APPLICATIONS OP STEAM-PUMPING.] 



APPLIED MECHANICS: 



879 



The performance of the Cornish engines has received 

 special attention, from the circumstance that a number 

 of mine proprietors placed their engines under the 

 superintendence of engineers, and had monthly reports 

 published as to the quantity of water lifted, the quantity 

 of coals consumed, and other particulars. Six of the 

 most effective engines reported on, presented the follow- 

 ing average results : 



Diameters of cylinder from 60 to 90 inches. 



Mean pressure of steam per square inch, 10 Iba. 



Length of stroke from 8 to 10 feet. 



Average number of strokes per minute, 1. 



Diameter of pumps, 9 to 18 inches. 



Average length of pump-stroke, 7 feet 6 inches. 



Average work, reckoned in Ibs. of water lifted 1 foot 

 high by the consumption of 1 bushel of coals, 40,500,000 

 Ibs., or the work of 1,227 horse-power. 



lu pumping docks, the quantity of water to be lifted 

 in a given time is generally great, but the height incon- 

 siderable, and the pumps may, therefore, be of large 

 diameter. As a practical example, we may take the 

 case e f a rectangular dock, 200 feet long, 40 feet broad, 

 and 2<) feet deep, the water being lifted 2 feet above the 

 highest level to give a fall for its drainage. The total 

 quantity to be lifted is 200 X 40 X 20 = 160,000 cubic 

 feet, or 160,000 X 62J = 10,000,000 Ibs. At the be- 

 ginning tit the work, the water has to be lifted only 2 

 feet ; at end it has to be lifted 22 feet ; and the mean 

 height of lift is, therefore, 11 feet, the work done being 



10000000 Ibs. X 11 

 equivalent to 3300(1 = 3 "^ norse P wer ; 



or, allowing ^th for friction and velocity, about 3660 

 horse-power. If the work be done in 1 hour or 60 



36GO 

 minutes, the power of the engine must be --/,,.- = 61 



horse-power, clear of all losses. As in a case like this, 

 the work at first is very light, and becomes greater as 

 the level of the water is lowered, and the height to be 

 lifted consequently increased, it is advisable to have 

 several pumps, all of which may be kept in action at 

 first, but which may be thrown out of action successively 

 as the load on them becomes increased, the strain of the 

 engine being thereby not greatly varied. 



