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


Conventional systems VS. Rainplus system

There are two types of rainwater drainage systems: conventional systems that are incorrectly called gravity systems, and the Rainplus® siphonic system, which is also known as a vacuum system or full section system.

Both use the force of gravity but in a decidedly different manner, resulting in differences in performance, design and calculation.


conventional drainage system

A conventional drainage system can be designed for large surface areas but does not cut off air flow into the pipe. For this reason pipes are sized for filling ratios of 20% or 33% (depending on national or local standards and regulations) allowing considerable amounts of air into the pipes of 80% or 67% of the pipe section.

In conventional roof drainage, the outlets are simple “funnels” installed on the roof covering and connected to the downpipes which are as high as the building and the water collectors which require a gradient of at least 1%, are dimensioned for a maximum filling factor of 70%.

When the water collectors are very long and it is not possible to provide the minimum slope necessary due to the limited space available, the only solution is to increase the size of the pipes with a consequent rise in installation costs.


Rainplus® siphonic drainage system

The Rainplus® siphonic drainage system is made up of special outlets that incorporate an anti-vortex plate that prevents air entering into the pipes. The outlets are connected via short pipes of relatively small diameters to the horizontal water collector which is located just under the building roof.

The collector pipe, generally installed at the highest possible position, runs horizontally (no fall angle is required) untill it reaches connection with the downpipe. The downpipe drops into the drainage line which is buried in the ground and conveys the water straight into a collection tank or the municipal stormwater mains.

The absence of air in the system allows it to run 100% full of water making use of the entire pipe section and vastly increasing flows that are 10 times faster when compared to conventional drainage systems.


Flow in a conventional outlet

In conventional roof drainage systems, the outlet does not incorporate any sort of insert or device, hence the flow entering the system is characterized by a vortex that pulls air into the pipes.


Flow in a Rainplus® outlet

With the Rainplus® siphonic drainage system, at design flow values, the roof outlets prevent air from entering and forming a vortex thus ensuring the system works at full capacity; in such conditions design can be based on the equations of fully developed flow rates operating at positive or negative pressures (Bernoulli’s energy conservation principle).


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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