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SAFETY PRECAUTIONS - 14020_168

Aviation Structural Mechanic E2 - How airplanes are built and how to maintain them
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Figure 5-3.—Transfer line connector/coupling. line. The reason is that as the LOX vaporizes, the vapors will warm, and excessive pressures may develop that can burst the conduit walls. For transfer efficiency, vacuum-jacketed lines with well-designed, low-heat input couplings are best for most uses. Unthinking use of two or three transfer sections coupled together where one could do the job wastes liquid and time. Several times as much line material has to be cooled down, and several times more heat transferring line surface area is contacted by the LOX. Additional heat influx means additional LOX vaporization; therefore, more liquid is needed to satisfy a given transfer demand. VALVES 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 5-3







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