Why does the operating resistance of small-diameter ball valves decrease significantly?
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The DN10 ball valves manufactured in our own factory have valve seats made of PTFE, and the compression amount of these seats has been set very high; as a result, when the valve is opened or closed, the steel ball leaves marks on the valve seats. However, once the handle is turned to the open or closed position, the resistance on the valve stem drops sharply to less than 1 nm. Could any expert tell me what the reason for this is?
Firstly, the internal damage to this valve is caused by impurities in the medium. The adjustment inside the valve must be done in accordance with the fit at the time of manufacture. Replacement should be done using original parts, provided that the valve core is not damaged. Additionally, ball valves are not recommended for regulating fluids. For reference.
Thank you, teacher. What we are working on is the simplest manual ball valve, with air as the medium. The sudden drop in resistance mentioned earlier occurred before conducting the pressure test; it was already this way after assembly. Due to a lack of prior experience, we were unable to determine the correct relationship between the seat compression amount, resistance, seat hardness, and the contact area of the steel ball. (The compression amount calculated according to the ball valve design specifications is very small; if the actual compression amount is used based on those calculations, the resistance to opening and closing the valve would be very low. Therefore, it is necessary to increase the compression amount.)
In your case, the problem lies in the design drawings: the sealing surface of the sphere does not fit properly with the valve seat. By increasing the compression force, it may seem as though sealing has been achieved, but in reality only a line of pressure is used for sealing. Therefore, as soon as the valve is opened, this line of pressure is no longer in place, and the valve seat loses contact with the sphere; as a result, the resistance drops significantly.