i 
 
 f 
 
 and another where a pump is used to force the water through the 
 mains, called forced circulation. The former is used for dwellings 
 and other buildings of ordinary size, and the latter for large buildings, 
 and especially where there are long horizontal runs of pipe. 
 
 For gravity circulation some form of sectional cast-iron boiler 
 is commonly used, although wrought-iron tubular boilers may be 
 employed if desired. In the case of forced circulation, a heater de- 
 signed to warm the water by means of live or exhaust steam is often 
 used. A centrifugal or rotary pump is best adapted to this pur- 
 pose, and may be driven by an electric motor or a steam engine, 
 as most convenient. 
 
 Types of Radiating Surface. Cast-iron radiators and circulation 
 
 coils are used for hot water as _^ } ^ 
 
 well as for steam. Hot-water *~| 
 radiators differ from steam 
 radiators principally in having 
 a horizontal passage at the top 
 as well as at the bottom. 
 This construction is necessary 
 in order to draw off the air 
 which gathers at the top of 
 each loop or section. Other- 
 wise they are the same as 
 steam radiators, and are well 
 adapted for the circulation of F ^ c 
 steam, and in some respects 
 are superior to the ordinary pattern of steam radiator. 
 
 The form shown in Fig. 85 is made with an opening at the top 
 for the entrance of water, and at the bottom for its discharge, thus 
 insuring a supply of hot water at the top and of colder water at the 
 bottom. 
 
 Some hot-water radiators are made with a cross-partition so 
 arranged that all water entering passes at once to the top, from which 
 it may take any passage toward the outlet. Fig. 86 is the more 
 common form of radiator, and is made with continuous passages at 
 top and bottom, the hot water being supplied at one side and drawn 
 off at the other. The action of gravity is depended upon for making 
 the hot and lighter water pass to the top, and the colder water sink 
 
 : Showing Construction of Radiator for 
 
 ot Water or Steam. Note Horizontal Pas- 
 sage along Top.
 
 100 
 
 HEATING AND VENTILATION 
 
 to the bottom and flow off through the return. Hot-water radiators 
 are usually tapped and plugged so that the pipe connections can be 
 made either at the top or at the bottom. This is shown in Fig. 87. 
 
 Wall radiators are adapted to hot-water as well as steam heating. 
 
 Efficiency of Radiators. The efficiency of a hot-water radiator 
 depends entirely upon the temperature at which the water is circu- 
 lated. The best practical results are obtained with the water leaving 
 the boiler at a maximum temperature of about 180 degrees in zero 
 weather and returning at about 100 degrees; this gives an average 
 
 . si;, r 
 
 Prod 
 
 mimon Form of Hot-Water Radiator. C'ircuhiti 
 iced Wholly through Action of Gravity, Hot 
 Water Rising to Top. 
 
 Fi;,'. 87. End Elevation of 
 Radiator Showing Taps 
 at Top and Bottom for 
 Pipe Connections. 
 
 temperature of 170 degrees in the radiators. Variations may be made, 
 however, to suit the existing conditions of outside temperature. We 
 have seen that an average cast-iron radiator gives off about 1.7 B.T.U. 
 per hour per square foot of surface per degree difference in tempera- 
 ture between the radiator and the surrounding air, when working 
 under ordinary conditions; and this holds true whether it is filled 
 with steam or water. 
 
 If we assume an average temperature of 170 degrees for the 
 water, then the difference in temperature between the radiator and 
 the air will be 170 70 = 100 degrees; and this multiplied by 1.7 = 
 
 296
 
 HEATING AND VENTILATION 
 
 101 
 
 170, which may be taken as the efficiency of a hot- water radiator 
 under the above average conditions. 
 
 This calls for a water radiator about 1 . 5 times as large as a steam 
 radiator to heat a given room under the same conditions. This is 
 common practice although some engineers multiply by the factor 1 . 6, 
 which allows for a lower temperature of the water. Water leaving 
 the boiler at 170 degrees should return at about 150; the drop in 
 temperature should not ordinarily exceed 20 degrees. 
 
 Systems of Piping. A system of hot-water heating should pro- 
 duce a perfect circulation of water from the heater to the radiating 
 
 Fig. 88. System of Piping Usually Employed for Hot- Water Heating. 
 
 surface, and thence back to the heater through the returns. The 
 system of piping usually employed for hot-water heating is shown in 
 Fig. 88. In this arrangement the main and branches have an inclina- 
 tion upward from the heater; the returns are parallel to the mains, 
 and have an inclination downward toward the heater, connecting 
 with it at the lowest point.. The flow pipes or risers are taken from 
 the tops of the mains, and may supply one or more radiators as 
 required. The return risers or drops are connected with the return 
 mains in a similar manner. In this system great care must be taken 
 to produce a nearly equal resistance to flow in all of the branches, so 
 that each radiator may receive its full supply of water. It will always 
 
 297
 
 102 
 
 HEATING AND VENTILATION 
 
 be found that the principal current of heated w T ater will take the path 
 of least resistance, and that a small obstruction or irregularity in the 
 piping is sufficient to interfere greatly with the amount of heat received 
 in the different parts of the same system. 
 
 Some engineers prefer to carry a single supply main around the 
 building, of sufficient size to supply all the radiators, bringing back 
 a single return of the same size. Practice has shown that in general 
 it is not well to use pipes over 8 or 10 inches in diameter; if larger 
 pipes are required, it is better to run two or more branches. 
 
 The boiler, if possible, should be 'centrally located, and branches 
 I | carried to differ- 
 
 ent parts of the 
 building. This 
 insures a more 
 even circulation 
 than if all the 
 radiators are 
 supplied from a 
 single long main, 
 in which case 
 the circulation 
 is liable to be 
 sluggish at the 
 farther end. 
 
 The arrange- 
 ment shown in 
 Fig. 89 is similar 
 
 I 
 
 Fig. TO. System of Hot-Water Piping Especially Adapted to 
 Apartment Buildings where Each Flat Has a Separate Heater. 
 
 to the circuit system for steam, except that the radiators have two 
 connections instead of one. This method is especially adapted to 
 apartment houses, where each flat has its separate heater, as it 
 eliminates a separate return main, and thus reduces, by practically 
 one-half, the amount of piping in the basement. The supply risers 
 are taken from the top of the main; while the returns should con- 
 nect into the side a short distance beyond, and in a direction away 
 from the boiler. When this system is used, it is necessary to enlarge 
 the radiators slightly as the distance from the boiler increases. 
 
 In flats of eight or ten rooms, the size of the last radiator may be 
 increased from 10 to 15 per cent, and the intermediate ones proper-
 
 SECTIONAL VIEW OF CAST IRON HOT WATER HEATER.
 
 HEATING AND VENTILATION 
 
 103 
 
 tionally, at the same time keeping the main of a large and uniform 
 size for the entire circuit. 
 
 Overhead Distribution. This system of piping is shown in Fig. 
 90. A single riser is carried directly to the expansion tank, from 
 which branches are taken to supply the various drops to which the 
 radiators are connected. An important advantage in connection 
 with this system is that the air rises at once to theuexpansion tank, 
 and escapes through the vent, so that air-valves are not required on 
 the radiators. 
 
 Expa-ns'io-n Tank 
 
 r-irst Floor 
 
 TT 
 
 Fig. 
 
 'Overhead" Distribution System of Hot- Water Piping. 
 
 At the same time, it has the disadvantage that the water in the 
 tank is under less pressure than in the heater; hence it will boil at 
 a lower temperature. No trouble will be experienced from this, how- 
 ever, unless the temperature of the water is raised above 212 degrees. 
 
 Expansion Tank. Every system for hot-water heating should be 
 connected with an expansion tank placed at a point somewhat above 
 the highest radiator. The tank must in every case be connected to a 
 line of piping which cannot by any possible means be shut off from 
 the boiler. When water is heated, it expands a certain amount,
 
 104 
 
 HEATING AND VENTILATION 
 
 depending upon the temperature to which it is raised* and a tank or 
 
 reservoir should always be provided to care for this increase in volume. 
 Expansion tanks are usually made of heavy galvanized iron of 
 
 one of the forms shown in Figs. 91 and 92, the latter form being used 
 
 where the headroom is limited. The 
 connection from the heating system 
 enters the bottom of the tank, and 
 an open vent pipe is taken from the 
 top. An overflow connected with 
 a sink or drain-pipe should be 
 provided. Connections should be 
 made with the water supply both 
 at the boiler and at the expansion 
 tank, the former to be used when 
 first filling the system, as by this 
 means all air is driven from the bot- 
 tom upward and is discharged 
 through the vent at the expansion 
 tank. Water that is added after- 
 ward may be supplied directly to the 
 
 expansion tank, where the water-line can be noted in the gauge-glass. 
 
 A ball-cock is sometimes arranged to keep the water-line in the tank 
 
 at a constant level. 
 An alt it u d c 
 
 (j a u (j c is often 
 
 placed in the base- 
 ment with the col- 
 ored hand or point- c% 
 
 er set to indicate ^ 
 
 the normal water- 
 
 line in the expari- ;i .t 
 
 sion tank. When 
 
 the movable hand 
 
 falls below the F 
 
 fixed one; more 
 
 water may be added, as required, through the supply pipe at the boiler. 
 
 When the tank is placed in an attic or roof space where there is danger 
 
 of freezing, the expansion pipe may be connected into the side of the 
 
 A Common Form of G I . 
 Iron Expansion Tank. 
 
 Form of Expansion Tank Used where Headroom 
 is Limited. 
 
 300
 
 HEATING AND VENTILATION 105 
 
 tank, 6 or 8 inches from the bottom, and a circulation pipe taken 
 from the lower part and connected with the return from an upper- 
 floor radiator. This produces a slow circulation through the tank, 
 and keeps the water warm. 
 
 The size of the expansion tank depends upon the volume of 
 water contained in the system, and on the temperature to which it is 
 heated. The following rule for computing the capacity of the tank 
 may be used with satisfactory results: 
 
 Square feet of radiation, divided by 40, equals required capacity of 
 tank in gallons. 
 
 Air=Venting. One very important point to be kept in mind in 
 the design of a hot-water system, is the removal of air from the pipes 
 and radiators. When the water in the boiler is heated, the air it 
 contains forms into small bubbles which rise to the highest points of the 
 system. 
 
 In the arrangement shown in Fig. 88, the main and branches 
 grade upward from the boiler, so that the air finds its way into the 
 radiators, from which it may be drawn off by means of the air-valves. 
 
 A better plan is that shown in Fig. 89. In this case the expan- 
 sion pipe is taken directly off the top of the main over the boiler, so 
 that the larger part of the air rises directly to the expansion tank and 
 escapes through the vent pipe. The same action takes place in the 
 overhead system shown in Fig. 90, where the top of the main riser 
 is connected with the tank. Every high point in the system and 
 every radiator, except in the downward system with top supply con- 
 nection, should be provided with an air-valve. 
 
 Pipe Connections. There are Various methods of connecting 
 the radiators with the mains and risers. Fig. 93 shows a radiator 
 connected with the horizontal flow and return mains, which are 
 located below the floor. The manner of connecting with a vertical 
 riser and return drop is shown in Fig. 94. As the water tends to 
 flow to the highest point, the radiators on the lower floors should be 
 favored by making the connection at the top of the riser and taking 
 the pipe for the upper floors from the side as shown. Fig. 95 illus- 
 trates the manner of connecting with a radiator on an upper floor where 
 the supply is connected at the top of the radiator. 
 
 The connections shown in Figs. 96 and 97 are used with the 
 overhead system shown in Fig. 90. 
 
 301
 
 100 
 
 HEATING AND VENTILATION 
 
 Where the connection is of the form shown at the left in Fig. 90, 
 the cooler water from the radiators is discharged into the supply pipe 
 again, so that the water furnished to the radiators on the lower floors 
 is at a lower temperature, and the amount of heating surface must be 
 correspondingly increased to make up for this loss, as already de- 
 scribed for the circuit system. 
 
 "ig 93 Radiator Connected with Hori- 
 zontal Flow and Return Mains 
 Located below Floor. 
 
 Fig. 94. Radiator Connected to Vertical 
 Riser and Return Drop. 
 
 For example, if in the case of Fig. 90 we assume the water to 
 leave at 180 degrees and return at 160, we shall have a drop in tem- 
 perature of 10 degrees on each floor; that is, the water will enter the 
 radiator on the second floor at ISO degrees and leave it at 170, and 
 will enter the radiator on the first floor at 170 and leave it at 160. 
 
 'pper-Floor Radiator with Sup- 
 ply Connected at Top. 
 
 Fig 96. Radiator Connections, Overhead 
 Distribution System. 
 
 The average temperatures will be 175 and 165, respectively. The 
 efficiency in the first case will be 175 70 = 105; and 105 X 1.5 = 
 157. In the second case, 165 70 = 95; and 95 X 1.5 = 142; 
 so that the radiator on the first floor will have to be larger than that 
 on the second floor in the ratio of 157 to 142, in order to do the same 
 work. 
 
 302
 
 HEATING AND VENTILATION 
 
 107 
 
 This is approximately an increase of 10 per cent for each story 
 downward to offset the cooling effect; but in practice the supply 
 drops are made of such size that only a part of the water is by-passed 
 through the radiators. For this reason an increase of 5 per cent 
 for each story downward is probably sufficient in ordinary cases. 
 
 Where the radiators discharge 
 into a separate return as in the case 
 of Fig. 88, or those at the right in 
 Fig. 90, we may assume the tempera- 
 ture of the water to be the same on 
 all floors, and give the radiators an 
 equal efficiency. 
 
 In a dwelling-house of two stories, 
 no difference would be made in the 
 sizes of radiators on the two floors; 
 but in the case of a tall office build- 
 ing, corrections would necessarily be made as above described. 
 
 Where circulation coils are used, they should be of a form which 
 will tend to produce a flow of water through them. Figs. 98, 99, and 
 100 show different ways of making up and connecting these coils. 
 In Figs. 98 and 100, supply pipes may be either drops or risers; and 
 
 Pig. 97. Another Form of Radiator 
 Connection, Overhead Distribu- 
 tion System. 
 
 fc 
 
 8 
 
 Fig. 98. Circulation Coil, One Method of Construction. Supply Pipes 
 may be Either Drops or Risers. 
 
 in the* former case the return in Fig. 100 may be carried back, if desired, 
 into the supply drop, as shown by the dotted lines. 
 
 Combination Systems. Sometimes the boiler and piping are 
 arranged for either steam or hot water, since the demand for a higher 
 or lower temperature of the radiators might change. 
 
 303
 
 108 
 
 HEATIXG AND VENTILATION 
 
 The object of this arrangement is to secure the advantages of a 
 hot-water system for moderate temperatures, and of steam heating 
 for extremely cold weather. 
 
 Fig. 99. Another Method of Building Up a Circulation Coil. 
 
 As less radiating surface is required for steam heating, there is 
 an advantage due to the reduction in first cost. This is of consider- 
 able importance, as a heating system must be designed of such dimen- 
 sions as to be capable of warming a building in the coldest weather; 
 
 L J 
 
 GjUl/U : 11 N 
 
 
 r? J 
 
 ^n 
 
 U^ 
 
 ; & 
 
 
 V U 
 
 1T> 
 
 
 n 5 ) 
 
 'fl 
 
 Ix 
 
 ( 
 
 
 V U 
 
 1 N 
 
 
 n> ) 
 
 ' :; ^J 
 
 fl J 
 
 
 Fig. 100. Circulation Coil with Either Drop or Riser Supply. In former case, return 
 may !><> carried into Supply Drop as shown by "Dotted Lines. 
 
 and this involves the expenditure of a considerable amount for radiat- 
 ing surfaces, which are needed only at rare intervals. A combination 
 system of hot-water and steam heating requires, first, a heater or boiler 
 
 304
 
 HEATING AND VENTILATION 109 
 
 which will answer for either purpose; second, a system of piping 
 which will permit the circulation of either steam or hot water; and 
 third, the use of radiators which are adapted to both kinds of heating. 
 These requirements will be met by using a steam boiler provided with 
 all the fittings required for steam heating, but so arranged that the 
 damper regulator may be closed by means of valves when the system 
 is to be used for hot-water heating. The addition of an expansion 
 tank is required, which must be so arranged that it can be shut off 
 when the system is used for steam heating. The system of piping 
 shown in Fig. 88 is best adapted for a combination system, although 
 an overhead distribution as shown in Fig. 90 may be used by shutting 
 off the vent and overflow pipes, and placing air-valves on the radiators. 
 
 While this system has many advantages in the way of cost over 
 the complete hot- water system, the labor of changing from steam 
 to hot water will in some cases be trouble- 
 some; and should the connections to the 
 expansion tank not be opened, serious re- 
 sults would follow. 
 
 Valves and Fittings. Gate-valves 
 should always be used in connection with 
 hot-water piping, although angle-valves may 
 be used at the radiators. There are several 
 patterns of radiator valves made especially 
 for hot-water work; their chief advantage 
 
 lies in a device -for quick closing, usually a Flg . 101> Radlator Valve for 
 quarter-turn or half-turn being sufficient to 
 
 open "or close the valve. Two different designs are shown in Figs. 
 101 and 102. 
 
 It is customary to place a valve in only one connection, as that is 
 sufficient to stop the flow of water through the radiator; a fitting 
 known as a union elbow is often employed in place of the second valve. 
 (See Fig. 103.) 
 
 Air=Valves. The ordinary pet-cock air-valve is the most reliable 
 for hot-water radiators, although there are several forms of auto- 
 matic valves which are claimed to give satisfaction. One of these 
 is shown in Fig. 104. This is similar in construction to a steam 
 trap. As air collects in the chamber, and the water-line is lowered, 
 the float drops, and in so doing opens a small valve at the top of the 
 
 305
 
 110 
 
 HEATING AND VENTILATION 
 
 chamber, which allows the air to escape. As the water flows in to take 
 its place, the float is forced upward and the valve is closed. 
 
 All radiators which are supplied by risers from below, should be 
 provided with air-valves placed in the top 
 of the last section at the return end. . If 
 they are supplied by drops from an over- 
 
 rig. 102. Another Type of Hot- 
 Water Radiator Valve. 
 
 Fig. 103. Union Elbow. 
 
 head system, the air w r ill be discharged at the expansion tank, and 
 
 air-valves will not be necessary at the radiators. 
 
 Fittings. All fittings, such as elbows, tees, etc., should be of 
 
 the long-turn pattern. If the common form is used, they should be 
 a size larger than the pipe, bushed 
 down to the proper size. The long- 
 turn fittings, however, are preferable, 
 and give a much better appearance. 
 Connections between the radiators 
 and risers may 'be made with the 
 ordinary short-pattern fittings, as 
 those of the other form are not \vell 
 adapted to the close connections nec- 
 essary for this work. 
 
 Pipe Sizes. The size of pipe 
 required to supply any given radiator 
 depends upon four conditions ; first, the 
 size of the radiator; second, its elevation 
 above the boiler; third, the length of 
 pipe required to connect it with the 
 
 boiler; and fourth, the difference in temperature between the supply 
 
 and the return, 
 
 Hot-Water Radiator. Operated 
 by a Float. 
 
 306
 
 HEATING AND VENTILATION 
 
 111 
 
 As it would be a long and rather complicated process to work out 
 the required size of each pipe for a heating system, Tables XXVI and 
 XXVII have been prepared, covering the usual conditions to be met 
 with in practice. 
 
 TABLE XXVI 
 
 Direct Radiating Surface Supplied by Mains of Different 
 Sizes and Lengths of Run 
 
 SQUARE FEET OP RADIATING SURFACE 
 
 
 100 ft. 
 Run 
 
 200 ft. 
 Run 
 
 300 ft. 
 Run 
 
 400 ft. 
 Run 
 
 500 ft. 
 Run 
 
 600 ft 
 Run 
 
 700 ft. 
 Run 
 
 800 ft. 
 Run 
 
 1,000 
 ft. Run 
 
 1 in. 
 
 30 
 
 
 
 
 
 
 
 
 
 H' 
 
 60 
 
 50 
 
 
 
 
 
 
 
 
 l!' 
 
 100 
 
 75 
 
 50 
 
 
 
 
 
 
 
 2 ' 
 
 200 
 
 150 
 
 125 
 
 100 
 
 75 
 
 
 
 
 
 2*' 
 
 350 
 
 250 
 
 200 
 
 175 
 
 150 
 
 125 
 
 
 
 
 3 ' 
 
 550 
 
 400 
 
 300 
 
 275 
 
 250 
 
 225 
 
 200 
 
 175 
 
 150 
 
 3i' 
 
 850 
 
 600 
 
 450 
 
 400 
 
 350 
 
 325 
 
 300 
 
 250 
 
 225 
 
 4 ' 
 
 1,200 
 
 850 
 
 700 
 
 600 
 
 525 
 
 475 
 
 450 
 
 400 
 
 350 
 
 5 ' 
 
 
 1,400 
 
 1,150 
 
 1,000 
 
 700 
 
 850 
 
 775 
 
 725 
 
 650 
 
 6 ' 
 
 
 
 
 1,600 
 
 1,400 
 
 1,300 
 
 1,200 
 
 1,150 
 
 1,000 
 
 7 ' 
 
 
 
 
 
 
 
 1,706 
 
 1,600 
 
 1,500 
 
 
 
 
 
 
 
 
 
 
 
 These quantities have been calculated on a basis of 10 feet difference 
 in elevation between the center of the heater and the radiators, and a differ- 
 ence in temperature of 17 degrees between the supply and the return. 
 
 TABLE XXVII 
 
 Radiating Surface on Different Floors Supplied by 
 Pipes of Different Sizes 
 
 SIZE OF 
 
 SQUARE FEET OF RADIATING SURFACE 
 
 
 1st Story 
 
 2d Story 
 
 3d Story 
 
 4th Story 
 
 5th Story 
 
 6th Story 
 
 1 in. 
 
 30 
 
 55 
 
 65 
 
 75 
 
 85 
 
 95 
 
 1M ' 
 
 60 
 
 90 
 
 110 
 
 125 
 
 140 
 
 160 
 
 iy 2 ' 
 
 100 
 
 140 
 
 165 
 
 185 
 
 210 
 
 240 
 
 2 < 
 
 200 
 
 275 
 
 375 
 
 425 
 
 500 
 
 
 2^' 
 
 350 
 
 -475 
 
 
 
 
 
 3 ' 
 
 550 
 
 __ 
 
 
 
 
 
 sy 2 ' 
 
 850 
 
 
 
 
 
 
 Table XXVI gives the number of square feet of direct radiation 
 which different sizes of mains and branches will supply for varying 
 lengths of run. 
 
 Table XXVI may be used for all horizontal mains. For vertical 
 risers or drops, Table XXVII may be used. This has been com- 
 
 307
 
 HEATING AND VENTILATION 
 
 puted for the same difference in temperature as in the case of Table 
 XXVI (17 degrees), and gives the square feet of surface which dif- 
 ferent sizes of pipe will supply on the different floors of a building, 
 assuming the height of the stories to be 10 feet. Where a single 
 riser is carried to the top of a building to supply the radiators on the 
 floors below, by drop pipes, we must first get what is called the average 
 elevation of the system before taking its size from the table. This may 
 be illustrated by means of a diagram (see Fig. 105). 
 
 In .1 we have a riser carried to the third story, and from there a 
 drop brought down to supply a radiator on the first floor. The 
 elevation available for producing a flow in the riser is only 10 feet, 
 the same as though it extended only to the radiator. The water in 
 the two pipes above the radiator is practically at the same temperature, 
 and therefore in equilibrium, and has no effect on the flow of the 
 water in the riser. (Actually there would be some radiation from the 
 pipes, and the return, above the radiator, would be slightly cooler, but 
 for purposes of illustration this may be neglected). If the radiator 
 was on the second floor the elevation of the system would be 20 feet 
 (see B}; and on the third floor, 30 feet; and so on. The distance 
 which the pipe is carried above the first radiator which it supplies 
 has but little effect in producing a flow, especially if covered, as it 
 should be in practice. Having seen that the flow in the main riser 
 depends upon the elevation of the radiators, it is easy to see that the 
 way in which it is distributed on the different floors must be con- 
 sidered. For example, in B, Fig. 105, there will be a more rapid 
 flow through the riser with the radiators as shown, than there would 
 be if they were reversed and the largest one were placed upon the first 
 floor. 
 
 We get the average elevation of the system by multiplying the 
 square .feet of radiation on each floor by the elevation above the 
 heater, then adding these products together and dividing the same 
 by the total radiation in the whole system. In- the case shown in 
 B, the average elevation of the system would be 
 (100 X 30) + (-50 X 20) + (25 X 10) = 
 
 100 + 50 + 25 
 
 and we must proportion the main riser the same as though the whole 
 radiation were on the second floor. Looking in Table XXVII, we 
 find, for the second story, that a l-|-inch pipe will supply 140 square 
 
 308
 
 HEATING AND VENTILATION 
 
 113 
 
 fc-ct; and a 2-inch pipe, 275 feet. Probably a 1^-inch pipe would 
 be sufficient. 
 
 Although the height of stories varies in different buildings, 10 
 feet will be found sufficiently accurate for ordinary practice. 
 
 INDIRECT HOT=WATER HEATING 
 
 This is used under the same conditions as indirect steam, and 
 the heaters used are similar to those already described. Special 
 
 3= I 
 
 A B 
 
 Fig. 105. Diagram to Illustrate Finding of Average Elevation of Heating System. 
 
 attention is given to the form of the sections, in order that there may 
 be an even distribution of water through all parts of them. As the 
 stacks are placed in the basement of a building, and only a short 
 distance above the boiler, extra large pipes must be used to secure a 
 proper circulation, for the head producing flow is small. The stack 
 
 309
 
 114 HEATING AND VENTILATION 
 
 casings, cold-air and warm-air pipes, and registers are the same as 
 in steam heating. 
 
 Types of Radiators. The radiators for indirect hot-water heating 
 are of the same general form as those used for steam. Those shown 
 in Figs. 52, 53, 5G, 106, and 107 are common patterns. The drum 
 pin, Fig. 106, is an excellent form, as the method of making the 
 connections insures a uniform distribution of water through the 
 stack. 
 
 Fig. 107 shows a radiator of good form for water circulation, and 
 also of good depth, which is a necessary point in the design of hot- 
 water radiators. They should be not less than 12 or 15 inches deep 
 for good results. Box coils of the form given for steam may also be 
 
 Fip. 10(5. "Drum Pin" Indirect Hot-Water Radiator. 
 
 used, provided the connections for supply and return are made of 
 good size. 
 
 Size of Stacks. As indirect hot-water heaters are used princi- 
 pally in the warming of dwelling-houses, and in combination with 
 direct radiation, the easiest method is to compute the surfaces required 
 for direct radiation, and multiply these results by 1 .5 for pin radiators 
 of good depth. For other forms the factor should vary from 1.5 
 to 2, depending upon the depth and proportion of free area for air- 
 flow between the sections. 
 
 If it is desired to calculate the required surface directly by the 
 thermal unit method, we may allow an efficiency of from 360 to 400 
 for good types in zero weather. 
 
 310
 
 HEATING AND VENTILATION 
 
 In schoolhouse and hospital work, where larger volumes of air 
 are warmed to lower temperatures, an efficiency as high as 500 B. T. U. 
 may be allowed for radiators of good form. 
 
 Flues and Casings. For cleanliness, as well as for obtaining 
 the best results, indirect stacks should be hung at one side of the 
 register or flue receiving the warm air, and the cold-air duct should 
 enter beneath the heater at the other side. A space of at least 10 
 inches, and preferably 12, should be allowed for the warm air above 
 the stack. The top of the casing should pitch upward toward the 
 warm-air outlet at least an inch in its length. A space of from 8 to 
 10 inches should be allowed for cold air below the stack. 
 
 As the amount of air warmed per square foot of heating surface 
 is less than in the case of steam, we may make the flues somewhat 
 smaller as compared 
 with the size of heater. 
 The following p r o - 
 portions may be used 
 under usual conditions 
 for dwelling - houses : 
 l square inches per 
 square foot of radia- 
 tion for the first floo*-, 
 lj square inches for 
 the second floor, and 
 1 square inches for 
 the cold-air duct. 
 
 Pipe Connections. In indirect hot-water work, it is not desirable 
 to supply more than 80 to 100 square feet of radiation from a single 
 connection. When the requirements call for larger stacks, they 
 should be divided into two or more groups according to size. 
 
 It is customary to carry up the main from the boiler to a point 
 near the basement ceiling, where it is air- vented through a small 
 pipe leading to the expansion tank. The various branches should 
 grade downward and connect with the tops of the stacks. In this 
 way, all air, both from the boiler and from the stacks, will find its way 
 to the highest point in the main, and be carried off automatically. 
 
 As an additional precaution, a pet-cock air-valve should be placed 
 in the last section of each stack, and brought out through the casing 
 by means of a short pipe. 
 
 Fig. 107. Indirect Hot- Water Radiator. 
 
 311
 
 IK) 
 
 HEATING AND VENTILATION 
 
 TABLE XXVIII 
 
 Radiating Surface Supplied by Pipes of Various Sizes Indirect Hot= 
 Water System 
 
 SQCAKK FEET or RAWATINO SI'HFACE 
 
 100 Ft. Hun 
 
 1 in. 15 
 
 
 
 H ' 30 
 
 25 
 
 
 H " 
 
 50 
 
 40 
 
 25 
 
 2" ' 100 
 
 75 
 
 60 
 
 2i " 
 
 175 
 
 125 
 
 100 
 
 3" " 
 
 275 
 
 200 
 
 150 
 
 34 " 
 
 425 
 
 300 
 
 225 
 
 4 " 
 
 GOO 
 
 425 
 
 350 
 
 5 " 
 
 700 
 
 575 
 
 (i ' 
 
 
 
 7 '' 
 
 
 50 
 90 
 
 140 
 200 
 300 
 500 
 800 
 1,200 
 
 Some engineers make a practice of carrying the main to the 
 ceiling of the first story, and then dropping to the basement before 
 branching to the stacks, the idea being to accelerate the flow of water 
 through the main, which is liable to be sluggish on account of the 
 small difference in elevation between the boiler and stacks. If 
 the return leg of the loop is left uncovered, there will be a slight drop 
 in temperature, tending to produce this result; but in any case it will 
 be exceedingly small. With supply and return mains of suitable 
 size and properly graded, there should be no'difficulty in securing a 
 good circulation in basements of average height. 
 
 Pipe Sizes. As the difference in elevation between the stacks 
 and the heater is necessarily small, the pipes should be of ample size 
 to offset the slow velocity of flow through them. The sizes mentioned 
 in Table XXVIII, for runs up to 400 feet, will be found to supply 
 ample radiating surface for ordinary conditions. Some engineers 
 make' a practice of using somewhat smaller pipes, but the larger sizes 
 will in general be found more satisfactory. 
 
 CARE AND MANAGEMENT OF HOT=WATER HEATERS 
 
 The directions given for the care of steam-heating boilers apply 
 in a general way to hot-water heaters, as to the methods of caring 
 for the fires and for cleaning and filling the heater. Only the special 
 points of difference need be considered. Before building the fire, all 
 the pipes and radiators must be full of water, and the expansion tank 
 
 312
 
 HEATING AND VENTILATION 
 
 117 
 
 should be partially filled as indicated by the gauge-glass. Should 
 the water in any of the radiators fail to circulate, see that the valves 
 are wide open and that the radiator is free from air. Water must 
 always be added at the expansion tank when for any reason it is 
 drawn from the system. 
 
 The required temperature of the water will depend upon the 
 outside conditions, and only enough fire should be carried to keep 
 the rooms comfortably warm. Ther- 
 mometers should be placed in the flow 
 and return pipes near the heater, as a 
 guide. Special forms are made for 
 this purpose, in which the bulb is im- 
 mersed in a bath of oil or mercury (see. 
 Fig. 108). 
 
 FORCED HOT=WATER CIRCU= 
 LATION 
 
 While the gravity system of hot- 
 water heating is well adapted to 
 buildings of small and medium size, 
 there is a limit to which it can be car- 
 ried economically. This is due to the 
 slow movement of the water, which 
 calls for pipes of excessive size. To 
 overcome this difficulty, pumps' are 
 used to force the water through the 
 mains at a comparatively high velocity. 
 
 The water may be heated in a 
 boiler in the same manner as for 
 gravity circulation, or exhaust steam 
 may be utilized in a feed-water heater 
 of large size. Sometimes part of the 
 heat is derived from an economizer placed in the smoke passage 
 from the boilers. 
 
 Systems of Piping. The mains for forced circulation are usually 
 run in one of two ways. In the two-pipe system, shown in Fig. 109, 
 the supply and return are carried side by side, the former reducing 
 in size, and the latter increasing as the branches are taken off. 
 
 . 108. Thermometer Attached to 
 jed-Pips near Heater, to Deter- 
 mine Temperature of Water. 
 
 313
 
 118 
 
 HEATING^AND VENTILATION 
 
 The flow through the risers is produced by the difference in 
 pressure in the supply and return mains; and as this is greatest 
 nearest the pump, it is necessary to place throttle-valves in the risers 
 to prevent short-circuiting and to secure an even distribution through 
 all parts of the system. 
 
 Fig. 110 shows the single-pipe or circuit system. This is similar 
 to the one already described for gravity circulation, except that it can 
 be used on a much larger scale. 
 
 A single main is carried entirely around the building in this 
 case, the ends being connected with the suction and discharge of the 
 pump as shown. 
 
 As the pressure or head in the main drops constantly throughout 
 the circuit, from the discharge of the pump back to the suction, it is 
 
 Fig. 109. "Two-Pipe" System for Forced Hot-Water Circulation. 
 
 evident that if a supply riser be taken off at any point, and the return 
 be connected into the main a short distance along the line, there will 
 be a .sufficient difference in pressure between the two points to produce 
 a circulation through the two risers and the connecting radiators. 
 A distance of 8 or 10 feet between the connections is usually ample to 
 produce the necessary circulation, and even less if the supply is taken 
 from the top of the main and the return connected into the side. 
 
 Sizes of Mains and Branches. As the velocity of flow is inde- 
 pendent of the temperature and elevation when a pump is used, it is 
 necessary to consider only the volume of water to be moved and the 
 length of run. 
 
 314
 
 TYPICAL HEATING INSTALLATION SHOWING SECTIONAL BOILER 
 AND RADIATOR. 
 
 American Radiator Company.
 
 HEATING AND VENTILATION 
 
 119 
 
 The volume is found by the equation 
 
 Q- K E 
 
 y ~ 500 7" 
 in which 
 
 Q = Gallons of water required per minute; 
 R Square feet of radiating surface to be supplied; 
 E Efficiency of radiating surface in B. T. U. per sq. foot per hour; 
 T Drop in temperature of the water in passing through the heating 
 system. 
 
 In systems of this kind, where the circulation is comparatively 
 rapid, it is customary to assume a drop in temperature of 30 to 40, 
 between the supply and return. 
 
 Having determined the gallons of water to be moved, the required 
 size of main can be found by assuming the velocity of flow, which 
 for pipes from 5 to 8 inches in diameter may be taken at 400 to 500 
 
 Fig. 110. "Single-Pipe" or "Circuit" System for Forced Hot- Water Circulation. 
 
 feet per minute. A velocity as high as 600 feet is sometimes allowed 
 for pipes of large size, while the velocity in those of smaller diameter 
 should be proportionally reduced to 250 or 300 feet for a 3-inch pipe. 
 The next step is to find the pressure or head necessary to force the 
 water through the main at the given velocity. This in general should 
 not exceed 50 or 60 feet,, and much better pump efficiencies will be 
 obtained with heads not exceeding 35 or 40 feet. 
 
 As the water in a heating system is in a state of equilibrium, the 
 only power necessary to produce a circulation is that required to 
 overcome the friction in the pipes and radiators; and, as the area of 
 the passageways through the latter is usually large in . comparison 
 with the former, it is customary to consider only the head necessary 
 to force the water through the mains, taking into consideration the 
 additional friction produced by valves and fittings. 
 
 315
 
 120 HEATING AND VENTILATION 
 
 Each Ions-turn elbow may be taken as adding about 4 feet to 
 the length of pipe; a short-turn fitting, about 9 feet; 6-inch and 
 4-inch swing check-valves, -50 feet and 25 feet, respectively; and 
 6-inch and 4-inch globe check-valves. 200 feet and 130 feet, respec- 
 tively. 
 
 Table XXIX is prepared especially for determining the size of 
 mains for different conditions, and is used as follows: 
 
 Ex<i-pif. Suppose that a heating system requires the circulation of 480 
 gallons of water per minute through a circuit main 600 feet in length. The 
 pipe contains 12 long-turn elbows and 1 swing check-valve. What diameter 
 of main should be used ? 
 
 Assuming a velocity of 4SO feet per minute as a trial velocity, we 
 follow along the line corresponding to that velocity, and find that a 
 5-inch pipe will deliver the required volume of water under a head 
 of 4.0 feet for each 100 feet length of run. 
 
 The actual length of the main, including the equivalent of the 
 fittings as additional length, is 
 
 600 - 12 X 9 i 50 = 75S feet ; 
 
 hence the total head required is 4.9 X 7.5S = 37 feet. As both 
 the assumed velocity and the necessary head come within practicable 
 limits, this is the size of pipe which would probably be used. If it 
 were desired to reduce the power for running the pump, the size of 
 main could be increased. That is. Table XXIX shows that a 6-inch 
 pipe would deliver the same volume of water with a friction head of 
 only about 2 feet per 100 feet in length, or a total head of 2 / 7.5S = 
 15 feet. 
 
 The risers in the circuit system are usually made the same size 
 as for gravity work With double mains, as shown in Fig. 109, they 
 may be somewhat smaller, a reduction of one size for diameters over 
 1^ inches being common 
 
 The branches connecting the risers with the mains may be pro- 
 portioned from the combined areas of the risers, ^"hen the branches 
 are of considerable size, the diameter may be computed from the 
 available head and volume of water to be moved. 
 
 Pumps. Centrifugal pumps are usually employed in connection 
 with forced hot-water circulation, in preference to pumps of the 
 piston or plunger type. They are simple in construction, having 
 BO valves, produce a continuous flow of water, and, for the low heads 
 
 316
 
 HEATING AND VENTILATION 
 
 121 
 
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 Capacity 
 
 
 
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 317
 
 122 HEATING AND VENTILATION 
 
 against which they are operated, have a good efficiency. A pump of 
 this type, with a direct-connected engine, is shown in Fig. 111. 
 
 Under ordinary conditions the efficiency of a centrifugal pump 
 falls off considerably for heads above 30 or 35 feet; but special high- 
 speed pumps are constructed which work with a good efficiency 
 against 500 feet or more. 
 
 Under favorable conditions an efficiency of 60 to 70 per cent is 
 often obtained; but for hot-water circulation it is more common to 
 assume an efficiency of about 50 per cent for the average case. 
 
 The horse-power required for driving a pump is given by the 
 following formula : 
 
 _ Hx VX 8.3 
 " 33,OOOX#' 
 in which 
 
 H = Friction head in feet; 
 
 V Gallons of water delivered per minute; 
 
 E = Efficiency of pump. 
 
 Centrifugal pumps are made in many sizes and with varying 
 proportions, to meet the different requirements of capacity and head. 
 
 Heaters. If the water is heated in a boiler, any good form may 
 be used, the same as for gravity work. In case tubular boilers are 
 used, the entire shell may be rilled with tubes, as no steam space is 
 required. 
 
 In order to prevent the water from passing in a direct line from 
 the inlet to the outlet, a series of baffle-plates should be used to bring 
 it in contact with all parts of the heating surface. 
 
 When steam is used for heating the water, it is customary to 
 employ a closed feed-water heater with the steam on the inside of the 
 tubes and the water on the outside. 
 
 Any good form of heater can be used for this purpose by providing 
 it with steam connections of sufficient size. In the ordinary form of 
 heater,, the feed-water flows through the tubes, and the connections 
 are therefore small, making it necessary to substitute special nozzles 
 of large size when used in the manner here described. 
 
 When computing the required amount of heating surface in the 
 tubes of a heater, it is customary to assume an efficiency of about 200 
 B- T. U. per square foot of surface per hour, per degree difference in 
 temperature between the water and steam. 
 
 818
 
 HEATING AND VENTILATION 
 
 123 
 
 It is usual to circulate the water at a somewhat higher tempera- 
 ture in systems of this kind, and a maximum initial temperature of 
 200 degrees, with a drop of 40 degrees in the heating system, may be 
 used in computing the size of heater. If exhaust steam is used at 
 atmospheric pressure, there will be a difference of 212 180 = 32 
 degrees, between the average temperature of the water and the steam , 
 giving an efficiency of 200 X 32 - 6,400 B. T. U. per square foot 
 of heating surface. 
 
 From this it is evident that 6,400 * 170 = 38 square feet of 
 direct radiating surface, or 6,400 -f- 400 = 16 square feet of indirect, 
 may be supplied from each square foot of tube surface in the heater. 
 Example. A building having 6,000 square feet of direct; and 2,000 
 square feet of indirect radiation, is to be warmed by hot water under forced 
 circulation. Steam at atmospheric pressure is to be used for heating the 
 water. How many square feet of heating surface should the heater contain ? 
 
 6,000 -=- 38 = 158; and 2,000 
 -=- 16 = 125; therefore, 158 + 
 125 = 283 square feet, the area 
 of heating surface called for. 
 
 When the exhaust steam is 
 not sufficient for the require- 
 ments, an auxiliary live steam 
 heater is used in connection 
 with it. 
 
 EXAMPLES FOR PRACTICE 
 
 1. A building contains 
 10,000 square feet of direct 
 radiation and 4,000 square feet 
 of indirect radiation. How 
 
 many gallons of water must be circulated through the mains per min- 
 ute, allowing a drop in temperature of 40 degrees? Axs. 165 .gal. 
 
 2. In the above example, what size of main should be used, 
 assuming the circuit to be 300 feet in length and to contain ten long- 
 turn elbows? The friction head is not to exceed 10 ft., and the 
 velocity of flow not to exceed 300 feet per minute. ANS. 4-inch. 
 
 3. What horse-power will be required to drive a centrifugal 
 pump delivering 400 gallons per minute against a friction head of 
 40 feet, assuming an efficiency of 50 per cent for the pump? 
 
 ANS. 8 H. P. 
 
 111. Centrifugal Pump Direct -Con- 
 nected to Engine, for Forced Hot- 
 Water Circulation. 
 
 319
 
 124 HEATING AND VENTILATION 
 
 4. A building contains 10,000 square feet of direct radiation and 
 5,000* square feet of indirect radiation. Steam at atmospheric pres- 
 sure is to be used. The initial temperature of the water is to be 200; 
 and the final, 160. How many square feet of heating surface should 
 the heater contain? Axs. 575 sq. ft. 
 
 5. How many square feet would be required in the above 
 heater (Example 4) if the initial temperature of the water were 180 
 and the final temperature 150? Axs. 399 sq. ft. 
 
 EXHAUST=STEAM HEATING 
 
 Steam, after being used in an engine, contains the greater part 
 of its heat ; and if not condensed or used for other purposes, it can 
 usually be employed for heating without affecting to any great extent 
 the power of the engine. In general, we may say that it is a matter of 
 economy to use the exhaust for heating, although various factors 
 must be considered in each case to determine to what extent this is 
 true. The more important considerations bearing upon the matter 
 are: the relative quantities of steam required for power and for 
 heating; the length of the heating seaso-n; the type of engine used; 
 the pressure carried; and, finally, whether the plant under con- 
 sideration is entirely new, or whether, on the other hand, it involves 
 the adapting of an old heating system to a new plant. 
 
 The first use to be made of the exhaust steam is the heating of 
 the feed-water, as this effects a constant saving both summer and 
 winter, and can be done without materially increasing the back- 
 pressure on the engine. Under ordinary conditions, about one-sixth 
 of the steam supplied to the engine can be used in this way, or more 
 nearly one-fifth of the exhaust discharged from the engine. 
 
 "We may assume in average practice that about SO per cent of 
 the steam supplied to an engine is discharged in the form of steam 
 at a lower pressure, the remaining 20 per cent being partly converted- 
 into work and partly lost through cylinder condensation. Taking 
 this into account, there remains, after deducting the steam used for 
 feed-water heating, .8 X f = .64 of the entire quantity of steam 
 supplied to the engine, available for heating purposes. 
 
 ^Tien the quantity of steam required for heating is small com- 
 pared with the total amount supplied to the engine, or where the 
 heating season is short, it is often more economical to run the engine
 
 HEATING AND VENTILATION 125 
 
 condensing and use the live steam for heating. This can be deter- 
 mined in any particular case by computing the saving in fuel by the 
 use of a condenser, taking into account the interest and depreciation 
 on the first cost of the condensing apparatus, and the cost of water, 
 if it must be purchased, and comparing it with the cost of heating 
 with live steam. 
 
 Usually, however, in the case of office buildings and institutions, 
 and commonly in the case of shops and factories, especially in north- 
 erly latitudes, it is advantageous to use the exhaust for heating, even if 
 a condenser is installed for summer use only. The principal objec- 
 tion raised to the use of exhaust steam has been the higher back- 
 pressure required on the engines, resulting in a loss of power nearly 
 proportional to the ratio of the back-pressure to the mean effective 
 pressure. There are two ways of offsetting this loss one, by raising 
 the initial or boiler pressure; and the other, by increasing the cut- 
 off of the engine. Engines are usually designed to work most econom- 
 ically at a given cut-off, so that in most cases it is undesirable to 
 change it to any extent. Raising the boiler pressure, on the other 
 hand, is not so objectionable if the increase amounts to only a few 
 pounds. 
 
 Under ordinary conditions in the case of a simple engine, a rise 
 of 3 pounds in the back-pressure calls for an increase of about 5 
 pounds in the boiler pressure, to maintain the same power at the 
 engine. 
 
 The indicator card shows a back-pressure of about 2 pounds 
 when an engine is exhausting into the atmosphere, so that, an increase 
 of 3 pounds would bring the pressure up to a total of 5 pounds which 
 should be more than sufficient to circulate the steam through any 
 well-designed heating system. 
 
 If it is desired to reduce rather than increase the back-pressure, 
 one of the so-called vacuum systems, described later, can be used. 
 
 The systems of steam heating which have been described are 
 those in which the water of condensation flows back into the boiler 
 by gravity. Where exhaust steam is used, the pressure is much below 
 that of the boiler, and it must be returned either by a pump or by a 
 return trap. The exhaust steam is often insufficient to supply the 
 entire heating system, and must be supplemented by live steam taken 
 directly from the boiler. This must first pass through a reducing 
 
 321
 
 126 HEATING AND VENTILATION 
 
 valve in order to reduce the .pressure to correspond with that carried 
 in the heating system. 
 
 An engine does not deliver steam continuously, but at regular 
 intervals, at the end of each stroke; and the amount is likely to vary 
 with the work done, since the governor is adjusted to admit steam in 
 such a quantity as is required to maintain a uniform speed. If the 
 work is light, very little steam will be admitted to the engine; and 
 for this reason the supply available for heating may vary somewhat, 
 depending upon the use made of the power delivered by the engine. 
 In mills the amount of exhaust steam is practically constant; in 
 office buildings where power is used for lighting, the variation is 
 greater, especially if power is also required for the running of elevators. 
 
 The general requirements for a successful system of exhaust 
 steam heating include a system 'of piping of such proportions that 
 only a slight increase in back-pressure will be thrown upon the engine; 
 a connection which shall automatically supply live steam at a reduced 
 pressure as needed; provision for removing the oil from the exhaust 
 steam ; a relief or back-pressure valve arranged to prevent any sudden 
 increase in back pressure on the engine; and a return system of some 
 kind for returning the water of condensation to the boiler against 
 a higher pressure. These requirements may be met in various ways, 
 depending upon actual conditions found in different cases. 
 
 To prevent sudden changes in the back-pressure, due to irregular 
 supply of steam, the exhaust pipe from the engine is often carried to 
 a closed tank having a capacity from 30 to 40 times that of the engine 
 cylinder. This tank may be provided with baffle-plates or other 
 arrangements and may serve as a separator for removing the oil from 
 the steam as it passes through. 
 
