(c)
Rotation of the reverse thrust lever actuates the switches for the directional valve control (S181, S182, S183, S184) in the microswitch pack. This energizes the solenoid circuit for the directional control valve (DCV).
(d)
The isolation valve circuit goes from the control switches for the thrust reverser, through an air/ground relay to the isolation valve solenoid.
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(e)
The syncronizing cable lock circuit is energized through the thrust reverser control switches and the deploy relay. In the energized condition the solenoid inside the sync lock pulls a armature which in turn pulls the two lock pins away from the teeth of a rotor. This allows the synchronizing cables to rotate.
(f)
The DCV circuit goes through an air/ground relay and fire switch, then through DCV control switches in the autothrottle microswitch pack to the DCV solenoid.
(g)
When the isolation valve solenoid is energized, the pilot valve is opened and fluid is ported to one end of the arming spool, shifting it to the open position. The PRESS port is connected to the CYLINDER port providing hydraulic fluid to the PRESS port of the directional control valve (DCV). The isolation valve RTN port is connected to CONT port which is connected to the RTN port of the DCV.
(h)
When the solenoid for the directional control valve is energized, the pilot valve is opened moving the spool to the deploy side. Fluid is ported to EXT and RET ports of the DCV. The DCV RTN port is not connected to the thrust reverser actuators.
(i)
Fluid flow through both extend and retract flow control tees allows pressurization of both rod end and head ends of the hydraulic actuators. Equal pressure is developed in both head and rod end cavities of all actuators.
(j)
Hydraulic flow, from the directional control valve and through the extend flow control tee enters the head end of the locking actuators through a locking device. As pressure builds in the lock chamber, a piston repositions, moving a lever that disengages the lock and allows hydraulic fluid to flow into the head end of the actuators. Once pressure builds, both the head end and rod end of the actuator will be at equal pressure. Since the head end of the actuator has a cross sectional area twice that of the rod end, sufficient force is generated to move the translating sleeve aft at a rapid rate. At the end of the stroke, a snubbing mechanism slows the movement to reduce the loads generated at the rod end when the actuator extends to the fully deployed position.
(k)
The non-locking upper and lower actuators operate in synchronization with the locking actuator. Hydraulic fluid entering the head end of the center actuator is ported directly to the head end of the two non-locking actuators. Pressure is thereby equal in all three actuators so they translate aft at an equal rate.
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(l) A mechanical flexible driveshaft system ensures all three actuators drive the sleeve in unison. The flexshafts are connected to synchronizing gear train of the actuators. As each actuator translates, movement of the head end piston forces an Acme nut aft. The Acme nut forces a threaded shaft to rotate at a rate proportional to piston movement. A pinion gear rotates with the shaft to drive a worm gear. The worm gear is connected to and drives the flexshafts. Any tendency of one actuator to increase or decrease speed will thus be countered by the other actuators. The flexshafts are routed through the hydraulic tubing connecting the locking and nonlocking actuator head ends.
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