Filter Micron Ratings
Caterpillar specifies actual filter capability, rupture strength, the capacity for holding dirt, flow resistance, filter area, etc.
Caterpillar does not specify filter or filter paper by micron rating. Micron ratings are easily confused for the following reasons:
– The test for micron ratings is not repeatable at different labs. One manufacturer may give a rating of 10 microns
(0.00039 in.), another at 2 microns (0.000079 in.) and a third may rate a particular filter media (paper) at 15 microns (0.00059 in.).
– There is no consistent relationship between micron rating and actual filtration efficiency. The entire filter needs to be tested, not just the media (paper).
– The micron rating does not show what happens to a filter over time. The test provides no information about how a filter will stand up under continual use.
Micron ratings are overemphasized; a 10-micron filter will not always stop a 10-micron particle. Many reputable filter manufacturing firms are drifting away from micron ratings to more conclusive tests. Smaller micron ratings are not necessarily better.
If all other factors (area) were equal, a smaller micron number media (paper) has a severe draw-back: it has less capacity before plugging and needs to be replaced more often. The size of the pores in the paper needs to be balanced
against the costs of the filter replacements.
Common questions are:
– What is the maximum particle size which can pass through Cat filters?
– What is the difference between nominal size and absolute size filters?
For example: A nominal 10 micron filter media (paper) will pass some particles up to about 50 microns in size. Theoretically, an absolute rating of 10 microns will stop all particles larger than 10 microns. In fact, filters with absolute micron ratings of 10 will pass some particles larger than 10 microns due to the irregularity of the paper weave. New filters may pass larger particles than they will after only a few hours of use.
As a rule, Caterpillar fuel filter media (paper) is about 3 microns nominal, 20 microns absolute. Oil filter media
(paper) is about 10 microns nominal, 50 microns absolute. These are approximate values only.
Filters are not effectively compared on the basis of micron rating alone. Evaluate filters on the basis of their ability to collect foreign material as a whole.