I would suggest using a Left/Right/Both/Off valve for a couple of
reasons.
Reason 1#
I have a Velocity that I converted to this. It had an issue when feeding
from both tanks to feed unevenly. The previous owner said he would land, let the
fuel settle out and take off again.
With the new system if one side feeds unevenly, I can fix it from the
pilots seat by switching to the fullest tank.
Reason #2:
You take off and lost or didn’t replace a fuel cap on one side. For the
sake of argument, let’s say it was the right tank.
If you have a cross feed via your plumbing or the valve (Both/Off) the vent
system tries to slightly pressurize both tanks. The left tank with the cap will
be at a pressure higher the the right tank with no cap. Over time the the
difference will push the fuel through the crossover into the right tank causing
the fuel to overboard. Once the left tank goes dry you un-port the fuel pickup
and now you have a right tank full of fuel that you cannot access. With a
Left/Right/Both/Off valve, you can switch to the right tank and access that
fuel. Again, a situation that can be resolved from the pilot’s seat using the
valve.
Reason #3
........ or you could use a Left/Right/Off valve and avoid both
scenarios.