Studies on Low-Erosion Butterfly Valves : Suppression of Erosive Vortex Cavitation

Abstract

In order to improve the reliability of butterfly valves, it is absolutely imperative to prevent fatal cavitation erosion and to control the flow rates precisely. In our previous studies, erosive vortex cavitation, which takes place within a limited part of the high-shear region, was found to play an important role in the erosion. This fact suggests to us a useful method for overcoming erosion. To date, many types of modified valves have been proposed, in which very uniquely-shaped buffers are attached on the orifice and nozzle sides of the valve disc, although data on the results of their practical use are unavailable. In this paper, therefore, the erosive shock-pressure distributions on the inner pipe-wall surface downstream from the valve disc and the corresponding cavitation-flow pattern are precisely measured in the typical bounded flow around butterfly valves by means of pressure-sensitive films and high-speed photography. It is found that the erosive pulses and the range of their occurrence in the shear regions can be significantly attenuated by introducing simple buffers.