Retrievable pilot operated gas lift valve

Claim 1

IN COMBINATION, A WELL TUBING STRING SECTION HAVING A PASSAGEWAY THERETHROUGH AND A LONGITUDINALLY EXTENDED TUBULAR RECEIVER OFFSET LATERALLY FROM AND OPEN AT OPPOSITE ENDS INTO SAID PASSAGEWAY AND PROVIDED WITH A GAS LIFT ENTRY PORT IN THE WALL THEREOF AND INTERMEDIATE SAID ENDS, SEALING SURFACES FORMED INTERNALLY OF THE RECEIVER ABOVE AND BELOW SAID INLET PORT AND ADAPTED FOR CO-OPERATION WITH MATING SEALING SURFACES ON A WELL TOOL, AN UPWARDLY FACING TOOL ENGAGEABLE SEAT ON SAID RECEIVER ADJACENT ITS UPPER END, A DOWNWARDLY FACING LATCH ENGAGEABLE SEAT ON SAID RECEIVER ADJACENT ITS LOWER END AND A WELL TOOL FOR LATCHED RECEPTION WITHIN SAID RECEIVER AND INCLUDING A BODY, A DOWNWARDLY FACING LOCATING SHOULDER ON THE BODY ADJACENT ITS UPPER END FOR ENGAGMENT WITH THE UPWARDLY FACING SEAT OF THE RECEIVER, A LATERALLY BIASED LATCH CARRIED BY THE BODY ADJACENT ITS LOWER END AND PROVIDED WITH AN UPWARDLY FACING ABUTMENT TO ENGAGE WITH SAID DOWNWARDLY FACING LATCH ENGAGEABLE SEAT, LONGITUDINALLY SPACED APART SEALING SURFACES PERIPHERALLY CARRIED BY THE BODY FOR BEARING SEALING ENGAGEMENT WITH THE INTERNAL SEALING SURFACES OF SAID RECEIVER, A PAIR OF LONGITUDINALLY SPACED APART ANNULAR VALVE SEATS POSITIONED BY THE BODY INTERNALLY THEREOF WITH THE UPPER VALVE SEAT FACING UPWARDLY AND THE LOWER VALVE SEAT FACING DOWNWARDLY, FLOW OUTLET MEANS IN THE BODY BELOW SAID LOWER VALVE SEAT, MEANS IN THE WALL OF THE BODY COMMUNICATING SAID LIFT GAS ENTRY PORT WITH THE INTERIOR OF THE BODY ABOVE EACH OF SAID VALVE SEATS, A SPOOLSHAPED MAIN VALVE MEMBER HOUSED BY THE BODY WITH THE UPPER HEAD END OF THE MEMBER SLIDABLY BEARING ON THE BODY WALL BELOW SAID UPPER VALVE SEAT AND WITH THE LOWER HEAD END OF THE MEMBER ARRANGED FOR UPWARD CLOSING ENGAGEMENT WITH THE LOWER AND DOWNWARDLY FACING VALVE SEAT, SPRING MEANS ACTIVE ON SAID MEMBER TO BIAS THE SAME UPWARDLY, SAID MEMBER HAVING A LONGITUDINAL FLOW PASSAGE THERETHROUGH OF LESSER FLOW AREA THAN THE FLOW AREA OF THE UPPER VALVE SEAT AND A NORMALLY DOWNWARDLY BIASED PILOT VALVE HOUSED BY THE BODY TO SEAT ON SAID UPPER SEAT AND BEING RESPONSIVE TO GIVEN LIFT GAS PRESSURE ABOVE SAID UPPER SEAT TO OPEN FOR PRESSURE GAS ACTION ON THE UPPER SIDE OF SAID UPPER HEAD END OF THE SPOOL-SHAPED MEMBER.