Abstract: Control apparatus 24 for use with a pressure-flow compensated variable displacement pump assembly 10 for saving energy by limiting the power output of the pump 12 to the load requirements, or to the pump drive capacity, comprising a pressure regulated variable orifice means 52 through which the pumped fluid to load flows, the orifice means being responsive to changes in pressure of the pumped fluid from the pump assembly to vary inversely the effective area of the orifice means, the flow compensator 28 of the pump assembly functioning to hold the pressure drop across the orifice means constant so that the flow across the orifice means also varies inversely with the pressure to limit to a preselected value the horsepower supplied by the pump assembly to load.

Abstract: An apparatus for causing a low force input movement from a control rod to cause a corresponding movement in an output member by force amplification through hydraulic pressure. A piston is provided that has a greater pressure area on one side than on its other side. Orifice means are provided between a pressure chamber and a control chamber and between the control chamber and the reservoir such that as said second orifice means is varied, the piston will move until a null position is reached.