Pressure compensated valve

Claim 1

A PNEUMATICALLY OPERATED VALVE COMPRISING A BODY ASSEMBLY DEFINING AN INLET CHAMBER AND AN OUTLET CHAMBER SEPARATED BY A PARTITION HAVING A VALVING ORIFICE THEREIN, A CONTROL CHAMBER PARTIALLY DEFINED BY SAID BODY ASSEMBLY AND COMPLETED BY A DIAPHRAGM, A VALVING ELEMENT FOR CONTROLLING FLUID FLOW THROUGH SAID ORIFICE, SAID VALVING ELEMENT INCLUDING A CLOSURE MEMBER ADAPTED WHEN IN A CLOSED POSITION TO SEAT ON SAID PARTITION SO THAT A PORTION THEREOF OVERLIES SAID PARTITION AND THE REMAINING PORTION THEREOF OVERLIES SAID ORIFICE, A STEM MOUNTED FOR RECIPROCATION WITHIN SAID ASSEMBLY AND HAVING ONE END SECURED TO SAID VALVING ELEMENT WITHIN SAID OUTLET CHAMBER AND THE OTHER END SECURED FOR AXIAL MOVEMENT WITHIN SAID DIAPHRAGM, AN AXIALLY EXPANDABLE BELLOWS ENCLOSING A PORTION OF THE LENGTH OF SAID STEM, SAID BELLOWS CONSTITUTING SEALING MEANS BETWEEN SAID STEM AND SAID ASSEMBLY AND ADAPTED TO RECEIVE THE PRESSURE IN ONE OF SAID CHAMBERS, A COMPRESSION SPRING SURROUNDING SAID STEM WITHIN SAID BELLOWS URGING SAID VALVING ELEMENT AWAY FROM SAID ORIFICE, AND A PRESSURE COMPENSATING MEANS COMPRISING A SECOND BELLOWS EXPANDABLE AXIALLY OF SAID STEM, SAID SECOND BELLOWS AND SAID DIAPHRAGM BEING CONNECTED FOR MOVEMENT IN UNISON, AND MEANS FOR COMMUNICATING THE PRESSURE IN ONE OF SAID CHAMBERS ADJACENT SAID VALVING ORIFICE TO SAID SECOND BELLOWS, IN WHICH THE FORCE GENERATED BY SAID SECOND BELLOWS OFFSETS AT LEAST A SUBSTANTIAL PART OF THE FORCE GENERATED BY THE PRESSURE AGAINST SAID PORTION OF SAID CLOSURE MEMBER AND OF THE PRESSURE OF SAID FIRST BELLOWS.