TJ UC-NRLF SB 33 OF THE so REESE LIBRARY OF, THE UNIVERSITY OF CALIFORNIA. Received^ Accessions No. _ 168 60,000 500 79 41 420 750 37 159 60,000 323 80 41 50,000 100 38 154 48,000 600 81 41 12,000 290 39 154 37,600 410 82 41 6,000 480 40 140 24,000 720 83 41 41 135 7.200 600 84 35 18,000 100 42 125 36,000 390 85 35 6,6tO 465 43 125 86 34 12,000 480 44 115 54,000 1,220 87 30 30,000 151 45 115 15,000 600 UNIVERSITY OF CALIFORNIA. A DESCRIPTION DIFFEKENTIAL EXPANSIVE PUMPING ENGINE. THE COMPOUND DIFFERENTIAL PUMPING ENGINE. THE Differential Engine exists in two distinct types, viz. : the single cylinder, and the compound engine; the latter admitting of being worked with high degrees of expansion, is capable of realizing the greatest economy of fuel. The chief peculiarity in the invention, is the simple manner in which the engine is made perfectly safe in working under all conditions of load, automatically varying its supply of steam in proportion as the load on the engine increases or decreases; the distribution of steam being such, that the pumping is performed without shock. In designing pumping machinery as also in designing steam machinery of all kinds the three great questions which should be relatively considered, are economy of fuel, economy of main- tenance, and economy of construction. Economy in fuel must always be a very important considera- tion; our steam engines consume annually 37,000,000 tons of coal, which at the present moment may perhaps be reckoned at an average of 15s. per ton, representing over 27,000,OOOZ. sterling; an economy of 25 per cent, would therefore effect a saving of nearly 7,000,OOOZ. annually. 6 A DESCRIPTION OF THE With colliery pumping engines it is not unusual to find a con- sumption of from 12 to 14 Ib. of coal per horse-power per hour. A good compound engine will work with less than a quarter of that amount of fuel. The saving to be effected on 400 horse-power of actual work, by the substitution of a compound engine for a non- expansive engine, would be, at the lowest estimate, 36 tons in 24 hours; which taken at 5. a ton at the pit's mouth would amount to the sum of 2700Z. per annum. As a question of first cost only the necessary boiler power must be taken into account, and it very often occurs that the total cost of engine and boilers is in favour of the most costly and most economical engine. The leading principle of economy is expansion, and the engine which will work with the greatest amount of expansion is, cceteris paribus, the most economical. There are, however, certain con- ditions necessary to economical working. The resistance to be overcome in pumping, is almost constant, and the force applied to overcome that resistance by the expansion of steam, varies. The condition of the two forces "is graphically represented in Fig. 1, FIG. 1. where the resistance of the pump is shown by a parallelogram, and the expansive force of steam, by a parabola. It is evident that the mean of the two forces must coincide, but the extremes greatly vary. The steam pressure is too great at the commence- ment of the stroke, and too small at the end. A means then is required whereby work may be stored up, whilst the piston is moving through the beginning of the stroke, and given out DIFFERENTIAL EXPANSIVE PUMPING ENGINE. again whilst it is further moving towards the end of the stroke. That function is performed in the Cornish engine by the inertia and momentum of the pit work beam column, and other inert matter ; and in the rotative engine, by that of the fly-wheel. It is evident that when a high degree of expansion is employed in a single cylinder an enormous strain (above the resistance of the pump) is put on the engine at the commencement of the stroke; and also that the maximum piston speed must be very great. These are two of the most serious difficulties surmounted by the Compound Differential Engine. A range of expansion which would produce a variation of strain of six to one in a Cornish engine, would only give two and a half to one in the Compound Engine ; that is to say, the strains are nearly three times as great in the Cornish engine. The importance of thus reducing the strains on the machinery is obvious. The engine may be made lighter, with greater security against breakages. The foundations become cheaper, whilst the speed of the engine is rendered more uniform. In the Compound Differential Engine, not only are the strains and maximum speeds reduced for a given ratio of expansion, but the effective piston speed is increased, because the engine is double instead of single acting. The following comparison of the two systems Cornish and Compound Differential are taken from actual tests in practice. Initial Pressure. Ratio of Expansion. Average Pressure. Maximum Piston Velocity per Minute. Relative Strains on Engine. Effective Piston Speed. Cornish Ditto Ib. 31 45 3 4* Ib. 16 19 feet. 600 500 1-8 2-26 100 80 Differential Ditto 43 80 ? 