Pilot's Operating Handbook
Section 7
Description
Edition 1 - January 15, 2018
Rev. 5
Page 7.9.2
Engine bleed air system
The engine bleed air system is designed to ensure the following functions :
- to
regulate the bleed air from the engine,
- to ensure a controlled airflow in the cabin,
- to adjust the bleed air temperature for cabin heating.
To regulate the bleed air from the engine
The engine bleed air system operates from either P2.5 or P3 engine bleed ports.
The system normaly operates on the P2.5 port as long as the pressure or temperature
demands are met by this port.
If one of these demands is not met, the system automatically switches to the P3 port.
When the pressure or temperature demand can be met by the P2.5 port, the system
automatically returns to using the P2.5 port.
The Inlet Pressure Port Sensor (IPPS) measures the pressure at the P2.5 port and
sends this value to the GASC. The GASC controls the Shut Off Valve (SOV) switching
function depending on the value received. The SOV switches from P2.5 to P3 and the
BLEED HI message is then displayed.
A Non Return Valve (NRV) prevents P3 air from entering the P2.5 port when the P3
port is opened.
To ensure a controlled airflow in the cabin
The bleed air flow is controlled by the Flow Control and Shut Off Valve (FCSOV) driven
by the GASC.
To adjust the temperature of the bleed air
The bleed air outlet temperature control is ensured by the By-Pass Valve (BPV) in
association with the Main Heat Exchanger (MHX).
Based on pilot's or passengers' TEMP selector position, the GASC computes the
appropriate cabin air inlet temperature target and compares it to the actual measured
inlet temperature in order to set the BPV position. The BPV diverts the required
amount of bleed air through the MHX in order to mix it with cabin air, and then provides
air at the cabin Inlet Temperature Sensor (ITS) target.
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