Digital valve controllers offer many benefits over simple valve positioners, including the ability to detect and report degrading valve performance in advance of outright failure. However, implementing a comprehensive diagnostics program to take advantage of these features can be a daunting task.
My article in the September 2024 issue of Processing, titled “Activate diagnostic alerts to leverage digital valve controller capabilities,” describes a simple four-step procedure to make use of the “big three” basic diagnostic alerts provided by Fisher™ FIELDVUE™ digital valve controllers, mitigating up to 80% of control valve failures before they occur.
Evolving valve control
Prior to the introduction of the pneumatic valve positioner around 1949, valve position often deviated from the control system setpoint. Pneumatic positioners remedied this by comparing the setpoint to the actual valve position and adjusting the position as necessary, dramatically improving process control.
Starting with the Fisher 3500 Positrol Valve Positioner in 1949, valve positioning technology has improved dramatically.
The transition to digital valve controllers in 1994 marked another significant inflection point in valve control. These devices use additional sensor readings and digital technology to detect degrading valve performance in advance of failure.
But not all end users are taking full advantage of this technology in their installed base, a situation that can be rectified by following the steps detailed below.
Maintenance methodology
When developing a maintenance program, operating facilities can adopt one or more of the following strategies:
- Corrective maintenance or run-to-failure. Do no maintenance until something fails and fix it at that time.
- Preventative maintenance. Fully rebuild equipment on a fixed schedule to avoid unplanned downtime.
- Condition-based or predictive maintenance. Use diagnostic technology to detect developing problems and schedule maintenance as needed.
In an optimized reliability-centered maintenance program, all three strategies have their place. Letting non-critical valves run to failure often makes sense since the cost of failure is very low. Routinely pulling and overhauling low to moderately critical valves also has merit as this method avoids significant downtime and unplanned failures. The remaining moderate to highly critical valves are likely good candidates for condition-based maintenance, provided the valve condition can be ascertained, and that is where the big three digital valve controller alerts come into play.
This diagram shows the common functional failure points of a control valve. The basic diagnostics available in nearly all Fisher digital valve controllers can detect and alert most of these failures — but only if they are enabled, configured and monitored.
Four steps to alert success
Fisher FIELDVUE digital valve controllers provide a variety of basic and advanced alerts, but these alerts must be enabled, configured, and monitored. This can be accomplished by executing the following steps:
- Classify each valve by criticality. When monitoring is performed manually, its frequency is generally determined by criticality, but digital valve controllers with automated alerts make frequent monitoring practical, even for less critical valves.
- Enable and configure the big three alerts for each valve. The Travel Deviation Alert occurs when the actual valve position does not match the setpoint within a few seconds, the Supply Pressure Alert occurs when plant air supply to the valve is inadequate, and the Drive Signal Alert occurs when the drive signal is higher or lower than expected at the current valve position.
- Monitor valves for new alerts. A HART-enabled maintenance program can detect alerts remotely and automatically, and then forward them to maintenance technicians. Otherwise, a routine manual scan of each valve may be required.
- Act upon alerts. Top-performing plants often have automated systems that generate work orders when an alert occurs. Technicians must troubleshoot and correct problems before they cause a failure.
Using just the big three alerts, operating facilities can detect up to 80% of control valve failures, significantly improving uptime and reliability. Nearly every Fisher digital valve controller can provide these alerts with a few simple parameter changes, making condition-based maintenance more accessible for all.
Visit the Digital Valve Controllers section on Emerson.com to know how you can meet your process reliability and performance goals by bringing intelligence to your entire valve assembly.
