Numerical modelling of air pressure transient propagation in building drainage systems, including the influence of mechanical boundary conditions

Air pressure transients within building drainage systems belong to a family of unsteady flow phenomena amenable to numerical modelling via the method of characteristics. The defining equations are solved for a range of transient conditions, including trap seal retention prediction and air admittance valve stack termination. An air admittance valve boundary condition is investigated, both numerically and experimentally. The resultant boundary equation is validated and the method of characteristic model is shown to be capable of predicting the valve's operational performance. The model is shown to be capable of development as a basis for air admittance valve design and acceptance criteria. © 1992.