Leakage analysis for electric valve

Translated by Alice - Welco Valve dated June 15, 2012.

Nowdays, the electric valve has been widely used in power plants, petrochemical, iron and steel metallurgy, food processing and water treatment industries, especially for large enterprises that need to automatic control. Electric valve has create the condition of remote control for the valve so that the automation and intelligent of production systems become possible. However, the electric valves in system often can not shut down tightly in operation. It has made a lot of trouble for valve user and operator, seriously affected the valve life.

Wedge gate valve, globe valve and butterfly valve, they are to reply on the operational force on the sealing surface to ensure sealing. And the sealing surface than the pressure is to rely on the valve operating torque can reach this. This kind of valve is to be operated by torque control. In actual practice, it may often cause the leakage when it is closed by electric. So for this aspect, it need to manually close the valve. In case of unforeseen circumstances, in order to ensure that the valve closed tightly, usually we need to use a long rod to force for closing it. This operating condition neither achieve the remote control and system automation, but also increased the operator's labor intensity and shorten the service life of valve. Because the valve is not closed tight, the medium of leakage will wash off the sealing surface in high-speed, it must be a apid damage of it. If we close the valve with a long rod, we can not control the torque and inevitably damage the sealing surface, such as high temperature electric gate valve and motorized triple offset butterfly valve etc. We can also call electric valve or motorized valve. It is the same type.

The electric valve can not close tightly, and people can manually shutting the valve. Obviously the problem is subject to the control system of electrical device.

At present, the electric valve is usually equipped with stroke control and torque control two sets of systems, it is built to travel for the control, and torque for the protection. For the stroke control valve, normal working hours, to travel to control valve fully open and fully closed position. If the travel is out of control, we need to use the manual torque protection for its operation which can be maintained to avoid valve damage. In order to ensure the safety valves and production systems. Torque control valve in the existing system, travel system can not afford protection role. Torque control failure or values ​​change, the valve operating torque will be increased rapidly in an instant, but no other protective measures. Therefore, this control system is not complete.

Even with the applicable control system, after the electric device and the valve assembly, is also accurate debugging and setting the control parameters. Generally, the electrical device at the factory, the rated output torque has been completed calibration. After calibration of torque, however, only indicates that the work capacity of electrical device, the torque is not the same as the valve closes. The valve closes the required torque in addition to the valve specification model, the actual work with the valve media, pressure and temperature, the user should re-adjustment and setting. However, most of valve users (including valve manufacturer) do not have the torque detection means, and can not be set torque value. And valve operation for some time after repair, the torque of electric device factory settings have been changed must be re-set. The case of lack of torque determination means, the valve user can only be adjusted in accordance with the valve fully open and fully closed position the valve opening direction, and set in the fully open and fully closed position limit switch action to ensure that the travel control can work properly. Then, the valve is closed, the trip off switch action based on, manual off valve, feel close torque increased to a certain range, adjust the action of torque switch. This set of results must be the valve opening and closing is still subject to the control of limit switch. The closing toruqe of valve can not be guaranteed, so the tightness of sealing is difficult to guarantee.

In many companies, valves and electrical installations are belong to two departments for managemen. Valve owned by the equipment sector management, and electric installations owned by the instrument sector management. Electric devices typically meter department responsible for adjusting the settings. Instrumentation sector natural focus in the control system work properly, as long as the stroke control adjustment, and automatic control of whole system will be able to work properly. As for the work to ensure that the valve closing moments do not get enough attention, often electric valve operation after the closure of leakage is simply regarded as the poor quality of valve. In fact, the electric valve closure is not tight and is caused by a variety of factors, both technical reasons, also organized management reasons. Only by taking a realistic and practical approach, one by one to solve these problems, in order to ensure that the valve performance.

In order to ensure the reliability of electric valve operation, valve commissioning training should be strengthened so that they can correctly grasp the reasonable debugging method for all kinds of valves. So that the electric valve closure tightness in the electric operation will be radically improved. The valve itself is good quality, the reliability of valve will be improved, and will also be welcomed by users.