9TH-STAGE AIR 9TH-STAGE AIR
LEFT 2.9 BLEED VALVE RIGHT 2.9 BLEED VALVE
OUTLET
INLET  SERVO
PORT
PORT  PORT
STABILITY BLEED PNEUMATIC RELAY VALVE 2 %N2 BEFORE IDLE AND STEADY STATE
2.9 Bleed System Simplified Schematic Figure 2 (Sheet 2)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
FAN AIRSTREAM
9TH-STAGE AIR
LEFT 2.9 BLEED VALVE
VENT
////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
FILTERED
15TH-STAGE
AIR

SOLENOID SOLENOID NO. 2 NO. 1
DE-ENERGIZEDDE-ENERGIZED VENT
2.9 BLEED VALVE SOLENOID
9TH-STAGE AIR
RIGHT 2.9 BLEED VALVE
OUTLET
INLET SERVO
PORT

PORT  PORT
STABILITY BLEED PNEUMATIC RELAY VALVE
DECEL OR IMPENDING SURGE
2.9 Bleed System Simplified Schematic Figure 2 (Sheet 3)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
(c)  
The 2.9 bleed valve solenoid No. 1 controls the supply of 15th-stage air pressure to the right 2.9 bleed valve as well as servo pressure to the relay valve through the internal inlet cavity of the 2.9 bleed valve solenoid No. 2.

 (d)  
During initial start, solenoid No. 1 is energized, and solenoid No. 2 is de-energized. The energized solenoid No. 1 blocks muscle pressure to the right 2.9 bleed valve and servo pressure to the internal inlet cavity of solenoid No. 2. The de-energized solenoid No. 2 blocks servo pressure to the relay valve. When servo pressure to the relay valve is lost, the relay valve shifts and vents muscle pressure from the left 2.9 bleed valve. When muscle pressure to a 2.9 bleed valve is lost, the bleed valve springs open and vents 9th-stage compressor air to the fan airstream.

 (e)  
When N2 is 2% before idle and steady state, solenoid No. 1 is de-energized and solenoid No. 2 is energized. The de-energized solenoid No. 1 supplies muscle pressure to the right 2.9 bleed valve, and servo pressure to the internal inlet cavity of solenoid No. 2. The energized solenoid No. 2 supplies servo pressure to the relay valve, which shifts to block the vent port and supplies muscle pressure to the left 2.9 bleed valve. When muscle pressure is supplied, the 2.9 bleed valves close.

 (f)  
If the engine is decelerated below 81 %N2, or if an impending surge is detected by the EEC, solenoid No. 2 is de-energized opening the left bleed valve for a maximum of 2 seconds by blocking servo pressure to the relay valve.

 (g)  
Except for initial start, solenoid No. 1 is always de-energized and the right bleed valve is closed.

 (h)  
If the engine is shutdown, both bleed valves will be spring loaded open as muscle pressure to the bleed valves equals ambient pressure.

 (i)  
If 2.9 bleed valve solenoid fails to function correctly, two messages are stored in the CMCS depending upon the area of solenoid failure: ENG-# START BLEED SOL WIRING/CONTROL VALVE FAIL (CH-X) and ENG-# STABILITY BLEED SOL WIRING/CONTROL VALVE FAIL (CH-X).

 NOTE: "ENG-#" denotes engine 1, 2, 3, or 4; "CH-X" denotes
____ Channel A or Channel B of the EEC.
 B. Control
 (1)  All operations of both systems are automatic and require no operator actions.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
COMPRESSOR BLEED CONTROL SYSTEM - INSPECTION/CHECK
__________________________________________________
 1.  General
　
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