VALVE ACTUATORS Process ControlsVALVE ACTUATORSRemote operation of a valve is easily managed by one of the four types ofactuators.EO 1.7 DESCRIBE the operation of the following types ofactuators:a. Pneumaticb. Hydraulicc. Solenoidd. Electric motorActuatorsFigure 35 Pneumatic Actuator: Air-to-Close/Spring-to-OpenBy themselves, valves cannotcontrol a process. Manual valvesrequire an operator to positionthem to control a process variable.Valves that must be operatedremotely and automatically requirespecial devices to move them.These devices are called actuators.Actuators may be pneumatic,hydraulic, or electric solenoids ormotors.PneumaticActuatorsA simplified diagram of apneumatic actuator is shown inFigure 35. It operates by acombination of force created by airand spring force. The actuatorpositions a control valve bytransmitting its motion through thestem.A rubber diaphragm separates theactuator housing into two airchambers. The upper chamberreceives supply air through anopening in the top of the housing.IC-07 Page 54 Rev. 0
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