1170

THEORY AND PRACTICE OF ENGINEERING.

Book II.

open the valve I, and pass with the air in the pump-barrel into theascending pipe: the piston then descending, the weight of the waterin the upper pipe will close; the upper valve and the vacuum formedin the pump-barrel will be successively filled with water as the pistondescends, which it will the more freely do, as it meets with no obstaclebut the weight of the valve K, which is very small. When the pistonre-ascends, the water supported by it will again pass into the ascendingpipe, and the pumping being continued, will arrive at the height required.

The Suction and Forcing Pump , fig. 1773., consists of a barrel, A 15 C 1),a suction pipe, C D F E, and a branch GKNO made in three pieces ;the first, G K, is cast with the pump-barrel, the second, IKML, formsthe elbow, and the third, LNOM, conducts the water to the reservoir.

At the junction I K is a clack valve, S, opening and shutting alternatelywith the valve K, at the bottom of the pump-barrel; the first, S, retainsthe water in the ascending branch, to prevent it from descending at thetime of suction.

The piston PQVT is solid, and traversed by an iron rod attached bytwo keys; it consists of two equal truncated cones united at their sum-mits ; each cone has a slightly cup-shaped band of leather.

As the piston must not descend lower than TV, because it wouldotherwise close the mouth GII of the ascending branch, there willnecessarily be condensed air in the space X T Z, which cannot be pre-vented, although an essential defect. When the piston is first raised,this air dilates in the pump-barrel and ceases to be in equilibrio withthat in the suction pipe, which forces open the valve 11 to expand also,and allows the water to ascend some feet. The valve S remains closed,and is with difficulty opened, because the air in the ascending branch, bywhich it is pressed, has more elasticity than that on the side of Z. Butwhen the piston descends, the valve R closes ; the air contained in the Tpump-barrel being pressed acquires an elasticity superior to that whichpresses the valve S, which it opens, and the air in the pump-barrel passesinto the ascending branch, as long as they are in equilibrio. On raising the piston the

V-o- ^

Fie. 1772.FORCE-PUMP.

valve S closes; the other, It, opensforced up the ascending branch. Con-tinuing to pump, the water reachesthe barrel, where it mixes with theair that could not be expelled, which Ais forced with part of the water bythe descent of the piston into theascending branch : that below pass-ing without difficulty into the pumpbarrel, whence it accompanies thepiston upwards, and the same actionis repeated

Pumps of this kind may be vari-ously constructed, and different po-sitions given to the suction and'"'ascending pipes, relatively to thepump barrel.

Fig. 1774. shows the suction pipeCDE, separated from the barrel towhich it is united above, in orderthat the piston, which differs in norespect from the preceding, exceptthat the rod is carried by a frame,may force the water from below up-wards, while the other forces it fromabove downwards. It is evident that,when first lowered, it will form avacuum in which the natural airenclosed in the space C B will dilate;that in the ascending branch will thenopen the valve C, and expand in thepump-barrel. On raising the pistonthe valve F will open, and the greaterpart of the air will be driven up the Fig. 1773ascending branch'G ; by continuing

the air in the suction-pipe again dilates, and is

I

rcnoN ANDFORCING PUMP.

Fig. 1774. suction and

PORCINO PUMP.