Newbie’s question regarding the structure of control valves
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In a pneumatic control valve (butterfly valve) like the one shown in the figure below, the left and right sides are the spring areas, while the middle part is the air inlet area; a baffle separates these two areas. What I would like to ask is, are the spring area and the intake area relatively completely sealed? Or is it normal for a little gas to enter the spring area? It seems that intake should be allowed; otherwise, how could the middle baffle move back and forth? A newbie question, thanks.
In these two pictures, you see single-acting control valves; in reality, the spring side of such valves has a connection to the atmosphere. It is recommended that you take a look at the actual valve, as this will help you understand the principle behind the valves shown in the pictures
For single-acting control valves with exhaust ports on the valve body, these ports are usually blocked with a silencer or protected by a rain cover
In the middle is a closed piston, with an O-ring to ensure dynamic sealing.
There are air inlets on the cylinder block on both sides of the piston to ensure air intake and exhaust. When the valve is opened, the purpose of introducing air into the intake area is to increase the air pressure so as to overcome the spring force and drive the valve to move; the spring side is compressed, and the gas in the cylinder on the spring side is expelled ； When the valve is closed, exhaust occurs in the intake area; the spring force is greater than the pressure in that area, which pushes the intake area to compress and thus closes the valve.
The butterfly valve is equipped with a pneumatic actuator; the working principle is shown in the diagram
Newbie: This is just a schematic diagram; it does not represent the actual working principle of the valve. To understand it, one needs to consider the actual structure of the valve’s cylinder.