Filter Fact
Cartridge Filter Ratings
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The variety of cartridge filters available and the method of ratings sometimes make selection of cartridges difficult. Before selecting a cartridge filter, it is important to understand cartridge filters, how they work and how they are rated.

Nominal Rating

The particle size corresponding to an 85% removal is called the Nominal Rating of the filter. However, different manufacturers rate their filters at different efficiencies.

This means that the same 5-micron, nominal-rated filter from two different manufacturers could mean different efficiency ratings. One could be 85% efficient at
5-micron, while the other could be only 70%.

Nominal rating is generally given to filters to be used for general filtration and turbidity reduction applications, such as pre-treatment for reverse osmosis (RO) or point-of-entry (POE) units and other pre-filtration applications.


Absolute Rating

For sub-micron and critical applications. Absolute Rating is used, and is defined as essentially 99.9% (3-log) rejection at the specified micron rating. This means the filter removes 99.9% of the particles of the stated size.

In other words, if a 5-micron absolute filter is challenged with 1000 particles of
5-micron it will filter out at least 999.

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