Racor 2020 Prefilters 10 or 30 micron? what to use ?

[BartW]

The Racor prefilters that I've alway's used on our big old V12 MAN Lumps are 30 micron,
The new filters I've got here for spare
and fitted a few weeks ago on one engine are 10 micron
engine ran fine with them, (we have two pre-filters in parallel on each engine)
what's best to use ? 10 or 30 micron.

no big difference according local MAN man, " 10 is better "

 

[JerseyDiver]

If the pre filters are easy to access go with the 10 and catch the crud there. The engine filter is likely 10 or possibly 5 ??

 

[boatmike]

The final filter on the engine will probably be 5 or less. When I bought my boat it had fuel contamination and 30 micron filters let a lot of contamination through to the final filters and slowed both engines considerably. If you have relatively clean tanks and fuel, 10 micron is fine and most contamination will be stopped there allowing the final filter to have a longer life. With the Racor filters it is relatively easy to dump contaminates and fit new filters anyway while most final filters are spin on types that can't be cleaned, only replaced. Go for 10 and inspect regularly.

 

[BartW]

OK, all understood,

I don't know how many micron the MAN filters are,
googling the part nrs didn't give the specs,
but I guess I'm ok,

so far I've alway's had clean fuel, (I think)
almost alway's bought from a respected supplier, who mostly offered a sample with each filling.
also our "decantation box" that I drain ones or twice every season, didn't reveal much dirt

thanks for clarifying

 

[Bandit]

Normally pre filters are 30 micron rock stoppers and the engine mounted ones are finer 10 or so.

 

[boatmike]

That's very misleading. If the fine filter on the engine was only 10 micron any contaminates smaller than this would (assuming fuel is contaminated to any extent at all) go straight through to the fuel pump which would not last long. Most engine final filters are 5 micron absolute or less and are there as final protection only assuming that most larger contaminates will have been stopped earlier. It is true that many boats have 30 micron filters fitted but 10 micron is more suitable and will have a reasonable life if the fuel is not heavily contaminated. One of the most common causes of engines not developing full power is final filters becoming contaminated and restricting fuel flow. Fine filters don't have a great deal of dirt holding capacity and become loaded very easily. If the only filters upstream of them are what you call "brick stoppers" and the fuel is contaminated they wont last long.

 

[Piers]

With advice from Parker Hannifin, I've always fitted 10 to the pre-filters. Why? It's easier to change these at sea rather than the hot engine's fine filters. 10 will not restrict fuel flow.