*
HPC rotor speed (N2)
*
Fan inlet temperature (T2).
During an engine start, the EEC sends a signal to the variable stator vane actuator. Servo fuel closes the vanes. As the engine speed increases, the EEC begins to open the vanes.
For a surge or rapid deceleration, the EEC sends a signal to the variable stator vane actuator to close the vanes.
Compressor Bleed Control
The 2.5 and 2.9 compressor bleed valves bleed LPC and HPC air overboard to increase the stability of the HPC. The EEC controls the 2.5 bleed valve actuator and 2.9 bleed valves as a function of:
*
TRA
*
LPC rotor speed (N1)
EFFECTIVITY
BEJ ALL
*
HPC rotor speed (N2)
*
Fan inlet temperature (T2)
*
Altitude.
During an engine start, the EEC sends a signal to the 2.5 bleed valve actuator. Servo fuel fully opens the bleed valve. A spring holds the 2.9 bleed valves open. When engine speed increases, the EEC sends a signal to the 2.5 bleed valve actuator; and servo fuel starts to close the bleed valve. Just before idle the EEC sends a signal to both 2.9 bleed valve solenoids. Servo air closes both 2.9 bleed valves.
During a surge or rapid deceleration, the EEC opens the 2.5 bleed valve and the left (stability) 2.9 bleed valve.
Thrust Balance Control
The thrust balance air shutoff valve sends 8th stage air to the low pressure turbine through the exhaust case to reduce axial loads on the number 1 bearing. The EEC controls the thrust balance air shutoff valve through the TVBC air shutoff valve solenoid as a function of HPT temperature.
Engine Bearing Cooling
The No. 3 bearing buffer air cooler uses 4th stage air to cool 12th stage air. The cooled air flows through an external tube to the No. 3 bearing compartment.
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AIR -FUNCTIONAL DESCRIPTION
BEJ ALL POST SB 777-71-0032
Turbine Vane and Blade Cooling
The TVBC system supplies 12th stage cooling air through valves and ducts to the HPT 2nd stage vanes and blades. The EEC controls the TVC air valve actuator and TVBC air shutoff valve solenoid as a function of HPT temperature.
During low power operation, the EEC sends a signal to the TVBC air shutoff valve solenoid. Servo air closes the TVBC air shutoff valves. The EEC also sends a signal to the TVC air valve actuator. Servo fuel pressure closes the TVC air valve. If the turbine temperature is too high, the EEC removes the solenoid signal. The TVBC air shutoff valves open. The EEC also begins to modulate the TVC air valve.
BEJ ALL
Turbine Vane and Blade Cooling
The TVBC system supplies 12th stage cooling air through valves and ducts to the HPT 2nd stage vanes and blades. The EEC controls the TVBC air shutoff valve solenoid as a function of HPT temperature.
During low power operation, the EEC sends a signal to the TVBC air shutoff valve solenoid. Servo air closes the TVBC air shutoff valves. If the turbine temperature is too high, the EEC removes the solenoid signal. The TVBC air shutoff valves open.
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本文鏈接地址：777 AMM 飛機維護手冊 發動機引氣 Engine Air PW 777 AIRCRAFT MAINTENANCE MANUAL(6)
