[f1rocket]

I have a question for anyone that has installed the Andair fuel valve that has the fittings for the fuel return line. Do you connect the fuel return line to the valve and the fuel valve sends the fuel to the opposite tank selected?

Or, do you have to run return lines from the valve to the tank to return the fuel? I hope it's not this way because that would seem extra complex. My hope is that the valve handles this internally.

Can someone shed some light? Thanks.

 

[RV7Factory]

Randy,

I have only researched the Andair duplex valves while designing my fuel system, so I have no hands-on knowledge. With that in mind, my understanding is that this particular Andair valve is essentially 2-valves stacked on top of one another, one for the feed, the other for the return. This requires seperate return lines back to the tanks, and is intended to return fuel to the tank from which it was drawn. Andair recommends against returning fuel to a specific tank (or opposite tank) to prevent overfilling the tank and possibly venting fuel.

If I am wrong, someone please correct me.

 

[DGlaeser]

andair duplex valve

RV7Factory is exactly correct. I have an Andair Duplex valve for my FI Subaru engine.

You will need to install return lines to each tank. Even if you've already built your tanks, it's not a super pain - quickbuilders do it all the time. Then you need to run the return line from the valve to the tank. It's not complex, just more work

You wouldn't want fuel returned to the opposite tank - if you start out with full tanks that would cause all returned fuel to be vented overboard. The easiest system, operationally, is to return the fuel to the tank in use.

 

[KPmarc]

To what end?

Randy:

What are you using the return line for? This makes a big difference.

If it's for routing the return from the purge valve back to the tank, you can have it either way--sending the fuel back to the tank from which it came or to the other tank. Really doesn't much matter because you won't be "exchanging" a lot of fuel, at least not enough to create a problem overfilling the tank that the purge is feeding into.

If it's for a return system like you need on the new ECI injection system, then you definitely should have the fuel go back to the same tank it's coming from. That system, like the Continental setup on which it's based, returns a given amount of fuel and vapor to the tank. I forget the amount, but it's probably 2-3 gph.

Older Bonanzas with inboard aux tanks had a funky setup as a result of the fuel return. The vapor would go back to the left tank when the left main was selected; and it would go back to the right tank if the right main was selected. But when drawing from the aux tanks, all return fuel went back to the left tank. As such, you had to run the left main down to half or less before using the auxes. When the auxes were depleted, the left main would be nearly full again. Free fuel!

Of course it doesn't have to be hard. On my Sportsman I have a Left-Both-Right single-plane selector. The purge return is teed into the right tank's feed line through a one-way valve. When I purge during a hot start, I simply switch to the left tank. Fuel goes from the left tank, through the selector, through the firewall, up through the boost pump, engine-driven fuel pump, servo and right up to the purge valve, then backward through the tee and then on up to the right tank.

I was initially skeptical that the purge system was worth the trouble. Until, that is, I put my hand on the exposed aluminum lines during a hot-start purge. I could not hold my hand against the lines the fuel was so hot. Amazing.

Hope that helps.

MC

 

[f1rocket]

I'm building a new Rocket and have the dual Andair valve. I'm trying to simplify the return line routing for the purge valve. My plan would be to just put a tee in each input line to the valve and run each return line from the valve directly to the appropriate tee in each input line, as opposed to all the way back to the tank. I was just hoping that the fuel valve kind of did this internally.

On my current Rocket, I do not have the dual Andair valve. For my purge line, I just teed it into the feed line from the right tank. This means that when I use the purge valve for a hot start, I should have the fuel selector on the left tank. It's not a big deal but I'm always looking for better ways to do stuff.

 

[KPmarc]

Simpler = better

Makes sense. I would say the way you have it now, in your current Rocket, is the simplest and most effective. Only downside--the ONLY one--is that you have to remember to switch to the non-purge-return side during the purge process. I would also make sure there's a check valve in the purge line, else you might end up with a wet line forward of the firewall that you can't shut off.

Yes, I know that with a low wing tank the fuel won't want to come up and forward. But I'd do it anyway.

As I said before, you're not running enough through the purge system to make overfilling a tank much of an issue.

MC

 

[f1rocket]

I would also make sure there's a check valve in the purge line, else you might end up with a wet line forward of the firewall that you can't shut off.MC

That's an excellent find. I never really thought about this but you are absolutely correct. I'm going to order a check valve and retro fit my existing installation. Thanks.

 

[KPmarc]

And I found it the hard way...

We didn't fully appreciate the significance of a check valve on a high-wing airplane until removing the return line from the purge valve assembly on the engine. Hmmm....why is fuel streaming all over the place?

I ended up using a part from McMaster-Carr. Search on part number 7768K26. Or check out catalog page 436.

--Marc