The medium flow control device has a pump-connected (11) outlet (17) with a built-in flow control valve (26). A flow control circuit working with this outlet dictates the medium flow, using an outlet valve (37) responding to the pressure gradient across the flow control valve. A piston (28) in a bore (27) defines the opening surfaces of the outlet and is loaded by a spring (30) to position the piston against an opposing force varying with oil flow from the pump. The spring comprises first and second springs in series (38,39), and the stiffness of the second spring should exceed that of the first. An adjuster stop (40) within the valve links the two springs and in so doing limits the compression of the first spring. The Piston, bore and stop work together to form a first spring chamber and the piston and stop form a second spring chamber.
