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Specific Speed

The net suction specific speed is a dimensionless number defined by centrifugal and axial pumps' inherent physical characteristics and operating point [1] . It is one of a number of factors used in selecting a pump for use and is mainly used to see if there will be problems with cavitation during the pumps operation on the suction side [2] . The net suction specific speed of a pump will define the range of operation in which a pump will experience stable operation [3] . The higher the net suction specific speed, then the smaller the range of stable operation. The envelope of stable operation is defined in terms of the best efficiency point of the pump.

The Net suction specific speed is defined as[4]:

\begin{align} N_{ss} &= \frac{N\sqrt{Q}} {\mbox{NPSH}_R^{0.75}} \\ \mbox{Where:}\\ N_{ss} &= \mbox{Net suction specific speed} \\ N &= \mbox{rotational speed of pump in rpm} \\ Q &= \mbox{flow of pump in US gallons per minute} \\ \mbox{NPSH}_R &= \mbox{NPSH required in feet at pumps best efficiency point} \\ \end{align}

References

1. ^ NPSH and Suction Specific Speed - Goulds Pumps - ITT Corporation. ITT Corporation. Retrieved on 2007-07-13.
2. ^ Specific speed. McNally Institute. Retrieved on 2007-07-13.
3. ^ Article #3: Suction Specific Speed (NSS). Pumping Machinery. Retrieved on 2007-07-13.
4. ^ Specific Suction Speed for Pumps. Engineering Toolbox. Retrieved on 2007-07-13.