Abstract: A hydraulic flow control apparatus is provided which is adapted to provide a constant pressure differential between a pump and an external load. The apparatus includes a housing, and a balance piston slideably mounted therein. The pump pressure acts to bias the piston in a direction toward a pump bypass position, and the piston is urged in the other direction and toward its operating position by the consumer pressure and a spring. Means are also provided whereby the pressure of the pump necessary to move the piston toward its bypass position and against the force of the spring, may be minimized during operation in the idling mode, to thereby minimize power consumption.