Bypass Seperators

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Silotank range of Bypass Separators are used where the risk of a large spillage and heavy rainfall occurring at the same time is small and it is deemed that full treatment of very high flows is not necessary. Bypass separators fully treat all flows, for the area served, generated by rainfall events of up to 6.5 mm/hr i.e. 99% of all rainfall events.

Common applications for Bypass Separators are

  • Surface Car Parks
  • Roadways
  • Lightly contaminated commercial areas

Each bypass separator design includes the necessary volume requirements to meet the recommendations laid down in Pollution Prevention Guidelines PPG3. These include

  • Oil Storage Volume (V = NSB x 15 litres)
  • Silt Storage Capacity (C = NSB x 100 litres)
  • Coalescing Filter

The nominal size of a bypass separator that is required for a catchment area (A) is obtained using the following formula:

  • NSB = 0.0018(A) m2

The flows generated by higher rainfalls will pass through the weir chamber and bypass the main separation chamber. Class 1 separators are designed to achieve a discharge concentration of less than 5mg/litre of oil under standard test conditions.




  • Manufactured from HDPE materials and therefore light and easy to install
  • Maintenance from ground level
  • A range of extension shafts available for deep inverts
  • All models are inclusive of silt storage volume
  • Vent point socket and cable duct at top of unit
  • Factory fitted hydrocarbon alarm probe holster

To specify a Bypass Separator the following information is needed

  • The calculated flow rate or the drainage area served. Our designs are based on the assumption that any interconnecting pipework fitted elsewhere on site does not impede flow into or out of the separator.
  • The required discharge standard
  • We recommend only installing Class 1 separators
  • Pipework type and size
  • The drain invert inlet depth



    • Over 30 years of excellence in design, manufacture, installation
      and maintenance for chemical & liquid storage solutions.

We can find a solution to suit your needs. For more information:

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