The choice of cartridge filters is application dependent. Cartridge filters are suitable for systems with less than 100 ppm of contaminants (i.e. less than 0.01% by weight of contaminants).
Cartridge filters are available as either surface or depth filters. Depth filters trap particles and contaminants throughout the entire thickness of the media, while surface filters (generally made of thin materials such as paper, woven wire, cloth, etc.) trap particles on the surface of the filter.
Surface filters are the most suitable if you are filtering a deposit of particles of similar size. If all the particles are 5 microns in size, then a 5 micron pleated filter is the best choice because it has more surface area than other filters. Depth filters have a smaller surface area than pleated surface filters, but the depth advantage is significant.
As a general rule the larger the filter area the greater the flow rate, the longer the filter life and the greater the dirt holding capacity. Filter cartridges are usually designed for single use, meaning that when the filter is clogged the cartridge has to be replaced.
Usually bag filters are used for dust removal in industries. Airflow can be directed from outside to inside of the filter (i.e. particle separation occurs on the outer surface of the filter) or from inside to outside, depending on the application. Bag filters typically collect particles on the inside surface of the bag.
Bag filters are normally designed to self-clean when plugged, but some bag filters for gas applications (e.g., dust removal) can be mechanically cleaned by shaking or backwashing with compressed air (so-called reverse flow bag filters).
Bag filters are mainly surface type filters. Surface filters are easier to backwash and clean, whereas depth filters are generally discarded after use.
Variations in filtration rate
Bag filters are generally designed for applications with filtration rates from 1 to 1000 microns.
Cartridge filters have filtration rates of 0.1 to 500 microns.
