I would appreciate some guidance on issues with control valves and transmitters
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I encountered an issue at work: the control valve operates normally when the flow rate is below 60%, and the transmitter functions properly as well. However, once the flow rate exceeds 60%, the control valve opens further and the flow rate decreases (the valve element itself is fine). The fluid flows from the pump outlet, passes through the transmitter, and then reaches the control valve; there are no problems with the other pipelines. I would appreciate some advice from those with more experience
I haven’t encountered this problem before; let’s wait for an expert to answer it! !
The zero point and range of the locator have not been set correctly; it needs to be recalibrated..................
Check what the actual output signal of the transmitter is at 60%. If the signal is normal, the problem lies in the flow totalizer; otherwise, the issue is with the transmitter and the connecting pipelines. Inspect the transmitter as well as the pressure guiding tubes to check for any blockages. Personal opinion, for reference only.
Was the description of this issue provided by the process team? I think you’d better verify it yourself
The valve is opened wider, but the flow rate is actually lower. Listen to it with your ears – it seems unlikely
You must work together with the process engineers on-site to determine, when the signal reaches over 60%, whether the valve stem should move forward or backward Can we also measure at this time whether the current changes in a consistent manner? Now you should know what the problem is! :lol
A larger opening results in a smaller flow rate. First, check the valve positioner to see if the stem displacement is correct under the given signal. You say there’s no problem with the valve core, so what kind of valve is it – a butterfly valve or a cage valve? If it is a cage type, is the connection between the valve stem and the valve core intact, and is there any signs of detachment? What is a flow meter? What kind of flow meter is it? Differential pressure, electromagnetic, or vortex street? Is there any leakage in the differential pressure? Is there any minor blockage? Is the transmitter’s linearity intact? After the valve is opened, does the pump’s output ensure that there are no bubbles in the pipeline and that it is filled to capacity? Does the vortex street cause severe vibrations in the pipeline when the valve is opened wide? Does the pump’s output ensure that there are no bubbles in the pipeline and that it is fully filled?
Is the flow rate highest when the valve position is at 60%? If the valve position is increased further, does the flow rate remain unchanged at the level corresponding to 60% opening? Is it still below the flow rate corresponding to 60% opening? If the flow rate remains unchanged, it is likely a problem with the valve; it is recommended to disassemble it for inspection offline. If the flow rate decreases, check the differential pressure transmitter. Check its output current and the corresponding differential pressure value, as well as the input current of the valve positioner. Is it consistent in the loop? The fault symptoms aren’t very specific, so it’s hard to say.
It’s not clear whether the poster observed this from the control room or on-site; first, it’s necessary to confirm whether the value of the control valve on-site is above 60%, which would result in a decrease in the flow rate indicated by the flow meter. If on-site verification shows everything is normal and it’s unknown what the medium is, then check whether changes in the state of the medium occur when the valve is opened, thereby causing changes in the flow rate
It is best to manually send a signal to the valve and go to the site in person to verify it; this situation occurs very rarely