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Valsir S.p.a
Waste and water
supply systems, underfloor heating system
and flush cisterns


The ultimate solution in case of rain

Rainplus® is defined as a siphonic rainwater drainage system because it is based on the same principle as a siphon. The siphon is in general a reversed U shaped pipe used to pour a fluid from one container to another located in a lower position.

When the pipe is full, the fluid contained in the longer stretch of pipe tends to fall due to its weight causing the suction of the liquid in the shorter section, which is lighter in weight.


This process only starts when the pipe is completely full and continues until a balance between the two containers is reached: either when the two containers reach the same level or when the fluid level in the higher container goes below the pipe inlet section.

The driving force that causes this effect is a result of the difference in height of the two containers: the bigger the difference, the stronger the driving force and, as a consequence, the greater the flow velocity in the pipe.

The performance of the Rainplus® siphonic drainage system is therefore decidedly better than a conventional system where the driving force is generated exclusively by the amount of water that accumulates on the roof. When the siphonic drainage system runs at full capacity, the “siphon effect” is triggered resulting in a driving force that is proportionate to the height of the roof and the end of the circuit, which is typically located at ground level.

Such power generates levels of positive and negative pressures in specific points of the circuit such as to rapidly increase the velocity and, as a consequence, the flow rates of the system (Bernoulli’s principle).

Bernoulli’s principle


In fluid dynamics, Bernoulli’s principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. Bernoulli’s principle is named after the Dutch-Swiss mathematician Daniel Bernoulli who published his principle in his book Hydrodynamica in 1738.


Valsir provides complete support both during the planning phase and on site, thanks to a first-class technical office made up of a team of highly experienced engineers, capable of dealing with the most complex system requirements.

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