Reasons for the automatic opening of a pneumatic control valve
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The pneumatic control valve was initially in the closed position; after manually increasing its opening degree from 1% to 10%, the valve suddenly opened fully on its own, for reasons unknown； As a layperson, I’m seeking advice from everyone here.
You haven’t been very specific; it’s important to know whether manual operation refers to control from a central panel or on-site. Based on manual operation via the central panel, here are my observations: First, the valve is equipped with interlocks, and once it reaches an opening degree of 10%, factors such as flow rate, temperature, and pressure can trigger these interlocks, causing the valve to open fully； The second is a locator failure ； Thirdly, it was an error in the central control system: instead of 10%, 100% was entered. If you are still in the construction phase, check the configuration module again
Thank you. It has been determined that the issue is caused by a fault in the locator, and there was a significant amount of oil inside it (it’s unclear where it came from). How can we prevent similar incidents from happening again?
It’s likely that there is oil in your instrument air system; the root cause is a failed or ineffective oil separator in your air compressor station. It is recommended that you first conduct a thorough inspection of the instrument air system, check the air filters on all valves, and carry out regular drainage at the end points as well as at various individual drainage locations ； Secondly, the air compression station addresses the oil issue at its root. Also, check whether there is any possibility of your instrument air system being connected to other process equipment; if there are devices that use instrument air as a sealing gas, those devices need to be inspected carefully
Reply to 3# ybtytyong: Add an oil-water separator to the input air supply of the locator, and discharge the liquid regularly~~~
It’s almost certain that the compressed air supplied by your instruments contains oil; increase the oil-water separation, and it’s best to use dry compressed air.
Water and oil contamination in instrument air is a problematic issue that needs to be investigated. I’m not sure about the source of your instrument air; it’s necessary to take samples from several different points to determine whether this is a common problem or an isolated case. If only the instrument air within this system is affected, then the pipelines need to be checked to identify where the oil is getting in – which pipeline is leaking. Many manufacturers are reluctant to install filters for instrument air, as they are confident in its cleanliness. However, chemical production processes can be complex, leading to many unexpected problems that require thorough analysis. Nitrogen pipelines can also contain various impurities, and as long as they are connected to the process system, there is a risk of air or liquid leakage
Instrument air is part of the utility system; people don’t pay attention to it when everything is fine, but once problems arise it becomes a hassle. Therefore, it’s necessary to pay more attention and conduct regular checks to prevent air leaks and breaches in the system.
What impact does a high oil content in the instrument air have on valve positioners? Could you be more specific?
I think it’s better to first check whether there are any issues with the logical configuration within the DCS. It’s possible that, due to timing problems during the operator’s operation of the control valve, the relevant data such as pressure and flow rate have not reached the requirements specified by the process within the allotted time after the valve is opened, which triggers the interlock mechanism.
Reply to 9# Zero Degree Freezing Point: The most obvious reason for oil contamination in the instrument air is the one mentioned by the original poster. The opening degree is abnormal. In severe cases, the control valve cannot be opened either