What is the principle behind increasing the pre-tightening force of a control valve? How do I operate it?
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I would like to ask the experts: What is the principle behind applying preload to control valves? How do I operate it?
Are you referring to frictional resistance? Is it called differently?
My understanding is that it’s like a belt with a narrow waist; the principle behind it is similar to that of elastic bands. The pre-tensioning of the packing in a water pump’s dynamic seal is the same as the pre-tensioning of the packing in a valve’s dynamic seal. For reference.
It’s a leakage issue within the valve; by increasing the pre-tightening force, the leakage decreases. It seems that the distance between the push rod and the valve stem is adjusted in the connecting block, but I’m not really sure about the details
That’s the idea. Could you give some guidance on the specific steps?
There is no fixed format for this; the only requirement is that there is no leakage during use, and the looser it is, the better. If it becomes so tight that it can no longer be tightened any further, the packing must be replaced. For situations with a large temperature difference, it is indeed difficult to master such operations, and this is the only approach available; it’s worth giving it a try.
Increase the compression amount of some springs to ensure that the valve can be fully closed at zero position. Each manufacturer has different requirements for preload force. Too low a pre-tightening force may prevent proper sealing, while too high a force can cause excessive stress between the valve core and the seat, leading to damage. For example, if the desired force on the valve is 0.2 Bar, the connection piece between the diaphragm head and the valve stem can be separated, and a pressure regulator can be used to supply an air pressure of 0.2 Bar; this will cause the diaphragm head to compress slightly, after which the connection piece can be reattached. At this point, the pre-tension is 0.2 Bar, because when the air supply pressure is completely removed, the spring exerts a pressure of 0.2 Bar downward.
The simple solution is to add a spring, or replace it with one that has greater force. But it takes into account the air source start-up pressure. It is not recommended to make changes on your own; it is safer to contact the manufacturer.