MIL-PRF-27720G
cleaning fluid pumped through the vent line will be sprayed against the inside top of the inner
shell to flush sediment and other contaminants from the tank. The total area of the spray holes
shall be at least as that of the cross sectional area of the vent line. The vent line shall have a
manual shutoff valve as near as possible to point where it enters the outer shell, but shall be
readily accessible to the operator. The line shall discharge toward the ground in a safe location
outside the control housing. The vent line shall terminate in a 1-inch, female pipe thread in an
area convenient for attachment of a purging unit hose or an overboard vent line during air
transportation (see 4.5.1, 4.5.11.3).
3.5.12 Control housing assembly.
3.5.12.1 Control housing. A control housing shall be provided on one end of the tank assembly
to house and protect the tank controls, instrumentation, and accessories. The housing shall be
readily removable from the tank assembly for maintenance. The housing top shall be shaped to
preclude the accumulation of snow, rain, or sleet. Ventilation openings shall be provided to
prevent accumulation of gasses or fog during operation. Doors or hinged panels shall be
provided and shall be equipped with latches for securing them in any position from fully closed
to wide open even when subjected to wind gusts up to 70 mph. Door or hinged panel latches and
position regulating devices shall be readily operable by personnel wearing heavy arctic mittens
(see 4.5.1, 4.5.16.9).
3.5.12.2 Control panel. The control housing shall provide for a control panel with all
instruments and controls readily visible and accessible. The controls, pressure gages, and
instruments shall not be installed where they can be contacted by leaking liquid oxygen or water
from vapor condensing on cold lines. All valve handles and gage faces shall be not less than
27.0 inches above ground level. All gages, instruments, and manually operated controls used in
normal operation of the unit shall be located on the control panel. The control panel shall be
protected by a panel or door when the tank is not in use for liquid transfer. The control panel
shall be shielded from rain and snow when the door or panel is open (see 4.5.1, 4.5.16.9).
3.5.13 Pressure buildup system. The tank assembly shall have a pressure buildup system to
pressurize the inner shell vapor space to 50 psig when the tank contains 25 gallons or more of
liquid oxygen. Operation of the buildup system shall not require control operation other than
closing of the vapor vent line valve and opening the pressure buildup manual control valve (see
4.5.1, 4.5.9).
3.5.14 Pressure relief devices. The tank assembly shall include pressure relief devices in any
line or component that can be isolated by closing valves, or where dangerous pressures can
develop. All pressure relief devices shall be installed in accessible locations and the design shall
ensure that a discharge of pressure will not cause danger to personnel or equipment damage.
Venting of oxygen vapor shall not cause freezing of the relief devices (see 4.5.1, 4.5.3).
Incorporation of safety valves shall be in accordance with section VIII of the ASME Boiler and
Pressure Vessel Code.
3.5.15 Valves.
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