Separators (Interceptors) & Accessories

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Oil separators are fitted to surface water drainage systems to prevent pollution by oils and to protect the environment. The Groundwater Regulations, for example, prohibit discharge into the ground and/or watercourses of pollutants such as hydrocarbons (oils, greases, fuel etc.). Oil Separators separate oil from the water, retaining it safely until it is removed. Oil separators need to be correctly designed, installed and maintained to be fully effective.

Do I need a Separator?

Vehicle Washpad[+]
Vehicle Washpad

Oil may be contaminating surface water at various sites. Sites need to have measures in place to prevent oil polluting the environment. These would include:

Examples of sites where oil contaminates surface water
Car Park

Car Park
Garage forecourt
Garage Forecourt

Which type and class of Separator do I need?

There are two Classes of Separator:

Class 1 Separator

Class 2 Separator

These are designed to achieve a discharge concentration of less than 5 mg/ litre of oil under standard test conditions and are required for discharges to surface water drains and the water environment. Many contain coalescing devices to trap oil droplets. These are designed to achieve a discharge concentration of less than 100 mg/litre of oil under standard test conditions and are suitable for dealing with discharges where a lower quality requirement applies. e.g. discharges to foul sewer.
Both classes can be produced as full retention or bypass separators.

Do I need Silt Capacity?

EA PPG3 clearly states; "On sites where high levels of silt are likely to enter the separator, the build up of silt must not be allowed to compromise the operation of either the separator or the by-pass device."

We therefore offer Separators with or without silt capacity and our large Silt Trap (see below) that can be installed upstream to meet EA requirements.


A Class 1 Full Retention Separator is required if you plan to discharge to surface water (i.e. river, watercourse, soakaway) and is the model we advise is installed for washpads situated away from the foul sewer.

A Class 2 Full Retention Separator is allowed for foul sewer discharges (but you must seek permission).

Use of detergents

It should be noted that the use of detergents (which emulsify the oil/water mix) should not be used in Separators that discharge to surface water.

There are three Types of Separator:

The Three Types of Separator
(typical examples pictured below) :

Full Retention Separator

Bypass Separator

Full Retention Separator

Treats the full flow that can be delivered by the drainage system, normally equivalent to rainfall intensity of 65 mm/hour.

Bypass Separator

Fully treats all flows generated by rainfall rates of up to 6.5 mm/hour (99% of all rainfall events). Flows above this rate are allowed to bypass the separator.

Forecourt Separator

Typical Forecourt Separator

A full retention separator specified to retain on site the maximum spillage likely to occur at a petrol filling station. A separator with an oil storage capacity of 7600 litres is usually required.

Closure Devices

Full retention separators must be provided with an automatic closure device which operates in the event of a sudden surge of a large quantity of oil entering the system or too high an accumulation. This device should work in conjunction with the oil alarm.

Audible Oil Alarm[+]
Audible Oil Alarm

Oil Alarm

Separators must be provided with a visual and audible oil alarm (similar to the one shown here), remotely located if necessary. This operates when the oil level reaches 90% of the oil storage volume and indicates that the separator needs immediate emptying for it to continue to work effectively.



Grass Trap / Debris Filter

Primary Filter

Grass trap / debris filter

Our Grass Trap / Debris Filter is ideal in a smaller washpad and enables grass clippings, sand or debris to be collected, allowing polluted water to enter the separator. Size 600 x 300 x 300mm with twin outlets and one or more may be used depending on pad size and water volumes.

Primary Filter

A primary filter, which fits into the trap top, is also supplied and a squeegee available.

Large Silt Trap

Large Silt Trap
For larger washpads, we recommend our large Silt Trap. Built to order and available in different sizes to suit various applications.

Flow chart of choosing a separator[+]
Choosing a separator

How do I select the right one?

Check our "Choosing the right separator" check sheet, contact us for class, type and sizing help (make sure you have to hand the dimensions of the area drained in square meters for us, please), see the Environment Agency Pollution Prevention Guidelines PPG3 for further guidance.

If you wish to operate a washdown area away from the public sewer and stay within the law, you may wish to consider installing a ClearWater Washpad Water Recycling System. Such systems are fast becoming the preferred option for many as they are considered future-proof, save valuable water and can be used in drought areas. 
Watch the new ClearWater video now
Separator Installation[+]

What about Installation?

We offer a comprehensive range of all classes and types of Separators and accessories, competitively priced, to suit most needs with professional installation if required.

Our qualified engineers also carry out separator servicing and maintenance as required by EA PPG3 and with full certification (often an insurance requirement).

Separator Servicing & Maintenance:

Separator Servicing

Example Service Certificate

For separators (interceptors) and accessories - talk to us!
Call Lo-call 0845 6003572 to discuss your requirements