Bleed Trip Sensors
Bleed trip sensors illuminate the respective BLEED TRIP OFF light when engine
bleed air temperature or pressure exceeds a predetermined limit. The respective
engine bleed air valve closes automatically.
Duct Pressure Transmitters
Duct pressure transmitters provide bleed air pressure indications to the respective
(L and R) pointers on the bleed air duct pressure indicator. The indicator is AC
operated. Differences between L and R duct pressure on the bleed air duct
pressure indicator are considered normal as long as there is sufficient air for
cabin pressurization.
Isolation Valve
The isolation valve isolates the left and right sides of the bleed air duct during
normal operations. The isolation valve is AC operated.
With the isolation valve switch in AUTO, both engine bleed air switches ON, and
both air conditioning pack switches AUTO or HIGH, the isolation valve is closed.
The isolation valve opens if either engine bleed air switch or air conditioning pack
switch is positioned OFF. Isolation valve position is not affected by the APU bleed
air switch.
APU Bleed Air Valve
The APU bleed air valve permits APU bleed air to flow to the bleed air duct. The
valve closes automatically when the APU is shut down. The APU bleed air valve
is DC controlled and pressure operated.
With both the APU and engine bleed air valves open, and the engines operating
at idle thrust, there is a possibility of APU bleed air backpressuring the 9th stage
modulating and shutoff valve. This would cause the 9th stage valve to close.
Bleed trip sensors illuminate the respective BLEED TRIP OFF light when engine
bleed air temperature or pressure exceeds a predetermined limit. The respective
engine bleed air valve closes automatically.
Duct Pressure Transmitters
Duct pressure transmitters provide bleed air pressure indications to the respective
(L and R) pointers on the bleed air duct pressure indicator. The indicator is AC
operated. Differences between L and R duct pressure on the bleed air duct
pressure indicator are considered normal as long as there is sufficient air for
cabin pressurization.
Isolation Valve
The isolation valve isolates the left and right sides of the bleed air duct during
normal operations. The isolation valve is AC operated.
With the isolation valve switch in AUTO, both engine bleed air switches ON, and
both air conditioning pack switches AUTO or HIGH, the isolation valve is closed.
The isolation valve opens if either engine bleed air switch or air conditioning pack
switch is positioned OFF. Isolation valve position is not affected by the APU bleed
air switch.
APU Bleed Air Valve
The APU bleed air valve permits APU bleed air to flow to the bleed air duct. The
valve closes automatically when the APU is shut down. The APU bleed air valve
is DC controlled and pressure operated.
With both the APU and engine bleed air valves open, and the engines operating
at idle thrust, there is a possibility of APU bleed air backpressuring the 9th stage
modulating and shutoff valve. This would cause the 9th stage valve to close.
