defines the suction geometry, or suction characteristics, of a pump. It is calculated

from the equation:

N = rotative speed in RPM

Q = capacity in GPM at BEP (For double suction impeller, Q=GPM/2)

NPSHR = NPSHR in Feet based on 3% head loss at BEP

In multi-stage pump the NPSHR is based on the first stage impeller NPSHR.

at 3560 RPM if it required 18 FT of NPSH at its BEP of 800 GPM?

Solution: NSS = [3560 x (800/2)^0.50 / (18)^0.75] = 8148

1. It is that it is commonly used as a basis for estimating the safe operating flow

range for a pump. The higher the NSS is, the narrower is its safe operating flow

range relative to its BEP. Many users prefer their pumps to have an NSS in the

range of 8000 to 11000 for improved MTBF or trouble-free operation.

2. It is commonly used as an indicator if a pump were susceptible to develop

internal flow recirculation problem. The higher the NSS number, the higher is its

susceptibility.

As the term implies, the suction specific speed of a pump is mainly influenced by

the suction design geometry of the pump including its suction nozzle diameter, the

casing suction area development, the impeller suction eye area, eye inlet

diameter, and suction vane angle.

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