A B737-800 PILOT COMMENTS THAT THE CREW OXYGEN SYSTEM APPEARED NORMAL ALTHOUGH THE ACR REPORTED THE BOTTLE VALVE NOT FULLY OPEN DURING PREFLT.

Narrative

I OPENED UP A COMPANY MESSAGE YESTERDAY REGARDING A B737-800 AIRCRAFT. IT WAS FOUND THAT THE FLIGHT DECK O2 VALVE IN THE E/E COMPARTMENT WAS NOT FULLY OPEN. THE COMPANY EMAIL IMPLIES THAT A NUMBER OF FLIGHT CREWS DID PROPERLY CHECK THEIR O2 SYSTEM BY NOTICING A DIP IN THE FLIGHT DECK O2 GAUGE. I CONDUCT ALL FLIGHT DECK O2 CHECKS IN THE SAME MANNER ON EVERY AIRCRAFT I AM FLYING (PER OUR FLIGHT HANDBOOK PROCEDURES). I DID NOT SEE ANY O2 PRESSURE CHANGE ON AIRCRAFT ON THE DAY IN QUESTION.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT THE VALVE HANDLE OF THE O2 BOTTLE INVOLVED WAS ONLY OPEN 3 TURNS INSTEAD OF THE FULL 6 TURNS PRESCRIBED IN THE MAINTENANCE MANUAL. THIS VALVE POSITION STILL ALLOWED FULL O2 FLOW BUT DID NOT MEET THE PREFLT REQUIREMENTS. THE VALVE POSITION IS A MAINTENANCE FUNCTION BECAUSE THE BOTTLE AND VALVE ARE LOCATED IN THE E AND E COMPARTMENT; INACCESSIBLE TO THE FLT CREW. HOWEVER; THE REPORTER'S ACR EXPECTS THE FLT CREW TO OBSERVE THE O2 BOTTLE PRESSURE FOR A PRESSURE DROP DURING O2 MASK CHECKING. HOWEVER; UNLESS THE BOTTLE VALVE IS NEARLY CLOSED; THE REPORTER STATED THAT THERE IS NEVER A DROP IN PRESSURE DURING THE CHECK; THEREFORE THE FLT CREW HAS ABSOLUTELY NO WAY OF KNOWING IF THE VALVE IS FULLY OR PARTIALLY OPEN.