The bypass valve isolates the hydraulic motor from hydraulic system pressure. The bypass valve also prevents a hydraulic lock and permits backdrive of the hydraulic motor.
A dual-coil bypass solenoid valve controls pilot pressure to the bypass valve, but only one coil of the solenoid is used. When the FSEUs energize the bypass solenoid valve, it removes pilot pressure from the open side of the bypass valve. This closes the bypass valve, which connects the hydraulic lines to both sides of the hydraulic motor.
The bypass valve is spring-loaded and hydraulically controlled to the closed position. The open side of the valve has a larger surface area for the pilot pressure than the close side of the valve. When the center hydraulic system pressure is low, springs automatically force the bypass valve to close. When the center hydraulic system pressure is high, the bypass valve opens.

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TRAILING EDGE FLAPS -PRIMARY CONTROL VALVE -FUNCTIONAL DESCRIPTION

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TRAILING EDGE FLAPS -FLAP/SLAT PRIORITY VALVE

Purpose

The flap/slat priority valve gives priority of hydraulic power to the primary flight controls over the flaps and slats. This priority valve makes sure that the primary flight control PCUs receive sufficient hydraulic power when both air driven pumps (ADPs) are not operating.
Location

The flap/slat priority valve is at the bottom of the keel beam in the right wheel well.
Physical Description

The flap/slat priority valve has a flow limiter and a control valve. When the pressure in the center hydraulic system is high, the control valve fully opens. The maximum flow through the flow limiter is then 43 gpm.
When the system pressure decreases, the control valve restricts the flow to the flap and slat primary control valves. In the fully restricted position, the control valve limits the flow to
0.4 gpm. Restriction of the flap/slat flow permits the control valve to modulate the system pressure to 1750 psi during high demand conditions.
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TRAILING EDGE FLAPS -FLAP/SLAT PRIORITY VALVE

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TRAILING EDGE FLAPS -FLAP POWER DRIVE UNIT (PDU)

Purpose

The flap PDU turns the flap torque tubes during operation in all three modes. The flap PDU has these LRUs:
*
A hydraulic motor

*
An electric motor

*
A gearbox.

Information on the hydraulic motor and the electric motor is shown later.
Location

The flap PDU is above the keel beam in the main landing gear wheel wells. Access to the hydraulic and electric motors is through the right wheel well. Access to the gearbox is through the left wheel well.
Gearbox

The gearbox transmits the power from the hydraulic or electric motors to the torque tubes.
The hydraulic motor or the electric motor rotates gears in the gearbox. These gears increase the torque from the motors. The gearbox turns the torque tube couplings on both sides of the PDU. These couplings turn the torque tubes.
During high-speed operation in the primary mode, the gearbox turns the torque tubes at 550 rpm. During low-speed operation, the gearbox turns the torque tubes at 110 rpm.
During operation in the secondary and alternate modes, the gearbox turns the torque tubes at 74 rpm.
Training Information Point
The gearbox contains oil and it is necessary to do servicing at specified times. You get access to the oil fill plug through the left wheel well.

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TRAILING EDGE FLAPS -FLAP POWER DRIVE UNIT (PDU)

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TRAILING EDGE FLAPS -PDU HYDRAULIC AND ELECTRIC MOTORS

Purpose

The PDU hydraulic and electric motors supply power to turn the gearbox and the torque tubes.
Location
The motors are on the flap PDU and connect to the gearbox.
Hydraulic Motor

The hydraulic motor operates in the primary mode. It receives hydraulic pressure from the flap primary control valve. During secondary and alternate mode operation, the primary control valve blocks hydraulic power to the motor. It also permits the hydraulic motor to be backdriven.
The hydraulic motor is a reversible, constant displacement, piston-type motor. The hydraulic motor has two hydraulic connections for pressure and return to the flap primary control valve. It also has one connection for case drain to the return line of the center hydraulic system. The hydraulic motor weighs 16 lb (7 kg). It is identical and interchangeable with the slat hydraulic motor.
　
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