Filter Medium – The Core of the Filter

Filter Medium | The Core of the Filter

Clean combustion requires clean fuel. The job of the filter medium, the core of the filter, is to clean the fuel.

Filters are your machine’s silent heroes. Hidden inside the vehicle the filter is not seen or heard. Yet the filters provide continuous protection. Under the hood of each filter, is the filter medium. This is doing the job of cleaning your fuel. Without this medium, there is no clean fuel, which means clean combustion won’t be possible.

The typical clearance for a high pressure common rail fuel injector is less than 5 microns. And with pressures of up to 2,500 bar, even the smallest dirt particles in the fuel can have the effect of a projectile and cause substantial damage.

MANN+HUMMEL uses a triple layer filter medium to meet this challenge. The first layer is a fully synthetic fibre layer. It enables an increase in the dirt holding capacity. The second layer is made from a combination of cellulose and ultra-fine glass fibres. It ensures a high separation efficiency to maximize the number of particles the filter can retain. A final cellulose layer with a support function prevents the escape of glass fibres.

New development from the test bench

After the definition of different parameters, each new development is set up on the test bench. That starts with a first sample of the filter medium in DIN A4 size. Using computers, the developers at MANN+HUMMEL are able to determine how many particles are held back by the filter medium. Using modern filter media, for example, only 3 of every 1,000 particles in the flow with a size of 4 micrometres are able to reach the other side of the filter. These particles are up to 18 times finer than a human hair.
In the next step the medium has to prove that, despite many arrested dirt particles, it will not clog prematurely. The developers examine the so-called dust holding capacity and for this purpose add soot particles to the filter on the test bench. This enables the researchers to get closer to real operating conditions and make very exact predictions as to how the filter medium will function under actual operation.

Filter medium manually crafted

Low volume tests are conducted in a suitable production plant. Here processing specialists and technicians work on the fine-tuning of the filter medium and details such as the use of suitable technology to join the filter medium to the end cap. 20 to 30 sample filters are made this way manually. Then the filters return to the test bench. If the results are not satisfactory, the materials and processing are adjusted, and further tests are carried out.

Step by step to the end result

In the last step the filter returns to the production plant, where high volume tests are conducted. Machines with huge rollers process roughly a tonne of the new filter medium, and several hundred filter elements are manufactured under series production conditions. With cutting, pleating, curing and other steps the new development has to prove that it will be able to handle non-stop processing and remain stable in the process. When this implementation is finally successful under series production conditions, the production plant and development department give the go-ahead, and a new filter medium is born.