13 24 228 220 1-4 1-37 168 150 8 A DESCRIPTION OF THE Fig. 2 is a velocity diagram from a Compound Differential Engine with 30-inch and 60-inch cylinders, making twelve strokes per minute, and expanding six times, and Fig. 3 that of a Cornish engine expanding twice. FIG. 2. Backward FarwarcL Stroke. \ / \ ! tx \ / 3 8-f \ / iP 3* K Jfoi;" 1 ' J : / i \ JEL 3 \ lit) \ /" / FLston, yx*^^_ \ C 2-9 7 Compound DifferentiaL Engine ,W"& 60' Cylinders FIG. 3. Water Stroke, Steam, Stroke Cornish; Engine 60 Cylinder In the Compound Engine, the initial pressure, ratio of ex- pansion, average pressure and effective piston speed are increased, whilst the strains on the engine and the maximum speed of the piston are reduced. DIFFERENTIAL EXPANSIVE PUMPING ENGINE. 9 In practice, the greatest economy is obtained with from six to eight fold expansion, when the initial pressure is about 100 Ib. per square inch absolute. That such a result might be expected on theoretical considerations is seen from an inspection of Fig. 4. The ordinates of the curve A, represent the work done with 10 A DESCRIPTION OF THE various grades of expansion, from one to fifteen ; whilst the straight lines inclined to the base line, cut off the portion of the work lost by useless resistances ; each division representing 4 Ib. If 2 Ib. be taken as the back pressure, and 2 Ib. the friction of the engine, and the friction be assumed to increase in the same proportion as the capacity of the cylinder, then the front line B, will cut off from the ordinates the portion of the work lost ; the remaining being the useful effect. It is readily seen how small is the increase of useful effect after expanding eight times. Next in importance to economy of fuel in pumping engines or frequently of more importance are safety in working, and immunity from stoppages. The distribution of steam should be effected in such a way, as to cause no shock or slip in the pumps ; and in the event of a sudden loss of load, the engine should be safe ; in short, the engine should be self-governing under extreme variations of resistance. To effect this, the Differential Yalve Gear was designed, which admits steam to the engine in pro- portion to the resistance to be overcome ; and in case of a sudden total loss of load, reverses the steam to catch the piston. The dis- tribution of steam is effected by coupling the motion of the engine with that of a piston having a uniform velocity. The engine is made to cut off steam by its motion, whilst the uniformly moving subsidiary piston is employed in admitting it. As long as the resistance to the engine is sufficient to prevent its motion becoming relatively equal to that of the subsidiary piston, steam is admitted up to the fixed point of cut off ; but should a loss of resistance, or a superior pressure of steam, cause the engine to acquire a speed relatively greater than the speed of the subsidiary piston, then the motion of the steam valve would be reversed earlier, and the supply of steam would be adjusted to the altered conditions. The modus operandi is best illustrated by the following diagrams. The action of the Differential Yalve Gear is illustrated in the diagrams Figs. 12 to 15, Plate 9. These diagrams are not drawn to scale, but are intended to show clearly the action of the gear ; whilst Fig. 11, Plate 10, shows a practical example of its applica- DIFFERENTIAL EXPANSIVE PUMPING ENGINE. 11 tion to a Compound Engine. The main slide valve G, Fig. 12, is actuated by the piston rod through a lever H, working on a fixed centre, which reduces the motion to the required extent and re- verses its direction. The valve spindle is not coupled direct to this lever, but to an intermediate lever L, which is jointed to the first lever H, at one end ; the other end M, is jointed to the piston rod of a small subsidiary steam cylinder J, which has a motion independent of the engine cylinder; its slide valve I, being actuated by a third lever N, coupled at one end to the intermediate lever L, and moving on a fixed centre P, at the other end. The motion of the piston in the subsidiary cylinder