REFLECTOR: Fuel Vent System - 3

[Andrew Ellzey]

John,

I think Bob stated it very well, I also beleive your junction block and check 
valve is too low in your system. I have attached a photo of my vent system for 
your review. As you can see, all of my vent lines are higher than my fuel tanks. 
Hope this helps,

Andy Ellzey




________________________________
From: Bob Jackson <bobj at computer.org>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Sun, January 30, 2011 7:45:01 PM
Subject: Re: REFLECTOR: Fuel Vent System - 3


John,
 
I don't think your in-cabin (back-up) vent is high enough on the inside of the 
firewall -- it need to be up as close to the ceiling as possible (or at least 
the vent outlet line coming out of it), otherwise fuel is going to slosh from 
the tanks, through the block, and out at least the normal main vent line (which 
looks like in your case goes out of the bottom of the fuselage, just forward of 
the bulkhead.  And worse yet, that sloshing could cause even a small amount of 
fuel to slosh out your red check valve into the cabin if the sloshing is 
energetic and cyclic enough to activate the check valve (which should normally 
remain closed unless a vacuum develops in the block).  When the main tanks are 
full, the full level will be at rest only an inch or two the level of your block 
(it will be almost at the of the top of the spar with full tanks).
 
 
Even if the back up cabin check valve isn't momentarily sloshing open (I don't 
see any blue fuel dye stains on the carpet, except a little behind the right 
fitting which looks like a one time occurrence, probably resolved by tightening 
the fitting)  -- then with the block looped so low to the top of the spar, 
you're going to have quite a lot of fuel coming out of the main vent with full 
fuel when you get it sloshing (on take-off or in turbulence).  Your main 
fuselage fuel vent line is also pretty close to the retract openings, so if fuel 
sloshes over the vent block that you show in the photo and out this vent line, 
air turbulence will also probably cause fumes extend out to the sides and to 
come in the retract openings and be smelled by your passengers.
 
I'm confused by the fact that you only apparently have one 'in' and one 'out' 
into your block -- that would indicate to me that maybe this section of the 
plumbing is only venting the sump tank (and maybe the 'overflow vents' that 
you're referring to in each wheel well are the vents for each of the main 
tanks).  If so, those are way too low as well.  

 
I would say you need to:
	1. Extend the routing of the two fuel vent/overflow lines you describe in each 
wheel well into the cabin,
	2. Buy or make a new aluminum block that has four openings to it,
	3. Route your newly extended vent lines from each wheel well into two of these 
aluminum block inlets,
	4. Route the vent line from the sump tank into a third aluminum block inlet,
	5. Route a new aluminum line from the top 'outlet' hole in the aluminum block 
in a loop that goes all the way to the top of the fuselage ceiling, and then 
down out of the fuselage as the main vent out,
	6. Add a 'tee' to this main vent out line down a foot or so from the ceiling, 
and plumb your red check valve off of this tee.
 
This is more or less the way Richard Gentil's photo shows his as being plumbed, 
except his must have all three inlet lines already teed together before going 
into the block, since he shows his check valve coming out of one of the block 
side outlets, and apparently his main vent line coming out of the other.  I 
don't think Richard's routing is quite as good because his check valve won't 
benefit from the vent loop I described that could go all the way to the top of 
the fuselage before heading to the vent hole on the bottom of the fuselage (and 
I think it would be more likely to also vent some fuel in the cabin 
occasionally).
 
You should do as Scott recommends and read the online manual section on fuel 
plumbing and follow it's recommendations.  Did you build the plane or buy it 
from someone else?
 
Just my 2 cents worth...
 
Bob Jackson
N2XF
 

________________________________

From:reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of 
aminetech at bluefrog.com
Sent: Sunday, January 30, 2011 10:48 AM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Fuel Vent System - 3
 
 

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