Experimental Characterization and Diagnosis of Different Problems in Control Valves.

In the perspective of developing an integrated system able to include loop performance assessment and early diagnosis of anomalies, an experimental characterization of more common problems encountered in industrial valves has been carried out on a pilot scale plant. The primary scope was to investigate the possibility of detecting different types of valve anomalies from the analysis of routine data, by taking into account additional variables made available by intelligent instrumentation and field bus communication systems. Experimental results show that different problems (as: stiction, change in valve dynamics, air leakage and periodic disturbances), cannot be easily detected by referring to classical loop variables. On the contrary, their presence can be promptly identified by means of Travel Deviation and Drive Signal values, made available by the valve positioner. A key role is plaid by the availability of the valve stem position.