Consultation on pneumatic control valve failures
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A pneumatic control valve in the plant has failed. The fault is manifested in such a way that when the DCS commands a 10% opening degree, the control valve does not move (although there is a sound of air flowing into the cylinder); whereas when a 15% opening degree is commanded, the control valve starts to move with a clicking sound. There are no issues with operation at an opening degree of over 15%, but it does not function at low opening degrees. What could be the cause of this? (The valve positioner has been checked and shows no faults.)
Based on the description, it is presumed to be a gas-controlled valve; there is collision due to the inclination of the twin springs inside the pneumatic actuator. It is recommended to check the springs in the pneumatic actuator, and pay attention to safety to prevent the springs from rupturing. For reference.
It might be that the valve core is stuck; take it apart to check
The valve core and seat are stuck and need to be disassembled for repair.
The key is whether it’s a gas-on valve or a gas-off valve; different valves result in different reasons
When closing the valve, the valve core gets stuck to the sealing surface; removing it for inspection does not provide a complete solution
First, remove the membrane head or cylinder to check the spring; if the spring is fine, then the valve is stuck
Personally, I think it might be due to the valve getting stuck when it is being closed. Additionally, if the pressure difference before and after the valve is too large, it can also prevent the valve from opening properly at low opening degrees.
Can you take a photo of me? We specialize in control valves and positioners, QQ3842726
The valve core is stuck. Additionally, the selection of the control valve and the operating flow rate are coordinated with each other.
Everyone, we’re really impressed by you guys! People have said that there is an intake sound at 10% opening, and the valve moves at 15%! It must be the pressure release valve! On the first floor, they seriously said it was a gas shut-off valve! This is usually due to wear or deformation inside the valve body, or sticking of the shaft sleeve! Take it apart and have a look!