Sorting Out Filtration – Filter Types and Media Selection for Increased Filter Life

If a filter is doing its job, its life will be limited.  Eventually it will have filtered out and collected enough particles to be severely restricted or totally block liquid flow.  When this happens, the filter or filtration media must be replaced.  A clogged filter will, at minimum, have process consequences as particle accumulations build up in the cleaning or rinsing solution, and, in the extreme, cause pump failure as the pump supplying the filter pump overheats against a “dead” head thereby ruining the seal.  Neither is a good thing.  However, since filter changes result in “down time” and additional expense for the
filter or filter media, it is a good idea to select a filter that will last as long as possible in a given application.

Illustration of Canister Filter
A typical canister filter with replaceable filter media cartridge

One simple solution, of course, is to increase the physical size or type of filter housing.  The two basic types of filter housings used in industrial and precision parts cleaning are the “canister” filter and the “bag” filter.   A canister filter is a long, cylindrical tube which houses a replaceable filter cartridge at its center.  Connections are made within the canister to force the liquid being filtered to flow through the filter media which comprises the filter cartridge.  A bag filter is also a long cylindrical tube, usually somewhat larger in diameter than a canister filter with a replaceable bag or sack through which the liquid being filtered is forced to flow.  Selecting a filter of a larger size usually provides more surface area for collecting particles and will result in longer periods between required service.

Illustration of Bag Filter
A typical bag filter with replaceable filter media bag

In some applications where space is limited or when it is not possible to retrofit a larger filter housing into an existing machine there is a need for other options.  Another way to  extend filter life is through the use of alternative filter media.  So far we have simply described media as something similar to window screen that allows smaller particles to pass and larger particles to be held back.  There are a couple of simple ways that the capacity of media to retain particles can be increased.  One way is to use a media comprised of many layers each with progressively smaller holes.  These are commonly called “depth” filters and are designed to retain particles in layers.  Larger particles are stopped by the outer, coarser layer while smaller particles penetrate deeper and are stopped and collected by finer and finer layers of filtration.  Because the collection of particles is distributed throughout the depth of the filter media (hence the name “depth filter”), more retained particles can be accumulated by the filter.  Many “wound” cartridges used in canister filters function as depth filters.  Another way to increase the capacity of a filter media to retain particles without clogging is to increase the surface area of the media.  “Pleated” filter cartridges, also used in canister filters, are an example of this type of construction.  A single layer of filter media is “pleated” and wrapped around a central core in such a way that the surface area available for filtration is many times what it would be if there was just a single, flat wrap.  Filter media used in bag filters offer similar options to those described above for cartridge filters.  Bag filters are also the option of choice in cases where large volumes of relatively large particles must be retained and collected.  The bag filter, inherently, has a larger surface area and larger reservoir for the collection for retained particles.

There are several other ways to increase filter efficiency and reduce maintenance costs many of which will be covered in the next and future upcoming blogs.

– FJF –

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