What are the methods to solve the poor stability of regulating valves


Published:

2023-01-16

If you encounter stability issues with the control valve during use, we propose five major solutions. The following content is hoped to be helpful to everyone.

If you encounter stability issues with the control valve during use, we propose five major solutions. The following content is hoped to be helpful to everyone.
1. Method of changing the direction of action of unbalanced force: In stability analysis, when the action of unbalanced force is known to be the same as the direction of valve closure, that is, when there is a tendency to close the valve, the stability of the valve is poor. When the valve operates under the above-mentioned unbalanced force conditions, the method of changing its direction of action is usually to change the flow closed type to the flow open type, which can easily solve the stability problem of the valve.
2. Avoiding unstable zone operation of valves: Some valves have poor stability when working at certain opening angles due to their own structural limitations. Double seat valve with an opening of less than 10%, causing instability due to open flow at the upper ball and closed flow at the lower ball; The stability is poor near the area where the slope of the unbalanced force changes alternately. Like butterfly valves, the alternating point is around 70 degrees; The double seat valve has an opening of 80-90%. When encountering such valves, working in unstable areas inevitably results in poor stability, and avoiding working in unstable areas is sufficient.
3. Replace the valve with good stability: The valve with good stability has a small change in unbalanced force and good guidance. Among commonly used ball valves, sleeve valves have this major feature. When the stability of single or double seat valves is poor, replacing them with sleeve valves will definitely improve their stability.
4. Increase spring stiffness method: The ability of the actuator to resist the impact of load changes on stroke depends on the spring stiffness. The greater the stiffness, the smaller the impact on stroke, and the better the valve stability. Increasing spring stiffness is a common and simple method to improve valve stability, such as changing the spring range of 20-100KPa to a high stiffness spring of 60-180KPa. This method is mainly used for valves with locators, otherwise, the valves used need to be equipped with locators.
5. Reducing response speed method: When the system requires the control valve to respond or adjust the speed not too fast, the response and adjustment speed of the valve are relatively fast. For example, if the flow needs to be fine tuned and the flow adjustment change of the control valve is significant, or if the system itself is already a fast response system and the control valve is equipped with a locator to accelerate the valve's action, this is unfavorable.
This will result in overshoot, vibration, etc. To address this, the response speed should be reduced. Change the linear characteristic to logarithmic characteristic; The ones with locators can be changed to converters or relays.