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21-51-00
ALL ú ú 01F Page 7 ú Feb 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
C23413
A
747-400
MAINTENANCE MANUAL
C. When the normal flow solenoid is energized, the flow control and shutoff valve is partially closed, reducing air flow through the valve by approximately 33%. The normal flow solenoid is controlled automatically by the pack temperature controllers.
D. The valve closed limit switch provides a pack off signal to the pack temperature controllers and to the ECS miscellaneous circuit card. The signal is used for pre-positioning ram air inlet and exit doors and turbine bypass valve before starting the pack (Ref 21-62-00).
E. Test ports located on the valve assembly allow a check of valve functions on the ground. The valve flow control schedule and the operation of the open/close actuator and shutoff and normal flow solenoids can be ground checked with the valve installed.
3. Pack Dump (SMACCS) Valve (Fig. 2)
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A. There is a pack dump valve (also refered to as a Smoke Mode Air Conditioning Control System, or SMACCS valve) for pack 1 and pack 3 located adjacent to and just downstream of the flow control and shutoff valve.
B. The valve is a 7-inch diameter disk type and is electrically operated with 115 volts ac power. A visual position indicator gives the valve position. The valve has an override handle for manual operation.
C. The pack dump valves restrict airflow to air conditioning packs 1 and 3. The valve restricts the airflow to the pack with a hole in the disk when the valve is closed.
4. Heat Exchanger (Fig. 2)
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A. The dual heat exchanger has primary and secondary cores. Both cores are of counterflow design of plate and fin construction. The primary heat exchanger cools engine bleed air from the flow control and shutoff valve and the secondary heat exchanger cools the air cycle machine compressor discharge air. Both heat exchangers transfer heat to ram air in flight, or to the fan-forced cooling air on the ground.
5. Air Cycle Machine (Fig. 2)
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A. The air cycle machine (ACM) houses a turbine, a compressor, and a fan, all mounted on the same shaft. Air from the secondary heat exchanger is expanded across the turbine to provide the rotational drive for the entire ACM assembly. The air which passes through the turbine is cooled by the expansion. The turbine can be bypassed when this cooling is not needed.
B. The compressor boosts the pressure of the air from the primary heat exchanger before it enters the secondary heat exchanger. A check valve allows the compressor to be bypassed when the turbine is not active.
C. The fan forces air through the ram air duct when the airplane is on the ground. In flight, ram air bypasses the fan through a cooling air check valve.
6. Fan Diffuser and Inlet Housing (Fig. 2)
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A. The fan diffuser and inlet housing is a fiberglass housing mounted on the air cycle machine to form the inlet volute and discharge diffuser for the cooling air fan.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
21-51-00
ALL ú ú 01F Page 8 ú Feb 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
B. A 3/8-inch mesh screen is located in the ACM fan inlet. It prevents foreign object damage to the ACM fan section or heat exchanger.
7. Compressor Bypass Check Valve (Fig. 2)
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A. The compressor bypass check valve is a spring-loaded flapper valve installed in the compressor bypass line. It permits flow to be bypassed around the compressor when the ACM turbine is bypassed.
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