Technical Booklet N Drainage·Page 19·3.3
Capacity of pipes
Drainage system capacity must be adequate for expected peak flow with minimum pipe diameters of 100 mm for WC drains and 75 mm for other cases. Table 3.2 and Diagram 3.1 specify minimum gradients and capacities for various pipe diameters.
The capacity of a system should be adequate to carry the expected peak flow at any point provided that the pipe diameter is not less than 100 mm where the drain carries water from a WC and 75 mm in all other cases. Table 3.2 gives the minimum gradient at which a pipe should be laid for a given peak flow. Diagram 3.1 gives the capacities which should be assumed for various diameters of drain laid at various gradients.
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