ProSafe-RS

Under normal conditions, valves that are integrated with a safety instrumented system (SIS) are not activated. (They are only actuated when the SIS initiates a process shutdown after an abnormality is detected in a process.) It is therefore necessary to periodically test valves to ensure that they are in good working order and will respond properly when needed.

This periodic check is called a “proof test,” and generally it involves a full stroke test (completely closing the valves). When a plant is up and running, the costly installation of a bypass is necessary to conduct a proof test. If this is not possible, the only other option for conducting this test is to shut down the plant. As a consequence, proof tests of the valves are usually conducted only once every several years.
 
An alternative to the full stroke test is the partial stroke test (PST), which involves slightly closing a valve to diagnose problems. A PST can be conducted without stopping a process, and it can be performed remotely from locations such as a control room.

By conducting a PST, plant owners can significantly reduce their maintenance costs. And by checking the valves more frequently than is possible with the full stroke test, they can anticipate great benefits such as increased reliability .

Note: although the PST does not eliminate the need for a full stroke test, it makes it possible to extend the proof test interval without sacrificing the required safety level.

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