Recently I got a rare but interesting question from a client, who asked if oil might be filtered too much and therefore get over-purified?

The answer, however, is not a simple yes or no. Although cleaner oil does reduces equipment wear and improve machinery reliability, sparing no efforts for unnecessarily low ISO cleanliness might be misleading.

First, you need to consider the machine’s requirements for clean oil. For example, hydraulic systems normally ask for higher oil purity than gearbox, which is determined by the equipment’s sensibility and criticality. Therefore, it is recommendable to match the fluid cleanness to the specific equipment.

After deciding on the oil cleanliness your machine need, then it’s time to choose a suitable filter to achieve your purity goal. Normally, people take filter’s micron rating as its efficiency, but we must realize that the filter’s beta ratio must also be considered in evaluating its performance. The micron rating tells the fineness of the filter element, while beta ratio tells the filter’s effectiveness of capturing particulates at the micron level. For example, a 5-micron filter doesn’t mean it can remove all particulates larger than 5 micron, only with a certain beta ratio, the efficiency of the filter media can be known. The bigger the beta ratio is, the more efficient your filter is.

If the filter is “too” fine, for example fuller’s earth filter, the purification process may even harmful for your oil, as some “large” additives(defoamants, demulsifiers, anti-wear,etc.) might be accidently removed. Therefore, for filter fineness selection, the most suitable for the particular equipment is the best. Each machinery system has unique needs for cleanliness, and should all be treated individually.