What engine(s) do you have? If it is a Lehman the secondary filters are about 6 to 8 microns. Most of the older engines use that as a secondary. If you have a new common rail then the secondaries would be 2 microns. I have SP225 Lehmans and use 10 micron in the Racors and the standard filters as secondaries, which are about the 8 micron. You could use 2 microns in the Racors but with the older engines 10 is probably fine. I don’t use the 30 micron because I would rather change the Racor element than the secondary.
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