^ COPYRIGHT DEPOSIT. J STEAM-BOILERS BY CECIL H. PEABODY and EDWARD F. MILLER Professor of Naval Architecture Professor of Steam and Marine Engineering Engineering Massachusetts Institute of Technology SECOND EDITION, 1904 AND THIRD EDITION, IQI2 BOTH REVISED AND ENLARGED BY EDWARD F. MILLER TOTAL ISSUE, ELEVEN THOUSAND NEW YORK JOHN WILEY & SONS London: CHAPMAN & HALL, Limited 1912 Copyright, 1807, 1908, 1912, BY C. H. PEABODY and E. F. MILLER I* 3 Stanbopc jpress F. H.GILSON COMPANY BOSTON, U.S.A. PREFACE TO THIRD EDITION In this book as revised we have attempted to give a clear and concise statement of facts concerning boilers and their auxilia- ries, and of the methods of designing, building, setting, manag- ing, and caring for boilers. The subjects of mechanical stokers, economizers, and steam piping have been treated at considerable length, and the use and calculation of induced draught fans quite fully explained. Much new material on chimney draught, the result of work extending over a period of years, has been added, as has also a chapter on coal handling and coal-handling machinery. Nearly every chapter has been enlarged and the number of illustrations more than doubled. The chapter on combustion has been extended to cover oil burning and to include the most recent analyses of American coals, together with a detailed description of coal calorimetry as applied to the determination of the heating value of coal pur- chased on a " heat unit " basis. The chapters on staying riveted joints and boiler testing have each been extended. While the book was planned primarily for the use of students in technical schools, and in the two revisions has been increased so as to meet the needs of the students at the Massachusetts Institute of Technology, it is felt that the book may prove useful to engineers in general. C. H. P. and E. F. M. September i, 191 2. CONTENTS. CHAPTER I. PAGE Types of Boilers i CHAPTER II. Superheaters 37 CHAPTER III. Fuels and Combustion 48 CHAPTER IV. Corrosion and Incrustation 103 CHAPTER V. Settings, Furnaces, Chimneys, Economizers, Mechanical Stokers, and Induced Draught Fans 129 CHAPTER VI. Power of Boilers 213 CHAPTER VII. Staying and Other Details 223 CHAPTER VIII. Strength of Boilers 249 v VI CONTENTS. CHAPTER IX. PAGE Boiler Accessories 326 CHAPTER X. Coal Handling and Coal-handling Machinery 383 CHAPTER XI. Shop-practice 408 CHAPTER XII. Boiler-testing 437 CHAPTER XIII. Boiler Design 468 APPENDIX 503 INDEX 529 STEAM-BOILERS. CHAPTER I. TYPES OF BOILERS. Steam-boilers may be classified according to theTr form and construction or according to their use. Thus we have horizontal and vertical boilers, internally and externally fired boilers, shell-boilers and sectional boilers, fire-tube and water- tube boilers: the several features mentioned may be combined in various ways so as to give rise to a large number of kinds and forms of boilers. Again, we have stationary, locomotive, and marine boilers, together with a variety of portable and semi-portable boilers. Locomotive boilers are always shell- boilers, internally fired, and with fire-tubes ; and the re- strictions of the service have developed a form that has changed little from the beginning, except in the direction of increased size and power. Marine boilers present a much larger variety of form and construction, depending on the steam-pressure used and the size and service of the vessel to which they are supplied. The Scotch or drum boiler is more widely used than any other form at present, but the tendency to use high-pressure steam has led to the introduction of vari- ous forms of water-tube boilers for marine work. The variety of forms and methods of construction of stationary boilers is very wide : each country and section of a country is likely to have its own favorite type. Thus in New England, where 2 S TEA M-B OILERS. the water is good, cylindrical tubular boilers are largely used; in some of the Western States, where water contains mineral impurities, flue-boilers are preferred; and in England, the Lancashire and Galloway boilers are favored; and again, various forms of sectional and water-tube boilers are now widely used. Cylindrical Tubular Boiler. — This type of boiler is shown by Figs, i and 2 and by Plate I. It consists essentially of a cylin- drical shell closed at the ends by two flat tube-plates, and of numerous fire-tubes, commonly having a diameter of three or four inches. About two thirds of the volume of the boiler is filled with water, the other third being reserved for steam. The water-line is six or eight inches above the top row of tubes. The tube-plates below the water-line are sufficiently stayed by the tubes ; above the water-line the flat plates are stayed by tJirougJi rods or stays as in Plate I, by diagonal stays like those shown by Fig. 91, page 229 or otherwise. A pair of cylindrical boilers in brick setting are shown by Figs. 44 and 45, on pages 130 and 131, with the furnaces under the front (right-hand) end. The products of combustion pass back over a bridge-zvall, limiting the furnace, to the back end, then forward through the tubes and up the uptake to the flue which leads to the chimney. The shell commonly extends beyond the front tube-plate, as shown at the right in Fig. 1, and is cut away to facilitate the arrangement of the uptake. The boiler is usually sup- ported by cast-iron brackets riveted to the shell ; the front brackets may rest on or be fixed to the supporting side walls, but the rear brackets should be given some freedom to avoid unduly straining the boiler by expansion. Thus the rear brackets may rest on rollers, which in turn bear on a horizontal iron plate. The expansion takes place toward the back end of the boiler, and to allow for this expansion a space is left between the back tube-sheet, and the arch of fire-brick back of the boiler. TYPES OF BOILERS. STEAM-BOILERS. TYPES OF BOILERS. 5 The boilers shown by Figs. 1 and 2 and by Plate I each have two steam-nozzles, one near each end. The safety-valve is usually attached to the front nozzle, which is above the fur- nace. The steam-pipe leading steam from the boiler is at- tached to the rear nozzle, which is over the back end of the boiler, where ebullition is less violent, and consequently there is less danger that water will be thrown into the steam-pipe. Boilers of this type commonly have a manhole on top near the middle, and a hand-hole near the bottom of each tube- sheet, as shown on Plate I, to give access to the interior of the boiler and to facilitate washing out. Many boilers are now made with a manhole near the bottom of the front tube- sheet, in addition to the one on top. All parts of the boiler can then be cleaned and inspected whenever desirable. Some of the lower tubes must be left out when there is a manhole in the tube-sheet, but this is of small consequence, as the lower tubes are not efficient, and enough heating-surface can be provided elsewhere. The omission of the lower tubes re- quires also special stays for the portion of the tube-sheet left unsupported. The feed-pipe for the boiler shown by Plate I enters the front head at the left, below the water-line, and runs toward the back end of the boiler, where it may end in a perforated pipe leading across the boiler. The feed-pipe may enter the top of the boiler, near the back end, and terminate in a similar perforated transverse pipe below the water-line. A blow-off pipe leads from the bottom of the shell near the back tube-sheet. On the blow-off pipe there is a plug or valve which may be opened when steam is up, to blow out mud and soft scale that may collect in the boiler. The boiler is com- monly set with a slight inclination toward the rear so that mud may collect near the blow-off pipe. The boiler may be emptied by allowing the water to run out at the blow-off pipe. About half of the shell, two thirds of the back tube-sheet, and all the inside surface of the tubes come in contact with 6 STEAM-BOILERS. the products of combustion and form the heating-surface ; all the heating-surface is below the water-line. The boiler-setting, shown by Figs. 44 and 45 on pages 130 and 131 is made of brick laid in cement or mortar; all parts that are directly exposed to the fire are lined with fire- brick. The walls have confined air-spaces to reduce transmis- sion of heat. The boiler front is commonly made of cast iron, and has fire-doors leading to the furnace, and ash-pit doors opening from the ash-pit, or space below the grate ; there are also large doors giving access to the tubes through the smoke-box at the front end of the boiler. The furnace is formed by the side walls, the bridge, and the lower part of the boiler front, which latter is lined with fire-brick above the grate. Doors through the rear wall give access to the space back of the bridge. The top of the boiler is covered by a brick arch or by non-conducting material. Two-flue Boiler. — The cylindrical flue-boiler differs from the tubular boiler mainly in replacing the fire-tubes by one or more large flues. Fig. 3 shows such a boiler with two Fig. 3. flues. This type of boiler is usually longer than a tubular boiler, but even so it has less heating-surface and is less efficient in the use of coal. Nevertheless the greater sim- plicity and accessibility for cleaning recommend it where feed water is bad. The setting of a flue-boiler resembles that for the cylin- TYPES OF BOILERS. drical tubular-boiler. The figure shows two loops at the top of the shell for hanging the boiler; a crude method of sup- porting, suitable only for small and short boilers. Plain Cylindrical Boiler. — In places where fuel is very cheap, especially where it is a waste product, as at sawmills, the plain cylindrical boiler is fre- quently used. Its external ap- pearance is similar to that of the two-flue boiler (Fig. 3), except that there are no flues and the ends are commonly hemispheri- cal or else curved to a radius equal to the diameter of the "* shell. Such plain cylindrical 2 boilers are also employed to util- ize the waste gases from blast- furnaces. They are commonly 30 to 42 inches in diameter and from 20 to 40 feet long. They have been made 70 feet long. With such extreme lengths spe- cial care must be taken to insure equal distribution of the weight to the supports and to provide for expansion. Lancashire Boiler. — This boiler, shown by Fig. 4, is a two- flue shell-boiler with furnaces in the tubes; it is therefore an p internally-fired boiler, in which it differs from the two pre- 8 STEAM-BOILERS. ceding types, which are externally-fired. The chief difficulty in the design of these boilers is to provide sufficiently large furnaces without making the external shell too large. As com- pared with the cylindrical tubular boiler, this boiler will be sure to have long, narrow grates, with a shallow ash-pit and a low furnace-crown : the boiler also appears to be deficient in heating-surface. In compensation, radiation and loss of heat from the furnace are almost entirely done away with, and the thick outside shell, with its riveted joints, is not exposed to the fire, as with the tubular boiler. The flues are made in short sections riveted together at the ends, thus forming a series of stiffening rings that add very much to the strength of the flues against collapsing. Conical through-tubes, ver- tical or inclined, give increased heating-surface, break up the currents of the hot gases, improve the circulation of the water, and strengthen the flues. These tubes are small enough at the lower end to pass through the hole cut in the flue for the upper end, and thus are readily put in or taken out for repairs. The flat plates at the ends of the shell are stayed by gusset-stays or triangular flat plates to the shell of the boiler. The boiler is provided with a manhole near the back end and a safety-valve near the front end. Steam is taken through a horizontal dry-pipe, perforated on the top. Galloway Boiler. — This boiler has two furnace-flues at the front end, like the Lancashire boiler. Beyond the furnace the two flues merge into one broad flue, having the upper and lower surfaces stayed by numerous conical through-tubes, like those shown in Fig. 4 for the Lancashire boiler. Cornish Boiler. — This boiler was developed in conjunction with the Cornish engine, and both boiler and engine long had a reputation for high efficiency. It differed from the Lanca- shire boiler in that it had but one flue; it formerly did not have cross-tubes. The one furnace of the Cornish boiler, with a given diameter of shell, can have better proportions than the two furnaces of the Lancashire boiler, but there is even TYPES OF BOILERS. q greater difficulty to get sufficient grate-area and heating-sur- face- The high economy shown by these boilers when used with the Cornish pumping-engine was due to a slow rate of combustion, and to the skill and care of the attendant, who was usually both engineer and fireman, and who was stimu- lated by a system of competition and awards, maintained by the mine-owners in that district. The Lancashire and the Cornish boilers are set in brickwork which forms flues leading around the outside shell, thus mak- ing the shell act as heating-surface. Fig. 5 gives a cross-sec- Fig. 5. tion of the Lancashire boiler and its setting. After the gases from the fires leave the internal flues they are directed into the flue a and come forward ; then they are transferred to the flue b and pass backward ; finally they come forward in the flue c, and are then allowed to pass to the chimney. This forms what is known as a wheel-draught. In some cases the gases divide at the rear and come forward through both side TO STEAM-BOILERS. flues a and b> and uniting pass back through c and thence to the chimney, forming a split -draught. Vertical Boilers.— Boilers of this type have a cylindrical shell with a fire-box in the lower end, and with fire-tubes run- ning from the furnace to the top of the boiler. Large verti- cal boilers have a masonry foundation and a brick ash-pit; small vertical boilers have a cast-iron ash-pit that serves as foundation. Vertical boilers require little floor-space; if properly designed they give good economy, or they may be made light and powerful for their size, when economy is not important. Fig. 6 shows a large vertical boiler designed by Mr. Manning. It is made 20 to 30 feet high, so that there is a large heating-surface in the tubes. The shell is enlarged at the fire-box co provide a larger furnace and more area on the grate. The internal shell which forms the fire-box is joined to the external shell by a welded iron ring called the founda- tion-ring. This internal shell should be made of moderate thickness to avoid burning or wasting away under the action of the fire. Being under external pressure, the shell of the fire-box must be stayed to avoid collapsing. For this pur- pose it is tied to the outside shell at intervals of four or five inches each way, by bolts that are screwed through both shells and riveted over cold, on both ends. The stays near the bottom have each a hole drilled from the outside nearly through to the inside end. Should any stay break or become cracked, steam will escape and give warning to the fireman. The tubes are arranged in concentric circles, leaving a space about ten inches in diameter at the middle of the crown-sheet ; the corresponding space in the upper tube- sheet provides for the attachment of the nozzle for the steam outlet. There are numerous hand-holes in the shell outside of the fire-box, some near the crown-sheet, and some near the foun- dation-ring, and these are the only provision for cleaning the TYPES OF BOILERS. II WATER L.EVEL '&m& Fig. 6. 12 STEAM-BOILERS. boiler, which consequently is adapted for the use of good feed-water only. The feed-pipe enters the shell at one side and extends across the boiler; it is perforated to distribute the feed-water. The sides of the fire-box, the remaining surface of the tube-sheet allowing for the holes for the tubes, and the inside of the tubes up to the water-line form the heating-surface: the inside of the tubes above the water-line form the super TYPES OF BOILERS. 13 heating- stir face, since it transmits heat from the gases to the steam and superheats it. This type of boiler has found favor at factories where floor-space is valuable, since a powerful battery of boilers may be placed in a small fire-room. A small vertical boiler adapted for hoisting, pile-driving, and other light work is shown by Fig. 7. It commonly has a short smoke-pipe, into which the exhaust steam from the engine is turned to form a forced draught and give rapid combustion. Under this treatment the upper ends of the tubes frequently give trouble by leaking. To avoid this diffi- culty the tubes are sometimes ended in a sunken or submerged tube-sheet which is kept below the water-line, as shown by Fig. 8. The space between the edge of the tube-sheet Fig. 8. and the outside shell is likely to be contracted, and not to give proper exit for the steam formed on the tubes and crown-sheet. Furthermore, the cone forming the smoke- chamber above the tube-sheet is subjected to external pres- sure and is likely to be weak. A form of vertical boiler having a sunken tube-plate is shown by Fig. 9. It was at one time much used for steam fire-engines, but to save weight it was so crowded with tubes 14 STEAM-BOILERS. and the water-spaces were so contracted that it gave much trouble when forced. Fire-engine Boiler. — A boiler for a steam fire-engine should be light and compact, able to make steam quickly and r r ^z ooo ooce po o o o __k o o ooooo fr Jr Fig. 9. to steam freely when urged. They have small water-space and large heating-surface for their size, but are not economi- cal in the use of fuel. It is customary to use cannel-coal for fire-engines, as it. burns freely without clogging. A forced TYPES OF BOILERS. 15 draught is obtained by exhausting steam up the smoke-pipe. When standing in the engine-house ready for duty the boilers are kept hot by connecting them to a heating- boiler in the basement. The connection is so made with snap-valves that it is broken by pulling the fire-engine out of position. 0000000008 llllll ssssssssss 0000000000 000000 0000000000 Fig. 10. Scotch Boilers. — A single-ended three-furnace Scotch marine boiler is shown in perspective by Fig. 10; Fig. it gives the working drawings of a similar boiler with two fur- naces. The arrangement of the furnaces in the flues, is simi- lar to that for the Lancashire boiler, shown, by Fig. 4. The furnace-flue leads into a combustion-chamber, from which 1 6 STEAM-BOILERS. the products of combustion pass through fire-tubes to the uptake, which is bolted onto the front end of the boiler. The flues are from three and a half to four and a half feet in diameter; the size of the boiler depends on the number and size of the flues. Large boilers have as many as four flues. A three-furnace boiler commonly has three combustion-chambers, while a four-furnace boiler may have two, into each one of which two furnaces lead. Double- ended boilers have furnaces at each end, and resemble two single-ended boilers placed back to back. A double- ended boiler is lighter, cheaper, and occupies less space than two single-ended boilers. In the best practice there are two distinct sets of combustion-chambers for the two sets of furnaces. To still further lighten double-ended boilers, common combustion-chambers for corresponding furnaces at the two ends have been used. The results from such boilers have not been satisfactory, more especially when used under forced draught in the closed stoke-holes of war- ships; there has been so much trouble from leaky tubes under such conditions that forced draught has been aban- doned in many cases, and ships have consequently failed to make the speed anticipated. The circulation of water is defective in all Scotch boilers, and more especially in double-ended boilers. Considerable time — three or four hours — is always allowed for raising steam. Frequently some arrangement is made for drawing cold water from the bottom of the boiler and returning it near the water- line, while steam is raised. Haste and lack of care are liable to cause leakage from unequal expansion. The flue has the highest temperature of any part of the boiler and consequently expands the most, so that some allowance for expansion must be made or it will strain the tube-sheets and cause leaks. The methods of providing for expansion and at the same time stiffening the flues against collapsing under external pressure are shown on pages 291 to 3 it, and will be described in de- tail later on. TYPES OF BOILERS. »7 .r&Ad..&.. v feyj tet Mk o5 pc O ^ z =* CO 03 O h- co ojs o * o o) o Sift c" 0/0 OO O^W^i • fi-s o °^° P is 9, /etl ,J»Vfc|I f °T°|°o c H = ■ .li * : o , o i8 STEAM-BOILERS. Locomotive-boilers. — The typical American locomotive- boiler is shown by Plate II. Fig. 12 gives a perspective view of a boiler of the locomotive type used for small factories, or where steam is required temporarily ; it has no permanent foundation, but is supported on brackets at the fire-box and by a pedestal-bearing on rollers near the back end. The locomotive-boiler consists essentially of a rectangular fire-box and a cylindrical barrel through which numerous tubes pass from the fire-box to the smoke-box, which forms a con- tinuation of the barrel, and from which the products of com- bustion pass up the smoke-stack. The fire-box is joined to the outer shell at the bottom by a forged rectangular foundation-ring, similar (except in shape) Fig. 12. to the foundation-ring of a vertical boiler. Near this ring are several hand-holes for clearing out the space between the fire- box and the shell, commonly called the water-leg. The boiler TYPES OF BOILERS. 19 also has a manhole at the top of the barrel. The water-leg is stayed by screwed stay-bolts riveted cold at the ends. The flat crown-sheet is stayed to a system of crown-bars which rest on the side sheets of the fire-box and are also slung from the shell. Plate III shows a locomotive-boiler with a flattened top over the fire-box to which the crown-sheet is stayed by through-bolts. The excessive compression brought to the sheets, forming the inner sides of the water-leg, by the crown-bars which get an end support at these sheets and the great depth required in the crown-bar in order to give the strength needed, have made it impracticable to use crown-bars on boilers carrying more than 200 lbs. of steam-pressure. The method shown by Plate III is commonly adopted on large boilers of this class. The stay-bolt has a tapering head which is drawn into a tapering hole in the crown-sheet. This makes a tight joint and does not increase to any extent the amount of metal in contact with the crown-sheet. The whole matter of staying will be discussed more fully in the chapter on staying. The tubes for a locomotive-boiler are smaller than for a sta- tionary boiler and are spaced much more closely. Generally about 2 -inch tubes are used in locomotives, although in some cases smaller tubes have been used. The tubes are spaced at the intersection of sets of parallel lines drawn at angles of 30 and 150 with reference to a horizontal line. By this means a greater number of tubes can be gotten into a given space than could be done by spacing in vertical and horizontal rows, as is customary in horizontal multitubular boilers like Figs. 1 and 2 and Plate I. This is to obtain a large heating- surface required by the high rate of combustion, which often exceeds one hundred pounds of coal per square foot of grate- surface per hour. The boiler works under a strong forced draught, produced by throwing the exhaust up the smoke-stack. The boiler is fastened rigidly to the frame of the locomo- 20 STEAM-BOILERS. tive at the smoke-box end; a small longitudinal motion on the frame at the fire-box end is provided by expansion-pads, shown by Fig. 4, Plate II. Locomotive Type of Boiler.— Reference has already been made in connection with Fig. 12 to a boiler of locomotive type used for stationary purposes. Plate IV shows a modification of the locomotive type designed by Mr. E. D. Leavitt to give high evaporative efficiency. The boiler represented has a barrel 90 inches in diameter, and it is 34 feet 4 inches long over all. The working pressure is 185 pounds. The fire-box of this boiler is spread at the bottom to give increased grate-area, and contains two separate furnaces, shown by the section A A on Plate IV. The products of combus- tion pass through openings, shown by section BB, into a com- bustion-chamber, which has the section shown at CC. From the combustion-chamber, the gases pass through tubes to the smoke-box and uptake. As far as the combustion-chamber the top of the boiler is flattened to facilitate the staying of the crown-sheets of the furnace, passages, and combustion-cham- ber; the barrel of the boiler beyond the combustion-chamber is cylindrical. The boiler is somewhat complicated in construction and staying, and must be handled with care, especially in starting, to avoid straining from unequal expansion. It is adapted for the use of good feed-water only. Boilers of the locomotive type were at one time used for torpedo-boats. The fire-box was made shallower than for locomotive-boilers, and forced draught in a closed stoke-hole was used, the rate of combustion being even higher than on locomotives. Whatever may have been the reasons, it was a fact that this type of boiler, which is very reliable on locomo- tives, gave much trouble in torpedo-boats. Water-Tube Boilers. — The boilers thus far considered have an external shell containing a large body of water. Heat is communicated to the water through the shells or through TYPES OF BOILERS. 21 the sides of internal furnaces, and also by carrying the gases through tubes or flues. The boilers and water contained, are heavy and cumbersome, and the shells under high pressure must be made very thick. If the boiler fails either through some defect or through carelessness of attendants, a disastrous explosion is likely to take place. If properly designed and made and if cared for by competent and careful attendants they are safe, reliable, and durable. The large mass of hot water tends to keep a steady pressure, though at the expense of rapidity of raising steam or of meeting a sudden demand for more steam. A large number of water-tube boilers of all sorts of shapes and methods of construction has been devised to overcome the admitted defects of shell-boilers. They all have the larger part of their heating-surface made up of tubes of moder- ate size filled with water. They all have some form of separa- tors, drum, or reservoir in which the steam is separated from the water; some of these boilers have a shell of consider- able size, thus securing a store of hot water and a good free- water surface for disengagement of steam. Such shell, drum, or reservoir is either kept away from the fire or is reached only by gases that have already passed over the surface of water-tubes. The tubes are of moderate or small diameter, and so can be abundantly strong even when made of thin metal. Even if a tube fails through defect in manufacture or through wast- ing during service, it will not cause a true explosion ; and yet the failure of a tube in a confined boiler or fire-room has fre- quently caused death by scalding. Water-tube boilers may be made light, powerful, and compact, and are well adapted for use with forced draught. Steam may be raised rapidly from cold water, but pressure falls as rapidly if the fire loses intensity, and fluctuations in pressure are likely to occur. The two greatest difficulties are to secure a proper circulation of water through the tubes 22 STEAM-BOILERS. and to properly separate the steam from the water. There are many joints that may give trouble by leaking, and some types have numerous hand-holes for cleaning the tubes, which may further increase the chances of petty leaks. A few water-tube boilers will be described as illustrations ; many others equally good will be passed by, since it will be impossible to describe all. Babcock and Wilcox Boiler.— This boiler, which is shown by Figs. 13 and 14, is a water-tube boiler having one or two cylindrical drums at the top from either end of which are suspended " headers" into which the tubes running from end to end are expanded. The headers are made of steel castings or forgings, box-like in shape, with holes for tubes staggered so that the tubes taken as a whole are in horizontal rows, but not in vertical rows — an arrangement that gives a better spreading of the products of combustion among the tubes. Opposite the end of each tube there is a hand-hole, as shown. Each header is connected with the corresponding header at the opposite end by the tubes making a "section." The capacity of a boiler of this class is increased by increasing the number of tubes in a section and by increasing the number of sections con- nected to the drum or drums at the top: thus a boiler 12 wide and 9 high would have 12 sections and 9 tubes in each header. If there were a very strong draught it might be advisable to have more tubes in a header. A double-deck boiler is one where a second header is joined to the end of the first header. The two headers are joined by a piece of tube which is expanded into each. Two headers, each 9 high, when joined in this way make 18 high. By means of a special tile made to fit between the tubes the gases are obliged to circulate, as shown by the arrows. The gases escape out of the back wall. In some cases where there is not much room the gases have been brought up between the drums at the back end, thus enabling the back wall to be TYPES OF BOILERS. 23 MMMliUUMMUUUUMHdlWlMMIIUl 24 STEAM-BOILERS. against the wall of the building. The lower half of the cylin- drical shell serves as heating-surface, but it is at such a height above the fire and is so shielded by the water-tubes that it is not liable to be overheated. The boiler is hung from cross-girders front and back, which in turn are supported on iron columns, and the brick setting is only a screen to retain the heat. The circulation of the water in the boiler is down from the shell at the rear to the water-tubes, forward and upward through the tubes, in which course it is partially vaporized and conse- quently has a less average density, then up into the shell at the front, where the steam and water separate; the water in the shell flows continually from the front to the rear to supply the current through the tubes. Beneath the back headers there is a mud-drum into which scale settles. The blow-off pipe leads from this mud-drum out through the setting. Heine Boiler. — This boiler, shown by Fig. 15, consists of one or two drums, depending on the size of the boiler, with a rec- tangular box-like water-leg connected at each end. These legs are built out of plate and riveted to the drum or drums. Tubes run from leg to leg. Opposite the end of each tube there is a hand-hole through which the tube may be expanded or cleaned from scale. The boiler is set with the back end com siderably lower than the front end, as shown by the cut. The gases are made to circulate, as indicated by the arrows. The feed-water is taken into a small drum inside the main drum. It becomes heated here and deposits some of the lime salts, which are generally found in feed-water. These deposits are blown out from time to time through the pipe shown. A similar blow-off connection is shown at the bottom of the back water-leg. The water circulation is from the front towards the back in the drum and from the back towards the front in the tubes. A mixture of steam and water rushes out of the tubes at the TYPES OF BOILERS. 25 front end and up into the drum where it strikes against a deflect- ing plate placed so as to keep water from being sprayed into the steam space. A similar plate is to be found in the drum of the Babcock and Wilcox boiler. The velocity into the drum is greater in the Babcock and Wilcox than in the Heine. The water-legs of the Heine boiler are stayed by hollow stays ^fjif^^^^ pis Fig. 15. expanded or screwed into the two plates at points located between the tubes. The Stirling Boiler. — This boiler, shown by Fig. 16, has three cylindrical drums at the top and a larger drum at the bottom, connected by tubes having a slight curvature at the ends. The two forward drums at the top have also a connec- tion below the water-line through pipes not indicated. All three upper drums have their steam-spaces connected by piping. The water-line is indicated by a dotted line. 26 STEAM-BOILERS. The feed-water is introduced into the rear upper drum, from which it passes down through the rear system of pipes, which act mainly as a feed-water heater, and enter the lower drum, where the water deposits any lime compound that it may contain, from whence it may be blown out at intervals. Fire-brick bridges cause the products of combustion to pass in succession through the three systems of water-tubes as shown by the arrows. Fig. 16. The circulation through the tubes is very rapid and the tubes being nearly vertical do not collect much scale. These two facts have made this boiler work satisfactorily TYPES OF BOILERS. 2 7 with bad feed-water when some other types of boiler would not answer at all. The water-level is not the same in all three drums when the boiler is working. The front drum will show a level 6 inches higher than the rear drum if the boiler is forced hard. Water Tube Marine Boilers. — With the advent of very high steam pressures on steamships there has been a tendency to replace the Scotch boiler by some form of water-tube boiler. The objects that are sought in water-tube boilers for steam- ships are a larger power for the weight and the ability to carry high pressures. It is still a question whether the water-tube boiler will or can replace the Scotch boiler. Fig. 17. Babcock and Wilcox Marine Type.— This boiler, shown by Fig. 17, is made up of sections connected at one end to the 2 8 STEAM-BOILERS. bottom of a drum running at right angles to the tubes, and at the other end to a tube leading into the side of the drum at the level of the water-line. The side sections are continued down to the level of the grate, the tubes being replaced by forged steel boxes of 6-inch square sections at the furnace sides. These boxes are located one above the other on the same angle as the tubes; they take the place of brickwork, insure a cool side casing, and prevent the adherence of clinkers. Placed across the bottoms of the front header ends and con- nected with them by 4-inch tubes is a forged steel box of 6-inch square section. This box is situated at the lowest corner of the bank of tubes and forms a blow-off connection or mud-drum, through which the boiler may be completely drained. The circulation of water in the tubes is from the front to the back, w"here the connecting-tube leading from each section to the drum discharges a mixture of steam and water against the baffle in the large drum. The path of the gases is shown by the arrows. The Belleville Boiler is represented by Fig. 18; it con- sists essentially of a series of coils of pipe made up with bends and elbows around which the products of combustion pass on the way to the chimney. At the top there is a steam-drum Ay connected by two circulating-pipes B and C, with a drum D at the bottom. From the mud-drum D a rectangular feed- supply runs across the front of the boiler to all the coils or elements of the boiler. Each element is continuous from the feed-supply to the steam-drum, and is made up of slightly inclined pieces of pipe with horizontal bends or connections at the end. The effect is much as though a helical coil were flattened into two vertical tiers of pipes. The amount of water in the boiler is so small that it cannot be run without an automatic feed-water regulator, which in turn requires the attention of an expert feed-water tender. The several ele- ments deliver a mixture of water and steam to the steam- TYPES OF BOILERS. 29 r-^fl^5 ■& 2)\PlPlPlPl&lPlp^\ o o - i «: > i i 1 I El H B ^ 30 STEAM-BOILERS. drum, which does not appear to act efficiently as a separator, as an external separator is placed between the boiler and the engine. The feed-water is supplied to the steam-drum and passes through the external circulating-pipes to the mud-drum, where it deposits much of its impurities. Thornycroft Boiler. — The boiler represented by Figs. 19 and 20 was built for the torpedo-boat destroyer, "Daring," by Mr. Thornycroft; boilers of slightly different forms have been fitted by him, in torpedo-boats and steam-launches. The boiler consists essentially of a large drum or separator at the top and three drums at the bottom, connected by a large number of bent-tubes. There is, inside of the casing, a large tube connecting the top drum to the middle drum at the bottom, and this drum is connected to the side drums by smaller pipes. The circulation is down from the top drum to the middle lower drum, and from that to the side drums, then up through all the bent water-tubes to the upper drum, where mingled water and steam is delivered against a baffle-plate above the water-line. Steam is drawn from a nozzle at the front end of the top drum. The arrangement of grates and fire-doors is shown in elevation and section by Fig. 19. The middle drum divides the grate into two parts; over that drum is a space which is in communication with the uptake, as shown by Fig. 20. The products of combustion pass among the tubes leading from the middle drum; the tubes to the outer drums intercept the radiant heat which would otherwise strike on the boiler- casing. The boiler-setting is an iron frame, and the casing is thin plate iron lined with incombustible non-conducting material. There are numerous doors through the casing for cleaning the tubes. This boiler has proved very successful with a forced draught, making steam freely and giving little trouble. The boiler contains so small an amount of water that steam may TYPES OF BOILERS. 31 3 2 STEAM-BOILERS. be raised quickly, and any demand for steam can be quickly met. On the other hand, the feed-supply must be regulated with care and skill, and the pressure is liable to fluctuate. Fig. 21. The Yarrow Boiler. — The form of boiler used by Mr. Yarrow for torpedo-boats, is shown by Fig. 21. It resem- bles in general arrangement a form used by Mr. Thorny- TYPES OF BOILERS 33 croft with one grate. It, however, differs radically in certain particulars, namely, in that the tubes are straight and that they enter the upper drum below the water-line, and in that there are no pipes outside the casing to carry water from the upper drum to the lower drum or reservoirs. Some of the tubes deliver water and steam to the upper drum, from which steam is drawn ; other tubes carry water from the upper drum to the lower drums. A given tube may act sometimes in one way and sometimes in the other. Naturally those tubes which receive the most heat and make the most steam deliver to the upper drum, and tubes that receive less heat carry down water. The air for the fire is drawn from an iron box or casing outside the boiler-casing, so that the heat escaping from the boiler-casing is largely carried back to the fire, and the fire- room, and also the rest of the vessel, is heated up less. The Almy Boiler. — This boiler, which is represented by Fig. 22, is made of short lengths of pipe screwed into return- bends and into twin unions. At the bottom is a large tube or pipe forming three sides of a square at the sides and back of the grate. From this water-space the tubes lead into a similar structure at the top. The steam and water are discharged into a separator in front of the boiler, from which steam is drawn; while the water separated therefrom, together with the feed- water, passes down through circulating-pipes to the bottom of the boiler. The boiler is provided with a coil feed-water heater above the main boiler. It is enclosed by a casing lined with non- conducting material. It is intended for general marine work. General Discussion. — In deciding on the type of boiler to be selected for any particular case there are a number of things to be considered. The following are the most important: 1. The pressure to be carried. 2. The quality of the feed-water. 34 STEAM-BOILERS, 3. The variation in load. 4. The size of the battery. 5. The amount of land available. 6. The cost of land. 7. The fuel to be used. In general, it may be said that the more simple the boiler Is, the better it is; that all parts of the boiler should be easily Fig. 22. accessible, and that the boiler should be so designed that it will not strain itself by unequal expansion. The thickness of the steel needed in the shell of a boiler must increase as the pressure increases, and also as the diameter increases, as will be shown later. It is not considered advisable TYPES OF BOILERS. 35 to transmit heat through plates over one half an inch in thick- ness. For high pressures this means that if shell boilers, like Figs. 1 and 2, are to be used the diameter must not be greater than 60 or 66 inches, thus limiting the horse-power of a single unit to from 80 to 125 boiler horse-power, depending on the kind of coal used and the rate of combustion. This type of boiler is the least expensive, and if there were ample room and if the land occupied were inexpensive, it might be advisable to instal a large number of these small units to make up the horse-power desired. If, however, land were ex- pensive, or if there were but a small amount of land available, then this type could not be considered. A vertical boiler, like the Manning, or some form of water- tube boiler, like the Babcock and Wilcox, the Heine, or the Stirling, would probably be selected. If the cost of land were extremely high water-tube boilers might be located on the second, third, and fourth floors of a build- ing and discharge steam into a common main supplying engines in the basement. This arrangement is common in power- and lighting-stations located in the middle of a city. There is no difficulty in making a building sufficiently strong to carry the weights. There should be a sufficient number of boilers in the battery, so that one could be shut down and the others carry the load. As a boiler can be run from 25 to 30 per cent over its rated capacity this means that there should be at least four boilers in the battery if the plant is to run continuously. It is not cus- tomary to install units of more than 350 or 500 horse-power even in the largest batteries. The quality of the feed-water must also be considered in deciding how many boilers there are to be in the battery. If the feed-water is very bad it may be necessary at times to have two boilers shut off from the line. More boilers are needed when the feed-water is of poor quality, not only for the reason mentioned, 36 STEAM-BOILERS. but also because of the poorer efficiency of the heating-surface due to deposits of scale. The heating value of the fuel also enters as a factor in deter- mining the number of boilers needed. If a steady pressure is to be maintained with as little fluctua- tion as possible, a boiler with a large water-space should be chosen. Such a boiler will meet a sudden demand for steam without much drop in pressure; on the other hand, it takes a long time to increase the pressure. The Scotch boiler and a modification of the same having the combustion-chamber in a space bricked in at the end of the boiler have been used successfully for the operation of draw- bridges, where the demand for steam is at the rate of 100 boiler horse-power for a period of from five to eight minutes two or three times an hour. The cost of boilers varies with the price of steel. At the present time, 1912, horizontal multitubular boilers cost, when set, about $11.50 per horse-power for boilers 60 to 66 inches in diameter. Water-tube boilers about 200 horse-power per unit cost from $15.50 to $16.50 per horse-power, set ready to connect to the steam-main. Scotch boilers cost about $16.50 per horse-power in sizes ranging from 100 to 150 horse-power. Tables giving the diameters, ratings, width, length, and heights of settings of many of the common types of boilers have been added to the appendix. We believe that these tables will be useful to any one who may be making the preliminary design of a boiler plant. CHAPTER II. SUPERHEATERS. Steam may be dry and saturated, primed or superheated. Dry and saturated steam and primed or "wet" steam, as it is sometimes called, at the same pressure have the same tem- perature. As bubbles of steam break through the surface of the water in a boiler some water is atomized into the steam-space where it floats just as moisture floats in the air. The amount by weight of such water floating in a total weight of one pound is called the priming. This priming is in certain types of boilers between .005 and .03. If heat is now added to the wet steam in the steam-space the water floating in the steam will vaporize and at the instant when all of this water has vaporized we have dry and saturated steam. If more heat is added the temperature of the steam will go up and the steam will become superheated; the amount of superheating in degrees being the difference between the tem- perature of the steam as observed and that of saturated steam of the same pressure. The specific heat of superheated steam is the amount of heat necessary to raise the temperature of one pound of superheated steam i° Fahrenheit. The specific heat has been found to increase with the pressure of the steam, and at any constant pressure to decrease as the number of degrees of superheating increases up to a certain point, 37 3* STEAM-BOILERS. differing somewhat for each pressure, beyond which the specific heat gradually increases. The degrees of superheat at which the values begin to increase are above any used in general engi- neering work. Specific Heat of Superheated Steam. — The following table gives the mean value of the specific heat of superheated steam for different degrees of superheat at a number of pressures. SPECIFIC HEAT OF SUPERHEATED STEAM. 6 < . !2 '3 D 1 d .2 1 & 03 > "o w H O J 5 Mean Value of the Specific Heat. Si" (Do +» ro *o£ 4J O cd_Q Degrees of Superheat ° F. IJ 10 50 IOO IS© 200 250 300 400 500 600 IO 3° 50 IOO I50 200 250 300 193.2 250.3 281.0 327-9 358.5 381.9 401 .1 417-5 l6l 219 25O 298 330 354 374 39i 3 1 4 5 3 2 3 981.4 944-4 922 .8 887.6 863.0 843-5 826.9 812.4 1142.7 1163.5 1173.2 1186.1 1193.0 1197.8 1 201 . 1 1203.7 .46 •49 •5i •57 .62 .69 • 77 •85 .46 .48 •5o •55 •59 •63 .68 .72 .46 .48 • 50 •53 •56 •59 .62 .64 46 48 49 52 54 56 58 (.0 46 48 40 5- 53 55 56 58 46 48 40 51 52 54 55 56 46 48 49 5i 52 53 54 55 47 48 48 50 5i 52 53 54 47 48 48 5o 5i 51 52 53 47 48 48 40 50 51 52 52 The use of this table will be explained by applying the values to one or two simple problems. How many heat units must be added to a pound of feed- water at ioo° F. in order to change it into steam at 200 pounds absolute pressure, the steam being superheated 250 ? To change a pound of water at 32 into saturated steam re- quires 1 197.8 heat units. As the specific heat of water is practi- cally unity, the amount required to change the pound of water at ioo° into saturated steam would be 100 — 32 = 68 heat units less. Hence 1 197.8 — 68 + .54 X 250 = 1264.8. The value .54 is the specific heat taken from the table. The temperature of steam in a boiler is 545. 2 F., the SUPERHEA TERS. 3 9 pressure is 175 pounds absolute, the feed- water is at 200 F. How many heat units are required to change a pound of feed- water into steam of this pressure and temperature? The temperature of saturated steam at 175 pounds may be found near enough for this illustration by assuming the tempera- ture between 150 and 200 pounds to vary uniformly with the pressure 38I.9-358-5 x ^ = g + = o p 5° as the temperature of saturated steam at 175 pounds. The superheat is 545.2 — 370.2 = 175 . a 8 1193.0 + ^- X 25 - (200 - 32) + .545 X 175 = 1122.8. 5° In a later chapter work of this sort is illustrated more fully. Attached Superheater. — There are two classes of super- heaters, the attached and the independently fired. The attached is connected to the boiler, receives its heat from the fire under the boiler, and in general does not give more than 150 degrees of superheat. Nearly all of the attached superheaters are connected to the steam and to the water-space of the boiler in such a way that they can be flooded while steam is being gotten up in the boiler. Some makes of attached superheaters may be flooded and the heating-surface used as additional steam-generating surface when the boiler is delivering saturated steam. Babcock and Wilcox Attached Superheater.— This superheater is shown by Fig. 23. It is located directly under the drums between the first and second gas passages. It is made of bent tubes expanded into steel headers, as shown. Steam is taken from the dry pipe in the top of each drum into the center of the top headers, and after passing through the tubes leaves at the outer end of the bottom header. From the 4Q STEAM-BOILERS. end of the bottom header a pipe leads up to a nozzle fastened to the drum of the boiler, but not connecting with the drum. In some instances these superheaters have been arranged to work Fig. 23. flooded with water when the boiler was not delivering superheated steam. Heine Attached Superheater. — Fig. 24 and the two cross-sections shown on the same cut gives the arrangement of the Heine superheater. The greater part of the products of combustion is made to circulate, as shown by the dotted arrows, and is utilized in generat- ing steam. A small part of the products of combustion is made to follow the path shown by the full arrows, and pass through the super- heater. The path of these gases will be made clear by the sec- tions BB and A A. Stirling Attached Superheater.— The attached super- heater is shown as the middle bank of small tubes in Fig. 25. The detail of this superheater is shown by Fig. 26, which is a cross-section taken through Fig. 25. SUPERHEATERS. 41 o ' 42 STEAM-BOILERS. Saturated steam from the front and rear drums enters the left- hand section of the upper drum (Fig. 26) through the holes shown near the top. This steam circulates through the tubes to and Fig. 25. from the lower drum, as shown by the arrows, and is drawn off at the right-hand end of the upper drum. There is a removable diaphragm in the lower drum and covers in the two diaphragms in the upper drum. These are provided SUPERHEATERS. 43 so as to make it possible for a man to get at the ends of any tubes which may need to be re-expanded. When using saturated steam the two by-pass valves in the diaphragms in the upper drum are opened and the lower drum Fig. 26. is connected with the bottom of one of the other drums through valves and piping provided for flooding. Independently -fired Superheater. — The independently- fired superheaters are intended to give higher temperatures to the steam than can be obtained by an attached superheater. 44 STEAM-BOILERS. Superheaters of this class give a thermal efficiency of about 60 per cent. Different makers use different amounts of heating- surface for the same capacity and the same degrees of superheat- ing. It seems that about 3 square feet are needed per boiler horse-power if the steam is to leave at about 6oo° F. and was not primed more than one per cent on entrance to the superheater. In order to keep the temperature of the superheated steam as uniform as possible it is customary to make use of a Dutch oven furnace, a furnace with a fire-brick arch over the grate. This arch, by giving up heat at one time and by absorbing heat at another time, tends to keep the gases more nearly at a uniform temperature. Foster Independently- fired Superheater. — This is shown in longitudinal view by Fig. 27. Fig. 28 gives a section through a tube and header and shows the cast-iron rings put on to give additional surface for absorbing heat, and also to prevent any rapid fluctuations in the temperature of the fire affecting the temperature of the steam. SUPERHEATERS. 45 The inner tube shown in this cut is sometimes closed togethcx at the ends but not tightly sealed. This tube, which is held in place by distance pieces in the shape of rivet-heads, causes the AAAJXATr Fig. 28. steam to flow rapidly through the annular space between it and the outer tube. The steam enters Fig. 27 at the top and leaves at the bottom. American Independently-fired Superheater. — The American superheater is shown by Fig. 29. Like the preceding it is built with a Dutch oven-furnace. A " tempering" door located in the bridge-wall may also be used for regulating the temperature of the gases. The superheater is made up of headers, which are steel cast- ings joined together by steel tubes. The tubes from the bottom of one header enter the top of the header opposite. The steam circulates as many times as there are headers in one row and passes out at the bottom. The bottom tubes are of Shelby drawn nickel-steel and in some cases are covered with tile or cast iron. The headers are supported one on top of another with steel balls in between. These balls provide for the expansion sf the tubes. 4 6 STEAM-BOILERS. * SUPERHEATERS. 47 A superheater of this make, installed at the Massachusetts Institute of Technology, designed to superheat 10,000 pounds of steam an hour at 250 pounds pressure with one per cent prim- ing, 250 F., had a grate-area of 15.6 square feet and 558.3 square feet of heating-surface. Steam Pipe-fittings for Superheated Steam. — Steel castings are probably the best fittings to use on pipe lines carry- ing highly superheated steam. Steel fittings are expensive and are not to be found in stock. There is evidence tending to show that cast iron, especially if of a poor grade, is affected in its strength by superheated steam: there is no evidence, however, showing that gun-iron fittings have deteriorated under the action of superheated steam. Fittings on superheated steam lines are subjected to greater strains on account of the larger amount of expansion of the pipe and on account of the greater changes in temperature. Composition loses its strength at high temperatures and is unsafe to use with superheated steam. CHAPTER III. FUELS AND COMBUSTION. THE fuels used for making steam are coal, coke, wood, charcoal, peat, mineral oil, and natural and artificial gas. Various waste and refuse products, such as straw, sawdust, and bagasse, are burned to make steam. All coals appear to be derived from vegetable origin, and they owe their differences to the varying conditions under which they were formed or to the geological changes which they have undergone. Anthracite Coal consists almost entirely of carbon and inorganic matters ; it contains little if any hydrocarbon. Some varieties, for example certain coals found in Rhode Island, appear to approach graphite in their characteristics, and are burned with difficulty unless mixed with other coals. Good anthracite is hard, compact, and lustrous, and gives a vitreous fracture when broken. It burns with very little flame unless it is moist, and gives a very intense fire, free from smoke. Even when carefully used, it is liable to break up under the influence of the high temperature of the furnace when freshly fired, and the fine pieces may be lost with the ash. Semi-anthracite or Semi-bituminous Coal is intermedi- ate in its properties between anthracite coal and bituminous coal; it contains some hydrocarbon, is less dense than anthra- cite, it breaks with a lamellar fracture, and it burns readily with a short flame. 4 8 FUELS AND COMBUSTION. 49 Bituminous Coals contain a large and varying per cent of hydrocarbons or bituminous matter. Their physical prop- erties and behavior when burning, vary widely and with all intermediate gradations represented, so that classification is difficult. Three kinds may, however, be distinguished, as follows : Dry bituminous coals, which burn freely and with little smoke and without caking. Caking bituminous coals, which swell up, become pasty, and cake together in burning. They are advantageously used for gas-making. Long -flaming bituminous coals, which have a strong ten- dency to produce smoke ; some do and some do not cake while burning. Coke is made from bituminous and semi-bituminous coal by driving off the hydrocarbons by heat. Coke made as a by-product in gas retorts, is weak and friable, and has little value for making steam. Coke made in coking ovens, by partial combustion of the coal which is coked, is of a dark- gray color, porous, hard, and brittle. It has a metallic lustre, and gives out a slight ringing sound when struck. Sulphur in the coal may be burned out in coking, if the coal is moist or if steam is supplied during coking, so that coke may be comparatively free from this noxious element even when made from a poor coal. Coke burns without flame and makes a fierce fire when forced. Lignite, or brown coal, is of more recent geological formation than coal, and is in a manner intermediate between coal and peat. It frequently contains much moisture and mineral matter. It is used where good coal is difficult to get, and while the better varieties form a useful fuel, the poorer qualities have little value. Peat, or turf, is obtained from bogs. It consists of slightly decayed roots of the swamp vegetation mingled with more or less earthy matter. For domestic use it is cut and 50 STEAM-BOILERS. dried in the air. It is little used for making steam, though when pulverized, dried, and compressed it makes a useful artificial fuel. Wood is used for making steam either in remote places where coal is hard to get and timber is plenty, or where saw- dust or other refuse wood is produced in quantity in manufac- turing operations. Wood is also used for kindling coal-fires. One cord of hard wood is equivalent to one ton of anthracite coal ; one cord of yellow-pine is equal to half a ton of coal ; other soft woods are, as a rule, of less value for fuel. Charcoal is made by charring wood ; it is but little used for making steam. Mineral Oil, in the form of crude petroleum or the refuse heavy oil left from the distillation of petroleum, is used for making steam, especially in the neighborhood of the Black Sea oil-field, and by steamers carrying oil from those fields. It is customary to throw the oil into the furnace in the form of finely divided spray through special spraying apparatus worked either with compressed air or with superheated steam. The use of superheated steam has its convenience only to recommend it, for it adds to the inert material to be uselessly heated. Special precautions must be taken, when petroleum is burned, to avoid flooding the furnace with oil and to pre- vent explosions of the vapor and burning of the oil in tanks or receptacles. Gases. — Natural gas from gas-wells has been used for making steam, usually in a crude and wasteful way. Some attempts have been made to use gas made from poor and smoky coal, in producer-furnaces like those used in metallurgi- cal operations ; but the gain to be expected is only the sup- pression of the smoke nuisance, which is rather a social than an economical problem. Artificial Fuels. — The small waste from coals and char- coals, sawdust, and other fine combustible material which cannot be sold in such shape, is sometimes made into cakes or FUELS AND COMBUSTION. 51 briquettes by mixing it with some adhesive material and then compressing it. The adhesive materials have been wood-tar, coal-tar, or else clay. Tar is available in limited quantities only, and clay is disadvantageous since it adds to the inert material, of which fine fuel is liable to have an excess. Artificial fuels have some advantages for special purposes, and can be stored compactly ; they are used mostly where good fuel is difficult to get. Composition and Heat of Combustion of Coals. — The com- position of American coals is given by three sets of tables : one by Mr. Henry J. Williams, page 57, gives the results of analyses made by him in 1897; a second table, pages 52 and 53, gives the analyses made at the coal testing plant of the United States Geological Survey; and a third table, pages 54 and 55, contains the results of analyses made by a number of chemists, and includes also the work of the U. S. Geological Survey. From this last table, which was given in a report of a committee on fuel supply appointed by the Boston Chamber of Commerce, the summary given on page 56 was made. The table on pages 54 and 55 has been made with the coals arranged in the order of the carbon hydrogen ratio. It will be noticed that the highest heating value of any of these coals occurs with a carbon hydrogen ratio of approxi- mately 18.7. As would be expected the coals with the larger percentage of ash show a smaller heating value. The tables on pages 54 and 55 and the summary on page 56 give the average of a great number of analyses, and, in judg- ing of the heating value to be expected from any particular coal, these results may be depended upon with more certainty than the results of one or two analyses on a sample of that coal. It is to be noted also that heating values above 14,600 B.T.U. are not numerous. 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S § • ci d o5 . u u u rh a) D 4> °£ES we gg •ooo POUU o rl £ £ -!i O PL, O O - £ - ■d -6 r, C8 c 00 w J! >> o, > C73 cd u a +5 O » cd « 5j h^ cd > <+--6 • S a o 56 STEAM-BOILERS. < g Ooo O 10 m rf O O O OO O O oo OO cow t^OsrJ-O O co O OOO lOO O O *^ t^ w r^M NCOO OO Ol 10 M O O NioO O lO ^O (JNOOOvO t» CO00 OO 00 -iO O OOO O O O O 1^00 O f^O O r^O Tf O is CO CO O CN O) CN CO CN CN CN CO CN Tf CN CN -tf- LO00 Tf tJ- u-> tJ-O OO to tJ-00 rf >0 ci crj rt crj cd 'O'O .... .v -J I..I ^U HI vj ^J U I. J Vo ^O i—j |_j >_^ K_^ I K-^ .»■« ?; cd ci d ci ci ci ci ci c ci *-> «-i .83" 3 C +f "£ 4-> >^ 3 C g G ^ _, o 3 3 p c g n o o o p 5 CD crj Tl rt ■rH ^ ^ b 00 SS o g 6 S^ OjO «h C hH itH cu O, ci V C o G > O c3l*° FUELS AND COMBUSTION. 57 m < O u < u I— I w rr. S o 3 o p O £ o < w HI < O °3 O no 00 On -T C4 o to s "c a 3 « NO O On m Tj- no r>. 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O oo en " t O O u^co Tf OO *3- in en O en en en s s s en en en xa jau^IM •|OA JU3D J3J cn «N in eno *H HO I-I 11 CN CN en en en O O in rf CO CO CO o o o co co CO OOO •qsy o o o o o O O f o o O rt *t -r en o o o o o o o o r^ o O O QOO OOO O O in in en o O en in cn cn n o OOO OOO CN CN O in rf in in o i-i *3- in *3" 1-cOq rtO OOO •*r en in DldODS -ojpA-H O O O »n O in O O r^- O O fiO o in cn O v~> eno -i cm OOO OOO CN (_> O o t 1-1 Tt O O vn O O i-i O O en O O en in in cn WtN m H h, d « « H mO O en O t> O n W O - N en Tt-o en CON N't en enco O r->- in M -H O en O o o en r~ OOO CO C- en r^ en cn s in O CN CO -f O ""> I-" CN CN CN inO m CO CN CN i-i co oo -t- « en o O en r» n o o -too a co en tn t h | n in O a o 8 s « ^ 6 i *»2 ty) > C e s g o o CJ **■* *•-< c a; a; a! c c cjo be hJ-J S.C S - 2 -a r^ O c . ° tu o a; o FUELS AND COMBUSTION. 59 Composition and Heat of Combustion of Petroleums. — The heat of combustion of petroleum is much higher than for coal. This is due largely to the greater amount of hydrogen contained in the petroleums. COMPOSITION OF PETROLEUMS. Carbon. Hydrogen. Oxygen. Specific Gravity. Heating Value, B.T.U. 849 86.3 86.6 87.1 13.7 13.6 12.3 11. 7 1.4 0.1 1.1 1.2 0.886 0.884 0.938 0.938 20,736 22,027 20,138 19.832 PROPERTIES OF CRUDE AND FUEL OIL. Oil. Field. c •8 O a M 2 c W a , X 0. H pq Authority. . 9266 0.9179 . 9240 0.9260 0.9416 I98 18,460 18,500 19,060 19.481 18,513 ) Prof. A. C. Scott, ) Univ. of Texas. ) U. S. Naval Liquid ) Fuel Board. Prof. W. C. Blasdale, Crude Fuel Beaumont, Tex.. . . Beaumont, Tex.. . . Whittier, Cal. . 84.6 833 10.9 12.4 I.63 O.50 2.87 3.83 I80 216 200 240 Univ. of California. Heat of Combustion. — The number of thermal units de- veloped by the complete combustion of one unit of weight of a fuel is called the heat of combustion. The heats of combustion of carbon in various forms as de- termined by Berthelot * are: Diamond 7859 calories Diamond bort 7860.9 calories Graphite 7901.2 calories Amorphous from wood 8137.4 calories * Comptes rendu, 1889. 60 STEAM-BOILERS. The following table gives the heat of combustion of some elements and simple gases. Carbon burned to C0 2 8,140 calories; 14,650 B.T.U. Carbon burned to CO 4400 B.T.U. Hydrogen 34, 500 calories; 62,100 B.T.U. Sulphur 4,032 B.T.U. Marsh-gas, CH 4 23,513 B.T.U. Olefiant gas, C 2 H 4 2I >343 B.T.U. Carbon monoxide 4>393 B.T.U. Determination of Heat of Combustion. — The heat of com- bustion of any fuel, whether liquid or solid, may be determined by burning the fuel in a properly constructed calorimeter. The most recent and the best results are those obtained by the use of the type known as the Mahler bomb. This is a strong receptacle of wrought iron or bronze, gold-plated or enamelled inside. The fuel to be tested is placed in a small platinum crucible, with an arrangement for igniting by electricity. The bomb is then filled with oxygen under the pressure of about twenty-five atmos- pheres, and is placed in a calorimeter-can containing water. There is oxygen in excess, so that the charge when ignited is completely consumed, and the resultant total heat of combustion is absorbed by the metal of the bomb and by the water in the calorimeter. The corrections for the calorimeter are determined by burning in it some substance like cane sugar, for which the heat of combustion is known. The processes of making com- bustion determinations are simple and direct; the difficulties are those incident to accurate measurements of temperatures, for which purpose the best physical thermometers are required. Consulting engineers as a rule send the samples of coal on which they want determinations of the heat of combustion made to some expert chemist or physicist who may make a specialty of such work. There are many cases, however, where great accuracy in the determinations is not required, hence an expert operator is not needed. FUELS AND COMBUSTION. 6 1 As a large and a constantly increasing number of manu- facturing establishments are now buying coal on the " heat-unit basis " and as the price of the coal is often fixed by its heating value, it becomes necessary to test samples from each carload of coal delivered. The number of samples to be tested becomes so large that it pays to install a complete outfit for coal testing. Such an outfit costs about $300 and can be operated by any skilled engineer. In the near future the determination of the heat of combus- tion of coal will be one of the regular duties of the chief engineer in charge of the operation of the power plant of an establishment. With this in mind it may not be out of place to give here in some detail a description of a coal calorimeter, its manipulation, standardization, and the method of making what calculations are needed in getting the heating value of a fuel. The cuts shown by Figs. 30 and 31 illustrate the Emerson Fuel Calorimeter, and are taken, as is also considerable of what follows, from a paper written by Mr. Emerson. The bomb, which is made of steel, consists of two cups joined by means of a heavy steel nut. The two cups are machined at their contact faces with a tongue and groove; the joint being made tight by means of a lead gasket inserted in the groove. The lining is of sheet metal, spun in to fit, or of a double- process high- temperature porcelain. The pan holding the combustible, shown at the centre of the bomb in Fig. 30, is made of platinum or nickel, and the support- ing wire of nickel. The jacket is a double-walled copper tank between the walls of which water is inserted. The calorimeter-can, which is as light as possible, is made of brass. The stirrer is directly connected to a small motor and is enclosed in a tube to facilitate its action in circulating the water. The stirrer is mounted on a post on the calorimeter jacket as is the thermometer holder. (62) Fig. 30. FUELS AND COMBUSTION. 63 The piping for the insertion of oxygen under pressure is fitted with a hand union at one end to make the connection with the bomb, and the other end has a special fitting, to fit the oxygen supply tank. In getting ready to make a determination of the heating value of a coal, one proceeds as follows: first, place the lower half of the bomb in the holder, shown at the left in Fig. 31, and Fig. 31. place also the shallow fuel pan in the wire support which holds it in the centre of the bomb. Twist one end of the fuse wire through the small hole at one edge of the fuel pan, leaving the short end of sufficient length to bend over the ring which supports the pan and make good con- tact with it. The long end of the wire is now extended across the fuel pan through a hole in a mica upright, shown in Fig. 30 as the vertical piece at the left of the pan, and attached to the D4 STEAM-BOILERS. binding post on the side of the bomb. This wire is bent down into the pan so as to be in contact with the fuel charge but it must not touch the pan except at the point of connection. Next, fill a test-tube with the sample, which has previously been crushed and powdered, and weigh the same accurately to a tenth of a milligram. Pour from this into the pan of the bomb until the pan is approximately half full. Weigh the test- tube again, and the difference gives the net quantity of fuel in the bomb. This weight should be at least five tenths of a gram, and should not exceed 1.2 grams. Nineteen hundred grams of distilled water are now placed in the calorimeter-can at a temperature about one and one half degrees below the jacket temperature which should be about the same as that of the room. The bomb is next placed in the calorimeter and the stirrer and the thermometer are lowered into position. The thermome- ter is immersed about 3 inches in the water, care being taken that the bulb does not touch the side of the can. The terminals of the electric circuit used for firing are now attached as shown in Fig. 30. For hard coal the maximum charge should not be greater than one gram. Hard coal should not be as finely divided as soft coal: if the sample of hard coal passes through an 80-mesh sieve it is fine enough. The upper half of the bomb is next placed in position and the nut screwed down by the use of a long wrench. The bomb is now ready to be filled with oxygen through the attachment shown in Fig. 31. The spindle on the bomb need only be opened one turn and the amount let into the bomb may be regulated by the value on the oxygen tank. When 300 pounds is shown by the gauge the value on the tank is closed and the spindle screwed down. The hand wheel on this spindle is now removed. This spindle serves also as one of the terminals for the electric circuit. After filling the bomb with oxygen it should be tested for leaks by immersing same in a glass jar filled with water. Care FUELS AND COMBUSTION. 65 bhould be taken not to tip the bomb lest some of the coal be spilled from the fuel pan. The stirrer is now started. After waiting three or four minutes for the temperature of the water and bomb to equalize, readings of the thermometer to yoVo or 2"oVo °^ a degree are taken at half-minute intervals for the next five minutes, when the firing switch is turned on for a second only. In a few seconds the temperature begins to rise rapidly and readings are taken as before, every half minute from the time of firing till the maximum temperature is reached, generally at an interval of less than six minutes' duration. After the maximum temperature is reached the rate of change of temperature is due only to radiation to or from the calorim- eter, and in order to make the corrections for this it is necessary to continue the readings at thirty second intervals for another five -minute period. The data obtained during the run is used as follows: The difference between the temperature at maximum and the temperature at firing gives the apparent rise in temperature in the calorimeter. To this apparent rise must be applied a cooling correction computed thus: The change in temperature during the preliminary five minutes of reading divided by the time (five minutes) gives the rate of change of temperature per minute due to radiation to or from the calorimeter and also any heating due to stirring, etc. This factor we will call Ri, in like manner the readings taken after final temperature give R 2 . The two rates of change of temperature give the existing conditions in the calorimeter at the start and at the finish of the run. Therefore, the algebraic sum of the two rates divided by two will give the mean (or average) value of the rate of change of temperature during the entire run due to radiations to and from the calorimeter. This value mul- tiplied by the time from firing to maximum will give the total cooling correction. The cooling correction thus determined has been found by long experience to be a very close approximation 66 STEAM-BOILERS. to the radiation effects encountered when working under these above conditions. This latter quantity is either added to or subtracted from the apparent rise taken from the data of the run, accordingly as the balance of heat radiation is to the surroundings or from the sur- roundings. This is at once determined from an inspection of the data. Cooling correction is expressed: p ■ p — X time from firing to maximum temperature. The corrected rise of temperature divided by the weight of fuel used will give directly the rise per gram of fuel. The rise per gram times the weight of water plus the " water equivalent " will give the calories per gram of fuel. The calorie referred to is the amount of heat necessary to raise one gram of water one degree centigrade. The result in calories per gram of fuel multiplied by the factor 1.8 gives the B.T.U. per pound of fuel. In the measurement of the heat of combustion of a fuel in a bomb calorimeter the immersed parts of the calorimeter, in- cluding the bomb, can, stirrer, etc., are carried through the same rise in temperature as the water. The amount of heat absorbed by these immersed parts for one degree rise in temperature is known as the " water equivalent." A set of observations as taken, together with the calculations, follow. September 17, 191 2. Run No. 2. Sample No. 728 (dried). Thermometer used, No. 2295. Weight of tube and coal = 7.9379 Weight of tube and coal = 7.0713 0.8666 gram Weight of water = 1900 grams. FUELS AND COMBUSTION. THERMOMETER READINGS. 6 7 Time, min. sec. Temperature. Time, min. sec. Temperature. Time, min. sec. Tempera- ture. 20.348 30 2 1 . OOO II 23.182 30 20.350 6 22 .600 30 23.178 I 20.352 30 22.900 12 23.174 30 20.356 7 23 . IOO 30 23.170 2 20.358 30 23.150 13 23 . 166 30 20.360 8 23 • 194 30 23. 162 3 20.362 30 23.196 Max. temp. 14 23-I58 30 20.364 9 23.196 30 23-154 4 20.368 3° 23-194 15 23.ISO 30 20.374 10 23-194 5 20.376 Firing temp. 30 23.190 Apparent rise in temperature = 2.820. Rate of change of temperature before firing = 0.0056 = Ri. Rate of change of temperature after maximum temperature — 0.0088 = R 2 (taken between times 10 and 15). Average rate of change of temperature during run = 0.0016. Total cooling correction = (0.0016 X 3.5 (min.)) = 0.006 (additive) . Total corrected rise in temperature = 2.826. Rise per gram of sample = 3.261. The water equivalent of bomb, calorimeter-can, stirrer, etc., = 490. Gram calories per gram of sample = (1900 + 490) X 3.261 = 7794- British Thermal Units per pound of sample = 7794 X 1.8 = 14,030. Note. Ri and R 2 are each for a five-minute period. The maximum temperature in the bomb was reached in 3.5 minutes. A bomb calorimeter when operating properly will give the true heat value of a given combustible if as a water equivalent factor we use that obtained from the weights and specific heats of the immersed parts, i.e., the sum of the products of the weight of each part times its specific heat. The testimony and the work of such physicists as Berthelot and Mahler have conclusively 68 STEAM-BOILERS. proven that this above method is correct. It is sometimes desirable to check this value by burning a combustible of known calorific value. Extreme care should be taken that such stand- ardizing substances should be of practically ioo per cent purity and absolutely free from chemically or physically combined water. The value of such a standard substance in calories per gram is divided by the rise in temperature in the calorimeter per gram of sample and the result is the water plus the water equivalent of the apparatus. The water being known, the water equivalent is thus determined. With a combustible of absolute purity this determination will check the value of the water equivalent as figured from the weights and specific heat of the material included in the immersed parts of the calorimeter. Cane sugar may be obtained at the Bureau of Standards at Washington, D. C, in a high degree of purity, and is probably the most desirable substance available for standardization. (When burning sugar carbon in the bomb use 400 pounds per square inch pressure of oxygen.) Naphthalene, although fre- quently used, is uncertain in its action if burned in a powdered or flaky condition. Upon ignition it burns with extreme rapidity, frequently scattering the charge without burning the same. The best results are obtained from this latter material if it is previously melted into a capsule. Naphthalene volatilizes to such an extent that upon ignition of the charge the naphthalene vapor in some cases explodes or detonates, and this is undesirable as it introduces a possibility of injuring the bomb. Benzoic acid is also useful as a standardization agent. Sampling Coal. — The original sample taken from the coal pile, shipload, or carload shipments must be large. A large sample insures that we will get in the original sample, at least, one that is a fair average of the whole, provided the selections are made with due care. If we are taking a sample from a 5 00- ton ship- ment the original sample should be not less than one ton. FUELS AND COMBUSTION. 