tank is one with a vacuum space between two walls.)
excess liquid or gas, and a pressure-relief valve system
Separate liquid level and pressure gauges, as well as
that is connected to the vent system.
pressure-relief devices, are provided for each tank.
Transfer of LOX from the cart to the aircraft LOX
These components are permanently mounted on a
converter is by pressure differential. Basically, a higher
portable three-wheel trailer, which is equipped with a
pressure is built in the LOX cart than what exists in the
manually operated parking brake and retractable caster
aircraft converter. Pressure in the cart is developed by
allowing LOX to flow into the buildup coil. The
The low-loss, closed-loop transfer system is
buildup coil acts as a heat exchanger, changing liquid
designed to retain oxygen vapor caused by heat losses
into gas through vaporization. The gaseous product
during transfer to the aircraft converter. The gaseous
fills the area, causing pressure within the storage tank
oxygen vapors vented from the transfer tank and
or transfer tank. When the pressure in the cart becomes
aircraft converter are returned to the storage tank for
greater than the pressure in the aircraft's system, the
cool down and retention.
transfer of LOX takes place.
The Storage Tank
Controls and Indicators
The storage tank is a 50-gallon (U.S.) capacity, and
Table 10-1 contains functional descriptions of the
the space between the double walls of the storage tank
components outlined previously in figure 10-6. Figure
and the transfer tank is evacuated down to 5 microns or
10-7 shows the physical layout of the controls and
less. The space between the walls also contains a
indicators. Refer to figures 10-6 and 10-7 and to table
multi-layer, high-vacuum insulation to minimize heat
10-1 as we describe how the system works and which
gain and boil-off of the liquid oxygen.
controls affect which functions. Note how LOX and
gas vapors flow in the system. Troubleshooting and
The Transfer Tank
maintenance will be easier if you can see the big
picture of how the system works, and which controls
The 15-liter-capacity transfer tank is a
affect which functions.
double-walled, vacuum-insulated dewar that is
permanently attached to the storage tank. The transfer
With the exception of the converter full indicator
tank is self-contained, and is gravity-filled from the
gauge (marked LIQUID or GAS) and the transfer tank
storage tank. The transfer tank has a pressure buildup
liquid level gauge, all gauges have a green band to
coil, a relief valve, a rupture disc, and various controls.
indicate safe operating pressures and a red band to
The primary function of the transfer tank is to hold
indicate unsafe pressures.
small volumes of liquid oxygen and to use cold gas
The pressures of internal systems used to fill and
pressure from the pressure buildup unit to transfer
service converters, and to protect LOX carts and LOX
LOX from the cart to the aircraft's LOX converter.
cart operators, are listed in table 10-2.
The Transfer Lines and Piping System
Filling the Servicing Trailer
The LOX cart's transfer lines carry LOX from the
storage tank to the transfer tank, and then to the
In most locations, servicing trailers are filled from
aircraft's LOX converter. The lines also carry vented
central supply tanks called LOX farms. The supply
oxygen gas from the aircraft's LOX converter back to
tanks have transfer hoses terminating in couplings that
the storage on the cart tank.
match the fill-drain line couplings on the trailers. For
the correct operating procedures for the supply tanks,
The closed-loop system of the transfer lines
refer to the tank's operations manual. LOX farm
contains vented oxygen gas during filling operations.
operators will prepare the station's supply tank to
The interconnected liquid and return gas lines are
transfer LOX to the servicing trailer.
vacuum-jacketed wherever practical, and are of
minimum length to reduce cool down and heat leak
In studying the procedure for filling a servicing
trailer, refer to figures 10-6, 10-7, and table 10-1.
When the supply tank is ready, use the following
The piping system consists of a fill line for filling
the storage tank, a vent system for overboard venting of
procedures to fill the servicing trailer: