PNEUMATIC SYSTEM SCHEMATIC
Air Supply Distribution System
Figure 1 (Sheet 2)
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B49948
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MAINTENANCE MANUAL
E. The precooler reduces the temperature of the bleed air extracted from the engines. It uses engine fan air to remove heat from the bleed air. The fan air temperature sensor measures the temperature of the bleed air downstream of the precooler and varies signal pressure to the fan air modulating valve. The fan air modulating valve controls the amount of fan air that goes through the precooler.
F. The bleed air from the precooler, goes up through the strut and the PRSOV before it enters the airplane pneumatic ducts. The PRSOV controls the pressure in the pneumatic ducts. This valve also prevents reverse flow back to the engine. It has an override function to permit reverse flow during engine start. The valve can be closed during engine operation to isolate the system or if there is an overheat condition.
G. The APU can supply air to the pneumatic system when the airplane is on the ground or as a secondary source during flight. The air from the APU goes through the APU isolation valve and the APU check valve. Then it enters the pneumatic crossover duct. When the isolation valve is closed, the APU will be isolated from the pneumatic system. The check valve prevents reverse air flow from the engines to the APU.
H. When the airplane is on the ground, a pneumatic ground cart can supply air for the pneumatically operated systems. The ground cart supplies compressed air through two 3-inch diameter connectors on the aft side of the left air-conditioning bay door (Fig. 3). Air enters through the connectors and then goes into the air supply crossover duct.
PRESSURE REGULATING
AND SHUTOFF VALVE
TO COWL
THERMAL ANTI-ICE
TO STRUT HYDRAULICAIR SUPPLY
RESERVIOR PRECOOLER FAN AIR
FAN AIR TEMPERATURE MODULATING
SENSOR VALVE
INTERMEDIATE TO STARTERPRESSURE
CHECK VALVE PRESSURE REGULATING VALVE
HIGH PRESSURE
SHUTOFF VALVE
HIGH PRESSURE BLEED PORTS (4 PLACES)
INTERMEDIATE PRESSURE BLEED PORTS (2 PLACES)
Engine Air Supply System
Figure 2
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AIR APU
CONDITIONING PACKS (3 LOCATIONS) PNEUMATIC GROUND AIR CONNECTORS
SEE A
FWD
CHECK VALVE INBD
GROUND AIR CONNECTORS
SEE B
PNEUMATIC GROUND AIR CONNECTORS
FLANGE
A
CONNECTOR
1
CHECK VALVE
GROUND AIR CONNECTOR
B
CONNECTOR 1
CONNECTOR WITH FLANGE 2 CONNECTOR WITHOUT FLANGE 2
Pneumatic Ground Air Connection
Figure 3
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I. The ENGINE BLEED control switches are installed on the bleed control module (P5 overhead panel) in the flight compartment (Fig. 4). The switches permit operation of the individual bleed air systems. The wing isolation valve switches (L ISLN and R ILSN) permit you to isolate either the left or right wing pneumatic manifolds. The APU switch will open the APU shutoff valve and permit the APU to supply pressure to the pneumatic system. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747-400 AMM 飞机维护手册 气动系统 PNEUMATIC SYSTEM(25)
