A methodology for determining actuator setup criteria and performing diagnostics for pneumatically operated valves

In response to industry concerns about proper valve operation, Combustion Engineering (C-E) has developed a methodology to determine actuator setup criteria and perform diagnostics on pneumatically operated valves. Performing this type of diagnostic evaluation on pneumatically operated valves will ensure the valve can perform its safety function, pass in-service inspections, and improve valve reliability, resulting in increased plant availability. The methodology C-E used to determine actuator setup criteria considers packing gland forces, seat loads, leakage classifications, system pressure forces, valve/actuator capabilities, including spring rate characteristics. Basic valve, actuator, and systems data are gathered and entered into a valve data base for future reference and calculations. The formulas and decision criteria have been incorporated into a programming section of the same data base. This program can then can be operated on a personal computer to calculate baseline actuator setup criteria for the bench, inherent, and installed conditions. A significant feature of C-E's methodology is that feedback from actual measured conditions can be input into the program to validate or correct for conservative estimates used to determine the baseline actuator setup criteria. These criteria are presented in terms of actuator air pressure requirements versus valve position and a signature trace