Although valves might appear to be of minor concern in a system, low-temperature valves often cause more trouble than any other element of the system. In addition to the general requirements for any valve, LOX valves must be able to function properly at extremely low temperatures without causing excessive boil-off losses to the liquid flowing through them. Insulation is the best method to meet these thermal requirements. Various materials have been used for insulation, but the best method is to vacuum insulate the valve. The valve illustrated in figure 5-4 is typical of this type. The method of operation will vary by manufacturer.

OXYGEN SERVICING EQUIPMENT

Learning Objective: Describe oxygen servicing equipment to include safety precautions, servicing trailers, and system servicing.

Figure 5-4.- Vacuum-insulated cryogenic valve.

Oxygen servicing equipment for both liquid and gaseous oxygen systems are discussed in this section. Since AMEs operate this equipment, they must be familiar with purging and sampling procedures as well as operation of the equipment while servicing aircraft oxygen systems.