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Technical Note: An Analytical Method for Evaluating Pumps for a Storage-Pump System

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Applied Engineering in Agriculture. 28(4): 559-565. (doi: 10.13031/2013.42085) @2012
Authors:   D. J. Sample, D. B. Powers
Keywords:   Cavitation, Digitize, Explicit, Friction factor, Hydraulic, Implicit, Pipeline, Pumps, Storage

Runoff can be captured and stored for a wide variety of uses; the practice is known as rainwater harvesting (RWH). Storage-pump systems are an efficient means of collecting runoff, storing it for later use, and pumping it to satisfy demand when needed in a RWH system. Evaluating pumps for storage-pump systems can be complex for two reasons. First, there are nonlinearities in the friction factor equation, which is needed to calculate head loss in the system. This head loss is used in both the demand curve and suction head relationship. Second, quickly assessing the pump characteristic curves is difficult because they are typically provided in non-digital form. This article compares various approximate explicit methods to a more exact, implicit solution for the friction factor. The system demand curve is calculated with both, and the relative error for a selected RWH example is provided. A tracing program is used to digitize a pump characteristic curve selected for this example. The Serghides (1984) method was selected due to a low relative error and is recommended for wide use in calculation of similarly configured systems. The reader can adapt this method by modifying this example to quickly assess the pumping and demand characteristics of their design.

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