Duplex fuel valve

[RV7A Flyer]

Originally Posted by Bevan

I have the Andair duplex valve and it is my understanding that there is no ?dead? position between the left and right positions. There cannot be for safety reasons. This being the case, putting the selector in between left and right would cause feeding from both.

This sounds...unsound. There either is a "Both" position/detent, or there isn't, and fooling around with it doesn't seem like a great idea to me.

Do it right, or don't do it all.

[Bcone1381]

Originally Posted by Andrew Anunson

It doesn't exist (or at least it shouldn't) for a good reason.

I don't think a Both setting makes sense with a duplex valve (valve with returns). Where is the return fuel going to go when you have the valve set to Both? It might go to the left or to the right... you'll never really know.

If you are going to run a system that requires a return (such as EFI) then you need to be in control of where the return fuel goes (which should be the tank it came from).... therefore you need a Left / Right valve.

Bob says (Patrol Book) if using a L-R fuel selector, take offs and landings should be made with the tank at least 1/2 full and no significance slip to avoid unporting the selected tank. I would make that a limitation in my airplane.

I know you don't want to use a header tank. You might consider the simplicity it can give though. Weighs less than 1/2 a tank of fuel. Allows for a simple on-off fuel selector valve.

I look forward to seeing what you decide.

[svyolo]

Hi Bcone;
I wish I had more experience with light aircraft and their systems. I really don't want to go off on a tangent.
It seems to me that a header tank is either designed for a specific purpose (aerobatics) or to make up for some fuel feed deficiency. The BH fuel system looks like it really needs to be run in "Both" for maneuvering flight, especially close the the ground. Right now I am leaning towards using "Both" for TO and landing, and using L or R if I need to balance fuel. I will probably be returning 55-70% of the fuel flow during cruise flight (13-18 gph returned to tanks).

If I use a header tank, I would probably still use BOTH for TO and Landing, even though the header tank gives me some margin for poor fuel feed from the main tanks. And then I would still have to balance the fuel in flight with L or R.

Seems to me to be the same amount of effort on the part of the pilot, but maybe I am missing something.

Newton responded to a couple of emails. They said their V9 valve is available and were trying to lead me in that direction vs the V4. Their reason was that the V4 "leaks" a little to bleed off pressure for a ROTAX requirement after shutdown. I don't see that being any problem with a constant displacement pump.

I think either the V4 or V9 will work.

[svyolo]

And the other 49% of me wants to mount a header tank.

[svyolo]

So, there I was. Down to 15 gallons of fuel. Decide to do a half a dozen touch and goes. Left pattern. Fuel selector in BOTH. Every time I turn, the high wing (right wing)is feeding 25 gph. The engine is using less than half of that. It is returning the rest to the left wing. The left wing is getting heavy very fast. I can't select the LEFT wing tank as it is the low tank in turns in a left hand pattern. I ask the tower for a right hand pattern. They ask why. I say "fuel balance". They say "Huhhhhh?"

I think I am up to 90% in favor of a header tank.

[Andrew Anunson]

Or just install a standard duplex valve. Manage your fuel and don't give "both" another thought.