Fault analysis of intermittent increase or decrease in flow rate display while valve position remains unchanged
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For example: in a control loop, when the valve is at 50% position, the flow rate shows 10 tons, but it rises intermittently to 11 tons. By reducing the valve opening to 45%, the flow rate drops back to the normal value of 10 tons. However, when the valve is returned to its original 50% position, the flow rate does not return to 11 tons but shows a certain deviation. The valve position is correct; what could be the reason from a detection perspective? The medium is crude benzene feed
1# hzyhyb: Correction – the flow rate cannot return to 10 tons
2# hzyhyb: Once again, there is no issue with the operating conditions; in other words, the amount of material supplied remains unchanged
Your valve position refers only to the set value of the valve, not the feedback value, right? If that’s the case, it’s easy to explain: it’s either the instrument air pressure is too low or the pressure reducing valve is faulty
There are merely three reasons: 1. Process-related reasons. 2. Valve-related reasons. 3. Causes related to the level gauge. 1. Wear of the valve core. 2. Level fault (caused by the medium). 3. The process medium is dirty.
Personally, I don’t see any problems. 1. It is normal for traffic to remain stable for a while. For example, set the valve to 50% and take a reading after half an hour. Turn it down to 45% again and take a reading after half an hour. II. Well, that could be the problem – instability of the medium, such as temperature, density, etc., as well as factors like the pump’s rotation speed.
Flow measurement errors and measurement feedback lag (for flow measurement regulation, it is necessary to ensure that the control valve is installed at an appropriate distance in front of the flow measurement element; otherwise, significant lag will occur. The installation position should be appropriate to minimize the lag as much as possible. ), all of which will cause adjustment errors. Furthermore, since the control valve has a certain backlash, the situation described by the original poster occurs. Furthermore, changes in temperature and pressure can affect flow rates, and this situation also occurs. Equipment changes and other process modifications can also affect flow regulation.
7# Steel florets flying: Why does the flow rate reading rise intermittently when the valve position on site remains unchanged and the process conditions stay the same? Why is the flow reading deviating significantly after the original on-site valve position changes and returns to its original state? What are the issues from a testing perspective?
Due to process-related reasons, I have encountered similar situations: the flow rate kept increasing even though the control valve did not move. When switching to a manual valve, the flow rate continued to rise as well, despite the manual valve not moving. The flow meter was found to be in good condition, and it was also confirmed that the flow rate indeed increased when the valve remained stationary. Therefore, it is necessary to analyze the reasons from a process perspective, to determine whether there is an issue with the pump. The flow rate also increases when using a manual valve; it has nothing to do with the control valve