Safety valve for wells

Claim 1

IN A SUBSURFACE SAFETY VALVE FOR STOPPING FLOW IN A WELL PRODUCTION CONDUIT AND TO BE HELD OPEN BY PRESSURE FLUID SUPPLIED THROUGH PIPING EXTENDED FROM ADJACENT THE WELL HEAD, AN ANNULAR VALVE SEAT TO BE FIXEDLY MOUNTED IN A PRODUCTION CONDUIT, A MOVABLE CLOSURE VALVE THEREFOR, MEANS MOUNTING THE VALVE FOR MOVEMENT IN A PATH BETWEEN AN OPEN POSITION AND A CLOSED POSITION ON SAID ANNULAR VALVE SEAT, A VALVE POSITION CONTROLLING ELEMENT SHIFTABLE INTO AND OUT OF THE PATH OF SAID VALVE AND THEREBY CONTROLLING ITS MOVEMENT, RELATIVELY MOVABLE PISTON AND CYLINDER MEMBERS ONE OF WHICH IS JOINED AND MOVABLE WITH SAID VALVE POSITION CONTROLLING ELEMENT AND THE OTHER OF WHICH IS FIXED RELATIVE TO THE ANNULAR VALVE SEAT, SAID CYLINDER MEMBER HAVING AXIALLY SUCCESSIVE INTERNAL CYLINDRICAL WALL PORTIONS, EACH OF DIFFERENT DIAMETER RELATIVE TO OTHERS AND PROVIDING A PAIR OF SPACED APART PISTON RECEIVING CHAMBERS, ONE OF LARGER DIAMETER THAN THE OTHER, AND AN ANNULAR WALL PORTION SEPARATING SAID CHAMBERS AND BEING OF SMALLER DIAMETER THAN THE CHAMBERS FOR CO-OPERATION WITH THE PISTON MEMBER IN AFFORDING A CHOKED PASSAGE COMMUNICATING THE CHAMBERS, SAID PISTON MEMBER HAVING SPACED APART PISTON HEADS IN SLIDING SEAL FIT WITH THE RESPECTIVE CHAMBERS AND PRESENTING OPPOSING FACES OF RELATIVE DIFFERENTIAL AREAS INTERNALLY OF THE RESPECTIVE CHAMBERS, SPRING MEANS CO-OPERATING WITH SAID MEMBERS AND BIASING THEIR RELATIVE MOVEMENT IN A DIRECTION TO SHIFT THE VALVE POSITION CONTROLLING ELEMENT OUT OF THE PATH OF SAID VALVE AND MEANS FOR INTRODUCING PRESSURE FLUID INTO THE SMALLER OF THE PISTON RECEIVING CHAMBERS FOR COMMUNICATION WITH THE LARGER CHAMBER THROUGH SAID CHOKED PASSAGE AND FOR ACTION ON THE OPPOSING PISTON FACES IN EFFECTING PROJECTION OF THE VALVE POSITION CONTROLLING ELEMENT INTO THE PATH OF THE VALVE IN OPPOSITION TO THE BIAS OF THE SPRING MEANS.