LESSONS IN LUBRICATION
Typical Oil
Filter Components
media. The media operate under several types of filtration mechanisms, including:
• Direct Interception and Depth Entrapment – Particle blockage
on the media due to the particles being larger than the taken
passages within the media.
• Adsorption – The electrostatic or molecular attraction of
particles between the particles and the media.
• Depth Retention – Contaminants are held either at the surface
of the media or within the labyrinth of passages within the
"depth" of the filter media. This creates several opportunities
for contaminants to become trapped.
The graph below shows how depth-type filtration is more efficient in capturing smaller particles when compared to surface-type
filters. This can be attributed to the deeper media providing more
• Inertial Impaction – Particles are impacted onto the filter media
by inertia and held there by adsorption as the oil flows around.
• Brownian Movement – This causes particles smaller than 1
micron to move irrespectively of the fluid flow and results in the
particles being adsorbed by media in close proximity. It is much
less prevalent, especially in viscous fluids.
• Gravitation Effects – These allow much larger particles to
settle away from fluid flow regions when there is low flow.
In addition, filter media can be designed to capture particles
through two distinct methods:
• Surface Retention – Contaminants are held at the surface of the
media. This provides an opportunity for the contaminant to
become trapped as it comes in contact with the media surface.
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Particle size retention characteristics of depth-type
and surface-type filter media.
