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Technical Reference

Basic Filtration Principles

Filter Media

Smaller media pores cause more flow resistance, in
Media is a term used to describe any material used
to filter particles out of a fluid flow stream. There are turn causing higher pressure drop.
four basic types used to remove contamination in
engine applications: While cellulose provides effective filtration for a
wide variety of petroleum-base fluids, in certain
A. Synthetic Media applications it results in poor filtration performance
as compared to synthetic media.
Synthetic fibers are man-made, smooth and
rounded of provide the least resistance to flow. Their C. Composite Media
consistent shape allows us to control the fiber size
and distribution pattern throughout the media mat to Composite media are where synthetic media and
create the smoothest, least inhibited fluid flow. cellulose media are put together to provide some
Consistency of fiber shape allows the maximum of the benefits of both for certain applications. In
amount of contaminant-catching surface area and some applications where flow rates are lower and
specific pore size cellulose media properties are desired, but more
control. The result
is media with Donaldson’s third generation of
predictable filtration Synteq fuel filter water separator
efficiencies at media uses both cellulose and
ENGINE LIQUID FILTRATION TECHNICAL REFERENCE
removing specified meltblown synthetic layer to
contaminants (e.g., achieve the highest levels of fuel
filtration performance
4 μm) and maximum
dirt holding capacity.

The low resistance capacity is required a composite media is used.
of synthetic media These are typically fuel applications. You get the high
to fluid flow makes capacity of synthetic media and the water separation
Donaldson Synteq™ synthetic filter characteristics of treated cellulose, to create a cost
media (left) is magnified hundreds of it ideal for synthetic
times under the scanning electron fluids, water glycols, effective and long life media.
microscope. The smooth rounded water/oil emulsions,
fibers provide low resistance to fluid D. Wire-Mesh Media
flow. and petroleum based
fluids. Wire-mesh media consists of stainless steel, epoxy-
coated wire mesh available in 3 mesh sizes:
B. Cellulose Media
• 100 mesh yields 150 μm filtration
Cellulose fibers are
actually wood chips, • 200 mesh yields 74 μm filtration
microscopic in size • 325 mesh yields 44 μm filtration
and held together by
resin. As you see in Typically wire-mesh filters will be applied to catch
the photo below, the very large, harsh particulate that would rip up a
fibers are irregular in normal filter. You may also find this media useful as a
both shape and size. coarse filter in viscous fluid applications.

Cellulose often has
lower efficiency
ratings, which means Cellulose filter media photo from
there are smaller scanning electron microscope
pores in the media. magnified hundreds
of times.

108 • Engine Liquid Filtration www.donaldson.com