Racor 1000 duplex system??

Twin filters are set up so the filters are identical. The purpose is to be able to switch on the fly should you have a problem. Unless of course you run them both at the same time like some people do…

i ve always run 30s in the Racors, and whatever secondary the manufacturer supplies, usually 2 microns.

Look back on your engines, at least one secondary filter should be mounted. If not we need to get you properly fixed.

When you want full fuel flow to your engine reliably, you filter your fuel in stages.
I came up with three stages; Course, medium and fine. Vacuum and pressure gauges on the system also.
I have the same older parallel Racors you have, as my dual mud filters @ 30mic. These alone have save many headaches using one at a time after bunkering ship fuel.
Next filter with a sight bowl also @ 17mic and final filter @ 8mic.
Later Racor filters may pass water (no more real fish oil used anymore) so I like the middle filter with another sight glass.

If I was to just use Racor 10 or 2 mic filters like others state they do, I would be still drifting offshore today and out of filters.

Every deployment, I carry eight or more 30m Racors and two of each of the other fuel filters.

Dual gen-sets draw from a single Racor 30m then to each owns 10m secondary.
Gen-set pick-up tubes do not go so far down into the fuel tanks. Don't pick up all that bottom junk & water.

Ah, MAN stuff.
Way different from my 47 year old Detroits.
But the fuel issues are the same; Must be clean.

I used to deliver boats up/down the FL east coast.
It was always a fun bet guessing how soon a mud filter would clog up on some of the cleanest dock queens.