Pneumatic Valve Actuators

Pneumatic valve actuators adjust valve position by converting air pressure into linear or rotary motion. Linear motion devices open and close gate, globe, diaphragm, pinch and angle-style valves with a sliding stem that controls the position of the closure element. Rotary motion devices move ball, plug and butterfly valves a quarter-turn (90°) or more from open to close.  There are several actuation methods for pneumatic valve actuators. Diaphragm actuators are used mainly with linear motion valves, but are suitable for rotary motion valves when used with some type of linear-to-rotary motion linkage. Piston cylinder actuators are suitable for both linear and rotary motion valves. Typically, rack- and-pinion actuators are used to transfer the linear motion of a piston cylinder actuator to rotary motion. Rack-and-pinion designs are also suitable for adjusting manually-operated valves. Scotch yoke devices are used to transfer linear motion to rotary motion. By contrast, vane actuators are suitable only for rotary motion valves. Link and lever actuators attach a splined or slotted lever to the valve shaft in order to transfer the linear motion of diaphragm or piston cylinder actuators to rotary motion.

Specifications for pneumatic valve actuators include stem diameter, actuation time, control signal input, acting type, fail-safe position, air supply pressure range, and operating temperature. Actuation time is the time required to fully close the valve. Milliampere, voltage, and pressure signals are common control signal inputs. Single-acting devices use air pressure to actuate the valve in one direction and a compressed spring to actuate the valve in the other. Double-acting devices use air pressure to actuate the valve in both directions. The failsafe position determines whether pneumatic valve actuators open or close the valve in the event of a power failure or the loss of the control signal. Air supply pressure range is the input pressure needed to achieve the desired torque or thrust output. Stroke length, number of turns, and actuator force are other important specifications for pneumatic valve actuators that move linear motion valves. Rotary motion devices indicate whether the full range of motion is a quarter-turn, a nominal 180° or 270° turn, or multiple turns for more than 360°.

National Electrical Manufacturers Association (NEMA) ratings indicate whether pneumatic valve actuators are suitable for hazardous or non-hazardous locations and designed for indoor or outdoor use. All NEMA enclosures protect personnel against incidental contact with the enclosed equipment. Type 4 and Type 4X NEMA enclosures are rated for indoor and outdoor use in non-hazardous locations. NFPA 70, a publication of the National Fire Protection Association (NFPA), is the basis of several NEMA ratings for hazardous locations. Type 7 and Type 8 NEMA enclosures are rated for indoor use and designed for Class I; Division 1; Groups A, B, C or D hazardous locations. Type 9 NEMA enclosures are designed for indoor use in hazardous locations classified as Class II; Division 1; Groups E, F, or G. 

Pneumatic valve actuators are available with a variety of features. Directing acting and reverse acting devices are commonly available. Overtorque protection uses a torque sensor to stop the power source when a safe torque level is exceeded. Travel stops or travel limits restrict or limit the actuator’s linear or rotary motion. Pneumatic valve actuators with an electromechanical limit switch (contacts) or non-contact proximity sensor allow position monitoring from a remote location. Valve actuators with local position indicators are also available. Some pneumatic valve actuators include integral pushbuttons and manual controls. Others include a handwheel, manual lever, or hydraulic hand pump that can be used to override the actuator in the event of an emergency.

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Part Numbers for Pneumatic Valve Actuators