 Any system of piping may be used; but great care should be 
 taken that as little resistance as possible is introduced at bends and 
 fittings ; and the mains and branches should be of ample size. Usually 
 the best results are obtained from the system in which the main steam 
 pipe is carried directly to the top of the building, the distributing pipes 
 being run from that point, and the radiating surfaces supplied by a 
 down-flowing current of steam. 
 
 Before taking up the matter of piping in detail a few of the more 
 important pieces of apparatus will be described in a brief way. 
 
 Reducing Valves. The action of pressure-reducing valves has
 
 HEATING AND VENTILATION 127 
 
 been taken up quite fully in "Boiler Accessories/' and need not be 
 repeated here. When the reduction in pressure is large, as in the 
 case of a combined power and heating plant, the valve may be one or 
 two sizes smaller than the low-pressure main into which it discharges. 
 For example, a 5-inch valve will supply an 8-inch main, a 4-inch a 
 6-inch main, a 3-inch a 5-inch main, a 2^-inch a 4-inch main, etc. 
 
 For the smaller sizes, the difference should not be more than one 
 size. All reducing valves should be provided with a valved by-pass 
 for cutting out the valve in case of repairs. This connection is usually 
 made as shown in plan by Fig. 112. 
 
 Grease Extractor. When exhaust steam is used for heating pur- 
 poses, it must first be passed through some form of separator for 
 removing the oil ; and as an additional precaution it is well to pass the 
 
 BY-PASS 
 
 Fig. 118. Connections of Reducing Valve in Exhaust-Steam Heating System. 
 
 water of condensation through a separating tank before returning it to 
 the boilers. 
 
 Such an arrangement is shown in Fig. 113. As the oil collects 
 on the surface of the water in the tank, it can be made to overflow 
 into the sewer by closing the valve in the connection with the receiving 
 tank, for a short time. 
 
 As much of the oil as possible should be removed before the 
 steam enters the pipes and radiators, else a coating will be formed on 
 their inner surfaces, which will reduce their heating efficiency. The 
 separation of the oil is usually effected by introducing a series of 
 baffling plates in the path of the steam; the particles of oil striking 
 these are stopped, and thus separated from the steam. The oil drops 
 into a receiver provided for this purpose and is discharged through a 
 trap to the sewer. 
 
 In the separator, or extractor, shown in Fig. 114, the separation is 
 accomplished by a series of plates placed in a vertical position in the
 
 12S 
 
 IIKATING AND VENTILATION 
 
 body of the separator, through which the steam must pass. These 
 plates consist of upright hollow columns, with openings at regular 
 intervals for the admission of water and oil, which drain downward 
 to the receiver below. The steam takes a zigzag course, and all of 
 it comes in contact with the intercepting plates, which insures a 
 thorough separation of the oil and other solid matter from the steam. 
 Another form, shown in Fig. 11."), gives excellent results, and has the 
 advantage of providing an equalizing chamber for overcoming, to 
 some extent, the unequal pressure due to the varying load on the 
 engine. It consists of a tank or receiver about 4 feet in diameter, 
 with heavv boiler-iron heads sli<rhtlv crowned to mve stiffness. 
 
 Water-line in 
 
 Receiving Tank ,...~ -ji 'Oil < 
 
 foReceivi-ngTe 
 4 
 
 Oil Over-Flovy 
 
 S-u.rfa.cc 
 
 Main Ret-u-m 
 From Trap 
 
 Fij.'. 113. Separator for Removing Oil from Exhaust Steam and Water Condensation. 
 
 Through the center is a layer of excelsior (wooden shavings of long 
 fibre) about 12 inches in thickness, supported on an iron grating, 
 with a similar grating laid over the top to hold it in place. The 
 steam enters the space below the excelsior and passes upward, as 
 shown by the arrows. The oil is caught by the excelsior, which can 
 be renewed from time to time as it becomes saturated. The oil and 
 water which fall to the bottom of the receiver are carried off through 
 a trap. Live steam may be admitted through a reducing valve, for 
 supplementing the exhaust when necessary. 
 
 Backpressure Valve. This is a form of relief valve which is 
 placed in the outboard exhaust pipe to prevent the pressure in the 
 heating system from rising above a given point. Its office is the 
 
 324
 
 HEATING AND VENTILATION 
 
 129 
 
 reverse of the reducing valve, which supplies more steam when 
 the pressure becomes too low. The form shown in Fig. 116 is 
 designed for a vertical pipe. The valve proper consists of two discs 
 of unequal area, the combined area of which equals that of the pipe. 
 The force tending to open the valve is that due to the steam pressure 
 acting on an area equal to the difference in area between the two discs ; 
 it is clear from the cut that the 
 pressure acting on the larger 
 disc tends to open the valve 
 while the pressure on the smal- 
 ler acts in the opposite direc- 
 tion. The valve-stem is con- 
 nected by a link and crank 
 arm with a spindle upon which 
 is a lever and weight outside. 
 As the valve opens, the weight 
 is raised, so that, by placing it 
 in different positions on the 
 lever arm, the valve will open 
 at any desired pressure. 
 
 Fig. 117 shows a different 
 type, in which a spring is used 
 instead of a weight. This 
 valve has a single disc moving RECEIVER 
 in a vertical direction. The 
 valve stem is in the form of a 
 piston or dash-pot which pre- 
 vents a too sudden movement 
 and makes it more quiet in 
 its action. The disc is held 
 on its seat against the steam 
 pressure by a lever attached 
 to the spring as shown. When 
 the pressure of the steam on the underside becomes greater than the 
 tension of the spring, the valve lifts and allows the steam to escape. 
 The tension of the spring can be varied by means of the adjusting 
 screw at its upper end. 
 
 A back-pressure valve is simply a low-pressure safety-valve 
 
 DISCHARGE 
 
 Pig. 114. Oil Separator Consisting of Vertical 
 
 Plates with Openings Giving Steam a 
 
 Zigzag Course.
 
 130 
 
 HEATING AND VENTILATION 
 
 designed with a specially large opening for the passage of steam 
 through it. These valves are made for horizontal as well as for 
 vertical pipes. 
 
 LIVE STEA 
 FROM REDUCING 
 VALVE 
 
 EXHAUST t 
 
 FROM ENC/NE 
 
 EXCELS/OR / 
 
 \STEAM TO 
 HEATING 
 SYSTEM 
 
 \HANDHOLE 
 
 ( >il Separ 
 
 >r Consisting of a Tank in which Steam is Filtered by Passing 
 Upward through a Layer of Excelsior. 
 
 Exhaust Head. This is a form of separator placed at the top 
 of an outboard exhaust pipe to prevent the water carried up in the 
 steam from falling upon the roofs of buildings or in the street below. 
 Fig. 118 is known as a centrifugal exhaust head. The steam, on 
 entering at the bottom, is given a. 
 whirling or rotary motion by the 
 spiral deflectors; and the water is 
 thrown outward by centrifugal force 
 against the sides of the chamber, from 
 which it flows into the shallow trough 
 at the base, and is carried away through 
 the drip-pipe, which is brought down 
 and connected with a drain-pipe in- 
 side the building. The passage of the 
 steam outboard is shown by the arrows. 
 Other forms are used in which the 
 water is separated from the steam by 
 deflectors which change the direction of 
 the currents. 
 
 Automatic Return=Pumps. In exhaust heating plants, the 
 condensation is returned to the boilers by means of some form of 
 return-pump. A combined pump and receiver of the form illus- 
 
 Kig. 1 16. Automatically Acting Back- 
 pressure Valve Attached to Ver- " 
 tical Pipe. For Preventing 
 Rise of Pressure in System 
 above any Desired 
 Point.
 
 HEATING AND VENTILATION 
 
 131 
 
 trated in Fig. 119 is generally used. This consists of a cast-iron or 
 wrought-iron tank mounted on a base in connection with a boiler 
 feed-pump. Inside the tank is a ball-float connected by means of 
 levers with a valve in the steam pipe which is connected with the 
 pump When the water-line in the tank rises above a certain level, 
 the float is raised and opens the steam valve, which starts the pump. 
 When the water is lowered to its normal level, the valve closes and 
 the pump stops. By this arrangement, a constant water-line is 
 maintained in the receiver, and the pump runs only as needed to care 
 for the condensation as it returns from the heating system. If dry 
 returns are used, they may be brought together and connected with 
 the top of the receiver. If it is desired to seal the horizontal runs, as 
 
 Pig. 117. Back-Pressure Valve Automatic- 
 ally Operated by a Spring. 
 
 Fig. 118. Centrifugal Exhaust Head. 
 
 is usually the case, the receiver may be raised to a height sufficient 
 to give the required elevation and the returns connected near the 
 bottom below the water-line. 
 
 A balance-pipe, so called, should connect the heating main with 
 the top of the tank, for equalizing the pressure; otherwise the steam 
 above the water would condense, and the vacuum thus formed would 
 draw all the water into the tank, leaving the returns practically empty 
 and thus destroying the condition sought. Sometimes an inde- 
 pendent regulator or pump governor is used in place of a receiver. 
 One type is shown in Fig. 120. The return main is connected at 
 
 327
 
 132 
 
 HEATING AND VENTILATION 
 
 the upper opening, and the pump suction at the lower. A float inside 
 the chamber operates the steam valve shown at the top, and the pump 
 works automatically as in the case just described. 
 
 If it is desired to raise the water-line, the regulator may be 
 elevated to the desired height and connections made as shown in 
 Fig. 121. 
 
 Return Traps. The principle of the return trap has been de- 
 scribed in "Boiler Accessories," but its practical form and application 
 
 Pig. 119. Combined Receiver and Automatic Pump for Returning Water of 
 Condensation to Boiler. 
 
 will be taken up here. The type shown in Fig. 122 has all its working 
 parts outside the trap. It consists of a cast-iron bowl pivoted at and 
 II. There is an opening through connecting with the inside of 
 the bowl. The pipe K connects through C with an interior pipe 
 opening near the top (see Fig. 123). The pipe D connects with a 
 receiver, into which all the returns are brought. A is a check-valve 
 allowing water to pass through in the direction shown by the arrow. 
 E is a pipe connecting with the boiler below the water-line. B is a
 
 HEATING AND VENTILATION 
 
 133 
 
 check opening to\vard the boiler, and K, a pipe connected with the 
 steam main or drum. 
 
 The action of the trap is as fol- 
 lows : As the bowl fills with water from 
 the receiver, it overbalances the 
 weighted lever and drops to the bot- 
 tom of the ring. This opens the valve 
 C, and admits steam at boiler pres- 
 sure to the top of the trap. Being at 
 a higher level the water flows by grav- 
 ity into the boiler, through the pipe E. 
 Water and steam are kept from passing 
 out through D by the check A. 
 
 \\Tien the trap has emptied it- VI9 ^SSS^JS^SSS M 
 
 . , , ,, . of a Receiver. 
 
 self, the weight of the ball raises it 
 
 to the original position, which movement closes the valve C and opens 
 the small vent F. The pressure in the bowl being relieved, water 
 flows in from the receiver through D, until the trap is filled, when the 
 
 K3 
 
 A U TO MA T/C VA L VE 
 
 TO PUMP 
 
 Fig. 121. Pump Regulator Placed at Sufficient Height to Raise Water- Line to 
 Point Desired. 
 
 process is repeated. In order to work satisfactorily, the trap should 
 be placed at least 3 feet above the water-level in the boiler, and the 
 
 329
 
 134 
 
 HEATING AND VENTILATION 
 
 pressure in the returns must always be sufficient to raise the water 
 from the receiver to the trap against atmospheric pressure, which is 
 theoretically about 1 pound for every 2 feet in height. In practice 
 there will be more or less friction to 
 overcome, and suitable adjustments must 
 be made for each particular case. 
 
 Fig. 124 shows another form of trap 
 acting upon the same principle, except 
 that in this case the steam valve is oper- 
 ated by a bucket or float inside the trap. 
 The pipe connections are practically the 
 same as with the trap just described. 
 
 Return traps are more commonly 
 used in smaller plants where it is desired Fig ]23 . Return Trap w}th Work . 
 to avoid the expense and care of a pump. 
 
 Damper=Regulators. Every heating and every power plant 
 should be provided with automatic means for closing the dampers 
 when the steam pressure reaches a certain point, and for opening 
 them again when the pressure drops. There are various regulators 
 designed for this purpose, a simple form of which is shown in Fig. 125. 
 
 Steam at boiler pres- 
 sure is admitted beneath a 
 diaphragm which is bal- 
 anced by a weighted lever. 
 When the pressure rises to a 
 certain point, it raises the 
 lever slightly and opens a 
 valve which admits water 
 under pressure above a dia- 
 phragm located near the 
 smoke-pipe. This action 
 forces down a lever con- 
 nected by chains with the 
 ii Trap damper, and closes it. 
 When the steam pressure 
 drops, the water-valve is closed, and the different parts of the 
 apparatus take their original positions. 
 
 Another form similar in principle is shown in Fig. 126. In this 
 
 Fig. 123. Showing Interior Detail of Retur 
 of Fig. 122. 
 
 880
 
 HEATING AND VENTILATION 
 
 135 
 
 case a piston is operated by the water-pressure, instead of a diaphragm. 
 In both types the pressures at which the damper shall open and close 
 are regulated by suitable adjustments of the weights upon the levers. 
 Pipe Connections. The method of making the pipe connections 
 in any particular case will depend upon the general arrangement 
 of the apparatus and the various conditions. Fig. 127 illustrates 
 
 s& 
 
 Pig. 134. Return Trap with Steam Valve Operated by Bucket or Float Inside. 
 
 the general principles to be followed, and by suitable changes may be 
 used as a guide in the design of new systems. 
 
 Steam first passes from the boilers into a large drum or header. 
 From this, a main, provided with a shut-off valve, is taken as shown; 
 one branch is carried to the engines, while another is connected with 
 the heating system through a reducing valve having a by-pass and 
 cut-out valves. The exhaust from the engines connects with the large 
 main over the boilers at a point just above the steam drum. The 
 
 331
 
 130 
 
 HEATING AND VENTILATION 
 
 branch at the right is carried outboard through a back-pressure 
 valve which may be set to carry any desired pressure on the system. 
 The other branch at the left passes through an oil separator into the 
 heating system. The connections between the mains and radiators 
 are made in the usual way, and the main return is carried back to the 
 return pump near the floor. A false water-line or seal is obtained by 
 elevating the pump regulator as already described. An equalizing 
 
 Fig. 125 
 D 
 
 125. Simple Form of Automatic Damper-Regulator. Operated by Lever Attached to 
 Diaphragm, for Closing Dampers when Steam Pressure Reaches a Certain Point. 
 
 or balance pipe connects the top of the regulator with the low-pressure 
 heating main, and high pressure is supplied to the pump as shown. 
 
 A sight-feed lubricator should be placed in this pipe above the 
 automatic valve; and a valved by-pass should be placed around the 
 regulator, for running the pump in case of accident or repairs. The 
 oil separator should be drained through a special oil trap to a catch- 
 basin or to the sewer; and the steam drum or any other low points 
 
 332
 
 HEATING AND VENTILATION 
 
 137 
 
 or pockets in the high-pressure piping should be dripped to the 
 return tank through suitable traps. 
 
 Means should be provided for draining all parts of the system 
 to the sewer, and all traps and special apparatus should be by-passed. 
 The return -pump should always be duplicated in a plant of any size, 
 as a safeguard against accident; and the two pumps should be run 
 alternately, to make sure that one is always in working order. 
 
 Fig. 136. Automatic Damper-Regulator Operated by Piston Actuated 
 by Water-Pressure. 
 
 One piece of apparatus not shown in Fig. 127 is the feed -water 
 heater. If all of the exhaust steam can be utilized for heating pur- 
 poses, this is not necessary, as the cold water for feeding the boilers 
 may be discharged into the return pipe and be pumped in with the 
 condensation. In summertime, however, when the heating plant is 
 not in use, a feed-water heater is necessary, as a large amount of heat
 
 138 
 
 HEATING AND VENTILATION
 
 HEATING AND VENTILATION 139 
 
 which would otherwise be wasted may be saved in this way. The 
 connections will depend somewhat upon the form of heater used: 
 but in general a single connection with the heating main inside the 
 hack-pressure valve is all that is necessary. The condensation from 
 the heater should be trapped to the sewer. 
 
 335
 
 336
 
 HEATING AND VENTILATION 
 
 PART III 
 
 VACUUM SYSTEMS 
 
 Low=Pressure or Vacuum Systems. In the systems of steam 
 heating which have been described up to this point, the pressure 
 carried has always been above that of the atmosphere, and the action 
 of gravity has been depended upon to carry the water of condensation 
 back to the boiler or receiver; the air in the radiators has been forced 
 out through air-valves by the pressure of steam back of it. Methods 
 will now be taken up in which the pressure in the heating system is 
 less than the atmosphere, and where 
 the circulation through the radiators is 
 produced by suction rather than by 
 pressure. Systems of this kind have 
 several advantages over the ordinary 
 methods of circulation under pressure. 
 First no back-pressure is produced 
 at the engines when used in connection 
 with exhaust steam; but rather there 
 will be a reduction of pressure due to 
 the partial vacuum existing in the radia- 
 tors. Second there .is a complete 
 removal of air from the coils and 
 radiators, so that all portions are 
 steam-filled and available for heating 
 purposes. Third there is complete drainage through the returns, 
 especially those having long horizontal runs; and there is absence of 
 water-hammer. Fourth smaller return pipes may be used. 
 The two older systems of this kind in common use are known as the 
 Webster and Paul systems; other systems of recent introduction are 
 described in the Instruction 'Paper on Steam and Hot- Water Fitting. 
 
 Webster System. This consists primarily of an automatic outlet- 
 valve on each coil and radiator, connected with some form of suction 
 apparatus such as a pump or ejector. One type of valve used is 
 
 Pig. 128, Air Outlet-Valve for Radi- 
 ator, Automatically Operated by 
 Expansion and Contraction 
 of Vulcanite Stem. 
 
 837
 
 142 
 
 HEATING AND VENTILATION 
 
 Fig. 129. Thermostat At- 
 tached to Angle- Valve with 
 Top Removed. 
 
 shown in section in Fig. 128, which 'replaces the usual hand-valve at 
 the return end of the radiator. It is similar in construction to some 
 of the air-valves already described, consisting of a rubber or vulcanite 
 stem closing against a valve opening when 
 made to expand by the presence of steam. 
 When water or air fills the valve, the stem 
 contracts and allows it to be sucked out 
 as shown by the arrows. A perforated 
 metal strainer surrounds the stem or ex- 
 pansion piece, to prevent dirt and sediment 
 from clogging the valve. 
 
 Fig. 129 shows the valve or thermostat, 
 as it is called attached to an ordinary 
 angle-valve with the top removed; and Fig. 
 130 indicates the method of draining the 
 bottoms of risers or the ends of mains. 
 
 Fig. 131 shows another form of this 
 valve, called a water-seal motor. This is 
 used under practically the same conditions 
 as the one described above. Its action is as follows : 
 
 Ordinarily, the seal .1 is down, and the central tube-valve is 
 resting upon the seat, closing the port K and preventing direct com- 
 munication between the interior of 
 the motor-body E and the outlet 
 L. The outlet is attached to a pipe 
 leading to a vacuum-pump, or 
 other draining apparatus, which 
 exhausts the space F above the seal 
 through the annular space between 
 the spindle B and the inside of the 
 central tube G. The water of 
 condensation, accumulating in the 
 radiator or coil, passes into the 
 chamber E, through the inlet C, rises in the chamber, and seals the 
 space between the seal-shell A and the sleeve of the bonnet D. The 
 differential pressure thus created causes the seal .1 to rise, lifting the 
 end of the central tube off the seat, thus opening a clear passageway 
 for the ejection of the water of condensation. 
 
 Fig. 13fl. Showing Method of Draining 
 
 Bottoms of Risers or Ends 
 
 of Mains.
 
 HEATING AND VENTILATION 
 
 143 
 
 When all the water of condensation has been drawn out of the 
 radiator, the seal and tube are reseated by gravity, thus closing the 
 port K, preventing waste or loss of steam; and the pressure is equal- 
 ized above and below the seal because of the absence of water. This 
 action, is practically instantaneous. When the condensation is small 
 in quantity, the discharge is intermittent and rapid. 
 
 The space between the seal A and the sleeve of the bonnet D, 
 and the annular space between the central tube G and the spindle B, 
 
 Fig. 131. Water-Seal Motor. 
 
 form a passageway through which the air is continually withdrawn by 
 the vacuum pump or other draining apparatus. 
 
 The action outlined continues as long as water is present. 
 
 No adjustment whatever is necessary; the motor is entirely auto- 
 matic. 
 
 One special advantage claimed for this system is that the amount 
 of steam admitted to the radiators may be regulated to suit the require- 
 ments of outside temperature; and is possible without water-
 
 144 
 
 HEATING AND VENTILATION 
 
 340
 
 HEATING AND VENTILATION 145 
 
 logging or hammering. This may be done at will by closing down on 
 the inlet supply to the desired degree. The result is the admission 
 of a smaller amount of steam to the radiator than it is calculated to 
 condense normally. The condensation is removed as fast as formed, 
 by the opening of the thermostatic valve. 
 
 The general application of this' system to exhaust heating is 
 shown in Fig. 132. Exhaust steam is brought from the engine as 
 shown; one branch is connected with a feed-water heater,, while the 
 other is carried upward and through a grease extractor, where it 
 branches again, one line leading outboard through a back-pressure 
 valve and the other connecting with the heating main. A live steam 
 connection is made through a reducing valve, as in the 'ordinary 
 system. Valved connections are made with the coils and radiators 
 in the usual manner; but the return valves are replaced by the special 
 thermostatic valves described above. 
 
 The main return is brought down to a vacuum pump which dis- 
 charges into a return tank, where the air is separated from the water 
 and passes off through the vapor pipe at the top. The condensation 
 then flows into the feed-water heater, from which it is automatically 
 pumped back into the boilers. The cold-water feed supply is con- 
 nected with the return tank, and a small cold-water jet is connected 
 into the suction at the vacuum pump for increasing the vacuum in -the 
 heating system by the condensation of steam at this point. 
 
 Paul System. In this system the suction is connected with the 
 air-valves instead of the returns, and the vacuum is produced by 
 means of a steam ejector instead of a pump. The returns are carried 
 back to a receiving tank, and pumped back to the boiler in the usual 
 manner. The ejector in this case is called the exhauster. 
 
 Fig. 133 shows the general method of making the pipe connections 
 with the radiators in this system; and Fig. 134, the details of connec- 
 tion at the exhauster. 
 
 A A are the returns from the air-valves, and connect with the 
 exhausters as shown. Live steam is admitted in small quantities 
 through the valves B B ; and the mixture of air and steam is discharged 
 outboard through the pipe C. D D are gauges showing the pressure 
 in the system; and E E are check-valves. The advantage of this 
 system depends principally upon the quick removal of air. from the 
 various radiators and pipes, which constitutes the principal obstruction 
 
 341
 
 I4r> 
 
 HEATING AND VENTILATION 
 
 to circulation; the inductive action in many cases is sufficient to cause 
 the system to operate somewhat below atmospheric pressure. 
 
 Where exhaust steam is used for heating, the radiators should 
 
 fMVi SYSTEM OF HCATIN* 
 
 Fit:. 133. Showing General Method Of Making Pipe and Radiator Connections in 
 Paul System. 
 
 be somewhat increased in size, owing to the lower temperature of 
 the steam. It is common practice to add from 20 to 30 per cent to 
 the sizes required for low-pressure live steam.
 
 HEATING AND VENTILATION 
 
 147 
 
 FORCED BLAST 
 
 In a system of forced circulation by means of a fan or blower 
 the action is positive and practically constant under all usual con- 
 ditions of outside temperature and wind action. This gives it a 
 decided advantage over natural or gravity methods, which are af- 
 A A 
 
 B B 
 
 Fig. 134. Details of Connections at Exhauster, Paul System. 
 
 fected to a greater or less degree by changes in wind-pressure, and 
 makes it especially adapted to the ventilation and warming of large 
 buildings such as shops, factories, schools, churches, halls, theaters, 
 etc., where large and definite air-quantities are required. 
 
 Exhaust Method. This consists in drawing the air out of a 
 building, and providing for the heat thus carried away by placing 
 
 343
 
 148 HEATING AND VENTILATION 
 
 steam coils under windows or in other positions where the inward 
 leakage is supposed to be the greatest. When this method is used, a 
 partial vacuum is created within the building or room, and all currents 
 and leaks are inward ; there is nothing to govern definitely the quality 
 and place of introduction of the air, and it is difficult to provide suit- 
 able means for warming it. 
 
 Plenum Method. In this case the air is forced into the building, 
 and its quality, temperature, and point of admission are completely 
 under control. All spaces are filled with air under a slight pressure, 
 and the leakage is outward, thus preventing the drawing of foul air 
 into the room from any outside source. But above all, ample oppor- 
 tunity is given for properly warming the air by means of heaters, 
 either in direct connection with the fan or in separate passages leading 
 to the various rooms. 
 
 Form of Heating Surface. The best type of heater for any 
 particular case will depend upon the volume and final temperature 
 of the air, the steam pressure, and the available space. When the 
 air is to be heated to a high temperature for both warming and venti- 
 lating a building, as in the case of a shop or mill, heaters of the general 
 form shown in Figs. 135, 136, and 137 are used. These may also be 
 adapted to all classes of work by varying the proportions as required. 
 They can be made shallow and of large superficial area, for the com- 
 paratively low temperatures used in purely ventilating work; or 
 deeper, with less height and breadth, as higher temperatures are 
 required. 
 
 Fig. 135 shows in section a heater of this type, and illustrates 
 the circulation of steam through it. It consists of sectional cast-iron 
 bases with loops of wrought-iron pipe connected as shown. The 
 steam enters the upper part of the bases or headers, and passes up 
 one side of the loops, then across the top and down on the other side, 
 where the condensation is taken off through the return drip, which 
 is separated from the inlet by a partition. These heaters are made 
 up in sections of 2 and 4 rows of pipes each. The height varies from 
 3^ to 9 feet, and the vidth from 3 feet to 7 feet in the standard sizes. 
 They are usually made up of 1-inch pipe, although l|-inch is commonly 
 used in the larger sixes. Fig. 136 shows another form; in this case 
 all the loops are made of practically the same length by the special 
 form of construction shown. This is claimed to prevent the short- 
 
 344
 
 HEATING AND VENTILATION 
 
 149 
 
 circuiting of steam through the shorter loops, which causes the outer 
 pipes to remain gold. This form of heater is usually encased in a 
 
 Fig. 135. Showing Circulation of Steam in Large Coil-Pipe Radiator for 
 Heating Mills, Shops, etc. 
 
 sheet-steel housing as shown in Fig. 137, but may be supported on 
 foundation between brick walls if desired. 
 
 845
 
 150 
 
 HEATING AND VENTILATION 
 
 Fig. 138 shows a special form of heater particularly adapted to 
 ventilating work where the air does not have to he raised above 70 or 
 SO degrees. It is made up of 1-inch wrought-iron pipe connected 
 
 with supply and return headers; each section contains 14 pipes, and 
 they are usually made up in groups of 5 sections each. These coils 
 are supported upon tee-irons resting upon a brick foundation. Heat- 
 
 346
 
 HEATING AND VENTILATION 
 
 151 
 
 ers of this form are usually made to extend across the side of a room 
 with brick walls at the sides, instead of being encased in steel housings. 
 
 Fig. 139 shows a front view of a cast-iron sectional heater for 
 use under the same conditions as the pipe heaters already described. 
 This heater is made up of several banks of sections, like the one shown 
 in the cut, and enclosed in a steel-plate casing. 
 
 Cast-iron indirect radiators of the pin type are well adapted for 
 use in connection with mechanical ventilation, and also for heating 
 
 Fig. 137. Large Coil-Pipe Radiator Encased in Sheet-Steel Housing. 
 
 where the air- volume is large and the temperature not too high, as 
 in churches and halls. They make a convenient form of heater, for 
 schoolhouse and similar work, for, being shallow, they can be sup- 
 ported upon I-beams at such an elevation that the condensation will be 
 returned to the boilers by gravity. 
 
 In the case of vertical pipe heaters, the bases are below the water- 
 line of the boilers, and the condensation must be returned by the use 
 of pumps and traps. 
 
 347
 
 152 
 
 HEATING AND VENTILATION 
 
 Efficiency of Pipe Heaters. The efficiency of the heaters used in 
 connection with forced blast varies greatly, depending upon the 
 temperature of the entering air, its velocity between the pipes, the 
 temperature to which it is raised, and the steam pressure carried in 
 the heater. The general method in which the heater is made up is 
 also an important factor. 
 
 In designing a heater of this kind, care must be taken that the 
 free area between the pipes is not contracted to such an extent that 
 an excessive velocity will be required to pass the given quantity of 
 
 GAL. /RON STOP 
 
 PLAN AT SUPPLY END 
 
 FRONT V/EW 
 1I!S. Heater Especially Adapted 
 
 S/DE V/EW 
 
 o Ventilation where Air does not Have to be Heated 
 70 to 80 decrees F. 
 
 air through it. In ordinary work it is customary to assume a velocity 
 of 800 to 1 ,000 feet per minute ; higher velocities call for a greater 
 pressure on the far., which is not desirable in ventilating work. 
 
 In the heaters shown, about .4 of the total area is free for the 
 passage of air; that is, a heater 5 feet wide and 6 feet high would 
 have a total area of 5 X 6 = 30 square feet, and a free area between 
 the pipes of 30 X . 4 = 12 square feet. The depth or number of rows 
 of pipe does not affect the free area, although the friction is increased 
 and additional work is thrown upon the fan. The efficiency in any 
 
 848
 
 HEATING AND VENTILATION 
 
 153 
 
 I 
 
 given heater will be increased by increasing the velocity of the air 
 through it; but the final temperature will be diminished; that is, 
 a larger quantity of air will be heated to a lower temperature in the 
 second case, and, while the total heat given off is greater, the air- 
 quantity increases more rapidly than the heat-quantity, which causes 
 a drop in temperature. 
 
 Increasing the number of rows of pipe in a heater, with a con- 
 stant air-quantity, increases the final temperature of the air, but 
 diminishes the efficiency of the heater, because the average difference 
 in temperature between the air and the steam is less. Increasing 
 the steam pressure in the 
 heater (and consequently its 
 temperature) increases both 
 the final temperature of the 
 air and the efficiency of the 
 heater. Table XXX has been 
 prepared from different tests, 
 and may be used as a guide 
 in computing probable results 
 under ordinary working con- 
 ditions. In this table it is 
 assumed that the air enters 
 the heater at a temperature of 
 zero and passes between the 
 pipes with a velocity of 800 
 feet per minute. Column 1 
 gives the number of rows of 
 pipe in the heater, ranging 
 from 4 to 20 rows; and columns 2, 3, and 4, show the final tempera- 
 ture to which the entering air will be raised from zero under various 
 pressures. Under 5 pounds pressure, for example, the rise in tem- 
 perature ranges from 30 to 140 degrees; under 20 pounds, 35 to 150 
 degrees; and under 60 pounds, 45 to 170 degrees. Columns 5, 6, and 
 7 give approximately the corresponding efficiency of the heater. For 
 example, air passing through a heater 10 pipes deep and carrying 20 
 pounds pressure, will be raised to a temperature of 90 degrees, and 
 the heater will have an efficiency of 1,650 B. T. U. per square foot of 
 surface per hour. 
 
 139. Front View of Cast-Iron Sectional 
 eater. The Banks of Sections are En- 
 closed in a Steel-Plate Casing.
 
 154 
 
 HEATING AND VENTILATION 
 
 TABLE XXX 
 Data Concerning Pipe Heaters 
 
 Temperature of entering air, zero. Velocity of air between the pipes, 
 800 feet per minute. 
 
 TEMPERATURE TO WHICH AIR WILL EFFICIENCY OF HEATING SURFACE iN-B.T.U 
 BE RAISED FROM ZERO PER SQUARE FOOT PER HOUR 
 
 Rows OF 
 PIPK DEEP Steam Pressure in Heater 
 
 Steam Pressure in Heater 
 
 5 Ibs. ! 20 Ibs. 
 
 60 Ibs. 
 
 
 5 Ibs. 
 
 2 
 
 o Ibs. 
 
 e 
 
 Ibs. 
 
 4 30 35 
 
 45 
 
 
 1,600 
 
 
 1,800 
 
 f 
 
 >,000 
 
 6 50 55 
 
 65 
 
 
 1,600 
 
 
 1,800 
 
 c 
 
 >,000 
 
 8 65 70 
 
 85 
 
 
 1,500 
 
 
 ,650 
 
 
 ,850 
 
 10 80 90 
 
 105 
 
 
 1,500 
 
 
 ,650 
 
 
 ,850 
 
 12 95 105 
 
 125 
 
 
 ,500 
 
 
 ,650 
 
 
 ,850 
 
 14 105 120 
 
 140 
 
 
 ,400 
 
 
 ,500 
 
 
 ,700 
 
 16 120 130 
 
 150 
 
 
 ,400 
 
 
 ,500 
 
 
 ,700 
 
 18 130 140 
 
 160 
 
 
 ,300 
 
 
 .400 
 
 
 ,600 
 
 20 140 150 
 
 170 
 
 
 ,300 
 
 
 ,400 
 
 
 ,600 
 
 For a velocity of 1,000 feet, multiply the temperatures given in 
 the table by . 9, and the efficiencies by 1.1. 
 
 Example. How many square feet of radiation will be required to raise 
 600,000 cubic feet of air per hour from zero to 80 degrees, with a velocity 
 through the heater of '800 feet per minute and a steam pressure of 5 pounds? 
 What must be the total area of the heater front, and how man}- rows of 
 pipes must it have? 
 
 Referring back to the formula for heat required for ventilation, 
 we have 
 
 000,000 X 80 __ 
 
 = 8/2,/2/ B. T. I . required. 
 55 
 
 Referring to Table XXX, we find that for the above conditions a 
 heater 10 pipes deep is required, and that an efficiency of 1,500 
 
 B. T. U. will be obtained. Then ' = 582 square feet of 
 
 1 ,oOO 
 
 surface required, which may be taken as 600 in round numbers. 
 
 600,000 . : 10,000 
 
 = 10,000 cubic feet ot air per minute: and - = 12. o 
 
 GO 800 
 
 square feet of free area required through the heater. If we assume 
 .4 of the total heater front to be free for the passage of air, then 
 
 12 5 
 
 = 31 square feet, the total area required. 
 
 350
 
 HEATING AND VENTILATION 
 
 155 
 
 For convenience in estimating the approximate dimensions of 
 a heater, Table XXXI is given. The standard heaters made by dif- 
 ferent manufacturers vary somewhat, but the dimensions given in 
 the table represent average practice. Column 3 gives the square 
 feet of heating surface in a single row of pipes of the dimensions given 
 in columns 1 and 2; and column 4 gives the free area between the 
 pipes. 
 
 TABLE XXXI 
 Dimensions of Heaters 
 
 WIDTH OF SECTION HEIGHT OF PIPES 
 
 SQUARE FEET OF 
 SURFACE 
 
 FREE AHEA THROUGH 
 HEATER IN SQ. FT. 
 
 3 feet 
 
 3 feet 
 
 6 inches 
 
 20 
 
 4.2 
 
 3 " 
 
 4 " 
 
 " 
 
 22 
 
 4.8 
 
 3 " 
 
 4 " 
 
 6 " 
 
 25 
 
 5.4 
 
 3 " 
 
 5 " 
 
 " 
 
 28 
 
 6.0 
 
 4 " 
 
 4 " 
 
 6 " 
 
 34 
 
 7.2 
 
 4 '" 
 
 5 " 
 
 
 
 38 
 
 8.0 
 
 4 " 
 
 5 " 
 
 6 
 
 42 
 
 8.8 
 
 4 " 
 
 6 " 
 
 " 
 
 45 
 
 9.6 
 
 5 " 
 
 5 " 
 
 6 " 
 
 52 
 
 11.0 
 
 5 " 
 
 6 " 
 
 " 
 
 57 
 
 12.0 
 
 5 " 
 
 6 " 
 
 6 " 
 
 62 
 
 13.0 
 
 5 " 
 
 7 " 
 
 " 
 
 67 
 
 14.0 
 
 6 " 
 
 6 " 
 
 6 " 
 
 75 
 
 15.6 
 
 6 " 
 
 7 " 
 
 " 
 
 81 
 
 16.8 
 
 6 " 
 
 7 " 
 
 6 
 
 87 
 
 18.0 
 
 6 " 
 
 8 " 
 
 
 
 92 
 
 19.2 
 
 7 " 
 
 7 " 
 
 6 ' : 
 
 98 
 
 21.0 
 
 7 " 
 
 8 " 
 
 " 
 
 108 
 
 22.4 
 
 7 " 
 
 8 " 
 
 6 
 
 109 
 
 23.8 
 
 7 " 
 
 9 " 
 
 " 
 
 116 
 
 25.2 
 
 In calculating the total height of the heater, add 1 foot for the 
 base. 
 
 These sections are made up of 1-inch pipe, except the last or 
 7-foot sections, which are made of l|-inch pipe. 
 
 Using this table in connection with the example 'just given, we 
 should look in the last column for a section having a free area of 12.5 
 square feet; here we find that a 5 feet by 6 feet 6 inches section has a 
 free opening of 13 square feet and a radiating surface of 62 square 
 
 351
 
 156 HEATING AND VENTILATION 
 
 feet. The conditions call for 10 rows of pipes and 10 X 62 = 620 
 square feet of radiating surface, which is slightly more than called for, 
 but which would be near enough for all practical purposes. 
 
 EXAMPLE FOR PRACTICE 
 
 Compute the dimensions of a heater to warm 20,000 cubic feet 
 of air per minute from 10 below zero to 70 degrees above, with 5 
 pounds steam pressure. 
 
 Axs. 1,164 sq. ft. of rad. surface 10 pipes deep. 
 25 scj. ft. free area through heater. 
 
 Use twenty 5 ft. by 6 ft. sections, side by side, which gives 24 
 square feet area and 1,140 square feet of surface. 
 
 The general method of computing the size of heater for any given 
 building is the same as in the case of indirect heating. First obtain 
 the B. T. U. required for ventilation, and to that add the heat loss 
 through walls, etc.; and divide the result by the efficiency of the 
 heater under the given conditions. 
 
 Example. An audience hall is to be provided with 400,000 cubic feet 
 of air per hour. The heat loss through \vaHs, etc.. is 250,000 B.T.U. per 
 hour in zero weather. What will be the size of heater, and how many rows 
 of pipe deep must it be, with 20 pounds steam pressure?' 
 
 400,000 X 70 
 
 o 
 
 Therefore 250,000 + 509,090 - 759,090 B. T. U., total to be supplied. 
 
 We must next find to what temperature the entering air must 
 be raised in order to bring in the required amount of heat, so that the 
 number of rows of pipe in the heater may be obtained and its corre- 
 sponding efficiency determined. We have entering the room for pur- 
 poses of ventilation, 400,000 cubic feet of air every hour, at a tempera- 
 ture of 70 degrees; and the problem now becomes: To what tem- 
 perature must this air be raised to carry in 250,000 B. T. U. additional 
 for warming? 
 
 We have learned that 1 B. T. U. will raise 55 cubic feet of air 
 1 degree. Then 250,000 B. T. U. will raise 250,000 X 55 cubic 
 feet of air 1 degree. 
 
 J>50,000j><j>5 = , 
 
 ^00,000^ 
 The air in this case must be raised to 70 + 34 = 104 degrees, to provide 
 
 352
 
 HEATING AND VENTILATION 157 
 
 for both ventilation and warming. Referring to Table XXX, we find 
 that a heater 12 pipes deep will be required, and that the corre- 
 
 sponding efficiency of the heater will be 1 ,650 B. T. U. Then 
 
 1,650 
 
 = 460 square feet of surface required. 
 
 Efficiency of Cast=Iron Heaters. Heaters made up of indirect 
 pin radiators of the usual depth, have an efficiency of at least 1,500 
 B. T. U., with steam at 10 pounds pressure, and are easily capable of 
 warming air from zero to 80 degrees or over when computed on this 
 basis. The free space between the sections bears such a relation to 
 the heating surface that ample area is provided for the flow of air 
 through the heater, without producing an excessive velocity. 
 
 The heater shown in Fig. 139 may be counted on for an effi- 
 ciency at least equal to that of a pipe heater; and in computing the 
 depth, one row of sections may be taken as representing 4 rows of 
 pipe. 
 
 Pipe Connections. In the heater shown in Fig. 135, all the 
 sections take their supply from a common header, the supply pipe 
 connecting with the top, and the return being taken from the lower 
 division at the end, as shown. 
 
 In Fig. 137 the base is divided into two parts, one for live steam, 
 and the other for exhaust. The supply pipes connect with the upper 
 compartments, and the drips are taken off as shown. Separate traps 
 should be provided for the two pressures. 
 
 The connections in Fig. 136 are similar to those just described, 
 except that the supply and return headers, or bases, are drained 
 through separate pipes and traps, there being a slight difference in 
 pressure between the two, which is likely to interfere with the proper 
 drainage if brought into the same one. This heater is arranged to 
 take exhaust steam, but has a connection for feeding in live steam 
 through a reducing valve if desired, the whole heater being under one 
 pressure. 
 
 In heating and ventilating work where a close regulation of 
 temperature is required, it is usual to divide the heater into several 
 sections, depending upon its size, and to provide each with a valve in the 
 supply and return. In making the divisions, special care should be 
 taken to arrange for as many combinations as possible. For example, 
 a heater 10 pipes deep may be made up of three sections one of 
 
 353
 
 158 
 
 HEATING AND VENTILATION 
 
 2 rows, and two of 4 rows each. By means of this division, 2, 4, 6, 8, 
 or 10 rows. of pipe can be used at one time, as the outside weather 
 conditions may require. 
 
 When possible, the return from each section should be provided 
 with a water-seal two or three feet in depth. In the case of overhead 
 heaters, the returns may be sealed by the water-line of the boiler or 
 by the use of a special water-line trap; but vertical pipe heaters 
 resting on foundations near the floor are usually provided with siphon 
 loops extending into a pit. If this arrangement is not convenient, a 
 separate trap should be placed on the return from each section. 
 The main return, in addition to its connection with the boiler or 
 
 L/VE STEAM 
 
 EXHAUST STEAM 
 
 TRAP TRAP 
 
 Fig. 140. Heater Made Up of Interchangeable Sections. 
 
 pump receiver, should have a connection with the sewer for blowing 
 out when steam is first turned on. Sometimes each section is pro- 
 vided with a connection of this kind. 
 
 Large automatic air-valves should be connected with each 
 section; and it is well to supplement these with a hand pet-cock, 
 unless individual blow-off valves are provided as described above. 
 
 If the fan is driven by a steam engine, provision should be made 
 for using the exhaust in the heater; and part of the sections should 
 be so valved that they may be supplied with either exhaust or live 
 steam. 
 
 354
 
 HEATING AND VENTILATION 
 
 159 
 
 Fig. 140 shows an arrangement in which all of the sections are 
 interchangeable. 
 
 From 50 to 60 square feet of sadiating surface should be provided 
 in the exhaust portion of the heater for each engine horse-power, 
 and should be divided into at least three sections, so that it can be 
 proportioned to the requirements of different outside temperatures. 
 
 Pipe Sizes. The sizes of the mains and branches may be com- 
 puted from the tables already given in Part II, taking into account 
 the higher efficiency of the heater and the short runs of piping. 
 
 Table XXXII, based on experience, has been found to give 
 satisfactory results when the apparatus is near the boilers. If the 
 main supply pipe is of considerable length, its diameter should be 
 checked by the method previously given. 
 
 TABLE XXXII 
 Pipe Sizes 
 
 SQUARE FEET OF SURFACE 
 
 DIAMETER OF STEAM PIPE 
 
 DIAMETER OF RETURN 
 
 150 
 
 2 inches 
 
 l\ inches 
 
 300 
 
 2* 
 
 1* " 
 
 500 
 
 3 
 
 2 
 
 700 
 
 8J 
 
 2 " 
 
 1,000 
 2,000 
 
 4 
 5 
 
 II " 
 
 3,000 
 
 6 
 
 3 " 
 
 Heaters of the patterns shown in Figs. 135, 136, and 137 are 
 usually tapped at the factory for high or low pressure as desired, 
 and these sizes may be followed in making the pipe connections. 
 
 The sizes marked on Fig. 136 may be used for all ordinary work 
 where the pressure runs from 5 to 20 pounds; for pressures above 
 that, the supply connections may be reduced one size. 
 
 FANS 
 
 There are two types of fans in common use, known as the cen- 
 trifugal fan or blower, and the disc fan or propeller. The former 
 consists of a number of straight or slightly curved blades extending 
 radially from an axis, as shown in Fig. 141. When the fan is in 
 motion, the air in contact with the blades is thrown outward by the 
 action of centrifugal force, and delivered at the circumference or 
 
 355
 
 160 
 
 HEATING AND VENTILATION 
 
 periphery of the wheel. A partial vacuum is thus produced at the 
 
 center of the wheel, and air from the outside flows in to take the 
 
 place of that which has been discharged. 
 
 Fig. 142 illustrates the action of a centrifugal fan, the arrows 
 
 showing the path of the air. 
 
 This type of fan is usually 
 
 enclosed in a steel - plate 
 
 casing of such form as to 
 
 provide for the free move- 
 ment of the air as it es- 
 capes from the periphery 
 
 of the wheel. An opening 
 
 in the circumference of the 
 
 casing serves as an outlet 
 
 into the distributing ducts 
 
 which carry the air to the 
 
 various rooms to be venti- 
 lated. 
 
 A fan with casing, is 
 
 shown in Fig. 143; and a 
 
 combined heater and fan, 
 
 with direct-connected engine, is shown in Fig. 144. 
 
 The discharge opening can be located in any position desired, 
 
 either up, down, top horizontal, bottom horizontal, o" at any angle. 
 
 Where the height of the fan room is 
 limited, a form called the ihrcc-qnarlcr 
 hominy may be used, in which the lower 
 part of the casing is replaced by a brick 
 or cemented pit extending below the floor- 
 level as shown in Fig. 145. 
 
 Another form of centrifugal fan is 
 shown in Fig. 146. This is known as the 
 cone fan, and is commonly placed in an 
 opening in a brick wall, and discharges air 
 from its entire periphery into a room called 
 a plenum chamber, with which the various 
 
 distributing ducts connect. 
 
 This fan is often made double by placing two wheels back to 
 
 Fig. 141. Centrifugal Fan or Blower. 
 
 Fig. 142. Illustrating Action 
 of Centrifugal Fan. The 
 Arrows Show the Path of 
 the Air. 
 
 356
 
 HEATING AND VENTILATION 
 
 161 
 
 back and surrounding them with a steel casing in a similar manner 
 to the one shown in Fig. 143. 
 
 Cone fans are particularly adapted to church and schoolhouse 
 work, as they are capable of moving large volumes of air at moderate 
 speeds. 
 
 Fig. 147 shows a form of small direct-connected exhauster com- 
 monly used for ventilating toilet-rooms, chemical hoods, etc. 
 
 Centrifugal fans are used almost exclusively for supplying air 
 for the ventilation of buildings, and for forced-blast heating. They 
 are also used as exhausters 
 for removing the air from 
 buildings in cases where 
 there is considerable resist- 
 ance due to the small size 
 or excessive length of the 
 discharge ducts. 
 
 General Proportions. 
 The general form of a fan 
 wheel is shown in Fig. 141, 
 which represents a single 
 spider wheel with curved 
 blades. Those over- 4 feet 
 in diameter usually have 
 two spiders, while fans of 
 large size are often pro- 
 vided with three or more. 
 The number of floats or 
 blades commonly varies 
 from six to twelve, depending upon the diameter of the fan. They 
 are made both curved and straight; the former, it is claimed, run 
 more quietly, but, if curved too much, will not work so well against 
 a high pressure as the latter form. 
 
