Analysis Of The Causes Of Poor Sealing Of Electric Valves
Nowadays, Lined Valve has been widely used in power plants, petrochemicals, steel metallurgy, food processing and water treatment industries, especially in large enterprises that need to implement automatic control. Electric valves create conditions for remote control of valves, making automation and intelligence of production systems possible. However, electric valves often have the phenomenon of loose closing during electric operation, which brings trouble to valve users and operators and seriously affects the service life of valves.
When closing, valves such as wedge gate valves, stop valves and sealed butterfly valves rely on generating sufficient sealing surface pressure on the valve sealing surface to ensure sealing, and the sealing surface pressure is achieved by the operating torque of the valve. This type of valve is a torque-controlled valve. In production practice, this type of electric valve often has the phenomenon of medium leakage after electric operation is closed. For this reason, it is necessary to manually close the valve. In case of unexpected circumstances, in order to ensure that the valve is closed tightly, it is usually necessary to use an extra-long force rod to forcefully close the valve. Such operating conditions can neither achieve remote control of the valve nor system automation, nor can they increase the labor intensity of the operator and shorten the service life of the valve. Because the valve is not closed tightly, the leaking medium will flush the valve sealing surface at high speed, which will inevitably cause rapid damage to the sealing surface. Using a force rod to forcefully close the valve cannot control the closing torque, and it is inevitable to damage the valve sealing surface.
The valve is not closed tightly by electric operation, but it can be closed tightly by manual force. This is a manifestation of insufficient valve closing torque. Obviously, the problem is related to the control system of the electric device.
Current valve electric devices are usually equipped with two systems, stroke control and torque control. It is based on "stroke as control and torque as protection", which is only applicable to stroke control type valves. For valves that require stroke control, when working normally, the stroke is used to control the full open and full closed positions of the valve. If the stroke control fails, there is also over-torque protection to maintain the operation of the valve and avoid valve damage. Thereby ensuring the safety of the valve and the production system. For torque control valves, in the existing system, the stroke system does not play a protective role. If the torque control fails or the value changes, the operating torque of the valve will increase rapidly in an instant, but there are no other protection measures. Therefore, this control system is not perfect.
Even if there is a suitable control system, after the electric device and the valve are assembled, the control parameters still need to be accurately debugged and set. Usually, the rated output torque of the electric device has been calibrated when it leaves the factory. However, the calibrated torque only indicates the working capacity of the electric device, which is not equivalent to the torque required for the valve to close. The torque required for the valve to close is related to the specifications and models of the valve, as well as the medium, pressure and temperature of the actual working of the valve. The user should readjust and set it. However, most valve users (including many valve manufacturers) do not have the means of torque detection and cannot set a reasonable torque value. Moreover, after the valve has been running for a period of time and has been repaired, the torque set by the electric device at the factory has changed and must be reset. In the absence of torque measurement means, valve users can only adjust the valve opening indication according to the fully open and fully closed positions of the valve, and set the stroke switch action at the fully open and fully closed positions to ensure that the stroke control can work normally. Then, on the basis of the valve closing and stroke closing switch action, manually close the valve, and when the closing torque is felt to increase to a certain extent, adjust the torque switch action. The result of this setting is that the opening and closing of the valve is still only controlled by the stroke switch. The closing torque of the valve cannot be guaranteed, so the tightness of the closure is difficult to ensure.
In many companies, valves and electric devices are managed by two departments. Valves are managed by the equipment department, while electric devices are managed by the instrument department. The electric device is usually adjusted and set by the instrument department. The instrument department naturally focuses on the normal operation of the control system. As long as the stroke control is adjusted well, the automatic control of the whole system can work normally. As for the work of ensuring the closing torque of the valve, it has not received enough attention, and the leakage phenomenon after the valve is electrically operated and closed is often simply regarded as poor valve quality. In fact, the loose closure of electric valves is caused by many factors, both technical reasons and organizational management reasons. Only by taking practical measures and solving these problems one by one can the performance of the valve be guaranteed.
In order to ensure the reliability of electric valve operation, the training of valve commissioning personnel should be strengthened so that they can correctly master the reasonable commissioning methods of various valves. In this way, the closing sealing of electric valves under electric operation will be fundamentally improved. As long as the quality of the valve itself is good, the reliability of the valve will be improved and it will definitely be welcomed by users.
