In this article, we will discuss and compare the Positioner-based and SOV (Solenoid operated valve)-based methods used for Partial Stroke Testing (PST) of emergency shutdown valves and HIPPS (High-integrity pressure protection system) valves. The two control methods are based on two different valve controller concepts.
The main difference between the two control methods is that the exhaust of the media (oil or air) passes through the positioner at the positioner-based method and through the SOV for the SOV-based method during PST or Emergency Shutdown (ESD).
The overall purpose of a PST is to ensure the valves ability to move on demand. When implemented successfully PST will extend the interval between shutdowns for full stroke testing and reducing failure on demand.
Historically, most PSTs have been conducted using positioner-based devices, which were originally developed for modulating control valves. In recent times, SOV-based devices developed specifically for PST have become more common. We will argue that the SOV-based solution for PST is a more reliable and efficient solution because it is less complex than the positioner-based solution.