Multipass Testing

Based on ISO 4572, the multipass test standard is used to measure a filter element's filtration efficiency and operational life. The following is a simple representation of a multipass test circuit:

As illustrated by the above diagram, 10mg/L of ACFTD (Air Cleaner Fine Test Dust) is uniformly introduced into the test filter element from the injection system and the number and size of particles are measured both entering and exiting the filter element. The results are expressed as a filter's Beta ratio (the relationship of the number of certain size particles found going in to the number flowing out of the filter). This Beta ratio is calculated as follows:

For example, if we have 1000 particles larger than "X" upstream and 50 particles downstream, we can express this as Beta x = 1000/50 = 20. The larger the value (in this case “20”), the better the filtration efficiency. When expressed as a percentage, this represents that the tested filter is capable of capturing 99.5% of all particles larger than "x" microns in size.

General paper filter media (expressed as nominal 10 micron media) which has a filtration efficiency expressed as Beta 10 >= 1.4 means that it is capable of capturing 28.6% of particles equal to or larger than 10 microns in size.

For added information, the following graphs are indicative of multipass test measurement results. The graph on the left represents filtration efficiency, the graph on the right represents filter life.

Yamashin routinely measures the filter life of an element according to the pressure drop across the filter. This is measured to a value of 100KPa (1kgf/cm2) from the filter's beginning test pressure value.