The following are general procedures for
servicing a high-pressure oxygen system.
NOTE: Since aircraft oxygen systems vary in
design, always check the applicable MIM or
maintenance requirements card prior to servicing
an aircraft oxygen system.
1. Prior to servicing (recharging) an aircraft
gaseous oxygen system, ensure that the following
conditions exist on the aircraft and the oxygen
The trailer and aircraft should be
The line valve on the oxygen servicing
hose should be closed.
All six trailer manifold control valves
should be closed.
Both pressure regulators and their
associated shutoff valves should be
All six individual cylinder valves should
be opened and the individual cylinder
2. Open the cylinder valve and then the
manifold control valve on the cylinder with the
lowest pressure above the aircraft system pressure.
3. Open the two shutoff valves on each side
of the pressure regulator valve that is to be used.
(The oxygen servicing trailer is equipped with two
pressure regulators so that in the event of the
failure of one, the other maybe used.)
4. Slowly open the pressure regulator valve
(by turning the control knob clockwise) and allow
the pressure to buildup to the trailer cylinder
pressure. The set pressure of the regulator may
be noted on the regulator gauge.
NOTE: A temperature connection charge is
given in the applicable MIM or on the side of the
servicing trailer. This chart is used to determine
the pressure to which the aircraft cylinders should
be filled. This pressure depends on the ambient
temperature, as maybe noted on the thermometer
on the trailer manifold stand.
5. Slowly open the service valve on the
servicing hose, and bleed the hose to ensure that
all loose foreign matter that might be within the
hose is expelled.
6. Close the service valve on the hose, and
attach a high-pressure adapter to the coupling nut
on the servicing valve.
7. Open the access panel to the aircraft
oxygen filler valve. Check the filler valve and the
area around the filler valve for any trace of oil,
grease, or any other foreign material. Clean the
area if necessary. Unscrew the dust cap from the
aircraft filler valve.
8. Connect the service hose high-pressure
adapter to the aircraft filler valve.
9. Slowly open the service valve on the hose.
When there is no longer a flow of gas (lower
manifold gauge is within 15 pounds of the
supply cylinder gauge), close the cylinder valve
and the manifold control valve, and repeat the
process with the cylinder with the next higher
pressure. Work cylinders in increasing order of
their pressure until the aircraft system pressure
has reached the desired reading.
NOTE: Oxygen under high pressure will
increase in temperature during the servicing
procedure. To obtain the desired pressure in the
aircraft system, cylinders should be filled slightly
above 1,800 psi (+50 to +200 psi), depending
upon the ambient temperature.
10. After fully charging the aircraft system,
close the service hose valve, shutoff valves,
pressure regulator, and associated shutoff valves,
manifold control valves, and cylinder control
valve, in that order.
11. Disconnect the servicing hose from the air-
craft filler valve, and relieve the hose pressure by
opening the service valve on the hose.
12. Close the service valve and stow the hose
in the trailer hose basket.
13. Replace the aircraft filler valve dust cap
and the access plate.