PUMPS 



491 



(2) The Lift and Force Pump (fig. 2). The 

 piston is solid, and the valve E, instead of being 

 earned by the piston, is fitted in the discharge- 

 pipe. During the downward motion of the piston 

 water is forced past the valve E ; it cannot return ; 



Fig. 2. 



Fig. 3. 



and water may thus be forced to considerable 

 heights. Sometimes (fig. 3) the piston is made to 

 fit, not the barrel, but the stuffing-box, B, which 

 can be tightened down on it so as to make the 

 tit good. An air-vessel, or a loaded hydraulic press 

 called an 'accumulator,' is fitted on the discharge- 

 pipe so as to minimise shock and intemiittence ; 

 and double pumps are very generally employed, 

 either directly driven by steam-engine pistons or 

 driven by a flywheel. Force-pumps are used for 

 deep wells and mines, hydraulic presses, boiler 

 feeds, creasoting timl>er, hydraulic lifts, steam fire- 

 engines both land and marine, and hydraulic power 

 supply. 



(3) The Pulsometer. Two chambers, A and B, 

 converge above and communicate with a single 

 steam-pipe ; a ball-valve shuts off either A or B, 

 but not both at the same time, from the steam ; 

 A and B each have a discharge outlet and a suction 

 inlet, both these having valves. The whole is 

 tilled with water ; the steam drives water from, 

 say, A into the discharge-pipe : condensation takes 

 place and the ball- valve is pulled over, so as to 

 shut off the steam from A : the steam then acts 

 in B in the same way as it bad done in A, while in 

 the meantime A, where there is a partial vacuum, 

 is being filled with water from the suction-pipe. 

 The two chambers thus act alternately. The 

 whole contrivance can be hung by chains and 

 let down to the required position ; and it is greatly 

 in use in contractors' work. 



(4) The Chain-pump. This pump is formed of 

 plates called lifts or buckets, fastened, now gener- 

 ally by their centres, to an endless chain and 

 moving upwards, in a case or 'barrel' which is in 

 places constricted so as just to let the buckets 

 pass. Chain pump are noisy and somewhat apt 

 to break down ; hut they can lift very gritty or 

 muddy material. Dredging-machines (q.v.) with 

 their buckets are a variety of this device. 



(5) Spiral Pumps. An Archimedes' Screw (q.v.) 

 is rotated round its axis so as to make water slip 

 np the inclined plane of the screw. They are very 

 economical in power, and they work so regularly 

 that they act as meters. 



(6) Centrifugal Pumps (figs. 4 and 5). The 

 water enters by the supply-pipes, A, A, which lead 



to the central orifices of the fan, B, B ; it then 

 traverses the passages, C, C, formed by the vanes 

 and the side covering-plates, D, of the fan. The 

 fan is made to rotate from the shaft, E. The water 

 acquires a rotatory motion while passing through 

 the passages of the rotating fan ; it then enters the 

 whirlpool-chamber, F, and is discharged by the pipe, 

 G, at the circumference of F ; and the velocity of 



Fig. 4. 



rotation of the fan determines the height to which 

 the water will rise in the discharge-pipe. This 

 velocity cannot conveniently be made to exceed a 

 certain limit ; hence the utility of centrifugal 

 pumps is practically limited to low lifts ; but as 

 they can be made very large they can deal with 

 enormous quantities of water ; and they are much 

 used for pumping 

 in docks, canals, 

 marsh and polder 

 draining, land- 

 reclaiming, and 

 the like. As 

 they have no 

 valves they are 

 little liable to 

 become choked. 

 In nearly all 

 modern centrifu- 

 gal pumps the 

 whirlpool - cham- 

 ber, F, the pur- 

 pose of which 

 was to reduce the 

 ultimate velocity 



of outflow and 

 correspondingly 

 to increase the 



Fig. 5. 



pressure, is dispensed with ; and the same end is 

 attained without wasting energy through friction 

 in the vortex, F, by shaping the vanes of the fan so 

 as to reduce the velocity. See Cotterill's Applied 

 Mechanics. 



(7) The Jet-pump, now not much used, is practi- 

 cally a Giffard's Injector (q.v.) worked by water 

 from a height instead of by steam. 



(8) The Persian Wheel. An under-shot wheel 

 (mill-wheel in which the water (lows under the 

 wheel) in which little buckets are carried by the 

 rim of the wheel so as to pick up water from the 

 stream and deliver it at the top of the wheel. 



(9) Scoop-wheels or flash wheels: equivalent to 

 breast water-wheels with reversed action ; driven 

 by windmills or by steam, they raise water in 

 their buckets and deliver it a few feet higher up ; 

 in some cases they have curved blades, and the 

 water is delivered at the centre of the wheel. 



See Pumps and Piimpinv Machinery, by Frederick 

 Culver, C.E. (Lond. 188G) ; also see AIR-PUMP. 



