CONTROL VALVE CAVITATION GUIDE

ONE OF THE IMPORTANT UNRESOLVED OPERATIONAL PROBLEMS AT NUCLEAR POWER PLANTS IS CAVITATION IN CONTROL VALVES. EACH YEAR COSTLY SHUTDOWNS ARE NECESSARY TO REPAIR VALVES DAMAGED BY CAVITATION. THE PROBLEM IS MORE THAN JUST AN ECONOMICAL BURDEN ON THE UTILITY, IT CAN CREATE SAFETY-RELATED PROBLEMS BECAUSE A VALVE DAMAGED BY CAVITATION MAY NOT BE ABLE TO PERFORM ITS INTENDED FUNCTION. THE PRIMARY REASONS THIS PROBLEM REMAINS UNRESOLVED ARE INCORRECT TEACHINGS ABOUT CAVITATION AND LACK OF RELIABLE DESIGNN INFORMATION. THE PREVAILING METHOD FOR ANALYZING A VALVE OF CAVITATION IS BASED ON AN INCORRECT UNDERSTANDING OF THE CAVITATION PROCESS. THE PREVAILING TEACHING IS THAT CAVITATION DOES NOT BEGIN UNTIL THE MEAN PRESSURE AT THE VALVE DROPS TO VAPOR PRESSURE AND REFERS TO THIS ONSET OF CHOKED CAVITATION WHERE NOISE, VIBRATIONS, AND CAVITATION EROSION DAMAGE ARE NEAR THEIR MAXIMUM. IT IS ACTUALLY ABOUT THE WORST FLOW CONDITION AT WHICH TO OPERATE A VALVE AND NOT THE POINT OF INCIPIENT CAVITATION. SOME VALVES (SUCH AS PRESSURE RELIEF VALVES) CAN OPERATE SAFELY AT THIS LEVEL OF CAVITATION FOR SHORT PERIODS OF TIME. HOWEVER, CONTROL VALVES THAT OPERATE FOR EXTENDED PERIODS OF TIME WILL EXPERIENCE CAVITATION EROSION DAMAGE IF OPERATED NEAR ONSET OF CHOKING. THERE IS A CRITICAL NEED FOR AN APPLICATION GUIDE THAT TEACHES CORRECT PRINCIPLES ABOUT CAVITATION, PROVIDES AN ACCURAGE AND SIMPLE DESIGN PROCEDURE AND PROVIDES ADEQUATE EXPERIMENTAL DATA FOR APPLICATION ENGINEERS TO BE ABLE TO COMPLETE ACCURATE ANAYSES OF EXISTING VALVES AND SELECT REPLACEMENT VALVES WHEN NECESSARY