Fuel Filters: One or Two?

rgmiller1974 · #1 09-12-2017, 01:39 PM

I have a question about fuel filters. The plans only show one filter, plumbed in between the selector valve and the boost pump. I was wondering if it would be a good idea to have two filters - one for each tank and plumbed in before the valve. That way, if one of the filters clogged, I could just switch over to the other tank.

Mostly, that worry comes from hanging out with a few Long-EZ and Cozy builders. The foam-and-fiberglass crowd have plenty of horror stories about construction debris from their tanks clogging their fuel systems. I think that's probably not as much of a concern for RV builders, especially those of us who bought quickbuild kits.

So? Are there any real advantages to using two filters? Or is it just more expense, weight and plumbing complexity for no real safety improvements?

Thanks,
-Ross

rv8ch · #2 09-12-2017, 01:56 PM

I think it would be easy to argue that done right, two filters would eliminate at least one failure mode. Some install the filters in the wing roots and just remove the wing root fairing to clean them, but it does add a bit of plumbing complexity.

snopercod · #3 09-12-2017, 02:55 PM

I'm a "foam and fiberglass guy" and would be glad to offer my 2 cents. If you flush your tanks several times before flight, I really don't think you need to worry about a filter clogging. I would worry more about the additional fittings and tubing leaking.

ctennis · #4 09-12-2017, 03:12 PM

I considered two in my RV-8, but never really figured out where I'd put them. The wing root area is tight. Like, really tight. I'm glad I didn't end up putting them in there.

At the end of the day, I have one in the spot where it calls for in the plans.

vic syracuse · #5 09-12-2017, 03:50 PM

Unless you live in an area where you know will have dirty fuel and need some extra filtering, the current fuel systems with one filter have been running pretty well on thousands of flying RV's. One of the highest contributing factors to Amateur-Built aircraft accidents is modification to the fuel system. So, unless you have some compelling reason to do it, it's probably not necessary.

Vic

Mark Dickens · #6 09-12-2017, 03:51 PM

I decided that I wanted them in the wing roots and mounted them as described here: http://www.marksrv8.com/2016/08/26/e...ters-part-two/

Rather than taking a dive into the cockpit to remove the filter with my back issues, I decided that laying under the wing on a creeper was more comfortable. Plus I have the redundancy. It's easy to work in the wing root space if you organize things right. I'm happy with my decision. I do have to drain the wing tanks first though to remove and inspect the filters, but that's no biggie with a little planning.

Carl Froehlich · #7 09-12-2017, 05:33 PM

+1 on what Vic said.

The AFP surface area is huge - and I've never found anything in it during the conditional inspection. If you are pumping that much trash that you have a problem, you could add a dozen filters and still have a problem.

Flush your tanks using a see through cheap auto filter when you do your tank fuel sender calibrations, flow tests and system flush. You will never have a problem.

Carl

Kahuna · #8 09-12-2017, 08:11 PM

I just converted an RV-8 system from 2 filters in the wing root to a single filter after the valve. I cant imagine dealing with draining the tanks every time you want to inspect and clean the filters in the wing roots. I suspect the owner
had the same problem as the filters had never been taken out to be cleaned as far as I could tell from the way they were mounted, and the lack of any reference to them in the logs that were fairly detailed.
Anytime you make something difficult, it increases the risk it does not get done.

rgmiller1974 · #9 09-17-2017, 10:16 AM

Thanks for the advice, everyone. I've decided to go with one filter. (Though Mark's installation looked really good.)
-Ross

SuperCubDriver · #10 09-17-2017, 01:18 PM

I mounted one Andair fuel filter in the left wing root behind the fuel selector and bofore the boost pump. The fuel is doing just one circle out the fuselage and in again on the other side of the filter. No need to drain the tanks. Super easy to get to the filter, no need to fold myself into the lower cockpit for cleaning/checking. The only minor issue is when disconnecting the filter a little fuel is dripping out and onto your face when not being careful.