What is valve actuator ?
Valve actuator is the element to open and close a valve . It is a must element for any valve .
There are mainly four types of actuators: manual, pneumatic, hydraulic, and motorized (electric ). Manually operated valves require someone to modify them using a lever, geared, or wheel to move the valve stem by hand. Usually, manual actuators are not expensive, and easy to operate. But, if the valve size is large, it is impractical to operate manually . and some valve installed in a remote or bad environment which is not suitable for manual operation. And some situations need faster operation than manual. So pneumatic, hydraulic, and motorized (electric ) actuators are required in these situations.
Pneumatic type valve actuator
Pneumatic type valve actuator use air (gas )pressure as the power source, it is the most popular actuation method, and capable of delivering the required forces with enough speed of travel . And it provide a fail-safe response on lose of drive power with spring sets, and it is more safe application when using in explosion hazards area. A pneumatic actuator may be spring-closed or spring-opened with air pressure overcoming the spring to provide movement. A double-acting actuator use air applied to the different inlet to move the valve in opening or close state.
The electric actuator uses an electric motor to provide torque to drive a valve. They are without noise, and use in non-explosion or safety area, and save energy. They can be used for on-off application for large isolating valves, and especially popular application for continuous positioning control by providing position feedback to a controller providing variable speed reversible drive action. They are widely applied in the power generation industry, water supply/treatment plants, pharmaceutical industry.
Hydraulic actuators convert fluid pressure into motion . They are similar to pneumatic actuators , while they are used liquid pressure to move the valve mechanism , and normally applied on linear or quarter-turn valves . And usually they are installed on gate or globe valve , and use a piston to convert fluid pressure into mechanical force. Most of hydraulic actuator can be supplied with fail-safe features to close or open a valve under emergency situation . Some actuator designs combine hydraulic and electric power in what is called a electro-hydraulic valve , such actuator are a good solution for isolated location where pneumatic supply pressure is not available while where precise control of valve plug position is needed .