Cavitation is a phenomenon in which low pressure in a liquid (below saturated vapor pressure*) leads to the formation of small, vapor-filled cavities. The principle is the same as boiling, but if the pressure is low enough, bubbles form even at room temperatures.
A pump is a machine that raises the pressure of water to discharge it, but there are certain areas, such as at suction ports, where pressure is low. If the pressure in that area falls below saturated vapor pressure, cavitation occurs.
Cavitation also includes the phenomenon in which gases, such as oxygen, that had dissolved in the liquid are released and vaporize in the low-pressure region of the liquid. This particular phenomenon is known as gaseous cavitation.
Cavitation occurring on a hydrofoil. It resembles the shape of a white cloud.
There are three main adverse effects of cavitation when it occurs inside a pump.
*Saturated vapor pressure:
The pressure of vapor at which liquid evaporates and reaches equilibrium at a certain temperature. The saturated vapor pressure of water at 100 °C is exactly 1 atm.
Cavitation image of hydrofoil obtained by computational fluid dynamics. The hydrofoil blades are color-coded by pressure
Basic Knowledge of Pump Cavitation Phenomena [Part 1] (Japanese only)
Basic Knowledge of Pump Cavitation Phenomena [Part 2] (Japanese only)
Basic Knowledge of Pump Cavitation Phenomena [Part 3] (Japanese only)