A Simple Test to Confirm Control Valve Stiction

Authors:	Shoukat Choudhury Md Ali A., University of Alberta, Canada Kariwala Vinay, University of Alberta, Canada Shah Sirish L., University of Alberta, Canada Douke Hisato, Mitsubishi Chemical Corporation, Japan Takada Haruo, Mitsubishi Chemical Corporation, Japan Thornhill Nina F., University College London, United Kingdom
Topic:	6.1 Chemical Process Control
Session:	Modelling, Estimation and Fault Detection for Process Control
Keywords:	Control loops, Control valves, Dead band, Process control, Nonlinearity, Static friction.

Abstract

Stiction is a common problem in the widely used spring-diaphragm type controlvalves in the process industry. Several methods are available for detecting stiction incontrol valves. After detection of stiction, a test is required to confirm that the valvein question is indeed suffering from stiction. This paper presents a simple closed looptest, based on changing only the controller gain, for confirming the presence of stiction.The method does not require that the loop be put in manual, which can otherwise upsetthe plant. The usefulness of this test is demonstrated through simulation studies and anindustrial application.