The primary purpose of portable transfer equipment is to provide a means of servicing oxygen systems installed in aircraft. There are currently two types of LOX servicing trailers in use by the Navy- the standard type 7 trailer, which vents gaseous and liquid oxygen overboard through the vent fitting of the LOX converter as it is being filled (fig. 5-5), and the TMU-70/ M low loss, closed loop trailer, which recaptures these vented losses (fig. 5-6). The TMU-70/ M trailer is manufactured by Cryogenic Engineering Company and has been selected for coverage in this training manual.

TMU-70\ M, Low Loss, Closed Loop Liquid Oxygen Servicing Trailer

During LOX servicing of aircraft converters, a lot of oxygen is lost because of the way the transfer is carried out. In addition to the economic loss, a safety hazard is created when LOX or oxygen vapors are released into the atmosphere near operating equipment and personnel. The low loss, closed loop system was designed to significantly reduce these losses and eliminate the safety hazards associated with venting oxygen in critical areas.

DESCRIPTION.- The TMU 70/ M is a completely self-contained unit with three major components: a 50-gallon Dewar tank, a 15-liter Dewar transfer tank, and a low loss, closed loop

Figure 5-6.- TMU-70/ M low loss, closed loop, liquid oxygen servicing trailer.

(LLCL) system of transfer lines. Separate liquid level and pressure gauges, as well as pressure relief devices, are provided for each tank. These components are permanently mounted on a portable three-wheel trailer, which is equipped with a manually operated parking brake and retractable caster wheel. The primary purpose of the TMU 70/ M is to service aircraft LOX converters. The LLCL

system is designed to recycle oxygen vapor caused by heat losses during transfer to the aircraft converter. The oxygen vapors vented from the transfer tank and aircraft converter are returned to the storage tank for cooldown and retention.

Storage Tank.- The storage tank is a 50-gallon (U. S.) capacity, double-walled Dewar. The space between the double walls of the storage tank and the transfer tank is evacuated down to 5 microns or lower and contains a multilayer, high-vacuum insulation to minimize heat gain and boil-off of the LOX.

Transfer Tank.- The 15-liter-capacity transfer tank is a double-walled, vacuum-insulated Dewar, permanently attached to the storage tank. It is self-contained and gravity filled from the storage tank. The transfer tank is equipped with a pressure buildup coil, relief valve, rupture disc, and controls. The primary function of the transfer tank is to hold small volumes of LOX and to utilize cold gas pressure from the pressure buildup unit to transfer LOX to the aircraft converter.

Transfer Lines and Piping System.- These lines carry the LOX from the storage tank to the transfer tank, and then to the aircraft converter. They also carry the vented oxygen gas from the aircraft's converter to the storage tank. The closed loop system of the transfer lines contains the vented oxygen gas during filling

operations. The interconnected liquid and return gas lines are vacuum-jacketed wherever practical and are of minimum length to reduce cooldown and heat leak losses.

The piping system consists of a fill line for storage tank filling, a vent system for overboard venting of excess liquid or gas, and a pressure relief valve system connected to the vent system.