Regulating valve oscillation

Typically, insufficient spring stiffness in the control valve leads to unstable output signals, and sudden changes in these signals can cause oscillations in the control valve. Another scenario is when the frequency of valve operation is the same as the system frequency, or when the pipes and base vibrate violently, causing the control valve to vibrate as well. Due to improper selection, the control valve operates at a low opening degree, resulting in sharp changes in flow resistance, flow rate, and pressure. When these changes exceed the valve’s stiffness, its stability deteriorates, and oscillations may occur in severe cases. The corresponding solution: Since there are various reasons for oscillations, each specific issue must be analyzed on its own. For vibrations of mild intensity, increasing stiffness can be used to eliminate them. If a high-stiffness spring is used, switch to a piston actuation structure. Severe vibrations in pipes and bases are eliminated by adding supports to reduce vibration interference ； If the frequency of the selector valve is the same as the system frequency, replace it with a valve of a different structure ； The oscillations that occur when the control valve operates at a low opening degree are caused by an inappropriate selection of the flow capacity C value; it is necessary to choose a value for C that is lower, or to use step control or mother-child valves in order to overcome the problems associated with operating the control valve at low openings.

There’s also that type of intelligent locator that indicates a leak, causing the valve to keep slamming shut repeatedly – does that count as vibration?

Valve oscillation can be caused by two factors. One is an mismatch in the gain of the positioner; an excessive gain leads to an overly high flow rate, causing the valve to oscillate back and forth around the set point. The other reason is an excessively large or small dead zone of the valve, which is mainly due to the packing being installed too loosely or too tightly after the valve is disassembled.

I have also encountered severe oscillations in control valves before. The inspection revealed that it was caused by a large pressure difference before and after the valve.

Check whether the tightening screws of the valve positioner are loose

Reply to 1# open786: For the control valve in use, when such problems occur, a simple solution is to reduce the pressure drop across the control valve by closing the upstream valve, which can help minimize oscillations

We adjust the screw in the middle of the amplifier, try turning it back and forth; if that doesn’t work, adjust it again. It’s a crude method. .

This is most likely a problem with selection and installation! !

Reply 1# open786: Generally, it is because the control valve is in a low-open position; it’s mainly a selection issue