Piping Design Section 04

Dimension S in Figures 7 and 9 is a minimum value based on the normal low water level at the pump or suction pipe bell, taking into consideration friction losses through the inlet screen and approach channel. Note that this dimension represents submergence at the intake, or the physical height of the water level above the intake relating to the prevention of eddy formations and vortexing. The channel floor should be level for at least a distance Y (see Figures 7 through 10) upstream before any slope begins. The screen or gate widths should not be substantially less than W, and heights should not be less than the maximum anticipated water level to avoid overflow. Depending on the approach conditions before the sump, it may be necessary to construct straightening vanes in the approach channel, increase dimension A and/or conduct an intake model test to work out some other combination of these factors.

Dimension W is the width of an individual pump cell or the center-to-center distance of two pumps if no dividing wall is used.

On multiple intake installations, the recommended dimensions in Figures 7 and 8 apply as noted above, and the following additional factors should be considered.

As shown in Fig. 10 (A), low velocity and straight in-line flow to all units simultaneously is a primary recommendation. Velocities In the sump should be approximately one foot per second, but velocities of two feet per second may prove satisfactory. This is particularly true when the design is based on a model study. Not recommended would be an abrupt change in the size of the inlet pipe to the sump or the inlet from one side introducing eddying.

In many cases, as shown in Fig. 10 (B), pumps operate satisfactorily without separating walls. if walls must be used for structural purposes or some pumps operate Intermittently, then the walls should extend from the rear wall approximately ten times the C dimension given in Fig. 7.

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Fig. 7 Sump Dimensions

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Fig. 8 Sump dimensions, Plain view, wet pit type pumps
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Fig. 9 Sump dimensions, elevation view, wet pit type pumps

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Fig. 10 Mulitple pump installations