The pneumatic piston-type control butterfly valve operates slowly
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Please help resolve this issue: The butterfly valve in the gas main pressure regulation section is operating slowly now; this problem did not exist with the new equipment, and it has been working slowly recently. This valve is a air-operated valve; its accessories include a filter pressure regulator, a positioner, a solenoid valve, a limit switch, a speed control valve, and an air-controlled valve! The air source pressure is normal, at 6 kilograms! Please help analyze the reasons!
Preliminary assessment: The O-rings on the piston inside the cylinder are worn, causing air leakage between the two cylinders; as a result, the output torque is insufficient and the thrust generated by the cylinder is not enough. The cylinder needs to be removed, opened, and the gasket replaced.
Is the instrument air clean, and is there any blockage in the speed control valve?
First, check the various components of the gas circuit for any leaks, and then try increasing the pressure of the gas supply to see what happens
It’s an O-ring or an accelerator; most likely it’s an O-ring. Provide the manufacturer with the model of the actuator, and just buy a set of O-rings to replace it.
The butterfly valves in the gas processing section operate slowly, but I’m not sure just how slow exactly; has it exceeded a certain limit?
Thank you all for your answers. I thought it was a problem with the attachment, but now that I’m here in person, it doesn’t seem that slow! I’ll open each attachment and clean it up tomorrow!
How does the pneumatic piston control valve compare in performance to the pneumatic spring diaphragm control valve?
According to you, this valve is just slow to respond, with no other faults, right? Air source: 0.6, along with a speed control valve and an air-controlled valve; it shouldn’t be slow under normal circumstances. Please check the design specifications; there it mentions the action time (valves with requirements regarding action time). If it has a spring, is the spring force too strong?
How long does it take to go from full open to full closed? What is your caliber? Also, are you referring to the valve reacting slowly (it takes a long time for it to start moving once a signal is given), or does it move slowly (when a strong signal is applied, the valve progresses slowly toward its corresponding opening degree)?
The person in charge at the site removed all the instrument accessories directly, and then fed filtered instrument air into the air pipe connection of the cylinder to check whether the opening and closing action of the piston cylinder was still slow. If it was slow, it indicated that there was a problem with the piston inside the cylinder, such as issues with the sealing of the piston seal or with the rotating parts of the mechanical mechanism within the cylinder. If it is normal, check the areas around it step by step to rule out possibilities.
It is possible that the O-ring seals (made of silicone rubber or fluororubber) inside the actuator cylinders have worn out, resulting in air leakage between the cylinders; our company has encountered this problem before.
Everyone’s attention is focused on actuators and pneumatic accessories; here, I’d like to offer another perspective, as this is also a problem we encounter frequently here. In other words, particles and impurities present in the process medium can easily get trapped between the valve stem of the butterfly valve and its shaft sleeve; over time this can lead to sticking, and once sticking occurs, the valve will operate more slowly. Our company uses triple-eccentric butterfly valves from a well-known brand; 8 of these valves have encountered this problem. By taking the valve off the production line, disassembling it and cleaning the valve stem, the issue is resolved.