Importance

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Abstract

A pump has an inlet, an outlet, and a fluid displacement mechanism operable to pump fluid from the inlet to the outlet. A cheek plate in the pump is movable to control a flow of fluid from the outlet back to the inlet and thereby to vary the fluid flow to a hydraulic system supplied by the pump. Acting on different and unequal surface areas of the cheek plate are two fluid pressure forces. One fluid pressure force is provided by fluid pressure in a cheek plate control chamber. The force acts with a spring biasing force to bias the cheek plate into a position blocking the flow of fluid from the outlet back to the inlet. The second fluid pressure force acts on the cheek plate against the spring force and the first fluid pressure force. A first orifice communicates the pump outlet with the hydraulic system, a second orifice communicates the system with the control chamber, and a third orifice communicates the control chamber with the pump inlet. The second and third orifices are sized relative to each other to provide, at a predetermined rate of flow to the system, a fluid pressure in the control chamber which has a ratio to system pressure generally equal to the ratio of (a) the area of the cheek plate surface on which the second fluid pressure force acts to (b) the area of the cheek plate surface on which the first fluid pressure force acts.

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First Claim