 The relative proportions of a fan wheel vary somewhat in the 
 case of different makes. The following are averages taken from fans 
 of different sizes as made by several well-known manufacturers for 
 general ventilating and similar work: 
 
 Width of fan at center = Diameter X .52 
 
 Width of fan at perimeter = Width at center X -8 
 
 Diameter of inlet = Diameter of wheel X .68 
 
 Fig. 143. Centrifugal Fan with Casing. 
 
 357
 
 HEATING AND VENTILATION 
 
 Fig. 144. Combined Heater and Centrifugal Fan with Direct-Connected Engine. 
 
 
 Fig. 145. Centrifugal Fan in "Three-Quarter Housing." Used where Headroom is 
 Limited; Extra Space Provided by Pit under Floor-Level. 
 
 358
 
 HEATING AND VENTILATION . 
 
 163 
 
 Fans are made both with double and with single inlets, the 
 former being called blowers and the latter exhausters. The size of 
 a fan is commonly expressed in inches, which means the approximate 
 height of the casing of a full-housed fan. The diameter of the wheel 
 is usually expressed in feet, and can be found in any given case by 
 dividing the size in inches by 20. For example, a 120-inch fan has a 
 wheel 120 -r- 20 = 6 feet in diameter. 
 
 Fig. 146. "Cone" Fan. 
 
 Discharges through Opening in Wall into a " 
 Connecting with Distributing Ducts. 
 
 Plenum Chamber" 
 
 Theory of Centrifugal Fans. The action of a fan is affected 
 to such an extent by the various conditions under which it operates, 
 that it is impossible to give fixed rules for determining the exact 
 results to be expected in any particular instance. This being the 
 case, it seems best to take up the matter briefly from a theoretical 
 
 359
 
 164 
 
 HEATING AND VENTILATION 
 
 standpoint, and then show what corrections are necessary in the 
 case of a given fan under actual working conditions. 
 
 There are various methods for determining the capacity of a 
 fan at different speeds, and the power necessary to drive it; each 
 manufacturer has his own formula? for this purpose, based upon 
 tests of his own particular fans. The methods given here apply 
 in a general way to fans having proportions which represent the 
 average of several standard makes; and the results obtained will be 
 
 Fi^'. 147. Small, Direct-Connected Exhauster for Ventilating Toilet-Rooms, Chemical 
 Hoods, etc. 
 
 found to correspond well with those obtained in practice under 
 ordinary conditions. 
 
 As already stated, the rotation of a fan of this type sets in motion 
 the air between the blades, which, by the action of centrifugal force, 
 is delivered at the periphery of the wheel into the casing surrounding 
 it. As the velocity of flow through the discharge outlet depends 
 upon the pressure or head within the casing, and this in turn upon 
 the velocity of the blades, it becomes necessary to examine briefly 
 into the relations existing between these quantities.
 
 HEATING AND VENTILATION 
 
 165 
 
 Pressure. The pressure referred to in connection with a fan, 
 is that in the discharge outlet, and represents the force which drives 
 the air through the ducts and flues. The greater the pressure with a 
 given resistance in the pipes, the greater will be the volume of air 
 delivered; and the greater the resistance, the greater the pressure 
 required to deliver a given quantity. 
 
 The pressure within a fan casing is caused by the air being 
 thrown from the tips of the blades, and varies with the velocity of 
 rotation; that is, the higher the speed of the fan, the greater will be 
 the pressure produced. Where the dimensions of a fan and casing 
 are properly proportioned, the velocity of air-flow through the outlet 
 will be the same as that of the tips of the blades, and the pressure 
 within the casing will be that corresponding to this velocity. 
 
 Table XXXIII gives the necessary speed for fans of different 
 diameters to produce different pressures, and also the velocity of air- 
 flow due to these pressures. 
 
 TABLE XXXIII 
 Fan Speeds, Pressures, and Velocities of Air-Flow 
 
 7. j. 
 
 
 H 
 
 Eg 
 
 ' 
 
 can 
 
 * r * s 
 
 3* 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 
 
 
 
 
 
 
 
 
 
 S> 
 
 
 
 REVOLUTIONS PER MINUTE 
 
 
 1 
 
 274 
 
 206 
 
 164 
 
 137 
 
 117 
 
 103 
 
 92 
 
 82 
 
 2,585 
 
 
 336 
 
 252 
 
 202 
 
 168 
 
 144 
 
 126 
 
 112 
 
 101 
 
 3,165 
 
 1 
 
 338 
 
 291 
 
 232 
 
 194 
 
 166 
 
 146 
 
 129 
 
 116 
 
 3,653 
 
 1 
 
 433 
 
 325 
 
 260 
 
 217 
 
 186 
 
 163 
 
 144 
 
 130 
 
 4,084 
 
 The application of this table will be made plain by a brief dis- 
 cussion .of blast area. 
 
 Blast Area. When the outlet from a fan casing is small, the air 
 will pass out with a velocity equal to that of the tips of the blades ; and 
 the pressure within the casing will be that corresponding to the 
 tip velocity. That is, a 3-foot fan wheel revolving at a speed of 274 
 revolutions per minute will produce a pressure within the fan casing 
 of I ounce per square inch, and will cause a velocity of flow through 
 the discharge outlet of 2,585 feet per minute (see Table XXXIII). 
 
 361
 
 166 HEATING AND VENTILATION 
 
 Now, if the opening be slowly increased, while the speed of the fan 
 remains constant, the air will continue to flow with the same velocity 
 until a certain area of outlet is reached. If the outlet be still further 
 increased, the pressure in the casing will begin to drop, and the 
 velocity of outflow become less than the tip velocity. The effective 
 area of outlet at the point when this change begins to take place, is 
 called the blast area or capacity area of the fan. This varies some- 
 what with different types and makes of fans; but for the common 
 form of blower, it is approximately of the projected area of the fan 
 
 opening at the periphery that is, - , in which D is the diameter 
 
 of the fan wheel, and w its width at the periphery. It has already 
 been stated under "General Proportions" that W = . 52 D, and w = .8 
 
 D X .8 IF Dx -8X -5279 
 
 \\ ; so that we may write A = - = .14 D~, 
 
 o o 
 
 in which A = the blast area, and D the diameter of the fan. 
 
 As a matter of fact, the outlet of a fan casing is always made 
 larger than the blast area; and the result is that the pressure drops 
 below that due to the tip velocity, and the velocity of flow through 
 the outlet becomes less than that given in the last column of Table 
 XXXIII for any 'given speed of fan. 
 
 Effective Area of Outlet. The size of discharge outlet varies 
 somewhat for different makes; but for a large number of fans ex- 
 amined it was found to average about 2.22 times the blast area 
 as computed by the above method. When air or a liquid flows 
 through an orifice, the stream is more or less contracted, depending 
 upon the form of the orifice. 
 
 In the case of a fan outlet, the effective area may be taken as about 
 .X of the actual area. This makes the effective area of a fan outlet 
 equal to .8 X 2.22 = 1.78 times the blast area. 
 
 Table XXXIV gives the effective areas of fans of different 
 diameter as computed by the above method. That is, Effective 
 area - .147J 2 X 1.78 = .25Z) 2 . 
 
 Speed. We have seen that when the discharge outlet is made 
 larger than the blast area, the pressure within the fan casing drops 
 below that due to the tip velocity; so that, in order to bring the pres- 
 sure up to its original point, the speed of the fan must be increased 
 above that given in Table XXXIII. 
 
 362
 
 EXCELSIOR PATTERN RADIATOR USED IN THE INDIRECT METHOD 
 OF WARMING 
 
 American Radiator Company 
 
 METHOD OF INDIRECT WARMING AND VENTILATION, SHOWING ROTARY 
 CIRCULATION OF AIR 
 
 American Radiator Company
 
 HEATING AND VENTILATION 167 
 
 TABLE XXXIV 
 Effective Areas of Fans 
 
 
 EFFECTIVE AREA OF OUTLET, IN 
 
 
 SQUARE FEET 
 
 3 
 
 2.3 
 
 4 
 
 4.0 ' 
 
 5 
 
 6.3 
 
 6 
 
 9.1 
 
 7 
 
 12.3 
 
 8 
 
 16.0 
 
 9 
 
 20.4 
 
 10 
 
 25.2 
 
 Tests upon a fan of practically "the same proportions as those 
 previously given, show that, when the effective outlet area is made 
 1 . 78 the blast area, the speed must be increased 1 . 2 times in order 
 to keep the pressure at the same point as when the outlet is equal 
 to or less than the blast area. 
 
 Capacity. The capacity of a fan is the volume of air discharged 
 in a given time, and is usually expressed in cubic feet per minute. 
 It is equal to the effective area of discharge multiplied by the velocity 
 of flow through it. 
 
 Example. At what speed must a 6-foot fan be run to maintain a pres- 
 sure of J ounce, and what volume of air will be delivered per minute? 
 
 From Table XXXIII we find that a 6-foot fan must run at a 
 speed of 194 revolutions per minute to maintain the given pressure 
 when the outlet is equal to the blast area, or 194 X 1 .2 = 233 revo- 
 lutions per minute under actual conditions. The velocity of flow 
 through the outlet at \ ounce pressure, is 3,653 feet per minute (Table 
 XXXIIJ) ; and the effective area of outlet of a 6-foot fan is 9 . 1 square 
 feet (Table XXXIV). Therefore the volume of air delivered per 
 minute is equal to 9.1 X 3,653 - 33,242 cubic feet. 
 
 Example. It is desired to move 52,000 cubic feet of air per 
 minute at a pressure of \ ounce. What size and speed of fan will 
 be required? Looking in Table XXXIII, we find that the velocity 
 through the fan outlet for ^-ounce pressure is 2,585, which calls for 
 an outlet area of 52,000 -^- 2,585 = 20.1 square feet. Looking in 
 Table XXXIV, we find this corresponds very nearly to a 9-foot fan, 
 which is the size called for. Referring again to Table XXXIII, the 
 speed necessary to maintain the required pressure under the given 
 conditions is found to be 92 X 1 .2 = 110 revolutions per minute.
 
 If.S HEATING AXD VENTILATION 
 
 Effect of Resistance. Thus far it has been assumed that the 
 fan was discharging into the open air against atmospheric pressure. 
 The effect of adding a resistance by connecting it with a series of 
 ventilating ducts, is the same as partially closing the discharge outlet. 
 Carefully conducted tests upon this type of fan have shown that the 
 reduction of air-flow is very nearly in proportion to the reduction 
 of the discharge area. That is, if the outlet of the fan is closed to 
 one-half its original area, the quantity of air discharged will be prac- 
 tically one-half that delivered by the fan with a free opening. The 
 effect of attaching a fan to the ventilating flues of a building like a 
 schoolhouse, church, or hall, where the ducts have easy bends and 
 where the velocity of air-flow through them is not over 1,000 to 1,200 
 feet per minute, is about the same as reducing the outlet 20 per cent. 
 For factories with deep heaters and smaller ducts, where the velocity 
 runs up to 1,500 or 1,800 feet per minute, the effect is equivalent to 
 closing the outlet at least 30 per cent, and even more in very large 
 buildings. 
 
 For schoolhouses and similar work a fan should not be run much 
 above the speed necessary to maintain a pressure of ounce at the 
 outlet. Higher speeds are accompanied with greater expenditure of 
 power, and are likely to produce a roaring noise or to cause vibration. 
 A much lower speed does not provide sufficient pressure to give proper 
 control of the air-distribution during strong winds. For factories, 
 a higher pressure of J to :] ounce is more generally employed. 
 
 Actually the pressure is increased slightly by restricting the out- 
 let at constant speed ; but this is seldom taken into account in venti- 
 lating work, as volume, speed, and power are the quantities sought. 
 
 E.rinnjilc. A school building requires 32.000 cubic feet of air per min- 
 ute. What size and speed of fan will be required? 
 
 If the resistance of the ducts and flues, is equivalent to cutting 
 down the discharge outlet 20 per cent, we must make the computa- 
 tions for a fan which will discharge 32,000 -r- .8 = 40,000 cubic feet 
 in free air. 
 
 Looking in Table XXXIII, we find the velocity for f-ounce 
 pressure to be 3,165 feet per minute; therefore the size of fan outlet 
 must be 40,000 -r 3,105 = 12.6 square feet, which, from Table 
 XXXIV, we find corresponds very nearly to a 7-foot fan. 
 
 364
 
 HEATING AND VENTILATION 169 
 
 Referring again to Table XXXIII, the required speed is found 
 to be 144 X 1.2 = 173 revolutions per minute. 
 
 Example. A factory requires 21,000 cubic feet of air per minute for 
 wanning and ventilating. What size and speed of fan will be required? 
 
 21,000 -f- .7 = 30,000, the volume to provide for with a fan 
 discharging into free air. Assuming a pressure of f ounce, the veloc- 
 ity will be 4,084 feet per minute, from which the area of outlet is 
 found to be 30,000 H- 4,084 = 7. 3- square feet. This, we find, does 
 not correspond to any of the sizes given in Table XXXIV. As 
 standard fans are not usually made in half-sizes above 5 feet, we 
 shall use a 5-foot fan and run it at a higher speed. 
 
 A 5-foot fan has an outlet area of 6 . 3 square feet, and at f-ounce 
 pressure it would deliver 6 . 3 X 4,084 = 25,729 cubic feet of air per 
 minute, at a speed of 260 X 1.2 = 312 revolutions per minute. 
 The volume of air delivered by a fan varies approximately as the 
 speed; so, in order to bring the volume up to the required 30,000, the 
 speed must be increased by the ratio 30,000 -r 25,729 - 1.16, 
 making the final speed 312 X 1.16 = 362 revolutions per minute. 
 In the same way, a 6-foot fan could have been used and run at a 
 proportionally lower speed. 
 
 Power Required. The work done by a fan in moving air .is 
 represented by the pressure exerted, multiplied by the distance through 
 which it acts. 
 
 Table XXXV gives the horse-power required for moving the 
 air which will flow through each square foot of the effective outlet 
 area, under different pressures. 
 
 This table gives only the power necessary for moving the air, 
 and does not take into consideration the friction of the air in passing 
 through the fan, nor that of the fan itself. 
 
 The efficiency of a fan varies with the speed, the size of outlet, 
 and the pressure against which the fan is working. Under favorable 
 conditions, with properly proportioned fans, we may count on an 
 efficiency of about .35. 
 
 Example. What horse-power will be required to drive an 8-foot fan at 
 such a speed as to maintain a pressure of ounce? 
 
 An 8-foot fan has an 6utlet area of 16 square feet (Table XXXIV) ; 
 and from Table XXXV we find that .5 horse-power is required to 
 move the air which will flow through each square foot of outlet under 
 
 365
 
 170 HEATING AND VENTILATION 
 
 TABLE XXXV 
 
 Power Required for Moving Air under Different Pressures 
 
 
 HORSE-POWER FOR MOVING AlR WHICH WILL 
 FLOW THROUGH E.A.CH SQUARE FOOT OF 
 
 EFFECTIVE OUTLET AREA 
 
 
 1 
 
 .18 
 .33 
 .50 
 
 .70 
 
 ^-ounce pressure. Therefore the power required to move the air 
 alone is 10 X .5 = 8, and the total horse-power is 8 -=- .35 = 23. 
 
 Effect of Resistance. In the above case, it is assumed that the 
 fan is discharging into free air. If a resistance is added, the effect 
 is the same as partially closing the outlet, and the volume of air 
 moved and the horse-power required are both reduced in very nearly 
 the same proportion. This reduction, as already stated, may be 
 taken as 20 per cent for schoolhouse and similar work, and 30 per 
 cent for factories. 
 
 For example, if the fan just considered was to be used for venti- 
 lating a schoolhouse, delivering air under a pressure of } ounce, the 
 necessary horse-power would be 'only 23 X .8 = 18.4. If used for 
 a factory, delivering air under a pressure rf ounce, the required 
 
 horse-power would be ^~-~~~ X -7 = 22.3. 
 
 General Rules. The methods above described may be briefly 
 expressed as follows: 
 CAPACITY Q = A X r X F, in which 
 Q = Cubic feet of air per minute: 
 A = Effective area of fan outlet (Table XXXIV); 
 ? = Velocity of flow through outlet; 
 
 (3,165 (j-ounce pressure)-for schoolhouses, etc.; 
 (4,084 (ij -ounce pressure) for factories; 
 p _ j -8 for schoolhouses, etc.; 
 
 | .7 for factories. 
 
 SPEED Take the speed from Table XXXIII, corresponding to the given 
 pressure and size of fan, and multiply by 1.2. 
 
 HOUSE-POWER H.P. = - 1 x P x F in whieh 
 .3o 
 
 H.P. = Horse-power; 
 
 A = Effective area of fan outlet; 
 
 p = Horse-power to move air which will flow through 1 square foot of fan 
 outlet under given pressure (Table XXXV);
 
 HEATING AND VENTILATION . 171 
 
 _ j .33 for schoolhouses, etc.; 
 
 j .7 for factories. 
 _._ j .8 for schoolhouses, etc.;' 
 ~ 1 -7 for factories. 
 
 EXAMPLES 
 
 1. A schoolhouse requires an air-supply of 30,000 cubic feet 
 per minute. What will be the required size of fan, its speed, and 
 the H. P. of engine to drive it? f 7 ft. in diameter. 
 
 Axs. 173 r. p. m. 
 [9 H.P. 
 
 2. What will be the size and speed of fan, and horse-power of 
 engine, to heat and ventilate a factory requiring 1,080,000 cubic feet 
 of air per hour? f6ft. in diameter. 
 
 ANS. j 260 r. p. m. 
 
 [8.8 H.P. 
 
 General Relations. The following general relations between the 
 volume, pressure, and power will often be found useful in deciding 
 upon the size of a fan: 
 
 (1) The volume of air delivered varies directly as the speed of the fan; 
 that is, doubling the number of revolutions doubles the volume of air de- 
 livered. 
 
 (2) The pressure varies as the square of the speed. For example, if 
 the speed is doubled, the pressure is increased 2X2 = 4 times; etc. 
 
 (3) The power required to run* the fan varies as the cube of the speed. 
 Thus, if the speed is doubled, the power required is increased 2X2X2 = 8 
 times; etc. 
 
 The value of a knowledge of these relations may be illustrated 
 by the following example: 
 
 Suppose for any reason it were desired to double the volume of 
 air delivered by a certain fan. At first thought we might decide to 
 use the same fan and run it twice as fast; but when we come to con- 
 sider the power required, we should find that this would have to be 
 increased 8 times, and it would probably be much cheaper in the 
 long run to put in a larger fan and run it at lower speed. 
 
 Disc or Propeller Fans. When air is to be moved against a very 
 slight resistance, as in the case of exhaust ventilation, the disc or pro- 
 peller type of wheel may be used. This is shown in different forms 
 in Figs. 149 and 150. This type of fan is light in construction, re- 
 quires but little power ai low speeds, and is easily erected. It may be 
 
 367
 
 172 
 
 HEATING AND VENTILATION 
 
 conveniently placed in the attic or upper story of a building, where 
 it may be driven either by a direct- or belt-connected electric motor. 
 Fig. 148 shows a fan equipped with a direct-connected motor, and 
 Fig. 151 the general arrangement when a belted motor is used. These 
 fans are largely used for the ventilation of toilet and smoking rooms, 
 restaurants, etc., and are usually mounted in a wall opening, as shown 
 in Fig. 151. A damper should always be provided for shutting off 
 the opening when the fan is not in use. The fans shown in Figs. 149 
 and 150 are provided with pulleys for belt connection. 
 
 Propeller Fan Direct-Connected to Moti 
 
 Fans of this kind are often connected with the main vent flues 
 of large buildings, such as schools, halls, churches, theaters, etc., 
 and are especially adapted for use in connection with gravity heating 
 systems. They are usually run by electric motors, and as a rule are 
 placed in positions where an engine could not be connected and also 
 in buildings where steam pressure is not available. 
 
 Capacity of Disc Fans. The capacity of a disc fan varies greatly 
 with the type and the conditions under which it operates. The rated 
 
 368
 
 HEATING AND VENTILATION 
 
 173 
 
 capacities usually given in catalogues are for fans revolving in free 
 air that is, mounted in an opening without being connected with 
 ducts or subjected to other frictional resistance. 
 
 As the capacity and necessary power are so dependent upon the 
 resistance to be overcome, it is difficult to give definite rules for 
 determining them. The following data, based upon actual tests. 
 
 . 149. Another Form of Propeller Fan, with Special Type of Blade. 
 
 apply to fans working against a resistance such as would be 
 produced by connecting with a system of ducts of medium length 
 through which the air was drawn at a velocity not greater than 600 
 or 800 feet per minute. Under these conditions, a good type of fan 
 will propel the air in a direction parallel to the shaft a distance equal to 
 about . 7 of its diameter at each revolution ; and from this we have 
 the equation : 
 
 369
 
 174 
 
 HEATING AND VENTILATION 
 
 Q = .7 D X R X A, 
 
 Q Cubic feet of air discharged per minute; 
 
 D = Diameter of fan, in feet ; 
 
 7? = Revolutions per minute; 
 
 A = Area of fan, in square feet. 
 In order to obtain the 
 best results, the linear velocity 
 />f air-flow through the fan 
 should range from 800 to 1 ,200 
 feet per minute. 
 
 Table XXXVI gives the 
 revolutions per minute for 
 fans of different diameter to 
 produce a linear velocity of 
 1,000 feet, the volume deliv- 
 ered at this speed, and the 
 horse-power required . 
 
 The horse-power is com- 
 puted by allowing .14 II. P. 
 for each 1,000 cubic feet of 
 air moved, when the velocity 
 through the fan is 800 feet 
 per minute; .10 II. P. for 
 1,000 feet velocity; and .1811. P. for 1,200 feet velocity. These 
 factors are empirical, and based on tests. 
 
 Fig. 150. Propeller Fan with Wheel on Shaft 
 for Belt Connection. 
 
 Fan Belt-Connected to Motor. 
 
 Example. Assuming a velocity of 800 feet per minute through a 4-foot 
 fan, what volume will be delivered per minute, and what speed and horse- 
 power will be required ? 
 
 370
 
 HEATING AND VENTILATION 
 
 175 
 
 TABLE XXXVI 
 Disc Fans, their Capacity, Speed, etc. 
 
 DIA. OF FAN, IN 
 INCHES 
 
 REV. PER MIN. 
 
 CUBIC FEET OF AIR 
 MOVED 
 
 HORSE-POWER 
 REQUIRED 
 
 18 
 
 952 
 
 1,700 
 
 .27 
 
 24 
 
 . 716 
 
 3,100 
 
 .50 
 
 30 
 
 572 
 
 4,900 
 
 .78 
 
 '36 
 
 476 
 
 7,100 
 
 1.2 
 
 42 
 
 408 
 
 9,400 
 
 1.5 
 
 48 
 
 343 
 
 12,000 
 
 1.9 
 
 54 
 
 317 
 
 15,800 
 
 2.5 
 
 60 
 
 286 
 
 19,400 
 
 3.1 
 
 72 
 
 238 
 
 28,300 
 
 4.5 
 
 The area of a 4-foot fan is 12.5 square feet; and at 800 velocity 
 the volume would be 12.5 X 800 - 10,000 cubic feet. Next solve 
 for the speed by the equation Q = .ID X R X A, which, when 
 transposed, takes the form 
 
 ;?- Q 
 
 ~ .1 D X A 
 
 Substituting the known quantities, we have: 
 
 _ 10,000 _ 
 ~.7X4X 12.5 ~ 
 
 The horse-power is 10 X .14 = 1.4. 
 
 Fan Engines. A simple, quiet-running engine is desirable 
 for use in connection with a fan or blower. The engine may be either 
 horizontal or vertical; and for schoolhouse and similar work, should 
 be provided with a large cylinder, so that the required power may 
 be developed without carrying a boiler pressure much above 30 
 pounds. In some cases, cylinders of such size are used that a boiler 
 pressure of 12 or 15 pounds is sufficient. The quantity of steam 
 which an engine consumes is of minor importance, as the exhaust can 
 be turned into the coils and used for heating purposes. If space 
 allows, the engine should always be belted to the fan. Where it is 
 direct-connected, as in Fig. 144, there is likely to be trouble from 
 noise, as any slight looseness or pounding in the engine will be com- 
 municated to the air-ducts, and the sound will be carried to the rooms 
 
 371
 
 17(5 
 
 HEATING AND VENTILATION 
 
 above. Figs. 152 and 153 show common forms of fan engines. The 
 latter is especially adapted to this purpose, as all bearings are enclosed 
 
 Fig. 152 A Common Form of Fan Engine. 
 
 and protected from dust and grit. A horizontal engine for fan use 
 is shown in Fig. 154. 
 
 In case an engine is belted, the distance between the shafts of 
 the fan and engine should not in general be much less than 10 feet 
 
 372
 
 HEATING AND VENTILATION 
 
 177 
 
 for fans up to 7 or 8 feet in diameter, and 12 feet for those of larger 
 size. When possible, the tight or driving side of the belt should 
 be at the bottom, so that the loose side, coming' on top, will tend to 
 wrap around the pulleys and so increase the arc of contact. 
 
 Motors. Electric motors are especially adapted for use in 
 connection with fans. This method of driving is more expensive 
 
 Fig. 153. Another Form of Fan Engine, with Bearings Enclosed to Protect Them 
 from Dust and Grit. 
 
 than by the use of an engine, especially if electricity must be pur- 
 chased from outside parties; but if the building contains its own 
 power plant, so that the exhaust steam can be utilized for heating, 
 the convenience and simplicity of motor-driven fans often more than 
 offset the additional cost of operation. 
 
 373
 
 178 
 
 HEATING AND VENTILATION 
 
 Direct-connected motors are always preferable to belted, if a 
 direct current is available, on account of greater quietness of action. 
 This is due both to the slower speed of the motor and to the absence 
 of belts. 
 
 Sufficient speed regulation can be obtained with direct -connected 
 machines, without excessive waste of energy, by the use of a rheostat. 
 
 If a direct current is not available, and an alternating current 
 must be used, the advantages of electric driving are greatly reduced, 
 as high-speed motors with belts must be employed, and, further- 
 more, satisfactory speed regulation is not easily attainable. 
 
 Fig. 154. Horizontal Engine for Fan Use. 
 
 Area of Ducts and Flues. \Vith the blower type of fan, the size 
 of the main ducts may be based on a velocity of 1,200 to 1,500 feet per 
 minute; the branches, on a velocity of 1,000 to 1,200 feet per minute, 
 and as low as GOO to SOO feet when the pipes are small. Flue veloci- 
 ties of 500 to 700 feet per minute may be used, although the lower 
 velocity is preferable. The size of the inlet register should be such 
 that the velocity of the entering air will not exceed about 300 feet per 
 minute. The velocity between the inlet windows and the fan. or 
 heater should not exceed about 800 feet. 
 
 The air-ducts and flues are usually made of galvanized iron, the 
 
 374
 
 HEATING AND VENTILATION 
 
 179 
 
 ducts being run at the basement ceiling. No. 20 and No. 22 iron 
 is used for the larger sizes, and No. 24 to No. 28 for the smaller. 
 
 Regulating dampers should 
 be placed in the branches lead- * 
 ing to each flue, for increasing or 
 reducing the air-supply to the 
 different rooms. Adjustable de- 
 flectors are often placed at the 
 fork of a pipe- for the same pur- 
 pose. One of these is shown in 
 Fig. 155. 
 
 Fig. 156 illustrates a com- 
 mon arrangement of fan and 
 heater where the type of heater Fig . 155 . Adjustable Deflector Placed at Fork 
 shown in Fig, 138 is used; and of pipe to Regulate Air-s upP i y . 
 
 Fig. 157 is a self-contained apparatus in which the heater is inclosed 
 
 in a steel casing. ' 
 
 Factory Heating. The application of forced blast for the 
 
 warming of factories and 
 shops, is shown in Figs. 
 158 and 159. The pro- 
 portional heating surface 
 in this case is generally 
 expressed in the 'number 
 of cubic feet in the 
 building for each linear 
 foot of 1-inch steam 
 pipe in the heater. On 
 this basis, in factory 
 practice, with all of the 
 air taken from out of 
 doors, there are generally 
 allowed from 100 to 150 
 cubic feet of space per 
 
 Fig. 156. Common Arrangement of Fan with Heater foot of P^P 6 ' according as 
 
 of Type Shown in Fig. 138. exhaust or live steam 
 
 is used, live steam in this case indicating steam of about 80 
 pounds pressure. If practically all the air is returned from the 
 
 375
 
 180 
 
 HEATING AND VENTILATION 
 
 buildings to the heater, these figures may be raised to about 140 as a 
 minimum, and possibly 200 as a maximum, per foot of pipe. The 
 
 heaters in Table XXXI may be changed to linear feet of 1 inch pipe 
 by multiplying the numbers in column three (suuare feet of surface) 
 bv three. 
 
 376
 
 HEATING AND VENTILATION 
 
 181 
 
 EXAMPLES FOR PRACTICE 
 
 1. A machine shop 100 feet long by 50 feet wide and having 3 
 stories, each 10 feet high, is to be warmed by forced blast, using 
 
 Pig. 158. Illustrating Application of Forced Blast for Warming a Factory. 
 
 exhaust steam in the heater. The air is to be returned to the heater 
 from the building, and the whole amount contained in the building 
 is to pass through the heater every 15 minutes. What size of blower 
 
 377
 
 182 
 
 HEATING AND VENTILATION 
 
 will be required, and what will be the H. P. of the engine required to 
 run it? How many linear feet of 1-inch pipe should the heater con- 
 tain? 
 
 J 4-foot blower. 
 Axs. -j 6 H. P. engine. 
 
 [ 1,071 feet of pipe. 
 
 Fig. 159. Centrifugal Blower Producing Forced Blast for Heating a Shop. 
 
 2. Find the size of blower, engine, and heater for a factory 
 200 feet long, 60 feet wide, and having 4 stories, each 10 feet high, 
 using live steam at 80 pounds pressure in the heater, and changing 
 the air every 20 minutes by taking in cold air from out of doors. 
 
 f 6-foot blower. 
 Axs. \ 13 H. P. engine. 
 
 [3,200 feet of pipe. 
 
 378
 
 UTTLE GIANT BOILER AS INSTALLED FOR FIRE DEPARTMENT SERVICE 
 
 Pierce, Butler & Pierce Mfg. Co.
 
 HEATING AND VENTILATION 
 
 183 
 
 In using this method of computation, judgment must be employed, 
 which can come only from experience. The figures given are for 
 average conditions of construction and exposure. 
 
 Double=Duct System. The varying exposures of the rooms of 
 a school or other building similarly occupied, require that more heat 
 shall be supplied to some than to others. Rooms that are on the 
 south side of the building and exposed to the sun, may perhaps be 
 kept perfectly comfortable with a supply of heat that will maintain 
 a temperature of only 50 or 60 degrees in rooms on the opposite side 
 of the building which are exposed to high winds and shut off from the 
 warmth of the sun. 
 
 Fig. 
 
 Hot-Blast Apparatus with Double Duct for Supplying Air at Different Temper- 
 atures to Different Parts of a Building. 
 
 With a constant and equal air-supply to each room, it is evident 
 that the temperature must be directly proportional to the cooling 
 surfaces and exposure, and that no building of this character can be 
 properly heated and ventilated if the temperature cannot be varied 
 without affecting the air-supply. 
 
 There are two methods of overcoming this difficulty: 
 The older arrangement consists in heating the air by means of a 
 primary coil at or near the fan, to about 60 degrees, or to the minimum 
 temperature required within the building. From the coil it passes 
 to the bases of the various flues, and is there still further heated as 
 required, by secondary or supplementary heaters placed at the base of 
 each flue. 
 
 379
 
 HEATING AND VENTILATION 
 
 183 
 
 In using this method of computation, judgment must be employed, 
 which can come only from experience. The figures given are for 
 average conditions of construction and exposure. 
 
 Double=Duct System. The varying exposures of the rooms of 
 a school or other building similarly occupied, require that more heat 
 shall be supplied to some than to others. Rooms that are on the 
 south side of the building and exposed to the sun, may perhaps be 
 kept perfectly comfortable with a supply of heat that will maintain 
 a temperature of only 50 or 60 degrees in rooms on the opposite side 
 of the building which are exposed to high winds and shut off from the 
 warmth of the sun. 
 
 Fig. 160. Hot-Blast Apparatus with Double Duct for Supplying Air at Different Temper- 
 atures to Different Parts of a Building. 
 
 With a constant and equal air-supply to each room, it is evident 
 that the temperature must be directly proportional to the cooling 
 surfaces and exposure, and that no building of this character can be 
 properly heated and ventilated if the temperature cannot be varied 
 without affecting the air-supply. 
 
 There are two methods of overcoming this difficulty: 
 The older arrangement consists in heating the air by means of a 
 primary coil at or near the fan, to about 60 degrees, or to the minimum 
 temperature required within the building. From the coil it passes 
 to the bases of the various flues, and is there still further heated as 
 required, by secondary or supplementary heaters placed at the base of 
 each flue. 
 
 379
 
 184 
 
 HEATING AND VENTILATION 
 
 With the second and more recent method, a single heater is 
 employed, and all the air is heated to the maximum required to 
 maintain the desired temperature in the most exposed rooms, while 
 the temperature of the other rooms is regulated by mixing with the 
 hot air a sufficient volume of cold air at the bases of the different flues. 
 This result is best accomplished by designing a hot-blast apparatus 
 
 so that the air shall be 
 forced, rather than drawn 
 through the heater, and 
 by providing a by-pass 
 through which it may 
 be discharged without 
 passing across the heated 
 pipes. 
 
 The passage for the 
 cool air is usually above 
 and separate from the 
 heater pipes, as shown in 
 Fig. 160. Extending 
 from the apparatus is a 
 double system of ducts, 
 usually of galvanized 
 iron, suspended from the 
 ceiling. At the base of 
 each fine is placed a mix- 
 ing damper, which is 
 controlled by a chain 
 from the room above, 
 and so designed as to 
 admit either a full vol- 
 
 
 Fig. 161. 
 
 Mixing Damper for Regulating Temperature 1lrnp o f 
 of Air Supplied by Double Duct System. 
 
 pj r n f,,]l 
 all > a ] 
 
 volume of cool or 
 
 tempered air, or to mix them in any desired proportion without affect- 
 ing the resulting total volume delivered to the room. A damper o 
 this form is shown in Fig. 161. 
 
 Fig. 162 shows an arrangement of disc fan and heater where the 
 air is first drawn through a tempering coil, then a portion of it forced 
 through a second heater and into the warm-air pipes, while the remain- 
 
 380
 
 HEATING AND VENTILATION 
 
 185 
 
 dor is by-passed under the heater into the cold-air pipes. Mixing 
 
 dampers are placed at the bases of the flues as already described, to 
 regulate the temperature in different rooms. 
 
 381
 
 1S6 HEATING AND VENTILATION 
 
 ELECTRIC HEATING 
 
 Unless electricity is produced at a very low cost, it is not com- 
 mercially practicable for heating residences or large buildings. The 
 electric heater, however, has quite a wide field of application in heating 
 small offices, bathrooms, electric cars, etc. It is a convenient method 
 of warming rooms on cold mornings in late spring and early fall, 
 when furnace or steam heat is not at hand. It has the special advan- 
 tage of being instantly available, and the amount of heat can be regu- 
 lated at will. The heaters are perfectly clean, do not vitiate the air, 
 and are portable. 
 
 Electric Heat and Energy. The commercial unit for electricity 
 is one watt for one hour, and is equal to 3.41 B. T. V. Electricity is^ 
 usually sold on the basis of 1,000 watt-hours (called Kilowatt-hours), 
 
 Fig. 163. Electric Car-Heater. 
 
 which is equivalent to 3,410 B. T. V. A watt is the product obtained 
 by multiplying a current of 1 ampere by an electromotive force of 1 
 volt. 
 
 From the above we see that the B. T. U. required per hour for 
 warming, divided by 3,410, will give the kilowatt-hours necessary for 
 supplying the required amount of heat. 
 
 Construction of Electric Heaters. Heat is obtained from the 
 electric current by placing a greater or less resistance in its path. 
 Various forms of heaters have been employed. Some of the simplest 
 consist merely of coils or loops of iron wire, arranged in parallel rows, 
 so that the current can be passed through as many coils as are needed 
 to provide the required amount of heat. In other forms, the heating 
 material is surrounded with fire-clay, enamel, or asbestos, and in some 
 cases the material itself has been such as to give considerable resist- 
 ance to the current. A form of electric car-heater is shown in Fig. 163. 
 Forms of radiators are shown in Figs. 164 and 165. 
 
 382
 
 HEATING AND VENTILATION 
 
 187 
 
 Calculation of Electric Heaters. The formula for the calcu- 
 lation of electric heaters is 
 
 H -P Rt x .24, . 
 
 in which 
 
 H = Heat, in calorics; 
 7 = Current, in amperes; 
 R = Resistance, in ohms; 
 t = Time, in seconds. 
 Examples. What resistance must an 
 electric heater have, to give off 6,000 B. 
 T. U. per hour, with a current of 20 am- 
 peres ? Fig. 164. Electric Radiator. 
 
 We have learned that 1 B. T. U. = 252 calories; so, in the 
 present case, 6,000 X 252 = 1,512,000 calories must be provided. 
 Substituting the known values in the formula, we have 
 
 1,512,000 = 20-' X R X 3,600 X .24, 
 from which 
 
 1,512,000 
 
 * = -34^600 =4 - 3 ' hmS - 
 
 A heater having a resistance of 3 ohms is to supply 3,000 B. T. U. per 
 hour. What current will be required ? 
 
 Fig. 165. Another Form of Electric Radiator. 
 
 3,000 X 252 - 756,000 calories. Substituting the known values in 
 the formula, and solving for I, we have 
 
 756,000 = P X 3 X 3,600 X .24, 
 from which 
 
 / = I/ 29L6 =17 + amperes. 
 
 Connections for Electric Heaters. The method of wiring for 
 electric heaters is essentially the same as for lights which require tin- 
 same amount of current. A constant electromotive force or voltage 
 
 383
 
 188 HEATING AND VENTILATION 
 
 is maintained in the main wire leading to the heaters. A much less 
 voltage is carried on the return wire, and the current in passing through 
 the heater from the main to the return, drops in voltage or pressure. 
 This drop provides the energy which is transformed into heat. 
 
 The principle of electric heating is much the same as that in- 
 volved in the non-gravity return system of- steam heating. In that 
 system, the pressure on the main steam pipes is that of the boiler, 
 while that on the return is much less, the reduction in pressure occur- 
 ring in the passage of the steam through the radiators; the water of 
 condensation is received into a tank, and returned to the boiler by a 
 pump. 
 
 In a system of electric heating, the main wires must be suffi- 
 ciently large to prevent a sensible reduction in voltage or pressure 
 between the generator and the heater, so that the pressure in them 
 shall be substantially that in the generator. The pressure or voltage 
 in the main return wire is also constant, but very low, and the genera- 
 tor has an office similar to that of the steam pump in the system just 
 described that is, of raising the pressure of the return current up 
 to that in the main. The power supplied to the generator can be 
 considered the same as the boiler in the first case. All the current 
 which passes from the main to the return must flow through the heater, 
 and in so doing its pressure or voltage falls from that of the main 
 to that of the return. 
 
 From the generator shown in Fig. 166, main and return wires 
 are run the same as in a two-pipe system of steam heating, and these 
 are proportioned to carry the required current without sensible drop 
 or loss of pressure. Between these wires are placed the various 
 heaters, which are arranged so that when electric connection is made 
 they draw the current from the main and discharge it into the return 
 wire. Connections are made and broken by switches, which take the 
 place of valves on steam radiators. 
 
 Cost of Electric Heating. The expense of electric heating must 
 in every case be great, unless the electricity can be supplied at an 
 exceedingly low cost. Estimated on the basis of present practice, 
 the average transformation into electricity does not account for more 
 than 4 per cent of the energy in the fuel which is burned in the furnace. 
 Although under best conditions 15 per cent has been realized, it 
 would not be safe to assume that in ordinary practice more than 5 
 
 384
 
 HEATING AND VENTILATION 
 
 1S9 
 
 per cent could be transformed into electrical energy. In heating 
 with steam, hot water, or hot air, the average amount utilized will 
 probably be about 60 per cent, so that the expense of electrical heating 
 is approximately from 12 to 15 times greater than by these methods. 
 
 TEMPERATURE REGULATORS 
 
 The principal systems of automatic temperature control now in 
 use,- consist of three essential features; First, an air-compressor, 
 reservoir, and distributing pipes; second, thermostats, which are 
 
 Fig. 166. General System of Wiring a House for Electric Heating. 
 
 placed in the rooms to be regulated; and third, special diaphragm or 
 pneumatic valves at the radiators. 
 
 The air-compressor is usually operated by water-pressure in 
 small plants and by steam in larger ones; electricity is used in some 
 cases. Fig. 167 shows a form of water compressor. It is similar 
 hi principle to a direct-acting steam pump, in which water under 
 pressure takes the place of steam. A piston in the upper cylinder 
 compresses the air, which is stored in a reservoir provided for the 
 purpose. When the pressure in the reservoir drops below a certain 
 
 385
 
 190 
 
 HEATING AND VENTILATION 
 
 point, the compressor is started automatically, and continues to 
 operate until the pressure is brought up to its working standard. 
 
 A ihermostat is simply a mechanism for opening and closing 
 one or more small valves, and is actuated by changes in the tempera- 
 
 ig. It". Air-Compressor Operated by Wa- 
 ter-Pressure. Automatically Controlled, 
 and Operating to Regulate Temperature 
 by Controlling: Radiator Valves. 
 
 Fig. 168. Thermostat Controlling Valves 
 on Radiators, and Operating through Ex- 
 pansion or Contraction of Metal Strip E. 
 
 ture of the air in which it is placed. Fig. 168 shows a thermostat 
 in which the valves are operated by the expansion and contraction 
 of the metal strip E. The degree of temperature at which it acts 
 may be adjusted by throwing the pointer at the bottom one way or 
 the other. Fig. 1G9 shows the same thermostat with its ornamental 
 
 386
 
 HEATING AND VENTILATION 
 
 191 
 
 casing in place. The thermostat shown in Fig. 170 operates on 
 a somewhat different principle. It consists of a vessel separated into 
 two chambers by a metal diaphragm. 
 One of these chambers is partially 
 filled with a liquid which will boil 
 at a temperature beiow that desired 
 in the room. The vapor of the 
 liquid 'produces considerable pres- 
 sure at the normal temperature of 
 the room, and a slight increase of 
 heat crowds the diaphragm over 
 and operates the small valves in a 
 manner similar to that of the metal 
 strip in the case just 'described. 
 
 The general form of a dia- 
 phragm valve is shown in Fig. 171. 
 These replace the usual hand-valves 
 at the radiators. They are similar 
 in construction to the ordinary 
 globe or angle valve, except that 
 the stem slides up and down in- 
 stead of being threaded and run- 
 ning in a nut. The top of the stem 
 connects with a flat plate, which 
 rests against a rubber diaphragm. 
 The valve is held open by a spring, 
 as shown, and is closed by admit- 
 ting compressed air to the space 
 above the diaphragm. 
 
 In connecting up the system, 
 small concealed pipes are carried 
 from the air-reservoir to the ther- 
 mostat, which is placed upon an 
 inside wall of the room, and from 
 there to the diaphragm valve at 
 the radiator. When the temperature of the room reaches the maxi- 
 mum point for which the thermostat is set, its action opens a small 
 valve and admits air-pressure to the diaphragm, thus closing off the 
 
 Fig. 169. Thermostat of Fig. 168 in 
 Ornamental Casing. 
 
 387
 
 102 
 
 HEATING AND VENTILATION 
 
 steam from the radiator. When the temperature falls, the thermostat 
 acts in the opposite manner,, and shuts off the air-pressure from the 
 diaphragm valve, at the same time opening a small exhaust which 
 allows the air above the diaphragm to escape. The pressure being 
 removed, the valve opens and again admits steam to the radiator. 
 
 Diaphragm Motors. Dampers are operated pneumatically in 
 a similar manner to steam valves. A diaphragm motor, so called, is 
 acted upon by the air-pressure; and this lifts a lever which is properly 
 connected to the damper by means of chains or levers, thus securing 
 the desired movement. 
 
 Dampers. When mixing- dampers are operated pneumatically, 
 a specially designed thermostat for giving a graduated movement 
 
 at Opcrat 
 
 if* through Expansion or Contraction of the Vapor 
 of a Volatile Liquid. 
 
 (o the damper should be used. By this arrangement the damper 
 is held in such a position at all times as to admit the proper proportions 
 of hot and cold or tempered air for producing the desired temperature 
 in the room with which it is connected. 
 
 Large dampers which are to be operated pneumatically, should 
 be made up in sections or louvres. Dampers constructed in this 
 manner are handled much more easily than when made in a single 
 piece. 
 
 It often happens, in large plants, that there are valves, and 
 dampers in places which are not easily reached for hand manipula- 
 tion. These may be provided with diaphragms and connected with 
 the air-pressure system for operation by hand-switches or cocks 
 
 338
 
 HEATING AND VENTILATION 
 
 19S 
 
 conveniently located at some centra/ point in the basement or boiler 
 room. 
 
 Telethermometer. This is a device for indicating on a dial 
 at some central point the temperature of various rooms or ducts in 
 different parts of a building. A special transmitter is placed in each 
 of the rooms and electrically connected with a central switchboard. 
 Then, by means of suitable switches, any room may be thrown in 
 circuit with the recorder, and the temperature existing in the room 
 at that time read from the dial. 
 
 Fig. 171. Exterior View, and Section Showing Interior Mechanism of Diaphragm Valve. 
 
 .Humidostat. The kumidostat is a device to be placed in one or 
 more rooms of a building for maintaining an even percentage of 
 moisture in the air. The apparatus consists of two essential parts 
 the humidostat and the humidifier. The former corresponds, to the 
 thermostat in a system of temperature control, and operates a pneu- 
 matic valve or other mechanism connected with the humidifier when 
 the percentage of moisture rises above or falls below certain limits. 
 The operating medium is compressed air, the same as for tempera- 
 ture control; and the two devices are usually connected with the same 
 pressure system. 
 
 389
 
 194 HEATING AND VENTILATION 
 
 The normal moisture of a room is 70 per cent, and should never 
 exceed that. In cold weather it will be necessary to reduce the 
 amount of moisture somewhat, owing to the "sweating" of walls and 
 windows. 
 
 The method of moistening the air will depend somewhat upon 
 circumstances. If the air for ventilation is delivered to the rooms at 
 a temperature not exceeding 70 degrees, the humidifier is best placed 
 in the main air-duct. ' If the air enters at a higher temperature, the 
 humidifier must be located in the same room with the humidostat. 
 
 The moistener or humidifier may be of any one of several forms. 
 "NVhere steam heating is used, and where the steam is clean and odor- 
 less and free from oil from engines, a perforated pipe (or pipes) in the 
 air-duct is the simplest and best humidifier. The outlets are properly 
 adjusted, and then the humidostat shuts off and lets on the steam 
 as required. Sometimes a water spray, particularly of warm water, 
 may be used in place of steam. "Wnen neither steam jet nor water 
 spray is advisable, an evaporating pan containing a steam coil may 
 be used, the humidostat controlling the steam to the coil, and the 
 water-level in the pan being kept constant by means of a. ball-cock. 
 
 AIR=FILTERS AND AIR=WASHERS 
 
 In cases where the air for ventilating purposes is likely to contain 
 soot or street dust, it is desirable to provide some form of filter for 
 purifying it before delivering to the rooms. If the air-quantity is 
 small and there is plenty of room between the inlet windows and 
 the fan, screens of light cheesecloth may be used for this purpose. 
 The cloth should be tacked to light but substantial wooden frames, 
 which can be easily removed for frequent cleaning. These screens are 
 usually set up in "saw-tooth" fashion in order to give as much sur- 
 face as possible in the least space. 
 
 Another arrangement, used in case of large volumes of air, 
 is to provide a number of light cloth bags of considerable length, 
 through which the air is drawn before reaching the heater. These are 
 fastened to a suitable frame or partition for holding them open. The 
 great objection to filters of this kind is their obstruction to the passage 
 of the air, especially wjien filled with dust, the frequent intervals at 
 which they should be cleaned, and the great amount of filtering sur- 
 face required. 
 
