21-30-00
ALL ú ú 01 Page 1 ú Nov 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
PRESSURIZATION CONTROL SYSTEM - DESCRIPTION AND OPERATION
_________________________________________________________
1. General_______
A. The pressurization control system is an electrically operated and electronically controlled system, which meters the exhaust of ventilating air to provide controlled pressurization of the passenger and control cabins, the electronic compartment, both cargo compartments, and the lower nose compartment. The pressurization control system consists of a pressure control panel, a pressure controller, and a cabin pressurization outflow valve (Fig. 1). The pressurization control system characteristics are as follows:
(1)
The system has four operating modes; automatic, standby, ac manual and dc manual. Automatic is the normal operating mode. Standby is a semiautomatic backup. The ac manual and dc manual modes are backups for automatic and standby modes. Normal operation is automatic and normally requires no adjustment by the flight crew throughout the flight except for barometric correction.
(2)
Both the ac manual mode and the dc manual mode provide direct control to the outflow valve through separate electrical actuators. The manual modes back up the automatic and standby systems.
(3)
In the automatic mode, the system accepts manual inputs of planned flight altitude and landing altitude before takeoff. It then determines the lowest possible cabin pressure that can be maintained during airplane high altitude flight and schedules any necessary change in cabin pressure during the flight without any action by the crew. The system can also be reset if a change in planned flight altitude or landing field altitude is made.
(4)
Cabin pressure rate of change is automatically controlled in AUTO. Rate of change may be manually controlled in STBY.
(5)
Barometric correction for automatic and standby pressure control assures that cabin pressure and landing field pressure are approximately the same at landing.
(6)
A mode selector switch on the control panel permits selection of four modes of operation plus a check position for system test.
(7)
The STANDBY system automatically takes over to control cabin pressure according to cabin altitude and rate of cabin pressure change settings if certain limits are exceeded in AUTO. In addition, a manual transfer can be made from AUTO to STBY, if desired, by use of the mode selector switch.
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21-31-00
ALL ú ú 01 Page 1 ú Jun 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
SAFETY RELIEF VALVE
VACUUM SEE A RELIEF VALVE
CABIN
PRESSURIZATION
OUTFLOW VALVE
SEE B EQUALIZATION VALVE SCREEN AFT CARGO COMPARTMENT
FORWARD
OVERHEAD PANEL
SEE C
PRESSURE A
CONTROLLER
AURAL WARNING
DEVICE BOX
AUXILIARY
STATIC PORT
CABIN
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