Can Oil be Overfiltered?

Noria Corporation

"We are having a discussion as to whether way lube can be overfiltered. We use 220 way oil on our mechanical presses, and the question was whether we could clean the oil too much. What is the standard way lube filtration recommendation, if there is one?"

The question of whether more is always better when it comes to filtration is a common concern. The answer isn’t as simple as you might think. It has been proven that cleaner oil decreases bearing and machine wear, thus increasing equipment life expectancy. However, there are issues to consider when striving for very low ISO cleanliness codes.

One of the first things to take into consideration is the machine’s tolerances and need for clean oil. Hydraulic systems are notorious for needing clean oil, especially when compared to an industrial gearbox. That’s not to say that gearboxes don’t require clean oil. It just depends on the machine’s age, criticality and equipment cost. In other words, the fluid cleanliness should be matched to these conditions.

After determining the required machine cleanliness, you must select a filter to achieve these levels. The filter’s micron rating is commonly referred to as the benchmark of filter performance, but this only tells half the story. The beta ratio completes the picture of the filter’s true performance and capability. While the micron rating tells you how fine or how coarse the filter media is, the beta ratio tells you how efficiently it catches particles at that micron value. For instance, while having a 3-micron filter is good, it doesn’t tell you much about the filter. It could be a 3-micron filter with a beta ratio of 2, which is only 50 percent efficient, or as high as 2,000, which is 99.999 percent efficient at the same micron value.

Some filters can actually filter at a sub-micron level. As they become more aggressive, filters can begin to strip out some additives, affecting lubricant health. For example, defoamants are among the most common additives to be filtered out, as they are quite large. Depending on the filter media, other additives may be at risk as well. If using a chemically active filter such as fuller’s earth, polar additives (extreme pressure, anti-wear, demulsifiers, etc.) can be stripped, affecting the lubricant’s additive package and ability to protect the machine’s surfaces.

While clean oil is always better, balancing the needs of the machine with the cost of cleaning the fluid can lead to greater reliability and fewer failures. Remember, when it comes to filtration, it isn’t a one-size-fits-all approach. All systems have unique requirements for cleanliness, and they should all be viewed independently.

Subscribe to Machinery Lubrication