During the pump operation, there is a drop of the liquid flow in the center of the rotor, causing the inflow of the liquid through the suction port. In the event of an excessive pressure decrease, in some parts of the rotor, the pressure can be lower than the saturation pressure corresponding to the temperature of the pumped liquid, causing the so-called cavitation, i.e. liquid evaporation. To prevent this, the pressure in the suction port (at the inlet of the pump) should be higher than the saturation pressure corresponding to the liquid temperature by the net positive suction head (NPSH).