.
STBY – Semiautomatic pressurization control; standby mode of
operation. Uses DC motor.
.
MAN AC – Manual control of the system using the AC motor.
.
MAN DC – Manual control of the system using the DC motor.
Air Systems -Pressurization System Description 737 Operations Manual
In the automatic mode of operation, airplane altitude is sensed directly from the static ports. In the standby mode, airplane altitude is sensed electrically from the air data computer (ADC). Barometric corrections to these pressures come from the Standby Altimeter. On some airplanes barometric corrections to these pressures come from the Captain’s altimeter in AUTO and the First Officer’s altimeter in STANDBY.
The controller receives additional information from the air/ground sensor and the cabin pressure altitude sensing port.
Cabin Pressure Control System Schematic
As installed NORMAL OPERATION IN FLIGHT
Airplanes with CPCS
2.40.2 Copyright . The Boeing Company. See title page for details. June 7, 2002
Air Systems -Pressurization System Description
737 Operations Manual
Airplanes with DCPCS
Cabin altitude is normally rate–controlled by the digital cabin pressure controller up to a cabin altitude of 8,000 feet at the airplane maximum certified ceiling of 37,000 feet. The cabin pressure controller controls cabin altitude in the following modes:
.
AUTO – Automatic pressurization control; normal mode of operation.
Uses brushless DC motor.
.
ALTN – Automatic pressurization control; alternate mode of operation.
Uses brushless DC motor.
.
MAN – Manual control of the system using DC motor.
In the automatic and alternate modes of operation, airplane altitude is provided by the air data computers (ADCs). The ADCs receive barometric corrections from the Captain’s and First Officer’s altimeters.
The controller receives additional information from the air/ground sensor, the cabin pressure altitude sensing ports, and the stall management computer.
Air Systems -Pressurization System Description
Cabin Pressure Control System Schematic
ENGINE N1/N2 OUTPUT
IN FLIGHT NORMAL OPERATION
Airplanes with DCPCS
Pressurization Outflow
Cabin air outflow is controlled by the main outflow valve, the forward outflow valve and the flow control valve. During pressurized flight, the flow control valve is closed, and the majority of the overboard exhaust is through the main and forward outflow valves. 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.
2.40.4 June 7, 2002
Air Systems -Pressurization System Description
737 Operations Manual
Flow Control Valve
The flow control valve opens to exhaust the cooling air from the E & E compartment overboard during ground operation, unpressurized flight and pressurized flight below a cabin differential pressure of 2.5 psi.
When the flow control valve closes, air is directed around the forward cargo compartment liner for inflight heating.
Outflow Valves Airplanes with CPCS
The main outflow valve can be actuated by either an AC or a DC motor. The AC motor is used during AUTO and MAN AC operation. The DC motor is used during STANDBY and MAN DC operation.
Airplanes with DCPCS
The main outflow valve is actuated by DC motors in any operating mode. With either system, the forward outflow valve closes automatically to assist in maintaining cabin pressure when the main outflow valve is almost closed or when the recirculation fan is operating. The forward outflow valve is the overboard discharge exit for air circulated around the forward cargo compartment. The main 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 main outflow valve.
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