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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

PACK 1 TURBINE 
BYPASS VALVE 
FWD 
PACK 2 RAM AIR 
INLET ACTUATOR 
PACK 1 RAM AIR 
INLET ACTUATOR 

PACK TEMPERATURE CONTROLLERS
PACK 1 DISCHARGE TEMPERATURE SENSOR
PACK 2 TURBINE BYPASS VALVE
PACK 1 RAM AIR OUTLET ACTUATOR PACK 2 DISCHARGE TEMPERATURE SENSOR
PACK 2 RAM AIR OUTLET ACTUATOR
PACK 3 DISCHARGE TEMPERATURE SENSOR
PACK 3 RAM AIR OUTLET ACTUATOR
PACK 3 TURBINE BYPASS VALVE
PACK 3 RAM AIR
INLET ACTUATOR

AIR CONDITIONING EQUIPMENT BAY

Air Conditioning Pack Temperature Control Component Location
Figure 2

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL

 3.  Turbine Bypass Valve (Fig. 2)
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 A.  The turbine bypass valve is a motor-driven 6-1/2 inch (165 mm) butterfly valve which can be placed in any position between fully closed and fully open by the pack temperature controller. When the valve is fully closed, all the ACM compressor discharge air flows through the turbine, providing maximum cooling of the pack discharge air. As the valve is progressively opened, less compressor discharge air passes through the turbine, and there is less cooling of the pack discharge air. When the valve is fully open, no air flows through the turbine and the ACM becomes inactive.
 B.  Ganged potentiometers are coupled to the bypass valve shaft for position feedback to both pack temperature controllers and for indication on the EICAS ECS maintenance page. The valve has an external position indicator and a hex stud for manual override.
 C.  A limit switch in the valve actuator is used in conjunction with switches in the ram air inlet and exit door actuators to shut down the pack in case of improper sequencing of the turbine bypass valve and either actuator.
 D.  On the ground with power applied the turbine bypass valve will automatically open approximately 30%. This prevents an inadvertent pack overheat if pneumatic power is applied without electrical power.
 4.  Ram Air Inlet Door and Actuator (Fig. 2 and Fig. 3)
_______________________________
 A.  Each ram air inlet actuator positions a hinged door which regulates the flow of cooling air into the ram air duct and through the heat exchanger. On the ground the pack temperature controller commands the inlet actuator to drive the door to the full open position.
 B.  CLX 001-004, 101 POST-SB 21-2388; CLX 005-099; On the ground after the pack temp controller commands the inlet door to the full open position, the inlet actuator will remain unpowered.
 C.  Each inlet or exit door actuator consists of an ac motor, gear train, and drive nut and lead screw which drive the ram air doors. Ganged potentiometers coupled to the drive nut provide position feedback to the pack temperature controllers and indication on the EICAS air conditioning system maintenance page. A limit switch in the actuator is used in conjunction with a switch in the turbine bypass valve to shut down the pack in case of improper sequencing of the actuator and the bypass valve.
 5.  Ram Air Exit Door and Actuator (Fig. 2 and Fig. 3)
______________________________
 A.  Each ram air exit actuator is identical to, and interchangeable with, the ram air inlet actuators. The ram air exit actuator positions an exit door assembly directly below the heat exchanger. The exit door meters the amount of air which passes through the heat exchanger and exhausts overboard. On the ground the pack temperature controller commands the exit actuator to drive the door to the full open position.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL