C1, TM 9-1240-318-35
Section IV. SEALING, PURGING, AND CHARGING
counterclockwise to the closed position.
Sealing is a process of creating an airtight instrument
nitrogen tank valve slowly until pressure is registered on
that will retain a desired amount of dry nitrogen over a
the high pressure gage (7).
period of time. Two types of seals are used; preformed
packing and sealing compound.
Note. Tank pressure must exceed 100 psi. If the
registered pressure is less than 100 psi, obtain and
a. Preformed packing is a rubber O ring
use a replacement tank.
compressed into a slot and allowed to expand against a
e. Open valve knob (9) located under the outlet
valve gages (10).
b. Sealing compound, MIL-S-11031, is used to seal
f. Slowly turn the pressure regulator valve
and lock all screws and rings authorized for replacement
clockwise until approximately 5 psi is registered on the
at direct support, general support, and depot
low pressure gage (11). Adjust outlet valve (8) until 5 psi
is registered on outlet valve gage. Check free end of the
attached hose assembly for free flow of nitrogen for
approximately ten seconds; then close valve knob to
stop the flow of nitrogen.
Purging is a procedure which eliminates the moisture
g. Remove the purging screws (12 and 13) and
content and contaminated air locked inside of a sealed
insert threaded purging adapter (14) to the purging
instrument by introducing dry nitrogen gas into the
screw hole. Connect free end of hose assembly to
interior of the instrument housing and allowing it to
escape by means of a vent at the opposite end of the
h. Open valve knob and allow nitrogen to flush
through the telescope at this pressure for five minutes.
i. Close valve knob and replace purging screw
(12) on telescope. Open valve knob to permit nitrogen
to flow into the instrument and continue to charge the
Charging is a process of forcing dry nitrogen gas into a
telescope at 5 psi for two minutes.
sealed optical instrument at a prescribed pressure for
j. Close the valve knob and record the internal
pressure on the outlet valve gage. The pressure should
fogging due to external temperature changes.
be between 4.5 to 4.9 psi. The reading will drop if the
telescope sight is not properly sealed. If loss of nitrogen
5-26. Purging and Charging.
is indicated, reseal the instrument.
(Depot Maintenance ONLY)
Note. After a five minute period, check the
internal pressure on the outlet valve gage. The
pressure should not drop in excess of 0.1 psi.
a. Place a tank of dry nitrogen (1) in back of the
pressure test fixture (2) and secure. Remove threaded
k. If ther e is no apparent pressure loss, remove the
cover from the valve outlet of tank. Open tank valve (3)
purging adapter and hose assemble; then replace the
momentarily to rid the valve scat of any foreign matter.
purging screw (13).
b. Check adapter (4) for cleanliness and proper
sealing of gasket. Securely attach this adapter to the
Note. Replace the purging screw as quickly as
tank valve and then attach pressure regulator (5) to
possible when removing purging adapter to retain as
adapter. Connect the pressure line to the pressure
much of the nitrogen charge as possible.
regulator and ensure that all connections are tightened
to prevent leakage.
I. If no further purging and charging is required,
c. Remove cap from snap-type coupler and
exhaust system as follows: close tank valve, open valve
connect hose assembly (6) to valve outlet by means of
knob, remove hose and replace cap to snap-type
the snap-type coupler.