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TM 5-4120-259-15
figure 13
fig. 30
figure 37
fig. 37
fig. 36
figure 13
(1)
( 2 )
95. System Evacuation
To minimize the time needed for evacuation
and for obtaining a completely dry system,
use the double evacuation procedure which
follows. (See figure 37 which shows connec-
tions and procedure.)
a. With a vacuum pump, reduce the system
to an absolute pressure of approximately
54
10,000 microns, 10 millimeters. The stop evacu-
ation and break vacuum with oil-pumped dry
nitirogen. This will cause any condensed vapor
to flash back into its original state of vapor
in which it can be removed by the pump.The
dry nitrogen serves as a carrier for the water
vapor.
b. The above procedure should be repeated
several times to assure a completely dry
system.
96. Replacing Tubing, Fittings or
Refrigerant Components
a. General. A careful ana!ysis of any
trouble should first be mde to determine if
replacement is necessary. The cause of failure
must be determined before replacement is
made.
b. Unbrazing Joints
(1) Release system charge to the atmos-
phere or refrigerant cylinder through
the System
charging valve,
figure
30.
(2) Connect a cylinder of oil pumped
dry nitrogen to the system charging
valve, figures 30 and 37, and, using
a nitrogen regulating valve, charge
the system with just enough nitrogen
to insure a constant flow of nitrogen
at all times when the system is open
and
while brazing or
unbrazing
joints. One to two psig is sufficient.
c. Cutting Copper Tubing.
Use a sharp wheel cutter, or hack-
saw of 32 teeth per inch. Avoid any
burns or malforming of the tube at
the cut.
Cut tubing square and remove all
burns from inside and outside with a
sharp fine file. Hold tubing so filings
will drop away from tube opening.
Caution: Care must be taken to pre-
vent filings or cuttings from entering
the tube. Particles which enter the
tube must be cleaned out before com-
pleting connections. Failure to do this
may result in damage to the system
through oil gumming and sludging,
chemical reaction, or direct scoring of
the cylinder walls and pistons.
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