757
MAINTENANCE MANUAL
(2)
The temperature control valve is a 3-inch diameter, electrically controlled and operated, butterfly-type valve. It has a rotary electromechanical actuator, a valve flow section, and a linear variable resistor assembly.
(3)
Description
(a)
The rotary electromechanical actuator controls the position of the temperature control valve. It has an electric motor, a manual override, two limit switches, a capacitor, an output shaft, and a visual position indicator. 1) The electric motor is connected to the output shaft through
a reduction gear, two worm gears, the sector gear, and a slip clutch. The electric motor is a dual-coil type so it can turn the output shaft in both directions. The electric motor uses 115v ac, 400 Hz, single phase power.
2) The manual override is connected to the output shaft by one of the worm gears and the sector gear.
3) The capacitor supplies more power to the electric motor when it starts to move.
4) The output shaft has two cams, which move the limit switches when the shaft turns.
5) The visual position indicator is a pointer attached to the end of the output shaft. As the shaft turns, the pointer moves to the words OPEN or CLOSED, on the cover of the rotary electromechanical actuator.
(b)
The valve flow section has a butterfly plate, and a butterfly shaft. The butterfly plate has two piston rings to seal against the valve flow body when it closes. It is attached to the butterfly shaft by a bolt. The butterfly shaft is attached to the output shaft of the rotary actuator. The butterfly shaft turns on two annular ball bearings in the valve body.
(c)
The linear variable resistor assembly has a wiper arm, a 1K ohm linear variable resistor, and a 10K ohm linear variable resistor. The wiper arm is attached to the butterfly shaft.
(4)
Function
(a)
When power is supplied to the electric motor, it turns the gears, which turns the output shaft. The output shaft turns the butterfly shaft. The butterfly shaft turns the butterfly plate, the visual position indicator, and the wiper arm of the linear variable resistor assembly. The 1K ohm resistor supplies a position signal to the EICAS computers. The 10K ohm resistor supplies a position signal to the automatic pack temperature controller.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757
MAINTENANCE MANUAL
(b)
When the butterfly plate is in the full open or the full closed position, the cams on the output shaft will close the applicable limit switch. When the limit switch is closed, it sends a position signal to the automatic-pack-temperature controller. Then the automatic-pack-temperature controller stops the supply of power to the temperature control valve.
(c)
If the supply of power is stopped, the slip clutch holds the butterfly plate in its last set position. If power is supplied again, the butterfly plate can turn again.
(d)
The valve can open or close manually. When the manual override knob is turned, the clutch lets the output shaft turn. Again, the clutch holds the butterfly plate in the set position.
L.
Automatic-Pack-Temperature Controller (Fig. 10A)
_____________________________________
(1)
Two interchangeable automatic-pack-temperature controllers are used to control the air cooling packs. One controls the right cooling pack system and the other controls the left cooling pack system. The automatic-pack-temperature controller is a box that has a microprocessor. The microprocessor controls the air-cooling-pack-outlet temperature and monitors the system for failures. The front panel of the controller has lamps to show if a failure occurs. The front panel also has switches and instructions to do the built-in test equipment (BITE).
(2)
The automatic pack temperature controllers are in the E3 rack of the main equipment center.
(3)
Each automatic-pack-temperature controller controls these components for each air cooling pack:
(a)
The temperature control valve
(b)
The ram-air-inlet-door and the ram-air-exhaust-door actuators of the ram-air-cooling system (Ref 21-53-00)
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