Pressure operated safety valve

Claim 1

A VALVE INCLUDING: A HOUSING HAVING A FLOW PASSAGE OPEN AT ITS UPPER END AND A LATERAL PORT COMMUNICATING SAID PASSAGE WITH THE EXTERIOR OF THE HOUSING BELOW ITS UPPER END; VALVE MEANS IN SAID HOUSING FOR CLOSING SAID PASSAGE TO FLUID FLOW THERETHROUGH FROM SAID PORT, SAID VALVE MEANS IN SAID HOUSING HAVING SEAT MEANS COENGAGEABLE WHEN SAID VALVE MEANS IS IN CLOSED POSITION PROVIDING A METAL TO METAL SEAL BETWEEN SAID VALVE MEANS AND SAID HOUSING; AND MEANS RESPONSIVE TO FLUID PRESSURE EXTERIORLY OF SAID HOUSING FOR MOVING SAID VALVE MEANS TO CLOSED POSITION WHEN THE PRESSURE EXTERIORLY OF THE HOUSING FALLS BELOW A PREDETERMINED VALUE COMPRISING BELLOWS MEANS DISPOSED IN SAID HOUSING AND CONNECTED TO SAID VALVE MEANS FOR MOVING SAID VALVE MEANS, SAID BELLOWS AND SAID HOUSING HAVING A CHARGE CHAMBER FOR HOLDING A CHARGE OF GAS UNDER PRESSURE BIASING SAID BELLOWS MEANS TO MOVE SAID VALVE MEANS TO CLOSED POSITION, SAID BELLOWS MEANS BEING EXPOSED TO FLUID PRESSURE FROM EXTERIOR OF THE HOUSING FOR MOVING SAID BELLOWS MEANS TO MOVE SAID VALVE MEANS TO OPEN POSITION WHEN THE PRESSURE EXTERIORLY OF THE HOUSING RISES TO A FIRST PREDETERMINED VALUE WITH RESPECT TO THE EFFECTIVE PRESSURE OF THE CHARGE IN THE BELLOWS, SAID BELLOWS MEANS MOVING SAID VALVE MEANS TO CLOSED POSITION WHEN THE PRESSURE ACTING ON THE BELLOWS FROM THE EXTERIOR OF THE HOUSING DECLINES BELOW A SECOND PREDETERMINED VALUE WITH RESPECT TO THE CHARGE OF GAS UNDER PRESSURE CONFINED WITHIN THE BELLOWS, SAID VALVE MEANS WHEN IN CLOSED POSITION BEING EXPOSED TO PRESSURE FROM EXTERIORLY OF THE HOUSING ENTERING SAID HOUSING THROUGH SAID LATERAL PORT WHEREBY SAID PRESSURE ACTS ON SAID VALVE MEANS TO MAINTAIN SAID VALVE MEANS IN SAID CLOSED POSITION.