The pneumatic butterfly valve sticks when fully closed

It can’t be the quick-flow valve body (VALUE) either; it must be handling a medium similar to steam

That’s just the nature of butterfly valves. Wipe the sealing surface with clean cotton yarn dipped in a little machine oil, then open and close it several times; if there is no sticking, then there is no problem. Check for air leaks in the actuator cylinder: Inject compressed air from both sides; after closing the inlet, the pressure should remain stable for a certain period of time. If there is a leak, the output of the actuator will not meet the requirements.

Klaus exhaust, steam jacket valve.

There’s no problem with the actuator; I think the limit of the time valve plate is too far back, causing the valve core to close too much.

:L is also a valve used in exhaust gas treatment. We have here a valve in a situation similar to what you described: after being operated four or five times with an increased air supply pressure, it got stuck in the middle position. The seal condition of the valve gate was as you said; after the manufacturer took it back for inspection, it was found that the shaft holes and attachments on the upper and lower parts of the valve (things similar to pins) had broken into several pieces, which caused the valve to get completely stuck

This is a common problem with disc valves, caused by their structure. The disc of the butterfly valve (i.e., the valve element) and the sealing surface of the valve seat form a frustum-shaped surface; when the valve is closed, in order to reduce leakage, the closing position is often as close as possible to the minimum position (near the radial center line). The sealing surfaces are available in two materials: hard seal and soft seal. With a hard seal surface, impurities in the medium tend not to detach after sticking to it, or the sealing surface may corrode, which increases frictional resistance. When the valve disc is closed near the radial center line, the leakage is reduced. However, when trying to open the valve again, insufficient torque from the actuator – due to the resistance from medium flow, the resistance between the valve stem and the valve seat, and the resistance at the sealing surface (with the latter two resistances increasing) – prevents the valve from opening. Therefore, when adjusting the limit position of the valve’s closed state, the electrical and mechanical limits need to be adjusted in coordination. It is not easy to close it too tightly within the required leakage range. At the same time, it ensures lubrication between the valve stem and the valve seat, as well as increases the torque of the actuator.

I agree with the view above – it’s a problem related to the torque output of the cylinder. Increasing the air pressure slightly can also be a solution. The limit pin is another factor to consider, but the valve is mainly regulated by the cylinder itself; by the time it reaches the position of the limit pin, the force should not be very high, otherwise the valve core (valve plate) would deform……

I think the main issue lies with the actuator. Of course, over time, the sealing surface of the butterfly valve can also be damaged due to erosion; increasing the size of the cylinder might be a solution

1. When a hard-sealed butterfly valve is closed, it is essentially a cone that is inserted into a conical hole (which is somewhat similar to how a needle valve operates when closed). To achieve the exact degree of compression required for the sealing surfaces to fit together at a specific location, the manufacturing requirements are extremely high. 2. The fit between the valve core and the valve disc of a butterfly valve is related to the temperature during the valve’s operation. The limit is set at the position where the valve maintains a sealing pressure at the highest temperature. Therefore, for the above two reasons, the limit should generally not come into effect during normal (room temperature) inspections. A very important reason why a butterfly valve cannot be opened after it has been closed is that closing it while it is still hot causes the valve body to contract, thereby locking the valve disc in place. Adding a layer of heat tracing and insulation around the outside of the valve seat can solve the problem to some extent ； Adjusting the limit to lock the valve disc at room temperature can also solve the problem. However, at this point, the problem of valve leakage occurs right after it is closed under operating conditions (before it has cooled down). It is necessary to decide whether to use it based on the process requirements.

The explanation on the 8th floor is quite clear: with this type of hard-sealed symmetric butterfly valve, closing it too tightly can lead to jamming. In my opinion, the sealing performance of the control valve is less important; flexibility is what really matters. Changing the limit is indeed the most direct way.