Improved stiction compensation in pneumatic control valves

The oscillations caused by static friction (stiction) in control valves cause losses in quality and expense of raw materials. The effects of friction can be reduced through compensation techniques, until the maintenance of the valve is made in the next programmed plant shutdown. In this work, a well-known stiction compensation method that reduces variability both at process variable and valve stem movement is revisited. Limitations of this method are overcome through two proposed methods using a similar approach. The effectiveness of the proposed compensators is demonstrated using simulation examples and a flow control loop in a pilot plant.

► Stiction compensation techniques can be used to reduce oscillations in control loops.
► We propose methods to reduce variability in the process variable and the valve steam.
► Compensation is illustrated with an example and with a flow loop of a pilot plant.
► The methods are applied to self-regulating processes and can handle disturbances.