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Shoptalk

Simple Facts about Liquid Filtration

SHOPTALK Understanding the How Big is a Micron?

Beta Rating System

This information is provided as an aid to
understanding fluid filter efficiency terminology
based on current ISO, ANSI and NFPA test
standards. It is not proprietary and may be 40 µm
reproduced or distributed in any manner for 80 µm
educational purposes. 25
µm
What Is Beta Ratio?
10 µm
100
Beta ratio (symbolized by ß) is a formula used µm 2 µm
to calculate the filtration efficiency of a particular
fluid filter using base data obtained from multi-pass
testing.

In a multi-pass test, fluid is continuously injected Micron Sizes of Familiar Particles
with a uniform amount of contaminant (i.e., ISO
medium test dust) then pumped through the filter Grain of table salt 100µm
unit being tested. Filter efficiency is determined Human hair 80µm
by monitoring fluid contamination levels upstream Lower limit of visibility 40µm
and downstream of the test filter at specific times.
An automatic particle counter is used to determine White blood cell 25µm
the contamination level. Through this process an Talcum powder 10µm
upstream to downstream particle count ratio is Red blood cell 8µm
developed, known as the beta ratio.
Bacteria 2µm
The formula used to calculate the beta ratio is: Silt <5µm

Beta ratio = particle count in upstream fluid
(x)
particle count in downstream fluid

where (x) is a given particle size

Indicates that testing was
done with APC’s calibrated
with NIST fluid
ß 10(c) = 1000

1000 times more
particles upstream
than downstream
that are 10 µm and
larger

Additional information on Beta Ratings and use in fuel
& lube filtration in Technical Reference section.

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