To lessen the level of contamination, several mechanisms can be used, including mechanical stoppage, magnetism, gravimetric deposit, and centrifugal separation. The mechanical stoppage method, which has two possible implementations, is the most efficient:

SURFACE FILTERING

By direct interception, that is. The filter keeps particles from entering the plant or system that are larger than the pores. Metal canvases or meshes are typically used in the production of surface filters.

FILTERING IN DEPTH

Fiber interlacing is used to create filters. When particles encounter apertures that are smaller than their diameter, such wraps create pathways of various shapes and sizes in which they are trapped. Papers impregnated with phenolic resins, metal fibers, or inorganic fibers are typically used to make depth filters.

The largest particle size that can pass through the meshes of the filtering grid is considered the metallic mesh filtration efficiency. A laboratory test known as the Multipass Test is used to determine the effectiveness of microfiber and paper filtration (ßx(c)). The ratio of the number of particles of a particular size found upstream and downstream of the filter is known as the efficiency value (ßx(c)).

Upstream particles number > X µm(c) /Downstream particles number > X µm(c) = ßx(c)
ISO 16889 specifies the test conditions, including the type of fluid to be used (MIL-H-5606), the type of contaminant to be used (ISO MTD), the fluid viscosity, and the test temperature.

During the Multipass test, additional significant features, such as filtration stability (ß stability) and dirt holding capacity (DHC), are tested in addition to the filtration efficiency value. The reason why filtering quality degrades as filter life increases is poor filtration stability. Reduced dirt-holding capacity shortens the filter’s lifespan.

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