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Vent line- a different way

RV7Guy

RV7Guy

Well Known Member
Some time back I remember seeing where some people had coiled the vent line tubing and kept it in the wing root area. The vent fixture was attached to the wing root fairing. It looks like a simpler alternative to the traditional run.

Anyone have information on this method?
 
Darwin,
I installed the fuel vents similar to the Rocket method. Due to the shorter skin overhang I riveted a piece of 063 for mounting the bulkhead vent fitting. I then drilled a clearance hole in the root fairing that goes over the vent. This allows the fairing to go on and off without having to disconnect the vent. If you do this I recommend temporarily attaching the fairing first to find where the holes lie and locatie the vent between attach points. I also drilled a # 60 hole in the top of the coil nearest to the fuel vent to act as an alternate air source in the event the vent became obstructed. I haven't flown yet, but have had the tanks full of fuel and run the engine. The vents work fine.

 
Just what I was looking for

Hi Rocky,

Thanks. This was exactly what I was looking for. Nice tip on have a secondary mounting flange. I'm going to do it this way.
 
It will drip...

.....much sooner this way. Van raises the top arc of the lines much higher his way. When you fill the tanks in the sun it will start dripping very shortly afterwards.

Van's way has the top of the vent line 18" higher than the coils.

Regards,
 
Actually, no drips . . .

pierre smith said:
.....much sooner this way. Van raises the top arc of the lines much higher his way. When you fill the tanks in the sun it will start dripping very shortly afterwards.
Van's way has the top of the vent line 18" higher than the coils.
Regards,
Click to expand...
I did mine this way and haven't had a drip yet - with temps into the 90's and full tanks.
 
Long term?

Seems like a way to have some gummy old fuel remaining in the vent coils forever, though I could be wrong.........
 
No long term problems...

captainron said:
Seems like a way to have some gummy old fuel remaining in the vent coils forever, though I could be wrong.........
Click to expand...
Since the vent line is where the air comes from to replace the fuel being used, they will clear out every time you run on that tank.
 
How about a check valve like the Lancair's use? Makes for a tidy installation, no coil of tubing to deal with. There's only a little dribbling when the tanks are full since the only fuel that can pass thru the check valve is thru the .040" bleed hole in the check valve's flapper door.
 
Status Update on Vent Coil

I posted some pictures of my install in the original thread. I thought folks would like an update after 200+ hours of using this installation.

It does run minor amounts of fuel out the vent when full and it's hot. Pierre is correct, at least for my installation anyway. Bob is also correct, I think some small check valves are in order here to cut the amount of drip down.

Overall, the amount of fuel is not that bad but can be noticable on a hot day, maybe a fuel tester cup's worth. However, I like the install better than running the lines up the side of the cockpit so I am willing to live with it.
 
f1rocket said:
...It does run minor amounts of fuel out the vent when full and it's hot...
Click to expand...
I have the standard vent tube setup on my RV-6, which has black wings. If someone fills the tanks all the way to the top I get a lot of fuel out of the vents if the airplane is sitting in the sun. That expanding fuel has to go somewhere. The simple solution is to leave some expansion space in the tanks.
 
Coefficient of expansion for gasoline - 0.000950/(degrees of change)

Lets say the fuel warms up 20 degrees in your tank, and you have 19 gallons in the tank. To solve for expansion:

ΔV=V0βΔT
ΔV=19gals.*0.000950*20
ΔV=0.361gallons

0.361 gallons, enough to make a mess on the floor if the tank's completely full. I usually fill up to about an inch below the filler neck.
 
Careful with check valves

If a check valve really seals, the expansion has to go somewhere and that could cause problems :eek: I'd rather have the gas come out the vent than take a chance with pressure buildup in the tanks.
Leaving some space in the tank is the best solution.
 
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