69 The most convenient place to sample coal is under conditions where it is being handled, i.e., by bucket elevator, belt conveyor, team load, or car. Shovelfuls taken every so often from belt or bucket conveyor, a shovelful or two from every other team load during cartage and from carload shipments, several well selected shovelfuls from each car, in each case will give satisfactory results. In carload shipment the heavy pieces of rock and slate gradually work toward the bottom of the car and due considera- tion of this fact is necessary in proper sampling of the same. For the boiler-test sample the fireman is instructed to lay aside a shovelful during each stroke period. In the case of a large coal pile, shovelfuls, all the way from the top to the bottom of the pile and on different sides, should be taken. Selections should be made 18 inches or 2 feet below the surface of the pile. A considerable portion of the sample should be taken from the larger pieces which are invari- ably found at the bottom of the pile. If of considerable size the pieces should be broken and parts of the fragments retained in the sample. Pieces encountered which contain practically nothing but slate or other forms of rock should not in each and every case be included in the sample. It is largely a matter of observation of the apparent percentage of such material that governs the sampler as to how much of the same he shall include in his sample. His judgment in this matter determines partly the success or failure of his work. The intrinsic impurities of the coal will be included in proper proportions if the sampler exerts a reasonable amount of care. If sampling is done at the mine, several points should be chosen from a map of the mine, which will give a fair sample of the whole. These points should be near the working face. A cut across the face 6 inches in width and 1 inch in thickness should be made at each point. This cut should be taken out complete except that which would be rejected by the mine worker. The samples taken from the several points should be thrown together, crushed, mixed, and treated according to the 70 STEAM-BOILERS. directions given below. In determining the quality of the average output of a mine the most convenient place to sample is from the cars as they come from the mine. The original sample is reduced in bulk and at the same time made to retain the same average quality by the process of quartering. The sample is spread out on an oilcloth, canvas, or smooth floor and thoroughly mixed by overhauling with a shovel. The large pieces should be crushed until the maximum is not greater than the size of an egg. Lines are drawn through the sample at right angles, thus dividing it into quarters. Two opposite quarters are taken out and the rest rejected. The part retained is again mixed, crushed, and requartered. In this man- ner the size of the sample is reduced and we do not destroy the average quality if our mixing is reasonably thorough. The maximum size of the pieces should be reduced as we decrease the size of the sample. Careful and thorough mixing is the first essential in this process of quartering. The crushing is usually done with a sledge or maul. The sample is reduced until about sufficient to fill a two-quart jar. This sample is run through a grinder and requartered after mixing on glazed paper or oilcloth, with repetitions of the same until the sample is reduced to about 40 grams. This ultimate sample is powdered with fine grinder or mortar and pestle until it passes completely through an 80-mesh sieve. The sample is immediately placed in a sealed bottle ready for test. Throughout the process of sampling, care should be taken that the sample shall not be long exposed to the air, as con- siderable moisture will be lost. The Purchase of Coal on Specifications. — During the past few years a great many coal consumers have taken up the pur- chase of coal on specifications with varying degrees of success. In this, as in most new movements, some difficulties have been encountered, and the results have not been satisfactory in every case. The principal reasons for failure have been in the appli- FUELS AND COMBUSTION. 7 1 cation of the method rather than in the method itself. Many misunderstandings have arisen on the one hand because the pur- chasers are prone to expect too much, to take faulty samples, or to act on inaccurate analyses of the coal delivered, and on the other hand because the coal companies are inclined to overesti- mate the excellence of coal they are able to deliver. The general method of buying coal on specifications is for the purchaser to ask for bids, to be based upon the delivery of coal of a specified analysis, allowing certain variations for the B.T.U. and the various constituents. Should the analysis show variations from the specifications, premiums are paid or penalties exacted in proportion to such variations above or below the standard. In some forms of specifications the bidder submits an analysis of coal he proposes to deliver, and the analysis of the successful bidder is taken as a standard for the contract. In some contracts the adjustment of price is based on the moisture, volatile, ash, sulphur, and B.T.U., while in others only the ash and B.T.U. are considered. The B.T.U. should always be one of the factors, as steam coal is purchased for the heat which may be developed from it. Moisture is also of great importance, as it represents so much valueless material; it should be ascertained when the selling weights are obtained. Volatile has two objectionable features: first, the production of smoke; second, reduction in boiler efficiency. These may be overcome by proper boiler installation and careful firing with a view to complete combustion. In the absence of these condi- tions it is best to avoid high volatile coals. It seems that the lower boiler efficiency due to higher volatile coals has been greatly overestimated, for the results of some 400 boiler tests, made by the United States Geological Survey, indicate that the boiler efficiency is about 2 per cent lower with coal containing 35 per cent volatile than it is with coal of 15 per cent volatile.* * Report by the Committee on Fuel Supply of the Boston Chamber of Com- merce, November, 1909. 72 STEAM-BOILERS. Ash affects both the capacity and the efficiency of a boiler, and the price of coal should vary with it. Ash not only replaces combustible material, but also reduces the efficiency of the boiler by clogging the grate, by carrying unburned coal with it to the ash-pit, and by its accumulation on the heating surface causes additional labor and extra expense for its removal. Sulphur in excess is penalized because its presence is believed to be a general indication of clinkering properties in coal. This indication is not always correct, as fluxing materials other than those accompanying sulphur are usually contained in ash. The average method of analysis does not, however, deter- mine these qualities, nor is it usually worth while to determine them. There is much diversity of specifications, even for similar coals and similar plants, and there is need for some standardiza- tion of their form as well as the method of their application. Coal Specifications. — Two forms of specifications are given below. The first one was drawn for the Massachusetts Insti- tute of Technology. This calls for a high-grade coal, like a Pocahontas or the best of what is known as New River coal. " Coal must be of a good quality of bituminous steam coal, free from dirt. A fair proportion of the coal is to be in the form of lumps. Analysis of the dry coal shall not show more than 22 per cent volatile matter, 7 per cent ash, 1^ per cent sulphur, and the calorific value shall not fall below 14,500. The coal is to contain less than 3 per cent of moisture. " The samples of coal shall be taken by the Institute or its representative and no other sample will be recognized. The con- tractor or his representative may witness the operation of the sampling if so desired. Samples of the coal delivered will be taken by the Institute or its representative as the coal is being delivered. The original sample shall be taken from the wagons while being unloaded. Two or more shovelfuls of coal shall be taken from each wagon load sampled, and at least three wagon loads will be represented in any one sample. The sample shall FUELS AND COMBUSTION. 73 be thoroughly mixed and quartered in the usual manner. The final sample is to be pulverized and passed through an 80-mesh sieve. A part of the final sample shall be put aside in an air- tight jar properly marked, for the contractor, so that he may verify results if he so desires. " The coal shall be tested by the Institute or its representa- tive, a bomb calorimeter being used. Should the contractor question the results, a sufficient quantity of the original sample is to be furnished him for testing if he so requests it. Should the heating value per pound of dry coal fall below 14,500 heat units, or should the moisture exceed 3 per cent, or the ash exceed 7 per cent, or the sulphur i| per cent, this contract may be ter- minated at the option of the Institute. " The contractor agrees to furnish coal to conform to the above specifications at a price of $ . . . per ton of 2000 pounds of coal." Another form of contract reads: " Coal shall be bituminous or semi-bituminous, of good quality free from excessive amount of foreign matter. Each bidder shall state in his proposal the standard heating value in British thermal units per pound of dry coal that he proposes to furnish and shall also give an analysis of it, showing the per- centage of moisture, volatile matter, ash, and sulphur. " The calorific value and the analysis of the coal of the accepted proposal shall be a part of the contract. The price and the heating value shall be used to compute the cheapest coal. Consideration, however, shall be given to the quality, and the company shall reserve the right to make award according to its best interest. " Samples of the coal shall be taken by the company. The samples shall in no case be less than 100 pounds, and shall be carefully selected so as to represent a fair average of the whole. No other sample will be recognized. The samples shall be re- duced by thoroughly mixing and quartering until a final sample is obtained for testing, which shall at once be placed in an air- 74 STEAM-BOILERS. tight jar or can and sealed for moisture determination. The contractor or his representative may be present to witness the operation of sampling. " The test shall be made by the company according to the method adopted by the American Chemical Society, using a bomb calorimeter. " Payments shall be made on the basis of price and analysis named in the proposal corrected for variations in moisture, ash, and calorific values as follows: " Deductions shall be made from the contract price at the rate of 2 cents per ton for each whole per cent of moisture above the contract specification. " Deductions shall be made from the contract price at the rate of 2 cents per ton for each whole per cent of ash above the limit specified in the contract. " Deductions shall be made from the contract price at the rate of 1 cent for each 50 B.T.U. which the coal develops less than the standard specified in the contract. " The company shall have the right to reject any coal having more than 22 per cent volatile matter, 10 per cent ash, 1.5 per cent sulphur, and a calorific value of more than 500 B.T.U. less than the standard specified in the contract, and the contractor shall remove the same at his expense." Volume of a Ton of Coal. — Kind of Coal. Cubic Feet to Ton. Soft coal 41 to 43 Buckwheat or pea 37 Nut 34 Furnace size 36 Coke 76 Volume of a Ton of Ash. — Cubic Feet to Ton. Ash not packed 43 to 50 FUELS AND COMBUSTION. 75 o 100c T*- ON \n •SS9JJ lUB^SUOQ ie uoiiipuo^ sno9 O O iflNtOrj-W -rf N O* MTtH-ti^a -04 * -sbq in ' %vdn oypadg to oodooo • o 6 o o • O O to • OOOO • • • CO •pauang O «o O m rO l o O O 00 0- Q •qq J 3 d ■fi'X'a m O w ^ ^f H H CN (N CN •qq i uang o^ -O •£ z£ }B sbq jo -qq i 00 ■00«HNON"1NHM a o jo -^ -113 ui auitqo^ N • MUM (NMMMM VO •iOMCO"3->-iNNcoON E •SS3JJ -sqq £-fri %v iO • o qoquiAg OOO CD a 3 jBjnD3jop\[ < ■^qSpM M H w 3 w PQ < •30UB ;sqng c a; buO r 2 c l-i r- > C 2- \ ^2 ■J. ■f - i +: 5= -- b a a 1- < < 76 STEAM-BOILERS. Chemistry of Combustion. — Calculations concerning the heat of combustion of fuels and the amount of air needed for com- bustion require a knowledge of the elements of chemistry. Elementary chemical substances are those that have not been decomposed, such as oxygen, hydrogen, and nitrogen. The ele- ments enter into chemical combination in fixed proportions by weight; these proportions are called the combining weights or the atomic weights of the elements. In the table on page 75 are given the most important chemical elements of fuels, their chemi- cal symbols, and their atomic weights. The table gives other useful information which will be referred to later. A chemical combination such as water is represented by a formula consisting of the symbols of the elements entering into the combination, each symbol having a subscript which shows the number of times the combining or atomic weight of the element occurs in the combination. Thus, water is repre- sented by H 2 0, which indicates that water is made up of two portions of hy- drogen and one portion of oxygen. It is commonly said that two atoms of hydrogen and one atom of oxygen unite to form one molecule of water. As the atomic weight of hydrogen is I and the atomic weight of oxygen is 16, we have water formed of two pounds of hydrogen to 16 pounds of oxygen. Again, carbon may unite with one portion of oxygen to form carbon monoxide or carbonic oxide, represented by CO ; or carbon may unite with two portions of oxygen to form carbon dioxide or carbonic acid, represented by C0 2 . Re- ferring to the table on page 60, it appears that the complete combustion to C0 2 gives more than three times the heat ob- tained from incomplete combustion to CO. But the resulting gas, C0 2 may be burned with one more portion of oxygen, and will finally form CO2. Assuming that the double process will yield the same amount of heat per pound of coal as is ob- tained by direct combustion to C0 2 , we may calculate the heat of combustion of one pound of carbon monoxide as follows: FUELS AND COMBUSTION. 77 In the combustion of carbon to CO, 12 pounds of carbon unite with 16 pounds of oxygen, forming 28 pounds of CO, hence one pound of carbon will form 5 = 2i lbs. of CO. 12 The heat developed by burning these 2 J- pounds of carbon monoxide, under our assumption, is 14650 — 4400 = 10250 B. T. U., so that each pound of carbon monoxide will yield 10250^21 = 4393 B. T. U., as given in the table on page 54. The complete combustion in either case will give 12 -f 2 X 16 _ 2 pounds of carbon dioxide for each pound of carbon. Calculation of Heat of Combustion.— If a fuel were a mechanical mixture of two chemical elements such as carbon and sulphur, the heat of combustion could obviously be found by calculating the parts separately and adding the results. For example, a mixture of 60 per cent carbon and 40 per cent sulphur would give 0.60 X 14650 = 8790.0 0.40 X 4032 = 1612.8 10402.8 B. T. U. for each pound of the mixture. Fuels, as a rule, contain carbon in a free state, and various compounds of carbon and hydrogen, and compounds of carbon, hydrogen, and oxygen. Now the rapid union of chemical ele- ments is usually accompanied by the evolution of heat, as in 78 STEAM-BOILERS. the combustion of oxygen and hydrogen. Conversely, heat is required to break up a chemical combination. The com- bustion of a fuel is a complex process, usually involving some breaking up of chemical compounds and the union of chemical elements with oxygen ; the exact nature of the process is far from certain even when the real chemical compounds and ele- ments of which the fuel is composed are known. As a rule we know only the final analysis of the fuel and do not know the compounds which enter into it. For this reason the only true way of determining total heat of combustion is by experi- ment. Nevertheless it is customary and convenient to make a calculation of the total heat of combustion by an arbitrary method, when the real heat of combustion of a fuel has not been determined. Dulong proposed that the heat of combustion should be calculated on the assumption that the oxygen in the fuel and enough hydrogen to unite with it and form water, could be set aside as inert, and that the remainder of the hydrogen and all the carbon could be treated as free elements. From the com- position of water and the atomic weights of hydrogen and oxygen it is clear that each pound of oxygen will require 2X1 i 16 of a pound of hydrogen. Dulong's method may therefore be expressed by the equation Total heat = 14,6500+ 62, 100 (H — £0) in which the letters C, H, and O represent the weights of car- bon, hydrogen, and oxygen in one pound of fuel. No con- fusion need arise because the letters are used with a different significance from that given them in chemical formulae. This equation does not give very satisfactory results. FUELS AND COMBUSTIOX. 79 Mahler has proposed an empirical formula for finding heats of combustions which in French units is Total heat = 8 140 C + 34, 500 H — 3000 ( O + N), in which C, H, O, and N represent the weights of the ele- ments carbon, hydrogen, oxygen, and nitrogen in a kilogram of fuel. The result is in calories. In English units Mahler's equation becomes Total heat = 14,650 C + 62, 100 H — 5400 (O + N), in which the letters represent the weights of the correspond- ing elements in one pound of the fuel. The result is in B. T. U. This equation gives results that agree very well with Mahler's experimental determinations, as shown by the table on page 58. For example, the total heat of combustion of Pittsburg bituminous coal, for which the ultimate analysis may be taken as = 0.7647, H = 0.0519, O — 0.0810, N = 0.0145, appears by Dulong's formula to be 14650 C + 62, 100 (H — i O) = 14,650 X 0.7647 + 62, 100 (0.05 19 — ° - ° IO \ = 13,720 B. T. U. Mahler's formula for the same coal gives 14,650 C + 62, 100 H — 5400 (O + N) = 14,650 X 0.7647 -f- 62, 100 X 0.05 19 — 5400 (0.08 10 -|- 0.0145) = i 3 , 9 ioB. T. U. Air required for Combustion. — If the moisture and car- bon dioxide in the air be neglected, and if, further, the argon So STEAM-BOILERS. is not distinguished from the nitrogen, then we have for the composition of the atmospheric air, By weight |2 Xygen °' 232 (Nitrogen 0.768 ( Oxygen 0.2094 By volume ■< . T . T ( Nitrogen o. 7906 For rough calculations it is customary to consider that the atmosphere is made up of one volume of oxygen and four volumes of nitrogen. This approximation is sufficient for calculation of air required by fuels, and for similar purposes. The air required for combustion of a given fuel may be estimated from its composition and from the composition of the air. A few examples will make the process clear. Thus, carbon burned to CO, requires two portions of oxygen, so that one pound of carbon will require •£•_,! pounds of oxygen. Since air is 0.232 part oxygen by weight, one pound of carbon will require 2$ -7- 0.232 = 11. 5 pounds of air for complete combustion. In like manner one pound of hydrogen will require 2 pounds of oxygen, or 8 -T- 0.232 = 34.5 pounds of air for complete combustion. Another method of calculation is based on the approxi- mate composition of air, i.e., one volume of oxygen and four of nitrogen. This method depends on the fact that the FUELS AND COMBUSTION. 8 1 weights of a cubic foot of different kinds of gases are propor- tional to their atomic weights ; so that if the weight of a cubic foot of hydrogen be taken for the basis 01 comparison and be called unity, then the weight of a cubic foot of oxygen will be 1 6, while that of nitrogen will be 14. We shall then have for the approximate composition of air one volume of oxygen having the weight 16, and four volumes of nitrogen having each the weight 14. In order to get one pound of oxygen we must take (16 + 4 X 14)^- 16 = 4J pounds of air. It has already been shown that one pound of carbon will require 2§ pounds of oxygen. By the method just stated it appears that a pound of carbon will require 2| X 4i = 12 pounds of air. This result is often quoted and is easily remembered. Since a pound of hydrogen requires 8 pounds of oxygen, this method gives 8 X A\ = 36 pounds of air for each pound of hydrogen. In calculating the air required for a fuel it is customary to use the convention proposed by Dulong for finding heat of combustion, namely, that each pound of oxygen in the fuel renders one eighth of a pound of hydrogen inert, and that the remainder of the hydrogen and all the carbon can be treated as free elements. In using this convention it is customary to take the approximate weights of air just calculated for a pound of carbon and a pound of hydrogen. The convention can then be stated in the form of an equation as follows: Air per pound ot tuel = 12 C + 36 (H — -JO), 82 STEAM-BOILERS. In which the letters C, H, and O represent the weights of carbon, hydrogen, and oxygen in one pound of the fuel. An application of this equation to Pittsburg coal gives a- <- . J 0.08 io\ Air = 12 X 0.7647 -f- 36(0.0519 — ) = 10.7 pounds. This result is somewhat larger than would be obtained were the more exact composition of the atmosphere given on page 59 used, together with the assumption that the oxygen ren- ders inert its equivalent of hydrogen ; but the method is not sufficiently well grounded to warrant much refinement. As a further illustration of the method the following cal- culation of the air required for one pound of defiant gas may be interesting. This gas, having the composition C a H 4 , con- sists of 2 X 12 6 — ■ = — carbon, 2 X 12+4X 1 7 hydrogen, 2 X 12 + 4X 1 7 and will require f X 12 -f- t X 36 = 1 5.4 pounds of air. Air for Dilution. — In order to secure complete combustion of coal in the furnace of a boiler it is necessary to supply an excess of oxygen, or, what amounts to the same thing, an excess of air. This excess varies from one half the quantity required for combustion to an equal quantity. Thus, roughly, from 18 to 24 pounds of air may be furnished per pound of car- bon and from 54 to 72 pounds of air per pound of hydrogen. Volume of Air for Combustion. — The table on page 75 gives the density or weight of one cubic foot of the several gases mentioned, also the reciprocal of the density or the volume occupied by one pound of the gas. This is called the specific volume of the gas. The specific volume of air is 12.39 at the pressure of the atmosphere and at the temper- With 50 per cent Dilution. With 100 per cent Dilution. 225 300 675 9OO FUELS AND COMBUSTION. 83 ature 32 F. The volume of a pound of gas increases as the temperature rises. At 6o° F. one pound of air will occupy- about 13 cubic feet. To find the volume of air required per pound of fuel we may simply multiply the weight by 13, for ordinary calculations. Thus we shall have for the air per pound of the principal elements in fuels: Without Dilution. Carbon 150 Hydrogen 450 These approximate values are sufficient for determining the dimensions of doors or passages through which air is supplied to the fire. This method applied to Pittsburg coal will give, approxi- mately, 10.7 X 13 ■■= 139 cubic feet of air for each pound of coal without dilution. With dilution of 50 per cent the air required will be about 210 cubic feet for each pound. Sometimes, in connection with boiler-tests or for other purposes, a more exact estimate of the amount of air is de- sired. The calculation for this purpose can be best explained by aid of an example. Example. — Required the weight and volume of air needed for combustion of Pittsburg coal with 50 per cent dilu- tion, the temperature of the atmosphere being yo° F. and the height of the barometer being 29 inches, when reduced to 32 F. This coal is composed of 76.47 per cent carbon, 5.19 per cent hydrogen, and 8.10 per cent oxygen. Assuming that the oxygen renders inert one eighth of its weight of hydrogen, there will be available 5. 19 = 4. 18 per cent o 84 STEAM-BOILERS. of hydrogen and 76.47 per cent of carbon. Since one pound of carbon requires 2§ pounds of oxygen, and one pound of hydrogen requires 8 pounds, the weight of oxygen required per pound of coal is 2f X 0.7647 + 8 X 0.0418 = 2.374 pounds. But air contains 23.2 per cent of oxygen by weight, so that the air required per pound of coal is 2.374-^-0.232 = 10.2 pounds. The specific volume of air is 12.39, so tnat each pound of coal will require 10.2 X 12.39 — I2 6 cubic feet of air at the normal pressure of the atmosphere and at 32 ° F. To find the volume of air required at the actual pressure of the atmosphere and the actual temperature, we have the facts that the volume of a given weight of air is inversely pro- portional to the absolute pressure and directly proportional to the absolute temperature. Now the absolute pressure of the atmosphere is 29 inches of mercury as given by the barometer, while the normal pressure is 29.92 inches of mer- cury. To get the absolute temperature we add 459.5 t0 tne temperature by the thermometer; the absolute temperature of 32 F. is 491.5, and that of 70 F. is 529.5. Under the con- ditions of the problem the air required per pound of fuel will have the volume, without dilution, of . 529.5 29.92 126X^^X^^ = 140 491.5 29.00 cubic feet. With 50 per cent dilution the volume will be 210 cubic feet. Determination of Air per Pound of Coal. — The amount of air supplied per pound of coal may be determined either by FUELS AND COMBUSTION. 85 measuring the air supplied to the furnace or by an analysis of the products of combustion. For the first method the following arrangement has been used in boiler-tests at the Massachusetts Institute of Tech- nology: The ash-pit doors are removed and a sheet-iron mouthpiece is fitted over the opening into the ash-pit. The air for combustion is supplied by a cylindrical sheet-iron con- duit leading into this mouthpiece. The area of the conduit should be at least equal to the area of the fire-door or fire- doors, and its length should be several times its diameter. The velocity of the air in the conduit is measured by an ane- mometer, from which the volume of air is readily calculated, and its weight determined from the temperature and pressure of the atmosphere. The joint between the mouthpiece and the furnace front must be luted to avoid leakage, and leaks or ad- mission of air to the furnace otherwise than through the sheet- iron conduit must be stopped or allowed for Anemometers, even when tested and rated, are liable to be affected by errors of two per cent or more. They are commonly tested by swinging them on a revolving arm through still air — a method that is proper for small or moderate velocities, but difficult to use, and is vitiated by the action of centrifugal force at high speeds. An ideal way of testing an anemometer would be to find its reading in such a conduit when the weight, and con- sequently the velocity, of the air per second is known. The weight may be determined by causing the supply of air to flow through a well-rounded orifice, to which calculations by the proper thermodynamic equations may be applied. This method for large conduits would involve the use of a very large air-compressor, which makes it hardly practicable. Orsat's Gas Apparatus.— This apparatus, which is well adapted to the analysis of flue-gases, determines the propor- tion by volume of the carbon dioxide, carbon monoxide, and oxygen in a mixture of gases. The remainder of tne flue- gases is commonly assumed to be nitrogen, but it includes 86 STEAM-BOILERS. unburned hydrocarbon, if there be any, and steam or vapor of water. In Fig. 32, A, B, and Care pipettes containing, respectively, solutions of caustic potash to absorb carbon diox- ide, pyrogallic acid and caustic potash to absorb oxygen, and cuprous chloride in hydrochloric acid to absorb carbon mon- oxide. At Wis a three-way cock to control the admission of gas to the apparatus ; at D is a graduated burette for measuring the volumes of gas, and at P is a pressure-bottle connected with D by a rubber tube to control the gases to be analyzed. The pressure-bottle is commonly filled with water, but glyc- Fig. 32. erine or some other fluid may be used when, in addition to the gases named, a determination of the moisture or steam in the flue-gases is made. The several pipettes A, B, and C are filled to the marks a, b, and c with the proper reagents, by aid of the pressure-bottle P. With the three-way cock W open to the atmosphere, the pressure-bottle P is raised till the burette D is filled with water to the mark m\ communication is then made with the flue, and by lowering the pressure-bottle the burette is filled with the gas to be analyzed, and two minutes are allowed for the burette to drain. The pressure-bottle is now raised till the water in the burette reaches the zero-mark and the FUELS AND COMBUSTION. 87 clamp k is closed. The valve W 'is now opened momentarily to the atmosphere to relieve the pressure in the burette. Now open the clamp k and bring the level of the water in the pres- sure-bottle to the level of the water in the burette, and take a reading of the volume of the gas to be analyzed ; all readings of volume are to be taken in a similar way. Open the cock a and force the gas into the pipette A by raising the pressure- bottle, so that the water in the burette comes to the mark m. Allow three minutes for absorption of carbon dioxide by the caustic potash in A, and finally bring the reagent to the mark a again. In this last operation, brought about by lowering the pressure-bottle, care should be taken not to suck the caustic reagent into the stop-cock. The gas is again measured in the burette and the diminution of volume is recorded as the volume of carbon dioxide in the given volume of gas. In like manner the gas is passed into the pipette B, where the oxygen is absorbed by the pyrogallic acid and caustic potash ; but as the absorption is less rapid than was the case with the carbon dioxide, more time must be allowed, and it is advisable to pass the gas back and forth, in and out of the pipette, several times. The loss of volume is recorded as the volume of oxygen. Finally, the gas is passed into the pipette C y where the carbon monoxide is absorbed by cuprous chloride in hydro- chloric acid. The solutions are as follows : A. Caustic potash, 1 part ; water, 2 parts. B. Pyrogallic acid, 1 gramme to 25 c.c. caustic potash. C. Saturated solution of cuprous chloride in hydrochloric acid having a specific gravity of 1.10. are- The absorption values per cubic centimetre of the reagents A Caustic potash absorbs 40 c.c. carbon dioxide. B. Pyrogallate of potassium absorbs 22 c.c. oxygen C. Cuprous chloride absorbs 6 c.c. carbon monoxide. 88 STEAM-BOILERS. Samples of gas for analysis by Orsat's apparatus should be taken from the back of the furnace, from the uptake, and from the chimney; the difference in composition of gases at the several points will give the basis for calculations of leakage. When it is not convenient to draw gases from the flue di- rectly into the measuring burette of the apparatus, samples of gas may be drawn into glass bottles with rubber stoppers, from which gas can be supplied to the burette. Calculation from a Gas Analysis. — The calculation of the amount of air supplied per pound of carbon and per pound of coal, from the known chemical constituents of the flue-gases, is best shown by an example. Example. — Let it be assumed that the analysis of the flue- gases resulting from the burning of Pittsburg bituminous coal gives by volume 13 per cent of carbon dioxide, 0.5 per cent of carbon monoxide, and 6 per cent of oxygen. It is con- venient to treat the percentages by volume as the number of cubic feet of the several gases in one hundred cubic feet of flue- gas. We will thus have — Density. Gas. Volume. (See page 5 5-) Weight. Carbon dioxide 13 0.12345 1.6043 Carbon monoxide 0.5 0.07806 -0.03903 Oxygen „ 6 0.08928 0.53568 Now one pound of carbon dioxide is composed of 2 X 16 $_ 12 -f- 2 X 16 11 of a pound of oxygen and 3/1 1 of a pound of carbon, and a pound of carbon monoxide is composed of 16 _ 4 12 -)- 16 ~~ 7 of a pound of oxygen and 3/7 of a pound of carbon. Conse- quently we have. FUELS AND COMBUSTION. 89 ft X I.6043 = I- 1668 ft X I.6043 =0.4375 4 X O.03903 = O.0223 f X O.03903 = O.O167 0.5357 Pounds of oxygen, 1.7248 Pounds of carbon, 0.4542 And as air consists of 0.232 part by weight of oxygen, the air per pound of carbon from the gas analysis is _lZ_z — 1_ 0.232 = 16.4 pounds. 0.4542 The coal in question contains 76.47 per cent of carbon, 5. 19 per cent of hydrogen, and 8. 10 per cent of oxygen. Of these elements Orsat's apparatus accounts for the carbon only ; the oxygen and hydrogen together with unburned volatile matter pass off with the nitrogen. The analysis shows 16.4 pounds of air for each pound of carbon ; consequently the carbon in one pound of coal will require 0.7647 X 16.4 = 12.5 pounds of air. Assuming that the oxygen in the coal renders one eighth of its weight of hydrogen inert, and that the re- mainder will require 36 pounds of air per pound of hydrogen, we shall have ,/ 0.08 io\ 36(0.0519 — ) = 1.5 of a pound of air required for the hydrogen. So that the total air per pound of coal is about 12.5 + l 'S = l 4 pounds. The calculation just given, involving the use of the densities of the several gases, is perhaps the most readily understood ; there is another method, which gives the same result and is more expeditious, depending on the fact that the weight of a gaseous compound referred to hydrogen as unity, is half its 90 STEAM-BOILERS. molecular weight. This quantity is called the vapor density of the compound. Thus the vapor density of carbon dioxide, C0 2 , is £(12 +2x16) = 22; and the vapor density of carbon monoxide, CO, is 1(12 + 16) = i 4 . Assuming as before that in each 100 cubic feet of flue-gases there are 13 cubic feet of C0 2 , 0.5 of CO and 6.0 of O, we have for the corresponding weights, based upon hydrogen as unity, 13 X 22 = 286 for CO a 0.5 X 14 = 7 for CO 6.0 x 16 = 96 for O Total, 389 The last result depending on the fact already noted, that the weights of elementary gases are proportional to the atomic weights. Now each pound of C0 2 contains 3/1 1 of a pound of carbon, and each pound of CO contains 3/7 of a pound of carbon, so that of the 286 parts by weight of C0 2 we shall have T 3 T X 286 = 78 parts of carbon, and of the 7 parts by weight of CO we shall have tX7 = 3 parts of carbon. The total weight of carbon will be 78+3 = 3i. The weight of oxygen is clearly 389-81 = 308. FUELS AND COMBUSTION. 91 The oxygen per pound of carbon is therefore 308^81 = 3.80, and the air per pound of carbon is 308 . — ^-0.232 = 16.4 pounds, as found by the previous calculation. Loss from Incomplete Combustion. — The presence of even a small amount of carbon monoxide in flue-gases is evi- dence of a very appreciable loss of efficiency, as may be seen by the following example, quoted from a test made on a 325- horse-power boiler at Lowell. The coal used was George's Creek Cumberland, fired by hand. An analysis of flue-gases by Orsat's apparatus showed 12.5 per cent of CO,, 1. 1 per cent of CO, and 6.4 per cent of O, by volume. Using the method of vapor densities for making the calcu- lation, it appears that the CO a contained T 3 T x 12-5 X 22 = 75 parts of carbon, and the CO contained f X 1.1 X H = 6.6 parts of carbon. Now 75 pounds of carbon burned to C0 2 gives 75 X 14,650 = 1,098,750 B. T. U., and 6.6 pounds of carbon burned to CO gives 6.6 X 4400 = 29,040 B. T. U., or a total for all the carbon of 1, 127,790 B. T. U. Had all the carbon been burned to CO, , the heat of com bustion would have been (75 + 6.6) 14,650 = 1, 195,440 B. T. U. 9 2 STEA M -BOILERS . The loss by incomplete combustion was consequently 1,195,440—1,127,790 . — X 100 = 5.6 per cent. 1,195,440 The actual loss may be placed at a little less figure than 5.6 per cent, since less air is required for burning carbon to CO than for CO„. Loss from Excess of Air. — The ideal condition would be to supply just enough air to burn all the carbon in the coal to C0 2 and all the free hydrogen to H 2 ; it is necessary to use somewhat more air than required for complete combustion to avoid the formation of CO and the attendant loss of heat. On the other hand, too great an excess of air occasions a loss, as that excess must be heated to the temperature in the chimney. As an example, suppose that Pittsburg coal can be com- pletely burned with 50 per cent excess of air, but that 100 per cent excess is allowed to pass through the grate. To simplify the problem we will neglect the effect of sul- phur and of the ash, more especially as it is not certain what their effect is ; we know only that it cannot be very impor- tant. Each pound of carbon will yield 3§ pounds of CO, and each pound of hydrogen will yield 9 pounds of H a O. There will therefore be 3f X 0.7647 = 2.8039 pounds of C0 2 ; 9X0.0519 = 0.4671 " " H 2 0. In the calculation for the weight of air (page 84) it has been shown that 2.374 pounds of oxygen and 10.2 pounds of air are required for combustion. There is therefore 10.2 — 2.374 = 7.826 pounds of nitrogen in the air for combustion. But each pound of coal contains 0.014 of a pound of nitrogen, so that the total nitrogen is 7.840 pounds. FUELS AND COMBUSTION. 93 Now the heat required to raise the temperature of one pound of a substance one degree, called the specific heat, is given in the table on page 75. For carbon dioxide the specific heat is 0.2169, and the heat required to raise 2.8039 pounds one degree is 2.8039 X 0.2 169 = 0.6082 B. T. U. The following are the calculations for the several compo- nents of the products of combustion : Weight. s P eci t fic s Heat. Carbon dioxide, C0 2 2.8039 X 0.2 169 = 0.6082 B. T. U. Steam, H a O 0.4671 X 0.4805 = 0.2244 " Nitrogen 7.840 X 0.2438 = 1. 91 14 " Air for dilution 50$.... 5.100 X 0.2375 = 1.2 112 " Total 3-9552 u If the external air is at 6o° F., and the gases in the chim- ney are at 560 F., then the heat in the chimney-gases above the temperature of the air is 500 X 3.9552 = 1978 B. T. U. The total heat of combustion of this coal by Dulong's formula is 13800 B. T. U. ; of this about 10 per cent will be lost by conduction and radiation. There will then remain to be transferred to the water in the boiler 13800 — (1380 + 1978) = 10442 B. T. U. This is about 76 per cent of the heat generated by combus tion. Suppose that the dilution is allowed to be 100 per cent, so that 5 additional pounds of air per pound of coal are ad- mitted to the grate. Then to the above total must be added 94 STEAM-BOILERS. 1.2112 B.T. U., making in all 5.1664 B. T. U. Multiply- ing by 500, the difference of temperature assumed 500 X 5- 1664 = 2583 B. T. U. Assuming, as before, 10 per cent for loss by radiation and conduction leaves 13800 - (1380 + 2583) = 9837 B. T. U. to be transferred to the water in the boiler. This is about 72 per cent, so that the loss by the excess of dilution is about 4 per cent. Hypothetical Temperature of Combustion, — A calcula- tion is sometimes made of the temperature of the fire on the assumption that the total heat of combustion is all applied to raising the temperature of the products of combustion, includ- ing the ash. In the case of Pittsburg coal it has been found that 3.9552 B. T. U. are required to raise the products of combustion one degree, allowing 50 per cent for dilution. This coal has J. 6 per cent ash, for which a specific heat of 0.2 may be allowed. We must therefore add to the total just quoted .076 X 0.2 = 0.0152 B. T. U., making in all 3.9704 B. T. U. Dividing the total heat by this quantity, we get 13800 4- 3.9704 = 3480 F. for the elevation of temperature. To this we will add the temperature of the air admitted to the furnace, say 6o° F., making 3540 F. for the hypothetical temperature of the fire. Such a temperature is never reached in the furnace of a boiler, for the combustion is not instantaneous and is not completed in the furnace, as flames commonly extend over FUELS AND COMBUSTION. 95 the bridge-wall or into the combustion- chamber; meanwhile there is an energetic radiation from the glowing fuel and flame, and a rapid transfer of heat from the hot gases to the heating-surface of the boiler. The better the fuel and the higher the hypothetical temperature of the fire the less chance is there that the actual temperature will approach it. In general the temperature in a furnace ranges between 2000 and 2600 F., when the boiler is running at its rated capacity. Decomposition of Steam. — Among the many devices gotten up either to increase the efficiency of a boiler, to increase its capacity, or to raise the temperature of the furnace, there is a class claiming to operate through the decomposition of steam. The hydrogen, liberated by the supposed decomposition, burning in the presence of the oxygen also liberated by the supposed decomposition, would, on account of the high heating value of the hydrogen (62,100 B.T.U. per pound), furnish a large amount of heat. Two facts have been overlooked however. First, it is impossible to decompose steam in any appreciable quantity for any length of time at a temperature under 3500 F., a tempera- ture never reached in a coal furnace as used under boilers ; and second, that even if steam were decomposed at 3500 F. every pound of steam so decomposed would require at the instant of breaking up the " heat of reaction," 6900 B.T.U. per pound, and this value is just what is recovered by the burning of sufficient hydrogen to make one pound of steam. This is evident from the following: one pound of H unites with 8 pounds of O to make 9 pounds of H 2 0, and yields 62,100 heat units; hence the heat per pound of steam formed is 62,100 -f- 9 = 6900. The method of making hydrogen by pass- ing steam over heated steel chips depends upon the oxygen of the steam being absorbed by the iron of the chips in forming sesquioxide or black oxide of iron, thus liberating some hydro- gen. This action ceases after the oxide is once formed. The introduction of a jet of steam either over the grate, under the grate, or in the flue will, in most cases, increase the net capac- 96 STEAM-BOILERS. ity of a boiler, and in some cases the use of a steam jet over the fire as an aspirator or an air injector may, by bringing in an additional air supply immediately following a firing, prevent in- complete combustion and consequently make a slight net increase in economy after having deducted the steam used. C0 2 Recorders.— In many boiler plants continuous analyses or intermittent analyses are made of the flue gas by some form of automatic C0 2 recorder. The advantages of such analyses is evident from what has been said previously about the losses resulting from excess air or too little air supplied for combustion. The two makes of carbonic acid recorders most commonly used are the Uehling and the Sarco. Uehling C0 2 Recorder.— This instrument is continuous in its operation and the principle on which it operates may be illustrated by Fig. 33 • An aspirator D operated by a steam jet draws flue gas through two orifices ,4 and B of equal size. If the drop in pressure : ^ y 'tjuiy Fig. 33- caused by the aspirator action in the chamber C is constant, as shown by the height of the liquid in the leg q, there will necessarily be a drop in pressure in the chamber C, as shown by the height in the leg p, due to the fact that the same weight of gas is passing through each orifice. If, however, C0 2 be absorbed between FUELS AND COMBUSTION. 97 the orifices A and B there will be less weight passing through B, and if the height of the liquid in the leg q remains constant the level in the leg p will change. The change of level of the liquid in the leg p serves to give an indication of the amount of C0 2 absorbed in the chamber C. The actual arrangement of the apparatus is shown diagram- matically by Fig. 34. A central receptacle of 8-inch pipe, 60 inches long, is nearly filled with water. The small central tube shown in the centre of this receptacle is open to the air at the top. The left-hand tube ends 6 inches above the lower end of the central tube, and the right-hand tube, shown dipping a few inches below the surface of the water, is just 48 inches above the lower end of the central tube. Opening the steam valve A allows steam to pass through the aspirator B and causes a drop in pressure in the small pipe lead- ing from B to the right-hand side of the cap on the top of the 8-inch pipe. On opening the valve in this pipe a drop in pressure occurs in the top of the receptacle equal in amount to that re- quired to draw air from outside down through the water in the central tube, which, as has been said, is open to the air at its top end. At the same time flue gas is taken in through the pipe D into the chamber E, where it goes through a dust-removing filter, then through the pipes F and H, and any surplus gas not passed through the orifice K is drawn down through the left-hand tube in the receptacle and bubbles up through the water to the top, where it is removed by the aspirator. Beneath the aspirator B there is a chamber / through which the gas passes on its way to the orifice K and also on its return, after passing through the absorbent in the chamber L on its way to the exit orifice A r . By thus jacketing both pipes with the waste steam used by the aspirator the temperature of the gases entering either orifice is the same, 212 , no matter what the pres- sure of the steam supplied to the aspirator may have been. The pressure in the absorber L is transmitted through the STEAM-BOILERS. To Recording •■% Gage | — i JL Fig. 34. FUELS AND COMBUSTION. 99 pipe M and its connections 55 either to a tube on the left reading per cent C0 2 or to a recording gauge. The absorbent may be either a dry carton changed once a week or a solution of caustic potash siphoned through L from the tank above. When a solution of caustic potash is used the absorber is rilled with pebbles or quartz, thus presenting a con- siderable amount of absorbing surface. Sarco C0 2 Recorder. — This recorder, shown by Fig. 35, auto- matically traps off, at regular intervals, 100 c.c. of gas from a continuous stream of gas. This trapped-off portion of gas is brought into contact with caustic potash, which absorbs the C0 2 , and a record is then automatically produced on a chart showing the amount of C0 2 in the respective samples of gas. Gas is drawn through the machine after passing through the filter and through the intake pipe D, at the right. The suction necessary to draw the gas through the apparatus is obtained by means of a jet of water falling from an overhead water supply tank, and passing through the ejector Q attached to the top of the recorder cabinet by means of a standard T. After actuating the ejector Q a portion of the water flows to the small tank L, which serves as a pressure regulator, and is provided with an overflow tube R. From this tank the water enters tube H in a fine stream, the strength of which is adjusted by the cock 5 (according to the number of records that may be desired per hour), and gradually fills the vessel K. Vessel K contains an ebonite float into which tube H admits falling water and from which siphon G extends. The water which enters K gradually fills it and compresses the air in the space above and surrounding the float. This pressure is transmitted to the solution of glycerine and water contained in lower part of K and forces it out into burette C. While this has been taking place the ejector Q has been drawing a continuous stream of gas right through D, C, and E in the direction indicated by the arrows. IOO STEAM-BOILERS. Fig. 35. FUELS AND COMBUSTION. IOI When the liquid rising in C has reached the inlet and out- let to this vessel, no further gas can enter the burette for the moment, and the ejector will now draw the gas through the seal F and out in the direction of the arrow for the time being. Before the liquid can close the centre tube in C the gas has to overcome the slight resistance offered by the rubber bag P and is therefore forced to assume atmospheric pressure. The moment the liquid has sealed the lower open end of this centre tube exactly ioo c.c. of the flue gas are trapped off in the outer vessel C and its companion tube, under atmospheric pressure. As the liquid rises further the gas is forced through the thin tube Z and into vessel A which is filled with a solution of caustic potash at 1.27 specific gravity. Upon coming in contact with the surface of the potash and the moistened sides of the vessel, the gas is freed from any car- bonic acid that may be contained in the sample, this being rapidly and completely absorbed by the potash. The remaining gas gradually displaces the potash solution in A, sending it up into vessel B. This has an outer jacket filled with glycerine and supporting a float N. Through the centre of this float reaches a thin tube through which the air in B is kept at atmospheric pressure. This float is suspended from the pen gear M by a silk cord and counterbalanced by the weights X. The liquid rising in B first forces a portion of the air therein out through the centre tube in the float and then raises the latter. This causes the pen lever to swing upwards, carrying the pen Y with it. The mechanism is so calibrated and adjusted that the pen will travel to the top, or^ero line, on the chart when only atmos- pheric air is passing through the machine and nothing is ab- sorbed by the potash in A . Thus, should any carbonic acid be contained in the gas sample it would be absorbed by the potash in A, not so much of this 102 STEAM-BOILERS. liquid would be forced up into vessel B, and the float would not cause the pen to travel up so high on the chart, in exact accord- ance with the amount of C0 2 absorbed. When the liquid in C has reached the mark near the top of the narrow neck of that tube, the whole of the ioo c.c. has been forced on to the surface of the potash, one analysis being thus completed. At this moment the power water, which simultaneously with rising in tube H has also travelled upwards in siphon G, will have reached the top of this siphon, which then commences to flow. Through the siphon G a much larger quantity of water is disposed of than flows in through the cock S, so that the vessel K is rapidly emptied again. The moment the pressure on this vessel is released the liquid from C returns into the lower part of the vessel K and the float N to its original position. As soon as the liquid in C has fallen below the gas in the outlets to this vessel the whole of the remain- ing gas is rapidly sucked out through E by the ejector Q. CHAPTER IV. CORROSION AND INCRUSTATION. THE water supplied to a boiler for forming steam may corrode the iron of the boiler, or it may deposit material that j can form a scale or incrustation ; both actions may go on at the same time. Pure water, free from air and carbon dioxide, has little or no solvent action on iron, even though some other metal, such as copper, which may with the iron form the elements of a galvanic couple, be present. On the other hand, iron will not rust if placed in an atmosphere of dry air or dry carbon dioxide. All natural water, rain-water, water from wells, rivers, lakes, or the sea, contains air in solution, and carbon dioxide is not infrequently found in such waters. Iron is rapidly acted upon by water containing air or carbon dioxide, and, on the other hand, iron rusts rapidly in air or carbon dioxide when moisture is present. Again, distilled water, as from the sur- face condenser of a marine engine containing more or less oil, or the substances resulting from the action of steam on oil, causes corrosion in boilers that are free from scale. To avoid rusting of boilers when not in use they ought to be either quite dry inside or they ought to be entirely filled with water — preferably water that has been freed from air by boil- ing. In the American Navy it has been the custom to dry out boilers and paint them inside with mineral oil preparatory to laying them up. In the English Navy the boilers are dried out, a pan of glowing charcoal is placed in the boiler to 103 io4 S TEA M-B OILERS. U31BM B3S-PB3Q .0 . 00 ,0 cn 'inui''m >• ■ ■ • « * • o> \ • ! ' ! o^ ! . n • • 00 • • • • • I ! ! 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J=*^ c v j2 aO . tfl ^> « cIsS S ^£ S £ ill 1§ 111 cd rt ct3 w^, ^^ . ^ ^^ -^ - : d^ • • : • : • 48 *=* 39 8 3 ;^S O M y C C C U^ c (J U c c c .2 .E .3 « 5 -0 -o S E E w en en 3 .5 '= C C D .d .d .d o3 03 CT3 E C rt 1 c- a O O O O O O V — 1- 3 3 cocy)c/)Ci a 3 x e rt 5 • »j w w "Z a u ■55 S« 73 O rl?~<— 24~ » Q © ® © =r m 1 -19-8- ^' : - '--:,. CONCRETE *.,_-;V, < Fig. work, about three feet wide, under the side, middle, and end walls only. I32 STEAM-BOILERS. On this foundation there are built the walls that support and enclose the boiler and the furnace. The outer walls at the sides and rear are double, with an air-space to check thr conduction of heat. The boilers are each supported by two brackets at each end; the front brackets rest on iron plates which are built into the side walls; the rear brackets have iron rollers interposed to allow for expansion. A brick, arch is sprung over the boilers to check the radiation of heat. The space between the side and end walls over the boilers may be filled with sand, for the same purpose. Coal ashes are sometimes used, but they are hygroscopic and liable to harbor moisture when the boilers are not working, and should not be used. Sometimes the tops of boilers are covered with brick and buried in sand; or the sand may be used without brick. These methods give ready access to the shell for inspection or repairs, but are not so good as a brick arch, as water can more readily get to the boiler if it should drip from leaky valves or fittings. The rear wall is carried a little higher than the top row of fire-tubes, then the space is bridged over from the side walls by a horizontal mass of brick-work, stiffened and supported by T irons. The smoke-box projects over the front wall, and has a rectangular uptake on top, lead- ing to a wrought-iron flue which carries the smoke to the chimney. The furnaces under the front ends of the boilers arc enclosed by the side walls, the front wall, and a bridge just beyond the first ring of the boiler-shell. The grates rest on the front wall and the bridge, as shown in vertical section by Fig. 45 and indicated in black on Fig. 44. There is a clear space of 24 inches between the grate and the boiler, and a clear space of 8 inches over the bridge. The top of the bridge is made of fire-brick, and all the walls of the furnaces and other spaces that are exposed to the fire are lined with fire-brick. The fifth or sixth course of fire-brick above the grate should be laid as headers, which serve to support the bricks above, while the brick SETTINGS. 133 below the headers are being renewed. All the remainder of the brickwork is of hard, well-burned brick. The ash-pit under the grate is paved with brick. The floor behind the bridge is covered with a layer of sand and paved with brick. The side walls are braced by three pairs of buck-staves, with through-rods under the paving and over the tops of the boilers. The boiler front is cast iron, with doors opening from the furnaces and from the ash-pits. There are also doors opening from the smoke-boxes to give access to the tubes. Doors through the rear wall give access to the space behind the bridge-wall. Between the front tube-sheet and wall in front of the boiler there should be a distance equal to the length of a tube; for it may be necessary in a few months to replace one or more tubes. Sometimes when there is insufficient room the boiler is placed opposite a door or a window. The tubes are cleaned from the front, that is to say, the soot is blown from the inside of the tubes by a steam-jet taken in through the swinging-doors of the front covering the tubes. Any number of boilers of this type can be set side by side in battery. If it is desired to get as much boiler power as is possible in a given space, using this type of boiler, it will be most economical to arrange the boilers in two lines with the fronts facing together with a distance equal to the length of a tube between the front tube-sheets. The setting for a two-flue boiler, or for a boiler with several large flues in place of the numerous fire-tubes of the tubular boiler, is substantially the same as those just described. Babcock and Wilcox Water-tube Boiler Setting. — This boiler is suspended from a framework built up of I-beams with I-beam columns at each corner. The brickwork carries no load whatever, the entire load coming to the foundation through the columns. These boilers may be set with the back wall against the back wall of the boiler-house, but it is better to keep at least 3 feet 134 STEAM-BOILERS. between the two and to bring the gases out through an opening in the back wall rather than to take the gases through the space between the two drums. By referring to Figs. 13 and 14 it is seen that in order to blow the soot from the outside of the tubes three openings are needed on the side of the setting. On account of this only two boilers can be set together, then there must be a space of from 4 to 5 feet. To make it possible to renew a tube in the boiler there should be a distance between the bottom hand-hole in the header and the wall equal to the length of a tube, the distance being measured in a line parallel with the tubes in the boiler. As a matter of fact the hand-holes being elliptical it is possible to get a tube in even if this distance measures 3 or 4 inches less than that called for by the above. Stirling Water-tube Boiler Setting. — This boiler is sus- pended in practically the same manner as the Babcock & Wilcox. Its tubes are cleaned from the side, and access to the drums is from the side, so only two of these boilers can be set together. Heine Water-tube Boiler Setting. — This boiler is sup- ported at the bottom of the water-legs. The front water-leg rests on cast iron columns, built into the brickwork and tied together by the casting carrying the fire- and ash-pit doors. The rear water-leg is supported by brickwork. Between the brick- work and the water-leg, plates and rollers are inserted to allow the boiler to expand. The tubes in this boiler are cleaned of soot by blowing jets of steam through the hollow stays which tie the sides of the water- legs together. There is a stay in the center of the space between four tubes. The tubes are blown in this way from the front and from the back. Any number of boilers may be set side by side, but there must be a space at the back of the boiler-setting. The hand-hole covers, covering the openings opposite a tube, FURNACES. 135 are round and can only be removed by dropping them down to the bottom of the water-leg where a larger hole is left. Marine Water-tube Boiler Settings. — Boilers like the Babcock & Wilcox, Thornycroft, Yarrow, and Almy are en- closed in a sheet-iron casing lined with blocks of non-conducting material. Asbestos, or a compound of which magnesia is a prin- ciple ingredient, is commonly used. Fire-brick and pumice-stone are used with the Thornycroft boiler to intercept heat that would be radiated downward. The spaces in ships under boilers, being more or less inaccessible, and being subject to the influence of heat and moisture, are liable to show excessive corrosion. Furnaces. — There are certain general conditions to which the construction of furnaces should conform if high efficiency is desired. Some of these depend on the requirements for good combustion, and some depend on the size, strength, and endurance of the human frame, since hand-firing is almost universal. Some of these conditions are violated in the design and arrangement of furnaces in certain types of boilers; deviation from them involves either a demand for greater strength and skill on the part of the fireman, or a loss of effi- ciency, or both. These conditions, with examples of good and bad practice, are as follows : There should be an abundant and uniform supply of air to the under surface of the grate. About the only cases where this condition is not easily fulfilled is in the design of furnace- flues of Lancashire boilers and Scotch marine boilers. A small supply of air is required over the grate for burn- ing smoky fuels like bituminous coal. This air is very com- monly supplied through a circular grid or damper in the fire- door. The fire-door is commonly protected from direct radi- ation by a perforated wrought-iron plate, which also serves to distribute the air coming through this grid. Since the air thus supplied is cold, it must be small in amount or x ^5 STEAM-BOILERS. it will chill the gases and check combustion instead of aiding it. Leakage of cold air into the furnace, or into the combus- tion-chamber or flues beyond the furnace, injures the draught and reduces the temperature of the products of combustion, and is a direct source of loss. All externally-fired boilers and water-tube boilers are liable to suffer from leakage of air. Locomotive and Scotch marine boilers are usually free from this defect. The incandescent fuel on the grate should not come in contact with a cold surface. Furnaces lined with fire-brick, such as are used for externally-fired boilers, conform to this requirement. Vertical boilers, marine boilers, locomotive- boilers, and all other boilers having the furnaces in fire-boxes or flues, violate this condition, as the plates in contact with the fire are kept nearly at the temperature of the water in contact with the other side, and are therefore much colder than the fire. There should be an abundant opportunity for complete combustion of gases coming from the fuel with hot air drawn through the fuel, before the flame is chilled by contact with cold surfaces. This condition is best fulfilled by having a clear space over the grate. Externally-fired boilers commonly have two feet or more between the grate and the boiler-shell immediately over it, and combustion may continue beyond the bridge. Locomotive- boilers have from four to six feet between the grate and the fire-box crown-sheet, but the flame is quickly drawn into and extinguished by the tubes. To aid combustion and to protect the lower part of the tube-sheet a brick arch is frequently carried across the fire-box, over which the flame must pass on the way to the tubes. The lack of space over the grate of flue-furnaces, as in the Scotch marine boilers, is only partially compensated by the combustion- chamber beyond the furnaces. Loss from external radiation is almost entirely avoided in FURNACES. 137 internally-fired boilers. Externally-fired boilers are subject to more or less loss from conduction and radiation. The fire-grate should not be longer nor wider than can be conveniently reached by the fireman in throwing on fuel and in cleaning the grate. A narrow grate should not be so long as a wide grate. In general, a hand-fired grate should not be more than six feet long, and if it is over four feet wide two fire-doors should be provided. These conditions are usually fulfilled by the design of externally-fired boilers, locomotive- boilers, and water-tube boilers. Attention has been called already to the difficulty of getting proper space for the grates in flue-furnaces. With the common diameters of the furnace- flues a length of five feet should not be exceeded. Flues in marine boilers have been made eight feet long; in such case the further end of the grate is sure to be inefficiently fired. To aid in firing, and to use the space below and above the grate to the best advantage for the supply of air and for combustion, the grate is commonly given an inclination down- wards of about 3/4 of an inch to the foot. As an extreme example of deviation from these propor- tions we may cite the Wooten locomotive fire-box, designed to burn anthracite slack. The grate is made about eight feet wide and twelve feet long. For convenience in throwing on coal and in cleaning the grates, the floor on which the fireman stands should be about two feet below the grate. This can usually be arranged for stationary boilers. The grate of a locomotive is commonly below the floor of the cab ; this facilitates throwing on the coal; some form of rocking grate is used to shake down the ashes. The side furnaces of Scotch marine boilers are com- monly too high for convenient firing, and the middle furnaces may be too low for convenience in cleaning the grate. Excessive heat in the fire-room should be avoided as far as possible; the labor of feeding and cleaning a furnace for rapid combustion is always severe, and when combined with great 138 STEAM-BOILERS. heat it soon exhausts the fireman. If land boilers are properly clothed to avoid radiation, and if the fire-room is airy and well ventilated, the heat will not be excessive. It is, however, very difficult to avoid excessive heat in the stoke- hole of a steamship. Of course the radiation from the glow- ing fuel when the fire-doors are open cannot be avoided, but it ought to be possible to clothe the fronts of marine boilers more perfectly than is now the common practice. Moreover, the ventilation of the stoke-hole is commonly defective ; the air pours down through the ventilators and makes cold spots immediately beneath them, while other parts of the stoke- hole are hot. Forced draught with closed stoke hole usually gives good ventilation ; with closed ash-pit it is liable to give defective ventilation. In certain types of water-tube boiler there is not sufficient space over the fire to enable the gases to mix. If the unmixed gases are chilled by coming in contact with the cold tubes in- complete combustion results. Analyses of furnace-gas samples taken at different parts of the gas passage often show CO and an excess of O. This shows that the gases were not mixed till the second or third gas passage was reached, where the tem- perature was too low for the CO to burn. The Dutch oven-furnace, previously referred to in the dis- cussion of independently-fired superheaters, has been applied to these boilers and has helped somewhat. By raising the boiler up and using the Dutch oven-furnace, as shown by Fig. 46, the gases may be made to travel 9 or 10 feet before coming in con- tact with the tubes. This setting gives very nearly complete combustion and is very efficient as a smoke-consuming device. A relieving arch in either side wall carries the fire-bricks above the arch and makes it possible to renew the fire-brick adjacent to the fire without disturbing the bricks above. Great care should be taken in laying the fire-bricks in a furnace of this sort. The bricks should be laid with as thin a FURNACES. 139 I 4 STEAM-BOILERS. layer of clay between them as will serve to give a uniform bear- ing. Fire-bricks which have been exposed to the weather during a storm or fire-bricks which have been left out in winter weather, will crumble as soon as they are heated in a furnace. But few masons seem to be aware of this fact. Grate-bars are commonly made of cast iron, as it is cheaper and lasts as well as wrought iron. Sometimes wrought- iron bars are used on locomotives and elsewhere, if they are expected to withstand rough usage. Cast-iron fire-bars are generally 5/8 to one inch thick at the top, and 5/16 to 5/8 of an inch thick at the bottom; they are about two inches deep at the ends, and three to five inches deep at the middle. To provide for wasting of the upper surface, they are made full width for some distance down from the top, thus forming a sort of head; then they are rapidly narrowed down to a web that is tapered gradually toward the bottom. The space between the bars depends on the draught and the nature of the fuel; with ordinary coal and natural draught 3/8 to 1/2 of an inch is allowed. Lugs or projections are cast at the ends and at the middle, so that the bars shall be properly spaced when laid side by side. With forced draught the bars may be 3/8 to 9/16 of an inch wide at the top, and the distance between the bars may be 1/16 to 1/4 of an inch. The area of the air- spaces through the grate-bars is ordinarily from 30 to 50 per cent of the area of the grate; if shavings are to be burned, a much greater air-space is needed and a grate, like Fig. 49, is often used. The combined area of the holes may be made as great as the projected area of the bar, thus giving 100 per cent air-space. A dead-plate two inches wide should be fitted to the furnace- tube of marine boilers to prevent admission of air at that place. The length of fire-bars should not exceed four feet; the length of a fire-grate may be made up of two or three short bars. Bars are commonly cast in pairs, or three or four may be cast together, to resist twisting and warping under heat. FURNACES. 141 The usual form of grate-bar cast in pairs with lugs at the side is shown by Fig. 47. The herring-bone grate is shown by Fig. 48; a grate used for sawdust, shavings or other inflammable material of this sort Fig. 47. Fig. 48. is shown by Fig. 49. Fig. 50 shows a form of grate designed by Prof. Schwamb for burning screenings at a high rate of com- bustion. The construction of the grate is shown by the section. A boss around each air opening allows ash to collect in the small recesses between the air openings on the top of the grate. This ash prevents clinkers from adhering to the bars. Bars of this sort have been used twenty-four hours a day for over two years under boilers forced 80 per cent over rating without trouble. Wrought-iron fire-bars are formed with a head and web, but are of uniform depth, as they are cut from a rolled bar; they are bolted together in sets of six, with washers to give the proper 142 STEAM-BOILERS. spacing. For marine boilers they may be 5/16 of an inch thick at the top, with spaces 3/16 of an inch wide, or less. Fig. 50. Rocking Grates. — The labor of breaking up the clinker which forms on grate-bars is very much reduced by employing some form of rocking grate. On locomotives, where the rate of combustion is high and where the fire should always be in good condition, some form of rocking grate is considered essential in American practice. In Fig. 51 A and B represent alternate grate-bars which are supported at semicircular notches at the ends. CO is a b' a' Fig. 51. cast-iron crank-shaft extending across the furnace at one end of the grate-bars. Shallow bars like A rest on cranks that are above the line CO, and deep bars like B rest on FURNACES. 143 cranks below that line, as shown at a, a' ', and a" > and at b and b' . The further ends of the grate-bars rest on another crank-shaft like CO '. At the lower right-hand corner of the figure c" represents the end of the crank-shaft and d repre- sents an upper crank carrying a shallow bar like A. At g is a head to which a lever may be applied to rock the crank- shaft. When the crank-shaft is rocked the alternate bars are thrown back and forth, and grind up the clinker so that it falls through the grate into the ash-pit. Firing. — Care, skill, and intelligence are required to burn coal rapidly and economically. There is a marked difference in the ability of trained firemen to make steam with a given boiler, and probably there is nothing more wasteful and costly than a poor or careless fireman. The method to be adopted in firing depends on the type of boiler, the kind of coal, and the rate of combustion. Three methods of firing may be distinguished: Spreading, which consists in distributing small charges of coal evenly over the surface of the fire at short intervals. In this method the object is to deliver the coal just where it is wanted, and then not disturb it. The fire can then be kept in just the right condition at all times, and probably the best results can be thus obtained, both in absolute quantity of steam and in economy, provided the coal used is well adapted to this method. Care must be taken to have the door open as little as possible, or an undue amount of cold air will be admitted through the fire-door. Anthracite coal should always be fired by spreading, and should be disturbed as little as possible after it is thrown in place. Unless the fire is urged, very little clinker will be formed, and the ashes are readily shaken out by a pick or hook run up between the fire-bars. The thickness of the fire may vary from four to twelve inches, depending on the size of the coal and the strength of the fire. Dry bituminous coal, and other bituminous coals, if not 144 STEAM-BOILERS. very smoky and if in small pieces, can be advantageously fired in this way. Each shovelful thrown on will give off volatile matter, which will burn with the excess of air corning through the fuel, and very little smoke will result. Side firing consists in covering all of one side of the fire with fresh fuel, leaving the other bright. The smoke given off from the fresh fuel can then be burned with the hot air coming through the bright fire. This method of firing is best carried on with two furnaces leading to a common combus- tion-chamber; the furnaces are fired alternately, at regular intervals, with moderate charges of coal. It is customary to admit air through the grid in the fire-door when the fuel is giving off gas. Coking the coal on a dead-plate, or on the grate just inside the fire-door, is perhaps the best way of burning a smoky coal. The volatile products driven off from the heap of coal near the furnace-door burn with the hot air, coming through the clear fire at the rear. As soon as the charge is coked it is pushed back and spread over the grate, and a new charge is thrown on. With bituminous coal the fire should be thicker than with anthracite coal; from 6 to 16 inches gives good results. The method too often followed by ignorant and indolent firemen, of throwing on as much coal as the furnace will hold and then sitting down to wait till the steam-pressure falls, needs to be mentioned only to condemn it. Mechanical Stokers, feeding coal regularly from a hopper, have been invented in a variety of forms from time to time. Since the hopper may be made of considerable size, manual handling of the coal may be entirely avoided, and one man can easily attend to a number of furnaces with little labor and exposure to heat. It would appear also that a more even and better-regulated combustion may be had than with hand-firing. The primary object, however, is to save labor and it is foolish to install a mechanical stoker in a plant, MECHANICAL STOKERS. 145 unless a saving can be made in the cost of labor or the capacity of the plant increased. There are many plants equipped with mechanical stokers where the hoppers are filled by the shovel. Often it is harder to shovel the coal into the hoppers of the stoker than it would be to throw the coal on to the grate, and as many firemen are needed as would be required to fire the boiler by hand. With some mechanical stokers working under forced draught the capacity of the plant may be increased considerably above what could be obtained by hand firing, but, in general, it does not pay to use stokers in plants of less than 1500 boiler horse- power, as the saving in labor is not great enough to pay for the necessary repairs and the interest on the first cost of the stokers. The Roney Stoker. — The Roney stoker, shown by Fig. 52, as applied to a B. & W. water-tube boiler, may be taken as an illustration of a mechanical stoker. The grate-bars extend across the furnace and form a serie's of steps down which the fuel slides, burning on the way down. Each grate-bar is hung on pivots at the ends, near the top, and has a rounded lug at the bottom that rests in a groove in a rocker-bar, as shown by Fig. 53. The rocker-bar has a slow and regular reciprocation de- rived from a small steam-engine, which tips the grate-bars so that the upper surfaces are inclined downward to make the fuel slide, and then rights them to check the motion of the fuel. The coal from the hopper falls onto a horizontal plate, from which it is pushed forward by a " pusher " that is driven by the steam-engine which drives the rocker-bar. The rate of feeding the fuel can be controlled by changing the stroke of the pusher, and by regulating the number of strokes of the pusher and of the rocker-bar per minute. The ashes, clinker, and other unburned refuse collect on a dumping-grate at the foot of the grate-bars. This grate is shown in normal position by heavy lines in Fig. 53> and in the dumping position by light lines. This grate appears to be well adapted to burn smoky fuel, 146 STEAM-BOILERS. Floor Line Fig. 52. mmm Fig. 53. MECHANICAL STOKERS. 