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APU AIR -APU AIR SUPPLY SYSTEM -FUNCTIONAL DESCRIPTION
When the ADPs and the air conditioning packs operate, the APUC selects the ADP/ECS mode and opens the IGVs the amount necessary to supply both of these systems.
Inlet Guide Vane Control Logic
After pneumatic mode selection, the APUC uses inlet temperature and inlet pressure data to adjust the IGV angle for the correct airflow. For the ECS and ADP/ECS modes, the APUC also uses ECS inputs and APU total operating hours to control the IGV position.
During APU start, the APUC closes the IGVs to keep APU loading to a minimum. At 95 percent RPM, the IGVs can open to supply pneumatic airflow.
Turbine Inlet Temperature Calculation
The APUC calculates turbine inlet temperature (T4) from these inputs:
*
Air inlet temperature (T2).
*
Air inlet pressure (P2)
*
Exhaust gas temperature (EGT)
*
Total pressure
*
RPM.
If a heavy APU load causes a T4 increase, the APUC starts to close the IGVs. If T4 continues to increase, the APUC can close the IGVs completely. This gives APU output priority to electrical power generation.
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APU AIR -APU AIR SUPPLY SYSTEM -FUNCTIONAL DESCRIPTION
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D633W101-BEJ Jan 05/2002
APU AIR -APU SURGE BLEED SYSTEM -INTRODUCTION
Purpose
The APU surge bleed system releases load compressor air that the aircraft pneumatic system does not use. This air flows outboard through the APU exhaust.
The APUC controls the surge bleed system.
Components
Surge bleed system components are on a common pneumatic cluster. These are the components:
*
Surge control valve and actuator
*
Inlet pressure sensor
*
Total pressure sensor
*
Differential pressure sensor.
Control
The APUC controls the surge bleed system.
Training Information Point
These are the surge bleed system LRUs:
*
Pneumatic cluster
*
Surge control valve
*
Pressure sensor pallet
*
Each pressure sensor.
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APU AIR -APU SURGE BLEED SYSTEM -INTRODUCTION
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D633W101-BEJ Jan 05/2002
APU AIR -APU SURGE BLEED SYSTEM -SURGE CONTROL VALVE
Purpose
The surge control valve releases pneumatic pressure from the load compressor. This keeps a minimum flow of air through the load compressor to prevent compressor surge.
Physical Description
The valve is a butterfly type valve that is spring-loaded open. The surge control valve actuator is on the bottom of the valve. A two-stage servo valve controls the actuator.
Location
The valve is on the aft part of the pneumatic cluster.
Functional Description
The APUC controls a torque motor on the servo valve. This motor controls high pressure fuel from the APU fuel system to open or close the surge control valve. The valve moves between 10 degrees (open) and 90 degrees (closed). An LVDT supplies valve position feedback to the APUC.
Air that flows through the surge control valve goes overboard through the exhaust duct.
Training Information Point
A valve position indicator shows valve position.
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APU AIR -APU SURGE BLEED SYSTEM -SURGE CONTROL VALVE
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APU AIR -APU SURGE BLEED SYSTEM -PRESSURE SENSORS
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