Just a cautionary note, dealing with unequal feed and feedback to tanks. It
  seems like you are feeding your engine directly from the in tank pumps . I
will  assume that you will be using only one pump at a time for tank
selection. Actually, it doesn't make any difference one or both

I'm not sure what you are doing with your vents,  however to assume  that
each tank has the same pressure in it and the resistance of the plumbing is
identical for each tank may lead you to a pile of trouble. You have teed
your  return to go beck to each tank assuming that the pressure is the same in
each.  It usually is not and what you will find is that  the tank with the
lower  pressure (from ram pressure to the vent, lack of same, or negative
pressure  (caused by improper installation) will fill from the tank with
higher
pressure
will get the return flow at a greater rate, as well as receiving fuel
this phenomena will give you unequal and seemingly capricious fuel quantity
(weight)differences as you fly



  You can't assume that they will equalize. This problem has
plagued many of the  "real" plane manufacturers.

Your non-return valves serve little purpose as the tanks will try to
equalize, all things being equal (but not!!) through the return and equalizing
lines.

furthermore, if the one-way valve, in either pump fails, for what ever
reason, that malfunctioning pump will act as a pressure regulator and
you will be pumping fuel
from the good pump and tank through the bad pump into the bad pump tank
draining  the good tank, filling the bad tank and possibly blowing that fuel
out of the  vent (when the tank gets full) but most importantly, reducing the
fuel system  pressure, to the engine, which may cause your engine to go to
sleep. This, in my  mind, is a major safety factor with that design.

Your system, although logical will probably suffer the phenomena of
constantly unbalanced fuel load (if you run both pumps at the same time) and
ambiguous fuel quantity understanding of what is in what tank (as it will  be
constantly shifting, in flight)  not in your control. This is not a good
thing for longer flights or flights where cognition of fuel quantity and
location may be critical.

Additionally, the way you have it situated, if you are using one pump at a
time, a pump failure would result in immediate engine stoppage.

Additionally, additionally, with a 1/2" equalizing line, when you bank, or
fly in an uncoordinated way (never happens) you will be loading the lower
tank  with fuel (weight) further adding to the unbalance-- If you fill your
tanks, and  let the plane sit on the ramp, not perfectly level, your precious
and expensive  fuel will drain out of the low tank and fuelinate on the
ground through the  low tank vent.

That being said,

Some suggestions: as a place to start

1. have low pressure pumps (or gravity from your tanks) feed into a
central sump tank from which your fuel is pumped into the engine.
2. tie all of your vents together (with some sort of manifold and run your
vent lines (to the exterior) from this manifold. (sump tank too, if you
decide  to use one). This technique will go a long way to equalizing the
pressure  between your right and left tanks.
3. dump the equalizing line, if you are using a sump tank.-- or make it a
smaller gauge if your are married to it
4. forgetting the shutoff valve has a couple of consequences, primarily,
you probably won't get it certified if you do that (you can always put one in
  and not use it) secondly, and more importantly, depending on the
arrangement  (gravity-wise), should you have a less than successful landing,
is
there
any  chance that the fuel will continue to flow (even at a low rate) to a
potential  fire location.



 Rich


The above is a kluged together correction of my previous post. I hope
I didn't just repeat it without the corrections.