Cavitation

A particularly dramatic pressure surge effect is vapour cavity formation and collapse which occurs when pressures surges allow the fluid to reach vapour pressure. This causes "cold boiling" which creates vapour cavities through the fluid. When pressures recover, the collapse of these cavities is extremely rapid, and can cause very high localised pressures that can burst pipes, accelerate fatigue and damage linings. 

While many 1D software packages attempt to model this behaviour, it is never reliably predicted. It is considered "very bad design" to allow such pressures to develop in a hydraulic system, as the results are chaotic, impossible to predict reliably and potentially catastrophic.



The following video describes the "Water Hammer Effect" but actually shows the impact of cavitation and cavity collapse. In long pipelines, the size of cavities can be much larger than these.

Cavitation






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