AIRCRAFT FILLING A LIQUID OXYGEN SYSTEM

 Filling A Liquid Oxygen System

Service carts for liquid oxygen normally carry the LOX in 25- or 100-liter containers. Servicing systems from these carts is similar to that described in the previous section on gaseous oxygen systems. And here again, cleanliness and care are of the utmost importance. Liquid oxygen has such a low boiling point that it must not be spilled on your skin; it would be sure to cause serious frostbite. Protective clothing and an eye shield must be worn.

Before servicing an empty LOX system or one that hasn't been in use for some time, you should purge it for a few hours with heated water pumped dry air or nitrogen.

Attach the service cart to the aircraft system and, after placing the build-up and vent valve in the vent position, open the valve on the service cart. As the LOX flows from the service cart into the warm converter, it vaporizes rapidly and cools the entire system. Considerable gaseous oxygen is released during the filling procedure, and it vents to the outside air through the build-up and vent valve. This venting of the gaseous oxygen will continue until liquid oxygen starts to flow out of the vent valve. A steady stream of liquid indicates that the system is full.

Be sure that the system vents freely as it is being filled and that frost forms only on the outlet and the hoses. If any frost forms on the supply con­tainer, it could be an indication of an internal leak, and since the pressure can build up extremely high, any trace of a leak demands that the equip­ment be shut down immediately and the cause of the frosting determined.

When you attach the liquid oxygen cart to the aircraft system, open the valve fully, then close it slightly. If you do not do this, it is possible that the oxygen flowing through the valve could cause the valve to freeze in the open position and it may be difficult or impossible to close.

There are two ways LOX converters are serviced. Some are permanently installed in the aircraft and are serviced from an outside filler valve. The build-up and vent valve is placed in the vent position, the service cart is attached to the filler valve, and liquid oxygen is forced into the system until liquid runs out of the vent line. When the system is full, the build-up and vent valve is returned to the build-up position to build up pressure in the converter. Other installa­tions have quick-disconnect mounts for the con­verters so the empty converter can be removed from the aircraft and replaced with a full one. Exchanging converters allows oxygen servicing to be done much more quickly and safely than can be done by filling the converter in the aircraft.

Inspecting the masks and hoses disposable masks such as those used with many of the portable systems should be replaced

with new masks after each use, but the permanent masks used by crew members are normally retained by the individual for his exclusive use. These masks are fitted to the face to exclude leakage and are usually treated as personal flight gear. They should be occasionally cleaned with a lukewarm detergent bath by washing them with a cloth wet with the detergent solution and then allowing them to dry at room temperature. The face portion of the mask may be disinfected with a mild antiseptic.

Check the masks and hoses for leaks, holes or rips, and replace them rather than attempting to repair any damaged component. When storing the mask in the airplane, be sure to protect it from dust and dampness, and especially from any type of grease or oil.