Types and selection of actuators
There are currently four types of actuators, which can use different driving energy and can operate various types of valves.
1. Electric multi-turn actuator
Electric-driven multi-turn actuators are one of the most common and reliable types of actuators
. A single-phase or three-phase motor drives a gear or worm gear and finally drives the stem nut, which causes the valve stem to move to open or close the valve. The multi-turn electric actuator can quickly drive large size valves. In order to protect the valve from damage, the limit switch installed at the end of the valve stroke will cut off the power of the motor. At the same time, when the safe torque is exceeded, the torque sensing device will also cut off the power of the motor. The position switch is used to indicate the switch status of the valve. A handwheel mechanism fitted with a clutch device allows manual operation of the valve in the event of a power failure.
The main advantage of this type of actuator is that all components are housed in one housing, and all basic and advanced functions are integrated in this waterproof, dustproof, explosion-proof housing. The main disadvantage is that in the event of a power failure, the valve can only remain in place, and the valve can only achieve a fail-safe position (fail open or fail closed) with a backup power system
2. Electric single-turn actuator
This kind of actuator is similar to the electric multi-turn actuator, the main difference is that the final output of the actuator is 1/4 revolution and 90 degree movement. The new generation of electric single-turn actuators
combines the complex functions of most multi-turn actuators. The single-turn actuators are compact in structure and can be installed on small-sized valves. Usually, the output torque can reach 800 kg meters. In addition, the required power supply should be relatively small. Small, they can be fitted with batteries for fail-safe operation.
3. Fluid-driven multi-turn or linear output actuator
This type of actuator is often used to operate globe valves (globe valves) and gate valves, which are operated either pneumatically or hydraulically. The structure is simple, the work is reliable, and it is easy to realize the fail-safe operation mode. Usually people use electric multi-turn actuators
to drive gate valves and globe valves, and only consider using hydraulic or pneumatic actuators when there is no power supply.
4. Fluid-driven single-turn actuator
Pneumatic and hydraulic single-turn actuators are very versatile, they do not require power and are simple in structure and reliable in performance. The fields of their application are very wide. Usually the output is from a few kilograms of rice to tens of thousands of kilograms of rice. They use cylinders and transmissions to convert linear motion into right-angle outputs. Transmissions usually include: forks, racks and pinions, and levers. The rack and pinion output the same torque throughout the full stroke range, they are ideal for small size valves, and the fork has high efficiency with high torque output at the start of the stroke, which is ideal for large diameter valves. Pneumatic actuators
generally install accessories such as solenoid valves, positioners or position switches to control and monitor valves.