Correct, but then I only know of 10u and then they drop to 2u. I maybe wrong, but I don't know of a 5u. Correct me if I am wrong.
10u is OK for a secondary, but as Pat pointed out, an injector will pass below 5-7, so you will still get the occasional particle that could clog.
setup would be firstly att eh tanks
. The tank would have a "sump" area that has a drain off valve for water to "fall" to and be able to be run off. Then two Racor's (best in my opinion) 30u primary with seperator in parrellel with a valve to switch over one to the other in an emergency
. Then I would have a secondary 10u Racor(single and Seperator not required). Then the engine mounted in a 2u. (or 5-6 if available) These small filters are cheap
and easily replaced and are a final safeguard ONLY. Because they are small, they can block quickly if you get a bug issue.
The two Racors are the main work horses and will stop 99% of all problems, have a large surface area so they will take a lot to block off and the primary would remove any water. Probably way overkill for most small engine installs, but recommended in any Engine power only installations, especially if you are big enough to venture out on your own.
But that is expensive and as I said, my "ideal". I can't afford that, so I have a Racor with seperator (10u) and the two secondaries on the engine. Not sure if they are 10's or 2's. Must check that.