NPSH calculation allows us to know if there is cavitation risk for a pump. Cavitation may damage the pump. Pump manufacturers provide the required NPSH for a given operating point, this
value must be compared with the available NPSH of the installation. To be sure that the pump will work properly, required NPSH mush be below available NPSH, also considering some safety margin.
Water temperature: ºC
(1) Vapor pressure: m
Density: kg / m 3
(2) Relative pressure -P- in the tank or suction pipe (*):
(3) Pump elevation above water level - Z - (**): m
(4) Pressure drop in the suction pump:
Altitude above sea level: m
(5) Atmospheric pressure:mbar
Available NPSH (2)+(3)+(5)-(4)-(1): m
(*) P is the relative pressure in the tank or pipe. If the tank is not pressurized, this value will be zero.
(**) Z is the difference between water level and the axis of the suction connection of the pump. If the pump is above water level, this value will be negative. .
If what we know is the relative pressure of point 1, the calculations are simpler as we can indicate P = pressure in point 1, Z=0 and pressure drop in inlet temperature also zero.