Centrifugal pumps

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 Excerpt: ... value of Bi is the sum of the widths for both sides in the case of the double suction impeller. The value of F3 is the area of the volute at the maximum section 360 from the beginning. Exact values of ai and /i are difficult to estimate. 54. Head-discharge Curves at Constant Speed.--The relation between head and rate of discharge! for eight different speeds is shown in Fig. 66. It will be noted that this particular pump has a rising characteristic and that values of head are obtained which are greater than u22/2g. While there are variations due to slight irregularities in the test data, the following values will be fair averages. For the shut-off head, to = 1.02 U22/2g; for the maximum head, h = 1.0Su22/2g; and for the head at the point of highest efficiency, h = 0.94M22/2g. For the curves in Fig. 61 the corresponding values of these factors are 0.96, 0.985, and 0.80 respectively. It will be noticed that for small rates of discharge the curves in Fig. 66 are concave upward and, after passing a point of Fig. 62.--Construction of 6-inch De Laval centrifugal pump. inflection, they assume the customary form of concave downward. The reason for this is that the "churning loss" shown in Fig. 58 prevents the head from rising as it would do otherwise. But this factor drops out as the rate of discharge increases. This feature is very common but is not usually noticed by observers because an insufficient number of points are recorded for these small flows to enable an accurate curve to be drawn. Thus, if the first point only after shut-off had been omitted from Fig. 64.--Impeller for Worthington turbine pump. most of the curves in Fig. 66, there would be no indication that the true curve should have a point of inflection. The same is true in Fig. 11 for an ...