<<Electric acuators do not give feedback on valve condition and cannot
overcome a

bit of extra resistance.  They work until they don't.>>

norm2 wrote:

I am planning on using a high pressure pump (Bosch) one on each tank.  These
have a checkvalve built into the output fitting.  To pump from the right
tank, power the right pump.  To pump from the left tank, power the left
pump.  The return fuel will be  handled with a Pollack 6 port fuel selector
valve.  Take the power leads from the pump to actuate the motor driven
valve, it will return fuel to the tank that is being pumped.  In the event
that both pumps are powered (for takeoff, landing, or one pump failure), the
valve stays where it is put.  There is a switch in the valve that is
typically used to select which fuel sender to display on the vehicle
dashboard.  This switch can be used to indicate to the cockpit where the
fuel is being returned.  Given that you know where you are drawing fuel
from, a simple error light could be configured to tell you that the valve is
stuck and you are returning to the opposite tank.  Even without a warning
device to tell you that the return valve has failed, the failure mode is
that the fuel is returned to one side only (a system that has been proposed
on this list many times, and I believe the system that Tracy uses), or if
stuck in the middle, to both tanks as a tee (also a system currently
debated, one which I think has problems but can be managed as a soft failure
mode).

  An alternative to this would be to use a ganged selector (electric or
manual) rather than relying on the check valves. An electric valve has

been

identified here previously and there is a good manual valve available

from

Andair (in the ridiculous price range mentioned previously).

The side of the electric selector valve typically used on the suction side
could be plumbed to create the option of feeding one of the high pressure
pumps from either tank, or from the primary tank plus a third tank.  But
some of the people on this list get cranked up pretty fast about extra tees
or backup tanks. I guess a person could always put a third high pressure
pump into the system, but that seems a bit much.

  Going with all electric valves in such a system makes it possible to

keep

all fuel system components out of the cockpit which to me would seem to

be

a worthwhile goal.

I have no problems with the low pressure fuel lines in the cockpit, my
concerns are more associated with making the fuel management as clean as
possible.  The 6 port mechanical valve handles it quite nicely, albeit with
a lot of plumbing in a tight area.  I also think there may be a way to use
the $20 Weatherhead valve that is typically used as a suction valve to
handle the return flow, and fit a switch to it to power the appropriate high
pressure pump.  My preference is to use the electric selector valve for
return fuel, and work through the failure modes by looking at failed pumps,
switches, circuit breakers, etc.

Another aspect of this whole fuel system/ fuel management business looks to
be that there are many ways to accomplish the task.  There are probably many
ways that do a good job of managing the failure modes, and will come down to
an individual making some decisions based upon 'what do I think will fail',
and am I comfortable with the backups to deal with that.  Beyond the
acceptable solutions, there are some solutions that work but have less
robust failure modes, and then there are some solutions that work but have
critical failure modes.  Hopefully all of this discours helps people achieve
fuel systems that fall into the robust and comfortable mode.  I do not think
it is possible that this mail list will ever come to consensus and create
the ultimate, robust, everybody warm and fuzzy fuel system.

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