PG-4 Indicates Low
The 0-15 psig pressure gage PG-4 measures
extremely low pressures from the item under test.
This gage is protected from high pressures by gage
guard GP-1, which is set between 11 and 14 psig.
To locate any leaks in this system, you will need
to perform the leakage test described earlier for
the test stand. You will not be required to
perform the leakage test for the accessories
section. In most cases by tightening the necessary
fittings, you will be able to remedy the low
readings on the PG-1 pressure gage.
Differential Pressure Gage
(DF-1) Indicates Low
The 0-100-in. H2O differential pressure gage
is a bellows-operated gage used to indicate
differential pressure when the pressure closing and
pressure opening valves are tested. The probable
cause for low readings on this gage is a leaky shut
off differential pressure valve V-8. If you are
lucky, you can correct it by tightening the fittings.
If this does not solve the problem, you will need
to replace the valve.
Bell Jar Leakage
You may also have problems with the bell jar.
The bell jar is used for testing components
having more than one possible area of leakage.
The bell jar consists of the bell jar itself, a relief
valve with a range of 5 to 15 psig, and a bell jar
coupling. The relief valve is designed to be
leakproof at 5 psi and set to relieve at 10 psig.
To perform the leakage test on the bell jar
assembly, proceed as follows:
1. Remove hose assembly 3 and nipple
assembly 14 (figure 1-5) from the bottom bell jar
coupling C-1. Disconnect the opposite end of the
hose from differential pressure connection NIP-7.
2. Ensure differential pressure bleed valve
V-7, test-pressure-gage-to-bell-jar valve V-2, and
system bleed valve V-5 are closed. Open differen-
tial pressure shutoff valve V-8.
3. Place the bell jar on the fixture and secure
it with a clamp. Plug bell jar top coupling C-2.
4. Slowly open oxygen supply valve V-6
until 100 in. H2O is indicated on differential
pressure gage DF-1. Close valve V-6. Leakage,
indicated by a drop in pressure on DF-1, shall not
be more than 2 in. H2O in 10 minutes.
5. Close the oxygen supply cylinder valve and
open system bleed valve V-5 to bleed the system.
When the test stand is secured, all valves
with the exception of system bleed valve
V-5 will be closed. Valve V-5 is left open
to prevent accidental build-up of pressure
in the system.
6. Secure all test stand valves. Leave system
bleed valve V-5 open.
REPAIRING AND REPLACING PARTS
Anytime you have a defective or damaged
part, it must be repaired or replaced. Informa-
tion on part numbers can be found in the
NAVAIR 17-15BC-20 manual.
Y o u m a y o n o c c a s i o n f i n d y o u h a v e a
defective piece of tubing. To replace any tubing
installed on this test stand (59A120), remember
that you are dealing with high-pressure oxygen.
Therefore, you must use tubing with a minimum
wall thickness of 0.049 to replace any defective
tubing. This tubing may be cut to length and
flared to replace any defective portion of tubing.
W A R N I N G
When you work with oxygen systems,
never use any parts that have been in con-
tact with oil, grease, or any other material
that is not approved for use in the presence
of high-pressure oxygen. Fire or explosion
may result when even the slightest trace of
combustible material comes in contact with
Heat Exchanger Panel
If the heat exchanger panel is defective, it may
be replaced. You may replace the panel by discon-
necting its connections and removing its seven
retaining screws. If a new heat exchanger is
used, you may drill or punch holes not exceeding
11/32 inch in diameter in the perimeter, beyond
the outer seam welds, for use in mounting. When
the holes are drilled at installation, you should
be careful to prevent the drill from puncturing the
The test stand nor its components require