Limiting method for pneumatic valves
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In production, limit issues with pneumatic valves are common. Does anyone know how pneumatic valves achieve limiting? Including upper and lower limits (two types: gas on and gas off). I hope everyone can give me some advice. Thank you
The positioning mechanisms for pneumatic valves can generally be divided into two types: mechanical positioning and positioning controlled by the main DCS system. However, for control valves used in field applications, mechanical positioning is usually adopted, as with mechanical positioning it is also necessary to ensure that the valve returns to its original position in case of a power or air supply failure (in the case of valves equipped with springs). Therefore, mechanical positioning is the method commonly used for valves intended for industrial use.
When ordering the valve, it’s sufficient to install two limit switches! !
What limit? The switch is still mechanical.
Mechanical limits have an adverse effect on the valve; it is forced into a fixed position and is still under stress, experiencing small fluctuations up and down, which leads to heat generation and wear. Over time this results in fatigue, so it is better to use electrical limits along with an appropriate dead zone. The instructions contain all the relevant explanations.
I also think the electrical limit control is better; all our pneumatic valves are like this
A valve with a manual operator can also be used, but I’ve only seen ones for setting upper limits; I haven’t seen any for setting lower limits
Limit switches come in mechanical, inductive, and spring-type versions.