Regulating valve failure

It’s recommended to replace the locator; it seems to have lost its sensitivity

1. It doesn’t function when the adjustment range is small; I’m not sure what your adjustment range is； 2. The accuracy of various positioners varies; it ranges from 0.5% to 1%. Even among different models from the same manufacturer, the accuracy differs, and the positioner will not move if the adjustment range is less than the specified accuracy level ； 3. Check whether a dead zone is set in the control system or actuator; no action will occur if the adjustment amplitude is less than the dead zone ； 4. The valve is also a small system; from the positioner and pneumatic accessories to the actuator and the valve itself, factors such as pressure loss and the level of friction within the valve can affect its regulating performance. In such cases, it may be necessary to use valve positioner diagnostic software (such as FISHER VALVE LINK, METSO DEVICE CARE, etc.) to retrieve information such as the opening signal, actual opening degree, output pressure, friction analysis, and transition time, in order to identify the problem. Larger deviations (>2%) are generally caused by sticking of the actuator and the valve body itself, that is, an increase in friction ； In applications where high adjustment accuracy is required, positioners with higher precision should be used, along with an optimized air circuit.

To what extent is the amplitude small? Does it mean that an action that was possible before can no longer be performed? Or something. Please describe it in detail.

Check for issues such as insufficient air supply pressure, stuck valve stem and spool, air leakage in the air circuit, large dead zone (low sensitivity), and wear in the torque transmission mechanism of the valve actuator. Check the smart locator to see if there have been any changes to the settings

The dead zone is set too large; adjust it again in the locator

Most common causes: 1. Stuck valve stem； 2. There is a transmission clearance in the positioner feedback rod.

Is the locator not properly adjusted, is it malfunctioning, or is the valve stuck? Be more specific about the question!

There are many reasons for this, but it’s not a big issue if the operation level is below 1%; after all, the normal operating range for valves should be between 25% and 75%, with other ranges being designed for specific purposes. If the process requires sensitivity of less than 1%, consider Fisher or Memosyn valves with a price of around 200,000 yuan (DN50); otherwise, well..……

The information on the 3rd floor is quite detailed; we encounter similar situations in our company as well. Generally, it’s because the dead zone of the valves isn’t adjusted properly, but our requirements aren’t that strict.