What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fuel tank vents

Larry DeCamp

Well Known Member
The plans suggest a tube up the firewall and down through the floor.

The “Rocket” vent is two coils at the root rib and out the floor.

There is testimony here that pressure under the wing will feed demand for air through a scarfed tube end, flush cut or even a static port shaped tip.

There is testimony here that a “mud dauber plug” can create a visual collapse of the tank skin.

apparently, any fuel that leaves the tank into the vent system will either go out into the air or sit in a tube at a depth of up the the thickness of the wing. And history suggests that pump suction is sufficient to pull air as needed through the liquid without hurting the tank. I assume solid slugs of fuel are not drawn back into the tank, but rather bubbles sneak by through or over the liquid. This logic also questions how a full tank in the hot sun has a place to overflow into unless the fuel in the coils has evaporated previously. Does the fuel ever go back in the tank ?

So why all the tubing artistry, what am I missing ?
 
Coiled up here...

I fought the gear tower route for the fuel vent line and lost terribly. So, instead, I coiled up the vent lines in the wing root (4 coils) per the Rocket system.

It works....
 
Zip tie

As for plugs I now subscribe to the uncut large zip tie. Should prevent mud daubers for entering and will let enough air into prevent tank collapse. I "test flew" one in the vent and did not notice I'd forgotten to remove it until after landing. Didn't notice any fuel pressure problems in flight.

I use red ones :)

Finn
 
So why all the tubing artistry, what am I missing ?

I think with full tanks you are more likely to see fuel coming out the vents with the coiled tubes. Even more so with no coils and just out the bottom of wing roots.

I previously suggested skipping vents through tanks and just a vent out through outmost tank rib and down through outside tank skin. Problems with that would be icing and drag. And of course fluel flowing out if parked with a wing down.

Finn
 
Flyboy vent

Flyboy sells a nice aerodynamic vent with a screen inside. Might be worth a knot.
Looks cool too. :D
 
Flyboy sells a nice aerodynamic vent with a screen inside. Might be worth a knot.
Looks cool too. :D

I got mine from JD Air and they are beautiful.
 

Attachments

  • 23EF21FE-FB22-44CD-BF02-AFF056E0362F.jpg
    23EF21FE-FB22-44CD-BF02-AFF056E0362F.jpg
    106.8 KB · Views: 130
Things tried, and failed

I was concerned about blocking the standard Van's fuel vent path, so I tee'd in a checkvalve at the highest point in the path to break any vacuum. Result was fuel vapor and spittling in the cockpit, so don't do that unless you route the 'in' of the checkvalve overboard also.

It's not unthinkable with 21 gallon tanks to get a half gallon or more of fuel out of a vent if you accidentally fuel to the top with cold fuel and leave the wings in the sun.

Next time I'll try the rocket method.
 
Last edited:
I was concerned about blocking the standard Van's fuel vent path, so I tee'd in a checkvalve at the highest point in the path to break any vacuum. Result was fuel vapor and spittling in the cockpit, so don't do that unless you route the 'in' of the checkvalve overboard also.
.

This sounds odd, as normally the check valve should be closed. I also have a check valve in the line, but mine’s inside the wing root. No fuel smell. Putting the ‘in’ of the checkvalve overboard partially defeats its purpose, if you encounter icing. I wonder if your checkvalve ‘in’ sits in an area of higher pressure than the normal vent?
 
Back
Top