Abstract: A scavenging system for a hydraulic circuit includes a sump passage connecting the sump to a reservoir, a solenoid-operated switching valve, a logic control circuit controlling operation of the switching valve and a passage connecting the reservoir to the inlet of a hydraulic pump that supplies the hydraulic circuit. A vacuum source, such as the intake manifold of an internal combustion engine or a vacuum pump, is connected through a ball check valve and vacuum regulator to a space in the reservoir above the fluid. Fluid level sensing switches sense the level of fliud within the reservoir and produce electronic signals used by the logic circuit to control the solenoid-operated switching valve. An oil filter cap allows the reservoir to be filled while maintaining vacuum within the reservoir. A heat exchanger located within the reservoir draws excess heat from the fluid by passing engine coolant through the exchanger.