Understanding Oil Filter Beta Ratios

When buying hydraulic oil filters elements, the filter industry developed standards to measure the true effectiveness of the filter. A filter that is marked or rated “10 micron” has some ability to capture particles as small as 10 micrometers. However, you do not know exactly what this means unless you also have a description of the test methods and standards used to determine the filter rating. The results from the different test methods may not be comparable as their method varies greatly.

 Two of the key standards are the filters“Micron” rating and the “Beta β” ratio. The “Micron” rating describes the normal particle size the filter removes.

What does the word micron mean? It is another term for micrometer (1 millionth of a meter).  A micrometer is a unit of linear measure in the metric system used to measure distance from one point to another. Its scientific notation is μ. Here are some objects that will give you a visual of comparative sizes:

  • Diameter of average human hair 70 microns
  • Lower limit of visibility (naked eye) 40 microns
  • White blood cells 25 microns
  • Talcum powder 10 microns
  • Red blood cells 8 microns
  • Bacteria 2 microns
  • Carbon black 0.6 microns
  • Tobacco smoke 0.5 microns

Beta ratio (b) is formulated by dividing the number of particles of a particular size in the upstream flow by the number of particles of the same size in the downstream flow:

where bx is the beta ratio for contaminant larger than x mm
Nu is the number of particles larger than x mm per unit of volume upstream
Nd is the number of particles larger than x mm per unit of volume downstream.

The beta ratio is an indicator of how well a filter controls particulate: i.e., if one out of every two particles (>x mm) in the fluid pass through the filter, the beta ratio at x mm is 2, if one out of every 200 of the particles (>x mm) pass through the filter the beta ratio is 200.
Therefore, filters with a higher beta ratio retain more particles and have higher efficiency.
Efficiency for a given particle size (Ex) can be derived directly from the beta ratio by the following equation:

Read more: http://www.lenntech.com/library/fine/beta/beta-ratio.htm#ixzz104rJzTX4

 An example would be a filter with a “β6 = 75” would be 98.67%  efficient at removing particles 6 micron and larger.  CALCULATION:   (75-1)/75 * 100 = 98.67%

Here is an efficiency tabel for your reference:

Beta ratio information can also be stated as β 5/10/20 = 2/20/75. In this example, the media tested removed

  • 50% of 5-micrometer or micron size particles
  • 95% of 10-micrometer or micron size particles
  • 98.7% of 20-micrometer or micron size particles
Beta Ratio  Efficiency















A filter’s beta ratio also does not give any indication of its dirt-holding capacity, the total amount of contaminant that can be trapped by the filter throughout its life, nor does it account for its stability or performance over time.

Nevertheless, beta ratios are an effective way of gauging the expected performance of a filter.

SAE J1858
ISO 4548-12,lube & oil
ISO16889, hydraulic or fuel
ANSI (American National Standards Institute)
NFPA (National Fluid Power Association)
Filter MAnufacturers Council

Joe Panfalone
Application Engineer
Phone (513) 671-3322
Web: www.exair.com
Twitter: www.twitter.com/exair_jp 
Facebook: http://www.facebook.com/exair


2 thoughts on “Understanding Oil Filter Beta Ratios

  1. Joe:

    This is extremely helpful information.I have attempted, without notable success, to obtain beta ratios on automotive oil filters for many years but the manufacturers wouldn’t provide the data although I assume they have it.(They do publish beta ratios on filters used in heavy truck and industrial engines.) Material I have read indicates that on older engines particles about 20 microns do the greatest damage but on newer engines which have smaller clearances and user lower viscosity oil e.g. SAE 5-20, particles in the 10 micro range do the greatest damage. Do you have any suggestions how I could obtain that data?

    1. Dennis,

      Here are a couple of links you may find useful, you may have seen them but it is some of the better information we have found. If the manufacturers are not giving up the information, it may be impossible to find. The information at autoeducation.com, speaking about efficiencies vs. beta ratios may shed some light on figuring it out.
      Thank you,
      Joe Panfalone

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