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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
UPPER SHROUD  CONTROL LINE FOR THE BLEED AIR  SEE  C  SEE  A 
AIR DUCT BLEED 
FWD 
TURBINE PLENUM  SEE  B 
A 
CONTROL LINE FOR THE BLEED AIR  BLEED AIR VALVE SOLENOID 
AIR DUCT BLEED ELECTRICAL PLUG 
CONTROL AIR LINE 
VALVE BLEED AIR  AIRPLANE DUCT PNEUMATIC 
AIR INLET LINE  INBD 
DIFFERENTIAL REGULATOR B Figure 1 (Sheet 1) APU Bleed Air System Component Location PRESSURE  FWD 

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
FORWARD OVERHEAD PANEL, P5
SEED
FLIGHT COMPARTMENT 
APU CONTROL 
THERMOSTAT 
RECIRC FAN 
OFF 
THERMOCOUPLE  NORMAL 
PROBE 
UPPER  40  60 
SHROUD  OVHT 
80 
PSI 
0  100 
EXHAUST  TEST 
PORT  L PACK  ISOLATION  R PACK 
SURGE BLEED  OFF  VALVE  OFF 
VALVE  NORMAL  CLOSE  NORMAL 
HIGH  AUTO  HIGH 
CONTROL LINE 
AIR LOAD FOR THE BLEED  ICE ANTI WING  TRIP OFF PACK  OPEN  TRIP OFF PACK  ICE ANTI WING 
WING-BODY  TRIP  WING-BODY 
OVERHEAT  OVERHEAT 
BLEED  BLEED 
TRIP OFF  TRIP OFF 
RESET 
OFF  OFF 
3-WAY 
SOLENOID  ON  ON 
VALVE  1  BLEED APU  2 
FWD  BLEED AIR 
SWITCH 
C  D 
APU Bleed Air System Component Location 
Figure 1 (Sheet 2) 

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 ú ú 01 Page 3 ú Mar 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FORWARD OVERHEAD PANEL, P5
SEED
FLIGHT COMPARTMENT
RECIRC FAN OFF
ETC NORMAL
THERMOCOUPLE PROBE 40 60 OVHT 80
PSI 0 100
UPPER
SHROUD
TEST
L PACK R PACK
ISOLATION OFF VALVE OFF
EXHAUST
NORMAL CLOSE NORMAL PORT
HIGH AUTO HIGH
WING WINGPACKPACK OPENANTI ANTI
TRIP OFF ICE TRIP OFF ICE
SURGE BLEED
WING-BODYWING-BODY TRIP OVERHEATOVERHEAT
VALVE
BLEED TRIP OFF BLEED TRIP OFF
3-WAY
RESET SOLENOID
OFF OFF
VALVE
ON ON 1 APU 2 BLEED FWD
BLEED AIR C SWITCH
D
APU Bleed Air System Component Location
Figure 1 (Sheet 3)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
B.  When the APU engine speed is more than 95%, the solenoid for the bleed air valve is energized. When the solenoid for the bleed air valve is not energized, the switcher valve moves the control air to the bottom of the actuator diaphragm. This keeps the main valve closed. Control air from upstream of the main valve moves to the two sides of the diaphragm of the rate control valve. The pressure of the two sides of the diaphragm is the same. This keeps the poppet valve closed. When the BLEED AIR switch is moved to the ON position, the solenoid for the bleed air valve is energized. This opens the check valve and closes the switcher valve. Also, the control air from the bottom of the actuator diaphragm moves to the top of the actuator diaphragm and opens the main valve. When the main valve opens, the pressure at the rate control valve will decrease in proportion to the quantity of bleed air from the APU. Since the adjustable orifice keeps to a limit the bleed air from the top of the rate control diaphragm, the rate control diaphragm will move down and open the poppet valve. Control air will bleed from the actuator to control the rate that the main valve opens. Also, this controls how much the main valve opens to prevent an overload on the APU. While the pressure of the control air bleeds from the top of the rate control diaphragm, the poppet valve will close slowly. While the poppet valve closes, the pressure from the control air in the actuator will increase and open the main valve more. When the poppet valve is fully closed, the main valve is fully open. The adjustable orifice is usually set to make the main valve open in 12 to 14 seconds.
　
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