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Siphonic rainwater drainage system

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Vestone, Italy
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Siphonic rainwater drainage system

Rainplus® is a siphonic rainwater drainage system designed to reach maximum drainage performance with the lowest levels of water accumulation on the roof. 
Valsir Rainplus® fully meets the demands of increasing rainfall levels being registered and guarantees the drainage of rainwater from medium to large size buildings in total safety.
The system uses the building height as the driving force to generate high speed flow rates thus maximizing drainage efficiency.
Rainplus® allows the entire quantity of rainwater to be directed to any part of the building whatsoever thus enabling the implementation of the most modern rainwater harvesting systems. The harvesting and conservation of water are parameters that are taken into consideration and contribute to obtainment of Green Building marks.
The advantages of this technology are numerous; such as the significant reduction in costs and installation times, as well as an increase in the performance of the entire drainage system.
The Rainplus® siphonic system is made up of special roof outlets that are designed and tested according to American Standard ASME A112.6.9 and European Standard EN 1253.
These outlets are connected to Valsir HDPE pipes and fittings, which are sized in order to work under negative pressures, at high flow rates and with a full bore. 

Further info from manufacturer on RAINPLUS
Further details
Characteristics of excellence
The advantages of Rainplus®

When compared to conventional systems, Rainplus® requires a lesser number of roof outlets and allows a substantial reduction in pipe diameters, in the number of fittings required and the number of downpipes: this results in savings of up to 80% on vertical pipes and from 20% to 30% across the entire system.

Space saving
The roof outlets are connected to single horizontal collector pipes that are fitted without fall and the downpipes are positioned anywhere along the building perimeter thus avoiding interference.

High performance
When in operation drainage pipes flow at 100% full over the entire system, draining velocity is therefore greater resulting in the self cleaning action of the pipework.

Eco sustainability
The ease in directing the pipes to storage tanks makes the collection of rainwater easier for reuse in irrigation systems, fire ponds and tanks for non-potable uses in general.

Time and labour saving
Construction programmes are accelerated due to reduced installation times and less groundwork is required due to the reduced number of embedded pipes.

Increased design flexibility
Complete control over downpipe location and absence of embedded pipes gives increased design flexibility of the siphonic system.

The Valsir Rainplus® system and HDPE are produced with completely recyclable materials which, at the end of their useful life can be recovered. The production processes employed are energy efficient and of reduced impact. Valsir has adopted the Green Building principles in terms of respect for the environment and conservation of resources, pipes and fittings are in fact certified by the prestigious Singapore Green Building.
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.
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.
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 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).
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).
Flow stages
EN 1253 and ASME A112.6.9 technical standards are used to evaluate the performance of a siphonic system and, as they define the measurement method of the flow rates as a function of the water depth on the roof, they allow the flow regime phases to be analyzed.
Stage 1
With a moderate flow, of 10 or 15% of the design rainfall intensity value, the roof outlet works as it would in a conventional system and the flow is defined “gravity flow”, in that air content in the pipes is elevated.

Stage 2
When the water discharged from the roof is between 10 to 15% and 60% of the full bore flow condition, water flow is discontinuous and the system therefore fluctuates from a gravitational flow regime to a full siphonic action. At these rainfall values the water that accumulates on the roof fills the outlet, cutting off air flow into the pipe and triggering the siphonic action.
The velocity of water discharged therefore increases which results in falling water levels, allowing air to be drawn into the piping network and breaking the siphon; for this reason this stage is called “plug flow”.

Stage 3
When the water discharged is between 60% and 95% of the design rainfall intensity value, the pipes are completely full of water although many air bubbles are still present. This stage is called “bubble flow” and features high flow velocities thanks to the siphonic effect.

Stage 4
When the flow is over 95% of the design rainfall intensity value, the siphonic effect operates at full capacity reaching maximum velocity with no air entering the pipes. This stage is called “full flow” and does not produce noise or vibrations.
Outlets and accessories
One of the key elements of the system is the Rainplus® outlet that has been designed and manufactured to meet the requirements and testing criteria set by the international standards EN 1253 and ASME A112.6.9.
The main components of the Rainplus® outlets are made of stainless steel or molded aluminium alloy, protected by a special resin that makes them longlasting.
wide range of drainage flows (up to 65 l/s with Rainplus® 110 and up to 14 l/s with Rainplus® 56);
Reduced roof water levels required to trigger the siphonic action;
No swirls thanks to the special profile of the antivortex disk and reduced pressure losses at the inlet;
Low noise levels and maximum operation stability;
Easy installation thanks to the reduced number of components and compact size. For example, Rainplus® 56, in the version with horizontal connection, can be installed inside the roof slab thanks to a height of just 104 mm;
Connection with the Valsir HDPE system is extremely reliable;
Suitable for installation in gutters, even of small dimensions, or on roofs covered with any type of waterproofing material.
Rainplus® Overflow Kit
Local regulations or standards on the design of rainwater systems may require emergency systems (also known as overflow systems) to be provided that are capable of draining unexpectedly intense rainfall that exceeds the design rainfall level.
Valsir supplies a patented product that allows a Rainplus® siphonic outlet to be transformed into an emergency siphonic outlet by simply adding an Overflow Kit that is adjustable in height and capable of maintaining the same drainage performance.
Bracketing systems
Valsir offers a wide range of bracketing systems and accessories for installing the entire drainage network. The Rainplus® bracketing system, composed of special clips together with support rails and relative accessories, is designed to resist the forces of heat contraction and expansion in the drainage network and is available in diameter 40 mm up to diameter 315 mm.
The Rainplus® system also includes clips with M10 expansion anchors, clips for M10 threaded rods also for mounting on support rails, clips for 1/2” and 1” threaded rods for wall and ceiling mounting.
The bracketing system range allows:
- Easy pre-fabrication;
- Rapid and simple ceiling mounting of long stretches of collector pipes;
- Mounting of entire drainage network using a reduced number of bracketing pieces;
- alignment of clips and Valsir HDPE pipes with the support rail;
- Capacity of absorbing heat expansion and contraction of the drainage network;
- Installation without the use of special tools;
- The clips are anchored to the pipes and support rail using high resistance bolts.
Pipes and fittings
The Valsir HDPE product line for the creation of siphonic drainage systems is available in diameters 40 mm up to diameter 315 mm and is characterised by a wide range of fittings such as access pipes, elbows, reducers and reduced branches.
The use of Valsir HDPE pipes and fittings offers numerous advantages:
Possibility of pre-fabricating system parts and mounting them on site thanks to the light weight of the components;
Savings in labour costs thanks to rapid installation times;
Possibility of choosing from the different connection types such as butt-welding or electrofusion couplings;
No material wastage makes it more economical;
Increased safety of the systems thanks to the excellent mechanical characteristics of Valsir HDPE.

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