Problems with control valves and DCS
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There is a control valve in the plant that was originally a air-operated open valve; it has now been changed to an air-operated closed valve using a positioner. After this change, a problem arose: the opening degree of the control valve as shown on the DCS was the opposite of what it should be in reality. On the DCS, the valve is set as an air-operated closed valve in the regulator’s feedback configuration. How can this problem be resolved on the DCS?
The last edit to this post was made by ssln123 on 2011-6-30 at 13:51. It should be clear from the start that a valve positioner only changes the direction of operation; it does not alter whether the valve operates in an air-open or air-close manner. All you need to do is change the direction of action of the regulator. At the same time, AO inversion must also be set so that the control valve position corresponds to the actual condition on site.
What was said upstairs is completely correct. The positioner cannot change whether the valve operates in open or closed mode. Only the action and reaction can be changed. The valve is specified as air-open or air-close at the time of manufacture. In other words, the direction of the return spring and diaphragm inside the valve determines whether the valve operates in an open or closed state when air is applied.
Reply to 2# ssln123: Hello. Where can I configure the forward and reverse action of the regulator? I found the control valve, but all I can choose from is air-open or air-close. Also, how do I set the inversion of the DDZ3 AO output? :P
The settings for different DCSs vary; follow the system operation instructions.
Do you know what system you are using? Please be more specific so that HAIYOU can tell you exactly what to do and help you. It seems that you are not clear on the concepts at the moment; it is recommended that you first learn about what constitutes opening and closing of gas flow, as well as the positive and negative effects of positioners, and the positive and negative effects of regulators. This will make it much easier for you to handle such issues in the future.
It’s best to change the on/off status of the air valve in the DCS configuration. I’m only familiar with HONEYWELL systems, where it can be done by selecting the options in the PID module settings.
Our factory uses the JX-300x model from Zhejiang University Zhongkong. Thank you to all the technicians for continuing to provide answers
The control valve positioner cannot change FO or FC; at most, when the current is 4 mA, the control valve can be switched to closed or open depending on the positioner. But when the wind stops, the control valve still remains in the same fault condition as at the time of manufacture. This is because the diaphragm design of the control valve is fixed; therefore, to change the fault condition, one must either alter the way air is supplied to the valve or replace its spool
Ask one question and you have to answer a bunch of others. After understanding the principle of action and reaction for opening and closing, you also need to master the regulator of the system you are using. In short, it seems the original poster still has a lot to learn.
Yeah, thank you all, masters. I’ll study harder