Siphonics Explained

The main component that differentiates a siphonic rainwater system from a conventional system is the outlet (or inlet) located at high level on the roof or in the gutter.

The three main parts of the outlet are;

• The body which is normally made of stainless steel and shaped by spinning or pressing.
• The air baffle which is made as an alloy casting (UV-System) or molded hi-density polyethylene or polypropylene.
• The leaf strainer, this is either a separate plastic component or integrated into the air baffle.

The heart of a siphonic drainage system is the air baffle. The function of the air baffle, which is disc shaped and solid without perforations, is to stop air from being entrained into the pipework at or before dimensional flows.  To increase the efficiency of the air baffle and further eliminating air entrainment, some systems also incorporate anti vortex fins in their design of the air baffle for example Ultraflow and UV-System. In combination air baffle/leaf strainers outlets the fins must be spaced to prevent the ingress of debris which may otherwise get caught in the pipework.

Roof outlets designed for gravity systems must not be installed in siphonic systems. When outlets without correctly designed air baffles or with no air baffles are installed in siphonic systems, air entrainment into the pipework is only prevented when the water above the outlet attains sufficient depth.  However, it is impossible to predict at what depth siphonic action will occur and to control the water depths on the roof or in the gutter with such outlets.