 390
 
 HKATING AND VENTILATION 
 
 195 
 
 An apparatus which is 
 coming quite generally into 
 use for this purpose, and ' 
 which does away with the 
 disadvantages noted above, 
 is the spray filter or air- 
 washer, one form of which 
 is shown in Fig. 172. Air 
 enters as indicated, and 
 first passes through a tem- 
 pering coil to raise it above 
 the freezing point in win- 
 ter weather; then passes 
 through the spray-chamber, 
 where the dirt is removed; 
 then through an eliminator 
 for removing the water; 
 and then through a second 
 heater on -its way to the 
 fan. 
 
 The water is forced 
 through the spray-heads 
 by means of a small cen- 
 trifugal pump; either belted 
 to the fan shaft or driven 
 by an independent motor. 
 
 HEATING AND 
 VENTILATION OF 
 VARIOUS CLASSES 
 OF BUILDINGS 
 
 The different methods 
 used in heating and venti- 
 lation, together with the 
 manner of computing the 
 various proportions of the 
 apparatus, having been 
 
 391
 
 196 HEATING ANT) VENTILATION 
 
 taken up, the application of these systems to the different classes 
 <;f buildings will now be considered briefly. 
 
 School Buildings. For school buildings of small size, the furnace 
 system is simple, convenient, and generally effective. Its use is con- 
 fined as a general rule to buildings having not more than six or eight 
 rooms. For large ones this method must generally give way to some 
 form of indirect steam system with one or more boilers, which occupy 
 less space, and are more easily cared for than a number of furnaces 
 scattered about in different parts of the basement. As in all systems 
 that depend on natural circulation, the supply and removal of air is 
 considerably affected by changes in the outside temperature and by 
 winds. 
 
 The furnaces used are generallv built of cast iron, this material 
 being durable, and easily made to present large and effective heating 
 surfaces. To adapt the larger sizes of house-heating furnaces to 
 schools, a much larger space must be provided between the body and 
 the casing, to permit a sufficient volume of air to pass to the rooms. 
 The free area of the air-passage should be sufficient to allow a velocity 
 of about 400 feet per minute. 
 
 The size of furnace is based on the amount of heat lost by radia- 
 tion and conduction through "walls and windows, phis that carried 
 away by air passing up the ventilating flues. These quantities may 
 be computed by the usual methods for "loss of heat by conduction 
 through walls," and "heat required for ventilation." With more 
 regular and skilful attendance, it is safe to assume a higher rate of 
 combustion in schoolhouse heaters than in those used for warming 
 residences. Allowing a maximum combustion of G pounds of coal 
 per hour per square foot of grate, and assuming that 8,000 B. T. U. 
 per pound are taken up by the air passing over the furnace, we have 
 6 X 8,000 = 48,000 B. T. U. furnished per hour per square foot of 
 grate. Therefore, if we divide the total B. T. U. required for both 
 warming and ventilation by 48,000, it will give us the necessary grate 
 surface in square feet. It has been found in practice that a furnace 
 with a firepot 32 inches in diameter, and having ample heating surface, 
 is capable of heating two 50-pupil rooms in zero weather. The sizes 
 of ducts and flues may be determined by rules already given under 
 furnace and indirect steam heating. 
 
 The velocity of the warm air within the uptake flues depends 
 
 392
 
 HEATING AND VENTILATION 19? 
 
 Upon their height and the difference in temperature between the 
 warm air within the flues and the cold air outside. The action of 
 the wind also affects the velocity of air-flow. It has been found by 
 experience that flues having sectional areas of about 6 square feet for 
 first-floor rooms, 5 square feet for the second floor, and 4\ square feet 
 for the third, will be of ample size for standard classrooms seating 
 from 40 to 50 pupils in primary and grammar schools. These sizes 
 may be used for both furnace and indirect gravity steam heating. 
 
 The vent flues may be made 5 square feet for the first floor, and 
 6 square feet for the second and third floors. They may be ar- 
 ranged in banks, and carried through the roof in the form of large 
 chimneys, or may be carried to the attic space and there gathered 
 by means of galvanized-iron ducts connecting with roof vents of 
 wood or copper construction. 
 
 In order to make the vent flues "draw" sufficiently in mild or 
 heavy weather, it is necessary to provide some means for warming 
 the air within them to a temperature somewhat above that of the 
 rooms with which they connect. This may be done by placing a 
 small stove made specially for the purpose, at the base of each flue. 
 If this is done, it is necessary to carry the air down and connect with 
 the flue just below the stove. 
 
 The cold-air supply duct to each furnace should be made f 
 the size of all the warm-air flues if free from bends, or the full 
 size if obstructed in any way. 
 
 The inlet and outlet openings from the rooms into the flues, are 
 commonly provided with grilles of iron wire having a mesh of 2 to 2 j 
 inches. Both flat and square wire are used for this purpose. Mixing 
 dampers for regulating the temperature of the rooms should be pro- 
 vided for each flue. The effectiveness of these dampers will depend 
 largely upon their construction; and they should be made tight 
 against cold-air leakage, by covering the surfaces or flanges against 
 which they close with some form of asbestos felting. Both inlet and 
 outlet gratings should be provided with adjustable dampers. One of 
 the disadvantages of this system is the delivery of all the heat to the 
 room from a single point, and this not always in a position to give the 
 best results. The outer walls are thus left unwarmed, except as the 
 heat is diffused throughout the room by air-currents. When there is 
 considerable glass surface, as in most of our modern schoolrooms, 
 
 393
 
 108 HEATING AND VENTILATION 
 
 draughts and currents of cold air arc frequently found along the out- 
 side walls. 
 
 The indirect gravity system of steam heating comes next in cost 
 of installation. Qnc important advantage of this system over furnace 
 heating comes from the ability to place the heating coils at the base 
 of the flues, thus doing away with horizontal runs of air-pipe, which 
 are required to some extent in furnace heating. The warm-air 
 currents in the flues are less affected by variations in the direction and 
 force of the wind where this construction is possible, and this is of 
 much importance in exposed locations. 
 
 The method of supplying cold air to the coils or heaters is im- 
 portant, and should be carefully worked out. The supply should be 
 taken from at least two sides of the building, or, if possible, from all 
 four sides. When it is taken from four sides, each inlet should be 
 made large enough to supply one-half the amount, or, in other words, 
 any two should give the total quantity required. It is often possible 
 to arrange the flues in groups so that all the heating stacks may be 
 placed in two or more cold-air chambers, depending upon the size 
 of the building. A cold-air trunk line may be run through the center 
 of the basement, connecting with the outside on all four sides, and 
 having branches supplying each cold-air chamber. 
 
 Cast-iron pin-radiators are particularly adapted to this class 
 of work. 
 
 The School-Pin, having a section about 10 inches in depth and 
 rated at 15 square feet of heating surface per section, is used quite 
 extensively for this purpose. Stacks containing about 240 square 
 feet of surface for southerly rooms, and 260 for those having a north- 
 erly exposure, have been found ample for ordinary conditions in zero 
 weather. 
 
 A very satisfactory arrangement is the use of indirect heaters 
 for warming the air needed for ventilation, and the placing of direct 
 radiation in the rooms for heating purposes. The general construc- 
 tion of the indirect stacks and flues may be the same; but the heating 
 surface can be reduced, as the air in this case must be raised only to 
 70 or 75 degrees in zero weather, the heat to offset that lost by con- 
 duction, etc., through walls and windows being provided by the 
 direct surface. The mixing dampers may be omitted, and the tem- 
 perature of the room regulated by opening or closing the steam valves 
 
 394
 
 
 
 DIRECT-INDIRECT METHOD OF WARMING TAKING A FRESH AIR SUPPLY 
 FROM OUTSIDE AND PASSING IT UPWARD 
 
 American Kadiator Company
 
 HEATING AND VENTILATION 199 
 
 on the direct coils, which should be done automatically. The direct- 
 heating surface, which is best made up of lines of lj-inch pipe, should 
 be placed along the outer walls beneath the windows This supplies 
 heat where most needed, and does away with the tendency to draughts. 
 In mild weather, during the spring and fall, the indirect heaters may 
 prove sufficient for both ventilation and warming. 
 
 Where direct radiation is placed in the rooms, the quantity of 
 heat supplied is not affected by varying wind conditions, as is the 
 case in indirect heating. Although the air-supply may be reduced 
 at times, the heat quantity is not changed. Direct radiation has the 
 disadvantage of a more or less unsightly appearance, and architects 
 and owners often object to the running of mains or risers through 
 the rooms of the building. Air-valves should always be provided 
 with drip connections carried to a sink or dry well in the basement. 
 
 When circulation coils are used, a good method of drainage is 
 to carry separate returns from each coil to the basement, and to place 
 the air-valves in the drops just below the basement ceiling. A check- 
 valve should be placed below the w r ater-line in each return. 
 
 The gravity system has the fault of not supplying a uniform 
 quantity of air under all conditions of outside temperature, the same 
 as a furnace, but when properly arranged, may be made to give quite 
 satisfactory results. 
 
 The fan or blower system for ventilation, w r ith direct radiation 
 in the rooms for warming, is considered to be one of the best possible 
 arrangements. 
 
 In designing a plant of this kind, the main heating coil should 
 be of sufficient size to warm the total air-supply to 70 or 75 degrees 
 in the coldest weather, and the direct surface should be proportioned 
 for heating the building independently of the indirect system. Auto- 
 matic temperature regulation should be used in connection with 
 systems of this kind, by placing pneumatic valves on the direct radia- 
 tion. It is customary to carry from 3 to 8 pounds pressure on the 
 direct system, and from 8 to 15 pounds on the main coil, depending 
 upon the outside temperature. The foot-warmers, vestibule, and 
 office heaters should be placed on a separate line of piping, with 
 separate returns and trap, so that they can be used independently 
 of the rest of the building jf desired. Where there is a large assembly 
 hall, it should be arranged so that it can be both wanned and venti- 
 
 395
 
 200 HEATING AND VENTILATION 
 
 lated when the rest of the building is shut off. This can be done by a 
 proper arrangement of valves and dampers. 
 
 When different parts of the system are run on different pressures, 
 the returns from each should discharge through separate traps into 
 a receiver having connection with the atmosphere by means of a vent 
 pipe. Fig. 173 shows a common arrangement for the return con- 
 nections in a combination system of this kind. The different traps 
 discharge into the vented receiver as shown; and the water is pumped 
 back to the boiler automatically when it rises above a given level in 
 the receiver, a pump governor being used to start and stop the pumps 
 as required. 
 
 A water-level or seal of suitable height is maintained in the main 
 returns, by placing the trap at the required elevation and bringing 
 the returns into it near the bottom ; a balance pipe is connected with 
 the top for equalizing the pressure, the same as in the case of a pump 
 governor. .Sometimes a fan is used with the heating coils placed at 
 the base of the flues, instead of in the rooms. Where this is done 
 the radiating surface may be reduced about one-half. This system 
 is less expensive to install, but has the disadvantage of removing the 
 heating surface from the cold walls, where it is most needed. 
 
 With a blower type of fan, the size of the main ducts may be 
 based on a velocity of from 1,000 to 1,200 feet per minute, and the 
 branches on a velocity of 800 to 1 ,000 feet per minute. 
 
 The velocity in the vertical flues may be from (iOO to TOO feet per 
 minute, although the lower velocity is preferable. 
 
 The size of the inlet registers should be such that the velocity 
 of the entering air will not exceed 350 to 400 feet per minute. 
 
 When the air is delivered through a register at the high velocities 
 mentioned, some means must be provided for diffusing the entering 
 current, in order to prevent disagreeable draughts. This is usually 
 accomplished by the use of deflecting blades of galvanized iron, set 
 in a vertical position and at varying angles, so that the air is thrown 
 towards each side as it issues from the register. The size of the 
 vent flues should be about the same as for a gravity system that is, 
 about 6 square feet for a standard classroom, and in the same pro- 
 portion for smaller rooms. 
 
 Vent-flue heaters are not usually required in connection with a 
 fan system, as the force of the fan is sufficient to supply the required 
 
 396
 
 HEATING AND VENTILATION 
 
 201 
 
 397
 
 202 HEATING AXI) VENTILATION 
 
 quantity of air at all times \vithout the aspirating effect of the vent 
 flues. 
 
 The method of piping shown in Fig. 173 applies especially to 
 buildings of large size. In the case of medium-sized buildings, it 
 is often possible to use pin radiation for the main heater, placing the 
 same well above the water-line of the boilers and thus returning the 
 condensation by gravity, without the use of pumps or traps. When 
 this arrangement is used, an engine with a large cylinder should be 
 employed, so that the steam pressure will not exceed 15 or 1S pounds, 
 and the whole system, including the direct surface, may be run upon 
 the same system. 
 
 This is a very simple arrangement, and is adapted to all build- 
 ings of small and medium size where the heater can be placed at a 
 sufficient height above the boilers. 
 
 Temperature control is usually secured automatically by placing 
 pneumatic valves upon either the direct or supplementary heaters. 
 Mixing dampers are sometimes used instead, in the latter case. Every 
 fan system should be provided with a thermometer of large size for 
 indicating the temperature of the air in the main duct just beyond 
 the fan. 
 
 The ventilation of the toilet-rooms of a school building is a 
 matter of the greatest importance. The first requirement is that the 
 air-movement shall be into these rooms from the corridors instead of 
 outward. To obtain this result, it is necessary to produce a slight 
 vacuum within, and this cannot well be done if fresh air is forced 
 into them. 
 
 One of the most satisfactory arrangements is to provide exhaust 
 ventilation only, and to remove the greater part of the air through 
 local vents connecting with the fixtures. * 
 
 Hospitals. The best system for heating and ventilating a hos- 
 pital depends upon the character and arrangement of the buildings. 
 It is desirable in all cases to do the heating from a central plant, 
 rather than to carry fires in the separate buildings, both on account 
 of economy and for cleanliness. 
 
 In the case of small cottage hospitals with two or three buildings 
 placed close together, indirect hot water affords a desirable system for 
 the wards, with direct heat for the other rooms ; but where there are 
 several buildings, and especially if they are some distance apart, it 
 
 398
 
 HEATING AND VENTILATION 203 
 
 becomes necessary to substitute steam unless the water is pumped 
 through the mains. For large city buildings, a fan system is always 
 desirable. 
 
 If the building is tall compared with its ground area, so that 
 the horizontal supply ducts will be comparatively short, the double- 
 duct system may be used with good results. Where the rooms are 
 of good size, and the number of supply flues not great, the use of 
 supplementary heaters at the bases of the flues makes a satisfactory 
 arrangement. Direct radiation should never be used in the wards 
 when it can be avoided, even in connection with an independent air- 
 supply, as it offers too great an opportunity for the accumulation of 
 dust in places which are difficult to reach. 
 
 It is common to provide from 80 to 100 cubic feet of air per 
 minute per patient in ordinary wards, and from 100 to 120 cubic feet 
 in contagious wards. 
 
 The usjial ward building of a modern cottage-hospital generally 
 contains a main ward having from 8 to 12 beds, and a number of 
 private rooms of one bed each. 
 
 In addition to these, there are a diet kitchen, duty-room, toilet- 
 rooms, bathrooms, linen-closets, and lockers. 
 
 For moderately sheltered locations, 30 square feet of 'indirect 
 steam radiation has been found sufficient in zero weather for a single 
 ward with one exposed wall and a single window, when upon the 
 south side of the building. 
 
 For northerly rooms, 40 square feet should be used. In exposed 
 locations, the heaters may be made 40 and 50 square feet for north 
 and south rooms respectively. The standard pin-radiators rated at 
 10 square feet of heating surface per section, are commonly used for 
 this purpose. In case hot water is used, the same number of sections 
 of the deep-pin pattern rated at 15 square feet each may be employed, 
 making a total of 45 and 60 square feet per room. For corner rooms 
 having two exposed walls and two windows, the amount of radiation 
 should be increased about 50 per cent over that given above. 
 
 The wards are usually furnished with fireplaces which provide 
 for the discharge ventilation. In case the fireplaces are omitted, a 
 special vent flue, either of brick or of galvanized iron, should be pro- 
 vided. These should not be less than 8 by 12 inches for single wards, 
 and the equivalent for each bed in a large ward. Each flue of this 
 
 399
 
 204 HEATING AND VENTILATION 
 
 kind should have a loop of steam pipe for producing a draught. A 
 loop of 1-inch pipe, 10 or 12 feet in height, is usually sufficient for 
 this purpose. 
 
 Other rooms than wards are usually heated with direct radia- 
 tors, the sizes of which may he computed in the same manner as for 
 dwelling-houses. 
 
 Steam tables for the kitchen, sterilizers, and laundry machinery, 
 require higher pressures than is necessary for heating. 
 
 In large plants the boilers are usually run at high pressure, and 
 the pressure reduced for heating. A good arrangement for small 
 plants is to provide sufficient boiler power for warming and ventilating 
 purposes, and run at a pressure of 3 to 5 pounds. In addition to 
 this, a small high-pressure boiler carrying 70 or SO pounds should be 
 furnished for laundry work and water heating. 
 
 Churches. Churches may be warmed by furnaces, by indirect 
 .steam, or by means of a fan. For small buildings the furnace is 
 more commonly used. This apparatus is the simplest of all and is 
 comparatively inexpensive. Heat may be generated quickly, and 
 when the fires are no longer needed, they may be allowed to go out 
 without danger of damage to any part of the system from freezing. 
 
 It is not usually necessary that the heating apparatus be large 
 enough to warm the entire building at one time to 70 degrees with 
 frequent change of air. If the building is thoroughly warmed before 
 occupancy, either by rotation or by a slow inward movement of 
 outside air, the chapel or Sunday-school room may be shut off until 
 near the close of the service in the auditorium, when a portion of the 
 warm air may be turned into it. When the service ends, the switch- 
 damper is opened wide, and all the air is discharged into the Sunday- 
 school room. The position of the warm-air registers will depend 
 somewhat upon the construction of the building, but it is well to keep 
 them near the outer walls and the colder parts of the room. Large 
 inlet registers should be placed in the floor near the entrance doors, 
 to stop cold draughts from blowing up the aisles when the doors are 
 opened, and also to be used as foot-warmers. 
 
 Ceiling ventilators are generally provided, but should be no 
 larger than is necessary to remove the products of combustion from 
 the gaslights, etc. If too large, much of the warmest and purest 
 air will escape through them. The main vent flues should be placed 
 
 400
 
 HEATING AND VENTILATION 205 
 
 in or near the floor and should be connected with a vent shaft leading 
 outboard. This flue should be provided with a small stove or flue 
 heater made specially for this purpose. In cold weather the natural 
 draught will be found sufficient in most cases. 
 
 The same general rules are to be followed in the case of 
 indirect steam as have been described for furnace heating. The 
 stacks are placed beneath the registers or flues, and mixing dampers 
 provided. If there are large windows, flues should be arranged to 
 open .in the window-sills, so that a sheet of warm air may be delivered 
 in front of the windows, to counteract the effects of cold down-draughts 
 from the exposed glass. These flues may usually be made 3 or 4 
 inches in depth, and should extend the entire width of the window. 
 Small rooms, such as vestibules, library, pastor's room, etc., are usually 
 heated with direct radiators. Rooms which are used during the 
 week are often connected with an independent heater so that they 
 may be warmed without running the large boilers, as would otherwise 
 be necessary. 
 
 When a fan is used, it is desirable, if possible, to deliver the air 
 to the auditorium through a large number of small openings. This 
 is often done by constructing a shallow box under each pew, running 
 its entire length, and connecting it with the distributing ducts or a 
 plenum space by means of a pipe from below. The air is delivered 
 at a low velocity through a long slot, as shown in Fig. 174. 
 
 The warm-air flues in the window-sills should be retained, but 
 may be made shallower, and the air forced in at a high velocity. 
 
 If the auditorium has a sloping floor, a plenum space may be 
 provided between the upper or raised portion and the main floor. 
 Sometimes a shallow basement 3 or 4 feet in height, with a cemented 
 floor, and extending under the entire auditorium, is used as an air 
 or plenum space. 
 
 If the basement is of good height and used for storage or other 
 purposes, it is necessary to carry galvanized-iron ducts at the ceiling 
 under the center of each double row of pews, and to connect \vith 
 each pair by means of branch uptakes. The size of these should 
 be equal to 3 or 4 square inches for each occupant. 
 
 Another method is to supply the air through a small register in 
 the end of each pew. This simplifies the pew construction some- 
 what, but otherwise is not so satisfactory as the preceding method. 
 
 401
 
 206 
 
 HEATING AND VENTILATION 
 
 If the special pew construction is too expensive, or for any othei 
 reason cannot well be used, and the fan is to be retained, the greater 
 part of the air is best introduced through wall registers placed about 
 8 feet above the floor, with exhaust openings at or near the floor. 
 By this arrangement the air is thrown horizontally toward the center 
 of the church, and much of it falls to the breathing level without 
 rising to the upper part of the room. 
 
 Halls. The treatment of a large audience hall is similar to that 
 of a church, the warming being usually done in one of the three ways 
 already described. Where a fan is used, the air is commonly delivered 
 
 through wall registers placed in 
 part near the floor, and partly at a 
 height of 7 or 8 feet above it. They 
 should be made of ample size, 
 so that there will be freedom from 
 draughts. A part of the vents 
 should be placed in the ceiling, 
 and the remainder near the floor. 
 All ceiling vents, in both halls and 
 churches, should be provided with 
 dampers having means for hold- 
 ing them in any desired position. 
 If indirect gravity heaters are 
 used, it will generally be necessary 
 to place heating coils in the vent 
 flues for use in mild weather; but 
 if the fresh air is supplied by 
 means of a fan, there will usually be 
 
 pressure enough in the room to force the air out without the aid of 
 other means. "When the vent air-ways are restricted, or the air is 
 impeded in any way, electric ventilating fans are often used. These 
 give especially good results in warmer weather, when natural venti- 
 lation is sluggish. The temperature may be regulated either by 
 using the double-duct system or by shutting off or turning on a greater 
 or less number of sections in the main heater. After an audience 
 hall is once warmed and filled with people, very little heat is required 
 to keep it comfortable, even in the coldest weather. 
 
 Theaters. In designing heating and ventilating systems for 
 
 Fig. 174. An Approved Method of De- 
 livering Warm Air to the Audi- 
 torium of a Church. 
 
 402
 
 HEATING AND VENTILATION 207 
 
 theaters, a wide experience and the greatest care are necessary to 
 secure the best results. A theater consists of three parts: the body 
 of the house, or auditorium; the stage and dressing-rooms, and the 
 foyer, lobbies, corridors, stairways, and offices. Theaters are usually 
 located in cities, and surrounded with other buildings on two or more 
 sides, thus allowing no direct connection by windows with the ex- 
 ternal air; for this reason artificial means are necessary for providing 
 suitable ventilation, and a forced circulation by means of a fan is the 
 only satisfactory means of accomplishing this. It is usually advisable 
 to create a slight excess of pressure in the auditorium, in order that 
 all openings shall allow for the discharge rather than the inward 
 leakage of air. 
 
 The general and most approved method of air-distribution is 
 to force it into closed spaces beneath the auditorium and balcony 
 floors, and allow it to discharge upward through small openings 
 among the seats. One of the best methods is through chair-legs 
 of special latticed design, which are placed over suitable openings in 
 the floor; in this way the air is delivered to the room in small streams, 
 at a low velocity, without draughts or currents. The discharge 
 ventilation should be largely through ceiling vents, and this may be 
 assisted if necessary by the use of ventilating fans. Vent openings 
 should also be provided at the rear of the balconies, either in the wall 
 or in the ceiling, and these should be connected with an exhaust fan 
 either in the basement or in the attic, as is most convenient. 
 
 The close seating of the occupants produces a large amount of 
 animal heat, which usually increases the temperature from 6 to 10 
 degrees, or even more; so that, in considering a theater once filled 
 and thoroughly warmed, it becomes more of a question of cooling 
 than one of warming to produce comfort. 
 
 The dressing-rooms should be provided with a generous supply 
 of fresh air, sufficient to change the entire contents once in 10 minutes 
 at least, and should have discharge flues of sufficient size to carry 
 awa^r this amount of air at a velocity not exceeding 300 feet per 
 minute, unless connected with an exhaust fan, in which case the 
 velocity may be doubled. The foyer, corridors, dressing-rooms, 
 etc., are generally heated by direct radiators, which may be con- 
 cealed by ornamental screens if desired. 
 
 Office Buildings. This class of buildings may be satisfactorily 
 
 403
 
 20$ HEATING AND VENTILATION 
 
 wanned by direct steam, hot water, or, where ventilation is desired, 
 by the fan system. Probably direct steam is used more frequently 
 than any other system for this purpose. Vacuum systems are well 
 adapted to the conditions usually found in this type of building, 
 as most modern office buildings have their own light and power 
 plants, and the exhaust steam can thus be utilized for heating pur- 
 poses. The piping may be either single or double. If the former 
 is used, it is better to carry a single main riser to the upper story, and 
 run drops to the basement, as by this means the steam and water 
 flow in the same direction, and much smaller pipes can be used than 
 would be the case if risers were carried from the basement upward. 
 
 Special provision must be made for the expansion of the risers or 
 drops in tall buildings. They are usually anchored at the center, 
 and allowed to expand in both directions. The connections with the 
 radiators must not be so rigid as to cause undue strains or to lift the 
 radiators from the floor. 
 
 It is customary, in most cases, to make the connections with 
 the end farthest from the riser; this gives a length of horizontal pipe 
 which has a certain amount of spring, and will care for any vertical 
 movement of the riser that is likely to occur. Forced hot-water 
 circulation is often used in connection with exhaust steam. The 
 water is warmed by the steam in large heaters similar to feed-water 
 heaters and is circulated through the system by means of centrifugal 
 pumps. This has the usual advantage of hot water over steam, 
 inasmuch as the temperature of the radiators may be regulated to 
 suit the conditions of outside temperature. 
 
 When a fan system is used the arrangement of the air-ways is 
 usually somewhat different from any of those yet described. Owing 
 to the great height of these buildings, and the large number of small 
 rooms which they contain, it is impossible to carry up separate flues 
 from the basement. One of the best arrangements is to construct 
 false ceilings in the corridor-ways on each floor, thus forming air- 
 ducts which may receive their supply through one or more large up- 
 takes extending from the basement to the top of the building. These 
 corridor air-ways may be tapped over the door of each room, the 
 openings being provided with suitable regulating dampers for gauging 
 the air-supply to each. Adjustable deflectors should be placed in 
 the main air-shafts for proportioning the quantity to be delivered 
 
 404
 
 HEATING AND VENTILATION 209 
 
 to each floor. If both supply and discharge ventilation are to be 
 provided, the fresh air may be carried in galvanized-iron ducts within 
 the ceiling spaces, and the remainder used for conveying the exhausted 
 air to uptakes leading to a discharge fan placed upon the roof of 
 the building. In both of these cases, it is assumed that heat is sup- 
 plied to the rooms by direct radiation, and that the air-supply is for 
 ventilation only. 
 
 Apartment Houses. These are warmed by furnaces, direct 
 steam, and hot water. Furnaces are more often used in the smaller 
 houses, as they are cheaper to install, and require a less skilful at- 
 tendant to operate them. Steam is probably used more than any 
 other system in blocks of larger size. A well-designed single-pipe 
 connection, with autcmatic air-valves dripped to the basement, is 
 probably the most satisfactory in this class of work. People who 
 are more or less unfamiliar with steam systems are apt to overlook 
 one of the valves in shutting off or turning on steam ; and where only 
 one valve is used, the difficulty arising from this is avoided. Where 
 pet-cock air-valves are used, they are often left open through careless- 
 ness ; and the automatic valves, unless dripped, are likely to give more 
 or less trouble. 
 
 Greenhouses and Conservatories. Buildings of this class are 
 heated in some cases by steam and in others by hot water, some florists 
 preferring one and some the other. Either system, when properly 
 designed and constructed, should give satisfaction, although hot 
 water has its usual advantage of a variable temperature. The 
 methods of piping are, in a general w r ay, like those already described, 
 and the pipes may be located to run underneath the beds of growing 
 plants or above, as bottom or top heat is desired. The main is gen- 
 erally run near the upper part of the greenhouse and to the farthest 
 extremity, in one or more branches, with a pitch upward from the 
 heater for hot water and with a pitch downward for steam. The 
 principal radiating surface is made of parallel lines of H inch or 
 larger pipe, placed under the benches and supplied by the return 
 current. Figs. 175, 176, and 177 show a common method of running 
 the piping in greenhouse work. Fig. 175 shows a plan and eleva- 
 tion of the building with its lines of pipe; and Figs. 176 and 177 give 
 details of the pipe connections of the outer and inner groups of pipes 
 respectively. 
 
 405
 
 210 
 
 HEATING AND VENTILATION 
 
 Any system of piping which gives free circulation and which is 
 adapted to the local conditions, should give satisfactory results. The 
 radiating surface may be computed from the rules already given. 
 As the average greenhouse is composed almost entirely of glass, we 
 
 Fig. 175. Plan and Elevation Showing One Method of Running Piping in a Greenhouse 
 
 may for purposes of calculation consider it such; and if we divide 
 the total exposed surface by 4, we shall get practically the same 
 result as if we assumed a heat loss of 85 B. T. U. per square foot of 
 surface per hour, and an efficiency of 330 B. T. U. for the heating 
 
 408
 
 HEATING AND VENTILATION 211 
 
 coils; so that we may say, in general, that the square feet of radiating 
 surface required equals the total exposed surface, divided by 4 for 
 steam coils, and by 2.5 for hot-water. These results should be in- 
 creased from 10 to 20 per cent for exposed locations. 
 
 CARE AND MANAGEMENT 
 
 The care of furnaces, hot-water heaters, and steam boilers has 
 been discussed in connection with the design of these different systems 
 of heating, and need not be repeated. The management of the 
 heating and ventilating systems in large school buildings is a matter 
 of much importance, especially in those using a fan system. To obtain 
 the best results, as much depends upon the skill of the operating 
 engineer as upon that of the designer. 
 
 Beginning in the boiler-room, he should exercise special care 
 in the management of his fires, and the instruction given in "Boiler 
 Accessories" should be carefully followed; all flues and smoke 
 passages should be kept clear and free from accumulations of soot 
 and ashes by means of a brush or steam jet. Pumps and engine should 
 be kept clean and in perfect adjustment, and extra care should be 
 taken when they are in rooms through which the air-supply is drawn,, 
 or the odor of oil will be carried to the rooms. All steam traps should 
 be examined at regular intervals to se'e that they are in working order; 
 and upon any sign of trouble, they should be taken apart and care- 
 fully cleaned. 
 
 The air-valves on all direct and indirect radiators should be 
 inspected often; and upon the failure of any room to heat properly, 
 the air-valve should first be looked to as a probable cause of the diffi- 
 culty. Adjusting dampers should be placed in the base of each flue, 
 so that the flow to each room may be regulated independently. In 
 starting up a new plant, the system should be put in proper balance 
 by a suitable adjustment of these dampers; and, when once adjusted, 
 they should be marked, and left in these positions. The temperature 
 of the rooms should never be regulated by closing the inlet registers. 
 These should never be touched unless the room is to be unused for 
 a day or more. 
 
 In designing a fan system, provision should be made for air- 
 rotation; that is, the arrangement should be such that the same 
 air may be taken from the building and passed through the fan and 
 
 407
 
 212 HEATING AND VENTILATION 
 
 Fig. 176. Connections of Outer Groups of Pipes of Greenhouse Shown in Fig. 175. 
 
 Fig. 177. Connections of Inner Groups of Pipes of Greenhouse Shown in Fig. 175. 
 
 408
 
 HEATING AND VENTILATION 213 
 
 heater continuously. This is usually accomplished by closing the 
 main vent flues and the cold-air inlet to the building, then opening the 
 class-room doors into the corridor-ways, and drawing the air down 
 the stair-wells to the basement and into the space back of the main 
 heater through doors provided for this purpose. In warming up a 
 building in the morning, this should always be done until about 
 fifteen minutes before school opens. The vent flues should then be 
 opened, doors into corridors closed, cold-air inlets opened wide, and 
 the full volume of fresh air taken from out of doors. 
 
 At night time the dampers in the main vents should be closed, 
 to prevent the warm air contained in the building from escaping. 
 The fresh air should be delivered to the rooms at a temperature of 
 from 70 to 75 degrees; and this temperature must be obtained by 
 proper use of the shut-off valves, thus running a greater or less number 
 of sections on the main heater. A little experience will show the 
 engineer how many sections to carry for different degrees of outside 
 temperature. A dial thermometer should be placed in the main 
 warm-air duct near the fan, so that the temperature of the air delivered 
 to the rooms can be easily noted. 
 
 The exhaust steam from the engine and pumps should be turned 
 into the main heater; this will supply a greater number of sections 
 in mild weather than in cold, owing to the less rapid con- 
 densation. 
 
 409
 
 PLUMBING. 
 
 PART I. 
 
 PLUMBING FIXTURES. 
 
 Bath Tubs. There are many varieties of bath tubs in use at 
 the present time, ranging from the wooden box lined with zinc or 
 copper which was in common use a number of years ago and is 
 still to be found in the old houses, to the finest crockery and 
 enameled tubs which are now used in the best modern plumbing. 
 In selecting a tub we should choose one with as little woodwork 
 about it as possible. Those lined with zinc or copper are hard to 
 keep clean and are liable to leak and are, therefore, undesirable 
 from a sanitary standpoint. The plain cast iron tub, painted, is 
 the next in cost. This makes a serviceable and satisfactory tub if 
 
 Fig. 1. 
 
 kept painted ; it is used quite extensively in asylums, hospitals, 
 etc. One of this type is shown in Fig. 1. These are sometimes 
 galvanized instead of being painted. 
 
 The "steel-clad" tub shown in Fig. 2 is a good form for a 
 low-priced article. This tub is formed of sheet steel and has a 
 lining of copper. This form is light and easy to handle ; it is an 
 open fixture the same as the cast iron tub and requires no casing. 
 It is provided with cast iron legs and a wooden cap. Probably 
 the most common form to be found in the average house at the 
 present time is the porcelain lined iron tub as shown in Fig. 3. 
 
 411
 
 I 
 
 PLUMBING. 
 
 This has a smooth interior finish and is easily kept clean. It will 
 not, however, stand the hard usage of those above described as 
 the lining is likely to crack if struck by any hard substance. 
 
 In Fig. 4 is shown a crockery or porcelain tub arranged for 
 needle and shower baths. This is a most sanitary article in every 
 respect and requires no woodwork of any kind; being made of one 
 
 Fig. 2. 
 
 piece, there is no chance for dirt to collect, it is a heavy tub anci 
 requires great care in handling. This material is very cold to the 
 touch until it has become thoroughly warmed by the hot water. 
 Fig. 5 shows a seat bath and Fig. 6 a foot bath, both of which are 
 
 Fig. 3. 
 
 very convenient and should be placed in all well equipped bath 
 rooms if the expense does not prohibit their use. 
 
 Water Closets. There is a great variety of water closets 
 from which to choose, many operating upon the same principle 
 but varying slightly in form and finish. The best are made of 
 
 412
 
 PLUMBING. 
 
 porcelain, the bowl and trap being in one piece without corners or 
 crevices so that they are easily kept clean, The top of the bowl 
 is provided with a wooden rim and cover. The general arrange- 
 ment of seat and flushing tank is shown in Fig. 7. A section 
 through the bowl is shown in Fig. 8. This type is known as a 
 
 Fig. 4. 
 
 syphon closet, and those made on this principle are probably the 
 most satisfactory of-any in present use. They are made in differ- 
 ent forms by various manufacturers but each involves the prin- 
 ciple which gives it its name. Water stands in the bottom as 
 ihown, thus forming a seal against gases from the sewer. 
 
 413
 
 6 
 
 PLUMBING. 
 
 When the closet is flushed, water rushes down the pipe and fills 
 the small chamber at the rear which discharges in a' jet at the 
 bottom as shown by the arrow. The syphon action thus set up 
 draws the entire contents of the bowl over into the soil pipe. In 
 the meantime a part of the water from the tank fills the hollow 
 rim of the bowl and is discharged in a thin stream around the 
 
 Fig. 5. 
 
 
 Fig. 7. 
 
 entire perimeter which thoroughly washes the inside of the bowl 
 each time it is flushed. Fig. 9 shows a form called the "wash- 
 out" closet. In this case the whole of the water is discharged 
 through the flushing rim but with greater force at the rear which 
 washes the contents of the upper bowl into the lower which over- 
 flows into the soil pipe. This is a good form of closet and is 
 widely used. A similar form, but without the upper bowl is 
 
 414
 
 PLUMBING. 
 
 shown in Fig. 10. This is known as the "wash down" closet 
 and operates in the manner already described. The water enters 
 the bowl through the flushing rim and discharges its contents by 
 
 Fig. 8. 
 
 Fig. 9. 
 
 overflowing into the soil pipe. This is a simple form of closet 
 and easily kept clean. 
 
 One of the simplest closets is the "hopper" shown in Fig. 11. 
 This consists of a plain bowl of porcelain or cast iron tapering to 
 
 Fig. 10. 
 
 Fig. 11. 
 
 an outlet about 4" in diameter at the bottom. It is connected 
 directly with the soil pipe as shown. The trap may be placed 
 either above the floor or below as desired. They are provided 
 with a flushing rim at the top similar to that already described. 
 This type of closet is the cheapest but at the same time the least 
 satisfactory of any of the different kinds shown. 
 
 415
 
 PLUMBING. 
 
 It is sometimes desirable to place a closet in a location where 
 there would be danger of freezing if the usual form of flushing 
 tank was used. Fig. 12 shows an arrangement which may bs 
 used in a case of this kind. The valve and water connections are 
 placed below the frost line and a pipe not shown in the cut is 
 carried up to the rim of the bowl. Whenthe rim is shutdown the 
 
 Fig. 12. 
 
 valve is opened by means of the chain attached to it and water 
 flows through the bowl while in use. When released, the weight 
 on the lever closes the valve and raises the wooden rim to its 
 original position. Any water which remains in the flush pipe is 
 drained to the soil pipe through a small drip pipe which is seen in 
 the cut. 
 
 Urinals. A common form of urinal is shown in Fig. 13. 
 The partitions and slab at the back are either of slate or marble 
 and the bowl of porcelain. They may be flushed like a closet. 
 Fig. 14 shows a section through the bowl and indicates the 
 
 416
 
 PLUMBING. 
 
 manner of flushing, partly through the rim and partly at the back. 
 The trap or seal is shown at the bottom. Another form is shown 
 in Fig. 15. In. this case the bowl remains partly filled with 
 water which forms a seal as shown. It is flushed both through 
 the rim and the passage at the back. In action it is the same as 
 the syphon closet shown in Fig. 8 and the bowl is drained each 
 
 Fig. 13. 
 
 Fig. 14. 
 
 time it is flushed, but immediately fills with water to the level 
 indicated. 
 
 An automatic flushing device is illustrated in Fig. 16. When 
 the water line in the tank reaches a given level, the float lever 
 releases a catch and flushes the urinal. The intervals of flushing 
 can be regulated by adjusting the cock shown in the inlet pipe, 
 near the bottom of the tank. 
 
 A simple form of urinal commonly used in schools and public 
 buildings is shown in Fig. 17. This is flushed by means of 
 
 417
 
 10 
 
 PLUMBING. 
 
 small streams of water which are dis- 
 charged through the perforated pipe 
 near the top of the slab at the back 
 and run down in a thin sheet to the 
 gutter at the bottom. 
 
 Lavatories. Bowls and lava- 
 tories can be had in almost any form. 
 Fig. 18 shows a simple corner lava- 
 tory, made of porcelain and provided 
 
 Fig. 17. 
 
 16. 
 
 with hot a n d 
 cold water fau- 
 cets. It has an 
 overflow, shown 
 by the s in a 1 1 
 openings at the 
 back and a rub- 
 ber plug for clos- 
 ing the drain at 
 the bottom. 
 
 The lavatory 
 shown in Fig. 
 
 19 is provided 
 wi t h in a rb ie 
 slabs and is more 
 expensive. Fig. 
 
 20 shows a sec- 
 tion through the 
 b o w 1 . T h e 
 waste pipe is at 
 the back, which 
 
 418
 
 PLUMBING. 
 
 11 
 
 brings the plug and chain well out of the way. A pattern still 
 more elaborate is shown in Fig. 21, and a section through the 
 bowl in Fig. 22. The waste pipe plug in this case is in the 
 form of a hollow tube and acts as an overflow when closed and 
 as a strainer when open. It is held open by means of a slot and 
 
 Fig. 18. 
 
 Fig. 19. 
 
 pin near the top. Fig. 23 shows a bowl so arranged that either 
 hot, cold or tepid water may be drawn through the same opening 
 which is placed well down in the bowl where it is out of the way. 
 
 Fig. 20. 
 
 Sinks. Sinks are made of plain wood, and of wood lined 
 with sheet metal, such as copper, zinc or galvanized iron. They 
 are also made of sheet steel, cast iron, either plain, galvanized or 
 enameled, and of soapstone and porcelain. Each has its advan- 
 tages and disadvantages. The wooden sink is liable to leak, 
 
 419
 
 12 
 
 PLUMBING. 
 
 and is difficult to 
 keep thoroughly 
 clean. The lined 
 sink is most satis- 
 factory when new, 
 but holes are quite 
 easily cut or 
 punched through 
 the lining and it 
 then becomes very 
 objectionable from 
 a sanitary stand- 
 point as the greasy 
 water and vege- 
 table matter which 
 works through the 
 opening causes the 
 woodwork to decay 
 rapidly and to give 
 off in the process 
 a gas which is not 
 only unhealthful but 
 the underside so that 
 
 Fig. 21. 
 
 tends to destroy the lining of the sink from 
 its destruction is rapid after a leak is once 
 started. The cast 
 iron sink is satisfac- 
 tory. The appearance 
 is improved by galvan- 
 izing, but this soon 
 wears off on the in- 
 side. Enameled 
 sinks are easily kept 
 clean but likely to 
 become cracked or 
 broken from hard 
 usage or from ex- 
 tremes of hot or cold ; 
 
 22 the porcelain sink has 
 
 the same defects; 
 
 420
 
 PLUMBING. 
 
 18 
 
 they are both however well adapted to places where they will 
 receive careful usage. 
 
 Taking all points into consideration the soapstone sink may 
 perl laps be considered the most satisfactory for all-around use. 
 
 Jt will not absorb moisture ; is not affected by the action of acids, 
 oil (.r grease will not enter the pores and it is not injured by hot 
 water nor liable to crack. 
 
 Fig. 24 shows the ordinary cast iron sink, made to be set in 
 a wooden casing ; this is not to be recommended however, and it is 
 
 Fig. 24. 
 
 much better to support them upon iron brackets or legs. Fig. 25 
 shows an enameled sink mounted in this way. A porcelain sink 
 with dish racks is shown in Fig. 26. This is a good form for a 
 pantry sink which is used only for washing cutlery, glassware, 
 
 421
 
 14 
 
 PLUMBING. 
 
 crockery, etc., and is not subjected to hard usage. A slop sink is 
 shown in Fig. 27. This, as will be noticed, is provided with an 
 extra large waste pipe and trap to prevent clogging. These sinks 
 are made of cast iron with different finishes and of porcelain. 
 
 Set tubs for laundry use are made of soapstone, slate, cast 
 
 Fig. 25. 
 
 iron (enameled or galvanized) and of porcelain. What has been 
 said in regard to kitchen sinks applies equally well in this case. 
 
 A set of enameled tubs is shown in Fig. 28. 
 
 Traps. A trap is a loop or water seal placed in a pipe to pre- 
 vent the gases from the drain or sewer from passing up through the 
 waste pipes of the fixtures into the rooms. A common form made 
 up of cast iron pipe and known as a "running trap" is shown in 
 Fig. 29. A trap of this form is placed in the main drain pipe of a 
 
 422
 
 PLUMBING. 
 
 building outside of all the connections to prevent gases from the 
 main sewer or cesspool from entering the building. A removable 
 cover is placed on top of the trap -to give access for cleaning. 
 
 The floor trap shown in section in Fig. 30 is made both of 
 brass and of lead. It is commonly used for kitchen sinks and is 
 placed on the floor just beneath the fixture. It is provided 
 with a removable trap screw or clean-out for use when it is desired 
 
 Fig. 26. 
 
 to remove grease or sediment from the interior. Fig. 31 shows a 
 common form for lavatories, which consists simply of a loop in the 
 waste pipe. These are usually made of brass and nickle plated 
 when used with open fixtures. A trap for similar purposes is 
 shown in Figs. 32 and 33. 
 
 Figs. 34 and 35 show a form known as the centrifugal trap on 
 account of the rotary or whirling motion given to the water by 
 the peculiar arrangement of the inlet and outlet. This motion 
 carries all solid particles to the outside and discharges them with 
 the water, thus keeping the trap clear of sediment. Where there 
 is likely to be a large amount of grease in the water as in the case 
 of waste from a hotel or restaurant it becomes necessary to use a 
 special form of separating trap to prevent the waste pipes from becom- 
 
 423
 
 PLUMBING. 
 
 big clogged. A grease trap designed for this purpose is shown in 
 Fig, 36. .Its action is readily seen as the fatty matter will be 
 separated, first by dropping into a large body of cold water and 
 then being driven against the center partition before an outlet can 
 be gained. The grease then rises to the surface where it cools 
 and can then be easily removed as often as necessary. 
 
 Sometimes a cellar or basement is drained into a sewer which 
 
 Tig. 27. 
 
 is liable to be filled at high tide or from other causes and a 
 special trap or check must be used to pi-event the cellar from 
 becoming flooded. Such a trap i* shown in Fig. 37. When 
 water flows in from below, the float rises, and the rubber rim 
 pressing against the valve seat prevents any passage through the 
 trap; the cut shows the valve closed by the action of high water. 
 Tanks or cisterns for flushing closets or other fixtures are 
 usually made of wood and lined with zinc or copper. These are 
 generally placed inside a finished casing. A common form is shown 
 
 424
 
 PLUMBING. 
 
 17 
 
 in Fig. 38. The arrangement of valves for supplying water to 
 the tank and for flushing the fixtures is shown in Fig. 39. The 
 large float or ball cock regulates the flow of water into the tank 
 from the street main or house tank. When the water in the tank 
 
 Fig. 28. 
 
 falls below a certain level the float drops and opens a valve, thus 
 admitting more water, and closes again when the tank is filled. 
 The closet is flushed by pulling a chain attached to the lever at 
 the right which opens the valve in the bottom of the tank and 
 admits water to the flushing pipe. In this form the valve remains 
 open only while the lever is held down by the 
 chain, the weight on the other end of the lever 
 closing the valve as soon as the chain is released. 
 Another form which is partially automatic is 
 shown in Fig. 40. When the chain is pulled 
 it raises the central valve from its seat and 
 allows the water to flow down the flush pipe 
 until the tank is nearly empty. When empty, the strong suction 
 seals the valve which remains closed until the ehain is again 
 pulled. In this type of valve a single pull of the chain is suffi- 
 cient to flush the closet without further attention. 
 
 A purely automatic flushing device is shown in Fig. 41. 
 
 Fig. 29.
 
 18 
 
 PLUMBING. 
 
 The chain in this case is attached to the rim of the seat so that 
 when it is pressed down, the valve in the compartment at the 
 bottom, connecting with the flush pipe is closed awd at the same time 
 
 Fig. 33. 
 
 communication is opened between the two compartments. When 
 the pull on the chain is released the valve connecting the flush 
 pipe is opened and the opening between the compartments closed

 
 PLUMBING. 
 
 19 
 
 Fig. 34. 
 
 Fig. 35. 
 
 427
 
 20 
 
 PLUMBING. 
 
 so that the water in the lower portion of the tank flows 
 through the flush pipe into the closet automatically, and. \vhen 
 empty no more can be admitted until the lever is again polled 
 down and the valve in the partition opened. 
 