147 as such fuel is well coked at the top of the grate, and the volatile parts driven off by coking can burn with the excess of air coming through the grate at the bottom. If the rate of feed is too fast, it is evident that unburned coal will work down onto the dumping-grate, and will appear in the ashes. If the rate of fuel is regulated so that no coal appears in the ashes, the fire becomes thin at the bottom, and an excess of air is liable to enter there ; certain tests on this grate have indicated such an excess of air, which is the side on which the fireman is liable to err, as he may not know how much waste he thus occasions, while he can see the coal in the ashes. Murphy Stoker. — A general view of the Murphy stoker as set with a Dutch-oven furnace is shown by Fig. 54. This stoker has been one of the most successful of the mechanical stokers installed in plants where the service is severe, and where the size of the units does not exceed 400 boiler horse-power. Coal is fed from the bottom of each magazine onto coking plates by a " stoker box " at either side. Each " stoker box " is given a reciprocating motion by means of a rack and pinion operated through the stoker engine. At the bottom of each fuel magazine there is a coking plate against which the upper ends of the inclined grates rest. The grates are made in pairs, one fixed and the other movable. The movable grates, pinioned at their lower ends, are moved alternately above and below the stationary grates by a rocker bar at their lower ends. The feeding mechanism is so arranged that the coal is fed faster at the back of the furnace than at the front, thus pro- ducing the same thickness of fire at the place where air spaces are most likely to occur. Any coal that may sift through the grates at the topmost point is collected in dust pits on either side of the furnace. From these pits the coal is hoed once a day. The stationary grates rest at their lower ends upon a grate MECHANICAL STOKERS. 149 bearer which is cast hollow and which receives the exhaust steam from the stoker engine. This steam escaping through small openings in the grate bearers besides keeping the bearers cool, serves to soften the clinker, which together with the ash is removed by a rotating clinker crusher located at the centre of the furnace between the lower ends of the inclined grate bars. Air is supplied to the coking plates through openings in the castings against which the fire-brick arch rests. Taylor Stoker. — The Taylor stoker is one of the underfed type. As it is supplied with air under pressure it is capable of being forced so that the boiler may develop three or four hun- dred per cent of its rating. Many power plants built recently have been planned to work with boilers running normally at two hundred per cent of their rating and at times of overload much more than this. Fig. 55 shows the general arrangement of the stoker and Fig. 56 gives three views of the furnace and operating mechanisms. Coal from the hopper is fed into the retorts from which two cylindrical rams in each retort, assisted by gravity, introduce it into the furnace at an angle to the fire surface. The upper rams push the green coal outward and upward, properly distributing it in the coking zone. The action of the lower rams is similar, but instead of bringing in fresh coal they push the fuel bed and refuse toward the dump plates at the rear. Each retort or fuel magazine is formed by two tuyere boxes; that is, the retorts and tuyere boxes alternate, the number depending upon the size of the boiler. A series of tuyeres is supported on each tuyere box, with openings in the vertical faces to distribute air to the fuel. These tuyeres, of cast iron, interlock when in position. Air for combustion enters the tuyere boxes from the wind box, and escaping from the tuyere openings mingles with the gases distilled from the coal and with the coked fuel pushed outward and upward by the rams. Both rams are actuated by connecting rods and links from a crank shaft which is driven from the speed shaft. The speed shaft in turn is driven by the fan engine. a — 152 5 TEA M -BOILERS. The dump plates, which are combination dump plates and fire guards, are hung on the rear of the wind box; these plates receive the burned-out refuse and are dumped periodically, as the conditions of service may require. The dump plates are operated from the front of the stoker, raised, latched in position, and released by a hand lever. When the Taylor stoker is equipped with extension grates, the intermediate grate, which lies between the mouth of the retorts and the dump plates, is used as an active grate or for ash storage, as conditions may require. The extension grate may be rocked, due to its direct connection to the operating mechanism of the stoker, the length of travel and position being subject to adjustment. The air supply to the extension grate is regulated by a hand wheel at the front of the furnace, and when once set is subject to the same automatic control as the air supply to the stoker itself. The horizontal distance from centre to centre of retorts is 2of inches. Fig. 57 shows Taylor stokers applied to a new form of boiler used by the Detroit Edison Company. This boiler was equipped with Roney and with Taylor stokers, and in each case the effi- ciency was very high. The tests on this boiler are referred to at the end of the chapter on boiler testing. The boiler was rated at 2365 horse-power. The American Stoker. — This stoker applied to a horizontal multitubular boiler is shown by Fig. 58. The grate ordinarily used with the boiler is replaced by a shallow iron trough, extend- ing nearly to the bridge-wall. The trough is not over one third of the width of the regular grate. Fire-brick are laid either side of the trough, thus blocking off the grate. Air from a blower is sent into the furnace through tuyere blocks located near the top of the trough. The jets of air issuing from these openings are inclined up- wards by a trifling amount. Fig. 57. (153) 154 STEAM-BOILERS. Coal is fed from the hopper to a worm rotated at a very slow speed by a steam cylinder. Fig. 59. The coal pushed along by the worm rises through the trough and makes a mound which gradually extends on to the brick either side of the trough. The fire is hottest at the surface of the mound opposite the MECHANICAL STOKERS. 1 55 tuyeres. Any carbon or volatile gases driven off from the green coal as it rises through the trough are completely consumed in their passage through the hot outer layers. Both this stoker and the one shown by Fig. 59 increase the capacity of a boiler. Many people do not realize that a boiler forced beyond its capacity must be kept clean in order for it to last as long as it would if run at normal rating. These stokers are good smoke-consumers. The ashes and clinkers have to be removed through the fire- doors. Any stokers to which air is admitted in this way, if improperly handled, may give a blowpipe effect. This is due to the air escaping through the coal in one spot instead of being distributed through the entire mass of coal. The heat generated by this action is localized and very intense. The Jones Under-fed Stoker. — This stoker, shown by Fig. 59, is similar in its action to the American. Air is forced into the ash-pit in this case. Coal is forced in intermittently by a steam piston. This piston may be operated by a hand-lever, or it may be timed to operate as many times an hour as the timing device is set for. The Green Traveling Link-grate. — Chain grates have been used to a considerable extent with the poorer grades of soft coal. Fig. 60 illustrates the Green traveling grate applied to a Heine boiler. Power from a shaft overhead oscillates the vertical rod at the left of the cut. A ratchet carried by the arm moved by this rod gives motion to a train of gears. The link-grate is moved by sprocket-wheels keyed to the shaft at the extreme left of the figure. The entire grate and frame may be withdrawn from the furnace. Columns Supporting Boilers with Stokers. — In many of the modern power houses the boilers are located in the story above the basement, which is frequently at ground level, thus making the boilers 20 feet or more above the ground. 156 STEAM-BOILERS. MECHANICAL STOKERS. 1 57 The Stirling boiler and boilers of the Babcock and Wilcox type are supported by a steel framework, from which the drums are hung, two boilers commonly being set together with one common middle wall. There are usually, however, three uprights at either end. Where the boilers are above the ground it is customary to use the steel columns of the building as the uprights at the front end of the boilers. If two boilers are set with one common wall evidently the middle upright may come partly in the brickwork. - Boilers which are forced have been known to melt down the middle wall near the furnace, and on this account it is not ad- visable to have a column act as the middle support. The column spacing, for every second bay, may be made equal to the width of two boilers, and a pair of channel beams strong enough to carry the front ends of the two boilers run from column to column. The space between sets of two boilers does not need to be over 10 feet, and the next column might be located at this dis- tance, thus making the column spacing unequal. Hanging boilers from channel beams attached to the columns brings an eccentric load on the columns which must be taken care of by proper bracing, placed between the columns in the short span. There are other ways of supporting boilers from the columns of a building by which an even spacing may be secured, but in general the columns are more 'apt to be in the way. Smoke Prevention has become a matter of great social importance in cities where much smoky coal is used. Though the loss through imperfect combustion of carbon to the form of carbon monoxide may be great, and though there may be an appreciable loss if the volatile parts of coal are driven off un- consumed, it is a fact that the loss in smoke, even when it is dense and black, is not enough to induce coal users to take the trouble to prevent the formation of smoke. Not infre- 158 STEAM-BOILERS. quently it has been found that the methods used to prevent smoke are accompanied by a loss instead of a gain. For ex- ample, smoke burning by the alternate firing of two furnaces, leading to a common combustion-chamber, may give a slightly greater efficiency if just enough hot air in excess is admitted through the clear fire, to burn the gases distilled from the fresh charge. If the clear fire must be kept too thin, and thus admit a large amount of air, in order that the smoke may be burned, there will be a loss of efficiency. Though it is not well proved, it is asserted that the mixture of finely divided carbon, in the form of smoke, with carbon dioxide may give a clear gas with the formation of carbon monoxide, and thus with a notable loss. The same difficulties arise when side firing and coking are re- sorted to with smoky fuels. One of the most perfect arrangements for smoke prevention which has yet been tried, consisted of a detached furnace with small grate-area and a deficient air-supply, so that the coal was distilled and burned to carbon monoxide; the resulting hot gases were then burned under a steam-boiler. The method was suggested by the producer-furnaces used for making gas for the open-hearth process of steel-making. The objections are the loss of heat by radiation from the detached furnace and the space occupied by that furnace. Though reported to be a success so far as the prevention of smoke was concerned, it does not meet with approval. It is a common experience that when laws against making smoke are enforced users of fuel have chosen to buy anthra- cite coal or coke, or in some cases have used crude petroleum oil. Ringelmann Smoke Chart. — The method of estimating smoke proposed by Professor Ringelmann consists in making a comparison of the color of the smoke with that of charts of different shades of gray. The charts are made by drawing a series of horizontal and of vertical black lines, 10 mm. apart, on a white ground. FURNACES. 159 The width of the black lines on Chart No. 1 is 1 mm. The width of the black lines on Chart No. 2 is 2.3 mm. The width of the black lines on Chart No. 3 is 3.7 mm. The width of the black lines on Chart No. 4 is 5.5 mm. The width of the black lines on Chart No. 5 is 10.0 mm. The last card is evidently all black. These five charts are placed in a line between the observer and the chimney and far enough from the observer so that he cannot distinguish the rulings on the charts which appear now as four shades of gray and black. Generally the charts are placed about 70 feet from the ob- server. The color of the smoke for any minute is noted by the num- ber of chart which matched it for that minute. The observations taken each minute are averaged or plotted and serve to give one some idea of the amount and grade of smoke produced. The position of the sun, the background, the condition as to weather, the direction and the intensity of the wind, all influence the readings. Although the method is not entirely satisfactory no better one as simple has as yet been suggested. Nearly every large city has some " smoke law " which may or may not be enforced. The law applying to Metropolitan Boston calls for a gradual reduction in the amount of smoke allowable. All stacks are classified into six classes: Class I includes all stationary stacks having an inside area at the top not exceeding the area of a circle 5 feet in diameter. Class II includes all stationary stacks having an area at the top greater than that of a circle 5 feet in diameter but not ex- ceeding that of a circle 10 feet in diameter. Class III includes all stacks having an area at the top greater than that of a circle 10 feet in diameter. Class IV includes all stacks of vessels having an inside i6o STEAM-BOILERS. area at the top not exceeding that of a circle 4 feet in diameter. Class V includes all stacks of vessels having an area at the top greater than that of a circle 4 feet in diameter. Class VI includes all stacks on steam locomotives. TABLE SHOWING THE DENSITY OF SMOKE, IN ACCORDANCE WITH THE RINGELMANN CHART, WHICH MAY BE EMITTED FROM THE VARIOUS CLASSES OF STACKS AND THE DURA- TION OF SUCH EMISSION. Class I 2 3 4 5 6 Locomotive Moving Train, 6 Cars or More. i 2; X, U d O 03 c 6 u c 6 O o5 a 6 O § h 03 O c ai d£ 21 io d O VI O On, 20 5) 10 ) 20 ) 5 ) 4 3 3 3 9 12 7 3 4 3 3 3 12 15 9 5 3 3 3 3 40 30 20 20 3 3 3 3 50 40 30 30 Down-draught Furnaces. — In connection with the subject of smoke prevention, attention should be called to down-draught furnaces, which have the connection with the chimney below the grate. The supply of air is through the fire-door to the top of the fire, which has a very attractive appearance, as it burns brightly at the upper surface unless obscured by fresh fuel. A natural inference is, that the combustion is perfect in a down- draught furnace, and that it should give a notable gain in economy of fuel, but a little consideration shows that such a furnace is subject to the same conditions as an ordinary furnace. If there is either an excess or a deficiency of air, the combustion will be imperfect; in the latter case, as with an ordinary furnace, FURNACES. It) I smoke may appear at the top of the chimney. Tests made on a boiler using first an ordinary and then a down-draught grate have commonly shown little if any advantage in favor of the latter. Down-draught furnaces, if properly arranged and fired, can be made to burn inferior fuels which have a large amount of volatile matter without making much smoke; this may be a matter of great importance in cities where laws against smoke are enforced. Hawley Down-draught Furnace. — This furnace consists of a water-grate, an ordinary grate beneath the water-grate, and an ash-pit beneath this. There are three sets of doors. The upper doors are kept open nearly all of the time. Coal is fired through the upper doors. The coal next to and in con- tact with the water-grate is the hottest, and any volatile products driven off from the green coal have to pass downward through the water-grate and over the fire on the lower grate before escap- ing into the space beyond the bridge-wall. The lower grate is supplied with coal which drops through the water-grate when the slice-bar is used. This fire is what would be called a dirty fire and shows clinkers and ash. As a general rule firemen are not apt to keep a sufficient depth of fire on this lower grate. A fire about 6 inches thick seems to give best results. The water-grate adds a large amount of very efficient heating- surface to a boiler, and in consequence increases the capacity of the boiler without reducing the economy. Oil Fuel. — Fuel oil is used for the gener ation of steam to a considerable extent in some parts of this country. It has cer- tain advantages over coal which may be briefly summarized as follows : Crude oil has a heating value 30 per cent greater than coal; it can be burned without smoke or ash or dust; more perfect combustion can be maintained than is possible with coal; a greater capacity can be obtained from the boiler; the pressure 1 62 STEAM-BOILERS. in a boiler can be raised very quickly or its power may be doubled in a few minutes; the cost of labor per boiler horse-power is very low. The disadvantages are the danger of explosions, especially with oils of low flash point when handled by an unskilled fire- man; the difficulty of storing the oil which must be placed, according to city requirements, 30 feet from the nearest building; and, on account of the intense heat generated in the furnace, the danger of burning the shell of a boiler, if that boiler is supplied with feed-water which is of a scale-making quality. To burn oil successfully the oil should be heated, atomized, sprayed into a fan-shaped jet, and the amount of air should be regulated, first, by the hand damper in the flue, and second, by opening the ash-pit doors an additional amount when any tend- ency to make smoke is noticed. A proper adjustment of the burner is necessary in any case. As the atomizing of the oil is generally done by means of steam it is customary to supply the steam to the atomizer and in some cases to the oil pumps through a reducing valve which maintains a constant pressure irrespective of any fluctuations in boiler pressure. Tests made on boilers using liquid fuel have shown a gross thermal efficiency of from 79 to 83 per cent with from 1.5 to 2.7 per cent of the total steam used by the burners. A furnace arranged for burning oil fuel is shown by Fig. 61. The burners placed just inside the bridge-wall send a fan-shaped flame forward. Air is taken in through holes shown at the back end of the grate which is covered at the front end as shown. Oil Burners. — Oil burners have been divided by the United States Naval Liquid Fuel Board into two general classes, each class being divided into five types. The two general classes are outside mixing and inside mixing burners, depending on whether the mixing of the oil and the atomizing agent occurs outside or inside the burner. The five types into which each class may be subdivided are. distinguished by the method by which the oil is atomized. OIL BURNERS. 163 These are designated as Drooling — where the oil oozes out onto the air or steam jet. Atomizing — where the oil is swept from the orifice by the jet of air or steam. Chamber — where oil mingles with steam or air in the body of the burner and the mixture issuing from the nozzle is broken into minute particles by the expansion of the air or steam. Fig. 61. Injector — where the action is similar to that of a steam injector. Mechanical — spraying done mechanically, no atomizing agent such as air or steam being used. A burner should be designed so as to allow of quick inspection and of the easy removal of any foreign material which may clog it and of the cheap and rapid renewal of any parts subject to wear. A few of the many different makes of burners are shown by Figs. 62 to 66. Fig. 62 is known as the Peabody No. 1 burner. This is an outside mixing burner of the drooling type, fan-shaped flame. 164 STEAM-BOILERS. The oil pipe is jacketed with steam and provision is made for blowing out foreign material which may lodge in the oil pipe with steam admitted through a by-pass. The tip, shown more clearly by the section, contains two very narrow slots separated by a diaphragm, the lower slot being for steam, the upper for oil. Steam Connection Burner Tip 1 £»<£ Oil Connection Fig. 62. The oil falls at right angles upon the steam jet which atomizes it. The mixing and atomizing is done entirely outside the burner. The Gem oil burner is shown by Fig. 63. This is an out- side mixing burner, drooling type, with rose-shaped orifice. The spraying is aided by slight centrifugal action from the internal helix. This burner is adapted for use where a very heavy con- sumption of oil is required. The Hammel oil burner, Figs. 64 and 65, is of the inside mixing class and of both the chamber and atomizing types. Referring to Fig. 64, oil enters at the left through the inclined passage into the mixing and atomizing chamber at the right-hand end of the burner. Steam enters the lower chamber and flows through three small slots, one of which is shown in the section, into the mixing chamber where it meets the oil. A plan view of Fig. 64 would show that the mixing chamber was V-shaped, with the long narrow opening at the front end. OIL BURNERS. I6 5 The Texas oil burner, shown by Fig. 66, is of the inside mix- ing class, chamber type. As the oil flows into the large mixing chamber it is picked up by the steam to which rotary motion has been imparted by a short helix in the steam passage just back of the oil inlet. The mixture then passes along the chamber through a spiral passage occupying about one half of its length, which sets up a strong centrifugal action which causes the oil to be thoroughly atomized and vaporized when it issues from the fan-shaped orifice in the small chamber at the tip of the burner. This orifice is made to give any width of flame required and the tip is easily renewable in case of wear. A discussion of oil burning is to be found in the journal for August, ion, of A.S.M.E., in an article FlG - 6 ^ by Mr. B. R. T. Collins. From this article much of the pre- ceding has been abstracted. Induced Draught and Forced Draught. — When a higher rate Fig. 64. Fig. 65. of combustion is required than can be had with natural draught, resort is had to forced draught, by aid of which 150 pounds of coal can be burned per square foot of grate-surface per hour. 1 66 STEAM-BOILERS. Three systems of forced draught are in common use, namely, with a closed stoke-hole, with closed ash-pits, and induced draught. Induced draught has long been used on locomotives, by the action of the exhaust-steam thrown through the smoke-stack. The same method is used to some extent on tug-boats. This method is simple and effective, but can be used only with non- condensing engines. Induced draught may be obtained by a centrifugal, or other form of blower, in the chimney. It is essential that an economizer should be used to cool the gases before they come to the blower. On steamships forced draught has been obtained by the aid of centrifugal fan-blowers. The method with closed ash-pit Fig. 66. has been used with success on merchant steamers and some war-ships. With this method air drawn from the fire-room passes through a blower and is delivered to the ash-pit, which has an air-tight door. If the pressure in the ash-pit exceeds the resistance to the passage of air through the fuel, flame comes out around the fire-door unless it is also made air-tight. When the fire-door is opened to throw on coal the blast must be shut off from that furnace and all others having a common combustion- chamber, or flame will shoot out into the fire-room in a dangerous manner. One reason why it has not been used on war-ships is the difficulty of properly ventilating the many small fire-rooms in which boilers are placed. The closed stoke-hole has been the customary way of getting FURNACES. 167 a forced draught on torpedo-boats and on other naval vessels. The stoke-hole is closed air-tight, admission and egress being through air-locks, and air from without is forced in through a centrifugal blower till the pressure exceeds that of the atmos- phere. When a fire-door is opened to attend to the fire, there is a strong inrush of air that is liable to make the tube-plates leak. So great difficulty has been experienced from this cause, when forced draught has been used with the Scotch boiler, that many naval officers doubt its advisability for large ships. The success of forced draught on the locomotive and on torpedo- boats with modified locomotive-boilers may be attributed partly to the type of the boiler and partly to the fact that there is only one boiler and one furnace. When two boilers are used on a torpedo-boat, each has its own chimney. On locomotives the induced draught is frequently equiva- lent to a column of water 5 or 7 inches high. Forced draught on torpedo-boats has approached these figures, but is usually less. Large ships usually have the forced draught restricted to 2 inches of water. On account of the resistance to the entrance of air to the fire-rooms of war-ships, through venti- lating shafts, gratings, etc., it has been common to assist the draught by running the blowers without closing the air locks. The increased cost of coal has led many to burn screenings or buckwheat coal by means of a forced draught. A blower driven by a steam-engine supplies air to the ash-pit at from 1/2 to 4 inches water pressure. A rapid rate of com- bustion is maintained, and even though the cheap coal is not burned as economically as it might be, still the poorer coal at the present prices shows a saving in the cost of making steam. The speed of the engine driving the blower is controlled by the pressure in the boiler, a damper regulator operating the throttle of the engine. When the damper regulator has closed the throttle, the engine is kept turning fast enough to pass the dead-centers by steam admitted through a small pipe with valve, which by-passes the throttle controlled by steam pressure. 1 68 STEAM-BOILERS. In the induced draught system, as arranged in large plants, the gases are drawn from the grate through an economizer into the exhaust-fan, which then discharges the gases at about 300 F. into the stack. The stack serves simply to carry the gases away. Howden's System. — The temperature of gases in the up- takes of marine boilers is frequently high, especially when forced draught is used. In Howden's system the products of com- bustion pass through vertical transverse tubes placed in an enlargement of the uptake. Air to supply the fire is forced over these tubes by a fan-blower and is thereby warmed, thus saving heat and giving quicker combustion. Care must be taken in using this system not to go too far, or the fire may become too hot and rapidly burn out the fire-grates and do other injury. Fire Cracks. — Fire cracks are often found on old boilers at the joints exposed to the fire. The two rivets at the left in Fig. 67 show such cracks. Fig. 67. These cracks are caused by the repeated buckling, between the rivets, of the plate exposed to the fire. This plate becomes much hotter than the plate back of it which is in contact with the water in the boiler, and any change in the temperature of the fire is felt by the plate. Innumerable repetitions of this action ultimately starts a crack which extends as shown. If a crack extends beyond a rivet it should be plugged to prevent the crack from extending FURNACES. 169 to the edge of the lap of the other plate. This plug is a piece of soft copper driven into a hole drilled about 3/8 inch diameter. The cracks are most always at the rivets, but sometimes a crack will be found between two rivets. In case a fire crack should leak much the leak may be stopped for a time by countersinking the plate, as shown by the right- hand rivet and driving in a very soft rivet. The metal of the rivet will flow out into the crack. • Cleaning Fires. — Three tools are used in clearing the grate: they are a long straight bar known as the slice-bar, a similar bar with the point bent at right angles to make a hook, and a long-handled rake with three or four prongs. The hook may be run along between the grate-bars from below, to clear the spaces from ashes and clinker. The slice-bar is thrust under the fire on top of the grate to break up the cinder; it is used also to stir and break up caking coals. The rake is used to haul the fire forward or to draw out cinder. To clean a fire the fireman breaks up the cinder with the slice- bar and rattles down the ashes; if necessary, he works the fire back toward the bridge and exposes the grate in front, which may then be thoroughly cleaned. Then he hauls the fire forward and cleans the back end of the furnace. Cinder which will not break up and pass through the grate is pulled out through the fire-door. Some firemen prefer to clean the grate one side at a time. After the grate is cleaned the fuel left is spread evenly over the grate and fresh fuel is thrown on. The fire should be allowed to burn down before cleaning, but a fair amount of glowing coal should be left to start a new fire briskly. Before beginning to clean the fire the draught should be checked by closing dampers or otherwise. Economizers. — An economizer cons sts of a series of vertical cast-iron tubes placed in the flue of a boiler between the boiler and the stack, and used to heat the feed-water with heat re- covered from the flue gases (Fig. 68). Any heat taken up in this way is just so much heat gained, 170 STEAM-BOILERS. provided the draught is not so reduced by the extra resistance offered to the passage of the flue gas as to lessen the capacity of the boiler. An economizer will show a greater saving on a plant which is forced than on a plant which is running at a moderate rate. Ordinarily a gross saving in coal of from 8 to 10 per cent will be made. It is not advisable, however, to install economizers in small plants unless these plants are being forced. To find whether or not an economizer will make a net saving, the interest on the money invested in the economizer and the amount allowed for its depreciation must be deducted from the gross saving. The life of an economizer is generally taken as 20 years, and the cost is from $4.25 to" $4.50 per boiler horse-power." From 3.5 to 5 square feet of economizer surface are commonly allowed per boiler horse-power. Economizers are made up of cast-iron tubes about 4 inches in inside diameter and 9 feet long. The tubes are turned at the end to a slight taper and are forced into top and bottom headers by hydraulic pressure. These headers are made to take different numbers of tubes, as is shown by the table of dimen- sions given in the Appendix. The lower headers project through the brick-work housing and are joined together by a " bottom branch pipe " running lengthwise of the economizer. This " bottom branch pipe " has on one side a series of flanges for making the connection with the bottom headers, and, on the opposite side, a series of clean-out openings, one opposite each header. Expansion of these connecting pipes at the bottom and at the top is provided for by U-shaped bends, as shown in Fig. 68. The feed- water enters this " bottom branch pipe " at the end of the economizer nearest the chimney and leaves the econo- mizer at the top, at the end nearest the boiler. The top headers are similarly connected. This pipe joining the top headers is placed above instead of at the end of the header and at the opposite side of the economizer. In some cases means are pro- 172 STEAM-BOILERS. vided for washing out the bottom headers, by sending a stream of water from a hose down through the tubes at the back end of the bottom headers, and letting it flow along the entire length of the bottom headers and out through the clean-out openings directly opposite the headers. In setting up an economizer, room should be left opposite these clean-out openings, so that a scraper can be put into each header to remove any scale which may lodge there, inasmuch as the headers are sometimes cleaned out in this way, instead of by washing. In order to repair a tube and replace it by a second tube without dismantling that section or that header, a slot is made in the upper end of the tube with a chisel, so as to enable the tube to be sprung together. The tube is then withdrawn from the bottom header in the following manner. A piece of iron, shaped as shown in the cut, is pushed down inside the tube and moved to one side so as to engage the bottom end of the tube, this piece being held by a rod with thread and nut at the top. A second piece like a wedge is held against the first piece. By screwing on the first nut the tube may now be withdrawn from the bottom header. The new tube is now in- serted, driven into the bottom header, and a conical wedge used to make the joint between the tube and the top header. Some- times a tube which has given trouble may be plugged and cut out of service. As broken tubes are withdrawn through the top of the economizer or in case of serious mishap, as the entire section is taken up through the top of the economizer, there should be sufficient room left over the economizer to allow for this. The arrangement of the brickwork should be such as to enable a section to be withdrawn without making it necessary to take down a large amount of masonry. The heating surface needed may be put either in one large economizer, through which all the gases from all of the boilers pass, or there may be a number of smaller economizers, known ECONOMIZERS. 173 as " unit economizers," one for each battery of two boilers. With the first arrangement, any accident to the economizer which might put it out of service would reduce the power of the boiler plant 8 or 10 per cent. The draught would be reduced to a con- siderable amount by this arrangement. In the second arrangement, as only one unit would be cut out, in case of accident, the reduction in power of the boiler plant would be inappreciable. The flue gas leaving the boiler should have a direct passage to the chimney around the economizer. Suitable dampers should be provided so that the gases may be sent either through the economizer or directly to the chimney. When the economizer is out of service both dampers at entrance and exit to the econo- mizer should be closed. Reducing the temperature of the flue gas by passing it through the economizer reduces the draught practically in the proportion that the absolute temperature of the flue gas is reduced. The draught is still further reduced by the friction of the gas in passing through the economizer, and, in the many instances where the draught is poor, it would be unwise to install an econo- mizer unless an induced draught fan were to be installed also. This loss of draught varies from 0.2 to 0.4 inch according to conditions. For ordinary cases 0.3 inch may be assumed as the loss. Usually on the side of the economizer there is a space about 1 2 inches wide left between the last tubes and the casing or brick- work, to allow of inspection. Sometimes there are two such passages, one either side of the economizer. These passages are closed by side dampers when the economizer is in use. Provision should be made for removing the soot from the bottom of the economizer. To remove the soot which collects on the tubes, scrapers are provided, these scrapers being in the form of loose collars which are alternately raised and lowered by chains operated from a shaft running along the top of the econo- mizer. If the economizer is only eight tubes wide, one shaft will 174 STEAM-BOILERS. serve, but if the economizer is ten or twelve tubes wide there should be two sets of shafts. The economizers must each be provided with a relief valve of sufficient size and with a blow-off valve. Two arrangements of economizers as applied to two types of boilers are shown by Figs. 69 and 70. Sometimes economizers become " steam bound," due to steam being generated in the tubes. This may happen if the feed pump has been stopped for any length of time while the boilers were running. If the economizer is steam bound it is difficult, or almost impossible, to get water through it, and the thumping and snapping which results is liable to start some of the joints. The economizer is always connected to the feed line in such a way that the feed may be by-passed around the economizer, and when the economizer becomes steam bound it should be cut out and allowed to cool until the steam has condensed. The rise of temperature of the feed-water in the economizer may be calculated as follows : Calculation of an Economizer. — T h = temperature of flue gas entering economizer. T c = temperature of flue gas leaving economizer. t h = temperature of feed-water leaving economizer. t c = temperature of feed-water entering economizer. 0.24 = specific heat of flue gas. 30 = number of pounds of water fed per boiler horse-power. 24 = pounds of flue gas per pound of coal. 9 = probable evaporation of water per pound of coal. (T h - T c ) X 24 X ^ X 0.24 = 30 (t h - 9 T h - T c =-~ (t h - = 1.562 (h - 0.64 . T,= T h -1.562(4-0. ECONOMIZERS. 175 For different evaporations, or for different weights of flue gas per pound of coal, the value to replace 1.562 may be easily figured. As the coldest gas is at that end of the economizer at which the cold water enters, and the hottest gas at the end where the water is hottest, there can be but little error in taking the difference of the mean temperatures of the gas and of the water. Let S = square feet of heating surface in the economizer per boiler horse-power or per 30 pounds of feed-water fed per hour. Let 3 = B.T.U. transmitted per square foot of surface per hour per degree difference of temperature between the gases out- side the tubes and the water inside the tubes. This value 3 would apply to a new economizer; as the metal gets old the inter- change of heat would be less, even as low as 2 B.T.U. per hour per square foot per degree difference in temperature. 30 (4 - = (^^ - '-^x 3 x 5 ■^(h -t c )=SlT h +T h - 1.562 (4 - ~k- h\ O _ h ~ tc 2 T h - 1.562 (t h -t c ) -t h -t c 2ot h - 2ot c = S U T h - 1.562 (t h - /,) - t h - t c \ _ 20 t c -f 2 ST h -f- 1.562 St c — St c 20 + 1.5625 + 5* _ 20 t c -f 2 ST h + 0.562 St c 20 + 2.562 6" The Green Economizer Company use the following formula: S(T h -t c ) k - L -+(^* In this w = pounds of feed-water per boiler horse-power. G = pounds of flue gas per pound of combustible. C = pounds of coal per boiler horse-power hour. This formula is practically the same as the one already worked out. 176 STEAM-BOILERS. Illustration. — Flue gas leaves a boiler and enters an econo- mizer at 550 F. The feed- water after passing through both a primary and a secondary heater enters the economizer at 200 F. What is the temperature of the feed-water leaving the economizer? What is the temperature of the flue gases leaving the econo- mizer? Assume in this case 4 square feet of heating surface in the economizer per boiler horse-power. _ 20 X 200 -f 2 X 550 X 4 + 0.562 X 4 X 200 20 + 2.562 X 4 k = 2Q2° T c = 1.562 (292 — 200) = 407 . The flue gas has been reduced 143 , and the feed-water in- creased in temperature from 200 to 292 . Figs. 69 and 70 show two different arrangements of Green economizers. Fans for Induced Draught and for Forced Draught. — As has been pointed out in the discussion of economizers, the cooling of the gases and the frictional resistance offered by the econo- mizer both tend to reduce the draught, and, in most cases, it is inadvisable to install an economizer unless an induced draught is maintained either by a centrifugal fan or by some other means. A centrifugal fan consists of a series of paddles rotated in a casing. Air is drawn in at the centre of the casing, around the shaft, either on one or on both sides, and is delivered at an out- let in the periphery. If the vanes of the fan be revolved at a certain speed with the end of the discharge pipe closed, the pressure produced in the pipe is the maximum possible at that speed. This pressure is frequently called the dynamic pressure. If, now, an outlet be made in the closed pipe, the fan will maintain this same total pressure until a certain area of opening is obtained. This area is called the " capacity area," or " blast area," and is approxi- k#^mwM»^^ i 7 8 STEAM-BOILERS. CROSS SECTION Fig. 70. FANS. 179 mately equal to the diameter of the fan in inches times the width in inches, divided by three. The " capacity area " depends somewhat on the shape of the discharge outlet. The " capacity area " for a hole in a flat plate is greater than that for a tapered discharge pipe. The power required to drive a fan with the outlet closed is from 30 to 37 per cent of that required when discharging through an opening equal to the " capacity area." Suppose that three glass U tubes, shaped as shown at a, b, and c in Fig. 71, be inserted in the discharge pipe of a fan. The tube a opens at right angles to the axis of the pipe. The tube b \CONTRACT£D J>/3CHARQ£. Fig. 71. has its opening pointing along the axis of the pipe and towards the fan, and the tube c has two openings, one like b and one like a. If the end of the discharge pipe is closed and the fan be run, the pressure in the discharge will cause the water in the U tubes a and b to rise in the legs open to the air. The readings of a and b will be the same. The level in c will show no change. If the end of the discharge pipe be opened, the pressure shown by a decreases, that shown by b remains nearly constant, and that shown by c is equal to the difference between b and a. On account of eddy currents, etc., the dynamic pressure shown by the U tube b is somewhat less for a moving column of air 180 STEAM-BOILERS. than for a still column such as is obtained with a closed dis- charge. The pressure shown by b is called the " dynamic pressure " (D.P.), that by a the " static pressure " (S.P.), and that shown by c the " velocity pressure " (V.P.). Evidently (D.P.) - (S.P.) = (V.P.). If the velocity pres- sure is known the velocity may be calculated from V = V 2 gh, where h equals the height in feet of a column of air at the same temperature as the air in the pipe, which will produce a pres- sure equal to the velocity pressure. V = velocity in feet per second. , _ 144 X velocity pressure X 0.036 * _ ~ T ' where d equals the density of the air at a pressure corresponding to the static pressure and 0.036 is the pressure of an inch of water on a square inch area. 144 X velocity pressure X 0.036 , x d 5.2 velocity pressure , , d velocity pressure = — (3) or the velocity pressure increases as the square of the velocity. The dynamic pressure increases also as the square of the velocity. The work done on the air per second is very nearly equal to the pressure on the square foot times the volume displaced per second plus the kinetic energy due to the velocity which has been imparted. Static pressure X 0.036 X 144 X V X a -\ V 2 . (4) a = area of discharge at the point where velocity V is measured. FANS. 181 Substituting for V 2 from equation (i) in the last term of (4), V X a X d 2 g X 144 X velocity pressure X 0.036 2g d This last term simplifies to the velocity pressure X 0.036 X 144 X V X a, which substituted in equation (4) gives: (static pressure + velocity pressure) X (0.036 X 144) XV Xa. (5) This evidently is equal to the dynamic pressure on the square foot times the volume moved. As the dynamic pressure varies with the square of the velocity, it is evident that the work increases with the cube of the velocity. To measure the velocity pressure, various forms of Pitot tubes have been used. Those made of bent glass are not reliable. A form used by Mr. D. W. Taylor is described in the Proceedings of the Naval Architects and Marine Engineers, November, 1905. It is substantially as shown by Fig. 72. Mr. Taylor made extensive tests on different types of fans. He found the efficiency of the fans tested to vary from 30 to 45 per cent, according to the speed and the delivery pressure. He deduced also by experi- 73-o.» Tube ffl.Ml'j^ V«/f* | T — 1 ' 1 . 1 rfr I A S/ct Zf'Long ,„ Outer ' I I PITOT TUBE. I iMBS TO J 1 ^_JM/IHOM£ TO\ ' I 01 Fig. 72. ment the value of the coefficient of friction in round galvanized iron pipes as it applies in the formula D 3600 H f = loss of head in feet of air due to air friction. D = diameter of pipe in feet. L = length of pipe in feet. F = velocity in pipe in feet per minute. / = 0.00008 by experiment. 182 STEAM-BOILERS. Substituting this value and reducing, L F 2 H f = ± ~ (6a) D 11,250,000 For rectangular pipes where Y = short side in feet and nY — long side in feet, the formula becomes H L±nA_FL_ . . . (6b) n Y 22,500,000 L = length of pipe in feet and F = velocity in feet per minute. A number of years ago Mr. F. R. Still of the American Blower Company wrote an article which appeared in the Journal of the Western Society of Engineers, 1902, on the performance of steel- plate fans. The curves shown by Fig. 73 are taken from that article. The letters (P.V.P.) mean peripheral velocity pressure; the other letters (D.P.), (S.P.), and (V.P.) are used to denote dynamic pressure, static pressure, and velocity pressure, as before. The curve marked K was plotted by an empirical formula. This curve is made use of in calculating the inlet area of an induced draught fan such as would be used for flue gases. '-? « / = area of fan inlet, square feet. n _ volume of gas per minute 1000 H = draught in inches of water. K = constant determined by experiment (to be taken from plot). The ratio of opening as ordinates means the percentage of the actual opening compared with that of the opening needed for free discharge, this being generally somewhat greater than the FANS. 183 Tiatio, of Openina., Te?- Cent. * ^ & X» * Fig. 73. 184 STEAM-BOILERS. "capacity area." The ratio of effect in per cent due to restrict- ing the discharge area is plotted as abscissae. From the plot it is seen that with a full opening the ratio of (V.P.) to (D.P.) = 1, or the (D.P.) = (V.P.). The static pressure (S. P.) for full opening = (D.P.) — (V.P.) = o. Suppose the opening to be restricted to 70 per cent of its full area, then (S.P.) = (D.P.) - 0.22 (D.P.) = 0.78 (D.P.) (S.P.) is also 0.62 (P.V.P.) The following tables are taken from " Mechanical Draft " by the B. F. Sturtevant Company. V is calculated by equation (2), page 180, the value of d appearing in that equation being calculated thus: 14.7 X 12.39 _ (i4-7 + (S-P-) X0.036) Xvolume _ 1 = , 49 J -5 459- 1 +5° ' volume The multiplier for different temperatures is found by noting that the velocity varies as -, and d varies inversely as the abso- d lute temperature, d for 70 would be 5 = 0.06 times the 529-5 value at 50 . 1 0.96 = 1.02, as found in the table. P As the velocity V varies as \ — the relative pressure necessary r a to produce the same velocity may be found thus : Taking 70 as before, = VP = V0.98 = 0.96, as given 1.02 in the table on the following page. FANS. 185 Static Pressure of Still Air or Velocity of Dry Air at 50 ° F. of Still Air or Velocity of Dry Air at 50 F. Velocity Pres- Velocity Pres- sure of Moving sure of Moving Air in Inches of Feet per Sec. Feet per Min. Air in Inches of Feet per Sec. Feet per Min. Water. Water. O. I 20.72 1243 0.9 62. IO 3726 O. 2 29 30 1758 I .0 65-45 3927 0.3 35 84 2150 I . I 68.48 4118 O.4 4i 43 2486 I . 2 71.68 43° 1 o-5 46 31 2779 1-3 74.60 4476 0.6 50 73 3043 1-4 77-41 4645 0.7 54 78 3287 1-5 80.12 4807 0.8 58 56 3514 If the air is at a temperature different from 50°, the velocity may be obtained by multiplying by the values given in the following table. Temperature of Air, ° F. Relative Ve- locity due to Same Pressure. Relative Pres- sure Necessary to Produce Same Veloc- ity. Temperature of Air, ° F. Relative Ve- locity due to Same Pressure. Relative Pressure Nec- essary to Produce Same Ve- locity. 30 O.98 I .04 200 I. 14 O.78 40 O.99 I .02 250 I 18 O.72 50 60 I .OO I .OI I .OO O.98 300 350 I I 22 26 O.67 O.63 70 I .02 O.96 400 I 30 0-59 80 I.03 O.94 450 I 34 0.56 90 I .04 0.93 500 I 37 0-53 IOO I 05 O.91 550 I 4i 051 I50 I .09 O.84 Suppose that it is desired to find the horse-power input to a fan in order for it to maintain a velocity of 3927 feet per minute through a restricted opening having an area 70 per cent of the capacity area which may be taken as 4 square feet. The air may also be assumed to be 70 in temperature. Referring to Still's curves: (V.P) f , v =0.22 for 70 per cent opening. 1 86 STEAM-BOILERS. From the table it appears that air at 50 under 1 inch velocity pressure will give velocity 3927, and at 70 the pressure required is 1.0 X 0.96 = 0.96 inch. (V.P.) 0.96 . - (D^) = (D^) = °- 22 mGh (D.P.) = 4.364 4.364 - 0.96 = 3.404 = (S.P.) „ 3927 X 2.8 X 4-364 X 144 X 0.036 Horse-power = Q2 — - ^2_^± ^t q_ __ T g^ 33,000 X 0.42 The use of the curves may be best explained by showing their application to a few cases. Suppose a fan to deliver 10,000 cubic feet of air per minute against a dynamic pressure of 1.33 inches, the discharge area being restricted 80 per cent. The mechanical efficiency is 37 per cent. rri, u 10,000 X 1.33 X 5.2 , The horse-power = — — = 5.67. 33,000 X 0.37 The ratio of (D.P.) to (P.V.P.) for 80 per cent opening is 0.66, hence (1 ^_ = o.66; (P.V.P.) = ,00 inches; ^ = f^ = °.4 5 ; (S.P.) = 0.90 inch; ^ ^^ = 0.22; (V.P.) = 0.44 inch; (D.P.) - (S.P.) = (V.P.) = 0.43 inch. If the outlet is now opened sufficiently to give an unrestricted discharge, A ' '\ = 0.33, or ' = 0.33; whence (V.P.) = (r.x.r.) 2.00 0.66 inch; (D.P.) = 0.66 inch; (S.P.) = o inch. The volume moved is of that n 0.80 efficiency of the fan becomes 22 per cent. The volume moved is of that moved before, and the 0.80 FANS. 187 10,000 X — — X 0.66 x 5.2 r^ , O.OO The horse-power = 5.91. 33,000 X 0.22 If the opening is now restricted to 20 per cent, the capacity becomes 2500 cubic feet per minute, and the dynamic pressure = . , . (D.P.) 2.10 inches since = 1.15. 2.00 m * . , (S.P.) (S.P.) The static pressure = 2.26 inches since , = (r.V.P.) 2.00 = I.I3- The velocity pressure = 0.04 inch. The efficiency of the fan is 27 per cent and the power is tt 2 5°° X 2 -3° X 5- 2 ^ Horse-power = -* Q *- = 3.36. 33,000 X 0.27 Should the outlet be entirely closed, the power is 37 per cent of that required for an unrestricted discharge, or 0.37 X 5.91 = 2.19 horse-power, and the static pressure, which is, in this instance, the same as the dynamic pressure, is 2.32 inches since ' = 1.16. 2.00 The following example will illustrate the method of making the calculations for an induced draught fan. Example. — Determine the size of an induced draught fan and the approximate power required to drive it for a boiler plant of 2000 boiler horse-power. Heating value of coal 14,650 B.T.U. per pound. Boiler efficiency 70 per cent. Flue gases leaving economizer and entering fan 400 F. Draught as shown by a U tube 1 .00 inch. Then 33*47 = 6^27 pounds of coal per hour. 14,650 X 0.70 D ' F * The volume of a pound of flue gas at 400 F. is approximately X 11.78 = 23.0 cubic feet. Allowing 21 pounds of air at 49i-5 the ash-pit per pound of coal, and assuming 5 per cent leakage 1 88 STEAM-BOILERS. into the setting, makes 22.05 pounds of air per pound of coal; and inasmuch as the coal is 90 per cent carbon, there results 22.95 pounds of flue gas per pound of coal. — — j 1 ^—*- 60 = 57,530 cubic feet of gas entering fan per minute. It is cus- tomary, when little is known about a plant in which a fan is to be installed, to assume that the resistance is equivalent to restricting the discharge outlet 25 per cent. Hence, in this problem, the various factors are referred to a " ratio of open- ing " of 75 per cent. From formula (7), page 182, the area of the inlet should be / = — ^ = 5 57-53 = 27.9 square feet, H 1 which corresponds to a diameter of 5.96 feet. (K = 0.485 is taken from the curve (Fig. 73).) The area of the inlet may be taken as 40 per cent of the area of the side of the wheel. The latter then will be — ^ = 69.7 square feet, 0.4 which corresponds to a diameter of 9.42 feet. Referring to Fig. 73, the ratio of dynamic pressure to peripheral velocity pressure, (D.P.) to (P.V.P.), at 75 per cent opening is 0.73. rru *• (S.P.) (P.V.P.) = °' 53 ' (D.P.) (P.V.P.) Q.73 = , . (P- p -) (S.P.) 0.53 x * 37 (S.P.) (P.V.P.) As (S.P.) in this particular case is 1; (D.P.) = 1.37 inches (D.P.) - (S.P.) = (V.P.) = 0.37 inch. The power required to drive the fan = 57,53o X 1.37 X 5-2 = H p 33,000 X 0.4 FANS. 189 The hot gas leaving the fan and entering the chimney is usually at less than atmospheric pressure, and the draught due to this column of hot gas reduces the work on the fan. In the case of an induced draught, the static pressure shown by the U tube a, Fig. 71, being less than atmospheric, the level of water stands higher in the inner leg than in the open leg. If one were to imagine the open legs of the tubes a and b, Fig. 71, sealed and exhausted of air, then, if the tubes were of sufficient length, the difference in water level would measure the absolute pressure; the differences between the absolute (D.P.) and (S.P.) would be positive and a measure of the (V.P.). In any case, the tubes c and d, as connected, measure the (V.P.). The peripheral velocity is V = V2 gh, where h is expressed in feet of gas. h = 1.37 X 62.4 = 1.37 X 5-2 12 0.0413 24.2 / I "^7 X ^ 2 V = v 2 £-^ — = 10=5.2 feet per second or V 0.0413 6312 feet per minute. 57j>53_ _ g H S q Uare f ee t for " blast area." 6312 The blast area is one third of the product of the diameter and the width; hence the width of the blades of the fan is <^lXi =2 . 9fee t. 9.42 The speed is ^ = 213 R.P.M. 9.42 X3.1416 The efficiency of the fan has been taken as 40 per cent f ror 1 the curves shown by Fig. 73. On account of the draught exerted by the chimney, the work needed to drive the fan would be somewhat less than 31 H.P. 190 STEAM-BOILERS. If the fan were engine-driven by an engine using 55 pounds of steam per indicated horse-power per hour, or -^ =61 pounds 0.9 per horse-power output (the mechanical efficiency of the engine being 90 per cent) , then the steam consumption of the fan engine would be 61 X31 = 1 89 1 pounds per hour. Assuming that 30 pounds of water, under the conditions of pressure and tempera- ture of feed, would, if evaporated per hour, be equivalent to a boiler horse-power, then the per cent of the total boiler horse- power required by the fan is — — X 100 = 3.15. 2000 If, now, the fan were motor-driven, and the current cost 18 pounds of steam per engine horse-power input to the generator, and if the generator and the motor each had an efficiency of 90 per cent, then the percentage input to the fan would be 18 X 31 . "5- 30 O.9X0.9 — - X 100 = 1. 15. 2000 Arrangement of Induced Draught Fan and Economizer. — The boiler plant of the Eastman Kodak Company is arranged as shown by Fig. 74. The induced draught fans, which are in duplicate, may draw the gas from five vertical boilers through either economizer, or by closing a damper in the main flue the fans may draw the gas from three boilers through one economizer and the gas from two boilers through the other economizer. In case of an accident to an economizer the first arrangement would be used. It is possible also to cut out both economizers and to run the gases directly into the stack either with or without the help of the induced draught fans. Another arrangement is shown by Fig. 75, which illustrates the plant of the Hollingsworth & Whitney Company at Water- ville, Maine. FANS. IQI Fig. 74. 192 STEAM-BOILERS. Flue to Economizer a" conomizer ti^= ^-1 1 7\ 7\ T\ 21 CD W\s.vxs^ss^^ Flue to Economizer O / Fig. 75. CHIMNEYS. 193 In this boiler room there are six horizontal multitubular boilers, which discharge into three circular flues running back over the boilers and entering one large circular flue, from which the gases may be passed through economizers on the way to the induced draught fans. In case of an accident to an econo- mizer the gases are put through the two economizers remaining. It is probable, however, that the greater part of the gas goes through the economizer which is nearer the fans. There is no by-pass around each economizer. The by-pass flue marked on the drawing serves the same purpose by allowing the gases to be sent through the other economizers. A study of the drawing shows that the dampers have been located with the above in view. Chimneys. — There are a number of different kinds of chim- neys in use to-day: the red-brick stack, the radial brick stack, the self-supporting steel stack, the guyed steel stack, and con- crete chimneys. The steel chimneys are sometimes lined with fire-brick and sometimes unlined. The life of a steel chimney depends upon the care taken of it; probably ten to twelve years is a fair estimate of the life of such a chimney. A steel chimney deteriorates much more rapidly when idle than when in use. A brick stack lasts a great many years. Radial brick chimneys are made of a special brick, much larger and thicker than the ordinary red brick, shaped to the curve of the chimney on two faces and radial on two faces. There are five or six holes about one inch square running vertically through these bricks. Radial brick chimneys are very numerous in Germany. Many are being built now in this country. They are known here as the Custodis, the Heinicke, and the Kellogg chimneys. Concrete reinforced by iron bars has been used for chimneys during the last few years. It has not always proved to be a success, in some cases, because of faulty design, in others, because of poor material and poor construction. 194 STEAM-BOILERS. Various formulae have been proposed for use in rinding the diameter and the height of a chimney needed for a given power, those given by Kent, by Christie, and by Gale being best known. The following table, figured by William Kent from his formula, is borne out by practice. The table is figured on the assumption that 5 pounds of coal are required per boiler horse-power. If less coal is required the capacity of the chimney is increased, and SIZES OF CHIMNEYS WITH APPROPRIATE HORSE-POWER OF BOILERS. (Kent.) Diam- Height of Chimneys and Commercial Horse-power. Side of Actual Area, eter in Inches. 50 60 70 80 90 IC no 125 150 175 : >oo Spuare Inches. Square Feet. I eet. Feet . Feet. Feet. Feet. Fe St. Feet. Feet. I 'eet. Feet. F eet. 18 23 25 27 16 1.77 21 35 38 41 19 2.41 24 49 54 58 "62 22 314 27 65 72 78 83 24 398. 30 84 92 100 107 113 •• 27 4.91 33 115 125 133 141 .. 30 5-94 36 141 15.2 163 173 1 82 32 7.07 39 183 196 208 2 19 35 8.30 42 216 231 245 2 58 271 38 9.62 48 311 330 3 ;8 365 '389 43 12.57 54 363 427 4 49 472 503 551 48 I5-90 60 505 536 5 65 593 632 692 748 . 54 19.64 66 658 6 u 728 776 849 918 981 59 2376 72 792 8 $5 876 934 [032 1 105 1 181 64 28.27 78 9 >5 1038 1 107 [212 1310 1 400 70 33l8 84 11 6.3 1214 1294 [418 1531 1 637 75 38.48 90 ... 13 44 1415 1496 [639 I770 1 893 80 44.18 96 ... 15 37 1616 1720 [876 2027 2 167 86 50.27 102 1946 2133 2303 2 462 90 56.75 108 2192 2402 2594 2 773 96 63.62 114 2459 2687 2903 3 003 101 70.88 120 2990 3230 ; 452 106 78.54 126 3308 3573 ; 820 112 86.59 132 3642 3935 4 205 117 95.03 138 3991 431 I 4 605 122 103.86 144 4357 4707 5 031 127 113. 10 its new rating may be obtained by multiplying the figure given in the table by 5 and dividing by the actual coal used per boiler horse-power. Mr. W. W. Christie in his work on " Chimney Design " gives the table of chimney capacities shown on page 195. This table is based on 4 pounds of coal per boiler horse-power rating. Coal per Hour per Square Foot of Chimney Area. — It is con- venient in judging the capacity of a chimney to know the pounds CHIMNEYS. 195 •5 a v rt 5. W TJ a cr—.x p. O O cm tJ- t^ O n tooo tooo rf O ■<* O 10OO mo m r^ t^oo m m cm cm cm ro t*3 fO to "t » t^.00 OO O O O O m ^t "^ 0> tON N 11 O NO 00 h\0 i- (O00 m N O 00 O to CM <0 i_i <0O 00 M Tt W M tM/00 O >0 H H H N N N tOtOfJ-t^ cm O -^-00 M M MONhM O On O CM O com O <0 to m O O O W)lON O <0O & N O CO CM MMMMCMCMCMCMCOtO"3-tO toiflH U)(> tJ-OO m Tt Tf to rf cm On O0 ^cm m to to OO <0 to ^ N O to O 00 O (H3±VM iO 83H0NN M.ld H8V QNV SOVNHrtd N33MX39 C13din03a XJVbQ JO 30HOJ 204 STEAM-BOILERS. If No. i anthracite buckwheat coal were to be burned at the rate of 20 pounds per square foot of grate per hour, the draught required would be: Fuel bed 0.45 inch Flue, 200 feet 0.20 inch Two bends 0.10 inch Boiler 0.20 inch Economizer 0.30 inch Total 1.25 inch Where the greater part of the resistance is due to the fuel bed, a forced draught fan blowing air under the grate is prefer- able to an induced draught fan. In such cases this fan need deliver the air with sufficient pressure to overcome the resistance offered by the fuel bed only; the gas above the grate being at atmospheric pressure makes what is sometimes known as a bal- anced draught. The pull exerted by the chimney is in most cases sufficient to carry the gases away. Furnace Draught , Inches of Water. Resistance in Inches of Water Total Draught, Coal burned per Hour per Square Foot of Grate. due to Inches of Water. Passage under Boiler and through Tubes. Passage over Top of Boiler. With Passage over Top. Without Passage over Top. 5 O.04 O.04 O.04 O. 12 O.08 8 . II •05 .04 . 20 .16 IO •13 .07 •05 •25 . 20 12 ■17 .07 •05 .29 .24 14 .19 • IO •05 •34 •29 15 . 20 . II •05 •36 •31 16 . 21 . 12 •OS •38 ■33 18 ■23 •13 •05 •42 36 20 •24 .16 .06 .46 .40 22 .26 .18 .06 •50 •44 25 .27 . 22 .06 •55 •49 28 •29 •24 .07 .60 •53 30 ■30 .27 .07 .64 •57 34 ■32 ■31 .08 •7i •63 36 ■33 •34 .08 •75 .67 40 ■36 ■38 .08 .82 •74 In the Transactions of the A.S.M.E., Vol. XVII, is given the results of some tests conducted by J. M. Whitham to determine CHIMNEYS. 205 the amount of draught needed for a certain type of boiler for various rates of coal consumption. The boiler on which the testing was done was one of 60-inch diameter, of the horizontal multitubular type with forty four 4-inch tubes 20 feet long. The grate area was 26.7 square feet, the grates being of the herringbone type with 46 per cent air opening. The distance from the grate to shell was 18 inches; from bridge wall to shell 10 inches. The gases were returned over the top of the boiler. Areas of Chimneys and Flues. — In common practice it is found that satisfactory results are obtained if the area of the section of a chimney is made 1/10 the area of all of the grates connected to the chimney, where the boilers are working under natural draught. The area of a chimney used for a small plant where there is only one or two boilers should be made 1/8 the area of the grate. The flue and the uptake of a boiler are generally made 1/7 to 1/8 the grate area. Forms of Chimneys. — Chimneys are made of brick or of steel plates. Steel chimneys are always round; large brick chimneys are usually round; small ones may be round or square. A round chimney gives a larger draught-area for the same weight of material, and it presents less resistance to the wind. Plate V gives the general arrangement and some detail of two chimneys: one of brick, 175 feet high, and the other of steel, 200 feet high. The brick chimney is built in two parts: the outer shell, which resists the pressure of the wind; and the lining, which forms the flue proper, and which may expand when the chimney is full of hot gases without bringing any stress on the shell. The shell has a foundation of rough stone and one course of dressed stone at the surface of the ground. The brickwork is splayed out inside to cover the stone foun- dation, and is drawn in at the top to the same diameter as the inside of the lining. The external form of the top is mainly a matter of appearance. The finish of large tiles at the top 206 STEAM-BOILERS. sheds rain and keeps water from penetrating the brickwork. The outside of the shell has a straight taper from the base nearly up to the head. A system of internal buttresses, as shown in section at Fig. 3 and Fig. 4 (Plate V), gives the requisite stiff- ness to the shell without an excessive amount of material. The lining carries its own weight only, being protected from the wind by the external shell; it has a uniform diameter of 6 feet inside, and varies in thickness from 1 2 inches at the bottom to 4 inches at the top. A rectangular flue with an arched top leads into the chimney at one side of the foundation. The shell of the steel chimney is made of vertical half-inch plates at the base, and is splayed out to give additional bearing on the foundation. Above this portion the shell has a straight taper to the top; the plates, each 4 feet wide, vary in thickness from 3/8 of an inch to 1/4 of an inch. At the top an external finish of light plate is given for the sake of appearance. The foundation is of red brick, with a course of stone at the surface of the ground, clamped by a wrought-iron strap. The shell is bolted through a foundation-ring made of cast-iron segments 4 inches thick, and a steel plate 2\ inches thick, by long bolts which take hold of anchor-plates bedded in the foundation. The lining of fire brick varies in thickness from 18 inches at the bottom to 4I inches at the top. It lies against and is carried by the steel shell. The internal diameter of the chimney is intended to be 10 feet; at places the size is a little larger on account of the arrangement of the lining. The lining is used to check the escape of heat through the steel shell. It adds nothing to the strength of the chimney; on the contrary, it must be carried by the shell. There is a chance that moisture may be harbored between the lining and the shell and give rise to corrosion. Large steel chimneys are comparatively recent, so that experience does not show whether lined or unlined chimneys are the more durable. Stability of Chimneys. — On account of the concentration of weight on a small area, and the disastrous results that would follow from defective work, the foundations of an important CHIMNEYS. 207 chimney should be carefully laid by an experienced engineer. A natural foundation is to be preferred, but piling and other artificial methods of preparing the earth for the foundation can be used when necessary. Good natural earth should carry from 2000 to 4000 pounds to the square foot. The base of the chimney should be spread out so that this pressure, or whatever the earth can safely bear, may not be exceeded. In calculating the stability of a chimney it is customary to assume the maximum pressure of the wind as 55 pounds per square foot on a flat surface. The pressure of the wind on a round chimney would theoretically be two thirds of that on a square chimney. It is commonly assumed, however, that the pressure on a round chimney is 0.57 of that on a square chimney of the same width, on a hexagonal 0.75, and on an octagonal 0.65. This method has long been in use, and it has been shown to give abundant stability. Experiments on wind-pressure are difficult and uncertain, and, curiously, the pressure determined by small gauges is commonly in excess of that shown by large gauges. Thus, certain experiments made during the construc- tion of the Forth Bridge gave a maximum wind-pressure of 35 pounds per square foot on a large gauge 20 feet long and 15 feet wide, while a small gauge showed a pressure of 41 pounds at the same time. The highest recorded pressure during violent gales, at the Forth Bridge, was that just quoted, namely 35 pounds to the square foot. Small wind-gauges have shown a pressure of 80 to 100 pounds to the square foot; but such results are discredited, both because it is known that small gauges give too large results, and because buildings were not destroyed as they would have been if exposed to such wind- pressures. To determine whether a chimney is stable, treat it as a cantilever uniformly loaded with 55 pounds to the square foot and find the bending-moments and resultant stresses. The stress will be a tension at the windward side and a compression at the leeward side. Calculate the direct stress due to the weight 208 STEAM-BOILERS. of the chimney, which will be a compression at either side of the chimney. For a brick chimney, subtract the tension due to wind-pressure at the windward side from the compression due to weight: if there is a positive remainder showing a resultant compression the chimney will be stable; otherwise not, because masonry cannot withstand tension. Again, add the compression due to wind-pressure to the compression due to weight, to find the total compression at the leeward side: if the result is not greater than the safe load on masonry, the chimney is strong enough. The safe load may be taken as 10 tons per square foot. Fig. 80 gives a graphical method of arriving at the stability of a chimney. At the point A, the centre of gravity of the trape- zoidal area against which the wind presses, a line is drawn at some convenient scale to represent the total wind-pressure on the side. From B a line BW, drawn at the same scale, represents the total weight of the chimney. Combine at point B these two forces, and if the resultant cuts the base at a point D, so that CD is less than 1/3 EE for square chimneys and less than 1/4 EE for round chimneys, there will be no tension on the mortar at the windward side, and the maximum intensity of compression will be twice the mean intensity. In the upper diagram at the right of the cut of the chimney the line YY represents the direct compression due to the weight of the chimney; the line XX the stresses due to the action of the wind. Combining these the line ZZ is obtained. This shows at the windward side a compression equal to EZ. The second diagram illustrates the case where the action of the wind just removes the compression at the windward edge, making EZ at the leeward edge equal to twice EY . The third cut shows a possible distribution of the stresses on a section which had cracked on the windward side. The calculation for the strength of a self-supporting steel chimney involves certain details of the design of a riveted joint CHIMNEYS. 209 and certain nice discriminations as to the action of such a joint when affected by a bending moment, which are out of place here. For example, it is clear that on the leeward side the com- pression on a lapped joint must be borne by the rivets and that the plate between the rivets is free from stress. A crude calcu- lation may be made as for a homogeneous cylinder, which is Fig. 80. subjected to compression and bending, using for the apparent working stress the safe stress of the steel, multiplied by the effi- ciency of the riveted joint, as determined by methods given in Chapter VIII. A calculation like that just described must be made for the 210 STEAM-BOILERS. section of the chimney at the base, for each section where there is a change of thickness or of construction, and for any other section where there is reason to suspect weakness or instability. A steel base built up from boiler-plate is shown by Fig. 81. This differs from the one shown on Plate V. The lining of a brick chimney is to be calculated for com- Fig. 81. pression due to weight, at the base and at each section where there is a reduction of thickness. The lining of a steel chimney must be counted in when the stress due to weight is determined. A separate calculation must be made for the stability of CHIMNEYS. 211 the foundation of a steel chimney. For this purpose find the total wind- pressure on the chimney and its mo- ment about an axis in the plane of the base of the foundation. Find also the total weight of the entire chimney with its lining, and of the foundation: this will be a vertical force acting through the middle of the foundation. Divide the moment of the wind-pressure by the weight of the chimney and foundation: the re- sult will be the distance from the middle of the foundation to the result- ant force due to the combined action of wind-pressure and weight. If this resultant force is inside the middle third of the width of the foundation, the chimney will be stable. This brief statement is intended to describe the method of calculating the stability of chimneys, and not to give full instructions. The design and calculation for an important chimney should be intrusted only to a compe- tent engineer who has had experience in such work. Radial Brick Chimneys. — This class of chimney is rapidly replacing the red brick chimney. It costs less, is more durable, and can be built in a shorter time than a red brick chimney. Although tall radial brick chim- neys are not figured to resist tension on the side towards the wind, the Air-^ Firebrick mm Fig. 82. 212 STEAM-BOILERS. adhesion of the mortar to the perforated radial brick is such that a pull of 4.4 tons per square foot is required to separate the joint. The ultimate crushing strength is about 362 tons per square foot. The radial bricks laid weigh about 118.5 pounds per cubic foot. It is customary in some types of radial brick chimney to figure 20 tons as the safe load in compression per square foot. In general these chimneys are not lined. There are cases, however, where a lining is required. The lining may be put in as shown in the cut of the Custodis chimney, Fig. 82. The weight of the fire-brick lining is carried by the shell of the chimney and by adding to its weight increases its stability. Foil moitar be Fig. 83. The method of bonding used in the Heinicke chimney is shown by the left-hand side of Fig. 83 ; the right-hand side shows how poor work might be done by an unscrupulous party if an inspector were not constantly on the watch. CHAPTER VI. POWER OF BOILERS. The power of a boiler to make steam depends on the amount of heat generated in the furnace, and on the propor- tion of that heat which is transferred to the water in the boiler. The amount of heat generated depends on the size of the grate, the rate of combustion, and the quality of the coal burned. The transfer of heat to the water in the boiler depends on the amount and arrangement of the heating-sur- face. In practice it is found that each type of boiler has certain general proportions which give good results ; any marked variation from these proportions is likely to give poor economy in the use of coal, or to lead to excessive expense in construction. The capacity of a boiler is commonly stated in boiler horse-power; the economy of a boiler is given in the pounds of steam made per pound of coal. Neither method is entirely satisfactory, but definite meaning is attached to the terms by definitions and conventions. Standard Fuel. — A comparison of the composition and of the total heats of the several kinds of coal given in the table on page 54 shows a great difference in the value of a pound of coal, depending on the district and mine from which it comes. In order to introduce some system into the com- parison of the performance of boilers in different localities it has been proposed that some coal or coals be selected as standards, and that all boiler-tests intended for comparison be made with a standard coal. For this purpose it has been 213 2 1 4 Sl^EA M -BOILERS. proposed to select Lehigh Valley anthracite, Pocahontas semi-bituminous, and Pittsburg bituminous coal. More def- inite comparisons would result if only one coal, such as Poca- hontas, were selected. The objections are, first, that some trouble and expense might be incurred in localities where this coal is not regularly on the market; and second, that a furnace designed for a given coal may not give its best results with a different kind of coal. There is a notable dif- ference between furnaces designed for anthracite coal and those designed for bituminous coal ; for the rest it appears that the use of a standard coal is a question merely of ex- pediency. In making a boiler-test it is not difficult to make an ap- proximate determination of the per cent of ash in the coal used. When that is done, the economy is usually stated in terms of water evaporated per pound of combustible, as well as per pound of coal. This gives somewhat more definite- ness to the statement ; but as no account is taken of the vola- tile matter in the coal, nor of the oxygen, this method also is indefinite. Value of Coal. — The actual value of a coal for making steam can be determined only by accurate tests with a fur- nace and boiler which are adapted to develop and use the heat that the coal can produce. While many boiler-tests have been made, and there is a good deal of material that could be used for the purpose, there has not yet been made a satisfactory statement of the value of the fuel in common use. It appears probable that the real value of a coal for mak- ing steam is proportional to the total heat of combustion. It this can be shown to be true, then coals should be sold on the basis of heat of combustion, just as steel is required to have certain physical properties which are determined by making proper tests. Quality of Steam. — When the economy of a boiler is stated in terms of water evaporated per pound of coal, it is assumed that all the water is evaporated into dry saturated POWER OF BOILERS. 