Loading... Please wait...

Filter Efficiency

Posted by

Filter ratings are often a misunderstood area of when choosing a filter. On several recent occasions, I have witnessed someone describing a filter by its nominal rating. A nominal rating is an arbitrary micrometer value given to the filter by the manufacturer. These ratings have little to no value. Tests have shown that particles as large as 200 microns will pass through a nominally rated 10-micron filter. If someone tries to sell you a filter based on an "excellent" nominal rating of five microns, run away.

A better rating to use when choosing filters is the absolute rating. An absolute rating gives the size of the largest particle that will pass through the filter or screen. Essentially, this is the size of the largest opening in the filter although no standardized test method to determine its value exists. Still, absolute ratings are better for representing the effectiveness of a filter over nominal ratings.

The best and most commonly used rating in industry is the beta rating. The beta rating comes from the Multipass Method for Evaluating Filtration Performance of a Fine Filter Element (ISO 16889:1999).  An easy way to unerstand it is know that for example a beta 2 filter only stops 1 particle for every 2 that enter the filter. In a beta 1000 filter only 1 particle with pass for every 1000 that enters. 

Here is a chart to demonstrate how the Beta Ratio equates to efficiency.


Last week I had a customer frustrated with the level of contamination in his oil  He said he was using a 10 micron filter.  I looked it up and found that it had a Beta Rating of 2!  I have never seen one in service.  I very disappointing find.  I got him a Beta 1000 Donaldson Filter and he is very happy to have learned the difference.  I know when I recommend a high efficiency filter the customer will end up with good results.

If you want to go crazy Donaldson makes several Beta 2000 filters.  The are found in the Donaldson Blue Can line.  The results are amazing!

Thanks for stopping by!