[1] Common commercial and industrial practices use dimensioned versions which are of equal utility.
Specific speed is an index used to predict desired pump or turbine performance.
It is this impeller's "shape" that predicts its flow and head characteristics so that the designer can then select a pump or turbine most appropriate for a particular application.
Once the desired specific speed is known, basic dimensions of the unit's components can be easily calculated.
Several mathematical definitions of specific speed (all of them actually ideal-device-specific) have been created for different devices and applications.
Low-specific speed radial flow impellers develop hydraulic head principally through centrifugal force.
Pump specific speed can be calculated using British gallons or using Metric units (m3/s and metres head), changing the values listed above.
[2] It is defined by centrifugal and axial pumps' inherent physical characteristics and operating point.
[4] The higher the suction specific speed, then the smaller the range of stable operation, up to the point of cavitation at 8500 (unitless).
[6] The specific speed of a turbine is given by the manufacturer (along with other ratings) and will always refer to the point of maximum efficiency.
[7] To derive the Turbine specific speed equation we first start with the Power formula for water then using proportionalities with η,ρ, and g being constant they can be removed.
Substituting this back into the power equation gives: To convert this proportionality into an equation a factor of proportionality, say K, must be introduced which gives: Now assuming our original proposition of producing 1 kilowatt at 1m head our speed N becomes our specific speed
In countries which use the metric system, the factor is omitted, and quoted specific speeds are correspondingly larger.
Once the desired specific speed is known, basic dimensions of the turbine parts can be easily calculated.