This paper presents the development of a method for condition monitoring and online fault detection on proportional directional valves. The systems that such valves are part of might be sensitive for unexpected maintenance or long duration stops. Consequently, the implementation of a fault detection and monitoring system can reduce maintenance costs and increase safety. The method is based on monitoring both the valve supply current and spool position related to the spool positioning control signal. Therefore, it is applicable for valves with embedded electronics including spool position measurement and internal controller. The supply current and spool position behavior depends on the friction, flow forces, solenoid current, and valve closed loop controller performance. Furthermore, valve static and dynamic characteristics are influenced by the spool size, overlapping and manufacturing tolerances. The effectiveness of the method to monitor and detect faults in valves with different sizes and constructive parameters is shown experimentally using five different proportional valves. The proposed method requires reference parameters characterizing the valve operation without faults. Standard tests are proposed to determine healthy valve parameters. For the method valuation and validation, experimental results with the valve operating under healthy conditions and with induced faults were compared. Faults were added in a way to represent spool locking and increase of friction forces between the spool and sleeve. The obtained results show the capability the method for the detection of faults classified as severe even if the valve controller attempts to compensate the faulty behavior.

This paper presents the analysis of an on-line fault detection method for proportional directional hydraulic valves applied on speed governors of hydroelectric power plants. This application area is very sensitive for unexpected maintenance or long duration stops since most of power plants are interconnected on an electrical power grid. A plant stop must be programmed previously and approved by a regulatory agency. Consequently, the implementation of a fault detection and monitoring system can reduce maintenance and operational costs as well as safety risks of equipment and operators. The developed method is based on monitoring both the valve supply current and spool position related to an input control signal. Therefore, it is applicable for so called servoproportional valves, it means, those including spool position measurement and with embedded electronics. Valve static and dynamic behaviour depends on spool friction, flow forces, solenoid force and valve closed loop controller. Such characteristics are influenced by the spool size, overlapping and manufacturing tolerances. In this paper, the effectiveness of the method to monitor and detected faults in valves with different sizes and constructive parameters is demonstrated experimentally using five proportional valves.

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