Valve stability is poor and how to solve the oscillation

(1) to change the direction of the unbalanced force Ft is usually used to change the flow direction of the method to change the direction of FI. Such as the dg ≥ 20mm through the single-seat valve from the flow closed to open type, can be easily solved the stability of the valve. (2) to avoid valve instability zone imbalance force FI occurs changes in the direction of the exchange, the valve easy to produce oscillation. Such as the butterfly valve, usually 5 ° ~ 10 °, 75 ° two changes occur, so the minimum opening should be greater than 20%, the full opening of 70 °; another example, double seat valve, generally less than 10% and 80% 90% open on the change, use should be avoided. (3) replacement of a good valve stability Good stability of the valve change in its unbalance small, good guidance, the sleeve valve has this feature. When single, double seat valve stability is poor, can be replaced with sleeve valve. (4) increase the stiffness of the spring This is to improve the stability of a common simple method, such as the 20 ~ 100kPa spring into 60 ~ 180kPa large stiffness spring. This method is mainly used with the valve locator, or else with another locator. (5) reduce the response speed When the system requirements of the valve response or adjustment speed should not be too fast (such as the flow needs to be fine-tuning) and the valve speed is faster, or the system itself is a fast response system, and the valve with locator to speed up Action, will have overshoot, oscillation occurs. In this regard, should reduce the response speed. There are ways: ① the linear characteristics of the logarithmic characteristics; ② with the locator can be changed to the converter, the relay. 876 pneumatic film regulating valve instability, resulting in oscillation, which are the reasons? ① regulator output signal is unstable. ② pipe or base violent vibration. ③ valve positioner sensitivity is too high. Circulation capacity C value is too large. Regulating valve in the small opening state work. ⑤ throttle pieces with the guide gap is too large. ⑥ stem friction, prone to hysteresis oscillation. ⑦ actuator rigidity is not enough, will produce oscillation in the whole trip; spring preload is not enough, will occur in the low-stroke oscillation.

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