Isolation valves perform the role of stopping flow in process manufacturing and production processes. They are commonly used in safety applications to take the process to a safe state.
In an Emerson Exchange 2017 presentation, Emerson’s Sean Raymond and Mike Hoyme discuss instruments that can make these valves operate more reliably. Common isolation valves include ball, triple-offset, butterfly and gate valves. Common valve actuators include pneumatic, hydraulic, electric and manual-operated. Spring-return can be used to make the valve fail-open or fail-close based on the applications.
Some challenges with isolation valves are packing wear, bearing and seal stiction and inactivity which leads to increased friction over time. Partial stroke testing can exercise movement of these valves periodically and be part of proof tests used in safety applications.
Accessories may include solenoid valves and valve position monitors to provide the open or closed state of the valve. Possible solutions to add feedback include 4320 wireless position monitors, digital valve controllers (DVC6200 and DVC6200 SIS). A 4320 position monitor can be added to existing applications with no wires and no additional I/O required. It provides stroke times, valve dwell time, alerts and a time stamp of opening and closing events.
Both DVC6200 and DVC6200 SIS provide full stroke diagnostics, event capture, alerts and online monitoring. The DVC6200 SIS adds partial stroke testing and a demand/reset time as a proof test of the demand on the valve in a safety instrumented function (SIF).
These digital valve controllers provide a baseline to show any degradations over time when the valve signature test is redone, perhaps 6 months or a year later. A full stroke diagnostic monitors the entire valve stroke from open to close to open or vice versa. This can help to spot frictional buildup due to corrosion or a mechanical issue in the valve.
By capturing events over time, these valve movements can be credited as a full stroke test by many manufacturers & producers. A partial stroke test (PST) moves the valve enough to verify that it is not stuck in the open or closed position. The process is performed by the digital valve controller during normal operations and done in a controlled fashion to minimize spurious trips and process upsets. During this PST, a safety demand can still occur to take the valve to a safe state.
Two of the most common alerts for isolation valves are the stroke times and PST status. These diagnostics are reported back to the control systems as a HART variable or read from the Asset Management System software.
By adding these diagnostics to isolation valves, it is possible to extend service intervals when used in safety applications. These diagnostics can improve overall reliability and help avoid spurious trips and unplanned downtime.
Are you applying diagnostics to your isolation valves and if so, what results have you seen that you can share with the Valve community?