Choking and Supercavitating Valves

The occurrence of choking flow or supercavitation downstream of valves can result in unsatisfactory performance. A valve chokes when the mean pressure immediately downstream drops to vapor pressure. For a given upstream pressure, the maximum discharge through the valve has been reached. Vibrations, noise, and possibly erosion damage due to cavitation reach their peak intensity near choking. Supercavitation occurs when the entire pipe cross-section for several diameters below the valve is filled with water vapor. When this occurs, the collapse of the cavitation and thus, the vibrations, noise, and erosion potential occur remote from the valve. Information is provided from which the conditions under which a valve will choke or supercavitate can be predicted. Data are presented for ball, gate, glove, and butterfly valves in sizes from 1 in. through 16 in. The testing covered ranges of pressure from 15-260 psi. Scale effects on choking cavitation due to variations in size and pressure are negligible.