Revolutionary Syphonic Drainage - Gutter Pumper

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Revolutionary syphonic drainage


Weir flow generates a vortex that spirals air down a pipe. This causes the water to also spiral down the inner wall rather than fall down the pipe. For this reason and unless blocked, downpipes never contain less than 2/3rds air!


The anti-vortex baffle stops a vortex spiralling air down the pipe, allowing the pipe to flow full of water. The effect of gravity on FULL FLOW generates a vacuum that sucks water into the outlet at high velocity, increasing flow rates by up to 1,000%.

Longer vertical drops generate greater velocity and flow rates.

Purging the air to achieve syphonic flow

Water above the baffle stops the vortex but it also traps a large air pocket in the pipe. The air pocket’s buoyant force, equal to the weight of the water it displaces, initially resists the hydraulic head and downward flow.

Inflowing water calves air bubbles off the air pocket and carries them downwards, reducing the air pocket until it has negative buoyancy and is purged from the pipe. Syphonic full flow is established in seconds.

Gutter Pumper fits 20 mm class 12 uPVC pressure pipe and fittings. The pipe’s internal diameter is 23.7 mm and its volume per metre is 0.441 litres.

Pipe must remain vertical or horizontal to maintain the prime but the horizontal pipe’s diameter can be increased at ground level to reduce friction loss over long runs if needed.

NOTE: Class 12 uPVC pressure pipes have the same outside diameter as the equivalent US uPVC schedule 40 pipes and use the same fittings. 1 inch = 25.4 mm.


The initial vertical drop is the distance between the gutter and the top of the initial horizontal pipe PLUS 25 mm for the Gutter Pumper inside the gutter. The minimum initial vertical drop possible is 70 mm when the elbow is fitted directly under the Gutter Pumper as shown below.

Friction loss between the Gutter Pumper and the second drop = the pipe length between the top of the Gutter Pumper to the second drop PLUS the equivalent pipe length for each elbow including the 90 degree elbow above the second drop.

90 degree elbow = 0.6 metres
45 degree elbow = 0.3 metres

The second vertical drop boosts the system’s flow rate when primed and the Gutter Pumper can prime the second drop after flowing through a pipe with a friction loss expressed as fifty times the length of the initial vertical drop. We also have a way to increase this length a further 30% for even longer runs of initial horizontal pipe. Examples, charts and a flow rate calculator that allows you to design your system for your required flow rate are found on the Fitting page.

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