Can Oil be Overfiltered?

When it comes to oil filtration, many people often wonder if more is always better. The answer isn’t as simple as you might think. It has been proven that cleaner oil decreases bearing and machine wear, increasing equipment life expectancy, but there are some things to consider when trying to meet ISO cleanliness codes.

The first thing to consider is a machine’s tolerances and need for clean oil. Different machines have different needs. For example, hydraulic systems typically require much higher standards of oil cleanliness compared to industrial gearboxes. This isn’t to say that gearboxes don’t need clean oil, but rather they can tolerate dirty oil better than hydraulic systems can. A machine’s age, criticality and equipment costs should all be considered when determining cleanliness levels.

Once cleanliness goals are set, it is time to choose a filter. Micron ratings are usually considered a benchmark when evaluating filter performance, but this rating only gives part of the story. To get a complete picture of a filter’s performance, the beta ratio must be considered.

• Micron rating — The size of particles that the filter can capture.
• Beta ratio — The efficiency of the filter’s particle capturing ability.

As they become more aggressive, filters can begin to negatively affect lubricant health and performance, usually by stripping out additives. For example, defoamants, because of their large size, are additives that are commonly stripped from the oil during filtration. Some forms of filter media, such as fuller’s earth, are chemically active and can strip polar additives from the oil.

Ultimately, when it comes to filtration, there is not a one-size-fits-all approach. Each machine has different cleanliness needs, and each machine should be viewed individually. As far as over-filtering goes, the goal of filtration is balance — more aggressive filtering is not always the solution to cleanliness needs.