In water-works for supplying towns, not only has the 

 water to be lifted to such a height that it may command 

 the highest level to which it has to rise, but it has also 

 to be conveyed through great lengths of pipe, often ex- 

 tending many miles. It is convenient to arrange, as 

 near as possible to the pump, a high reservoir, of such 

 altitude as may be sufficient to cause the necessary flow 

 in the great length of pipe connected with it. This is 

 effected by pumping the water through an elevated 

 siphon, open at the top to permit the issue of air that 

 may be mingled with the water. The pump, in making 

 its stroke, has thus to put in motion only the column of 

 water contained in the ascending limb of the siphon, 

 instead of the whole mass contained in the pipes. But 

 iii order still farther to relieve the pump and engine 

 from the strain required to put in sudden movement 

 eveu this mass of water, the pump is provided with a 

 capacious air-vessel a dome-shaped vessel the upper 

 part of which contains air, and the lower part communi- 

 cates with the discharge-pipe of the pump. When the 

 pump discharges its contents, the air in the vessel is 

 compressed by the influx of water below it ; and while 

 the pump is making its return stroke, the elasticity of 

 the compressed air continues the flow of the water that 

 had been forced into the vessel. The air thus acts as a 

 spring, yielding to the force of the discharge from the 

 pump, and sustaining the pressure on the flow-pipe at 

 intervals when the pump is inactive. When the pump 

 is double-acting, or discharges at both the up.stroke and 

 the down-stroke, the intervals of inaction are only those 

 occupied by the turn of the stroke, and the air-vessel has 

 less to do than when the pump is single-acting. Two 

 single acting pumps, of which the one discharges while 

 the other is drawing, produces a like effect. Upon the 



whole, we believe that for simplicity, economy of cost 

 and of working, a good double-acting engine, with 

 double-acting pump, is preferable to two single-acting 

 engines and pumps, each of half the power, or to one 

 single-acting of equivalent power. We know of no ad- 

 vantage possessed by the single-acting engine, which 

 cannot be fully secured in the double-acting engine. It 

 has so happened, that many single-acting engines have 

 been made of large dimensions and long stroke, and that 

 the expansive power of the steam has been employed by 

 cutting it off at an early part of the stroke, to such an 

 extent as to secure great economy of fuel. But in the 

 double-acting engine, particularly when the duplicate 

 cylinder, with high-pressure and low-pressure action, is 

 applied, the same economy of fuel can be secured, and 

 the bulk and weight of the whole are greatly reduced. 



An operation, nearly allied to that of pumping water, 

 is the production of the air-blast required for furnaces. 

 At the iron-works, which constitute so important a part 

 of our industry, a very great amount of power is employed 

 for this purpose. The smelting furnaces, in which the 

 metal is separated from the earthy ingredients of the ore, 

 are supplied with the air required for intense combustion 

 forced into them by pumps, which are worked generally by 

 steam-engines. The volume of air supplied is very great, 

 ranging from 1,500 to 2,000 cubic feet per minute ; but 

 its pressure is inconsiderable, seldom exceeding 3 Ibs. per 

 square inch above atmospheric pressure ; and the pumps 

 are therefore made of large capacity. In many places, 

 the air. on its Way to the furnace, is heated to a high 

 temperature, so as to maintain a more intense combus- 

 tion, and thereby extract a greater quantity of metal 

 from the ore at a rapid rate. But it is found that the 

 metal so produced, called hot-blast iron, though cheaper 

 than cold~blast iron, is of inferior quality for all pur 

 poses where strength and tenacity are required. When 

 the blast is not required at so high a pressure as that 

 which is necessary for smelting furnaces for ordinary 

 foundry furnaces, and for blowing forge fires the 

 current of air is usually produced by a fan. The an- 

 nexed plate represents a construction of fan which has 

 obtained considerable, and we believe well-merited, 

 repute for efficiency and durability. The fixed portion 

 of this fan consists of a framing, which is generally 

 bolted securely down to a block of stone or heavy timber, 

 in order to avoid vibration, and a cylindrical casing, 

 with circular openings on either side, and a mouth at 

 one part of the circumference, which is connected to 

 the pipe or channel for conveying the air-blast to the 

 furnace. The framing is formed with long and carefully 

 made bearings, in which a spindle revolves concentric 

 with the cylindrical casing. On this spindle are fixed a 

 number of recurved arms, fronted by plates bent to fit 

 them, and the whole enclosed within two conical sides, 

 which have lips projecting and fitting into the circular 

 openings in the casing. The spindle and the arm-plates 

 and conical sides being put in rotation at a high velocity 

 1,000, 1,500, or sometimes 2,000 revolutions per 

 minute air enters by the circular openings of the casing, 

 passes between the two cones, and issues at their cir- 

 cumference into the casing, whence it proceeds with con- 

 siderable velocity to the furnace. The force which pro- 

 duces the current of air is the centrifugal tendency of 

 every particle to flv from the axis when it is put in rapid 

 rotary motion, and the recurved blades act not only to 

 carry the particles of air round in a circular direction, 

 but also to drive them outwards from their inclined sur- 

 faces. The side casings of the blades are made conical, 

 so that the area or channel through which the air passes 

 should be nearly uniform throughout its course. 



[On a similar principle, Messrs. Gwynne's centrifugal 

 pump is constructed. The folio plate represents one of 

 these engines, which was at work in the Exhibition at 

 London, in 1862, and which raised a complete torrent of 

 water by the great power it exerted. It is peculiarly 

 suitable for draining purposes, and, generally, for lifting 

 water in great quantities to moderate heights. ED.] 



II. DRIVING MACHINERY. Where the power re- 

 quired is small, or where fuel is cheap and water scarce, 



