Hand-operated valves are usually equipped with a handwheel attached to the valve's stem or Yoke nut which is rotated clockwise or counter clockwise to close or open a valve. Globe and gate valves are opened and closed in this way.
Hand-operated, quarter turn valves, such as Ball, Plug or Butterfly, has a lever for actuate the valve.
There are applications where it is not possible or desirable, to actuate the valve manually by handwheel or lever. These applications include:
Large valves that must be operated against high hydrostatic pressure
Valves they must be operated from a remote location
When the time for opening, closing, throttle or manually controlling the valve is longer, than required by system-design criteria
These valves are usually equipped with an actuator.
An actuator in the broadest definition is a device that produces linear and rotary motion of a source of power under the action of a source of control.
Basic actuators are used to fully open or fully close a valve. Actuators for controlling or regulating valves are given a positioning signal to move to any intermediate position. There a many different types of actuators, but the following are some of the commonly used valve actuators:
Electric Motor Actuators
For more information about Actuators see main Menu "Valves" -Valve Actuators-