With the trend of mechatronics and the development of microelectronics technology and computer technology, more and more problems are emerging in using valve, such as low control precision, inconvenient field debugging and imperfect diagnosis methods, etc. All these make the original electric valve be increasingly unable to meet the development needs of modern industry and finally approach to elimination. So, for electric valve, one of the important mechanical industry products, it is very important to make an effective transformation to improve its intellectualized degree and to have computerized control process, digital communication faction, intelligent diagnosis treatment and remote detection.

 

There are only three actual valve positions for a valve: on, off and middle position and valve position is controlled by the output torque of valve motor. At present, our country often works on this working mode- “travel switch controls valve motor, torque switch protects valve”. However, travel switch and torque switch are usually installed on electric actuator, which makes the valve position signal can not get directly from valve shift. Thus, the indicated valve for valve position will be inaccurate and the valve cannot be closed or opened completely. If the selection of output torque is too small, it would be different to close/open the valve and finally make the motor burned; if it is too big, the local structure of valve will be destroyed easily once the control of the electric actuator is fail.

 

On the other hand, with this working mode, the micro groove will be appeared in pipeline walls because of the long-term action oppression from straight travel globe valve and gate and that will make the valve cannot be closed completely which will lead to leakage problem. Leakage is one source of the industrial pollutions. Valve Leakage can make the medium flow out and give rise to the growth of consumption, the increase of cost and the decrease of economic benefits of enterprises. What’s more, it is easy to cause fire, explosion, poisoning, personal injury or death and other accidents because of the outflow of inflammable, explosive, toxic and harmful medium. Strong corrosive medium leakage can accelerate the corrosion rate of plant and equipment and shorten their service life. Therefore, leakage problems can not be ignored, because it seriously threaten the safety and process of production. For a long time, solution for this problem is always started with valve. Optimize the design of valve structure, choose right valve material on the basis of different process conditions, enhance the level of quality control in valve manufacturing process and improve the type of valve according to process conditions in chemical production process. Although these methods have effectively eliminated the leakage, however, if we can start with changing the control mode of valve position, it will have a better result because we can control the valve position directly and take steps for it according to the feedback information. At the same time, it is required to change the control mode to meet the requirements of automatic production.