Lube oil, called the life blood of an engine, is called on to do more than most people are aware. We all know that it keeps engines running by reducing internal friction in the engine. It does this by actually keeping moving parts separated with a thin fluid layer. It helps protect internal metal surfaces for corrosion. Engine lube is also called on to fill several other important roles. It assists in removing heat from the engine. It forms a seal between piston rings and cylinder walls. Detergent additives in the lube clean internal surfaces. And finally, very importantly, it carries debris to filters.
Once you understand the importance of an engine’s lubricant, it only makes sense to keep that oil as healthy as possible. That’s the role of the engine’s filtration system. The filter’s job is to remove solid contaminants such as dirt, carbon and metal particles from the oil before they can damage bearings, journal and cylinder wall surfaces in the engine. Don’t expect your engines to deliver a long service life if filtration systems are not doing an effective job.
Exactly what kind of particle are we talking about? First we need to understand how particles are measured, and, from that information, how filters are rated. Like most things scientific, particles are generally measured in microns—one millionth of a meter. The symbol often used for a micron is the Greek letter mu, µ. To give you an idea of how small that is, one inch is equal to 25,400 microns. Conversely, one micron is equal to 0.000039 inches.
Engines are in no danger from any large particles – by large, consider any particle with a diameter larger than that of a human hair, about 70µ. Such particles are relatively easy to filter out of the lubricant stream. They are, in fact, larger than most of the clearances within an engine and, therefore, would not be able to enter the contact areas between most moving components to cause any wear problems.
Small particles, those in the 5 to 25µ range, are of the greatest concern because particles of this size are able to enter between internal engine parts and cause accelerated wear. Moreover, because of their small size, they are difficult to remove from the oil stream.
The Society of Automotive Engineers (SAE) published a technical paper titled Correlating Lube Oil Filtration Efficiencies With Engine Wear in which it reported the relationship between filtration levels and abrasive engine wear. The paper summarized the test results by saying, “Compared to a 40μ filter, engine wear was reduced by 50% with 30μ filtration. Likewise, wear was reduced by 70% with 15μ filtration. Controlling the abrasive contaminants in the range of two to 22μ in the lube oil is necessary for controlling engine wear.”
Such filters are readily available, but it’s important to understand how filters are rated and what those ratings mean. Just because a filter claims to have a 15µ rating, that doesn’t let you know much more than it is capable of capturing some particles as small as 15µ unless you also know what standard was used to determine that rating.
David Cline, product manager for oil filtration systems at Racor Filtration, said, “A filter element box that states the filter it contains has 98% efficiency is meaningless unless it states at what micron level. This is only part of the equation because a very high efficiency element may not have the capacity necessary to properly perform through the recommended oil change interval. Once a filter becomes restricted to a pre-set point, dirty oil is directed around the media sending dirty oil directly to the engine to maintain lubrication.”
According to the Filter Manufacturers Council, the two common media ratings are a nominal micron rating and an absolute micron rating. A nominal rating usually means the filter’s media can capture a given percentage of particles of a stated size. For example, a filter might be said to have a nominal rating of 50% for particles 10 micrometers in size or larger.
An absolute micron rating can be determined by passing a test fluid containing particles of a known size through a small piece of filter media then measuring what is captured. An absolute rating is often expressed in the form of a percentage of each size of particles captured.
Even with this data there still is not enough information to let you know with certainty how well a filter’s media will perform in the field. Fortunately, there is an accepted test procedure called beta (β) ratio testing that yields readily comparable test results. Baldwin engineers tell us, “Beta ratio testing is an accurate and objective way to compare performance of liquid filters. This test measures the filter’s ability to remove particles of given sizes from the fluid stream, thus identifying how efficient the filter is at removing specific sizes of contaminant particles.”
