Cavitation erosion characteristics around a hollow-jet valve

In this paper, to make clear the mechanism of cavitation erosion around a hollow-jet valve, cavitation erosion test was conducted in a hollow-jet model valve. The eroded surfaces of specimens were observed by Scanning Electron Microscope (SEM) at different times of the test. Cavitation aspects were also observed photographically by a high-speed camera. It was found that the erosion occurs in cavitating flows around a hollow-jet valve with two patterns. One is characterized by a big plastic crater, which seems to be generated by one blow event of a cavitating vortex collapse near a specimen surface. Another is due to a small brittle irregular pit formed by the cumulative effects of many weaker blows. The former is the main cause to lead serious erosion. The high-speed photographic observations of the cavitation aspects showed that more cavitating vortices in middle cavitation number state occur than these in other states. The erosion tests also illustrated that the middle state is the most dangerous for cavitation erosion around a hollow-jet valve.