On the head-discharge relation of a "duckbill" elastomer check valve

Abstract

Duckbill-shaped elastomer check valves are often installed on wastewater effluent diffusion systems and stormwater outfalls to prevent baekflow or sea water intrusion. Unlike fixed diameter ports, the jet velocity varies nonlinearly with port discharge flow. A new theory to predict the hydraulic characteristics of a duckbill elastomer check valve (DBV) is presented, and it provides a theoretical basis for the correlation of all DBV hydraulic data. It is shown that a DBV can be considered as a smooth converging nozzle. By modelling the duckbill valve as a two-dimensional rubber membrane, a theory is developed to relate the DBV material properties and flow conditions to the valve deformation. The valve opening area is predicted as a function of the driving pressure head: a linear head-discharge relation is predicted. The predictions are in excellent agreement with ex peri mental data. The derived head-discharge relation can be readily incorporated into a diffuser internal hydraulics code to determine the variation of discharge flow and jet velocity along a multiport diffuser fitted with duckbill check valves.