What type of filter cartridge do I need?
To separate impurities from liquids one can use a wide range of filter cartridges. Those cartridges vary regarding the filter material, the dirt retention capacity and dirt absorbing capacity. Any type of filter cartridge provides certain character-istics and is better or less suitable for the specific application. The following information provides a little help what type of filter will fit your special application best:
Depth filter cartridges with nominal efficiencies are used as prefilters or to remove general impurities and turbidity. Depth filter cartridges with absolute efficiencies have their applications in more advanced filtration processes and as safety filters.
Generally speaking, depth filter cartridges are better-suited for clarification than surface filters such as pleated filters, sieves, strainers and screens, which are more appropriate for classification. Sieves and screens can be cleaned or back-washed, but not depth filters and pleated filters.
Depth filter:
A depth filter does not only hold back the dirt load on the surface but also within its inner porous structure. (like a sponge) The outer layers of the filter cartridges are coarser to trap the larger size particles and the inner layers are finer to hold back the smaller particles. So a depth filter cartridge works well in applications with impurities with a wide range of particle sizes. So the various particles can be trapped in the different layers. However with high throughput rates depth filters can might build high pressure drops and it can occur that they get compressed. So particles might be released again. This is the so-called particle break-through.
Pleated cartridges:
Pleated cartridges are in contrast to depth filters sheer surface filters. The particles are to be retained at the surface due to the micron rating of the filter media and not within the structure of the filter media itself. The main feature of a pleated filter is the surface. The surface corresponds to ten times the size of the final layer of a depth filter. Respectively the advantage of a pleated filter is the better throughput at low pressure drop.
Combined Filter:
When we combine the good features of a depth filter with the good features of a surface filter we receive a pleated cartridge with thick filter media and a reduced number of pleats. Though the surface is correspondingly smaller than with a sheer pleated cartridge the cartridge reaches the required depth filter effect. Combined filter cartridges offer a good dirt holding capacity, high throughput rates with concurrent very good absolute retention rate.
Sieves, screens and strainers:
Coarse impurities can be retained using sieves, screens and strainers.Those materials often are used to protect downstream components like pumps, measuring probes or nozzles. The particles retained on the surface can be removed again. Sieves, screens and strainers do only have a very low holding capacity but they can easily be cleaned or flushed back and are therefore reusable.
