What is HydroMax Siphonic (Syphonic) Roof Drainage

Hydromax™ Siphonic Rainwater System

In order to appreciate the function and benefits of a Siphonic Rainwater System it is important to understand how a traditional gravity rainwater system operates.

As rain falls on the roof, the rainwater spreads out to the lowest level it can find. As the depth of water on the roof or gutter increases, it generates a force to move the water flow towards holes or openings called roof outlets that convey the water to a lower level. The roof outlets are connected to pipes that drop to ground level and into the underground drainage system.

To enable the water to move into the rainwater downpipe from the outlet a large amount of air is required. A vortex forms naturally and the water spirals down the outer wall of the pipe therefore transporting the water flow extremely inefficiently. Current European regulations limit the water/air mix within the pipe to 1/3 water and 2/3 air. This form of water movement results in a large bore pipe moving a lot of air and a little water.

The flow rate is very slow as the water is rotating round and round as it drops instead of flowing directly in the intended course.

The preferred requirements of the architect or building user for free use of the space within buildings is sacrificed due to having limited choice as to the positioning of the numerous rainwater downpipes which are generally determined by the outlets in the roof.

When using the HydroMax™ siphonic roof drainage system, the technology, custom and practice in managing the discharge of rainwater from roofs is changed. A siphonic system maximises the flow of water through the pipes by eliminating air within the pipework and uses the full available building height to drive the water directly through the pipework. Running with full-bore flow by means of simple sphonic action ensures efficient drainage of the rainwater to a connection into the underground drainage system in your preferred location. By using this method you can position the downpipe(s) in location(s) to suit the design team and or client's requirements.

The number of downpipes is normally significantly reduced effecting another benefit (and a large cost saving) through a reduction in underground drainage requirements.

A constituent part of the HydroMax™ siphonic system is the special HydroMax™ siphonic roof drain. The HydroMax™ drain (outlet) is designed so that as soon as the rainwater reaches the hallow deth to the underside of the inducer plate, the unique inducer prevents air-ingress into the pipework as a first step towards making the system run under siphonic principles. Instead of multiple downpipes, small diameter tailpipes join a series of outlets to a collector pipe positioned at high level below the roof area. This horizontal collector pipe (installed absolutely level) connects from the required number of roof outlets and runs to a chosen position before dropping for connection into the underground drainage system.

We described above that the first step towards operating siphonically is the elimination of air entry by the HydroMax™ siphonic roof outlet. As the pipe is filled with air before the rainfall storm event commenced, our second step is to remove this air from the pipe.This is achieved by sizing the tail pipes, collector pipes and downpipe to fill up quickly, a process that is called priming. The tail pipes are, when compared to an inefficient gravity system, relatively small. This enables quick priming of the tail pipe. The water flows in a plug form to the downpipe. The third and last step towards the creation of the siphon occurs when this plug of water accelerates (due to gravitational forces) as it drops down the downpipe. This acceleration pulls the full-bore flow and any remaining air through the system thus creating the siphon. There are no moving parts within our 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 the full bore of all the pipes in the system fill up quickly. The pipework sizing is determined using the very latest and most sophisticated hydraulic design calculation software - HydroTechnic™, owned and copyright of HydroMax.

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How does a HydroMax™ Siphonic Roof Drainage system work?

A HydroMax™ Siphonic Roof Drainage system utilises the full height of the building to provide the energy to create a powerful siphonic action. A collection of elements combine to create the HydroMax™ Siphonic Roof Drainage System.

The piping system is empty prior to a storm event occurrence. As the rainfall event starts, our unique HydroMax™ Siphonic Roof Drain prevents further air-entry into the pipework system whilst its Anti-Vortex fins also stop Vortex formation. Our technically advanced HydroTechnic™ analytical design software program has unsurpassed accuracy to determine the pipework diameters necessary to rapidly fill and prime the pipework system to provide optimised performance.

HydroMax™ will utilise significantly smaller pipe diameters than that required in a traditional gravity system. As the small diameter pipes prime and the water reaches the vertical downpipe, the water accelerates due to the forces of gravity. This acceleration creates the negative pressures that give the system its ‘Siphonic’ title and the forces literally suck the water off the roof until the rainfall event abates.