Piston operated valve

Claim 1

A VALUE FOR CONTROLLABLY INTERRUPTING THE FLOW OF FLUID THERETHROUGH COMPRISING A HOUSING DEFINING A FIRST CHAMBER HAVING AN INLET THERETO AND AN OUTLET THEREFROM, AN ANNULAR VALVE SEAT SURROUNDING SAID OUTLET, A PEDESTAL PORTION OF SAID HOUSING SURROUNDED BY SAID SEAT EXTENDING PERPENDICULARLY TO THE PLANE OF SAID SEAT AND HAVING AT LEAST ONE TRANSVERSE OPENING THERETHROUGH A VALVE ELEMENT MOVABLE IN SAID CHAMBER RELATIVE TO SAID SEAT, SAID VALVE ELEMENT BEING TUBULAR AND SURROUNDING SAID PEDESTAL PORTION OF SAID HOUSING, SAID VALVE ELEMENT BEING SLIDABLE ON SAID PEDESTAL AND SEALABLY CONNECTED THERETO, SAID HOUSING HAVING A BORE THEREIN, A CYLINDRICAL PISTON SLIDABLY AND SEALABLY DISPOSED IN SAID BORE AND DEFINING A SECOND CHAMBER ISOLATED FROM SAID FIRST CHAMBER, MEANS CONNECTING SAID PISTON TO SAID VALVE ELEMENT, SAID CONNECTING MEANS BEING PERFORATED TO EQUALIZE THE PRESSURE ON SAID PEDESTAL WITH THE PRESSURE IN SAID FIRST CHAMBER, SAID PISTON HAVING AN EFFECTIVE CIRCULAR FACIAL AREA DIRECTED TOWARD SAID OUTLET AND EXPOSED TO THE PRESSURE IN SAID FIRST CHAMBER IN ALL POSITIONS OF SAID VALVE ELEMENT, SPRING MEANS ACTING ON SAID VALVE ELEMENT IN A VALVE CLOSING DIRECTION, AND MEANS FOR APPLYING A CONTROL FLUID PRESSURE TO SAID SECON CHAMBER AND TO SAID PISTON TO URGE SAID VALVE ELEMENT IN A VALVE CLOSING DIRECTION.