Siphonic Rainwater Drainage

World leaders in rainwater roof drainage systems

A quality space saving rainwater drainage system

Using our extensive knowledge of the siphonic industry, RwpClearflow has developed a high flow capacity siphonic rainwater outlet capable of taking flows up to 46 l/s per outlet. That’s nearly twice the amount of some earlier siphonic outlets.

The product has been developed to work with all modern day construction methods and material types, allowing the outlet and adjoining siphonic system to be used in virtually any new build or refurbishment.

Advantages of siphonic systems

  • Reduced diameter down pipes
  • Reduced number of down pipes
  • Less underground drainage connection points
  • More aesthetically pleasing
  • Easier co-ordination
  • Space saving
  • Extremely efficient
  • Reduces your carbon footprint
  • Cost effective

To speak to a rainwater specialist about our siphonic rainwater drainage system, call us now on 0114 247 1800 or send us a message via our contact form.

What are the benefits of siphonic rainwater drainage?

A balanced siphonic system is designed, activated and controlled by the siphonic outlet, analytical design software, pipe work system and material.

The pipe work material and jointing system again needs to meet a required level of performance due to the velocity and negative pressures produced and be able to withstand the forces and contain the rainwater at all times.

As siphonic systems flow at high velocity under suction they offer a great benefit over traditional gravity systems:

  • less outlets,
  • less roof penetrations,
  • smaller pipe diameters,
  • horizontal pipe runs (no drop required)

This all leads to a more efficient installation and removing the need for awkwardly positioned internal gravity down pipes. It also provides a vast reduction in networks of underground drainage systems that are required to collect gravity drops

For a further understanding, to discuss a concept design, tender or live contract, call us now on 0114 247 1800 or send us a message via our contact form.

What is siphonic rainwater drainage?

Siphonic Drainage Systems are analytically calculated pipe work systems, designed to receive and discharge a given volume of rainwater from roofs in line with the Clients R10 specification and BSEN 12056.

Siphonic rainwater outlets are designed and tested to allow rainwater to flow freely into the pipework below, whilst also building the level of rainwater around the outlet to rise and restrict the flow of air into the system. At this point the horizontal pipe work below becomes full (primed), and the falling column of water in the down-pipe below causes suction in the system, drawing the rainwater through at a designed and controlled flow velocity.

As the system empties the water around the outlet drops it allows air to enter the system, breaking the siphonic action. As the rain continues the process starts again and the cycle continues until such time as the rainfall intensity decreases.

As with traditional gravity systems there are no moving parts or pumps. The terminology "traditional" or "gravity" and "siphonic systems" can be misunderstood as it’s the head of water and gravity drop within the vertical stack which creates the suction in a siphonic system. Siphonic systems are created by gravity and the controlled flow of air and water.

We design, supply and install all rainwater systems

At RWP Clearflow we take care of the whole process for you. Our experienced rainwater drainage design team and rainwater systems technicians are dedicated to producing drawings and installs in line with our client’s requirements.

Call us for your free consultation now on 0114 247 1800


In-house design

Product supply

Quality installations

Reliable support

Rainwater specialists

Technical assistance