Fuel return lines. Don't make this mistake

[clutch22]

I need school'd on fuel systems. I guess I didn't plan out my fuel system selection ahead of time and have been putting it off. (My QB wings are all sealed up.)

I'm wondering if it is possible to retrofit a fuel return to my tanks if I go with EFII. Does the return line need to be plumbed all the way to the outboard end of the tanks so that the fuel in the tank doesn't have pressure against the returning fuel, or does it have enough pressure to just dump it in at the inboard tank rib?

Sorry if this is a dumb question.

P.S. I hope I'm not changing the subject too much on this topic. I just thought if it is possible to retro-fit, then I'm sort of in the same boat you guys are in except I dont have an existing interfering fitting/hole in my rib.

Thanks!

[majuro15]

From talking to Robert at EFII (call him, he's extremely helpful), it doesn't need to go outboard in the tank. A lot of folks are just having the fitting dump into the first bay. I originally had mine going to the second bay just to help cooling the fuel down a bit, but others that are flying say they haven't had any issues.

If you plan ahead, I think you will be able to retrofit your tanks through the sender hole.

[rocketman1988]

You don't even need the sender hole. I have the QB wings and am going to use the EFII system. After discussing it with Robert, I ended up using an aluminum flange with 1/4" NPT threads.

Pick a location, carefully drill the center hole and rivet holes. I used grease in the flutes of the drill bit to capture the chips, along with a vacuum at the drill site.

Debur, ProSeal, and rivet using closed end rivets.

Now you have a 1/4" NPT tank bung that you can install any fitting necessary...

[JDanno]

If you are really worried (paranoid) about cool fuel, fire sleeve the fuel lines through the tunnel. It can get really hot in there especially if the heater is on.

[clutch22]

Originally Posted by rocketman1988

You don't even need the sender hole. I have the QB wings and am going to use the EFII system. After discussing it with Robert, I ended up using an aluminum flange with 1/4" NPT threads.

Pick a location, carefully drill the center hole and rivet holes. I used grease in the flutes of the drill bit to capture the chips, along with a vacuum at the drill site.

Debur, ProSeal, and rivet using closed end rivets.

Now you have a 1/4" NPT tank bung that you can install any fitting necessary...

Thanks. I like this method. And as long as there's no problem with the system pumping the return fuel into the first bay then it should work just fine. What I'm still confused about is if the return line is pressurized through another pump. It looks like maybe the EFII fuel pump is two pumps (1 for the fuel going to the engine and 1 for the fuel return line. Is this right?)
For example, would it have a problem overcoming any positive fuel pressure from a full fuel tank as it enters the tank.

[majuro15]

The EFII pump is a dual pump system with one primary and one back up. Both have plenty of power to overcome any fuel in the tank if the return line is plumbed in somewhere below the fluid level. If really concerned, plumb in a one way check valve close to the tank, but don't think that's necessary.

The flange idea is another option and may be the way I go as well.

[clutch22]

Okay okay. I think I have things straight now. Thanks!

[rocketman1988]

Just make sure that your return line is 3/8" with -6 fittings to match the supply. The EFII system is a full flow system, i.e. the return line needs to be able to flow as much as the supply line.

The location of the return to the tank is non critical, though he said to keep it several inches from the supply fitting.

I don't think there will be any issues with hot fuel in the tunnel as the EFII system continuously flows fuel from the tank and back to the tank.

It is a double electric pump, one primary and one backup...no mechanical pump on the engine.

Don't forget that you will need to use a duplex fuel selector valve...you need to switch the return lines as well as the supply lines. I used an Andair valve.

[Lynnb]

Can anyone help me out with what parts/fittings/tubing are needed for this? Do you just order an extra set of vent line parts from vans?

[rocketman1988]

I think each application is going to be different depending on the system being used and personal preference. In my case, I am using the EFII fuel injection and ignition, so for the fuel system I used:

EFII double electric fuel pumps mounted in the tunnel

Two EFII pre filters mounted one under each seat

Andair duplex fuel selector valve and extension

EFII Pressure Regulator...mounted on firewall

Two 1/4" NPT aluminum flanges, one for each tank return

Closed end blind rivets for flange installation

Firewall bulkhead fitting

Tunnel bulkhead fittings

Fuselage bulkhead fittings

B Nuts and sleeves

5052 aluminum tube for lines

Adel clamps

And a substantial amount of time to fabricate the lines

If I did it again, I would probably just get Tom at TS Flightlines to make all the lines.