 Fig. 37. 
 
 Faucets. There are many different forms of faucets in 
 use. The most common is the c6mpression cock shown in Fig. 
 42. This has a removable leather or asbestos seat which 
 requires renewing from time to time as it becomes worn. 
 Fig. 43 shows a similar form, in which the valve seat is 
 free to adjust itself, being held in place by a spring. Another 
 
 Fig. 38. 
 
 Fig. 39. 
 
 style often vised in hotels and other public places is the self-closing 
 faucet. These are fitted with springs in such a way that they 
 remain closed except when held open. Two different forms are 
 shown in Figs. 44 and 45. 
 
 There are various arrangements for mixing the hot and cold 
 water for bowls and bath tubs before it is discharged. This is 
 
 423
 
 PLUMBING. 
 
 21 
 
 accomplished by having both faucets connect with a common nozzle. 
 Such a device for a lavatory is shown in Fig. 46. 
 
 Fig. 40. 
 
 Fig. 41. 
 
 Fig. 42. 
 
 Fig. 48. 
 
 SOIL AND WASTE PIPES. 
 
 Cast=Iron Pipe. There are many different forms of soil pipes 
 and fittings, and one can best acquaint himself with these by 
 looking over the catalogues of different manufacturers. Figs. 47 
 and 48 show two lengths of soil pipe ; the first is the regular 
 pattern, having only one hub, and the second is a length of double- 
 hub pipe ; this can be used to good advantage where many short 
 pieces are required. 
 
 Figs. 49 to 57 show some of the principal soil pipe fittings. 
 Figs. 49, 50, 51, 52 and 53 show quarter, sixth, eighth, sixteenth 
 
 429
 
 PLUMBING. 
 
 and return bends respectively, and by the use of these almost any 
 desired angle can be obtained. Different lines of pipe may be 
 connected by means of the Y and T-Y branches shown in Figs. 
 
 Fig. 44. 
 
 Fig. 46. 
 
 54, 55, 56 and 57. The T-Y fitting, Fig. 56, is used in place of 
 the Y branch, Fig. 54, in cases where it is desired to connect two 
 pipes which run perpendicular to each other. 
 
 The double T-Y, Fig. 57, is conven- 
 ient for use in double houses where a single 
 soil pipe answers for two lines of closets. 
 Pipe Joints, Great care should be 
 given to making up the joints in a proper 
 manner, as serious results may follow any 
 defective workmanship which allows sewer 
 gas to escape into the building. In mak- 
 ing up a joint, first place the ends of the 
 pipes in position and fasten them rigidly, 
 then pack the joint with the best picked 
 oakum. In packing the oakum around 
 the hub, the first layer must be twisted into a small rope so that 
 it will drive in with ease and still not pass through to the inside 
 of the pipe where the ends join. 
 
 Fig. 
 
 430
 
 PLUMBING. 
 
 In a 4-inch pipe the packing should be about 1 inch in thick- 
 ness and calked perfectly tight so that it will hold water of itself 
 without the lead. Just before the packing is driven tightly into 
 
 Fig. 47. 
 
 Fig. 48. 
 
 Fig. 49. 
 
 Fig. 50. 
 
 Fig. 51. 
 
 Fig. 52. 
 
 Fig. 53. 
 
 Fig. 54. 
 
 the hub, the joint should be examined to see that the space around 
 the hub is the same, so that the lead will flow evenly and be of 
 the same thickness at all points, as the expansion and contraction 
 
 431
 
 24 
 
 PLUMBING. 
 
 will work an imperfect joint loose much sooner than one in which 
 the lead is of an even thickness all the way around. Only the 
 best of clean soft lead should he used for this purpose. In calking 
 in the lead after it has been poured, great care must be exercised, 
 as the pipe, if of standard grade, is easily cracked and will stand 
 but little shock from the calking chisel and hammer. 
 
 Fig. 58 shows a section through the calked joint of a cast 
 iron soil pipe. 
 
 Fig. 56. 
 
 Fig. 57. 
 
 Wrought Iron Pipe. This is used but little in connection 
 with the waste pipes except for the purpose of back venting where 
 it may be employed with screwed joints the same as in steam 
 work. It is sometimes used where only small drain pipes are 
 
 Fig. 58. 
 
 necessary, but is not desirable as it is likely to become choked 
 with rust or to be eaten through by moisture from the outside. 
 
 Brass Pipe. Brass pipe, nickle plated, is largely used for 
 connecting open fixtures, such as lavatories or bath tubs, with the 
 soil pipe. It is common to use this for the exposed portions of 
 the connections and to use lead for that part beneath the floor or 
 in partitions. The various fittings are also made of brass and 
 finished in a similar manner. 
 
 432
 
 PLUMBING. 
 
 25 
 
 Lead Pipe. For sinks, bath tubs, ]aundry tubs, etc., noth- 
 ing is better for carrying off the waste water than lead pipe, for 
 the reason that it has a smooth interior surface which offers a 
 small resistance to the flow of water, and does not easily collect 
 dirt or sediment. It can also be bent in easy curves which is an 
 advantage over fittings which make abrupt turns ; this is especi- 
 ally important in pipes of small size. 
 
 Pipe Joints. There are two. common methods of making 
 joints in lead pipe, known as the " cup joint " and the " wipe 
 joint." The first is suitable only on small pipes or very light 
 pressures. This is made by flanging the end of one of the pipes 
 and inserting the other, then filling in the flange with solder by 
 means of a soldering iron, see Fig. 59. In making this joint great 
 
 SOLDER 
 
 Fig. 59. 
 
 Fig. 60. 
 
 care should be taken that the ends of the pipes are round and fit 
 closely so there will be no chance for the solder to run through 
 inside the pipe and form obstructions for the collection of 
 sediment. 
 
 The different stages of a wipe joint are shown in Fig. 60. 
 The ends of the pipes are first cleaned and then fitted together 
 as shown in the second stage. The solder is melted in a small 
 cast iron crucible and is carefully poured on the joint or thrown 
 on with a small stick called a "spatting stick." As the solder 
 cools it becomes pasty and the joint can be worked into shape by 
 means of the stick or a soft cloth, or both, depending upon the 
 kind of joint and stage of operation. The filial shape and smooth 
 finish is given with the cloth. The ability to make a joint of this 
 kind can be attained only by practice, and printed directions are 
 
 433
 
 26 
 
 PLUMBING. 
 
 of little value as compared with observation and actual practice. 
 This is the strongest and most satisfactory joint that can be made 
 between two lead pipes or a lead and brass or copper pipe. In 
 the latter case the brass or copper should be carefully tinned as 
 far as the joint is to extend by means of a soldering iron. 
 
 Where lead waste pipes are to be connected with cast iron 
 soil pipts a brass ferule should be used. Different forms of these 
 are shown in Figs. Gl and 02. The lead pipe is wiped to the 
 finished end of the ferule while the other end is calked into the 
 hub of the cast iron pipe in the manner already described. The 
 ferule should be made heavy so as not to be injured in the proc- 
 
 F/N/S/-/ED 
 
 HUB 
 
 Fig. 61. 
 
 ess of calking. Cup joints should never be used for this 
 purpose. 
 
 Tile Pipes. Nothing but metal piping should be used inside 
 of a building, but in solid earth, starting from a point about 10 
 feet away from the cellar wall, we may use salt-glazed, vitrified, or 
 terra cotta pipe for making the connection with the main sewer. 
 This pipe is made in convenient lengths and shapes and is easily 
 handled. Various fittings are made similar in form to those 
 already described for cast iron. In laying tile pipe each piece 
 should be carefully examined to see that it is smooth, round, and 
 free from cracks. The ends should fit closely all around, and each 
 length of pipe should fit into the next the full length of the hub. 
 In making the joints nothing but the best hydraulic cement should 
 be used, and great care should be taken that this is pressed well 
 
 434
 
 PLUMBING. 27 
 
 into the space between the two pipes. All cement that works 
 .through into the interior should be carefully removed by means of 
 a swab or brush made especially for this purpose. The earth 
 should be filled in around a pipe of this kind before the cement is 
 set or else the joints are likely to crack. Fine soil should be filled 
 in around the pipe to a depth of 3 or 4 inches, and rammed down 
 solid, and the ditch may then be filled in without regard to the 
 pipe. No tile pipe should be used inside of a house or nearer 
 than about 10 feet for the reason it might not stand the pressure 
 in case a stoppage should occur in the sewer. This kind of pipe 
 is not intended to carry a pressure and when used in this way 
 is seldom entirely filled with water. Joints between iron and tile 
 piping are made with cement in the manner described for two 
 sections of tile. 
 
 Cesspools. It is often desired to install a system 'f plumb- 
 ing in a building in the country or in a village where there is no 
 system of sewerage with which to connect. In this case it becomes 
 necessary to construct a cesspool. This is always undesirable, but 
 if properly constructed and placed at a suitable distance from the 
 house and in such a position that it cannot drain into a well or 
 other source of water supply it may be used with comparative 
 safety. Especial care should be taken in the construction, and 
 when in use it should be. regularly cleaned. One form of cess- 
 pool is shown in Fig. 63. This consists of two brick chambers 
 located at some distance from the building and in a position where 
 the ground slopes away from it if possible. The larger chamber 
 has a clean-out opening in the top which should be provided with 
 an air-tight cover. An ordinary cast iron cover may be made 
 sufficiently tight by covering it over with 3 or 4 inches of earth 
 packed solidly in place. A vent pipe should be carried from the 
 top to such a height that all gases will be discharged at an eleva- 
 tion sufficient to prevent any harm. 
 
 The smaller chamber is connected with the first by means of 
 a soil pipe as shown. This chamber is arranged for absorbing the 
 liquids and for this purpose is provided with lengths of porous 
 tile radiating from the bottom as shown in the plan. The house 
 drain connects with the larger chamber, which fills to the level of 
 the overflow, .then the liquid portion of the sewage drains over 
 
 435
 
 28 
 
 PLUMBING. 
 
 into chamber No. 2 and is absorbed through the porous tile branches. 
 The solid part remains in chamber No. 1, and can be removed 
 from time to time. A suitable trap should of course be placed 
 in the house drain in the same manner as though connected with 
 a street sewer. The safety of the cesspool will depend much upon 
 its location, its general construction and care and the nature of the 
 soil. 
 
 TRAPS AND VENTS. 
 
 Traps. The best method of connecting traps, and their 
 actual value under all conditions, are matters upon which there is 
 
 Fig. 63. 
 
 much difference of opinion. Cities also vary in their require- 
 ments to a greater or less extent, so that it will be possible to 
 show in a general way only the various principles involved and to 
 illustrate what is considered good practice, in the average case, at 
 the present time. 
 
 A separate trap should in general be placed in the waste pipe 
 from each fixture, although several of a kind, such as lavatories, 
 etc., are often drained through a common trap, as shown in Fig. 64. 
 
 In addition to the traps at the 'fixtures a main or running 
 trap is placed in the main soil pipe outside of all the connections; 
 
 436
 
 PLUMBING. 
 
 29 
 
 this is sometimes placed in a manhole just outside the building, 
 but more commonly in the cellar before passing through the wall ; 
 the former method is much to be preferred, as the trap may be 
 cleaned without admitting gases or odors to the house. The run- 
 ning trap has been shown in Fig. 29, and is provided with a 
 removable cap for cleaning. 
 
 The agencies which tend to destroy the water seal of traps 
 
 Fig. 04. 
 
 are siphonage, evaporation, back pressure, capillary action, leakage 
 and accumulation of sediment. 
 
 Siphonage. This can best be illustrated by a few simple 
 diagrams showing the principles involved. In Fig. 65 is shown a 
 U tube with legs of equal length and filled with water. If we 
 
 Fig. 
 
 66. 
 
 Fig. 67. 
 
 invert the tube, as shown in Fig. 66, the water will not run out, 
 because the legs are of equal length, and contain equal weights 
 of water, which pull downward from the top with the same force, 
 tending to form a vacuum at the point A. If one of the legs is 
 lengthened, as in Fig. 67, so that the column of water is heavier on 
 one side than on the other, it will run out, while atmospheric pressure 
 will force the water in the shorter tube up over the bend, as there 
 
 437
 
 30 
 
 PLUMBING. 
 
 would be no pressure to resist this action should the column of 
 water break at this point. This action is also assisted by the 
 adhesion of the particles of water to eacli other. The column of 
 water in the tube may be likened to a piece of flexible rope 
 hanging over a pulley; when equal lengths hang over each side it 
 will remain stationary, but if drawn over one 
 side slightly, so that one end is heavier than 
 the other, the whole rope will be drawn over 
 the pulley toward the longer and heavier 
 end. The first cause, due to atmospheric 
 pressure, is the principal reason for the action 
 of siphons, but the latter assists it to some 
 extent. If the shorter leg of the siphon be 
 dipped in a vessel of water, as shown in 
 Fig. 68, the atmospheric pressure, which be- 
 fore acted on the bottom of the water in the 
 tube, is' transferred to the surface of the 
 water in the vessel, and the flow through the tube will con- 
 tinue until the water level in the vessel falls slightly below the 
 end of the tube and admits air pressure, which breaks the siphon 
 
 action. Fig. 69 shows the same principle . . 
 
 applied to the trap of a sink or bowl. 
 If the bowl is well rilled with water, 
 sc that when the plug is removed from 
 the bottom, the waste pipe for some 
 distance below the trap is filled with 
 a solid column of water, a siphon action 
 will be set up like the one just de- 
 scribed, and the trap will be drained. 
 Frequently a sufficient amount of water 
 runs down from the fixture and sides of 
 the pipe above the trap to partially re- 
 store the seal. This direct action of 
 
 Fig. 68. 
 
 Fig. 69. 
 
 the water of a fixture in breaking its own trap seal by siphoning 
 is called "self-siphonage." 
 
 A more common form, where two or more fixtures connect with 
 the same waste pipe, is shown in Fig. 70. In this case the seal 
 of the lower closet is broken by the discharge of the upper. The 
 
 438
 
 PLUMBING. 
 
 falling column of water leaves behind it a partial vacuum in the 
 soil pipe, and the outer air tends to rush into the pipe through 
 the way of least resistance, which is often through the trap seals 
 of the fixtures below. The friction of the rough sides of a tall 
 soil pipe, even though it be open at the roof, will sometimes 
 cause more resistance to air flow than the trap seals of the fixtures, 
 with the result that they are broken, and 
 gases from the drain are free to enter the 
 building. 
 
 Three methods have been employed to 
 prevent the destruction of the seal by siphon- 
 age. The first method devised was what is 
 known as " back venting," and this is largely 
 in use at the present time, although careful 
 experiments have shown that in many cases 
 it is not as effective as it was at first sup- 
 posed to be, and is considered by some 
 authorities to be a useless complication. It 
 is, however, called for in the plumbing regu- 
 lations of many cities, and will be taken up 
 briefly in connection with other methods. 
 
 Back Venting. This consists in con- 
 necting a vent pipe at or near the highest 
 part of the trap, as shown in Fig. 71. The 
 action of this arrangement is evident; in 
 place of the waste pipe receiving the air 
 necessary to fill it, through the basin, after 
 the solid column of water has passed down, 
 it is drawn in through the vent pipe, as 
 shown by the arrows, and the seal remains, or should remain, 
 unbroken. It also prevents " self-siphonage " by breaking the 
 column of water and admitting atmospheric pressure at the 
 highest point or crown of the trap. The vent not only pre- 
 vents the seal from being broken, as described, but allows any 
 gases which may form in the waste pipe to escape above the roof 
 of the house. In order to be effective, the back vent should be 
 large, but even when of the same size as the waste pipe, the flush- 
 ing of a closet will oftentimes break the seal, especially if the 
 
 Fig. 70. 
 
 439
 
 32 
 
 PLUMBING. 
 
 vent pipe is of considerable length. The vent often becomes 
 choked, either with the accumulation of sediment near the trap or 
 by frost or snow at the top ; in this case its effect is of course 
 destroyed. Another disadvantage of the back vent is the hasten- 
 ing of evaporation from the trap and the unsealing of fixtures 
 which are not often used. 
 
 The second method of guarding against the loss of seal by 
 
 V 
 
 Fig. 71. 
 
 Fig. 72. 
 
 siphonage is to make the body of the trap so large that a sufficient 
 quantity of water will always adhere to its sides after siphoning 
 to restore a seal. The pot or cesspool trap shown in Fig. 72~is 
 based on this principle. 
 
 The third method consists in the use of a trap of such form 
 that it will not siphon, and will at the same time be self-cleaning. 
 Among other types the centrifugal trap, shown in Figs. 34 and 35, 
 is claimed to fulfil these conditions. The pot trap, while less 
 affected by the siphoning action, is more or less objectionable on 
 account of retaining much of the sediment and solid part of the 
 sewage which falls into it. 
 
 Local Vents. A local vent is a pipe connected directly with 
 a closet or urinal for carrying off any odor when in use. It has 
 no connection with the soil pipe, unless the trap seal becomes 
 broken, and is not provided for the purpose of carrying off gases 
 from the sewer. A urinal provided with a local vent is shown in 
 Fig. 73. 
 
 Sometimes a small register face back of the fixture, and eon- 
 
 440
 
 PLUMBING. 
 
 necting with a flue in the wall, is used in place of the regular 
 local vent. In order for a vent flue of either form to be of any 
 value, it must be warmed to insure a proper circulation 01 air 
 through it. This is done in some cases by placing a gas-jet at 
 the bottom of the flue, in others a steam or hot water pipe is 
 run through a portion of the flue, and in still others the vent 
 is carried up beside a chimney flae, from which it may receive 
 sufficient warmth to assist the circulation to some extent. 
 
 Main or Soil Pipe Vent. It 
 is customary to vent the main soil 
 pipe by carrying it through the 
 roof of the building, and leaving 
 the end open. This is shown in 
 Fig. 74. On gravel roofs which 
 drain toward the center, the soil 
 pipe is sometimes stopped on a 
 level with the roof, and serves as 
 a rain leader. In other cases the 
 roof water may be led to the soil 
 pipe in the cellar. If the latter 
 method is used, the water should 
 pass through a deep trap before 
 connecting with the drain. These 
 arrangements tend both to flush 
 out the soil pipe and "trap and 
 prevent the accumulation of sedi- 
 ment. 
 
 Fresh Air Inlets. The fresh air inlet shown just above the run- 
 ning trap Fig. 74 is to cause a circulation of air through the soil 
 pipe, as shown by the arrows. The connection should be made just 
 inside of the trap, so that the entire length of the drain will be 
 swept by the current of fresh air. It is sometimes advised to 
 extend the fresh air pipe up to the roof, because foul air may at 
 times be driven out by heavy flushing of the drain pipe, but where 
 this is done there is much less chance for circulation, as the inlet 
 and outlet are nearly on a level, and the columns of air in them 
 are more likely to be balanced. By carrying the inlet six or eight 
 feet above the ground both objections are overcome to some extent, 
 
 Fig. 73. 
 
 441
 
 PLUMBING. 
 
 unless this brings it near a window, which, of course, would not 
 be safe. The main trap does not require a back vent, for should 
 it be siphoned under ordinary conditions, it will always be filled 
 
 Fig. 74. 
 
 again within a few minutes; and if the main soil pipe is open at 
 the top and all fixtures are properly tapped, no harm would come 
 from the slight leakage of gas into the drain under these condi- 
 
 442
 
 NICKEL PLATED BRASS SHOWER BATH. 
 
 The Federal Company.
 
 PLUMBING. 35 
 
 tions, and some engineers recommend the omission of the running 
 trap. 
 
 Where a house drains into a cesspool instead of a sewer, it is 
 far more necessary that the system should be trapped against it 
 as it gives off a constant stream of the foulest gases. The usual 
 form of running trap serves to protect the house, but the cesspool 
 should have an independent vent pipe leading to some unobjection- 
 able point and carried well up above the surface of the ground. 
 
 Disposal of Sewage. In cities and towns having a system 
 of sewers, or where there is a large stream of running water near 
 by, the matter is a simple one. In the first case, the house drain 
 is merely extended to the sewer, into which it should discharge at 
 as high a point as possible, and at an acute angle with the direction 
 of flow. When the drain connects with a stream it should be 
 carried out some distance from the shore and discharge under 
 water, an opening for ventilation being provided at the bank. 
 Where there are neither sewers nor streams, the cesspool must be 
 used. When the soil is sufficiently porous the method shown in 
 Fig. 63 may be employed. Sometimes the sewage is collected in 
 a closed cistern and discharged periodically through a flush tank 
 into a series of small tiles laid to a gentle grade, from 8 to 12 
 inches below the surface. By extending these tiles over a sufficient 
 area and allowing from 40 to 70 feet of tile for each person, a 
 complete absorption of the sewage takes place by the action of the 
 atmosphere and the roots. 
 
 PIPE CONNECTIONS. 
 
 The Bath Room. There are different methods of connect- 
 ing up the fixtures in a bath room, depending upon the 
 general arrangement, type, the~kind of trap used, etc. Fig. 75 
 shows a set of fixtures connected up with vented traps. Both the 
 soil and vent pipes are carried above the roof with open ends. 
 No trap or fixture should be vented into a chimney, as is quite 
 commonly done ; this may work satisfactorily when the flues are 
 warm, but in summer time, when the fires are out, there are quite 
 likely to be down drafts, which cause the gases to be carried into 
 the vooms through stoves or fireplaces. The vent pipe, although 
 usually carried through the roof independently, is sometimes 
 
 443
 
 36 
 
 PLUMBING. 
 
 connected with the soil pipe above the highest fixture ; the soil 
 pipe is often made a larger size through the attic space and above 
 the roof in order to increase the upward tlow of air through it. 
 Fig. 76 shows a set of bath room connections in which non-siphon- 
 ing traps are used without back venting ; this is a simpler and less 
 expensive method of making the connections and is especially 
 recommended by some engineers. Its efficiency of course depends 
 upon the proper working of the traps. 
 
 Fij?. 75. 
 
 The bath room itself should be well lighted, and if possible, 
 in a location where it will receive the sun. It should be arranged 
 so that it may be heated to a higher temperature than other rooms 
 in the house if desired, and it should also be thoroughly ventilated, 
 the vent register being placed 5 or 6 feet above the floor in order 
 that it may carry off any steam which rises from the bath tub. 
 The walls, doors, etc., should be finished in a way to make them 
 as nearly waterproof as possible ; some form of good enamel paint 
 answers well for this purpose. Paper should never be used on 
 the walls, nor carpets on the floors, which should be of hard wood. 
 Where the ^xpense is not a matter of importance, glazed tile may 
 be used for the floor and walls. Means should always be provided 
 
 444
 
 PLUMBING. 
 
 for ventilating the bathroom without opening the door into the 
 
 other rooms, and the greatest care should be taken to keep not 
 
 only the fixtures, but the room itself, in the most perfect order. 
 
 Urinal Connections. The common form of urinal connection 
 
 Fig. 76. 
 
 is shown in Fig. 14. The overflow from the trap ends in a tee, 
 the lower outlet of which connects with the soil pipe and the 
 upper with the vent pipe. Where several 
 urinals are erected side by side it is usual to 
 omit the individual traps, using the direct 
 outlet connection shown in Fig. 77. These 
 connect with a common waste pipe and drain 
 through a single trap to the soil pipe. 
 
 Kitchen Sink Connections. Fig. 78 
 shows the usual method of making the con- 
 nections for a kitchen sink. The waste and 
 vent are of lead, connected with the main 
 cast-iron soil and vent pipes by means of 
 brass ferules and wiped joints. 
 
 Soil and Waste ^Pipes. The various fixtures have been 
 taken up, together with the different kinds of traps which are used 
 in connection with them, and also the general methods of making 
 the various connections for waste and vent. We will next take 
 
 Fig. 77. 
 
 445
 
 38 
 
 PLUMBING. 
 
 up some of the points in regard to the manner of running and 
 supporting 1 the different pipes, together with the proper sizes to he 
 used under different conditions. 
 
 The waste pipes of necessity contain more foul matter and 
 therefore more harmful gases than the fixtures, so that especial 
 care must be taken in their arrangement and construction. It is 
 advisable to keep all piping as simple as possible, using as few 
 connections as is consistent with the proper working of the 
 system. 
 
 The fixtures on each floor should be arranged to come directly 
 over each other, so as 
 to avoid the running of 
 horizontal pipes across or 
 between the floor beams. 
 The sizes of pipes com- 
 monly used require such 
 a sharp grade that there 
 is not sufficient space, 
 in ordinary building con- 
 struction, between the 
 floor boards and ceiling 
 lath below for horizontal 
 runs of much length. 
 One soil pipe is usually 
 sufficient for buildings 
 of ordinary size, and in 
 cold climates is nec- 
 essarily carried down inside the building to prevent freezing. 
 One or more waste pipes from sinks, bathtubs, etc., are usually 
 required in addition to the soil pipe These may be connected 
 directly with the soil pipe (through traps), if located near it, or 
 may be carried to the basement vertically and then joined with 
 the main drain pipe inside the running trap. These should also 
 be placed on the inside wall of the house, and, if necessary to 
 conceal them, the boxing used should be put together in such a 
 manner that it may be easily removed for inspection. 
 
 The main soil pipe should also be placed where it can be 
 
 446
 
 PLUMBING. 
 
 seen, so that leaks may be easily discovered ; it is commonly run 
 along the basement wall and supported by suitable brackets or 
 hangers. If carried beneath the cellar floor, it should run in a 
 brick trench with removable covers. In running all lines of pipe, 
 whether vertical or horizontal, they should be securely supported 
 and, in the case of the latter, properly graded. Some of the 
 various kinds of hangers and supports used are shown in Figs. 79 
 and 80. The grade of the pipes should be as sharp and as uniform 
 as possible. The velocity in the pipes should be at least two feet 
 per second to thoroughly clean them and prevent clogging. Gen- 
 erally speaking, the pitch of the pipes should not be in any case 
 less than 1 foot in 50. In running lines of soil pipe, it is best to 
 
 Fig. 79. Fig. 80. 
 
 set the joints ready for calking in the exact positions they are' 
 to occupy and resting upon the supports which are intended to 
 hold them permanently. In this way there is less liability of sag- 
 ging or loosening of the joints after calking. In the running of 
 vertical pipes, care should be taken to have them as straight as 
 possible from the lowest fixture to the roof. 
 
 It is very necessary that the pipes be given such an align- 
 ment that the water entering them will meet with no serious 
 obstructions. Where vertical pipes join those which are horizon- 
 tal, they should be given a bend which will turn the stream gradu- 
 ally into the latter, thus preventing any resistance and the result- 
 ing accumulation of deposits. Horizontal pipes may be joined 
 with vertical pipes without a bend, as the discharge will be suffi- 
 ciently free without it. However, it is customary to use a Y or 
 T branch, giving a downward direction to the flow when connect- 
 ing a closet or other fixture where there is likely to be much solid 
 matter in the sewage. Offsets should always be avoided as far 
 as possible, as they obstruct the flow of both water and air. 
 
 447
 
 40 PLUMBING. 
 
 Pipe Sizes. The most importer t requirements in the case 
 of discharge pipes are that they cany away the waste matter as 
 thoroughly as possible without stoppage of flow or eddying, and 
 that they be well ventilated. In order to accomplish this they 
 must be given such sizes as experience has shown to be the best. 
 When water having solid matter in suspension half fills a pipe, the 
 momentum or force for clearing the pipe will be much greater than 
 when it forms only a shallow stream in one of a larger size, so that 
 in proportioning the suas of soil pipes and drains care must be 
 taken that they are no',, made larger than necessary, for if the 
 
 Fig. 81. 
 
 stream becomes too shallow the pipes will not be properly flushed 
 and deposits are likely to accumulate. The amount of water used 
 in a house of ordinary size, even w r hen increased by the roof water 
 from a heavy rain, will easily be cared for by a 4-inch pipe having 
 a good pitch. While a pipe of this size would seem to be sufficient, 
 it is found by experience that it is likely to become clogged at 
 times by substances which through carelessness find their way into 
 the drain, so that it seems best to use a somewhat lai-ger size. 
 For city buildings in general, it is recommended that the main 
 drain should not be less than 5 or 6 inches in diameter, and in 
 ordinary dwelling houses not less than 5 inches. The vertical 
 soil pipes need not be larger than 4 inches, except in very high 
 buildings. 
 
 Waste pipes may vary from li inches to 2 inches. The 
 waste from a single bowl or lavatory should be 1| inches in 
 diameter, from a bathtub, kitchen sink or laundry tub 1 * inches, 
 from a slop sink 1| inches. Smaller pipes should never be used. 
 In laying out the lines of piping, provision should be made for 
 clearing the pipes in case of stoppage. Fig. 81 shows how this 
 
 448
 
 PLUMBING. 
 
 41 
 
 may be done. Clean-out plugs are left at the points indicated by 
 the arrows, so that flexible sticks or strips of steel may be inserted 
 to dislodge any obstruction which may occur. 
 
 The fresh-air inlet to the main drain pipe has already been 
 referred to. This should be located away from windows, where 
 foul air would be objectionable ; in cities they may be placed 
 at the curb line and covered with a grating. Sometimes 
 they are arranged as shown in 
 Fig. 82. The opening is made 
 in the usual way, and a hood 
 placed over the inlet, and a pipe 
 leading from this is carried 
 through the roof. When the 
 circulation of air is upward 
 through the main soil pipe the 
 opening acts in the usual way, 
 that is, as a fresh-air inlet, but 
 should there be a reversal of 
 the current from any reason, 
 which would discharge foul air 
 from the sewer, it would be 
 caught by the overhanging 
 
 hood and carried upward through the connecting vent pipe to a 
 point above the roof. A general layout for house drainage is 
 shown in Fig. 83. 
 
 PLUMBING FOR VARIOUS BUILDINGS. 
 
 Dwelling Houses. The bathroom fixtures, laundry tubs and 
 kitchen sink, with the possible addition of a slop sink, make up the 
 usual fixtures to be provided for in the ordinary dwelling house. 
 In houses of larger size these may be duplicated to some extent, 
 but the general methods of connection are the same as have already 
 been described and need not be taken up again in detail. 
 
 Apartment Houses. These are usually made up of duplicate 
 flats, one above the other, so that the plumbing fixtures may be the 
 same for each. It is customary to place the bathrooms in the 
 same position on each floor, so that a single soil pipe will care for 
 all. 
 
 449
 
 PLUMBING. 
 
 Hotels. Here, as in the case just described, the bathrooms 
 are placed one above another, so that a single soil pipe may care 
 for each series, and the problem then becomes that of duplicat- 
 ing the layout for an apartment house. In addition to the 
 private baths there is a public lavatory or toilet-room, usually on 
 the first floor or in the basement. T as is fitted up with closets, 
 
 urinals and bowls. The closet seats and urinals are placed side 
 by side, with dividing partitions, and connect with a common soil 
 pipe running back of them and having a good pitch. Each fixture 
 should have its own trap. The flushing of the fixtures is often 
 made automatic, so that pressing down the wooden rim of a closet 
 
 450
 
 PLUMBING. 
 
 seat will throw a lever which on being released will flush the 
 closet. Urinals are commonly made to flush at regular intervals 
 by some of the devices already shown. The lavatories are made 
 up in long rows, as shown 
 in Fig. 84. 
 
 Railroad Stations. The 
 plumbing of a railroad 
 station is similar to that 
 of a hotel, although even 
 greater care should be 
 taken to make the fixtures 
 self-cleansing, as the 
 patrons are likely to in- 
 clude many of the lowest 
 and most ignorant class of 
 people. Special attention 
 should be given to both 
 the local ventilation of the 
 fixtures and the general 
 ventilation of the room. 
 
 Schoolhouses. The 
 same general rules hold in 
 the case of school buildings 
 as in hotels and railroad 
 stations. As the pupils 
 are under the direct super- 
 vision of teachers and jani- 
 tors it is not necessaiy to 
 have- the fixtures auto- 
 matic to as great an extent 
 as in the cases just de- 
 scribed, and it is customary 
 to flush the closets by 
 means of tanks, and pull 
 chains or rods, the same as in private dwellings. The urinals 
 may be automatic or a small stream of water may be allowed 
 to flow through them continuously during school hours. A good 
 form for this class of work is shown in Fig. 85. 
 
 451
 
 44 
 
 PLUMBING. 
 
 Shops and Factories. Some simple type of fixture which 
 can be easily sared for is best in buildings of this kind. 
 
 TESTING AND INSPECTION. 
 
 All plumbing work of any importance should be given two 
 tests ; the first, called the " roughing test," applies only to the 
 
 452
 
 PLUMBING. 45 
 
 soil, waste and vent pipes, and is made before the fixtures are 
 connected. The best method of making this test is to plug the 
 main drain pipe just outside the running trap, and also all open- 
 ings for the connections of fixtures, etc., and then fill the entire 
 system with water. This may be done in small systems through 
 the main vent pipe on the roof, and in larger ones by making a 
 temporary connection with the water main. If any leaks are 
 present they are easily detected in this way. In cold weather, 
 when there would be danger of freezing, compressed air under a 
 pressure of at least ten pounds per square inch may be used in 
 place of water. Leaks in this case must be located by the sound 
 of the issuing air. The water test is to be preferred in all cases, 
 as it is easier to make, and small leaks are more easily 
 detected. 
 
 The final test is made after the fixtures are in and all work 
 is completed. There are two ways of making this test, one known 
 as the "peppermint test," and the other as the "smoke test." In 
 making either of these, the system should first be flushed with 
 water, so that all traps may be sealed. If peppermint is used, 4 
 to 6-ounces of oil of peppermint, depending upon the size of the 
 system, are poured down the main vent pipe, and then a quart or 
 two of hot water to vaporize the oil. The vent pipe is then 
 closed, and the inspector must carefully follow along the lines of 
 piping and locate any leaks present by the odor of the escaping 
 gas. Another and better way is to close the vent pipe and 
 vaporize the oil in the receiver of a small air pump, and then 
 force the gas into the system under a slight pressure. The re- 
 ceiver is provided with a delicate gage, so that after reaching a 
 certain pressure (which must not be great enough to break the 
 trap seals) the pump may be stopped and the pressure noted. If, 
 after a short time, the pressure remains the same, it is known that 
 the system is tight ; if, however, the pressure drops, then leaks 
 are present and must be located, as already described. Ether is 
 sometimes used in place of peppermint for this purpose. 
 
 In making the smoke test the system is sealed, and the vent 
 pipes closed in the same manner as for the test just described; 
 smoke from oily waste or some similar substance is then forced 
 into the pipes by means of a bellows. When the system is filled 
 
 453
 
 46 PLUMBING. 
 
 with smoke, and a slight pressure produced, the fact is shown by 
 a iloafc, which rises and remains in this position if the joints are 
 tight. If there are leaks, the float falls as soon as the bellows 
 are stopped. Leaks may be detected in this way, both by the 
 odor of the smoke and by the issuing jets from leaks of any size. 
 Special machines are made for both the peppermint and smoke tests. 
 The water test is preferable for roughing in, and the smoke 
 test for the final. Every system of plumbing should be tested at 
 least once a year. 
 
 SEWERAGE AND SEWAGE PURIFICATION. 
 
 An abundant supply of pure water is a necessity in every town 
 and city ; and such a supply having been secured brings up the 
 question of its disposal after being used. This is plainly the re- 
 verse of its introduction. As it was distributed through a net- 
 work of conduits, diminishing in size, with its numerous branches, 
 so it may be collected again by similar conduits, increasing in size, 
 as one after another they unite in a common outlet. 
 
 This fouled water is called seivage, and the conduits which col- 
 lect it constitute a sewerage system. In general, sewage is dis- 
 posed of in two ways ; either it must be turned into a body of 
 water so large as to dilute it beyond all possibility of offence, 
 and where it cannot endanger human life by polluting a public 
 water-supply, or it must be purified in some manner. 
 
 The conduits which carry water collected from street surfaces 
 during and after rains, or ground water collected from beneath 
 the surface, are called drains. When one set of conduits removes 
 sewage and another carries surface and ground water, it is said 
 that the separate system of sewerage is in use. Where one system 
 conveys both sewage and drainage water it is called the combined 
 system. Various modifications of these two systems are possible, 
 both for whole cities and for limited areas within the same town 
 or city. 
 
 A sanitary sewerage system cannot be installed until a public 
 water-supply has been provided. It is needed as soon as that is 
 accomplished, for while the wells can then be abandoned the volume 
 of waste water is greatly increased by the water-works system. Its 
 foulness is also much increased through the introduction of water- 
 
 454
 
 PLUMBING. 47 
 
 closets. Without sewers and with a public water-supply cesspools 
 must be used, and with these begins a continuous pollution of the 
 soil much more serious than that which commonly results from 
 closets and the surface disposal of slops. 
 
 Among the data which should first be obtained in laying out 
 a sewerage system are : 
 
 First. The area to be served, with .its topography and the 
 general character of the soil. A contour map of the whole town 
 or city, showing the location of the various streets, streams, ponds 
 or lakes, and contour lines for each 5 feet or so of change in ele- 
 vation, is necessary for the best results. The general character of 
 the soil can usually be obtained by observation and inquiry among 
 residents or builders who have dug wells or cellars, or have ob- 
 .jerved work of this kind which was being done. The kind of 
 soil is important as affecting the cost of trenching and its wetness 
 or dryness, and this, together with a determination of the ground- 
 water level, will be useful in showing the extent of underdraining 
 necessary. 
 
 Second. Whether the separate or combined system of sewer- 
 age, or a compromise between the two is to be adopted. These 
 points will depend almost wholly upon local conditions. The size 
 and cost of combined sewers is much greater than the separate 
 system, since the surface drainage in times of heavy rainfall is 
 many times as great as the flow of sanitary sewage. In older 
 towns and cities it sometimes happens that drains for removing' 
 the surface water are already provided, and in this case it is only 
 necessary to put in the sanitary sewers ; or again, the latter may 
 be provided, leaving the matter of surface drainage for future con- 
 sideration. 
 
 If the sewage must be purified, the combined system is out 
 of the question, for the expense of treating the full flow in times 
 of maximum rainfall would be enormous. Sometimes more or less 
 limited areas of a town may require the combined system, while 
 the separate system is best adapted to the remainder ; and again 
 it may be necessary to take only the roof water into the sewers. 
 As already stated, local conditions and relative costs are the 
 principal factors in deciding between the separate and combined 
 systems. 
 
 455
 
 48 PLUMBING. 
 
 Third. Whether subsoil drainage shall be provided.--- In 
 most cases this also will depend upon local conditions. It is al- 
 ways an advantage to lower the ground-water level in. places 
 where it is sufficiently high to make the ground wet at or near the 
 surface during a large part of the year. In addition to rendering 
 the soil dry around and beneath cellars, the laying of uuderdrains 
 is of such aid in sewer .construction as to warrant their introduc- 
 tion for this purpose alone. This is the case where the trenches 
 are so wet as to render the making and setting of cement joints 
 difficult. The aim in ail good sewer work is to reduce the infil- 
 tration of ground water into the pipes to the smallest amount; 
 but in very wet soil, tight joints can be made only with difficulty, 
 and never with absolute certainty. Cases have beon known where 
 fully one-half the total volume of sewage discharged consisted of 
 ground water which had worked in through the joints. 
 
 Fourth. The best means for the final disposal of the 
 sewage. Until recently it was turned into the nearest river or 
 lake where it could be discharged with the least expense. The 
 principal point to be observed in the disposal of sewage is that 
 no public water-supply shall be endangered. At the present time 
 no definite knowledge is at hand regarding the exact length of 
 time that disease germs from the human system will live in water. 
 The Massachusetts legislature at one time said that no sewer 
 should discharge into a stream within 20 miles of any point where 
 it is used for public water-supply, but it is now left largely in the 
 hands of the State Board of Health. There may be cases where 
 sewage disposal seems to claim preference to water supply in the 
 use of a stream, but each case must be decided on its own merits. 
 Knowing the amount of water and the probable quantity and 
 character of the sewage, it is generally easy to determine whether 
 all of the crude sewage of a city can safely be discharged into the 
 bodj' of water in question. Averages in this case should never 
 be used; the water available during a hot and dry summer, when 
 the stream, or lake is at its lowest, and the banks and beds are ex- 
 posed to the sun, is what must be considered. Where sewage is 
 discharged into large bodies of water, either lakes or the ocean, it 
 is generally necessary to make a careful study of the prevailing 
 currents in order to determine the most available point of discharge, 
 
 456
 
 PLUMBING. 49 
 
 in order to prevent the sewage becoming stagnant in bays, or the 
 washing ashore of the lighter portions. Such studies are com- 
 monly made with floats, which indicate the direction of the exist- 
 ing currents. 
 
 Fifth. Population, water consumption and volume of sewage 
 for which provision should be made, together with the rainfall 
 data, if surface drainage is to be installed. The basis for population 
 studies is best taken from the census reports, extending back many 
 years. By means of these the probable growth may be estimated 
 for a period of from 30 to 50 years. In small and rapidly grow- 
 ing towns it must be remembered that the rate of increase is gen- 
 erally less as the population becomes greater. 
 
 It is desirable to design a sewerage system large enough to 
 serve for a number of years, 20 or 30 perhaps, although some 
 parts of the work, such as pumping or purification works, may 
 be made smaller and increased in size as needed. 
 
 The pipe system should be large enough at the start to serve 
 each street and district for a long period, as the advantages to be 
 derived from the use of city sewers are so great that all houses 
 are almost certain to be connected with them sooner or later. It 
 is often necessary to divide a city into districts in making esti- 
 mates of the probable growth in population. Thus the residential 
 sections occupied by the wealthiest classes will be comprised of a 
 comparatively small population per acre, due to the large size of 
 the lots. The population will grow more dense in the sections 
 occupied by the less wealthy, the well-to-do and finally the tene- 
 ment sections. In manufacturing districts the amount of sewage 
 will vary somewhat, depending upon the lines of industry 
 carried on. 
 
 The total water consumption depends mainly upon the popu- 
 lation, but no fixed rule can be laid down for determining it 
 beforehand. It is never safe to allow less than 60 gallons per 
 day per capita as the average water consumption of a town if 
 most of the people patronize the public water-supply. In general 
 it is safer to allow 100 gallons. The total daily flow of sewage is 
 not evenly distributed through the 24 hours. The actual amount 
 varies widely during different hours of the day. In most towns 
 there should be little if any sewage, if the pipes are tight enough 
 
 457
 
 50 PLUMBING. 
 
 to prevent inward leakage, between about 10 o'clock in the 
 evening and 4 in tbe morning. From | to ? of the daily flow 
 usually occurs in from 9 io 12 hours, the particular hours varying 
 in different communities. This is not of importance in designing 
 the pipe system, but only affects the disposal. 
 
 Rainfall data is usually hard to obtain except in the cities 
 and larger towns. In cases of this kind the data of neighboring 
 town or cities may be used if available. Monthly or weekly 
 totals are of little value, as it is necessary to provide for the 
 heaviest rains, as a severe shower of 15 minutes may cause more 
 inconvenience and damage, if the sewers are not sufficiently large, 
 than a steady rain extending over a day or two. A maximum 
 rate of 1-inch per hour will usually cover all ordinary conditions. 
 The proportion which will reach the sewers during a given time 
 will depend upon local conditions, such as the slope of land, 
 whether its surface is covered with houses and paved streets, 
 cultivated fields or forests, etc. 
 
 Sixth. Extent and cost of the proposed system. This is a 
 matter largely dependent upon the local treasury, or the willing- 
 ness of the people to pay general taxes or a special assessment 
 for the benelits to be derived. 
 
 DESIGN AND CONSTRUCTION. 
 
 The first step is to lay out the pipe or conduit system. For 
 this the topographical map already mentioned will be found 
 useful. This, however, should be supplemented by a profile of all 
 the streets in which sewers are to be laid, in order to determine 
 the proper grades. In laying out the pipe lines, special diagrams 
 and tables which have been prepared for this purpose may be 
 used. In the separate system it is generally best to use 8" pipe 
 as the smallest size to lessen the risk of stoppage, although 6" 
 pipe is ample for the volume of sanitary sewage from an ordinary 
 residence street of medium length. Pipe sewers are generally 
 made of vitrified clay, with a salt-glazed surface. Cement pipe is 
 also used in some cities. The size of pipe sewers is limited to 
 30 inches in diameter, owing to the difficulty and expense of 
 making the larger pipe and the comparative ease of laying brick 
 sewers of anv size from 24 or 30 inches up. In very wet ground, 
 
 458
 
 COMBINED NEEDLE AND SHOWER BATH ARRANGED FOR HOT AND COLD WATER. 
 
 The Federal Company.
 
 PLUMBING. 51 
 
 cast iron pipe with lead joints is used, either to prevent inward 
 leakage or settling of the pipe. 
 
 The pipes should be laid to grade with great care and a good 
 alignment should be secured. Hole's should be dug for the bells 
 of the pipe, so that they will have solid bearings their entire 
 length. If rock is encountered in trenching, it will be necessary 
 to provide a bed for the pipe which will not be washed into fis- 
 sures by the, stream of subsoil water which is likely to follow the 
 sewer when the ground is saturated. 
 
 Underdrains. Where sewers are in wet sand or gravel, 
 underdrains may be laid beneath or alongside the sewer. These 
 are usually the ordinary agricultural tiles, from 3 inches in 
 diameter upward. They have no joints, being simply hollow 
 cylinders, and are laid with their ends a fraction of an inch 
 apart, wrapped with a cheap muslin cloth to keep out the dirt 
 until the matter in the trench becomes thoroughly packed about 
 them. These drains may empty into the nearest stream, provided 
 it is not used for a public water-supply. 
 
 flanholes. These should be placed at all changes of grade 
 and at all junctions between streets. They are built of brick and 
 afford access to the sewer for inspection ; in addition to this they 
 are sometimes used for flushing. They are provided with iron 
 covers which are often pierced with holes for ventilation. 
 
 Sewer Grades. The grades of sewers should be sufficient 
 where possible, to give them a self-clearing velocity. Practical 
 experiments show that sewers of the usual sections will remain 
 clear with the following minimum grades: Separate house con- 
 nections, 2 per cent; (2-feet fall in each 100 feet of length) 
 small street sewers, 1 per cent ; main sewers, 0.7 per cent. These 
 grades may be reduced slightly for sewers carrying only rain or 
 quite pure water. 
 
 The following formula may be used for computing the mini- 
 mum grade for a sewer of clear diameter equal to "d" inches 
 and either circular or oval in section. 
 
 Minimum grade, in per cent = , , . 
 5 + 5 
 
 Flushing Devices. Where very low grades are unavoidable 
 
 459
 
 52 PLUMBING. 
 
 and at the head of branch sewers, where the volume of flow is 
 small, flushing may be used with advantage. 
 
 In some cases water is turned into the sewer through a man- 
 hole, from some pond or stream, or from the public water-works 
 system. Generally, however, the water is allowed to accumulate 
 before being discharged, by closing up the lower side of the man- 
 hole until the water partially fills it, then suddenly releasing it 
 and allowing the water to rush through the pipe. Instead of 
 using clear water from outside for this purpose, it may be sufficient 
 at some points on the system to simply back up the sewage, by 
 closing the manhole outlet, thus flushing the sewer with the sewage 
 itself. Where frequent and regular flushing is required, automatic 
 devices are often used. These usually operate by means of a self- 
 discharging siphon, although there are other devices operated by 
 means of the weight of a tank which fills and empties itself at 
 regular intervals. 
 
 House Connections. Provision for house connections should 
 be made when the sewers are laid, in order to avoid breaking up 
 the streets after the sewers are in use. Y branches should be put 
 in at frequent intervals, say from 25 feet apart upwards, according 
 to the character of the street. When the sewer main is deep 
 down, quarter bends are sometimes provided, and the house con- 
 nection pipe carried vertically upwards to within a few feet of the 
 surface to avoid deep digging when connections are made. Where 
 house connections are made with the main, or where two sewers 
 join, the direction of flow should be as nearly in the same direc- 
 tion as possible, and the entering sewer should be at a little higher 
 level in order to increase the velocity of the inflowing sewage. 
 
