Introduction

Duckbill-shaped rubber check valves are often installed on wastewater effluent diffusion systems and stormwater outfalls. A duckbill valve is essentially a flow sensitive variable-are valve. At no flow condition, the flaps of the valve remain closed. As the flowrate increases, pressure is exerted on the flaps of the valve, and the valve opens more, Duckbill valves differ from conventional fixed-diameter round ports significantly: I) the valve jet velocity varies nonlinearly with the flowrate; reasonably high velocities can be maintained even at very small flowrates; ii) the head-discharge relation is however approximately linear. These valves can prevent sea water sediment, and aquatic life from entering the outfall, and achieve optimal mixing of the underwater effluent discharge with the receiving water.

Lip-shaped opening of a duckbill valve under normal flow conditions