5.  Operation
_________
 A.  Static air or ram air goes into the first-stage impeller from the compressor plenum. The first-stage impeller compresses the air. The compressed air moves through diffuser and crossover ducts to the second-stage compressor. The second-stage compressor also compresses the air. This compressed air moves through the second diffuser to the turbine plenum. Some of the air flows to the combustion chamber. The remaining air is available for bleed air. The fuel atomizer supplies fuel to the combustion chamber. The igniter plug supplies a spark for the ignition of the fuel-air mixture. Ignition is only necessary to start the APU. From the combustion chamber, the hot combustion gases move through the torus assembly where a series of nozzles turns the gases to the turbine wheel. The hot gases turn the turbine wheel. The turbine wheel changed the energy of combustion to mechanical power. The APU uses the mechanical power to turn the compressors, APU electrical generator and other necessary components. The hot gases from the turbine wheel come out of the APU through the exhaust port.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 APU ENGINE - MAINTENANCE PRACTICES
__________________________________
 1.  General
_______
 A.  This procedure gives the steps to manually turn the APU. To manually turn the APU, you remove the starter motor and turn the APU by the use of a socket on the starter drive pawl nut.
 TASK 49-21-00-982-001
 2.  Manually Turn the APU (Fig. 201)
_____________________
 A.  References
 (1)  AMM 49-41-11/401, Starter Motor
 B.  Access
 (1)  
Location Zones
 703 APU Compartment

 (2)  
Access Panels
 3804 APU Cowl Door

 C.  Procedure
 S 022-004
 (1)  Remove the starter motor (AMM 49-41-11/401).
 (a)  Install 3/8 inch socket onto starter drive pawl nut. Turn socket clockwise with 1/4 inch drive wrench.
 NOTE: When you turn the starter drive pawl nut
____ clockwise, the APU will turn.
 NOTE: When you turn the starter drive pawl nut
____ counterclockwise, the nut may come loose.
 S 412-005
 (2)  Install the starter motor (AMM 49-41-11/401).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

737-300/400/500
MAINTENANCE MANUAL

SEE  A
SEE  B  FWD 
CSEE MANUALLY TURN THE APU LOCATION TO  MOUNT PAD  STARTER DRIVE PAWL NUT A 

STARTER
MOTOR

B
FWD
LOCATION TO MANUALLY TURN THE APU
C
Location to Manually Turn APU Figure 201
F82502
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
APU ENGINE - INSPECTION/CHECK
_____________________________
 1.  General
_______
 A.  This procedure gives the steps to do an inspection of the internal parts of the APU engine. To do this inspection, you use a borescope set to see the APU engine.
 B.  The inspection looks at these internal parts of the APU engine:
 (1)  
The combuster unit.

 (2)  
The turbine torus assembly.

 (3)  
The guide vanes of the turbine nozzle assembly.

 (4)  
The blades of the turbine wheel.

 (5)  
The trailing edge of the turbine exducer.

 (6)  
The housing assembly for the second stage diffuser.

 TASK 49-21-00-206-006
　
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