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Siphonic Roof Drainage

HydroMax® continue to be leaders in the market with all our roof drains tested to the British Standard BS 8490 and/or ASME A112.6.9 Siphonic roof drain product test standard and market leading design software including our HydroTechnic™ Revit API plug-in.

Gravity storm drainage relies on a large core of air within rainwater pipes to allow water to flow through the pipes. The air and water enters the gravity roof drain in a vortex flow which builds significant ponding or head of water above the gravity roof drain. The ratio in vertical pipes is 30% water and 70% air. This air flow requirement results in large diameter pipes and a restriction in pipe routing with sloping horizontals and multiple rainwater downpipes required.

Gravity drainage is inefficient and restricts design team and client choice of pipe routing.

With Siphonic Roof Drainage, the HydroMax® siphonic roof drain’s purpose is to eliminate air-ingress into the piping system thus filling with water only and allowing full-bore flow. We utilise the building height to create vacuum (negative) pressure which, in turn, creates high-capacity water flow through smaller diameter pipes.

HydroMax® Siphonic Systems are Self-Priming during the storm event and Self-Draining after the storm event. Using the HydroMax® Siphonic Roof Drainage method allows you to run horizontal pipes flat for long runs giving flexibility to position the fewer downpipes in locations to suit the design team and or client’s requirements.

The reduction in downpipes significantly reduces underground drainage requirements with environmental and cost saving benefits. The pipes are empty before a rainfall storm event. As rain falls and enters the piping system through the HydroMax® Siphonic Roof Drain, the design of the roof drain with air baffle and anti-vortex plate inducer prevents further air entering the pipe and promotes water filled pipework.

Priming of the system is achieved by sizing the tail pipes, collector pipes and downpipe to fill up quickly. The tail pipes are relatively small when compared to an inefficient gravity system, This enables quick priming of the tail pipe. We design with the horizontal pipe being flat to further speed up the priming process.

When the water flows reaches the downpipe, the column of water accelerates due to gravitational constant as it falls down the vertical downpipe. This acceleration creates vacuum pressures and pulls the full-bore flow and any remaining air through the system thus creating the siphon. There are no moving parts within our HydroMax® siphonic system – Hydraulics and the height of the building do all the work!

To ensure the hydraulics function efficiently, the pipework diameters are selected so that all the pipes in the system fill up quickly to run full-bore.

The pipework sizing is determined using the very latest and most sophisticated hydraulic design calculation software programs – HydroTechnic™ web-based app and HydroTechnic™ Revit API plug-in. Both apps are owned and copyright of HydroMax®.

Our strategy is to partner with leading companies who provide local market knowledge coupled with technical expertise.

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