B737 Undifferentiated or Other Model
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 210; Flight Crew Total 29640; Flight Crew Type 18486
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
Approximately 2 hours into the flight; the FO (First Officer) noticed that our oxygen pressure was below 400 psi. I conferenced Dispatch and [Maintenance] and decided to [advise ATC] and divert to ZZZ. By the time we landed it had dropped to 250 psi. Maintenance there found a leaking valve on the bottle head. The pressure on preflight was above 600 which was well above the temperature corrected limit of 470 for 2 pilots. The FO noted just before takeoff that the pressure was unchanged. I had checked inbound write ups and the current [Maintenance Release] but didn't notice in the log history that the oxygen had recently been serviced or I would have queried Maintenance in ZZZ1 prior to departure.
We received our paperwork about 30-40 minutes prior to push and had to hurry up and download everything. Captain called several times for the flight plan. We got to the aircraft. I did the safety checks and noticed the oxygen pressure was 600 psi. I said something to the Captain. We both looked up the minimum for the temperature outside and came up with 470 so we said we are good to go. We pressed and were rushed a little because we got to the aircraft a little late; due to traffic and security and received our flight plan very late.Just prior to takeoff we checked the oxygen and it was still at 600 psi. About 2 hours into the flight the Captain went back for a bathroom break and I looked up and noticed the pressure was down to 300 psi. I said something to the Captain at that point [and] we tried making contact with Dispatch and [Maintenance]. After what seemed like a very long time; we sent another message to Dispatch. Still no call from Dispatch; [but] finally the Captain was able to find a frequency and got a patch through to Dispatch. [Maintenance] just told us to write it up when we got to ZZZ. We told him the oxygen will be depleted by time we got there. Maybe we can fly below 10;000 without oxygen but if we have smoke and fumes in the aircraft; we need oxygen. Captain tried explaining there is a problem and we need to divert. [Maintenance] said ok; we will have [Maintenance] standing by for you.
B737 flight crew reported that the oxygen pressure on the crew oxygen bottle decreased rapidly in flight; resulting in a diversion.