 Depth of Sewers Below the Surface. No general rule can 
 be followed in this matter except to place them low enough to 
 secure a proper grade for the house connections, which are to be 
 made with them. They must be kept below a point where there 
 would be trouble from freezing, but the natural depth is usually 
 sufficient to prevent this in most cases. 
 
 Ventilation of Sewers. There is more or less difference in 
 opinion in regard to the proper method of ventilating sewer mains. 
 Ventilation through house soil pipes is generally approved where 
 the sewers and house connections are properly constructed and 
 
 460
 
 PLUMBING. 53 
 
 operated, and where the houses on a given street are of a uniform 
 height, so that the tops of all the soil pipes will be above the high- 
 est windows. Where the houses are uneven in height, or where 
 the sewerage system or connections are not well designed or con- 
 structed, it is recommended that main traps should be placed on 
 all soil pipes, and that air inlets and air outlets be placed on the 
 sewers at intervals of from 300 to 400 feet. 
 
 The Combined System. The principal differences between 
 this and the separate system are in the greater size of conduits 
 and the use of catch-basins or inlets for the admission of surface 
 water. They are generally of brick, stone or concrete, or a 
 combination of these materials, instead of vitrified pipe. 
 
 Another difference is the provision for storm overflows, by 
 means of which the main sewers when overcharged in times of 
 heavy rainfall may empty a part of their contents into a nearby 
 stream. At such times the sewage is diluted by the rain-water, 
 while the stream which receives the overflow is also of unusually 
 large size. 
 
 Size, Shape and Material. The actual size of the sewer, 
 and also to a large extent its shape and the material of which it is 
 constructed, depends upon local conditions. Where the depth of 
 flow varies greatly it is desirable to give the sewer a cross-section 
 designed to suit all flows as fully as possible. 
 
 The best form to meet these requirements is that of an egg 
 with its smaller end placed downward. With this form the 
 greatest depth and velocity of flow is secured for the smallest 
 amount of sewage, thus reducing the tendency to deposits and stop- 
 pages. Where sewers have a flow more" nearly constant and equal 
 to their full capacity the form may be changed more nearly to that 
 of an ellipse. F*or the larger sewers brick is the most common- 
 material, both because of its low cost and the ease with which any 
 form of conduit is constructed. Stone is sometimes used on steep 
 grades, especially where there is much sand in suspension, which 
 would tend to wear away the brick walls. Concrete is used where 
 leakage may be expected or where the material is liable to movement, 
 but is more commonly used as a foundation for brick construction. 
 
 A catch-basin is generally placed at each street corner and 
 provided with a grated opening for giving the surface water access 
 
 461
 
 54 PLUMBING. 
 
 to a chamber or basin beneath the sidewalk, from which a pipe 
 leads to the sewer. Catch-basins may be provided with water 
 traps to prevent the sewer air from reaching the street, but traps 
 fire uncertain in their action, as they are likely to become unsealed 
 through evaporation in dry weather. To prevent the carrying of 
 sand and dirt into the sewers, catch-basins should be provided 
 with silt chambers of considerable depth, with overflow pipes 
 leading to the sewer. The heavy matter which falls to the 
 bottoms of these chambers may be removed by buckets and carted 
 away at proper intervals. 
 
 Storm Overflows. The main point to be considered in the 
 construction of storm overflows is to ensure a discharge into 
 another conduit when the water readies a certain elevation in the 
 main sewer. This may be carried out in different ways, depending 
 upon the available points for overflow. 
 
 Pumping Stations. The greater part of the sewerage 
 systems in the United States operate wholly by gravity, but in 
 some cases it is necessary to pump a part or the whole of the 
 sewage of a city to a higher level. The lifts required are usually 
 low, so that high-priced machinery is not required. In general 
 the sewage should be screened before it reaches the pumps. 
 
 Where pumping is necessary, receiving or storage chambers 
 are sometimes used to equalize the work required of the pumps, 
 thus making it possible to shut down the plant at night. Such 
 reservoirs should be covered, unless in very isolated localities. 
 The force main or discharge pipe from the pumps is usually short, 
 and is generally of cast iron put together in a manner similar to 
 that used for water-supply systems. 
 
 Tidal Chambers. Where sewage is discharged into tide 
 water it is often necessary to provide storage or tidal chambers, so 
 that the sewage may be discharged only at ebb tides. These are 
 constructed similar to other reservoirs, except that they must 
 have ample discharge gates, so that they may be emptied in a 
 short time. They are sometimes made to work automatically by 
 the action of the tide. 
 
 SEWAGE PURIFICATION. 
 
 Before taking up this subject in detail it is well to consider 
 what sewage is, from a chemical standpoint. 
 
 462
 
 PLUMBING. 55 
 
 When fresh, it appears at the mouth of an outlet sewer 
 as a milky-looking liquid with some large particles of matter 
 in suspension, such as orange peels, rags, paper and various 
 other articles not easily broken up. It often has a faint, 
 musty odor and in general appearance is similar to the suds-water 
 tfrom a family laundry. Nearly all of the sewage is simply water, 
 the total amount of solid matter not being more than 2 parts in 
 1,000, of which half may be organic matter. It is this 1 part in 
 1,000 which should be removed, or so changed in character as to 
 render it harmless. 
 
 The two systems of purification in most common use are 
 " chemical precipitation " and the " land treatment." Mechanical 
 straining, sedimentation and chemical precipitation are largely 
 removal processes, while land treatment by the slow process of 
 infiltration, or irrigation, changes the decaying organic matter into 
 stable mineral compounds. 
 
 Sedimentation. This is effected by allowing the suspended 
 matter to settle in tanks. The partially clarified liquid is then 
 drawn off leaving the solid matter, called " sludge" at the bottom 
 for later disposal. This system requires a good deal of time and 
 large settling tanks ; therefore it is suitable only for small quanti- 
 ties of sewage. 
 
 Mechanical Straining. This is accomplished in different 
 ways with varying degrees of success. Wire screens or filters of 
 various materials may be employed. Straining of itself is of little 
 value except as a step to further purification. Beds of coke from 
 6 to 8 inches in depth are often used with good results. 
 
 Chemical Precipitation. Sedimentation alone removes only 
 such suspended matter as will sink by its own weight during the 
 comparatively short time which can be allowed for the process. 
 
 By adding certain substances chemical action is set up, which 
 greatly increases the rapidity with which precipitation takes place. 
 
 Some of the organic substances are brought together by the 
 formation of new compounds, and as they fall in flaky masses 
 they carry with them other suspended matter. 
 
 A great number and variety of chemicals have been employed 
 for this purpose, but those which experience has shown to be most 
 useful are lime, sulphate of alumina and_some of the salts of iron. 
 
 463
 
 56 PLUMBING. 
 
 The best chemical to use in any given case depends upon the 
 character of the sewage and the relative cost in that locality. 
 Lime is cheap, but the large quantity required greatly in- 
 creases the amount of sludge. Sulphate of alumina is more 
 expensive, hut is often used to advantage in connection with 
 lime. Where an acid sewage is to be treated, lime alone should be 
 used. 
 
 The chemicals should be added to the sewage and thoroughly 
 mixed before it reaches the settling tank ; this mav be effected by 
 the use of projections or baffling plates placed in the condui'; 
 leading to the tank. The best results are obtained by means of 
 long', narrow tanks, and they should be operated on the continue/us 
 rather than the intermittent plan. The width of the tank should 
 be about one-fourth its length. In the continuous method the 
 sewage is constantly flowing into one part of the tank and dis- 
 charging from another. In the intermittent system a tank is lilled 
 and then the flow is turned into another, allowing the sewage in 
 the first tank to come to rest. In the continuous plan the sewage 
 generally flows through a set of tanks without interruption until 
 one of the compartments needs cleaning. The clear portion is 
 drawn off from the top, the sludge is then removed, and the tank 
 thoroughly disinfected before being put in use again. The satis- 
 factory disposal of the sludge is a somewhat difficult matter. The 
 most common method is to press it into cakes, which greatly 
 reduces i.s bulk and makes it more easily handled. These are 
 sometimes burned but are more often used for fertilizing purposes. 
 In some cases peat or other absorbent is mixed with the sludge 
 and the whole mass removed in bulk. In other instances it is run 
 out on the surface of coarse gravel beds and reduced by draining 
 and drying. In wet weather little drying takes place and during 
 the cold months the sludge accumulates in considerable quantities. 
 This process also requires considerable manual labor, and in many 
 cases suitable land is not available for the purpose. The required 
 capacity of the settling tanks is the principal item in determining 
 the cost of installing precipitation works. 
 
 In the treatment of house sewage provision must be made for 
 about T V the total daily flow, and in addition to this, allowance 
 must be made ^or throwing out a portion of the tanks for cleaning 
 
 464
 
 PLUMBING. 57 
 
 and repairs. In general, the tank capacity should not bo much 
 less than | the total daily flow. 
 
 In the combined system it is impossible to provide tanks for 
 the total amount, and the excess due to storm water must dis- 
 charge into. natural water courses or pass by the works without 
 treatment. 
 
 Broad Irrigation or Sewage Farming. Where sewage is 
 applied to the surface of the ground upon which crops are raised 
 the process is called "sewage farming." This varies but little 
 from ordinary irrigation where clean water is used instead of 
 sewage. The land employed for this purpose should have a 
 rather light and porous soil, and the crops should be such as 
 require a large amount of moisture. The application of from 
 5,000 to 10,000 gallons of sewage per day per acre is considered 
 a liberal allowance. On the basis of 100 gallons of sewage per 
 head of population this would mean that one acre would care for 
 a population of from 50 to 100 people. 
 
 Sub-Surface Irrigation. This system is employed only 
 upon a small scale and chiefly for private dwellings, public insti- 
 tutions and for small communities where for any reason surface 
 disposal would be objectionable. The sewage is distributed 
 through agricultural drain tiles laid with open joints and placed 
 only a few inches below the surface. Provision should be made 
 for changing the disposal area as often as the soil may require by 
 turning the sewage into sub-divisions of the distributing pipes. 
 
 Intermittent Filtration. This method and the broad irriga- 
 tion already described arc the only purification processes in use on 
 a large scale which can remove practically all the organic matter 
 from sewage without being supplemented by some other method. 
 The process is a simple one and consists in running the sewage 
 out through distributing pipes onto beds of sand 4 or 5 feet in 
 thickness with a system of pipes or drains below for collecting the 
 purified liquid. In operation the sewage is first turned on one 
 bed and then another, thus allowing an opportunity for the liquid 
 portion to filter through. As the surface becomes clogged it is 
 raked over or the sludge may be scraped off together with a thin 
 layer of sand. The best filtering material consists of a clean, 
 sharp sand with grains of uniform size such that the free space 
 
 465
 
 58 PLUMBING. 
 
 between them will equal about one-third the total volume. When 
 the sewage is admitted to the sand only a part of the air is driven 
 out, so there is a store of oxygen left upon which the bacteria 
 may draw. This is not a mere process of straining but the forma- 
 tion of new compounds by the action of the oxygen in the air, 
 thus changing the organic matter into inorganic. Much depends 
 upon the size and quality of the sand used. The grains that have 
 been found to give the best results range from .1 to .5 of an inch 
 in diameter. The work done by a filter is largely determined by 
 the finer particles of sand and that used should be of fairly uni- 
 form quality, and the coarser and finer particles should be well 
 mixed. The area and volume of sand or gravel required are so 
 large -that the transportation of material any great distance cannot 
 be considered. Usually the beds are constructed on natural 
 deposits, the top soil or loam being removed. The sewage should 
 be brought into the beds so as to disturb their surface as little as 
 possible, and should be distributed evenly over the whole bed. 
 
 The under drains should not be placed more than 50 feet 
 apart, usually much less, and should be provided with manholes 
 at the junctions of the pipes. Before admitting the sewage to the 
 beds it is usually best to screen it sufficiently to take out paper, 
 rags and other lloating matter. The size of each bed should be 
 such as to permit an even distribution of sewage over its surface. 
 
 Where the nitration area is small, it must be divided so as to 
 permit of intermittent operation ; that is, if a bed is to be in use 
 and at rest for equal periods, then two or more beds would be 
 necessary, the number depending on the relative periods of use 
 and rest. Some additional area should also be piovided for emer- 
 gency, or for use while the beds are being scraped. If a large 
 area is laid out, so that the size of the beds is limited only by 
 convenience in use, then an acre may be taken as a good size. 
 
 The degree . of purification depends upon various circum- 
 stances, but with the best material practically all of the organic 
 matter can be removed from sewage by intermittent nitration at a 
 rate of about 100,000 gallons per day. 
 
 Theie is often much opposition to sewage purification by 
 those living or owning property near the plants ; but experience 
 has shown that well-conducted plants are inoffensive both within 
 
 460
 
 PLUMBING. 59 
 
 and without their enclosures. The employees about such worts 
 are as healthy as similar classes of men in other occupations. The 
 crops raised on sewage farms are as healthful as those of the same 
 kind raised elsewhere, and meat and milk from sewage farms are 
 usually as good as when produced under other conditions. Good 
 design and construction, followed by proper methods of operation, 
 are all that are needed to make sewage purification a success. No 
 one system can be said to be the best for all localities. The 
 special problems of each case must be met and solved by a selec- 
 tion from among the several systems and the combinations of 
 systems, and parts chosen that are best adapted to the conditions 
 at hand. 
 
 467
 
 PLUMBING. 
 
 PART II. 
 
 DOHESTIC WATER SUPPLY. 
 
 Hydraulics of Plumbing. Although the principles of Hy- 
 draulics and Hydrostatics are discussed in " Mechanics," it will 
 be well to review them briefly, showing their application to the 
 various problems under the head of " Water Supply." 
 
 If several open vessels containing water are connected by 
 pipes, the water will eventually stand at the same level in all of 
 them, regardless of the length or the size of the connecting pipes. 
 
 The pressure exerted by a liquid at any given point is the 
 same in all directions, and is proportional to the depth. 
 
 A column of water at 60 temperature having a sectional area 
 of one square inch and a height of one foot, weighs .43 pound, and 
 the pressure exerted by a liquid is usually stated in pounds per square 
 inch, the same as in the case of steam. If a closed vessel is con- 
 nected, by means of a pipe, with an open vessel at a higher level, 
 so that it is 10 feet* for example, from the bottom of the first 
 vessel to the surface of the water in the second, the pressure on 
 each square inch of the entire bottom of the lower vessel will be 
 10 X .43 = 4.3 pounds, and the pressure per square inch at any 
 given point in the vessel or connecting pipe will be equal to its 
 distance in feet from the surface of the water in the upper vessel 
 multiplied by .43. If a pipe is carried from a reservoir situated 
 on the top of a hill to a point at the foot of the hill a hundred feet 
 below the surface of the water, a pressure of 100 X -43 43 
 pounds per square inch will be exerted at the lower end of the 
 pipe, provided it is closed. When the pipe is opened and the 
 water begins to flow, the conditions are changed and the pressure 
 in the different parts of the pipe varies with the distance from the 
 open end. 
 
 In order for a liquid to flow through a pipe there must be a 
 certain pressure or " head " at the inlet end. The total head caus- 
 ing the flow is divided into three parts, as follows: 1st, the 
 
 469
 
 PLUMBING. 
 
 velocity head : the height through which a body must fall in a 
 vacuum to acquire the velocity with which the water enters the 
 pipe. 2d, the entry head : that required to overcome the resist- 
 ance to entrance into the pipe. 3d, the friction head: due to the 
 frictional resistance to flow within the pipe. In the case of long 
 pipes and low heads the sum of the velocity and entry heads is so 
 small that it may be neglected. 
 
 Table I shows the pressure of water in pounds per square 
 inch for elevations varying in height from 1 to 185 feet. 
 
 Table II gives the drop in pressure due to friction in pipes of 
 different. diameters for varying rates of flow. The figures given 
 are for pipes 100 feet in height. The frictional resistance in 
 smooth pipes having a constant flow of water through them is pro- 
 portional to the length of pipe. That is, if the friction causes a 
 drop in pressure of 4.07 pounds per square inch in a l|-incli pipe 
 100 feet long, which is discharging 20 gallons per minute, it will 
 cause a drop of 4.07 X 2 = 8. 14 pounds in a pipe 200 feet long; or 
 4.07 -f- 2 = 2.03 pounds in a pipe 50 feet long, acting under the 
 same conditions. The factors given in the table are for pipes of 
 smooth interior, like lead, brass or wrought iron. 
 
 Example. A 1-i-inch pipe 100 feet long connected with a 
 cistern is to discharge 35 gallons per minute. At what elevation 
 above the end of the pipe must the surface of the water in the 
 cistern be to produce this flow? 
 
 In Table II we find the friction loss for a 1 i-inch pipe dis- 
 charging 35 gallons per minute to be 5.05 pounds. In Table I we 
 find a pressure of 5.2 pounds corresponds to a head of 12 feet, 
 which is approximately the elevation required. 
 
 How many gallons will be discharged through a 2-inch pipe 
 100 feet long where the inlet is 22 feet above the outlet? In 
 Table I wo find a head of 22 feet corresponds to a pressure of 9.53 
 pounds. Then looking in Table IT we find in the column of Fric- 
 tion Loss for a 2-inch pipe that a pressure of 9.46 corresponds to 
 a discharge of 100 gallons per minute. 
 
 Tables I and II are commonly used together in examples. 
 
 A house requiring a maximum of 10 gallons of water pel 
 minute is to be supplied from a sp'/ing which is located 600 feet 
 distant, and at an elevation of 50 feet above the point of dis- 
 
 470
 
 PLUMBING. 
 
 TABLE 
 
 Head 
 in 
 feet. 
 
 Pressure 
 pounds per 
 square inch. 
 
 Head 
 in 
 feet. 
 
 Pressure 
 pounds per 
 square inch. 
 
 Head 
 in 
 
 feet. 
 
 Pressure 
 pounds per 
 square inch. 
 
 1 
 
 .43 
 
 46 
 
 19.92 
 
 91 
 
 39.42 
 
 2 
 
 .86 
 
 47 
 
 20.35 
 
 92 
 
 39.85 
 
 3 
 
 1.30 
 
 48 
 
 20.79 
 
 93 
 
 40.28 
 
 4 
 
 1.73 
 
 49 
 
 21.22 
 
 94 
 
 40.72 
 
 5 
 
 2.16 
 
 50 
 
 21.65 
 
 95 
 
 41.15 
 
 6 
 
 2.59 
 
 51 
 
 22.09 
 
 96 
 
 41.58 
 
 7 
 
 3.03 
 
 52 
 
 22.52 
 
 97 
 
 42.01 
 
 '8 
 
 3.46 
 
 53 
 
 22.95 
 
 98 
 
 42.45 
 
 9 
 
 3.89 
 
 54 
 
 23.39 
 
 99 
 
 42.88 
 
 10 
 
 433 
 
 55 
 
 23.82 
 
 100 
 
 43.31 
 
 11 
 
 4.76 
 
 56 
 
 24.26 
 
 101 
 
 43.75 
 
 12 
 
 5.20 
 
 57 
 
 24.69 
 
 102 
 
 44.18 
 
 13 
 
 5.63 
 
 58 
 
 25.12 
 
 103 
 
 44.61 
 
 14 
 
 6.06 
 
 59 
 
 25.55 
 
 104 
 
 45.05 
 
 15 
 
 6.49 
 
 60 
 
 25.99 
 
 105 
 
 45.48 
 
 16 
 
 6.92 
 
 61 
 
 26.42 
 
 106 
 
 45.91 
 
 17 
 
 7.36 
 
 62 
 
 26.85 
 
 107 
 
 46.34 
 
 18 
 
 7.79 
 
 63 
 
 27.29 
 
 108 
 
 46.78 
 
 19 
 
 8.22 
 
 64 
 
 27.72 
 
 109 
 
 47.21 
 
 20 
 
 8.66 
 
 65 
 
 28.15 
 
 110 
 
 47.64 
 
 21 
 
 9.09 
 
 66 
 
 28 ; 58 
 
 111 
 
 48.08 
 
 22 
 
 9.53 
 
 67 
 
 29.02 
 
 112 
 
 48.51 
 
 23 
 
 9.96 
 
 68 
 
 29.45 
 
 113 
 
 48.94 
 
 24 
 
 10.39 
 
 69 
 
 29.88 
 
 114 
 
 49.38 
 
 25 
 
 10.82 
 
 70 
 
 30.32 
 
 115 
 
 49.81 
 
 26 
 
 11.26 
 
 71 
 
 30.75 
 
 116 
 
 50.24 
 
 27 
 
 11.69 
 
 72 
 
 31.18 
 
 117 
 
 50.68 
 
 28 
 
 1.2.12 
 
 73 
 
 31.62 
 
 118 
 
 51.11 
 
 29 
 
 12.55 
 
 74 
 
 32.05 
 
 119 
 
 51.54 
 
 30 
 
 12.99 
 
 75 
 
 32.48 
 
 120 
 
 51.98 
 
 31 
 
 13.42 
 
 76 
 
 32.92 
 
 121 
 
 52.41 
 
 32 
 
 13.86 
 
 77 
 
 33.35 
 
 122 
 
 52.84 
 
 33 
 
 14.29 
 
 78 
 
 33.78 
 
 123 
 
 53.28 
 
 34 
 
 14.72 
 
 79 
 
 34.21 
 
 124 
 
 53.71 
 
 35 
 
 15.16 
 
 80 
 
 34.65 
 
 125 
 
 54.15 
 
 36 
 
 1 5.59 
 
 81 
 
 35.08 
 
 126 
 
 54.58 
 
 37 
 
 16.02 
 
 82 
 
 35.52 
 
 127 
 
 55.01 
 
 38 
 
 16.45 
 
 83 
 
 35.95 
 
 128 
 
 55.44 
 
 39 
 
 16.89 
 
 84 
 
 36.39 
 
 129 
 
 55.88 
 
 40 
 
 17.32 
 
 85 
 
 36.82 
 
 130 
 
 56.31 
 
 4.1 
 
 17.75 
 
 86 
 
 37.25 
 
 131 
 
 56.74 
 
 42 
 
 18.19 
 
 87 
 
 37.68 
 
 132 
 
 57.18 
 
 43 
 
 18.62 
 
 88 
 
 38.12 
 
 133 
 
 57.61 
 
 44 
 
 19.05 
 
 89 
 
 38.55 
 
 134 
 
 58.04 
 
 45 
 
 19.49 
 
 90 
 
 38.98 
 
 135 
 
 58.48 
 
 471
 
 PLUMBING. 
 
 charge. What size of pipe will be required? From Table I we 
 find an elevation or head of. 50 feet will produce a pressure of 21.65 
 'pounds per square inch. Then if the length of the pipe were 
 only 100 feet, we should have a pressure of 21.65 pounds avail- 
 able to overcome the friction in the pipe, and could follow along the 
 line corresponding to 10 gallons in Table II until we came to the 
 
 TABLE II. 
 
 
 J 
 
 n. 
 
 i 
 
 m. 
 
 1 
 
 in. 
 
 11 
 
 in. 
 
 11 
 
 in. 
 
 2 
 
 in. 
 
 2J 
 
 in. 
 
 3 
 
 n. 
 
 rged per 
 
 ft 
 
 
 1 
 
 
 h 
 P. 
 
 
 1 
 
 
 1 
 
 
 1 
 
 
 Pi 
 | 
 
 
 ! 
 
 a 
 
 ~ 
 | 
 
 H 
 
 | 
 
 
 
 
 I 
 
 a 
 
 OQ 
 
 o 
 
 a 
 
 1 
 
 c 
 
 
 o 
 
 a 
 
 I 
 
 HH 
 
 a 
 
 I 
 
 
 
 
 >, 
 
 a 
 
 >, 
 
 s 
 
 >> 
 
 fl 
 
 ^ 
 
 a 
 
 >J 
 
 a 
 
 X 
 
 a 
 
 K^ 
 
 
 1 
 
 35 
 
 C 5 
 
 11 
 
 a 
 
 p> 02 
 
 II 
 It 
 
 Velocit 
 second 
 
 .2-c 
 
 *i a 
 
 ll 
 
 .tJ-c 
 
 og 
 
 >8 
 
 .2-0 
 "5 
 
 Si 
 
 Velocit 
 second 
 
 Frictio 
 pounds 
 
 Velocit 
 second 
 
 Frictio 
 pounds 
 
 Velocit 
 second 
 
 Frictio 
 pounds 
 
 Velocit 
 second 
 
 .2-a 
 
 3 
 
 P. 
 
 11 
 
 0) " 
 
 > cfl 
 
 Frictio 
 pounds 
 
 5 
 
 8.17 
 
 24.6 
 
 3.63 
 
 33 
 
 2.04 
 
 .84 
 
 1.31 
 
 .31 
 
 .91 
 
 .12 
 
 
 
 
 
 
 
 in 
 
 163 
 
 96.0 
 
 7.25 
 
 13.0 
 
 4.08 
 
 3.16 
 
 2.61 
 
 1.05 
 
 1.82 
 
 .47 
 
 1.02 
 
 .12 
 
 
 
 
 
 IS 
 
 
 
 10.9 
 
 
 6.13 
 
 6.98 
 
 3.92 
 
 2.38 
 
 2.73 
 
 .97 
 
 1.53 
 
 .27 
 
 
 
 
 
 20 
 
 
 
 14.5 
 
 50.4 
 
 8.17 
 
 12.3 
 
 5.22 
 
 4.07 
 
 3.63 
 
 1.66 
 
 2.04 
 
 42 
 
 
 
 
 
 25 
 
 
 
 18.1 
 
 78.0 
 
 10.2 
 
 19.0 
 
 6.53 
 
 6.40 
 
 4.54 
 
 2.62 
 
 2.55 
 
 .67 
 
 1.63 
 
 .21 
 
 1.13 
 
 .10 
 
 an 
 
 
 
 
 
 12.3 
 
 27.5 
 
 7.84 
 
 9.15 
 
 5.45 
 
 3.75 
 
 3.06 
 
 .91 
 
 
 
 
 
 35 
 
 
 
 
 
 14.3 
 
 370 
 
 9.14 
 
 1204 
 
 6 36 
 
 5.05 
 
 3.57 
 
 1.25 
 
 
 
 
 
 111 
 
 
 
 
 
 16.3 
 
 48.0 
 
 10.4, 
 
 16.10 
 
 7.26 
 
 6.52 
 
 4.09 
 
 1.60 
 
 
 
 
 
 4ft 
 
 
 
 
 
 
 
 11.7 
 
 20.2 
 
 8.17 
 
 8.15 
 
 4.60 
 
 2.02 
 
 
 
 
 
 ",! I 
 
 
 
 
 
 
 
 13.1 
 
 24.9 
 
 9.08 
 
 10.0 
 
 5.11 
 
 244 
 
 326 
 
 .81 
 
 2.27 
 
 85 
 
 75 
 
 
 
 
 
 
 
 19.6 
 
 56.1 
 
 13.6 
 
 22.4 
 
 7.66 
 
 5.32 
 
 4.90 
 
 1.80 
 
 3.40 
 
 .74 
 
 [00 
 
 
 
 
 
 
 
 
 
 18.2 
 
 39.0 
 
 10.2 
 
 9.46 
 
 6.53 
 
 3.20 
 
 4.54 
 
 1.31 
 
 1 "l 
 
 
 
 
 
 
 
 
 
 
 
 12.8 
 
 14.9 
 
 8.16 
 
 4.89 
 
 5.67 
 
 1 99 
 
 1 M 1 
 
 
 
 
 
 
 
 
 
 
 
 15.3 
 
 21.2 
 
 980 
 
 7.00 
 
 6.81 
 
 285 
 
 175 
 
 
 
 
 
 
 
 
 
 
 
 17.1 
 
 28.1 
 
 11.4 
 
 9.46 
 
 7.94 
 
 3>5 
 
 200 
 
 
 
 
 
 
 
 
 
 
 
 20.4 
 
 37.5 
 
 13.1 
 
 12.47 
 
 9.08 
 
 5.02 
 
 friction loss corresponding most nearly to 21.65, and take the size of 
 pipe corresponding. But as the length of the pipe is 600 feet, the 
 friction loss will be six times that given in Table II for given sizes 
 of pipe and rates of flow ; hence we must divide 21.65 by 6 to ob- 
 tain the available head to overcome friction, and look for this 
 quantity in the table, 21.65 -^- 6 3.61, and Table II shows i.s 
 that a 1-inch pipe will discharge 10 gallons per minute with a 
 friction loss of 3.16 pounds, and this is the size we should use. 
 
 EXAHPLES FOR PRACTICE. 
 
 1. What size pipe will be required to discharge 40 gallons 
 per minute, a distance of 50 feet, with a pressure head of 19 feet? 
 
 Ans. 1| inch. 
 
 472
 
 PLUMBING. 
 
 2. What head will be required to discharge 100 gallons per 
 minute through a 2* -inch pipe 700 feet long? 
 
 Ans. 52 feet. 
 PIPING. 
 
 Wrought iron, lead and brass are the principal materials 
 used for water pipes. Wrought-iron pipe is the cheapest and 
 easiest to lay, but is objectionable on account of rust and the 
 consequent discoloration of water passing through it. When it 
 
 TABLE III. 
 
 | 
 
 3 
 
 1 
 
 
 5 
 
 Q> 
 
 , 
 
 S 
 
 per square 
 urface. 
 
 per square 
 surface. 
 
 
 
 H 
 
 "3 
 1 
 
 
 1 
 
 
 a 
 
 a 
 
 "5 . 
 
 
 
 5 
 
 n 
 
 il outside c 
 
 I 
 
 il inside di 
 
 
 nal circum 
 
 ,h of pipe 
 of inside - 
 
 ,h of pipe 
 , of outside 
 
 oj 
 
 13 
 a 
 
 \ 
 
 "3 
 a 
 
 h of pipe< 
 bic foot. 
 
 ht per foot. 
 
 1 
 ?! 
 
 13 
 
 t 
 
 > 
 
 I 
 
 5 
 
 ns per foot 
 
 I 
 
 1 
 
 5 
 
 1 
 
 1 
 
 i 
 
 |l 
 
 r 
 
 1 
 
 H 
 
 1! 
 
 tt 
 1 
 
 I 
 
 ! 
 i 
 
 O 
 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 feet 
 
 feet 
 
 in. 
 
 in. 
 
 feet 
 
 pounds 
 
 
 
 
 . 
 
 .40 
 
 .068 
 
 .27 
 
 .85 
 
 1.27 
 
 14.1 
 
 9.44 
 
 .05 
 
 .13 
 
 2500. 
 
 .24 
 
 27 
 18 
 
 
 .0006 
 .0026 
 
 'I 
 
 .54 
 
 .088 
 
 .36 
 
 1.14 
 
 1.69 
 
 10.5 
 
 7.05 
 
 .10 
 
 .23 
 
 1385. 
 
 .42 
 
 U 
 
 
 .0057 
 
 . 
 
 .67 
 
 .091 
 
 .49 
 
 1.55 
 
 2.12 
 
 7.67 
 
 5.65 
 
 .19 
 
 .36 
 
 751.5 
 
 .56 
 
 1 1 
 
 
 .0102 
 
 : 
 
 .84 
 
 .109 
 
 .62 
 
 1.95 
 
 2.65 
 
 8.13 
 
 4.50 
 
 .30 
 
 .55 
 
 472.4 
 
 .84 
 
 14 
 
 
 .0230 
 
 
 
 1.05 
 
 .113 
 
 .82 
 
 259 
 
 3.29 
 
 4.63 
 
 3.63 
 
 .53 
 
 .86 
 
 270.0 
 
 1.12 
 
 ll 
 
 
 .0408 
 
 1 
 
 1.31 
 
 .134 
 
 1.05 
 
 3.29 
 
 4.13 
 
 3.68 
 
 2.90 
 
 .86 
 
 1.35 
 
 166.9 
 
 1.67 
 
 ll 
 
 
 .0638 
 
 
 166 
 
 .140 
 
 1.38 
 
 4.33 
 
 5.21 
 
 2.77 
 
 2.30 
 
 1.49 
 
 2.16 
 
 96.2 
 
 2.26 
 
 11 
 
 
 .0918 
 
 ij 
 
 1.90 
 
 .145 
 
 1.61 
 
 5.06 
 
 5.96 
 
 2.37 
 
 2.01 
 
 2.04 
 
 2.83 
 
 70.6 
 
 2.69 
 
 11 
 
 
 .1632 
 
 X 
 
 2.37 
 287 
 
 .154 
 .204 
 
 2.06 
 247 
 
 6.49 
 7.75 
 
 7.46 
 9.03 
 
 1.85 
 1.54 
 
 1.61 
 1 33 
 
 3.35 
 
 4.78 
 
 4.43 
 6.49 
 
 42.3 
 30 1 
 
 3.66 
 5.77 
 
 8 
 8 
 
 
 .2550 
 .3673 
 
 :i 
 
 3.50 
 
 .217 
 
 3.06 
 
 9.63 
 
 10.1 
 
 1.24 
 
 1.09 
 
 7.39 
 
 9.62 
 
 19.5 
 
 7.54 
 
 8 
 
 
 .4998 
 
 3J 
 
 4.00 
 
 .226 
 
 3.55 
 
 11.1 
 
 12.5 
 
 1.07 
 
 .95 
 
 988 
 
 12.5 
 
 14.5 
 
 9.05 
 
 H 
 
 
 .6528 
 
 f 
 
 4.50 
 
 .237 
 
 402 
 
 12.6 
 
 14.1 
 
 .95 
 
 .85 
 
 12.7 
 
 15.9 
 
 11.3 
 
 10.7 
 
 X 
 
 
 .8263 
 
 6 
 
 6 
 
 5.56 
 6.62 
 
 .259 
 .280 
 
 5.04 
 6.06 
 
 15.8 
 19.0 
 
 17.4 
 20.8 
 
 .75 
 
 .63 
 
 .57 
 
 20.0 
 28.9 
 
 24.3 
 34.4 
 
 7.2 
 4.9 
 
 IS 
 
 8 
 '8 
 
 
 1.469 
 1.999 
 
 is employed for this purpose it is customary to use galvanized 
 pipe, that is, pipe which has been covered with a thin coating of 
 zinc or zinc and tin. This prevents rust from forming where the 
 zinc is unbroken, but at the joints where threads are cut, and at 
 other places where the zinc becomes loosened, as by bending, the 
 pipe is likely to be eaten away more or less rapidly, depending 
 upon the quality of the water. Zinc, when taken into the 
 system, is poisonous, and for this reason galvanized pipes should 
 not ordinarily be used for drinking water. 
 
 473
 
 8 
 
 PLUMBING. 
 
 Table III gives the various dimensions of wrought-iron pipe. 
 In using pipe of this kind, it is well to allow something in size 
 for possible choking by rust or sediment. While galvanized 
 pipe does not rust, for a time at least, there is likely to be 
 a roughness which causes an accumulation of more or less 
 sediment. 
 
 TABLE IV. 
 
 Lead Pipe. 
 
 
 
 
 
 if 
 
 
 s 
 
 1 
 
 
 
 p. 5 
 
 
 "S 
 
 
 
 "Q 
 
 be ?- 
 
 
 g 
 
 1 
 
 
 2 
 
 s 
 
 
 2 
 
 "3 
 
 .2 
 3 
 
 I 
 
 
 a 
 
 1 I 
 
 
 1 
 
 a 
 55 
 
 a 
 
 ft 
 
 &o 
 
 r 
 5 
 
 
 a 
 
 1 
 
 2 
 
 
 g 
 
 1 
 
 3 
 
 .75 
 
 .18 
 
 1 Ib. 12 oz. 
 
 1968 
 
 492 
 
 3 
 
 .55 
 
 .087 
 
 10 
 
 1085 
 
 271 
 
 i 
 
 1.00 
 
 .25 
 
 3 
 
 1787 
 
 446 
 
 * 
 
 .63 
 
 .065 
 
 10 
 
 625 
 
 156 
 
 | 
 
 1.10 
 
 .23 
 
 3 8 
 
 1548 
 
 387 
 
 f ' 
 
 .84 
 
 .10 
 
 1 4 
 
 708 
 
 177 
 
 
 1.33 
 
 .29 
 
 4 14 
 
 1462 
 
 365 
 
 1 
 
 .93 
 
 .09 
 
 1 3 
 
 505 
 
 126 
 
 1 
 
 1.60 
 
 .30 
 
 6 
 
 1230 
 
 307 
 
 1 
 
 1.18 
 
 .09 
 
 1 8 
 
 325 
 
 81 
 
 H 
 
 1.80 
 
 .275 
 
 6 12 
 
 962 
 
 240 
 
 H 
 
 1.44 
 
 .095 
 
 2 
 
 322 
 
 80 
 
 H 
 
 2.08 
 
 .29 
 
 8 
 
 742 
 
 185 
 
 
 1.74 
 
 .12 
 
 3 
 
 245 
 
 61 
 
 if 
 
 2.12 
 
 .19 
 
 5 
 
 460 
 
 116 
 
 if 
 
 2.0 
 
 .125 
 
 3 10 
 
 318 
 
 79 
 
 2 
 
 2.60 
 
 .30 
 
 10 11 
 
 611 
 
 152 
 
 2 
 
 2.18 
 
 .09 
 
 4 
 
 200 
 
 50 
 
 Iron pipe having a lining of tin Jg inch or more in thickness 
 is now manufactured, but being a comparatively new product, its 
 wearing qualities have not yet been thoroughly tested. 
 
 Lead Pipe is the best and most widely used for domestic 
 water supply. Although poisonous under certain conditions, as 
 
 474
 
 s 
 
 S5 >> 
 
 2* 
 w 
 S^ 
 
 I!
 
 PLUMBING. 
 
 when new and bright and when used with very pure water, it 
 usually becomes coated with a scale which makes it practically 
 Harmless. It is more costly than iron pipe, and requires more 
 skill in laying and making up the joints. It is less likely to burst 
 from the action of frost, as it is a soft metal and stretches 
 with the expansion of the ice in the pipe. When it does 
 break under pressure it generally occurs in small holes not 
 over an inch long, which are easily repaired without removing 
 any part of the pipe, while in the case of iron pipe the cracks 
 generally extend the entire length of the section in which the 
 
 TABLE V. 
 
 Tin-lined Lead Pipe. 
 
 1 
 
 I 
 
 1 
 
 1 
 
 1 
 
 | 
 
 | 
 
 j 
 
 | 
 
 1 
 
 3 
 "3 
 
 2jf 
 
 Sf 
 
 * 
 
 ! 
 
 ojf 
 
 $ 
 
 |I 
 
 $ 
 
 |! 
 
 a 
 
 
 
 A 
 
 A 
 
 A 
 
 43 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 i 
 
 I 
 
 <o 
 
 '3 
 
 <a 
 
 a) 
 
 " 
 
 w 
 
 3 
 
 
 lb. oz. 
 
 lb. oz. 
 
 lb. oz. 
 
 lb. oz. 
 
 lb. oz. 
 
 lb. oz. 
 
 lb. oz. 
 
 lb. oz. 
 
 Ib.oz. 
 
 
 1 8 
 
 i 5 
 
 1 2 
 
 1 
 
 13 
 
 10 
 
 
 8 
 
 
 i 
 
 3 
 
 2 
 
 12 
 
 1 4 
 
 1 
 
 13 
 
 
 11 
 
 9 
 
 6 
 
 3 8 
 
 2 12 
 
 8 
 
 2 
 
 1 12 
 
 8 
 
 1 4 
 
 1 
 
 12 
 
 1 
 
 4 8 
 
 3 8 
 
 \ 
 
 2 4 
 
 2 
 
 12 
 
 1 8 
 
 1 4 
 
 1 
 
 1 
 
 6 
 
 4 12 
 
 ' 
 
 3 4 
 
 2 8 
 
 
 
 
 1 8 
 
 
 
 6 12 
 
 5 12 
 
 12 
 
 3 12 
 
 3 
 
 8 
 
 
 2 
 
 
 M 
 
 9 
 
 8 
 
 4 
 
 5 
 
 4 4 
 
 8 
 
 
 3 4 
 
 
 
 
 9 
 
 
 
 
 
 
 
 
 water is frozen, and new pipe will be required. Lead pipe 
 is commonly made in six different thicknesses or weights, desig- 
 nated as AAA, AA, A, B, C and D, in which AAA is the 
 heaviest and D the lightest. Table IV gives the principal prop- 
 erties of the heaviest and lightest weight for lead pipe of different 
 diameters. 
 
 Tin-lined lead pipe is used to some extent for conveying 
 water for domestic purposes. The principal objection to this pipe 
 lies in the difficulty experienced in making the joints. Tin melts 
 at a considerably lower temperature than lead, so that in making 
 wipe joints it is likely to melt before the lead and block up the 
 passage through the pipe. Another objection is due to the fact 
 
 475
 
 10 
 
 PLUMBING. 
 
 that the tin lining and the outer lead covering are simply pressed 
 together, and it often happens that in bending the pipe the lining 
 pulls away from the lead, thus both obstructing and weakening 
 the pipe. When used for hot water, the uneven expansion of the 
 two metals may separate the two layers, and so cause the same 
 difficulties already mentioned. 
 
 Table V gives some of the properties of tin-lined lead pipe. 
 
 WATR LEVEL 
 /N WCLL 
 
 Fig. 2. 
 
 The strength of tin-lined pipe is about the same as that of lead 
 pipe, the greater strength of the tin being offset by the lighter 
 weight of the pipe made in this way. 
 
 Brass Pipe. Brass is one of the best materials for hot- 
 water pipes, and should be used where the cost is not the control- 
 ling feature. It is commonly employed for connecting pumps and 
 boilers and for the steam-heating coils inside laundry-water 
 heaters. It is often used for the connections between the kitchen 
 hot-water tank and range, and when nickel plated is extensively 
 employed in connection with bathroom fixtures. The sizes and 
 thicknesses are approximately the same as wrought-iron pipe. 
 
 47G
 
 PLUMBING. 11 
 
 PUHPS. 
 
 The principle upon, which the pump operates has already 
 been taken up in the Instruction Paper, " Mechanics." The 
 more common forms are known as the "lift pump," the "suction 
 pump" and a combination of the two called the "deep well 
 pump." 
 
 Fig. 1 shows a pump of the first kind. In this pump A is 
 the cylinder, B the plunger, C the bottom valve and D the 
 plunger valve. When the plunger is drawn up, a vacuum is 
 formed in the cylinder, and water flows in through C to fill it. 
 When the plunger is forced down, valve D opens and allows the 
 water to flow through the plunger while C remains closed. As 
 this operation is repeated, the water is raised by the plunger at 
 each stroke until the entire length of the pump barrel is filled, 
 and it will then flow from the spout in an intermittent stream. 
 
 In the suction pump shown in Fig. 2, the cylinder and valves 
 are the same, but they are placed at the top of the well and are 
 connected with the water below by means of a pipe, as shown. 
 When the pump is operated, a vacuum is formed in the cylinder 
 and'pipe below the plunger, and the pressure of the atmosphere 
 upon the surface of the water forces it up the pipe and fills the? 
 chamber, after which the action becomes the same as in the case 
 of a lift pump. The pressure of the atmosphere is approximately 
 15 pounds per square inch, which corresponds to the weight of a 
 column of water 34 feet high, which is the height that the water 
 may be raised theoretically by suction. 
 
 When the surface of the water is a greater distance than this 
 below the point of discharge, a pump similar to that shown in Fig. 
 3 must be used. A is a cylinder with plunger and valves similar 
 to those of a suction pump. The cylinder is supported in the well 
 at some point less than 34 feet above the surface of the water ; E 
 is an air chamber connecting with the upper part of the pump 
 cylinder, and F a discharge pipe leading from the bottom of the 
 air chamber E. The action is as follows : water is pumped into 
 the bottom of the air chamber, and as it rises and seals the end 
 of the discharge pipe, the air in the upper part of the chamber 
 is compressed, and as soon as sufficient pressure is obtained the 
 water is forced out through the discharge pipe F. The pressure 
 
 477
 
 12 
 
 PLUMBING. 
 
 required in the air chamber depends upon the height to which the 
 
 water is raised. 
 
 The Hydraulic Ram. This is a device for automatically 
 
 raising water from a lower to a higher level, the only requirements 
 
 within certain limits being that 
 the ram shall be placed at a given 
 distance from the spring or source 
 of supply and at a lower level, 
 depending upon the height to 
 which the water is to be raised 
 and the length of the pipe through 
 which it is to be forced. The 
 distance from the source or 
 spring to the ram should be at 
 least from 25 to 50 feet, in order 
 to secure the required velocity 
 for proper operation. A differ- 
 ence in level of 2 feet, or even 
 less, is sufficient to operate the 
 ram ; but the greater the differ- 
 ence, the more powerful is its 
 operation. For ordinary pur- 
 poses, where the water is to be 
 conveyed from 50 to 60 rods, 
 about -J0- to -^ of the total amount 
 
 used can be raised and dis- 
 charged at an elevation ten 
 times as great as the fall from 
 the spring to the ram. 
 
 In Fig. 4, A represents 
 
 Fig. 3. 
 
 the source or spring, B the supply pipe, C a valve opening up- 
 ward, D an air chamber, E a valve closing when raised, and F 
 the discharge pipe. When the water in the pipe is at rest, 
 the valve E drops by its own weight and allows the water 
 to flow through it. As soon as a sufficient velocity is reached 
 by the water, its momentum or force raises the valve against its 
 seat and closes it. The water being thus suddenly arrested in its 
 
 478
 
 PLUMBING. 
 
 13 
 
 passage flows into the chamber D, where its sudden influx com- 
 presses the air in the top of the chamber, and this in turn forces 
 the water upward through the discharge pipe F. As soon as the 
 water in the pipe B becomes quiet, the valve E again opens and 
 the operation is repeated. Bends in either the drive or discharge 
 pipe should be avoided if possible. If elbows are necessary, the 
 extra long turn pattern should be used in order to give as little 
 resistance as possible. These machines are made of iron and 
 
 TIC. aoo' 
 Fig. 5. 
 
 Fig. 4. 
 
 brass. The valve and stem are of 
 bronze, on account of its wear- 
 ing qualities. 
 
 Cisterns and Tanks. Water 
 cisterns and tanks are made of 
 various materials and in different 
 shapes and sizes, according to 
 the special uses for which they are required. A durable and 
 satisfactory tank may be made of heavy woodwork or plank 
 bolted together with iron rods and nuts and then lined with some 
 sheet metal, such as copper, lead or zinc. Copper or lead makes 
 the best lining, as the zinc has a greater tendency to corrode and 
 become leaky. If copper is used, it should be tinned on the out- 
 side. Fig. 5 shows a wooden tank in plan, with the method of 
 locking the joints in the copper lining. All naib should be 
 so placed as to be covered by the copper, and the joints soldered 
 with the best quality of .solder, which should be allowed to 
 into the seams. If the tank is lined with lead, a good 
 
 470
 
 1 1 
 
 PLUMBING. 
 
 should be used (about six pounds per square foot) and the joints 
 carefully wiped by an experienced workman. If used for the 
 storage of drinking water, this form of lining is open to the same 
 objections as lead 'pipe, but if kept filled at all times, and espe- 
 cially if the water contains mineral matter to any extent, there is 
 very little danger, as a coating is soon formed over the surface of 
 the lead, protecting it from the action of the water. 
 
 Fig. C. 
 
 Cast-iron sectional tanks can be had in almost any size or 
 shape. A tank of this form is shown in Fig. 6. It is made up of 
 plates which are planed and bolted together, the joints being made 
 tight with cement. The sections are made in convenient sizes, so 
 that they may be handled easily and conveyed without difficulty 
 through small openings to any part of the house. These tanks 
 are easily set up, and are practically indestructible. Wrought- 
 iron tanks are often used, but are not as easily handled as either 
 of the kinds just described. Table VI will be found useful in 
 computing the size of cylindrical tanks. 
 
 COLD-WATER SUPPLY. 
 
 Systems. There are two general methods of supplying a 
 building with water, one known as the " direct supply " system, 
 and the other as the "indirect" or "tank" system. 
 
 In the direct system each fixture is connected with the 
 supply pipe and is under the same pressure as the street main, 
 
 480
 
 PLUMBING. 
 
