norm2 wrote:

<<For instance, suppose your pump puts out 30 GPH and the engine uses 15 GPH
at cruise power.>>

The drawing for the Bosch pump that I found shows that it pumps 48 gallons
per hour.  Are there injection pressure pumps available that have a lower
flow rate?  The other thing to watch is the electrical power consumed by
having multiple pumps running at the same time.

Start with full  30 gals left and  30 gals right, and all returned fuel

goes

to the
left tank, you would start, taxi, TO and climb on the left tank.  This
simplified example ignores the extra fuel burn in climb.

                           LEFT              RIGHT
START                 30                     30
1 hour on L          -15                       0
@ end of 1 ho       15                      30
1/2 hr on Rt        +7.5                    -15
@ end of 1.5 hr     22.5                   15
1 hr on Left          -15                       0
@ end of 2.5 hr      7.5                    15
1/2 hr on Rt           +7.5                 -15
@ end of 3 hr         15                      0
time to look for field, with all remaining
fuel in the left tank, no more fuel mgmt req'd
except landing before you run out.  :-)

If the pump is putting out 48 gallons per hour, you have a net transfer of
33 gallons per hour.  Your schedule then looks like 1 hour left, 15 minutes
right, 1 hour left, 15 minutes right, ...  The large flow rate makes the
timing more critical, or you are going to pump fuel overboard.  Another
solution is to vent the left tank to the right tank, and the right tank to
atmosphere.  That way if you do overfill the left tank, it overflows to the
right side.

The last fuel tank system I designed had dual tanks (300 gallon total) with
a 4 inch diameter crossover hose so that we could fill at 50 gallons per
minute.  These systems are setup to draw from one tank, return to the
opposite side (for heat dissipation), crossover hose between tanks to
equalize fuel level, crossover vent lines at top to equalize air pressure,
and single atmosheric vent (with rollover check valve for upset protection).
If you can buy into a single sump system, a few crossover lines takes care
of the return fuel issues quite nicely.

To further this discussion we really need to get some good numbers on flow
rates of the available pumps.  A pump that flows about 5 gallons per hour
over what the engine consumes at max power would make the timing much
easier.

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