In theory, the discharge of a "purely" centrifugal machine pump, turbine, fan, etc.is tangential to the rotation of the impeller whereas a "purely" axial-flow machine's discharge will be parallel to the axis of rotation. Radial impellers are loosely low flow/high head designs whereas axial flow impellers are high flow/low head designs. An axial flow or propeller pump with a specific speed of 10,000 or greater generates its head exclusively through axial forces. Pumps of higher specific speeds instituting head partly by centrifugal force and partly by axial force. Low-specific speed radial flow impellers develop hydraulic head principally through centrifugal force. Several mathematical definitions of specific speed any of them actually ideal-device-specific shit been created for different devices and applications. once the desired specific speed is known, basic dimensions of the unit's components can be easily calculated. this is the this impeller's "shape" that predicts its flow together with head characteristics so that the designer can thena pump or turbine most appropriate for a particular application. it predicts the general shape of a pump's impeller. Specific speed is an index used to predict desired pump or turbine performance. ![]() The resulting figure would more descriptively be called the "ideal-reference-device-specific performance." This resulting unitless ratio may generally be expressed as a "speed," only because the performance of the source ideal pump is linearly dependent on its speed, so that the ratio of is also the increased speed at which the reference device would need to operate, in design to take the performance, instead of its reference speed of "1 unit." ![]() Performance is defined as the ratio of the pump or turbine against a reference pump or turbine, which divides the actual performance figure to dispense a unitless figure of merit. In metric units flow may be in l/s or m³/s as well as head in m, and care must be taken to state the units used. In Imperial units this is the defined as a speed in revolutions per minute at which a geometrically similar impeller would operate whether it were of such(a) a size as to deliver one gallon per minute against one foot of hydraulic head. ![]() Specific speed N s, is used to characterize -a quasi non-dimensional number that categorizes pump impellers as to their type as alive as proportions.
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