Reduction of cavitation around a butterfly valve (cavitation reduction by a partly enlarged pipe)

The purpose of this study is to reduce cavitation noise occurring around a butterfly valve. The main cause of cavitation occurrence is an abrupt decrease of the fluid pressure behind a valve. To recover the pressure behind the valve in our experiment, the pipe was partly enlarged from just ahead of the valve shaft forward downstream. From the results of the noise measurement and visualization, the size of the ditch was determined and it was found that the effect of noise reduction was greatest when the length and the depth of the ditch were 1 and 0.2 times the width of the duct, respectively. The effect of the ditch was very clear in the experiments using an actual valve and piping. It was confirmed that the sound pressure level can be reduced by about 8 dB even with severe cavitation. When a partly enlarged pipe was used, secondary cavitation occurred from the edge of the ditch. It was found that the effect of the noise of secondary cavitation was about 2 dB to 4 dB. However, this noise could be eliminated by changing the shape of the ditch.