Project Description

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ABP Food Group; Petrol Interceptor/Separator Case Study

BMS Design Detail

BMS are the largest manufacturer of petrol/oil interceptors in Ireland and have unmatched ability to supply both large holding tanks and large capacity interceptors.  BMS can customise the interceptors to suits practically any inlet/outlet pipe size.  One of the features of this project was the requirement for particularly large interceptors.  All BMS Interceptors are manufactured to the European Standard EN858 Parts 1&2 and under an NSAI validated ISO 9001:2015 Quality Management System:

Supply Details

(a) 1. No BMS PF19 Class 1 Full Retention Interceptor (NSF 200 / Max Flow 200 l/s / 71,000 l Capacity)

(b) 1. No BMS PF15 Class 1 Full Retention Interceptor (NSF 132.6 / Max Flow 132.6 l/s / 47,000 l Capacity)

(c) 1 No. BMS PB5 Class 1 Bypass Interceptor (NSB 47 / Max Flow 47 l/s / 17,000 l Capacity)

(d) 1 No. BMS PB3 Class 1 Bypass Interceptor (NSB 16 / Max Flow 16 l/s / 3,000 l Capacity)

Construction/Installation Details: BMS designed, manufactured and delivered all the Interceptors.

BMS have introduced a full set of Petrol Interceptor/Holding Tank Sizing & Selection Charts to help you easily size and select an Interceptor/Holding Tank suitable for your requirements. They can be downloaded at this link.

Operation/Maintenance Details

The BMS Full Retention Interceptor is designed to retain the full contents of an oil spill or contamination up to flows of 50 mm/hr.

The BMS Bypass Interceptor will separate and retain silt and pollutants such as oil and petrol up to flows of 5 mm/hr.  In storm conditions, when periods of peak flow are experienced, it will treat a certain percentage of the maximum flow whilst at the same time allowing the excess to by-pass the retention chamber of the unit.

As contaminated water enters the first chamber, pollutants float to the surface. Due to the unique internal design; vortex formation occurs at the by-pass pipe resulting in the pollutants being skimmed off the surface and become trapped allowing the uncontaminated water to discharge from the interceptor.

When storm flow intensity increases, the vortex pipe floods thus restricting the flow from the first chamber to the retention chamber. As a result of the increase in water level in the first chamber, hydraulic pressure increases, forcing the majority of the water through the by-pass weir and into the chamber to discharge.

A BMS Full Retention Interceptor comes with an automatic closure device in the event of a large oil spill.  The interceptor can then be emptied by suction tanker and reset.  Similarly any silt and oil in a BMS Bypass Interceptor can be removed by suction tanker.          

Petrol/Oil Interceptor Terminology

  • Full Retention Interceptor: Designed to treat the full flow delivered by a drainage system up to 50 mm/hr.
  • Bypass Interceptor: Designed to treat flows of up to 5 mm/hr.  This covers 99% of rainfall.
  • Class 1 Interceptor: Designed to achieve a concentration of 5 mg/l of petrol/oil at discharge under normal conditions, includes a coalescer and a closure mechanism.  A Class 1 Interceptor is usually required for discharge to any surface water.
  • Class 2 Interceptor: Designed to achieve a concentration of 100 mg/l of petrol/oil at discharge under normal conditions.  Normally used when discharge is to a foul sewer.
  • Petrol/Oil Separator: Another word used to describe an interceptor.
  • NS: Nominal Size. Each interceptor is allocated a nominal size based on EN858.  This will indicate the nominal flow that the interceptor is sized for e.g. 4 l/s.  A full retention interceptor with a capacity of 4 l/s would be designated NS04 while a By-Pass interceptor with the same capacity would be designated NSB04.

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Project Details




ABP Food Group/McMahon & Associates Consulting Engineers


McMahon & Associates, 50 Dobbin Street, Armagh, BT61 7QQ.


When ABP Food Group embarked on a program of upgrading their facilities their Consulting Engineers; McMahon & Associates contacted BMS regarding their Petrol/Oil Interceptor requirements.  BMS designed, manufactured and delivered a number of large Full Retention and Bypass Petrol/Oil Separators on a phased basis.


€15,000 +