When liquids flow, flow processes may cause local pressures that are smaller than the corresponding vapour pressure of the liquid. In this case, the liquid evaporates and vapour bubbles are formed. When the pressure re-increases the vapour bubbles implode.
Cavitation in pumps
Visualisation of cavitation effects in a transparent pump; how speed, inlet pressure, flow rate and temperature affect cavitation.
Visualisation of the formation of vapour bubbles in a Venturi nozzle.