Size Determination of Partly Full Conduits

The transition from partly full to full pipe (sealing) is accompanied by vibrations of the structure and surging of the flow. The experimental study was done in a 4-in. (100-mm) square conduit with three different circular bends, with various deflectors, and with various concentrations of air. Sealing depends on the Froude number of the flow. To maintain partly full flow, more space is needed above the water-flow area with an increase of Froude number. With short-tube control, the ratio of the radius of curvature along the center line to the bend diameter and the deflector thickness at the crown of the bend determine the water-flow area in the horizontal conduit. Ventilation of the horizontal conduit delays sealing while aeration of the water flow hastens sealing. With weir control, waves on the flow surface hasten sealing and highly aerated flow delays sealing. Ratios of radius of curvature to the bend diameter larger than 2.0 are recommended, since they generate fewer waves.