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In-Line Fluid Filter Micron Ratings and Recommendations

In-Line Fluid Filter Micron Ratings and Recommendations

How Fine a Filter Do I Need?

Fluid filters are typically rated according to the nominal size of the openings in the filter media. Screen filters can also be rated by the mesh size (or "mesh count"). Mesh sizes can be confusing because they refer to the number of openings per inch. A larger mesh number translates to smaller opening sizes.
Mesh Count and Micron Ratings
Mesh Micron Inches Particle Size Filter Example
  1270 0.05 Won't pass through the eye of a sewing needle Canton Coarse Inline Screen Filter
  400 0.0157 Coffee grounds Internal Filter for Facet Cylindrical Pumps
50 297 0.0117 Beach sand Canton 50 Mesh Inspection Filter Element
60 250 0.0098 Sawdust Setrab 250 Micron In-Fitting Screen
100 149 0.0059 Table salt Setrab Magnetic Inline Screen Filter
  115 0.0045 120 grit sandpaper Fuel Funnel Screen Filter
200 74 0.0029 Silt 1/8 NPT to 5/16" Hose Barb Fuel Filter
  40 0.0016 Lower limit of visibility Canton 40 Micron Cleanable Oil Filter Element
  31 0.0012 Pollen Fuel Safe Sock Filter for Fuel Pickups
  25 0.001 White blood cells Flow Ezy 25 Micron Fuel Filter
  8 0.0003 Red blood cells Canton 8 Micron Oil Filters
  5 0.000197 Dust Fram HPGC-1 High-Performance Fuel Filter
  1 0.000039 Bacteria Canton Fuel Filter
Specific Recommendations:

Differential or transmission cooler: 149 to 1270 micron. This filter needs to protect the cooler passages from clogging.

Engine oil pre-filter (inspection filter): 40 to 1270 micron. This filter needs to protect the suction side of the pump from damage.

Engine oil main filter: 8 to 40 micron. Crankshaft journals are often finish-polished using 23 micron abrasives.

Fuel system pre-filter (before the pump): 25 to 400 micron. This filter only needs to catch larger particles to prevent the final filter from clogging prematurely.

Fuel system final filter (after the pump): 1 to 74 micron. High-performance fuel injector manufacturers recommend a 10 micron or finer filter.

General rules of thumb:

For any given size, a coarse filter will flow better than a fine filter. This is why coarse filters are usually recommended for thicker fluids. Increasing the filter size can (partially) compensate for the lower flow of a finer filter.

In any application, it is hard to go wrong with a coarse pre-filter followed by a fine filter. The fine filter protects the machinery, and the coarse filter protects the fine filter from clogging too quickly. Installing the coarse filter before the pump will also protect the pump from damage.

Racing Oil Filters
Racing Fuel Filters

This article was first published on 3/11/2013.

It was most recently modified on 3/26/2015.