The History of Oil Filtration
By Wayne Owen
This article will cover “full-flow” oil filters as well as “By-pass” oil filters
One important function of motor oil is to capture and suspend contaminants and wear particles, preventing premature wear on an engine's internal parts. Acting alone, motor oil would quickly become saturated with these contaminants and wear materials and would require very frequent changing, perhaps as often as every 500 miles! In order to effectively guard against wear, it is an engine’s oil filter which allows motor oil to last for an extended period of time.
The earliest automobiles did not have any sort of oil filtration, and it was common to change oil every 500 to 2,000 miles. Later, as pressure lubrication became standard on automobiles, some kind of oil filtration was necessary in order to protect the oil pump from damage and wear. Early designs were quite primitive, often consisting of nothing more than steel wool, wire meshes or screens placed in the oil pump intake. Many designs were cleanable and reusable.
The earliest adaptation of the modern oil filter came about in 1923, when Ernest Sweetland introduced his invention known as the “Purolator”, a combination of the words "Pure Oil Later." Incorporated into the lubricating system after the oil pump and before the oil flows into the engine bearings, the original Purolator featured an upright series of seven twill weave cloth-covered, perforated plates encased in a heavy-duty cast container. It also had a sight feed glass on one side, enabling the owner to see the oil flow and change the filter when flow slowed to a trickle.
James A. Abeles saw enough potential in the Purolator to convert a New York City garage into a company called Motor Improvements Inc., developed primarily to manufacture Purolator filters. The Maxwell Chalmers Company also saw promise in this new product, installing a Purolator on a Maxwell Automobile which was test-driven on a round-trip from Detroit to the West Coast in 1924. The longer oil drain intervals, cleaner oil and reduced engine wear offered by the Purolator ensured endorsement by the automotive industry, and they soon became standard on many popular automobiles of the day, including Studebaker, Pierce Arrow, Hupmobile, Peerless, Cadillac, Oakland, Gardner, Moon, Jordan, Buick and Dodge. (Only Buick, Dodge and Cadillac, are still in business today.)
Oil filter technology continued to progress over the years and in the late 1930's, cotton waste material was introduced as filtration media, providing the first filter replacement capability. Various woven fabrics were also used in some filter designs. By 1946, as disposable filter models became the norm and interest in saving production costs increased, materials such as pleated paper and cellulose became the filtration media materials of choice, materials that are still widely used in today's oil filters. Many of today’s oil filters use advanced Synthetic and Glass blend filtering media, which allows higher efficiency, capacity and longevity, while meeting the high flow demands of modern engine designs.
Prior to 1943, most oil filters were of the "by-pass" variety, only filtering about 10 percent of the oil at a time.
Full-flow Oil Filters
The first full- flow oil filter, capable of filtering 100 percent of the motor oil, was introduced in 1943 and became standard on mass production vehicles by 1946.
The modern disposable “Spin-On” oil filter design was introduced in 1955, replacing “cartridge” type filters which had to be placed in a special housing or canister. These types of filters became known as spin-on “throwaway” filters and made changing filters much easier, and more convenient. The Technology progressed throughout the 1960’s and spin on oil filters soon became standard on virtually all American, European and Japanese Automobile designs.
Today's spin-on oil filters resemble metal cans that encase the filtration media, which capture and hold the various organic and inorganic contaminants and wear-metals within the motor oil. Organic contaminants include bacteria and other organisms that make up “sludge”, while inorganic contaminants include dust, dirt and metallic particles.
An Engine’s oil pump pumps
motor oil from the oil sump to the oil filter before the oil reaches the
engine’s components, such as crank shaft, valves, pistons, etc. The flow
of oil passes from the outside of the filtering media to the inside of the
filtering media through the center mounting stud. Cleansed oil is then
distributed by oil passages throughout the engine. (Figure 1)
Cleansing of the oil is determined by the design and type of filtering media used. Advanced engine designs place tough demands on an engine’s “full-flow” filter, most of which are capable of efficiently filtering out only coarser wear particles, generally greater then 20 to 25 microns.
Figure 1
NOTE: A Micron or Micrometer is nothing more than a very small unit of linear measurement. To better relate to this unit of measurement, consider the following examples:
· A micron is a unit of length equal to one millionth of a meter.
· 1 micron equals 0.0000039 inch.
· The diameter of a human hair is 50 to 100 microns.
· The smallest particle visible without magnification is 40 microns.
