Bypass& Full Retention Separator Range

A bypass separator treats flow up to a set rate (typically the peak rate from a 10mm/hour storm) and diverts anything above that straight to discharge, making it suitable for surface water drainage where the pollution risk is generally low. A full retention separator treats the entire flow through the unit, including storm water, so it's specified where there's a higher risk of spillage or contamination — forecourts, car washes and fuel storage sites, for example.

Sizing is based on the peak flow rate into the separator, calculated from the drained catchment area, the surface type and local rainfall intensity, then matched against the Nominal Size (NS) rating in BS EN 858-1. For full retention units you also need to account for any additional flows such as vehicle washdown. Where you're unsure, give us your drainage area and site type and we can help you identify the right Klargester AquaOil model.

Installing a separator is usually covered by drainage or environmental permit requirements rather than planning permission, but this depends on your local authority and the Environment Agency's discharge consent for the site. Commercial sites such as garages, workshops and waste transfer stations will typically need a trade effluent or surface water discharge consent regardless of the separator itself. It's worth checking with your local authority and the Environment Agency before installation to confirm what's required for your specific site.

Klargester AquaOil separators are installed below ground on a prepared, level concrete base, backfilled per the manufacturer's installation guide to avoid distortion of the GRP shell. Units sited under trafficked areas such as car parks or forecourts need the appropriate cover and frame rated for the expected loading (pedestrian, light vehicle or heavy goods traffic) — this needs to be specified at order stage, not added afterwards.

Separators need regular inspection and periodic emptying by a licensed waste carrier to remove accumulated oil and silt, with frequency depending on site risk and throughput — high-use forecourts and car washes will need more frequent servicing than a quiet distribution yard. Most Klargester units can be fitted with a warning probe or alarm that alerts you when the oil storage capacity is nearing its limit, which takes the guesswork out of scheduling.

Sites with a high risk of regular spillage or contamination — scrapyards, waste transfer stations, fuel storage sites and vehicle workshops — generally require a full retention Class I separator, since all flow needs treating rather than just the storm-diluted portion. A bypass separator is more appropriate for lower-risk sites like general car parks or business park roadways, where only surface water run-off needs treatment.