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. 5-20