There are systems that will subtract the fuel return, but dont
bother. Here
is what I recommend. It is what I did an I find it works very well.
Route your SINGLE return line to a tank you consider your 'main'
tank. Not
a headder, but your largest tank. The fuel valve now has to select
only
which tank you are drawing from, but you will obviously be using
your main
tank most of the time. When you select one of the other tanks, the
fuel
then is in essence being transferred to the main tank. That is OK.
Will
transfer at a known rate of about a gallon/min. It is imperative
that you
set some sort of alarm to avoid overflowing the main tank. I
actually have
a fuel flow transducer on my RETURN line, and I set it to remind me
after I
have transferred the desired number of gallons to the main tank.
This is simple and reliable. Only one simple return line, simple fuel
select valve, and only necessitates an alarm for when using one of
the other
tanks.
As a fuel totalizer, use something that tallies the injector
workload such
as Ed Anderson's EFI monitor or Tracy Crooks EM2. I have Ed's and
it does a
very accurat job of keeping track of the fuel.
JMHO
--
David Leonard
Dave -
First:
Thanks for screwing up my "simple" PWM EFI fuel pump plans. Now I
have to return something, somewhere, somehow. I'm still working on
the PWM project though.
Second:
One of the best all-electric solutions I've considered for your
(damned) return line is to use 2 solenoids after the "T" for the
return - one left, one right. The left & right electric switches
control which EFI pump is powered, AND which solenoid opens to allow
returned fuel to flow to the respective tank. More parts, more amps.
Is it still worth it? I'm gonna find out.
In all seriousness, I don't think the PWM controlled EFI fuel pump is
going to be worth the effort & complexity unless used in a RETURN-LESS
system.
However, I want to address the issues you brought up earlier. The PWM
EFI system fuel rail can have a return to the main tank with a simple
inline ball valve. This will be used to purge contaminants and vapors
when necessary. Otherwise it is essentially a return-less system.
Simple. Reliable.
What are your thoughts?
-Vince Orton
Hi Vince,
Can your "returnless" PWM system have a return line.....of sorts. Since
the purpose of the return is only to "burp" the system, you need to pass
air or gas bubbles. Copper tubing for refrigeration purposes is available
in very small inside diameters. On the order of .020 to .040, and in lengths
to 20 feet. The idea in refrigeration is a combination of dia and length
yields a known restriction the freon must pass thru. If a size and length
could be chosen to pass "air" and gasoline at an extreemly small rate--say
a pint an hour at max system pressure-- the return line could be routed to
any tank. A four hour flight would then put an additional HALF gallon into
a tank, likewise on that four hour flight your "in use" tank would be short
a half gallon. Flying to envelop limits that are going to be hindered by a
half gallon over a four hour flight is just not prudent anyway. Dave M
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