Most oil filters have “Anti-drain back” valves located within the filter so when the engine is shut off, oil will be trapped inside the filter. This action minimizes time required to initiate oil pressure at startup, and also keeps contaminated oil from draining back when the filter is mounted in an inverted or horizontal position. Also located within the typical “full-flow” filter is a by-pass Valve- a safety valve that opens when the media is too restrictive to allow an adequate flow of oil. An example would be in the event that the media becomes saturated with debris, or at startup with a cold viscous fluid. Typically, the by-pass valve opens when 8-12 psi pressure drop across the media is obtained.
To fully understand this, one must be exposed to two terms relating to pressure. The first is system pressure, which is the force applied to any surface in the system by the fluid. System pressure is commonly reported in pounds per square inch (psi). The second is differential pressure. Differential pressure is the difference in system pressure measured in two different areas of the system. Any device that exists in a system that can offer restriction to flow will exhibit a pressure differential. For example, the restriction to flow that may exist in a filter media will result in a difference in pressure between the inlet side of the media and the outlet side.
To determine the differential pressure of the media, one first measures the system pressure of the oil as it enters the media, and again measures the pressure as it exits. Subtract the outlet pressure from the inlet and the difference is the differential pressure. Differential pressure is reported as pounds per square inch differential (psid) or delta pressure.
Now let’s see how this by-pass valve works. (Figure 2) As stated, the construction of the typical spin-on full flow filter allows for the by-pass valve to open when the differential pressure is typically between 8-12 psid. If the inlet pressure were (60 psi) and the pressure on the outlet side of the media were (55 psi), the result would be a pressure differential of (5 psid) and would not be sufficient to cause the valve to open.
Figure 2
Full Flow Oil Filtration
Full-Flow oil filtration is the most commonly used today. With this type, the filter is placed between the engine oil pump and the engine components. (Figure 3) In this configuration, all oil reaching the engine components is subjected to at least some form of filtration prior to delivery.
In full-flow systems, the rate of oil
flow through the filter is significantly higher than in a by-pass system. To accommodate this higher flow, the filtration media used must be more open and free-flowing than in a by-pass filter.
Figure 3
Due to the flow versus efficiency, full-flow filtration is less effective at removing small contaminants than by-pass filtration. Full-flow systems are generally concerned only with removing particles large enough to cause immediate damage (>40 micron). If too restrictive, the filter could starve the engine components of oil.
Oil Filtration Performance Indicators
There are many terms and test methods used to indicate the performance of an oil filter. The two most widely accepted methods are those outlined in Society of Automotive Engineers (SAE) HS-J806B and J1858 protocols.
SAE HS J806B-Reviews the ability of a filter to remove a known contaminant from the fluid stream over a period of time. Results are reported as the percent of contaminant (by weight) removed over a period of time (Time weighted efficiency). Capacity (life) is also determined by noting the amount of contaminant required to increase the resistance across the media a given degree. Capacity is reported in grams of contaminant. As the contaminant used varies in its specific particle size the efficiency can be reviewed over time, and tends to produce a more accurate picture as to how the filter will perform in a given application.
SAE J1858-reviews the ability of a filter to remove contaminants of a specific size from the fluid stream at a specific moment in time. The test can be repeated to suggest efficiencies over the life of the filter. Results are reported as a ratio between the number of particles of a given size entering the filter and the number of the same size particles exiting the filter. The difference between the two is referred to as the BETA ratio. BETA ratios are reported in numbers from 1 to 75.
To achieve a BETA ratio number, the number is determined by examining the number of specific size particles before filtration, and dividing it by the number of same size particles after filtration.
Example: If we know that there were 2,000 10 micron-sized particles in a system before filtration, and only 1,000 remained after filtration, a BETA ratio of 2 would be assigned to the filter for 10 micron particles. This would be expressed as BETA 10=2 or B10=2. A BETA ratio of 2 is equal to a 50% removal efficiency. 4 equals 75% and 50 equals 98% efficiency. BETA ratios higher than 75.0 indicate little improvement in filtration efficiency.
NOTE: One can only compare filter test results when they have been obtained by using the same test methods.
By-Pass Oil Filters
The first and original most widely used in the automotive industry is the by-pass or partial-Flow System.
These type systems are referred to as partial-flow because they only filter a portion of the oil pump output volume at any given time (5-20 percent). As mentioned earlier in this article, this type oil filtration was used exclusively in automotive applications prior to 1943.
