Post by Scoutpilot on Apr 5, 2015 9:22:26 GMT -5
In order to understand air cleaners, we have to understand dust. That’s a big topic, so here’s a short course. And since there is a lot of good information to be found on the web, I have borrowed liberally from sources like the G503, The CJ3A Page and others.
Dust size is measured in micrometers (usually shortened to microns), and the actual shape and weight of the dust particle is dependent upon on the type of dust it is. Chaff, road dust, snow, all have unique characteristics that affect their behavior in the air stream and their effect on engines and air cleaners. A micron is one millionth of a meter. So for comparison, the diameter of a human hair varies from about 40 microns to 120 microns. Humans lose the ability to see dust particles at about 40 microns. It’s important to filter the small dust particles even if you can’t see them.
Dust has weight, mass, hardness and shape. Air cleaners, no matter what type, exploit these characteristics to capture dust. Dust larger than 15-20 microns, depending on its characteristics, is generally not so much of a problem either, as it is typically too large to be airborne long enough to get to your engine. Therefore, the dust that is most important to catch is the 3-15 micron dust, as this dust will stay airborne and can also damage your engine.
The air filter prevents the abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination.An oil bath air cleaner consists of a sump containing a pool of oil, and an insert which is filled with fibre, mesh, foam, or another coarse filter media. When the cleaner is assembled, the media-containing body of the insert sits a short distance above the surface of the oil pool. The rim of the insert overlaps the rim of the sump. This arrangement forms a labyrinthine path through which the air must travel in a series of U-turns: up through the gap between the rims of the insert and the sump, down through the gap between the outer wall of the insert and the inner wall of the sump, and up through the filter media in the body of the insert. This U-turn takes the air at high velocity across the surface of the oil pool. Larger and heavier dust and dirt particles in the air cannot make the turn due to their inertia, so they fall into the oil and settle to the bottom of the base bowl. Lighter and smaller particles are trapped by the filtration media in the insert, which is wetted by oil droplets aspirated there into by normal airflow.
Oil bath air cleaners were very widely used in automotive and small engine applications until the widespread industry adoption of the paper filter in the early 1960s. Such cleaners are still used in off-road equipment where very high levels of dust are encountered, for oil bath air cleaners can sequester a great deal of dirt relative to their overall size without loss of filtration efficiency or airflow. However, the liquid oil makes cleaning and servicing such air cleaners messy and inconvenient, they must be relatively large to avoid excessive restriction at high airflow rates, and they tend to increase exhaust emissions of unburned hydrocarbons due to oil aspiration when used on spark-ignition engines.
Manufacturers included AC, Donaldson, Oakes and Fram. The oil bath air cleaner in our Willys as a system runs about 85% efficient on Arizona Test dust, and you have to service them often. You can get away with 85% efficiency on gas engines because the tolerances in the engine allow it.
Now all that said, don't go pulling off your Donaldson oil bath and putting on a teeny-tiny paper filter, the key words are system. The pre-cleaner part of the system usually takes out about 80% of the dust, if you look at the Donaldson on the Willys you see the air enters near the fire wall through a series of holes, these force the air to circle around the air cleaner to separate out the water in the air stream, then it goes into the air cleaner where it is forced to do a 90 degree turn above the oil bath, this does separate out the heavier particles, gravimmetrical separation, then the air goes up to the oil soaked steel mesh where the finer dust is trapped. By replacing this system with a K&N style paper filter at the carb, you eliminate the system aspect and force that itty bitty piece of paper to absorb all of the air and all of the dust. It can't possibly do it and becomes overwhelmed.
Think about this, restriction to flow is a function of how much material you are trying to put through a given size hole, the Willys air cleaner is 9 inches in diameter, those little K&Ns are 4 inches? That means the air is going 4 times as fast through that filter vs the Oil bath. It just can't perform. The faster the air is moving, the more dust it will carry with it, slow the air down and the dust drops out.
The critical parts of the air cleaner are described in this section: The inlet section, the pre-cleaner section, the oil cup, mesh assembly and outlet. Dust has weight, therefore when it is moving it has inertia. The inlet section of the air cleaner does two things, sending air in the direction we want it to go, and accelerating the air prior to the pre-cleaner section. In this air cleaner the pre-cleaner creates a tortuous path, a 180 degree turn that uses the inertia of the dust to separate it from the air stream and drop it into the oil cup where it is captured.
AC "pancake type" introduced with the production start in late 1941. Instructions placed on a small decal (black letters on red background).
2- Oakes "decal type" introduced in early 1942. Instructions placed on a large decal (silver letters on black background).
3- Oakes "plate type" introduced in mid 1942. Instructions embossed onto a steel plate which was attached by spot-welds.
