Torrential rain and inadequate sewage systems have made flooding an increasingly common problem

allagamento_antiriflusso_danni.gif     Whether the cause is climate change or the irresponsibility of humankind, the fact is that flooding in buildings caused by heavy rain is becoming an increasingly common and serious problem in Italy. When many millimetres of rainwater are suddenly unleashed, the water simply cannot drain away fast enough, causing the flow to back up into drainage systems in buildings. Very often, even though the causes of the problem are well known, radical modifications to the sewage system are not possible, so it becomes necessary to implement a solution directly in the building itself to provide protection against the risk of flooding. The solution is the backflow prevention valve.

What is backflow, and what causes it?

Referring to the communicating vessels principle – whereby water will maintain the same level in all the branches of a hydraulic circuit – backflow occurs when the maximum level in a hydraulic circuit, above which there is overflow from the circuit itself, is exceeded. Therefore, if there are any sanitary fittings below the backflow level (generally in basements, cellars and underground garages, but also in sub-street level apartments), flooding may occur during sewage system overload situations. The following are possible causes of backflow:
  • An inadequately sized sewage system
  • High sewage volumes caused by short but heavy rainfall
  • Increased rainwater volumes channelled into drains due to increased building density and urbanisation
  • Drainage overloading caused by peaks in simultaneous usage in high density urban areas
  • Malfunctions and obstructions downstream in the sewage system
Backflow protection is required both where white water and black water are separate and where there is mixed water drainage.

The backflow prevention valve – a solution protecting the safety of the home

The backflow prevention valve is installed in a dedicated accessible and inspectable well. The function of the valve is to act as an effective barrier preventing any backflow of water from the sewage system during any possible overload event. The backflow prevention valve contains a stainless steel plate which pivots into the direction of the outgoing water flow from the building to the sewage system. In the event of backflow, the plate is mechanically closed by the pressure of the water. The valve has a lever that can be used to permanently lock the plate in the hermetically sealed position. A backflow prevention valve must be included in the design and sizing process for the drainage system of a new building. Its use is also strongly recommended in existing buildings, where work on the piping connecting the building drainage system to the sewage mains is possible, and there is adequate physical space for creating a well to contain the valve. Backflow prevention valves must be certified compliant with the European standard EN 13564-1:2003, which ensures conformity with specific requisites concerning, for example: drainage flow efficacy, rigidity, resistance, water tightness, connection conformity and correct operation of the open/close mechanism.