A Bypass Separator is a tank used in low risk areas such as a car park or roadway and they are designed to treat the first 10% of surface water runoff. The first flush from the surface is typically the most contaminated. The runoff enters the unit where any solids present sink to the bottom and are retained in the first chamber.
Oil and water are then passed through to the second chamber where they are partially separated. As rain water builds and the surface water entering the separator exceeds the design flow, further runoff is diverted to bypass the second chamber and exit the separator.