Section 56.—PUMPING AND RAISING WATER.
(See also [p. 124].)
[2332]. Quadruple-acting pump with two pistons, one attached to a rod the other to a sleeve worked by lever A and links B B.
[2333]. Variable delivery single-acting pumps; the eccentrics can be shifted round the shaft 180° by a sleeve and pin motion similar to [No. 2467]. When the eccentrics are opposite each other the pump does not deliver any water, but when the eccentrics are side by side the pump delivers the full contents of both rams. There is one suction and one delivery valve.
[2334]. Screw pump for applying heavy pressure to a ram; sometimes used as an adjunct to give the final heavy pressure to an hydraulic press after the pumps have forced the ram as far as their power permits.
[2335]. Duplex-action pump, in which both piston and cylinder move in opposite directions, but the gear may be applied to two pistons in one pump (fixed), as [No. 2332].
[2336]. French pump, with bucket pistons, maintains a direct flow without reversing or check.
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[2337]. Oke’s patent sewage pump, simple and accessible, three valves.
Slide valves or piston valves are occasionally used to distribute the water in pumps, but must have no lap or lead, and be accurately adjusted.
Air vessels are used on the delivery side of a pump to cushion the discharge of water and prevent concussion, water being incompressible. They are also sometimes useful on the suction side, where the lift is considerable. A piston and spring may be employed instead of an air vessel. See [No. 2121].
Pumps required to run constantly, but deliver water intermittently only, are worked (a) by an air valve on the suction side which, when open, stops the water suction; (b) by a pass valve between suction and delivery which, when open, passes the delivery into the suction again; and (c) by a waste valve on the delivery.