LOX SERVICING TRAILERS
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 Navythe 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
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
(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
aircrafts 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.
Controls And Indicators. The controls and
indicators of the TMU-70/M are illustrated and