 16 
 
 unless a reducing valve is introduced. This system is not always 
 desirable, as the street pressure in many places is likely to vary, 
 especially where the water is pumped into the mains. A variable 
 pressure is injurious to the fixtures, causing them to leak much 
 sooner than if subjected to a steady pressure. Where the pres- 
 sure in the street main exceeds 40 pounds per square inch, a 
 reducing valve should be used if the direct system is to be 
 employed. 
 
 TABLE VI. 
 
 Capacity of Cisterns, in Gallons, for each 10 inches in Depth. 
 
 Diam- 
 eter in 
 feet. 
 
 Gallons. 
 
 Diam- 
 eter in 
 feet. 
 
 Gallons. 
 
 Diam- 
 eter in 
 feet. 
 
 Gallons. 
 
 2.0 
 
 19.5 
 
 6.0 
 
 176.3 
 
 10 
 
 489.6 
 
 2.5 
 
 30.5 
 
 6.5 
 
 206.8 
 
 11 
 
 592.4 
 
 3.0 
 
 44.6 
 
 7.0 
 
 239.9 
 
 12 
 
 705.0 
 
 3.5 
 
 60.0 
 
 7.5 
 
 275.4 
 
 13 
 
 827.4 
 
 4.0 
 
 78.3 
 
 8.0 
 
 313.3 
 
 14 
 
 959.6 
 
 4.5 
 
 99.1 
 
 8.5 
 
 353.7 
 
 15 
 
 1101.6 
 
 5.0 
 
 122 A 
 
 9.0 
 
 396.5 
 
 20 
 
 1958.4 
 
 5.5 
 
 148.1 
 
 9.5 
 
 461.4 
 
 25 
 
 3059.4 
 
 The following factors for changing a given quantity of water 
 from one denomination to another will often be found useful : 
 
 Cubic feet X 62% = Pounds 
 Pounds -*- 62> = Cubic feet 
 Gallons X 8.3 = Pounds 
 Pounds -^ 8.3 = Gallons 
 Cubic feet X 7.48 = Gallons 
 Gallons H- 7.48 = Cubic feet 
 
 For domestic purposes the indirect system is much better. 
 In this case the connection with the street main is carried directly 
 to a tank placed in the attic or at some point above the high- 
 est fixture, and all the water used in the house discharged into 
 it. The supply of water is regulated by a ball-cock in the 
 tank which shuts it off when a certain level is reached. All the 
 plumbing fixtures are supplied from the tank, and are therefore 
 
 481
 
 16 
 
 PLUMBING. 
 
 under a constant pressure. This pressure depends upon the dis- 
 tance of the fixture below the tank. The pipes and fixtures in a 
 house supplied with the tank system will last much longer and 
 
 Jv 
 
 TO f?ANG BO/LR 
 
 J 
 
 give much better results than if connected directly with the street 
 main. The tank is also found useful for storage purposes in case 
 of repairs to the street mains, which is often a matter of much 
 inconvenience. 
 
 Fig. 7 sho\v s the general arrangement of the cold-water pipes 
 of an indirect supply system. On the right is shown the service 
 
 482
 
 PLUMBING. 
 
 17 
 
 pipe, which is carried directly from the street to the attic, and 
 then connected with a ball-cock located inside the house tank. 
 A supply pipe is taken from the bottom of the tank and carried 
 downward through the building for supplying the various fixtures. 
 A stopcock should be placed in the supply pipe for closing off 
 the tank connections in case of repairs to the house-piping or 
 fixtures. 
 
 Tank Overflow Pipe. In order to prevent any possibility 
 of overflow, every house tank should be supplied with an overflow 
 pipe of sufficient size to carry off easily the greatest quantity of 
 water that may be discharged into it. The overflow from a house 
 tank should never be connected directly with a sewer or soil pipe, 
 even if provided with traps, for the water may seldom flow 
 
 SERVICE 
 
 OCK 
 
 LEAD STREET 
 
 PIPE). \ jf^. MAIN 
 
 Fig. 8. 
 
 through this pipe, thus allowing the trap to become unsealed 
 through evaporation. It is much better to let the end of the 
 overflow pipe be open to the atmosphere or drop over some fixture 
 which is in constant use. 
 
 Service Pipe Connections. Fig. 8 shows the usual method 
 of connecting the service pipe with the street main. The service 
 cock is connected directly with the main, and should be carefully 
 blocked, so that any pressure of earth from above will not break 
 the connection or strain the cock. To do this properly, the earth 
 under the pipe should be rammed down solid after the connections 
 are made, and the pipe at this point should be supported on sound 
 
 483
 
 18 
 
 PLUMBING. 
 
 wooden blocks. If galvanized iron is used for the service pipe, it 
 should in all cases be connected to the main service cock with a 
 short piece of lead pipe two or three feet long, for the reason that 
 lead will give or sag with the pressure of the earth without break- 
 ing. The remainder of the pipe should be carefully embedded in 
 the earth, to prevent uneven strains at any particular point. 
 Connections between the lead and iron pipes should be made by 
 means of brass ferrules and wiped joints. A stopcock should 
 be placed in the service pipe just inside the cellar wall, and in a 
 position where it will be accessible in case of accident. A drip 
 should be connected with the stopcock for draining the pipes 
 when water is shut off. 
 
 In protecting pipes against 
 freezing it is well to pack them 
 in hair, felt, granulated cork or 
 dry shavings where they pass 
 through the floor. This is shown 
 in Fig. 8. When the service 
 pipe comes in below the cellar 
 floor, it may be arranged as shown 
 in Fig. 9. The cock should be 
 placed about 18 inches below the 
 cellar bottom in a wooden box 
 with hinged cover, so that it 
 may be easily reached. 
 In many cities and in certain elevated situations the pres- 
 sure in the mains is not sufficient to carry the water to the 
 house tanks in the attics of the higher buildings, and it becomes 
 necessary to use some form of automatic pump for this purpose. 
 The screw pump shown in Fig. 10 is especially adapted to uses of 
 this kind when equipped with an electric motor and automatic 
 starting and stopping devices. A float in the tank operates an 
 electric switch by means of a chain and weights, as shown. A 
 centrifugal or rotary pump is also satisfactory for this work. 
 
 Another device which may be attached to a steam pump is 
 shown in Fig. 11. When the water line in the tank reaches 
 a given height, the aoat closes a butterfly valve in the 
 discharge pipe, thus increasing the pressure within it; this 
 
 484
 
 PLUMBING. 
 
 19 
 
 in pressure acts on the bottom of a piston by means of a connect- 
 ing pipe, and in raising the piston, shuts off the steam supply to the 
 pump. When the water line in the tank is lowered, the float falls 
 
 and the butteifly valve 
 opens, relieving the pres- 
 sure in the pipe and al- 
 lowing the steam valve to 
 open by the action of the 
 counterweights attached 
 to the lever arm of the 
 valve, as shown. The 
 automatic valve is shown 
 in section in Fig. 12. 
 Another means of rais- 
 ing water to an eleva- 
 tion for domestic pur- 
 poses, especially in the 
 country, is by the use of 
 a windmill. A large 
 storage tank is placed at 
 a suitable height so that 
 a sufficient supply may 
 be pumped on windy 
 days to last over inter- 
 vening periods of calm 
 weather. 
 
 HOT- WATER SUPPLY. 
 
 All modern systems 
 of plumbing include a 
 hot-water supply to the 
 various sinks, bowls, 
 bathtubs and laundry- 
 tubs throughout the 
 house. 
 
 Fig. 10. 
 
 Fig. 13 shows the usual arrangement of a kitchen boiler and 
 water-back with the necessary pipe connections. The boiler is 
 
 435
 
 20 
 
 PLUMBING. 
 
 Fig. 11. 
 
 486
 
 PLUMBING. 
 
 21 
 
 commonly made of copper and supported upon a castriron base. 
 It may be located in the kitchen near the range, or may be 
 concealed in a nearby closet. The "water-back," so called, is 
 a special casting placed so as to form one side of the fire box in 
 
 the range. The cold-water supply pipe to the boiler usually 
 enters at the top and is carried down to a point near the bottom, 
 as shown by the dotted lines. Connection is made between the 
 bottom of the boiler and the lower chamber of the water-back. The 
 upper chamber is connected at a point about one-third of the way 
 up in the side of the boiler, as shown. The circulation of water 
 
 487
 
 22 
 
 PLUMBING. 
 
 through the boiler and supply pipes is the same as already de- 
 scribed for hot-water-heating sj-stems. The range fire in contact 
 with the water-back heats the water within it, which causes it to 
 rise through the pipe connected witli the upper chamber and 
 
 HOT WATER TO BU/LD/NG 
 
 COLO WATER 
 SUPPLY 
 
 Ai Jt 11 
 
 WATER BACK. 
 /N RANGE 
 
 Fig. 13. 
 
 flow into the boiler or tank ; in the meantime cooler water flows 
 in at the lower connection to take its place, and the circulation 
 thus set up is constant as long as there is a fire in the range. 
 
 The "boiler," so called, is not a heater, but only a storage 
 tank. As the water becomes heated it rises to the top of the tank 
 and is carried to the different fixtures in the building through a 
 pipe or pipes connected at this point. The cold-water supply pipe 
 is connected with the house tank so that the pressure in the boiler 
 
 488
 
 PLUMBING. 
 
 is that due to the height of the tank above it. When any of the 
 hot-water faucets are open^ the pressure of the cold water in the 
 supply pipe forces out the hot water at the top of the boilers 
 and rushes in to take its place. There is no connection 
 between the circulation through the water-back and the pressure 
 in the cold-water supply pipe. The circulation is due only to the 
 difference in temperature be- 
 tween the water in the pipe 
 leading from the top of the 
 water-back and the water in 
 the lower part of the boiler, 
 and difference in elevation of 
 the connections with the 
 boiler. The nearer the top of 
 the boiler the discharge from 
 the water-back is connected, 
 the more rapid will be the BLOW^<. 
 circulation and the greater 
 the quantity of water which 
 will be heated in a given 
 
 time. The cold-water supply simply furnishes a pressure to force 
 the hot water through the pipes to the different fixtures, and re- 
 places any water that is drawn from the boiler. 
 
 Care should always be taken to have the pipes between the 
 water back and the boiler free from sediment or any other ob- 
 struction. If the water-back from any cause should become shut 
 off from the boiler, an explosion would be likely to occur if there 
 was a hot fire in the range. Freezing of the pipes is sometimes a 
 cause of accident. The sediment which accumulates more or less 
 rapidly should be regularly blown off through the blow-off cock 
 provided for this purpose at the bottom of the boiler. The best 
 time for doing this is in the morning, before the fire is started. 
 The device shown in Fig. 14 is intended to prevent the sediment 
 from collecting in the pipes or from being drawn into the water- 
 back, making the water roily when a large amount is drawn off at 
 one time. It consists of a smaU cylinder or chamber connected 
 to the bottom of the boiler in such a way that the sediment will 
 fall into it and not be disturbed by the circulation of the water 
 through the pipes. 
 
 Fig. 14. 
 
 489
 
 24 
 
 PLUMBING. 
 
 Double Water-back Connections. It is often desirable to 
 connect a boiler with two water-backs, one in the kitchen range 
 and another in a laundry stove in the cellar for summer use. 
 Fig. 15 shows the common method of making the connections. 
 In this case either may be used separately, or both together with- 
 out any adjustment of valves. The blow-off cock at the bottom 
 
 Fig. 15. 
 
 of the lower water-back should be opened quite often to clear it 
 of sediment, as it will collect much faster at this point than at the 
 bottom of the boiler. 
 
 Double Boiler Connections. It quite frequently happens that 
 the kitchen boiler does not have sufficient capacity for the entire 
 house, and it is not desirable to use a larger boiler on account 
 
 490
 
 PLUMBING. 
 
 26 
 
 V I / 
 
 of the limited space in the kitchen. In such cases a second boiler 
 may be connected with the laundry stove if one is provided, and 
 the water pipes from both boilers be connected together at some point 
 so that they may 
 both discharge hot 
 water into the same 
 general supply. 
 
 Stopcocks should 
 be placed in the 
 pipe connections as 
 shown, so that 
 either boiler may 
 be shut off for 
 repairs without in- 
 terfering with the 
 operation of the 
 other. Waste cocks 
 should always be 
 used for this pur- 
 pose, so that when 
 closed there will 
 be a connection be- 
 tween the boiler 
 and the atmos- 
 phere. This will 
 prevent damage to 
 the boiler in case 
 those in charge 
 should forget to 
 open the cocks 
 when starting up a 
 fire in the stove 
 with which the 
 boiler is connected. 
 
 
 
 V 1 
 
 1 
 
 
 \ 
 
 ] 
 
 Fig. 16. 
 
 Circulation Pipes. It is often desirable to produce a con- 
 tinuous circulation in the distributing pipes so that hot water may 
 be drawn from the faucets at once, without waiting for the cooler 
 water in the pipe between the boiler and the faucet to run out. 
 
 491
 
 26 
 
 PLUMBING. 
 
 This is accomplished by connecting a small pipe with the hot- 
 water pipe near the faucet, and connecting it with the bottom of 
 the boiler as shown in Fig. 17. This makes a circuit, and a con- 
 stant circulation is produced by the difference in temperature of 
 the water in the supply and circulation pipes. 
 
 TER SUPPLY 
 
 Fig. 
 
 Ripe Connections* Brass or copper pipe with screwed fit- 
 tings should always be used for making the connections between 
 the boiler and water back. Where unions are used they should 
 have ground joints without packing. Lead pipe is too soft to 
 
 492
 
 PLUMBING. 
 
 27 
 
 stand the high temperature to which these pipes are sometimes 
 subjected. 
 
 Laundry Boilers. In laundries, hotels, etc., where a large 
 amount of hot water is used, it is necessary to have a larger 
 storage tank and a heater with more heating surface than can be 
 
 Fig. 18. 
 
 obtained in the ordinary range water-back. Fig. 18 shows an 
 arrangement for this purpose. 
 
 The boiler may be of wrought iron or steel of any size de- 
 sired, and is usually suspended from the ceiling by means of 
 heavy strap iron. The heaters used are similar to those employed 
 for hot water warming. The method of making the connections 
 is indicated in the illustration. 
 
 493
 
 PLUMBING. 
 
 The capacity of the heater and tank depends entirely upon 
 the amount of water used. In some eases a large storage tank 
 and a comparatively small heater are preferable^ and in others 
 the reverse is more desirable. 
 
 The required grate surface of the heater may be computed as 
 fallows : first determine or assume the num"ber of gallons to be heated 
 per hour, and the required rise in temperature. Reduce gallons 
 
 STEAM CO/L 
 
 COLO WATER 
 SUPPLY 
 
 Fig. 19 
 
 to pounds by multiplying by 8.3, and multiply the result by the 
 rise in temperature to obtain the number of thermal units. As- 
 suming a combustion of five pounds of coal per square foot 
 of grate, and an efficiency of 8,000 thermal units per pound 
 of coal, we have 
 
 Grate Surface in sq. ft. = g^L^L^H X 8.3 X rise intemp^ 
 
 o X 8,000 
 
 Example. How many square feet of grate surface will be 
 required to raise the temperature of 200 gallons of water per 
 hour from 40 degrees to 180 degrees ? 
 
 2QO X 8.3_X_(180-40) 
 
 5 X 8000 
 
 In computing the amount of water required for bathtubs it 
 is customary to allow from 20 to 30 gallons per tub, and to con- 
 
 494
 
 PLUMBING. 
 
 29 
 
 0^55=3 
 
 sider that the tub may be used three or four times per hour as a 
 maximum during the morning. This will vary a good deal, de- 
 pending upon the character of the building. The above figures 
 are based on apartment hotel practice. 
 
 Boilers with Steam Coils. In large buildings where steam 
 is available, the water for domestic purposes is usually warmed by 
 placing a steam coil of brass or 
 copper pipe in the storage tank. 
 This may be a trombone coil made 
 up with brass fittings, or a spiral 
 consisting of a single pipe. Heaters 
 of these types are shown in Figs. 
 19 and 20. The former must be 
 used in tanks which are placed 
 horizontally, and the latter in 
 vertical tanks. If the steam is 
 used at boiler pressure, the con- 
 densation may return directly to 
 the boiler by gravity ; but if steam 
 at a reduced pressure is used, it 
 must be trapped to the receiver of 
 a return pump or to the sewer. 
 
 The cold water is supplied 
 near the bottom of the tank, and 
 the service pipes are taken off 
 at the top. A drip pipe should 
 
 be connected with the bottom, for draining the tank to the 
 sewer. Gate valves should be provided in all pipe connections 
 for shutting off in case of repairs. Sometimes a storage tank is 
 connected with a steam-heating system for winter use, and cross 
 connected with a coal-burning heater for summer use where 
 steam is not available. Such an arrangement is 1 shown in 
 Fig. 21. 
 
 The efficiency of a steam coil surrounded by water is much 
 greater than when placed in the air. A brass or copper pipe will 
 give off about 200 thermal units per square foot of surface per 
 hour for each degree difference in temperature between the steam 
 and the surrounding water. This is assuming that the water is 
 
 COLD WATR 
 SUPPLY 
 
 Fig. 20.
 
 30 
 
 PLUMBING. 
 
 circulating through the heater so that it moves over the coil at a 
 moderate velocity. In assuming the temperature of the water we 
 must take the average between that at the inlet and outlet. 
 
 Example. How many square feet of heating surface will be 
 required in a brass coil to heat 100 gallons of water per hour 
 from 38 degrees to 190 degrees, with steam at 5 pounds pressure? 
 
 Fig. 21. 
 
 Water to be heated = 100 X 8.3 = 830 pounds. 
 Rise in temperature 190 38 = 152 degrees. 
 Average temperature of water in contact with the coils 
 
 190 
 
 114 degrees 
 
 496
 
 PLUMBING. 
 
 31 
 
 Temperature of steam at 5 pounds pressure := 228 degrees. 
 The required B. T. U. per hour = 830 X 152 = 120,160. 
 Difference between the average temperature of the water and 
 the temperature of the steam = 228 114 = 114 degrees. 
 
 B. T. U. given up to the water per square foot of surface per 
 hour = 114 X 200 = 22,800, and 
 126,160 
 22,800 
 
 =r 5.5 square feet. Ans. 
 
 EXA/1PLES FOR PRACTICE. 
 
 1. How many linear 
 feet of 1-inch brass pipe will 
 be required to heat 150 gal- 
 lons of water per hour from 
 40 to 200 degrees, with steam 
 at 20 pounds pressure ? 
 
 Ans. 21.8 feet. 
 
 2. How many square 
 feet of grate surface will be 
 required in a heater to heat 
 300 gallons of water per hour 
 from 50 to 170 degrees? 
 
 Ans. 7.4 square feet. 
 
 3. A hot-water storage 
 tank has a steam coil con- 
 sisting of 30 linear feet of 
 1-inch brass pipe. It is 
 desired to connect a coal-burn- 
 ing heater for summer use 
 which shall have the same 
 capacity. Steam at 5 pounds 
 pressure is used, and the 
 water is raised from 40 to 180 
 degrees. How many square 
 feet of grate surface are re- 
 quired? Ans. 5.9 sq. ft. 
 
 4. A hotel has 30 bathtubs, which are used three timep 
 apiece between the hours of seven and nine in the morning. The 
 
 Fig. 22. 
 
 497
 
 32 
 
 PLUMBING. 
 
 hot-water system has a storage tank of 400 gallons. Allowing 20 
 gallons per bath, and starting with the tank full of hot water, how 
 many square feet of grate surface will be required to heat the 
 additional quantity of water within the stated time, if the temper- 
 ature is raised from 50 to 130 degrees? If steam at 10 pounds 
 pressure is used instead of a heater, how many square feet of 
 heating coil will be required? . j 11. (> sq. ft. grate. 
 
 I 1.5.:) sq. ft. coil. 
 
 Temperature Regulators. Hot-water storage tanks having 
 special heaters or steam coils snould be provided with some means 
 for regulating the temperature of the water. Fig. 22 shows ;i 
 simple form attached to a coal-burning heater. It consists of a 
 
 Fig. 23. 
 
 casting about nine inches long, tapped at the ends to receive a 
 2-inch pipe, and containing within it a second shell called the 
 steam generator. (See Fig. 28.) The outer shell is connected 
 with the circulation pipe as shown in Fig. 22. The generator is 
 filled with kerosene, or a mixture of kerosene and water, depend- 
 ing upon the temperature at which it is wished to have the regu- 
 lator operate. The inner chamber connects with the space below 
 a flexible rubber diaphragm. The boiling point of the mixture in 
 the generator is lower than that of water alone, and depends upon 
 the proportion of kerosene used, so that when the temperature 
 of the water in the outer chamber reaches this point, the mixture 
 boils, and its vapor creates a pressure which forces down the 
 diaphragm and closes the draft door of the heater with which it 
 is connected - 
 
 498
 
 PLUMBING. 
 
 33 
 
 A form of regulator for use with a steam coil is shown iw 
 Fig. 24. This consists of a rod made up of two metals having 
 different coefficients of expansion, and so arranged that this differ- 
 ence in expansion will produce sufficient movement, when the 
 water reaches a given temperature, to open a small valve. This 
 
 Fig. 24. 
 
 allows water pressure from the street main with which it is con- 
 nected, to flow into a chamber above a rubber diaphragm, thus 
 closing the steam supply to the coil. When the water cools, the 
 rod contracts', and the pressure is released above the diaphragm, 
 allowing the valve to open and thus again admit steam to the 
 coil.
 
 34 PLUMBING. 
 
 GAS FITTING. 
 
 Next to heating and ventilation and plumbing there is uo 
 part of interior house construction requiring so much attention as 
 the gas piping and gas fitting. 
 
 Gas piping in buildings should be installed according to 
 carefully drawn specifications, and only experienced workmen 
 should be employed. The gas fitter should work from an accurate 
 sketch plan showing the location of all gas service and distributing 
 pipes in the building and the locations of the meter and shut-off 
 cock. The plan should also indicate the exact location and size 
 of the risers and the position of the lights in the different rooms. 
 
 Service Pipe and Meter. The service pipe by which the gas 
 is conveyed to a building is always put in by the gas company. 
 The size of tins pipe is governed by the number of burners to be 
 supplied, but it should never in any case, even for the smallest 
 house, be less than 1 inch in diameter. This may be slightly 
 larger than is necessary, but the cost is only a little more and the 
 liability of stoppages is much less ; this also allows for the future 
 addition of more burners, which is often a matter of much con- 
 venience. Service and distributing pipes for water, or naphtha 
 gas, should be from 15 to 20 per cent larger than for coal gas. 
 The material for the main service pipe, from the street to the 
 house, should be either lead or wrought iron. As a rule, wrought- 
 iron pipe with screwed joints is preferable to lead, because it is 
 less likely to sag in the trench, thus causing dips for the accumu- 
 lation of water of condensation. Care must be observed in the 
 use of wrought-iron pipe to protect it by coating with asphalt, or 
 coal tar, to prevent corrosion. The pipe should also be well sup- 
 ported in the trench. Service pipes should preferably rise from 
 the street gas main toward the house in order to allow all conden- 
 sation to run back into the mains. This, however, cannot always 
 be done, owing to the relative levels of the street main and the 
 meter in the house. The latter should be placed in a cool, well- 
 lighted position, at or below the level of the lowest burner, which 
 is usually in the cellar. If the meter is below the gas main, the 
 service pipe must grade toward the house and should be provided 
 with a drip pipe, or "siphon," before connecting with the meter. 
 
 500
 
 PLUMBING. 35 
 
 When water accumulates in the siphon, the cap is removed and 
 the pipe drained. The gas company usually supplies and sets the 
 meter, which should be of ample size for the number of lights 
 burned. 
 
 A stopcock, or valve, is placed by the company in the service 
 pipe, so that the gas may be shut off from each building sepa- 
 rately. This is usually placed outside near the curb in the case 
 of buildings requiring a pipe 11 inches in diameter, or larger. In 
 the case of theaters or assembly halls it is often required by law 
 as a safeguard in case of fire. The meter is connected with both 
 the service pipe and the main house pipe by means of short con- 
 nections of extra heavy lead pipe. A cock is placed near the 
 meter, and in large buildings this is arranged so that a lock may 
 be attached to it when the gas is shut off by the company. Gate 
 valves are preferable for gas mains, as they give a free opening 
 equal to the full size of the pipe. 
 
 PIPES. 
 
 Distributing Pipes. The distributing pipes inside of a house 
 are usually of wrought iron, except where exposed in rooms, or 
 
 Fig. 25. Fig. 26. Fig. 27. Fig. 28. 
 
 carried along walls lined with enameled brick, or tile, in which 
 case they may be of polished bass, or copper. The chief re- 
 quirements for wrought-iron distributing pipes are that they be 
 carefully welded and perfectly circular in section. The first is 
 important in order to avoid splitting when cutting or threading 
 them on the pipe bench. 
 
 All gas pipes are put together with screwed joints, a thread 
 'being cut upon the outside. When the pipe is irregular in sec- 
 tion the threading will be more or less imperfect, and as a result 
 the joints will be defective. A good gas fitter must examine all 
 pipe as it is delivered at the building, and observe the section 
 
 501
 
 PLUMBING. 
 
 either by means of the eye or by the use of calipers. Plain 
 wrought-iron pipe is likely to rust upon the inside, especially 
 where the gas supplied is imperfectly purified, and for this reason 
 it is often advisable to use rustless, or galvanized pipe, for the 
 smaller sizes. 
 
 Fig. 29. 
 
 Fittings and Joints. The fittings used in gas piping are 
 
 similar to those employed in steam work, such as couplings, 
 elbows, tees, crosses, etc. (see Figs. 25, 26, 27 and 28). Other 
 fittings not so extensively used are the union, the flange union, 
 
 the running socket and right 
 and left couplings. Fig. 29 
 shows a screwed union and 
 Fig. 30 a flange. These fit- 
 tings are of cast iron, or of 
 malleable iron, the latter being 
 preferred for the smaller sizes. 
 Fittings may be either gal- 
 vanized, or rustless, as in the 
 
 Fig. 30. 
 
 case of pipe, and it is especially necessary that they be free from 
 sand holes. In making pipe joints the gas fitter should make use 
 of red lead, or red and white lead mixed, to make up for any pos- 
 sible imperfections in the threads ; this, however, should be used 
 sparingly so that the pipe may not be choked or reduced in size. 
 The use of gas fitters' cement should be prohibited. It is impor- 
 tant that each length should be tightly screwed into the fitting 
 before the next length is put on. It is always a wise precaution 
 
 5C3
 
 PLUMBING. 37 
 
 to examine eacli length of pipe before it is put in place, to inakt; 
 sure it is free from imperfections of any kind. 
 
 Running Pipes and Risers. All large risers should be ex- 
 posed, and it is desirable to keep all piping accessible aa far as 
 possible so that it may be easily reached for repairs. All hori- 
 zontal pipes should be run with an even though slight grade 
 toward the riser, and all sags in the pipes must be avoided to prevent 
 the collection of water, and for this reason they should be well sup- 
 ported. Floor boards over all horizontal pipes should be fastened 
 down with screws so that they may be removed for inspection of the 
 pipes. When it becomes necessaiy to trap a pipe, a drip with a 
 dram cock must be put in, but this should always be avoided un- 
 der floors or in- other inaccessible places. When pipes under floors 
 run across the timbers, the latter should be cut into near the ends, 
 or where supported upon partitions, in order to avoid weakening 
 the timbers. All branch outlet pipes should be taken from the 
 side or top of the running lines, and bracket pipes should be run 
 up from below instead of dropping from above. Never drop a 
 center pipe from the bottom of a running line ; always take such 
 an outlet from the side of the pipe. Where possible it is better 
 to cany up a main riser near the center of the building, as the 
 distributing pipes will be smaller than if carried up at one end. 
 Where this is done the timbers will not require so much cutting, 
 and the flow of gas will be more uniform throughout the system. 
 
 When a building has different heights of post it is always 
 better to have an independent riser for each height rather than to 
 drop a system of piping from a higher to a lower post and grading 
 to a lower point and establishing drip pipes. Drips in a building 
 should be avoided if possible and the whole system of piping be 
 so arranged that any condensed gas will flow back through the 
 system and into the service pipe. All outlet pipes should be 
 securely fastened in position, so that there will be no possibility 
 of their moving when the fixtures are attached. Center pipes 
 should rest on a solid support fastened to the floor timbers near 
 the top. The pipe should be securely fastened to the support 
 to prevent movement sidewise. The drop must be perfectly plumb 
 and pass through a guide fastened near the bottom of the timbers 
 in order to hold it rigidly in position. (See arrangement, Fig. 31.) 
 
 503
 
 38 
 
 PLUMBING. 
 
 Unless otherwise directed, outlets for brackets should be 
 placed 5|- feet from the floor except in the cases of hallways and 
 bathrooms, Avhere it is customary to place them 6 feet from the 
 floor. Upright pipes should be plumb, so that nipples which pro- 
 ject through the walls will be level; the nipples should not 
 
 Fig. 31. 
 
 project more than | inch from the face of the plastering. Lathes 
 and plaster together are usually about | inch thick, so the nipples 
 should project about 1-i inches from the face of the studding. 
 
 Gas pipes should never be placed on the bottoms of floor 
 timbers that are to be lathed and plastered, because they are inac- 
 cessible in case of leakage or alterations. 
 
 Pipe Sizes. All risers and distributing pipes, and all 
 
 504
 
 PLUMBING. 
 
 branches to bracket and center lights should be of sufficient size 
 to supply the total number of burners indicated on the plans. 
 Mains and brandies should be proportioned according to the num- 
 ber of lights they are to supply, and not the number of outlets. 
 
 No pipe should be less than | inch in diameter, and this size 
 should not be used for more than two-bracket lights. No pipe 
 for a chandelier should be less than 1 inch up to four burners, 
 and it should be at least | inch for more than four burners. The 
 following table gives sizes of supply pipes for different numbers 
 of burners and lengths of run. 
 
 TABLE VII. 
 
 Size of Pipe. 
 Inches. 
 
 Greatest Length 
 of Run. 
 Feet. 
 
 Greatest Num- 
 ber of Burners 
 to be Supplied. 
 
 f 
 
 20 
 
 2 
 
 
 30 
 
 4 
 
 
 
 50 
 
 15 
 
 1 
 
 70 
 
 25 
 
 1| 
 
 100 
 
 40 
 
 H 
 
 150 
 
 70 
 
 2 
 
 200 
 
 140 
 
 2* 
 
 300 
 
 225 
 
 3 
 
 400 
 
 300 
 
 4 
 
 500 
 
 500 
 
 Testing Gas Pipes. As soon as the piping is completed, it 
 should be tested by means of an air pump ; a manometer or mer- 
 cury gage is used to indicate the pressure. In the case of large 
 buildings, it is better to divide the piping into sections, and test 
 each separately. All leaks revealed must be repaired at once, and 
 the test repeated until the whole system is air tight at a pressure 
 of from 15 to 20 inches of mercury, or 7J to 10 pounds per 
 square inch. 
 
 The final test is of great importance. This test is to provide 
 against future troubles and dangers from leaks resulting from 
 sand holes in the fittings, split pipe, imperfect threads, loose joints 
 or outlets left without capping. If the building is new, a careful 
 inspection should first be made to see that all outlets are closed, 
 then the valve in the service pipe closed and the air pump at- 
 tached to any convenient side-light. To the same outlet or an 
 
 505
 
 40 PLUMBING. 
 
 adjacent one attach the mercury column gage used by gas. fitters, 
 and having a column from 15 to 20 inches in height. Care must 
 be taken that there are no leaks in the gage or its connections ; a 
 tight-closing valve must be placed between the gas pipe and the 
 temporary connections with the pump, so that it may be shut off 
 immediately after the pump stops, thus preventing any leakage 
 through the pump valves or hose joints. When all is ready, 
 pump the system full of air until the mercury rises to a height of 
 at least 12 inches in the gage; then close the intermediate valve 
 between the pump and the piping. Should the mercury column 
 " stand " for five minutes, it is reasonable to assume that the pipes 
 are sufficiently tight for any pressure to which they will afterward 
 be subjected. 
 
 If the mercury rises and falls with the strokes of the pump, 
 it indicates a large leak or open outlet near the pump. But 
 should there be a split pipe or an aggregation of small leaks, the 
 mercury will run back steadily between the strokes of the pump, 
 though more slowly than it rose. Should it rise well in the glass 
 and sink at the rate of 1 inch in five seconds, small leaks in fit- 
 tings or joints may be expected. 
 
 A leak that cannot be detected by the sound of issuing air 
 may usually be found by applying strong soap-water with a brush 
 over suspected joints or fittings ; the leak in this case being indi- 
 cated by the bubbles blown by the escaping air. Sometimes it is 
 necessary to use ether in the pipes for locating leaks, if the pipes 
 i\re in partitions or under floors. The ether is put into a bend of 
 the connecting hose, or in a cup attached to the pump, and forced 
 in with the air. By following the lines of the pipe, the approxi- 
 mate position of a leak may be determined by the odor of escap- 
 ing ether. 
 
 If the house is an old one or has been finished, the meter 
 should be taken .out and the bottom of the main riser capped. 
 Next remove all fixtures and cap the outlets. Then use ether to 
 locate the leaks before tearing up floors or breaking partitions. 
 
 GAS FIXTURES. 
 
 Burners. Illuminating gas is a complex mixture of gases, 
 of which various chemical compounds of carbon and hydrogen 
 
 506
 
 PLUMBING. 41 
 
 form the principal light-giving properties. Gas always contains 
 more or less impurities, such as carbonic oxide, carbonic acid, 
 ammonia, sulphureted hydrogen and bisulphides of carbon. 
 These are partly removed by purifying processes before the gas 
 leaves the works. 
 
 When the gas-jet is lighted, the hydrogen is consumed in the 
 lower part of the flame, producing sufficient heat to render the 
 minute particles of carbon incandescent. The hydrogen, in the 
 process of combustion, combines with the oxygen from the air, 
 forming an invisible vapor of water, while the carbon unites with 
 the oxygen, forming carbonic acid. 
 
 Fig. 32. Fig. 33. Fig. 34. 
 
 Various causes tend to render combustion incomplete : there 
 may be excessive pressure of gas, lack of air or defective burners. 
 An excess of pressure at the burners causes a reduction of the 
 amount of illumination ; on the other hand, if the pressure is in- 
 sufficient, the heat of the flame will not raise the carbon to a 
 white heat, and the result will be a smoky flame. It therefore 
 follows that for every burner there is a certain pressure and corre- 
 sponding flow of gas which will cause the brightest illumination. 
 
 There is a great variety of burners upon the market, among 
 which the following are the principal types : 
 
 The single-jet burner, the bat's-wing burner, the fish-tail 
 burner, the Argand burner, the regenerative burner and the in- 
 candescent burner. 
 
 The Single-jet burner (Fig. 32) is the simplest kind, having 
 
 507
 
 42 PLUMBING. 
 
 only one small hole from which the gas issues. It is suitable 
 only where a very small flame is required. 
 
 The Batfs-wing or slit burner (Fig. 33) has a hemispherical 
 tip with a narrow vertical slit from which the gas spreads out in a 
 thin, flat sheet, giving a wide and rather low flame, resembling in 
 shape the wing of a bat, from which it is named. The common 
 kind of slit burners are not suitable for use with globes, as the 
 flame is likely to crack the glass. 
 
 The Union-jet or Fish-tail burner (Figs. 34 and 35) consists 
 
 _VL f| f a flat tip slightly depressed or concave in the center, 
 
 IPjL with two small holes drilled, as shown in Fig. 35. Two 
 
 jajl jets of equal size issue from these holes, and by impin- 
 
 \ / S m S upon each other produce a flat flame longer and 
 
 ~ i narrower in shape than the bat's- wing, and -not unlike 
 
 the tail of a fish. Neither of these burners require a 
 chimney, but the flames are usually encased with glass globes. 
 
 The Argand burner (Fig. 36) consists of a hollow ring of 
 metal connected with the gas tube, and perforated oh its upper 
 surface with a series of fine holes, from which the gas issues, 
 forming a round flame. This burner requires a glass chimney. 
 As an intense heat of combustion tends to increase the brilliancy 
 of the flame, it is desirable that the burner tips shall be of a mate- 
 rial that will cool the flame as little as possible. On this account 
 
 Fig. 37. Fig. 38. 
 
 metal tips are inferior to those made of some nonconducting 
 material, such as lava, adamant, enamel, etc. Metal tips are also 
 objectionable because they corrode rapidly, and thus obstruct the 
 passage of the gas. Figs. 37 and 38 show lava tips for bat's- 
 wing and fish-tail burners. Burner tips should be cleaned occa- 
 
 505
 
 PLUMBING. 
 
 sionally, but care should be taken not to enlarge the slits or 
 holes. 
 
 In all regenerative burners the high temperature due to the 
 combustion in a gas flame is used to raise the temperature of the 
 gas before ignition, and of the air before combustion. These 
 powerful burners are used for lighting streets, stores, halls, etc. 
 
 Fig. 39. 
 
 Fig. 40. 
 
 In the incandescent burner the heat of the flame is applied in 
 
 raising to incandescence some foreign material, such as a basket 
 
 of magnesium or platinum wires, or a funnel-shaped asbestos wick 
 
 or mantel chemically treated with sulphate of zirconium and 
 
 other chemical elements. A burner of this kind 
 
 is shown in Fig. 39, where the mantel may be 
 
 seen supported over the gas flame by a wire at 
 
 the side. Fig. 40 shows another form of this 
 
 burner in which a chimney and shade are used 
 
 in place of a globe. Burners of this kind give 
 
 a very brilliant white light when used with 
 
 water gas unmixed with naphtha gases. The 
 
 mantel, however, is very fragile, and is likely 
 
 to lose its incandescence when exposed to an 
 
 atmosphere containing much dust. 
 
 The Bunsen burner shown in Fig. 41 is a 
 form much used for laboratory work. It bums 
 with a bluish flame, and gives an intense heat 
 without smoke or soot. The gas before ignition is mixed with a 
 certain quantity of air, the proportions of gas and air being 
 regulated by the thumbscrew at the bottom, and by screwing the 
 
 Fig. 41. 
 
 509
 
 44 
 
 PLUMBING. 
 
 outer tube up or down, thus admitting a greater or less quantity 
 of air at the openings indicated by the arrows. This same principle 
 is utilized in a burner for brazing, the general form of which is 
 
 shown in Fig. 42. 
 in the open air. 
 
 A flame of this kind will easily melt brass 
 
 Fig. 42. 
 
 Cocks. It is of greatest importance that the stopcocks at 
 the fixtures should be perfectly tight. It is rare to find a house 
 piped for gas where the pressure test could be successfully ap- 
 plied without first removing the fixtures, as the joints of folding 
 
 43. 
 
 Fig. 44. 
 
 brackets, extension pendants, stopcocks, etc., a/e usually found to 
 leak more than the piping. The old-fashioned, "all-around" cock 
 should never be allowed under any conditions whatever; only 
 those provided witli stop pins should be used. Various forms of 
 cocks with stop pins are shown in Figs. 43, 44 and 45. All 
 
 510
 
 PLUMBING. 
 
 45 
 
 joints should be examined and tightened up occasionally to pre- 
 vent tl<e : r becoming loose and leaky. 
 
 Fig. 46. 
 
 Fig. 47. 
 
 Brackets and Chandeliers. Poor illumination is frequently 
 caused by ill-designed -or poorly constructed brackets or chande- 
 liers. Gas fixtures, almost with- 
 out exception, are designed solely 
 from an artistic standpoint, with- 
 out regard to the proper condi- 
 tions for obtaining the best illumi- 
 nation. Fixtures having too many 
 scrolls or spirals may, in the case 
 of imperfectly purified gas, accu- 
 
 Fig. 45. 
 
 Fig. 48. 
 
 mulate a large amount of a tariy deposit which in time hardens 
 and obstructs the passages. Another fault is the use of very 
 small tubing for the fixtures, while a third defect consists in 
 the many leaky stopcocks of the fixtures, caused either by defec-
 
 46 
 
 PLUMBING. 
 
 tive workmanship, or by the keys becoming worn and loose. 
 Common forms of brackets are shown in Figs. 46 and 47, the lat- 
 ter being an extensive bracket. There is an endless variety of 
 chandeliers used, depending upon the kind of building, the finish 
 of the room and the number of lights required. Figs. 48, 49 and 
 50 show common forms for dwelling houses, Fig. 50 being used 
 for halls and corridors. 
 
 Fig. 50. 
 
 Globes and Shades. Next to the burners, the shape of the 
 globes or shades surrounding the flame affects the illuminating 
 power of the light. In order to obtain the best results, the flow of 
 air to the flame must be steady and uniform. Where the supply 
 is insufficient the flame is likely to smoke ; on the other hand, too 
 strong a current of air causes the light to flicker and become dim 
 through cooling. 
 
 Globes with too small openings at the bottom should not be 
 used. Four inches should be the smallest size of opening for an 
 ordinary burner. All glass globes absorb more or less light, the 
 
 518
 
 PLUMBING. 
 
 47 
 
 loss varying from 10 per cent for clear glass to 60 per cent or 
 more for colored or painted globes. Clear glass is therefore much 
 more economical, although where softness of light is especially de- 
 sired the use of opal globes is made necessary. 
 
 COOKING AND HEATING BY GAS. 
 
 Cooking by gas as well as heating is now very common and 
 
 there is a great variety of appliances for its use in this way. 
 
 Cooking by gas is less expensive and less troublesome than by 
 
 coal, oil or wood and is 
 
 more healthful on account 
 
 of the absence of waste 
 
 heat, smoke and dust. A 
 
 gas range is always ready 
 
 for use and is instantly 
 
 lighted by applying a 
 
 match to the burner. The fire, when kindled, is at once capable 
 
 of doing its full work ; it is easily regulated and can be shut off 
 
 the moment it has been 
 used, so that if properly 
 managed there is no 
 waste of fuel as in the 
 case of coal or wood. 
 The kitchen in the sum- 
 mertime may be kept 
 comparatively cool and 
 comfortable. Gas stoves 
 are made in all sizes, 
 from the simple form 
 shown in Fig. 51 to the 
 most elaborate range for 
 hotel use. A range for 
 
 family use, with ovens and water heater, is shown in Fig. 52. 
 
 Figs. 53 and 54 show the forms of burners used for cooking, 
 
 the former being a .griddle burner and the latter an oven 
 
 burner. 
 
 A broiler is shown in Fig. 55 ; the sides are lined with asbes- 
 tos, and the gas is introduced through a large number of* small 
 
 Fig. 52. 
 
 619
 
 48 
 
 PLUMBING. 
 
 openings. The asbestos becomes heated and the effect is the same 
 as a charcoal fire upon both sides. 
 
 Heating by Gas. Gas as a fuel has not been used to any 
 great extent for the warming of whole buildings, its application 
 
 Fig. 54. 
 
 being usually confined to the heating of single rooms. Unlike 
 cooking by gas, a gas fire for heating is not as cheap as a coal fire 
 when kept burning constantly. In other ways it is effective and 
 convenient. It is especially adapted to the warming of small 
 apartments and single rooms where heat is only wanted occasion- 
 
 Fig. 53. 
 
 ally and for brief periods of time. 
 In the case of bedrooms, bath- 
 rooms or dressing-rooms, a gas fire 
 is preferable to other modes of 
 warming and fully as economical. 
 It may be used on cold winter days 
 as a supplementary source of heat 
 in houses heated by stoves or by 
 furnaces. Again, a gas fire may be used as a substitute for 
 the regular heating apparatus in a house, in the spring or fall, when 
 the fire in the furnace or boiler has not yet been started. It is 
 often employed as the only means for heating smaller bedrooms, 
 guest rooms, bathrooms, and for temporary heating in summer 
 hotels where fires are required only on occasional cold days. 
 
 The most common form of heater is that shown in Fig. 56. 
 This is easily carried from room to room and may be connected 
 
 514
 
 PLUMBING. 
 
 49 
 
 with a gas-jet, after first removing the tip, by means of rubber 
 tubing. The heater is simply a large burner surrounded by a 
 sheet-iron jacket or funnel. Another and more powerful form is 
 the gas radiator, shown in Fig. 57. This is arranged with a 
 flue for conducting the products of combustion to the chimney, as 
 shown in the section Fig. 58. Each section of the radiator con- 
 sists of an outer and an inner tube with the gas flame between the 
 
 Fig. 56. 
 
 Fig. 57. 
 
 two. This space is connected with the flue, while the air to be 
 heated is drawn up through the inner tube, as shown by the 
 arrows. 
 
 Fig. 59 shows an asbestos incandescent grate, and Fig. 60 a 
 grate provided with gas logs made of metal or terra-cotta and as- 
 bestos. The gas issues through small openings among the logs, 
 and giv3s the appearance of an open wood fire. 
 
 Hot-water Heaters. The use of gas cooking ranges makes it 
 necessary to provide separate means for heating water. This is 
 accomplished in several ways. The range shown in Fig. 52 has a 
 boiler attached which is provided with a separate burner. 
 
 Fig. ol shows a gas heater attached to the ordinary Kitchen 
 
 515
 
 f>0 
 
 PLUMBING. 
 
 boiler. A section through the heater is shown in Fig. 62. This 
 consists of a chamber surrounded by an outer jacket with an aii 
 space between. Circulation pipes, through which the water passes, 
 are hung in the inner chamber just above a powerful gas-burner 
 placed at the bottom of the heater. 
 
 A heater of different form for heating larger quantities of 
 
 Fig. 58. 
 
 Fig. 60. 
 
 water is shown in Figs. 63 and 64. This consists, as :n the c^se 
 just described, of a circulation coil suspended above a series of 
 burners, '"he supply of gas admitted to the burners is regulated 
 by r,n automatic valve, which is opened more or less as the fio\\ of 
 wat* 3 : through the heater is increased or diminished. When no 
 
 516
 
 PLUMBING. 
 
 61 
 
 water is being used, the gas is shut off from the burners, and only 
 a small "pilot light/' which takes its supply from above the auto- 
 matic valve, is left burning. As soon as a faucet in any part of 
 the building is opened and a flow of water started through the 
 heater, the automatic valve opens, admitting gas to the main burn- 
 
 OUTLET 
 
 W/TH 
 
 ASBESTOS 
 L/N/NG 
 
 SHEET /RO 
 JACKET W/T 
 ASBESTOS 
 L/N/NG 
 
 DEAD A/f? 
 
 SPACE 
 
 LD WATER 
 K^BUM CHAMBER 
 VL J -HOT WATER 
 * CHAMBER 
 
 COLD WATER 
 -HOT WATER 
 
 COLO WATER 
 /NLET 
 
 Fig. 61. 
 
 Fig. 62. 
 
 ers, which is ignited by the pilot light, and in a few moments hot 
 water will flow from the faucet. The heater shown has a capacity 
 of 9 gallons per minute from a temperature of 55 to 130. 
 
 Another type is that known as the instantaneous water heater, 
 one form of which is shown in Fig. 65. This is made especially 
 for bathrooms, and will produce a continuous stream of hot water 
 whenever desired. The heater is shown in section in Fig. 66, in 
 
 617
 
 52 
 
 PLUMBING. 
 
 which A is the gas valve, B the water valve, D the pilot light, 
 FF the burners, I a conical heating ring, J a disc to retard and 
 spread the rising heat, K a perforated copper screen, and L a 
 revolving water distributer. In this heater the water is exposed 
 directly to the heated air and gases in addition to its passing over 
 the heated surface of the ring I. The upward arrows show the 
 path of the heat, and the downward arrows the passage of the 
 water. 
 
 Fig. 64. 
 GAS nETERS. 
 
 The meter should be placed in such a position that it is easily 
 accessible and may be read without the use of an artificial light. 
 It is connected into the system between the service pipe and main 
 riser to the building, the connections being made as shown in 
 Fig. 67. 
 
 Different meters vary but little in the arrangement of the 
 dials. In large meters there are often as many as five dials, but 
 those used for dwelling houses usually have but three. Fig. 68 
 shows the common form of index of a dry meter. The small index 
 haml, D, on the upper dial is not taken into consideration wheu 
 
 5)8
 
 PLUMBING. 
 
