Civil Engineering - Waste Water Engineering - Discussion

Size and Arrangement of Pipes: As per IS 4111-3 (1985)

In the pipe syphon, the fore-bay should be so designed that the various pipes come into action successively. This may be arranged by the provision of distribution weirs.

If there is sufficient head to permit good velocities, a single pipe of appropriate size can be used with little trouble. Where every little head and a widely varying flow make it difficult to obtain favourable velocities, a pipe large enough to carry the maximum flow will have the sewage barely moving through it during low flow. Several pipes in parallel will normally overcome this difficulty.

A separate sewerage system carrying only sewage may have two parallel pipes - one pipe large enough to take the minimum dry-weather flow at a good velocity with a second pipe to take the difference between the minimum and maximum dry-weather flow.

The partially separate or combined sewers will generally have three parallel pipes; one of the pipes of the inverted syphon is large enough to take the minimum dry weather flow at a good velocity. With a second pipe to take the differences between the minimum and maximum dry weather flow and a third to carry stormwater.

Where the fluctuation in the flow of stormwater in a combined sewer is too large, more than three pipes will often give a better result.

Two sloping pipe legths joined by a flat pipe length (2 sloping pipe + 1 flat pipe).

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