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Message
Al, I
don't believe that what I am seeing is mostly vapor (although there is possibly
some). If your theory is correct then lowering the pressure at the
regulator would decrease the pressure drop and less vapor would be made and the
return flow would decrease. This is opposite what I have
found.
Also,
my totalizer obviously cannot be used to account for my total fuel, but it is a
very useful reminder for fuel management. I start a flight with the
totalizer set to say 40gal. So after about an hour it beeps to remind
me to switch tanks. But since all my return flow goes to the left tank,
switching to the right tank effectively transfers fuel from the right to left
tank. When I switch I set the totalizer to remind me when a particular
quantity of fuel has been transferred to the left tank, usually about 5
gal. It then beeps again in a few min. to remind me to switch back to
the left tank. I find these transferred quantities to be very
representative of the amount of gas I know to be in the right
tank.
The
ratings on those pumps are probably for max fuel consumption. They would
need to make this number conservative given the variability in flow depending on
fuel pressure and other factors.
Also,
even if it is mostly bubbles (foam), there is still 40-80 gal/hr of something
going through that return line so it should be big enough to handle
it.
Dave
Leonard
That may be what
the meter is reading, but (I believe) not representative. I don’t have
the data handy, but I once pulled up some specs on the pump (or equivalent)
that I got from Tracy, and I think about 30 gph was max, and maybe less at
40psi. One reason for exceptional high readings from a Floscan type
meter downstream from a pressure regulator is there are almost always bubbles
in the fuel as some low vapor pressure fractionates flash due to the sudden
pressure drop, especially if there has been some heating as the fuel traversed
the fuel rails.
Al
Wow, is
that true Dave? That seems high, but I have no way of measuring
it. I run both pumps all the time (aside from testing them
individually during preflight), so I guess my fuel stays pretty well
stirred :-)
Rusty
(yes I know you don't need to run both all the time)
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