Page 18 - Parker - The Handbook of Hydraulic Filtration

Filter Media Types and Ratings
Filtration Fact
Surface media can be
cleaned and re-used. An
ultrasonic cleaner is
usually the best method.
Depth media typically
cannot be cleaned and
it is not re-usable.
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The filter media is that part of Depth Media
the element which removes the
contaminant. For depth type filter media, fluid must
take indirect paths through the materi-
Media usually starts out in sheet form, al which makes up the filter media.
and is then pleated to expose more sur-
Particles are trapped in the maze of
face area to the fluid flow. This reduces openings throughout the media.
pressure differential while increasing
Because of its construction, a depth
dirt holding capacity. In some cases,
type filter media has many pores of
the filter media may have multiple
various sizes. Depending on the distrib-
layers and mesh backing to achieve
ution of pore sizes, this media can have
certain performance criteria. After
being pleated and cut to the proper a very high captive rate at very small
particle sizes.
length, the two ends are fastened
together using a special clip, adhesive,
or other seaming mechanism. The most The nature of filtration media and the
common media include wire mesh, contaminant loading process in a filter
cellulose, fiberglass composites, or element explains why some elements
other synthetic materials. Filter media last much longer than others. In gener-
is generally classified as either surface al, filter media contain millions of tiny
or depth. pores formed by the media fibers. The
pores have a range of different sizes
and are interconnected throughout the
Surface Media
layer of the media to form a tortuous
For surface type filter media, the fluid path for fluid flow.
stream basically has a straight through
flow path. Contaminant is captured on
the surface of the element which faces
the fluid flow. Surface type elements
are generally made from woven wire.
Since the process used in manufactur- 74 m
ing the wire cloth can be very accurate-
ly controlled, surface type media have a
consistent pore size. This consistent
pore size is the diameter of the largest
hard spherical particle that will pass
through the media under specified test
conditions. However, the build-up of
contaminant on the element surface
Surface Media
will allow the media to capture parti-
cles smaller than the pore size rating.
Likewise, particles that have a smaller
diameter, but may be longer in length
(such as a fiber strand), may pass
downstream of a surface media.