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 servicing trailer. a. b. c. d. e. The trailer and aircraft should be properly grounded. 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 closed. All six individual cylinder valves should be opened and the individual cylinder pressures noted. 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. 5-21