B737 Flight Crew OXY
Hi LEM,
The B737NG crew oxy bottle shut off valve is located on the bottle itself (in the E & E bay accessed via the fwd cargo hold by removing the lwr centre bulkhead panel)it is upstream of the pressure transducers so this Boeing FCOM is correct for the B737NG aircraft.We use it as a test after servicing of crew oxy to ensure that the bottle shut off valve is fully open.This test does work for a NG.
The B737 CLASSIC is different (this a/c has options for different configurations depending on who ordered the airframe so do be carefull),the crew shut off valve is located in the flight deck physically and between the pressure regulator and the masks/demand regulators in the system,the pressure transducer is on the bottle side of the S.O.V so this test will not show if the bottle valve is closed as you said.
But the big difference is you have a valve that is accessable in flight on the classic`s.
Sorry i don`t have diagram`s available on a computer to help explain.