Calibration of control valves

This post was last edited by ylb913 on 2015-12-13 21:00. Is it not a butterfly valve? We can’t adjust the fans of the sulfur exhaust incinerator even a few times in a year or two.

You use proportional control, right? It’s probably the large fluctuations in air volume that cause wear

First, check the quality of the valve you purchased; you can conduct a pressure test first

For the proportional control valve, are the initially calculated CV value, opening degree, flow rate, and so on correct?

I’m not sure about this; we are operators, and after replacing it with a new one, the flow rate became too high

What type of valve do you use on site? Is it a control valve, a control butterfly valve, a control ball valve, or something of that kind? First, let me know what type of valve it is. If it’s a straight-stroke control valve, it’s possible that the positioning mechanism has shifted due to vibrations during transportation (in other words, when a signal is sent to close the valve fully, the valve does report that it’s closed, but in reality it isn’t fully closed yet). In such cases, the power supply can be turned off and manually tried to close the valve further; if it can be closed further, then it’s simple – just reset the positioning mechanism and have the valve go through a full open-to-full closed cycle, and that should solve the problem. As for ventilation butterfly valves, these are designed specifically for ventilation, with flue gas being the common medium used. For valves with larger diameters, the internal leakage rate can be as low as 1%, while for those with smaller diameters, the leakage rate is around 3%. Due to structural limitations of this type of valve, there’s nothing much that can be done. First, confirm what type of valve is being used on site

It is a straight-stroke control valve; it’s a newly installed valve. The old valve before it could only cause a change in air flow of around ten cubic meters for each unit change, while now it causes a change of seventy to eighty cubic meters per unit change.

There could be two reasons for this. The first reason is that the flow characteristics have changed; for example, the old valve had a proportional flow characteristic, while the new valve manufactured by the current supplier has a linear flow characteristic. This information can be found on the label attached to the valve. The second reason is that when the old valve was manufactured, the CV value was calculated based on the conditions at the installation site, and the valve core was designed with a reduced diameter. However, when manufacturing the new valve, the supplier did not perform such calculations and simply produced it according to the standards for control valves. For instance, if the valve size is DN50, the manufacturer of the old valve might have chosen a valve core with a diameter of DN25; thus, the valve core in the old valve had a diameter of DN25. In contrast, the manufacturer of the new valve did not carry out any such calculations and directly used a valve core with a diameter of DN50. As a result, the valve cores are different. This information can be found on the labels of the valves; you can check the label of the new valve on-site and then look at the label of the old valve to understand the situation.

If it is a single-seat valve, then the valve core is made larger to restore flow and pressure; perform some calculations. Based on your description, it can’t possibly be a V-ball or a control butterfly valve. Install flow-blocking plates in the pipeline or modify the valve core again