By combining both full-flow and by-pass filtration into one system, one can obtain additional performance without the compromises in the individual system.
(Figure 4)
Small particle removal efficiency for example can be achieved without sacrificing oil flow. Combining the two systems also increases filtration capacity providing longer filter element life, and increases additional oil supply resulting in longer oil life as well as lowering oil operating temperatures. There are various styles of by-pass systems on the market today. Some feature centrifuge or thermal action, spinning or boiling out contaminants, while others feature extremely efficient media that remove smaller contaminants.
Figure 4
Originally marketed as a way to effectively extend equipment life, the use of by-pass filters is also effective in keeping oil clean and capable of extended drain intervals. Of course anyone extending oil drains should use periodic oil analysis to determine lubricant serviceability.
OIL Analysis
Let’s look at oil analysis for engines. To make sure you’re taking full advantage of oil analysis, you should examine your sampling procedure and ask if it is representative, timely and well documented. A sample of oil should be analyzed shortly after it is taken since it will represent a point in time of the engine condition, and become less significant the longer it sits. Most laboratories recommend taking an oil sample while the oil is hot. This will assure dirt particles will not have settled out.
The oil sample should be taken from a source where no contaminants can enter the sample bottle. The best place other than a by-pass oil system return line is from the oil dipstick, using a plastic hose and a suction device. These devices can sometimes be obtained from the lab you use.
In most situations the real value of the data is in determining trends rather than in the accuracy of any one individual test. In general there are two different classes of analytical tests, those that measure the physical properties of the oil, and those that measure the level of contamination.
Physical properties are a good indication of the condition of the oil, and are often used to determine oil drain intervals. Some of the most common physical property tests are: viscosity, total acid number (TAN) and total base number (TBN).
Kinematic viscosity (ASTM D-445) determined at 40 Deg. C and/or 100 Deg.C is a measure of the flow rate of an oil in relation to time, and is expressed in centistokes (cSt) 1 square mm/1 second = 1 cSt. This data is used to assign an SAE grade to oil. Example: 40 grade oil has to fall between 12.50 cSt @100 C minimum, to 16.29 cSt @ 100 C maximum. Normally a 25% increase in viscosity is a warning that the oil is reaching the end of its useful life.
TAN (ASTM D974) determines the level of acidity by mixing in an indicator solution and then adding potassium hydroxide (KOH) until the solution changes color. The acidity is expressed as the milligrams of KOH required to neutralize a gram of oil (mgKOH/g).
TBN (ASTM D2896) determines the level of alkalinity in oil, which indicates the ability of the oil to continue to neutralize corrosive acids. The test measures the change in electrical conductivity. A higher TBN oil is considered better in neutralizing acids than a lower TBN oil. It is best to measure the change in TBN from new oil of the same type and brand you are using. The TBN of engine oil may be obtained from data sheets, or measured by analyzing a sample of new oil. Some manufacturers put the TBN number on the labels. A 50% reduction in TBN is a warning that the additives are becoming depleted and an oil change should be considered.
Common contamination tests include: water content, fuel dilution, dirt ingestion and wear metals analysis. Water contamination can usually be detected visually, but a water content test (ASTM D1744)) is sometimes used as well.
Fuel dilution is serious in that it can significantly reduce oil viscosity and increase engine wear. Since most engine oils gradually increase in viscosity over their useful life, a noticeable reduction in viscosity is a strong indication of fuel dilution.
Wear metals are metals used in the manufacture of the engine that will wear in normal use, such as Iron (Fe), Chromium (Cr), Lead (Pb), Copper (Cu), Tin (Sn), Aluminum (Al), Nickel (Ni), Silver (Ag). Analysis of the types and levels of wear metals can be used to determine which engine components are wearing and if the level of wear is becoming critical. Most tests measure wear metal levels spectrographically.
The most common: is emission spectroscopy. In this procedure a small oil sample is burned in a high temperature flame, and the equipment detects different levels of light emitted. The equipment is calibrated to simultaneously measure the emitted light from as many as 18 different wear metals and contaminants.
Another wear metal test called the atomic absorption analysis will provide the greatest level of accuracy for each element examined, but is more costly as well as time consuming as it requires one pass through the machine for each element tested. Either of these two wear metal tests are expressed in Parts Per million by weight (PPM).