215 steam. But the steam which leaves the boiler may contain some water, or it may be superheated. The moisture carried along by steam is called priming. The steam from a properly designed boiler, working within its capacity, seldom carries more than three per cent of priming. Under favorable circumstances steam from a boiler will be nearly dry. If steam, after it passes away from the water in the boiler, passes over hot surfaces it will be superheated ; that is, raised to a temperature higher than that of saturated steam at the same pressure. Vertical boilers with tubes through the steam- space give superheated steam. If steam is to be superheated to any considerable extent, it must be passed through a superheater, either attached or independently-fired, as described in Chapter II. Boilers of the Manning type and boilers equipped with attached superheaters generally give more superheat when forced. This is because of the higher temperature of the escaping gases. Although the consumption of an engine, figured on pounds of steam, is less with superheated steam than with saturated steam, it does not necessarily follow that the coal per indicated horse- power per hour is less. A number of plants investigated by the writers have shown an increased coal consumption. Certain types of turbine must be supplied with superheated steam, if any economy is to be obtained, on account of the fact that any water in the shape of priming in the steam or any water resulting from the expansion of the steam acts like a water-brake. In some turbines it is estimated that one per cent priming causes two per cent loss in economy. Steam-space. — The steam-space and the free surface for the disengagement of steam should be sufficient to provide for the efficient separation of the steam from the water. Cylin- drical tubular boilers frequently have the steam-space equal to one third of the volume of the boiler-shell. Marine return- tube boilers usually have a smaller ratio of steam-space to water-space. 2 1 6 STEA M -BOILERS. The more logical way appears to be to proportion the steam-space to the rate of steam-consumption by the engine. Thus the ratio of the volume of the steam-space of cylindri- cal boilers to that of the high-pressure cylinder of multiple- expansion engines varies from 50 : 1 to 140 : 1. The ratio of the steam-space of a simple locomotive-engine to the volume of the two cylinders is about 6J : 1. The capacity of the steam-space is sometimes equal to the volume of steam consumed by the engine in 20 seconds. It was found in some experiments with marine boilers having a working-pressure less than 50 pounds per square inch, that a considerable quantity of water was carried away by the steam when the steam-space was equal to the volume of steam con- sumed in 12 seconds, but that no water was carried into the cylinders when the steam-space was equal to the volume of steam used in 1 5 seconds and that no trouble from water was ever experienced when the steam-space was proportioned for 20 seconds. All the preceding discussion refers to engines that run at a considerable speed of rotation — not less than 60 revolutions per minute. Engines that make but few revolutions per min- ute and take steam for only a portion of the stroke require a larger proportion of steam-space. As an example we may cite the walking-beam engines for paddle-steamers. Equivalent Evaporation. — The heat required to evapo- rate a pound of water depends on the temperature of the feed- water, the pressure of the steam, and the per cent of priming. For example, if water is supplied to a boiler at 140 F., and is evaporated under the pressure of 80.3 pounds by the gauge, with 2 per cent of priming, the heat required will be calculated as follows: The heat of the liquid at 140 F., or the heat required to raise a pound of water from 32 F. to that temperature, is 108.0 B. T. U. The heat of the liquid at 95 pounds abso- lute, corresponding to 80.3 pounds by the gauge, is 294.6 POWER OF BOILERS 21 7 B. T. U. Consequently the heat required to raise the feed -water up to the temperature of the boiler is 294.6-108.0=186.6 B. T. U. The heat of vaporization, or the heat required to change a pound of water into steam, at 95.0 pounds absolute, is 890.5 B. T. U. But 2 per cent of water is found in the steam which comes from the boiler, leaving 98 per cent of steam; consequently the heat required is 0.97x890.5=872.7 B.T. U. The total amount of heat is therefore 186.6+872.7 = 1059.3 B.T. U. Suppose that each pound of coal evaporates 9 pounds of water, then the heat per pound of coal transferred to the boiler is 9X1059.3=9534 B.T. U. Now the heat required to vaporize a pound of water at 212 F., under the pressure of the atmosphere, is 969.7 B. T. U. Dividing the thermal units per pound of coal by this quantity gives 9534-969.7=9-83, which is called the equivalent evaporation from and at 212 F. This method of stating the economy of a boiler is equivalent to using a special thermal unit 969.7 as large as the thermal unit defined on page 59. In making calculations involving quantities of wet steam it is convenient to consider the amount of steam present, rather than the percent of priming. In the example just con- sidered, there are 0.02 of water or priming, and 0.98 of steam. The part of a pound which is steam is represented by x. If the heat of vaporization at the pressure of the steam in the boiler is represented by r, the heat of the liquid at that pressure by q, and the heat of the liquid at the temperature of the feed-water by q ; and if, further, there are w pounds of 2l8 STEAM-BOILERS. water evaporated per pound of coal, — then the equivalent evaporation is w(xr + q — g 9 ) 969.7 The highest equivalent evaporation per pound of coal is about 12 pounds, and to accomplish this result about 80 per cent of the total heat of combustion must be transferred to the water in the boiler. The complete combustion of a pound of carbon develops 14,650 B. T. U. ; if all this heat could be applied to vaporizing water at 21 2° F., then the amount of water evap- orated would be 14,650 -T- 969.7 = 1 5— |— pounds. Few, if any, coals have a greater heat of combustion, con- sequently this figure may be considered to be the maximum equivalent evaporative power of coal. Should any test appear to give a larger evaporative power, or even a power approaching this result, it may be concluded either that there is an error in the test, or that there is a large amount of priming in the steam. Some tests of early forms of water-tube boilers without proper provisions for separating water from the steam, appeared to give extraordinary results; which results were due to the presence of a large amount of priming in the steam. At that time the methods used for determining the amount of priming were difficult and uncer- tain, and were frequently omitted in making boiler-tests. Boiler Horse-power — It has always been the habit to rate and sell boilers by the horse-power. The custom appears to be due to Watt, and at that time the horse-power of a boiler agreed very well with the power of the engine with which it was associated. ' The traditional method of rating boilers, coming down from that time, was to consider a cubic foot, or 62^ pounds per hour, of water evaporated into steam, POWER OF BOILERS. 219 as equivalent to one boiler horse-power. This rating is now antiquated, and is seldom or never used. It was customary to consider 30 pounds of water evaporated per hour from a temperature of ioo° F., under the pressure of 70 pounds by the gauge, as equivalent to one horse-power. This standard was recommended by a committee of the Ameri- can Society of Mechanical Engineers.* The standard now is equivalent to the vaporization of 34.5 pounds of water per hour from and at 2 12 F. ; it is frequently so quoted. It is also equivalent to 33,470 B. T. U. per hour. Since the power from steam is developed in the engine, and since the economy in the use of steam depends on the engine only, and may vary widely with the type of engine, it appears illogical to assign horse-power to a boiler. The method appears to be justified by custom and convenience. Rate of Combustion. — The rate of combustion is stated in pounds of coal burned per square foot of grate-surface per hour. It varies with the draught, the kind of coal, and the skill of the fireman. In general a slow or moderate rate of combustion gj'ves the best results, both because the combustion is more likely to be complete and because the heating-surface of the boiler can then take up a larger portion of the heat generated. A very slow rate of combustion may be uneconomical, because there is a large excess of air admitted through the grate, and because there is a larger proportionate loss of heat by radia- tion and conduction. It is claimed that forced draught may be made to give complete combustion with a small amount of air in excess, and that it should give better economy than slower combustion. It will be remembered that a small amount of carbon monoxide due to incomplete combustion will cause more loss than a large amount of air in excess. It is true also that the harder a boiler is forced, the higher * Trans., vol. vi, 1881. 220 STEAM-BOILERS. the temperature of the escaping gases becomes and, consequently, the percentage of the heat of the coal carried off in this way increases. A series of tests made by J. M. Whitham and reported in Trans. A.S.M.E., Vol. XVII, show that the thermal efficiency of a 6o-inch horizontal tubular boiler, with (44) 4-inch tubes 20 feet long, did not change over 3 per cent between rates of coal consumption varying from 7 to 21 pounds per square foot of grate per hour. Heating-surface. — All the area of the shell, flues, or tubes of a boiler which is covered by water, and exposed to hot gases, is considered to be heating-surface. Any surface above the water-line and exposed to hot gases is counted as superheating- surface. The upper ends of tubes of vertical boilers are in this condition. For a cylindrical tubular boiler the heating-surface in- cludes all that part of the cylindrical shell which is below the supports at the side walls, the rear tube-plate up to the brick- arch which guides the gases into the tubes, and all the inside surface of the tubes. The front tube-plate is not counted as heating-surface. For a vertical boiler like the Manning boiler (page 11) the heating-surface includes the sides and crown of the fire- box and all the inside surface of the tubes up to the water- line. Surface in the tubes above the water-line is superheat- ing-surface. A certain 200-horse-power boiler of this type has 1380 square feet of heating-surface and 470 square feet of super- heating-surface. The heating-surface of a locomotive-boiler consists of the sides and crown of the fire-box and the inside surface of the tubes. The heating-surface of a Scotch boiler consists of the surface of the furnace-flues above the grate and beyond the bridge, the inside of the combustion-chamber, and the inside surface of the tubes. POWER OF BOILERS. 221 The effective surface of any tube-plate is the surface remain- ing after the areas of the openings through the tubes is deducted. Relative Value of Heating-surf ace. —A review of the kinds and conditions of heating-surface in various kinds of boilers, or even in a particular boiler, shows that the value of heating- surface varies widely. It does not appear possible to assign values to different kinds of heating-surface. We will note only that surfaces like the shell of a cylindrical boiler over the fire, like the inside of a fire-box, or like the flues of a marine boiler, which are exposed to direct radiation from the fire, are the most energetic in their action. Surfaces like combustion- chambers and tube-plates, against which the flames play, are nearly if not quite as good. The inside of small flues and tubes is less favorably situated, more especially as the flame is, under ordinary conditions, rapidly extinguished after it enters such a flue or tube. The length of the flame in small tubes depends on the draught, and with very strong forced draught may extend completely through tubes of some length. The value of heating-surface in a tube rapidly decreases with the length. It is doubtful if there is any advantage in making the length of a horizontal tube more than fifty times the diameter. Tubes of vertical boilers should have twice that length. Ordinary Proportions. — The table on the following page gives the ordinary proportions of various types of boilers. The higher rates of evaporative economy are associated with slower rates of combustion and with larger ratios of heating sur- face to grate-surface. No attempt is made to distinguish the kind or location of heating-surface; it must be understood that the ordinary ar- rangements and proportions for the several types are followed if this table is to be used in designing boilers. For example, it cannot be expected that heating-surface gained by length- ening the tubes of a locomotive-boiler will add materially to the efficiency of the boiler. 222 STEAM-BOILERS. Type of Boiler. Lancashire Cylindrical multitubu- lar Vertical, Manning Locomotive Locomotive type, sta- tionary Scotch marine Water- tube with cylin- der or drum Water-tube with sepa- rator Rate of Com- bustion. 8 to 12 8 to 15 10 to 20 50 to 120 average 75 8 to 15 35 to 45 9 to 15 15 to 67 average 20 Square Feet of Heating- surface per Foot of Grate. 25 to 30 35 to 40 *48+i6 60 to 70 40 to 45 30 35 to 45 30 to 40 Average Equivalent Evaporation. 8 to IO 9 to 10.5 9 to 10.5 6 . 7 to 8.5 9 to 10.5 7 to 9 9 to 10.5 7 to 9 Square Feet of Grate per Boiler H.P. 0.36 0.30 O.23 O.07 0.30 o. 11 O. 25 0.22 Heating- surface per Boiler H.P. 7.0 ". s II .1 4-5 12.6 3-3 11 .0 7-3 * 48 heating-surface, 16 superheating-surface. This table has been compiled from a large number of ex- amples, and may be taken to represent current good practice. The last two columns giving the grate-surface and heating- surface have been computed on the basis of one horse-power for 34.5 pounds of water evaporated per hour from and at 212° F. CHAPTER VII. STAYING AND OTHER DETAILS. ALL plates of a boiler that are not cylindrical or hemispher ical require staying to keep them in shape. For example, the cylindrical shell of a cylindrical tubular boiler does not require staying, because the internal pressure tends to keep it cylindrical. On the other hand, the pressure tends to bulge out the flat ends, and they must be held in place against that pressure. Many different methods of staying will be found in the different types of boilers seen in practice, and there are fre- quently several ways of staying the same kind of a surface. A few methods will be described in a general way. The placing of stays and arrangement of details is an important part of the design of a boiler, and must be worked out for each special design. Cylindrical Tubular Boiler. — The parts of the tube-sheets at the ends of a cylindrical tubular boiler, through which the tubes pass, are sufficiently stayed by the tubes themselves. The flat ends above the tubes require staying. Also, if there is a manhole at the bottom of the front end, the space thus left unsupported requires staying, and there is a corresponding space at the back end. An elaborate set of tests was made by Messrs. Yarrow* and Co., to determine the holding-power of tubes expanded into a tube-sheet. It was found that from 1 5,000 to 22,000 pounds * London Engineering, Jan. 6, 1893. 223 224 STEAM-BOILERS. were required to pull out a two-inch steel tube ; in some cases the tube gave way by tension inside the head into which it was expanded. The staying of a flat surface consists essentially in hold- ing it against pressure at a series of isolated points, which are arranged in a regular or symmetrical pattern. A simple case of staying is found in the side sheets of a locomotive fire-box. Here the stays, which are arranged in horizontal and vertical rows, are screwed and riveted. If possible, the pitch or dis- tance between the supported points should be the same, but this is possible only when arranged in rows as just men- tioned. The allowable pitch depends on the thickness of the plate. For cylindrical tubular boilers the pitch of the supported points of the flat ends above the tubes is 3.5 to 5 inches. The outside fibre-stress in the plate stayed may be from 6000 to 9000 pounds per square inch ; the calculation of this stress involves a knowledge of the theory of elasticity, and will be referred to later. It is not advisable, for this type of boiler, to assign a sepa- rate stay to each supported point of the flat surface under discussion, consequently the points are grouped, each point of the group being riveted to some support inside the boiler, and then the supports are held by proper stays. A good method of staying the flat end of a cylindrical boiler is shown by Plate I, and also, with some further details, by Fig. 84. There are two 6-inch channel-bars of proper length, that are riveted to the flat head. The rivets tie the plate to the channel-bars and thus support the plate at iso- lated points. The channel-bars in their turn are supported by stays that run directly through the boiler and have nuts and washers at each end. The channel-bars act as beams, and must be capable of carrying the load due to the pull on the rivets, and the through-stays must carry the loads on the beams. A short piece of angle-iron is riveted to the upper side of the upper channel-bar; it carries five additional rivets in the flat STAYING AND OTHER DETAILS. 225 head, and adds an additional load to the upper cliannel-bar. The points where the through-stays pass through the head are supported directly by the stays through the washers and nuts. The lower channel-bar is a continuous girder with four spans and five supports. The stays form three supports and the other two are at the inner edge of the flange of the head. The upper channel-bar is a girder with three spans and foui FRONT HEAD FOR 60 BOILER 84-3" TUBES Fig. 84. supports. The calculation of the stresses in the channel- bars is somewhat unsatisfactory, largely because the support at the flange of the head is uncertain; and this support must be left with some flexibility, and consequently with soem uncertainty, as too great rigidity leads to grooving. In arranging such a staying, we begin by determining the allowable pitch of the points supported by the rivets, assuming them to be in equidistant horizontal and vertical rows. This allowable pitch must not be exceeded, but the pitch may be made less either horizontally or vertically, or in both ways. A space of at least three inches is left between the top 22 6 STEAM-BOILERS, row of tubes and the lowest row of jivets, and a similar space is left at the sides. This is to avoid grooving, The two upper through-stays are fifteen and a half inches apart on centres. They must be wide enough apart to allow a man to pass through. The stay-rods are upset at the ends so that the diameter at the bottom of the threads is greater than the diameter of the body of rod. The washer outside the plate may be made of copper, in which case it is made cup-shaped so as to bear on a narrow ring, and is made tight by calking ; or the washer is made of iron, and is bedded in red lead to make a joint. Sometimes cap-nuts are used outside the head to prevent the escape of steam that may leak around the screw- threads. Long stay-rods are sometimes supported at the middle. A method of staying otherwise similar to that just de- scribed, uses two angle-irons in place of a channel-bar. A washer of special form is used to give a proper bearing, for the inner nut on the through-stay, against the angle-irons. Fig. 85 shows a different method of staying for cylin- drical boilers. The left half of the figure represents the end elevation, and the right half represents a section through the manhole; this is a common method for boiler drawings. The supported points are arranged in sets of four, and are tied to forgings known as crowfeet. Fig. 86 represents such a crowfoot with four rivets, known as a double crowfoot; a single crowfoot with only two rivets is shown by Fig. 87 When crowfeet are used they may be arranged in various patterns, in the example given there is a horizontal row of five double crowfeet just above the tubes, and three other double crowfeet are arranged in a circular arc. At the ends of the arc there are two braces like Fig. 88, which are used instead of single crowfeet. From each crowfoot a diagonal stay is carried to the boiler-shell. These stays are flattened at the farther end and bent to lie against the side of the shell, to STAYING AND OTHER DETAILS. 227 which they are riveted with two or three rivets ; the arrange- ment is similar to that of the right-hand end of the brace 0^ l°\ ._.. J r - J t ° --- Fig. 86. Fig. 87. shown by Fig. 88. At the crowfoot the stay has a forked head through which a bolt passes under the arch of the 228 STEAM-BOILERS. double crowfoot. A nut holds the bolt in place and pre vents the head of the stay from spreading. Fig. 90. A combination of channel-bar and crowfeet is shown by Fig. 80. The double crowfeet are represented as made of boiler-plate, bent up as shown by Fig. 90. STAYING AND OTHER DETAILS. 22g A method of staying, suitable only for boilers which work under low steam-pressure, is shown by Fig. 91. Short pieces of T iron, arranged radially, are riveted to the head. Each T iron is supported from the cylindrical shell by two OOOOOO OOOOOO OOOOOO OOOOOO Fig. 91. diagonal stays; one of the stays is represented by Fig. 92. One end of the stay is split, and is pinned to the T iron; the other end is flattened, and riveted to the shell. The shell of a cylindrical boiler, whether it is a tubular or a flue boiler, is made of a series of sections or rings. Each Fig. 92 ring is made of one or two plates riveted along the edge, or longitudinal seam. This seam has at least two rows of rivets; more complicated joints are commonly used to give more strength to the seam. Alternate rings of the shell are made smaller so that they may be slipped inside the rings at each of their ends. The seams joining adjacent rings are com- monly single-riveted. The longitudinal seams are kept above 230 STEAM-BOILERS. the middle of the boiler, so that they are not exposed to the fire. The first ring at the front end is always an outside ring, so that the first ring-seam has the outside edge pointing away from the fire; there is consequently less liability of injury to the seam from the flames that pass under the boiler toward the back end. Fig. 93 shows what is known as the Huston brace. It takes the place of the braces shown by Figs. 88, 90, and 92. It is made without welds. All horizontal multitubular boilers, 60 inches or over in diam- eter, should have a manhole in the front head, as shown by Fig. 227 in Chapter XIII. The manhole frame is itself sufficiently stiff to reinforce the bottom of the front head, but the back head must > Fig, 93. be stayed. Ten or twelve tubes must be omitted in order to make room for the manhole. Fig. 94 shows a good method of staying the back head between the tubes and the shell. Two pieces of angle iron are riveted to the plate with a dis- tance piece or ferrule made of a piece of pipe or tube between the plate and the bottom of the angle irons. These ferrules hold the angle iron off from the plate 2 to 3 inches. This distance allows of a free circulation of water and pre- vents an overheating of the plate. A space 2 inches deep will be sufficiently great to prevent scale from bridging over the space between the angle iron and the plate. Rivets are pitched from 5 to 8 inches along the angle irons. Bolts commonly made with tapering heads fitting conical holes in the plate pass between the angle irons and are drawn tight by nuts. Two stay-rods flattened at one end are fastened to the angle irons, as shown. These rods lead at a slight angle through the STAYING AND OTHER DETAILS. 231 232 STEAM-BOILERS. front head, one at either side of the manhole frame, and are fastened by nuts. The threaded ends are upset to a diameter greater than the centre of the rod. The angle at which the rods run across the boiler is so slight that there is no trouble with the nuts at the front head. These rods should never be tied to the bottom shell. Huston braces should not be used or any system which ties to the shell. Vertical Boilers. — The tube-sheets of a vertical boiler as is evident from inspection of Figs. 6 and 7, are usually stayed sufficiently by the tubes. Should the upper tube-sheet be much larger than the crown of the fire-box, it may need staying be- tween the tubes and the shell. Stays like Fig. %& may be used for this purpose. The circular fire-box of a vertical boiler is subjected to external pressure, and is prevented from collapsing under that pressure by tying it to the outer shell by screwed stay-bolts, which are put in and set like the stay-bolts for a locomotive- boiler. Locomotive-boiler. — The parts of a locomotive-boiler that require staying are the fire-box and the flat ends. The tube-sheets are sufficiently stayed by the tubes, but there is a part of the tube-sheet at the smoke-box end and a part of the flat end above the fire-box which requires support. The prob- lems here resemble those met in staying the tube-sheets of a horizontal cylindrical boiler, and similar methods are used. Thus in Plate II there are shown eight through-stays, each I-J of an inch in diameter. These stays pass through the girder staying of the crown-sheet, and have a simple nut and washer outside the end-plates of the boiler. At the smoke-box end, as shown by Figs. 1 and 3, Plate II, there are two diagonal stays taking hold of single crowfeet and running to the middle of the barrel. At the fire-box end there are four crowfeet or short angle-irons, made by bending up boiler plate ; two are shown by the right-hand elevation of Fig. 2 on Plate II. The outer crowfeet have five rivets, and the others six. From the outer crowfeet diagonal stays run to the shell at the ring just STAYING AND OTHER DETAILS. 233 in front of the fire-box. From the inner crowfeet stays run to the middle ring of the boiler. There are also two stays like Fig. 88, which run to the shell above the fire-box. Finally, there is a crowfoot and stay at the middle of the row of eight through-stays, this stay fastening to the two end crown-bars. Below the tubes there is a place in the fire-box tube-sheet which requires support. This is given by three braces like Fig. ^S, as shown by Figs. 1 and 2, Plate II. The shell of the boiler, shown by this plate, is higher over the fire-box than it is at the barrel, and a ring of peculiar shape is required to join the two parts together. This ring is cylindrical below and conical on top ; at the sides there are flattened spaces which require stiffening to prevent them from springing, and thus start grooving of the plates. For this purpose there are three T irons riveted to the shell at the flattened place mentioned, as shown by Fig. I, Plate II. The upper ends of the T irons on opposite sides of the boiler are tied together by transverse stays above the tubes. Coming now to the fire-box of the boiler represented by Plate II, we find that at the front, rear, and sides it is tied to the external shell by screwed stay-bolts set in equidistant hor- izontal and vertical rows. The holes for these stay-bolts are punched or, better, drilled before the fire-box is in place. After it is in place and riveted to the foundation-ring a long tap is run through both plates, the fire-box plate and the shell, and thus a continuous thread is cut in the plates. A steel bolt is now screwed through the plates, cut to the proper length, and riveted cold at each end. Owing to the screw-thread on the bolts, this riveting is imperfect, and likely to develop cracks at the edge. The thread should be removed from the middle of the bolts, as they are then less liable to crack under the peculiar strains set up by the unequal expansion of the fire- box and outside shell. The stay-bolts are very likely to be cracked or broken on account of the expansion of the fire-box; to detect such a 234 STEAM-BOILERS. failure of a bolt, or to show when excessive corrosion has taken place, the stay-bolts are often drilled from the outer end nearly through to the inner end. In case of failure steam will blow out of the defective stay ; serious injury has often been avoided by this method. The crown-sheet of the fire-box is exposed to intense heat, and is covered with only a few inches of water. The problem of properly staying this flat crown-sheet without interfering with the supply of water to it is one of the most difficult problems in locomotive-boiler construction. Figs. I and 2, Plate II, show the method of staying a crown-sheet with a sys- tem of girder-stays. Above the crown-sheet there are fourteen double girders, which are supported at the ends by castings of special form, shown by Figs. 2 and 6; the castings rest on the edges of the side sheets and on the flange of the crown-sheet* In addition the girder-stays are slung to the shell by sling- stays. At intervals of four and a half inches the crown-sheet is supported from the girders by bolts, having each a head in- side the fire-box, as shown by Fig. 5, and a nut at the top bearing on a plate above the girder. These plates are turned down at the ends to keep the two halves of the girder from spreading. There is a copper washer under the head of each bolt, inside the fire-box, to make a joint. Between the girder and the crown-sheet each bolt has a conical washer or thimble to maintain the proper distance between the girder and crown- sheet. This thimble is wide above to bear on the girder, and small below to avoid interfering with the flow of water to the crown-sheet, and also so as to cover as little surface as possible on account of the danger of burning the crown-sheet wherever the metal is thickened. The whole system of girders is tied together, and the girder nearest the fire-door is tied to the outside shell, thereby serving as stage for the head. It is evi- dent that such a system of staying is heavy, cumbersome, and complicated. It is also uncertain in its action, since the equal- ization of stresses depends on a nice adjustment of the mem- STAYING AND OTHER DETAILS. 235 bers of the system, which adjustment is liable to derangement from expansion of the fire-box. The girders or crown-bars are sometimes run lengthwise instead of transversely, but as the fire-box is longer than wide such an arrangement is inferior. To avoid the cumbersome method of staying the crown- sheet, which has just been described, the fire-box end of the boiler has been made flat on top, as shown by Fig. 95. The Fig. 95. crown-sheet can now be stayed to the outside shell by through- stays having nuts and copper washers at each end. The flat side sheets of the shell above the fire-box are also stayed by through-stays, and there are also three longitudinal through- stays in the corners of the shell over the fire-box where it protrudes beyond the barrel. This forms what is known as the Belpaire fire-box, from the inventor. Fig. 96 shows an attempt to combine the use of through- stays, like those of the Belpair fire-box, with a cylindrical top above the crown-sheet. It will be noted that the stays are neither perpendicular to the crown-sheet nor radial when they pierce the shell, and they must be subjected to an awkward side pull at both places. The locomotive-boiler represented by Plate III has a Belpair fire-box, and shows in addition some peculiarities of 236 STEAM-BOILERS. staying. Thus the flat end-plate above the fire-box has four T irons riveted to it. Each T iron is tied to the shell by two diagonal stays. Each stay has the usual double head at the T iron; the other end lies between, and is pinned to the flanges of pieces of plate that are riveted to the shell of the boiler. This arrangement is shown by the transverse and longitudinal sections through the fire-box. It will be noticed that the lower diagonal stays from the end-plate interfere with four transverse through-stays. These stays are STAYING AND OTHER DETAILS. 2 37 Sr^ M cut off and carry short vertical yokes, which are connected by two smaller rods, one above and one below the diagonal stays. The rings forming the barrel of the locomotive are made progressively smaller from the fire-box to the smoke-box; the slight taper toward the front end of the locomotive is found convenient in the design of the machine. Fig. 97 shows two ways of making the furnace-mouth of a locomotive-boiler. In one way the end- plate of the boiler-shell and the corre- sponding plate of the fire-box are flanged in the same direction, and are riveted out- side of the boiler. In the other case the two plates are flanged into the water-space and the overlapping edges are riveted. Jacobs-Shupert Fire-box. — This fire-box is made up of U-shaped sections of steel be- tween which are riveted stay sheets, as shown by Fig. 98. These stay sheets are perforated with radial slots through which the braces holding the heads pass. A boiler with this type of fire-box cannot be exploded through low water and the consequent overheating of the crown sheet. This was shown by tests made on June 20, 191 2, by Dr. W. F. M. Goss, an account of which appeared in Power, July 2d. Two full-sized locomotive boilers, designed for high-speed passenger service, were each subjected to severe low-water tests. Both boilers were identical in size and in design, except that one had a Jacobs-Shupert fire-box while the other had an ordinary radial stay fire-box. For the tests both boilers were mounted in a field some dis- tance apart, and were operated and observed from a bomb- proof hut a considerable distance away. Oil was used for fuel. The level of water in the boilers was read by means of a telescope. Fig. 97- 238 STEAM-BOILERS. Each boiler was in turn run at its maximum rating, about 1400 horse-power, and the water level allowed to drop gradually. The steam pressure in the Jacobs-Shupert boiler varied from 215 to 225 pounds during the first 27 minutes, then gradually dropped to 50 pounds at the end of the test. The test lasted about 55 minutes, during which time the water level dropped to more than 25 inches below the crown sheet. Examination showed that the fire-box was in good condition. The radial stay boiler was tested in the same manner. The pressure varied from 220 to 230 pounds and was 228 pounds at the time the boiler exploded. At the end of 23 minutes the .SECTION BACK FLUE SHEET Fig. 98. water level had fallen 14^ inches below the crown sheet when an explosion occurred. The crown sheet had pulled away from the stays. Marine Boiler. — The parts requiring staying in the Scotch boiler are the flat ends, the furnaces, and the combustion- chambers. The flat ends above the tubes are stayed by through- stays with nuts inside and with washers and nuts outside the plate. The boiler shown by Fig. 11, page 17, has two rows of through-stays — four in the upper and six in the lower row; two of the upper row pass through the fitting which carries the steam-nozzle. It is found in practice that the tube-sheets of a marine STAYING AND OTHER DETAILS. 2 39 boiler are not sufficiently stayed by plain tubes expanded into the sheets. It is customary to make a portion of the tubes thicker than the others, and to provide these thick tubes with thin nuts outside the tube-plates, so that they may act more effectively as stays. The thick tubes in Fig. n are indicated by heavy circles. Sometimes every other tube of each second row is made a thick tube; that is, something more than one fourth of the tubes are stay- tubes. Usually the number is fewer than this. Below the tubes the front plate is supported in part by the furnace-flues, and in part by through-stays running to the r~r 4) U=UJ tgST ^L> Fig. 99. combustion-chamber. There are two such stays above the furnaces and three below the furnaces in the middle of Fig. 11, each if inches in diameter. There are also two stays 2| inches in diameter, one at each side and above the furnaces. These last stays have one point of attachment to the front end-plate, but each has two points of attachment to the combustion- chamber. For this purpose the rear ends of the stays are bolted to V-shaped forgings, similar to that shown by Fig. 99. 240 STEAM-BOILERS. The furnace-flues are corrugated to stiffen them, and thus maintain their form under the external pressure to which they are subjected. The corrugations in Fig. n are made up of alternate convex and concave semicircles; other forms of cor- rugations and other methods of stiffening flues, together with a discussion of the strength of flues, will be given in the next chapter. The front ends of the furnace-flues in Fig. n are made as large as the outside of the corrugations; the rear ends are as small as the inside of the corrugations. Such an arrangement makes it easy to remove the furnaces without disturbing the other parts of the boiler and without destroy- ing the flues. The combustion-chambers of a Scotch boiler are made up of flat or curved plates subjected to external pressure, and must be stayed at frequent intervals to prevent collapsing. The sides and bottom of the combustion-chamber in Fig. n are stayed to the cylindrical shell of the boiler by screwed stay-bolts, spaced 7 inches on centres. The back of the com- bustion-chamber is stayed in like manner to the back end of the boiler, and thus both of these flat surfaces are secured. The plates used for making the combustion-chamber are thicker than those used for a locomotive fire-box, and consequently the stays are spaced wider and are larger in diameter. The top of the combustion-chamber is stayed by stay-bolts and bridges in a manner that suggests the crown-bar staying of a locomotive fire-box. The space is, however, narrower and the staying is less complicated. Complex Stays. — Sometimes the points to be connected by stays are so numerous that too many through-stays will be required if all points are stayed separately. Thus in Fig. 99 there is a tee-iron riveted to a flat plate, and supported at intervals, as indicated by the two bolts passing through it. Instead of using a through-stay for each bolt, the bolts are coupled by two V-shaped forgings, which forgings are bolted to a through-stay at the angle of the V. There is enough free- STAYING AND OTHER DETAILS. 241 dom of the bolts in their holes to give equal distribution of the pull on the through-stay. By an extension of this method several points may be supported by one stay-rod. Gusset-stays. — The flat ends of the Lancashire boiler, shown by Fig. 4, page 7, are secured to the cylindrical shell by gusset-stays; such a stay is shown more in detail by Fig. 100. A plate is sheared to the proper form, and is riveted H^^ Fig. 100. between two angle-irons along the edges that come against the shell and the flat end. The angle-irons in turn are riveted to the shell or to the flat plate. Gusset-stays have the advan- tages of simplicity and solidity. They interfere less with the accessibility of the boiler than through-stays or diagonal stays. Their chief defect is that they are very rigid and are apt to localize the springing of the flat plates, which is caused by unequal expansion of the furnace-flues and shell. Conse- quently, grooving near gusset-stays is very likely to be found in Lancashire and Cornish boilers. Gusset-stays are also used to some extent in marine boilers and in locomotive- boilers. Spherical Ends. — The ends of cylindrical boilers, or of steam-drums, are commonly curved to form a spherical sur- face, in which case they retain their form under internal pres- sure and do not need staying. If the radius of the spherical surface is equal to the diameter of the cylindrical surface, the same thickness of plates may be used for both. If the spherical surface has a longer radius, the thickness may be increased. Such dished heads of boilers and steam-drums are struck up 242 STEAM-BOILERS. between dies while at a flanging heat, and are then flanged to give a convenient riveting edge. Steam-domes are short, vertical cylinders of boiler-plate fastened on top of the shell of horizontal boilers. Plates II and III show steam-drums on locomotive-boilers. A steam- drum may be used to advantage when the steam-space is so shallow that there is danger that the ebullition may throw water into the pipe leading steam from the boiler. Locomo- tives usually have steam-domes, for not only is the steam- space shallow, but there is danger of splashing of the water in the boiler, especially if the track is rough or sharply curved. Stationary boilers ought to have steam-space enough with- out domes; marine boilers sometimes have domes, but they are less common than formerly. The additional steam-volume in a steam-dome is insignificant, so that a dome should not be added to increase steam-space of a boiler. The main objection to a steam-dome is that it weakens the boiler-shell, which must be cut away to form a junction with it. The shell may be reinforced, to make partial compensation, by a ring or flange of boiler-plate. Such a flange is clearly shown on Plate III, where the longitudinal seam of the ring carrying the dome is purposely placed at the top of the boiler. A similar arrangement is made for the dome on Plate II. Dry-pipe. — Any pipe inside of a boiler for the purpose of leading steam from the boiler is known as a dry-pipe; the pressure in such a pipe is frequently less than that of the steam in the boiler, consequently there is a tendency to dry the steam in the pipe. Dry-pipes are found in locomotive and marine boilers and sometimes in stationary boilers. The dry-pipe of a locomotive opens near the top of the dome. It runs vertically down till it is well below the shell of the barrel, then it runs horizontally through the steam-space and out through the smoke-box tube-sheet. The throttle-valve is at the inlet of the dry-pipe. It is controlled through a bell- STAYING AND OTHER DETAILS. 243 crank lever by a rod which enters the head of the boiler from the cab. The marine boiler shown by Fig. 11 has a dry-pipe which is joined to a steam-nozzle at the front end of the boiler. This dry-pipe is pierced with numerous longitudinal slits on the upper side; the sum of the area of such slits is seven-eighths of the area through the stop-valve in the steam-pipe. Steam-nozzle. — The stationary boiler shown on Plate I has a cast-iron steam-nozzle at each end. The steam-pipe leading steam from the boiler is bolted to the rear nozzle, and the safety-valves are placed above the front nozzle. Nozzles are often made of cast steel. The best are forged without welds from one piece of steel. Manholes. — A manhole should be large enough to allow a man to pass easily inside the boiler. That on Plate I is 15 inches long and 11 inches wide, and has its greatest dimen- sion across the boiler. The manhole there shown is placed inside the shell of the boiler. Both the ring and the cover are forged Irom steel without a weld. Fig. 101 shows a form of manhole that is placed outside the shell. Fig. ioi. This form is commonly made of cast iron, but manholes of similar form made of steel castings are used to some extent. The manhole-ring should be strong enough to give compen- sation for the plate cut away from the ring on which it is placed. The manhole-cover is placed inside the ring so that it is 244 STEAM-BOILERS. held up to its seat by the steam-pressure. The cover is drawn up to its seat by a bolt and removable yoke. Sometimes there are two bolts each with its yoke. A cast-iron manhole natu- rally has a cast-iron yoke, and a forged manhole has a wrought- iron or steel yoke. The manhole-cover is made steam-tight by a rubber gasket; the form of the cover and its seat are such that the gasket can- not be blown out by the pressure of the steam. Hand-holes are provided at various places on boilers to aid in washing out and cleaning. Thus the boiler on Plate I has a hand-hole near the bottom at each end, and there are several hand-holes near the foundation-ring of the vertical boiler, shown by Fig. 6. The hand-hole covers on Plate I are placed directly against the plate which is not reinforced. Each is held up by a bolt and a small yoke, which has a bearing on the plate completely round the hole. If the yoke has insuffi- cient bearing on the plate, the latter is liable to be damaged and leaks will occur. The hand-holes on the marine boiler shown by Fig. n are reinforced by small plates outside the boiler-heads. Washout Plugs. — Instead of hand-holes, washout plugs, 2 or 2§ inches in diameter, are provided near the corners of the foundation-ring of a locomotive fire-box. Such plugs are simply screwed into the outside plate of the boiler. Examples are shown by Plates II and III. Methods of Supporting Boilers. — Horizontal cylindrical boilers are commonly supported on the side walls of the brick setting, by brackets which are riveted to the shell of the boiler. Thus the. boiler shown on Plate I has two such brackets on each side; this boiler is about 16 feet long. If a boiler is as much as 18 feet long, three brackets are used. The front brackets rest directly on the brickwork, but the other brackets rest on iron rollers, to provide for the expansion of the boiler. The brackets are set so that the plane of support is a little above the middle of the boiler. STAYING AND OTHER DETAILS. 2 45 Fig. 102 shows a common form of bracket, made of cast iron, which is riveted to the shell above the flange of the bracket. $x O O o o o oo o oo — 4-f ooo Fig. 102. Fig. 103. A better form with rivets both above and below the flange is shown by Fig. 103. Fig. 104. Fig. 105. A detachable bracket, like that shown by Figs. 104 and 105, may be used when the boiler must be put into a building through Fig. 106. Fig. 107. a small aperture. Fig. 104 gives an end and side elevation and plan of the body of the bracket; Fig. 105 gives a side elevation 246 STEAM-BOILERS. and plan, with section, of the flange. After the boiler is in place the flange is thrust up into the dovetail groove in the body of the bracket. The pressure of the flange against the dovetail groove, intensified by the wedging action of the inclined sides, Fig. 108. [ Co; "0" Fig. 109. / ^*^ Fig. hi. Fig. 1 10. Fig. 112. is liable to be excessive. To overcome this difficulty the bracket shown by Figs. 106 and 107 has been used. Fig. 106 shows the end elevation and a view from below, of a casting which is riveted to the shell. Fig. 107 shows the same views of a casting which catches into the hollow under Fig. 106 and bears at the STAYIXG AND OTHER DETAILS. 247 top against this same casting, the rivets bolting it to the shell being countersunk. Horizontal boilers, and especially plain cylindrical boilers, are sometimes hung from a support above the boiler, as shown by Figs. 108, 109, and no. Fig. 108 shows a lug, made of boiler-plate, riveted to the shell of the boiler. The lugs are placed in pairs and the boiler is hung from these lugs by bolts that are supported between trans- & ± Sid •ygfgiaaitsfrg (2) K3 Fig. 113. verse beams over the boiler. Fig. 109 differs in substituting a loop for the lug. Fig. no shows a method of suspension with two short pieces of plate above the lug, to give some flexibility and provide for expansion. Figs, in and 112 show methods of suspending a boiler from the top. These methods are proper only for boilers which have a small diameter. Whenever possible it is better to suspend a boiler rather than to support it by brackets. The top of a bracket comes 3 or 4 inches below the longitudinal joint. If, due to any settlement of the brickwork, the bracket bears near its outer edge, there is a bending moment of considerable magnitude transmitted to the shell. This tendency to pull the shell out just at the bottom of the 248 STEAM-BOILERS. bracket and to push the shell in at the top of the bracket produces very severe strains in boilers of large diameter and of great weight. Boilers over 20 feet long require three sets of supports. If brackets are used it is probable that the middle set will either take more or less than one third the weight. The proper way to support such a boiler is as shown in Fig. 113. Three lugs, like Figs. 108 and 109, or preferably like Fig. no, are fastened to each side of the boiler. Rods from the front lugs pass up between two I-beams, resting on piers built up above the side walls of the setting, and fasten to the beams, as shown. Rods from the middle and rear lugs are attached on each side to an equalizer, which is in turn hung from I-beams in the same way as at the front. As these connections are free to turn, the load is always distributed in the same proportion between the lugs. CHAPTER VIII. STRENGTH OF BOILERS. The determination of the thickness of boiler-plates, the size of stays, and other elements affecting the strength of a boiler, involves a knowledge of the properties of the materials used and a knowledge of the methods of calculating stresses in the several members of the boiler. A brief statement of these subjects, as applied to boilers, will be given here. Materials Used. — The materials used for making boilers are mild steel, wrought iron, cast iron, malleable iron, copper, bronze, and brass. In order to insure that materials used for making a boiler shall have the proper qualities, it is customary to require that specimens shall be tested in a testing-machine, and that they shall have certain definite properties, such as ultimate tensile strength, elastic limit, and contraction of area at fracture. In order that these properties shall be properly developed, it is essential that specimens shall be of right size and shape, and that the testing shall proceed in a correct method. Testing-machines. — The frame of a testing-machine carries two heads, between which the test-piece is placed, and to which it is fastened by wedges or other clamping devices. One head, called the straining-head, is drawn by screws or by a hydraulic piston, and pulls on the test-piece. The other head, called the weighing-head, transmits the pull to some weighing device. Boiler materials are commonly tested in a machine which has the pull applied by screws, driven through gearing by hand or by power; the pull is weighed by a system of levers and knife-edges, arranged like those of a platform 249 250 STEAM-BOILERS. scale. Such a machine should be able to exert a pull of fifty or a hundred thousand pounds. Testing-machines that give a direct tension are commonly arranged to give also a direct compression. There are also machines arranged to give transverse loads, like the load applied to a beam. Forms of Test-pieces. — A test-piece of boiler-plate should be at least 1^ inches wide, planed on both edges, and should be about two feet long. A piece which is less than eighteen inches long is not fit for testing. Test-pieces eighteen inches to two feet long may be cut directly from bars or rods for making stays or bolts. If a. rod is so large that the available testing-machine will not break it, it is of course possible to turn it down to a smaller diameter, but it would be preferable to send such a rod to a machine that is powerful enough to break it at full size. Test-pieces of cast metal may be cast in the form of rectangular bars, which should be at least one inch wide and an inch thick. If the bars are rough or irregular it may be necessary to plane the edges, or perhaps to plane them all over. Test-pieces of boiler-plate should be cut from the edge of at least one plate of each lot of plates. Sometimes speci- fications require pieces from each plate used for a given boiler. Pieces should be cut from both the side and the end of a plate, for there is a grain developed by rolling either iron or steel boiler-plate, and tests should be made both with the grain and across the grain. Very hard material may require shoulders on the test- pieces to enable the testing-machine to get a proper hold. But iron or steel that is so hard as to require shoulders is much too hard for boiler-making; consequently there will be no reason for providing test-pieces of boiler iron or steel with shoulders. If test-pieces have shoulders, they should be at least ten inches apart. STRENGTH OF BOILERS. 25 1 Methods of Testing. Fig. ii4- -A test-piece of proper length is first measured to determine the breadth and thickness or else the diameter, as the case may be. A length of eight inches is laid off near the middle of the test- piece, and clamps for measuring the stretch of the piece are ap- plied at the ends of this eight-inch length, as shown by Fig. 114. The piece is then secured in the machine and a load is applied. The distance between the clamps is now measured by a micrometer caliper with an extension-piece. The method of doing this is to place the head of the micrometer against a point on the flange of the clamp at one end, and adjust the length of the micrometer so that it shall just touch the cor- responding point on the other clamp. A little practice will en- able the observer to measure to one or two ten-thousandths of an inch. As the load is increased the test-piece stretches, the in- crease of length being proportion- al to the increase of the load. The stretch is measured on both sides of the test-piece for each increase of load applied. If the test-piece is not straight or exactly aligned in the machine there may be some irregularity in the stretching at 252 STEA M -BOILERS . first, but after a considerable load is applied the piece stretches uniformly until about half the maximum load that the piece can carry has been applied. During the progress of the test a point is reached beyond which the stretch in- creases more rapidly than the load ; this is known as the elastic limit. After the elastic limit is reached the clamps are removed and the test proceeds without them, but at about the same rate of loading. A load is soon reached which the piece cannot permanently endure, shown by the fact that the scale- beam will fall though the straining-head remains at rest. This is called the yield point. The piece may, however, carry a considerably higher load if the straining-head is kept moving to take up the stretch. Finally, the piece begins to draw down rapidly, somewhere near the middle of its length, and when the piece breaks, the fracture shows about half the area of the piece before testing. Hard materials may draw down little, or not at all; the limit of elasticity may approach the strength of the material. The jaws or wedges of the testing-machine interfere with the stretching or flow of the material gripped by them. The influence of the wedges may extend two or three inches beyond their edge in the testing of boiler-plate. If a piece has shoulders they will have a like effect. Consequently the points at which a clamp is secured to a test-piece should be two or three inches from a shoulder or from the wedges of the machine. The wedges of a machine of a capacity of fifty or a hundred thousand pounds are four or five inches long. They will grip on three inches at the end of a test-piece, but not on less. The test-piece must have eight inches for measuring stretch, two or three inches at each end for flow, and three to five inches at each end in the wedges. Conse- quently the piece must be eighteen or twenty-four inches long. The method just described is slow and laborious, and STRENGTH OF BOILERS. 253 requires two observers — one to measure stretch and one to weigh. For commercial work an automatic device is often used which registers loads and corresponding elongations. Such devices commonly record the yield point instead of the elastic limit; these two points should never be confused. Stress. — The number of pounds of force per square inch is called the stress. The stress is uniform on a piece under direct tension, and is equal to the load divided by the area of transverse section. Stress may be expressed in other units, such as tons per square foot or kilograms per square milli- meter. Strain. — The stretch of a piece, under direct tension, per unit of length is called the strain. If the original length is / a and the stretch is a, then the strain is — = s. The Limit of Elasticity is the limiting stress beyond which the strain increases more rapidly than the stress. The limit is not perfectly definite, and can be determined approxi- mately only. A load greater than the elastic limit will pro- duce an appreciable permanent elongation after the load is removed. A stress less than the elastic limit will produce only a slight permanent elongation; such elongation may be inappreciable. Yield Point. — The stress at which the scale-beam of a testing-machine will fall while the straining-head is at rest is called the stretch limit. Ultimate Strength. — The maximum stress that a piece will endure in a testing-machine is called the ultimate strength of the material. The strength depends somewhat on the rate of testing. The more rapidly the testing proceeds the higher will be the apparent strength. It is desirable that some standard rate of testing may be adopted by engineers so that results may be strictly comparable. The Modulus of Elasticity is the result obtained by dividing the stress by the strain. If the stress is/ pounds 254 STEAM-BOILERS. per square inch and the strain is s per inch, then the modulus of elasticity is e = £ s Reduction of Area. — The area of the test-piece of boiler- plate at the rupture is much less than that of the piece before testing. This reduction is important, as it shows the ductility of the metal, and its ability to change shape without too much distress under the influence of unequal expansion of different members of a boiler. Ultimate Elongation. — After the test-piece is broken the two parts are laid down in a straight line with the broken ends in contact, and the length of the distance between the points of attachments of the measuring clamps is measured. The ratio of the elongation to the original length (eight inches) is called the ultimate elongation, The ultimate elon- gation is generally given in per cent. This is important, for the same reason given for the contraction of area. Compression. — The preceding definitions are given for tension only, for sake of simplicity and brevity; they may be applied to pieces in direct compression if the term stretch or elongation is replaced by compression. Shearing. — Stresses have thus far been considered to be at right angles to the sections of the pieces to which they are applied, and produce either tension or compression at that section. A stress that is not at right angles to a section will tend to produce sliding at that section. A stress that is parallel to a section will tend to produce sliding only, and is called a shearing-stress. If a shearing-stress is uniformly dis- tributed, its intensity may be found by dividing the total force or load by the area of the section. The rivets of a riveted seam are subjected to a shearing- stress. STRENGTH OF BOILERS. 255 Steel Specifications. — At the present time all boiler-plates are made of steel. The American standard specifications for steel of the Ameri- can Society of Testing Materials are universally adopted in the United States. That part of the specifications relating to boiler and rivet steel will be quoted in full. OPEN-HEARTH BOILER-PLATE AND RIVET STEEL. Adopted Aug. 16, 1909. Process of Manufacture. 1. Steel shall be made by the open-hearth process. 2. There shall be three classes of open-hearth boiler-plate and rivet steel; namely, flange or boiler steel, fire-box steel, and extra soft steel, which shall conform to the following limits in chemical and physical properties. Flange or Fire-box Extra Soft Boiler Steel, Steel, Steel, Per Cent. Per Cent. Per Cent. tju u l 11 * „ „„ j ( Acid 0.06 Acid 0.04 Acid 0.04 Phosphorus shall not exceed . . . < -r, ■ ^ . ^ ^ . ^ ^ I Basic 0.04 Basic 0.03 Basic 0.04 Sulphur shall not exceed 0.05 0.04 0.04 Manganese 0.30 to 0.60 0.30 to 0.50 0.30 to 0.50 Tensile strength, lbs. per sq. in. 55,0001065,000 52,000 to 62,000 45,0001055,000 Yield-point, in lbs. per sq. in., shall be not less than \ T. S. \ T. S. \ T. S. Elongation, per cent in 8 inches, shall be not less than 1,500,000 1,500,000 1,500,000 T. S. T. S. T. S. (need not exceed 30%.) Quenchbend'. '. '. '. '. \ '. '. '. '. '. '. \ \ \ \ \ l8 °° flat *° flat ^° ^ ' (a) Yield- point. — For the purposes of these specifications the yield-point shall be determined by the careful observation of the drop of the beam or halt in the gauge of the testing machine. 3. Boiler Rivet Steel. — Steel for boiler rivets shall be of the extra soft class as specified in paragraph 2. 4. Modifications in Elongation for Thin and Thick Material. — For material less than 5/16 inch and more than 3/4 inch in thickness the following modifications shall be made in the re- quirements for elongation. (b) For each increase of 1/8 inch in thickness above 3/4 256 STEAM-BOILERS. inch a deduction of i shall be made from the specified percent- age of elongation. (c) For each decrease of 1/16 inch in thickness below 5/16 inch a deduction of 2J shall be made from the specified percent- age of elongation. 5. Chemical Determinations. — In order to determine if the material conforms to the chemical limitations prescribed in paragraph 2 herein, analysis shall be made by the manufacturer from a test ingot taken at the time of pouring of each melt of steel, and a correct copy of such analysis shall be furnished to the engineer or his inspector. A check analysis may be made by the purchaser or his representative from a broken tensile test- specimen representing each heat of flange or extra soft steel on an order, and for each plate as rolled of fire-box steel, in which cases an excess of 25 per cent above the required limits in phos- phorus and sulphur will be allowed. 6. Test Specimen for Tensile Test.— The standard tensile test specimen of 8 inch gauged length shall be used to deter- mine the physical properties specified in paragraphs 2 and 3. The standard shape of the tensile test specimen for sheared plates shall be as shown in Fig. 115. WAtoutS^ §M (/j, representing the stress by s. Consequently we shall have 2 X 3.i4i6rAy = 3.1416^/. pr •'• s = 2t' It is evident that the stress from the end pull is half the stress on the section at the side of a cylinder, and conse- quently a cylinder made of homogeneous material without joints will always be ruptured longitudinally. It is also evident that the stress from the end pull will be the same if the end of the cylinder is closed by a spherical surface, or by any other figure, instead of a flat plate. Thin Hollow Sphere- — A section taken through the cen- tre of a sphere is in the same condition as a transverse sec- tion of a thin cylinder, and will be subjected to the same stress, if the sphere has the same thickness and is subjected to the same internal pressure. Formerly the ends of plain cylindrical boilers were made hemispherical, but such ends are difficult to make and are needlessly strong if of the same thickness as the cylindrical shell. It is now the practice to curve such ends to a less radius than that of the cylindrical shell. If the radius of the head is equal to the diameter of the shell, then with the same thickness of plate the stress will be the same per square inch, provided there are no seams in head or shell. The heads usually do not have a seam, and the shells always have a seam; the margin of strength in the head, when the same thickness of plate is used, under this condition may be offset against the possible injury done to the head in shaping it. STRENGTH OF BOILERS. 269 The construction known as a bumped-np head has the edge flanged into a cylindrical form to make a joint with the shell, and to avoid the awkward stress that would be thrown onto the cylindrical shell if the true cylindrical and spherical surfaces were allowed to intersect. If it is inconvenient to curve the head to a radius as small as the diameter of the cylinder, then a thicker plate may be used, with a longer radius. Rivets. — The plates of a boiler are joined at the edges by rivets; rivets are also used in stays and other members. The usual form of rivets is shown by Fig. 118. If the diameter of the rivet is D> then the proportions may be g3[ A D ■4; R D — 1.2 C D 0.7 D = 3/4. The length of the rivet will depend on the number and thickness of the plates through which it is to pass. The rivet represented by Fig. 118 has a pan head. Of the rivets shown by Fig. 119, A, B, and C have pan heads, and D and E have round or hemispherical heads. The form of the point of a rivet will depend on the way in which the rivet is driven and on the shape of the tools or dies used for forming the point. The rivet A has a straight 270 STEAM-BOILERS. conical point ; this is the only form that can be made when the rivet is driven by hand with flat-faced hammers. The rivet B has the head formed by a die or snap. The rivet is driven by a few heavy blows of a hammer, and the head is roughly formed ; then a die or snap is placed on the point and driven to form the point by a sledge-hammer. C shows a rounded conical point commonly used for machine-driven rivets. The heads of such rivets may have a similar form. D represents the usual form of countersunk rivets: the hemispherical head is not a peculiarity of such rivets; it is Fig. 119. occasionally used with any form of point. The rivet E has some fulness or projection at the point beyond the counter- sink. After a rivet is driven, both ends are called heads; the distinction of heads and points is made here for convenience in description. The straight conical form A is liable to be too flat and weak. Its height should be three-fourths the diameter of the rivet. When rivet-holes are punched in plates they are slightly conical, as shown by B,Fig. 119, which shows the two smaller ends of the rivet-holes placed together to facilitate the proper filling of the hole by the rivets. The other rivet-holes are straight, as they would be if drilled. STRENGTH OF BOILERS. 271 Riveted Joints. — The proportions of riveted joints, such as diameter and pitch of rivets, are determined in part by practice and in part by a method of calculation to be explained later. In practice it is found necessary to limit the pitch of the rivets, and consequently the diameter, to be used w.ith a given thickness of plate, in order that the joint may be made tight by calking. This limitation frequently makes the joint weaker than it otherwise would be. The edges of plates are either lapped over and rivetec 1 , or brought edge to edge and then joined by a cover-plate which is riveted to each of the two plates. The first method makes a lap-joint and the second a butt-joint. Fig. 120 shows a single-riveted lap-joint and Figs. 121 and 122 show double-riveted lap-joints. The rivets in Fig. 121 are said to be staggered; the form shown by Fig. 122 is called chain- riveting. Butt-joints with two cover-plates are shown by Figs. 125, 126, and 127. The outer cover-plate is narrow, with rivets placed close enough together to provide for sound calking. The inner plate is wider, and as its edges are not calked they may have a row of more widely spaced rivets. These joints, and those shown by Figs. 123 and 124, are designed with the view of securing more strength than can be had with a plain lap-joint like Fig. 121, or than can be had with a butt-joint with cover- plates of equal width. Efficiency of a Riveted Joint. — The strength of a riveted joint is always less than that of the solid plate, because some of the plate is cut away by the rivets. This is very evident in the case of a single-riveted joint, such as that shown by Fig. 120. It will be found to be true for more complicated joints, such as those shown by Figs. 125, 126, and 127. The efficiency of a riveted joint is the ratio of the strength of the joint to the strength of the solid plate. The strength and efficiency of a given riveted joint can be 272 STEAM-BOILERS. properly determined only by direct test on full-sized speci- mens, which have considerable width. Tests on narrow specimens are liable to be misleading. Tests on boiler-joints are expensive, and can be made only on large and power- ful testing-machines. Tests have been made on behalf of the United States Navy Department at the Watertown Arsenal on a large number of single-riveted joints, on a con- siderable number of double-riveted joints, and on a few special joints. A few tests have been made elsewhere on full- sized joints. These tests give us important information that can be used in designing joints for boilers, but we cannot in general select a joint directly from the tests. Methods of Failure. — A riveted joint may fail in one of several methods, depending on the proportions, such as thick- ness of plate and the diameter and pitch of the rivets. This can be clearly seen in case of a single-riveted joint like that shown by Fig. 120. Such a joint may fail: (1) By tearing the plate at the reduced section between the rivets. If the rivets have the diameter d and the pitch /, then the ratio of the area of the reduced section to that of the whole plate is i> — d P (2) By shearing the rivets. (3) By crushing the plate or the rivets at the surface where they are in contact. (4) By cracking the plate between the rivet-hole and the edge of the plate, or by some method of failure due to in- sufficient lap. A riveted joint never fails by this method in practice, because the lap can always be made sufficient. The failure of more complicated joints may occur in various methods, which will be considered In connection with the calculation of some special joints. STRENGTH OF BOILERS. 273 Drilled or Punched Plates. — In the better class of boiler- shops it is now the practice to drill rivet-holes in plates after the plates are in place, so that the holes are sure to be fair. Sometimes the holes are punched to a smaller diameter and then drilled out to the final size after the plates are in place. The result is the same as though the holes were drilled in the first place, as the metal near the hole, which was injured in punching, is all removed. The metal remaining between drilled holes does not have its properties changed by the drilling. On the contrary, the metal between punched holes is always injured more or less. In general, soft ductile metal is injured less than hard metal, and further, soft-steel plates are injured less than wrought-iron plates. When boiler-plates are punched and then rolled to form cylindrical shells, some of the holes are liable to come unfair, so that a rivet cannot be passed through. In such cases the holes should be drilled to a larger size, and a rivet of corre- sponding diameter should be substituted. Careless or reck- less workmen sometimes drive in a drift-pin, and stretch or distort the unfair holes so that a rivet can be forced through. The plate is liable to be severely injured by such treatment, and the rivet cannot properly fill the rivet-holes. Unfortu- nately it is difficult or impossible to detect bad work of this kind after the rivets are driven. Tearing. — The metal between the rivet-holes in a riveted joint cannot stretch as a proper test-piece does in the testing- machine, and consequently it shows a greater tensile strength than a test-piece from the same plate. Some tests on single or double riveted joints with small pitches show an excess of strength from this cause, amounting to ten per cent or more. The excess appears to be uncertain and irregular, so that if any allowance is made for it, it should be by a skilled designer after a careful study of all the tests that have been made. Ordinarily it will be safer to use the tensile strength shown by test-pieces in the testing-machine, especially for joints like Fig. 12.-2, which have a large pitch for some of the rivets. 274 STEAM-BOILERS. Shearing". — In general it is fair to assume the shearing strength of rivets of iron or steel to be between T V and T % of the tensile strength of the metal from which the rivets are made. Crushing. — It is customary to assume that the pull on a riveted joint is evenly distributed among the rivets in the joint, and to divide the total pull by the number of rivets to find the shearing or crushing force acting on one rivet. It is further customary to assume that the intensity of the crushing force on the surface where the rivet bears on the plate, may be found by dividing the total force on one rivet, by the product of the diameter of a rivet and the thickness of the plate. The crushing-stress on rivets in joints that fail by crushing is found by experiment to be high and irregular. In some cases it has amounted to 150,000 pounds per square inch; in a few tests it is less than 85,000 pounds. It is probable that 95,000 pounds may be used with safety in calculating riveted joints for boilers. Now the stress on the bearing-surface will seldom be so much as one third the ultimate strength, even during a hydraulic test of a boiler, and it is not probable that a joint will be injured in this way unless the stress approaches the ultimate strength. Friction of Riveted Joints. — It is evident that there must be considerable friction between plates that are firmly clamped together by rivets driven hot. It has been proposed to take some account of this friction in calculating riveted joints, or even to allow the friction to be the determining element in proportioning riveted joints. Such a method is shown by experiment to be unsafe, for slipping takes place at all loads, beginning at loads that are much smaller than a safe load, and the effect of friction disappears before a breaking load is reached. Lap. — The distance from the centre of the rivet-hole to the edge of the plate is called the lap. The lap is usually once and a half the diameter of the rivet, a proportion that appears to be satisfactory. STRENGTH OF BOILERS. 275 Diameter of Rivet. — The minimum diameter of punched holes is determined by the consideration that the punch should not be broken. In the ordinary methods of punching boiler-plates the diameter of the punch should at least be as much as the thickness of the plate. It very commonly is once and a half the thickness of the plate. Drilled rivet-holes may have any diameter. They never have a diameter less than the thickness of the plate. The maximum diameter of rivet to be used with any kind of riveted joint will in general be determined by the considera- tion that the tendency to crush the plate in front of the rivet should not be greater than the shearing strength of the rivet. The maximum diameter thus found is liable to give too large a pitch. Pitch.— The maximum pitch for a given plate along a calked edge should be determined by the consideration that the plate should be held up rigidly enough to make a tight joint without excessive calking. The pitch of rivets, like those in the outer row of the joint shown by Fig. 127, need not be governed by this rule. There does not appear to be any explicit rule deduced either from practice or experiment for determining the proper pitch of rivets. Single-riveted Lap-joint. — In the joint shown by Fig. 120 let the thickness of the plate be t, the diameter of the rivet d, and the pitch p y all in inches. Let the tearing strength of the plate be f t — 55,000, the shearing strength be f s = 45,000, and the resistance to crushing be ft — 95> 000 > a ^ f° r milci steel. Assume the proportions Fig. 120. ^=15/16, t = y/\6, p — 2\. It will be sufficient to consider a portion of the plate having a width equal to the pitch. The failure of such a strip may occur in one of three ways: .1 2j6 STEAM-BOILERS. 72 ist. Shearing one rivet. The area to be sheared is — x lAldd* or — . The resistance to shearing is found by multi- 4 plying this area by the shearing strength of the rivet : nd % x n X 15 X 15 X 45, 000 T" /s = 4X163T16- = 3I '° 63 ' 2d. Tearing plate between rivets. The effective width of the strip under consideration, allowing for the rivet-hole, is p — d, and the thickness of the plate is t ; the resistance to tearing is {p - d)tf t = (2}.- f£) T V X 55,ooo = 31,580. 3d. Crushing of rivet or plate. The conventional method is to assume the effective bearing area to be equivalent to the diameter of the rivet multiplied by the thickness of the plate. The resistance is considered to be dt fc = H X T \ X 95,000 = 38,970. The strength of a strip of the plate 2\ inches wide is 2 i X T 7 6 X 55,ooo= 54, HO. The calculated resistance to shearing is less than the resistance to tearing or compression. The apparent effi- ciency of the joint is 31,063 100 X = 57-4 P er cent - ^ 54,140 If it De assumed that the resistance to tearing of the section between rivets will have an excess of ten per cent over the resistance of a piece in a testing-machine, then the resistance to tearing between rivets will appear to be 34,740 This figure is not far from the resistance to shearing, though still inferior. If it be further assumed that the whole plate STRENGTH OF BOILERS. 