What is Oil Filtration
By Dennis Morgan
This is a seemingly simple question with seemingly simple answers. The problem however is because so many different products exist in the marketplace, either confusion abounds or there is an attempt to oversimplify in order to cut through the confusion.
The answer to the question is simple enough – filtration is using some method to remove suspended contamination from oil for either the protection of equipment (screening) or extending the life of the oil (cleaning). The solutions to oil filtration are not so simple and that’s where the confusion begins.
First there are two types of oil filtration – PRIMARY oil filtration (screening) and SECONDARY filtration (cleaning). The two types of oil filtration serve two very different purposes and are very different as a result.
Primary filtration is designed for equipment protection and is usually installed by the original equipment manufacturer. This type of filtration is almost always full flow with a bypass valve and is designed to keep out large particle contamination (many times 25 micron and larger). This is why it is referred to as oil screening. Its purpose is not to keep the oil clean at very low ISO cleanliness levels but to keep large particles from damaging the lubricated equipment. Generally, primary filtration will be installed in the equipment lubrication circuit, either in the pressure line going out to the lubrication point(s) or the return line from the lubrication point(s). Because of this, primary filtration cannot be constructed in such a way to restrict flow to a level that would deny the equipment proper lubrication. The philosophy is that dirty oil is better than no oil and many times, dirty oil is exactly what the equipment receives. The filter media is generally very porous and when the media becomes blocked with contamination, the internal bypass valve will open allowing unfiltered oil to exit the filter and reach the equipment.
Secondary filtration is designed for extending the life of the oil by cleaning it. This is also referred to as oil purification. The advantage of oil purification is not only extending the life of the oil, but also extending the life of the equipment with clean oil. There are several methods of oil purification, too numerous to address in this article. Sometimes original equipment manufacturers will include secondary filtration but rarely. Generally secondary filtration will be an add on aftermarket system and will be an off-line, side stream or kidney loop configuration. Secondary filtration will also usually clean oil down to very low ISO cleanliness levels that primary filtration cannot. Some examples of oil cleaning or purification are centrifugal, magnetic, vacuum dehydration, depth filter media or full flow filter media.
Primary filtration is important and with very rare exceptions, OEM filtration should not be altered. Secondary filtration can add great benefit to the equipment owner by extending the life of the oil in the system and the equipment. Primary filtration will help protect the equipment investment whereas secondary filtration helps to maximize the return on the equipment investment and maximize the return on the oil investment. With the continued rise in equipment costs, down time costs and oil re-placement costs, adding secondary filtration to equipment can be a very smart decision for the equipment owner.
