Air Systems -Air Conditioning System Description
737 Flight Crew Operations Manual
Air Conditioning Distribution Schematic
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June 1, 2003 2.31.7
Air Systems -Air Conditioning System Description 737 Flight Crew Operations Manual
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Copyright . The Boeing Company. See title page for details.
2.31.8 June 1, 2003
737 Flight Crew Operations Manual
Introduction
Cabin pressurization is controlled during all phases of airplane operation by the cabin pressure control system. The cabin pressure control system includes two identical automatic controllers available by selecting AUTO or ALTN and a manual (MAN) pilot–controlled mode.
The system uses bleed air supplied to and distributed by the air conditioning system. Pressurization and ventilation is controlled by modulating the outflow valve and the overboard exhaust valve.
Pressure Relief Valves
Two pressure relief valves provide safety pressure relief by limiting the differential pressure to a maximum of 9.1 psi. A negative relief valve prevents external atmospheric pressure from exceeding internal cabin pressure.
Cabin Pressure Controller
Cabin altitude is normally rate–controlled by the cabin pressure controller up to a cabin altitude of 8,000 feet at the airplane maximum certified ceiling of 41,000 feet.
The cabin pressure controller controls cabin pressure in the following modes:
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AUTO – Automatic pressurization control; the normal mode of operation.
Uses DC motor.
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ALTN – Automatic pressurization control; the alternate mode of
operation. Uses DC motor.
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MAN – Manual control of the system using DC motor.
The air data inertial reference units (ADIRUs) provides ambient static pressure, baro corrected altitude, non corrected altitude and calibrated airspeed to both automatic controllers. The ADIRUs receive barometric corrections from the Captain’s and First Officer’s BARO reference selectors.
The automatic controllers also receive throttle position from both stall management computers and signals from the air/ground sensors.
Copyright . The Boeing Company. See title page for details.
Air Systems -Pressurization System Description 737 Flight Crew Operations Manual
Cabin Pressure Control System Schematic
Pressurization Outflow
Cabin air outflow is controlled by the outflow valve and the overboard exhaust valve. A small amount is also exhausted through toilet and galley vents, miscellaneous fixed vents, and by seal leakage.
Copyright . The Boeing Company. See title page for details.
2.40.2 April 28, 2000
Air Systems -Pressurization System Description
737 Flight Crew Operations Manual
Outflow Valve
The outflow valve is the overboard exhaust exit for the majority of the air circulated through the passenger cabin. Passenger cabin air is drawn through foot level grills, down around the aft cargo compartment, where it provides heating, and is discharged overboard through the outflow valve.
Overboard Exhaust Valve
On the ground and in flight with low differential pressure, the overboard exhaust valve is open and warm air from the E & E bay is discharged overboard. In flight, at higher cabin differential pressures, the overboard exhaust valve is normally closed and exhaust air is diffused to the lining of the forward cargo compartment.
YA613 - YA809 However, the overboard exhaust valve is driven open if either pack switch is in high and the recirculation fan is off. This allows for increased ventilation in the smoke removal configuration.
YC153 -YK104 However, the overboard exhaust valve is driven open if either pack switch is in high and the right recirculation fan is off. This allows for increased ventilation in the smoke removal configuration.
YD651 - YD655
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