mode, in which gaseous oxygen is fed from the
Fill Sequence
converter, and the demand mode, in which oxygen
The fill sequence begins automatically when the
flows from the converter as a liquid and vaporizes to a
servicing trailer hose filler nozzle is connected to the
gas in the feed line.
filler port on the filler, buildup, and vent valve. The
In the economy mode of operation (fig. 7-17,
hose nozzle, when attached to the fill valve, actuates a
supply sequence, view C), limited demand upon the
plunger within the valve, which places the valve in the
system allows the converter to supply gaseous oxygen
fill and vent condition (fig. 7-17, fill sequence, view A).
directly as a result of drawing off the gaseous oxygen
The valve, when in this position, provides an opening
stored within the top of the converter. At approximately
from the top of the converter to the atmosphere. This
82 psi, the pressure-opening valve unseats and allows
opening is used to vent gaseous oxygen during filling
gaseous oxygen to flow from the converter to the supply
and liquid oxygen after the converter is full.
system. Oxygen then flows from the upper (gas)
During transfer, liquid oxygen flows into the
portion of the converter, rather than the liquid side.
converter through a passage located in the bottom of the
When the amount of oxygen demanded by the crew
converter. This arrangement allows gaseous oxygen to
exceeds the supply of the economy mode, the
vent through the converter top as it is being displaced
pressure-opening valve closes. As the crew continues to
by liquid flow in the bottom. When the converter is full,
draw upon the oxygen supply, the supply system
liquid flows overboard through the vent line, giving an
pressure becomes lower than that of the converter.
indication that the converter is full. Removal of the
When a pressure differential of 5 psi occurs, the
filler hose nozzle from the fill valve automatically
differential check valve opens (fig. 7-17, supply
places the converter in the buildup sequence.
sequence, views C and D) and allows liquid oxygen to
flow into the supply line, creating the demand mode.
Buildup Sequence
Converter pressure will build up while the system is
operating in the demand mode. As the pressure again
The buildup sequence (fig. 7-17, buildup sequence,
approaches 82 psi, the pressure-opening valve will
view B) begins when the filler hose is removed from the
again unseat, switching the supply sequence back into
converter. This sequence provides for rapid pressure
the economy mode. The converter automatically
buildup to system operating pressure.
switches itself back and forth between the economy
and demand modes while supplying oxygen to the
During this sequence, LOX from the converter fills
crew.
the buildup coil by gravity feed. Liquid in the coil
absorbs heat from the ambient air around the coil and
SYSTEM MAINTENANCE
vaporizes, causing the pressure to build up. The
gaseous oxygen formed in the coil then circulates
Extreme care must be exercised when installing
through the pressure-closing valve and back to the top
units in an oxygen system. The life of the pilot and crew
of the converter. This causes more fluid to flow into the
depends on the thoroughness with which the AME does
buildup coil. This circulation continues to build up
this job. All maintenance of LOX systems must be done
pressure until approximately 75 psi is reached. At this
in accordance with the instructions contained in the
pressure, the pressure-closing valve is forced closed.
applicable MIM. The AME assigned to do the LOX
Pressure continues to build up within the system at a
system maintenance also should be familiar with the
slower rate, and at approximately 82 psi, the
various instructions pertaining to handling LOX and
pressure-opening valve opens. When this occurs,
maintenance of the related equipment.
oxygen is available at the supply outlet. A pressure
relief valve, which is set at approximately 110 psi, is
The actual removal and installation procedures
installed in the converter system to relieve excessive
used in maintaining LOX systems will vary from one
pressure.
aircraft to another; however, the following precautions
will apply to almost any aircraft system.
Supply Sequence
1. Use only tubing assemblies that have been
tested, cleaned, capped, and properly identified as
The supply sequence of the liquid oxygen system
oxygen lines.
consists of two modes of operation--the economy
7-19
