Gas lift check valve

Claim 1

IN A GAS LIFT SYSTEM FOR WELLS, A STRING OF TUBING HAVING AN AXIAL BORE THRERTHROUGH; A GAS LIFT VALVE MOUNTED IN THE TUBING IN COMMUNICATION WITH THE BORE; A HOUSING ATTACHED IN THE TUBING IN SPACED RELATIONSHIP ABOVE THE GAS LIFT VALVE; A LATCHING RECESS PROVIDED IN SAID RECESS; A TRIEVABLE LOCKING DEVICE ARRANGED TO LATCH IN SAID RECESS; A CHECK VALVE SUSPENDED BELOW THE LOCKING DEVICE; AND HAVING A TUBULAR EXTENSION THEREBELOW IN REMOVABLE SEALING ENGAGEMEMT WITH THE HOUSING AND IN COMMUNICATION WITH THE TUBING STRING BORE THEREBELOW; AN UPWARDLY OPENING VALVE MEMBER IN AXIAL ALIGNMENT WITH THE BORE, FORMING A PART OF THE CHECK VALVE, NORMALLY SEATING IN THE UPPER END OF THE TUBULAR EXTENSION; A FLOW PASSAGE THROUGH THE HOUSING ABOUT THE VALVE MEMBER AND ABOVE THE TUBULAR EXTENSION ARRANGED TO COMMUNICATE WITH THE TUBULAR EXTENSION AND THE TUBING STRING THEREABOVE WHEN THE CHECK VALVE IS OPEN THE SAID VALVE MEMBER NORMALLY CLOSING THE FLOW PASSAGE TO THE FLOW OF FLUID THERETHROUGH; THE SAID VALVE MEMBER BEING MOVABLE FROM ITS SEAT BY GAS PRESSURE INJECTED INTO THE TUBING THROUGH THE GAS LIFT VALVE SO AS TO ESTABLISH COMMUNICATION THROUGH THE FLOW PASSAGE AND THE TUBULAR EXTENSION BETWEEN THE TUBING STRING BORE ABOVE AND BELOW THE HOUSING; AND ANOTHER FLOW PASSAGE COM-