2.9 BLEED VALVE SOLENOID

F
E
L-A4249
Compressor Bleed Control System Component Location
Figure 1 (Sheet 3)

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6.  Stability Bleed Pneumatic Relay Valve (Fig. 1)
_____________________________________
 A.  The stability bleed pneumatic relay valve is installed on the aft face of the intermediate case at the 5 o'clock position, above the 2.9 bleed valve solenoid.
 B.  The relay valve is a pneumatically signaled and pneumatically operated air selector valve. The relay valve supplies muscle pressure (15th-stage air), filtered by PS3 air filter, to and makes sure rapid opening of the left 2.9 bleed valve. For more information on PS3 air filter, refer to HPC Secondary Flow Control System (AMM 75-33-00/001).
 C.  The relay valve has three threaded ports (inlet, outlet, and servo ports) and a screened vent port. When servo pressure (15th-stage air) is cutoff from the solenoid, muscle pressure to the left 2.9 bleed valve is vented through the vent port.
 7.  Operation
_________
 A.  Functional Description
 (1)  2.5 Bleed System
 (a)  
The electronic engine control (EEC) controls the 2.5 bleed system as function of thrust lever angle, low pressure rotor speed (N1), high pressure rotor speed (N2), inlet total temperature (TT2), mach number, and altitude.

 (b)  
During engine start, the EEC regulates fuel pressure to the actuator translating the valve forward to the full open position. When the valve opens, 4th-stage compressor air is vented into the fan airstream. The valve starts to close at approximately 70 %N2 and is fully closed at approximately 85 %N2.

 (c)  
During quick engine decelerations, or if there is a possible surge, the 2.5 bleed valve will go to the fully open position.

 (d)  
During reverse thrust operation, the 2.5 bleed valve will go to the fifty percent flow position.

 (e)  
If 2.5 bleed valve actuator fails to function correctly, three messages are stored in the central maintenance computer system (CMCS), depending upon the area of actuator failure: ENG-# BLEED 2.5 TORQUE MOTOR WIRING/ACTUATOR FAIL (CH-X), ENG-# BLEED

 2.5 ACTUATOR UNIT FAIL (CH-X), and ENG-# BLEED 2.5 ACTUATOR LVDT WIRING/UNIT FAIL (CH-X).
 NOTE: "ENG-#" denotes engine 1, 2, 3, or 4; "CH-X" denotes
____ Channel A or Channel B of the EEC.
 (2)  2.9 Bleed System (Fig. 2)
 (a)  
The EEC controls the 2.9 bleed system as function of N2 and TT2 for the left 2.9 bleed valve, and as a function of N2 and low pressure compressor exit total air temperature (TT2.5) for the right 2.9 bleed valve.

 (b)  
The EEC supplies 28 volts dc to the solenoids.

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////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
FILTERED 
15TH-STAGE 
AIR 
SOLENOID  SOLENOID 
NO. 2  NO. 1 
ENERGIZED 
DE-ENERGIZED 
VENT 
VENT 
2.9 BLEED VALVE SOLENOID 
FAN AIRSTREAM  FAN AIRSTREAM 

9TH-STAGE AIR
9TH-STAGE AIR LEFT 2.9 BLEED VALVE
RIGHT 2.9 BLEED VALVE OUTLET
INLET SERVO PORT
PORT  PORT
VENT
STABILITY BLEED PNEUMATIC RELAY VALVE INITIAL START
2.9 Bleed System Simplified Schematic Figure 2 (Sheet 1)
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