J, is controlled by a cataract cylinder K, on the same piston rod, by which the motion of this piston is made uniform throughout the stroke ; and the regulating plug Q, can be adjusted to give any desired time for the stroke. The intermediate lever L, Plate 12, has not any fixed centre of motion, its outer end M, being jointed to the piston rod of the subsidiary cylinder J, the main valve G consequently receives a differential motion compounded of the separate motions given to the two ends of the lever L. If this lever had a fixed centre of motion at the outer end M, the steam would be cut off in the engine cylinder at a constant point in each stroke, on the closing of the slide valve by the motion derived from the engine piston rod ; but inasmuch as the centre of motion at the outer end M, of the lever shifts in the opposite direction with the movement of the subsidiary piston J, "the position of the cut off point is shifted and depends upon the position of the subsidiary piston at the moment when the slide valve closes. At the beginning of the engine stroke, the subsidiary piston is moving in the same direction as the engine piston, as shown by the arrows in Fig. 12 ; and in the instance of a light load as illustrated in Fig. 13, the engine piston having less resistance to encounter, moves off at a higher speed, and sooner overtakes the subsidiary piston, moving at a constant speed under the control of the cataract ; the closing of the main valve G, is consequently accelerated, causing an earlier cut off. But with a 12 A DESCRIPTION OF THE heavy load, as in Fig. 14, the engine piston encountering greater resistance moves off more slowly, and the subsidiary piston has time consequently to advance further in its stroke before it is overtaken, thus retarding the closing of the main valve G, and causing it to cut off later. At the end of the engine stroke Fig. 15, the relative positions become reversed from Fig. 12, in readiness for the commencement of the return stroke. The subsidiary piston J, Fig. 11, Plate 10, being made to move at a uniform velocity by means of the cataract K, the cut off consequently takes place at the same point in each stroke, so long as the engine continues to work at a uniform speed ; but if the speed of the engine becomes changed in consequence of a variation in the load if, for instance, the load be reduced, causing the engine to make its stroke quicker, the subsidiary piston has not time to advance so far in its stroke before the cut off takes place, and the cut off is therefore effected sooner, as in Fig. 13. On the contrary, if the load be increased, causing the engine stroke to be slower, the additional time allows the subsidiary piston to advance further before the cut off takes place, and the cut off is consequently later, as in Fig. 14. From the foregoing description of the Valve Gear, it will be understood that every erratic motion of the engine, alters the relative position of the valves with respect to the main piston, and in that way the engine checks itself. So perfect is the action of this gear, that when properly adjusted, the full load may be thrown suddenly off the engine, without any injury resulting. The effect of a sudden loss of load, is to reverse the action of the valves, and to throw the steam against the motion of the piston, stopping it before the end of the stroke. Many instances of this have occurred in practice when a pump rod has broken, a pump valve has failed, or a pipe has burst. At the Croydon Waterworks the load was suddenly thrown off the engine, when it was running at full speed, by the acci- dental lifting and tilting over of one of the pump valve seatings ; but the engine was instantly checked by the automatic action of DIFFERENTIAL EXPANSIVE PUMPING ENGINE. 13 the gear, and no more shock was caused to the engine than if the accident had not occurred. Such an accident happening with a Cornish engine would have caused a most serious breakdown. At the St. Helens Waterworks the mains burst without causing the slightest damage to the Differential Engine; and several such instances have occurred in practice. LIBRARY UNIVEESITY OF CALIFORNIA. X ../ A DESCRIPTION OF THE THE DIFFERENTIAL VALVE GEAR, AS APPLIED TO BEAM AND BULL ENGINES, &c. The illustration on the opposite page represents a perspective view of the gear. It consists of a lever a, called the main lever, by means of which motion is given to the valves through a rod 6. The motion of the engine is given to the outer end of the lever, through