Surface filters are employed wherever chief priority is placed on reliable and cost-effective treatment of air with high dust concentration. Prerequisites for the application of surface filters are relative humidity < 90%, as well as dust that is not moist (ideally, dry dust). Surface filters are almost always built in the form of dust collectors.
Principle of operation:
For both cartridge and bag-cassette dust collectors, the basic principle is the same. The systems intake the air from outside and guide it to the interior. The particles to be filtered out of the air are separated out on the surface of the filter medium. A dust cake forms on the upstream surface of the filter, which additionally provides a separation effect. Once the pre-selected pressure is reached, a blast of compressed air from the inside toward the outside blows the cake away, and the filter medium is clear for operation again.
It is important here, however, that the compressed air does not blow away all the filter cake, and that some of the cake remains on the filter medium. Otherwise, it may happen that fine dust becomes lodged in the filter medium. This happens, for example, when the pre-selected pressure difference (to trigger the blow-off of the dust cake) is too low.
Principle of blowing off accumulated dust cake on a filter bag
If the filter system filters only superfine dust, a pre-coating material must be applied during commissioning of the system, in order to provide an artificial dust cake. The superficial filtering velocity (also known as the air/cloth ratio) depends on the fineness, the consistency, and the type of the surface filter.