Frequently Asked Questions
Q. What is it?
A. The Downstream Defender® is a hydrodynamic separator
which is incorporated into a reinforced concrete chamber;
the system is designed to remove settleable solids, grits
and silts, and oil and other floatables from Stormwater runoff.
Q. What are the sizes available and what are their weights?
A. We produce 7 sizes of unit from 1.0 m to 3.0 m
in diameter to treat flows up to 160 l/s. Details of each
size of unit and the flows they can treat are outlined on
the Performance page and in the
Downstream Defender® brochure. The weight
of each unit is also given in this brochure.
Q. What is the difference between the design flow and the
capacity flow?
A. The design flow is the maximum flow that can pass through
the unit while achieving typical removal efficiencies of
around 80% of grits and floatables. Above this flow
rate and up to the capacity flow, a proportion of the inflow
will by-pass the treatment process and the removal efficiency
will be reduced. The unit cannot pass more than the capacity
flow without surcharging of the sewerage system.
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 requirements required
for a Class II oil interceptor. 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 it is installed before the interceptor it will remove
grits and silts to ensure that the interceptor operates to
it's maximum efficiency.
Q. Can it be modified from the specifications shown in the
brochure?
A. The Downstream Defender® cannot be modified as it relies
on certain critical dimensions and minimum pipe sizes in order
to be able to function correctly. It is a requirement that
the inlet and outlet pipes are in-line and there should be
at least 2-3 m of straight pipe on either side of the
unit.
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