Don't  forget that you have to account for the returning fuel as well.
Total
flow in my system is 40 gal/hr but depends a little on where you set  your
fuel pressure.  If I turn on both fuel pumps at once, my total  fuel flow
is
almost 80gal/hr.

Dave Leonard

OK,

What are you really monitoring here.

If it is fuel pressure, you want your sensor as close to the endpoint
of  the
run as possible. Any other place is subject to question as any restriction
anywhere in the line from where the sensor is, to the carb, fuel rail, or
spider  will give you a fuel pressure reading, but you have no idea of if
that
pressure  is really doing anything for you.

With respect to the flow scan, measuring the flowage out of the tanks, as
has been stated is useless. Your sender should be, again placed as close
to the
end point as possible for any reliable results (ie leakage etc) Some fuel
injection systems shunt the fuel back to the tanks before going to the
fuel rail
or spider (Airflow) and some give total flow to fuel rail and a relief
valve
at  the end relieves itself to the tank. In the latter case,m what you
need
is an  additional flowscan unit on the return line and some logic to
subtract
the  return pulses from the supply pulses, and your reading will be
accurate.
Ron  Mowerer of Rocky Mountain instruments, I believe, has such logic
already
in  production.

If you are going to measure something, make sure that the indication that
you are getting means something. Otherwise, why measure.

Rich (first posting on this list)

Unfortunately, Rich, you couldn't be more wrong.  I have a flow-scan in the
fuel return line, and have found it to be an extremely valuable sensor.
True, it does not tell me how much fuel my engine is using, better to use a
computer to do that based on injector cycle.  But the sensor in the return
line does give me a wealth of info about the function of my fuel system.

Output from my fuel pumps (the ones that Tracy Sells - and similar to the
stock mazda pumps) is supposed to be constant given constant head pressure
and line voltage.  If I start to accumulate stuff in my fuel filter, it
shows up as decreased return flow long before it becomes an issue for flight
or would be picked up on fuel pressure or a differiental fuel flow system.
When my fuel pump failed, it was a gradual failure that was manifest by
decreased return flow.  I was able to switch to the back-up pump before
having any loss of fuel pressure (which could have caused an engine out on
final approach, for example).

Decreased return flow could also be an indication of a leak in the system.
If switching to my back-up pump did not solve the issue, I might have
suspected a leak and landed at the closest airport.

Having that sensor there lets me check the health of both fuel pumps and the
fuel filter during run-up.  I really had no idea the sensor would be so
valuable when I installed it - but I installed it because it come with my
RMI engine monitor.

That sensor also helps me with fuel management because of an unusual trait
of my fuel system - all return flow goes to the left tank (A system that
many advise against, but has worked well for me and was much easier to
install.)

All of that is beside the point, however, because the point of my post was
to point out that just because your engine is using 10gal/hr, you still need
3/8" line because it needs to be able to flow 40-80gal/hr if you are using
the return flow type system.

BTW, I HIGHLY recommend the return flow type system for aircraft use.  Using
such a system virtually eliminates any possibility of problems with vapor
lock or water contamination.  Those are otherwise significant problems in
aircraft, especially if you use mogas like I do.

Paul, thanks for asking.  I'm reinstalling the empenage as we speak, then
the final project is making a new empenage fairing.  Engine is rebuilt and
installed with the new radiator.  I have an oil shut-off valve on the turbo
oil inlet in case the turbo lets go again I can just shut off the oil feed
and keep flying n.a. if need be.  New interior is finished, lots of touch up
paint, fixed a lot of minor issues I discovered on the thorough disassembly
and re-build.  Nice big cowl flap in place, and a muffler. Lots of cosmetic
improvements. Moving to the airport soon and will be flying again by the end
of Aug.  The guy I hired to paint the plane ran off with my money, I was
lucky to get my wings back at all.  Going to a real paint shop in Nov.