Electrically controlled pressure relief valve including a hydraulic bias

A pressure relief valve comprising a pressure inlet, a relief line adapted to communicate with a reservoir, a valve seat interposed between said inlet and said relief line, a closing element for controlling the communication between said pressure inlet and said relief line through said valve seat, said closing element having an area to which the system pressure is applied in a direction to open said closing element, spring means biasing said closing element into engagement with said valve seat, the bias force of said spring means being controlled by a proportional magnet having an armature which acts on said spring means through an actuating element, said spring means being contained within a spring retaining chamber adapted to be connected to the reservoir, characterized by means provided for applying system pressure to the inner space of said proportional magnet, said actuating element defines a piston having one face engaged with said spring means in said spring retaining chamber and means for applying system pressure to the piston face opposite said spring retaining chamber and a seal between said spring retaining chamber and said piston for sealing the piston face opposite said spring retaining chamber from said spring retaining chamber.