A-A
Intermediate Pressure Check Valve
Figure 7
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A
747-400
MAINTENANCE MANUAL
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ACTUATOR PRESSURE REGULATINGPRESSUREVALVE ACTUATORTUBE HOUSING PRESSUREREGULATING VALVE
SEE A SEE B PRESSUREFWD REGULATINGVALVE
A
POSITION SWITCHESCLOSED
MANUAL
OPERATION
HEX NUT
AMBIENT
1
2
3
TERMINALBLOCK
VISUAL
UP POSITION
POSTION
OPEN ACTUATOR SERVO PRESSURE(FROM PRESSURECONTROLLER)
ENGINEBLEED TO PRECOOLERAIR
SWITCHES VALVEVALVE
INDICATOR
INLET OUTLET
SCHEMATIC
PRV
B
B
Pressure Regulating Valve
Figure 8
A
747-400
MAINTENANCE MANUAL
A. The PRV is installed on the engine in the 10 o'clock position. The PRV is a 5.5 inch butterfly valve. A piston type actuator drives the butterfly valve through a link and crank. The valve contains two plunger-type position switches. Both the open and closed position switches send signals to the ASCTU. The PRV is similar to the HPSOV.
(1)
The PRV has a valve shaft extension that will permit you to manually open or close the valve with a wrench. The valve actuator case has a lockpin that can be removed. If the valve must be locked in the closed position, the lockpin is removed from the actuator case. This lets the valve control pressure go to ambient. The pin is installed through the valves' manual control linkage into a threaded hole to lock the valve in the closed position. The valve housing has markings, (OPEN and CLOSED), to give visual indication of the valve position.
(2)
The pneumatic servo pressure from the pressure controller will cause the PRV to move to the open or closed position. This pressure enters the valve actuator and acts against a spring and inlet pressure loaded piston. Sufficient servo pressure (10 psi minimum) from the controller is needed to operate the actuator piston and the attached links and cranks to open the valve. The valve is spring loaded to the fully closed position if no servo pressure is supplied.
6. Pressure Controller (Fig. 9)
___________________
A. The PRV (or pressure) controller is installed on the engine in the 7 o'clock position on the foward face of the main gearbox. The PRV controller senses pressure upstream and downstream of the PRV, receives inputs from the ASCTU, and sends pneumatic signals to the PRV. These pneumatic signals will cause the PRV to open or close.
(1)
The PRV controller has a cast aluminum body with an internal sensing diaphragm, and a shutoff solenoid. It has three pneumatic ports:
-supply pressure from upstream of the PRV
-regulated pressure from downstream of the PRV
-actuation pressure that is sent to the PRV.
(2)
The PRV controller adjusts PRV servo air pressure when PRV downstream pressure changes. This controls the position of the valve. The PRV downstream pressure is regulated to maintain precooler inlet pressure at 59-69 psig. If there is an overpressure condition in the precooler inlet, the controller sends actuation pressure to ambient. This will cause the PRV to close.
7. Engine Bleed Air Precooler (Fig. 10)
__________________________
A. The engine bleed air precooler is installed on the bottom of the strut and above the engine compressor case. The precooler is an air-to-air heat exchanger of the crossflow type. The precooler consists of layers of fins that are separated by parting plates and closure bars. The engine bleed air from the HP/IP manifold enters through the inlet duct. The fan air inlet and outlet are single connections, one on each side of the precooler. There is a pressure sense port on the precooler outlet flange that supplies servo pressure to the fan air modulating valve. There is a second pressure sense port on the precooler inlet flange that supplies the manifold pressure reference for the PRV controller. The approximate weight of the precooler is 130 lb (59 Kg).
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