Corrective Measures

Problems in pump sumps such as severe vortexing, intense swirl, or uneven flow distribution at the bell can be reduced or eliminated by deriving proper corrective methods using models. Because no single remedial method to correct these problems exists, it is important to try several suitable methods in the model to derive an effective and practical one.

FIGURE 7 Yarn streamers around the suction bell of a model intake to observe flow direction into the bell (Courtesy of Alden Research Laboratory, Inc.)

Even though the pump bell velocity and submergence are very important parameters contributing to problems, it is seldom possible to change these values. Hence, the corrective measures are usually incorporated in the geometry of the pump pit and include the introduction of suitable appurtenant devices.

Severe free surface vortices may be prevented by providing a uniform approach flow to the pumps while maintaining a sufficient submergence. Required submergences can be predicted by empirical equations available in the literature.31 Relocation of pumps, introduction of horizontal grids below the water surface, changing of wall and floor clearances, improvements in approach channel configurations, and changes in lengths and spacing of piers are some of the common techniques for reducing vortex activity. Surface vortices can also be controlled by installing a curtain wall immediately upstream of the pump. Figure 8 indicates various methods of eliminating poor flow conditions as given in Reference 7.

Submerged vortices are usually eliminated by installing splitter vanes or floor cones under the bell. Variations in floor and wall clearances can also be effective and should be tried in the model. Figure 9 shows a 1:4 scale model of a two-bay pump intake—each pump designed to draw 25,000 gpm (1.575 m3/s). Flow distributor walls are installed to assure a nearly uniform flow to the pumps, and splitters and fillets are provided to guide the flow into the pump bells without any sub-surface vortices.

The choice of corrective measures should always be made with the pump use in mind. For example, in testing pump intakes that will be used for sewerage, corrections that will allow trash build up, such as vanes or grids, should be avoided. It is also important that a continuous dialogue exist between the intake designer and the test laboratory so the most practical and inexpensive solution for a specific installation can be obtained with a minimum of effort.

FIGURE 8A through I Common method of eliminating vortexing problems in pump pits (Hydraulic Institute ANSI/HI 2000 Edition Pump Standards, Reference 7)

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FIGURE 9 A 1:4 geometric model of a two-bay intake showing flow distributors, splitters, and fillets to eliminate objectionable vortices (Courtesy of Alden Research Laboratory, Inc)

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Renewable Energy Eco Friendly

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