If the zero point of the air-operated control valve is not set correctly, can increasing the distance between the actuator and the valve stem help?
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The zero point of the air-operated control valve is not set correctly; can increasing the distance between the actuator and the valve stem help? Will this work if done that way?
Can’t it be closed tightly? Check the design parameters and actual operating conditions; if the pressure difference increases when it is closed, that means the spring force is insufficient. Your solution only addresses the zero-point issue – what happens when the valve is fully open? Is the force provided by the diaphragm or cylinder still sufficient?
Pneumatic shut-off valve: the zero position is not accurate; in my understanding, this means that it’s not possible to ensure a fully open state. In other words, when the signal is 4 milliamps, the valve stem does not rise completely; in such cases, the usual approach is to use pliers to turn the valve stem upward by a few degrees. Then observe whether the valve can close completely at 20 milliampere hours; if it can close completely, that’s sufficient. If the valve cannot be closed completely, and the valve stem has not reached the bottom by 20 milliamps, follow the same procedure: use pliers to turn the valve stem downward a little. To make the operation easier, it is usual to turn the valve stem while it is not fully closed, as otherwise it will be difficult to turn; after that, observe the condition of the valve.
You can also try to close it when there is no load; if it can be closed, that indicates that the pressure difference is too high, there is an issue with the valve selection, or something inside the valve is blocking it； If it still cannot be closed, it’s a problem with the valve; you can try increasing the distance between the valve stem and the actuator to see if that helps. It could also be an issue with the positioner, in which case the positioner should be recalibrated.
Sure, the length of the valve stem can be adjusted. First, determine whether it really doesn’t close tightly, and rule out other reasons such as insufficient air supply pressure or inaccurate scales
You need to rule out the possibility that nothing is actually stuck inside the valve first
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