I A P 2 0 2 3 . 0 0 1 - A F M / I R I S T E X A N I I P A G E | 71
FOR SIMULATION USE ONLY – NOT A TRAINING AID
PRESSURIZATION SYSTEM
The pressurization system includes a control valve, a safety valve, a control valve
regulator, a differential pressure (delta P) regulator, and a solenoid dump valve.
The control valve regulator operates in conjunction with the control valve to provide
pressure control.
The control valve is interconnected to a 28 VDC dump solenoid which requires
power to close. The delta P regulator operates in conjunction with the safety valve
to provide redundant control at maximum differential pressure.
For normal operation, electrical power is removed from the dump solenoid through
the landing gear weight-on-wheels switch when the aircraft is on the ground. When
the aircraft becomes airborne, electrical power is applied to the dump solenoid
valve. This allows the control valve regulator to open and close the control valve as
necessary to control cockpit pressure.
As the aircraft approaches 8000 feet pressure altitude, the control valve regulator
will open and close the control valve to maintain cockpit pressure.
An 8000-foot cockpit altitude is maintained until a differential pressure of 3.6±0.2
psi is reached at 18,069 feet. Cockpit pressure altitude at 31,000 feet is 16,600 feet.
If cockpit pressure altitude rises above 19,000 feet, an amber CKPT ALT caution
illuminates. If cockpit differential pressure exceeds 3.9 to 4.0 psi, a red CKPT PX
warning illuminates. Cockpit differential pressure and cockpit altitude are displayed
on the EICAS display in each cockpit.
The cockpit pressure altitude is presented in feet and is placarded COCKPIT ALT, FT.
The cockpit differential pressure display, placarded ΔP, PSI, is just below the
cockpit pressure altitude display.
The pressurization control switch, placarded PRESSURIZATION, is a guarded three-
position toggle switch on the environmental control panel in the front cockpit. The
switch positions are NORM, DUMP, and RAM/DUMP.
The switch guard must be raised to select the DUMP or the RAM/DUMP position.
When the pressurization control switch is in the NORM position, the pressurization
system operates automatically.
Selecting DUMP removes power from the dump solenoid which opens the dump
solenoid electrically and opens the control valve mechanically; however, bleed air
inflow continues. Selecting RAM/DUMP opens the control valve, opens the fresh air
valve, and closes the defog valve if open; however, bleed air inflow continues.
Placing the BLEED AIR INFLOW switch to OFF will stop bleed air inflow and allow
the increase of ram air flow into the cockpit.
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