As a final control element, a control valve directly touches the process and is subject to wear and tear over time. Predictive diagnostics can help detect abnormal conditions developing in time to address them before unplanned shutdowns or slow downs occur. In a Plant Engineering article, Advanced valve diagnostics drive savings, Jordan Mandernach and Emerson’s Brent Baker teamed up to share these diagnostics in digital valve positioners can help drive safety, reliability and efficiency improvements in the process.
Brent and Jordan open highlighting the issues surrounding predictive maintenance.
Predicting impending problems is often quite difficult to achieve in practice, with the biggest impediment to success usually a lack of information. How can one easily determine when a critical control valve is starting to fail?
Proportional-integral-derivative (PID) control loops can mask control valve performance issues.
The control loop is in automatic, so as valve performance degrades, the PID controller simply compensates and obscures the issue. The loop continues to function until the valve fails completely, often upsetting the process, or forcing a shutdown of the unit, or even the entire plant.
The challenge with the traditional maintenance approach is that often:
…a valve is pulled and serviced, only to find it is fully functional and requires little or no maintenance work. In other cases, valve internals are reworked incorrectly, creating new problems that did not exist before.
With a digital valve controller, such as the Fisher FIELDVUE DVC6200, it is equipped:
…with an array of sensors… [and] is uniquely placed to monitor the control valve and detect abnormal conditions as they develop.
Data from these digital valve controllers can be communicated:
…to an asset management system to alert personnel so they can inspect the valve prior to failure.
Even before installing the control valve into service:
…a digital positioner can be used to create a valve signature for a new valve… This signature captures details on packing friction, air usage, valve travel, and other parameters—all of which can be compared to future valve signature test results. Often a comparison will quickly highlight developing issues, such as instrument misalignment, air supply issues, and actuator leaks.
Read the article for more on real-time monitoring for performance issues such as excessive friction, reduced or lost air supply, and failing components in the valve. The authors also highlight diagnostics such as partial stroke testing, establishing predictive maintenance programs, and sharing return on investment (ROI) case studies.
Visit the Digital Valve Controllers section on Emerson.com for more on the capabilities and applications for the critical diagnostic devices.
