Actuator

Written by Jerry Ratzlaff on . Posted in Valve

An actuator, abbreviated as ACTR, is a device used to open, close, or control valves.  The most commonly used types are electrical, hydraulic, and pneumatic.  For high torque applications, electro-hydraulic actuators may be utilitzed.  Actuators are mounted to the valves by a linkage.
Actuators may be quarter turn or multi-turn.  They might fail in place, fail open or closed or continue to run, depending on the set up.  Actuators are sized depending on their application.  butterfly valves, for example, require the highest torque immediately after opening and the torque requirements depend on the orientation of the valve.

 

actuator Types

  • Electric Actuator  -  Electric valve actuators are devices that use electricity as the power source to stroke a valve.  They are available as quarter turn, which are used in valves like ball valves, or sliding stem, which are used in globe valves.   Unless specified, electric actuators are usually fail in place, which means they stay in the same position when power is lost.  In the event the valve is configured as Fail Closed or Fail Open, additional components are added to the electric actuator to assist in closure.  The most typical being a large capacitor that stores enough energy to fail the valve to the proper position.
    • Electromechanical Actuator  -  Actuators that convert electric signals into rotary or linear movements and may even be capable of a combination of both.
    • Electrohydraulic Actuator  -  Actuator powered electrically but gives movement to a hydraulic accumulator.  The accumulator then provides the force for movement, usually seen in heavy industrial equipment.
  • Manual Actuator  -  Manual actuators are knobs, cranks, gear operators or hand levers.  Movement may be quarter turn or multi-turn, depending on the required actuation.  During design and construction of a project, valves or actuators may end up in hard to reach locations.  Chain wheels are used to access these valve from a floor location in a safe operating manner.
    • Hydraulic Actuator  -  A fluid filled cylinder with a piston suspended at the center.
      • Piston Type Cylinders  -  Used for applications that require both push and pull functions.
        • Single Acting Cylinder  -  Uses fluid pressure to apply force in only one direction. 
        • Double Acting Cylinder  -  The fluid under pressure can be applied to either side of the piston to apply force and provide movement.
        • Tandem Cylinder  -  Consists of two or more cylinders arranged one behind the other but designed as a single unit.
      • Ram Type Cylinder  -  A ram-type cylinder is usually considered one in which the cross-sectional area of the piston rod is more than one-half the cross-sectional area of the movable element.
        • Single Acting Ram  -  Applies force in only one direction.
        • Double Acting Ram  -  Both strokes of the ram are produced by pressurized fluid.
        • Dual Ram  -  Consists of a single ram with a cylinder at either end.  Fluid can be directed to either cylinder, forcing the ram to move in the opposite direction.
        • Telescoping Ram  -  A series of rams are nested in the telescoping assembly.
    • Mechanical Actuator  -  Mechanical force is applied, such as pulling or pushing.
      • Chain Operator  -  Allows an operation of valves, actuators, or gear boxes in high, hard-to-reach by means of a slight pull on the chain.

      • Handwheel  -  A wheel operated by a pulling motion.
    • Pneumatic Actuator  -  Pneumatic actuators use compressed air controlled by a separate solenoid valve, while motor actuators use an electric gear motor.  Actuators may be used when valves are remotely located (such as on pipelines), located in hazardous areas, and when manual operation would be time consuming (like with large valves).  Pneumatic Actuators will typically have one of the following characteristics:
      • Air to Open - An actuator installed in this configuration requires air to open.  If the actuator is a rack and pinion actuator and is single acting, it must have a spring to force the valve closed when there is no air in the actuator.  Air to open type actuators require air pressure and some known volume to open the valve.  Actuators that require air to open are typically denoted as "fail closed".
      • Air to Close - Air to Close is of a different configuration than the ATO type actuator described above.  Air to Close means that constant pressure must be held on the acutator to keep the valve closed.  If air pressure is lost the actuator will automatically open. Actuators that require air to close are typically denoted as "fail open".
    • Rack and Pinion Piston Rotary Actuator  -  Consists of a body and two reciprocating pistons with an integral rack for rotating the shaft mounted in roller or journal bearings.  The shaft and bearings are located in a central position and are enclosed with a bearing cap.  The pistons, one on each side of the rack, are enclosed in cylinders machined or sleeved into the body.  The body is enclosed with end caps and static seals to prevent external leakage of pressurized fluid.
    • Thermal and Magnetic Actuator  -  Consist of shape memory alloys that can be heated to produce movement.

 

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