Dirt is probably the most common engine oil contaminant, and high levels can lead to excessive engine wear. The most effective way to detect dust or dirt contamination is to monitor silicon levels by spectrochemical analysis, though some tests can indicate total solids by centrifugal separation or filtering through a fine membrane filter. Contamination levels will vary according to the type of engine and the application, with off-highway equipment often having the highest levels. Again, it is important to measure the change in silicon or solids levels, rather than look at any individual analysis.
Each engine manufacturer has data on the normal wear of each of the elements for a given oil drain interval. Examples: Cummins, Iron (Fe) 50, GMC 6.2 Iron (Fe) 250, Mack Iron (Fe) 150. Remember in reviewing a report, ask yourself: is the elemental level proportional to the time on the oil? Example: 6,000 miles on oil, Iron at 25 PPM is OK for the above engines. 12,000 miles on the same oil, Iron at 40 PPM is still OK. 30,000 miles on the oil, Iron at 40 PPM would be poor. Still within limits, but poor.
Additive levels may also be measured with spectrographic metals analysis. Normal metals analysis will detect the levels of zinc, phosphorous, calcium and barium, which are common elements in most additive packages. A 50% reduction in parts-per-million of these elements indicates the oil should be changed.
Most labs will compare the wear trends to similar operations using the same type equipment in order to more reliably predict component failure. Because of this, it is important and valuable to work with a lab that has years of experience, as well as hundreds of thousands of samples in their files to compare data.
Periodic oil analysis is an important element in extending oil drain intervals and prolonging engine life, however looking at trends is the best solution to achieving this.
According to the (SAE) Society of Automotive Engineers paper 881825, AC Spark Plug and Detroit Diesel Corp. performed a joint study of the relationship between the level of engine oil filtration and Engine wear rates, and found finer filtration reduced the rate of engine wear.
Diesel and gasoline engine wear rates were established by building a diesel and gasoline engine with fully inspected wear components and inspecting them after the test. In both engines, the upper and lower main bearings, oil rings and compression rings were inspected. In the diesel engine, the cam lobe profile and cylinders were also inspected, while the piston pin bushings, piston pins and cylinder liners of the gasoline engine were inspected.
The total test duration was eight hours. To accelerate wear, 50 grams of AC Fine Test Dust were added, in slurry form, to the crank case every hour.
Diesel engine wear tests were performed using filters with high efficiency ratings for particle sizes: 40 microns, 8.5 microns and 7 microns.
Gasoline engines wear tests were performed using filters with high efficiency ratings for particle sizes of the following sizes: 40 microns, 30 microns and 15 microns.
ANALYSIS
The researchers found clearances in the Diesel and Gasoline Engines varied between 2 and 22 Microns during engine operations. That means particles in the 2 to 22 Micron size range are most likely to damage Engine parts. Particles smaller than 2 Microns will slip through the bearing clearances without damaging bearing surfaces.
CONLUSIONS
The researchers drew the following conclusions:
Abrasive engine wear can be substantially reduced with an increase in single-pass efficiency. Compared to a 40-micron filter, Engine wear was reduced by 50 percent with 30-micron filtration. Likewise, wear was reduced by 70 percent with 15-micron filtration.
Controlling the abrasive contaminants in the range of 2 to 22 microns in the lube oil is necessary for controlling engine wear, and the micron rating of a filter as established in a single-pass efficiency type test, does an excellent job indicating the filter’s ability to remove abrasive particles in the engine lube oil system.
The smallest particles most popular full-flow filters capture with high efficiency are sized 25 to 40 microns, depending on the filter brand. By-pass oil filters capture smaller particles as small as one micron with efficiency ratings of 71 percent.
Two of the largest automotive bearing manufacturers, Clevite and Federal-Mogul rate injection and circulation of abrasive material (dirt) as the number one cause of bearing failures.
Clevite Federal-Mogul
Dirt 44.9% Dirt 42.9%
Miss assembly 13.4% Miss assembly 15.3%
Misalignment 12.7% Misalignment 9.8%
Insufficient Lubrication 10.8% Insufficient Lubrication 15.3%
Overloading 9.5% Overloading 8.7%
Corrosion 4.2% Corrosion 4.5%
Other 4.5% Other 5.4%
Clevite Reference Manual #AM-208-1 Federal-Mogul Engine Bearing
Service Manual
The bottom line is to use good maintenance practices along with high quality oil filters and engine oils rated for the engine application.
NOTE: Portions of this article were obtained from various publications of Amsoil Inc., Analysis Inc., Lubes-N-greases, and Hart’s Lubricant World.