 53 
 
 reading the meter, but is used merely for testing.- The three dials, 
 which record the consumption of gas, are marked A, B and C, and 
 each complete revolution of the index hand denotes 1,000, 10,000 
 and 100,000 cubic feet respectively. It should be noted that the 
 index hands on the three dials do not move in the same direction ; 
 
 Fig. 65. 
 
 A and C move with the hands of a watch, and B in the opposite 
 direction. The index shown in Fig. 68 should be read 48,700. 
 Suppose after being used for a time, the hands should have the 
 position shown in Fig. 69. This would read 64,900, and the 
 amount of gas used during this time would equal the difference 
 in the readings : 64,900 48,700 = 16,200 cubic feet 
 
 019
 
 PLUMBING. 
 
 GAS HACHINES. 
 
 While tlie manufacture of gas for cities and towns is a matter 
 beyond the scope of gas fitting, it may nut be out of place to take 
 up briefly the operation of one of the forms of gas machines 
 
 Sf/f V/Ce PtPE 
 
 Fig. 66. 
 
 which are used for supplying .private residences or manufacturing 
 plants. 
 
 The general arrangement of the apparatus is shown in Fig. 
 
 Fig- 69. 
 
 70, which consists of a generator, containing evaporating pans or. 
 chambers, and an automatic air pump, together with the necessary 
 piping for air and gas. The gas made by these machines is com- 
 
 !T20
 
 PLUMBING. 
 
 55 
 
 521
 
 56 
 
 PLUMBING. 
 
 monly known as carbureted air gas, being common air impregnated 
 with the vapors of gasoline. It burns with a rich bright flame 
 similar to coal gas, and is conducted through pipes and fixtures in 
 the same manner. 
 
 Referring to Fig. 70, the automatic air pump is seen in the 
 cellar of the house, and connected to it and running underground 
 are the air and gas pipes connecting it with the generator, which 
 may be a hundred feet or more away if desired. When the m*t<- 
 
 chine is in operation, the pump 
 forces a current of air through 
 the generator, where it becomes 
 carbureted, thus forming an 
 illuminating gas that is return- 
 ed through the gas pipe to the 
 house, where it is distributed to 
 the fixtures in the usual way. 
 The operation is automatic, gas 
 being generated only as fast and 
 in such quantities as required 
 for immediate consumption. 
 The process is continuous while 
 the burners are in use, but stops 
 as soon as the lights are extin- 
 guished. Power for running 
 the air compressor is obtained 
 by the weight shown at the 
 right, which must be wound up 
 at intervals, depending upon the 
 amount of gas consumed. An 
 air compressoi to be run by wa- 
 ter power is shown in Fig. 71. 
 
 The action of this machine is entirely automatic, the supply of 
 water being controlled by the rising and falling of the holder A. 
 which, being attached by a lever to the valve B, regulates the 
 amount of water supplied to the wheel in exact proportion to 
 the number of burners lighted. If all the burners are shut off, 
 the pressure accumulating in the holder A raises it and shuts the 
 water oif. If a burner is lighted, the holder falls slightly, allow- 
 
 Fig. 71.
 
 PLUMBING. 
 
 ing just enough water to fall upon the wheel to furnish the amount 
 of gas required. A pump or compressor of this kind requires 
 about two gallons of water per hour for each burner. The advan- 
 
 tages of a water compressor over one operated by a weight are 
 that it requires no attention, never runs down and is ready for 
 immediate use at all times. 
 
 The generator is made up of a number of evaporating pans or 
 chambers placed in a cylinder one above another. These chambers 
 
 523
 
 58 
 
 PLUMBING. 
 
 are divided by supporting frames into winding passages, which 
 give an extended, surface lor evaporation. Fig. 72 shows the 
 generator when set with a brick pit and manhole at one side. It 
 is supplied with mica gages for showing the amount of gasoline in 
 each pan, and with tubes and valves for distributing it to the differ- 
 ent pans as required. In small plants the generator is usually 
 buried withuiit the pit being provided, but for larger plants the 
 
 setting shown in 
 Fig. 72 is recom- 
 mended. Car- 
 bureted air gas 
 of s t a n d a r d 
 quality contains 
 15 per cent of 
 vapor to 85 per 
 cent of air. A 
 regulator or 
 mixer for sup- 
 plying gas hav- 
 ing these pro- 
 portions is 
 shown in section 
 in Fig. 73. It 
 consists of a 
 cast-iron case in 
 which is sus- 
 pended a sheet- 
 metal can, B, 
 filled with ai r 
 
 and closely sealed. The balance beam E, to which this is hung, is 
 supported by the pin H, on agate bearings. Since the weight of the 
 can B is exactly balanced by the ball on the beam E, movement of B 
 can only be caused by a difference in the weight or density of the 
 gas inside the chamber A and surrounding the can B. If the gas 
 becomes too dense, B rises and opens the valve C, thus admitting 
 more air: and if it becomes too light, C closes and partially or 
 wholly shuts off the air, as may be required. 
 
 Fig. 
 
 524
 
 REVIEW QUESTIONS. 
 
 PRACTICAL TEST QUESTIONS. 
 
 In the foregoing sections of this Cyclopedia 
 numerous illustrative examples are worked out in 
 detail in order to show the application of the various 
 methods and principles. Accompanying these are 
 examples for practice which will aid the reader in 
 fixing the principles in mind. 
 
 In the following pages are given a large number 
 of test questions and problems which afford a valu- 
 able means of testing the reader's knowledge of the 
 subjects treated. They will be found excellent prac- 
 tice for those preparing for College, Civil Service, or 
 Engineer's License. In some cases numerical answers 
 are given as a further aid in this work. 
 
 525
 
 REVIEW QUESTIONS 
 
 ON THE SUBJECT OF 1 
 
 MACHINE DESIGN. 
 
 PART I'. 
 
 The drawings made in accordance with the problems below 
 should be traced in ink on tracing cloth 18 by 24 inches in size, 
 and having a border line ^ inch inside the edge of the paper. 
 
 PROBLEMS. 
 
 1. Suppose a 30-inch, pulley is substituted for the 42-inch 
 in the problem given, and that the pulley on the motor remains 
 10A inches as before, how fast must the motor run to give the rope 
 the same speed, 150 feet per minute ? 
 
 2. Will the horse -power of the motor be changed with this 
 new condition ? Explain fully. 
 
 3. Calculate the width of double belt for above condition. 
 
 4. What is the torque on the motor shaft for above condition? 
 
 5. Calculate the size of shaft in the small pulley for above 
 condition. 
 
 6. Calculate the size of shaft in the 30- inch pulley for above 
 condition. 
 
 7. Design and draw both pulleys for above condition, mak- 
 ing complete working drawings, and giving all calculations in full. 
 
 8. Taking the original problem as given in the text, suppose 
 it is desired to increase the large gear to 45 inches diameter, cal- 
 culate the load on the tooth, and a suitable pitch and face to take 
 this load. 
 
 9. How many teeth must the pinion have to give the same 
 speed of rope, 150 feet per minute, assuming that the motor 
 runs 470 revolutions per minute, for condition in Problem 8 ? 
 
 10. Calculate the bore of pinion for this case. 
 
 11. Design and draw the gears for the conditions of Prob- 
 lems 8 and 9, giving all calculations in full. ' .
 
 MACHINE DESIGN 
 
 12. When there is but 3.000 pounds on the rope, what are 
 the tensions in each end of the brake strap, assuming that the size 
 of drum and other conditions remain the same ? 
 
 13. llo\v much pressure on the foot lever would it take to 
 hold this load of 3.000 pounds on the rope ? 
 
 11. Suppose we put a bearing 9 inches long on the drum 
 shaft; the distance, center to center of bearings, would then be 3 
 feet 5| inches, gears, drum, brake, and load being same a.? in the 
 original problem of the text. Calculate the diameter of the drum 
 shaft. 
 
 15. Suppose the height of bracket, center to base, to be 15 
 inches; length and diameter of bearing, as in Problem 14; and that 
 we use a separate bracket for the drum bearings, not connected 
 with the pinion -shaft bearings. Design and draw such a bracket. 
 
 10. Calculate, design, and draw all the parts for a machine 
 similar to that of the text, from the following data: 
 
 Load on rope 4.000 pounds. 
 
 Speed of rope 175 feet per minute. 
 
 Length of rope to be reeled in .... 250 feet. 
 
 NOTE. Problems 12, 13 and 15 are comparatively simple, following 
 closely the steps of the text in their solution. 
 
 Problem 16, likewise, is supposed to be worked out on the same lines as 
 the text, but is wholly original in its nature, being based on entirely new data. 
 It is not expected that this problem will be attempted except by well-advanced 
 students who can give considerable time to working it out completely. It will 
 be found, however, an excellent exercise in original and yet simple design.
 
 REVIEW QUESTIONS 
 
 U 11 .1 E C T OF 1 
 
 HEATIXG AXD VEXTILATIOX 
 
 A. K T I . 
 
 1. What advantage does indirect steam heating have over 
 direct heating? What advantages over furnace heating? 
 
 2. What are the causes of heat loss from a building? 
 
 3. Why is hot water especially adapted to the warming of 
 dwellings? 
 
 4. What proportion of carbonic acid gas is found in outdoor air 
 under ordinary conditions? 
 
 5. A room in the N. E. corner of a building of fairly good con- 
 struction is 18 feet square and 10 feet high ; there are 5 single windows 
 each 3 by 10 feet in size. The walls are of brick 12 inches in thickness. 
 With an inside temperature of 70 degrees, what will be the heat loss 
 per hour in zero weather? 
 
 C. State four important points to be noted in the care of a fur- 
 nace. 
 
 7. A grammar school building, constructed in the most thor- 
 ough manner, has 4 rooms, one in each corner, each being 30 ft. by 
 30 ft. and 14 ft. high, and seating 50 pupils. The walls are of wooden 
 construction, and the windows make up -3 of the total exposed surface. 
 The basement and attic are warm. How many pounds of coal will be 
 required per hour for both heating and ventilation in zero weather, if 
 8,000 B. T. U. are utilized from each pound of coal? 
 
 S. What two distinct types of furnaces are used? What are 
 the distinguishing features? 
 
 9. What is meant by the efficiency of a furnace? What effi- 
 ciencies are obtained in ordinary practice? 
 
 529
 
 HEATING AND VENTILATION 
 
 10. What are the principal parts of a furnace? State briefly 
 the use of each. 
 
 11. A brick house of the best construction, 20 ft. by 40 ft., has 
 3 stories, each 10 feet high. The walls are 12 inches in thickness; 
 and 3 the total exposed wall is taken up by windows, which are double. 
 The basement is warm, but the attic is cold. The house is to be 
 warmed to 70 degrees when it is ten degrees below zero outside. How 
 many square feet of grate surface will be required, assuming usual 
 efficiencies of coal and furnace? 
 
 12. A high school is to be provided with tubular boilers. What 
 H. P. will be required for warming and ventilation in zero weather if 
 there are GOO occupants, and the heat loss through walls and windows 
 is 1,500,000 B. T. V. per hour? 
 
 13. What are the three essential parts of any heating system? 
 
 14. Is direct-steam heating adapted to the warming of school- 
 houses and hospitals? (rive the reason for your answer. 
 
 15. The heat loss from a dwelling-house is 280,000 B. T. U. per 
 hour. It is to be heated with direct steam by a type of sectional boiler 
 in which the ratio of heating- surface to grate surface is 28. What will 
 be the most efficient rate of combustion, and how many square feet of 
 grate surface will be required? 
 
 10. What is the use of a blow-off tank? Show by a sketch how 
 the connections are made. 
 
 17. How are the sizes of single-pipe risers computed? 
 
 18. What weight of steam will be discharged per hour through 
 a 6-inch pipe 300 feet long, with an initial pressure of 10 pounds, and a 
 drop of f pound in its entire length? 
 
 10. What is an air-valve? Upon what principles does it work? 
 
 20. What size of steam pipe will be required to discharge 2,400 
 pounds of steam per hour a distance of 900 feet, with an initial pres- 
 sure of GO pounds, and a drop in pressure of 5 pounds? 
 
 21. What objection is there to a single-pipe riser system? How 
 is this sometimes overcome in large buildings? 
 
 22. What patterns of valves should be used for radiators? 
 What conditions of construction must be observed in making the con- 
 nections betweeii the radiator and riser? 
 
 530
 
 REVIEW QUESTIONS 
 
 ON THE SUBJECT OF 1 
 
 HEATING AND VENTILATION 
 
 PART II. 
 
 1. How would you obtain the sizes of the cold-air and warm- 
 air pipes connecting with indirect heaters in dwelling-house work? 
 
 2. What is an 'aspirating coil, and what is its use? 
 
 3. What efficiencies may be allowed for indirect heaters in 
 schoolhouse work? How would you compute the size of an indirect 
 heater for a room in a dwelling-house? 
 
 4. How is the size of a direct-indirect radiator computed? 
 
 5. A schoolroom on the third floor is to be supplied with 2,400 
 cubic feet of air per minute. What should be the area of the warm- 
 air supply flue? 
 
 0. What is the chief objection to a mixing damper, and how 
 may this be overcome? 
 
 7. How many square feet of indirect radiation will be required 
 to warm and ventilate a schoolroom when it is 10 degrees below zero, 
 if the heat loss through walls and windows is 42,000 B. T. U., and the 
 air-supply 120,000 cubic feet per hour? 
 
 8. What is the difference in construction oetween a steam 
 radiator and one designed for hot water? Can the steam radiator 
 be used for hot water? State reasons for answer. 
 
 9. How may the piping in a hot-water system be arranged so 
 that no air-valves will be required on the radiators? 
 
 10. What, efficiency is commonly obtained from a direct hot- 
 water radiator? How is this computed? 
 
 11. How should the pipes be graded in making the connections 
 with indirect hot-water heaters? Where should the air-valve be 
 placed? 
 
 531
 
 HEATING AND VENTILATION 
 
 12. Describe briefly one form of grease extractor. 
 
 13. What is the office of a pressure-reducing valve in an exhaust- 
 steam heating system? 
 
 14. Upon what principle does a pump governor operate? 
 
 15. "What type of pipe fittings should always be used in hot- 
 water work? 
 
 10. How is the water of condensation returned to the boilers 
 in exhaust steam heating? 
 
 17. How many cubic feet of air per hour will be discharged 
 through a flue 2 feet by 3 feet, and 00 feet high, if the air in the flue 
 has a temperature of SO degrees and the outside air GO degrees? 
 
 IS. In a hot-water heating system, what causes the water to flow 
 through the pipes and radiators? How does the height of the radiator 
 above the boiler affect the flow? 
 
 10. What precaution should always be taken before starting 
 a fire under a steam boiler? 
 
 20. What is the free opening in square feet through a register 24 
 inches by 4S inches? 
 
 21. Why are return pumps or return traps necessarv in exhaust- 
 steam heating plants? 
 
 22. What efficiency may be obtained from indirect hot-water 
 radiators under usual conditions? What is the common method of 
 computing indirect hot-water surface for dwelling-house work? 
 
 23. State briefly how a return trap operates. 
 
 24. What is the use of an 'expansion tank, and what should be 
 its capacity? 
 
 25. Describe the action of one form of damper regulator. 
 
 20. What is the principal difference between a hot-water heater 
 and a steam boiler? What type of heater is best adapted to the 
 warming of dwelling-houses? 
 
 27. Upon what four conditions does the size of a pipe to supply 
 any given radiator depend? 
 
 28. What is the use of an exhaust head? 
 
 20. A hospital ward requires 00,000 cubic feet of air per hour 
 for ventilation, and the heat loss through walls and windows is 140,000 
 B. T. U, per hour. How many square feet of indirect steam radiation 
 will be required in zero weather? 
 
 30. For what purpose is a back-pressure valve used? 
 
 532
 
 REVIEW QUESTIONS 
 
 OX THE SUBJECT OF 
 
 HEATING AND VENTILATION. 
 
 PART III 
 
 1. A main heater contains 1,040 square feet of heating surface 
 made up of wrought-iron pipe, and is used in connection with a fan 
 which delivers 528,000 cubic feet of air per hour. The heater is 20 
 pipes deep, and has a free area, between the pipes, of 11 square feet. 
 If air is taken at zero, to what temperature will it be raised with steam 
 at 5 pounds' pressure. 
 
 2. An 8-foot fan used for schoolhouse ventilation runs at a 
 speed of 124 r. p. m. What horse-power of engine is required? What 
 horse-power would be required if the fan were speeded up to 134.6 
 r. p. m.? 
 
 3. What precaution must be taken in connecting the radiators 
 in tall buildings? 
 
 4. Give the size of heater from Table XXXI which will be 
 required to raise 672,000 cubic feet of air per hour, from 10 below 
 zero to 95, with a steam pressure of 20 pounds. If the air-quantity 
 is raised to 840,000 cubic feet per hour through the same heater, what 
 will be the resulting temperature with all other conditions the same? 
 
 5. A fan running at 150 revolutions produces a pressure of ^ 
 ounce. If the speed is increased to 210 revolutions, what will be the 
 resulting pressure? 
 
 6. A certain fan is delivering 12,000 cubic feet of air per minute, 
 at a speed of 200 revolutions. It is desired to increase the amount to 
 18,000 cubic feet. What will be the required speed? If the original 
 power required to run the fan was 4 H. P., what will be the final power 
 due to the increased speed? 
 
 7. What size fan will be required to supply a schoolhouse 
 
 533
 
 HEATING AND VENTILATION 
 
 having 300 pupils, if each is to be provided with 3,000 cubic feet of 
 air per hour? What speed of fan will be required, and what H. P. of 
 engine? 
 
 8. What advantages has the plenum method of ventilation over 
 the exhaust method? 
 
 9. A church is to be warmed and ventilated by means of a fan 
 and heater. The air-supply is to be 300,000 cubic feet per hour. 
 The heat loss through walls and windows is 200,000 B. T. U., when it 
 is zero. How many square feet of heating surface will be required, 
 and how many rows of pipe deep must the heater be, with steam at 5 
 pounds' pressure? 
 
 10. A schoolhouse requiring 600,000 cubic feet of air per hour 
 is to be supplied with a cast-iron sectional heater of the pin type. How 
 many square feet of radiating surface will be required to raise the air 
 from 10 below zero to 70 above, with a steam pressure of 10 pounds? 
 
 11. What velocities of air-flow in the main duct and branches 
 are commonly used in connection with a fan system? 
 
 1 2. A main heater is to be designed for use in connection with 
 a fan. How many square feet of radiation will be required to warm 
 1,000,000 cubic feet of air per hour, from a temperature of 10 below 
 zero to 70 above, with a steam pressure of 5 pounds and a velocity 
 of 800 feet per minute between the pipes of the heater? How many 
 rows of pipe deep must the heater be? 
 
 13. State in a brief manner the essential parts of a system of 
 automatic temperature control. 
 
 14. What advantage does an indirect steam-heating system have 
 over furnace heating in schoolhouse work? 
 
 15. The air in a restaurant kitchen is to be changed every 10 
 minutes by means of a disc fan. The room is 60 by 30 by 10 feet. 
 Give size and speed of fan, and H. P. of motor. 
 
 16. What forms of heating are best adapted to the warming of 
 apartment houses? 
 
 17. Give an approximate method for finding the heating surface 
 required for greenhouses, both for steam and hot water. 
 
 18 How does the cost of electric heating compare with that by 
 steam and hot water? 
 
 19. Describe briefly the construction of an electric heater, and 
 the principle upon which it works. 
 
 534
 
 HEATING AND VENTILATION 
 
 20. A school building of 4 rooms is to be supplied with 600,000 
 cubic feet of air per hour. The heat loss from the building is 300,000 
 B. T. U. per hour in zero weather. Give the square feet of grate sur- 
 face required in the furnaces. 
 
 21. What is a double-duct system as applied to forced-blast 
 heating? What are its advantages? 
 
 22. What is a thermostat? Give the principles upon which two 
 different kinds operate. 
 
 23. Describe briefly the connections to be made in a system 
 of electric heating. In what way do they correspond to the piping 
 in a system of steam heating? 
 
 24. State certain points to be observed in the introduction of 
 air for the ventilation of churches'and theaters. 
 
 25. A shop 100 feet long, 50 feet wide, and having 5 stories, 
 each 10 feet high, is to be warmed by forced blast using steam at 80 
 pounds' pressure. The full amount of air passed through the heater 
 is to be taken from out of doors, and the entire air of the building 
 changed 3 times an hour. Give linear feet of 1-inch pipe required 
 for heater, and size of fan and engine. 
 
 26. In what cases would you use a disc fan in preference to a 
 blower? 
 
 27. The heat loss from a room is 12,000 B. T. U. per hour. 
 How many kilowatt-hours will be required to furnish the necessary 
 heat? 
 
 28. What is one of the best systems for the heating and venti- 
 lation of school buildings of large size? 
 
 29. What form of heating system would you recommend for a 
 four-room school? 
 
 30. A factory 250 feet long by 50 feet wide has two stories, each 
 10 feet high. Each floor is to have a separate fan and heater, but the 
 fans are to be driven by the same electric motor. The lower floor is 
 to be supplied with air from out of doors, and is to have a complete 
 change of air every 20 minutes. On the upper floor the air is to be 
 returned to the heater from the room, and the entire contents is to 
 pass through the heater every 20 minutes. Exhaust steam is to be 
 used in both heaters. Give sizes of fans, heaters, and motor. 
 
 31. What is a telethermometer? 
 
 32. Describe two methods of moistening air. 
 
 635
 
 \ r I K W Q UK S T I O X S 
 
 PLUMUIXCi. 
 
 PART I. 
 
 1. What causes a trap to ". siphon.'' and in what three ways 
 may it be prevented? 
 
 2. What size of soil pipe should be used for an ordinary- 
 sized dwelling, and what pitch should bo given to the horizontal 
 portion ? 
 
 3. What quantity of water per capita should be allowed in 
 designing a sewerage system? 
 
 4. What form of cross-section of conduit gives a maximum 
 velocity of flow to smrJl quantities of sewage? 
 
 o. Describe the manner of making house connections with 
 the m;iin sewer. 
 
 !). Show by sketch the general method of running the 
 waste and ye:it pipes in a dwelling house, and indicate the proper 
 location of traps. 
 
 T. What are the two principal methods of sewage purifi- 
 cation ? 
 
 8. Describe the method of making up the joints in cast 
 iron soil pipe. 
 
 9. In what way may the seal of a trap be broken besides 
 siphonage? 
 
 10. What two tests are usually given to a .system of plumb- 
 iiiir'/ State the use of each. 
 
 536
 
 PLUMBING. 
 
 11. What grade should be given to main sewers and 
 branches ? 
 
 12. Give two methods of flushing sewers. 
 
 13. Describe briefly some of the usual arrangements in the 
 plumbing of hotels. 
 
 14. What is sewage farming ? Describe the process briefly. 
 
 15. What is the difference between a "cup joint" and a 
 44 wipe joint?" State the conditions under which you would use 
 each. 
 
 16. What is the use of a fresh-air inlet in connection with 
 a soil pipe, and how is it connected ? 
 
 17. Describe the " Smoke Test." 
 
 18. Should a trap or fixture be vented into a chimney ? 
 Give the reasons for your answer. 
 
 1 9. What material is commonly used for sewer pipes of 
 different sizes ? 
 
 20. When are underdrains required and how are they con- 
 structed ? 
 
 21. What precautions should be taken in back venting 
 traps ? 
 
 22. What chemicals are commonly used in the precipitation 
 of sewage ? 
 
 23. How should you connect a lead pipe with a cast or 
 wrought iron pipe? 
 
 24. Define the " separate " and " combined " systems of 
 sewerage. 
 
 25. What is the principal point to be observed in the dis- 
 posal of sewage ? What precautions should be taken when it is 
 discharged into a stream ? 
 
 26. What is the sedimentation process ? 
 
 27. What precautions should be taken in locating a cess- 
 pool? Describe briefly one form of construction. 
 
 28. Name some of the most important data to be obtained 
 before laying out a system of sewerage. 
 
 29. In designing a system of surface drains what maximum 
 conditions should be provided for? 
 
 30. Under what conditions may sub-surface irrigation be 
 used to advantage? 
 
 537
 
 R K V I K W Q U K S T I O N" S 
 
 O V T IT l-i !ST* J5.T KC"T O 1* 
 
 PLUMBING. 
 
 PART II. 
 
 1. A hotel requires a water supply of 200 gallons of water 
 per minute during' a certain part of the day. It receives its 
 supply from a reservoir 1,000 feet distant, and located 116 feet 
 above the house tank, in the attic of the building. What size of 
 wrought-iron pipe will be required to bring the water from the 
 reservoir ? 
 
 Ans. 3 inch. 
 
 2. What is the best kind of pipe for domestic water supply 
 under ordinary conditions? When may it be objectionable? 
 
 3. A 1-inch pipe is to discharge 40 gallons of water per 
 minute from a cistern placed directly above it. What must be 
 the elevation if we assume the friction in the pipe and bends to 
 be equivalent to 100 feet? 
 
 Ans. Ill feet. 
 
 4. A house tank is situated 15 feet above a faucet upon 
 the fifth floor of the building. If the stories are 8 feet high, what 
 will be the difference in pressure in pounds per square inch 
 between this faucet and one in the basement? 
 
 Ans. 17.3 pounds. 
 
 5. Describe the action of an hydraulic ram. 
 
 6. A pump has a steam cylinder 6 inches in diameter and 
 a watet- cylinder 5 inches in diameter. What steam pressure will 
 be required to raise water to an elevation of 135 feet, neglecting 
 friction in the pipe ? 
 
 Ans. 40.3 pounds. 
 
 538
 
 INDEX 
 
 The page numbers of this volume will be found at the bottom of the 
 pages; the numbers at the top refer only to the section. 
 
 
 Page 
 
 
 Page 
 
 A 
 
 
 Blow-oil tank 
 
 264 
 
 Air 
 
 
 Boiler connections 
 
 263 
 
 analysis of 
 
 204 
 
 Bolts 
 
 163 
 
 force for moving 
 
 207 
 
 Brackets 
 
 59, 184 
 
 required for ventilation 
 
 205 
 
 Brass pipe 
 
 432, 476 
 
 velocity of 
 
 207 
 
 British thermal unit 
 
 209 
 
 Air-compressor 
 
 385 
 
 Broad irrigation 
 
 465 
 
 Air distribution 
 
 208 
 
 Bunsen burner 
 
 509 
 
 Air-filters 
 
 390 
 
 Burners 
 
 
 Air-leakage 
 
 210 
 
 argand 
 
 508 
 
 Air- valves 
 
 254, 305 
 
 bat's wing 
 
 508 
 
 Air- vent ing 
 
 301 
 
 Bunsen 
 
 509 
 
 Air-washers 
 
 390 
 
 fish-tail 
 
 508 
 
 Argand burner 
 
 508 
 
 single- jet 
 
 507 
 
 Atmosphere, composition of 
 
 203 
 
 C 
 
 
 Automatic return-pumps 
 
 326 
 
 
 
 
 
 Cap screws 
 
 172 
 
 B 
 
 
 Carbonic acid gas 
 
 203 
 
 Back-pressure valve 
 
 324 
 
 Cast-iron pipe 
 
 429 
 
 Back venting 
 
 439 
 
 Catch-basins 
 
 461 
 
 Balance-pipe 
 
 327 
 
 Centrifugal fan 
 
 355, 359 
 
 Bath room pipe connections 
 
 443 
 
 Centrifugal pumps 
 
 316 
 
 Bath tubs 
 
 411 
 
 Centrifugal whirling 
 
 123 
 
 Bat's- wing burner 
 
 ' 508 
 
 Cesspools 
 
 435 
 
 Beams 
 
 24 
 
 Chemical precipitation 
 
 463 
 
 Bearings 
 
 184 
 
 Chimney flues 
 
 224 
 
 Belting 
 
 
 Circulation coils 
 
 241 
 
 horse-power transmitted by 
 
 95 
 
 Cisterns and tanks 
 
 479 
 
 material of 
 
 97 
 
 Clamp coupling 
 
 162 
 
 speed of 
 
 97 
 
 Claw coupling 
 
 162 
 
 Belts 
 
 89 
 
 Cold-air box 
 
 224 
 
 initial tension in 
 
 98 
 
 Cold-air ducts 
 
 278 
 
 problems on 
 
 99 
 
 Cold-water supply 
 
 480 
 
 Bessemer steel 
 
 127 
 
 Combined stresses 
 
 117 
 
 Bevel gears 
 
 140 
 
 Combustion chamber. 
 
 220 
 
 Blast area 
 
 361 
 
 Compression 
 
 25 
 
 Note. For page numbers see foot of p 
 
 ages. 
 
 
 
 539
 
 11 
 
 IXDEX 
 
 Page 
 
 Page 
 
 Cone fans 
 
 356 
 
 Design 
 
 
 Constructive mechanics 
 
 24 
 
 stands 
 
 184 
 
 Cotters 
 
 180 
 
 studs 
 
 163 
 
 Couplings 
 
 159 
 
 tabulation of torsional moments 
 
 43 
 
 
 
 theoretical 
 
 20 
 
 D 
 
 
 worm gears 
 
 146 
 
 Damper-regulators 
 
 330 
 
 Diaphragm motors 
 
 388 
 
 Dampers 273, 
 
 388 
 
 Diaphragm valve 
 
 387 
 
 Deflection of shaft 
 
 121 
 
 Direct hot-water heating 
 
 200, 293 
 
 Design 
 
 18 
 
 air-venting 
 
 301 
 
 application of 
 
 35 
 
 efficiency of radiators 
 
 296 
 
 base of machine 
 
 69 
 
 expansion tank 
 
 299 
 
 bearings 
 
 184 
 
 overhead distribution 
 
 299 
 
 belt width 
 
 43 
 
 pipe connections 
 
 301 
 
 belts 
 
 89 
 
 piping 
 
 297 
 
 bevel gears 
 
 140 
 
 radiating surface 
 
 295 
 
 bolts 
 
 163 
 
 systems of circulation 
 
 294 
 
 brackets 
 
 184 
 
 valves and fittings 
 
 305 
 
 brackets and caps 
 
 59 
 
 Direct-indirect radiators 
 
 200, 2S7 
 
 brake-relief spring 
 
 69 
 
 Direct -steam heating 
 
 198, 238 
 
 conditions and forces 
 
 18 
 
 cast-iron radiators 
 
 239 
 
 cotters 
 
 180 
 
 circulation coils 
 
 241 
 
 couplings 
 
 159 
 
 pipe radiators 
 
 241 
 
 data on sketch 
 
 44 
 
 piping systems 
 
 245 
 
 delineation 
 
 22 
 
 Disc fans 
 
 355, 367 
 
 driving gears 
 
 38 
 
 capacity of 
 
 368 
 
 drum and brake 
 
 63 
 
 Domestic water supply 
 
 469 
 
 foot lever 
 
 69 
 
 Driving gears 
 
 38 
 
 friction clutches 
 
 153 
 
 Drum and brake 
 
 63 
 
 gear guard 
 
 69 
 
 Drum shaft 
 
 49 
 
 gears 
 
 55 
 
 
 
 general drawing 
 
 70 
 
 E 
 
 
 height of centers 
 
 44 
 
 Efficiency 
 
 
 keys and pins 
 
 174 
 
 of cast-iron heaters 
 
 353 
 
 length of tarings 
 
 44 
 
 of furnace heating 
 
 221 
 
 original 
 
 82 
 
 of indirect heaters 
 
 270 
 
 pinion bore 
 
 49 
 
 of pipe heaters 
 
 348 
 
 practical modification 
 
 21 
 
 of radiators 
 
 243, 296 
 
 preliminary layout 
 
 51 
 
 Electric heat and energy 
 
 382 
 
 preliminary sketch 
 
 38 
 
 Electric heating 
 
 202, 382 
 
 pulley bores 
 
 47 
 
 Electric motors 
 
 373 
 
 pulleys 41, 53, 
 
 100 
 
 Exhaust head 
 
 326 
 
 rope and drum 
 
 38 
 
 Exhaust method of forced blast 
 
 343 
 
 shaft diameters 
 
 44 
 
 Exhaust steam heating 
 
 201, 320 
 
 shafts 49, 
 
 114 
 
 automatic return-pumps 
 
 326 
 
 specification 
 
 22 
 
 back-pressure valve 
 
 324 
 
 spur gears 
 
 128 
 
 damper-regulators 
 
 330 
 
 Note. For page numbers see foot of pages. 
 
 
 
 
 540
 
 INDEX 
 
 
 Page 
 
 
 Exhaust steam heating 
 
 
 Furnace heating 
 
 exhaust head 
 
 326 
 
 radiator 
 
 grease extractor 
 
 323 
 
 Furnaces 
 
 pipe connections 
 
 331 
 
 care and management of 
 
 reducing valves 
 
 322 
 
 chimney flues 
 
 return traps 
 
 328 
 
 cold-air box 
 
 Expansion of pipes 
 
 252 
 
 location of 
 
 Expansion tank 
 
 299 
 
 registers 
 
 
 
 return duct 
 
 F 
 
 
 smoke-pipes of 
 
 
 
 warm-air pipes 
 
 Factory heating 
 
 375 
 
 
 Fan engines 
 
 371 
 
 G 
 
 Fans 
 
 355 
 
 Gas 
 
 area of ducts and flues 
 
 374 
 
 cooking by 
 
 blast area 
 
 361 
 
 heating by 
 
 capacity 
 
 363 
 
 Gas fitting 
 
 effect of resistance 
 
 364, 366 
 
 Gas fixtures 
 
 power required 
 
 365 
 
 brackets 
 
 
 
 
 pressure 
 
 361 
 
 *~ 
 
 speed 
 
 362 
 
 chandeliers 
 
 Faucets 
 
 428 
 
 cocks 
 
 Firepot 
 
 219 
 
 globes 
 
 Fish-tail burner 
 
 508 
 
 shades 
 
 Flange coupling 
 
 160 
 
 Gas machines 
 
 Force for moving air 
 
 207 
 
 Gas meter 
 
 Forced blast 
 
 202, 343 
 
 Gas pipes 
 
 efficiency of pipe heaters 
 exhaust method 
 
 348 
 343 
 
 testing 
 Gate-valves 
 
 form of heating surface 
 
 344 
 
 Gears 
 
 plenum method 
 
 344 
 
 Globe valve 
 
 Forced hot-water circulation 
 
 313 
 
 Grates 
 
 pumps for 
 
 316 
 
 Grease extractor 
 
 Forces 
 
 24 
 
 H 
 
 Fresh air inlets 
 
 441 
 
 Heat loss from buildings 
 
 Friction 
 
 27 
 
 by air-leakage 
 
 Friction clutches 
 
 153 
 
 by ventilation 
 
 problems on 
 
 159 
 
 through walls and windows 
 
 Furnace heating 
 
 215 
 
 Heating, boilers used for 
 
 combination systems 
 
 229 
 
 Heating of 
 
 combustion chamber 
 
 220 
 
 apartment houses 
 
 efficiency 
 
 221 
 
 churches 
 
 flrepot 
 
 219 
 
 conservatories 
 
 furnaces 
 
 216 
 
 greenhouses 
 
 grates 
 
 218 
 
 halls 
 
 heating capacity 
 
 222 
 
 hospitals 
 
 heating surface 
 
 221 
 
 office buildings 
 
 Note. For page numbers see foot of pages. 
 
 III 
 
 Page 
 
 220 
 197 
 230 
 224 
 224 
 223 
 229 
 225 
 223 
 226 
 
 613 
 
 514 
 500 
 506 
 511 
 506 
 511 
 510 
 512 
 512 
 520 
 
 500, 518 
 501 
 505 
 305 
 55 
 254 
 218 
 323 
 
 209 
 210 
 214 
 209 
 232 
 
 405 
 400 
 405 
 405 
 402 
 398 
 403 
 
 541
 
 IV 
 
 INDEX 
 
 
 Page 
 
 
 Heating of 
 
 OQO 
 
 Lavatories 
 Lead, definition of 
 
 school buildings 
 
 40 
 
 Lead pipe 
 
 theaters 
 Heating and ventilation 
 Heating capacity of furnace 
 
 197-409 
 
 Leather belting 
 strength of 
 table 
 
 Heating surfaces 
 
 197 
 
 Local vents 
 
 Heating systems 
 
 00 
 
 Lock nuts 
 
 direct hot water 
 direct-indirect radiators 
 
 200 
 
 Lubrication 
 
 direct steam 
 
 198. 238 
 
 M 
 
 electric 
 
 202 
 
 Machine design 
 
 exhaust steam 
 
 201 
 
 calculations 
 
 forced blast 
 
 202 
 
 definition of 
 
 furnaces 
 
 197 
 
 empirical data 
 
 indirect hot-water 
 
 201 
 
 handbooks in 
 
 indirect steam 
 
 199 
 
 production of 
 
 stoves 
 
 197 
 
 theory of 
 
 vacuum 
 
 337 
 
 Machine screws 
 
 Hook-tooth gear 
 
 138 
 
 Machine tools 
 
 Horse-power of shafting 
 
 124 
 
 Machinery 
 
 Horse-power transmitted by telling 
 
 95 
 
 classification of 
 
 Horse-power for ventilation 
 
 238 
 
 mill and plant 
 
 Hot-water heaters 
 
 290, 515 
 
 motive-power 
 
 Hot-water supply 
 
 485 
 
 structural 
 
 circulation pipes 
 
 491 
 
 Manholes 
 
 double boiler connections 
 
 490 
 
 Mechanical straining of sewage 
 
 double water-back connections 
 
 490 
 
 Mill and plant machinery 
 
 pipe connections 
 
 492 
 
 Moments 
 
 Humidostat 
 
 389 
 
 Mortise teeth 
 
 Hydraulic ram 
 
 478 
 
 Motive-power machinery 
 
 Hydraulics of plumbing 
 
 469 
 
 Motors, electric 
 
 1 
 
 
 Muff coupling 
 
 Indirect hot-water heating 
 
 201, 309 
 
 N 
 
 Indirect radiators 
 
 268 
 
 Nickel steel 
 
 Indirect steam heating 
 
 199. 207 
 
 Nitrogen 
 
 direct-indirect radiators 
 
 287 
 
 Nuts 
 
 heaters for 
 
 268 
 
 
 pipe connection? 
 
 285 
 283 
 
 ( )ne-pipe circuit system 
 
 registers 
 Intermittent filtration 
 
 465 
 15 
 
 One-pipe relief system 
 Open-hearth steel 
 
 Invention 
 
 
 Original design 
 
 K 
 
 
 Oxygen 
 
 Keys and pins 
 
 174 
 
 P 
 
 L 
 
 
 Paul vacuum system of heating 
 
 Laundry boilers 
 
 493 
 
 Pinion bore 
 
 \otc.-For pane numbers sec font of 
 
 pages. 
 
 
 Page 
 
 418 
 
 148 
 
 433, 474 
 
 95 
 98 
 440 
 171 
 27 
 
 11 
 15 
 15 
 14 
 13 
 173 
 75 
 
 74 
 81 
 77 
 78 
 459 
 463 
 81 
 24 
 137 
 77 
 373 
 161 
 
 127 
 203 
 163 
 
 250 
 
 248 
 127 
 82 
 
 341 
 49 
 
 542
 
 INDEX 
 
 
 Page 
 
 
 Page 
 
 Pipe connections 
 
 443 
 
 Pulley rim 
 
 101 
 
 kitchen sink 
 
 445 
 
 Pulleys 
 
 41, 53, 100 
 
 soil and waste pipes 
 
 445 
 
 problems on 
 
 113 
 
 urinal 
 
 445 
 
 special forms of 
 
 112 
 
 Pipe radiators 
 
 241 
 
 Pumping stations 
 
 462 
 
 Pipes 
 
 
 Pumps 
 
 477 
 
 brass 
 
 432, 476 
 
 
 
 cast-iron 
 
 429 
 
 R 
 
 
 expansion of 
 
 252 
 
 Radiator connections 
 
 251 
 
 lead 
 
 433. 474 
 
 Radiators 
 
 220, 239 
 
 tile 
 
 434 
 
 efficiency of 
 
 243 
 
 wrought iron 
 
 432 
 
 Reducing valves 
 
 322 
 
 Piping 
 
 473 
 
 Registers 
 
 229, 283 
 
 Pitch, definition of 
 
 148 
 
 Return duct 
 
 225 
 
 Pitch cylinders 
 
 130 
 
 Return pipes 
 
 262 
 
 Plenum method of forced blast 
 
 344 
 
 Return traps 
 
 328. 
 
 Plumbing 
 
 411-524 
 
 Rope and drum 
 
 38 
 
 design and construction 
 
 458 
 
 
 
 catch-basin 
 
 461 
 
 S 
 
 
 house connections 
 
 460 
 
 Screws 
 
 163 
 
 manholes 
 
 459 
 
 Sectional boilers 
 
 235 
 
 pumping stations 
 
 462 
 
 Sedimentation 
 
 463 
 
 sewers 
 
 459 
 
 Service pipe connections 
 
 483 
 
 storm overflows 
 
 462 
 
 Set screws 
 
 172 
 
 tidal chambers 
 
 462 
 
 Sewage, disposal of 
 
 443 
 
 underdrains 
 
 459 
 
 Sewage purification 
 
 454, 462 
 
 Plumbing for 
 
 
 broad irrigation 
 
 465 
 
 apartment houses 
 
 449 
 
 chemical precipitation 
 
 463 
 
 dwelling houses 
 
 449 
 
 intermittent filtration 
 
 465 
 
 factories 
 
 452 
 
 mechanical straining 
 
 463 
 
 railroad stations 
 
 451 
 
 sedimentation 
 
 463 
 
 schoolhouses 
 
 451 
 
 sub-surface irrigation 
 
 465 
 
 shops 
 
 452 
 
 Sewerage 
 
 454 
 
 Plumbing fixtures 
 
 411 
 
 Sewers 
 
 459 
 
 bath tubs 
 
 411 
 
 Shafts 
 
 114 
 
 faucets 
 
 428 
 
 centrifugal whirling 
 
 123 
 
 lavatories 
 
 418 
 
 combined stresses 
 
 117 
 
 sinks 
 
 419 
 
 deflection 
 
 121 
 
 tanks 
 
 424 
 
 horse-power of 
 
 124 
 
 traps 
 
 422 
 
 material used in 
 
 127 
 
 urinals 
 
 416 
 
 problem on 
 
 128 
 
 water closets 
 
 412 
 
 simple bending 
 
 117 
 
 Plumbing tests 
 
 452 
 
 simple torsion 
 
 117 
 
 Propeller fans 
 
 367 
 
 tension 
 
 118 
 
 Pulley arms 
 
 103 
 
 Shrouding a tooth 
 
 137 
 
 Pulley bores 
 
 47 
 
 Simple bending 
 
 117 
 
 Pulley hub 
 
 105 
 
 Simple torsion 
 
 117 
 
 Note. For page numbers see foot of 
 
 pages. 
 
 
 
 043
 
 VI 
 
 INDEX 
 
 Single-jet burner 
 
 Sinks 
 
 Siphonage 
 
 Smoke-pipes 
 
 Soil pipe vent 
 
 Soil and waste pipes 
 
 brass 
 
 cast-iron 
 
 lead 
 
 pipe joints 
 
 tile 
 
 wrought iron 
 Spline 
 
 Split pulleys 
 
 Spur gear rim, arms, and hub 
 Spiir gears 
 Stacks and casings 
 Stands 
 Steam boilers 
 
 sectional 
 
 tubular 
 
 Page 
 
 507 
 419 
 487 
 223 
 441 
 429 
 432 
 429 
 433 
 430 
 434 
 432 
 175 
 108 
 135 
 128 
 273 
 184 
 ' 232 
 285 
 232 
 
 Steam-heating boilers, care and manage- 
 ment 288 
 
 Storm overflows 462 
 
 Stoves 197 
 
 Strain, definition of 29 
 
 Stress, definition of 29 
 
 Structural machinery 78 
 
 Stub tooth 1 38 
 
 Studs 163, 172 
 
 Sub-surface irrigation 465 
 
 Tables 
 
 air required per person 206 
 
 air required for ventilation 206 
 
 ah- changes required 207 
 
 air-flow through flues 282 
 
 blow-off, sizes for 264 
 
 boiler data 234 
 
 bolts, strength of 168 
 
 cistern capacity 481 
 
 direct hot-water heating data 307 
 
 disc fan data 371 
 
 effective areas of fans 363 
 
 fan speeds 361 
 
 feed pipes, sizes for 264 
 
 Note. For page numbers see foot of pages. 
 
 Tables 
 
 flrepot dimensions 
 gas pipe data 
 gear design data 
 grate area data 
 
 Page 
 
 223 
 505 
 140 
 233 
 
 heat loss, factors for calculating 211 
 
 heat losses in B. T. U. 210 
 
 heater dimensions 351 
 heating surface supplied by various 
 
 sizes of pipe 260 
 
 heating systems, relative cost of 200 
 
 indirect hot-water heating data 312 
 
 indirect radiating surface data 287 
 
 keys, proportions for 180 
 
 lead pipe 474 
 
 leather belting, sizes of 98 
 
 mains, data for 317 
 
 oval pipe dimensions 228 
 
 pipe heater data 350 
 
 pipe sizes 355 
 
 pipe sizes from boiler to main header 263 
 
 pipe sizes for radiator connections 262 
 power required for moving air under 
 
 different pressures 366 
 radiating surface supplied by steam 
 
 risers 261 
 
 radiator efficiency 243 
 
 register sizes for different pipes 229 
 
 return, sizes for 264 
 
 return pipe sizes 262 
 safe-working stresses for different 
 
 speeds 134 
 
 steam flow 257, 258 
 
 tin-lined lead pipe 475 
 
 torsional moments 43 
 
 warm-air pipe dimensions 226 
 
 water pressure 471,472 
 
 wrought-iron pipe dimensions 473 
 
 Tank overflow pipe 483 
 
 Tanks 424 
 
 Tap bolts 172 
 
 Telethermometer 389 
 
 Te,mperature regulators 385, 498 
 
 Tension 25, 118 
 
 Theoretical design 20 
 
 Thermostat 338, 386 
 
 Through bolts 172 
 
 544
 
 INDEX 
 
 VII 
 
 
 Page 
 
 
 Page 
 
 Tidal chambers 
 
 462 
 
 Ventilation 
 
 
 Tile pipes 
 
 434 
 
 horse-power for 
 
 238 
 
 Torsion 
 
 25, 117 
 
 of hospitals 
 
 398 
 
 Traps 
 
 422, 436 
 
 of office buildings 
 
 403 
 
 Tubular boilers 
 
 232 
 
 principles of 
 
 203 
 
 
 
 of school buildings 
 
 392 
 
 D 
 
 
 of sewers 
 
 460 
 
 Underdrains 
 
 459 
 
 of theaters 
 
 402 
 
 Urinals 
 
 416 
 
 Vents 
 
 436 
 
 
 
 local 
 
 440 
 
 V 
 
 
 soil pipe 
 
 441 
 
 Vacuum systems of heating 
 
 337 
 
 
 
 Paul system 
 
 341 
 
 W 
 
 
 Webster system 
 
 337 
 
 Warm-air flues 
 
 277 
 
 Valves 
 
 254 
 
 Warming systems 
 
 197 
 
 Velocity of air, measurements of 
 
 207 
 
 Water closets 
 
 412 
 
 Vent flues 
 
 279 
 
 Water-seal motor 
 
 338 
 
 Ventilation 
 
 
 Water-tube boilers 
 
 235 
 
 air required for 
 
 205 
 
 Web gears 
 
 139 
 
 of apartment houses 
 
 405 
 
 Webster vacuum system of heating 
 
 337 
 
 of churches 
 
 400 
 
 Woodruff key 
 
 179 
 
 of conservatories 
 
 405 
 
 Worm 
 
 146 
 
 of greenhouses 
 
 405 
 
 Worm gear 
 
 146 
 
 of halls 
 
 402 
 
 Wrought iron pipe 
 
 432 
 
 Note. For page numbers see foot of 
 
 pages. 
 
 
 
 \v 
 
 545
 
 7 '3
 
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