We have a level control valve on a sulfuric acid tank that has a pneumatic positioner on it. It's a teflon lined bellows valve. We have experienced several failures of the bellows, even after tuning the loop. We are considering using a teflon lined rotary valve in this application, and I wondered if I could get even better life out of the new valve if I did not use a positioner? Thanks Jim Moore

 

NEVER choose a valve without a positioner if it will control a level. Without a positioner, your valve will have some backlash and coupled with the integrating dynamics of your level process, the valve will cycle and could fail faster. With a positioner, your valve will have less backlash and will oscillate less. If you want to make sure you have no limite cycle or your valve put cascade control on your level controller.

 

Thanks for your help Ben, we will go with a positioner.

Jim Moore