Centrifugal Pump,  Design,  Performance,  S

Specific Speed (Ns)

The geometry, or shape, of a pump impeller. The formula for specific speed (Ns) is:

For US Units:

N is pump speed in rpm; Q is capacity in gallons per minute at the best efficiency point; and H is total head in feet per stage at the best efficiency point.

For Metric Units:

N is pumps speed in rpm; Q is capacity in liters per second at the best efficiency point; and H is total head in meters per state at the best efficiency point.

Use the following relationships to convert Ns values between those with US units, Imperial units (gpm), metric units (m3/h, L/s) and vice versa:

Ns(US gpm, ft.) = 0.861 Ns(m3/h, m)

Ns(British gpm, ft.) = 0.787 Ns(m3/h, m)

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