REFLECTOR: Fuel System -- Return Fuel Flow

[nmflyer1 at aol.com]

Brian, 


I am using an Airflow Performance F.I. Setup on my V-6. My setup is like this:


Out of the sump


Through the flow meter


Through the filter to a 4-way fitting. 


1 is the inlet line


2 sides of that fitting go to the separate fuel pumps (1 each).


The 4th side of that fitting is for the return line.


Out of the pump(s) the line goes up to the regulator.  


The regulator has: In, Out, Return (return sends fuel below demand & pressure back to the 4-way fitting)


After that, the line proceeds to the FI unit and has a pressure sensor (for the gauge) in line.


This is the way that Airflow recommended for my set-up. They said that it allows for fuel return without creating bubbles in the sump tank. They also said that the small amount of fuel returning to the 4-way right before the pumps would be mixed with "new" fuel, and therefor keep the fuel temps low enough as to not be a problem. 


My set up is a little different, as you can see. Hope this helps. 


Kurt  



-----Original Message-----
From: Brian Michalk <michalk at awpi.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Thu, Dec 8, 2011 3:30 am
Subject: REFLECTOR: Fuel System -- Return Fuel Flow


In my arrangement, I an using electronic fuel injection, with my fuel 
rail running at 45PSI.  I have a Bosch electric pump delivering what I 
think is .7 gpm (I need to verify this), and a mechanical positive 
displacement pump delivering 1.7gpm.

My fuel pressure regulator returns the fuel to the sump tank, which is 
also where the feed line is for the fuel pumps, so the fuel circuit is 
sump->pumps->FPR->sump.  Since I'm fixed gear, my sump is a little less 
than five gallons.

My question is, what are other people doing for their fuel return 
configuration that are using actual regulators.  The vapor return system 
on some of the aviation pumps returns very little fuel, I believe, so 
it's not the same thing.

Is a five gallon sump big enough?  Will it fill up with foamy fuel 
vapors?  This is avgas, not automotive fuel.
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