(c)  
The valve slide directs hydraulic fluid to the hydraulic motor until the input crank moves the slide to a position where hydraulic fluid is cut off.

 (d)  
The solenoid on the control valve moves a sleeve which surrounds the valve slide. When the solenoid is powered by FSEU-1 due to a flap load relief condition the solenoid moves the sleeve and opens up the ports to the hydraulic motor.

 (7)  
Position of the flap control valve input crank is controlled by cams in the PDU.

 (a)  
Movement of the flap control lever causes rotation of the input drum of the flap PDU. Connected to this drum is the input cam. A cam follower is moved when the input cam rotates. This cam follower is linked to the input crank of the control valve and determines valve position.

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757 MAINTENANCE MANUAL
 (b)  
A followup cam is driven by the gearbox in the PDU. When the flaps are driven the gearbox rotates the followup cam which moves a cam follower. This cam follower is linked to the input crank on the control valve. As the flaps approach their commanded position the followup cam moves the linkages to return the control valve slide to its null position, shutting off hydraulic power to the motor.

 (c)  
A drum attached to the followup cam drives the cables which control slat PDU operation. Unless the flap PDU gear train has been driven there is no movement of the followup cam and the slats will not move.

 (8)  
The bypass valve removes hydraulic power from the PDU during alternate flap operation or during protective flap drive system shutdown.

 (a)  
The bypass valve is a 3-port, 2-position, motor-operated rotary valve. It has a manual override lever to allow hydraulic bypass during maintenance operations.

 (b)  
When in the bypass position the bypass valve connects the extend and retract ports of the hydraulic motor, preventing the hydraulic motor from jamming the flap drive system.

 (9)  
The resolver on the PDU transmits information on the angular position of the PDU gear train to FSEU-3. The FSEU uses this position information to control the alternate electric motor.

 (10)
 The PDU must be rigged to ensure that the PDU will move the flaps to the commanded position.

 (a)  
A rig pin inserted in the flap PDU input cam is used to adjust the cables between the flap lever and the PDU.

 (b)  
Correct alignment of the followup cam is found by lining up a mark on the PDU with a mark on the output drum.

 (c)  
Hydraulic null for the control valve is approximated by lining up a mark on the input crank with a mark on the valve body. The hydraulic null is adjusted to the followup cam by pressurizing the hydraulic system, allowing the system to stop at hydraulic null and adjusting the linkage to the control valve input crank so that the followup cam is aligned at the same time the control valve is hydraulically nulled.

 E.
Flap/Slat Depressurization Module (Fig. 10)

 (1)  
The flap/slat depressurization module is installed in the left main gear wheel well directly forward of the flap PDU. The hydraulic flow to the flap and slat hydraulic motors passes through the depressurization module.

 (2)  
The primary function of the depressurization module is to remove hydraulic power from the flap and slat drive systems during cruise or in the event of drive system failures. Depressurization at cruise reduces valve erosion and minimizes the possibility of uncommanded flap/slat motion. In the event of a flap asymmetry condition or uncommanded motion problem, the flap/slat systems are shut down hydraulically as described in 27-58-00, Trailing Edge Flap System Position Indicating - Description and Operation.

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757
MAINTENANCE MANUAL

SEE A
PRESSURE SWITCH
CAP OR PLUG
HYDRAULIC RETURN LINE
　
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