Types of Filtration / Industrial Vacuum Filters
Types of Filtration
Many Nifisk and CFM vacuum cleaners utilize mechanical filtration. In mechanical filtration, particles are captured and retained by means of a physical barrier. Our vacuum cleaners accomplish this by a series of cloth, polyethylene and/or paper filters that cleanse the vacuum's working/intake air of particulate and exhaust clean air back into the surrounding environment.
Factors Affecting Mechanical Filtration
Four factors affect mechanical filtration of a substance in a vacuum cleaner: the particle size of the substance being collected, the air velocity or speed at which the substance is traveling, the filter media capturing the substance, and finally the running time or amount of time the filter has been used.
The smaller the particle, the more difficult to filter. Small particles can easily penetrate filter media that is too porous for the particulate.
Nilfisk and CFM filtration systems are designed to capture microscopic particles, down to and including 0.12 microns at 99.999% efficiency. This includes invisible particles that can adversely affect your product or enter your lungs and cause medical problems.
Air speed, or velocity, refers to the pace at which particles move though the hose and into the vacuum cleaner. The faster the particles travel, the deeper they will penetrate the filter media. A particle traveling at a high speed may have the force to push through the pores of the filter material. However, a particle traveling at a slower speed is easier to capture on or between the fibers or weave of the filter media.
A vacuum cleaner naturally moves air at a high velocity, but in a relatively low volume. Nilfisk and CFM vacuums utilize cyclonic filtration which, combined with an oversized main filter, slows the air down as it enters the machine before impacting the filter. This enables a more efficient filtration system.
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 and CFM 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.
A multi-stage, oversized, graduated filtration system is built into ALL Nilfisk and CFM vacuum cleaners. This series of progressively finer filters capture increasingly smaller particles as the working air travels through the vacuum cleaner.