Filtration Ratings Defined
Filtration Ratings Defined:
Filter rangs are an oen misunderstood area of contaminaon control. The most commonly used rang is the Beta Rao, which is defined as the rao of the number of parcles upstream of the test filter versus the number downstream, greater than a given size. Using the Beta Rao, a 5 micron filter with a Beta 1000 Rang, will have on average 1000 parcles larger than 5 micron upstream of the filter for every one 5 micron or greater parcle downstream.
The efficiency of the filter can be calculated directly from the Beta Rao since the % efficiency is simply (beta-1)/beta x 100. A Beta 1000, 5-micron filter is thus said to be 99.99% efficient at removing 5 micron and larger parcles.
Caution must be exercised when using Beta Ratios since they do not take into account field operating conditions such as pressure surges and changes in temperature, which can affect real life performance. A filter’s Beta Ratio also does not give any indication of its dirt holding capacity, the total amount of material that can be trapped by the filter throughout its life, nor does it account for how the capture efficiency changes over me. Nevertheless, Beta Raos are an effecve way of gauging the expected performance of a filter.
The ISO standard for Mul-pass filter tesng (ISO 16889) has changed to require filter manufacturers to determine the average parcle sizes which yield Beta Raos equal to 2, 10, 75, 100, 200, and 1000, again using the mul-pass test stand approach. The new standard gives a beer interpretaon of a filter’s overall performance.
Of course, regular monitoring of fluid cleanliness using ISO parcle counng should be used to determine the efficiency of the filter in actual field condions.