Cap Fuel Vent vs. Plumbed Fuel Vent

[Stuart Grant]

Building a Legacy RV-12, now working on Service Bulletins and Service Letters and then jumping into the Finish Kit. I have a pre-built fuel tank from June 2013 that I just opened up to do SB-13-12-19 Fuel Tank Attach Modification and SL-00070 Optional Fitting for Fuel Tank Inspection Hole. Since I am going to be drilling holes and resealing the tank I am wondering if you all think there might be some advantage to modifying the tank for the newer plumbed vent line - IF that is approved and actually possible. Anyone know why the fuel tank venting was changed? Was it something to do with fumes crazing the Lexan rear window?

Thanks!
Stuart Grant
Miami, FL
N412SG Reserved
'53 C-180 Sold 2010

 

[funflying]

I added the vent while doing the service bulletin much like you have mentioned. I know others noticed more fuel smell in the hangar and some talked about being able to fuel quicker, without splash back, with the new vent line.

For me if I’m using fuel from a self-service I have to watch the speed or it will still backup the filler neck and get gas all over. If I’m getting it from a truck I tell the operator to take it easy and no problem. When I use my Fast-Flo system I have no issues with fuel coming out.

Odor in the hangar, well when the day starts cool, and as the temperature warms I smell fuel from the vent but that’s what it should do. I don’t have fuel coming out but the tank is rarely full unless I know I’m flying for a couple hours. I still use my original drilled vented fuel cap also.

 

[Piper J3]

I have an early SN RV-12 with original vented fuel cap. I did the service bulletin to strengthen the tank mounting but decided to keep the filler cap with small vent hole. I now have 840TT with no problems. My reasoning (right or wrong) is the small vent hole will have less air-exchange in the tank when temperatures fluctuate in the hanger, Re: cold nights and warm days. I use Mogas 93E10. Alcohol is hydrophilic and absorbs moisture out of the air. High humidity will aggravate the problem. Best solution is to fly regularly and let water mixed with the fuel burn through the engine…

 

[Stuart Grant]

Thanks Patrick and Jim.

Either way, I will do my best to avoid allowing water buildup. I pumped thousands of gallons of Mogas into my 180 in the days before ethanol.

My tank is open and rivets removed and holes drilled for the Inspection Port. Now waiting for PolyGone sealant remover and a scraping tool. Looking in the tank, it seems like it would be easy to add the fuel vent fitting.

Curious to know why Van's might have made the change. Is the plumbed dual vent line also an overflow in case the tank is accidentally over-filled? Hope someone might remember the history... Thanks

EDIT: Found a great Kitplanes article on the complexity/issues involved in aircraft fuel venting here --- https://www.kitplanes.com/time-to-vent/
Also found that Van's sells a kit to do the vent modification which I ordered.

 

[DaveWelch]

Stuart,
I cannot for the life of me, find the earlier threads specifically about the added vent line. There was of course plenty of discussion, speculation, and opinions about spills, splashes on canopy, and moisture intrusion as well as rainwater thru the filler caps with vent holes.
In my opinion the added vent line is a worthwhile and low risk addition especially if you're in the middle of tank mods anyway. I believe it has save me from more than one "burp" of gasoline onto my canopy (which is much harder to replace if it gets crazed).
3-cents,
Dave

 

[MartySantic]

I added the fitting with a cap to the top of the tank the last time I had it opened but have not plumbed it yet.

 

[Crbunt]

Drilling fuel cap

Not sure if this is necessary with the added vent line but was wondering if anyone has the instructions on how to drill the fuel cap for the RV12? Had to order a new one and they are unvented and the Van's site says they should be modified per section 37. Can't find the section that refers to drilling it to vent it.
Thanks
Rick

 

[MMiller]

If your build complies with, and is equipped with, the additional fuel tank venting system, a drilled and vented fuel cap is not recommended. In this case an existing vented fuel cap should be plugged or replaced with a non vented fuel cap as this was the number one source of water entering the fuel system.

If you have an older and unmodified build that doesn’t have a separate fuel tank vent line, the vented fuel cap modification is required. The screenshot below explains the fuel cap modification and is from section 37, page 7 revision 0, of the plans dated 04/06/09

 

[rvbuilder2002]

If your build complies with, and is equipped with, the additional fuel tank venting system, a drilled and vented fuel cap is not recommended. In this case an existing vented fuel cap should be plugged or replaced with a non vented fuel cap as this was the number one source of water entering the fuel system.

If you have an older and unmodified build that doesn’t have a separate fuel tank vent line, the vented fuel cap modification is required. The screenshot below explains the fuel cap modification and is from section 37, page 7 revision 0, of the plans dated 04/06/09

And if you do have a legacy RV-12 that requires a vented cap because of no separate tank vent, if the cap is always installed with the latch lever positioned at the 6 o’clock / bottom, the risk of water entry is extremely low.

 

[Crbunt]

Fuel Cap

Thanks for all the help. I'm pretty sure mine does have the fuel vent added. It's a 2011 and the previous owner/builder was pretty OCD about complying with any and all updates. I do appreciate the quick reply's...one of the main reasons I'm on this site is the wealth of knowledge I find.
Thanks
Rick

 

[MMiller]

And if you do have a legacy RV-12 that requires a vented cap because of no separate tank vent, if the cap is always installed with the latch lever positioned at the 6 o’clock / bottom, the risk of water entry is extremely low.

Scott, I followed that 6 o’clock procedure for 13 years without a problem, until it was a problem, multiple times in fact. The 3 o’clock position is a better option, but the current tank vent design is an even better choice, in my opinion.

Have a look at the attached drawings below showing the fuel cap cross section relative to its installation angle in the filler neck.

 

[Mich48041]

I position the latch lever at 12 o’clock and cover it with a strip of electrical tape.
Water would have to run uphill to enter the cap vent hole. Over 400 hours hobbs time.
The tape has never come off while flying. I have only flown in rain a few times.

 

[Fisherpd]

Careful

I position the latch lever at 12 o’clock and cover it with a strip of electrical tape.

Don't do too good a job blocking the vent hole. It may not vent.

 

[Piper J3]

All this talk about water ingress into the fuel tank.....

PA-12 and some Super Cubs use a pressurized fuel cap.

Or, J-3 Cub with rain/condensation trickling down wire attached to cork float...
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