----- Original Message -----
From: "Marvin Kaye" <marv@lancaironline.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, March 15, 2003 9:42 AM
Subject: [FlyRotary] Re: Fuel Injection


> Posted for "sqpilot@earthlink" <sqpilot@earthlink.net>:
>
> >The regulator controls the pressure in the entire
> fuel
> > rail system, not just the point it is hooked to.  It regulates by
bleeding
> > off enough fuel to reduce system pressure to the desired point.
>
>     Hi, Tracy....thank you for that detailed explanation.  The light
finally
> came on, and I understand it now. Unfortunately, I have only had
carburetors
> in the past, and the EFI is all new to me.  One last question came to mind
> as I was imagining the fuel returning to the sump tank.  Is it normally a
> large volume of fuel that returns to the tank, or just a trickle.  I ask
> that because I need to consider how large of a sump tank to incorporate
into
> my fuselage.  Thanks again, Tracy.    Paul Conner
>


Hi Paul,

    Here is my perspective on size of your sump tank.  I used a quart size
sump tank mounting on my firewall to return my unused fuel from the pressure
regulator.  It has worked fine for me, however, I would recommend:

1.   As large a size as feasible and not smaller than one gallon (larger
gives you more of a heat sink)

2.  That the Sump tank  be located outside the engine compartment or if not,
at least, make certain it has lots of cooling air (blast tube).

3.  Also, I would make certain I had a boost pump to put pressure in the
sump should it start to show signs of the fuel becoming heated (percolating,
fluctuation fuel pressure, etc.), probably with a larger sump this would not
be necessary.

4.Also, the feed from the sump to the EFI pumps should be such that the
pumps have fuel at their inlets at you minimum fuel conditions (in other
words the pumps should be as low as possible or slightly higher than a
gasolator (if you use one to trap water)) as pumps like to push fuel not
suck it {:>).

Since the returned fuel has been heated by its passage through the fuel
system, the fuel in the sump pump will accumulate this heated fuel and on a
hot day (with my small quart size sump mounted on the firewall) I can see
indications of it wanting to percolate.  Turning on my boost pump precludes
that from happening, but with a larger sump tank located elsewhere, there
probably would not be any tendency to do that.

        Even though my setup works fine for me, returning fuel to the main
tanks is of course the most desirable route if feasible.  If not - a sump
will work, just need to be carefully thought out.

Ed Anderson