Liquid Filter Media Micron Rating

Micron ratings of liquid filtration media whether woven or nonwoven tend to be quite ambiguous depending on the test method and the conditions used. The most widely accepted method has been the AC Fine or AC Coarse Test Dust (ACFTD or ACCTD now replaced by ISO tests) challenge test for most media, especially for cartridges. Even so, most vendors employ slightly different conditions so comparison between vendors is difficult.

To bridge this gap, outside test labs such as IBR and IFTS provide uniform test methods and procedures that filter users can employ. In addition, they also provide unambiguous efficiency ratings vs. micron size to at least remove some of the uncertainties associated with the overused terms “nominal” and “absolute”. However, these challenge tests are relatively costly; and as a consequence, two relatively new methods are being used to assess the “micron rating”.

The first is Capillary Flow Porometry (CFP) which gives the Mean Flow Pore (MFP) size and the Bubble Point (B.Pt.) (i.e., the maximum pore size that can be related to the absolute micron rating from challenge testing via certain tortuosity factors). The second is the Whitehouse/Gilson Sonic Sifter method which gives the 97% efficiency (or cut-point) based on NIST certified glass beads.

Both of these methods provide an unambiguous “micron rating”, but of course, cannot determine the media’s life nor dirt holding capacity (DHC) like an actual ISO challenge test can.

If you are interested in learning more about Filter Testing, attend the Mid-Atlantic Chapter meeting on October 25th.

© 2007 American Filtration & Separations Society All rights reserved