the rod c, by means of a lever of the first order ; the long end of which is attached to the plug-rod or any moving part of the engine, where it gets the motion of the piston on a reduced scale; the other end d, deriving its motion from the subsidiary cylinder e, and being controlled by means of the cataract /. The cylinder has a slide valve which is worked by means of a tappet arm on the rod of the piston of a secondary cylinder ; the motion of the secondary piston is also controlled by a secondary cataract. The slide valve is, however, free to move with the motion of the hand lever tv 1010" FIG. 6. ^ Temperature of Pluses 188' Temperature of Stearw 'SGO* ferligtraJturc of Condenser WC Zero of Fahrenheits Scale < Absolute T^ero When Fahrenheit constructed his scale, which is found on most English thermometers, the absolute zero was unknown. It has since been ascertained, and temperatures reckoned from it are called absolute temperatures, vide Fig. 6. c 2 20 A DESCRIPTION OF THE Let T = highest absolute temperature. t = lowest The maximum theoretical efficiency of any heat engine is T -t TABLE SHOWING A COMPARISON OP THE USEFUL WORK DONE BY EQUAL WEIGHTS OF STEAM WITH DIFFERENT DEGREES OF EXPANSION AND DIFFERENT BACK PRESSURES. NON-CONDENSING ENGINES, STEAM PRESSURE CONDENSING ENGINES, STEAM PRESSURE 60 LB. 60 LB. PER SQUARE INCH. PER SQUARE INCH. ^!*- Back Pressure. Grades of Expansion. Useful Work. Back Pressure. a. 9- u. 6. 9- u. 6. a. 50-7 2 69-4 16 4 134-8 2 35-7 35-7 4 78-8 8 168-8 2 23-1 23-1 8 56-8 u 16 193-6 2 14-1 50-7 2 61-4 20 4 126-8 4 35-7 35-7 4 62-8 > 8 152-8 4 23-1 23-1 8 24-8 > 16 161-6 4 14-1 a average pressure per square inch. u = g (a - 6). NOTE. The gain as shown above for condensing engines between eightfold and sixteenfold expansion is so small that it is more than covered by the loss caused by the extra cooling effect of the larger engine. It is evident that for a sixteenfold expansion the engine must have double the capacity of that for an eightfold expansion. The above reasoning also applies to non-expansion engines, for it is self-evident that the higher the average pressure throughout the stroke the less the proportion lost by back press'jre. An engine working with an average pressure of 10 Ib. per square inch will lose 20 per cent, by back pressure, whereas if the average pressure were 20 Ib., the loss would only be 10 per cent. With practical men it is too common a notion that low- pressure steam is as economical as high pressure for the same ratio of expansion, but, as we have already seen, there is not a greater fallacy. DIFFERENTIAL EXPANSIVE PUMPING ENGINE. 21 HOKSE-POWER. An actual horse-power equals 33,000 Ib. raised 1 foot high per minute, or 33,000 units of work, which I shall denote by the letters H.-P. The term nominal horse-power, written N. H.-P., has a varied signification according to the fancies of different engineers, and is therefore made very confusing. It is a term which might be dispensed with, and the actual H.-P. universally adopted as the standard, to advantage. The Admiralty rule for N. H.-P. is 7 A V D*V N ' H - P ' = gpob or "GOO- V = velocity of piston in feet per minute. A = area of cylinder. D = diameter of cylinder. S = stroke of engine in feet. Ordinary rules D 2 !/~$~ N. H.-P. = v for high-pressure engines. JLo * o D 2 N. H.-P. = - for condensing engines. For ordinary horizontal high-pressure non- condensing engines D z D 2 of commerce, an approximate rule is N. H.-P. = r^, and H.-P. = , which is approximately right for an initial pressure of 50 Ib. and cut off at half stroke, with 300 feet piston speed per minute. PRACTICAL NOTES AND FORMULA FOR PUMPS AND PUMPING ENGINES. To find the quantity of water delivered from a given pump or pipe- Let d the diameter in inches, then : = the quantity delivered per foot, stroke, or flow in 30 gallons, a little under the theoretical quantity. 22 A DESCRIPTION OF THE A good working velocity of flow for water in the pipes is 200 feet per minute, and the speed of pump piston or ram most suitable for the "Differential Expansive" Pumping Engine, is equal to J L x 60, where L = the length of the stroke in feet. d = diameter of pipe in inches for 200 feet flow per minute. p - diameter of plunger in inches double-acting. q = number of gallons delivered per minute. q = d 2 x 6-66 = 200 ~, for a velocity of 200 feet per * oU minute. n = number of gallons delivered per hour. n = d 2 x 400. q = number of gallons of water raised per minute. H = the height to which it is raised in feet. H.