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T81263
A 737-300/400/500MAINTENANCE MANUAL
Flap Alternate Drive System Circuit
Figure 10
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T81297
A 737-300/400/500MAINTENANCE MANUAL
7. Priority Valve
______________
A. The operating speed of the trailing edge flaps is controlled by a flow limiting valve installed in the pressure line to the flap control valve upstream from the control valve. A priority valve controls the rate of fluid flow to the flap hydraulic motor. The priority valve reduces the flow of hydraulic fluid to flaps when pressure drops below level required to maintain all airplane systems. At normal temperatures with hydraulic pressure between 2700 and 3000 psi fluid flow to the motor is regulated at 10.0 gpm. When pressure drops to 2400 to 2700 psi, fluid flow is rapidly decreased. Below 2400 psi, flow of hydraulic fluid drops to 0.7 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 three ports from which hydraulic lines extend to the flap control valve and flap hydraulic motor. 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 the normal position and restores hydraulic operation of the flap system.
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 symmetrical (Fig. 9 and 10).
C. The bypass valve is also controlled by the flap control cable tension switch system which moves the valve to the bypass position to stop flap movement if the control cable breaks.
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 fluid 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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A
737-300/400/500MAINTENANCE MANUAL
10. Flap Power Unit_______________
A. The flap power unit transfers mechanical energy from the flap hydraulic motor and alternate drive unit to the flap drive system (Fig. 1). The power unit is an aluminum housing containing a reduction gear, two pinion gears, an output shaft with a worm gear, a worm wheel, and a worm wheel shaft. The reduction gear is splined to the output shaft. The flap hydraulic motor and the flap alternate drive unit are attached to the power unit. During normal flap system operation, power from the hydraulic motor is transmitted through a pinion gear to the reduction gear. During flap alternate drive operation, power from the alternate drive unit is transmitted through a second pinion gear to the reduction gear. Rotation of the reduction gear drives the flap system through the power unit output shaft.
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