| Positioners
Instrument attached to a pneumatic valve actuator,
providing accurate, automatic modulating control of the
valve between the open and closed positions by increasing,
decreasing, and balancing the air supply to the actuator as
determined by a varying input signal generated by an
external instrument source. While the operation positioners
may vary, the basic function will be either the pneumatic
positioner, designed to receive a 3 to 15 PSI signal, or the
electro-pneumatic, designed to receive a 4 to 20 milliamp
signal.
Manual Over-ride
Any mechanical device by which an automated valve may be
manually operated. On smaller actuators, this may simply be
wrench flats on the output shaft of the actuator. larger
actuators may require a more sophisticated system, such as
declutchable handwheels, manual gears, or jack screws, or
hydraulic hand pump over-ride.
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