Actuator

Written by Jerry Ratzlaff on . Posted in Valve

An actuator 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.

types of actuators

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. 

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.

Chain Wheel Operator Photos


 

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".

Abbreviations

  • ACTR - Actuator