777 AMM 飞机维护手册 发动机引气 Engine Air PW 777 AIRCRAFT MAINTENANCE MANUAL(7)

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Turbine Case Cooling
Fan air flows through valves and the manifolds to cool the HPT and LPT cases. The EEC controls the TCC air valve actuator as a function of altitude and N2.
During takeoff, climb, and cruise, the EEC sends signals to the torque motors in the TCC air valve actuator. Servo fuel pressure moves the HPT and LPT valves.
Engine External Accessories Cooling
Fan air continuously flows through accessory cooling tubes to specific engine components for cooling.
The nacelle zone ventilation shutoff valve controls the flow of fan air to cool the area outside of the HPC and the diffuser cases. The EEC controls the valve as function of altitude. Servo air pressure closes the valve.
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AIR -FUNCTIONAL DESCRIPTION

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AIR -FUNCTIONAL DESCRIPTION

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AIR -COOLING -INTRODUCTION

Purpose
The cooling system supplies and controls the airflow for internal and external cooling. The cooling system has these subsystems:
*
Engine external accessories cooling

*
Engine bearing cooling

*
Turbine case cooling

*
Turbine vane and blade cooling.

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AIR -COOLING -INTRODUCTION

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AIR -ENGINE BEARING COOLING -GENERAL DESCRIPTION

Purpose
The engine bearing cooling system pressurizes the bearing carbon seals and cools the No. 3 bearing compartment.
General Description
Compressor air pressurizes the main bearing carbon seals to make sure that the oil does not enter the air stream. Low pressure compressor (LPC) bleed air pressurizes the carbon seals around the No. 1 and 2 bearing. Ninth stage HPC bleed air pressurizes the No. 1.5 bearing carbon seal. LPC air also pressurizes the No. 4 bearing carbon seal.
The No. 3 bearing cooling system uses cooled 12th stage HPC bleed air to pressurize the No. 3 bearing carbon seals.
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