Selection Techniques and Necessary Considerations for Explosion proof Electric Valves
7175 Views
2019-03-06
1. Selection of control valves: At present, the control valves commonly used in engineering are mainly electromagnetic valves and electric valves. But they all have defects in use, such as electromagnetic valves being easily blocked by foreign objects, high water resistance, and requiring long-term maintenance by dedicated personnel; Although electric valves have no water resistance, due to the need for necessary control circuits, the impact of waterproof steam erosion on their service life is also a major problem that hinders promotion.
2. How to overcome the impact of scale on valve use Whether it is an electromagnetic valve or an electric valve, scale not only causes valve leakage, but even affects the normal operation of the valve in severe cases. Therefore, how to eliminate the impact of scale has become a common concern among industry professionals.
The scope of the control valve process is too broad to explain to you one by one here. I hope you can personally check the information on this aspect. However, due to differences in the design of the actuator and the use of filling materials, the poor performance of the control valve can still be summarized as follows: 1. The presence of dead zones in the process can cause process variables to deviate from the original set point. So the output of the controller must increase enough to overcome the dead zone, and only this corrective action will occur. 2. ① The main factors affecting the dead zone. Friction, displacement, valve shaft torsion, dead band of amplifier. Various control valves are different in sensitivity to friction, such as rotary valves, which are very sensitive to friction caused by high seat loads. Therefore, this should be noted when using them. However, for some sealing styles, a high seat load is necessary to achieve a closing level. Haha, in this way, the design of this valve is very poor, which can easily cause a large dead zone, and the impact on process deviation is obvious and decisive Wear and tear. It is inevitable that the valve will wear during normal use, but the wear of the lubrication layer is severe. According to our experimental verification, the lubrication rotary valve only undergoes a few hundred cycles of action, and the lubrication layer can be almost used with just a brush (to exaggerate, otherwise writing an article would be very frustrating). In addition, the load caused by pressure can also lead to wear of the sealing layer, which are the main factors leading to increased friction. What about the results? The performance of the control valve is devastating! ③ The friction force of the packing is the main source of friction force in the control valve, and the friction force caused by different packing materials varies greatly, The different types of actuators also have a fundamental impact on friction, and generally speaking, spring diaphragm actuators are better than piston actuators.
3. Design issues with locators. From a design perspective, the design of the actuator and locator must be considered together. How to design a good locator? From its important characteristics, it must be a high gain device. Its gain is composed of two parts: static gain and dynamic gain. The method to improve static gain is to design a preamplifier. For example, nozzle baffle device. So, some friends would like to ask how to obtain dynamic gain? It is obtained through a power amplifier, which is a spool valve (general). Someone has already used microprocessors to set up locators. It seems that the valve will still talk and tell us where it's broken in the future. At that time, it was easy to do maintenance. Return to the point. A high-performance positioner with both high static and high dynamic gain can provide better overall performance in reducing process deviation for any given valve component.
