Causes of surge in control valves and solutions
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Please discuss the causes of surging in pneumatic diaphragm control valves and the solutions to it.
It’s that the inlet pressure is high and the outlet pressure is low. Connect a secondary line for venting at the inlet
Sometimes the smart locator identifies the wrong type of sensor head!
There’s logic upstairs! It’s because the pressure difference is too large; the membrane tip cannot hold back the pressure, resulting in surge. It is recommended to replace it with a diaphragm head with greater thrust. Or change the type of valve to ones that can withstand high pressure differences, such as sleeve valves or V-ball valves
If the actuator diaphragm is aged or the spring stiffness is low, replace the actuator.
Adjust the Xp knob on the locator.
1. It may be that the pressure difference before and after the control valve is too large, preventing the diaphragm head from exerting sufficient pressure and resulting in surging. It is recommended to replace the diaphragm head with one that provides greater thrust, or to switch to a different type of valve such as a sleeve valve that can handle high pressure differences. It’s possible that the PID parameters of the control valve are not suitable; therefore, the gain settings need to be adjusted
The common cause is improper adjustment of the valve positioner; issues such as high sensitivity, inflexible feedback levers, and excessive output flow can all lead to oscillations.
I think it might be due to process-related reasons, mainly an excessive pressure difference before and after the control valve. It is also not possible to rule out issues with the control valve itself; during maintenance, it was confirmed that the valve was in good condition because there was no pressure in the process pipeline, but the operating conditions are different when the system is put into normal use! Additionally, if the gas supply pressure is unstable and fluctuates, it can also lead to the aforementioned situation.
We have encountered this issue with the control valves of tooling in our projects; adjusting their sensitivity can resolve it.
It’s possible that the part of the valve positioner responsible for positioning is damaged! It might be that the supply pressure is too high; adjust the pressure reducing valve (check the valve’s label for the required supply pressure for adjustment)
First, consider process-related factors. Taking our own facility as an example, with mixed refrigerant cycle compressors, sometimes the composition ratio in the process pipelines does not meet the required standards, which affects the turbine speed of the drive compressor and thus leads to severe surging. Instrument-related reasons: Issues stemming from the valve itself, such as certain signal problems with the valve actuator or fluctuations in the pressures measured by the pressure gauges at the inlet and outlet of the surge valve. A good solution is to regularly check these gauges and calibrate them, as well as to adjust the anti-surge parameters of the controller every few years.