Types of Filtration
Filtering efficiency is affected by the relationship between the surface area of the filter media and the volume of air trying to pass through it. This relationship is known as the air-to-cloth (ATC) ratio. The lower the ATC, the more efficient the filtering system. Likewise, the higher the ATC, the less efficient the filtering system.
The larger the filter area, the more efficient a vacuum cleaner filters because there is more area to trap particles and less frequent filter clogging. Small filters clog quickly and a large airflow through such a filter will cause the debris to penetrate the filters.
The optimum condition is a slow airflow through a large filter. Designed with this in mind, Nilfisk vacuum cleaners are equipped with oversized main filters to lower the air-to-cloth ratio.
Over time, debris will build up on the surface of a filter and embed itself into the filter material. This clogging action is known as filter blinding, or loading. A filter is most efficient just before it clogs because the pores of the filter are smaller, therefore becoming a finer filter. However, performance of the vacuum cleaner does not increase because there is little or no airflow to lift and move debris.
Several Nilfisk vacuum cleaners utilize the method of chemical filtration. Chemical filtration actually changes the physical characteristic of a gas or vapor. For example, Nilfisk mercury vacuums work on this type of filtration principle, adsorbing toxic mercury vapors and exhausting clean air into the environment. For more information on chemical filtration, and which Nilfisk vacuum cleaners utilize this method, contact your local Nilfisk Representative, or our Customer Service Department.