Pump cavitation will occur when the static pressure of a flow down to below the saturated steam pressure. To avoid pump cavitation endeavored not to have any part of the flow inside the pump which has a lower static pressure than the saturated steam pressure at a temperature of the liquid.
In this case need to be considered that there are two kinds of pressure which plays important role. First, the pressure is determined by environmental conditions in which the pump is installed, and the second, pressure is determined by the state of flow within the pump.
Related to two things above, can be defined a Net Positive Suction Head (NPSH) which is used as a standard to measure the safety of pump from cavitation. There are two kinds of Net Positive Suction Head (NPSH) as the following below:
2. Net Positive Suction Head Required (NPSHR) of pump
The way to avoid pump cavitation is the NPSHA (Net Positive Suction Head Available) is greater than the NPSHR (Net Positive Suction Head Required).