First Flush Delta Post/Wall Diverter

Blue Mountain Co

12.00 LBS
Calculated at Checkout
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Product Overview

Large volume first flush diversion made easy. The First Flush Delta Post / Wall incorporates a revolutionary chamber design that uses 4" inch (100mm) pipe for simple installation and high volume diversion. Every 39.37 inches (1m) of Delta chamber = 19.25 gallons (73 liters of diversion)!

Size 4" inch (100mm) WDPW110


First Flush Delta Extra Chamber

Delta High Volume Chamber

Easily divert large volumes of first flush with the Delta High Volume Chamber. Using multiple 4" inch (100mm) pipes to create the diversion chamber, the Delta’s revolutionary design makes installation simple. The Delta chamber is customizable up to 78.75" inches (2 meters). Every 39.37" inches (1m) of Delta chamber = 19.25 gallons (73 liters) of diversion.

For larger volumes, consider the Delta manifold installation configurations.

Delta Postwall Kit

Integrated ball and seat

This unique design ensure that the first flush ball remains close to the seat, even in high flow events, ensuring the diverter seals as soon as the chamber is full. No more lost balls when cleaning your outlet either!


Arv Web Kit

Divert larger volumes

By allowing you to determine the frequency of first flush, the Advanced Release Valve ensures that the Delta’s first flush diversion is optimized. The transparent, rapid release exit funnel reduces build up and blockages while allowing for easy visual inspection.





  1. It is a requirement to install a rain head upstream of any downpipe feeding the Delta Post/Wall First Flush. Large debris must not enter the First Flush chambers to prevent blockages and damage to the Advanced Release Valve.
  2. Select an installation point for your Delta Post/Wall First Flush. Your diverter chamber must be installed vertically when using the supplied Wall Brackets. Consider the location of the First Flush Plus Tee in your Rain Harvesting line and the space required for your assembled Delta Chamber. The First Flush Plus Tee can be installed in the horizontal or vertical orientation to suit your installation. The outlet and Advanced Release Valve must also be accessible for maintenance and inspection. (Refer to Figures 1a, 1b and 1c for suggested installation orientations).

    Figure 1
    Suggested Installation Orientations

  3. Remove Delta components from packaging and lay out parts ready for assembly.
  4. Using one of your Post/Wall brackets, screw the lower bracket to the wall at your chosen installation point. The outlet of your Advanced Release Valve must sit at least 150mm (6″) from the ground when fully assembled, so securing your lower bracket approx. 600mm (24”) above the ground should achieve this adequately.
  5. Determine chamber length using the calculation chart provided, based on your Rain Harvesting roof collection area and considered pollution level (see Delta Diversion Chamber Calculator Tab below.
  6. Using a tape measure, mark, cut and deburr 6 equal lengths of 100mm (4”) pipe to be used as the Chamber Pipes.

    NOTE: It is critical that all the Chamber Pipes are exactly equal length. It is also recommended to apply a small chamfer to the outside ends of the 6 Chamber Pipes to improve ease of insertion into the Chamber Sockets.

  7. Using priming fluid, clean all internal sockets of both Delta End Caps and each external end of the six Chamber Pipes.
  8. Working with one Delta End Cap, apply solvent weld glue internally to a Chamber Socket and then externally to one of the Chamber Pipes. Bring the two together ensuring the pipe is inserted fully into the socket and hold until firm. Repeat this step for all remaining pipes until all six Chamber Pipes are glued into one Delta End Cap.

    NOTE: All sockets of the Delta End Cap are stepped internally. The inner socket is for use with 100mm UPVC pipe and the outer socket for 4” SCH40 pipe. Only apply solvent weld glue to the socket relating to the pipe in use.

  9. Slide the Chamber Support Spacer over the open end of the Chamber Pipes and position approx. 200mm (8”) from the unglued end.
  10. Before completing the next step consider the installation position of your Delta and how the inlet and outlet should be oriented (Figure 2 – Delta Post/Wall – Inlet/Outlet Positions)

    Figure 2
    Delta Post/Wall Inlet/Outlet Positions

  11. Working quickly, apply solvent weld glue to each of the six internal Chamber Sockets of the remaining Delta End Cap and then externally to the six Chamber Pipes. Quickly bring the Delta End Cap together with the six pipes by first aligning three pipes and sockets on one side and then rolling onto the remaining three pipes. Using some force, push the Delta End Cap down onto the Chamber Pipes ensuring the pipes enter the socket fully and hold in position until secure (Figure 3 – Delta Diagram).

    NOTE: refer to solvent weld glue manufacturers specifications and curing times.

    Figure 3
    Delta Diagram

  12. Move the Chamber Support Spacer down the Chamber Pipes to approximately the half way position ensuring the pipes will be supported evenly.
  13. Insert Cage/Seat & Ball into the inlet (upstream) Delta End Cap, ensuring it is oriented correctly (Figure 4).

    Figure 4
    Inserting the Cage/Seat and Ball

  14. Place your assembled Delta in the Post/Wall Bracket and support the chamber as you fit your upper bracket around the inlet on the upper Delta End Cap and screw it to the wall or post.

    CAUTION: failure to support the unit in the upright position while attaching the upper bracket could crack the bottom Chamber End Cap.

  15. Measure your existing pipe and cut to create space for the First Flush Plus Tee. Ensure all cut edges are clean and smooth then use priming fluid to clean all external pipe ends and internal sockets of the First Flush Plus Tee.
  16. Install the First Flush Plus Tee to the existing pipe and extend the branch line of the Tee with 100mm (4”) pipe to the inlet of the upper Delta End Cap using solvent weld glue.
  17. Using a minimum of 170mm of 100mm pipe (3.5” of 4”) and solvent weld glue, attach the 100mm-90mm (4”-3”) Socket Reducer to the outlet (downstream) Delta End Cap.
  18. Install the Primary Filter Screen, Transparent Rapid Release Exit Funnel, and Advanced Release Valve by following the instructions in this guide.

    • Delta Diversion Chamber Calculator

    • Maintenance

      It’s important to ensure that your first flush diverter outlet remains clear of any debris. If your outlet becomes blocked, the chamber will not empty and the first flush of water will not be diverted when it rains.

      To ensure the flow of water out through your Advanced Release Valve, periodically remove from the Transparent Rapid Release Exit Funnel to check for any build-up of matter. Remove primary filter plus ball, and clean if required.

      Periodically check that the Advanced Release Valve batteries have charge. This is indicated by the flashing light.

      To protect your Advanced Release Valve from freezing or “winterizing”, remove the timer prior to the first frost or freeze and store it indoors until spring. Remember to remove the batteries from the battery compartment.

      For best results and minimal maintenance, rain heads with 0.955mm aperture mesh such as Leaf Eater Rain Heads
      must be installed upstream of the Delta First Flush to limit the entry of debris that can reach your diverter.