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Understanding Beta Ratings of Liquid Filters

Modern engines are developing at an unprecedented rate and frequently require highly efficient filtration. Donaldson fuel, lube oil, coolant and hydraulic filters are engineered to meet the specific requirements of equipment manufacturers and are required to have exacting efficiency ratings.

We all talk in micron sizing (1 micron = 1 millionth of a meter) but we need to understand that micron sizing is of little importance without some measure of the media’s efficiency on a given particle size. It could be said that a roll of toilet paper may stop 10 micron particles, but at what efficiency or what percentage of 10 micron particles would that roll of paper stop?

To remove confusion, manufacturers should describe the performance of the media used inside a filter by its 'beta ratio'. ISO 16889 (International Standard) lists eight common Beta ratios used to report filter efficiency: Beta 2, 10, 20, 75, 100, 200, 1000 and 2000. So what does each one mean and why have so many?

The ISO test method involves using particle counters and test fluid that has contaminants added to it. Contaminants of a given known particle size are counted both before and after the filter.

Beta Ratio How Many Particles of a Given Size Will Pass Through the Filter? Actual Filter Efficiency
2 1 out of every 2 particles 50%
10 1 out of every 10 particles
90%
20 1 out of every 20 particles
95%
75 1 out of every 75 particles
98.7%
100 1 out of every 100 particles
99%
200 1 out of every 200 particles
99.5%
1000 1 out of every 1000 particles
99.9%
2000 1 out of every 2000 particles
99.95%

When someone asks you for a 5 micron filter you should always ask them, "At what Beta ratio?". Clearly a media with a ratio of Beta 1000 is far more efficient than one with a rating of Beta 2 on that given particle size.

Your shirt sleeve may well have a Beta ratio higher than 2000 on particles the size of marbles. The same sleeve may have a Beta ratio of less than 2 on particles the size of talcum powder. Beta ratings can be used to explain the efficiency of filtration for all fluids, oil, diesel, petrol etc; it’s simply a measurement.

It is important that both the micron sizing and Beta ratio is matched to the application. Tighter and more efficient media than specified by the manufacturer can result in shortened element life and greater pressure increases. In some extreme cases of mis-application, this can even result in the unintentional removal of additives from oils. Less efficient media will generally result in a longer element life, but does so by allowing a higher percentage of contaminant to pass straight through the filter. This may result in a dramatic shortening of component life.

Did You Know?

Based on the image shown below, the filter has only allowed 1 particle out of every 10 greater than 5 micron to pass through. Therefore, this filter will have a rating of Beta 10 - 5 micron.

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