Technical Reference
Filter Efficiency Ratings This information is provided as an aid to
Efficiency The beta ratio is commonly used to calculate the filtration efficiency of a filter and can be converted into an percentage of efficiency at a give particle size.
understanding fluid filter efficiency terminology based on current ISO and SAE test standards. It is not proprietary and may be reproduced or distributed in any manner for educational purposes. What is Beta Ratio? Beta ratio (symbolized by ß) is a formula used 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 with a uniform amount of contaminant (i.e., ISO medium test dust), then pumped through the filter unit being tested. Filter efficiency is determined by monitoring oil contamination levels upstream and downstream of the test filter at specific times. An automatic particle counter is used to determine the contamination level.Through this process an upstream to downstream particle count ratio is developed, known as the beta ratio.
Efficiency Performance Formula
Efficiency (x) = ß - 1 ß (x) is a given particle size
ß
Efficiency
2 5
50 % 80 % 90 % 95 %
10 20 75
98.7%
100
99 %
ß 75 is 98.7% for particles 5µm and greater
1000
99.9%
ß (5) = 75 is same as 98.7%@ 5µm
What is a micron? The common unit of measurement in the filtration industry is the micron or micrometer. One micron equals forty millionths of an inch (.00004). In comparison, a human hair is approximately 70 micrometers.
Beta Ratio Formula
particle count in upstream fluid particle count in downstream fluid
Beta ratio (x) =
How Big is a Micron?
where (x) is a given particle size
100 µm
ß(5) = 75
40 µm
25 µm
80 µm
1 particle > 5 microns (downstream of filter)
10 µm
4 µm
Fluid in
Micron Sizes of Familiar Particles Grain of table salt 100 µm Human hair 80 µm Lower limit of visibility 40 µm White blood cell 25 µm Talcum powder 10 µm Red blood cell 8 µm Bacteria 2 µm Silt <5 µm
10 particles > 5 microns (upstream of filter)
56 • Engine Liquid Filtration
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