What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fuel Return Line - AN Fittings

gkochers

Member
Friend
Well, I'm sure this is because I'm a total noob when it comes to AN fittings that it took me several tries to figure this out. I thought I'd share my saga for those that haven't gone through it yet.

I'm not necessarily planning on running EFII, but I thought it couldn't hurt to put in an extra bung in the tank for fuel return. I bought extra VA-141 fuel flanges from Van's and figure I would just cap them off for now.

I had a little trouble figuring out which AN fittings to buy on Van's website so I thought I'd do some research and concluded that I just needed a 3/8" pipe to nipple adapter and a cap to seal it off. I referred to Section 5 and several web sources and concluded I needed an AN816-6D. Ordered it from Spruce for about $8 each - they didn't fit. I didn't even consider that it's a 3/8" fuel line, but the pipe fitting in the bung is what I eye-balled to be 1/2". The AN816-6D has 3/8" on both ends.

So, more online research, and I confidently concluded that I needed an AN816-6-8D to transition from the 3/8" tube (the -6) to the 1/2" fuel flange (the -8D). This was a little harder to find, but Skygeek showed them in stock for about $10 a piece and I ordered them. Skygeek must have not really had them in stock because it took the 2 weeks to ship them. I knew before I even pulled them out of the little paper wrapper it was not the right part. The 3/8" nipple was correct, but the pipe end was huge! What am I missing here? NPT pipe size is what I was missing.

NPT sizes are discussed in Section 5, and I just didn't pay enough attention. It shows 3/8" NPT as closer to 5/8" OD. I confirmed that's what my fuel flange measured. So then why wasn't the original AN816-6D correct? 3/8" nipple and 3/8" NPT, right? No - standard transitions apparently are downsized on the pipe side. So, an AN816-6D is really the same as an AN816-6-4D. I guess everyone probably knows that except me.

So finally figured out that I need an AN816-6-6D and Spruce carries those. 3/8" nipple to a 3/8" NPT. The part arrived today, and it fits! A month-long saga of AN fittings has ended. The parts aren't expensive, but I was paying almost as much in shipping every time I ordered the wrong one. I was getting frustrated.

Hopefully this will save someone out there some heartache. And maybe I just got lucky finally and someone else can better explain the sizing of pipe to nipple transitions.
 
If you haven’t already installed it, be careful where you put that bung on the inboard end of the tank.
There’s a limited number of spots that don’t interfere with spar bolts, control rods etc.
 
Hi Greg, If a fuel return system is something that's documented in the plans, I would do it exactly as Van's recommends.

I was trying to recall any use of NPT in my fuel system return lines, and could not think of any, so I went back and looked at my ancient blog, and here's what I did:

http://www.rv8.ch/fuel-return-line/

The reason I did it this way was to return the fuel to the outboard part of the fuel tank, to reduce possible foaming and to allow the fuel to cool. No idea if this is really needed, but it was recommended to me at the time by the engine supplier.

If I understand what you are doing, you will put the fuel back in the tank near the pickup. I'd check with Ross and/or Robert to see if this is what they recommend.

One stupid thing I did, which it seems you are not doing, is I made the return lines all -5 tubing, since some of the fuel will be used by the engine. This was a very bad idea, since getting -5 parts was really hard. I'd use -6 as it seems you are doing. Tubing is fun!
 
Mickey---the plans dont specifiy a return location, I think because Vans didnt support the electronic injections with returns. BUT, the tank end rib T-1003B L/R do have a provision for using the VA141 bung for the return on the top of the rib.

Tom
 
The space available to locate the return line is very restricted on a 10 tank compared to other models. The builder has to allow for the lateral rib & control linkage in a tight area. He should look forward in the plans to see how all that fits before drilling into the tank.
 
Back
Top