Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)
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Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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High Speed Pumps 175 History and Description of an Unconventional Pump Type Developmental work on the pump type central to the discussions in this chapter was initiated in Germany prior to World War II to meet urgent wartime requirements and after 1947 continued in Britain. Need for a simple, lightweight, and easily manufactured pump suited to produce high heads at low flow rates existed in connection with aircraft and rocket propulsion systems. An unorthodox high-speed centrifugal pump concept resulted and was described by Barske in papers published in 1955 and 1960. This pump is described as an open impeller type and is exemplified as highly unorthodox by Barske himself who states: "To a skilled designer the pump which forms the subject of this paper will, at first glance, appear most unfavorable and may well be regarded as an offense against present views of hydrodynamics." Reasons exist, however, to break with conventional design practice to meet objectives which would otherwise be difficult to achieve. Intentionally flaunting the rules, in fact, provides a pump design that can equal or exceed the performance of conventional pumps in the head-flow design range for which it is intended and for which it is best suited. Typical Barske-type pump construction is illustrated by the sketch in Figure 11-1. The salient features of the design start with a simple open impeller, which rotates within a case bored concentrically with the impeller centerline. A single emission throat with a conical diffuser section is oriented tangentially to the case bore. Conical difftisers provide high recovery efficiency because of their minimal wetted area. A cone angle of 10° is commonly used, providing good recovery potential and reasonable cone length requirements. Radical departure from conventional design practice exists in the exceptionally tall blade geometry used, with the impeller tip height, b 2 , set equal to or moderately greater than the emission throat diameter, dj. Blade angle, 8, is unimportant except that the flow area in the impeller eye must at least equal the area of the suction passage. Further obvious deviation from normal practice is the use of plain radial blades, with no attempt made to match inlet flow streamlines. Performance trends of the Barske pump are generally as indicated in Figure 11 -2A. The head at zero flow, or shutoff, is about equal to the design head, with a head peak a few percent higher than design in the neighborhood of half design flow. This curve shape is referred to as an unstable curve and is often viewed as undesirable, as described in Chapter 1. A stable curve is one in which the head rises continuously as flow is reduced from design to shutoff. Head drops rapidly for flows above design, and zero head or cutoff normally occurs around 130% of design

Figure 11-1. open impeller centrifugal pump.

Figure 11-1.<br />

open impeller centrifugal pump.

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