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CHAPTER 75
Engine Air
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D633A101-GUN Oct 10/2002
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CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
Purpose
The engine air system has these control functions:
* Turbine clearance
* Compressor airflow.
Turbine Clearance Control
The engine air system adjusts the clearances between the high
pressure turbine (HPT) blades and shroud and the low pressure
turbine (LPT) blades and shroud. Usually, the engine air system
decreases the clearance between the rotors and the turbine
case. This helps the engine use less fuel. The engine air system
also increases the clearance between the high pressure turbine
blades and shroud during some power conditions. This makes
sure the HPT blades tips do not rub against the case.
Compressor Airflow Control
The engine air system adjusts the low pressure compressor
(LPC) and the high pressure compressor (HPC) air flows for all
power conditions. These adjustments prevent an engine stall.
Abbreviations and Acronyms
* ADIRU - air data inertial reference unit
* DEU - display electronic unit
* EEC - electronic engine control
* EGT - exhaust gas temperature
* HMU - hydromechanical unit
* HPC - high pressure compressor
* HPT - high pressure turbine
* HPTACC - high pressure turbine active clearance control
* LPC - low pressure compressor
* LPT - low pressure turbine
* LPTACC - low pressure turbine active clearance control
* LVDT - linear variable differential transformer
* P0 - aircraft static air pressure
* PT - aircraft total air pressure
* RVDT - rotary variable differential transformer
* TAT - aircraft total air temperature
* TBV - transient bleed valve
* TRA - thrust lever resolver angle
* T3 - compressor discharge air temperature
* T25 - HPC inlet air temperature
* VBV - variable bleed valve
* VSV - variable stator vanes
* TCC - turbine case support temperature
ENGINE AIR - INTRODUCTION
EFFECTIVITY
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CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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ENGINE AIR - INTRODUCTION
ENGINE AIR - INTRODUCTION
EFFECTIVITY
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CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
75-00-00-010
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ENGINE AIR - INTRODUCTION
75-00-00
Page 4
D633A101-GUN Oct 10/2002
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
General
The electronic engine control (EEC) receives airplane system
data from the display electronic units (DEUs). The EEC uses this
data to control the engine air system. The EEC changes the
bleed airflows to change the turbine blade tips clearances. The
EEC also controls compressor airflows to prevent stall. The EEC
operates the air valves and the actuators through the
hydromechanical unit (HMU). HMU servo fuel pressure moves
the valves and the actuators.
The engine air system has these subsystems:
* Turbine clearance control
* Compressor airflow control.
See the engine and fuel control chapter for more information on
the EEC. (CHAPTER 73)
Turbine Clearance Control
The engine air system controls turbine tip clearance when it
controls the amount of cooling air that goes onto the turbine
case. Turbine blade tip clearances decrease when the turbine
case is cooled.
These are the turbine clearance control sub-systems:
* High pressure turbine active clearance control (HPTACC)
* Low pressure turbine active clearance control (LPTACC)
* Transient bleed valve (TBV).
The HPTACC system sends HPC 4th-stage and 9th-stage air to
the high pressure turbine (HPT) shroud support. The air flows
through an HPTACC valve.
The LPTACC system sends fan discharge air to the low
pressure turbine (LPT) case. The air flows through the LPTACC
valve.
The TBV sends HPC 9th stage air to the low pressure turbine
stage 1 nozzles for these two conditions:
* Engine start
* Engine acceleration.
The TBV prevents HPC stall during start and acceleration.
Compressor Airflow Control
These are the compressor airflow control subsystems:
　
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