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Figure 10.1
Simultaneity curves for sewer design flows |
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10.3.6
Minimum Velocity and Slope |
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The low content of fine particles in the effluents of interceptor tanks permits velocities as low as 20 cm/s in sewers. Nevertheless, it is not advisable to adopt a slope of less than 0.1 per cent, because of practical installation limitations. This slope allows velocities of more than 20 cm/s for 75 mm diameter and larger pipes flowing full and receiving a unit load of 0.33 1/s. For 50 mm PVC pipes the minimum slope is a little less than 0.2 per cent. As velocities increase when the pipes are not full, the minimum slopes adopted were 0.2 per cent for 50 mm pipes and 0.1 per cent for larger pipes. Tractive tension theory was used to verify that these parameters were suitable for a particle size of 0.02 mm. |
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