Under certain conditions, areas of low pressure can occur sometimes locally in a flowing fluid (liquid or gas). If the pressure in such areas falls below the vapour pressure, there will be local boiling and a cloud of vapour bubbles will form, it is known as cavitation.
Cavitation can cause serious problems, since the flow of liquid can sweep this cloud of bubbles on into an area of higher pressure where the vapour bubbles will collapse suddenly. If this occurs in contact with a solid surface, very huge damage can result due to the very large force with which the liquid hits the surface.
Cavitation can affect the performance of hydraulic machinery such as pumps, turbines and propellers. The impact of collapsing vapour bubbles can cause erosion of metal surfaces.
Cavitation can also occur if a liquid contains dissolved air or other gases, since the solubility of gases in a liquid decreases as the pressure decreases. Gas or air bubbles will be released in the same manner as vapour bubbles, with the same damaging effects. Usually, this release occurs at higher pressures and therefore, before vapour cavitation commences.