The pneumatic double-acting diaphragm valve cannot be fully closed on its own; it needs to be manually operated to close completely. Seeking help
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The double-acting pneumatic diaphragm valves used in the water treatment workshop fail to close properly when operated pneumatically; they only close fully when turned with a handwheel (without any feeling of sticking). The normal pressure in the pipeline is around 3 kilograms, with a maximum of no more than 6 kilograms ； I’ve tried gas pressures of 4.5 to 6 kilograms. In the workshop, the stainless steel gas supply pipe runs in a winding path from the solenoid valve control box to the diaphragm valve, covering a distance of about 3 or 4 meters. The diameter of this stainless steel gas supply pipe is Φ8, with an inner diameter of roughly 6; I’m not sure if this will have any impact. I plan to replace it with a Φ10 hose that runs from the valve control box to the valve to see if that works. I would like to ask whether this is a problem with the valve manufacturers? This manufacturer has been working with us since 2005, and such problems have never occurred before. Now the manufacturer itself can’t determine whether it’s an issue on their end... I would be extremely grateful if experts could help analyze this situation! :'(
This post was last edited by ylb913 on 2018-7-13 at 21:32. The pneumatic diaphragm valve does not close properly; we set it to the closed position, switch to secondary line control for the control valve, close the manual valves before and after it, adjust the threads in the middle of the valve stem to see if the valve can reach the closed position. If it can, it means it wasn’t closed fully enough – it needs to be pushed all the way to the closed position. Even set the valve position to a certain level, such as 0.1% closed (I didn’t pay attention to this; I’m not sure, but I know that 0.1% is an important value. With one of our butterfly valves, if it’s closed at 0%, it gets stuck and it becomes difficult to open it again; setting the limit at 0.1% eliminates this problem), and then manually lower the valve position further.
I hadn’t thought about that aspect... I always assumed the limit setting was fine; I’ll give it a try tomorrow!
Looking forward to the original poster resolving the issue and sharing the solution
It was a design issue: the diaphragm blocked the air inlets and outlets. We had the manufacturer come and weld a U-shaped groove in each of these openings to prevent blockages. Once the air could flow properly, the system could be closed again. The problem was resolved today.
The limit switches and handwheel both indicate that the travel distance is sufficient; the pipe pressure is also low, so it’s basically a limit switch issue
It means there’s air inside that hasn’t been released, I’ve learned it!