What is Partial Stroke Test (PST)?

There are 2 types of Stroke Tests: Full and Partial.
Full Stroke Tests are executed once in a few years / TARs / Outages.
Partial Stroke Tests are executed in a running plant. It is closing valves 5-20%.
During the partial stroke test, the valve is stroked a portion of its total travel to verify it is not stuck and to uncover other dangerous failures. It exercises the shutdown valve to verify it will operate and move to its safe position in the case of a safety demand.