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Post/Wall/Stand Mounted First Flush Water Diverter


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The First Flush Post/Wall Stand Water Diverter is a versatile unit that can be mounted on a wall, post or stand, to hold larger volumes of water. It can be adapted to suit a wide range of applications and will manage single or multiple pipes coming from the roof to divert between 20 litres and 150 litres of water.

The kit is easy to freight, and the diverter volume can be made on-site to match exact requirements – just add the appropriate length of 300mm pipe. The kit includes a saddle and a galvanised steel wall-mounting bracket. A galvanised steel stand is an optional alternative to post or wall mounting.

Features and Benefits

  • Prevents sediment, bird droppings, spiders, insects, mosquito eggs and debris from entering the rainwater tank.
  • Improves water quality, and protects pumps and internal appliances.
  • Ideal to use in conjunction with a rain head.
  • Easy installation, just adds 300mm pipe length and glue.
  • No mechanical parts.
  • Inlet fits 90mm pipe or 100mm female fitting.

How much water to divert

It is important to prevent heavy sediments and other roof pollutants from entering the rainwater tank. It is recommended that the amount of water diverted should be a minimum of 20 litres per 100 square metres of roof area (or 0.2L per m2). In calculating the amount of water to divert, consideration can be given to (1) the surface area of the roof, and (2) the number of pollutants on the roof and gutters.

The following factors can be used as a guide in determining the volume of water to be diverted.

  • Pollution Factor For The Roof
    • Minimal pollution – Divert 0.5 litres per square metre (open fields, no trees, no bird droppings, clean environment)
    • Substantial pollution – Divert 2 litres per square metre (leaves and debris, bird droppings, various animal matter)
  • Diversion Factor for a first flush water diverter – m2 Roof Area x Pollution Factor = Litres to be diverted
    • Example for a minimal polluted roof of 100m2 – 100 x 0.5 = 50 litres to be diverted
    • Example for a heavily polluted roof of 100m2 – 100 x 2 = 200 litres to be diverted

As a rule of thumb, the more water that is diverted the better the quality of water in the tank.

Multi pipe feed systems

These water diverters can handle more than one pipe

Single or multiple pipes coming from the roof can be connected into a “T” and coupled together so that the first flush from the roof enters the diverter chamber. The pipes are connected from the “T” to the tank.


Installation Instructions

Determine the length of pipe required using the table opposite.

Inlet End: The ball seat #6 is inserted into the top of the end cap as shown.

  • For 90mm infeed – insert the ball seat #6 and attach the infeed pipe hard down on top of ball seat #6.
  • For 100mm infeed – insert the ball seat #6 and glue the 90mm keeper ring (28mm long) hard down on top of the ball seat #6 to keep it firmly in place.

Outlet End: The outlet requires only a 90mm pipe. Assemble as shown making sure to insert ball #7 before attaching cap #12. Select one of the four control valves #13 and fit it into hose connector #14. Save the remaining valves for possible later use.

Stands: It is important to line up the centre of the chamber outlet with the weld on the stand. Make sure that the stand is bolted down securely and that the pipework connected to the top of the diverter chamber is appropriately secured so that the diverter is stable and the unit is not stressed by bad alignment.


Click here to view the product specifications fact sheet

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