MIL-PRF-26139D
3.9.1 Air compressor. The air compressor for the canopy seal system shall be the type that is
currently acceptable for industrial use. A maximum pressure relief valve set at 70 PSIG shall be
provided in the system.
3.10. Pressurization system. The pressurization system shall consist of the following:
3.10.1 Blower. An positive displacement blower with intercooling shall be provided to supply
400 CFM standard air (30.6 PPM) at 12.5 PSI measured at the discharge end of the outlet hose.
The bearings used in the blower shall be easily replaceable.
3.10.1.1 Drive shaft clearance. Means shall be provided for sealing the external and internal
drive shaft clearance holes in the end plates to prevent leakage.
3.10.1.2. Installation and removal. Alignment of blower to engine shall not require special tools
for installation or removal.
3.10.2 Intake silencer. The blower intake shall be equipped with an air-intake/ cleaner/silencer
device that does not protrude more than 3 inches from the tester exterior surface.
3.10.3 Blower outlet silencer. A silencer shall be provided to reduce noise and dampen the
pulsation of the blower discharge air.
3.10.4 Aftercooler. An air-to-air aftercooler capable of providing the required cooling and
volume of air shall be provided. The aftercooler shall have sufficient capacity to cool blower
discharged air to within 25° F of existing ambient temperature while delivering maximum flow
and pressure.
3.10.4.1 Aftercooler fan. An aftercooler fan shall be provided to supply the necessary cooling
air to the aftercooler.
3.10.4.2 Aftercooler fan inlet. The aftercooler fan inlet shall be equipped with adjustable
louvers which lock in any degree of opening.
3.10.4.3 Aftercooler fan exhaust. The aftercooler fan exhaust shall extend to the outside of the
tester housing and be protected.
3.10.5 Pressure regulating device. A pressure regulating device shall be provided to
automatically regulate the pressure in the aircraft cabin being pressurized, and shall be installed
between the aftercooler and flowmeter. For all pressure conditions, and where flow is varied
between 50 and 400 CFM, the valve shall limit the rate of pressure change to 500 foot pounds
per minute (FPM) as registered on the pressure equalization indictor. For all pressure conditions,
and where flow is varied between 10 and 50 CFM, the pressure regulating valve shall limit the
rate of pressure change between 750 FPM. The valve shall also limit pressure changes to
between 1,500 FPM during adjustments of the pressure regulator to a new pressure setting.
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