REFLECTOR: Fuel System -- Return Fuel Flow

[Alex Balic]

HI Brian-
I have the same setup on my Subaru- but with 2 electric pumps and not
mechanical- the fuel returns to the sump- I know that there has been
discussion about foaming, but I have not experienced this on my limited
running, probably, the liquid fuel is sufficiently more dense to force the
vapor out through the vent if there is any- you might want to temporarily
install some clear tubing on the return line ( the pressure is low) and see
what is going into the sump. 

Alex

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brian Michalk
Sent: Thursday, December 08, 2011 9:32 AM
To: Velocity Aircraft Owners and Builders list
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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