29-11-08
 ALL  ú ú 01 Page 2 ú Dec 10/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

ELECTRICAL 
COMPONENT 
AIR FILTER  ASSEMBLY 
AND WATER 
SEPARATOR 
SEE  C 

SHUTOFF AND SPEED 
CONTROL VALVE UNIT 
SHUTOFF VALVE 
POSITION SWITCH 
GEARBOX 
ENGINE BLEED 
AIR PNEUMATIC 
DUCT 
____NOTE:  SYSTEM 1 SHOWN, 
SYSTEM 4 SIMILIAR  FWD 
C 
Air-Driven Pump Turbine Drive 
Figure 1 (Sheet 2) 

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 29-11-08
 ALL  ú ú 01 Page 3 ú Dec 10/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 C.  The control system has a shutoff and speed control valve unit, a governor, an acceleration control unit, an electrical component assembly, and a three-position control switch. The electrical component assembly has a run-continuous solenoid valve and a run-on-demand solenoid valve. It accepts signals from the control switch in the flight compartment and the HYDIM.
 (1)  
The shutoff and speed control valve unit has two butterfly valves and their actuators installed on the same housing. The shutoff valve is below the speed control valve. The shutoff valve has a position switch that is used by the central maintenance computer system (CMCS).

 (2)  
The governor has a speed controller which is attached by a gear to the turbine rotor. The speed controller controls the turbine speed by adjusting the pressure in the speed control valve actuator. This will change the position of the speed control butterfly valve.

 (3)  
The acceleration control unit controls the acceleration of the turbine assembly when it is started. This will decrease the shocks to mechanical and hydraulic systems.

 3.  Operation (Fig. 2)
_________
 A.  Functional Description
 (1)  
The operation of the turbine drive is controlled by the position of the switch in the flight compartment. If the switch is put in the OFF position the turbine drive will not operate and it will stop if it is in operation.

 (2)  
When the control switch is in the AUTO position, the ADP will operate during the conditions that follow:

 -
The pressure of the EDP output decreases below 1,400 psi for more than 0.3 second. The ADP will operate for 14 seconds after the EDP output increases above 1,600 psi

 -
The trailing edge flaps are in operation

 -
The trailing edge flaps are put in a non-zero position and the airplane is in the air. The ADP will operate for 10 seconds after the flaps are put in the zero position

 -
The fuel cutoff actuator is in the CUTOFF position.

 (3)  
An air pressure signal is then sent through the air filter and water separator. The acceleration control unit receives the signal and decreases the acceleration rate. The shutoff valve is then put in the open position to permit engine bleed air to flow to the turbine drive. The turbine drive will get to 70 percent of its output speed in 1.2 seconds. The governor unit will control the speed when the turbine drive is in operation.

 (4)  
A malfunction of the governor unit or the speed control valve will cause the turbine drive to overspeed. The overspeed trip valve will stop the turbine drive when the speed gets to 32,000-34,000 rpm. This will prevent damage to the turbine assembly. The overspeed trip valve must be reset before the turbine drive can operate again (Refer to 29-11-08/201 for the reset procedure).

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 29-11-08
 ALL  ú ú 02 Page 4 ú Feb 10/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

Air-Driven Pump Turbine Drive Control Switches Location
Figure 2

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