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|  MIL-T-82571A(0S)
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4.4.5.4 Breech mechanism air loss test. Gradually charge each breech
mechanism (using the test equipment of 4.4.4.3 and 4.4.4.4) at a rate not
exceeding 250 psig per minute to a pressure of 2000 psig pneumatic, and per-
mit the mechanisms to cool for a period of 2 hours. The breech mechanisms
shall then be bled to a pressure of 1600 plus or minus 10 psig. After a 24-
hour period, observe the pressure, using gage 4.4.4.4. The pressure loss
in each breech mechanism shall not exceed 5 percent.
4.4.5.5 Bore size of barrel test. The "GO" bore gage (4.4.4.5) shall
pass through each barrel with an axial force not to exceed 150 pounds.
4.4.5.6 Ground circuit continuity. Continuity shall exist between ter-
minal 4 of TB104 in the junction box and the junction box case as well as
any of the two control box cases, breech interlock housings, and muzzle door
mechanism housings.
4.4.5.7 Dielectric strength. For the purpose of this test the muzzle
door heater switch shall be placed in the ON position and the muzzle door
thermoswitches shall be cooled with CO2 to close the contacts. The tube
assembly shall withstand a potential of 1000 volts, 60 Hz ac applied between
ground (terminal 4 of TB104 in the junction box) and all input terminals as
shown on the external electrical schematic (NAVORD Dwg 1448449), with the
exception of the muzzle door heater terminals, for one minute without evidence
of breakdown. The input terminals may be connected together for this test.
The muzzle door heaters shall withstand a potential of 500 volts 60 Hz ac
applied between the input terminals and ground for a period of one minute
with-':t evidence of breakdown.
4.4.5.8 Insulation resistance test. For the purpose of this test the
the assembly shall be in the same condition as required for the dielectric
strength test (4.4.5.7) with the exception that the muzzle door heater
switch shall be in the OFF position. Immediately after the hipot test, the
insulation resistance between the hipotted points shall be 3 megohms minimum
at 500 vdc and the insulation resistance between terminals 10 and 11 of TB104
and ground (terminal 4 of TB104) shall be 1 megohm minimum at 500 vdc.
4.4.5.9 Muzzle door heater circuit operating current. With 115 plus or
minus 0.5 volts 60 Hz ac applied to terminals 1 and 2 of TB1O4 in the junction
box, the muzzle door heater switch in the ON position, and the thermoswitches
of Barrel No. 1 closed by cooling with C02, measure the current. Permit the
thermoswitch of Barrel No. 1 to return to the OPEN position and close the
thermoswitches of Barrel No. 2 by cooling the switches; again measure the
current. The current in each muzzle door heater circuit shall not exceed
8.4 amperes. If necessary, the muzzle door may be opened to permit access
to the thermostats.
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