Selecting a filter

There are many different considerations when sizing the right filter for any given application. Whilst this list is not exhaustive, we would always want to consider the following factors.

Is water separation needed?

If not, then a strainer or simple fuel filter may be sufficient, if it is then a specific water separator should be used.  
Maximum fuel flow rate  
Often mistaken for fuel consumption, this figure is vital to selecting the right filter. The easiest way to get this figure is to find out the maximum capacity of your fuel transfer/lift pump. Whilst fuel consumption is important for any customer, the flow can be four times the consumption. Always select a filter with a capacity higher than or equal to the maximum fuel flow. The fuel flow can be lower than a filters maximum capacity, but conversely selecting a filter which is too small for the flow rate will dramatically increase the pressure restriction.  
Restriction – Delta P  
Fuel flow restriction or pressure restriction can be vital to some applications where the fuel pressure at the engine is closely monitored. The lower the delta P figure, the less restriction the filter will put into the fuel. In a transfer system it is typically less important.  
Marine or non-marine application?  
Depending on the location of the fuel filter in question, different rules exist as to what materials can be used in its construction. For example, an ocean going leisure craft has to periodically have an RCD inspection (recreational craft directive), this states the fuel filters used must meet the fire-proofing standard ISO10088. Likewise the British waterways expect the same requirement for all inland craft. This means one of our metal bowl filters or a clear bowl with a metal heat-shield. Other applications such as generator or truck filters do not have such requirements and so standard clear bowl filters can be used.  
Port sizes / pipe sizes  
Not all customers need a specific flow rate; some just want to match to their existing pipe work dimensions. For example, a customer with a 2” pipe who only needs to strain fuel does not always want to throttle the pipe down to 1” to match the ideal filter. Separ UK offer a range of filter solutions to meet their needs, from a wide range of filters to match the specific requirement to a massive range of fittings to ensure compatibility to any standard pipe dimensions.  
Straining element size  
What micron rating is actually required? If the application is for fuel in storage or as a pre-filter, then typically 30 micron is sufficient. What does that mean? 1 micron is one millionth of a meter, meaning there are 1000 microns in a millimetre. A human hair is typically 0.06mm (60 micron); 30 micron is therefore about half the width of an average human hair. Some customers need very fine straining, to 10, 5 or even lower micron ratings – some only need something coarse to stop large contaminate; in the region of 100, 300 or even 400 micron. Separ UK has the right filtration solution to match their requirements, and in most cases, the filter elements themselves can be changed at a later stage should the customer subsequently need to change their specification.  
Simplex or Duplex  
Looking at a typical marine customer as an example, if they had two engines on their boat, they would need a simplex filter for each engine’s fuel system. A simplex filter is one with a single body and a single path for the fuel to flow through. However If the customer had a boat with a single engine, we would strongly recommend a duplex filer – this has two paths for the fuel to flow though, where only one is in use at any time. Should the customer experience fuel contamination in the twin engine boat, it is highly unlikely both fuel systems would block at the same time, in the single engine boat however; a simple movement of the duplex’s changeover lever and the second flow path becomes live. The first path is now clear for servicing, without having to stop the engine.  



Need help selecting a filter?

See our guide to help you select the most suitable filter for your needs.

Technical Support

How it works

See how the Separ filter works to separate water and particulate from fuel. 

SWK2000 flow diagram transparancy

How to Order

Call or email us to place your order. We accept ALL major credit and debit cards, bank transfer and also PayPal. 

Contact Us TabPhone copy


Expert advice

Unsure which spare parts you require? Or if a Separ filter will meet your requirements? 

Talk to our expert team. Call 01923 276 007



Delivery options

We have a wide range of shipping options available to suit your destination and budget.



Wooden-Crate-psd42799 copy

Contact Us

3 Kingley Park, Station Road, Kings Langley, Herts, WD4 8GW

Tel: +44 (0)1923 276007

Fax: +44 (0)1923 267463

Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Here to Help

Product guides

Fuel Specs


Selecting a Filter