154

MODERN STEAM PRACTICE.

than 30 feet from the surface of the water in the shaft or pit to bedrained, 28 feet being a convenient height; that is to say, when thewater passes through the valve to the top of a solid bücket. Butwhen a hollow bücket is adopted, with the discharge valve fittedthereto, the distance from the level of the water to the height towhich the bücket ascends in the pump barrel should not exceed28 feet; consequently the suctionvalve in the pipe will be lower down.

In the former of these arrangementsthe water is drawn through the suc-tion valve on the down stroke of thesolid bücket, and in the up strokethe suction valve closes, and thewater is discharged through a valveplaced in the stand pipe above thesuction valve, until the return ordown stroke of the bücket, when thedischarge valve closes simply bythe weight of water upon it; the

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Fig. 91.—Forcing Set. Plunger 18 inches in diameter, arranged with one door for each valve.

A, Suction pipe. b, Suction-valve seating. c, DeKvery-valve seating. d, Plunger, e, Air valve.f, Stand pipe. g, Stuffing-box piece and gland.

suction valve' then opens, and the pump barrel is filled as before;and so on. With the hollow bücket the water is drawn through thesuction valve in like manner, but with this difiference, that the