A B737-700 HAD THE CREW OXYGEN BOTTLE REPLACED AND TESTED IN ACCORDANCE WITH MAINT MANUAL. TWO DAYS LATER CREW RPTED CREW OXYGEN BOTTLE PRESSURE DROP. FOUND BOTTLE NOT FULLY OPEN.

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ON JAN XA; I CHANGED THE CREW OXYGEN BOTTLE DUE TO LOW PRESSURE. ON JAN XC; THE FLT CREW REPORTED A DROP IN BOTTLE PRESSURE WHILE PERFORMING THE SYSTEM TEST. CONTRACT MAINT REPORTED FINDING THE BOTTLE NOT FULLY OPEN. IT IS POSSIBLE THAT I WAS DISTRACTED WHILE SERVICING THE BOTTLE AND DID NOT OPEN THE BOTTLE FULLY. I WAS IN A NEW BID LOCATION AND DID NOT HAVE A NEW ROUTINE ESTABLISHED. HOWEVER; I DID COMPLY WITH A SYSTEM TEST AFTER INSTALLING THE BOTTLE WITH NO PROBS INDICATED. THIS ACFT FLEW IN THE MORNING WITH NO PROBS REPORTED BY THE CREW. I BELIEVE THE CREW WOULD HAVE TESTED THE OXYGEN SYSTEM. THIS ACFT FLEW ON THE SECOND MORNING WITH NO PROBS REPORTED BY THE CREW. I BELIEVE THIS CREW WOULD HAVE ALSO TESTED THE OXYGEN SYSTEM. LATER IN THE SECOND DAY THE CREW REPORTED A DROP IN BOTTLE PRESSURE. I BELIEVE THERE ARE MORE QUESTIONS TO BE ASKED. AFTER THE BOTTLE WAS 'FULLY OPENED' BY CONTRACT MAINT WHAT WAS THE BOTTLE PRESSURE? DID THE PRESSURE RETURN TO A PREVIOUSLY NOTED PRESSURE? DID THE PRESSURE STAY THE SAME? DOES CONTRACT MAINT KNOW THAT A PROPERLY OPENED OXYGEN BOTTLE IS NOT FULLY OPEN? HOW MUCH WAS THE VALVE TURNED TO ACHIEVE FULLY OPENED? I BELIEVE THIS ACFT COULD HAVE EASILY HAD EITHER AN INDICATION PROB OR AN ACTUAL LOW PRESSURE. IT HAS BEEN BROUGHT TO MY ATTENTION THE COMPOSITE OXYGEN BOTTLES HAVE BEEN KNOWN TO HAVE VALVES THAT CAN BE DIFFICULT TO OPEN FULLY. WITH THIS INFO PREVIOUSLY KNOWN; HAS ANYTHING BEEN DONE TO CORRECT THOSE VALVES?CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FOLLOWING: THE COMPOSITE CREW OXYGEN BOTTLE WAS REPLACED AND TESTED PER THE MAINT MANUAL. THE BOTTLE VALVE IS DIFFICULT TO TURN TO THE OPEN POSITION AND WAS TURNED TO WHERE THE VALVE COULD NO LONGER BE TURNED ANYMORE TO THE OPEN POSITION. THE AIRPLANE WAS FLOWN FOR TWO DAYS WITH SEVERAL CREW CHANGES AND LATER IN THE SECOND DAY IT HAD A PRESSURE DROP REPORTED. A CONTRACT TECH RPTED THE VALVE WAS NOT FULLY OPEN AND CLRED THE RPT BY TURNING VALVE TO THE FULL OPEN POSITION OR WHERE THE VALVE STOPPED TURNING. A MEETING WAS HELD WHERE PREVIOUS IDENTICAL RPTS OF THE SAME PROB WERE REVEALED TO THE RPTR. IN EVERY CASE THE BOTTLE AND VALVE ASSEMBLY TESTED OK AND THE AIRPLANE WAS DISPATCHED. WITHIN A FEW FLTS THE CREW OXYGEN PRESSURE DROP WAS RPTED AND THE VALVE WAS FOUND NOT FULLY OPENED. RPTR STATED THAT MANAGEMENT BELIEVES THAT TECHNICIANS ARE AT FAULT.