When the regulating valve vibrates, the system piping will pulsate, causing accessories and components to loosen and generate noise. In severe cases, it may even lead to valve seat vibration and detachment, resulting in the system being unable to operate normally, and sometimes even unable to start.

    The vibration of a regulating valve is related to its frequency. When the frequency of an external force matches or is close to the system's resonant frequency (the ideal undamped vibration frequency), the external force performs positive work on the system throughout the entire cycle, forcing the vibration energy to reach its maximum. This situation is called resonance, and the external force at this time is referred to as a resonant force. It can be seen that the condition for resonance must be the same or close to the system's natural frequency. If this condition is disrupted, it will disrupt resonance, thereby eliminating vibration and noise. So, when designing a system, can we prevent their frequencies from being the same through calculation? The answer is no. Since the resonant frequency is usually impossible to calculate, it can only be eliminated during actual operation when resonance occurs. It should be noted that resonance itself is a coincidence, not a quality issue with the regulating valve. Many people believe that it is caused by the regulating valve and do not try to eliminate resonance. This idea is wrong.

    1. Solution to regulating valve vibration

    Based on extensive experience in regulating valve maintenance, the following methods for reducing or eliminating valve vibration are summarized:

    1. Mild resonance

    ① Improve the valve stiffness, such as selecting a high-stiffness spring or switching to a piston actuator.

    ② Increase damping, that is, increase the frictional force of vibration. For example, the valve plug of the sleeve valve can be sealed with an "O" ring, and graphite packing with high frictional force can be selected.

    ③ Increase the guiding dimensions and reduce the fitting clearance. The guiding dimensions of the plunger valve core are generally small, while the fitting clearance of all valves is generally large (0.4~1mm), which contributes to the generation of mechanical vibration. Therefore, when slight mechanical vibration occurs, this method can be used to mitigate it.

    2. Moderate resonance

    In a throttle opening with high-speed flow and rapid pressure changes, the frequency of the vibration source of the regulating valve can be altered by changing the shape of the throttle component.

    ① Change the shape of the throttle component. Turn the valve core surface within the vibration opening range by 0.5~1mm, and file or mill the window or valve core opening by 0.5~1mm.

    ② Replacement of throttling components to change the flow characteristics, mostly to linearity; replacement of valve cores, changing plunger-shaped valve cores to "V-groove valve cores, changing double-seat plunger valve cores to sleeve-shaped, changing windowed sleeves to small-hole sleeves, etc.

    3. Excellent resonance performance, with a wide resonance opening range

    Another type of throttling valve can be replaced, such as changing a double-seat valve to a sleeve valve, or vice versa. Valves with different structures naturally have different resonant frequencies. Changing the type of valve is an effective method to fundamentally eliminate resonance.

    II. Solutions to poor stability and oscillation of regulating valves

    In the industrial field, when the stability of the regulating valve is poor and oscillation occurs, we can take the following measures:

    To change the direction of the unbalanced force Ft, the method of changing the flow direction is commonly used. For example, for a straight-through single-seat regulating valve with dg ≥ 20mm, changing from a flow-closed type to a flow-open type can easily solve the stability issue of the regulating valve.

    2. To avoid unstable areas of the regulating valve itself, in addition to changes in the direction of unbalanced force (ft), the regulating valve is prone to oscillation. For example, butterfly valves usually alternate between 5-10° and 75°, so the minimum opening should be greater than 20%, while the full opening is 70°. Another example is double-seat regulating valves, which are generally used alternately within the range of 10% and 80-90% of the opening. These should be avoided during use as much as possible.

    3. Replacing a regulating valve with good stability. A regulating valve with good stability exhibits small changes in unbalanced force and good guidance, and a sleeve regulating valve possesses these characteristics. When the stability of single-seat or double-seat regulating valves is poor, a sleeve regulating valve can be used as a substitute.

    4. Increasing spring stiffness is a common and simple method to enhance stability, such as replacing a 20-100kPa spring with a high-stiffness spring of 60-180kPa. This method is primarily used for control valves with positioners; otherwise, a positioner is required.

    5. Reducing Response Speed When the system requires that the response or adjustment speed of the regulating valve should not be too fast (such as when the flow needs to be fine-tuned), but the speed of the regulating valve is relatively fast, or the system itself is a fast-response system, and a positioner that accelerates the action is installed on the regulating valve, overshoot will occur, causing oscillation. To address this, the response speed should be reduced. The methods are as follows: 1. Change the linear characteristic to logarithmic characteristic. 2. For systems with positioners, convert them to converters, relays, etc.