Abstract: A flow control valve has a slidable valve member and a variable orifice structure. The valve member slides in response to a pressure differential, created by fluid flow through the variable orifice, to bypass fluid in a positive displacement pump. The variable orifice is a self-contained unit including a longitudinally movable pin having a variable cross section disposed in an aperture. The pin position in the aperture controls the size of the orifice and thereore imposes a flow restriction which creates the pressure differential. The flow control valve is useful with power steering hydraulic pumps and systems where it is desirable to reduce the amount of hydraulic fluid which is delivered to the steering mechanism when the pump input speed exceeds a predetermined value.