RATE
SENSOR
LOAD COMPRESSOR
SCROLL HOUSING
FWD FWD B
A
APU Diverter and IGV Control System Components Figure 1 (Sheet 1)
M45075
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
SEE D
SEE E
DIVERTER VALVE
FWD DIVERTER VALVE MUFFLER
APU COMPARTMENT C
FWD
D
INLET GUIDE VANE ACTUATOR
FWD
E
APU Diverter and IGV Control System Components Figure 1 (Sheet 2)
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49-52-00
ALL ú ú 01 Page 3 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
4. Rate Sensor (Fig. 1)
___________
A. The rate sensor provides a flapper position proportional to rate of change of the venturi throat in the diverter valve control (Ps2). The rate sensor operates by sensing the pressure in the ventruri throat on one side of the control piston, while the other side of the piston senses the same pressure through a laminar restrictor. The sense line, the pneumatic tube that connects the rate sensor and the diverter valve control, delivers the Ps2 pressure. The flapper is attached directly to a lever arm which pivots on ball bearings. Compressor outlet pressure (P2) exceeding the pressure through the restrictor will cause the lever arm to move, which in turn repositions the flapper and provides air pressure (Pmdv) to open the diverter valve.
5. Inlet Guide Vane Actuator (Fig. 1)
_________________________
A. The IGV actuator is a torque motor driven, servo-type, hydraulic actuator which uses servo requlated fuel from the FMU as hydraulic fluid. The actuator is controlled by a "deflector jet" servovalve. The servovalve has an electromagnetic torque motor, which responds to signals from the APU controller. The servovalve controls the position of the actuator piston which is connected to the inlet guide vanes. The vanes modulate airflow to the load compressor according to aircraft demand.
6. Operation (Fig. 2)
_________
A. When airplane pneumatic demand is reduced, the diverter control system opens the diverter valve to dump the excess delivery flow into the APU exhaust. Certain APU operating conditions, such as main engine starts, require high air pressure but minimum airflow. When these conditions exist, the diverter valve control opens the diverter valve to dump load compressor delivery air through the diverter duct to the exhaust duct. The rate sensor supplements the diverter valve control when a sudden reduction in airflow demand occurs, such as when the airplane environmental control system is shut off. A sudden reduction in flow demand causes a very rapid pressure rise in the load compressor. The rate sensor fully opens the diverter valve to relieve pressure in the load compressor. The diverter valve control then positions the valve at the required valve position. The control system for the inlet guide vane (IGV) provides the force to position the inlet guide vanes in response to signals from the APU controller. The inlet guide vanes are controlled by the IGV actuator which provides the necessary mechanical force for rapid vane positioning. The IGV actuator moves in a direction and at a rate determined by signals from the APU controller.
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