Net positive suction head

In physical terms the concept of the German term "Haltedruckhöhe" (retaining pressure head) is the same as the NPSH (net positive suction head) value. There may be a difference in the numerical values (Z_S) between "retaining pressure head" and NPSH because different reference levels are defined for their calculation. See Fig.1 NPSH

In practice, only the NPSH value is used.