More and more factories adopt automation control. Manual operation is taken place of by mechanical or automated equipment. The actuator is required for not only playing as interface interaction for controlling mechanical motion of system and valve, but also enhancing security performance and environmental protection performance. In some dangerous occasions, automated actuator can reduce harms to personnel. Some special valves are requested to be opened or closed urgently under particular situations. Valve actuator can prevent danger from being expanded further and can reduce factory losses to the minimum. For high pressure large diameter valves, required actuator should have extremely large output torque, then, the torque must improve mechanical efficiency and use high output motor so that it can steadily operate large diameter valve. For valves having low torque, small electronic valves come out.
Compared with common electric valves, small electronic valves have the advantages of light weight, compact structure and complete functions.
The most extensive definition for actuator is a kind of actuating devices which can provide rectilinear or rotational motion. It uses some driven powers and operates under functions of some controlling signal. Actuator utilizes liquids, gases, power or other energies and transfers them into driving function through motor, air cylinder and other devices.
Actuator is used to dive valve to move on-off position. Actuator used for control valves can be able to drive valves to move any positions. Although most of actuators are used for on-off valves, the design of current actuators highly exceeds than on-off functions. They contain position sensor, torque sensor, electrode protection, logic control device, digital communication module and PID control module. All of those devices are installed inside a compact shell.
To successfully realize process automation, most of all is to ensure valve to meet particular requirements of processes and media inside pipeline. Manufacturing processes, techniques and media can decide categories of valves, types of valve cores, internals of valves, structure and materials of valves.
After choosing valve, choosing of actuator should be taken into consideration based on requirements of automation. The actuator can be considered based on two kinds of basic valve operation types.
Rotational valve:
This type of valves includes swing valve,
ball valve,
butterfly valve and ventilation door or baffle. Those valves require that actuator can turn in quarter.
Multi-turn valve:
This kind of valves can be non-swing lift stem or swing non-lift stem. Or the valve needs multi-turn to drive valve to move to on-off position. This type of valves contains straightway valve (
globe valve),
gate vale and knife gate valve. As a kind of choice, liner output pneumatic or hydraulic cylinder or thin film actuator can be also used to drive above valves.
Advantages of electric actuator:
The main advantages of electric actuator is that high stability and applicable constant thrust. The largest thrust caused by actuator can be as high as 225,000kgf. Such high trust only can be realized by hydraulic actuator while the price of hydraulic actuator is much higher than electric actuator. Electric actuator has good yaw stiffness. Output thrust or torque is basically constant which can overcome unbalanced for of media, realizing accurate control for technical parameters. so, the controlling actuate is higher than pneumatic actuator. If equipped with servo amplifier, interchange of direct and reactive direction can be realized easily. Shutoff signal also can be set easily to keep position of valves (maintaining, fully-opened or fully-closed). When failure is occurred, the valve must stay at normal position which cannot be realized by pneumatic actuator. pneumatic actuator realizes keeping position with the help of integrated protection system.
