norm2 wrote:

So, how about this:

Put an injection pressure pump from the left tank to a junction block that
feeds the FI manifold,
another injection pressure pump from the right tank to the same junction
block,
return from the pressure relief valve to a return tank (perhaps 2 gallon
capacity),
there are a pair of solenoid valves at the top of the return header tank.
When the left pump is on, the solenoid valve that allows the fuel to return
to the left tank is open.  When the right pump is on, the right return
solenoid is open.
Place an orificed line around one of the solenoid valves to provide a fuel
path in the event that both solenoid valves die.

Standard pocedure says to only run one fuel pump at a time, but if one of
the solenoid valves would fail, you could run both pumps so as to keep a
return path open.

Now-  with the return header tank you have an option.  You can install a
third injection pressure pump on this tank to give you a 'last ditch supply'
of 20 minutes of fuel or so.  Such that if you drain the left tank, drain
the right tank, you now know that you have a certain fixed amount to find a
place to put down.

Failure analysis-  You can loose any two of the three pumps and still have
power-  right up to the point that the tank feeding that pump goes dry.

All of the tanks are independent of each other, such that a birdstrike that
takes out the bottom of one of the main tanks does not create a drain on the
entire system.

If the return solenoid valves die, the orificed line keeps the pressure from
going to pump regulated pressure, it would return to a default tank.  The
orificed line also serves as a vent for the header tank should you utilize
the third pump in a fuel emergency.

One of the problems with these Bosch FI pumps is that they circulate a lot
of fuel, and returning them to a same side tank all of the time will
overfill that tank.  But with a plan that consideres where the fuel ends up,
I suppose that you could return to one side only.  I like the idea of using
a second FI pressure pump rather than a transfer pump, as it gives you a
backup.

Questions, comments, or concerns?

Regards-
Norm

 
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