Fault diagnosis in industrial control valves and actuators

The research paper reports on experimental work carried out on an industrial type globe valve with a diaphragm type actuator. The effects of a blocked vent hole which is in the upper diaphragm casing, on the overall valve performance, are reported. A high resolution pressure sensor together with the latest valve diagnostic system, developed by Fisher-Rosemount, were extensively used to monitor the variation in the pressure that was developed in the upper diaphragm casing as a result of different amounts of vent hole blockage. Furthermore,the effects on several parameters including valve travel, spring rate, frictional force and the available seat load were established. Valve internal leakage is a common malfunction with industrial control valves. The causes of such leakage are numerous, including damaged plug or seat, insufficient seat load or reduced spring rate. The reduction in the available seat load due to the increased packing friction was considered in detail and significant results are reported. The paper concludes by highlighting some of the limitations of the existing diagnostic system and outlines the future work which involves the development of a user-friendly expert system based on fuzzy rules and is capable of diagnosing faults in control valves more accurately.