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By Pass Separator
By-Pass Separators (BS EN 858-1 Compliant)
Compact, high-efficiency surface water drainage separators engineered for low-risk applications such as commercial car parks, roadways, and light industrial sites. Treats initial contaminated rainfall while safely bypassing heavy storm flows.
Targeted Surface Water Runoff Containment
Cowens **By-Pass Separators** are engineered specifically for areas where there is a low risk of major oil spills, but where surface water runoff routinely contains trace oils, fuels, and suspended silt from vehicle traffic.
Operating on the principle that the highest concentration of pollutants occurs during the initial period of rainfall (the “first flush”), the system treats runoff flows up to a designed rainfall intensity (typically 6.5 mm/hr). During extreme heavy storm events, excess water is safely bypassed around the separation chamber to prevent site flooding and avoid disturbing trapped hydrocarbons.
Ideal Applications
- Commercial Car Parks & Retail Parks: Filtering drip oil and tire grit from parking bays.
- Access Roads & Light Industrial Estates: Treating storm drainage before local discharge.
- Distribution Depot Hardstandings: Low-risk vehicle movement zones.
- Residential Hard Surfaces: Shared driveways and communal parking areas.
Technical Specifications
| Parameter | Specification / Capability |
|---|---|
| Regulatory Compliance | Designed and tested to British & European standard BS EN 858-1 / 858-2 |
| Separator Classification | Class 1 (Discharge < 5 mg/L oil) with coalescer OR Class 2 (Discharge < 100 mg/L oil) options |
| Design Rainfall Intensity | Treats full flow up to 6.5 mm/hr rainfall; automatically bypasses higher storm rates |
| Construction Material | Durable, corrosion-free GRP (Glass Reinforced Plastic) or reinforced steel tank shell |
| Monitoring & Alarms | Compatible with Cowens CB2022 / CB2800 high oil level solar or mains alarm systems |
Frequently Asked Questions
What is the difference between a By-Pass and a Full Retention Separator?
A **By-Pass Separator** treats initial light rainfall and allows heavy storm surges to bypass the separation chamber (used in low-risk areas like car parks). A **Full Retention Separator** treats 100% of the rainfall runoff without bypassing, required in high-risk areas like fuel storage depots where major spill risks exist.
Are oil level alarms legally required for bypass separators?
Under BS EN 858-1 standards, separators must be fitted with an automatic oil level alarm system (such as the Cowens CB2022) to alert site managers when accumulated oil needs to be pumped out.
How often should a by-pass separator be serviced?
By-pass separators should be visually inspected every 6 months and undergo a full maintenance service (including sludge removal and coalescer filter cleaning) annually or whenever the alarm activates.
