Discussion on valve opening degree?
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For control valves under the same operating conditions, some DCS systems do not indicate an open state when the value is below 5%, while others do not indicate an open state until the value is below 10%. What is the reason for this problem? How to adjust? Is it difficult to include scales to indicate the degree of valve opening?
Check the output pressure; sometimes a 5% valve position is not easily detectable. If the values are 5% and 10%, while other values such as 25%, 50%, 75%, and 100% are normal, it’s possible that the operating pressure is too low ； Or a card ； Or the valve position may be incorrect; adjusting it could be considered
The question isn’t very clear. In DCS, the on/off position of a valve can be defined based on its opening degree. Do you mean that the scale indicating the valve is open refers to the degree of opening of the valve? None of these are difficult; as long as the valve is a control valve with an opening degree feedback to the DCS, it’s fine.
In our coal chemical industry, the standard requirement is that the valves be shown as fully closed when the opening degree is below 5%. Under normal operating conditions, and with proper valve selection initially, the valve opening should generally be between 30% and 70%. If there is a valve position transmitter on site, it can display the actual opening degree of the valve.