Actuators serve the general purpose of controlling movements within machines. However, there are various kinds of actuators that produce varying motions and use different power sources. And this article covers five common types of actuators and their applications with examples.

Types of Actuators

1.  Manual

A manual actuator employs levers, gears, or wheels to move the valve stem with a certain action. Manual actuators are powered by hand.

The main advantages of manual actuators are inexpensive, typically self-contained, and easy to operate by humans.

The main disadvantages is that some large size ball valves are impossible to operate manually and some valves may be located in remote, toxic, or hostile environments that prevent manual operations in some conditions. As a safety feature, certain types of situations may require quicker operation than manual actuators can provide to close the valve.

 

2. Pneumatic

Air (or other gas) pressure is the power source for pneumatic valve actuators. They are used on linear or quarter-turn valves. Air pressure acts on a piston or bellows diaphragm creating linear force on a valve stem. Alternatively, a quarter-turn vane-type actuator produces torque to provide rotary motion to operate a quarter-turn valve. A pneumatic actuator may be arranged to be spring-closed or spring-opened, with air pressure overcoming the spring to provide movement.

Advantage:

(1) Most of the actuators used in industrial control occasions are pneumatic actuators, because it is more economical to use air source as power than electric and hydraulic, and the structure is simple, easy to master and maintain. From the point of view of maintenance, pneumatic actuators are easier to operate and calibrate than other types of actuators, and the front and back can be easily interchanged on the spot.

(2) From the point of view of maintenance, pneumatic actuators are easier to operate and calibrate than other types of actuators, and the front and back can be easily interchanged on site.

(3) Its biggest advantage is safety. When using the positioner, it is ideal for flammable and explosive environments, and if the electrical signal is not explosion-proof or intrinsically safe, there is a potential fire hazard due to ignition.

Disadvantage:

Slow response, poor control accuracy, and poor anti-deviation ability, which is due to the compressibility of gas, which is the need for air to fill the cylinder and empty it when using a large pneumatic actuator.

 

3. Hydraulic

Hydraulic actuators convert fluid pressure into motion. Similar to pneumatic actuators, they are used on linear or quarter-turn valves. Fluid pressure acting on a piston provides linear thrust for gate or globe valves. A quarter-turn actuator produces torque to provide rotary motion to operate a quarter-turn valve.

The main advantages of Most types of hydraulic actuators can be supplied with fail-safe features to close or open a valve under emergency circumstances. Hydraulic pressure can be supplied by a self-contained hydraulic pressure pump. In some applications, such as water pumping stations, the process fluid can provide hydraulic pressure, although the actuators must use materials compatible with the fluid.

The main disadvantages is that Hydraulic actuators are expensive, bulky, complex and requires special engineering, so most of them are used in some special occasions such as power plants and petrochemicals.

 

4. Electric

Electric valve actuator mounted on a pressure reducing needle valve. The electric actuator uses an electric motor to provide torque to operate a valve. They are quiet, non-toxic and energy efficient. However, electricity must be available, which is not always the case, they can also operate on batteries.

Main applications of electric actuators:

(1) Power Plant. (2) Process control. (3) Industrial automation.

The main advantages of electric actuators are a high degree of stability and the output thrust or torque is basically constant. It can well overcome the unbalanced force of the medium and achieve accurate control of the process parameters, so the control accuracy is higher than that of pneumatic actuators.

The main disadvantage is that the structure of the electric actuators are more complex and more prone to failure. Due to its complexity, the technical requirements for field maintenance personnel are relatively higher.

 

5. Spring

Spring-based actuators hold back a spring. Once any anomaly is detected, or power is lost, the spring is released, operating the valve.

The main advantages of they don’t require a powerful electric supply to move the valve, so they can operate from restricted battery power, or automatically when all power has been lost.

The main disadvantage is that they can only operate once, without resetting, and so are used for one-use purposes such as emergencies.