All cartridge filters have micron ratings that indicate the smallest sized particle they are capable of removing. One micron, symbolized by the Greek letter μ, is also known as a Milimicron, which is 1/1,000,000 meter. One micron = 0.000039 inch. Micron ratings for filter cartridges range from 50 microns (all filter cartridge types) down to 0.035 microns (Pleated membrane cartridges).
Absolute vs. Nominal Filter Ratings
The micron size ratings can be “Nominal” or “Absolute.” A nominal rating indicates that the filter cartridge will remove 95% of the particles of that micron size. An absolute rating indicates that the filter will remove 99% of the particles. (Absolute ratings are available only on pleated filter cartridges.)
Applications
Cartridge filters are effective in the removal of moderate amounts of particles from liquids in the size range of 50 to 0.035 microns. When filtering large amounts of solids at high flow rates, other treatment methods such as self-cleaning multimedia filters may be required as pre-filters, followed by cartridge filtration, if needed.
The most popular micron sizes are the 5-micron general-purpose filter cartridge, and 0.2 sub-micron “Absolute” pleated filter cartridge for final filtration on high purity water systems.