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# Filtration

## Filtration

(OP)
I there a difference between absolute filter efficiency rating and beta ratio?  Is there a ASTM standard related to this subject?

Thanks

Tom

### RE: Filtration

The effciency of an absolute rated filter is directly related to the Beta ratio.

Beta ratios are given for specific micron ratings.  For example, a B10 = 200 means that a filter has a Beta ratio of 200 for a 10 micron size.  a B5 = 200 would have Beta ratio of 200 for a 5 micron size.

The efficiency of the filter is determined by taking the Beta ratio minus one, dividing it by the Beta ratio, and then multiplying by 100.  An example for a Beta ratio of B10=200 is -->  [(200 - 1) / 200] X 100 = 99.5%.  So this filter is 99.5% efficient in removing particles of 10 micron size.

Regards,

Schlebb

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