Home | Siphonic Roof Drainage | How Does HydroMax® Siphonic Roof Drainage Work

HydroMax® Siphonic Roof Drainage – Simple and Effective

Being a self-draining piping system, at the start of a rainstorm the pipework is empty as shown above. As the rain enters the HydroMax roof drain, the tail-pipes will quickly fill and supply water into the horizontal collector pipe.

Hydromax System with Tailpipes primed. The tailpipe will supply water into the flat horizontal carrier pipe. The water in the main carrier pipe will initially flow in what is termed a gravity flow pattern with air and water in the pipe as shown below.

Gravity Flow Pattern – Air Above Water

As more rain falls, the drains supply greater volumes of water into the carrier pipe. When the water reaches the vertical downpipe, gravitational constant means the water accelerates down the vertical pipe which creates suction. This change in energy within the system to vacuum (or negative) pressures results in the rainwater being pulled into plugs that fill the pipe for short lengths as it is drawn towards the downpipe.

This is termed as Plug Flow. The plugs also push out pockets of air entrapped between the full bore plugs as shown below.Research at Herriot-Watt University and testing by HydroMax® has shown that this flow pattern is typically achieved at 10% to 15% of the design rainfall intensity. Importantly, at this 10% to 15% of design rainfall rate, self-scouring velocities are achieved – Ensuring regular self-cleansing of the pipe system.

As the rainfall rate intensifies, the water almost fills the entire pipe with very little air ingress. This flow pattern results in the small amount of air being carried out in bubbles entrained in the water flow. This flow pattern is named Bubble Flow.

When the air baffle inducer prevents air ingress, the pipes become fully primed.
This is termed Full Bore flow. At full-bore flow with high, self-scouring velocities, the HydroMax® system is now utilising the full height of the building to create suction and pull the water efficiently off the roof.

Fully Primed HydroMax System

A gravity downpipe will run with a core of air resulting in large diameter pipes with inflexible routing.

A HydroMax® downpipe will be full and flowing at high self-cleaning velocities.

Based on a single storey building a HydroMax® downpipe in siphonic flow will drain 10 to 15 times more flow than you would obtain in the same diameter under traditional gravity flow.

HydroMax® provides an extremely efficient drainage system maximizing the carrying capacity of the pipes

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

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