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  #1  
Old 08-20-2017, 08:48 PM
NYTOM NYTOM is offline
 
Join Date: Jun 2005
Location: Raleigh, North Carolina
Posts: 954
Default 6A fuel venting question

With fuel delivery being the number one problem with early flights of experimentals Im extremely concerned that mine is properly installed.
My question concerns the tank vent lines.
From the print it appears that the vent connection between the tank and fuselage line drops in elevation a little from the tank which Im afraid could cause it to trap any liquid that got into the line before it loops up to the top of the fuselage and back down to the vent. I would think you would want any liquid caught in the line to either drain out the vent or drain back onto the tank. But then I got to thinking maybe a trap is supposed to be there. Any definitive thoughts? Something simple like this done wrong could make for a bad day.
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  #2  
Old 08-20-2017, 09:58 PM
gasman gasman is offline
 
Join Date: Mar 2007
Location: Sonoma County
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As fuel is pulled from the tank, air must replace it or the tank will collapse (suck in). If there is fuel in the line, the tank will pull air past the fuel in the line or pull the fuel back into the tank before it pulls the walls of the tank in..... path of least resistance.

Fuel in the line is OK. Just don't plug it with dirt or bugs.
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  #3  
Old 08-20-2017, 10:45 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by gasman View Post
As fuel is pulled from the tank, air must replace it or the tank will collapse (suck in). If there is fuel in the line, the tank will pull air past the fuel in the line or pull the fuel back into the tank before it pulls the walls of the tank in..... path of least resistance.

Fuel in the line is OK. Just don't plug it with dirt or bugs.
+1

The real threat is icing on the bulkhead fitting that terminates the run under the fuse or muddaubers nesting in the line. I installed a check valve mid-run to vent with >1 psi vacuum on my left tank. It's a one way check valve, so fumes can't enter the cockpit.

Larry
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  #4  
Old 08-21-2017, 07:42 AM
NYTOM NYTOM is offline
 
Join Date: Jun 2005
Location: Raleigh, North Carolina
Posts: 954
Default I guess I was worried for nothing.

Thank you for the responses. I'm connecting these today. Coming from the Great White North I've always been concerned with any place ice could form and cause trouble. I can understand that a little fuel in the vent line wouldn't cause any problems but thought eliminating any chance of a trap might be a good idea. Wasn't sure if the connection drop down from the tank that's shown in the plans was actually required.
In a perfect world our fuel is always water free. Too bad we didn't all live in a perfect world.
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  #5  
Old 08-21-2017, 06:35 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
Posts: 1,114
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Quote:
Originally Posted by lr172 View Post
+1

The real threat is icing on the bulkhead fitting that terminates the run under the fuse or muddaubers nesting in the line. I installed a check valve mid-run to vent with >1 psi vacuum on my left tank. It's a one way check valve, so fumes can't enter the cockpit.

Larry
I also add a vacuum breaker check valve to each tank vent line. The valve resides on the wing root. From the valve I run 3/8" instead of 1/4" line to the exit below the wing. The 3/8" line is large enough that when cut on an angle I can expoxy on a piece of aluminum screen over the tubing to keep the bugs out. So a barrier to bugs, and a backup vent path if I get ice.

Carl
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