277 outside of the joint will show a tearing strength of only 55,000 pounds per square inch, the efficiency of the joint will appear to be more than five per cent greater than that given above. It is probably wise to ignore the excess of strength due to the fact that the plate between the rivets will not draw down for reasons that have already been stated at length. Double-riveted Lap-joint. — The rivets in this joint may be staggered as shown by Fig. 121, or chain-riveting may be Fig. 121. used as in Fig. 122. If the rivets are staggered and the two rows are too near together, it is possible that the plate may Fig. 122. tear down from a rivet in one row to the nearest rivet in the next row, and thus have, after tearing, a jagged edge. With the usual proportions such a failure will not occur, but the plate will tear between rivets in the same row, if it fails by 278 STEAM-BOILERS. tearing. The calculation for efficiency will consequently be the same for both methods of riveting. Let the dimensions be t = ;/i6, d = 13/16, / = 2j. The joint may fail in one of three ways: 1st. Shearing two rivets. The assumed strip having a width equal to the pitch will be held by two rivets ; this is apparent at once for chain-riveting. For staggered rivets such a strip will contain one whole rivet and half of two others, so that the same rule holds. The resistance of two rivets to shearing will be 2nd 2 . - ^ ■ f g = 46,660. 4 2d. Tearing between two rivets. The resistance is {p — d)tf t = 40,600 3d. Crushing in front of rivets. Just as for shearing, we have here the resistance at two rivets equal to 2dtf= 67,540. The strength of the plate for a width of the pitch is ptf = 60,160. The plate will apparently fail by tearing, and the effi- ciency of the joint will be 40,600 ^ 100 X 7 ^ - = 67.5 per cent. 60,160 The increase of efficiency of the double-riveted lap-joint over the single-riveted joint is clearly due to reducing the diameter of the rivet and increasing the pitch. A further increase of efficiency could be obtained by using three rows of rivets ; this, however, is practicable only for thick plates, as we are liable to get too wide a pitch for sound calking. Single-riveted Lap-joint, Inside Cover-plate — In this joint the plates are lapped and joined by a single row of rivets; STRENGTH OF BOILERS. 270 and a plate is worked inside and riveted through the shell with a single row of rivets, which are spaced twice as far apart as the rivets in the lap. In making up the joint all three rows of rivets may be driven at the same time. The lapped joint only is calked ; the pitch of rivets through the lap must con- sequently be small enough to give sound calking. The outer rows of rivets are not controlled by this rule. We will here consider a strip having the width a, Fig. 123, equal to twice the pitch of the rivets in the lap. Such a strip will be held by two rivets in the lap and by one rivet in an outer row. Assume the following dimensions: Thickness of shell and of cover-plate, t = 5/16. Diameter of rivets (iron), d — 3/4. Pitch of rivets in lap, p = 1 j. Pitch of outer rows of rivets, P— 3J. Shearing resistance of iron rivets per square inch or f s = 38,000 lbs. The joint may fail in one of five ways : ( * > JO c |> c > lope )O0QP © c )-«-( . P y ) — 1 Fig. 123. 1st. Tearing between outer row of rivets. The resistance is (P-d)tf t - 47,270. 280 steam-boilers, 2d. Tearing between inner row of rivets, and shearing outer row of rivets. The resistance is (/>- 2d)tf t + *ff, = 5i, I5 o. 4 Since the rivets are iron, f = 38,000. 3d. Shearing three rivets. The resistance is ^-7-/5=50,350. 4 4th. Crushing in front of three rivets. The resistance is $tdf e = 66,800. 5 th. Tearing at inner row of rivets and crushing in front of one rivet in outer row. The resistance is {P -2d)tf + tdf = $6,641. The strength of a strip of plate 3^ inches wide is I tf t = 60, 160. The least resistance is offered by the first method, giving for the efriciency 47,270 IOOX 6o7T6o := 7 8 - 6 P ercent - If the inside cover-plate is thinner than the shell, addi- tional complication will be introduced into the calculations for resistance. Double-riveted Lap-joint with Inside Cover-plate. — The arrangement of this joint is shown by Fig. 124. Assume the dimensions: Thickness of shell and of cover-plate, / = 7/16. Diameter of rivets (steel), d = 3/4. Pitch of rivets in lap, 2\\. Pitch of outer rows of rivets, P = 4. STRENGTH OF BOILERS. The methods of failure are: 1st. Tearing at outer row of rivets. Resistance (P - d)tf t = 78,210. 2d. Shearing four rivets. 47td* Resistance — - f s = 79,56c. 281 1 J I i— < |> o 6 m fo°J%°o°o M ) c^p-^ © [1 1 __ U^ Fig. 124. 3d. Tearing at inner row and shearing outer row of rivets. A strip having the width of the pitch of the outer row of rivets will be weakened at the rivets in the lap to the extent of one rivet-hole and half another rivet-hole. The resist- ance is Ttd 2 (P-Hd)tf t + —f 8 = 89,080. 4th. Crushing in front of four rivets. Resistance \tdf — 124,640. 5 th. Tearing at inner row of rivets and crushing in front of one rivet. Resistance (P- \\d)tf t + tdf = 100,350. 282 STEAM-BOILERS. Strength of strip 4 inches wide, Ptf t =9 6 >2 50. T-/V • 78,2IO Efficiency = IOO X 6 =81.3 per cent. Double-riveted Butt-joint. — The joint shown by Fig. 125 has a cover-plate inside and another, narrower, outside. There are two rows of rivets on each side of the joint. The inner rows are nearer together and pass through both cover- plates. Fig. 125. The outer row of rivets are wider apart and pass through the inner cover-plate only. The dimensions assumed are: Thickness of the plate and of both cover-plates, t = 7/16. Diameter of rivets (iron), 15/16 inch. Pitch of inner row of rivets, 2f. Pitch of outer row of rivets, 5J. There are five ways in which the joint may fail : 1st. Tearing at outer row of rivets. The resistance is (P-d)tf t = 103,770. STRENGTH OF BOILERS. 283 2d. Shearing two rivets in double shear and one in single shear. If the plate pulls out from between the cover-plates shearing off the rivets, then the rivets in the inner row must be sheared through on both sides of the plate, or they are in double shear. The outer row of rivets are sheared at only one place. There are, consequently, five sections of rivets to be sheared for a strip as wide as the larger pitch. The resist- ance is 5nd> — — /,= 131,100. 4 3d. Tearing at inner roiv of rivets and shearing one of the outer row of rivets. The resistance is 72 {P-2d)tf t +—f,= 107,430. 4th. Crushing in front of three rivets. The resistance is $tdf e — 116,880. 5 th. Crushing in front of two rivets and shearing one rivet. The resistance is 7Td* 2tdf + — /, = 104, 140. 4 The strength of a strip 5J inches wide is Si X T \ Xft= 126,560. The efficiency is 103,770 100 — 7 — 7 r- = 82 per cent. 126,560 r Triple-riveted Butt-joint. — The joint shown by Fig. 126 has three rows of rivets on each side. Two rows pass through both cover-plates, and the third or outer row passes through the inner cover-plate only. 284 STEAM-BOILERS. The dimensions are: Thickness of shell, t = 7/16. Thickness of both cover-plates, t c = 3/8. Diameter of rivets (steel), d = 15/16. Pitch, inner rows, / = 3§. Pitch, outer row, P= J\. Fig. 126. The joint may fail in one of five ways : 1st. Tearing at outer row of rivets. The resistance is (P-d)tf t = 151,890. 2d. Shearing four rivets in double shear and one in single shear. The resistance is Qnd* f s = 279,450. • 3d. By tearing at middle row of rivets {where the pitch is 3-f inches) and shearing one rivet. The resistance is (P- 2d)tf + 7t —f i = 160,340. STRENGTH OF BOILERS. 285 4th. By crushing in front of four rivets and shearing one rivet. The resistance is n d* 4dtf c + / = 186,830. 4 5th. By crushing in front of five rivets. Four of these rivets pass through both cover-plates and will crush at the shell-plate. The fifth rivet passes through the inner cover- plate only, and will crush at that plate, since the cover-plates are thinner than the shell-plate. The resistance is A dtf + dt c f c = 189,170. The strength of a strip of plate 7\ inches wide is Ptf= 174,370. The efficiency is 151,890 100 X — = 87 per cent. Quadruple Riveted Butt-joints with two cover-plates. Fi^.127 shows such a joint. Thickness of shell, t = iJ2 inch. Thickness of both cover-plates, ^ = 7/16 inch Diameter of rivets (steel), J =15/16 inch. Pitch of inner row, p = 2> I inches. Pitch of second row, p = $\ inches. Pitch of third row, T = jh inches. Pitch of outer row, P = i5 inches. The joint may fail in one of eight ways: 1st. Tearing at the outer row of rivets. The resistance is (P -d)tf t = 386,700. 2d. Tearing at the third row and shearing one rivet in the outer row. The resistance is ltd 2 (P — 2d)tf t -\ f s = 400,410. 286 STEAM-BOILERS. 3d. Tearing at the second row of rivets and shearing three rivets. The resistance is nd 2 (P-4^)^+3-T/ s = 4 ° 2,56a & & ' > Fig. 127. 4th. Double shearing eight rivets and single shearing three. The resistance is nd* 19— -/, = 590,200. 5/A. Crushing in front of eight rivets and single shearing three. The resistance is izd 2 ■ &dtf c + 3— -/, = 449M40. STRENGTH OF BOILERS. 287 6th. Crushing in front of eleven rivets. The resistance is I ld// c = 489,840. jth. Tearing at the third row of rivets and crushing in front of one rivet in the outer row. The resistance is (P- 2 d)tft + dtf c = 413,880. 8th. Tearing at the second row of rivets and crushing in front of three rivets. The resistance is (P - 4d) tf + 2,dtf c = 442,960. The strength of the solid plate is Ptf t = 412,500. The efficiency is '- = 93.7 per cent. Designing Riveted Joints. — One element of the design of a riveted joint is to secure as high an efficiency for the joint as is consistent with other requirements, such as a proper pitch for calking. A consideration of the example of a single-riveted lap- joint will show that the efficiency can be improved by increas- ing the diameter of the rivet and by increasing the pitch. In the first place, since the joint will fail by tearing between the rivets, simply increasing the pitch with the same size of rivet will give a greater efficiency. If the pitch is increased till the rivet fails, the failure will be by shearing. Now the resistance to crushing is represented by dtf c , while the resistance to shearing is represented by nd % 2 88 STEAM-BOILERS. that is, the resistance to crushing increases proportionally as the diameter, while the resistance to shearing increases as the square of the diameter. The shearing resistance increases the more rapidly, and can be made equal to the crushing resist- ance by using a larger rivet. Of course this will demand a further increase of pitch. In the case of the single-riveted lap-joint now under dis- cussion, the proper proportions for a joint that shall be equally strong against shearing, tearing, and crushing can be calculated directly. The usual way is to determine the diameter of the rivets by making them equally strong against shearing and crushing. Equating the expressions for crushing and shearing resistance, we have dtf e = — /„ or d---. 4 J,n For the case in hand with steel plates 7/16 of an inch thick, and steel rivets, the diameter will be rf= 95 I ooo4XA =I . 45,000 7t ' Having the diameter of the rivets, we may now calculate the pitch by equating the shearing and tearing resistances, which gives —/. = (*- or P-J t -^+ d ' For the case in hand we have 45,000 7T 1.17 , ^ = S5.°°04 xA +, ' iy " 3 - X The efficiency of the joint is the ratio of the resistance to STRENGTH OF BOILERS. 289 tearing between the rivets to the strength of a strip of plate having a width equal to the pitch, so that the efficiency is flp-d)t = p-d fspt P ' In the case in hand the efficiency is 1 3.2 — 1. 17 00 3.2 63.4 per cent. But the pitch calculated in this method is too great for proper calking with a plate of the given thickness. The double-riveted lap-joint has three possible ways of failure, which lead to two equations for finding the diameter and pitch of rivets. Equating the shearing and crushing resistance for two rivets, we have 2- r f, = 2dtf„ or d = J ^ ^, 4 Js n which will give the same size rivet for a plate of a given thickness as would be found for a single-riveted joint. Now this method has been found to lead to too large a rivet for a single-riveted joint, where a strip having a width equal to the pitch carries one rivet. In the double-riveted joint such a strip carries two rivets, and consequently it is the more cer- tain that the method proposed will give too large a rivet, and of course too large a pitch for proper calking. The advan- tage of double riveting is that smaller rivets may be used to provide the requisite shearing resistance, and the plate may be less cut away at the section between rivets. In designing a double-riveted lap-joint it is customary to assume a diameter for the rivets and then determine the pitch by equating the shearing resistance of two rivets to the tear- ing resistance between the rivets. If the resulting pitch is too large for proper calking, the diameter of the rivets must be 290 STEAM-BOILERS. reduced. If, on the contrary, the resulting pitch is less than may be allowed, a slightly larger diameter and pitch may be used. A design of a joint like the single-riveted lap-joint with inside cover-plate, which has a wide and a narrow pitch, involves some difficulty and complexity. The fundamental idea of such a joint is to make the resistance to tearing at the inner row of rivets (when the pitch is small) plus the shearing of the outer row of rivets greater than the resistance to tear- ing at the outer row of rivets (when the pitch is larger). To insure this condition we may proceed as follows: Equate the resistance to tearing at the outer row of rivets to the resist- ance to tearing at the inner row plus the resistance to shearing one rivet at the outer row. This gives (P - d)tf t = (P - 2d)tf t + ^/„ 4 whence d=% The result is the minimum diameter of rivets allowable. We may now choose a slightly larger diameter of rivets, and then determine the pitch in three different ways, namely, by equating the resistance to tearing at the outer row of rivets, in succession, to the resistance to shearing of three rivets, to the resistance to crushing in front of three rivets, and to the resistance to tearing between the inner rows of rivets and compression before one rivet. The smallest pitch obtained will be the correct one to use with the given diam- eter of rivet. Should the efficiency of the joint be unsatis- factory, an attempt may be made to raise the efficiency by increasing the diameter of the rivets. STRENGTH OF BOILERS. 201 In the preceding pages it has been assumed that the strength of a rivet in double shear is twice that of a rivet in single shear. Many designers use a lower value per square inch in double shear than in single shear. There is but little evidence to show that there is any justification for this. The effects of crushing and shearing are so combined that it is difficult to get any data on double shear that is reliable. A careful study of all the tests made at the Watertown Arsenal, and of those made at the Massachusetts Institute of Tech- nology, failed to give any evidence that would warrant using a lower value per square inch for double shear than for single shear. Practical Considerations. — In proportioning a riveted joint, the following considerations, some of which have already been mentioned, must receive attention: The pitch of rivets near a calked edge must not be too great for proper calking. Rivets must not be too near together for convenience in driving. Punched holes must have a diameter greater than the thickness of the plate. A riveted seam must contain a whole number of rivets. Again, it is desirable that similar seams, as for example the longitudinal seams for the several rings of a cylindrical boiler, shall have the same pitch. It is evident that the design of a boiler-joint cannot be considered apart from the general design of the boiler. Flues. — The tendency of internal pressure in a thin hol- low cylinder is to give it a true cylindrical shape; conse- quently, with fair workmanship, the formulae for thin hollow cylinders may be applied to the calculation of boiler-shells subjected to internal pressure. But the tendency of external pressure is to exaggerate any imperfection of shape, and cylindrical flues fail by collapsing. 292 STEAM-BOILERS. The pressure at which a flue will collapse can be found by direct experiment only. The earliest and for a long time the only tests on the collapsing of flues were those made by Fairbairn, and pub- lished in the Transactions of the Royal Society, in 1858. All of the tubes tested were 0.043 of an inch thick; they varied in diameter from 4 inches to 12 inches, and in length from 20 inches to 60 inches. From these tests he deduced the em- pirical formula 806,300 X t 219 in which / is the length of the tube in feet and 5° 7.87 33- 42 42 54 33 36 36 36 43 3 276 360 420 300 36 86 24 24 48 23 e a •C2 Collapsing Pressure in Pounds per Square Inch. Ss« ■°a c o C/l en V c M r° en C- 1 c V- 't5 5-SE c >. — c « 0*: SQPu V i_ Oh be B '00 O «5 8 + boX ■Sex. f . « g « ollapsing Coeffi- cient reduced to Steel of 27 Tons Tensile. £ § w O u u U 1st ring 6 ft. 5! in. total i" ¥ » length. 2d ring 1882 Length of rings : i8i". 10", 19", and 20" 7 ft. \ in. total 4 11" 3d ring 15" 3S ' 4th ring 1" 43 9/64 3d ring at 700 1st ring at 840, 2d ring 64,213 61,918 1887 length. Length of each ring, 23" 4 43-09 at 760, 3d ring at 840, 4th ring at 835 64,240 61,945 Note. — No record of tensile strength of steel ; 28 tons per square inch assumed. The collapsing coefficients are calculated on external diameter of furnace over plane part. STRENGTH OF BOILERS. 297 00 TJ G rt O" CN OO M — 1 3 fc — TJ vO SuisdB||03 IN >-. cn co r^ 4 00 0" 00 CO in co •ajnssajj c O O CO O co 0> O SuisdHno3 O 00 00 ~ <* -r •ijejAub IB CN CJ CN N Cl a J313UIKIQUI co co CO CO co CO •JJiaJS31B9Jr) O UI -t- rr r^ 1- »/-> 10 IT) O CO r^ r^ •UIBja UB3J^ in 4 4 CO -f CO -t- co co co CO co CO co c O CO co CO in •a co co -1- -1- in in C § U CT3 O in o> M r-s CN 2 co -t- r^ r^ "* H co co Tt -r in jo qiSu3q in vo J* H vO 1S3JB3JQ *saoii -BSnjao") C rj i_ M N C) 1-1 1-1 jo uaquinM ^ ^ v iota ; Its Jrz •aDHUjnj 5 r-H l-lOB 5 H ^|N H jo qiSuaq C r» co co r^ 00 CN O \C ) vO O O O O vb 1— M — _ „ — O O^ O a^ c 1 O -co OO 00 CO 00 c JN O O -H V a « ) - - . "* w w M _T m _T M 1-1 M M c 1 0* - " -o ^' xa J3 J3 > 4> t) u CJ aj U 5? ; 55 fa fa fa fa fa fa H tj 1 H 298 S TEA M-B OILERS. 1! '35 o Oh •0 1- V u Collapsing- Coefficient reduced to Steel of 27 Tons Ten- sile. OO O O OO O O ^ O <* N in in « vO 00" O*co" in in m in «j- in Ultimate Tensile Strength of Steel Assumed. 00 CO CO 00 CO W M N N W oX m r-~co co OOO i-o OO O t^M OO* 0* (> 0" N invO in in in ex . as On" in O O O in en in r^ r- m co 00 O in in Mean Diam- eter in Inches. m (N 00 -i-O M *-i O en CJ O^ C>CO CT> O c c rt U5 1- " v u> a Oco W O «3" m **f tJ- tJ- in in in rf ^ en d! 3- J J »• j 'lo «shf»tai»H'«*»> ,0 H invO O O vO O O O O vO (A H Q May, 1888 Do Do * Do S2 eg H 3 c STRENGTH OF BOILERS. 299 00 3 X O T3 K 3 .2 o C/3 y ° v g <-> S « _ -a J Y f 3 p. V V had a 75 a 8.S ~£ ~2 O E Dh •suox ^ jo [331g ojpsonp -3J JU3IDIJJ3 -03 SuisdB[[o3 00 (> •1331S jo qiSuajig 3[;s -U3JJ 31BUlUIfl ■ x •*■ a x J }U3IDIJJ3 03 SuisdBi[o3 •3JnSS3J,J J§uisdEi[o3 XlIE JB J3}301B -IQ UI3DU3J3J -}}(J JS31E3JQ UIBJJ JO 3piS -VnQ J3;3oieiq H^ •spug }B ]Bl J jo ipSusT ;S3}H3if) •suonB3njJ03 jo jaqmn^ 3DBU ■jit j jo qiSusq <3 H PJOD3J O^J "* Tf TT 3°° S TEA M-B OILERS. '55 °=5 o o "31ISU3J, SUOl Lz jopajs oj paonpai 'B 3 °D SuisdEno3 VI (A jd ja "O *E *C g t! t> 2 ~ SXUh NONCOCO>-iNi-i co inco m co co c* O OO r^ m hoo - O m -i •-" ir> in co in inO O •pug jpng co ci O co co O r^ •3-co*- h- CO m O^O m in co co T m inO "3IPPIW m -t-O N inO^woo co inco O coco coco invnM coininOO pug lUOJg s t** m CT> coo a co -t in in in pug Wld jo q^Suag isajBajf) •suoijbS tujo3 jo aaqtun^ •roBiung jo qiSuaq m|we9|e cocor^r^r^r^r^ r% i"» r^co oo co co co oo Ooooooo o t»xj° »^a co co co oo ** M r» r- r^ r^ r^ r-. - - oo oo co oo co oo N « CO OO ■» OO OO CO STRENGTH OF BOILERS. 301 Purves's Patent Furnaces. Official Tests made at Sir John Brown & Co. 's Works at Sheffield in 1889. T\»ce of Test. 889. it) rt Dec. 23, 1890. 9i 9i 9! 9* a *i u o .307 .362 .461 .466 .585 .578 .522 > -C o u u C U •- Q is s 5 * u w rt O 38.78...., 38.70 38.70 38.72 38.63 38.65.... 38.75I.-.-- . K," cu bt> c .S^q 2- u * &s x o'-c = 3 O «5 u U 675 700 870 950 1,065 »>*45 1,020 85,265 74,834 73.034 78,935 70,326 -A -^ . 75,718 « tx 28.8 28.O 27-3 29-3 23.7 iv. r.- 3 o '55 5 c w.£_ 4) C VL| — *j u " 71 " « ,. U 79,935 72,161 72,231 72..?3& C6,i6o 75,446 Corrugations spaced 9" apart. Not very full records kept. Note.— The collapsing coefficients are calculated on diameters of furnaces over flats. 3 02 STEAM-BOILERS. U ct C u 3 00 J c IN tt ^r ** ""> tn tn rf "ri- spug ib jbu jo Ul3U311S3?B3JO -suo.UBSru.103 jo aaquinM •3DBU -jnji jo inSuaq en en en en en en in en O M O r^ CM r-N r^ in en vO CO en -r ■* m in Qn O** O^ s O^ C7* vO O O o o Q P STRENGTH OF BOILERS. 303 Discussion of Results of Tests on Flues. — The stress in a thin hollow cylinder subjected to external fluid pressure may be calculated by an equation having the same form as that for a cylinder subjected to internal pressure; the equa- tion may be deduced by a similar method. Thus the stress will be s r in which / is the pressure per square inch, r is the radius and / is the thickness, both in inches. In the table we have a column giving the coefficient of collapse calculated by the expression PD T' in which Pis the pressure, D is the diameter, and 7* is the thickness. The coefficient appears consequently to be twice the compressive stress in the flue at the time of collapsing. This coefficient is fairly regular for each style of furnace, and is somewhere near the tensile strength of the metal from which the flue is made; in some cases it is less and in some more than the tensile strength. Now soft steel in the form of short cylinders will begin to flow when the compressive stress in a testing-machine is about equal to the strength of pieces used for tensile tests. In other words, the tensile and compressive strengths are about equal. The furnaces tested appear, then, to have collapsed when the compressive stress was half the ultimate compressive strength of the metal. Now the limit of elasticity for both tension and compression, for soft steel, is about half the ultimate strength, so that the collapse occurred somewhere about the elastic limit. We should not, however, attribute too much importance to this considera- tion, but it will be better to follow ordinary practice and consider the equations used for calculating* the safe working 3°4 STEAM-BOILERS. pressure on flues to be empirical, and to depend directly on experiment. Rules for Working Pressure on Flues. — There are three sets of rules for working pressure on flues, which need be considered, namely, those of the British Board of Trade, those of Lloyd's Marine Insurance Underwriters, and those of the United States Inspectors of Steam-vessels. These rules are changed from time to time, and include certain directions to inspectors that need not be given here; if a boiler is built for inspection under these or any other rules the only safe way is to obtain the current edition of the rules and see that the boiler conforms thereto, and also that the boiler is properly proportioned according to the best information that can be obtained by the designer. Rules for Plain Flues. — The rules for flues as given by the United States Board of Supervising Inspectors — Steamboat In- spection Service — as amended January, 191 1, are: Plain, Lap- welded Steel Flues, 7 to 18 Inches Diameter. Working pressures and corresponding minimum thicknesses of wall for long, plain, lap-welded, and seamless steel flues, 7 to 18 inches diameter, subjected to external pressure only, shall be determined by the following table and formula: Working Pressure in Pounds per Square Inch. Outside Diameter [00 [20 140 ] 60 180 200 220 of Flue. Inches. Thickness of Flue in Inch es. Safety Factor, 5. 7 152 160 .168 177 .185 193 201 8 174 183 193 202 211 220 229 9 196 206 217 227 237 248 258 10 218 229 241 252 264 275 287 11 239 252 265 277 290 303 316 12 261 275 289 303 317 330 344 13 283 298 313 328 343 358 373 14 301 320 337 353 369 385 402 15 323 343 361 378 396 413 430 16 344 366 385 404 422 440 459 17 366 . 389 409 429 448 468 488 18 387 ' 412 433 454 475 496 5i6 STRENGTH OF BOILERS. 305 Thicknesses in this table were calculated by formula _ [(F X P) + 1386] D 86,670 where D = outside diameter of flue in inches. T = thickness of wall in inches. P = working pressure in pounds per square inch. F = factor of safety. This formula is applicable to lengths greater than six diame- ters of flue, to working pressures greater than 100 pounds, to outside diameters of from 7 to 18 inches, and to temperatures less than 650 F. When flues are constructed of plates made in sections and efficiently riveted together, not less than 24 inches in length, minimum thickness 0.25 of an inch, over 6 and not exceeding 18 inches in diameter, the working pressure shall be calculated by the following formula: p _ 8100 T D where P = the working pressure in pounds per square inch. T = the thickness in inches. D = outside diameter in inches. The working pressure allowable on seamless, riveted, or on lap- welded flues over 18 inches in diameter up to and including 28 inches in diameter, made in sections not less than 24 inches in length, efficiently riveted together, sections not to exceed three and one half times the diameter of the flue, when subjected to external pressure only, shall be determined by the following formula: c c P= ^[(18.75 XT) -(LX1.03)] where P = the working pressure in pounds per square inch. D = the outside diameter of the flue in inches. L = the length of flue in inches not to exceed 3^ diameters. T — thickness of wall in sixteenths of an inch. 306 STEAM-BOILERS. Furnace Strength. — The United States Board of Supervising Inspectors give the following rules, amended January, 191 1, for figuring the strength of different furnaces. The tensile strength of steel used in the construction of cor- rugated or ribbed furnaces shall not exceed 67,000 and be not less than 54,000 pounds; and in all other furnaces the minimum tensile strength shall not be less than 58,000 and the maximum not more than 67,000 pounds. The minimum elongation in 8 inches shall be 20 per cent. All corrugated furnaces having plain parts at the ends not exceeding 9 inches in length (except flues especially provided for), when new, and made to practically true circles, shall be allowed a steam pressure in accordance with the following formula : D Leeds Suspension Bulb Furnace. F _ CXT D where P = pressure in pounds. T = thickness in inches, not less than five sixteenths of an inch. D = mean diameter in inches. C = a constant, 17,300, determined from an actual de- structive test under the supervision of the Board, when corrugations are not more than 8 inches from centre to centre, and not less than 2\ inches deep. Morison Corrugated Type. CX_I D where P = pressure in pounds. T = thickness in inches, not less than five sixteenths of an inch. STRENGTH OF BOILERS. 307 D = mean diameter in inches. C = 15,600, a constant, determined from an actual de- structive test under the supervision of the Board of Supervising Inspectors, when corrugations are not more than 8 inches from centre to centre and the radius of the outer corrugations is not more than one half of the suspension curve. [In calculating the mean diameter of the Morison furnace, the least inside diameter plus 2 inches may be taken as the mean diameter, thus — Mean diameter = least inside diameter + 2 inches.] Fox Type. P _CXT D where P = pressure in pounds. T = thickness in inches, not less than five sixteenths. D = mean diameter in inches. C = 14,000, a constant, when corrugations are not more than 8 inches from centre to centre and not less than 1 J inches deep. Purves Type. P _CXT D where P = pressure in pounds. T = thickness in inches, not less than seven sixteenths. D = least outside diameter in inches. C = 14,000, a constant, when rib projections are not more than 9 inches from centre to centre and not less than if inches deep. Brown Type. r _ CXT D where P = pressure in pounds. T = thickness in inches, not less than five sixteenths. 308 STEAM-BOILERS. D = least outside diameter in inches. C = 14,000, a constant (ascertained by an actual de- structive test under the supervision of this Board), when corrugations are not more than 9 inches from centre to centre and not less than if inches deep. The thickness of corrugated and ribbed furnaces shall be ascertained by actual measurement. The manufacturer shall have said furnace drilled for a one-fourth-inch pipe tap and fitted with a screw plug that can be removed by the inspector when taking this measurement. For the Brown and Purves furnaces the holes shall be in the centre of the second flat; for the Morison, Fox, and other similar types in the centre of the top corrugation, at least as far in as the fourth corrugation from the end of the furnace. Type Having Sections 18 Inches Long. CX_T D where P = pressure in pounds. T = thickness in inches, not less than seven sixteenths. D = mean diameter in inches. C = 10,000, a constant, when corrugated by sections not more than 18 inches from centre to centre and less than 2\ inches deep, measuring from the least inside to the greatest outside diameter of the corrugations, and having the ends fitted one into the other and substantially riveted together, provided that the plain parts at the ends do not exceed 12 inches in length. Adamson Type. When plain horizontal flues are made in sections not less than 18 inches in length, and not less than five sixteenths of an inch thick, and flanged to a depth of not less than three times STRENGTH OF BOILERS. 309 the diameter of rivet hole plus the radius at furnace wall (inside diameter of furnace), the thickness of the flanges to be as near the thickness of the body of the plate as practicable. The radii of the flanges on the fire side shall be not less than three times the thickness of plate. The distance from the edge of the rivet hole to the edge of the flange shall be not less than the diameter of the rivet hole, and the diameter of the rivets before driven shall be at least one fourth inch larger than the thickness of the plate. The depth of the ring between the flanges shall be not less than three times the diameter of the rivet holes, and the ring shall be substantially riveted to the flanges. The fire edge of the ring shall terminate at or about the point of tangency to the curve of the flange, and the thickness of the ring shall be not less than one half inch. The pressure allowed shall be determined by the following formula : Adamson Furnaces in Sections of not less than 18 Inches in Length. P= ^'[(18.75 XT) -(1.03 XL)] where P = working pressure in pounds per square inch. D = outside diameter of furnace in inches. L = length of furnace in inches. T = thickness of plate in sixteenths of an inch. Cylindrical riveted flues and furnaces made in sections of not less than 18 inches in length fitted one into the other and substantially riveted, combustion chambers for vertical sub- merged tubular boilers in the shape of a frustum of a cone, con- structed to a practically true circle, shall be allowed a steam pressure according to the following formula: P = SijS [(18.75 XT) -(1.03 XL)] 3 1 STEA M -BOILERS. where P = working pressure in pounds per square inch. D = outside diameter of furnaces in inches, or outside mean diameter of cone top in inches. L = length of furnace or flue in inches. T = thickness of furnace or cone top in sixteenths of an inch, not to be less than five sixteenths of an inch. When diameter of plain furnaces and flues used in vertical type of boilers or mean diameter of cone tops exceeds 42 inches, they shall be deemed a flat surface and must be stayed in ac- cordance with rules governing flat surfaces. If a greater work- ing pressure than given by formula is desired for mean diameters under 42 inches, the flues or cone tops shall be substantially stayed for such additional pressure. Fire-tubes. — The thickness usually given to fire-tubes to in- sure sound welding and to provide for expanding into the tube- sheets is in excess of that required to prevent collapsing. There appears, however, to be no experiments to show the actual collapsing pressure for such tubes. The joint made by expanding the tubes into the tube-sheets of locomotive and cylindrical tubular boilers has been found both by experiment and practice to be strong enough to secure the tube-sheet without additional staying. Girders. — When a flat surface cannot conveniently be stayed directly, it is customary to stay the surface to girders properly supported at the ends or elsewhere. The crown-bars of the locomotive boiler shown on Plate II, and the girders over the combustion-chamber of the marine boiler shown by Fig. 11, page 17, may be taken as examples. Again, the channel irons which are riveted to the flat heads of the cylindrical boiler shown by Plate I act as girders. The load which a girder of given material can safely carry depends on the form and dimensions of the girder, and on the manner of supporting and loading the girder. Some girders, like those over the combustion-chamber in Fig. 11, may be STRENGTH OF BOILERS. 3II calculated by the simple theory of beams; others, like crown- bars for locomotives and the channel-bars on Plate I, can be properly calculated only by the theory of continuous girders. A proper understanding of the theories of beams and of continuous girders can be obtained from standard works on applied mechanics. An adequate statement of even the theory of beams is out of place in a work on boilers; an incomplete statement is unadvisable, since it is liable to be misleading. One simple example will be worked out as an illustration of the use of the beam theory in boiler-design. As an example, we will take the girders over the combus- tion-chamber of the marine boiler shown by Fig. 11, page 17. The girders are spaced 7 inches apart, and each carries three stays spaced 6J inches apart. The load on each stay-bolt at 160 pounds steam-pressure is j X 6 J X 160 = 7000 pounds, and the total load on one girder is 21,000 pounds- The sup- porting force at each end of the girder is 10,500 pounds. The span of the girder is 22 J- inches, and the half-span is \\\ inches. The bending-moment at the middle of the girder due to the supporting force acting upward, and to the load on one bolt acting downward, is 10,500 x u| — 7000 X 6£ = 74,375 = M. Each girder is made of two plates each 5/8 of an inch thick, and 7 inches deep. The moment of inertia of the section of the girder at the middle is T V X 2 X f X 7 3 = /- The distance of the most strained fibre is 7~2 = 3£=^. 312 STEAM-BOILERS. The working fibre-stress is consequently f _My_ 74 375 X 3J _ g / - / -_ VX 2XfX7 3 ~ 7 7 pounds per square inch. Stayed Flat Plates. — The method of calculating the stresses in a flat plate supported at regular intervals by stays or stay-bolts, such as the sides of a locomotive fire-box, is treated in the theory of elasticity, under the heading of " indefinite plates which are firmly held at a system of points dividing them into rectangular panels." A complete solution of this problem is possible only when the panels are squares, that is, when the rows of stays are equidistant longitudinally and transversely. If the steam-pressure is represented by/, the thickness of the plate by /, and the pitch of the stays by a y then the direct working stress, which is a tension at certain places and a compression at others, is given by the formula S= 9?* The maximum deflection is given by the equation I pcf in which E is the modulus of elasticity of the material. If the sheets of a locomotive fire-box, or other stayed plates, have a direct tension or compression, proper allowance must be made for it. If stays or stay-bolts are in rows that are not equidistant each way, as for example the through-stays in the steam- space in Fig. ii, page 17, then the largest pitch maybe used in the above equations. The actual stress will in such case be less than the calculated stress by an unknown amount. If, STRENGTH OF BOILERS. 313 further, stays are arranged irregularly, the greatest distance in any direction may be used in the equations, but the calcu- lated stress may then be very different from the actual stress; it is, however, always the larger. As an example, we may calculate the stress in a side sheet of the locomotive fire-box shown on Plate II. Here the rows of rivets are four inches apart each way, the plate is 5/16 of an inch thick, and the steam-pressure is 170 pounds. The maximum stress is /= l(Af I7 ° = 6l9 °- Now the crown-bars are bedded on and are partly sup- ported by the side sheets of the fire-box. The crown-sheet is 72 inches long and 45! inches wide, and has an area of 72 X 45ft = 3285 square inches, and is subjected to a pressure of 3285 X 170 ■= 558,450 pounds. The distribution of this load between the side sheets and the sling-stays can be determined only by the cal- culation of the crown-bars as continuous girders, and may be disturbed by the expansion of the fire-box and by other causes. If it be assumed that the side sheets carry half the load on the crown-bars, then one side sheet will carry one fourth of 558,050, or 139,512 pounds. The side sheet is 72 inches long and 5/16 of an inch thick, so that the stress per square inch from the load on the crown-bars is 139,512 -r- 72 X A = 62QO pounds, — about as much as the stress calculated above. The 314 S TEA M-BOIL ERS. total compression on the side sheet is therefore about 12,400 pounds per square inch. This calculation, which appears sufficiently simple, illus- trates the danger of making calculations by formulae without knowing how they are derived and how they should be applied. The formula for staying given above is often quoted without any reference to tensile or compressive stress on the stayed sheet, from other causes; the use of such a formula by one who is unfamiliar with the theory of elasticity may lead to serious error in design. Factor of Safety.— The reciprocal of the ratio of the working pressure of a boiler to the pressure at which the boiler or any part of a boiler may be expected to fail quickly, is called the factor of safety for the boiler or for that part of the boiler. It is commonly recommended by writers that a factor of safety of six shall be used for boilers; probably such a factor would be economical for a boiler that is expected to work continuously for many years, as it allows a margin for deteri- oration. If the stresses coming on the parts of a boiler can be determined, a general factor of five will give sufficient security. If the boiler is carefully watched, a factor of four may be used; many boilers are worked with this factor. The use of an excessively large factor of safety, for example of the factor nine for flues calculated by Fairbairn's equation, shows a lack of confidence in the method. It is proper to make allowance for corrosion of parts like stays: this may be done either by using a larger factor of safety, or by a direct allow- ance; thus all stays, whatever their diameters, may have an eighth of an inch added to the diameter to allow for corrosion. It is of course proper in any structure to make small but im- portant members, such as stays in boilers, large enough to place them beyond any suspicion of failure. Hydraulic Tests of Boilers. — It is customary to subject new boilers to a water-pressure considerably in excess of the working pressure, to discover any leaks at riveted joints, at STRENGTH OF BOILERS. 315 the tube-sheets, or elsewhere; should there be any gross defect of design or workmanship it will be developed by this hydraulic test. Old boilers after repairs are subjected to a hydraulic test for the same purpose, but the pressure is not carried so high as for new boilers. The pressure applied during a hydraulic test is seldom more than once and a half the working pressure, and as most boilers have an actual factor of safety of not more than five, and frequently of four, it is apparent that the recommenda- tion of some authors, that the test pressure should be twice the working pressure, cannot ordinarily be followed without danger of injuring the boiler. With a factor of safety of six there should be no danger of injuring the boiler by applying a hydraulic pressure equal to twice the working pressure. It should be borne in mind that some of the worst stresses that come on the different parts of the boilers are due to unequal expansion and contraction, and that such stresses are not set up during a hydraulic test. Finally, the fact that a boiler has successfully withstood a hydraulic test is not a con- clusive proof that it is safe; too many unfortunate explosions of boilers, more frequently old boilers, after a hydraulic test, have shown this. The safety of a boiler is to be insured by careful and cor- rect design, honest and thorough workmanship, and intelli- gent care in service. Forms and methods of design and construction that do not admit of ready calculation should be avoided; in no case should the ordinary hydraulic test be relied upon to guarantee the strength of parts that cannot be calculated with a fair degree of certainty. If such forms are used in any case, they ought to be tested separately to a pressure of two or three times the working pressure, and some examples of each form and size ought to be tested to destruc- tion. The boiler undergoing a hydraulic test snould be carefully inspected, and any notable change of shape or leakage should 1 6 S TEA M- BOILERS. be investigated to discover the cause. Frequently small leaks that are developed during a test are stopped at once by calking or otherwise, but it is preferable to mark the place of the leak and calk after the pressure is removed. This of course requires another test to find out if the calking is suc- cessful. The pressure is usually applied by filling the boiler entirely full of water and then pumping in enough water, by hand or by power, to supply the leaks and develop the pressure required. If the pumping is done by hand, it is desirable to carefully remove all air from the boiler to avoid the labor of compressing air up to the test pressure. If the pumping is done by power, the saving of work is of less consequence, and a little air remaining in the boiler will act as a cushion, and lessen the shocks due to the strokes of the pump. New boilers are tested on the boiler-shop floor; old boilers are commonly tested in their settings, and in such case the inspection during a test is less convenient and efficient. It is sometimes recommended that hot water shall be used for testing a boiler; but there seems to be no advantage in so doing, as it is unequal expansion, and not merely rise of temperature, that sets up the unknown stresses that are so destructive to the boiler. Of course the use of hot water makes an efficient inspection during the test difficult if not impossible. When there is no other way of applying the hydraulic test to a boiler in its setting, the boiler may be quite filled with water, and then a light fire may be started in the furnace. The expansion of the water will develop the required pressure at a much less temperature than that of steam at the same pressure, and with less danger should the boiler fail. This method cannot be recommended for general use; and in case it is followed care must be taken not to exceed the desired pressure. STRENGTH OF BOILERS. 317 Hydraulic Test to Destruction. — In 1888 a boiler-shell, made to represent a part of the shell of a gunboat boiler, was tested by hydraulic pressure at the Greenock Foundry,* with the intention of bursting it. The shell was 1 1 feet long and 7 feet 8 T 3 g- inches mean diameter. It was made of three sec- tions of 19/32 plate, triple-riveted, with butt-joints and double cover-plates at the longitudinal joints, and lapped and double riveted at the ring seams. The rivets were staggered for both longitudinal and ring seams. The end-plates were 20/32 thick, and stayed with through-stays and washers, spaced 14 inches on centres. The stays were ij inches in diameter; the screws at the ends of the stays were 2 \ inches in diameter. Finally, it may be said that the shell was designed to fulfil the Admiralty specifications for a working pressure of 145 pounds per square inch. The workmanship was of the same degree of excellence usual for boiler-work at that establish- ment. First Test. — The shell was first subjected to the working pressure of 145 pounds, and showed a slight alteration of form due to the tendency of internal pressure to give it a true cylin- drical form. The pressure was then raised to the Admiralty test pressure of 235 pounds, and then to 300 pounds without developing leaks. There were some minor changes of form due to the increase of pressure. The pressure was then removed and the shell returned to its original dimensions. Pressure was then raised to 330 pounds, when there was a slight leak at the manhole door. At 450 pounds pressure the leak at the manhole door exceeded the capacity of the pumps. There was also a slight leak at the corners of two butts. The manhole was then strengthened — no other repairs were made. Second Test. — Pressure was raised to 350 pounds and developed a small leak at the manhole. There were slight * Trans. Inst. Naval Arch., vol. xxx. p. 285. 3i8 STEAM-BOILERS. leaks at the butt-straps, which were calked at the end of the test. The manhole, however, leaked so that the test was stopped. Third Test. — After additional bolts were put into the manhole cover the pressure was raised to 350 pounds with- out leakage. At 360 pounds the manhole began to leak, and at 580 pounds the test was stopped on that account. The butt-straps opened visibly at the calking and leaked more than before. Fourth Test. — The butt-joints were again calked and additional pumps were employed. The shell was again tight at 350 pounds and the pressure was carried to 620 pounds, at which there was a good deal of leakage at the butt-straps. Only one or two rivets showed signs of leakage; there appeared to be no difference between the hand and machine riveting in this respect. At the pressure of 620 pounds the entire capacity of the pumps was required to supply the leakage. The distortion of the shell was very marked at the higher pressures, and increased with the pressure; thus the ends bulged an inch at 520 pounds, about \\ inches at 580 pounds, and nearly two inches at 620 pounds. The sides bulged more irregularly, but to the extent of nearly an inch at 620 pounds. The stays drew down uniformly 1/64 of an inch at 520 pounds, 2/64 at 580 pounds, and 4/64 at 620 pounds. They increased in length 2^ inches at 520 pounds, 3J inches at 580 pounds, and 3f inches at 620 pounds; this accounts for the bulging of the end-plates. The mean tensional strength of the plates from which the shell and butt-straps were made may be taken at 61,500 pounds. At 620 pounds the tension on the plates between the rivet-holes was 57,504 pounds, or 93 \ per cent of the strength oi the solid plate, and there was no serious disturb- ance of the structure. The ring seams increased in diameter about \ of an inch, and the shell bulged out between them. STRENGTH OF BOILERS. 319 The various portions of the boiler acted in harmony and showed no special weakness at any point. The butt-joints had the rivets spaced 5f inches on centres to give a percen- tage of 83.7 per cent of the plate, and this may have caused the leakage found there. The riveting appeared to be reliable at the extreme pressure reached. This test seems to show that a boiler will give signs of weakness long before it will fail. Such signs of weakness should be carefully investi- gated : if there is any local weakness or deterioration, repairs or alterations may be made ; if there are evidences of general deterioration, the working pressure must be reduced, or better, the boiler may be replaced by a new one. Boiler-explosions. — The great destruction of life and property that is liable to be caused by a violent boiler-explo- sion makes it imperative that the causes should be carefully investigated, to the end that explosions may be prevented. With this in view the boiler and its parts, and any wreck or evidence of destruction caused by the explosion should be left undisturbed until the scene of the explosion can be examined by a competent engineer. Of course if any persons are injured by the explosion they must be rescued and cared for immediately, and also any building or structure that is so injured as to threaten life or safety must be attended to at once; but it should be borne in mind that the examination by the engineer for the purpose of determining the cause of the explosion is also in the interest of humanity, since its aim is to avoid future explosions. All idle or simply curious per- sons should be excluded from the scene of the explosion, more especially as such persons are apt to disturb or even carry away things that may be of importance in the study of the cause and history of the explosion. If the explosion is accompanied by loss of life or injury to person or property, it will be followed by a le^al investigation in which the testi- mony of the engineer or engineers who have examined the scene of the explosion will be of prime importance, as it will 320 S TEA M-BOILERS. have a large influence in locating responsibility for the disaster. While various causes may lead to boiler-explosion, it is unfortunately true that by far the greater part of violent explosions are due to the fact that the boiler is too weak to endure service at the regular working pressure. A new boiler may be weak through defective design or workmanship; there can be no excuse for the explosion of a new boiler from weakness, and such explosions in good practice are rare. An old boiler is liable to become weak through local or general corrosion or other deterioration; this amounts to saying that a boiler will eventually wear out. The length of time that a boiler will endure service depends (i) on the design, (2) on the thickness of plates and the quality of the metal, (3) on the workmanship, (4) on the care given it, and (5) on the quality of the feed-water. Definite figures cannot be given for the life of a boiler, since it depends on so many things. The following table gives the number of years several kinds of boilers can endure regular service if they are properly built and cared for: Lancashire, low-pressure 1 5 to 20 years. Locomotive type, stationary 12 to 1 5 Locomotive-boilers 8 to 12 Vertical boilers 10 to 15 Vertical boiler with submerged tubes 14 to 18 Horizontal cylindrical tubular 15 to 20 Scotch marine boiler 1 2 to 1 5 Water-tube boiler 12 to 16 Pipe or coil boiler 5 to 8 By water-tube boiler is here meant a boiler with a shell or drum containing a considerable body of water. By pipe or coil boiler is meant a boiler made up of pipe and pipe- fittings, with a separator. STRENGTH OF BOILERS. 321 Horizontal boilers will require one, and vertical boilers two extra sets of tubes, before the shell is condemned. A loco- motive-boiler will require two extra sets of tubes, and the entire fire-box will be renewed once in the life of the boiler. If boilers are subjected to careless or ignorant abuse., they may be used up in a fraction of their proper time of service, especially if cheaply built. This will account for the numer- ous explosions of sawmill boilers and agricultural boilers. It has been pointed out that leakage is frequently a sign of weakness; a perversion of this idea leads to the assumption that a boiler is safe as long as it can be kept from leaking. Too many boiler-explosions have this history: The boiler, after long and satisfactory service, began to leak; a cheap man was employed to repair the boiler, the repairs consisting mainly of excessive calking to stop the leaks; soon after the repairs, perhaps the first time the boiler was fired up, it exploded violently. A fit conclusion of the history is to ascribe the explosion to some obscure cause or to carelessness of the attendant, if he was killed by the explosion. Serious injury may be caused by overheating any part of the heating-surface, due to low water, to defective circulation, or to deposits of non-conducting substance on the plates or tubes. The overheated member, or plates, of the boiler may burst or collapse, and such failure may lead to an explosion of the boiler, but frequently the escape of steam and water will check the fire and relieve the pressure on the boiler. Local failures are dangerous to the boiler attendants, especially in a confined fire-room, as on shipboard. Unless there is direct evidence of overheating, either from known circum- stances before the explosion or from signs on the boiler after explosion, the cause of the failure should be sought elsewhere. If a boiler shows signs of low water or of overheating the fire should be checked by any effectual means. The most ready way of checking the fire is to close the ash-pit doors and throw ashes onto the fire. If there are no ashes at hand, then 322 S TEA M-B OIL ERS. fresh fuel may be used instead, since its first effect is to deaden the fire. There will be time for caring for, or drawing the fire before the fresh fuel is fairly in combustion. An attempt to draw the fire without first deadening it is liable to give a fierce combustion for a short time; moreover, more time is required to draw the fire. If the furnace has a dumping-grate, the fire may be immediately thrown into the ash-pit without waiting to deaden it. The damper should be left open so that if a rupture occurs the steam may escape up the chimney. Mean- while the steam made by the boiler should be disposed of by allowing the engine to run or by any other means, for exam- ple by opening the safety-valve, provided that it is merely a case of overheating, not accompanied by excessive pressure. It will probably be well to start the feed-pumps or to increase the supply of feed-water. Should the introduction of feed- water be badly arranged so that a large volume of cold water will be thrown onto a heated plate, it is possible that starting the feed-pump may cause a contraction which will start a rupture. It has been found by experiment that boiler-flues that have been purposely allowed to become bare and overheated have been saved by suddenly directing a stream of cold feed- water upon them, though such treatment may make them leak at the joints. The heat stored in such hot plates is insignificant as compared with the heat in the water and steam in the boiler. Excessive pressure, especially if it is enough to give good reason to fear an explosion, is more difficult to deal with ; the chances of success are less and the risks are greater than when the water is low, but the pressure is not excessive. If possi- ble the fire should be checked and the pressure relieved. The first may be done by throwing on ashes or cold fuel, and the second by running the engine at full load. It is at least doubtful whether starting the feed-pump will reduce the pressure fast enough to do much good, and on the other hand STRENGTH OF BOILERS. 323 there may be cases where such action would start an explo- sion. It is not best to open the safety-valve, since the sudden opening of a large safety-valve gives a shock which may determine the explosion. Some explosions have been re- ported that occurred immediately after the safety-valve opened. A large amount of energy is stored in the steam and water in a boiler in the form of heat. An idea of the amount of energy in any given case may be obtained by a simple calcu- lation. Thus the cylindrical boiler shown on Plate I, at 150 pounds pressure by the gauge, will contain 6600 pounds of water and 22 pounds of steam. The total weight of water and steam is 6622. The fractional 22 weight which in steam is 77— =.00332. Should the boiler ex- plode the mixture of water and steam would expand adiabati- cally to atmospheric pressure. A portion of the water would have vaporized. The percentage of the entire weight which is steam after the explosion has taken place may be found by equat- ing the entropy at the two points. Calling #1 the fractional weight which is steam at the start and x 2 the fractional weight at 212 ; ri and r 2 the heats of vapori- zation at boiler pressure and at 212 respectively, 7^ and T 2 the absolute temperatures, and d\ and 6 2 the entropies of the liquid we have that ~^ + 0i=^t"~ + ^2. If we call the boiler pressure 165 pounds absolute .00332X856.9 12X9691 365.9+459-5 + ' 535_ 459.5+2i2 + - 3l25j oc 2 = -15, or about 15 per cent is steam. The work done comes from loss of intrinsic energy and is in this case equal to 6622 XrjS(qi +X!pi -q 2 -x 2 p 2 ), 324 STEAM-BOILERS. where q\ and ^2 are the heats of the liquid at the two pressures and p\ and p 2 are the internal latent heats. Substituting values for these, the expression reduces to 6622 X 778(337. 7 + .00332 X 772.9— 180.3 — .15X896. 9) = 130,000,000 foot-pounds. If the entire explosion took place in two seconds, work was developed at the rate of 120,300 horse-power. If a calculation is made for this same boiler, assuming that the boiler was "dry," or just filled with steam, the energy developed would be between 5 and 6 million foot-pounds instead of 130 million. A person can sometimes judge as to whether the boiler was dry or not at the time of the explosion b™ the amount of destruc- tion caused by the explosion. The more water a boiler contains the greater the damage done by an explosion. An explosion of a boiler carrying low pressure for heating will, if there is a considerable amount of water in the boiler, develop a number of millions of foot-pounds of energy. Lap-seam Boilers. — It has already been mentioned that pressure on the inside of a cylinder tends to bend out any flat places and to make the shell a true circle, while pressure on the outside of a cylinder tends to make the cylinder collapse. Any flat places in such a cylinder will make the cylinder collapse at a much less pressure. This has been shown by experiments on upright boilers. The fire-box always begins to collapse at the seams where one part of the circle laps over the other part because at this spot there is a flattened area. If in the staying of the water-leg of a vertical boiler an extra line of screwed stay-rivets be put through this joint the collapsing pressure will be raised from 15 to 20 per cent. The longitudinal joint on a horizontal multitubular boiler comes from 2 to 6 inches above the top of the brackets support- ing the boiler. There is considerable stress thrown into the joint by the load on the brackets. The tendency of the pressure inside of the boiler and the tension in the shell is to pull the flattened STRENGTH OF BOILERS. 325 area at the joint into a true circle. The bending takes place at the rivet holes. The force tending to pull the joint into a circle varies every time the boiler pressure changes. These repeated bendings may after a long period start a crack which gradually gets deeper and finally determnies the life of the boiler. Sometimes an internal inspection of the boiler may show such cracks, but more often the crack starts between the two plates where one laps over the other. A crack in this place could not be found either by an internal inspection or by an external inspec- tion. A cold-water test might show this defect if the water pressure was made great enough. A number of boiler explosions have resulted from cracks of this sort. A lap-seam boiler may wear out before this repeated bending action at the joint starts a crack. If the plate used was ductile and the workmanship was good such probably would be the case, CHAPTER IX. BOILER ACCESSORIES. In this chapter will be described various fittings, attach- ments, and accessories for steam-boilers. Valves are used to control and regulate the flow of fluids in pipes. They are variously named after their forms or uses, such as globe valves, angle-valves, straightway valves, and check-valves. Fig. 129. Globe Valves are named from the globular form of their cases. The case is separated into two parts by a diaphragm with a passage through its horizontal part, as shown in Fig. 129. The fluid enters at the right, passes under the valve, and 326 BOILER ACCESSORIES. 327 out at the left. The valve is shut by screwing down the handle on the valve-spindle. A stuffing-box around the valve-spindle prevents leakage of fluid. In this valve the seat -ffl, J J = I \ 5 PIPE TAP Fig. 130. is rounded, and the valve face is a ring of a peculiar composi- tion, let into the valve at R. When the valve is shut, this composition is squeezed down onto the seat and makes a tight joint. If the fluid enters the valve from the right-hand side, the 328 STEAM-BOILERS. valve-spindle may readily be packed to prevent leakage while the valve is closed. If the fluid entered the valve at the other end, it would be necessary to shut off the fluid from the entire pipe in order to pack the valve. Angle-valves. — This form of valve, shown by Fig. 130, has an inlet at the bottom and an outlet at one side, it may take the place of an elbow at a bend in piping. The valve is made in two parts. The upper part carries a ring of soft metal which forms the bearing-surface. The lower part has ribs or wings which enter the opening through the valve-seat and guide the valve to its seat. The valve-spindle has a Fig. 131. sorew at the upper end which passes through a yoke entirely outside of the body of the valve. The body of the valve is made of cast iron. The valve, BOILER ACCESSORIES. 3 2 9 valve-seat, valve-spindle, and stuffing-box follower are made of brass or composition. This form of valve is frequently used tor the stop-valve between the boiler and the main steam-pipe. Straightway or Gate Valve. — This form of valve gives a straight passage through the valve, and offers very little resistance to the flow of fluids when it is open. Fig. 131 represents a Chapman valve, in which the valve is wedge- Fig. 132. shaped and is forced against a wedge-shaped seat. The valve- spindle is held at a fixed height by a collar, and draws up or forces down the valve to open or close it. The body of the valve is of cast iron ; the valve, valve-spindle, and stuffing-box are ot brass; the valve-seat is a soft composition. Fig. 132 represents a Peet valve, which has the faces of the valve-seats parallel. The valve itself is made in two pieces, 33o STEAM-BOILERS. between which is a peculiar casting, U shaped at the bottom and with wedge-shaped lips at the top. When the valve is shut this casting rests on the bottom of the valve body, and the two halves of the valve are thrown against the parallel valve-seats by the wedge-shaped lips of the casting. When the valve is opened this casting hangs between the two halves of the valve by the under side of the wedge-shaped lips. Check-valves allow fluids to pass in one direction, but not in the other. Fig. 133 represents a lift check- valve; it Fig. 133. Fig. 134. resembles a globe valve without a valve-spindle. Fluid entering at the left will lift the valve and pass out at the right. Should the current be reversed the valve will be promptly closed. Fig. 134 represents a swing check-valve. It offers less resistance to the flow of fluid than the valve shown above, and there is less chance that foreign matter will lodge on the valve-seat. The valve has some looseness where it is fastened to the swinging arm, so that it may properly seat itself. A feed-pipe must always have a check-valve to keep the boiler-pressure from acting on tne pump, or injector, when it is not at work. It automatically opens to allow water to pass into the boiler. There should also be a stop-valve (a globe or gate valve) near the boiler which can be shut at will; thus when the check-valve shows signs of leaking the stop-valve BOILER ACCESSORIES. 33 1 may be shut, and then the check-valve may be opened and examined. Safety-valves are intended to prevent the pressure oi steam from rising to a dangerous point. In order to accom- plish this, the effective opening of the valve should be suffi- cient to discharge all the steam that the boiler can make when urged to its full capacity. The effective opening is equal to the circumference of the valve-seat multiplied by the lift of the valve, if the valve-seat is flat ; if the valve-seat is conical, the lift should be measured at right angles to the seat. Then if / is the vertical lift and if a is the angle which the seat makes with the vertical, the effective lift is / sin a, The lift of a safety-valve rarely exceeds i/io of an inch. A two-inch pop safety-valve, made by the Crosby Gauge and Valve Co., and tested at the laboratory of the Massachusetts Institute of Technology, was found to lift from 0.07 to 0.08 of an inch. The valve had a conical seat with an angle of 45 . The actual flow was about 95 per cent of the calculated flow for this valve. The amount of steam that a boiler can make may be estimated from the grate-area, the rate of combustion, and the evaporation per pound of coal. The first item is fixed, and the other two, though somewhat indefinite, may be estimated from the type of boiler and the conditions under which it works. For example, a factory boiler having a grate 5 feet by 6 feet may be assumed to burn 18 pounds of coal per square foot of grate-surface per hour, and to evaporate 8 pounds of water per pound of coal. It will therefore generate 5X6X18X8 At, — fin v fin =1.2 pounds of steam per second. The amount of steam which will be delivered by a safety* 332 STEAM-BOILERS. valve may be calculated by an empirical formula proposed by Rankine and frequently called Napier's equation. It may be written W = aK 70 in which W is the weight of steam in pounds delivered per second, A is the effective area of discharge in square inches, and p is the absolute "pressure of the steam in pounds per square inch. The formula for calculating the diameter of a safety valve may be put into the form G X R X 9 = irdlp 3600 ' 70 where G = grate area in square feet, R = coal burned per sq. ft. of grate per hour, d = diameter of valve in inches, / = lift of valve in inches, p = absolute pressure on a square inch, .95 = a multiplier determined by test, as explained on the preceding page, 9 = probable actual evaporation per pound of coal. The expression above is for a flat-seated valve. For a 45-degree seat substitute .707 / for / in this formula. If the value d, in any case, figures out to be over 4 inches, two smaller valves having a total circumferential length equal to that of the one large valve should be used. A common rule requires that there shall be an area of 1/3 of a square inch through the valve-seat for each square foot of grate-surface. BOILER ACCESSORIES. 333 This rule will apply only to a certain rate of coal consump- tion: 15 to 20 pounds per hour per square foot of grate or 130 to 160 pounds of steam made per hour from a square foot of grate. The method, given on the preceding page, wherein the actual amount of steam made is considered, is the only correct method of calculating the size of a safety-valve. Lever Safety-valve. — The general arrangement and some of the details of a well-made safety-valve are shown by Fig. 135- Co WEIGHT 115 LBS. CENTER OF GRAVITY OF LEVER WEIGHT OF LEVER 42 LBS. 'WEIGHT OF VALVE AND SPINDLE 15 LBS. Fig. 135- The body of the valve is of cast iron, and has an opening at one side from which the escaping steam is led out of the boiler-room through an escape-pipe. The valve and valve-seat are of brass or composition; the bearing-surface is at an angle of 45 with the vertical. The load is applied by a steel spindle, to a point beneath the bearing-surface so that the valve is drawn down to its seat. The spindle passes through a brass ring in the cover to the valve-casing. The load is applied by a lever with a fulcrum at A and a weight at D. It is steadied by guides cast on the cover of the casing; in the figure the valve and body are shov/n in section but the spindle, lever, guides and weight are shown in eleva- tion. It is important that the pins at A and B shall be loose in their bearings, and that the spindle shall be free where it. 334 STEAM-BOILERS. passes through the top of the valve-case, so that the valve may not fail to rise even if the working parts are rusted a little. After a safety-valve has blown off it is liable to leak a little, and such leakage is likely to injure the bearing-surface. In this way safety-valves sometimes get leaky and trouble- some. The proper way is to regrind the valve and make it tight, but if the boiler attendant is careless he may try to stop the leak by jamming the valve on its seat. This may be done by hanging on extra weight, or wedging a piece of wood or metal against the lever. To remove temptation, it is well to have the guides for the lever open at the top, and also to cut off the lever to just the proper length so that the weight cannot be slid farther out. A short lever and a heavy weight are better, for this reason, than a lighter weight and a longer lever. In order to make a calculation of the pressure at which a safety-valve will blow off, we must know the diameter of the valve, the weight of the valve and valve-spindle, the length of the lever and the weight hung at its end, and the weight and centre of gravity of the lever. This last may be found by calculation, or more simply by balancing the lever on a knife-edge. In the example shown by Fig. 135 the valve has a diameter of 5 inches and an area of 3.1416X 5 3 , *—*- 1 = 19.635 4 square inches, on which the steam presses. The valve and spindle weigh 15 pounds; this is applied directly at the valve. The weight of 115 pounds at the end of the lever, is 56 inches from the fulcrum at A. It is equiva- lent to a weight of 115X56 , — t ±- = 1610 4 BOILER ACCESSORIES. 335 pounds at the valve. The weight of the lever is 42 pounds, applied at the centre of gravity C 7 20 inches from the fulcrum. It is equivalent to a weight at the valve of 42 X 20 = 210 4 pounds. The total equivalent weight, or the load on the valve, is 15 -f- 1610 + 210 = 1835 pounds. Since the area of the valve is- 19.635 square inches, the steam-pressure per square inch required to lift the valve will be 1835 -f- 19.635 = 93.46 pounds. Problems concerning the loading of a safety-valve may be conveniently stated and solved by taking moments about the fulcrum ; that is, by multiplying each weight or force by its distance from the fulcrum. Let the weights of the valve, spindle, lever, and weight be represented by V, 5, L, and W. Let a be the distance of the weight from the fulcrum and b be the distance from the fulcrum to the valve, while c is the distance of the centre of gravity of the lever from the fulcrum. The moment of the weight is Wa, and the moment of the lever is Lc. The moment of the valve and spindle is (V-\-S)b. All three moments act downward, and their total effect is equal to their sum, Wa + Lc + (V+S)b. If the diameter of the valve is d, then the area is \nd % . Representing the steam-pressure above the atmosphere by/, the force acting on the valve is nd % 3$6 STEAM-BOILERS. and the moment of that force is ■ pb. 4 F This moment acts upward and, when the valve lifts, will be equal to the total downward moment. So that the equa- tion for calculating the load on a lever safety-valve is pb = Wa + Lc + (V+ S)b. This equation gives for the steam-pressure at which the valve shown by Fig. 135 will lift 4 [Wa + Lc+ ( V-S)b] P ~ nd'b _ 4(1 1 5 X 5 6 + 42 X 20 -f 1 5 X 4) ''' P -' 3.1416 X 5 2 X 4 •'• P = 93-46 pounds, as found by the previous calculation. For a second example let us find the distance at which the weight of the valve shown by Fig. 135 must be placed from the fulcrum in order that the valve will blow off at 50 pounds above the atmosphere. Solving the general equation for a, we have nd 2 pb—- Lc- (V+S)b a = W 50 X A X ^— — X5 -42X20-15x4 . a = ± . ii5 \ a = 26.32 inches. BOILER ACCESSORIES. 337 For a third example find the weight which should be hung at the end of the lever if the valve is to blow off at 30 pounds above the atmosphere. Here we have nd* pb -Lc-{V-\-S)b W= ± . 30 X 4 X 3 ' 141 X 5 a - 42 X 20 - 1 5 X 4 W 56 W = 26 pounds. These last two problems can of course be stated and solved much after the first manner applied to the first problem, but the work, which will amount in the end to the same thing, cannot be so well arranged nor so easily done. Pop Safety-valve. — A defect of the common lever safety-valve is that it does not close promptly when the steam-pressure is reduced, and it is apt to leak after it has returned to its seat. The valve shown by Fig. 136 has a groove turned in the flange which projects beyond the bearing-surface, and there is another groove between the outer edge of the valve-seat and a ring which is screwed onto the valve-seat. When the valve lifts the escaping steam is twice deflected, once by the groove in the valve and again by the groove at the valve-seat. The reaction of the steam assists the pressure of the steam on the under surface of the valve, and suddenly opens the valve to its full extent. The valve stays wide open till the steam- pressure in the boiler has fallen a few pounds below the blow- ing-off pressure, and then the valve shuts as suddenly as it opens. The ring which is screwed onto the valve-seat has a number 338 STEAM-BOILERS. of holes drilled through it to allow steam to escape from the groove at its upper surface. It may also be screwed up or Fig. 136. down to adjust its position; a screw at the side of the case clamps it when adjusted. The action of the valve is regulated BOILER ACCESSORIES. 339 by the number of holes in the ring and by its vertical posi- tion. This valve is loaded by a helical spring. The thrust of the spring and the load on the valve is regulated by a sleeve which is screwed down through the top of the valve-case. It is of course possible to load a plain safety-valve in a similar way, or to load a pop-valve with a lever and weight. The valve is extended up in the form of a thin shell to guard the spring from the escaping steam. The valve-spindle is ex- tended through the top of the case, and may be pulled up by a lever when it is desired to ease the valve off from its seat. A drip at the lower right-hand side of the case draws off water which may collect in the case. The valve and its seat, the adjusting-ring on the seat, the valve-spindie, and the bearing-pieces on the spring are all brass. There is also a brass ring inside the shell that extends down from the cover and incloses the spring. There should be a little clearance between this brass ring and the shell on the valve so that the valve shall not be cramped. The entire valve-casing, which is made in four parts, is of cast iron. It is evident that the annular space between the bearing- surface and the edge of the groove of the valve in Fig. 136 is subjected to a pressure, when the valve is open, which depends on the rates of flow to and from this space. Some pop-valves depend mainly, if not wholly, on such an additional pressure for their action, and it is claimed by some makers that all pop-valves do. The closeness of regulation by a pop- valve may be controlled by determining the width of the an- nular space and by adjusting the grooved ring outside the valve-seat. Valves have been made with only two pounds for the range of pressure between opening and closing; thus, a pop-valve may open at 100 pounds pressure and close at 98 pounds. A safety-valve should be set by trial, to blow off at the required pressure as shown by a correct steam-gauge. A safety-valve should occasionally be lifted from its seat to 340 STEAM-BOILERS. insure that it is in proper condition. An unexpected opening of a safety-valve or continued leakage shows lack of attention to duty on the part of boiler attendants. While the safety- valve for a boiler should be able to deliver all the steam it can make, it may be considered that the proper function of a safety- valve is to give warning of excessive pressure. The safety of the boiler must always depend on the faithfulness and intelli- gence of the boiler attendants. The discharge of a safety-valve is often piped outside the boiler-room. Such pipes should be dripped to keep them free of water. Each safety-valve should be piped outdoors sepa- rately. Locomotive Pop Safety-valve. — A locomotive muffled pop safety valve, as made by the Crosby Steam Gauge & Valve Co., is shown by Fig. 137. The " blow down " is varied by screw- ing the outer muffle casing up or down, thereby varying the amount of opening given the four holes leading into the central discharge chamber. At A is shown a slight modification of the inner edge of the seat face which has been patented by Professor Miller. By this slight rounding of the sharp edges commonly found at this point in safety-valves, the discharge through the valve with the same lift may be increased from 10 to 15 per cent. Various rules have been proposed for figuring the discharge capacity of safety-valves. In general these rules assume either a definite lift or make the lift some fraction of the diameter or some fraction of the diameter plus a constant. By putting the assumed lift, or the equation for the lift in terms of the diameter, in the equation given on page 332, and at the same time by applying a proper multiplier to Napier's formula, a simple expression for the discharge of a safety-valve may be worked out in terms of the diameter and the pressure, all the constants being put into one factor. In the recent volumes of the Transactions of the A.S.M.E. are given the results of two series of tests on the discharge BOILER ACCESSORIES. 