Precoat filter

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Precoat are filters that the filtration of particles a filter aid use, usually diatomaceous earth or perlite , which are stranded as filter medium. The filter holder is a pressure or hinged belt filter . The filter band used is rather coarse.

Fine filtration is achieved by first applying a precoat (e.g. cellulose ) to the filter surface. With the help of the precoat, a fine filter cake is formed , the pores of which are much finer than those of the filter support.

First, the suspended filter aid is washed up using a carrier liquid . As soon as a filter cake has built up, the liquid to be filtered (the unfiltrate) is switched to. The filtrate or the clarified liquid flows downwards. If the back pressure increases, the filter cake tends to seal , i.e. H. If a limit value is exceeded, the filtration process would be interrupted and regeneration would have to be initiated. To delay this, the proportion of filter aid is increased until the differential pressure increase is lower.

The precoat filters can be used where very fine particles have to be removed from a liquid : for oil in the metalworking industry or for beer and wine to filter out yeast and other sediment .

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