Airframe system

Liquid Oxygen Systems (LOX)

Civilian aircraft do not generally use liquid oxygen, or LOX, systems because of the difficulty in handling this form of oxygen, and because it is not readily available to the fixed-base operators who service general aviation aircraft. The military, on the other hand, uses liquid oxygen almost exclusively because of the space and weight savings it makes possible. One litre of liquid oxygen will produce approximately 860 litres of gaseous oxygen at the pressure required for breathing.

The regulators and masks are the same as those used for gaseous oxygen systems, the difference in the systems being in the supply. Shown in Figure 9.8 is a sketch of a typical LOX converter and supply system. Liquid oxygen is held in the spheri­cal converter and in normal operation the build-up and vent valve is back-seated so some of the LOX can flow into the build-up coil where it absorbs enough heat to evaporate and pressurize the sys­tem to the amount allowed by the container pres­sure regulator, normally about 70 psi. This gaseous oxygen maintains a relatively constant pressure in the converter and supplies the oxygen to the regulator.

When the supply valve on the regulator is turned on, LOX flows from the converter into the supply evaporator coil where it absorbs heat and turns into gaseous oxygen.

If, for any reason, excessive pressure should build up in the system, it will vent overboard through one of the relief valves.