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(d)
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MAINTENANCE MANUAL
3) The actuator linkage assembly has an actuator arm and a connecting link. They connect the actuator diaphragm to the butterfly shaft. Movement of the actuator diaphragm causes the butterfly shaft to turn.
The closed-position-switch assembly
1) The closed position switch assembly is in the pneumatic actuator. It is attached to the side of the actuator housing assembly. The switch is closed by the actuator arm when the butterfly plate is closed.
The visual position indicator
1) The visual position indicator is a pin connected to the butterfly shaft assembly. The pin turns toward the words OPEN or CLOSED, which are on the upper bearing cover.
The zero-differential-pressure valve
1) The zero-differential-pressure valve has a servo cover assembly, a diaphragm assembly, a poppet valve, a valve seat, two springs, and a servo housing assembly. The poppet valve and the valve seat are used to adjust the valve. The springs push against the diaphragm assembly in opposite directions. The diaphragm assembly divides the zero-differential-pressure valve into two chambers. Chamber M bleeds to the throat-pressure-sensing probe. Chamber C bleeds to the adjustable orifice E and the solenoid assembly A. If the pressure in chamber C becomes too great, it bleeds into chamber D of the slave servo valve.
The slave servo valve
1) The slave servo valve has a pressure sensor assembly, an actuator lever assembly, two springs, and a bleed nozzle port. The actuator lever assembly includes a diaphragm that divides the slave servo valve into two chambers. Chamber D bleeds to chamber C and to ambient. Chamber Q bleeds to ambient and through the bleed nozzle port, if it is open. The bleed nozzle port bleeds to the solenoid-B-inlet connection. The two springs push on opposite ends of the lever to balance the actuator lever assembly.
2) The pressure sensor assembly has an aneroid and a spring that push against the actuator lever assembly. (An aneroid is a sealed, flexible container that becomes larger or smaller in relation to the adjacent air pressure). When the aneroid expands, the actuator lever assembly is pushed against the bleed nozzle port. Thus, the port will be closed.
3) The slave servo valve also has an altitude adjustment H, a slave servo valve adjustment L, and a bleed nozzle adjustment K.
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757
MAINTENANCE MANUAL
(h) The electro-magnetic-control valve
1) The electro-magnetic-control valve has a torque motor, a flapper, a supply nozzle port, and a control-pressure-nozzle port. When the torque motor is energized, it moves the flapper against the supply nozzle port. Thus, the port is closed. The supply nozzle port bleeds to the inlet-pressure-sense probe. The control-pressure-nozzle port bleeds to the adjustable orifice G.
(i) The solenoid valves (A and B) 1) The solenoid valve assembly A has a solenoid and a ball valve assembly. The solenoid has an electro-magnetic coil, an armature, an actuator rod, and a spring. The armature is attached to the actuator rod, which can push the ball in the ball valve assembly. The actuator rod pushes the ball when the solenoid is energized. When the solenoid is not energized, The spring pushes on the actuator rod to keep it away from the ball. 2) The ball valve assembly has two seats and a ball. The ball valve assembly bleeds to the adjustable orifice F, the adjustable orifice G, and chamber C of the zero-differential-pressure valve.
3) The solenoid valve assembly B is a momentarily controlled solenoid. The solenoid has two electro-magnetic coils and armatures, with opposite forces. The armatures are attached to the manual control rod. The manual control rod moves manually or automatically when a three second electrical pulse gives the solenoid a signal. The adjustable latch assembly holds the manual control rod in the last set position. The ball valve assembly has a spring-loaded seated-ball valve, two seats, and a ball. The ball valve assembly bleeds to the solenoid-B-inlet connection, ambient, and the mechanical- manual-override valve.
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