Sewer restoration: Installation of an air cushion inverted siphon

Air cushion inverted siphons regulate the flow speed of the waste water, ensuring that it flows fast enough to prevent dirt and sand from building up in the pipes. This prevents deposits from accumulating and ensures that the system runs smoothly, with no faults and very low maintenance requirements. The air cushion inverted siphon in Pforzheim has operated without faults since installation, reliably routing water to the treatment plant.

But what exactly is an air cushion inverted siphon? The solution is comprised of a pipe installed at a slight incline; water is fed into it via vertical pipes. Water flowing into and out of the component is regulated by a siphon, which means that air can be pumped in. If the amount of waste water flowing in is low, air can enter and the enlarged air cushion will reduce the cross section of the pipe, causing the water to flow faster. This prevents dirt from building up. If the amount of water flowing in increases, the amount of air can be reduced to optimize the flow.

The Arcadis restoration of the sewer system in Pforzheim was a project of enormous dimensions: Rain and waste water flow through the system at a rate of up to 9,000 liters per second, with levels fluctuating significantly depending on the weather. The project involved excavating 15,000 m³ of material and moving 2,000 m³ of rock; 1,800 m³ of reinforced concrete was put in place and 300,000 m³ of groundwater was pumped. The routing of the siphon pipe, around 15 meters below the Enz and Nagold rivers, was a particularly challenging aspect of this restoration project.