January 20, 2018
Removing particles from air is a requirement for many reasons and the cleanliness depends on the final application of the air. The most common requirement is to remove particles which were generated by a manufacturing process so that the air may be released to the environment and meet federal or local cleanliness standards.
The size of particles is usually measured in micrometers, or microns (u). One u is one millionth of a meter, or one thousandth of a millimeter. Particles generated from a grinding or cutting operation may be 100 u to over 1000 u in size. Mist from cooling oil or spray booth operations may be less than 5 u in size. Large particles may be removed from an air stream by centrifugal force, as is done in cyclones.
Most commonly, particles are trapped by the pores of the filter material where the particles are larger than the openings in the filter. The filter is a mat of fibers woven or compressed to trap the particles as the air is blown through the filter.
The particles may get trapped on the surface of the filter material or may get trapped once inside the filter material, depending on the type of filter used. As the filter material blocks the particles, the particles build up, reducing the amount of air flow possible through the filter for a given filter area and air pressure. The particles, therefore, have to be removed periodically from the filter. This can be achieved by shaking the filter, or by blowing air backwards through the filter. Both methods are used in industrial filter applications. The purging by vibration or air is usually done on a timed schedule.