-P. effective horse-power of engine without friction. 7i - head of water in feet. p = pressure in Ib. per square inch. / = pressure in Ib. per square foot. p = h x 0-433. h =p X 2-31. /= li x 62-4. 1 cubic foot of water = 6*24 gallons = 62 4 Ib. = 557 cwt. = 028 tons = 6 gallons approximately. 1 gallon = 10 Ib. or 0*16 cubic foot. 1 cwt. of water = 1*8 cubic foot =11-2 gallons. 1 ton of water = 35-9 cubic feet = 224 gallons. Weight of sea water = weight of fresh water x 1 * 028. A cylinder of spring water 1 inch diameter and 1 fathom long = 2-045 Ib. DIFFERENTIAL EXPANSIVE PUMPING ENGINE. 23 DUTY OF PUMPING ENGINES. A cylinder of spring water, 1 inch diameter and 1 fathom long, weighs 2- 045 Ib. L = length of stroke. N = number of strokes in one month. H = height of lift in fathoms. d = diameter of pumps. q = number of bushels of coal consumed in one month. Duty = number of Ib. lifted 1 foot high per bushel of coal. D = The calculation was formerly made for bushels of coal, eaclj. weighing 94 Ib., but it is now usual to use the cwt t in the place of the bushel. The usual mode of expressing the efficiency of a steam engine is in terms of coal burnt per horse-power or units of work per hour, but as the efficiency of the boiler is not in such a cape distinguished from that of the engine, it is important t^at a rulp should be established by which the efficiency of either might be readily ascertained. The efficiency of the boiler may be expressed in Ib. of water evaporated per Ib. of fuel, whilst the efficiency of the engine should be denoted in units of work done per 1 Ib. of steam used. A formula for that purpose may be thus constructed : Let 28 = number of cubic inches of water in 1 Ib. of steam. I sz initial pressure of steam. S = its specific volume. B = ratio of expansion employed. , (1 + Hyp. Log. E) I a = average pressure per square inch = ^ 7? " ~ * U = units of work done by 1 Ib. of steam, (28 x S X .R) then U = a - - - r - - 1 24 A DESCRIPTION OF THE Let I = 100 Ib. per square inch, then : S = 270. See table, page 32. The following table shows, in units of work, the comparative values of different degrees of expansion with a constant initial pressure equal to 100 Ib. per square inch ; worked out by means of the above formula, which for 100 Ib. initial pressure stands thus : U = a (630 X -R). Ratio of Average Pressure Initial Pressure. Expansion = R. Units of Work. (1 + Hyp. Log. R) 1 R Ib. 100 63000- Ib. 100 100 1-25 77017-50 97'8 100 1-66 94958-64 90-8 100 2-00 106596- 84-6 100 3-00 132111- 69-9 100 4-00 150192- 59-6 100 5-00 164115- 52-1 100 8-00 193536- 38-4 100 10-00 207900- 33-0 The formula for the duty of pumping engines * would then (H X (>2 o3 ^ cw . . . . t+ .JS5 "% I! s . rf o ^ O Ed s - 36 A DESCRIPTION OF THE DIFFERENTIAL TUMPING ENGINE. WEIGHT OF WROUGHT IRON. The weight of 1 cubic inch of wrought iron = 0*28 Ib. Number of cubic inches -8000 - = tons ' Number of cubic inches 400~ Number of cubic inches (jrs. 100 Number of cubic inches 3-5 Ibs. WEIGHT OF CAST IRON. The weight of 1 cubic inch of cast iron = 0*26 Ib. Number of cubic inches 8640 = tons. Number of cubic inches "532~ = owts " Number of cubic inches 108 = qrs. Number of cubic inches -,-, 3-85 1 cubic foot of cast iron = 448 Ib. = ith ton = 4 cwt. 1 foot superficial 1 inch thick = '. o Let n = number of cubic inches of cast iron. W = weight in Ib. W = j -f- (4 x the number of hundreds expressed by the first, or left hand figure in product), thus : Let n = 1728 cubic inches, 1798 ~ = 432 and 4 x 4 = 16 .-. W = 432 + 16 = 448 Ib. L I B R A R Y - - UNIVERSITY OF CALIFORNIA. J L I B ft A R Y i; N 1 V 10 K S 1 T V O F CALIFORNIA. J LI BRAKY CALIFORNIA- VERTICAL ENGINE AS APPLIED IN WATERWORKS &C TypeN? 4. Plate 5. VERTICAL DEEP WELL ENGINE AS APPLIED IN WATERWORKS. Type N^ 5. HENRY OAVEY L I B R A It Y UNIVERSITY OK CALIFORNIA. I LIBRA R Y U N I V K U S I T V F CALIFORN 1 A. Plate 7. Type N 7. PUMPING ENGINES. Fig. 16. COMPOUND DIFFERENTIAL ENGINE AND HYDRAULIC ENGINE APPLIED UNDERGROUND. COMPOUND DIFFERENTIAL ENGINE HENRY DAVEY LIBRARY UNIVERSITY OF CALIFORNIA. Plate 8 IMPROVED PLUNGER PUMPS Pumps 'Z(f dwu & JO f* Stroke lift 120 feel. HENRY DAVEY Plate 9. COMPOUND DIFFERENTIAL ENGINES. Diagrams Illustrating Action of Differential! Vdlve^ Gear. FIG. 13. Light Load, Early Cudi-off. FIG. 15. End of Engine Stroke. HENRY DAVEY LIBRARY U N I V E Li S 1 T V ( ) F LIBRARY UNIVERSITY OF CALIFORNIA. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. tt-O LD 21-100m-7,'39(402s)