----- Original Message -----
From: "Neil Kruiswyk" <neilak@rogers.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, February 12, 2004 5:57 PM
Subject: [FlyRotary] Re: EFI Fuel Pressure


> Scott,
>
> You're only dealing with a column of fuel 40" high and not the
> weight of all 5 gallons.  Assuming the return line is 3/8th inch ID
> (which would be on the big side), 40 inches works out to a grand total
> of 4.4 cubic inches of fuel, or, a grand total of .11 lbs/sq in.
>
> (Did I remember my grade 11 math correctly?)

Close, but no cegar!

The 40 inch high collum is all that counts.  Makes no difference if it's a
3/8" line or 3" line.  The pressure at the bottom of the colum would be just
under 2 psi.  But the column that applies here is how high above the
pressure regulator does the return fuel have to go.  If you plum it to the
top of the tank, it will have to lift the fuel that high always-very
consistent.  If you plum it to the middle or even the bottom of the tank, it
only has to pump it to the existing fuel level.  Sure, it will very but only
by the pressure differential of the vertical height of the tank at the rate
of about 25 inches per psi.

Bob Darrah