Fall (drainage)

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In construction and in sewage technology, a fall is a height offset in a sewer system . If a higher-lying pipeline flows into a lower-lying one underground, a vertical drop at points can serve to overcome this height difference. Often falls are realized in connection with shaft-shaped structures. One then speaks of a fall shaft or crash structure .

Technical background

The European standard EN 752, drainage systems outside of buildings, warns of the consequences of excessive flow velocities in sewers on steep slopes. The standard points out the importance of fall structures and fall shafts, as a result of which "sewers with great gradients can be avoided".

Lying sewer pipes must not have a gradient greater than 1:20. This is the only way to ensure safe emptying of the line. In the event of a greater gradient and thus increased flow velocity, liquid and solid components would separate and the solids would clog the line. In the case of large differences in height that cannot be achieved with due consideration of the maximum gradient, slopes (≥ 45 °) are built in, on which no deposits are possible.

In the case of property drainage in buildings, the private underground pipe is often considerably higher than the public sewer in the street. Therefore, a fall is often provided in order to reach the lower level of the sewer. This often happens in connection with a control shaft between the building and the street, near the property line. This shaft is then designed as a fall shaft.

Due to turbulence phenomena can lead to increased crash into buildings odor emissions come.

Executions

Depending on the location of the fall in relation to a shaft, one also speaks of an external or internal fall. While external drops are installed in the ground next to the shaft, internal drops are located within a shaft.

Since drainage systems are usually created using standardized molded parts, there are also ready-made solutions for the formation of falls. Particular attention must be paid to accessibility for maintenance purposes, as a fall for cleaning and inspection is a potential obstacle. An inspection opening must be provided at its upper point to ensure that the kinked line can be cleaned if necessary. This is already integrated in ready-made solutions.

There are special shapes of the falls, adapted to the different installation situations, fall heights and materials. In order to reduce the speed of the fall at greater heights and to prevent negative flow effects, there are falls with a laterally offset inflow, so that the wastewater rotates down the wall of the (vertical) pipeline in a vortex and the speed through the internal turbulence decreases sharply at the outlet.

Norms and standards

  • DIN 18306 - drainage canal works
  • DIN 4032 - concrete pipes and fittings (no longer valid)
  • DIN V 1201 - manholes made of concrete, steel fiber concrete and reinforced concrete
  • ATV - DVWK - worksheet - A 157, November 2000, sewer structures:
  • DIN V 4034 - Shafts made of precast concrete and reinforced concrete parts
  • DIN 4045 - wastewater technology; Terms
  • DIN 16928 - Pipelines made of thermoplastics; Pipe connections, pipe parts, laying, general guidelines
  • DIN 19534 - Pipes and fittings made of plasticizer-free polyvinyl chloride (PVC-U) with plug-in socket for sewers and pipes
  • DIN 19850 - Fiber cement pipes, fittings and manholes for underground sewers
  • DIN EN 295 - clay pipes and fittings as well as pipe connections for sewer pipes
  • DIN EN 588 - fiber cement pipes for sewers and sewers
  • DIN EN 752 - drainage systems outside of buildings
  • DIN EN 1401 - Plastic piping systems for underground pressureless sewers and pipes - Plasticizer-free polyvinyl chloride (PVC-U)
  • DIN EN 1916 - pipes and fittings made of concrete, steel fiber concrete and reinforced concrete
  • DIN EN 1917 - manholes made of concrete, steel fiber concrete and reinforced concrete

Individual evidence

  1. ↑ "Fall shaft" and "Fall structure" according to DIN EN 752-4: 1997 Drainage systems outside of buildings 9.3
  2. ↑ DIN EN 752-4: 1997 Drainage systems outside of buildings 9.3
  3. ↑ Franz-Bernd Frechen, Wolfram Franke: Determination of odor emissions from fall structures in the sewer system using the odor emission potential GEP . Hazardous substances - keeping the air clean , Volume 75 (2015) 10, pp. 417-420.