341 Fig. 137. 34 2 STEAM-BOILERS. capacity of safety-valves, one series made by Mr. Philip G. Darling and another series by Prof. E. F. Miller. Many engineers specify valves having a 45-degree seat without considering that such valves must lift from their seats 1.4 times the amount that would be required for flat-seated valves of the same diameter discharging the same weight of steam. This extra lift besides bringing additional stresses to the spring, which is already under severe stress, also adds to the force of the shock or blow caused by the return of the valve to its seat. The only advantage of a high lift is an increase in the dis- charge capacity, and this advantage is frequently more than offset by the disadvantages mentioned. Water-column. — The position of the water-level in a boiler is indicated either by a water-glass or by gauge-cocks or by both. These may be connected directly to the front end of the boiler, or they may be placed on a fitting known as a water -column or combination. Fig. 138 shows a good form of water-column. It is a cast-iron cylinder connected to the steam-space at the top and to the water-space near the bottom. The normal position of the water-level is near the middle. There is at the bottom a globular receiver into which deposits from the water may settle and be blown out at will. In one side of the water-column are brass fittings for the water-glass, which is a strong tube of special make. The glass tube passes through a species of stuffing-box in the brass fitting. The joint is made tight by a rubber ring which fits on the tube and is compressed by a follower screwed onto it. Each fitting has a valve by which steam may be shut off when the tube is cleaned or replaced. A cock at the bottom drains water from the tube; for this purpose the lower valve is closed and the cock is opened. If either valve leading to the water-glass is closed, the level of the water will rise in the tube. If the upper valve is closed, the steam in the upper part of the glass is gradu- BOILER ACCESSORIES. 343 ally condensed by radiation, and is replaced by water entering from below. If the lower valve is closed, the condensation of steam from radiation will accumulate and gradually fill the glass. Gauge-glasses are very brittle and, though carefully an- nealed, are under considerable stress from unequal cooling. Be- fore a tube is put in it may be cleaned by pouring acid through it, or by drawing a bit of waste through on a string. A wire should never be forced through a glass tube, for the slightest scratch may start a break which will end in reducing the tube to small pieces. When a tube is in place it may be cleaned by closing the lower valve and opening the drainage-cock and allow- ing steam to blow through. When a boiler is left banked overnight the water-glass should be shut off, since a breakage may result in drawing the water in the boiler down to the level of the lower end of the tube. In addition to the water-glass, which shows at all times the level of the water, the water-column carries three gauge-cocks. One is set at the desired water-level, one a little above, and one a little below. Steam from the steam-space, through the upper gauge-cock, becomes superheated as it blows into the atmos- phere and looks blue. The lower cock discharges hot water from the water-space, which flashes into steam as it escapes, but it has a white color, which is very distinct from that of the jet from the steam- space. A good fireman occasionally tests the position of the water-level by using the gauges to be sure that the indication by the water-glass is not erroneous. Engineers on locomotives, and boiler attendants where very high-pressure steam is used, often prefer to depend entirely on the gauge- cocks, and dispense with the water-glass, which may be annoy- ing or dangerous when it breaks. The water-column shown by Fig. 138 has an alarm-whistle, which shows above the main casting, at the right. It is con- trolled by two floats inside the cylinder; one float at the top 344 STEAM-BOILERS. opens the valve leading to the whistle when the water-level is too high, the other near the bottom blows the whistle when the water-level is too low. A ribbed glass, about if inches wide and 10 to 12 inches long, is frequently used in place of the ordinary gauge glass. This glass forms the front of a metallic box coated white on the interior. WATER CONNECTION Fig. 138. The glass up to the water line, due to interference of light, appears black, and above the water line white. This glass makes it easy for a fireman, who is more or less blinded after looking at the fires, to tell where the water is. Steam-gauges. — The pressure of the steam in a boiler is shown by a steam-gauge constructed as shown by Figs. 139, 140, and 141. The essential part is a flattened brass tube bent BOILER ACCESSORIES. 345 into the arc of a circle as shown by Fig. 139. The section of the tube may be an oval, or it may have two longitudinal corrugations as shown by Fig. 140. Pressure inside of such a tube makes it bulge and tends to straighten it. One end is fixed and is in communication Fig. 139. Fig. 140. with the space where the pressure is to be measured. The other end is closed and is free to move. It is connected by a link to a lever which bears a circular rack in gear with a pinion. The motion of the free end of the tube is multiplied and is shown by the motion of a needle on the pinion. The scale on the dial is marked by trial to agree with the indica- tions of a mercury column or of a standard gauge. A hair- spring on the pinion (not shown in Fig. 139) takes up the back- lash of the multiplying-gear. The long, flexible spring-tube is liable to vibrate to an undue extent when the gauge is exposed to the jarring of a locomotive. To avoid this difficulty, two short stiffer tubes have their ends connected to a more effective multiplying device, shown by Fig. 141. The greater number of joints in this device makes it less sensitive than the other form. Since the spring-tube changes its shape if the temperature changes, hot steam should not be allowed to enter it. An 346 STEAM-BOILERS. inverted siphon or U tube filled with water is, therefore, inter- posed between the gauge and the steam from the boiler. Fig. 141. Safety-plugs, or Fusible Plugs, as shown by Fig. 142, are made of brass and provided with a core of fusible metal. If the plate into which they are screwed is in danger of over- heating, the fusible metal will melt and run out, and steam and water will blow into the furnace. If the fire is not put out, it will at least be checked and the attention of the fire- man will be attracted. The melting-point of fusible metals is not always certain, and the plugs not infrequently blow out when there is no ap- parent cause. On the other hand, they sometimes fail to act when the plate is overheated. If the plug is covered with incrus- tation, the fusible metal may run out without giving warning. The following are some of the places where a fusible plug is used : In the back head of a cylindrical tubu- lar boiler, about three inches above the top row of tubes. In the crown-sheet of a locomotive fire-box. In the lower tube-sheet of a vertical boiler; or sometimes in one of the tubes a Fig. 142. little above that tube-sheet. BOILER ACCESSORIES. 347 In the lower side of the upper drum of a water-tube boiler. The fusible composition has a conical form so that it can- not be blown out by the pressure of the steam. Foster Reducing-valve. — When steam is desired at a less pressure than that of the boiler, it is passed through a reducing-valve like that shown by Fig. 143. The valve H is held open by the spring at/, acting through the toggle-levers Fig. 143. a, until the steam-pressure in the exit-pipe B, pressing on the diaphragm D, is able to overcome the spring and close the valve. The pressure at which this may occur is determined by the tension of the spring, which may be regulated by the screw at K. It is expected that the valve will be drawn up so as to admit just the proper amount of steam to the exit-pipe B to maintain the de- sired pressure in it. Valves for this purpose are liable to work intermittently, i.e. they close till the pressure falls 348 STEAM-BOILERS. below the proper point, then they open and raise the steam- pressure above that point. The valve is a species of throt- tling-valve, and therefore cannot be expected to remain tight. If the machinery supplied by the reducing- valve is liable to be injured by excessive pressure, there must be a stop-valve beyond the reducing-valve. The stop-valve must be closed when no steam is drawn, and must be used to regulate the supply of steam until the amount drawn exceeds the leakage of the reducing-valve. As practically all reducing-valves make use of a diaphragm, or a spring, they all must give out after a certain number of vibra- tions of the spring or diaphragm. When a reducing-valve gives out there is invariably full pressure established beyond the reduc- ing-valve. A safety-valve large enough to take care of the capacity of the pipe should be placed beyond the reducing-valve. If high-pressure and low-pressure boilers deliver into one main there must be on the low-pressure main safety-valves large enough to take care of all the steam made by the high-pressure boilers. The Damper-regulator, shown by Fig. 144, places the damper in the flue leading to the chimney under the control of the steam-pressure, so that if the pressure of the steam falls, the damper is opened wider to quicken the fire. The pressure of the steam in the boiler is communicated through the pipe a to the lower surface of a diaphragm, and lifts the loaded lever b, which stands half-way between the stops at the middle of its length when the steam-pressure is at the proper point. Should the steam-pressure rise above the proper point, it raises the lever and opens a small piston-valve at c, and water from a hydrant flows into d and presses on a piston which lifts the weights at e and so shuts the damper. The weighted head e of the piston is connected by a chain to the lever/, and closes the valve c as it rises, and so shuts off the water from the hydrant. If the pressure in the boiler drops the lever b as it descends BOILER ACCESSORIES. 349 pulls down the piston-valve in c far enough to open a dicsharge- port, which allows the water under the piston in d to flow to waste. The weights at e are made heavy enough to overhaul the damper and to overcome the piston friction in d. fl m ^ "* m-f Fig. 144. The diameter of the brass pipe d is fixed by the water-pressure available for working the regulator. Should the water-pressure fail, the regulator would not operate and the damper would be held open. Oftentimes damper-regulators are supplied with water from the fire-tanks located on the roofs of many of our factories. A regulator of the same form attached to a throttle-valve 35° STEAM-BOILERS. acts as a reducing- valve, and regulates the pressure below the valve with a variation of less than one pound. Fig. 145 shows the steam-valve used when the Locke regulator acts as a reducing- valve. The valve is a double valve which is nearly balanced, but with a slight tendency to rise under steam-pressure, as the lower valve is the larger. The cylin- drical part of the valve is cut into V notches, so that the supply of steam is regulated to a nicety when the valve is partially open. The cylindrical portion of the valve protects the valve-seat and the valve-face so that the valve may remain tight when closed. Steam-traps. — The object of a steam-trap is to drain con- densed water from steam-pipes without allowing steam to escape. As a rule a trap is placed below the pipe to be drained so that the drip from the pipe will run into it. Some traps that return the condensed water to the boiler do not conform to this rule. Some traps, such as the McDaniels, the Baird, and the Walworth, have a valve under the control of a float, which will allow water to pass but not steam. Fig. 145. Fig. 146. The McDaniels trap is shown by Fig. 146. The drip enters at C and escapes through the exit at E when the valve BOILER ACCESSORIES. 351 G is open. This valve is raised by the spherical float when the water rises to a sufficient height. When the water is drained from the pipe served by the trap, the water-level in the trap falls and the valve G is closed. D is a counter- weight to balance the weight of the spherical float. The valve at G can be opened by screwing down the screw at A r _ ■-■^% Fig. 147. Fig. 148. on to the counterweight. The trap can be emptied through the valve at F. The Baird trap, Fig. 147, has a spherical float D which 35 2 STEAM-BOILERS, controls a piston-valve at J. The inlet is at C, and the outlet at /. The screws A and B allow the valve J to be opened or closed by hand. The Walworth trap (Fig. 148) has a floating bucket into which the drip overflows after the outer case is partially- rilled. When the bucket sinks it opens a passage through the central spindle, and the water in the bucket is driven out through this spindle. The hand-wheel and screw at the top control a valve which is closed when the trap is working. The Flynn trap (Fig. 149) depends for its action on a head of water acting on a flexible diaphragm. Water may enter at the top or the bottom at ori- fices marked A. It fills the pipe B and the globe C as high as the end of the pipe E, and pro- duces a pressure of about a pound per square inch on the under side of the diaphragm at D. The spring at G produces a pressure of about half a pound per square inch on the upper side of the diaphragm. Conse- quently the valve leading from the chamber F to the escape- pipe H is closed so long as the pipe E remains empty. But when the water overflows the top of the pipe E and fills the chamber F, the water- pressure on top of the diaphragm will be the same as that on the bottom, and the spring at G will open the valve and allow water to escape. If the supply of water Fig. 149. at A ceases, the pipe E will be emptied and the valve will be closed under the influence of the pressure on the under side BOILER ACCESSORIES. 353 OUTLET Fig, 150. In the trap as actually constructed the pipe E is about 28 inches long ; in the figure it is made shorter in proportion. The Curtis trap (Fig. 150) has an expansion-chamber at C which JU inlet is closed by a diaphragm A at the bottom, and is filled with a very volatile fluid. So long as the ex- pansion-chamber is immersed in water the pressure of the fluid on the diaphragm is balanced by the spring on the valve-spindle B. If the water is drained away and the chamber is exposed to the temper- ature of steam (212 F. or more), the fluid vaporizes and exerts enough pressure on the diaphragm to compress the spring and close the exit-valve. Return Steam-trap. — The traps thus far considered usu- ally discharge against the pressure of the atmosphere. They may discharge into a closed tank against a pressure that is higher than the atmosphere, but in all cases the pressure in the pipes drained by the trap must be higher than the discharge-pressure. Return steam-traps are arranged to discharge directly into the boiler. The Bundy return-trap, shown by Fig. 151, is set three feet or more above the water-line in the boiler. It is so made that it is first opened to the pipe to be drained, and fills up under the pressure in that pipe. It is then put in commu- nication with the steam-space and with the water-space of the boiler, and the water previously collected drains into the boiler. The trap consists of a pear-shaped receptacle or closed bowl, hung on trunnions, through which the bowl is filled and emptied. When empty the bowl is raised by a weight and lever; when filled with water it Overbalances the weight and 354 STEAM-BOILERS. falls. The ring around the bowl limits the motion. The condensed water from the pipe or system of pipes to be drained enters the trap through the check-valve B, which pre- vents water from flowing back from the trap into the pipe to be drained. The trap is emptied through the check-valve A, which prevents water from the boiler from flowing into the Fig. i 5i . trap. At C is a valve under the control of the trap, which receives steam by a special pipe from the boiler. When the trap is empty and is lifted by the weight and lever, the valve C is thrown down and is shut ; water then flows in through the valve B from the pipe to be drained, and air escapes from an air-valve below C> which is open in this position of the trap. A check-valve on the" air-pipe prevents air from en- BOILER ACCESSORIES. 355 tering the trap if a vacuum happens to be formed in it. When the bowl is filled it falls and opens the steam-valve C, and steam enters the bowl through a curved pipe shown in Fig. 151. The pressure in the bowl is now equal to that in the boiler, and the water collected flows into the boiler by gravity. Separators. — If steam is carried to a distance in pipes, a considerable amount of water of conden. I ^J sation accumulates. It is undesirable to have this water delivered to a steam- engine in any case, but if the water ac- cumulates in a pocket or a sag in the piping, it may come along with the steam in a body whenever there is a sudden change of steam-pressure, and then the engine will be in danger of injury. A good way of removing such water is to allow the steam to come to rest in a steam-drum of suitable size, from which the water is drained by a steam- trap ; the steam meanwhile may flow from a pipe at the top of the drum. A small steam-drum used as separator is likely to fail, from the fact that the steam does not come to rest, or because the entering and leaving currents of steam are not properly separated. The Stratton separator, shown by Fig. 152, brings in the steam at one side of a cylinder, with a whirling motion that throws the water onto the side of ^ ^4,^,^r Fig. 152. the cylinder; dry steam escapes through a pipe in the middle. A good steam-separator will remove all but one or two per cent of moisture from steam, even though the entering steam is very wet. Attention has already been called to the use of separators 356 STEAM-BOILERS. with some forms of water-tube boilers which do not have a sufficient free water-surface for the disengagement of steam. The three separators shown by Figs. 153, 154, and 155 may be used on the steam-pipe to separate water from the steam, or on the exhaust-pipe of an engine fco collect the water and oil. Fig. i 53 . Fig. 153 represents the Curtis baffle-plate separator. The entering steam is divided into three portions, which flow as shown by the arrows. Water or oil coming in contact with the plates adheres to the plates and is collected in the space at the bottom. The Triumph separator, shown by Fig. 154, removes oil or water by centrifugal action and by a settling-chamber. The direction of flow is shown by the various arrows. Fig. 155 illustrates the Detroit separator. The steam is directed against a corrugated annular plate to which water and BOIL ER A CCESSORIES. 357 oil adheres. A settling-chamber in the shape of an enlargement of the casting allows floating particles to be deposited by gravity. Tests made with these separators connected to the exhaust- pipe of an engine have shown that by their use 80 per cent of the cylinder oil used in the engine may be taken out of the exhaust. Fig. 155. Most of this oil is mixed with water in such a way that it cannot be separated from the water. Oil-filters. — If exhaust steam is used for heating and the condensation in the system is returned as feed-water to the boiler it is of great importance that this water should be free from oil. An oil-separator will take out 80 per cent of the oil. The greater part of the 20 per cent remaining may be taken out by a straw-filter. The returns from the heating system are passed through a box about 8 feet long and 2 feet square in section, open at the top. There are partitions across the box so that the water enter, ing at one end flows over one partition and under the next, over the third, and so on. The entire box is filled full of hay or straw. Water is taken 358 STEAM-BOILERS. into the feed-pump from the opposite end of the box. If this straw is changed once in two weeks, or oftener if necessary, not enough oil will get into the boilers to cause any trouble. Feed-water Heaters. — The feed-water supplied to a boiler SAFETY VALVE BLOW * FEED TO BOILER EXHAUST FEED FROM PUMP m^mMZmjgmS&S^g^^S^gm^ u MUD BLOW-OFF Fig. 156. may be heated up to the temperature of the exhaust-steam by passing it through a feed-water heater. Feed-water heaters are sometimes made open, i.e., the steam from the engine BOILER ACCESSORIES. 359 mingles with and heats the feed-water. Such heaters have the disadvantage that the oil from the engine is carried into the boiler. A closed feed-water heater resembles a surface condenser, and as the steam and water do not mingle, there is no danger of carrying oil from the engine into the boiler. The Wain- wright heater, shown by Fig. 156, has the heating-surface of corrugated copper or brass tubes, of peculiar make, to allow for expansion. The steam from the engine passes around the tubes and the feed-water passes through the tubes. The Berryman feed-water heater, shown by Fig. 157. is arranged to have the exhaust-steam pass through a series of inverted U tubes, around which the feed-water circulates. Live-steam feed-water heaters take steam from the boiler to raise the tem- perature of the feed-water up to, or nearly to, the temperature in the boiler. The principal advantage appears to be that unequal contraction, due to the in- troduction of cold water, is avoided. It is claimed that with some forms of boilers a better circulation is obtained by aid of such a heater. The use of a feed-water heater for removing lime-salts from feed-water has been discussed on page no, and an ex- ample of such a feed-water heater wai: illustrated in connection therewith. Feed-pipes. — The temperature of the feed-water is usually much below the temperature in the boiler. It thus becomes essential to so locate the inlet, and to so distribute the water, that un- due local contractions may not occur; this is of special im- 360 STEAM-BOILERS, portance when the supply is intermittent. The feed-pipe for the cylindrical tubular boiler, shown by Plate I, enters che shell near the water-line, through the front head. It is carried along one side of the boiler for about three fourths of its length, and then is carried across over the tubes and opens downward. A feed-pipe is often perforated to give a better distribution of the feed-water. The shell is reinforced by a piece of plate riveted on the outside, where the feed-pipe enters the boiler. The end of the pipe has a long thread cut on it, so that it can be secured through the reinforcing-plate and the boiler-shell, and may then receive a pipe-coupling which connects it to the continu- ation of the feed-pipe inside. Sometimes the feed-water is delivered to an open trough inside the boiler, from which it overflows in a thin sheet. Or a perforated pipe may deliver the water in form of spray in the steam-space. Either method has the advantage that the water comes in contact with steam and is heated before it mingles with the water in the boiler. There is the disadvan- tage that the steam-pressure may fall off when the feed-water is turned on or is increased. It has already been pointed out that the feed-pipe should have a globe valve near the boiler, and a check-valve between the globe valve and the feed-pump. Feed-pumps. — Boilers are commonly fed by a small direct- acting steam-pump placed in the boiler-room. The steam- consumption per horse-power per hour of such pumps is very large, and yet the total steam used is insignificant. They are cheap and effective, and easily regulated. If the boiler-pressure is over 100 pounds an outside packed plunger is preferable to a piston-pump. The pump should be of the duplex type and the plungers at the water end should be covered with a composition or brass sleeve. A section through the water end of such a pump is shown by Fig. 158. BOILER ACCESSORIES. 361 Power pumps driven from a large engine are more econom- ical, provided their speed can be regulated; they not infre- quently are arranged to pump a larger quantity than required for feeding the boiler, the excess being allowed to flow back to the suction side of the pump through a relief- valve. When one pump supplies several boilers, a series of diffi- culties is liable to arise. First, if the boilers are fed singly in rotation, the large intermittent supply of feed-water is likely to give rise to local contraction and the water-level in the boiler fluctuates; there is liability that the water-level will fall too Fig. 158. low, endangering the heating-surface, or there may be excessive priming when the water-level is high. It appears advisable that the feed should be delivered to all the boilers simultaneously, the supply to each boiler being regulated by its stop-valve; each branch pipe to a particular boiler should be provided with its own check-valve, and the water-level and rate of feeding of each boiler must be carefully watched by the fireman, or by a water-tender if there are many boilers. Injectors. — An injector is conveniently used for feeding a boiler if the feed-water is not too hot; it has the incidental ad- vantage that it heats the water as it feeds it into the boiler. An 362 STEAM-BOILERS. injector should be connected up with unions/so that it may readily be taken down for inspection. At sea an injector is commonly used when the boilers are fed from the sea or from a supply- tank. Every boiler should have two independent sources of supply of feed-water, so that there may be some resource if the usual supply gives out. There may be two pumps, or a pump and an injector. A locomotive usually has two injectors. Fig. 159. As the amount of water delivered by an injector can be varied only by a small amount, and as an injector has to be large enough to supply a boiler at the time of maximum demand, it follows that under the ordinary working conditions of the boiler the injector must be used intermittently. Fig. 159 illustrates a Koerting injector. This injector has two sets of tubes; the lower or lifting-tube and the upper or forcing-tube. After opening the steam-valve in the pipe S, the injector is started by pulling the handle about ij inches to the left. This uncovers the lower steam-nozzle or lifting-nozzle. BOILER ACCESSORIES. 363 As soon as water appears at the overflow 0, the handle is pulled back as far as it will go. This, after opening the lower steam-nozzle to its full amount, opens the upper steam-nozzle, and at the same time pushes down the overflow-valve through a link running along the side of the injector. It will be noticed that the water must meet with considerable resistance in passing through the various passages in the injector. Power Pumps. — Where there is more exhaust steam from the auxiliaries than is needed to heat the feed-water, there is no reason why a steam pump should be used to feed the boilers. A power pump driven by the main engine or driven by a motor supplied with current from the main engine will, under such conditions, be much more economical. A belt-driven plunger pump is illustrated by Fig. 160. It is evident that in order to change the amount of water sent to the boiler by one of these pumps, either the speed must be varied, which may be accomplished by driving through a variable speed motor, or a by-pass must be connected so that some of the discharge water may be taken back into the suction. Where a pump is run at constant speed, and the regulation of the quantity of water fed to the boilers is accomplished through a by-pass, the amount of power required to drive the pump is the same whether the by-pass is opened much or little. In some plants three pumps are installed, the capacity of the three being equal to the maximum demand for feed-water ever made. When the load is light one pump only is run, and the quantity of water delivered by it to the boiler regulated by the by-pass; as the load increases two pumps are put on, one run- ning with the by-pass closed and the other with the by-pass closed as much as may be required. There must always be an auxiliary feed pump, which should invariably be steam driven. Turbine Driven Stage-Centrifugal Feed Pump. — The pressure obtained in a single-stage centrifugal pump depends upon the linear speed of the outer ends of the impellers. 364 STEAM-BOILERS. BOILER ACCESSORIES. 365 If a steam turbine, running at speeds between 2000 and 4000 revolutions per minute, be used to drive the impeller of such a pump, considerable centrifugal force will be developed even with a small diameter of impeller. By delivering water from the first stage of the centrifugal under 40 pounds pressure, which we will assume was the pressure developed in that stage, into the suction of the second stage, the second stage is put under 40 pounds pressure to start with, and the centrifugal force developed by the impeller in this stage adds 40 pounds, making the pressure at delivery from the second stage 80 pounds. Fig. 161. By adding a sufficient number of stages, water may be pumped against 250 pounds pressure. There are no discharge valves in this type of pump, and there is no suction valve when the water comes to the pump under a head. There is no danger of getting an excessive pressure in the piping should the delivery valve be closed, as the water after reaching a certain pressure, depending on the speed of the tur- bine driving the pump, would be carried around with the im- pellers in the pump. The pump is sure and reliable as a feed pump. 366 STEAM-BOILERS. BOILER ACCESSORIES. 367 Fig. 161 shows a side view of a turbine and pump, the pump being at the left-hand end. Fig. 162 is a section taken through the stage centrifugal pump. The water enters the pump, Fig. 161, from beneath, and is delivered at the opposite end of the pump. In Fig. 162 water enters at the centre on the left-hand side, and its path through the four stages is shown clearly by the arrows. To increase the efficiency diffuser rings are placed in each stage between the impeller and the outer chamber. These rings are generally fixed, but in some few cases they have been made movable. Blow-off Pipe. — The blow-off pipe draws from the lowest part of the boiler, or from some place where sediment may be expected to collect. On the blow-off pipe there is a cock or a valve which is opened to blow out water from the boiler. Some- times there are both a cock and a valve. A cock has the dis- advantage that it may give trouble by sticking; a valve may leak and the leak may not be detected. The pipe should be carried beyond the cock, so that the attendant is not liable to be splashed with hot water, but the pipe should end in the boiler-room or where discharge through the pipe on account of a leaky cock or valve may be sure to attract attention. Each individual boiler should have its own blow-off pipe. The blow-off pipe where it passes through the back connec- tion is covered with magnesia, asbestos, or fire-brick. In spite of this protection the blow-off pipe may burn off. The device shown by Fig. 163 is used to overcome this difficulty. When the blow-off cock is shut and the valve on the vertical branch is open, there is a continuous circulation of water which keeps the pipe from burning. The valve on the vertical branch is closed before the blow-off cock is opened. If a blow-off pipe burns off and water begins to escape, the feed-pump should be run at full capacity to keep water in 3 68 STEAM-BOILERS. the boiler and guard the plates from burning, if that is possible. The fire should then be checked by throwing on wet ashes or by other means, unless escape of steam from the break in the blow-off pipe prevents. Blow-off Tanks. Boilers located in the thickly settled dis- tricts of a city are obliged to discharge the water coming from the blow-off pipe into the city sewer. In most cities one is not allowed to discharge hot water into the sewer as it disintegrates the tile sewer pipe and causes other troubles. Fig. 163. Tn such cases a blow-off tank is placed at a sufficient height over the boiler so that it will drain by gravity into the sewer. This tank is made of steel plate, and is provided with a manhole, an open vent pipe, and with inlet and outlet pipes connecting with the blow-off pipe and with the sewer. There should be a valve in the outlet pipe. The size of the tank determines the amount of water which can be blown out at one time. After the water collected in the tank has cooled sufficiently the outlet valve is opened and the water discharged into the sewer. BOILER ACCESSORIES. 369 Piping" to carry steam from a boiler to an engine, for heating buildings- and for other purposes is too important to be considered as accessory to the boiler. A iew remarks, how- ever, may not be out of place. The coefficient of expansion of steel pipe is .0000065. This means that for each degree increase in temperature the pipe expands this fraction of its length. Thus a pipe at 70 F. measures 100 feet. What will be the expansion of this pipe if used to carry superheated steam at 165 pounds absolute pressure with 150 superheat? At 165 pounds absolute the temperature is found from the 0-Six% holes h'balanced expansion joint Fig. k tables to be 365°.o. F.; add 150 to this, giving 5i5°.o. as the tem- perature of the steam. The increase of temperature is 515.9 — 70 or 445°-9- 445°.oX.ooooo65Xioo'Xi2" = 3.48' the expansion in the 100 feet. In a long line of high-pressure piping where the expansion is 6 or more inches, the expansion may be taken up in an expansion- joint like that shown by Fig. 164. The flanges at either end are connected to the pipe. 370 STEAM-BOILERS. The drawing needs no explanation. An expansion- joint, like Fig. 164, is in use on a 20-inch pipe at the Merrimack Mills at Lowell, Mass. The following figures on expansion were obtained by the chief engineer: Length of 20-inch and 16-inch pipe, 277 feet 8 inches. Temperature of outside air, 56 F. Expansion of the pipe at 50 pounds gauge, 4 Jf inches. At 100 pounds gauge, 5|| inches. At 150 pounds gauge, 6|f inches. In long runs of pipe not over 6 inches in diameter, the expan- sion may be allowed for by screwed fittings, as shown by Fig. 165. • Fig. 165. The pipes shown broken are anchored at either end. The length of the pieces running at right angles depends upon the amount of expansion to be taken care of. As arranged there is no chance to pocket water in the expan- sion-joint. A drip should be provided at the end of the pipe bringing steam into the joint. A common way of allowing for expansion is illustrated by Fig. 166, which shows the connection from a boiler to the main steam-pipe. When the main steam-pipe expands or contracts, the short nipple between it and the angle-valve turns a little at one or at both ends; in like manner the vertical pipe turns a little at the nozzle or at the elbow. The motion is so small and so distributed as not to give any trouble unless the expansion to be provided for is very large. BOILER ACCESSORIES. 37 1 Fig. 1 66 is so arranged that there is no space where water can collect when the boiler is shut off from the main steam- pipe. If the stop-valve were in the vertical pipe, as is some- times the case, then the pipe over the valve would fill up with water when the boiler is shut off, and that water would be O A Fig. 166. suddenly blown into the steam-main when the stop-vaive is next opened. A pipe so situated should always have a drip- pipe to draw off condensed water before the valve is opened. As a special example we may mention the pipe leading to an engine, which always has a drip-pipe above the throttle-valve. Pipes that are likely to be troubled by condensation should be continuously drained by a steam-trap. Horizontal pipes are sometimes arranged so that water may collect in them, due to a sag in the pipe or to the fact that they do not properly drain through a side branch. Though the water may lie quiet in such a pocket while the draught of steam is steady, a sudden increase in the velocity of the steam, or a rapid opening of the valve supplying steam to the pipe, will sweep the water up and carry it along with the steam. The danger from the inrush of water to an engine is readily seen, but it is not so well known that the water thus violently thrown 372 STEAM-BOILERS. against elbows and other fittings give rise to leaks, if it does not burst the fittings. It is to be remembered that steam offers little or no resistance to the movement of water in a pipe, as it is readily condensed either from a slight increase of pressure or by mingling with colder water. Again, water at the temper- ature corresponding with the pressure easily separates, forming bubbles of steam, which as easily collapse, and the shock of impact of the water gives rise to pressures that search out all weak places in the pipe, even at some distance. Steam-piping should be pitched in the direction of the flow of the steam sufficiently to drain out the condensation. Should a large pipe be connected to one of smaller diameter, the bottom of the inside of the pipes must be kept on the same level. For this purpose eccentric flanges and tees with eccentric outlets may be used. To-day nearly all of the high-pressure piping is put up with elbows made of bent pipe instead of cast-iron or gun-iron flanged fittings. The bent pipe, by giving, allows for expansion, and it also reduces the friction loss in passing through the quarter turn. The radius of the bends is commonly made equal to five diam- eters of the pipe. To get some idea as to the stiffness of these bent pipes the following tests on bent pipes were made at the Massachusetts Institute of Technology by two seniors under the direction of one of the writers: The figures marked Pipes Nos. 1-9 give the size and weights. The load was applied at the points marked by the arrows, and deflections were measured at points indicated by the dash and dot lines. Fig. 167 illustrates the best practice in connecting a boiler to the main. The pipe is given a slight pitch towards the main. There are two straight-way valves with advancing stems and a blanked tee in the line. The three may be bolted together. The valve operated by the chain has a by-pass (not shown). If a boiler is piped to the main in this way there is no danger BOILER ACCESSORIES. 373 m n fi-cr fa «fe^ Weight = 552 lbs. Outeide dia. 6.625 Inside dia. 6.065 Weight =133 lbs, Outside dia.S.SQQ, Inside dia. 3.067 374 STEAM-BOILERS. PIPE No. i. Outer dia. 5". Inner dia. 4.25" PIPE No. 2. Outer dia. 6.625". Inner dia. 6.065' Total Motion in Inches. Load, Pounds. At Outer At Inner Line. Line. 200 .060 .025 400 .125 .050 600 .185 .076 800 .250 I05 1000 •3" 133 1200 .372 .160 1400 -435 .185 1600 .499 .213 1800 .561 .240 2000 .625 .265 Total Motion in Tnches. Load, Pounds. At Outer At Middle At Inner Line. Line. Line. 600 .29 .16 .08 1200 -58 -31 .16 1800 .87 •45 -23 2400 1. 16 .61 31 3000 1.50 .78 ■39 3600 1.88 .96 .48 PIPE No. 3. Outer dia. 6.625". Inner dia. 6.065' Load, Pounds. Total Motion in Inches. At Outer Line. At Second Line. At Third Line. At Inner Line. 200 400 600 800 1000 1200 1400 1.20 2.35 3-55 4.70 5-9° 7-3° 9-i5 0.83 1-65 2-45 3-30 4-15 5.20 6.50 0.50 0.97 1-45 i-95 2-55 3.20 4.00 0.17 0-34 0.80 O.67 0.86 1. 10 1-5° PIPE No 4. Out. dia. 6.625". In. dia. 6.025' Total Motion in Inches. Load, Pounds. At Outer Line. At Inner Line. IOOO .050 -OI5 2000 .107 .030 3000 4000 5000 6000 .167 • 230 -293 -365 -045 .060 .080 .100 7000 -442 .123 8000 8500 .542 .603 • *55 .174 PIPE No. 5. Outer dia. 5.563." Inner dia. 5.045' Load, Pounds. Total Motion in Inches. At Outer Line. At Inner Line. IOOO 2000 3000 35°° .205 .407 .612 .740 .058 •"5 .177 .216 BOILER ACCESSORIES. 375 PIPE No. 6. Outer dia. 8.62". Inner dia. 7.62". PIPE No. 7. Out. dia. 7.625". In. dia. 7 023' Total Motion in I nches. Load, Pounds. At Outer At Middle At Inner Line. Line. Line. 1000 •175 .108 050 2000 •345 217 . 100 3000 .516 •3 2 4 .151 4000 •695 -435 .205 5 coo .860 •542 .255 6000 I.032 .652 ■3°7 7000 I 206 .761 .360 8000 1 375 .872 .410 8500 1.463 -932 .440 PIPE No. 8. Out. dia. 3.500". In. dia. 3.067". Load, Pounds. lotal Motion in Inches. At Outer Line. At Middle Line. At Inner Line. IOO 200 300 400 ,820 I.620 2.420 3.280 -441 .880 1.320 1. 912 -1 24 .248 .380 .500 Total Motion in Inches. Load , Pounds. At Outer At Inner Line. Line. IOOO .182 .080 2000 390 . 160 3000 .628 • 252 4000 .892 .366 5000 1.225 •5IO 5500 I.480 .618 PIPE No. 9. Out. dia. 3.500". In. dia. 3.067' Total Motion in Inches. Load, Pounds. At Outer Line. At Inner Line. 200 .158 ■037 400 600 3 11 466 .071 . 106 800 620 . 142 IOOO 775 .178 1200 95° .228 1400 I 215 319 Fig. 167. in going inside the boiler even though there may be 200 pounds pressure in the main. By shutting both valves and uncovering 376 STEAM-BOILERS. the outlet on the blanked tee there is no possibility of steam leaking back into the boiler. The outlet of the tee may be on the side or on the bottom. Piping must be anchored at some point. Generally there must be an anchorage near the engine. Each system of piping has to be considered by itself, and no general rule can be given. A simple form of anchor is shown by Fig. 168. If a pipe passes through a brick wall a clamp may be made to fasten to the pipe and to bear against the wall. Fig. 169 shows a method used in supporting large pipes. The top roller is generally omitted. Small piping, up to 8 or 10 inches, is frequently hung by rings. Figs. 170, 171, and 172 show three of the forms of flanged joint used on high-pressure piping. Fig. 172 is known as the Van Stone joint. Bursting Pressure of Extra Heavy Flanged Fittings, — — An investigation as to the strength of fittings was made by the Crane Company and the results of their tests published in The Valve World of Nov., 1907. From their tests they deduced the following formula: T = thickness of metal; Z> = inside diameter; B = bursting point; £ = 65 per cent of tensile strength of the metal up to 12 inches diameter and 60 per cent for sizes over 12 inches diameter. T pXS=B. For working pressure divide B by a factor of from 4 to 8 as desired. Vibration of Steam-pipes. — Steam pipes-connected to high- speed engines seldom vibrate much. Pipes leading to slow- speed engines often vibrate badly. BOILER ACCESSORIES. 377 Fig. 1 68. Fig. 169. Fig. 170. Fig. 171. Fig. 172. 378 STEAM-BOILERS. An engine, rigid on its foundation, may set up vibrations in a pipe through pulsations caused by the checking of the velocity of the steam at cut-off. Such vibrations are most apt to oocur in pipes which are amply large for the engine. In most cases of vibration, if the stop-valve on the boiler is closed so as to make a slight drop in pressure at the engine, 2 or 3 pounds, the vibration will cease. A large drum placed close to the engine with a throttling-valve in the steam-pipe entering the drum will accomplish the same result. The valve close to the drum will then be used to stop the vibration Area of Steam-pipe. — In order that the loss of pressure in a steam-pipe due to friction may not be excessive, it is customary to limit the velocity to 5000 or 6000 feet per minute where steam is taken intermittently, as, for example, in the pipe sup- plying a slow-speed reciprocating engine. Pipes for steam turbines and for high-speed reciprocating engines may, on account of the steady flow, be figured on 10,000 feet velocity. Example. — Required the diameter of the main steam-pipe leading from a battery of boilers having an aggregate of 3000 boiler horse-power. Assume the pressure to be 100 pounds by the gauge, or about 115 pounds absolute. Assume also that a boiler horse-power is equivalent to 30 pounds of steam per hour. Then the steam drawn from the boiler in one hour is 30 X 3000 = 90,000 pounds. The steam per minute is consequently 1500 pounds. Now one pound of steam at 115 pounds absolute has a volume of 3.862 cubic feet. Consequently 1500 X 3.88 = 5820 cubic feet of steam per minute must pass through the steam- main. With a velocity of 5000 feet per minute the area of the pipe must be 5820 + 5000 = 1. 164 STEAM-BOILERS. 379 square feet, or 167.6 square inches. The corresponding diameter is 14^ inches. The next larger size of pipe is 16 inches, which will be used. In calculating the size of the steam-pipe needed for a battery of boilers the lowest pressure at which the boilers will ever work- must be considered, for a pipe which will carry 500 H.P. at 150 pounds pressure will carry only about 3/4 of 500 at 100 pounds pressure with the same velocity. Flow of Steam in Pipes. — Various formulae have been proposed for use in figuring the weight of steam a pipe will deliver with a cretain drop in pressure. An article by Prof. G. F. Gebhardt in Power, 1907, compares all of these formulae. It would seem that the formulae proposed by Mr. G. H. Babcock give results which agree very closely with results ob- tained by experiment. In this formula w = the weight of steam in pounds per minute; d = diameter of pipe in inches; L = length of pipe in feet ; P = the drop in pressure in pounds per square inch; ;y = the mean density in pounds per cubic foot; V = velocity in feet per minute. ^ = 15,950 3.6\' K-¥) 380 STEAM-BOILERS. Steam Meters. — There are a number of different kinds of steam meters in use to-day. The most common are the St. John, the Dodge or General Electric, and the Gebhardt. The last two consist of a Pitot tube used to measure velocity. The tube is the same in principle as that already explained in connection with the subject of induced draught-fans, but is made much stiffer and stronger. The greater the velocity of the steam in the pipe the more reliable are the readings. In the large boiler plants built recently, it has been the custom to connect a steam meter of the Pitot-tube type in the pipe leading from each boiler into the main. These meters tell at a glance what each boiler is doing, and have proven a great help to the men in charge of the different fire rooms. The meters are generally self-recording, and these, together with recording steam gauges, C0 2 recorders, high and low water alarm whistles, and recording volt-meters and ammeters, make it possible for an engineer to tell from his office the condition of his entire plant. Pipe-covering. — The steam-pipes should be covered with some non-conducting material to prevent radiation of heat. Magnesia, asbestos, mineral wool, hair-felt, etc., have been used for such coverings. Generally a sectional covering is used on the straight pipe and plastic on the fittings. It is probable that four tenths of a heat-unit will be lost per square foot of pipe surface per hour per degree difference of temperature between the steam inside the pipe and the air, if any good covering from 1 inch to i\ inches in thickness is used. A bare pipe would lose from 2.5 to 3 heat-units in radiation from each square foot per hour and per degree difference of temper- ature. The saving to be made by covering the pipes is apparent. Tube-cleaners. — To remove the scale which collects on the inside of the tubes of water-tube boilers supplied with a poor grade of feed-water, turbine tube-cleaners are used. BOILER ACCESSORIES. 381 Figs. 173 and 174 show the Liberty tube-cleaners. The head shown by Fig. 173 is for hard scale and also for use in a bent tube. \a p Fig. 173. Fig. 174 shows a different head attached to the turbine. The turbine blades are seen in Fig. 174. Water from a hose is taken into the outer casing. The water in escaping passes through the turbine, which rotates at high velocity, throwing out the arms with cutters by centrifugal force. The scale removed is washed away by the water. Fig. 174. The Weinland turbine cleaner is shown by Figs. 175 and 176. The lower right-hand figure is in section. The porcupine head, which is used on heavy scale, is shown at the left. This, like the preceding, operates with a i^-inch hose. A cleaner for removing soot from the inside of fire-tubes is shown by Fig. 177. This is attached to a long rod and pushed through the tube. 3 82 STEAM-BOILERS. Fig. 175. Fig. 176. Fig. 177. CHAPTER X. COAL HANDLING AND COAL-HANDLING MACHINERY. Coal-conveying Apparatus. — Until recently but little of value has been written on the subject of conveyors. An article by Mr. W. G. Hudson in the Engineering Magazine, vol. 37, 1909, and articles by Messrs. G. E. Titcomb, S. B. Peck, and C. K. Baldwin, in 1908 Transactions of A.S.M.E., cover the subject quite fully. Much of what follows has been abstracted from these articles. Conveyors for the continuous nandling of coal or other material may be divided into two general classes : (a) Those which push or pull their load, the weight of the load not being borne by the moving parts of the conveyor. (b) Those which actually carry the material handled. Conveyors of the first class push or pull the material handled in a trough. The friction of the conveyor itself and of the material conveyed on the trough both consume power and cause wear. Hence the field of usefulness of conveyors of this type is confined to relatively small conveyors with light service; or in the larger installations, to the handling of materials with a low coefficient of friction, and which are not abrasive in their action, such as coal, grain, etc. Flight Conveyors. — One of the oldest forms which, from its simplicity and comparatively low first cost, is still one of the most extensively used, consists merely of an endless chain to which are attached, at intervals, scrapers or flights. The im- proved forms of this conveyor, now most generally used, have sliding shoes or rollers attached to the flights or the chains, supported on runways. The flights are allowed to come very close to the trough bottom, but not actually in contact with it, 383 384 STEAM-BOILERS. thus reducing the friction upon the trough to the minimum amount. The accompanying figure (Fig. 178) illustrates a single-strand flight conveyor. Fig. 178. CONVEYING CAPACITIES OF FLIGHT CONVEYORS. S. R. Peck, A.S.M.E., 1910. In tons (2000 pounds) of coal per hour at 100 feet per minute. Horizontal. Inclined. Size of Flight. Spaced. Pounds per Flight. IO°. 24 Inches. 20 °. 24 Inches. *>•. 18 Inches. 18 Inches. 24 Inches. 24 Inches. 4X10 4X12 5Xl2 5X15 6X18 33f 42! 69I 30 38 46 62 80 120 22^ 28! 345 46^ 60 90 105 135, 1725 15 19 23 31 40 60 70 90 115 18 24 ■ 28! 4o| 492 72 84 120 150 I4l 18 22i 312- 4o£ 57 66£ 96 120 10? I3f i6£ 22^ 31* 48 56 72 90 8X18 8X20 8X24 10X24 The horse-power required for handling anthracite coal may be determined from the following formula, this taking no account of gearing or other driving connections. A TL + BWS H.P. = 1000 COAL HANDLING AND COAL-HANDLING MACHINERY. 385 T = net tons per hour. L = length, centre to centre, in feet. W = weight of chain and flights (both runs) in pounds. S = speed per minute in feet. A and B are constants depending on the inclination from the horizontal. (See values below.) TT OOOOO O O O O Hor. 5 10 15 20 25 30 35 40 45 A 0.343 0.42 0.50 0.585 0.66 0.73 0.79 0.85 0.90 0.945 B 0.01 0.01 0.01 0.01 0.009 0.009 o-OOQ. 0.008 0.008 0.007 The common working speeds are from 100 to 200 feet per minute, and the capacities are as shown by the table, these con- veyors in some cases handling upwards of 500 tons per hour. As an illustration, suppose it is desired to elevate hard coal 50 feet by a flight conveyor inclined 30 degrees, the capacity of the conveyor being 30 tons per hour at 100 feet speed per minute. From the table it is evident that at a speed of 100 feet per minute the flight should be 6 inches by 18 inches and spaced 24 inches apart. The length of the conveyor, centre to centre, would be at least 100 feet. Calling the weight of the chain 20 pounds per foot, and the weight of the flights spaced every 2 feet, 40 pounds, as given, the total weight per foot figures as 40 pounds. Substituting, in the formula given, the _ 0.79 X 30 X 100 + 0.009 X 200 X 40 X 100 1000 = 7-77- Pivoted-bucket Carriers. — Where the design of the plant re- quires conveying machinery adapted to the combined service of handling coal and ashes, the pivot-bucket carrier is hard to excel. The handling of ashes is very hard on conveying ma- chinery, and the construction of the carrier permits replacement of the several parts as corrosion or wear proceeds. 386 STEAM-BOILERS. Typical of this combined service is the recent installation in the new Wanamaker power house in Philadelphia. Here the inaccessible position of the storage bunkers makes it imperative that the conveying machinery should be reliable. Coal is de- livered by wagons at the street level to a reciprocating feeder, and is carried by a Dodge carrier up and over the storage bins. The lower horizontal run of the machine brings it beneath the ash discharge gates, so that ashes may be handled between the intervals of coaling. Steam sizes of anthracite coal are burned exclusively. This carrier operates at a speed of 42 feet per minute. The vertical lift is 114 feet. Power required when operating un- loaded, 6 horse-power; loaded, at 40 tons per hour, 16 horse- power, showing good efficiency. The buckets are of malleable iron, about 1/4 inch thick and 24 by 24 inches in plan. The ends of the shafts carrying the buckets form the chain pins. The inner links are bushed to obtain the necessary bearing surface, oil ducts extending into the bearings from the ends of the shafts. The bushings are protected by chilled cast-iron collars which engage the driving sprockets. The flanged self -oiling rollers, spaced midway in the links, support the carrier on the horizontal runs and do not engage the sprockets. Pivoted-bucket carriers for elevating coal in power-plant service have become quite popular. Their advantages are slow speed, silent operation, adaptability to change of direction with- out transfer, high efficiency, and easy renewal of worn parts. Their disadvantages are danger of buckets sticking or upsetting and jamming in the supports, and the difficulty of preventing spill at the loading and turning points. Protection against jamming may be had by connecting with the driving machinery through a safety pin whose margin of strength beyond the power requirements is very slight; or better, by designing the supports so that the buckets will clear in whatever position they may come around. COAL HANDLING AND COAL-HANDLING MACHINERY. 387 Uncleanly loading is guarded against in various ways in the several latest designs of carriers, of which the following may be noted. In the Hunt carrier, Fig. 179, the buckets are spaced an inch Fig. 179. or so apart and are loaded by a special device consisting of a series of connected funnels at the loading chute, Fig. 180, in Fig. 180. synchronism with, and dipping into, the carrier buckets, so that each bucket received its proper charge only. The Webster carrier has buckets with carefully planed lips, and the pitch of the buckets being very slightly less than the pitch of the carrier chain links, thus depending on close contact to eliminate the leakage. The McCaslin carrier, made now by the Mead, Morrison 3 88 STEAM-BOILERS. Manufacturing Company, uses overlapping buckets. These lap the wrong way after tripping for discharge, and are reversed by a " righting mechanism " before again passing the loading point. The Dodge carrier, Fig. 181, uses small auxiliary buckets hung beneath the apertures between the main buckets to catch the drip and return it to the main buckets at the first upturn. Fig. 181. The auxiliary buckets are shown fastened rigidly to the inner links. These auxiliary buckets are horizontal and at right angles to the chain on vertical lifts. Fastened to the end of the main carriers or buckets there is a cam which serves to dump the bucket, the arrangement being similar to that shown by the next illustration. The Peck carrier, Fig. 184, uses overlapping buckets similar to the McCaslin, but they are attached to the links extended beyond the points of articulation. This arrangement unlatches the buckets at the turns by giving them a path of greater radius than the chain joints, thereby doing away with a righting device otherwise necessary with the overlapping bucket. None of these devices for preventing spill at the loading and COAL HANDLING AND COAL-HANDLING MACHINERY. 389 turning points are particularly effective. The difficulty is in- herent in this type of conveyor whose many advantages, how- ever, far outweigh their defects. The alternative of the pivoted-bucket carrier for handling coal is the standard arrangement of an elevator with rigid steel buckets discharging into a flight conveyor which crosses above the bunkers, and is provided with discharge gates at convenient intervals; or instead of a flight conveyor, a belt with movable tripper, Figs. 182 and 183. This is a well tried-out system, o^R Fig. 182. Fig. 183. thoroughly reliable, and by many preferred to the run-around carrier on the ground, of lower first cost and simpler construc- tion. The elevator conveyor system is not adapted to handling ashes, which, however, should be taken care of by separate machinery whenever possible to do so. Screw conveyors for boiler-house service are sometimes used where the capacities are not large. In their favor it may be said that they are compact and lowest in first cost. Against them are the objections negligible in small installations, but increas- 390 STEAM-BOILERS. ingly undesirable in larger ones, that they are wasteful of power, unreliable if handling bituminous coal, and of high maintenance cost. The general arrangement of a " rectangular " pivoted bucket conveyor is shown by Fig. 184. Coal discharged from a car or from a cart falls into a hopper, from which it is fed by a reciprocating feeder into a crusher where the large lumps are broken up. From the crusher the coal is taken directly into the conveyor or into the feeding mechanism which fills the conveyor. » Somewhere in the system there must be a tightener, which in this cut is shown as located at the lower right-hand corner. The reciprocating feeder consists simply of a movable plate, at the bottom of the hopper, which is pushed forward and back through the action of an eccentric. On the forward stroke coal is fed into the crusher. The length of the plate is such that coal in the hopper will not flow over the left-hand edge when the feeding plate is still. Maryland Steel Company's Coal-handling Equipment. — An interesting example of coal handling in large capacities is ex- hibited by the equipment of the Otto coke plant of the Mary- land Steel Company, which has been very successful in its operation. Coal is delivered from four track hoppers, equipped with automatic feeders, to two double-strand monobar scraper lines 117 feet centres, with suspended flights every 3 feet. These conveyors deliver the coal to two crushers, and the product is elevated by two gravity discharge elevators, with 24- by 42-inch buckets spaced 3 feet apart. These discharge upon a 30-inch belt conveyor running horizontally 253 feet to the storage bins. The capacity of this installation, with all the machinery in operation, is 220 tons per hour, or, holding one elevator, crusher, and feeding conveyor in reserve, no tons per hour. The total cost of repairs in material and labor averages four tenths to five tenths of a cent per ton handled, and the 39 2 STEAM-BOILERS. labor cost of operating, about nine tenths of a cent per ton. The installation has been handled with intelligence and care, and to this, without doubt, much of the credit for its excellent record is due. Power readings at the motor are as follows: Machine. Each feeding conveyor 117 feet cen- tres: 30 feet rise, 10 by 42 inch suspended flights spaced 3 feet; speed 105 feet per minute Each pair of automatic feeders: Each plate 3 feet 6 inches wide by 11 feet long, stroke 6 inches. . . Each crusher: Two rolls 47 inches diameter by 36 inches long Each elevator: 94 feet vertical lift, 16 feet horizontal run, V-buckets 24 by 42 inches spaced 3 feet apart; speed 105 feet per minute. . Belt conveyor 253 feet centres ^cl- inch belt; speed 650 feet per min- ute. Moving tripper with belt empty runs up power of belt con- veyors to 14 horse-power. Size of Motor. Starting Load. Power Empty. H.P. H.P. H.P. 25 20 5-8 5 5 3 50 43 8 40 27 8 Running Load. H.P. 52 12-17 When the test was made, coal was being handled at the rate of 215 tons per hour, i.e., 107 J tons to each feeding conveyor, crusher, and elevator, and 215 tons per hour upon the belt. The life of a belt handling crushed coal is 18 months. The 1/4-inch steel troughs for the monobar conveyors are good for about 20 or 22 months. An occasional flight must be replaced. The knuckles of the chain are of very ample wearing surface and of long life. The elevator is of unusually heavy construc- tion, with hardened chain pins and chilled driving rollers. The rate of wear here is very slight except at the pinions of the motor and countershaft. The brunt of the work comes upon the crushers whose business it is to reduce run-of-mine bitumi- nous to 1 inch and under. COAL HANDLING AND COAL-HANDLING MACHINERY. 393 Power Required to Drive a Bucket Conveyor. — The power required to drive a bucket conveyor is rather difficult to figure, inasmuch as the same conveyor at different times requires dif- ferent amounts of power for the same work. From what data the authors have been able to secure through actual tests, it seems that for a bucket conveyor making a rectangular circuit with lift of from 40 to 80 feet of from 20 to 50 tons capacity, and at a speed of from 40 to 55 feet per minute, the horse- power required may be calculated by multiplying the capacity in tons per hour by the lift in feet and by 0.004. The conveyor when running empty will require from 40 to 60 per cent of the power running loaded. The smaller the capacity, the larger the percentage of power empty to power loaded. The crusher through which the coal passes before going to the conveyor often requires as much power as the conveyor. Cost of Handling Coal. — The cost of labor for handling coal (not including interest and depreciation) is given by Peck in Trans. A.S.M.E., 1910, as if cents per ton, this being an aver- age value obtained from a number of large plants handling from 1000 to 9000 tons per month. The coal was received in 50-ton self-cleaning cars and dumped into the hoppers leading to the conveyor. In some few instances the coal had to be shoveled out of the cars. The cost for such conditions ran up to 2 cents or over per ton. Gebhardt in " Steam Power Plant Engineering " says that " an average figure for handling coal by barrow is 1.6 cents per ton per yard, up to a distance of 5 yards, then about 0.1 cent per ton per yard for each additional yard. "With automatic conveyors the operating cost, not including the wages of firemen and water tenders, varies with the size of plant and the type of conveyor, and ranges anywhere from a fraction of a cent per ton to 4 or 5 cents per ton. The larger the plant and the greater the amount of coal burned, the lower will be the cost per ton. In comparing the relative costs of manual 394 STEAM-BOILERS. and automatic handling, fixed charges of at least 15 per cent of the first cost of the mechanical equipment should be charged against the latter, in addition to the cost of operation. " In large central stations equipped with stokers and con- veyors and consuming 200 tons or more of coal in 24 hours, the cost of handling the coal from coal car to ash car, including wages of fireman and water tenders, will range between 10 cents and 18 cents per ton." Belt Conveyors. — The earliest conveying belts were perfectly flat, being supported by plain cylindrical rollers such as are still used for the returning run. In order to increase the conveying capacity without the material spilling off the edges of the belt, the rollers were somewhat dished, or made concave in form, causing the belt to assume the form of a shallow trough. In theory this is open to the criticism, that but one diameter of the concave roller can travel at the speed of the belt, and some slipping must therefore take place at every other diameter of the periphery. Careful observations have shown, however, that the belts invariably fail in other ways before any injury from this slipping becomes apparent. Before this fact was demonstrated, however, a supporting device, consisting of three independent rollers, the middle one horizontal, and the side rollers inclined some 35 or 40 , came into very general use, this arrangement giving the belt the form of a deep trough and adding greatly to its carrying capacity. Further modification of this was the substitution of two in- clined centre idlers for the one horizontal idler. This, while giving a relatively deep trough, overcame the sharp bends in the belt incident to the three-roll support and permitted the belt to assume a uniform curve. For belts of large capacity, the four-roll idler may, therefore, be considered the best modern practice. For smaller belts and moderate capacities, there is nothing better than the old concave roller referred to, which troughs the belt but slightly, and, therefore, insures the greatest durability. COAL HANDLING AND COAL-HANDLING MACHINERY. 395 The conveying belts themselves are of cotton duck, woven solid; or of a number of plies varying from three to eight, stitched or cemented together with a composition of rubber and known as rubber belts. Canvas belts are plain duck, or are treated with some preservatives and painted with some compound. For many kinds of service they meet every requirement. For severe duty, where the cotton fabric, which is the strength of the belt, must be protected as perfectly as possible from dust, moisture, and cutting or wearing action, the rubber belts are preferable, and are usually made with a cushion of from 1/10 inch to 1/4 inch, more or less, pure rubber on the carrying side, which protects the fabric until this cushion is worn away. Special types of belts have been extensively used, some having fewer plies of canvas and a heavier cushion of rubber in the centre where the belt is designed to receive and carry its heaviest load, and others having the fabric made thinner at the points where it is intended the belt should be bent to form a trough. Experience seems to show that the greatest durability is at- tained by avoiding a localized bending. The belt conveyor has a wide field of usefulness and is deservedly popular both with manufacturer and user. It is simple, smooth, and noiseless in operation, and may be run at relatively high speeds, from 300 to 800 feet per minute, with con- sequent large conveying capacity. On account of the expense of the belt, and the large number of supporting rollers which revolve at high speed, the initial cost and the power consumed in operation are much greater than would be supposed, and not materially less than heavier and more cumbrous looking con- veyors of other types, performing equivalent service. The most serious objection to belt conveyors, and the one which has prevented their even more general use, is the lack of durability of the belts, their liability to destruction from acci- dental causes, and the expense of their frequent renewal. Capacity of Belt Conveyors. — Belt conveyors may be built to handle practically any quantity of material which may be fed 396 STEAM-BOILERS. to them. The following table gives the capacity, maximum size of lumps, and advisable speed for the different widths of belts. BELT CAPACITY AND SPEED. Width of Belt. Maximum Size of Pieces. Maximum Advis- able Speed in Feet per Minute. Capacity in Cubic Feet at the Maxi- mum Advisable Belt Speed. 12 2 300 1,380 14 25 300 1,890 16 3 300 2,460 l8 4 350 3.640 20 5 350 4,480 22 6 400 6,200 24 8 400 7,400 26 9 450 9,810 28 12 450 11,250 30 14 450 I3.050 32 15 500 16,500 34 16 500 18,500 36 18 500 21,000 38 19 550 25.300 40 20 550 28,050 42 20 550 30,800 44 22 600 37,200 46 22 600 40,800 48 24 600 44,400 Speed and Size of Belts. — When the quantity to be con- veyed is small, and the pieces large, the size of the material fixes the width of the belt, and the speed should be as low as possible to carry safely the desired load. When the quantity is great, the capacity fixes the width, and in this case also the speed should be as low as possible. A belt at slow speed may be loaded more deeply than one at high speed, and when a narrow belt is run much above the advisable speed, the load thins out and the capacity does not increase as the speed. The maximum length of the different widths of conveyors is determined by the fibre stress in the belt, and is, therefore, closely related to the load and speed. Naturally level conveyors COAL HANDLING AND COAL-HANDLING MACHINERY. 397 may be built longer than those lifting material. Conveyors 1000 feet from centre to centre, handling 400 tons per hour, have been most satisfactorily operated. Another important factor in the design of conveyors at high speed handling large quantities is the flow of material in the chutes. A 36-inch conveyor handling 750 tons of coal per hour, with a belt speed of 750 feet per minute under a 10,000-ton pocket, could not be loaded from a single chute, because it was not possible for the coal to attain a speed of 750 feet per minute in the chute. It was necessary, therefore, in order to obtain a full load, to open seven gates, each placing a layer of coal on the belt until the desired load was obtained. During a test this belt carried about 800 tons per hour. Power Required for Belt Conveyors. — The power required to drive a belt conveyor depends on a great variety of conditions, such as the spacing of idlers, type of drive, thickness of belt, etc. In figuring the power required, it is important to remember that the belt should be run no faster than is required to carry the desired load. If for any reason it is necessary to increase the speed, the figure taken for load should be increased in pro- portion and the power figured accordingly. In other words, the power should always be figured for the full capacity at the chosen speed, as follows: C = power constant from table, page 398; T = load in tons per hour; L = length of conveyor between centres in feet; H = vertical height in feet that material is lifted; S = belt speed in feet per minute; B = width of belt in inches. For level conveyors, Hp _ CX TXL 1000 For inclined conveyors, Hp _ CXTXL TXH 1000 1000 398 STEAM-BOILERS. Add for each movable or fixed tripper horse-power in col- umn 3 of table below. Add 20 per cent to horse-power for each conveyor under 50 feet in length. Add 10 per cent to horse-power for each conveyor between 50 feet and 100 feet in length. The above figures do not include gear friction, should the conveyor be driven by gears. POWER REQUIRED FOR GIVEN LOAD. 1 2 3 4 5 Width of C C H.P. Belt. For Material For I Material Required for Minimum Maximum Weighing from 25 Weighii lg from 75 Each Movable Plies of Plies of Lbs. to 75 Lbs. per Lbs. tc ) 125 Lbs. or Fixed Trip- Belt. Belt. Cu. Ft. per ( : u . Ft. per. 12 •234 147 1 3 4 14 220 143 1 3 4 16 220 140 3 4 4 5 18 209 138 I 4 S 20 305 136 ll 4 6 22 199 133 I§ 5 6 24 195 131 if 5 7 26 187 127 2 5 7 28 175 121 2\ 5 8 30 167 117 2| 6 8 32 163 115 2| 6 9 34 161 114 3 6 10 36 157 112 si 6 10 With the load and size of material known, choose from the capacity table the proper width of belt and proper speed. The above formulae give the horse-power required for the conveyor when handling the given load at the proper speed. With the horse-power and the speed known, the stress in the belt should be figured by the following formula in order to find the proper number of plies. Stress in belt in pounds per inch of width = ' — ^5j ^ S X B With this value known, the number of plies may be determined, COAL HANDLING AND COAL-HANDLING MACHINERY. 399 using 20 pounds per inch per ply as the maximum. Columns 4 and 5 of this table give the maximum and minimum advisable plies of the different widths of belt. Belts between these limits will trough properly and will be stiff enough to support the load. The maximum number of plies determines the maximum length of each width of conveyor. Belt conveyors may be driven from either end. Somewhere in the system there must be a tightener to allow for the stretch of the belt. The troughing idlers should be placed dependent upon the weight of material carried as follows: For belts 12 to 16 inches wide, from 4J to 5 feet apart. For belts 18 to 22 inches wide, from 4 to 4 J feet apart. For belts 24 to 30 inches wide, from 3^ to 4 feet apart, and For belts 30 to 36 inches wide, from 3 to 3! feet apart. The life of the belt depends a great deal upon the care which it receives, upon the material handled, and upon the quality of the belt to begin with. In general the life of the belt may be taken as from three to eight years. The Darley Conveyor. — A system for handling coal or ash by a current of air flowing in a pipe has been in use in some plants during the last three years. A description of a system arranged for handling ash will show the method of operation. A pipe is laid under the floor in front of the boilers with an open- ing through the floor into the pipe in front of each ash-pit door, each opening being closed unless ash is being hauled from the ash-pit into it. The end of the pipe under the floor is open to the air. The other end of this pipe connects with a riser which leads up to the top of a closed steel storage tank in which the ash is to be stored. An exhaust fan or a Root exhauster draws air out of the tank, thus creating a flow in the pipe in front of the boilers. Any ashes, clinker, or even bricks dumped in through the holes in front of the boilers will be carried along by the air and delivered into the closed tank elevated 20 to 40 feet above the boilers. After the exhauster has been stopped the 400 STEAM-BOILERS. ashes may be discharged from this tank into a car or cart by opening an ash valve in the bottom. To quench the hot ash and to prevent dust from being drawn over into the exhauster, a jet of water is sent in on the ash as it is entering the closed tank. The fittings, especially those at the corners where the direc- tion changes, wear rapidly. The elbows are made with renew- able chilled backs or in some cases a tee is used in place of an elbow. The plugged end of the tee filling up with ash causes the wear to come on the ash. Coal Crushers. — The construction of a coal crusher is shown by Fig. 185. The casing is removed so as to show the rolls. The front roll can move back with its bearings compressing the springs when a railroad spike or a coupling pin jams in be- tween the rolls. To allow for such motion the teeth of the driv- ing gears are made of the involute type and are of extreme length. Rolls 17 inches diameter by 24 inches long will reduce run- of-mine bituminous with lumps not exceeding 10 inches by 10 inches to 2\ inches size or less, at the rate of 30 tons per hour; and will require about 5 horse-power. Rolls 28 inches diameter 24 inches long will handle about 50 tons per hour and consume about 10 horse-power. Rolls 28 inches diameter 36 inches long will handle 70 tons per hour and require 15 horse-power. COAL HANDLING AND COAL-HANDLING MACHINERY. 401 Coal Valves. — Figs. 186 to 190 illustrate some of the types of valve used. General Arrangement for Handling and for Storing Coal in the Boiler House. — Figs. 191 and 192 illustrate two different equipments. The cuts need little explanation. A coal supply sufficient for from four to fourteen days may be stored in the coal bins overhead. From these bins or pockets the coax is fed by gravity to the mechanical stokers. The amount of coal used is weighed on its way from the pocket to the stoker by some form of weighing hopper, which may or may not be automatic; in general, similar to those shown by Figs. 195 and 196, and arranged as shown in Fig. 192. The ash may be taken into ash cars, as shown in Fig. 192, or be taken into cars which are later dumped into a hopper, from which a bucket conveyor elevates the ash to a storage hopper. Such an arrangement is shown in Fig. 191, in which the ash conveyor runs up in a vertical shaft, side of the coal conveyor, and turns to the right, where it, together with its driv- ing mechanism, may be seen in the landing over the large hopper into which the ashes are ultimately dumped. The storage bin is commonly designed as in Fig. 191, re- cently, however, a form of bin known as the parabolic bin has found favor among engineers. Such a bin is easy to calculate and brings but little side stress on the columns. The true shape of the curve would be found to be somewhere between a parabola and a transformed catenary. The parabola may be constructed as in Fig. 193 and its area figured as 2/3 xy, Fig. 194. The Brown Hoisting Machinery Company construct a bin of this type as follows: Two parallel plate girders are supported by the steel columns at the top of the pocket. From these girders, at intervals of 3 feet to 4 feet 10 inches, are suspended a series of steel supporting straps each curved approximately to the shape of a parabola. The straps are made strong enough to Fig. i 88. Fig. 189. Fig. 190. (402) 404 STEAM-BOILERS. Fig. 192. COAL HANDLING AND COAL-HANDLING MACHINERY. 