Under light rainfall a siphonic drainage solution works just as a conventional one. Since the pipe volume in a siphonic solution is less than a comparable conventional solution, a point is reached where the system is inundated and the water level in the gutter will rise. Once the water level covers the air baffle, air can no longer enter the system allowing water to completely replace it. This transitional state between convention and siphonic drainage is known as 'priming'. The water flow in the system will go through a series of changes as the air is evacuated from the system. Once water has completely filled the system, the system will enter the 'full bore' state. The full bore state is highly efficient must be controlled through effective design to ensure the system as a whole operates as the location and site demands.

Siphonic System with low rainfall intensity

Siphonic Roof Drain working at full bore