Hydraulics of “Duckbill” Elastomer Check Valves

Abstract

Duckbill-shaped elastomer check valves are sometimes installed on storm-water or sewage outfall ports to prevent backflow or seawater intrusion. Unlike fixed diameter ports, the jet velocity varies nonlinearly with port discharge flow. An analysis of all available experimental data on the head-discharge characteristics of check valves shows that the collective data can be effectively correlated with the parameters of the approach flow in the discharge port. Two dimensionless relations are obtained for the effective percentage jet opening area and the valve head loss. The relations are derived from data for nominal port diameters in the range of 100–305 mm (4–12 in.), and appear to hold generally for elastomer check valves. The head-discharge relations can be used to determine the jet discharge velocity and opening area that are needed as input to numerical plume models for environmental impact assessment and outfall design. The results can also be conveniently incorporated into a diffuser hydraulics code. In general, the calculations show that the use of duckbill check valves leads to a more uniform port discharge distribution, higher jet velocities, and higher energy head requirements.