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|  MIL-P-27431B(USAF)
3.5.5 Power requirements. The purging unit shall be designed to operate on not
more than 1500 watts electrical power supplied at 115 5V, 60 or 400 cycles, single
phase.
3.5.6 Explosion proofing. The purging unit shall incorporate provisions to
preclude the initiation of an explosion when exposed to class 1, group D atmospheres
and operated in class 1, division 2 hazardous locations as defined by Pamphlet 70.
3.5.7 Design pressures. The heat exchanger assembly and hose assembly shall be
designed to withstand working pressures up to 500 psig and shall show no leakage or
deformation when subjected to a proof pressure of 1,000 psig. Neither assembly shall
burst at less than 2,000 psig.
3.5.8 Safety. No electrical components and wiring shall be exposed to the
flowing oxygen gas. The heating element shall not be directly exposed to the flowing
oxygen gas without a sealed protective sheath that will prevent a failure from
providing an ignition source. Heating elements within a heat exchange medium and not
in direct contact with oxygen, do not require a sheath.
3.6 Performance.
3.6.1 Purge kit. The purge kit shall be assembled, connected, and instrumented
per Figure 3. Inlet oxygen shall be applied at any pressure between 40 and 100 psig.
Electrical power shall be applied at 115 5 V, 60 or 400 cycles, single phase. The
purging unit shall control effluent oxygen to within the following conditions at an
ambient temperature of 30F:
a.
A minimum flow rate of 300 Standard Liters Per Minute (SLPM) at 100
psig. Flow shall not exceed 400 SLPM.
b.
A minimum flow rate of 100 SLPM at 40 psig.
A temperature of 250 to +0 F at any flow condition from 0 SLPM to -30
c.
the maximum obtained at 100 psig.
3.6.1.1 Standard gas. For the purpose of this specification, standard gas is
defined as dry air, oxygen, or nitrogen at 760 mm Hg pressure and 70 F. Oxygen
shall be per MIL-0-27210; Nitrogen per BB-N-411 Type 1 Class 1, Grade B; air per
BB-A-1034 Source 1 Grade A or Source II Grade C.
3.6.1.2 Hot purging. The assembly shall be designed to provide a safe means of
hot purging both liquid and gaseous systems and accessory items using a prime inlet
Source of Grade 1 aviators breathing oxygen per MIL-0-27210.
3.6.2 Gas temperature and flow rate. When operated in any ambient temperature
from -30 to +125F, the gas temperature and flow rate at the inlet to the filler
valve, shall reach specified conditions in a time not to exceed 10 minutes after
power is first applied. No component shall be damaged by interruption of gas flow
with specified electrical power applied for periods up to and including 8 hours.
3.7 Details of components.
3.7.1 Heat exchanger assembly. As a minimum the heat exchanger assembly shall
consist of a heating element or elements, thermostatic controls, a protective outer
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