Oftentimes, an actuator is attached to the valve to administer pressure control and flow control in applications where it is crucial. These settings are very critical and must be precisely observed to maintain the precision and efficiency of the whole system. A motor box is operated by pneumatic pressure or an electric current which administer control over the valves. The valve actuator moves the valve positioning in order to keep to setting that was entered by the operator. Actuators are now very important to modern plants. There are many types of actuator; manual valve actuator, hydraulic valve actuator, pneumatic valve actuator and electric valve actuator. These actuators are built differently but all of them provide the necessary control that is required from them.
Manual Valve Actuators
A manual valve actuator employs levers, gears, or wheels to facilitate movement while an automatic actuator has an external power source to provide the force and motion to operate a valve remotely or automatically. Power actuators are a necessity on valves in pipelines located in remote areas; they are also used on valves that are frequently operated or throttled. Valves that are particularly large may be impossible or impractical to operate manually simply because of the sheer horsepower requirements.
Some valves may be located in extremely hostile or toxic environments that preclude manual operation. Additionally, as a safety feature, certain types of power actuators may be required to operate quickly, shutting down a valve in case of emergency.
Hydraulic and Pneumatic Valve Actuators
Hydraulic and pneumatic actuators are often simple devices with a minimum of mechanical parts, used on linear or quarter-turn valves. Sufficient air or fluid pressure acts on a piston to provide thrust in a linear motion for gate or globe valves. Alternatively, the thrust may be mechanically converted to rotary motion to operate a quarter-turn valve. Most types of fluid power actuators can be supplied with fail-safe features to close or open a valve under emergency circumstances.
Electric Valve Actuators
The electric actuator has a motor drive that provides torque to operate a valve. Electric actuators are frequently used on multi-turn valves such as gate or globe valves. With the addition of a quarter-turn gearbox, they can be utilized on ball, plug, or other quarter-turn valves.