Inverted Siphon of Drainage Network

In the underground drainage system of a city, when the pipeline encounters a river, railway or subway, how can the sewage be transported over mountains and hills? At this time, a special structure called an inverted siphon comes in handy. It is like an "underground overpass" that allows the water flow to cleverly avoid obstacles and complete "hurdle-style" transportation.

I. What is an inverted siphon?

An inverted siphon is a U-shaped or V-shaped curved pipe that uses the principle of "water flows to lower places" to allow sewage to pass through the bottom of obstacles. For example, when a drainage pipe needs to cross a river, the pipe will first be buried deep down, pass under the riverbed, and then climb up. The overall shape is like an inverted rainbow (siphon), hence the name "inverted siphon".

II. How does it work?

1. Gravity Drive

Sewage flows into the inverted siphon from the water inlet and naturally flows downward due to the height difference. After passing through the obstacle, the pipe gradually rises, and the pressure generated by the upstream and downstream water level difference "pushes" the sewage to the outlet.

2. Anti-silt design

The flow rate in the pipe should generally be greater than 0.6 m/s to prevent silt deposition and blockage. Some inverted siphons are also equipped with flushing ports or double pipes to facilitate dredging and maintenance.

3. Sealing pressure resistance

The inverted siphon is buried deep (often more than 5 meters) and is made of reinforced concrete or high-strength plastic to avoid being fractured by ground loads.

III. Why do we need an inverted siphon?

1. Protecting infrastructure

Avoid installing open pipes above rivers or roads to reduce the risk of pipelines being hit by ships or vehicles.

2. Maintaining smooth water flow

Traditional climbing pipes are prone to garbage accumulation, while inverted siphons use a "down first, then up" path to allow water to flow more smoothly.

3. Save land resources

Hidden underground, it does not affect ground buildings and ecological landscape.

IV. About the Design of Inverted Siphon

●Double-pipe inverted siphon: If two pipes are designed to be used alternately, the other can still operate when one is blocked.

●Caisson-type inverted siphon: vertical shafts are built on both sides of the river to facilitate maintenance personnel to enter and clean.

●Intelligent monitoring: Modern siphons are equipped with flow meters and cameras to monitor water levels and flow rates in real time, and to determine whether the siphon is faulty through monitoring.