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March 2016 • SMT Magazine 85 variables and performance figures for practical sizing of air filters: • Incoming particle characteristics • Initial pressure drop and pressure drop progression • Lifetime or possible duration of usage Filter performance (degree of separation/ efficiency), pressure drop and particle type are the most essential criteria for selecting best suit- able air filter. In addition, the first two criteria have a critical influence on energy issues, which should also be considered. Coarse Particulate Filters/ Saturation Filters Coarse particulate filters are commonly used as pre-filters. Primarily, they separate coarse dust types >10 µm. In industrial applications, con- figurations as filter mats, filter cassettes, pocket filters, metal mesh filters or wire frame filters are well proven. Since coarse particulates are mainly dry dusts, this filter selection is based on the percussion effect, i.e., due to their inertia forces particles are bound on the filter surface. After the formation of a so-called filter cake and respective saturation, the filters can be cleaned/ dedusted and reused. The precondition is a con- stant air flow. The benefit of saturation filters is the low initial investment and high flexibility, but set against high maintenance and operation costs. Fine Particulate Filters/Storage Filters Fine dust filters are primarily used for sep- arating airborne pollutants > 1 µm. Although they are available as pocket filters or compact cassettes, their utilisation as cleanable or regen- erative filters (e.g., in the form of cartridge fil- ters) has been proven in industrial applications. Long life is the benefit of cartridge filters (i.e., fIltratIon tEChnology Figure 3: Principle saturation filter system.