MODERN STEAM PRACTICE.

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valve, subjected as it is to the full head of water in the stand ordelivery pipe. This valve can also be used to test if the dischargevalve closes properly, the engine being stopped for that purpose;the plug tap above the suction valve and the one on the air pipe areopened, and a communication through the small pipe already men-tioned is effected between the pump and the suction pipe. If thedischarge valve passes water the loaded valve at once lifts, beingacted on by the full hydrostatic head in the delivery pipe. Thisvalve is therefore of great use in testing the efficient working of

the pump.

The pump valves are gen-erally of the double or treblebeat kind. They are intro-duced to obviate the objec-tions inherent in the flapand conical type of valve,due to the great lift neces-sary in the former to passthe water, and also on ac-count of the full head ofwater in the stand pipe,which, acting on a largearea, causes the valve to shutwith great violence, tendingto shatter the machineryand foundations. This evilis greatly obviated in thedouble-beat valve, as it isadapted to pass a large bodyof water with a moderatelift, which is the principalobject to be attained in allvalves subjected to hydro-static pressure. The valveFig. 94.—Doubie-beat Valve . consists of a metallic cylin-

A, Valve seat. B, Valve . c c, Wooden beats. der, COntraCted at the top,

D } Guide piece. e, Flange and bolts. 1 • 1

having a central ring witharms radiating from it, and passing down the side of the cylinder tostrengthen it; there is an inside projection at the top of the valve,which is truly faced in the turning lathe, as is also the bottom edge

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