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|
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.