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Old 04-03-2009, 12:26 PM   #1 (permalink)
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Filters: Micron Ratings What Do They Mean?

Micron Ratings What You Should Know & Ask

I would like to clarify some points regarding Microns and Micron ratings for the non engineers, scientists and Tribologists among us (most of us).

Micron ratings are how oil, fuel, hydraulic and other liquid filters efficiency are measured. What is a Micron? It’s the size measurement given to microscopic particles. A human hair for instance is 40-80 microns wide.

When talking about Micron ratings there are two different ratings commonly referred to or given to a filter.

The Nominal Rating which is basically this. The smallest size particle the filter will catch 50% of the time on a consistent basis. The Nominal rating is just a way to get a lower number in the marketing and really doesn’t mean anything to you and I where our trucks are concerned. For instance the Baldwin B7039 is a direct replacement for the Motorcraft FL1995 oil filter. Baldwin’s B7039 has a Nominal rating of 12 microns. That means that 12 Microns is the smallest particle it will catch 50% of the time. Who cares about 50% of the time?

The next and most important rating is the Absolute Rating. The absolute rating is this. The smallest particle the filter will catch 98.7% of the time. This is the rating you should be asking for when you are researching your filters. For instance the Baldwin B7039 has an Absolute Rating of 25 Microns. The smallest particle it will catch 98.7% of the time is 25 microns.

However my explanation of the Absolute Ratings needs to be broken down a little more. Let us talk about Beta ratios and how they work as they are critical to really knowing how the filter can actually perform and are not as easily manipulated as a Nominal or Absolute number can be the unknowing consumer.

“Nominal” ratings are ok when nothing else is known; as some info is always better than no info. And “nominal” ratings can help compare one filter to another, but only at 50% efficiency.

There is a much better way to compare filters, though. Beta ratios are a multi-level rating of the efficiency of a filter. Some filters can be very good at one particle size, but poor at another. Beta ratings allow us to understand how a filter performs overall. While it is not an exact correlation, it can be presumed to reasonably represent both the “nominal” and near-absolute ratings. I say “near” because it is not set in stone where the rating is done. But the general concept is that the Beta rating gives a wider range of efficiency visualization. A very common Beta rating is “2 / 20 = x / y”

Beta ratings are read in a particular way, and some basic math must be applied. Betas are stated as two fractions, each representing a ratio. Please understand that it is NOT the actual fraction you are using, but rather the numbers as individual values. They are merely stated as a “fraction” for the purpose of easy short-hand notation.

You must take the first number (upper number) as an inverse to the number “1” (one), and then subtract that resultant percentage from a whole of 100%. This applies for the upper and lower numbers individually. Then you use the second fractional value as individual number to know what micro size the rating is stated at. Here’s an example.

Beta rating of: “2 / 20 = 13 / 23”

The “2” is taken as a percentage, when divided into “1”; i.e. 1 / 2 (one-half), or 50% missed. So 100% particles minus 50% missed = 50% caught.

The “20” is taken as a percentage, when also divided into “1”; 1/20 (one-twentieth) or 5%. So 100% particles minus 5% missed = 95% caught.

The “13” is the particle size at the 50% rating. In other words, 50% of the time the filter catches particles that are at, or larger than, 13 microns in size.

The “23” is the particle size at the 95% rating. In other words, 95% of the time the filter catches particles that are at, or larger than, 23 microns in size.

Using this formula allows you to understand how a filter does its job with both large and small particles, and how efficient it is at those particular ratings. It is a much better view of the filter’s abilities as a whole.

If you can find out the Beta Ratio on your filter I suggest you do so. If you can’t get the Beta Ratio on your filter the Absolute rating for your filter will be the next best thing to find out. Brand shouldn’t play a role in your decisions for a filter Beta Ration or Absolute Micron rating should. If you care about your truck and want to make it last for a long time use the best Beta Ratio (if available) or Absolute Rating filters you can buy regardless of cost. It’s the best thing for your investment in a Diesel truck. If you want to improve on what is available to you, install a bypass or Dual bypass filtration system. It is said by oil industry experts and Tribologists that if you can filter to and below 5 microns you will virtually eliminate the wear particles that cause damage to the internals of our engines. From that point you will wear out the additive package in the oil and not the oil itself or your engine.

Thank you to my sources for this writing:

Dave Newton (dnewton)
The Baldwin Filter Company
Amsoil Corporation

Thank You for taking the time to read this,


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Old 04-06-2009, 05:29 AM   #2 (permalink)
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Very good write up, Dane.

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