405 carry the weight of the lining of the bin and the coal which the bin is intended to hold. The bin is lined with " ferro-inclave " reinforced concrete from 2 inches to 4 inches thick on the inside, and later similarly coated on the outside. \ i i 1 Fig. 194. Fig. 193. The reinforcing steel is of peculiar shape, well adapted to this kind of construction. Weighing Hoppers. — Two makes of travelling weighing hopper are shown — that made by the C. W. Hunt Company, by Fig. 195, and that by the Link Belt Company, by Fig. 196. The weighing system of Fig. 196 consists of two shafts or rods, one of which is shown as AAB in the left-hand view, to each of which is attached two short cranks A A, which act as levers. By referring to the right-hand view it will be noticed that the outer ends of these cranks are hung by links and knife edges from the moving framework above. The hopper is carried by two bars which are hung from knife edges on these four levers in such a way that as coal comes into the hopper it tends to cause the inner ends of these levers to lift. Fastened to each shaft or rod there is at one end of each a lever B, and these two levers pull up on a common rod which is connected with the weighing lever at the bottom. 406 STEAM-BOILERS. COAL HANDLING AND COAL-HANDLING MACHINERY. 407 Fig. 196. CHAPTER XI. SHOP-PRACTICE. The method of work in a boiler-shop depends on the size and arrangement of the shop and on the class of work. There are, however, certain general principles which can be recognized in all modern shops. The materials, especially the plates, are received at one end of the shop, near which is a storeroom, and a bench for laying out work. The plates, after they are laid out, pass in succession to the several machines, where they are sheared, punched or drilled, planed, rolled, and riveted. The machines for performing these operations are arranged in order with proper spaces for handling and working. Space is provided where boilers may be assembled and receive their tubes and furnaces. Machines which, like the punch, have much work to do, compared with other machines, may be duplicated. There should be an efficient system for handling the material at the machines and for passing it on from one machine to the next. A good arrangement is to have a swing-crane near each machine ; the spaces served by the several cranes overlap, so that one crane takes material from the next, and so on. It is advantageous, especially in large shops, to have a travelling crane that can handle the largest boiler made, and which can serve any part of the shop. Flanging and smithing are usually done in a separate shop or room. A few machine-tools are needed for doing work on steam-nozzles, manhole rings and covers, etc. A boiler-shop will have an office, a drawing-room, and a 408 SHOP-PR A C PICE. 4 00 pattern-room, also a storeroom for patterns. These may be conveniently located in the second story. A Boiler-shop. — The application of the general princi- ples just stated and the explanation of details can be best given by aid of an example. A medium-size shop for making cylindrical boilers has been chosen for this purpose; the shop is capable of making any shell boiler of moderate size. This shop will employ sixty or seventy men and can turn out two ioo-horse-power boilers per day. It will take about three days to finish one boiler, so that there may be six or more boilers in process of construction at one time. The shop which is represented by Fig. 197 has one end on the street and has a driveway or yard at one side. Plates are received at the street-door by a travelling crane and stored near at hand. The same crane takes plates to the laying-out bench and from there to the crane which serves the shearing- machine. Along one side of the shop are arranged in suc- cession a shearing-machine, two punches, a plate-planer, a *et of plate-rolls, and a riveting-machine. Between the punches and nearer the wall is a flange-punch ; near the planer is a forge for scarfing. This series of machines is served by four swing-cranes, and there are also two hydraulic cranes near the riveting-machine. These cranes, which are at the top of a tower thirty feet high, are operated from the working platform of the riveter. There are two shipping- doors where the finished boilers are delivered to teams, and at each door there is a jib-crane for handling the boilers. These jib-cranes and the hydraulic cranes at the riveter have a capacity of eight or ten tons; the swing-cranes may be much lighter. A shop where large marine boilers are made will have more powerful cranes. The machine-shop is near the receiving-door. Here are the lathes, planers, and drills for doing work on manholes, nozzles, and other fittings ; also a bench for fitting up boiler- fronts. Two drills for boring tube-holes in tube-plates, and 4io S TEA M-B OILERS. SH313AIH «0J I I dwnd onnvaaAH I 1 (~\ ocr z wi ' s in b W 111 2z i / *\ ! ; HONnd | v -~| \ y \ Hovnd x % □ j HONnd| NObi i33hs hoj govuois siNoaj aod 30VBOJ.S » lo o IE C n\l H = =ID Q. - cc o g ° I UJ CO z < co u ij 2 «T = i Sq O I < £ 2 3 -a 133H1S SHOP-PR A C TICE. 411 a boring-mill for facing off the flanges of boiler-heads, are placed in the entrance to the machine-shop, where work can be conveniently brought to them from the boiler-shop. At the end partition of the machine-shop are places for storing boiler-front castings and sheet-iron. The corner of the boiler- shop near the machine-shop is known as the cold-iron shop ; here the uptakes, flues, and dampers are made. This shop has a shearing-machine, three punches, and a set of rolls suitable for sheet-iron work; also a bench with hand-vises. At the rear of the boiler-shop there is in one corner a store- room for tubes, stay-rods, channel-bars, and finished fittings. In the opposite corner are the forge-shop and the engine- room. These are separated from each other and from the boiler-shop by glass partitions which do not cut off the light, and yet keep the smoke and dust from the forge out of the other rooms. The main line of shafting is near the wall over the shear- ing-machine, punches, and rolls. The shafting for the ma- chine-shop and cold-iron shop is driven by a belt from the main shaft, near the front end of the building. A space is left near the riveter where the plates from the rolls can be assembled and bolted together before going to the riveter. In front of the riveter there is a space about 60 feet wide and 120 feet long where boilers are deposited after leaving the riveter. Here the boilers receive their stays and tubes, here they are calked and receive all fixtures that are perma- nently attached to the shell. At this place the boilers are tested by hydraulic pressure, usually to one and a half times the working pressure. When complete the boilers are painted and oiled, ready for shipment. To illustrate the method of building a boiler more in detail, the different steps in making a horizontal boiler will be followed in order. Flanging Heads. — Regular sizes of boiler-heads flanged at one operation by machinery can now be bought on the 4 12 STEAM-BOILERS. market, and all except the largest shops are in the habit of buying them. The flanging-machine has a former and a die between which the plate is formed under hydraulic pressure while at the proper flanging temperature. No strains due to unequal heating or cooling are set up in this process, and the plate, which is allowed to cool gradually, does not need to be annealed. Irregular sizes and shapes are made in the shop on a special cast-iron anvil, which is about six inches deep, flat on top, and curved at one side to about the radius of the head to be flanged. The corner of the anvil or former is rounded so as not to cut the plate. It is placed near a special low forge where the plate is heated. In flanging, the plate is first marked at short distances on the inner circle of the bend with a prick-punch. A portion of the plate is then heated to a good heat, and the plate is taken to the anvil or former. After adjusting so that the depth of flange overhangs the right distance from the edge of the former, the heated portion of the plate is beaten down Fig. 19S. — Lifting-dogs. against the side of the former by wooden mauls and then smoothed with a flatter and sledge. The plate is then heated in a new place and another portion bent. To straighten the head and also to remove the strains set up by this way of flanging, it should be heated to a dull red and allowed to cool gradually. The lifting-dogs represented by Fig. 198 are used in lift- SHOP-PRACTICE. 413 ing and placing the head during the flanging, and in handling plates during other operations. Fig. 199 represents crane-lifts which are used when plates are lifted and carried by cranes. Fig. igg. After the head is flanged, holes for rivets, stay-rivets, and tubes are marked, and all the rivet-holes are punched. Flange-punch. — The holes in the flange are punched by a special machine shown by Fig. 200. The punch is carried Fig. 200. by a horizontal wrought-iron plunger which is operated by a cam. The die is carried by a hooked extension of the frame. The head is held horizontal with the flange down ; the flange is dropped between the punch and the die and the lever is 4 i4 S TEA M-B OILERS. solid piece of tool-steel. pulled to throw the cam into play ; the plunger then makes a stroke and punches a hole. The machine is driven by a belt, with a fast-and-loose pulley. On the shaft with these pulleys is a heavy fly-wheel. A pinion and spur-gear give a slow powerful stroke to the gear which moves the cam. Punch and Holder. — The punch (Fig. 2 oi) is made of a It has a flat head and a conical shoulder by which it is held onto the plunger, a short straight body, and a slightly coned point. The point is larger at the cutting edge than back toward the straight body, to avoid friction in the hole. A tit in the middle of the face of the punch catches in the centre- punch mark and centres the hole punched. The holder is made of wrought iron. It screws onto the end of the plunger, grips the punch by the conical shoulder on its head, and draws it down firmly against the plunger. Tube-holes. — There are two ways of cutting the holes for the tubes in boiler-heads. Some- times a small hole is punched at the centre of the hole. A tool like that shown by Fig. 202 is then put in the drill-press. The post in the middle is run through the small hole previously punched or drilled, and the two cutters rapidly cut out the tube-hole to the proper size. The other way is to punch the tube-holes at once to the proper size by a helical punch shown by Fig. 203. The die is made in the form of a ring with a flat face, so that the punch begins to cut at the cor- rifl Fig. 202. Fig. 203. SHOP-PR A CTICE. 4 1 5 ners, and the metal is removed by a shearing cut. Though not always done, the holes ought to be punched a little under size and then reamed out to give a fair surface against which the tubes may be expanded. Finishing the Flange. — The boiler-heads are placed on the platen of a boring-mill like that shown by Fig. 204, and the edge of the flange is turned off. The heads of marine boilers are often turned to a true cylinder at the flange to insure that they shall exactly fit the cylindrical shell into which they are riveted. This also gives a good surface to calk against. Boring-mill. — A simpler machine than the boring-mill shown by Fig. 204 would answer to turn off the flanges of the boiler-heads. But the machine is useful in other ways and may do the work which is commonly done on a large lathe. The platen is driven much in the same manner as the head of a lathe, through gearing and cone pulleys, to provide for various speeds. This gearing is not well shown in the figure, as it is hidden by the frame. The cutting-tool is ad- justed and controlled much like the tool of a planer. The tool-carriage is on a horizontal cross-head which is supported at the side frame and on a round vertical bar at the middle. The tool can be traversed in and out on the cross-head, and the cross-head may be raised or lowered. For doing some classes of work the cross-head may be set vertically on the guides that are shown on the horizontal bars of the frame near the right-hand end. Or, again, a tool may be carried by the central rod, which can be fed down by the screw at the top. Laying on the Plates. — The first and one of the most important steps in the work on the shell is the marking out of the plates. Generally one man in each shop does all the laying out. After squaring the sheet, he marks off the length and locates the rivet-holes by means of gauges. These 4i6 S TEA M-B OILERS. gauges have to be made by trial, a suitable allowance being made in them on account of the thickness of the plate for the Fig. 204. change in length due to rolling. There is a gauge for each course, or a set of gauges for each size boiler, and also sets SHOP-PR A CTICE. 4 1 7 for the same size, but with different thickness of shell. The plates are marked either with a piece of soapstone or with a slate-pencil. Rivet-holes are prick-punched at the centre. Shearing. — When the plate is laid out it is taken from Fig. 205. the bench to the shears and any superfluous stock is cut off. A shearing-machine is shown by Fig. 205. The lower knife is fixed and the upper knife is moved by an eccentric inside the head. The eccentric-shaft is coupled to the gear-shaft by a clutch that is controlled by a treadle. The weight of the sliding-head is counterbalanced by a weight and lever at the top. Lugs are shown on the casting near the knives ; when the machine is required to do extra-heavy work, wrought-iron bolts are put through the lugs and screwed up to strengthen the frame. The machine is driven by a belt with a fast-and-loose pul- ley ; the shaft carrying these pulleys has a pinion gearing into a large gear to give the necessary power for shearing. A fly- wheel steadies the motion of the machine; it must be able to supply the power for shearing-plates without a large reduction in speed. 4i8 S TEA M-B OILERS. Punch. — After the plate is sheared to size it is taken to one of the punches and all the rivet-holes are punched. Larger openings for man-holes and other fittings are cut out by punch- ing overlapping holes, thus leaving a ragged edge which is afterwards chipped smooth. The plate is not entirely cut away at such large openings, but the piece to be removed is left hanging at three or four places until after the plates are rolled into cylindrical form. If the pieces were removed, there would be less resistance to the rolls at such places and the plates would have a conical form instead of a true cylindrical form. The punches resemble the shears shown by Fig. 205, with a punch and die instead of the knives. Machines are often so made that they either punch or shear. Planing. — After the plate is sheared and punched the edges are planed to a slight angle to give a good calking edge. The planer shown by Fig. 206 has a long narrow bed on which the edge of the plate is laid and to which it is clamped by a follower; the follower is forced down by screws which pass through a beam as shown. The tool-carriage is drawn- back and forth by a leading-screw; the tool is made to cut on both strokes, and is fed by hand between the cuts. Scarfing. — When the plates are joined by a lap-joint the proper corners of each plate are heated in a portable forge near the planer, and are drawn down or scarfed so that the overlapping plates may come close together and not leave a space. Plate-rolls. — The plates for forming the cylindrical shell are bent to shape cold by running them through bending-rolls The horizontal roll represented by Fig. 207 has two parallel rolls below that are driven in the same direction by gearing. The upper roll is adjusted at each end separately, and some care is required or the shell will receive a conical shape instead of a true cylindrical shape. The bearing at one end of the SHOP-PRACTICE. 419 420 STEAM-BOILERS, SHOP-PRACTICE. 421 roll can be swung out, as shown by the figure, to remove the plate after it is rolled. The rolls may be driven in either direction by crossed and open belts. The plate to be rolled has one edge introduced Fig. 208. between the upper and lower rolls, the upper roll is brought down and the rolls are started up. The plate is run through nearly to the other edge then the top roll is screwed down 422 STEAM-BOILERS. farther and the rolls are reversed. Thus the plate is run back and forth and the top roll is gradually drawn down till the plate acquires the proper form. The extreme edges of the plate are not bent in this process; they are commonly bent afterwards by hammering them with sledges. Some rolls have a special device for bending the edges ; it consists of two short overhanging rolls about fifteen inches long, one concave and the other convex. The ends of the plate are fed through these rolls sideways, and are bent before they are introduced into the long rolls. Vertical rolls, shown by Fig. 208, are coming into use in boiler-shops. They take up less floor-space, and the plate after it is rolled up into cylindrical form is easily hoisted off from the front roll. For this purpose the front roll is counterbal- anced and the top end can be swung out clear from the hous- ing. The figure shows the rolls as erected by the builders; in the boiler-shop the plate at the lower end of the rolls is flush with the floor of the boiler-shop. The width of plate that can be rolled by either horizontal or vertical rolls depends on the length of the rolls. The length of the rolls and the reach of the riveter (to be men- tioned later) determine the width of plate that can be handled in the shop. Assembling and Riveting. — When the plates for a boiler have been punched, planed, and rolled they are assembled in courses, and bolted together ready for riveting. Formerly boilers were commonly punched and riveted ; now it is cus- tomary to punch the rivet-holes one eighth of an inch smaller than the finished size and then drill to the right size after the boiler is assembled. This is more expeditious than drilling directly, and as all the metal affected by punching is removed it gives as good results. It is the custom in most shops to drill the holes out at the riveting-machine immediately before the rivets are driven and thus each rivet-hole is sure to be true. SHOP-PRACTICE. 423 The shells of heavy marine boilers are drilled after the plates are assembled without previous punching. A few holes are drilled before the plates are rolled and serve for bolting the plates in place when the boiler is assembled. There are two forms of machines for drilling marine-boiler shells. In one the boiler is placed horizontal on rollers so that it may be readily turned, There are two or three upright frames each carrying a drill. The frames may be adjusted lengthwise of the boiler, and the drills may be set at any height or turned at an angle. When a longitudinal seam is drilled the boiler is rotated to bring a row of rivets to a drill, and the frame is trav- ersed from hole to hole. When a ring-seam is drilled the drill is brought to the proper place, and the boiler is rotated so as to bring the rivet-holes in succession to the drill. The other machine has the boiler placed on one end and the verti- cal frames carrying the drills can be rotated into place, and the boiler can be turned on a vertical axis. If plates are punched and riveted without drilling, the holes should be punched from the side of the plate which comes in contact with the other plate. The reason for this is that the die is always a little larger than the punch and the hole is slightly conical, larger at the side where the die holds up the plate. If the smaller ends of the holes in two plates are brought together, then the rivet fills the hole better and draws the plates up more perfectly as the rivet cools. It is clear that three or more overlapping plates should always be drilled, as punched holes cannot always be brought together in a proper manner. This is aside from the desirability of drill- ing all rivet-holes. Returning now to the assembling of a cylindrical boiler, the process is as follows: The back head is put in the rear course or ring of the shell, and is bolted with six or eight bolts through the punched holes. The head and ring are hoisted up to the drill near the riveter, and six or eight holes are drilled at about equal distances around the seam holding the 4 2 4 STEAM-BOILERS. head into the ring or course, and rivets are driven by the machine in these holes. The bolts are now taken from the punched holes, and all the remaining holes are drilled and riveted, completing the ring-seam through the flange of the back head. The reason for driving a few rivets first, at equal intervals, is that the errors of spacing, when any exist, are distributed, and are removed during the subsequent drilling; while such errors might accumulate and give trouble if the seam were riveted in succession beginning at one point, without first driving a few rivets at intervals. After the ring-seam through the flange of the head is completed, the longitudinal seam or seams are drilled and riveted. Here again a few rivets are driven at intervals before the seam is riveted up. A few holes at the ends of the seams are left for convenience in joining onto the next course. The head and first course are now lowered onto the next course, which has been assembled in readiness. A few bolts are put through the punched holes, and the two courses are hoisted up, drilled and riveted in the way already described for the rear course. When all the courses are riveted together the front head is put in with the flange out so that the rivets in that flange can be driven on the machine. The closing seams on a boiler which, like the Scotch boiler, has both heads set with the flange in, must be riveted by hand. Rivets are heated in a small forge near the riveter and are passed to a man inside the boiler, who picks them up in tongs, thrusts them through the holes from within and guides the head of a rivet up to the die which is inside the boiler. Sometimes the rivets are thrust through from without, in which case the man inside the boiler guides the point to the die. On the platform of the machine stand the riveter and two or three helpers. They adjust the boiler so that the rivet is brought between the dies, and the riveter pulls the SHOP-PRACTICE. 425 lever which controls the ram, and the outer die is driven against the rivet, forming the head and closing up the rivet in the joint. The holes are drilled about one sixteenth of an inch larger than the rivets. The pressure of the dies varies from 20 to 70 tons, depending on the thickness of the plate ; enough to compress the rivet and fill the hole completely. The rivets, as they cool, shrink and draw the plates firmly together. Riveting-machines. — There are four types of riveting- machines used for boiler-work, depending on the method of moving the ram or plunger which carries the movable die. The motion may be derived from — 1. A cam and toggle. 2. A hydraulic cylinder, 3. A combination of a hydraulic cylinder with a cam and toggle. 4. A steam-cylinder. The cam and toggle riveter is now seldom used. In it the ram carrying the movable die is driven by a toggle-joint that'is closed by a cam, which in turn is driven by a belt and gearing. The adjustment for different thicknesses of plate is made by a wedge behind the ram, which can be set by aid of a screw. The pressure on the rivet is controlled by the elas- ticity of the frame of the machine and the setting of the wedge ; it cannot be regulated satisfactorily. The hydraulic riveter, in one form or another, is most com- monly used at the present time. With it a definite pressure can be applied to each rivet whatever the thickness of plate. Fig. 209 represents a hydraulic riveter with a reach of 96 inches which can apply a pressure of 150 tons. It consists essentially of two heavy cast-iron levers or beams, bolted together near the middle and at the lower end. One beam carries the fixed die at its upper end ; the other carries the ram and hydraulic cylinder. The stroke of the ram can be adjusted and is controlled by a single lever. The ram moves 426 STEAM-BOILERS. in straight girders, and may apply an eccentric pressure with- out rotating or springing. Some hydraulic riveters have a hydraulic closing device Fig. 209. for holding the plates together while the rivets are driverio Even when furnished it is commonly not used. The reach of a riveting-machine is the distance from the dies to the bed-plate at the middle of the machine. It limits the width of plate that can be riveted by the machine. A portable hydraulic riveter is shown by Fig. 210, which has a reach of 12 inches and can apply a pressure of 75 tons. SHOP-PRACTICE. 427 It can be swung into position by a crane and can be turned to any angle by the gear at the trunnion. This type of ma- chine is used largely for bridge work; it is sometimes used for riveting nozzles, manhole-rings, brackets, and reinforcing- plates onto boilers. The power for working a hydraulic riveter is derived from either a steam-pump or a power-pump. A heavy geared Fig. 210. power-pump is shown by Fig. 211; it is run continuously and delivers water to an accumulator from which water is supplied to the hydraulic cylinder which moves the ram. The accumulator consists essentially of a loaded piston or plunger. Water is pumped into the cylinder of the accu- 428 STEAM-BOILERS. mulator, and is drawn out by the hydraulic cylinder as needed. When the accumulator reaches the end of its stroke it closes a valve on the pipe from the pump so that it receives no more water; at the same time it opens a by-pass from the delivery to the suction of the pump which continues to rum but has at that time very little resistance to overcome. When Fig. 211. some water has been withdrawn from the accumulator the by- pass is closed and the valve on the delivery-pipe is opened. When a steam-pump is used there is a device for shutting off steam from the pump when the accumulator is near the end of its stroke, and letting it on again when more water is required. An accumulator, shown by Fig. 212, is loaded by scrap- iron in a plate-iron cylinder. Inside the plate-iron cylinder is SHOP-PRACTICE. 429 a cast-iron cylinder which is closed at the top and which moves on a fixed plunger. This plunger passes through a stuffing- box and is carried by a cast-iron bed-plate. When water is pumped into the cylinder through a passage in the fixed plunger, the whole weight of the cylinder, plate-iron casing, and scrap-iron load are lifted. The pressure required to do 43° STEAM-BOILERS. this depends on the load ; it is the pressure which is exerted on the plunger of the hydraulic cylinder moving the ram. The frame of I beams at the sides forms a guide for the accumulator-cylinder and its load. Another form of accumulator, loaded with heavy cast-iron blocks and without any exterior guides, is shown by Fig. 213. Fig. 213. The hydraulic riveter with toggle and cam combines the simplicity of the cam-and-toggle machine with the advantage of a definite and determinable pressure on the rivet, which is the best feature of the hydraulic machine. The toggle bears against the ram at the front end, and against the plunger of a hydraulic cylinder at the back end. The cylinder is connected with an accumulator which is loaded to give the desired pres- sure on the rivet. Suppose that pressure to be 30 tons; then SHOP-PR A CTICE. 43 1 when the cam closes the toggle, the rear end, resting against the hydraulic plunger, remains at rest, and the front end drives the ram and compresses the rivet till a pressure of 30 tons is reached. When that pressure is reached the hydraulic plunger yields, forces water into the accumulator and raises the load on it. When the cam releases the toggle, the hy- draulic plunger moves forward and the load on the accumula- tor falls and drives water into the cylinder. The stroke of the hydraulic plunger may be very short, as the principal part of the stroke of the ram is made before the plunger yields. There is no loss of water except by leakage, which may be made up from time to time by a hand-pump. This machine gives a definite pressure on the rivet whatever the thickness of the plate, like the plain hydraulic riveter. It has no pump and the accumulator is smaller. If the plunger has a large area, the load on the accumulator need not be very great. Hand-riveting. — In a modern boiler-shop almost all the riveting is done by machine because it is cheaper and, espe- cially on heavy work, is more likely to be well done. There are, however, a good many rivets on any boiler that must be driven by hand. In such case the rivet, which may be heated entirely or at the point only, is thrust through the hole from within and is held up by a man inside, who has for this pur' pose a hammer or weight which weighs about 20 pounds on a long handle. He has also an iron hook which he hooks into a rivet-hole, and against which he gets a purchase to hold the rivet up while it is driven. Two men with hammers that weigh about 5 pounds drive the rivet, striking in turn. A few heavy blows are struck to close the joint and partially form the head, then the head is finished in the shape of a straight- sided cone with lighter hammers. If the rivet is long enough to form a good head, and if it is driven with care and skill, hand-riveting may be equal to machine-riveting. If the heads are ill-formed, or if they are too low, the work may be very inferior. Snap-riveting. — This method of riveting, which is espe- 432 S TEA M-B OILERS. cially convenient for driving rivets in contracted spaces, has some resemblance to machine-riveting. The rivet is thrust through the hole and held up from within the boiler. The joint is closed and the head is roughly formed by a few blows of a heavy hammer, then a snap or die is held on the rivet and driven with sledge-hammers. For large rivets the sec- tion of the snap should be a parabola, and the head should be relatively small in diameter and high, because this form causes the rivet to fill the hole better and makes sounder work. Tube-expanders. — The tubes are expanded into the tube- sheets to make a steam-tight joint, beginning at the least acces- sible end. They are commonly a little too long and are cut off at the projecting end by a tube-cutter. The tubes extend through the heads a slight amount, and are beaded over, after they are expanded, by a special tool. The expanders most commonly used are known as the Prosser and the Dudgeon expanders. The Prosser expander, represented by Fig. 214, is made up Fig. 214. of a number of steel segments held in place by a spring on a cylindrical extension of the segments. The acting part of the segments have the form to be given to the tube after it is expanded. The inside of the segments forms a straight hol- low cone into which a steel taper pin fits. The expander is forced into the tube and is expanded by driving in the pin with a hammer. This should be done gradually so as not to distress the metal of the tube tpo much, and the expander should be frequently slacked back and shifted part way round on account of the spaces between tne segments. SHOP-PRACTICE. 433 The Dudgeon expander, Fig. 215, has a set of rolls, three or more, in a frame. The rolls are forced out against the sides of the tube by driving in a taper pin. The pin and frame are CZ rotated as the pin is driven, and the rolls gradually force the tube against the tube-plate. Fig. 216 shows a self -feeding tube expander of the same type as the Dudgeon. Fig. 216. Although the two expanders accomplish much the same result, the action is different. The Prosser causes an abrupt stretching of the tube while the Dudgeon rolls the tube out grad- ually. One expander seems to be as good as the other. The expanded end of the tube conforms to the shape of the segments of the Prosser expander or to the shape of the rolls used in the Dudgeon. In general, the tube ends expanded by the two expanders will appear as in Figs. 217 and 218, which are drawn out of proportion to show the difference more clearly. An inexperienced person who may be using a tube expander for the first time may judge when a tube has been expanded sufficiently to be tight by watching the plate around the tube 434 STEAM-BOILERS. to see when fine hair-like cracks appear in the scale which covers the outside of the plate. When these lines show it means that the tube has been made to fill the hole and that the hole has begun to be stretched. After the tubes are expanded the ends are beaded over by a special tool known as a boot-tool. Beading adds a little to the holding power of a tube. Tube ends which are directly over a furnace, as is the case in vertical Fig. 217. Fig. 218. boilers like the Manning, should always be beaded. This bead- ing keeps the end of the tube in such cases from being eaten away by the fire. A vacuum may possibly be found in a boiler, if it is allowed to cool without admitting air. The Prosser method has an advantage in such case, when the tubes act as struts between the heads. The Dudgeon method will then act by friction only. The rollers might be shaped to give an expansion just inside the plate, instead of making them straight; there is, however, no evidence of trouble from this source in practice. SHOP-PRACTICE. 435 Calking. — The riveted seams of a boiler are made steam - tight by calking, which consists in driving the lower part of the planed edge forcibly against the plate beneath. Fig. 219 shows the form of calking-tool used in hand-calking, the posi- FiG. 219. tion in which it is held, and the way the extreme edge of the plate is compressed against the plate beneath. The acting sur- face of the tool, which is about an men wide, is ground at an angle of somewhat less than 90 , and the edge is rounded slightly so that it will not cut the lower plate. The tool is slid along the under plate against the edge of the upper plate and struck with a hammer. If the tool is ground to a sharp edge and used carelessly, a groove may be cut in the under plate and serious injury may be done. A pneumatic calking-machine or tool is now used for doing most of the calking in boiler-shops. In general prin- ciple it resembles a rock-drill, and consists of a cylinder in wfiich works a piston and rod on the end of which is the calking-tool. Air is supplied for working the piston, at a pressure of 60 or 80 pounds, through a flexible tube. It makes about 1500 working-strokes a minute, 3/16 of an inch long. The calker, which is about 2J inches in diameter out- side and 15 inches long over all, is held by a workman who presses it slowly along the seam to be calked. The edge of the tool is well rounded so as not to injure the lower plate. 436 STEAM-BOILERS. Work can be done four times as rapidly with the pneumatic calker as by hand. Cold-water Test. — After the boiler is calked it is tested to about once and a half the working pressure, with cold water. During the test the boiler is carefully watched to detect any notable change of shape or other sign of faulty design or construction, and important leaks are marked ; small leaks are of no consequence, as they will fill up with rust. Important leaks must be calked after the pressure is relieved ; if necessary, pressure may be applied again to see if they are stopped. If the boiler is examined by a boiler-inspector, he makes his inspection before the boiler is painted, and stamps certain letters on the head or over the fire-door to show that the boiler has passed inspection. Finally the boiler is painted and oiled ready for shipping. CHAPTER XII. BOILER-TESTING. The main object of a boiler-test is to determine the amount of water evaporated per pound of coal, or, more ex- actly, the amount of heat transferred to the boiler per pound of coal burned. For this purpose it is necessary to deter- mine : i. The number of pounds of water pumped into the boiler during the test. 2. The number of pounds of coal burned, and the weight of ashes left. 3. The temperature of the feed-water when it enters the boiler. 4. The pressure of the steam in the boiler. 5. The per cent of moisture in the steam discharged from the boiler. It is desirable to determine the conditions of combustion, such as the draught, the weight of air supplied per pound of coal, the composition of the products of combustion, and the temperature of the escaping flue-gases. It is also desirable to have determinations made of the composition of the coal and its total heat of combustion, but, as was explained in Chapter II, these determinations should usually be intrusted to a chemist and to a physicist. Water. — The best and most satisfactory way is to weigh the feed-water directly, in proper tanks or barrels on scales. There should be two barrels or tanks large enough so that the filling, weighing, and emptying may proceed without haste. 437 43 g STEA M -BOILERS. The scales should be adjusted and tested with a standard weight and should be known to be correct and sensitive. Good commercial platform scales are sufficient for this pur- pose. The weighing-barrels should be placed high enough to discharge into a tank or reservoir from which the feed-water is drawn by a pump or injector. This tank should hold more than both weighing-barrels, so that when it is about half empty an entire barrelful of water may be discharged into it without danger of overfilling it and wasting water. The bar- rels are emptied through large quick-opening lever- valves ; this point should receive attention, as any delay caused by small valves is ver}^ annoying. The weighing-barrels are filled either from a water system or by a special pump from a well or reservoir. When a direct- acting steam-pump is used, a quarter-inch by-pass should be carried from the delivery-pipe to the suction-pipe; the pump will then run slowly when the valves on the pipes leading to the weighing-barrels are shut ; when one of these valves is opened the pump starts away promptly, and it slows down again when the valve is shut. If a power-pump is used, it may be convenient to arrange so that it shall run all the time at full power, discharging into the well or reservoir when neither barrel is filling. Weighing water, though simple enough, requires care and intelligence, as any blunder will spoil the test. The observer should proceed systematically. He will naturally start with both barrels filled, weighed and recorded before the test begins. When the level in the feed-tank has fallen so that it can receive a barrelful of water he will open the discharge- valve from one barrel, which should be marked and designated as Barrel No. I. When that barrel is emptied, he will close the valve and weigh the barrel ; the weight empty is set down and subtracted from the weight full to get the weight dis- charged. The record of weights is kept in a table con- BOILER-TESTING. 439 taining columns for the name of the barrel, weights full, weights empty, weights discharged, and time at which dis- charged. The weight of the barrel empty must be taken each time, as the barrel will not drain completely in the time that can be allowed. Water may now be turned on to fill Barrel No. I, and Barrel No. 2 may be emptied, as occasion demands. Then one barrel may be filling when the other is emptying, and the work may proceed rapidly but without confusion. The errors that a novice is liable to are either to forget to record the weight of a barrelful of water, or to empty a barrel that has not been weighed. It is convenient and almost necessary to have some sort of an index or telltale to show the water-weigher where the water-level is in the feed-tank. For this purpose we may use a float, with a string that runs up over a pulley and is kept taut by a small weight moving over a scale, which is placed in front of the weighing-barrels. This float is not used to determine the level of the water in the feed-tank at the begin- ning and end of the test. At the beginning of the test the level of the water in the feed-tank is marked, and at the end of the test the level is brought to the same mark, so that all the water delivered by the weighing-barrels is drawn out of the feed-tank by the feed-pump. A good way of marking the water-level is to fasten to the side of the tank a piece of wire bent into a hook, with its point projecting slightly above the water-level. This hook will commonly be placed in position before the test begins, and the tank will be filled up to the level so marked before water is drawn from the feed-tank. If water cannot be weighed directly, it may be measured in tanks of known capacity which are alternately filled and emptied. Or the water may be measured by a good water- meter, which must be tested under the conditions of the test to determine its error. Care must be taken to keep the meter 44-0 STEAM-BOILERS. free from air or it will record more than the amount of water which actually passes. Boiler-tests on steamships can scarcely be made without using meters. At the time when the test begins, the water-level is noted at the water-glass, and at the end of the test the water-level is brought to the same place. The best way is to fix a wooden scale near the water-glass and record the height of the water above an arbitrary point on the scale. Sometimes a string is tied around the glass at the water-level when the test is started ; in such case the distance of the string from some fixed point on the fittings of the water-glass must be recorded, so that the string can be replaced if it happens to be moved or if the glass tube breaks. If the water is not brought exactly to the same level at the end as at the beginning of the test, the difference is noted and allowance is made. It has already been pointed out that the apparent height of the water depends to a certain extent on the rate of vaporization and on the rapidity of circulation in the boiler; consequently the boiler must be making steam at the same rate at the times when the water-level is observed for beginning and ending the test. All pipes leading water to or from the boiler, except the feed-pipe, must be disconnected. Steam may be taken for any purpose and through any pipe, so far as the boiler-test is concerned. Frequently the steam used by an engine is determined by weighing the feed-water for a boiler which is used exclusively for that engine. If the boiler is fed by an injector, the steam for running the injector should be taken from the boiler, for it will be condensed by the feed-water and returned to the boiler. A very small amount of the heat (less than two per cent) in the steam supplied to an injector is used in pumping the feed-water; the remainder is used in heating the feed- water and is returned to the boiler. The temperature of the feed-water must be taken before it goes to the injector. If the BOILER-TESTING. 441 boiler is fed by a direct-acting steam-pump, that pump should be run with steam taken from some other source. If that cannot be done, then the steam used by the pump must be determined and allowed for, unless the exhaust from the pump can be turned into and condensed by the water in the feed-tank, in which case the pump is in the same condition as an injector. The best way of determining the amount of steam used by a steam-pump is to condense it in a small sur- face condenser, and to collect and weigh the condensed water. Or the steam may be run into a barrel filled with cold water, which is weighed before and after steam is run in. This method requires that the barrel shall be emptied when the water begins to vaporize, and filled afresh with cold water. Steam used by a calorimeter for determining the amount of water in steam must be ascertained also; the methods will be given in connection with a description of the instruments. Coal and Ash. — The coal required during a boiler-test should be brought in as required in barrows; it may be fired from the barrow or dumped and fired from the floor. The barrow should be weighed full and empty, and the difference should be recorded together with the time ; the latter to serve as a check on the record and make sure that a barrow-load is not neglected. The weight of the barrow is usually the same throughout the test. Any coal left unburned is weighed back It is essential that the condition of the fire shall be tne same at the beginning and at the end of the test. There are two methods in vogue for trying to attain this result ; if the test is 24 hours long or more, the condition of the fire is esti- mated by its appearance; if the test is 10 or 12 hours long, the test is started and stopped with the grate empty. These are for tests of factory boilers with a combustion of 15 to 20 pounds of coal per square foot of grate per hour. For tests on marine or locomotive boilers, where the rate of combustion may be twice or five times as rapid, the duration of a test may be correspondingly reduced. 44 2 STEAM-BOILERS. Coal in solid mass will weigh 70 or 80 pounds to the cubic foot; when lying on a grate it will weigh 50 or 60 pounds. It is difficult to estimate the thickness of the bed of coal on a grate nearer than two inches. But a layer of coal two inches thick will weigh 8 or 10 pounds, which is about half the rate of combustion for a factory boiler. If a test is only ten hours long, the error resulting from a wrong estimate of the thick- ness of the fire may readily be five per cent. If the test lasts twenty-four hours, the error will probably not be more than two per cent, provided a proper method is used. If the condition of the fire is estimated at the beginning and end of the test, the fire should be cleaned and freed from ashes and clinker shortly before the test begins, and should then be spread in rather a thin even layer of clean glowing coal. Its height above the grate should be estimated with reference to some mark in the furnace that can be recognized readily. Just as long before the end of the test the fire should be cleaned and levelled in the same manner, and the thickness should be estimated with reference to the mark chosen at the beginning. The fireman is sure to have a clean bright fire at the beginning of the test, but he is apt to have a fire with much the same appearance that is half clinker at the end. The error from estimation may be very serious in such case, even though the test is 24 hours long. If the test is started and stopped with the grate empty, the boiler must be brought into good working condition about an hour before the test is to start, with all the brickwork thoroughly heated. The fire is allowed to burn low, and the steam-pressure is maintained by reducing the draught of steam from the boiler. Twenty or thirty minutes before the test starts, the fire is drawn or dumped and the grate and ash- pit are cleaned out. A new fire is started with wood, and coai is thrown on as soon as the wood is well alight. The time when coal is thrown on is counted as the beginning of the test. If the steam-pressure falls while the fire is drawn, BOILER-TESTING. 443 the stop-valve may be nearly or quite closed to keep it from falling much below the working-pressure. Toward the end of the test the fire is allowed to burn low, and at the end of the test it is drawn out on the boiler-room floor and quenched with as little water as may be, not enough to leave it wet. The unburned coal is picked out by hand and weighed back, the clinker and ashes are separated and weighed together with the clinker withdrawn during the test and the ashes in the ash-pit. If any appreciable amount of coal falls through the grate, a sample from the ash-pit may be picked over by hand to es- timate the proportions of unburned coal in the ash. The coal in the ash is allowed for in calculating the per cent of ash in the coal, but is not added to the coal weighed back, for there is no way of burning coal thus lost through the grate. When a test is started with a wood fire, more or less coal is apt to fall through the grate in starting. This is drawn from the pit and fired over again. It is customary to allow the fire to burn low before draw- ing the fire at the end of the boiler-test, both because it brings the fire more nearly to the condition at the beginning, and because it is a hard and unpleasant job to draw a thick fire. But the fire should be maintained at its normal condition until the end of the test approaches, and should be a good fire when drawn. Extraordinary results may be obtained by allowing the fire to burn nearly out at the end of the test, a very considerable amount of steam being formed by heat given out by the boiler-setting. It is unnecessary to say that such results are entirely misleading. The wood used for starting the fire is weighed and allowed for on the assumption that a pound of wood is equivalent to 0.4 of a pound of coal. The total weight of wood used is not large. Temperature of Feed-water — The temperature of the feed-water is taken by a thermometer in a cup filled with oil, screwed into the feed-pipe close to the check-valve. If the 444 STEAM-BOILERS. temperature varies, it may be read every five minutes: if it is found to be steady, less frequent intervals will do. Pressure of Steam. — The steam-pressure must be very nearly the same at the beginning and end of a test, and should remain nearly constant throughout the test. Read- ings are commonly taken every fifteen minutes, but the fire- man should be required to keep the pressure nearly constant at all times. The steam-pressure is taken by a spring-gauge like that shown by Fig. 139 on page 345. The gauge should be compared with a mercury column or a standard gauge both before and after the test, and a correction should be applied if necessary. If the pipe carrying pressure to the gauge fills up with water, allowance for the pressure of that column of water must be made. Each foot of water will give a pressure of about 0.43 of a pound per square inch. The reading of the barometer should be taken two or three times during a test. The reading in inches of mercury can be reduced to pounds per square inch by multiplying by the weight of a cubic inch of mercury, which is about 0.491 of a pound. Very commonly the pressure of the steam is obtained indirectly by aid of a thermometer set in the steam-pipe. The absolute pressure corresponding to the temperature is then obtained from a table of the properties of saturated steam. The thermometer is readily standardized, and is not so likely to become unreliable as a steam-gauge. Most vertical boilers and some water-tube boilers give superheated steam ; in such case there should be both a thermometer and a gauge on the steam-pipe, to indicate tem- perature and pressure. The excess of the temperature by the thermometer above that corresponding to the absolute pressure of the steam, as found in a table of properties of steam, is the degree of superheating. Specific Heat of Superheated Steam. — The mean value BOILER-TESTING. 445 of the specific heat of superheated steam is given in Chapter II. The value is commonly represented by c p . The value increases with the pressure and at the same pressure decreases as the super- heat increases. For example, let the pressure by the gauge be 65.3 pounds, and let the temperature be 350 F. by the thermom- eter. The absolute pressure corresponding to 65.3 pounds is 80 pounds, at which saturated steam has the temperature of 3 12°. I F. The superheating is consequently 350 F. — 3i2°.i F. = 37 . 9 F. The heat due to the superheating is o.53 X 37-9 = 20.1 B. T. U. When the steam is superheated, the formula for equivalent evaporation is changed from the form given on page 148 to c P (t s — t) + r + q — q w 7 , 9697 in which t t represents the actual temperature of the super- heated steam, and / is the temperature corresponding to the absolute pressure of the steam determined from the reading of the gauge. Priming. — A boiler which has sufficient steam-space and free water-area will deliver steam which contains less than two per cent of moisture. Professor Denton* has pointed out that a jet of steam blowing into the air from a petcock will give a characteristic blue color if there is less than two per cent of water in the steam. If there is more than two per cent of moisture, the jet will be white. Since steam seldom contains less than one per cent of moisture under the usual conditions of ordinary practice, it is possible by this method to estimate the condition of steam with a probable error of one per cent. * Trans. Am. Soc. Mech. Engs., vol. x. p. 349. 446 STEAM-BOILERS. The most ready way of determining the condition of steam is by the aid of a throttling-calorimeter, devised by Professor Peabody,* which depends on the fact that the total heat of steam increases with the pressure, so that dry steam be- comes superheated when the pressure is reduced by throttling. If the steam is only slightly primed, superheating will still take place, and the amount of priming can be determined from the temperature and pressure of the steam after it is throttled. If there is much moisture in the steam, it fails to superheat. A good form of this apparatus is shown by Fig. 220, consisting of a reservoir A to which the steam to be tested is admitted through a ? = °°-°< H = °-5, S = a-** Heat of combustion of coal as fired ..... Total equivalent evaporation from and at 212 F. . . . Equivalent evaporation from and at 212° F. per pound of dry coal . Equivalent evaporation from and at 212 F. per pound of combustible Equivalent evaporation from and at 212 F. per square foot of heating surface per hour. .... Coal burned per square foot of grate surface per hour Boiler horse-power developed, A. S. M. E. rating Maximum assumed possible error of test . Air per pound of coal from analysis of flue gases Air required per pound of coal from the formula I 12 C -+- 36 \H — —j Excess air supplied ..... Heat carried off by flue gases per pound of coal Heat taken up by water in boiler per pound of coal Total heat furnished per pound of coal Heat radiated per pound of coal . Heat carried off by flue gases Thermal efficiency of boiler plant . Heat lost by radiation, etc. . 226.5 °&7 per cent. 3°'7 pounds. IO -9 pounds. 182 per cent. 2,485 B.T.U. 1 0,033 B.T.U. 14,555 B.T.U. 2,037 B.T.U. 17 ■ 1 per cent. 68. q per cent. I4-Q per cent. GAS ANALYSIS: Per cent by volume. CO a o 2 CO Bet. bridge wall co 2 o 2 CO Ash-pit . and back end Above grate . Back end . . . At bridge wall Uptake 6.4 12.0 O.I DRAUGHT AND TEMPERATURES. Setting. Ash-pit Above grate At bridge wall Between bridge wall and back end . Back end . Uptake Inches of Water. F. 301 Stack. feet above grate. Inches of Water. F. Remarks: The coal was of poor quality. Fires were hard to clean, as there were bad clinkers. The firing was good. BOILER-TESTING. 459 Total equivalent evaporation from and at 212 F.: (.99ir-\-q) at absolute ^boiler-pressure is 1181.7 B.T. L'. (q) at temperature of feed-water (75. 9 F.) is 44.0 " Heat necessary to vaporize a pound of feed-water into steam primed .9 per cent is 1137. 7 B.T.U. .137-7 X746 457 = 87577opounfe 969.7 is the latent heat of steam at 212 F. Equivalent evaporation from and at 21 2 F. per pound of dry coal : 87^770 n = 10.48 pounds. 83544 Equivalent evaporation from and at 21 2° F. per pound of dry combustible : 8 7577° -^—.s 11.49 pounds. Equivalent evaporation from and at 212 F. per square foot of heating surface per hour: 8 7577° •. -^-^ =1.72 pounds. 4558X112 v Coal burned per square foot of grate surface per hour _?il43_ = 8 . l8 pounds. 92.4 X 112 460 STEAM-BOILERS. Boiler horse-power developed (A.S.M.E. rating). (See page 218.) "37-7 X 746457 112 x 33 + 70 226.5 Maximum assumed possible error of test. — It is assumed that an error of one inch may be made in estimating the thickness of each fire at the beginning and at the end of the test and that these errors are cumulative, thus making the total error two inches over the entire grate. For soft coal the weight of a cubic foot is about 48 pounds. 92.4 X 48 X j 2 — 739- 2 pounds error. 739.2 X 100 84643 0.87 per cent. Thermal efficiency of boiler plant. — This is the ratio of the heat taken up by the water in the boilers per pound of coal fired to the heat given up by a pound of coal as fired. H37.7X746457XIOO — -^—. = 68.9 per cent. 14555 X 84643 Air per pound of coal from analysis of flue-gases. (See pages 88, 8 9 , 90.) C0 2 = 6.4X22 = 140.8; T 3 T X 140.8 = 38.4 C 2 = 12.9 X 16 = 206.9 CO = 0.1X14= i-4j fX 1.4= 0.6 C 348.6 39-oC ' 348.6 — 39 = 309.6 o 2 . BOILER-TESTING. 461 — ^1- = 7.94 pounds of oxygen per pound of carbon. 39 '—^1 — 34. 2 pounds of air per pound of carbon. .232 As the coal is 90 per cent carbon, the air per pound of coal is 30.8 pounds. Air required per pound of coal from formula : i2C-l-36^H— -J = 12 X .9 + 36^.005 + '-^^ 1 = 10.9 pounds Excess of air supplied- (30.8 — 10.9)100 10.9 182 per cent. Heat carried off by the gases per pound of coal. — There were 30.8 pounds of air and .9 pounds of carbon, making 31.7 pounds of gas for each pound of coal burned. The proportion of the gases by weight may be figured from the flue-gas analysis : C0 2 6.4 X22- 140.8 2 12.9 x 16 = 206.9 CO 0.1 X 14 = 1.4 N 2 80.6 x 14 = 1128.4 100. o 1477.5 ■ — X 31.7 =" 3-02> the weight of CO J477-5 — X 31.7 = 4-44> the weight of O J477-5 — - X 31.7 = 0.03, the weight of CO J 477-5 - X ^1.7 = 24.21, the weight of N, 1477-5 46 2 STEA M-BOILERS. The temperature of the flue was 391 F., while the air in the boiler- room was 6i° F.; a difference of 330 F. Multiplying the weights of the gases by their specific heats and by the number of degrees increase in temperature. (See pages 75-93.) Weight. S P eci f c Temperature BT ° Heat. Increase. CO2 3.02 .2169 330 216.2 2 4-44 .2175 330 318.6 CO 03 .2450 330 2.4 N 2 24.21 .2438 330 1947-8 2485.0 No allowance has been made for the moisture in the coal or for the moisture in the air. This moisture might amount to 90 or 95 heat-units in a total of 2500. A much simpler method of finding the heat carried off by the flue- gases, although not as accurate as the one given above, is sufficiently accurate for most work. There are 31.7 pounds of gas per pound of coal; call the average specific heat of flue-gas .235. The heat carried away is then 31. 7X330X. 235 = 2474, which varies from 2485 by but 11 heat-units. Heat taken up by the water in the boiler per pound 0} coal as fired: II37.7 X 746457 =I0033B ,t.u. 84643 Heat radiated per pound of coal: I 4555- I °033- 2 485 = 2037 B.T.U. Heat carried off by flue gases: 2485 X IO ° 14555 = 17. 1 per cent. Heat lost by radiation: 2037 x 100 14555 = 14.0 per cent. BOILER-TESTING. 463 Heat Balance. — The heat given up by the coal is accounted for as heat put into making steam, as heat carried off by the flue-gases, and as heat radiated from the setting to the air. The heat taken up in making steam and that carried off by the flue-gas may be calculated from the data obtained during the test, but the heat lost by radiation can only be found by subtract- ing the sum of the preceding from 100. This should be from 8 to 15 per cent, depending on how hard the boiler is being forced, and on the amount and thickness of the brickwork. A Scotch boiler will show only 2 to 4 per cent loss by such radiation. Should the radiation come out negative it shows inaccuracy in the test. This inaccuracy may be due to errors in weighing coal or to the conditions at the start and at the end not being the same. At times, even though an engineer does his best to con- duct a test fairly, he may be cheated by the fireman. It is not out of place to point out here some of the ways by which an unfair result may be obtained by an honest engineer. 1. By forcing the boiler abnormally for two or three hours before the test begins, thus storing up heat in the brickwork which is given out later when the boiler is under test. This may be obviated by keeping the boiler at its test rating for two hours before starting the test. 2. If a boiler is working hard the water-level is lifted more than when the boiler is steaming easily. By crowding the boiler for a few minutes just as the test begins and by checking the boiler at the end of the test the indication by the glass may be made to vary one inch with the same amount of water in the boiler at the start and at the finish. As the level in the boiler is judged by the height in the glass, too much water would be put into the boiler near the end of the test when the rate of evaporation decreased. If the boiler is kept working at the same rate and at the same pressure through- out the test, the error from this source would be avoided. 3. In many vertical boilers the water connection of the com- 464 STEAM-BOILERS. bination carrying the gauge glass comes from the shell just above the crown-sheet. This makes a column of water outside the boiler perhaps 10 feet in height. This column is balanced by the water inside the boiler. Just before beginning the test the fireman will blow out the combination (to satisfy you that it is working freely). The piping and glass now fill with hot water, and the level in the boiler and the level in the glass are the same. As there is no circulation in the pipe leading to the water end of the combina- tion, the water gradually cools and a column of cold, or com- paratively cold, water is balancing a column of hot water in the boiler. If the level in the glass is made the same at the end of the test as at the beginning, the level in the boiler will be from 6 to 10 inches higher than at the beginning. By having the com- bination blown just before the end of the test this error is avoided. 4. Sometimes plans to cheat the engineer are deliberately made. The engineer may insist that the blow-off pipe and all feed-pipes, excepting those from his weighing-tanks, be blanked, and yet he may get an impossible evaporation. A small pipe 1/4 inch in diameter starting below the water- line may lead up inside of the steam-pipe and run perhaps 100 feet, where it appears on the outside of the pipe as a drip-pipe for removing condensation from the pipe. It is evident that if this " drip-valve" is manipulated most any evaporation could apparently be obtained. If an engineer has any doubts about the honesty of the parties concerned he may protect himself against any cheating similar to that referred to above by cutting the boiler under test from the steam-main and by blowing all the steam generated into the air through an orifice of known area. The weight of steam (figured by Rankine's or Napier's for- mula) flowing through the orifice plus the steam used in the calorimeter plus the steam used by the feed-pump should equal the feed-water weighed. BOILER-TESTING. 465 Thermal Efficiency of a Boiler. — It has already been pointed out that the thermal efficiency of a boiler is the ratio of the heat utilized by the boiler from a pound of coal to the heat given up by a pound of coal. A thermal efficiency of 100 per cent would mean that there was no radiation from the brickwork setting, and that the flue gas left the boiler at the temperature of the room. It may be of interest to figure what efficiency might be ex- pected under the most favorable conditions. The amount of air needed to burn a pound of bituminous coal theoretically figures approximately 12 pounds, as will be seen by reference to Chapter III. The flue gases leaving a boiler which is working at capacity will be in the vicinity of 450 F., and if the temperature of the room be taken as 50 , the amount of heat per pound of coal carried off by the flue gas is 12.85 X (450 - 5°) X 0.24 = 1234. The 12 pounds of air unites with 0.85 pound of carbon in the coal, making 12.85 pounds of flue gas. An average grade of soft coal gives up 14,650 B.T.U. per pound, and if the minimum radiation from the setting be taken as 5 per cent (it is more often 8 to 10), then the heat lost in this way is 0.05 X 14,650 = 733 B.T.U. 1234 + 733 = 1967; 14,650 - 1967 = 12,683; 12,683 ^ J AfiS° = 0-865 or 86.5 per cent. Actually at least 18 pounds of air are required as a minimum per pound of coal, because it is impossible to distribute the theoretical amount in such a way that all parts of the fuel bed get the proper allowance. A similar calculation made with 18.85 pounds of flue gas, instead of 12.85, an d with 5 per cent radiation, gives 82.7 per cent as a result which might be obtained. Some recent tests of long duration, made by Prof. D. S. Jacobus, an expert of the highest standing, on a boiler of large 466 STEAM-BOILERS. furnace capacity compared with the radiating surface of brick- work, Fig. 57, have shown efficiencies as high as 80 per cent. These tests were made with the boiler equipped with both the Roney and the Taylor stokers. The results were practically the same. The upper line in Fig. 224 shows the variation in efficiency as the capacity was increased. The lower lines give the per cent of steam used by the stokers. 83 3 80 u 1 t 76 £74 72 Sb D 5 w 3 -£ 3 Ta yi« r R HH O u Cm 70 90 110 130 150 170 190 210 Per Cent of Rating on Basis of 10 Sq.Ft.of Boiler Heating Surface =1 Horse Power Fig. 224. Graphic Log Sheet. — Some of the ways by which an honest but inexperienced engineer may be tricked, have been noted under " Heat Balance." It is always advisable to carry along a graphic log sheet and fill this out hour by hour as the test progresses. Any ir- regularity in the water line, if not met by a corresponding irregularity in the coal line, at once gives warning that something is wrong. The log sheet at a glance shows whether or not conditions were stable during the test. Profile paper or the regular cross-section paper ruled to tenths may be used for this work. Fig. 225 shows such a log sheet. 01 S 001 s 5 t 2 3 I aaowrm J.UVHO 3H0WS 001 06 08 aonwo •S3Bd WV319 35 03 81 9t tl SONHOd 0001 N 31 OT 8 9 i 3 NOIldWnSNOO 1VOO SS OS S* 0* S8 sawnod oooi ni Ofi S3 03 St 01 S NOIldWnSNOO H3XVM 009S 002S 0081 00H 0001 *JoS3Hniva3dW3X 3fVH QNV 30VNUnd 009 1 ! 001 08 09 01- 03 S3tjrUVU3dW31 H3XVM Q33J qnw woo« wsiioa 'saisina CHAPTER XIII. BOILER DESIGN. In order to bring together the principles and methods which have been given in the preceding chapters, they will be applied to the design of a boiler. Designing of any sort is an art that is guided and controlled by practical considerations and theoretical principles, and which can be acquired by prac- tice only. The design of a boiler, like many other designs, is further modified to meet the requirements of government boards of inspection, or to conform to the inspection-rules of insurance companies. These rules and requirements vary from place to place and from time to time; they must be known to the designer, but they have no place in a text-book. A simple and common type of boiler has been chosen for design ; the methods, with proper modification, can be applied to other types, and the general principles illustrated are much the same for all types. Type of Boiler. — The kind of boiler used in a given locality depends on custom, on the kind of water used, and on the cost and quality of fuel. Deviation from common prac- tice should be made only for sufficient reason. Where water is bad or where fuel is cheap, the plain cylindrical boiler or a flue-boiler will be chosen. With clean, soft water the cylin- drical tubular boiler, like that shown by Plate I, has been found to be convenient, economical, and cheap. All these boilers have external furnaces, so that the shell is in part exposed to the fire. Now plates exposed directly to the fire should not be more than half an inch thick; 3/8 of an inch is preferable. Though thicker plates are sometimes used, this 468 BOILER DESIGN. 469 consideration limits the size of boilers of this type when high pressures are used. The importance of high efficiency for the longitudinal riveted joint becomes apparent in this connec- tion. Internally-fired boilers, like the Lancashire or the Scotch marine boiler, are not limited in diameter by this reason. The marine boiler sometimes has plates an inch and a quarter thick ; the fact that so great a thickness is undesirable some- times serves as a check on the size of such boilers. General Proportions. — Whatever may be the type of boiler chosen, there must be provided — 1. Sufficient grate-area to burn the fuel required under the available draught. 2. Suitable combustion-space to properly burn the fuel. 3. Sufficient area of flues or tubes to carry off the products of combustion. 4. Sufficient heating-surface to absorb the heat generated. 5. Proper water-space to prevent too great a fluctuation of the water-level when there is an irregular demand for steam. 6. Suitable steam-space to prevent too great a fluctuation of pressure when steam is taken at intervals, as for the cyl- inder of a steam-engine. 7. Sufficient free-water area for disengagement of steam. The last three conditions are not fulfilled by most water- tube boilers; some such boilers depend on a separator for disengaging steam from water. Problem for Design. — Let it be required to determine the main dimensions and some of the details of a hori- zontal cylindrical tubular boiler to develop 80-horse power A. S. M. E. standard (page 218). Let the working-pressure be 150 pounds per square inch by the gauge, and the test- pressure 225 pounds, or once and a half the working-pressure. Assume that anthracite coal will be used, and that it will give an equivalent evaporation of 9 pounds of water per pound of coal from and at 212 F. Assume further that 12 470 STEAM-BOILERS. pounds of coal will be burned per square foot of grate-surface per hour. The heating-surface may be about thirty-seven times the grate-surface. Tubes 16 feet long will be used, which length should not much exceed sixty times the diameter. The area through the tubes will be made about 1/7.5 °f the grate-area. Grate - area. — The A. S. M. E. standard requires that 34.5 pounds of water per hour shall be evaporated from and at 212 F. for each horse - power. The total equivalent evaporation will consequently be 80 X 34.5 = 2760 pounds per hour. With an equivalent evaporation of 9 pounds of water per pound of coal the coal burned will be 2760 -r- 9 = 307 pounds per hour. With a rate of combustion of 12 pounds of coal per square foot of grate surface per hour, the grate-area must be 307 -T- 12 =25.6 square feet. Tubes. — A common rule for finding the diameter of tubes is to allow one inch for each four feet of length when soft coal is used, and five feet when hard coal is used. A tube three inches in diameter will very nearly fulfil this condition. The table of proportions of flue-tubes in the Appendix, gives the area of the internal transverse section of such a tube as 6.08 square inches; the external area is 7.07 square inches. The internal circumference is 8.74 inches, and the external circumference is 9.42 inches. BOILER DESIGN. 47 1 The aiea through the tubes has been chosen as 1/7.5 of the grate-area, equal to 25.6 X 144 . , = 492 square inches. Since the area through one tube is 6.08 square inches, there will be required 492 -7-6.08 = 80.8, or, more properly, 81 tubes. It may be found convenient in laying out the tube-sheet to use more than this number of tubes; a less number is of course improper. Steam-space. — A good rule for this type of boiler is to allow from 0.8 to 1 cubic foot of steam-space per horse- power, which gives from 64 to 80 cubic feet for this boiler. We will assume 80 cubic feet. For sake of comparison, calculations will be made also by rules given on page 216. Thus for certain boilers working at moderate pressures it is found that the steam-space may be made equal to the volume of steam used by the engine in 20 seconds. Suppose that this boiler, though designed for 150 pounds pressure, may run at 70 pounds pressure, and may supply an 80 horse-power engine which uses 30 pounds of steam per horse-power per hour. Now the volume of one pound of steam at 70 pounds by the gauge, or 85 pounds absolute, is 5.16 cubic feet. So that the engine will use 80X30X5.16=12,384 cubic feet of steam in an hour, or 20 -7— X 12384=68 3600 ° cubic feet in 20 seconds. This is about the lower limit by the rule used above. It is clear that the steam-space would 472 STEAM-BOILERS. be very small if determined by this rule for an engine using steam at 150 pounds pressure. Another rule makes the steam-space from 50 to 140 times the volume of the high-pressure cylinder of the engine; 50 for very high pressure and high speed, 140 for slow speed and low pressure. For medium speeds and pressures 60 to 90 may be used. The boiler under consideration may supply steam to a triple-expansion engine which has a high-pressure cylinder 9 inches in diameter by 30 inches stroke, so that the volume is 1. 105 cubic feet. According to this the steam-space needed is 66 to 99 cubic feet. Diameter of Boiler. — For this type of boiler the steam- space is commonly made one third and the water-space two thirds of the contents of the boiler. To the contents of the boiler there must be added the space occupied by the tubes to find the volume of the cylindrical shell. Now we have de- cided to use 81 tubes 3 inches in diameter and 16 feet long. The area of the external transverse section has been found to be 7.07 square inches. The space occupied by the tubes is consequently 81 X 7-07 X 16 144 = 64 cubic feet. To this add steam-space, 80 and water-space, 160 Making in all, 304 " " The cylinder is 16 feet long, so that its transverse area is 304 -h 16 = 19 square feet; which corresponds to a diameter of 59.02 inches, or nearly 60 inches. This will be taken as the trial diameter; it may re- quire change in proportioning other parts of the boiler. The method of determining the main dimensions of a BOILER DESIGN. 473 boiler from the steam-space will require modification if it is applied to any other type of boiler. Even when applied to a given type it leaves much to the judgment of the designer, who may find difficulty in using it unless he is accustomed to working on that particular type. If the designer has at hand the dimension of several boilers of a given type, he may pre- fer to select the main dimensions for a new design directly, with the reservation that such dimensions may be modified as the design proceeds. This is commonly done by the designers of marine and locomotive boilers. Heating-surface. — The heating-surface of a cylindrical tubular boiler consists of all the shell below the supports at the side wall, all the inside of the tubes, and part of the rear tube-plate. Usually half of the cylindrical part of the shell is heating-surface. In the case in hand the heating-surface, exclusive of the tube-pfate, will amount to cu 11 l w 3.I4I6 X 60 X 16 Shell - X = 125.7 sq. ft. _ t o 8.74 X 16 Tubes.... 81 X — — = 943.9 " " Total 1069.6 " " The grate-surface is to be 25.6 square feet, so that the ratio of grate-surface to heating-surface will be at least as good as 25.6 : 1069.6 :: 1 : 41J. The actual ratio will be more favorable as it will appear advisable to use more than 81 tubes, and the back tube-sheet remains to be allowed for. Water-level. — It is now necessary to determine the posi- tion of the water-level to see if there will be sufficient free- water surface and sufficient distance from the water-level to the shell above it. 474 STEAM-BOILERS. Since the whole boiler is cylindrical, the area of the head of the boiler exposed to steam and to water will have the same ratio as that of the steam-space to the water-space. Consequently the area of the head above the water-level must be one third of the total area of the head less the combined areas of the tubes. The area of a circle having a diameter of 60 inches is 2827.4 square inches. The area of 81 tubes each having an external cross-section of 7.07 square inches will be 81 x 7-07 = 572.7 square inches. The area of the head exposed to steam is consequently 2827.4- 572 .7 = ;s j 6 3 square inches. We need now to know the height of a seg- ment of a 60-inch circle, which has the area of 751.6 square inches. The second problem in the explanation of the use of a table of segments (see Appendix) gives for the tabular number corresponding to the area 751.6 0.2088; 60 X 60 for which the ratio of the height to the diameter is 0.312. The height of the segment is therefore 0.312 X 60 = 18.7 inches. This gives sufficient height above the water, and sufficient free-water surface. The water-level will be 30 - 18.7 = 11. 3 inches above the centre of the boiler. Factor of Safety. — It has been pointed out that the actual factor of safety of boiler-shells is usually four or five when the boiler is built. The apparent factor of safety for some parts BOILER DESIGN. 