SUPADIVERTA - syphonic rainwater diverter

SUPER EFFICIENT SYPHONIC DRAINAGE

Syphonic drainage has allowed Supadiverta to be designed as a compact slim line unit capable of harvesting large volumes of rainwater with great efficiency and versatility.

Revolutionary syphonic drainage systems require fewer and smaller downpipes and are widely used in large modern buildings for their greater efficiency, cost savings and greater architectural design freedom. Syphonic drainage systems can easily achieve flow rates ten times greater than same sized conventional systems.

For more detailed information about syphonic drainage, a recommended site is www.hydromax.com
- select Hydromax Siphonic, Understanding Hydromax
- this is a direct link to the document


OF INTEREST: Conventional downpipes never drain with less than two thirds air!

SYPHONIC DRAINAGE & SUPADIVERTA – HOW DOES IT WORK?
A full flow of water (no air) draining through an unconnected (no vertical pipe) Supadiverta 20 mm outlet flows at approximately 18 litres per minute (lpm) but if a vortex was to draw air down the outlet, the flow would slow to about 12 lpm.
HOWEVER, connecting even a short .5 metre length of vertical 20 mm PVC pressure pipe to the outlet will dramatically increase the FULL FLOW rate to 41 lpm and to approximately 58 lpm if a 1 metre length is used.
Lengthening the pipe increases the hydraulic head and each 1 metre of head generates approximately 9.8 kPa or 1.47 psi static head pressure BUT if the same vertical drop was fitted to an outlet that was drawing air through a vortex, the flow rate would decrease to approximately 6 lpm as the unpurged air pockets in the pipe will prevent generation of a hydraulic head AND act as physical barriers to restrict flow.
Each Supadiverta outlet has an anti vortex baffle that blocks the vortex whenever the water rises above the baffle and once the connecting pipe work is then purged of air, the generated head pressure causes the FULL FLOW of water to flow at increased velocity through the connecting pipes. The increased flow velocity in turn creates a vacuum that sucks the water into the outlet at far greater volumes than possible with normal gravity weir flow.

MORE WATER – FLOWING FASTER!

NOTE: Static head is the measure of water pressure in a pipeline that is not flowing. Water flowing through a pipe is subjected to friction loss which consumes energy, the reason why smaller and longer pipes flow slower. The static head minus the friction loss is referred to as the total dynamic head.
IMPORTANT: A vertical drop must remain vertical and not increase in diameter in order to prime. To understand why, we recommend looking at the page 12-14 diagrams in this linked document provided by Siphonic Roof Drainage Association in the UK http://www.siphonic-roof-drainage.co.uk/

FLOW VELOCITIES

Syphonic flow velocities are generally restricted to less than 8 metres per second (mps) for good reason. Once velocities exceed little more than 9 mps, the generated sub atmospheric pressures causes the water to cavitate (form bubbles), literally boiling the water at low pressure. For this reason, High Density Polyethylene (HDPE) syphonic downpipes able to withstand negative pressures are also designed with varying diameters and/or vacuum breaks when used in tall buildings to prevent this happening.

Supadiverta owners need not worry about this happening as Supadiverta is designed to operate with lower head pressures and flow velocities than larger and longer syphonic downpipes on tall buildings!

Class 12 PVC pressure pipe or polypipe is recommended for use with Supadiverta.

OF INTEREST: At the correct vacuum, iced water will boil and produce steam – all at the same time!

FRICTION LOSS

The flow rates generated by the vertical drops are reduced by the energy lost in connected pipe work but friction/energy losses are minimised by connecting the vertical drops to larger horizontal pipes.

The simple adage is: Larger pipes = less friction loss = greater total dynamic head = higher flow rates

For polypipe, 19mm vertical drops are most often connected to 25mm (78% greater volume) horizontal polypipe, depending on intended usage. Polypipe has the advantage of low cost, ease of fitting, is easily altered and is versatile.

For the recommended class 12 PVC pipe, the 20mm vertical drops can be connected to 25 mm, 32 mm, 40 mm and even 50mm class 12 PVC pipe fittings. Larger PVC pipes maintain higher flow rates, are still inexpensive and more suited to permanent connections

Poly and PVC pipe can also be mixed and matched

OF INTEREST: Doubling a pipe’s diameter increases the internal volume X 4 and if the same head pressure is maintained the flow rate increases about 6 times. Class 12 PVC pressure pipe is sold as a ‘nominal size’… the actual internal diameter (I.D.) is larger! For example, 32mm pipe I.D. is actually 37.5mm I.D. See the table of actual I.D.’s, their volume per metre and flushing flow rates.

SELF CLEANING PIPEWORK

Flow rates in excess of .8 metres per second (mps) promote a self cleaning action and Bubble Flow, one of the four syphonic priming stages, has a scouring action.
To see photos and a brief description of the priming process, see this document at www.akatherm.com

NOTE: Horizontal pipes should be fitted with drain valves to enable flushing in between rain events.

FRICTION LOSS CHARTS

To access friction loss/flow rate charts for Poly and PVC pipe, visit…
http://www.agf.gov.bc.ca/resmgmt/publist/500Series/590304-2.pdf

NOTE: The above linked document gives flow rates in U.S. gallons, head pressures as PSI and pipe diameters as inches. The flow rate / friction loss calculations are the equivalent of 100 feet (approximately 31 metres) of pipe work. The following conversions apply:-

Friction losses caused by pipe fittings must also be added to a pipe’s length when calculating friction loss/flow rates.
The table below shows the friction losses as an equivalent measure of pipe length in metres.