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will keep cabin pressure higher that the atmospheric pressure when the aircraft is operating at altitudes above 8,000 feet.
+ maintains cabin pressure by controlling the amount of air vented from the cabin.
- using AC AIR to pressurize the ACFT.
+provides aircrew/ suitable environment during FLIGHT.
PURPOSE OF CABIN PRESSURIZATION:
+ DE-ENERGIZED : NORMAL.
- maintains cabin pressure at various aircraft altitudes.
- located outside of the pressurized cabin on the left side of the bulkhead just forward of the cabin.
- fixed-isobaric, single differential type regulator. ( fixed setting of 10.91)
- set pressure of 5 PSI in the differential range of pressurization.
- two components : a regulator & outflow valve.
- regulates pressure in the cabin by venting air to the atmosphere.
Cabin Air Pressure Regulator Valve
- controls cabin pressures in both unpressurized & isobaric ranges.
- contains an evacuated bellows that maintains 10.91 PSI (8,000ft)
- throughout the isobaric range (8,000 to 23,000ft)
- Differential Range: 23,000 ft and extends to maximum operating alititude. ( 5 PSI )
: used to perform ground operational checks of the cabin pressurization system.
3 POS GND TEST VALVE
- safety wired to the FLIGHT Position. (NORMAL)
-blocks vent ports for the isobaric cntrl sec. (used to check 5 PSI Diff Setting)
- Keeps outflow valve on seat
- Control Chamber cannot vent
Test only DIFF ON
- blocks ALL vent ports. (overrides normal reg. functions of cntrl valve)
* When pressure relief and dump valve should open and relieve cabin pressure *
Test only ALL OFF
3 control functions:
+ located on the right forward bulkhead.
If regulator fails to control pressure @ 5 PSID, then dump valve will take over & relieve excess cabin pressure when it reaches 5.35 to 5.50 PSID.
- Negative pressure relief ( normal control function )
+ also used to dump cabin pressure during emergencies.
- incorporating a solenoid that is energized by placing the air-source sw to DUMP or RAM pos.
+ Energizing the relief & dump valve solenoid will cause the valve to open & dump cabin pressure.
Cabin Pressure Relief & Dump Valve
- used to indicate cabin pressure in terms of cabin pressure altitude versus aircraft altitude.
@ 20,000 IT will indicate cabin pressure in terms of a cabin altitude of 8,000 feet.
Atmospheric Pressure at 20,000 feet is 6.76 PSI.
Cabin Pressure is 10.91 PSI @ 8,000
- the indicator provides cabin pressure altitude indications from 0 to 50,000 feet.
Cabin Pressure Altitude Indicator
- normally open isobaric switch.
- located in the lower forward area of the cabin.
- illuminates if the cabin pressure is too low.
- provides a signal to the cabin pressure caution light
SW CLOSES: when cabin pressure decreases to 5 PSIA or exceeds 27,000 feet
- sw will remain closed until pressure reaches 5.85 PSI. (23,400 ft)
Cabin Low Pressure Switch
- Metering Valve
- Rocking Arm
DIFF CONTROL SEC-
- only electrical component
2) DUMP - ac still runs.
3) MANULY - SQAUT SW.
The Differential control section consist of a Differential Control _______ & Differential Control ________ Valve.
Diaphragm & Metering