Operation Manual Part 2

Aerosoft – Digital Aviation
CRJ-70 & CRJ-900
AOM PART 2
Systems Description
VOL
5
5-1-41
26-Jul-2017
SAFETY VALVES
Two safety valves prevent the differential pressure exceeding its maximum.
• Maximum positive differential pressure limit 8.6 PSI (tolerance ±0.1PSI)
• Maximum negative differential pressure limit -0.5 PSI
GROUND VALVE
On ground the ground valve is normally open if passenger and/or service doors are open. The valve limits
differential pressure drop due to discharging air from the avionics cooling. As soon as the passenger and
service doors are closed and locked, or the pre-pressurization mode is initiated, the valve is driven to the
CLOSED position.
In case the ground valve fails to open on ground an OVBD COOL FAIL status message appears on the EICAS
status page.
CABIN ALTITUDE LIMIT
To prevent an increase of cabin altitude after passing 14’500 ft. (±500 feet) with the aircraft, the outflow valve
closes automatically.
EMERGENCY DEPRESSURIZATION
As soon as the EMER DEPRESS pushbutton is pressed, the outflow valve is driven open. In case the aircraft
cruises at a higher altitude, the altitude limiter will limit cabin al to 15’000ft.