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The basic performance characteristics of pumps and fans are the capacity, head, and pressure they develop and also the energy their pumping (rotating) elements add to the flow. The pumping elements (vanes, pistons) of a pump perform in the fluid flow and add energy to the latter. The basic relationship of the centrifugal pump theory is directly inferred from “The Advanced Theory of Machines Driven by Water”, a theoretical work by the academician L. Euler (a member of the Russian Academy of Sciences) published in the second half of the 18th century. To the present day Euler’s equation underlines the design of fluid machinery of the centripetal or centrifugal type. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits. Centrifugal pumps are capable of varying their capacity and pressure over a broad range; the relationships between the main parameters of these pumps are widely different. However the suction conditions of the pump may impose specific restrictions. This is due to a peculiar phenomenon known as cavitation that can possibly occur in particular areas of the pump suction passages. The elements of an axial- flow machine vane differently removed from the center are rotating at different speeds. Because of this, the head produced by vane of constant width and invariable entry and discharge angles changes along the vane length. This phenomenon makes liquid particles shift in a radial direction in the flow passage of impellers and downstream of the latter and decreases the efficiency of the machine. In this work, We will shed the light on centrifugal pumps and fans, their principle of operation, applications and some points of performance in an attempt to acquaint the reader with an overall knowledge of this field.
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