Rotork Upgrades Partial Stroke Testing Systems

Rotork Fluid Systems has completed a project to retrofit improved partial stroke testing capabilities on heavy-duty pneumatic valve actuators installed at a European oil refinery. The 14 Rotork GP range quarter-turn valve actuators were originally supplied to the Raffineria Milazzo on the north coast of Sicily in 1995. Occupying an area of 212 hectares, the complex refinery facility produces low-sulphur products. In 2008, Rotork was asked to upgrade the performance of the electrically operated partial stroke testing systems that had been fitted to the actuators when they were first supplied.

Partial stroke testing enables the performance and condition of infrequently operated valves to be monitored without fully closing them in plant areas where such closings would disrupt routine plant operations. The original partial stroke testing systems were in need of mechanical and electrical modifications to improve the precision of their performance in line with increased operational efficiencies in the refining processes. To achieve this, all 14 actuators were disassembled and shipped to the Rotork Fluid Systems factory at Lucca, where they were modified and repainted, before being returned to site and refitted within a total timescale of approximately four weeks.

The modified partial stroke test systems are now initialised by selecting the test mode and operating a pushbutton on a new control box for each actuator. The pushbutton activates a solenoid valve to release air from the actuator cylinder until it reaches a preset position of 15deg in the closing direction. At this point, a newly fitted limit switch disengages the closing-direction solenoid and activates the open-direction solenoid to enable the valve to return to its fully open position. In this way, the valve is never allowed to travel beyond the 15deg closing position, which would compromise the plant process and potentially shut down the refining reactors.