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Numerical modelling of the priming of a siphonic rainwater drainage system

The operation of siphonic rainwater systems, and in particular their priming action, is described. Current industry recognised design procedures are discussed. The initial priming of a test facility developed to replicate current design practice is described in detail, and related to the expected performance of systems installed in the field. The impartance, hydraulically, of several specific elements of the system operation are emphasised in terms of the priming action. Additionally, problems encountered at start-up, due to air in both the system and the inflow, are highlighted. A numerical model is discussed that represents system priming, and conclusions are drawn regarding the data presented here and how they relate to the siphonic roof drainage industry as a whole.