475 like stay-bolts may be greater, but such factors are illusory because the stays may be subjected to considerable irregular stress from unequal expansion. The apparent stress on stay- rods and bolts, from steam-pressure only, is frequently limited by inspection-rules or by law. The factor of safety of a boiler which has been at work for some years is much affected by corrosion, which acts upon different parts of the boiler very differently, even when the corrosion is uniform. Thus a plate half an inch thick will have 7/8 of its original strength after it has lost 1/16 of an inch by corrosion. The weakest part of the plate, that is, the riveted joint, seldom suffers as much from corrosion as the whole plate at a distance from the joint, because the plate is protected to some extent by the rivet-heads. Some forms of joint have an internal cover-plate, which protects the plate at the joint and the joint may be nearly as strong after corrosion as before. Very often old weak boilers fail by tearing the corroded plate outside the riveted joint. Stay-rods and bolts suffer much more from corrosion than plates. Thus a rod one inch in diameter has an area of 0.7854 of a square inch. After corrosion to the extent of 1/16 of an inch has taken place the diameter is 7/8 of an inch and the area is 0.6013, which is 0.6013 -^ 0.7854 = 0.766 ot the original area. Compare this with the plate which retains 7/8 or 0.875 oi i ts thickness after the same amount of corrosion. Of course a smaller stay will suffer more, and a larger one less, in proportion. After the sizes of the parts of a boiler are decided upon it is well to make calculation to see that a factor of safety of four will remain after a reasonable amount of corrosion. Or, as in the case of stay-rods, the size may be calculated with a proper factor, and then the diameter may be increased to allow for corrosion. 476 STEAM-BOILERS. Thickness of Shell. — The final decision of the proper thickness of the shell for the boiler under consideration can- not be made until the efficiency of the joint is known; but the efficiency of any of the complex joints now in vogue can be found only when the thickness of the plate is known. It is therefore convenient to assume a factor of safety of about six and make a preliminary calculation. Thus for the boiler in hand w r e will get for the thickness t= 150x30 55,000 ~ 6 * of an inch. A similar calculation with a factor of five gives 150 X 30 _ n f7 t — = 0.4.1 55,000-- 5 of an inch. The shell will be either 7/16 or 1/2 an inch thick. Seven sixteenths will give an apparent factor of safety of 55 ,000 x 7/ig = ., 150 X 30 " After the allowance for the efficiency of the joint has been made this factor will be found to be about 4f . Longitudinal Joint. — The shell-plate is made as thin as possible because it will be exposed to the fire. Consequently the efficiency of the longitudinal riveted joint must be high if the real factor of safety is to be satisfactory. The strength of triple-riveted joints like that shown on page 284 ranges from 85 to 90 per cent. The joint with two cover-plates shown by Fig. 226, will be chosen. Following the method given on page 284, it appears that this joint may fail in one of five ways, for which the resistances are as follows: A. Tearing at outer row of rivets: Resistance = (P — d)tft. BOILER DESIGN. 477 B. Shearing four rivets in double shear and one in single shear: _ . Qitd' 1 „ Resistance = /,. 4 C. Tearing at the middle row of rivets and shearing one rivet: Resistance = (P — 2d)tf t -\ f s . 4 J/ > r^ ( ;) (( 1 Fig. 226. D. Crushing four rivets and shearing one: nd? Resistance = ^dtf c -\ f s . E. Crushing five rivets: Resistance = Adtf c + dt c f c . The diameter of rivet will be found by equating the resistances A and C. 7td* . , Aift 4 X tVX 55. QQQ : q . . a = —7- = = 0.00. n f s ^45,000 478 STEAM-BOILERS. The rivet which was used was 1 3/1 6 of an inch when driven. There are several methods in which we may find the way in which the joint will fail, and then find therefrom the effi- ciency. One is that shown on page 285 by assuming a pitch and calculating the resistance of the joint to failure in each of the five several ways. Another method is to equate the five several resistances two and two and calculate the pitch; the least pitch thus found must not be exceeded. Thus Equating B and C, A = {P _ 2d)tfi +*Al u 4 4 At ft 8 X 3.Hi6x(^|) 4X i6 45,000 , 13 X — + 2 X -1= 9- 7 55,ooo r 16 Equating A and B, ■■■ p = 9 -£i+< 9X3.Hi6(l|) J 45,000 L 3 7 55,000 * 16 4X F6 Equating A and D, 4 BOILER DESIGN. 479 ft At ft 3.14.6 x(^V 13 95,000 _ m6^ 4^000 £3 ~ 4 X i~6 X 55^55 + " A y 7 " X 5 5,ooo + .6 - 7 ' 4 " Equating A and E, (P-d)tf t = 4 dtf c + QQQ , 13/16 X 3/8 Qj^ooo 13 __ " 4X 16 X 55,000 + 7/16 ~ X 55,000+16 h * Here t the thickness of the cover-plate, is taken to be 3/8 of an inch. The greatest allowable pitch at the outer row of rivets is evidently 7.4 inches. Instead of going to the labor of solving all four of the above equations, we may find by some other method how the joint is likely to fail, and make up an equation involving those resistances only. Thus a rivet in the outer row may fail by shearing or by crushing at the cover-plate, which is here made thinner than the shell-plate. Equating the re- sistances of the two methods, we have 4 or for a cover-plate 3/8 of an inch thick d = AXi 95^oo =iQi 7t 45,000 A rivet 1.01 inch in diameter wiil consequently be just as 480 STEAM-BOILERS. likely to fail by crushing as by shearing. But the resistance to shearing increases as the square of the diameter, while the resistance to crushing increases as the diameter. It is there- fore evident that a rivet larger than i.oi of an inch will fail by crushing, while a smaller rivet will fail by shearing. A similar calculation at the inner row, when the rivet bears against a cover-plate both inside and outside, and will consequently crush against the shell-plate, gives ——f s = tdf c ; ^ = lXA x ?5^oo = o6- 7t 45,000 Here a rivet larger than 0.6 will crush, and one smaller will shear. It is now evident that a 13/16 rivet will shear at the outer row and will crush at the inner row. That is, for this joint the failure will occur by the method D, but not by the methods B or E. Then equating the resistances A and D, and solving for P y we get for the pitch at the outer row 7.4 inches as before. The corresponding pitch at the calking edge of the outer cover-plate is 3.7 inches; we will choose for that pitch 3-jj- inches, making the pitch at the outer row 7J inches. The efficiency of the joint is ioo ^"" d = 100 X ^~^ = 88.8 per cent. In the preceding article the apparent factor of safety based on the whole strength of the shell-plate is 5,35. Al- lowing for the efficiency of the longitudinal joint, the real factor of safety when the boiler is new is 0.888 X 5-35 =4.75. BOILER DESIGN. 481 With this style of joint the shell-plate is protected from corrosion by the inner cover-plate, and the joint will lose little if any efficiency from corrosion. If it be assumed that the plate loses 1/16 of an inch by corrosion during the life of the boiler, then the strength of the plate will be one seventh less after corrosion, and the corresponding factor of safety will be 5-35 X f = 4-6, which may be considered to be sufficient. Ring-seam — The stress on a transverse section of a homogeneous hollow cylinder from internal fluid pressure is one half the stress on a longitudinal section. It will in gen- eral be found that a single- or a double-riveted ring-seam is sufficient for any cylindrical boiler-shell. Marine boilers commonly have double-riveted ring-seams; externally-fired horizontal boilers seldom have the shell more than half an inch thick, and for that thickness, or less, single-riveted ring- seams are used. It is found in practice that ring-seams of horizontal ex- ternally-fired boilers may have a pitch of about 2 T \ inches for all thicknesses of plate from 1/4 to 1/2 of an inch. The diameters of rivets for such seams may be made about the size given in the following table : Thickness of plate £ -fa f T 7 ¥ J Diameter of rivet i \i i i $ The ring-seam in question has a circumference of about 3.1416 X 60 = 188.2 inches, which will allow us to use 84 rivets with a pitch of about 2.24 inches. This joint will fail by shearing the rivets. The efficiency of the joint is consequently the ratio of the resistance of a single rivet to shearing, to the resistance of 482 STEAM-BOILERS. a strip of plate as wide as the pitch. Consequently the efficiency is nd* 4 fs = i X 3-i4i6 X (H) 2 X 45.QQO = ptf t 2.24 x -iV x 55,000 * 433, which is more than half of the efficiency of the longitudinal seam, and will consequently be sufficient. Lap. — The lap, or distance from the centre of the rivet to the edge of the plate, is usually taken as 1.5 times the diam- eter of the rivet used, which makes the distance of the edge of the hole from the edge of the plate equal to the diameter of the rivet. For the single-riveted ring-seam this makes the lap equal to 1-5 XH= 1-22. It is customary to calculate the width of lap required on the assumption that the metal between the rivet and the edge of the plate may be treated as a beam of uniform depth, fixed at the ends and loaded at the centre by the force which would be required to shear or crush the rivet, taking, of course, the larger. The width of the beam is the thickness of the plate, the depth is the distance from the edge of the hole to the edge of the plate, and the length is the diameter of the rivet. Rivets in single-riveted seams fail by shearing. The load is consequently the shearing resistance 7td* The maximum bending moment for a beam of uniform section fixed at the ends and uniformly loaded is equal to the load multiplied by one eighth of the span. The moment of resistance is equal to A BOILER DESIGN 483 in which /is the cross-breaking strength (about 55,000), /is the moment of inertia of the section, and y is the distance of the most strained fibre from the neutral axis. Here we have T th 2 h 12 2 representing the distance from the edge of the hole to the edge of the plate by h. Equating the bending moment to the moment of re- sistance, 4 o 3 x 3-1416 x 13 45,ooo X z = 0.77 ' f r r\r\r\ ' ' 6xlx.6 ! 55 ' 00 ° ID for the case in hand. The lap is consequently Q-77+1 X J| = i.i8 2 ID inches for the ring-seam, which is somewhat less than that by the arbitrary rule that it should be once and a half the diam- eter. A similar calculation for the cover-plates with the same diameter of rivet, but with a plate 3/8 of an inch thick, gives for the lap 1.24 or i-|- of an inch, while the arbitrary rule gives 1.03 of an inch. It is probable that the lap may be consider- ably smaller than is given by the calculation by the beam theory, but for lack of direct experimental knowledge on this question it is not wise to make the lap much less than the calculation gives; we will consequently use ij of an inch for the lap of the cover-plates. 484 STEAM-BOILERS. The rivets of the inner rows pass through both cover-plates and are in double shear, and consequently fail by crushing as is shown on page 480. The load to be used for calculating the lap is therefore the resistance to crushing in front of the rivet ; that is, we here have for the load tdf c . The equation of bending moment and moment of resistance gives 1 tti -dxtdf c =f—. v/g-iVJ^s?- 4 X 45>°°o The lap is consequently 0.926 + ^ X y 6 = 1.27, or a little more than ij. The lap used is if of an inch. Tube-sheet. — The next step in the design is to lay out the tube-sheet on the drawing-board. If possible, the tubes should be arranged in horizontal and vertical rows as shown on Plate I. The distance between the tubes should not be less than three fourths of one inch ; one inch is better. On Plate I the horizontal rows are spaced one inch apart, while the vertical rows are only three fourths of an inch apart ; wider spacing for horizontal rows is more favorable for the free cir- culation of water and the disengagement of steam. The cir- culation is improved by having a space in the middle as shown on Plate I If a very large number of tubes are required for a given boiler, they may be arranged in vertical rows and in rows at 30 with the horizon, as on Plate II. This arrangement is commonly used for locomotive boilers, but is not favored for stationary boilers. The common range of fluctuation allowed for the water- BOILER DESIGN. 485 line with this type of boilers is six inches, three above and three below the mean water-level. The tops of the tubes are set about three inches below low water-level. The tubes should nowhere be nearer than three inches from the shell, and the bottom row should be from four to six inches from the bottom of the boiler. The hand-hole near the bottom of the head should be placed as low as possible; the flat surface for the gasket should be at least 3/4 of an inch wide. No tube should be nearer than an inch from its edge. The tube plate is usually from 1/16 to 1,8 of an inch thicker than the shell-plating. The internal radius of the flange should not be less than half an inch. For plates half an inch thick or less the outside radius is commonly made one inch. In applying these principles to the tube-sheet for a boiler 60 inches in diameter, as shown on Plate I, it appears that 84 tubes may be used, spaced four inches horizontally and 3J vertically and with a space at the middle for circulation, pro- vided that the top of the upper row of tubes is 6\ inches above the centre-line of the boiler. This brings the water- level 6i+6= 12 i inches above the middle of the boiler, instead of 11. 3 as caL culated on page 474; that is, the water-level is raised 1.2 of an inch or 1/10 of a foot. At 12 inches above the middle, the boiler is about 4-J feet wide; the layer of water added has consequently a volume of 1/10 X 4-5 X 16 = 7.2 cubic feet. The effect is to reduce the steam-space from 80 cubic feet (see page 471) to 72.8 cubic feet. But the rule used gave from 64 to 80 cubic feet, so that 72.8 cubic feet is a fair allowance. If the tubes were spaced nearer together in the horizontal rows and the space for circulation were 4 86 STEAM-BOILERS. omitted, the required number of tubes could be easily provided for without raising the water-level. If in any case a satisfactory ar- rangement of tubes cannot be made with the diameter assumed from preliminary calculations of steam- and water-space, or from some other method, then a larger diameter must be used. If a manhole is put in the front head the tube-sheet is as shown in Fig. 227. There are now 74 tubes instead of 84, and BOILER DESIGN. 487 the heating-surface is reduced by 116.5 square feet, leaving a total of 978.8 square feet, or about 12.5 square feet to a horse- power. The head under the tubes is stayed by angle irons tied to the head by two through rods. This staying is figured in the same manner as the channel-bars, which are considered later in this chapter. Area of Uptake. — The area of the uptake, like the total area through the tubes, is made from 1/7 to 1/8 of the grate area. On page 471 the area through the tubes was found to be 492 square inches. The uptake may be made 12 inches deep, measured from front to rear. It will then be 492 ~ 12 =41 inches wide, measured transversely. The opening through the top of the projecting shell at the front end will be made 12 inches deep, as shown on Plate I, and must be cut down till it is 41 inches wide. The projecting end of the shell is made long enough so that a space of about one inch is left between the uptake and the calking edge of the front tube- sheet. Length of Sections. — The length of the rings or sections of the cylindrical shell is limited by the reach of the riveting- machine and by the width of plate obtainable. The sec- tions are often made the same length, though there is no other reason for this than the convenience in ordering material. The two rear sections on Plate I are each made 68 inches from centre to centre of riveted joints, or, allowing ij- of an inch for lap at each end, the plates when finished are 70 J inches wide The front section is 14+ 54f + ii = 6 9 % inches wide. In this case the plates could all be ordered about 72 inches wide. The front course which comes over the fire is an outside course, so that the flames may not strike directly against the 488 S TEA M-BOILERS. edge of the plate at the ring-seam. The length of the grate is commonly about one third of the length of the boiler, which brings the first ring-seam over the bridge, where the fire is the hottest. It is well to avoid this by making the front section shorter, and the other sections longer. Manholes, Hand-holes, and Nozzles.- — These fittings should be strong enough and stiff enough to carry the stresses which come from the direct steam-pressure and from the ten- sion in the pieces to which they are fastened ; for example, the manhole-ring must be able to take the place of the piece of plate cut away at the hole. All these fittings can now be bought in the form of steel forgings, made by a hydraulic flanging or forging machine. Gun-iron and cast steelare, however, much used. The determination of stresses in a manhole-ring, even if approximate methods are used, is both difficult and uncertain, and will not be considered here. Forms and dimensions that have been used in good practice may be taken for a guide in designing. A rule used by boiler-makers for forged rings, which, like that shown on Plate I, lie close to the shell-plate, is to make the section of the ring, exclusive of the lip, equal at least to the section of the plate cut away. The aid given by the lip against which the cover bears is considered to offset eccentric loading, etc. The ring of a steam-nozzle may be treated in the same way, though it is more efficiently aided by the cylindrical portion. Gun-iron manhole-rings should be \\ of an inch thick, and nozzles may be \\ of an inch thick. An approximate calculation of the stress in the manhole- cover may be made by treating it as a beam supported at the ends and loaded by the steam-pressure and by the pull of the bolt at the middle; this last must be assumed, as it cannot be known. The calculated stress will be in excess of the actual stress, since the plate is supported all around. The handhole- plate may be treated in a similar way. Handhole-covers are frequently drawn up by a taper key instead of a bolt and nut, BOILER DESIGN. 489 because the nut is exposed to the fire, and often cannot be removed with a wrench, after it has been in place some time. The bearing-surfaces of the manhole-cover and the lip against which it bears should be machined to make them true and smooth, though this is not always done. The hand- hole-cover may be finished, but it bears directly against the plate, which of course is not finished. In any case the joint is made tight by a gasket which may be 3/4 of an inch wide for the hand-hole and from that width to an inch for the man- hole. Staying", — As is pointed out on page 312, the calculation of stresses in a flat plate supported at intervals can be determined only by the application of the theory of elasticity; and the only determinate case is that in which the supported points are in equidistant rectangular rows, dividing the sur- face into squares. This case applies directly to the staying of the fire-box of a locomotive by stay-bolts. Whatever system of arranging the supported points is finally chosen, it is convenient to make a calculation for the determinate case, with the points in equidistant rows, in order to get a standard with which the chosen system may be compared. The equation for finding the stress in a flat plate supported at points in equidistant rectangular rows is in which a is the distance of points in a row, / is the thickness of the plate, and p is the steam-pressure in pounds per square inch. In the design in hand t = 9/16 of an inch and p = 150 pounds. Assuming /=tV X 55,ooo= 5500, and solving for a, we have IVJ? / 9X 5500 X 9"X~9 „ , • t, ^ = V2"7 :== V2Xi50Xi6xi6 :=7 + mches - 4QO S TEA M-B OILERS. If the distance between supported points is made less than 7 inches, whatever the system of arrangement may be, we may be confident that the stresses will not exceed 5500 pounds; in this case stresses in the plate are due only to the pressure on the plate, since the shell of the boiler is self-sup- porting. In the several ways of staying the flat ends of boilers shown on pages 225 to 229 the plate is riveted to channel- bars, angle-irons, or crowfeet, which in turn are supported by stay-rods. The rivets are in direct tension, and are subject to initial stresses due to the contraction when they cool; it is customary to limit the apparent working stress to 6000 pounds. Rivets less than 3/4 of an inch are seldom used, since in practice they are found to be too much affected by initial stress due to cooling. Large rivets are also considered to be undesirable. We will choose here 13/16 for the rivets. If each rivet sustains the pressure on a square a inches wide, then the stress per square inch on the rivet will be ~rf s = 150 X a\ 4 in which d is the diameter and f s is the tensional stress. Assuming f s = 6000 and d = 13/16, and solving for a x , we have a ^\l n x 13 X 13 X 6000 — 4.55 inches. 150 X 16 X 16 This gives for the limiting distance of rivets 4.55 inches. Of course a less distance may be used if convenient. In some cases the pitch of the rivets may be controlled by the system of staying. For example, the rods used with crowfeet are seldom more than \\ of an inch in diameter, because larger rods may bring too large a local stress where they are riveted to the cylindrical shell. Rods one inch or *m inch and an eighth are frequently used. A double crow- BOILER DESIGN. 49 1 foot has four rivets, each of which will carry one fourth of the load on the stay-rod. A stay-rod \\ inches in diameter, and limited to a stress of 7500 pounds, may carry a pull in the direction of its length ot 7500 X = 9204 pounds. If the rod makes an angle of 20 with the shell-plate, the pull which it will exert perpendicular to the head will be 9204 cos 20 = 9204 X 0.93969 = 8649 pounds, so that each rivet will carry about 2162 pounds. If each rivet supports a square having the side # a exposed to the pressure of steam at 150 pounds, then 2162 = 150 X af, or /2162 n . „ = v t& = 3 in Laying out Stays. — Having selected the form of staying to be used, the plan must be laid out on the drawing-board, giving proper attention to practical considerations, such as the way in which the stays are to be inserted, and taking care that accessibility is not too much interfered with. Fig. 228 repeats the upper part of the head of the boiler shown by Plate I, with certain additional dotted lines, which will be referred to in the explanation of calculations. The area to be stayed is considered to be limited by the upper row of tubes, and by a dotted line drawn i\ of an inch from the inside of the shelL This line is drawn at the right only; it is very nearly the place where the rounded corner of the flange joins the flat surface of the head. The distance of the lowest row of rivets from the top row of tubes, and of the outer row of rivets from the dotted line, may be as great as their maxi- mum distance from each other. Rivets should not be placed nearer than 3 inches from the tubes, lest the expansion of the 49 2 S TEA M-B OILERS. tubes should start leaks. Rivets may be placed near the dotted line, if that is convenient. For example, the outer- most row of rivets in crowfoot staying (Fig. ,85, page 227) may be at a distance a^ from the dotted line; for \\ inch stay- rods 39° = > or - =2.17. The makers of steel beams, channel-bars, and angle-irons publish handbooks which give the sizes and properties of the standard forms, including the moment of inertia / and the ratio -, which is called the moment of resistance. From such y a handbook it appears that the moment of resistance of the channel-bar 6" X 2\" X \" is 1.08, and that the moment of resistance of the 3^ // X 3" angle-iron is 1.55; the sum 2.63 is larger than the required moment of resistance given above. These forms are consequently used as shown on Plate I. Brackets. — The boiler shown on Plate I is supported on four cast-iron brackets, each of which is 10 inches wide in the direction of the length of the boiler, and 15J inches long measured circumferentially. Each bracket is riveted to the shell by nine rivets 15/16 of an inch in diameter. Boilers over 16 feet long commonly have six brackets. The brackets are made wide and long in order that the local strains due to carrying the weight of the boiler may not be excessive. The rivets are larger than are used about the boiler, as the pitch is not restricted as in a calked seam. 5 00 STEAM-BOILERS. The brackets are set above the middle line of the boiler so that the flanges may be protected by brickwork. In the case in hand they are 3^ inches above the middle; as much as 4^ inches is commonly used. The brackets are arranged so that the weight of the boiler and accessories is equally divided among them, and so that there is as little bending-moment as possible on the shell of the boiler. When four brackets are used they may be some- what less than a fourth of the length of a tube, from the tube- plates. The load on the brackets may be estimated by calculating the weight of the boiler when entirely full of water, and add- ing the weight of all parts that are supported by the boiler, such as pipes, valves, and brickwork or covering, that may rest on the boiler. One fourth of this load is assigned to each bracket. This load on a bracket should be uniformly dis- tributed over the bearing-surface of the flange, which is com- monly 8 or 9 inches wide. But to guard against the effect of unequal bearing, it is well to assume the bracket to bear near the outer edge — say two inches from the edge. Such an assumption will bring the bearing-force on a bracket on Plate I, 10 inches from the shell. This bearing-force tends to rotate the bracket about its upper edge, and this tendency is resisted by the rivets under the flange, which must be large enough to resist the resulting pull on them. The other rivets are added to give sufficient resistance to shearing all the rivets. There are seldom less than nine rivets in a bracket, all as large as those below the flange, even though fewer would suffice. The bracket is usually made of cast iron, and the dimensions are commonly controlled as much by the condi- tions required for a sound casting as by calculations for strength. The strength may be calculated, treating it as a cantilever, allowing for the web connecting the flange to the body of the casting. Specifications and Contract. — The engineer intrusted BUILER DESIGN. r OI with the design of a boiler prepares a set of working drawings and a set of specifications which give all necessary instructions concerning the material to be used and the methods of con- struction to be followed. The drawings and specifications form a part of the contract with the boiler-maker. Boiler-makers commonly design standard forms of boilers, and in answer to inquiry will furnish a statement or set of specifications for a desired boiler in form of a letter, which letter forms the contract for the boiler. On the next page is given the contract and specifications for the boiler shown on Plate I. 502 STEAM-BOILER. IRON WORKS CO. Boston, Mass., Feb. /, 1897. Gentlemen : Your letter of received. We will build One (/) Horizontal Tubular Boiler. One Boiler, viz., Sixty (bo) inches diameter by seventeen 2/12 (17&) feet iong. Containing 84 Tubes 3 inches diameter, by sixteen (ib) feet long. Shell of Boiler of O. H. Fire-box Steel, y/ib" thick, not less than 33,000 nor over 60,000 lbs. Tensile Strength. Not less than 36% reduction 0/ area, and 23% elongation in 8". Heads of Boiler of O.H. Flange Steel q/ib" thick. Longitudinal Seams Butt Jointed, with double covering-plates, Triple Riveted. Rivet-holes drilled in place, i.e., Rivet-holes punched i / 4" small, courses rolled up, covering-plates bolted on courses. Heads in courses ■with all holes together perfectly fair. Then rivet-holes drilled to full size. Longitudinal braces without welds, with upset screw ends. Two (2) or three (3) Lugs on each side, and to be provided with wall-plates and expan- sion-rolls. Manhole (internal frame) on top. This frame a steel casting. Two (2) 5" Nozzle* on top, A Hand-hole in each head, Fusible Safety Plug in back head. Bottom at back end reinforced and tapped for 2" blowout Internal Feed Pipe placed in Boiler Co.'s style, With Boiler, Castings for setting, viz.; C. I., Overhung Front, Mouth-pieces, Division Plates, Grate Bars, shaking pattern bo" X bo" . Grate Bearers, Ash-pit Door for the brickwork, Back Return Arched T Bars, the Anchor Bolts for Front. One (1) set of six (6) Buckstaves and Tie Rods with the boiler. With the Boiler One (1) 4" Pop Safety Valve, (3)3/4" Gauge Cocks, One (1) b" Steam Gauge, One (1)3/4" Water Gauge and One (1) Combination Column Boiler tested 223 lbs. per square inch. Inspected and Insured in the sum of $400.00 for one year, by Steam Boiler Inspection & Insurance Co The Boiler Castings and Fixtures as herein specified by name, delivered F. O. B. cars, or at vessel's wharf, or on sidewalk of building, Boston, Mass., for the sum of six hundred and seventy (byo.oo) dollars net. Very respectfully yours, IRON WORKS CO. P. S. — Specimens will be furnished, one lengthwise and one crosswise, from each plate. To be at least 18" long and planed on edge 1" or i\" wide. These specimens shall show no blowhole defects and shall bend double cold, at a red heat, and at a flanging heat. APPENDIX. 50.3 5°4 APPENDIX. HORIZONTAL RETURN TUBULAR Heat- ing- Surface Shell. Tubes. Number. No. Horse- power. Diam- eter. Length, O. H. Length, Flush. Length, Diam- eter. With Man- With- out hole. Man- hole. I 21 254 36 11 11 10 3 28 2 25 3°4 36 J 3 13 12 3 28 3 33 403 42 13 J 3 12 3 38 4 39 469 42 15 15 14 3 38 5 55 604 48 15 2 15 2 14 3 50 6 62 690 48 17 2 17 2 16 3 50 7 49 548 48 15 2 15 2 14 3h 38 8 56 625 48 17 2 17 2 16 3h 38 9 67 739 54 15 2 15 2 14 3 62 IO 76 844 54 17 2 17 2 16 3 62 ii 86 949 54 19 2 19 2 18 3 62 12 64 704 54 i5 2 15 2 14 3h 5° 13 73 803 54 17 2 17 2 16 3h 50 14 82 9°3 54 19 2 19 2 18 3l 50 15 87 875 60 15 2 15 2 14 O 3 74 82 16 99 999 60 17 2 17 2 16 3 74 82 i7 112 1123 60 19 2 19 2 18 3 74 82 18 76 765 60 15 2 15 2 14 3i 54 62 19 87 873 60 17 2 17 2 16 3* 54 62 20 98 981 60 19 2 19 2 18 3* 54 62 21 124 1247 66 17 6 17 2 16 3 94 104 22 140 1401 66 19 6 19 2 18 3 94 104 2 3 i55 1556 66 21 6 21 2 20 3 94 104 24 113 ii33 66 i7 6 17 2 16 3* 72 80 25 127 1273 66 19 6 19 2 18 3i 72 80 26 141 1414 66 21 6 21 2 20 3* 72 80 27 99 996 66 17 6 17 2 16 4 54 62 28 111 1119 66 19 6 19 2 18 4 54 62 29 124 1242 66 21 6 21 2 20 4 54 62 30 158 1588 72 17 6 17 2 16 3 122 130 31 178 1785 72 19 6 19 2 18 O 3 122 130 3 2 198 1982 72 21 6 21 2 20 3 122 130 • 33 144 1448 72 17 6 17 2 16 3* 94 102 34 162 1628 72 19 6 19 2 18 3i 94 102 35 180 1807 72 21 6 21 2 20 3* 94 102 36 129 1292 72 17 6 17 2 16 4 72 80 37 145 . i45 2 72 19 6 19 2 18 4 72 80 38 161 1612 72 21 6 21 2 20 4 72 80 39 209 2090 78 19 6 18 3 144 i54 40 41 42 43 44 45 46 47 232 195 216 2321 1952 2167 1821 78 78 78 78 78 84 84 84 21 6 20 3 3i 3* 4 4 3 3 3} 144 *54 19 21 6 18 O 114 122 6 20 114 122 182 19 21 6 18 92 92 180 100 202 2022 6 20 100 257 286 236 2579 2864 2367 19 21 6 18 O 190 6 20 180 190 1 5° 19 6 18 140 48 49 262 215 2629 2i55 84 84 21 6 20 3* 4 140 *5° 19 6 18 no 114 5° 239 2302 84 21 6 20 4 no 114 APPENDIX. 505 BOILERS. (ROBB-MUMFORD BOILER Co.) Thickness, 125 Pounds. Thickness. 150 Pounds. Size of Safety Grates. Weights. Shell. Heads Style Joint. Shell. Heads Style Joint. Valve Width L'gth Boiler Only. Castings. Total. 1/4 3/8 D.L. 2 36 3° 2730 2030 4760 1/4 3/8 D.L. 2 36 36 3120 2080 5200 S/16 3/8 D.B. n/32 3/8 D.B. 2 42 36 4670 2670 7340 5/l6 3/8 D.B. 11/32 3/8 D.B. 2 42 42 5270 2740 8010 11/32 7/16 D.B. 13/32 7/16 D.B. 2i 48 42 6800 3540 10340 H/32 7/16 D.B. 13/32 7/16 D.B. 2h 48 48 758o 4000 1 1 580 11/32 7/16 D.B. 13/32 7/16 D.B. 2* 48 42 6740 3540 10280 n/32 7/16 D.B. 13/32 7/16 D.B. 2* 48 48 7520 4000 1 1 520 11/32 7/16 T.B. 13/32 7/16 T.B. 2§ 54 48 8120 4300 12420 11/32 7/16 T.B. 13/32 7/16 T.B. 3 54 54 9100 4770 13870 11/32 7/16 T.B. 13/32 7/16 T.B. 3 54 60 1 0000 5*9° 15190 11/32 7/16 T.B. 13/32 7/16 T.B. *\ 54 48 8210 4300 12510 11/32; 7/16 T.B. 13/32 7/16 T.B. 3 54 54 9210 4770 13980 n/32 7/16 T.B. 13/32 7/16 T.B. 3 54 60 10120 5 J 9o IS3IO 3/8 1/2 Q.B. 7/l6 1/2 Q.B. 3 60 54 10270 4920 1 5190 3/8 1/2 Q.B. 7/16 1/2 Q.B. 3 60 60 11420 53°° 16720 3/8 1/2 Q.B. 7/16 1/2 Q.B. 3 60 66 12480 594o 18420 3/8 1/2 Q.B. 7/16 1/2 Q.B. 3 60 54 10060 4920 14980 3/8 1/2 Q.B. 7/16 1/2 Q.B. 3 60 54 1 1 180 5*7° 16250 3/8 1/2 Q.B. 7/i6 1/2 Q.B. 3 60 60 12200 579o 17990 I3/3 2 1/2 Q.B. 15/32 1/2 Q.B. 3 66 60 14500 579o 20290 I3/3 2 1/2 Q.B. 15/32 1/2 Q.B. 3h 66 66 1593° 6410 22340 13/32 1/2 Q.B. 15/32 1/2 Q.B. 3* 66 72 17380 6540 23920 13/32 1/2 Q.B. 15/32 1/2 Q.B. 3 66 60 14410 579o 20200 13/32 1/2 Q.B. 15/32 1/2 Q.B. 3 66 60 15840 6170 22010 13/32 1/2 Q.B. !5/3 2 1/2 Q.B. 3i 66 66 17270 6410 23680 13/32 1/2 Q.B. !5/3 2 1/2 Q.B. 3 66 60 14210 579o 20000 I3/3 2 1/2 Q.B. 15/32 1/2 Q.B. 3 66 60 15610 6170 21780 1 3/3 2 1/2 Q.B. 15/32 1/2 Q.B. 3 66 60 17020 6170 23190 7/16 1/2 Q.B. 17/32 9/16 Q.B. 3* 72 66 17170 6540 23710 7/i6 1/2 Q.B. 17/32 9/16 Q.B. 3* 72 72 18910 7290 26200 7/16 1/2 Q.B. 17/32 9/16 Q.B. 4 72 84 20650 758o 28230 7/16 1/2 Q.B. 17/32 9/16 Q.B. 3h 72 66 17100 6540 23640 7/16 1/2 Q.B. 17/32 9/16 Q.B. 3h 72 72 18820 7290 26110 7/16 1/2 Q.B. 17/32 9/16 Q.B. 3* 72 78 20560 7440 28000 7/16 1/2 Q.B. 17/32 9/16 Q.B. 3* 72 66 16960 6540 23500 7/i6 1/2 Q.B. 17/32 9/16 Q.B. 3* 72 66 18670 7150 25820 7/i6 1/2 Q.B. 17/32 9/16 Q.B. 3l 72 72 20390 7290 27680 1/2 9/i6 T.B. 9/16 9/16 Q.B. 4 78 78 22580 8550 3 1 *3° 1/2 9/16 T.B. 9/16 9/16 Q.B. 4 78 90 24620 8860 3348o 1/2 9/i6 T.B. 9/16 9/16 Q.B. 4 78 78 22710 8550 31260 1/2 9/16 T.B. 9/16 9/16 Q.B. 4 78 84 24770 8660 33430 1/2 9/16 T.B. 9/16 9/16 Q.B. 4 78 72 22960 8400 3 1 3 6 ° 1/2 9/16 T.B. 9/16 9/16 Q.B. 4 78 78 25060 8550 33 6 io 1/2 9/16 Q.B. 19/32 5/8 Q.B. 4t 90 84 25700 9440 35140 1/2 9/16 Q.B. 19/32 5/8 Q.B. 4l 90 96 28100 9790 37890 1/2 9/16 Q.B. 19/32 5/8 Q.B. 4* 90 84 25670 9440 35i 10 1/2 9/16 Q.B. 19/32 5/8 Q.B. 4* 90 90 28070 9620 37690 1/2 9/16 Q.B. 19/32 5/8 Q.B. 4* 90 78 25700 9260 34960 1/2 9/16 Q.B. 19/32 5/8 Q.B. 4* 90 84 28110 0440 37550 506 APPENDIX. t) m ■i 1, W///////A % ir APPENDIX. 507 •saapog jo jaja'urBiQ 1 S TOO OOO TOO WOO TOO H (1 K)K)tt lOO \Q t- r^OO 0\ O •acrejjng a^J0 jo qjxfuag fe W .JOJNfOfOTTiO w>o t-> t^OO uaaMjag aoedg b ^TOTOfOTOTOTOT , 1 W M M W M W *» W N fO fO T T W i/HO O r- «~00 •saa^naQ uo aaijog En g • • -VO OO OO O OO OO M * * " . . . . loo O t^t>.00 ONOvO C £ ' * " JO J3JU30 0; n u AV ap»»nO QQ gOwTt^OONO «*>o c\ «^ "IFAV aiJpug 0^ -lapog Ri a; 3 ovftawoiwaoio c 1— 1 •aoBjang a^JQ jo mpiAi &H 00 M J N M f) r<5 T T W> v>\0 O t-» t~O0 -ag aoBcIs-jpy c 'A 'IFAi J^nao fe; - • • -OOOOOOOOOO l_4 • • -NNP)WM(N(MN«W "IF AY 9 P!S J° apisni gOOOOMMOONtlMNnNNd iFAV 9 PTS jo ap ; sino K gOOOOMOOMNtlNNNNPIfl s-s o> C ^ 1*1 •?UOJjJ 3ai3uBq ' -J3A0 s •^uojj •*» gOO(N'NNN-r^»^.t-.t-r^t-- •■iajiog 0; a;uiQ &s £ oo oo oO Tr-J-^i^r^r^r^r^t^i— ^wwwcsNNCNNNNNNN "11* AV jo aou^ 0.% Ja[iog Eq w OC O O O tttTtTttf t apismo jo ssau^attjj^ q gOOOOOOOOOONNNNNMNN •apisuj 'IP* AY ^a jo ssainpiifj. ^OOMOOMOONt(«N«NCI« WH aouds .ay h-< Iqttttfftttt*^') jo •sjajtog jaiauuBiQ -1 j£ TOO N 00 TOO MOO TOO ^ N t^njift too O r~ t^oo On ^ pq <3 000000000000000 000000000000000 MOOMNNVOrolO n<3 O l-» O O : O'C 6 OOOOOOOOOOOOOOO 000000000000000 O w O "HO O O O O wi ui t<> Tf rn if f*5 u->vO ton ro-trtTtPO^Tj-t^OM 2 » s s«- o g w c « c *m o t~ w r^oo woo woo woo woo w xxxxxxxxxxxxxxx e3 o • 1 ° ? 6 we a OOOOOOOOOOOOOOO OOOOOOOOOOOOOOO (Of)t "lO O O r- t^oo 00 00 00 00 00 OOOOOOOOOOOOOOO OOOOOOOOOOOOOOO t-- O w>00 fOOTOOOOOiO"-. 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M OOOOOOOOOOOOOOOOO r OOOOOOOOOOOOOOOOO m en m too mcocMCMCMONc^O ^ro ^t^u C3\w 5 g wuiuilfllflvo inO 00 lnininminwminin 1— 1 73 V "ft 3 O a r 'oooc cocoo mmcM cm Tr^oooooo inu- •OnO t^t^t^r^oooo O O m m cm cm cocomm •9 3 Q J3 M ^ rt4 hH -!■» hi-* h|-» H-» hW H-* hH qi^CMt~CMt^CMl^CMr^CMr>CMr^CMr~CMt^CM .joo 000 000 000 000 000 000 000 000 rTMNMNlHMMOMMI-lOl-IMMWMP) (J O < - 5 M C • W!H|« H|N i+M r*» HtN Hfe» HIM H« »*« C ONOnOnOOnOnOnOOnOnOnOnOnOnOnOnOnOn • i^ONt-ONt~ONt~0\t^ONt^ONt^CNr-ONr^Ov a wi\cOvOM3 CM CM CM CM O O O O CM 01 CM CM O O (-) fa MHMMMMWHMMM HWMMWMMMCMCMCMCMCMCMCMCMCOCO "el O c3 1 OhiO-TOOOnOOhOOOnOOhiOnO OOOmONOOmOOcoOmONOOOOmO w PQ < PQ S3 c Cv bi) c .JO00O00O00O00O00O00O00O00O00 feMHM MMMM«MH««MMMHM» coo oOOmcoONTwiH 000 r~ m m moO cm cm cm cococococoTmmm mo «-» t^oo s OnCnOnOnCnOnOnOnOnOnOOnOnOnCnOnOnC ^3 t"OOminoO«^r~'H/TroooooooOt^»~ • cocoTtmmmmt^ r-oo 00 On on O cm cm: oj >0>0 f- r^00 00 On On CM cm T TO >OMM h h 3 OJ gOOOOOOOOOOOOOOOOOO *J O r-O t^O r^O t^O t^O r~0 t^O t^O t» fa 1 0)"g "o3 bl)B3 S » 00 co in O in cm t^O J-->-iOO>Hininc~0 m Tft^N T m O00 coOO "If (Ml O t^N\0 O m w co co "I inO O cm wjvO O O O -.i-imhim>hmhcmcmcmcm,cmcococococo oOcomOmocMr~ot^MOO>-.mmt^O M tNN tM O00 CO00 m-H/OCM O t^CMO OHiiHcocommoOCMiooOOOcomON •AH3XJ,V^ [ 3NQ NI H aiiog 3nq 5M APPENDIX. oo W o m w n w U M W A w i-i o II 88 o o o o o o o 88 O O 82 o o o O O o o o o o o 88 •?1 lO M On ■<*■ Tf Ov r- cs oo Tf ■* "<*■ OnvO ^-00 £3 vO t^. vO t^ t>» t^ t^OO 00" ON 00 ON On O ON 6~ o" o" s* HI Is o o o o o o O O o o o o O O 88 o o C^J co o o o o o o o o o o o o io to «a On O Ov O CS ro 00 Tt" On to CS Tt VO vO vO t^ -C 3 O cs O co HI Tt CS -^t VO ON t^ O cs M (O HI Tt ^Z CS CS IN CS cn cs CS CS CS CS CS CO co co CO CO CO CO « 5 M "S o o o o o o O O o O O O O o o O £ 8 8 o o o o o o o O O O O o o O O CS vO "3-vo 00 vO 00 vO cs O M-ftO 00 o cs oo M CS tO t^ o VO ON cs vo ^f o t^. cs Tf HI VO vo 00 r^ c vo VO vovO vO vo r-» r*. On O O M cs ro CO tJ- tovo 'ft HI a J3 CO a v ■&& M M M H OfO voio vO vo o o cs cs vo vO o o V Q M M M HI cEhh n-i o ■ HI M hM vO vO o o o rt- rf- cs Tf cs cs O n- 9 CT co oo VO Tf- ON CS O co r~~ t^ o oo' OO* rj- M lO to cs O CS ~ cs CO O O t^ O ON £oq CS CS CS CS cs to CO co ^ ^ Tf VO lOvO vo vo t>. t>. f§2 "S •A^axxvg aNQ NI sxa-iiog; oavx APPENDIX. GREEN'S FUEL ECONOMIZER. 515 Dimensions, Area between c £. Valves. «-£ Inside Walls. Tubes. X ■ II 4) 3 ■gOQ *o 3 si °3 83 .2 £ ® eS & u 2/3 H *o u (0 ,0 ■ s s 8.9 & 14 01 •-so a * III ^ Q to * 3 3 oq z Feet. Feet. Feet. Feet. Feet. Feet. Feet. Sq.ft. Lbs. E H. P. Inches. 32 4 4-10 3-4 4-1 4-10 16.6 23,85 31.10 8 384 1,984 • 5 2 i-5 48 4 7- 3 12 576 2,976 •5 2 i.5 64 4 9- 8 16 768 3,968 • 5 2 1 -5 80 4 12- 1 20 960 4,960 •5 2 1.5 96 4 14-6 24 1152 5.952 I 2 1.5 JI2 4 1 6-1 1 28 1344 6,944 1 2 i.5 128 4 19- 4 32 1536 7,936 1 2 1. 5 144 4 21-9 36 1728 8,928 1 2.5 2 l6o 4 24- 2 40 1920 9,920 2 2.5 2 176 4 26- 7 44 21 12 10,912 2 2.5 2 192 4 29- 48 2304 11,904 2 2.5 2 208 4 3i- 5 52 2496 12,896 2 2.5 2 48 6 4-10 4-8 5-5 6-2 21.85 29. 10 3 6 -.3 5 8 576 2,976 •5 2 X S 72 6 7- 3 12 864 4,464 • 5 2 1 5 96 6 9- 8 16 1152 5,852 2 i-5 I20 6 12- 1 20 1440 7,440 1 2 i-5 144 6 14-6 24 1728 8,928 1 2-5 2 168 6 16-11 28 2016 10,416 2 2.5 2 192 6 19- 4 32 2304 11,904 2 2.5 2 2l6 6 21-9 36 2592 13.392 2 2-5 2 240 6 24- 2 40 2880 14,880 2 2-5 2 264 6 26-7 44 3168 16,368 2.5 2-5 2 288 6 29- 48 3456 17,856 2-5 2.5 2 312 6 3i- 5 52 3744 19,344 2.5 2.5 2 336 6 33-IO 56 4032 20,832 2 -5 2-5 2 360 6 36- 3 60 4320 22,320 3 3 2.5 96 8 7- 3 6-0 6-9 7-6 27.00 34.25 4i... 5 12 1152 5,952 1 2 1 -5 128 8 9- 8 16 1536 7,936 1 2 i-5 l6o 8 12- 1 20 1920 9,920 2 2.5 2 192 8 14-6 24 2304 11,904 2 2-5 2 224 8 1 6-1 1 28 2688 13,888 2 2-5 2 256 8 19- 4 32 3072 15,872 2 2.5 2 288 8 21- 9 36 3456 17,856 2-5 2.5 2 320 8 24- 2 40 3840 19.840 2-5 2.5 2 352 8 26— 7 44 4224 21,824 2-5 3- 2.5 384 8 29-0 48 4608 23,808 2.5 3 2-5 416 8 3i- 5 52 4992 25,792 2-5 3 2-5 448 8 33-io 56 5376 27,776 3 3 2.5 480 8 36- 3 60 576o 29,760 3 3 2-S 160 10 9- 8 7 ." 4 8-1 8-10 32.25 39 4 -.5o 46.75 16 1920 9,920 2 2-5 2 200 10 12- 1 20 2400 12,400 2 2-5 2 240 10 14- 6 24 2800 14,880 2 2-5 2 280 10 1 6-1 1 28 336o 17,360 2-5 2-5 2 320 10 19- 4 32 3840 19,840 2-5 3- 2-5 360 10 21- 9 36 4320 22,320 2.5 3- 2-S 400 10 24— 2 40 4800 24,800 2.5 3- 2-5 440 10 26- 7 44 5280 27,780 2.5 3- 2-5 480 10 29- 48 576o 29,780 2.5 3- 2.5 520 10 3i- 5 52 6240 32,240 3 3. 2-5 560 10 33-IO 56 6720 34,720 3 4. 3 600 10 36- 3 60 7200 37,200 3 4. 3 640 10 38- 8 64 7680 39,680 3 4. 3 680 10 41- 1 68 8160 42,160 3 4. 3 720 10 43- 6 72 8640 44,640 4-5 4. 3 760 10 45-n 76 9120 47.120 4-5 4. 3 800 10 48- 4 80 96oo|49,6oo 1 5 4- / 3 5i6 APPENDIX. STANDARD SIZES OF STURTEVANT Ma- chine No. I 2 3 4 5 6 7 8 9 io ii 12 13 14 i5 16 i7 18 i9 20 21 22 23 24 25 26 27 28 29 3° 31 32 33 34 35 36 37 38 39 40 4i 42 43 44 45 46 4? 48 49 No. of Pipes. 3 2 48 64 80 96 112 128 40 60 80 100 120 140 160 180 200 72 9 6 120 144 168 192 216 240 264 288 112 140 168 196 224 252 280 308 33 6 3 6 4 392 128 160 192 224 256 288 320 352 384 416 448 480 No. of Sec- tions. Ex- ternal No. of ! Heat- Pipes in 1 ing- Section. surface. Sq. ft. 8 12 16 20 24 28 32 8 12 16 20 24 28 32 36 40 12 16 20 24 28 3 2 36 40 44 48 16 20 24 28 32 36 40 44 48 52 56 16 20 24 28 32 36 40 44 48 52 56 60 400 600 801 1001 1 201 1401 1601 499 749 999 1248 1499 1747 1997 2247 2496 897 1196 1496 1795 2094 2393 2692 2991 3290 3589 1394 1743 2092 2440 2789 3137 3486 3835 4183 4532 4880 I59 2 1990 2388 2786 3185 3583 398i 4379 4777 5i75 5573 597i Capacity in Pounds of Water. 2,016 3,° 2 4 4,032 5,°4o 6,048 7,056 8,064 2,520 3,78o 5,040 6,300 7,56o 8,820 10,080 n,34o 12,600 4,536 6,048 7,56o 9,072 10,584 12,096 13,608 15,120 16,632 18,144 7,056 8,820 10,584 12,348 14,112 15,876 17,640 19,404 21,168 22,932 24,696 8,064 10,080 12,096 14,112 16,128 18,144 20,160 22,176 24,182 26,198 28,224 30,240 General Dimensions. Length. Ft. In. 4 7 9 12 14 16 19 4 7 9 12 14 16 19 21 24 7 9 12 14 16 19 21 24 26 29 9 12 14 16 19 21 24 26 29 3i 33 9 12 14 16 19 21 24 26 29 3i 33 36 10 3 8 1 6 11 4 10 3 8 1 6 11 4 9 2 3 8 1 6 11 4 9 2 7 o 8 1 6 11 4 9 2 7 o 5 10 8 1 6 11 4 9 2 7 o 5 10 3 Width. Ft. In. 3 2* 3 ioJ Height in Feet and Inches. Section. IO 2j 4 6* 5 A 5 i°i IO 2\ Section and Gearing. IO 2\ 12 6 « < « < «« 11 12 6 APPENDIX. 5 J 7 STANDARD ECONOMIZERS. No. Ex- L ternal Capacity General Dimensions. Height in Feet and Ma- No. No. of Heat- ■ ,n . ing- Pounds surface. „ T °' Water. Inches. chine No. ox Pipes. of Pipes in Section. Lciic^^* Width. Sec- tions. Section. Section and Sq. ft. Ft. In. Ft. In Gearing. 50 180 20 9 2,237 ",34° 12 I 6 6J IO 2\ 12 6 51 216 24 9 2,685 13,608 14 6 ' ' 52 252 28 9 3,132 1 15,876 16 11 " 53 288 32 9 3,580 18,144 19 4 i < 54 3 2 4 36 9 4,027 20,412 21 9 " 55 360 40 9 4,475 22,680 24 2 < < 56 396 44 9 4,922 ■ 24,948 26 7 « i 57- 432 48 9 5,370 27,216 29 < < 58 468 52 9 5,817 29,484 31 5 < « 59 5°4 56 9 6,265 : 3^752 33 10 t < 60 540 60 9 6,712 34,020 36 3 < < 61 576 64 9 7,160 36,288 38 8 ' ' 62 200 20 10 2,484 12,600 12 1 7 „ 2 * IO 7.\ 12 6 63 240 24 10 2,981 15,120 14 6 " 64 280 28 10 3,478 ! 17,640 16 11 ( « 65 320 32 10 3^974 [ 20,160 19 4 « ( 66 360 36 10 4,471 22,680 21 9 • « 67 400 40 10 4,968 25,200 24 2 ( ( 68 440 44 10 5,465 27,720 26 7 " 69 480 48 10 5,962 30,240 29 *' 70 520 52 10 6,458 32,760 3i 5 I ( 7i 560 56 10 6,955 35.28o 33 10 ( < 72 600 60 10 7.45 2 37,8oo 36 3 " 73 640 64 10 7.949 40,320 38 8 " 74 680 68 10 8,446 42,840 41 1 " 75 396 36 n 4,9i5 24,949 21 9 7 M ioJ IO 2\ 12 6 76 440 40 11 5,46i 27,720 24 2 ( i 77 484 44 11 6,008 3°,497 26 7 •« 78 528 48 11 6,554 33,268 29 " 79 572 52 11 7,101 36,045 3i 5 " 80 616 56 11 7,646 38,811 33 10 <« 81 660 60 11 8,i93 41,588 36 3 < ( 82 704 64 11 8,739 44,359 38 8 " 83 748 68 11 9,286 47,136 41 1 1 84 792 72 11 9,832 49,907 43 6 < 85 836 76 11 10,379 52,684 45 11 t { 86 880 80 11 10,925 55,455 48 4 c ( 87 528 44 12 6,549 33,262 26 7 8 6\ IO 2\ 12 6 88 576 48 12 7,145 36,289 29 ( « 89 624 52 12 7,74i 39,317 3 1 5 < ( 90 672 56 12 8,337 42,344 33 10 II 9i 720 60 12 8,933 45,37i 36 3 ( « 92 768 64 12 9,529 48,398 38 8 ** 93 816 68 12 10,125 5i,425 41 1 It 94 864 72 12 10,721 54,452 43 6 (« 95 912 76 12 n,3i7 57,479 45 11 ( t 96 960 80 12 ",913 60,506 48 4 • 1 97 1008 84 12 12,489 63,432 5o 9 II 98 1056 88 12 i3,° 6 5 66,357 53 2 •4 i8 APPENDIX. LOGARITHMS. Nat. Proportional Parts. Nos. 1 2 3 4 5 6 7 8 9 0000 0043 0086 0128 1 2 3 4 5 6 7 8 9 10 0170 0212 0253 0294 0334 0374 4 8 12 17 21 25 29 33 37 11 0414 0453 0492 0531 0569 0607 0645 0682 07190755 4 8 11 15 19 23 26 30 34 12 0792 0828 0864 0899 0934 0969 1004 1038 1072 1 106 3 7 10 14 17 21 24 28 31 13 "39 "73 1206 1239 1271 1303 1335 1367 1399 1430 3 6 10 13 16 19 23 26 29 14 1461 1492 1523 1553 1584 1614 1644 1673 1703 1732 3 6 9 12 15 18 21 24 27 15 1761 1790 1S18 1847 1875 1903 i93i 1959 1987 2014 3 6 8 11 14 17 20 22 25 16 2041 2068 2095 2122 2148 2175 2201 2227 22532279 3 5 8 11 13 16 18 21 24 17 2304 2330 2355 2380 2405 2430 2455 2480 2504 2529 2 5 7 10 12 15 17 20 22 18 2553 2 577 2601 2625 2648 2672 2695 2718 27422765 2 5 7 9 12 14 16 19 21 19 2788 3010 2810 3032 2833 2856 2878 2900 3118 2923 3^39 2945 3160 29672989 318113201 2 4 7 9 " 13 16 18 20 20 3054 3075 3096 2 4 6 8 11 13 15 i7 19 21 3222 3243 3263 3284 3304 3324 3345 3365 3385 3404 2 4 6 8 10 12 14 16 18 22 3424 3444 3464 3483 3502 3522 354i 356035793598 2 4 b 8 10 12 14 15 17 23 3617 3636 3655 3674 3692 37" 3729 374737663784 2 4 6 7 9 11 13 15 17 24 3S02 3820 38383856 3374 3892 3909 3927 3945 3962 2 4 5 7 9 11 12 14 16 25 3979 3997 40 1 4 '403 1 4048 4065 4082 4099 41164133 2 3 5 7 9 10 12 14 15 26 4150 4166 4183 4200 4216 4232 4249 4265 4281 4298 2 3 5 7 8 IO 11 13 15 27 43M 4330 43464362 4378 4393 4409 4425 44404456 2 3 5 6 8 9 11 13 14 28 4472 4487 45024518 4533 4548 4564 4579 4594 4609 2 3 5 6 8 9 11 12 14 29 4624 477' 4639 4736 46544669 4683 4698 4713 4728 4742 4757 1 3 4 6 7 9 10 12 13 30 48oo'48i4 4829 4843 4S57 4871 4886 4900 1 3 4 6 7 9 10 11 13 31 49M 4928 49424955 4969 4983 4997 501 1 5024 5038 1 3 4 6 7 8 IO II 12 32 5051 5065 5079I5092 5105 5"9 513- 5M5 5I595I72 1 3 4 5 7 S 9 II 12 33 5185 5198 5211 5224 5237 52505263 5276 5289 5302 * 3 4 5 6 8 9 IO 12 34 5315 5328 53405353 5366 53785391 5403 54165428 1 3 4 5 6 8 9 10 11 35 5441 5453 5465^478 5490 5502 5514 5527 5539'555i 1 2 4 5 6 7 9 10 11 36 5563 5575 5587 5599 5611 562315635 5647 5658 5670 1 2 4 5 6 7 8 10 11 37 5682 5694 5705 5717 5729 574U.5752 5763 5775 5786 1 2 3 5 6 7 8 9 10 38 579S 5809 5821 5832 5843 58555866 5877 5888 5899 1 2 3 5 6 7 8 9 10 39 59" 5922 5933 5944 5955 5966 5977 5988 5999 6010 1 2 3 4 5 7 8 9 10 40 6021 6031 6042 6053 6064 6075 6085 6096 6107 6117 1 2 3 4 5 6 8 9 10 41 6128 6138 6149 6160 6170 6180 6191 6201 6212 6222 1 2 3 4 5 6 7 8 9 42 6232 6243 6253 6263 6274 6284^)294 6304 63146325 1 2 3 4 5 6 7 8 9 43 '6335 6345 6355 6365 6375 63S5|6395 6405 64156425 1 2 3 4 5 6 789 44 6435 6444 6454 6464 6474 6484.6493 6503 6513:6522 i 2 3 4 5 6 7 8 9 45 6532 6542 6551 6561 6571 6580 6590 6599 6609' 66 1 8 1 2 3 4 5 6 7 8 9 46 6628 6637 6646 6656 6665 6675)6684 6693 6702 6712 1 2 3 4 5 6 7 7 8 47 6721 6730,6739 6749 6758 6767 6776 6785 67946803 1 2 3 4 5 5 678 48 6812 6821 6830 6839 6848 6S57 6S66 6875 68S4 6893 1 2 3 4 4 5 678 49 6902 691 1 6920 7007 6928 7016 6937 6946 6955 6964 6972 7059 6981 7067 1 2 3 4 4 5 678 50 6990 6998 7024 7033 7042 7050 1 2 3 3 4 5 678 51 7076 7084 7093 7101 7110 7118 7126 7135 7M3 7152 1 2 3 3 4 c •678 52 7160 7168 7177 7185 7193 7202 7210 7218 7226 7235 1 2 2 3 4 c 6 7 7 53 7243 7251 7259 7267 7275 7284 7292 7300 730SJ7316 1 2 2 3 4 5 667 54 7324 7332 7340 7348 7356 7364 7372 7380 7388 '7396 1 2 2 3 4 5 667 APPENDIX. LOGARITHMS. 5*9 Nat. Nos. 1 2 3 4 7 8 9 Proportional Parts. 5 6 12 3 4 5 6 7 8 9 55 7404 7412 7419 7427 7435 7443 7451 7459 7466 7474 122 3 4 5 5 6 7 56 7482 7490 7497 7505 75i3 752o|7528 7536 7543 755i 122 3 4 5 5 6 7 57 7559 7566 7574 7532 7589 7597 7604 7612 7619 7627 i 2 2 3 4 5 5 6 7 58 76.34 7642 7649 7657 7664 7672 7679 7686 7694 7701 112 3 4 4 5 6 7 59 7709 7716 7723 773i 7738 7745 7752 7760 7767 7774 1 1 2 3 4 4 5 6 7 60 7782 7789 7796 7803 7S10 78187825 7832 7839 7846 1 1 2 3 4 4 5 6 6 61 7853 7860 7868 7375 7882 7889 7896 7903 7910 79 J 7 112 3 4 4 5 6 6 62 7924 7931 7938 7945 7952 7959 79 66 7973 798o 7937 1 1 2 3 3 4 5 6 6 63 7993 Sooo 8007 8014 S021 8o28;8o35 8041 8048 8055 1 1 2 3 3 4 5 5 6 64 S062 SI2Q S069 S136 8075 S082 8089 8096 8102 8109 8116 8122 1 1 2 3 3 4 5 5 6 65 8142 8149 8156 8162 Si 69 8176 8182 S189 1 1 2 3 3 4 5 5 6 66 Siqq 8202 S209 8215 8222 S228 8235 8241 8248 8254 1 1 2 3 3 4 5 5 6 67 8261 3267 8274 8280 8287 8293 8299 8306 8312 8319 1 1 2 3 3 4 5 5 6 6$ S325 8331 3338 3344 3351 8357 8363 3370 8376 8382 112 3 3 4 4 5 6 69 8388 3395 8401 8407 8414 8420 8426 3432 8439 3445 112 2 3 4 4 5 6 7C 8451 3457 8463 8470 8476 8482 848S S494 8500 8506 112 2 3 4 4 5 6 71 85t3 35^9 8525 8531 8537 8543 3549 8555 8561 3567 112 2 3 41 4 5 5 72 85 73 3579 8585 8591 8597 8603 S609 S615 S62: 8627 1 1 2 2 3 4, 4 5 5 73 8633 8639 8645 8651 8657 S663 8669 3675 8681 8686 112 2 3 4! 4 5 5 74 8692 8751 8698 3756 8704 8762 8710 8768 S716 8722 8727 8733 8739 8745 112 2 3 4 4 5 5 75 3774 8779 8785 8791 8797 8S02 112 2 3 3 4 5 5 76 8808 -S14 8820 882; 8831 8837 8S42 8848 S854 8859 1 1 2 2 3 3 4 5 5 77 8865 S871 8S76 S882 8887 8S93 SS99 S904 8910 8915 1 1 2 2 3 3 4 4 5 78 8921 3927 8932 8938 8943 8949 8954 S960 S965I8971 1 1 2 2 3 3 4 4 5 79 S976 8982 8987 3993 8998 9004 9009 9015 9020,9025 1 1 2 2 3 3 4 4 5 80 9031 9036 9042 9047 9053 9058 9063 9069 90749079 1 1 2 2 3 3 4 4 5 81 9085 9090 9096 9101 9106 9112 9117 9122 91289133 1 1 2 2 3 3 4 4 5 82 9'3« 9M3 9149 9 T 54 9159 91659170 9175 9180,9186 112 2 3 3 4 4 5 83 9191 9196 9201 9206 9212 9217 9222 9227 9232 9238 1 1 2 2 3 3| 4 4 5 84 9243 9294 924S 9299 9253 9304 9258 9309 9263 9315 92699274 93209325 9279 9284 9289 112 2 3 3 4 4 5 85 9330 9335 9340 1 1 2 2 3 3 4 4 5 86 9345 935o 9355 9360 9365 9370 9375 93S0 9385 9390 112 2 3 3 4 4 5 87 9395 9400 9405 94io 9415 94209425 9430 9435 9440 1 1 223 3 4 4 88 9445 94509455(9460 9465 94699474 94799484 948g 1 1 223 3 4 4 89 9494 9499 9504;9509 9513 95^9523 95289533953S 1 1 2 2 3 3 4 4 90 9542 954795529557 9562 95669571 95769581 9586 Oil 223 3 4 4 91 9590 9595 9600 9605 9609 961419619 9624'96289633 Oil 2 2 3 3 4 4 92 9638 96439647,9652 9657 9661 9666 9671 9675 968c 1 1 223 3 4 4 93 9685 9689 96949699 9703 97oS 9713 9717 97229727 1 1 223 3 4 4 94 9731 9736 974ij9745 9750 9754 9759 9763 97689773 1 1 223 3 4 4 95 9777 9732 97S6'979i 9795 9800 9805 9809 9S-4 9S18 1 1 223 3 4 4 96 9823 9827 9832 9836 9841 9845 9850 98549S599S63 1 1 223 3 4 4 97 9868 9872 98779881 9886 g3go 9894 9S99 9903 990S 1 1 223 3 4 4 98 9912 9917 9921 9926 9930 9934 9939 9943 99439952 1 1 223 3 4 4 99 9956 9961 9965 9969 9974 9978 9983 9987 9991 9996 Oil 223 3 3 4 520 APPENDIX. Explanation of the Table for Finding the Area of Segment of a Circle. — The areas given in the table are for a circle I inch in diameter. The diameter is divided into iooo parts, and the area for segments of different heights can be taken directly from the table, since the ratio of the height of the segment to the diameter of the circle is the same as the height of the segment. For a circle whose diameter is other than unity. Given the diameter of the circle and the height of segment. Re- quired area of segment. Divide height of segment by diameter ; find area given in the table opposite this ratio ; multiply this area by the square of the diameter and the result is the re- quired area. Example. — Dia. of circle = 60", height of segment =18". 18 -f- 60 = .30; area in table opposite .30 is . 198 17. .19817 X 60 X 60 = area of segment = 713.4 sq. in. Given the diameter of the circle and the area of a segment, to find the height. Divide the area of the segment by the square of the diam- eter. Find in the table the area nearest to this, multiply the ratio corresponding to this by the diameter of the circle, and the result is the required height of the segment. Example. — Area of segment = 713.4 sq. in. Diameter of circle = 60". Required the height of the segment. '—— = .19817. Ratio opposite this is .300. .300 X 60" = 18", the required height. Example — Area of segment = 640 sq. in. Diameter of circle — 50". 640 = .2560; nearest ratio, .362. 50 X 50 .362 X 50 = 18.10", the required height. APPENDIX. 521 TABLE FOR FINDING AREAS OF SEGMENTS OF A CIRCLE. " O V t; v *j O 1) j «OM <-> V ■a:a c u J3 *j — bc w H c u c a bo V CO sri C u s:a c £g0 C a bX) co "v c; - ; a M u CO "5 Ci] = |2 ? ° a bf w CO "S& a be CO 3 2 .12977 2 .17287 2 .21853 2 .26611 2 .31502 3 .13060 3 .17376 3 .21947 3 . 26708 3 .31600 4 •I3M4 4 •17465 4 . 22040 4 .26805 4 .31699 .225 .13227 •275 •17554 .325 •22134 •375 .26901 •425 •31798 6 .13311 6 .17644 6 .22228 6 .26998 6 •31897 7 •13395 7 •17733 7 .22322 7 •27095 7 .31996 8 •13478 8 .17823 8 •22415 8 .27192 8 • 32095 9 .13562 9 .17912 9 .22509 9 .27289 9 •32194 .230 .13646 .280 .18002 •33o .22603 .380 •27386 •43° •32293 1 .13731 1 .18092 .22697 1 .27483 • 32392 2 .13815 2 .18182 2 .22792 2 .27580 2 •32491 3 .13900 3 .18272 3 .22886 3 .27678 3 •32500 4 .13984 4 .18362 4 .22980 4 •27775 4 .32689 •235 .14069 • 285 .18452 •335 •23074 • 38 | .27872 •435 •32788 6 •I4I54 6 .18542 6 .23169 6 .27969 6 .32S87 7 •14239 7 .18633 7 .23263 7 . 28067 7 •32987 8 •^4324 8 .18723 8 •23358 8 .28164 8 • 33086 9 .T4409 9 .18814 9 •23453 9 .28262 9 •33185 .240 .14494 .290 .18905 •34o •23547 •39o •28359 •440 •33284 1 .14580 1 .18996 1 .23642 1 •28457 •33384 2 .14666 2 .19086 2 •23737 2 •28S54 2 •33483 3 •1475 1 3 .19177 3 •23832 3 .28652 3 •33582 4 .M837 4 .19268 4 .23927 4 .28750 4 .33682 .245 .14923 •295 • 193 6 ° •345 .24022 •395 .28848 •445 •33781 6 ■ 15009 6 •19451 6 .24117 6 ■28945 6 .33880 7 •15095 7 .19542 7 .24212 7 .29043 7 •3398o 8 .15182 8 .19634 8 •24307 8 .29141 8 • 34079 9 .15268 9 .19725 9 .24403 9 •29239 9 •34179 .250 •'5355 .300 .19817 •35° •24498 .400 •29337 •450 •34278 1 • I 544> 1 .19908 1 •24593 1 •29435 1 •34378 2 •15528 2 . 20000 2 .24689 2 • 2 9533 2 •34477 3 .15615 3 .20092 3 .24784 3 •29631 3 •34577 4 .15702 4 .20184 4 .24880 4 .29729 4 .34676 •255 •15789 •305 .20276 •355 .24976 •405 .29827 •455 •3477 6 6 .15876 6 .20368 6 .25071 6 . 29926 6 .34876 7 •15964 7 .20460 7 .25167 7 .30024 7 •34975 8 . 16051 8 •20553 8 •25263 8 . 30122 8 •35075 9 .16139 9 .20645 9 •25359 9 .30220 9 •35*75 522 APPENDIX NATURAL TRIGONOMETRIC FUNCTIONS. CIRCLES Deg. Sine. T angent. Cot. Cos. Deg. .OOOO .OOOO Infinite I. OOOO 90 I •OI75 0175 57.290 .9998 89 2 •0349 0349 28.636 •9994 88 3 •0523 0524 19.081 .9986 87 4 .0698 0699 14-301 .9976 86 5 .0872 0875 11.430 .9962 85 6 .1045 1051 9-5M4 •9945 84 7 .1219 1228 8.1443 •9925 83 8 .1392 1405 7.H54 •9903 82 9 .1564 1584 6.3138 .9877 81 10 .1736 1763 5.6713 .9848 80 ii .1908 1944 5.1446 .9816 79 12 .2079 2126 4.7046 .9781 78 13 .2250 2309 4.3315 • 9744 77 J 4 .2419 2493 4.0108 • 9703 76 15 .2588 2679 3-7321 .9659 75 16 .2756 2867 3.4874 .9613 74 17 .2924 3057 3.2709 • 9563 73 18 .3090 3249 3.0777 .9511 72 19 •3256 3443 2.9042 •9455 7i 20 .3420 3640 2-7475 •9397 70 21 .3584 3839 2.6051 .9336 69 22 •3746 4040 2.4751 .9272 68 23 •3907 4245 2.3559 .9205 67 24 .4067 4452 2.2460 • 9135 66 25 .4226 4663 2.1445 .9063 65 26 .4384 4877 2.0503 .8988 64 27 .4540 5095 1.9626 .8910 63 28 .4695 5317 1.8807 .8829 62 29 .4848 5543 1 . 8040 .8746 61 30 .5000 5774 1. 7321 .8660 60 3i .5150 6009 1.6643 .8572 59 32 .5299 6249 1 . 6003 .8480 58 33 .5446 6494 1-5399 .8387 57 34 •5592 6745 1.4826 .8290 56 35 .5736 7002 i.428r .8192 55 36 .5878 7265 1.3764 .8090 54 37 .6018 7536 1.3270 .7986 53 38 .6157 7813 1.2799 .7880 52 39 .6293 8098 1-2349 •7771 5i 40 .6428 8391 1.1918 .7660 50 4i .6561 8693 1. 1504 • 7547 49 42 .6691 9004 1.1 106 •7431 48 43 .6820 9325 1.0724 .7314 47 44 .6947 9 6 57 I-Q355 .7193 46 45 .7071 I OOOO I. OOOO .7071 Sine. 45 Deg. Cos. Cot. Tangent. Deg. Diam. Circumf. Area, Inches. Inches. Sq. In. 12 371 113$ 14 44 154 16 5o£ 20I 18 56i 254^ 20 621 3I4| 38o£ 22 69* 24 75# 452| 26 8i| 53i 28 88 6i 5 f 30 94i 7o6| 32 ioo| 8o4i 34 io6i 907| 36 "3* 1017J 38 Ii9f "34& 40 I25f 1256$ 42 132 i385i 44 138^ 1520^ 46 I44| i66i| 48 I50f 1809! 50 157* ] 963? 52 1 63I 2123! 54 169I 2290^ 56 i75| 2463 58 1824, 2642J 60 i88| 2827I 62 i 94 f 3019^ 64 201 3217 66 207I 342ii 68 213S 363 if 70 219I 3848^ 72 226£ 4071I 74 2 3 2| 43co£ 76 238J 4536| 78 245 477Sf 80 25if 5026! 82 257$ 5281 84 263! 554if 86 2701 58o8| 88 276^ 608 2£ 90 282f 636lf 92 289 66 4 7£ 94 2951 6939! 96 3orf 7J38* 98 307! 7543 100 3I4& 7854 102 32of 8171* APPENDIX. ROUND RODS OF WROUGHT IRON. 5 2 3 Weight Diameter Diameter Excess of Effective Diameter Circumfer- Area in of Rod of Upset of Screw Threads Area of in Inches-. ence in Inches. Sq. Inches. One Foot Long. Screw End. Inches. at Root of Thread. Inches. per Inch. Number. ScrewEod over Bar. Per Cent. 1/16 .1963 .0031 .OIO 1/8 .3927 .0123 .041 3/16 •5890 .0276 .092 1/4 .7854 .0491 . T64 5/16 .9817 .0767 .256 3/8 I.1781 .1104 .368 7/16 1-3744 .1503 .501 1/2 1.5708 .1963 .654 3 1 .620 IO 6* 9/16 1 . 7671 .2485 .828 t .620 IO 21 5/8 1.9635 .3068 I.023 7 .731 9 37 11/16 2.1598 .3712 I.237 I .837 8 48 3/4 2.3562 .4418 1-473 .837 8 25 13/16 2.5525 .5185 I.728 T l •940 7 34 7/8 2.7489 .6013 2.OO4 3 I.065 7 48 I5/I6 2.9452 .6903 2.301 I.065 7 29 1 3.1416 .7854 2.6l8 If 1. 160 6 35 1/16 3-3379 .8866 2-955 If 1. 160 6 19 1/8 3-5343 .9940 3-313 l£ I.284 6 30 3/i6 3.7306 1. 1075 3.692 T l I.284 6 17 1/4 3.9270 1.2272 4.O9I If I.389 5s 23 5/16 4.1233 i.353o 4.510 If I.490 5 29 3/8 4.3197 1.4849 4-950 T 3 I.49O 5 18 7/16 4.5160 1 .6230 5.4IO I| 1. 615 5 26 1/2 4.7124 1.7671 5.890 2 I. 712 4l 30 5/8 5-1051 2.0739 6.913 ■* 1.837 4h 28 3/4 5.4978 2.4053 8.018 4 1 . 962 4h 26 7/8 5.8905 2.7612 9.204 2f 2.087 4* 24 2 6.2832 3-1416 IO.47 2| 2.175 4 18 1/8 6.6759 3.5466 11.82 2| 2.300 4 17 1/4 7.0686 3.9761 13.25 2^ 2-550 4 28 3/8 7.4613 4.4301 14.77 3 2.629 3* 23 1/2 7.8540 4.9087 16.36 3i 2.754 3i 21 5/8 8.2467 5.4II9 18.04 3i 2.879 3* 20 3/4 8.6394 5.9396 19.80 31 3.OO4 3* 19 7/8 9.0321 6.4918 21.64 31 3.225 3? 26 3 9.4248 7.0686 23.56 3f 3.3I7 3 22 524 APPENDIX. LAP-WELDED BOILER-TUBES. V U (A c is £2 if * £3 fc, « j aJ a Q £•=■ 35 a 5 _ — u? C.C c c/T (A X en „ M s & <£ c 2c/j CO £ cu *-> & ~ v- ctf « &L £ K £ c c 1- J at; be c £3 . s« — CO u V 0. fa <*5 fa to fa fa fo fa «o o *-« «~rs » «m3 » «~n2 4> «~:2» •k."^ 4) O 3 > > 3 > O 3 > 5 > °3 £ i 0)M o3 a S 0) ^0*0 0)1— 1 d ft a 0) 1— 1 °3 ft a 0) »M C9 a 0)i—! eg ft a Hi £ ffi H w H H H M H w H X 32 0.0 76 44.1 121 89.0 166 1340 211 179.3 256 224.9 33 I .0 77 45-i 122 90.0 167 1350 212 180.3 257 225.9 34 2 .O 78 46. 1 123 91 .0 168 136.0 213 181. 3 258 226.9 35 3° 79 47-1 124 92 .0 169 137.0 214 182.3 259 227.9 36 4.0 80 48.I 125 93 170 138.0 215 183.3 260 229.0 37 5 81 49-1 126 94.0 171 139.0 216 184.3 261 230.0 38 6.1 82 50.1 127 950 172 140 .0 217 185.3 262 231 -o 39 7-1 83 Si. 1 128 96.0 173 141 .0 218 186.3 263 232.0 40 8.1 84 52.1 129 970 174 142 .0 219 187.4 264 2330 41 9-i 85 53-1 130 98.0 175 143.0 220 188.4 265 234 42 10. 1 86 54-1 131 99 176 144.0 221 189.4 266 235.0 43 11 . 1 87 55-i 132 100 .0 177 1450 222 190.4 267 236.1 44 12 . 1 88 56.1 i33 IOI .0 178 146 .0 223 191. 4 268 237.1 45 I3-I 89 57-1 134 102 .0 179 147.0 224 192 .4 269 238.1 46 14. 1 90 58.1 i35 103 .0 180 148.0 225 193-4 270 239.1 47 15. 1 9i 59-1 136 104 .0 181 149.0 226 194.4 271 240.2 48 16. 1 92 60.1 137 105.0 182 150. 1 , 227 195-4 272 241 .2 49 17. 1 93 61. 1 138 106 .0 183 151-1 228 196.5 273 242 .2 5o 18. 1 94 62 . 1 139 107 .0 184 152 . 1 229 197.5 274 243-2 51 19. 1 95 63.1 140 108.0 185 153. 1 230 198.5 275 244.2 52 20. 1 96 64. 1 141 109.0 186 154. 1 231 199-5 276 245-3 53 21 . 1 97 65.0 142 IIO.O 187 155. 1 232 200.5 277 246.3 54 22 . 1 98 66.0 143 III .0 188 156. 1 233 20T .5 278 247-3 55 23.1 99 67.0 144 112 .O 189 157.1 234 202 .5 279 248.3 56 24.1 100 68.0 145 113 .O 190 158. 1 235 203 .6 280 249-4 57 25-1 IOI 69.0 146 114. O 191 159.1 236 204.6 281 250.4 58 26.1 102 70.0 147 IIS.O 192 160. 1 237 205 .6 282 251.4 59 27.1 103 71.0 148 Il6. O 193 161 .1 238 206.6 283 252.4 60 28.1 104 72.0 149 117 .O 194 162 . 1 239 207 .6 284 2 53-4 61 29. 1 105 73-0 150 IlS. O 195 163 .1 240 208.6 285 254.5 62 30.1 106 74.o 151 IIQ. O 196 164 . 1 241 209 .6 286 255.5 63 3i. 1 107 75.o 152 I20.0 197 165 . 1 242 210.7 287 256.5 64 32.1 108 76.0 i53 121 .O 198 166.2 243 211 .7 288 257.5 65 33-1 109 77.o 154 122 .O 199 167 .2 244 212.7 289 258.6 66 34-1 no 78.0 155 I23.0 200 168.2 245 213-7 290 259.6 67 35-1 III 79-0 156 I24.O 201 169. 2 246 214.7 291 260.6 68 36.1- 112 80.0 i57 125 .O 202 170.2 247 215 7 292 261 .6 69 37-1 "3 81 .0 158 I20.O 203 171 . 2 248 216.7 293 262 .7 7o 38.1 114 82 .0 159 127 .O 204 172.2 249 217.7 294 263.7 7i 39.1 115 83.0 160 I28.O 205 173.2 250 218.8 295 264.7 72 40. 1 116 84.0 161 I29.O 206 174.2 251 219.8 296 265.7 73 41. 1 H7 85.0 162 I300 207 175.2 252 220.8 297 266.7 74 42.I 118 86.0 163 131 .O 208 176.2 253 221 .8 298 2678 75 43- 1 119 87.0 164 I32.0 209 177.2 254 222.8 299 268.8 120 88.0 165 I33-0 210 178.3 255 223.8 300 269.8 VOLUME AND WEIGHT OF DISTILLED WATER. Temp. Weight of a Temp Weight of a Temp. Weight of a Degrees Cubic Foot Degrees Cubic Foot Degrees Cubic Foot Fahr. in Pounds. Fahr. in Pounds. Fahr. in Pounds. 32 62.417 90 62.110 160 61 .007 391 62 .425 100 62 .000 170 60 . 801 40 62.423 no 61 .867 180 60.587 50 62 .409 120 61 . 720 190 60.366 60 62.367 130 61.556 200 60. 136 70 62 .302 140 61.388 210 59894 80 62.218 150 61 .204 212 59.707 APPENDIX. PROPERTIES OF SATURATED STEAM. 5 2 7 Pressure Pounds per Square Inch. Temperature Degrees F. Heat of Liquid above 32 . Heat of Vaporization or Total Latent Heat. Heat Contents above Water at 32 F. Volume in Cubic Feet of One Pound. 5 162.3 I30.3 IOOO. II30-3 78.3 IO 193 . 2 161. 3 981 •4 II42 7 38.4 15 213 .0 181. 3 969 1 1150 4 26.3 20 227 9 196.4 959 4 "55 8 20. 1 25 240 . 1 208.7 95i 4 1 160 1 16.3 30 250 •3 219. 1 944 4 1 163 5 13-7 35 259 •3 228. 2 938 2 1 166 4 11. 9 40 267 ■3 236.4 932 6 1 169 10.5 45 274 5 243-7 927 5 1171 2 9-39 50 281 250.4 922 8 "73 2 8-51 55 287 1 256.6 918 4 "75 7-78 60 292 7 262 .4 914 3 1 1 76 7 7.17 65 298 267.8 910 4 1178 2 6.65 70 303 272.9 906 6 "79 5 6.20 75 307 6 277.7 903 1 1 180 8 S-81 80 312 1 282 . 2 899 8 1182 5-47 85 316 3 286.5 896 6 1 183 1 5-i6 90 320 3 290.7 893 5 1 184 2 4.89 95 324 2 294.6 890 5 "85 1 4.64 100 327 9 298.5 887 6 1 186 1 4-43 105 331 4 302.1 884 8 1 186 9 4-23 no 334 8 305 .6 882 1 1187 1 405 ii5 338 1 309.0 879 5 1 188 -5 3-^ 120 34i 3 312.3 876 9 1 189 . 2 3-72 125 344 4 315-5 874 5 1 190 .0 3.58 130 347 4 318.6 872 1 1 190 •7 3-45 135 35o 3 3215 869 8 1191 •3 3-33 140 353 1 3244 867 4 1191 .8 3-22 145 355 8 327-3 865 2 1192 •5 3.12 150 358 5 330-° 863 "93 .0 3.01 155 361 1 332.7 860 9 "93 .6 2.92 160 363 6 335-3 858 8 1 194 . 1 2.83 165 366 1 337-9 856 8 "94 -7 2-75 170 368 5 340.4 854 8 "95 . 2 2.67 175 37o 9 342.8 852 8 "95 .6 2.60 180 373 2 345-2 850 9 1 196 1 2-53 185 375 4 347-5 849 1196 5 2-47 190 377 6 349-8 847 i iiq6 9 2.41 195 379 8 352.1 845 3 "97 4 2.36 200 381 9 354-3 843 5 "97 8 2. 29 205 384 356-4 841 7 1 198 1 2.24 210 386 358.6 840 1198 6 2.18 215 388 360.6 838 3 1198 9 214 220 390 362.7 836 6 "99 3 2.09 225 39i 9 364-7 834 9 "99 6 2.04 230 393 8 366.6 833 3 "99 9 2.00 235 395- 7 368.6 831. 7 1200 3 1 .96 240 397- 5 37o.5 830. 1 1200. 6 1.92 245 399- 3 372.4 828. 5 1200. 9 1.88 250 401 . 1 374-2 826. 9 1201 . 1 1.85 PLATE L PLATE II. LOCOMOTIVE BOILER 160 LBS. PRESSURE SECTION THROUGH FIRE BOX REAR ELEVATION SECTION C-C LOOKING BACK- SECTION A-A LOOKING FRONT. 108! 10 SECTION B-B LOOKING FRONT. INDEX Page 429 Accumulators . 109 Acetic acid , Adamson joints Air for combustion ' 9 dilution , . . 181 friction in pipes loss from excess 9 per pound of coal supply for boiler, measurement of 455 Almy boiler 33 American independently-fired superheaters 45 stoker Anchorage for pipes 377 Angle- valves 3 Anthracite coal Area, reduction of Area of circles 5 378 steam-pipe °' uptake Areas of segments of circles 52 ° Arrangement of induced draft * 91 Artificial fuels 5 ° Ash-pit doors Ash, volume of ton of 74 Assembling and riveting boilers 4 22 Atmosphere, composition of Atomic weight ' ° Attached superheaters 39 Babcock & Wilcox attached superheater 39 boiler 22 boiler setting x 33 marine type 2 ? Back-pressure valve 35 •D I20 Ba g s „o Belleville boiler 25 529 530 INDEX Page Belt-conveyor 389, 394 power required for 397 Bending tests 256 Bituminous coal 49 Blow-off pipe 5, 367 tanks 368 Blowing out brine, loss from 126 Blue heat 260 Boiler accessories 326 Almy 33 assembling and riveting 422 Babcock & Wilcox 22 Belleville 28 calculation of efficiency test of 459 cold water test of 436 Cornish 9 design 468 efficiency test of 45 7 explosion of 319 explosions, energy developed by 323 fire engine 14 general discussion of ^ graphic log sheet of test on 466 horse power 218, 219 Heine 24 horizontal multitubular Plate I, 2, 3, 4 hydraulic test to destruction 317 Lancashire 7 locomotive Plates II, III, 18, 20 Manning 10, 1 1 method of making evaporative test on 437 plain cylindrical 7 Scotch 15 settings for, table of sizes 507 shop arrangement of 409 sizes of Babcock & Wilcox (table) 513 Heine (table) 510 horizontal tubular (table) 504 Stirling (table) 509 vertical (table) 508 specifications and contract for 500 Stirling 25 testing 437 Thornycroft 30 thermal efficiency of 465 two flue : 6 INDEX 53 1 Page Boiler, types of I vertical IO Yarrow 3 2 Boilers, cost of 3° lap seam 3 2 4 life of 320 method of supporting 224 ordinary proportions of 221 strength of 249 Boiler-plate, chemical determinations 256 open hearth 255 test specimen of 256 Boiler-setting 129 Babcock & Wilcox boiler 133 cylindrical tubular boiler 130 Heine boiler 134 Stirling boiler 134 Boiler-tubes, sizes of (table) 524 Boring mill. 415 Brace, diagonal 228 Brackets, calculation of 499 Brass 263 Bridge wall 2 Brine, loss from blowing out 126 Bronze 263 Bucket conveyor, power required by 393 Butt-joint, double-riveted 282 quadruple-riveted 285 triple-riveted 283 Calking 435 Calorimeters 446 Calorimeter tests 447 Carbon, heat of combustion of 60 monoxide, heat of combustion of 60 Carbonic oxide, heat of combustion of 60 Carbonate of lime in feed water 106 soda in feed water 107 Cast iron 261 Channel-bar, layout of 494 staying 225 Charcoal 50 Check valves 330 Chemical determination of steel 256 Chemistry of combustion 76 Chimney, area 205 532 INDEX Page Chimney, capacity 197 draught 196 calculations of 200 needed 201 temperature 198 Chimneys 191 cost of 196 forms of 205 radial brick 211 stability of 206 Kent's and Christie's (tables) 194, 195 Circles, areas of 522 Cleaning fires 168 C0 2 recorders 96 Sarco 99 Uehling 96 Coal bin — parabolic 401 Coal, composition and heat of combustion of 51-58 conveying apparatus 383 cost of handling 393 crushing 400 handling 383 handling and storing : . . . 401 purchase of on specifications 70 sampling 68 specification, sample of 72 tests, U. S. Geological survey 52-55 valves 401 volume of ton of 74 weighing hoppers 405 Coke 49 Cold water test 436 Combination 342 Combustion, air required for ' 79 chemistry of 76 loss from incomplete 91 rate of 219 volume of air required for 82 Complex stays 240 Composition 263 Composition and heat of combustion of coals 51 foreign coals (Mahler) 58 coals (Williams) 57 coals (tables) 52-58 Compression 254 Conveyors, belt type 389, 394 INDEX 533 Page Conveyors, belt type, capacity and speed of 396 capacity of flight 384 Darley type 399 Dodge type 388 flight 383 horse power of flight 384 Hunt type 387 McCaslin type 387 Peck type 388 pivoted bucket 385 power to drive belt 397 bucket 393 size of belts 396 Copper 262 Cornish boiler 9 Corrosion 122 and incrustation 103 prevention of 126 Corrugated furnace 297 Cost of boilers 36 of chimneys 196 Crane lifts 413 Crow-foot staying 227 Crude oil, heat of combustion of 59 properties of 59 Crushers for coal 400 Crushing 274 Crushing strength 274 Cylinder, end tension of 267 rim tension of 266 thin hollow 266 Cylindrical tubular boiler Plate I, 2 setting 130 staying of 223 Damper regulator 348 Darley conveyors 399 Decomposition of steam 95 Design of a boiler 468 Determination of air per pound of coal 84 Diagonal braces 228 stays 265 Dished heads 241 Doors of water-legged boilers 237 Double-riveted butt joint 282 lap joint 277 534 INDEX Page Double-riveted lap joint with inside cover plate 278 Down-draught furnace 160 Draught by fans 1 76 Draught fans, induced or forced 176 gauge 453 Howden's system 168 induced and forced 165 required 201 split 10 wheel 9 Dry pipe 242 Dudgeon expander 433 Dutch-oven furnace 138 Dynamic head 179 Economizers 169 calculation of 174 sizes of Green's (table) 515 sizes of Sturtevant's (table) 516 Efficiency of riveted joints 271 Efficiency test of boiler 459 calculation of 459 Elastic limit 253 Elasticity, modulus of 253 Elements, atomic weights of 75 End tension of cylinder 267 Elongation, ultimate 254 Explosions of boilers 319 Equalizer 247 Equivalent evaporation 216 Evaporative test, sample of 457 Excess air, loss from 92 Factor of safety • 314 Fans, calculation of induced draught 187 for induced draught and for forced draught 176 Farnley furnace 298 Feed containing oil 115 pipe 5, 359 pump 360 power type 363 stage centrifugal 363 Feed-water, analyses of (table) 104 carbonate of lime in 106 mineral impurities in 105 organic impurities in 119 index 535 Page Feed-water, sulphate of lime in 106 temperature of 443 use of soda ash in 107 use of tannic acid in 109 Feed-water heaters 358 lime extracting no Filter for oil 357 removing oil from feed 115 Fire cracks 168 Fire-engine boiler 14 Fire tubes 310 Fires, cleaning 168 Firing, methods of 143 Fittings, bursting pressure of 376 Flange punch 413 Flanging 411 Flat plates, strength of stayed 312 Flight conveyors 383 capacity of 384 horse power of 384 Flow of steam 451 in pipes 379 Napier's formula 332 Rankine's formula 332 Flue, area 205 Flue gas analysis 85 calculation of 88 Flue gases, sampling of 452 Flues 291 rules for working pressure on 304 strengthened 294 tests of furnace 295 Forced draught fans 176 Forms of test piece 250 Foster superheater 44 Foundations 129 Fox's corrugated furnace 297 Friction of air in pipes 181 Fuel oil, heat of combustion of 59 properties of 59 Furnace, Adamson type 309 Brown type 308 Farnley type 298 Fox type 307 flues, tests on 295 Leed's bulb type 306 536 INDEX Page Furnace, Morison type 302 Purve's type 307 short sections 308 strength 306 temperature hypothetical 94 Furnaces 135 down-draught 160 Dutch oven 138 Hawley down-draught 161 Fusible plugs 346 Gas analysis, calculation from a 88 by Orsat apparatus 85 Gases 50 Gate valve 329 Grate area 470 General discussion of boilers 33 Girders 310 Globe valves 326 Grate bars 140 Grates, rocking 142 Graphic log sheet 466 Green traveling link grate 155 Grooving 123 Gun iron 261 Gusset-stays ' 8, 241, 266 Hand holes _. 244 Hand riveting 431 Hawley down-draught furnace 161 Heat balance 463 Heat of combustion 59 calculation of 77 determination of 60 Dulong's formula 78 Mahler's formula 79 of coals 5 1-58 crude oil 59 fuel oil 59 petroleum 59 Heat of the liquid 526 Heat of reaction 95 Heater for extracting lime from feed water 110 Heating surface 220 relative value of 221 Heine attached superheater 40 INDEX 537 Page Heine boiler 24 boiler setting 134 Holmes's furnace 299 Homogeneity tests 257 Horizontal multitubular boiler Plate I, 2, 3, 4 Horse-power boiler rating 218 Howden's system of draught 168 Hunt conveyor 387 Huston brace 230 Hydrogen, heat of combustion of 60 Incomplete combustion, loss from 91 Independently fired superheater 44 Induced draught fans 176 arrangement of 190 calculation of 187 Induced draught fan and economizer 191 Induced draught and forced draught 165 Injectors 361 Jacobs-Shupert fire-box 237 Jones underfed stoker 155 Kent's chimney sizes 194 Kerosene and petroleum oils in feed water 122 Laminations 259 Lancashire boiler 7 Lap 274, 482 Lap-joint double-riveted 277 inside cover plate 280 single-riveted 275 inside cover plate 278 Lap seam boilers 324 Leeds bulb furnace 306 Lever safety valve 333 Life of boilers 3 20 Lifting dogs 412 Lignite 49 Lime-extracting feed-water heater no Locomotive boilers Plates II, III, 18, 20 staying of 232 Locomotive door frames 237 pop safety valve 340 Logarithms, table of 518 Log sheet of boiler test 466 Longitudinal joint 476 538 INDEX Page Malleable iron 262 Manholes 243 Manning boiler 10, 1 1 Marine boilers, staying of 238 water tube 27 type, Babcock and Wilcox 27 water-tube boilers, settings of 135 Marsh gas, heat of combustion of 60 Material, methods of testing 251 Mechanical stokers 144-158 columns for building with 155 Methods of supporting boilers 244 testing material 251 Mineral impurities in feed water , 105 Mineral oil 50 Modulus of elasticity 253 Morison's furnace 302 Murphy stoker 147 Napier's formula 332 Oil burners * . . 10 filters 357 filter for feed 115 fuel 161 scale 115 Olefiant gas, heat of combustion of 60 Open-hearth boiler plates 255 Organic impurities in feed water 199 Orsat's gas apparatus 85 Pancake 118 Parabola, area of 405 Parabolic coal pocket 401 Peat 49 Petroleums, composition and heat of combustion of 59 Pipe, blow-off 367 covering 380 joints, Van Stone 377 methods of anchoring 377 supporting 377 Pipes, vibration of steam 376 Pipe fittings, bursting strength of 376 for superheated steam 47 Piping 369 INDEX 539 Page Piping, elasticity of 373 expansion of ' 369 methods for allowing for expansion of 369 Pitch 275 Pitot tube 181 Pitting 123 Pivoted bucket carriers 385 Plain flues, rules for 304 Plate planers 4 J 8 rolls 418 Plates, drilled or punched 273 tearing of 273 Power pumps 363 Pressure of steam 444 Priming 445 Proportion of rivets 269 Prosser expander 432 Pump for riveting 428 Punch 418 Punch and holder 414 Purchase of coal on specifications 70 Purve's furnace 300 Pyrometers 454 Quadruple-riveted butt joints 285 Quality of steam 214 Radial brick chimneys 211 Rankine's formula 332 Rate of combustion 219 Reducing valve 347 Reduction of area 254 Resistance in flue passages 204 Return steam trap 353 Rim tension in cylinder 266 Ringelmann smoke chart 158 Ring seam 481 Rivet, diameter of 275 Rivet-heads, forms of 270 Riveted joints 271 designing of 287 efficiency of 271 friction of 274 method of failure of 272 practical considerations 291 Riveting machine, portable 427 54° INDEX Page Riveting machine, pump for 428 Riveting machines 425 Rivets 261 pitch of 275 proportion of 269 shearing and crushing 274 Rocking grates 142 Rolls for plate -. 418 Roney stoker 145 Safety plugs 346 Safety valves 331 lever type 333 calculation of 336 locomotive pop 340 pop type 337 discharge of 332 Sampling coal 68 Sarco CO2 recorder 99 Saturated steam, properties of (table) ' 527 Scale from lime salts 106 sea water 113 Scarfing 418 Scotch boilers 15 Sea water, composition of : 112 used in boilers 113 Segmentof a circle, area of (table) 520 Semi-anthracite coal 48 Semi-bituminous coal 48 Separators 355 Setting for Babcock and Wilcox boiler 133 Heine boiler 134 horizontal multitubular boiler 130 marine water-tube boiler 135 Stirling boiler 134 Shearing 254, 274 plates . 417 strength 274 Shears for plate 417 Shop practice 408 Single-riveted lap joint 275 inside cover plate 278 Smoke chart, Ringelmann 158 Smoke law for Metropolitan Boston 159 Smoke prevention 157 Snap riveting 431 Soda-ash for feed water 108 INDEX 541 Page Soils, bearing pressure of 130 Specific heat of substances (table) 75 superheated steam 38 Specifications and contract for boiler 500 for purchase of coal 70 steel 255 Sphere, thin hollow 268 Spherical ends 241 Split draught 10 Static head 1 79 Stay bolts 263 rods 493, 264 calculation of 497 Staying 491 channel bar 225 crow-feet 227 cylindrical tubular boiler 223 laying out of 491 locomotive boilers 232 marine boilers 238 under tubes of back head 231 vertical boilers 232 with manhole in head 231 Stays, diagonal 265 gusset ' 266 Steam 253 decomposition of 95 domes 242 fittings for superheated 47 flow in pipes 379 flow of 451 gauges 344 meters 380 nozzles 243 pressure of 444 quality of •. . . 214 space 215, 471 superheated 37 Steam pipe, area of 378 sizes of, table 525 Steam pipes, vibration of : 376 Steam separators 355 Steam traps 350 bucket type 351 expansion type 353 diaphragm type 352 542 INDEX Page Steam traps, float type 350 return type 355 Steel specifications 254 Still's curves for fans 180 Stirling, attached superheater 45 boiler 24 setting 138 Stokers, mechanical 144-159 Strength of boilers 243 ultimate 253 Stress 253 Submerged tube sheet 13, 14 Sulphate of lime in feed water 106 Sulphur, heat of combustion of 60 Superheated steam 37 pipe fittings for 47 specific heat of 38 Superheaters, attached 39~44 Babcock and Wilcox 39 Heine 40 independently fired 44 _ 47 Stirling 40 Supports for boilers with stokers 155 Tannic acid for feed water 109 Taylor-Pitot tube 180 Taylor stoker 149 Temperature of furnace, hypothetical 94 gases in chimney 198 Test piece, forms of 250 Testing machines 249 Tests for bending 256 homogeneity 257 Thermal efficiency of a boiler 465 Thickness of shell 476 Thin hollow cylinder 266 sphere 268 Thornycrof t boiler 30 Throttling calorimeter 446 Trigonometric functions 522 Triple-riveted butt-joints 283 Tube cleaners 380 expanders 432 holes, drill for 414 punch for 414 sheet, layout of. 484 INDEX 543 Page Tube sheet, submerged 13, 14 Tubes, sizes of (table) 524 Turbine driven stage centrifugal feed pump 363 Two-flue boiler 6 Types of boilers 1 Uehling C0 2 recorder 96 Ultimate elongation 254 strength 253 Uptake, area of 487 U. S. Geological Survey coal tests 52-55 U. S. Inspectors, rules for flues 304 Value of coal 214 Valves, angle 328 back-pressure 350 check 330 coal 401 gate 329 globe 326 reducing 347 safety 331 Van Stone joints 377 Vertical boiler 10, 11, 12 Velocity head 179 Vertical boilers, staying of 232 Vibration in steam pipes 376 Volume of air required for combustion 82 ton of ash 74 ton of coal 74 Washout plugs 244 Water column 342 Water leg 18 Water, volume of 526 weight of 526 Water-tube boilers 20-28 marine boilers 27 Weighing hoppers 405 Wheel draught 9 Wood 50 Wrought iron 260 Wrought-iron bars, weight of (table) 523 Yarrow boiler 32 Yield point 253, 255 OCT 4 1912