The chemical drier should reinspected after every 12 cylinders are used, and the chemical agent should be replaced at the first sign of change in the indicator. The blue-colored indicating agent is applied on top of the white dry-ing agent. When moisture is present, the indicating agent will change color from blue to pink. The indicating agent can be easily inspected by removing the servicing hose and unscrewing the top cap of the drier container.

CAUTION Relieve all pressure prior to inspection/ replacement of the chemical agent.

The drying agent is removed by removing the hose connecting the lower cap and the lower manifold and unscrewing the drier lower cap. All traces of the contaminated agent should be removed and the lower cap replaced, and the lower manifold hose connected. The drying agent should be quickly placed in the drier so that it does not pick up moisture from the air. Care should be given to the replacement of the indicating agent. The top cap should be screwed in place immediately after observing the condition of the indicator so that the moisture or humid air does not cause the indicator to change color. The caps on the drier should be screwed down until they bottom. The caps should be removed and replaced by hand only. It is not necessary to tighten the caps extremely tight. The caps are sealed with O-ring packings, which usually give good service. If leakage occurs, the O-ring should be replaced. Refer to the applicable Operation and Service Instruction Manual (which includes the Illustrated Parts Breakdown) for the part number of the O-ring. NOTE: All maintenance on the oxygen ser-vicing trailer should be performed in accordance with the instructions contained in the applicable Operation and Service Instructions Manual or set of Maintenance Requirements Cards.

Daily/ Preoperational Inspections

Maintenance requirements for the gaseous oxygen servicing trailer are provided on daily, preoperational, or periodic maintenance re-requirement cards. These cards provide the minimum requirements necessary to maintain the equipment and ensure that no item is overlooked. They do not contain instructions for repair, adjustment, or means of rectifying defective conditions. The cards are arranged in a work area sequence similar to aircraft maintenance requirements cards so that the inspections can be held in an efficient manner. The daily requirements should be accom-plished prior to the first use of the equipment for that day. It may be necessary to repeat some of the requirements prior to each use of the equip-ment.

Gaseous Oxygen System Servicing 

The danger involved in the transfer of gaseous oxygen as well as its importance to the pilot requires that it be handled with care. The following general safety precautions should be followed for safe operation of the oxygen servic-ing trailer:

1. Only qualified operators should operate the trailer for recharging aircraft oxygen systems. Complete familiarity with the trailer is a basic prerequisite to safe operating techniques.

2. The aircraft electrical system must be turned off, and no other servicing should be conducted on the aircraft while servicing the ox-ygen system.

3. Never permit oil, grease, or other readily combustible materials to come in contact with oxygen cylinders, valves, regulators, gauges, or fittings.

4. The servicing hose and aircraft connection fittings must be thoroughly inspected prior to servicing. Any trace of oil, grease, or foreign material must be carefully removed.

5. The servicing hose should always be bled prior to connecting with the aircraft oxygen system.

6. Open all valves slowly.

7. Always know the pressure existing in the aircraft system to be filled and the pressure in all cylinders to be used in the refueling process before starting the recharging operation.

8. Ensure that the line valve on the discharge end of the servicing hose is closed at all times when not actually servicing aircraft.

9. Never have more than one cylinder control valve open during operation.

10. The servicing hose must never be tightly stretched to reach a connection. Position the trailer so that the hose is not under tension.

11. When disconnecting the transfer hose from an aircraft fitting, loosen the connection slowly to prevent rapid bleeding of the trapped oxygen.

12. A malfunctioning pressure regulator should be disconnected from the line by closing its associated shutoff valves. The trailer can then be operated with the remaining pressure regulator.

13. When moving the trailer from place to place, cylinder valves should be closed.

Before servicing an aircraft gaseous oxygen system, you should take care to ensure that the six manifold control valves on the trailer control panel are closed. If these valves are partially opened, the cylinder pressure will equalize from one to the other.

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. The trailer and aircraft should be properly grounded

b. The line valve on the oxygen servicing hose should be closed.

c. All six trailer manifold control valves should be closed.

d. Both pressure regulators and their associated shutoff valves should be closed

e. 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.