The test uses contaminant of known particles sizes added in measured quantities to a fluid which is pumped through the filter under test. Measured samples of fluid are then taken from the upstream and downstream sides of the filter. The contaminant in the samples is measured for particle sizes and quantities of each size or range of sizes. From these upstream and downstream measurements, a beta ratio is determined by dividing the number of particles of a particular size in the upstream sample by the number of particles of the same size in the downstream sample. That is,
βx = # particles upstream
# particles downstream
where β = beta ratio
x = specific particle size
For example, for a test in which there are 20,000 15µ particles upstream from the test filter and only 1,000 particles of that size downstream, the beta ratio is calculated as:
β15 = 20,000 / 1,000 = 20
To convert beta ratio to efficiency, use the formula:
[(β15 – 1)/β15] x 100 = efficiency.
Our test filter’s efficiency of filtering 15µ particles, therefore, can be calculated to be:
[(20 – 1) / 20] x100 = 19 / 20 = 95%.
According to the Filter Manufacturers Council, the testing process used to determine beta ratio provides an accurate, comparable test method to describe the efficiency of a media’s ability to remove certain size contaminants. It can also determine the total contaminant holding capacity of the filter as well as some of its differential pressure capabilities. Its use eliminates the inaccuracies and confusion caused by the use of “micron ratings.”
When people use the term extended oil drain interval, they’re actually referring to both the oil and the filter, since filters are normally changed along with the lubricant. Edward Covington, vice president of Quality Assurance at Wix Filters, said, “As you go longer in time, miles or fuel consumption, things start to change. Generally speaking, the longer the service interval, the more sophisticated the material choices have to be. For example, synthetic media is more resistant to acids, heat and long-term effect than cellulose. The other side of that is that the filter has to provide adequate filtration over that same period of time. Just looking at the efficiency of a filter is not the whole story. You have to look at the material selection itself to determine if you can go for that length of time while providing the right filtration for the engine.”
Darry Stuart, president and CEO of DWS Fleet Services, echoes that advice saying, “I recommend, in all cases, that fleets use premium filters if you’re going to try to extend oil drains. The best filter available from the supplier of your choice will give you a bit of a safeguard.”
The small additional price that fleets need to pay for premium filters is well worth the cost. According to Wix, they generally offer thicker base plates, sturdier element supports, heavy-duty center tubes and cans, and superior filter media compared to standard filters using cellulose media.
The challenge for filter manufacturers is balancing fluid flow, filtering efficiency and component life. All filter manufacturers have succeeded in developing premium filter designs using synthetic media for superior filtration over a longer service life than filters using only cellulose media.
For example, Donaldson has its Donaldson Blue (formerly known as Donaldson Endurance), which it describes as “providing enhanced durability for extended drain intervals while maintaining or improving efficiency and capacity.” According to Martin Barris, product director at Donaldson, “When used in combination with extended life oils and an oil analysis program, the synthetic media, the type of elastomer and other design choices for these products can help extend oil drain intervals significantly, reducing the overall cost of operation.”
Amsoil offers its Ea Filter line that uses “nanofibers to provide greater efficiency than any other filters available.”
And the proprietary filtration media in Wix ecoLAST filters is described as capable of “sequestering acids in the oil and having no similar competition in the market.”
But even high efficiency full flow filter elements can become loaded to the point of opening the internal safety bypass valve allowing unfiltered oil to enter the engine. If your fleet is experiencing such problems, your solution may well lie in the use of a bypass filter system. Stuart said, “If I had my way, I would use a deeper oil pan and a bypass filter on every vehicle. Any additional filtration that you can add at a reasonable cost is desirable.”
Racor’s Cline describes the benefits offered by a bypass system saying, “By utilizing a separate bypass filtration system, we can clean the oil to at least the same cleanliness level it had right out of the bottle from the manufacturer. The bypass becomes the work horse in the lube system collecting 99% of the contaminants as well as absorbing moisture.”
Dual flow filters, which incorporate full flow and bypass filters within a single spin on canister, are also available. For example, Baldwin Filters’ High Velocity Dual-Flow lube filters are described as providing improved engine protection during extended oil drain intervals, high idle time and harsh operating conditions when compared to standard spin on filters.
You clearly have the opportunity to use highly effective lube filtration systems to help protect your fleet’s assets. Since the important money goes for labor and lubricant, it only makes sense to step up to the best filter systems available.
This column appeared in the February 2014 edition of Fleet Equipment. You can read the entire issue on your phone or tablet by downloading the Fleet Equipment app.