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How does the system work?

BESSFLOW 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 BESSFLOW 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).


In fluid dynamics, Bernoulli’s principle states that for an in viscid flow, an increase in the speed of the fluid occurs sim ultaneously 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.

BESSFLOW — RAINPLUS is a siphonic rainwater drainage system that has been designed to guarantee maximum drainage performance with the lowest levels of water accumulation on the roof. This technology guarantees water drainage on medium to large size buildings in total safety.


Stage 1: Gravity Flow

The flow is between 10% to 15% of the design rainfall intensity value. The roof outlet works in a conventional system that air content in the pipes is elevated.

Stage 2: Plug Flow

The flow is between 10% to 60% of the design rainfall intensity value. The water that accumulates on the roof and filling up the outlet which trigger the siphonic action. However, the increasing of water speed discharge that results in falling water Levels to break the siphon.

Stage 3: Bubble Flow

The flow is between 60% to 95% of the design rainfall intensity value. Pipes are completely full of water, but air bubbles are may still present.

Stage 4: Full Flow

The flow is over 95% of the design rainfall intensity value. Pipes are completely full of water with no air entering and does not produce noise or vibrations.

In Comparison To Conventional System

  Conventional System (Gravity System) Siphonic System
Flow in the Outlet Pipes’ filling ratio of rainwater up to 20% or 33% ; amount of air into pipes up to 80% or 67% (Vortex Flow). NO AIR will be entered the pipes to ensure the system works at 100% full of water which causing the Siphon principle (Suction Force).
Number of Downpipe / Outlet Downpipe increased according to the number of outlets. Each outlet is connected through short pipes of relatively small diameter to the runner pipe.
Size of Downpipe Due to limited filling ratio available, conventional system only depends on the size of downpipes. Small diameter pipes are sufficient to discharge the rainwater due to the absence of air in the system allows it to work 100% full of water and vastly increasing flows, that are 10 times faster.
Piping Design Runner pipe always requires a gradient of at least 1% gradient fall. The size of the pipes is the only solution due to limited space available. There is no fall angle is required due to Siphon principle. Runner pipes could be installed at the highest possible position until it is connected to the downpipe which increasing design flexibility.