Filter Micron Ratings Explained: Absolute vs Nominal
A micron rating only means something when you know how it was measured. Here is the difference between nominal and absolute.
What a micron is
A micron (micrometre) is a thousandth of a millimetre. Many of the particles that wear hydraulic pumps and valves are far too small to see, which is why filter ratings are given in microns.
Nominal ratings
A nominal rating says the element catches some particles of the stated size, without a single agreed test behind it. Two elements with the same nominal rating can perform very differently.
Absolute ratings
An absolute rating comes from a defined multi-pass test that counts how many particles of each size get through the element. It is the better basis for comparing elements for critical circuits.