The shutdown valve is the valve that is designed to open along the period of operation. May we already know that almost all companies don’t want to stop their production, they want to run the operation as maximum. Based on that circumstance, the SDV is staying steady open for a long time, and because of the flowing fluid, it could be stuck on the SDV’s seat and cause the ball stuck and could not be closed. for that reason, there is a maintenance procedure to test the functionality without shutting down the process line, by using a partial stroke test.
in the video is the electric mean of a partial stroke unit, embedded in an open-close indicator. It just needs to plug the magnet stick to run the partial stroke test.