Air pressure transient propagation in building drainage vent systems, an application of unsteady flow analysis

Abstract

Air pressure variations within building drainage systems as a result of appliance discharge may result in the loss of trap seal protection by induced syphonage and/or overpressure. Air pressure transient propagation may be described by the quasilinear hyperbolic partial differential equations of continuity and momentum, solvable numerically by the method of characteristics. This paper develops these governing equations and illustrates the numerical model validation for a drainage system and vent network, including a wide range of commonly found boundary conditions. Trap seal response and retention are modelled and the technique shown to be applicable to both code and standard preparation and systems design.