737-300/400/500
MAINTENANCE MANUAL

SEE  A 
DUCT  BOLT (EXAMPLE)  SEE  B 
GASKET NO. 1  FWD
BRACKET  A 
GASKET NO. 2 
CONNECTOR  NUT  SEE C CONNECTOR 
C 
SERVICE CONNECTION WARNING!_______ SWITCH AIR COND. PACKS OFF BEFORE SUPPLYING AIR. SWITCH BATTERY PWR. ON AND PNEUMATIC GROUND  LATCH 
CAUTION MAX. AIR PRESS: 60 PSIG MAX. AIR TEMP : 450`F _______ D  PNEUMATIC GROUND SERVICE CONNECTOR ACCESS DOOR  FWD  SEE  D  B  LATCH 
Pneumatic Ground Service Connection Figure 6 

C96721
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 36-11-05
 ALL  ú ú 01 Page 15 ú Nov 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 B.  Before air is supplied, the battery switch must be selected ON and the air conditioning pack valves selected OFF. AC power must be available for air conditioning use. The maximum pressure and temperature of the air supply provided to the ground service connection must not exceed 60 psi and 450°F, respectively.
 C.  The check valve installed inside the connector housing prevents loss of pressurized air through the connector during operation of the airplane pneumatic system. Caution must be used in the removal and replacement of connector so that the two gaskets are not damaged or misaligned during operation.
 10. APU Check Valve (Fig. 7)_______________
 A.  A check valve is installed in the APU bleed air duct just downstream of the APU bleed air valve. The check valve prevents backflow of air from the pneumatic crossover duct to the APU.
 11. APU Bleed Air (Shutoff) Valve (Fig. 7)_____________________________
 A.  The APU bleed air valve is a modulating valve that is used to control bleed air flow from the APU to the airplane pneumatic system. The valve is located at the bleed air duct on the aft side of the APU compartment forward bulkhead. The pneumatically operated solenoid-controlled valve is controlled by a switch on the pilot's forward overhead panel.
 B.  When the APU is in operation at or above 95 percent, APU bleed air can be obtained with the APU bleed switch put to the ON position. The air from the APU is automatically regulated by APU components and by APU bleed valve modulation. This is to make sure that maximum APU bleed air is available without overloading the APU. A pressure relief valve provides safety relief at 80 psi.
 12. APU Pressure Relief Valve (Fig. 7)_________________________
 A.  The APU pressure relief valve is a spring loaded closed, bleed-off type regulator, which contain a poppet valve, valve seat, and spring. Its purpose is to vent off excess pressure in the pneumatic duct to prevent an overpressure condition which can cause the ducting to rupture. The relief valve is mounted to a boss on the APU pneumatic duct in the tail compartment and is set to relieve at approximately 80 psig. The pressure relief valve can be accessed through the stabilizer trim access door.
 13. Bleed Air Isolation Valve (Fig. 8)_________________________
 A.  The bleed air isolation valve is installed in the center of the crossover duct to separate the left and right pneumatic systems or to connect them when necessary. The isolation valve is a 115-volt, single-phase, motor-operated butterfly valve. The valve normally stays closed unless a cross-feed of bleed air is necessary.
 B.  The valve is controlled by a three-position (OPEN-AUTO-CLOSE) switch on the P5 panel. It is connected electrically through the left and right pack switches and also through the No. 1 and No. 2 engine bleed switches.
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 36-11-05
 ALL  ú ú 01 Page 16 ú Jul 15/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
APU CHECK VALVE
APU MANIFOLD DUCT
APU CHECK VALVE
SEE A SEE B
FWD
V-BAND CLAMP HINGE PIN
(2 LOCATIONS) BOSS
A
APU PRESSURE RELIEF VALVE
PACKING RING
LOCKWIRE
MOUNTING BOSS
APU PRESSURE RELIEF VALVE
SEE C
APU MANIFOLD 
DUCT 
　
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