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Hi George,
The correct way (at least as I see it) is to have some sort of "surge" tank
that is at least a
litre or so in capacity. The return line from the fuel rail dumps back into
the "surge" tank. The "Surge" tank is then connected via a bleed line from
the very top back to the main tank. Normal "Surge" tank volume is anywhere
between 0.5 & 2 litres, depending on the engine capacity.
See: http://www.sdsefi.com/techsurge.htm
The logic of this system is that it allows any air to be displaced out of
fuel rail back to top of the "Surge" tank and then vented back to the main
tank. This is particularly important if the "Surge" tank is run dry, and
is equally important during re-filling of the main tank and re-priming. On
an aircraft system, I'd be making this the lowest point in the system, and
have a false floor and a drain valve at the very bottom to remove any water.
Similar in principle to a "Gascolator" in carby systems.
Additionally, anywhere you get an air lock (as opposed to a vapour lock),
you will have trouble passing fuel, so any unavoidable high points/loops
etc in the system should have some sort of bleed nipple.
Anyway, at the risk of repeating myself, please go and have a look at the
following website. This will be the third time I've posted this URL, but
nobody seems to take any notice ... they continue to ask the same questions
that this site answers most eloquently ...
http://www.sdsefi.com/air27.htm
This bloke knows what he's talking about. Please heed him. Do your fuel
system this way and you won't have a problem. Do it any other way and it
could turn around and bite you on your nether parts some day.
Cheers,
Leon
----- Original Message -----
From: "George Graham" <rx7ez@yahoo.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, June 22, 2005 1:50 AM
Subject: [FlyRotary] EFI Fuel Testing
> Buly wrote:
>
> >Hi George, most of the injectors face down. I think if there
> are >bubbles,
> >they will remain on top of the fuel rail and be returned back
> to >the tank?
>
> Now we begin to approach what I am trying to get at!
>
> If the return fuel is returned to the tank, then no problem,
> however, what happens when the fuel is returned to a sump tank?
>
> My question is: How big must the tank be in order to ensure
> that only liquid fuel feeds the fuel pump, hence no vapor lock.
>
> George Graham
> Mazda Rx7ez N4449E
> Homepage <http://bfn.org/~ca266>
>
>
>
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