4- Oakes "standard type" introduced in late 1942. Instructions directly stamped in raised letters on the air cleaner case itself.
The parts of these cleaners.
Dust size is measured in micrometers (usually shortened to microns), and the actual shape and weight of the dust particle is dependent upon on the type of dust it is. Chaff, road dust, snow, all have unique characteristics that affect their behavior in the air stream and their effect on engines and air cleaners. A micron is one millionth of a meter. So for comparison, the diameter of a human hair varies from about 40 microns to 120 microns. Humans lose the ability to see dust particles at about 40 microns. It’s important to filter the small dust particles even if you can’t see them.
Dust has weight, mass, hardness and shape. Air cleaners, no matter what type, exploit these characteristics to capture dust. Dust larger than 15-20 microns, depending on its characteristics, is generally not so much of a problem either, as it is typically too large to be airborne long enough to get to your engine. Therefore, the dust that is most important to catch is the 3-15 micron dust, as this dust will stay airborne and can also damage your engine.
The air filter prevents the abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination.An oil bath air cleaner consists of a sump containing a pool of oil, and an insert which is filled with fibre, mesh, foam, or another coarse filter media. When the cleaner is assembled, the media-containing body of the insert sits a short distance above the surface of the oil pool. The rim of the insert overlaps the rim of the sump. This arrangement forms a labyrinthine path through which the air must travel in a series of U-turns: up through the gap between the rims of the insert and the sump, down through the gap between the outer wall of the insert and the inner wall of the sump, and up through the filter media in the body of the insert. This U-turn takes the air at high velocity across the surface of the oil pool. Larger and heavier dust and dirt particles in the air cannot make the turn due to their inertia, so they fall into the oil and settle to the bottom of the base bowl. Lighter and smaller particles are trapped by the filtration media in the insert, which is wetted by oil droplets aspirated there into by normal airflow.
Oil bath air cleaners were very widely used in automotive and small engine applications until the widespread industry adoption of the paper filter in the early 1960s. Such cleaners are still used in off-road equipment where very high levels of dust are encountered, for oil bath air cleaners can sequester a great deal of dirt relative to their overall size without loss of filtration efficiency or airflow. However, the liquid oil makes cleaning and servicing such air cleaners messy and inconvenient, they must be relatively large to avoid excessive restriction at high airflow rates, and they tend to increase exhaust emissions of unburned hydrocarbons due to oil aspiration when used on spark-ignition engines.
Manufacturers included AC, Donaldson, Oakes and Fram. The oil bath air cleaner in our Willys as a system runs about 85% efficient on Arizona Test dust, and you have to service them often. You can get away with 85% efficiency on gas engines because the tolerances in the engine allow it.
Now all that said, don't go pulling off your Donaldson oil bath and putting on a teeny-tiny paper filter, the key words are system. The pre-cleaner part of the system usually takes out about 80% of the dust, if you look at the Donaldson on the Willys you see the air enters near the fire wall through a series of holes, these force the air to circle around the air cleaner to separate out the water in the air stream, then it goes into the air cleaner where it is forced to do a 90 degree turn above the oil bath, this does separate out the heavier particles, gravimmetrical separation, then the air goes up to the oil soaked steel mesh where the finer dust is trapped. By replacing this system with a K&N style paper filter at the carb, you eliminate the system aspect and force that itty bitty piece of paper to absorb all of the air and all of the dust. It can't possibly do it and becomes overwhelmed.
Think about this, restriction to flow is a function of how much material you are trying to put through a given size hole, the Willys air cleaner is 9 inches in diameter, those little K&Ns are 4 inches? That means the air is going 4 times as fast through that filter vs the Oil bath. It just can't perform. The faster the air is moving, the more dust it will carry with it, slow the air down and the dust drops out.
The critical parts of the air cleaner are described in this section: The inlet section, the pre-cleaner section, the oil cup, mesh assembly and outlet. Dust has weight, therefore when it is moving it has inertia. The inlet section of the air cleaner does two things, sending air in the direction we want it to go, and accelerating the air prior to the pre-cleaner section. In this air cleaner the pre-cleaner creates a tortuous path, a 180 degree turn that uses the inertia of the dust to separate it from the air stream and drop it into the oil cup where it is captured.
AC "pancake type" introduced with the production start in late 1941. Instructions placed on a small decal (black letters on red background).
2- Oakes "decal type" introduced in early 1942. Instructions placed on a large decal (silver letters on black background).
3- Oakes "plate type" introduced in mid 1942. Instructions embossed onto a steel plate which was attached by spot-welds.
4- Oakes "standard type" introduced in late 1942. Instructions directly stamped in raised letters on the air cleaner case itself.
The parts of these cleaners.