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Fuel return line

togaflyer

Well Known Member
I have the quick build wings. I do not need a return line, but Im considering installing a return line fitting in the tanks and capping it (for somewhere down the road.) What fittings do I need to order. Can I install the fitting by way of the cut out hole for the fuel float or do I need to cut out another access, where should it be located. Finally, is it really worth the hassle.
 
I have the quick build wings. I do not need a return line, but Im considering installing a return line fitting in the tanks and capping it (for somewhere down the road.) What fittings do I need to order. Can I install the fitting by way of the cut out hole for the fuel float or do I need to cut out another access, where should it be located. Finally, is it really worth the hassle.

You could do all that, yes.

No - it is not worth it.

I had a return line on my 8A plumbed back to the left tank from the AirFlow Performance spider purge valve. I used it perhaps twice over 10 years for actual purge (but I used it at every shutdown to bleed off the fuel pressure). I did not have a return line on the RV-10 as the stock engine from Van's comes with Precision fuel injection. It does not have a purge valve. You could back fit it but I never had a need. Hot starts and such were not a problem.

Carl
 
Easy...

Install a 1/4" NPT bung in each root. Can be done from outside of tank. Drill holes, Pro seal and use sealed blind rivets. Then just use a brass pipe plug to seal it up. I am using a full flow return for my EFII system and it's what I did with my QB wings...
 
top shelf.

We have been through this and you can put it where you wish. The way we were tout to install a dual return line system is go back to the highest point in the tank away from the pick-up location. We run an Andair Douplex valve for just this style fuel system. We used the same flang that you have on the bottom of the fuel tank for the drain valve and installed it at the most outboard top of the back of the tank. Just as they are place in the bottom of the tank for the drain. As others have said you can plug it as you wish or use it for return fuel flow. Doing it this way keeps what few air bubbles may be dumping back into the tank away from the pickup and also reduces the back pressure on the return line for foot of head do to standing fluid on top of the return line to tank opening. Just the way it has been done for a long time out on the ramp.
Hope this helps, Yours, R.E.A. III #80888
 
My return line goes into the tank at the root rib same as the pickup and vent. On the inside of the tank, it is routed up to the top of the tank in the first bay where a tee fitting takes any air bubbles out to the filler cap area where the vent tube also terminates. The other end of the tee fitting is left open. This is the end of the line for returning fuel.

Bevan
 
The other way to skin this cat is to Tee your return line into the line from the tank to the selector. If you have return fuel, it'll either go downstream to the engine or upstream to the tank, depending on how much fuel the engine is pulling from that tank at the time.
 
The other way to skin this cat is to Tee your return line into the line from the tank to the selector. If you have return fuel, it'll either go downstream to the engine or upstream to the tank, depending on how much fuel the engine is pulling from that tank at the time.

I wouldn't recommend this solution. Return means return to the tank, not to the pump inlet. If you have air or vapor in the return line, say because you ran a tank dry, it's going to take a very long time for the engine to catch again as that air goes around in a circle for a while and the pump cavitates.

You don't want any air/vapor to ever enter the pump or get into the injectors. Returning directly to the tank is the best way to prevent this from happening.
 
Is return to the first bay (ie, just a bulkhead fitting through the end rib) good enough,
Absolutely!
or should the return be extended farther into the tank volume?
No benefit there but some builders choose to bring the return line outlet all the way to the other end of the tank.

I have a "constant flow" return system and fuel returns into the first bay at the wing root. For obvious reasons it is located at the top where as the pick up is located at the very bottom. Worst case scenario would be returning hot fuel or bubbles to the tank and last time I checked, bubbles float to the top as does fuel that is warmer than what is in the tanks. I use 91 octane E10 for most phases of flight and have not encountered any adverse effects having the return line plumbed into the first bay.
 
I wouldn't recommend this solution. Return means return to the tank, not to the pump inlet. If you have air or vapor in the return line, say because you ran a tank dry, it's going to take a very long time for the engine to catch again as that air goes around in a circle for a while and the pump cavitates.

You don't want any air/vapor to ever enter the pump or get into the injectors. Returning directly to the tank is the best way to prevent this from happening.

Thanks, Ross. My intended use is as a return for a purge valve. I don't see any issues with the approach I suggested as long as the return goes to one side and I'm pulling fuel from the other while purging.

Comments?
 
Thanks, Ross. My intended use is as a return for a purge valve. I don't see any issues with the approach I suggested as long as the return goes to one side and I'm pulling fuel from the other while purging.

Comments?

That's exactly how I have my AFP purge line plumbed. It "T's" into the right tank supply line below the fuel selector. For any boost pump operations with the purge valve closed, like starting, I select the left tank (checklist item). For this specific purpose, this configuration works just fine -- no issues whatsoever.
 
If you're talking EFI systems where very high volumes of fuel are returned, I would not return it anywhere but the tank selected for feed through something like an Andair duplex valve. (feed from left, return to left and vice versa). This avoids pumping fuel overboard if not returned to the selected tank.

Dumping the return fuel back into the first inboard bay is fine if it's several inches above the feed line since air rises.

Because fuel is pumped around the warm engine, fuel picks up heat. You want this heat to be sunk off in the large fuel mass in the tanks before being picked up in the pump again.

My advice is to not take chances with another layout. Do it the proven way, not an easier way. Air/vapor at the fuel pump inlet is really bad news on an EFI engine and you don't need something like that at 50 feet over the trees at the end of a runway.
 
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