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ACO Siphonic drainage

Roof areas without traffic larger than 150 m2, such as for example production buildings, hangars or sports stadiums, are suitable for siphonic drainage. When the rainfall is heavy enough, the gullies create reduced pressure in the pipe system. This means that increased drainage performance level can be achieved compared to simple gravity drainage. Siphonic drainage can be used on membrane, concrete and gravel roofs, as well as on green roofs with extensive planting.

When sizing and installing a siphonic system, there are a series of guidelines to be followed. That is why our own internal Application Technology department will be happy to carry out the calculations relating to the system for you, including the isometric diagram of the pipe layout and creating a list of the materials required.

Syphonic drainage systems operate with specially designed flat roof drains which, unlike gravity drainage systems, are configured to work with completely full pipes (degree of fill h/d 1.0). This can only be achieved by assuring amongst other things that no air is sucked in with the rain water to form bubble vortexes in the pipe systems.

Special components are used in the ACO Jet flat roof drains to prevent these vortexes from forming. Once the dimensioning rainfall volumes are reached which get the syphonic system operational, the system works with completely filled pipes which rapidly and safely drain the roof.

Syphonic drainage systems can be used to drain a roof if the following criteria are fulfilled:

  • Adequate difference in height of at least 4 metres between the roof and the buried drains.
  • Drainage of large roof surfaces requiring a minimum outflow capacity of 1.0 l/s.
  • If it is possible for each of the drains connected to a downpipe to be hydraulically matched to one another.
  • Initiation height of at least 0.3–0.4 m between the inflow level to the centre of the inclined pipe.
  • Distance between two drains max. 20 metres.

Typical example for application siphonic drainage

Cast iron (EN-GJL‑200)

Consists of an iron-carbon alloy where the carbon is embedded in strips within the metallic base. This so-called graphite mesh gives cast iron its exceptional resistance to corrosion and therefore makes it ideally suitable for use in wastewater technology.

Stainless steel (grade 304)

Is a term used to describe an alloyed or unalloyed steel with a particular level of purity. Steel is resistant to water, steam and air humidity and is used for many different purposes. Typical areas of application are e.g. roof drainage for large production buildings.

Cast iron - Modular system
Stainless steel - Modular system

Flat roof drainage systems must always be laid out in accordance with the reference rainfall figures. The reference rainfall can be exceeded during periods of heavy rainfall. This can cause water to pool on the surface of a flat roof.

An independent emergency drainage system for flat roof drains is therefore required in accordance with DIN 1986-100, Chapter 5.9.

This norm stipulates that emergency drainage systems can either drain freely through parapets, or that emergency drainage systems must be installed as gravity drainage systems or as planned completely full pipes with syphonic drainage.

Standard emergency drainage

ACO Turboflow emergency drainage

The specially designed ACO Turboflow for emergency drainage is already operating at an water-build height of 20 mm in the vacuum range. The weight of the water on the roof is reducing to a minimum in comparison to a conventional drainage system.