5. Operation
_________
A. Functional Description
(1)
All of the engine bleed air goes through the precooler before it goes into the airplane pneumatic ducts. The quantity of cool fan air that goes through the precooler is controlled by the position of the fan air modulating valve. The fan air temperature sensor measures the temperature in the pneumatic duct and controls the position of the fan air modulating valve.
(2)
The fan air modulating valve (FAMV) is opened and closed by the signal pressure from the fan air temperature sensor (FATS) and by bleed air pressure from the precooler. When the temperature of the bleed air sensed by the FATS is below 320°F (160°C), the FAMV is closed. When the temperature is above 380°F (193°C), the FAMV is fully open. The fan air modulating valve will regulate if the sensed temperature is between 320°F (160°C) and 380°F (193°C). The indicated temperature on the EICAS ECS maintenance page may vary between 250°F (121°C) and 380°F (193°C) while the fan air modulating valve regulates between open and closed.
(3)
The pressure signal will change in proportion to the temperature. The pressure signal is sent through the signal pressure tube. The cooling air tube supplies the sensor with pressurized air; the air in this tube is cool and decreases the temperature of the sensor.
(4)
After the fan air modulating valve receives the pressure signal, it uses precooler pressure to change the position of the butterfly valve. As the valve moves to the open position, more fan air is permitted to go through the precooler. The fan air then flows overboard through a duct in the core cowl.
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36-12-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
PRECOOLER AND FAN AIR MODULATING VALVE
SEE A
PW 4000
PRECOOLER
FAN AIR MODULATING VALVE
FWD
PRECOOLER AND FAN AIR MODULATING VALVE
A
Engine Bleed Precooler System Figure 1 (Sheet 1)
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36-12-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
FAN AIR TEMPERATURE SENSOR
SEE B
PW 4000 (INBOARD NACELLE STRUT)
FAN AIR TEMPERATURE SENSOR
SEE B
PW 4000 (OUTBOARD NACELLE STRUT)
FAN AIR TEMPERATURE SENSOR
FAN AIR TEMPERATURE SENSOR B
Engine Bleed Precooler System
Figure 1 (Sheet 2)
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36-12-00
ALL ú ú 03 Page 4 ú Jun 18/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
ENGINE BLEED AIR PRECOOLER - REMOVAL/INSTALLATION
_________________________________________________
1. General_______
A. This procedure contains two tasks. The first task removes the precooler. The second task installs the precooler. This procedure also contains a test for the precooler installation.
B. The precooler is installed on the bottom of the strut above the engine compressor case. To get access to remove the precooler, it is necessary to do the steps that follow:
(1)
Open the two halves of the thrust reverser.
(2)
Open the panel for the left core cowl.
(3)
Remove the panel for the right core cowl.
(4)
Open the access panel for the fan air temperature sensor.
(5)
Remove the fan air modulating valve and the three tubes that connect to it.
C.
It is necessary to replace the O-rings on the two tee fittings that are installed on the precooler.
D.
The precooler installation is the same on each engine.
TASK 36-12-01-004-001
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