The vibration of the control valve is generally divided into two states, one is the overall vibration of the control valve, that is, the whole control valve vibrates frequently on the pipeline or the base. The other is the vibration of the valve core of the regulating valve. It can be seen from the frequent movement of the valve stem up and down. The following analysis on the causes of these two kinds of vibration and the treatment measures are as follows:

1. Overall vibration of control valve

The reasons for the vibration of the whole control valve on the pipeline are as follows: the violent vibration of the pipeline or the base is easy to cause the vibration of the whole control valve; in addition, it is related to the frequency, that is, when the external frequency is equal to or close to the natural frequency of the system, the forced vibration energy reaches the maximum value and generates the common vibration. These two factors sometimes influence each other, which will make the vibration more and more intense, make the pipeline run out, the accessories or components loose, and make a clattering sound. In serious cases, it will cause the valve rod to break, the valve seat to fall off, and the system will not work. Based on this situation, the pipes and bases that cause vibration should be reinforced, which also helps to eliminate the interference of external frequency.

2. Sometimes, the flow velocity of the measured medium increases sharply, which makes the differential pressure between the front and back of the regulating valve change sharply. When the rigidity of the valve is exceeded, the stability of the valve becomes worse, which also causes serious vibration of the whole regulating valve. But this kind of oscillation is not necessarily caused by the small opening of the valve. This vibration is usually accompanied by shrieks. The stability of the regulating valve is poor. Once the interference of internal or external unbalanced force exceeds the rigidity of the regulating valve, and the regulating valve itself does not have the ability to eliminate this interference, it will produce oscillation. At this time, it is necessary to increase the stiffness of the regulating valve, for example, to increase the spring of 20-100kpa, or to increase the stability of its operation, which has certain advantages.

The installation position of the regulating valve shall be far away from the vibration source. If it is unavoidable, preventive measures shall be taken. The vibration of the whole control valve can be basically adjusted with the external given signal before reaching the resonance. Because the relative displacement of the external given signal to the valve core does not change or change very little due to the vibration of the whole regulating valve, the reason is that they are a whole. When the stop valves at both ends of the regulating valve are opened or closed violently, the sharp flowing wave measuring medium will produce strong reflection shock wave, which will impact the regulating valve core. When this force is greater than the downward pressure of the diaphragm on the valve core, it will make the valve core move up and generate vibration, especially in the case of small signal, because the preload is small, it is easier to make the valve core vibrate. When the opening of the regulating valve is too small, the differential pressure between the front and back of the regulating valve is too large, so that the flow rate at the throttle increases and the pressure decreases rapidly. If the pressure drops to the saturated vapor pressure of the liquid at this temperature, the liquid will be gasified, flash will be formed, bubbles will be formed, strong pressure and shock wave will be formed when the bubbles break, and air hammer will be produced. This pressure can generally reach tens of megapascals. The air hammer impacts the valve core to form honeycomb and strong pitted surface and vibrate the valve core. Generally, the causes of valve core vibration are as follows: the output signal of regulator is unstable. If the sensitivity of the valve positioner is too high, the output of the regulator will change slightly or drift, and the output signal of the positioner will be very large immediately. Cause the valve to oscillate.