Whether your air filter is fitted to a car, a truck, a tractor or a digger air filter efficiency will be measured in the same manner.
Older equipment might have used an oil-bath air cleaner but today it is almost entirely dry-type air filters that are used. They are more efficient and easier to service. They generally use treated cellulose media, pleated to give as much surface area as possible within the filter container. The more media is used the greater the air-flow that the filter can handle and the longer the service life before cleaning or element change.
As little as 100 gm of dirt passing into a diesel or petrol engine can “dust” it to the degree where it needs to be reconditioned. A dry-type air filter, from any of the major reputable manufacturers, will have an efficiency in excess of 99.9%. In other words for every 100 gm of dirt hitting the air cleaner element less than 0.1 gm will pass through and into the engine.
But how is its efficiency measured?
Under laboratory conditions special test dust, typically a carefully defined mix of different particle sizes, often from the Arizona desert, is mixed with the air flow entering the air cleaner assembly. Any dust that passes through will be caught on a massive absolute filter which would first have been weighed. After the test period the absolute filter is weighed again. This weight difference is then compared with the difference in weight of the air filter element itself before and after the test. The efficiency is a simple calculation and is expressed as a percentage.
The most commonly used test dust is defined as coarse and has the following particle size distribution by weight;
Size in microns Percentage
0 –5 12 +/- 2
5 – 10 12 +/- 3
10 – 20 14 +/- 3
20 – 40 23 +/- 3
40 – 80 30 +/- 3
80 – 200 9 +/- 3
Before deciding on which air cleaner to use always check what its efficiency is – for the sake of your repair bills at least!