Frequently Asked Questions

Q. What is it?

A. The Downstream Defender® is an advanced hydrodynamic vortex separator manufactured from High Density Polyethylene. The system is designed to remove settleable solids, grits and silts as well as oil and other floatable material from Stormwater runoff.

Q. What are the sizes available and what are their weights?

A. We produce 4 sizes of unit from 1.2m to 3.0m in diameter to accept inlet flows up to 750 l/s. Details of each size unit are outlined on the Performance Page. Dimensioned drawings of each size of unit are available on request. Lift weights of each component are given in the relevant Installation guidelines.

Q. What is the difference between the Treatment Flow and the Hydraulic Capacity?

The treatment flow rate is the point at which the unit achieves the typical removal efficiencies as shown on the Performance Page. The Downstream Defender® has an internal bypass to pass high flow rates associated with extreme rainfall events. The hydraulic capacity of the unit is the maximum flow rate that can pass through the Downstream Defender® without surcharging the upstream drainage network. At this flow rate a proportion of the flow will bypass the active treatment zone of the unit.

Q. Is the Downstream Defender® an equivalent to an oil interceptor?

A. The Downstream Defender® has been independently tested and has been found to meet the removal requirements required for a Class II oil interceptor under certain flow conditions. For sites where a Class I interceptor is required, the Downstream Defender® will still be a useful addition as a "first line of defence". If the Downstream Defender® is installed before the interceptor, it will remove grits, silts and some of the hydrocarbons to ensure that the interceptor operates to it's maximum efficiency.

Q. What is pollutant re-entrainment?

A. Removal of pollutants from the Stormwater is only part of the solution. Pollutant re-entrainment is defined as the tendency for pollutants that were previously removed under low flow conditions to be stirred up and discharged from the treatment device under high intensity storm conditions (i.e. high flows).
The Downstream Defender® is proven to prevent pollutant re-entrainment.

Q. Can the units be modified from the specifications shown in the brochure?

A. No. The internal components within the Downstream Defender® unit act to enhance the separation process and to isolate the captured pollutants from the treatment flow path in order to prevent re-entrainment. As the separation process is driven entirely by the hydraulic processes within the unit, the Downstream Defender® relies on certain critical dimensions and fixed pipe sizes in order to function correctly and these cannot be modified.
The angle of the outlet pipe is variable through a 180 degree arc (from 90 degrees to 270 degrees to the inlet pipe). 2-3m of straight pipe should be connected to either side of the Downstream Defender® unit before any further changes in angle or pipe dimension are made.