Surface filtration mainly adopts screen material and depth-type filtration felt material. Their differences are as follows:
Screen materials, like nylon monofilament, metal monofilament, etc. directly hold impurities back at the surface of filtering media. The advantage is due to its single filament structure, it can be cleaned for times, so its operation cost is low; and its disadvantage is with only one filter media, which is easy to be blocked by particles. This type of filter products is most suitable for coarse filtration with filter rating between 25-1200 microns.
Felt materials, like needle-punched felt, melt-blown nonwovens, etc. are common three-dimensional depth filtering media. It features loose fiber structure and high porosity, which increases retention rate a lot to impurities. This filtering media belongs to compound retention model material, namely larger particles are captured on the fiber surface and fine particles captured in the depth media, so it has high filtering efficiency, in addition, the high temperature surface treatment, i.e.: instant sintering technique, which can effectively prevent fibers from scattering by high speed liquid in filtration. Felt media belongs to disposable filtering material with its filter rating range form 0.1-200 micron.
Comparison between surface & depth filtration
The two ways of filtration depend on filtering material. The way of membrane filtering material, for instance, is surface filtration, which can be cleaned after it being blocked, it is for multi-times usage; fiber materials are piled up by fiber raw material, impurities can accumulate in its inside structure first then on its surface, which is not allowed to use the second time.
Initial filtering flow rate, which is determined by material aperture, the degree of fiber accumulation can be same, but along with particles accumulation for which it is faster on surface filtration instead of depth-type filtration, so it is faster to block of surface filtration comparing to depth-type one, but for service life, depth-type is much longer than that of surface one.
