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Harvard has two types of filters (surface and depth filters); filters that work by direct interception of particles, and filters that work by direct interception and absorption. Each filter type offers a slight advantage over the other in regards to how it is used and the media that it allows to flow through it.

Filter Types Available

  • Surface Filters
  • Depth Filters

Surface Filters

Surface filters work by direct interception of particles larger than the pore size of the media. Dirt is trapped on the upstream side of the media with the holding capacity limited by the number of media pores. When new, media resistance of flow is small, but as the filter builds up with contaminants, the resistance to flow rapidly increases.

Depth Filters

Depth filters work by both direct interception of particles and absorption (molecular attraction of particles). These filters use several types of media to achieve the goal of holding particles. The fluid must take a longer path through the filter before exiting. Normally, these filters have large holding capacities and initially have a higher resistance to flow.

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