B.  A flap control quadrant located directly above the flap control unit transfers cable motion through a shaft, a link and a bellcrank to position the trailing edge flap control valve slide. Pressurized fluid from the control valve drives the flap hydraulic motor. As the hydraulic motor drives the flap system, it also drives the power unit follow-up drum. Follow-up motion is transmitted by flap follow-up cables (WFFA and WFFB) to the control valve follow-up drum. Rotation of the control valve follow-up drum transmits motion through a cam, cam roller, and link to the bellcrank. Rotary motion from the bellcrank returns the control valve to the neutral position preventing fluid flow to the flap hydraulic motor. The control valve follow-up drum also transmits motion through a second cam and cam roller to control the leading edge flap control valve.
C.  The flap control unit is mounted on the right wheel well ceiling near the aft bulkhead. Mounted on the forward end of the follow-up shaft is an actuating cam for the flap limit switches, the landing gear warning horn switches, the takeoff warning switch, the mach trim switch, and the flap 10-degree switch.

G11577
531  Flap Control Unit 
Aug 15/71  Figure 5  27-51-0 
Page 11 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

6.  Flap Control Valve
A.  The flap control valve is a mechanically operated slide valve used to control directional movement of the trailing edge flaps. The valve is attached to the flap control unit located in the right wheel well. The control valve is driven by the control unit linkage.
B.  The control valve consists of a housing, a sleeve and a slide assembly. Ports are provided in the housing and sleeve for passage of fluid to and from the flap hydraulic motor. Moving the valve slide outboard from its neutral position pressurizes valve port B and connects valve port A to the hydraulic system A return line. This allows the flaps to retract. When the valve slide is moved inboard from its neutral position, valve port A is pressurized and valve port B is connected to the return line. In this valve slide position, the flaps will extend. When the valve slide is in the neutral position, the flow of hydraulic fluid to the flap hydraulic motor is blocked.
C.  The control valve includes a hydraulic solenoid valve activated by the flap load limiter system. The solenoid valve, when energized, repositions the flap control valve to the 30-unit position from the 40-unit position.
7.  Flow Limiting Valve
A.  The operating speed of the trailing edge flaps is controlled by a flow limiting valve which is installed in the pressure line to the flap control valve upstream from the valve. The valve controls the rate of fluid flow to the flap hydraulic motor. At normal temperatures with a hydraulic pressure between 200 and 3000 psi, fluid flow to the motor is regulated at 9.0 to 10.5 gpm.
8.  Flap Bypass Valve
A.  The flap bypass valve is a motor-operated, two position valve which interconnects the flap hydraulic motor pressure and return ports during operation of the flap alternate drive system (Fig. 1). The valve is mounted on the aft bulkhead in the right wheel well. The valve contains 3 ports from which hydraulic lines extend to the flap control valve and flap hydraulic motor (Fig. 9). The valve is controlled by the alternate flaps arm switch which, when moved to ARM, supplies 28-volt dc power to move the valve to the bypass position. In this position the down line from the flap control valve is blocked and the flap hydraulic motor ports are connected together to allow fluid circulation within the motor. Moving the alternate flaps arm switch to OFF moves the bypass valve to its normal position and restores hydraulic operation of the flap system.
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27-51-0 Page 12  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Feb 15/78 

B.  The bypass valve is also controlled by the flap asymmetry shutoff relay which moves the valve to the bypass position to stop flap movement when left and right wing flap extension or retraction is not symmetric (Fig. 8B and 9).
9.  Flap Hydraulic Motor
A.  A reversible hydraulic motor attached to the flap power unit drives the flap system during normal operation. The nine cylinder, piston type motor converts hydraulic pressure to mechanical energy. The externally splined motor driveshaft mates with the power unit input shaft. Two hydraulic lines from the flap control valve connect to inlet ports on the motor. A case drain line connecting the motor to the hydraulic return system through a check valve allows lubrication of the motor. The flow of pressurized fluid through the motor actuates the pistons and rotates the output shaft. Rotation of the output shaft drives the power unit.
　
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