AIR -COMPRESSOR BLEED CONTROL -2.9 BLEED VALVE SOLENOID AND PNEUMATIC RELAY VALVE

EFFECTIVITY BEJ ALL  75-32-00 
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AIR -COMPRESSOR BLEED CONTROL -2.9 BLEED VALVES AND THERMOCOUPLE PROBES

Purpose
The 2.9 (start/stability) bleed valves bleed 12th stage air from the high pressure compressor to increase compressor stability. The air bleeds into the fan airflow and the turbine exhaust.
Location
The 2.9 bleed valves are on the HPC case. The start bleed valve is at the 1:00 position and the stability bleed valve is at the 11:00 position.
There are two 2.9 bleed valve thermocouple probes on each valve.
Functional Description
Each valve is a poppet-type valve. A spring holds the valve open. PS3 servo air pressure pneumatically closes the valve.
The start bleed valve bleeds air to the fan airstream. The stability bleed valve bleeds air through a duct to the turbine exhaust.
The thermocouple probes send the air temperature in the bleed valve to each EEC channel. The EEC uses the air temperature to monitor the bleed valve position.
EFFECTIVITY BEJ ALL  75-32-00 
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D633W101-BEJ  Sep 05/2002 

AIR -COMPRESSOR BLEED CONTROL -2.9 BLEED VALVES AND THERMOCOUPLE PROBES

EFFECTIVITY BEJ ALL  75-32-00 
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D633W101-BEJ  Sep 05/2002 

PW4000 SERIES ENGINES

777 AIRCRAFT MAINTENANCE MANUAL

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75-32-00

Page 10 D633W101-BEJ Sep 05/2002

AIR -COMPRESSOR BLEED CONTROL -FUNCTIONAL DESCRIPTION

2.5 Bleed System -General
The EEC sends a signal to a dual-coil torque motor in the 2.5 bleed valve actuator to move a pilot valve. The pilot valve controls the servo fuel that moves the actuator piston.
Two RVDTs monitor the position of the actuator. Each RVDT sends data to an EEC channel. The EEC sends the position of the actuator and fault data to the EDIU. The EDIU sends the data to the AIMS.

2.5 Bleed System -Normal Operation
During an engine start, the 2.5 bleed valve is fully open. This lets maximum LPC airflow go overboard. At 70 -84 percent N2, the bleed valve starts to close. The valve continues to close as N2 speed increases to let more LPC airflow go into the HPC.

2.5 Bleed System -Non-normal Operation
The EEC commands the 2.5 bleed valve actuator to fully open the 2.5 bleed valve during any one of these conditions:
*
EEC makes a decision that a surge is about to occur

*
Rapid deceleration of the engine

*
EEC torque motor signal failure.

EFFECTIVITY BEJ ALL

2.9 Bleed System -General
The EEC sends a signal to the solenoids in the 2.9 bleed valve solenoid assembly. The solenoids control filtered PS3 air that closes the 2.9 bleed valves.
　
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