Incorporating Downstream Defender® III

Capture and retain sediment, oils and floatables from stormwater runoff over a wide range of flows in a small footprint.
Downstream Defender® is an advanced hydrodynamic vortex separator that reliably captures and retains sediments, oil, trash and floatables from surface water runoff. 

A compact, low-maintenance stormwater treatment best management practice (BMP), the Downstream Defender® enables engineers to deliver effective pollutant removal at a single point in the drainage system. 

The Downstream Defender® III or DD3 is the latest advanced hydrodynamic vortex separator that provides impressive and reliable removals of fine and coarse particles, hydrocarbons and floatable debris from stormwater runoff, delivering high levels of treatment over a wide range of flow rates. It has built-in internal bypass for high-intensity rainfall events which may exceed the design treatable flow rate of the system.  

Available in a range of sizes, it can be used as part of a treatment train or as a standalone device.  The Downstream Defender® has large storage volumes for pollutants captured from stormwater runoff whilst also offering protection to the surrounding drainage network from accidental spills of oils, hydrocarbons and light liquids. 

The Downstream Defender®is independently tested, verified and approved throughout many countries around the world.  

Targeted Pollutants:

  • Total suspended solids (TSS) i.e. Sedimentation 
  • Fine particles
  • Floatable debris
  • Liquid and sediment bound hydrocarbons
  • Sediment bound heavy metals
  • Sediment bound nutrients


The Downstream Defender® III reliably treats runoff from any impermeable surfaces including highways, car parks and industrial areas:

  • As part of Sustainable Drainage Systems (SuDS), Water Sensitive Urban Design (WSUD), LID or LEED systems.
  • Areas where high solids and trash/litter capture are a must.
  • Control of silting upstream of wetlands, ponds and basins

Downstream Defender® III is a registered trade mark of Hydro International.

Save space and money

The Downstream Defender® delivers high removal of pollutants across a wide range of flows in a much smaller footprint than conventional or other swirl-type devices. A smaller footprint means an easier install that is cost effective and less work.

No risk of pollutant wash out

The Downstream Defender® is proven to prevent wash out of captured pollutants. Carefully designed internal components isolate the pollution storage areas ensuring what is captured is retained, even during high flows.  


The Downstream Defender® can accommodate a change in outlet pipe direction to suit site specific requirements, helping meet Building Regulations without the need to construct a second manhole.

Cut headloss

Low headloss means more site flexibility and provides the option for a shallower site.

  1. Stormwater is introduced into the side of the vessel, generating a rotating flow that spirals around the outside of the dip plate.
  2. Oils, litter and floatable debris rise to the water surface and are trapped in the oil and floatables storage volume.
  3. As flow continues to spiral down around the dip plate cylinder, low energy vortex motion directs sediment inward along the benching skirt and into the protected sediment storage zone.
  4. The benching skirt and centre cone redirect the rotating flow up and inward between the centre shaft and dip plate cylinder away from the stored sediment.
  5. The outlet pipe discharges treated effluent from within the dip plate cylinder ensuring the longest possible residence time.
  6. Excess flows by-pass the vortex treatment chamber and also both the sediment and oil storage zones.  These excess flows pass forward untreated via the orientated outlet pipe.

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    Stormwater Treatment Solutions
    is a division of All Purpose Pumps