Linear actuators push a stem, from spring-and-diaphragm units on control valves to large pistons on gate valves; rotary actuators turn a shaft through 90 degrees via scotch yoke, rack and pinion or vane mechanisms. Electric actuators use a motor and gearbox with torque and limit switches. An actuator is sized for the worst-case thrust or torque with margin, including breakaway torque after the valve has sat for months.
Actuator's sized for clean gas, but that ball valve sat six months in the dirt, it needs another 30 percent breakaway torque.
Also heard as
- operator
- valve operator
Related terms
Positioner
A device on a control valve that compares the control signal with actual valve position and adjusts air to match.
Spring-return
Describes a single-acting actuator that uses air to move one way and a spring to move back and fail safe.
Double-acting
Describes an actuator that uses air or oil pressure to drive in both directions, with no return spring.
Scotch yoke
A rotary actuator mechanism that turns the straight push of a piston into a 90 degree shaft rotation through a slotted yoke.
MOV
Motor-operated valve: a valve driven by an electric actuator with a motor, gearbox, torque switch and limit switches.