How do you calculate the size of a Petrol/Oil Separator needed for a site?

The last in our customer questions regarding Petrol/Oil Interceptors/Separators is; How do you calculate the size of a Petrol/Oil Separator needed for a site?

Firstly you need to determine if you require a Bypass Interceptor or a Full Retention Interceptor; this is answered in a previous Customer Question answer; What are the different types of Petrol/Oil Interceptor (Separator) and what is the difference between them?  Secondly you need to determine if you require a Class 1 or Class 2 Interceptor; this is also answered in our last customer question answer; What is the difference between a Class 1 & Class 2 Separator?

After selecting the interceptor size and type, the correct size of interceptor is based on the flow into it based on rainfall onto a given surface area, this is known as nominal size or NS.

Each interceptor is allocated a nominal size based on EN858; the European Standard for Interceptor Design and Sizing.  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.

(Please note Petrol/Oil Separator and interceptor mean the same thing)

Example 1

An interceptor required for a 25,000 m2 car park discharging into a local authority surface water sewer.

As there is a low chance of oil spillage a Bypass Interceptor would be most appropriate.

As discharge is to a surface water sewer a Class 1 Interceptor, which is designed to achieve a concentration of 5 mg/l of petrol/oil at discharge under normal conditions and includes a coalescer and a closure mechanism is most appropriate. A Class 1 Interceptor is usually required for discharge to any surface water.

Based on EN858 a drainage are of 25,000 m2 gives a nominal size (NS) of 45 l/s.

So in this case BMS would select a BMS NSBP50 l/s Class 2 Bypass Interceptor, which is the closest available in our range.

Example 2

An interceptor required for a 1,700 m2 fuelling area discharging direct to surface water.

Due to the high risk or fuel spillage a Full Retention Interceptor designed to contain the full contents of a full spill is required.

As discharge is to a surface water a Class 1 Interceptor, which is designed to achieve a concentration of 5 mg/l of petrol/oil at discharge under normal conditions and includes a coalescer and a closure mechanism is most appropriate. A Class 1 Interceptor is usually required for discharge to any surface water.

Based on EN858 a drainage area of 2,600 m2 gives a nominal size (NS) of 47 l/s.

So in this case BMS would select a BMS NSFR50 l/s Class 1 Full Retention Interceptor, which is the closest available in our range.  Please note that the Nominal Size of a Full Retention Interceptor can also be denoted as NSF e.g. NSF; 47 l/s.

BMS manufacture produce a full range of ‘plug & play’ interceptors/separators from 1,000 – 100,000 litres manufactured in corrosion and rot proof GRP under ISO 9001:2008 to European Standards and are Irelands leading producer.

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 as part of updated Brochure. It can be downloaded at this link:

BMS Petrol Oil Interceptor Brochure and Selection Charts

A BMS NSFR60 Class 1 Full Retention Interceptor arriving on site in Malta

 

About BMS

BMS is a quality manufacturer of package products for wastewater and stormwater treatment:

  • Established: 1986

  • Global Reach: Exported to over 50 countries.

  • Family Business: A third-generation company with deep expertise.

BMS Product Range

BMS provides a wide array of surface water and wastewater treatment products, including:

View the full product catalogue here

Additional Services by BMS

  • Free Design Service: For sewage treatment, pump stations, and surface water management.

  • Operation and Maintenance: Full services for existing installations, including repair, advice, and testing.

  • Free CPD Presentations: Available for sewage treatment and surface water management, delivered at your location.

We would be delighted to discuss any requirements you might have, and we are available to meet you at your convenience.  Contact us today.

© Butler Manufacturing Services 2024.

Tommy Bulter

M.Pharm (Hons) MBS (Hons) Cert. H&S (Allison)
• 15 year’s + experience in Management in Waste/Surface Water, R&D & H&S.
• Project Management specialist, Marketing specialist, Pharmacist, Wastewater and pump specialist.

https://butlerms.com
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