Anonymous
Our experience at ExxonMobil says that the use of retrofit limit switches on wedge plug valves is not reliable over time. They get damaged and fouled. Unfortunately the only realistic way to reliably address the problem is install valves with a factory-installed, self-contained postion switch design. Another option is to have a mechanic clean and calibrate the devices on a daily basis.
Use of field-installed retrofit limit switches on Wilson-Snyder valves is even more problematic. We do not recommend such an operation, since reliability is essential in this safety application. The alternatives are, of course, an expensive MOV ball valve, or strict application of procedures, involving the use of two field technicians to check each other, plus review with the console supervisor.
Mitch Moloney 703-846-5095