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BAV. The ECU sends signals to the SCV to make sure sufficient
air flows through the load compressor to prevent a surge.
Training Information Point
ECU BITE checks these bleed air system components:
* BAV
* IGVA
* SCV
* Pressure sensors.
APU BLEED AIR SYSTEM - INTRODUCTION
EFFECTIVITY
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APU BLEED AIR SYSTEM - INTRODUCTION
APU BLEED AIR SYSTEM - INTRODUCTION
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Purpose
The APU bleed air valve (BAV) isolates the APU bleed air
system from the airplane pneumatic manifold.
Physical Description
The APU bleed air valve has these components:
* Valve flow body with butterfly plate
* Spring-loaded pneumatic actuator
* Control solenoid and electrical connector
* Position indicator (visual)
* Limit switch assembly.
Location
The APU bleed air valve is in the forward right side of the APU.
Access is through the APU cowl door.
Mechanical Valve Position Indication
The APU bleed air valve has a visual position indicator on the
bottom of the BAV flow body. The APU BAV also has a visual
position indicator on the top of the limit switch assembly.
APU BLEED AIR SYSTEM - APU BLEED AIR VALVE
EFFECTIVITY
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APU BLEED AIR SYSTEM - APU BLEED AIR VALVE
APU BLEED AIR SYSTEM - APU BLEED AIR VALVE
EFFECTIVITY
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APU BLEED AIR SYSTEM - APU BLEED AIR VALVE
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General
The bleed air valve (BAV) is a butterfly type valve that isolates
the APU load compressor from the airplane bleed air system.
Operational Indications
These are the indications in the flight compartment:
* EGT indicator
* Duct pressure gage
* Dual bleed light.
Exhaust gas temperature (EGT) increases when the BAV opens.
As the inlet guide vanes (IGV) open, more air goes to the load
compressor (L/C). As more air enters the L/C duct, the pressure
increases. The EGT increase is less than for APUs on previous
737s because air is from the L/C and not from the engine
compressor.
The duct pressure gage gives the left and right bleed manifold
pressures. You know if the BAV is open if the duct pressure is
more than 0 when the APU is the only source of bleed air.
See the pneumatic system for more information on duct
pressure indication. (SECTION 36-20)
The dual bleed light comes on when these conditions occur:
* APU bleed air valve is open
* Engine 1 or 2 bleed switch is ON and the isolation valve is
open.
See the pneumatic system for more information on the dual
bleed light. (SECTION 36-20)
Control
The APU bleed air switch sends a signal to the ECU. The APU
bleed air switch is on the air conditioning/bleed air controls
panel. The switch positions are OFF and ON.
The APU ECU controls the ON and OFF signal to the APU bleed
valve solenoid. The BAV opens when the solenoid is energized
from the ECU and pneumatic power is available from the load
compressor.
The APU ECU energizes the solenoid when these conditions
occur:
* APU bleed air switch is in the ON position
* APU is not in cool down cycle
* APU speed is more than 95 percent
* Altitude is less than 17,000 ft (5,200 meters), if altitude comes
from the ADIRU
* Altitude is less than 21,000 ft (6,401 meters), if increasing
altitude and altitude comes from inlet pressure sensor (P2)
* Altitude is less than 19,000 ft (5,791 meters), if descending
and altitude comes from inlet pressure sensor (P2).
APU BLEED AIR SYSTEM - APU BLEED AIR VALVE - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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