Abstract: A housing contains a slidable spool operable to port a first pressurized fluid line to a fluid motor, and a housing reservoir has a float movable with a fluid level. The motor drives a pump which "pumps down" the reservoir. A second pressurized fluid line is directed through a primary fixed orifice and against one end of the spool, acting against a spring bias, and is permitted to exit through an end orifice to the reservoir. The float moves in response to the fluid level and operates to shut off the end orifice flow, thereby building up backpressure to shift the spool, and thus varying outlet flow from the valve in accordance with the reservoir level. Therefore, the reservoir is pumped down in accordance with reservoir build-up.

Abstract: An electrohydraulic servo system is compensated by an electrical control system and has a position related feedback loop and a servovalve with a differential pressure transducer connected as a feedback loop between the output and return lines that extend to a hydraulic motor or other driven means from said servovalve.