REFLECTOR: Fuel Flow Sensor

Al Gietzen ALVentures at cox.net
Fri Jul 1 01:11:58 CDT 2005


 

My setup is a little different than most Velocities. My 173 FGE has a
2-electric fuel pump manifold with an inlet line, engine line, and regulated
return line. The regulator keeps the engine pressure side at 25psi, the rest
"T's" back in before the inlet line but after the filter. 

My fuel Injection is on TOP of my aluminum V-6. All the plumbing is on the
cabin side of the firewall except from the bulkhead fitting to the fuel
servo. 

 

 

This doesn't address the issue of where the flow sensor would work the best;
but addresses what I think is a much more important issue.  As I understand
your system, you have your EFI pump(s) recirculating the fuel through the
engine compartment and fuel rail and directly back to the pump inlet; and
you have the pump drawing the fuel through a filter, and proposing the
addition of the flow sensor upstream of the pump.  

 

I also expect that you planning to use automotive fuel; and that you will be
flying at hot days and high altitude.  Others have raised the issue of
potential vapor lock - I would raise that to an ALARM.  I think there could
be a concern with avgas, but definitely a concern with mogas.  Mogas is
formulated with higher vapor pressure.  Even at room temp, mogas components
can flash to vapor at about 9-10 psia (altitude of about 14,000'), so need
to assure that you have positive pressure to the pump inlet.

 

I would recommend a couple of rules of thumb on a recirculating EFI mogas
system.  Return the fuel to a sump of a couple of gallons or more to avoid
temp rise, and make sure there is not going to be a situation where the pump
is going to have to "suck" fuel. Filters upstream from the pump should best
be no finer than a fine mesh screen, and in our case, best upstream from the
sump tank.

 

I'll get off the soapbox now.  It's probably past my bedtime.

 

Be safe.

 

Al

 

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