charles.harbert wrote:

There are at least 4 solutions, but it really gets down to "do you want
individual tank valves, or not". Here are some thoughts on your solutions.

 1)  Make the fuel return to a 'T" connector downstream of the fuel

valve. -   I   I have also heard that the reason for not using
this solution has to do with overheating of the fuel in the line and possible
vapor lock (again, this doesn't make sense to me because the physics say that
this fuel will not get significantly warmer than direct flow fuel).

*The fuel in the line going to the injectors sits in a very warm area and can be
overheated creating vapor lock, especially at low flow (idle) rates. Modern FI
systems increase the bypass flow at low flow rates, then bypass much less at
full throttle. The elec FI pumps are positive displacement (constant capacity)
so they must be relieved, plus pressurizing to 30-40 psi adds heat. I would not
recommend using a "T" because it usually will tend to fill one tank, or the
other, creating an inbalance.

2)  Have the fuel always come from one tank and use a pump to transfer between

tanks.

*This will work, but as Tracy says you need to remember to transfer and then
shut it off. This is a fuel management problem and I think adds additional
complexity to a fairly straightforward problem.

3)  Dual line fuel control valves are available which will return fuel to the
tank from which it came.  I believe that this is the standard aircraft
solution but the valves are expensive and complicated.

*If your going to have 3 gas lines running inside the cabin to the fuel
selector, what's the difference of adding another 3 for fuel return to the
proper tank. I'd bet you can get these valves cheap from an aircraft salvage
supplier. This is the best way for people who like valving.

4)  Build a header tank supplied from both tanks.

*This is the system I have and like (for people who don't want tank valves, aka
"John Denver proof"). The tanks feed a sump tank which feeds twin elec FI pumps
(Airflow Performance), with the return fuel back to the sump tank. No valves and
the tanks drain evenly for good balance. Some planes have a problem with uneven
drainage, so you may need to find out from other owners.  My 6 gal sump tank has
a low fuel warning light. I shut off fuel to the engine by turning off the fuel
pumps. This is a KISS system.

All of these systems will work, and you can decide what you like best. Just make
sure you test the system extensively  before you fly it. A lot of planes have
crashed on t/o because of loss of fuel flow.

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