The purpose of FILTERS --- according to general definition:
Is to keep contamination transported in the air and oil out of the compressors.
Compressors together with gearboxes, fluid-power system (hydraulic & pneumatic), internal combustion engines and industrial machinery have a common problem:
"Wherever moving parts contact or mesh with one another, FRICTION results."
This friction has to be reduced. to this end, a suitable, mineral or synthetic oil, is used to provide a sliding film between the moving or rotating parts of the machines. This is only possible if the lubricating oil stay clean and remain clean. If foreign particles, even if they are microscopic in size, are transported with it.
Such particles can reach the moving or rotating parts inside the compressor in the form of sand or dust in the oil or air intake.
Whenever friction occurs, fine metallic abrasives are created, found it's way in the oil, creating even more metallic particles to get into the compressor oil or coolant.
Critical areas within the compressors are the compressor case (housing), screw rotors, seals, bearings, gears, valves etc. In addition, compression does not occur without leaving residues. If this is nor filtered out, the foreign particles acts as an abrassive mass, which can considerably accelerate wear on the moving parts.
Also, dirt particles when in excessively high concentrations though they are not as hard, can be dangerous for compressor. It can damage the compressor due to inadequate lubrication and cooling.
A well-maintained and effective oil filtration system along with good air filtering, is the best guarantee of long compressor life.
Main-flow filters and air inlet filters are usually designed for 25 micron particles filtration and 10 micron for bearings