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Vapor return line (low pressure system)

hohocc

Well Known Member
I'm getting to the tail end of my fuel tanks and to keep open the possibility of using mogas it would be wise to have a vapor return line. I'll be using a Rotec tbi so it's a low pressure fuel system.
According to 27 years of the Rvator this ideally should go back to one of the tanks, so needs to be dealt with before closing the tanks.
Using the search function hasn't found much (maybe the wrong search terms used), but would anyone be able to suggest some part numbers for fittings required at the tank, and while you are at it, at the point just prior to the carb/tbi?
Thanks in advance!
 
I ran a return line on my 6. Don't use mogas, but it helped to circulate cool fuel through the system before a hot start. I ran mogas once at 90+ * and this saved my bacon. It was sputtering pretty good before I opened up the return to get cooler fuel in the servo.

Just run a -4 line back to the tank with a valve somewhere in line and reachable by pilot and just put a -4 AN bulkhead fitting in the tank, sealed with proseal. I tapped the return right at the entrance to the servo. Actually, I tapped in there for fuel pressure and take the return off at the pressure sensor. My return runs through an .040" orrifice to ensure that the fuel pump can fully deliver the engine in case I leave the return open. This means it takes a bit longer to flush fuel, but is much safer.

Larry
 
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You're smarter than I. I am also using the rotec TBI, but I didnt install the return line before sealing the tank.

I'm using a restrictor fitting (the same one used on the oil pressure sensor) and then just running a line back to the left tank.

I'm just going to rivet/proseal about a 1/2'' piece of aluminum on the tank and then thread an AN fitting directly onto the tank. I'm not saying what I'm doing is right, but thats what i'm doing and I dont see why it wont work.
 
My buddy is running the Ellison throttle body on his -7 and he just ran an 1/8? return line back to the left tank. Being that small it doesn?t affect his fuel pressure enough to make a difference in the required fuel delivery pressure but it?s plenty to sweep out all of the vapors and hot fuel. It really made a HUGE difference in his hot starts and he doesn?t have to worry about vapor lock during full power takeoffs when the engine is hot. He has his plumbed through a manual on/off valve but I think it would actually be a cleaner and simpler installation to use a simple solenoid shutoff valve. For the most part you?d only have it open if the electric fuel pump is running so you could use the same toggle switch that powers your electric fuel pump to open and close the solenoid. This would also insure that you?re always moving that hot fuel on takeoff and landings without even thinking about opening a manual valve because you?re always going to have your electric fuel pump on during takeoff and landing....and with that small metered 1/8? return line, loss of too much fuel pressure would never be a problem.

Mark
 
Duplex.

We run a fuel system that needs return fuel, just like on the old Conty's. This was done one of two ways, run a line back to a gascolator not far behind the engine or all the way back to a fuel tank. WE chose to run a line back to both tanks and use an Andair duplex valve. This was done after the tanks were built and had been mounted on the wings. We took the tanks off and mounted the flange fitting that you use as a drain valve fitting in the bottom of the tank, to the outside upper corner of the rear face of the tank. You just drill a hole for the fuel to flow back in, drill the rivet holes. clean everything up and Pro-seal it on with pop-rivets. Then run your lines threw the "Z" brackets along the back of the tank. This gives us fuel back to the highest point with as little back pressure and puts the return away from the fuel pick-up so there is more time for the fuel to cool while mixing with the fuel in the tank and also dissipate any air that might be in the returning fuel. The duplex valve keeps the returning fuel going back to the tank from where it was drawn. No accidental over fills that way. Its your call on how you wish to do this, it has been done a number of different ways down through the years. Yours, R.E.A. III # 80888
 
Duplex.

We run a fuel system that needs return fuel, just like on the old Conty's. This was done one of two ways, run a line back to a gascolator not far behind the engine or all the way back to a fuel tank. WE chose to run a line back to both tanks and use an Andair duplex valve. This was done after the tanks were built and had been mounted on the wings. We took the tanks off and mounted the flange fitting that you use as a drain valve fitting in the bottom of the tank, to the outside upper corner of the rear face of the tank. Yu just drill a hole for the fuel to flow back in, drill the rivet holes. clean everything up and Pro-seal it on with pop-rivets. Then run your lines threw the "Z" brackets along the back of the tank. This gives us fuel back to the highest point with as little back pressure and puts the return away from the fuel pick-up so there is more time for the fuel to cool while mixing with the fuel in the tank and also dissipate any air that might be in the returning fuel. The duplex valve keeps the returning fuel going back to the tank from where it was drawn. No accidental over fills that way. Its your call on how you wish to do this, it has been done a number of different ways down through the years. Yours, R.E.A. III # 80888
 
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