Minimum Self-Cleansing Velocities for Inverted Sewer Siphons

Laboratory experiments were carried out to determine minimum self-cleansing velocities for preventing deposition of sediment in upward sloping and vertical pipes of inverted siphons. Tests were made using sediment sizes of 0.78mm and 4.3mm in a pipe of 150mm diameter for eight angles of inclination between 0deg; and 90°. The criterion for self-cleansing was defined as the minimum velocity needed to prevent the formation of separated dunes in the pipes. For a given sediment concentration the self-cleansing velocity was found to be a maximum at pipe slopes between about 30° and 37.5°. Analysis of the data enabled the results to be described by a single formula valid for any slope of pipe between horizontal and vertical.