Options a available fuel return line retrofit?

I need to retrofit fuel return lines to both tanks on my 7A, and I was hoping to see what might be available before machining my own parts for retro-fitting fuel return lines to both tanks. I have created a good design for retrofit to existing tanks without removing tanks or wings from the aircraft, but it won’t be easy.

Can anybody steer me toward any other products intended for this job before I launch into a custom-fabricated installation? Thanks- Otis

Hartstoc said:

I need to retrofit fuel return lines to both tanks on my 7A, and I was hoping to see what might be available before machining my own parts for retro-fitting fuel return lines to both tanks. I have created a good design for retrofit to existing tanks without removing tanks or wings from the aircraft, but it won?t be easy.

Can anybody steer me toward any other products intended for this job before I launch into a custom-fabricated installation? Thanks- Otis

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Depends on the flow requirement, but for mine I just used the flange fitting that Vans uses for the drain. Bough two extra and installed them on the rib. Only 1/8 NPT though, good for a bleed off, but maybe not an FI pressure regulator.

Otis---try VA141 flanges that Vans uses on the RV14 tanks. NPT threaded, and riveted on. No need to remove the outer rib and use a bulkhead fitting.
Getting to it with the wings on the plane will be 'interesting'.

Tom

EFII sells a machined bung that accepts a -6 ORB fitting. With some careful work I retrofitted them to my 9A tanks (tight wingroot space) while installed on the plane. A right-angle drill is essential, and proseal the fitting in place.
The Van?s drain flange would install the same way. I found specialized screws that are designed for thin sheet metal, with fine threads rather than typical coarse pointy sheet metal screws. Sealed pop rivets were my first choice, but I couldn?t find a puller that would fit in the available space in the 9 wingroot.

Ross at SDS suggests a bulkhead fitting with statoseals, also an elegant solution but would have required removing the tank access panel.

No leaks in 150+ hours, though some metal drilling swarf has come out the drain despite my best precautions.

Can you pull the access panels in the root end of the tanks and install the return fittings in the access panels?

If I'm honest with myself, I often spend more time taking shortcuts than just going the distance. Tank work might fit that description. As bad as pulling a tank seems, trying to do this kind of mod in the tank-fuselage gap sounds much worse, to me. I've had my -4's tanks off several times, and even if I doubled the time required to account for the-7's baffle screws, I'd still spend less total time than I would working in that little gap. Of course, YMMV...

which FI system?

Are you looking for a return for a Bendix type system or purge line return from a AFP system? I plumbed my AFP purge return into a vent line a tank level. You can push fuel out the vent if you over-purge. Not an option with a Bendix type. A bung into the tank would be ideal for both.

Just remove the tank

rv7charlie said:

If I'm honest with myself, I often spend more time taking shortcuts than just going the distance. Tank work might fit that description. As bad as pulling a tank seems, trying to do this kind of mod in the tank-fuselage gap sounds much worse, to me. I've had my -4's tanks off several times, and even if I doubled the time required to account for the-7's baffle screws, I'd still spend less total time than I would working in that little gap. Of course, YMMV...

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Gotta agree completely with Charlie on this one - it would probably be easier to just remove the tanks. This will allow you to see what's happening, to clean the tanks of any chips, etc.

rv8ch said:

Gotta agree completely with Charlie on this one - it would probably be easier to just remove the tanks. This will allow you to see what's happening, to clean the tanks of any chips, etc.

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The trouble with tank removal is that my wings have a perfect paint job that includes the tank screws and I don?t want to remove them. I?m zeroing in on a method that I think will work well and that I will document here. It will involve some custom machined parts that I?ll make on the bridgeport, and will employ methods of cutting the access holes and punching the connector holes that do not generate shavings or chips. I?ve determined that access to the forward raised circle on the inboard rib is quite good via the gap if you work from below propped up by a well designed inclined ?chair?. It won?t be fun but I think it will work well.

I need full-flow return lines because I?m installing a twin-redundant electric pump system and removing the engine driven pump completely. I?ll be installing Airflow Performance fuel injection and pressure will be maintained at 28-34PSI by relief valves. The majority of the active pump?s output will return to the tank it came from. Continuous short-loop recirculation is not an option for full time use of electric pumps. It is actually a pretty bad idea even for occasional use boost pumps.- Otis