A pump design valve represented by the total suction head (in feet) of liquid available (absolute value at pump’s suction port) less the absolute vapor pressure (in feet) of liquid being pumped. NPSHr is the absolute pressure head a pump must have at its suction port. NPSHa (available) is the absolute pressure head that is available at the pump suction port, a system-design value.
See also PEI/RP800.
