Utilized in industrial process industries including water, oil, and power plants, valve actuators provide automated operation of valves along a system of pipes. The use of actuated valves allows technicians to control an entire process system remotely, limiting the requirement for direct human interaction. Different types of actuators exist, determined by their operating mechanisms; these take the form of either a pneumatic, electric, or hydraulic valve actuator.
Hydraulic actuators are most commonly utilized to operate butterfly valves that require a rotation of less than 360 degrees within the pipe to provide the fluid level control. The hydraulic valve actuator converts electrical signals into fluid pressure within the hydraulic cylinder to provide the movement. If needed, technicians can retrofit hydraulic actuators easily to existing manual operation valve controls.
The main format of a hydraulic valve actuator used in the process industry is the rack-and-pinion style actuator. This style of actuator provides rotational movement by adjusting the hydraulic pressure within the actuator piston arm. It can rotate the valve flange by extending the arm and returning it to the original position by retracting the arm. With this limited movement, hydraulic actuators are not utilized for multirotation valve control.
There are three different styles of valve actuator available, each specific to different valve designs. The first of these are multiturn actuators, which control gate valves. These valves can turn a full 360-degree rotation and are controlled by electric valve actuators due to the unlimited single-direction rotation that is required.
Partial-turn actuators work in a similar fashion to multiturn actuators but are only required to rotate through an angle of approximately 90 degrees. Butterfly valves are the most common type controlled by partial-turn actuators, and these can be controlled by either an electric, pneumatic, or hydraulic valve actuator. One key area in which multiturn and partial-turn actuators differ is in their requirements to withstand thrust. As multiturn valves are not restricted in their rotation, the actuator must be able to withstand the thrust force it experiences. Partial-turn valves are supported by parts of the valve body and therefore are not required to withstand thrust.
The third type of actuated valve control is the linear actuator. These linear actuators operate by blocking the pipe and are therefore most commonly seen on control valves. This type of valve works by pressing a plug into the pipe and exerting a similar level of force to the thrust acting upon the valve face. Most actuated valves are also fitted with hand wheels to allow manual control if required.