Andair check valve

[akarmy]

When people are doing the return line, is it normally plumbed back to the header tank?

Yes in my case it goes into the top of the header tank for the return.

[jiott]

Ditto for me too-to the top of the header tank.
This is what the instructions say to do when you buy the Kitfox optional return line kit.

[jiott]

I know some guys run the line into the top of their gascolator and I guess this works. However, one of the main purposes of the return line is to recirculate cool fuel from the tank back to the engine to help prevent vapor lock. Recirculating it only to the gascolator (usually mounted in the hot engine compartment) seems to partly defeat this purpose.

[PapuaPilot]

You definitely want to send the return fuel to the header tank. The reason is to get rid of any vapor. That is the reason it goes in the top of the header tank.

It would not be wise to put it back in the gascolator.

[jrevens]

I could be mistaken, but I believe that RANS says to run it back to the gascolator. At least I've seen it done that way on several S-19s. I wonder if there is any value at all in doing that? If the gascolator is down low on the firewall, as they usually are, the fuel in it is probably cooler than that in the fuel line running on top of a hot engine. Also then, you are mixing the warmer returning fuel with the cooler fuel entering the gascolator, possibly giving close to the same effect, with shorter hose runs & one less line running through the cockpit.

[Dutch]

Correct me if I'm wrong. I allways thought the reason for the return line was to relieve the pressure of the expanding fuel between the fuel pump and the carbs after shut down. Thats why I routed it back to a metered port on top of the gascollater. I reasoned that the 8 or 9 lb would easily push the fuel back up line.

Dutch

[Dave S]

Ideally, I believe the instructions from Rotax say to route the relief line back to the fuel tank.

The idea behind that is to get any vapors (if they exist) out of the incoming fuel stream.

The Kitfox tactic favors the return/relief line going back to the header tank which has a vent to the fuel tank; and, has sufficient thermal mass in the amount of fuel stored in the fuel tank to recondense any gasolive vapors anyway.

Don't know anything about the Rans & gascolator deal; but, I would estimate that someone has evaluated, to some degree, the option of going to the gascolator and found that it works in that design (I hope?)......however, the line to the gascolator entirely depends on sufficient thermal mass at the gascolator (gascolator + fuel) to recondense gasoline vapors (which has far less thermal mass than a kitfox header tank)....since it does not have a vent daisy chained back to the fuel tank through a header or other venting system there is no way to exclude vapors from the fuel line to the engine if the stuff does not recondense in the gascolator...theoretically anyway.

So, why do people plumb a system short of the fuel tank?.....probably for simplictity and avoiding the extra work/plumbing that would be needed to go there......on a kitfox, there are no addittional ports for a return line at the wing tanks; but there is at the header which is also vented so it serves the same purpose as going to the wing tank. On the Rans, I don't know; but most gascolators have a primer outlet - if it isn't being used...it may be a target of opportunity for a return line - but it is not vented; and, the proximity of the primer port to the fuel pickup port to the engine in a gascolator is pretty darn close.

Dutch is correct on this point " I allways thought the reason for the return line was to relieve the pressure of the expanding fuel between the fuel pump and the carbs after shut down."

PaPua Pilot is correct on this "You definitely want to send the return fuel to the header tank. The reason is to get rid of any vapor. That is the reason it goes in the top of the header tank."

Jott is correct on this " one of the main purposes of the return line is to recirculate cool fuel from the tank back to the engine to help prevent vapor lock. Recirculating it only to the gascolator (usually mounted in the hot engine compartment) seems to partly defeat this purpose."

The trick here, as the Kitfox factory installation tactic has determined and suggests in its installation guide, is to: 1) Cure the pressure build-up between the fuel pump and carbs with a bleed/return line; while 2) Not taking a chance of sucking vapors back into the fuel line to the engine through a short circuit.

Mission accomplished by running the line back to the header tank where the bleed fluid can be recondensed and if not, vented to the fuel tank.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp Drive