How Filter Quality Affects Oil Analysis

Noria Corporation

"How does the quality of a filter impact oil analysis results (contamination and ferrous wear)? Is it correct to say that using filters with different beta ratios in the same equipment will result in different analysis results? Is there any correlation in setting alarm levels and filter beta ratios?"

The quality of the filter is directly proportional to the cleanliness and wear rate of the system. The higher the beta for the same micron pore size will result in a faster cleanup rate. Thus, it is better able to control ingression of solids in the system. The main system ingression sources typically are seals, breathers and oil top-ups, and wear debris. When catalytic wear metals are removed from the oil, the lubricant will experience longer oxidative life.

Therefore, expect to see better cleanliness results on the hard particle measurements, as well as lower levels of wear debris in the system, assuming that the oil is in good condition and there are no other problems like water ingress or misalignment or imbalance.

In terms of setting alarm levels, the first step is to set the alarm levels to achieve a reasonable and realistic gain in lubricant and machine life. Using any of several methods, this can be done to optimize your requirements based on financial, safety, environmental and reliability goals.

On that basis, the appropriate filter can be selected. Most filter manufacturers have methods to determine the required element size and pore rating to not only meet the cleanliness target, but also to match the lubricant viscosities at an operating temperature that would affect the flow rate. Most companies have established a beta ratio of 200 for their quoted pore size, although recent changes mean that they must also quote a beta value for a number of size ranges to establish performance.

Over the life of the machine, a better-quality filter, which is generally more expensive, will prove to be more cost-effective than a cheaper filter, owing to the relationship between filter performance and the system wear rates. To add value to that, many high-performance filters offer an associated improved dirt-holding capacity.

Subscribe to Machinery Lubrication