Oil Filtration is one of the most commonly followed maintenance-related activities in industry today. Operating personnel are generally aware about the brand and technical specifications of filters such as filter element type, flow rate, and filter nominal ratings. While these parameters are important, one parameter which is not discussed very often is the Beta Ratio of a filter. The more commonly used description for the efficacy of a filter is its nominal filter rating. However, filter Ratings are probably the misunderstood elements of applied tribology today.
Nominal Ratings: In my experience, asset operators are often mis-led into a false sense of security by the ‘Nominal Filter Rating’ certified by the manufacturers of lube oil filtration systems. Simply put, an oil filter rating ‘claim’ by the filter manufacturer in the OEM manual is akin to the commonly heard “99.99% germs killed” claim by a few toothpaste, disinfectant and soap manufacturers to appease germaphobes: a marketing gimmick- to be viewed with suspicion!
Nominal Ratings have little veracity. On a visit to Rubber Manufacturing Unit once, I noticed a gearbox with a 10 micron filtration unit installed. Upon further investigation and a few lab oil tests later, I emailed the GM Maintenance that the particles that found their way through these filters were larger than 30 microns. The GM instantly called me seeking a justification. Beta Ratio: A “nominal” rating is a value given by filter manufacturers based on a percentage of particulate weight removed during testing. Nominal ratings are unreliable as micron sizes of these particulate matter as well as testing methods can vary. What they don’t tell you is the percentage of particulate contaminants above a certain size that pass through the filter. This is where the Beta Ratio comes in. Tribologists at organizations like Noria Corporation have long argued that the Beta Ratio of Oil Filters must be calculated to accurately measure the effectiveness of your oil filter.
The Beta Ratio is a number derived by dividing the number of particles in the upstream (before filtration) of a particular size divided by the number of particles downstream (after filtration) of a particular size. The Beta rating comes from the Multi-pass Method for evaluating performance of a fine filter element (ISO 16889:1999) (Advanced Fluid Systems)
Why Beta is the true Alpha: Assuming you have a 10 micron filtration system and wish to calculate the Beta Ratio of your filter. Let’s break down the steps:
- The first step towards calculating the Beta Ratio of your filter is to collect samples of your oil upstream(before they go through the filter) and downstream(after they go through the filter).
- To calculate the Beta Ratio, you need to use the formula: 𝛃 = Number of Particles Upstream above 10 micron/ Number of Particles Downstream above 10 micron.
- Once you get the Beta Ratio, you can express it in the form of a efficiency % (𝛃 -1)/(𝛃) *100
- Assuming you have 2000000 particles upstream and 20000 particles Downstream, you get a ratio of 𝛃100.
- The Efficiency off your filter will be (100-1)/(100) * 100 = 99%. So 99% of all particles above 5 micron will be captured by your filter.
(Image Courtesy: Advanced Fluid Systems)
Particles larger than 10 micron before filtration vs Particles larger than 10 micron after filtration
Similarly, if a 10 micron filter has 2,00,000 particles downstream, instead of 20,000, the 𝛃 Ratio would be 90%, a substantial difference from 99% in the illustrated example. The Table Below (by Machinery Lubrication) is a simple illustration of the 𝛃 Ratios and Their associated Efficiencies.
(Image Courtesy: Noria Corporation)
Conclusion: Along with the Absolute Ratings (An absolute rating gives the size of the largest particle that will pass through the filter or screen), Beta Ratios are a good way to qualitatively judge the efficacy of filters. However, in addition to the Beta Ratio, one must also consider observing the dirt-holding capacity (the contaminant particulate matter) of the filter and its Pressure-Flow rating.
At Neptunus, we provide filtration units with elements that have a Beta Ratio of upto 925, or an efficiency of 99.89%. You can write to us at email@example.com or visit us at www.neptunus-power.com for more information.