I have a backcountry sc kit and i`m getting ready to cover the wings now. An a&p friend mentioned that we should run a vent line with a check valve from the 1/4 in. hole in the top front side of the tank out to the wing-tip for better venting. i plan to use the vented fuel caps so would this be necessary?
fuel tank vent
- Thread starter kirkangus
- Start date
100 series Cessnas run a line from the fuel tank (with a one way valve in line)
to just behind the wing strut positioned in such a way that it won't force water
into the tank if it is raining but still add positive pressure to the fuel
tank. The one way valve keeps fuel from running out if the wing tank is
full or at an incline... That system seems to work well to me. They also
have a 3/8 line from tank to tank to equalize pressure.
MNSC360
to just behind the wing strut positioned in such a way that it won't force water
into the tank if it is raining but still add positive pressure to the fuel
tank. The one way valve keeps fuel from running out if the wing tank is
full or at an incline... That system seems to work well to me. They also
have a 3/8 line from tank to tank to equalize pressure.
MNSC360
skywagon8a
MEMBER
SE Mass MA6
Don't forget that a vent needs to work in two directions. The Cessnas have a valve built into the cap for this purpose. If you don't have the ability to vent in both directions you could collapse the tank with altitude changes.
If you want to vent it out of the wing tip you should plumb it to vent out the opposite wing. Your vent hole is on the outboard side of the tank. When this is then plumbed up over the top of the tank to the opposite wing tip the fuel will need to flow up hill before it can run downhill to the wing tip. I don't believe that you will need a check valve in this case. This will reduce the possibility of fuel siphoning out if you are parked sideways on a slope. This is the way airliners are built.
If you want to vent it out of the wing tip you should plumb it to vent out the opposite wing. Your vent hole is on the outboard side of the tank. When this is then plumbed up over the top of the tank to the opposite wing tip the fuel will need to flow up hill before it can run downhill to the wing tip. I don't believe that you will need a check valve in this case. This will reduce the possibility of fuel siphoning out if you are parked sideways on a slope. This is the way airliners are built.
mike mcs repair
Registered User
chugiak AK
kirkangus said:
why???????????????????????????????
why not just use a good vented cap like the -18????
WhiskeyMike
MEMBER
West Boxford MA
fuel vent
Just complicating the simplest and most reliable system. Fuel vents in wings with check valves - like in 4 tank LR Scouts, can malfunction. Atlee's vented caps are the end of any problem. Bugs can get into more sophisticated fuel vent systems and cause fuel starvation.
Just complicating the simplest and most reliable system. Fuel vents in wings with check valves - like in 4 tank LR Scouts, can malfunction. Atlee's vented caps are the end of any problem. Bugs can get into more sophisticated fuel vent systems and cause fuel starvation.
DW
Registered User
pacific northwest
So your flying along with just the two caps vented and the cap on the tank your useing plugs --the engine sputters and you switch tanks and fly on---So now your flying along with vented caps and a crossover vent tank to tank and the engine sputters so you change tanks ---OH S!#t one of the caps has been plugged and you had no way of noing.
Then there's the---parking on a hill with the crossover vent--yea I know put a valve in it. I would think you would be better off with two vents on each tank no crossover.
Then there's the---parking on a hill with the crossover vent--yea I know put a valve in it. I would think you would be better off with two vents on each tank no crossover.
Works fine for me... other than using SS vented caps (from FAD, not the candy cane ones) my fuel system is 100% stock as it has been for all of its 2057 hours. The only problem I ever had was with the stock caps when a gasket went bad once and it messed some fabric finish up from the unnoticed fuel drool. New caps fixed that.NimpoCub said:
bob turner
Registered User
We had one Super Cub with problems on one tank. Investigation of the machined aluminum cap showed no blockage, and a number of sharp IAs looked at it. Cure was a new cap - I am still baffled.
J-3 needed that little curved "pffft" on top to feed reliably. Provides a positive pressure.
J-3 needed that little curved "pffft" on top to feed reliably. Provides a positive pressure.
thanks guys, so i guess i`m going with the candy cane caps,,,,interesting though,,,,the vent tube on the right wing of my 180 siphons fuel when full for a few minutes during flight,,,nothing serious but noticeable,,,,i usually switch to the right tank and burn off 10 gal or so then it seems okay,,,, that will be another question for later,,,,
Roger Peterson
Registered User
Sweeny, Texas
Only problem I have had with the curved 1/4 inch vent tubes on the gas caps is when someone puts one on backwards, it only takes 15 min to run it dry of fuel.
Roger Peterson
Registered User
Sweeny, Texas
But by unhooking your seat belt and getting as close to the sky-lite as possible, you are able to see the stream of gas heading rearward.
12Geezer2
Registered User
Eau Claire, WI
A friend called one day to tell me his J-4 quit shortly after take-off. He was in a good location so had an uneventful landing although the pucker factor was a bit high. I helped him investgate. Seems he had just installed a new FAA approved VENTED gas cap that was not built quite right and indeed was NOT vented. A careful modification with a small drill cured the problem. NEW parts don't always mean GOOD parts. 
WhiskeyMike
MEMBER
West Boxford MA
fuel vents
At the risk of looking stupid - since when are Cub tanks vented other than in the caps? Once we had a plugged cap vent and the tank tried to collapse. Luckily the fuel came out and the engine ran. Found the cap way beneath the top surface of the wing and when it came off, the tank popped back up. Since then we have Atlee vented caps on everything. If you trust someone else to fuel the plane, and don't check the caps, just look back to the side, and you'll see gas pouring out from the bassakwards caps. If you intend to use any auto fuel in warm weather ever, you'd do well to use the forward facing Atlee caps as well, to keep the fuel flowing nicely. Used to operate an early model Cessna AgWagon with wing tanks, and it quit dead cold all of a sudden one day. Hit the fuel boost and got home. Next week an AD came requiring vented caps. K.I.S.S.
At the risk of looking stupid - since when are Cub tanks vented other than in the caps? Once we had a plugged cap vent and the tank tried to collapse. Luckily the fuel came out and the engine ran. Found the cap way beneath the top surface of the wing and when it came off, the tank popped back up. Since then we have Atlee vented caps on everything. If you trust someone else to fuel the plane, and don't check the caps, just look back to the side, and you'll see gas pouring out from the bassakwards caps. If you intend to use any auto fuel in warm weather ever, you'd do well to use the forward facing Atlee caps as well, to keep the fuel flowing nicely. Used to operate an early model Cessna AgWagon with wing tanks, and it quit dead cold all of a sudden one day. Hit the fuel boost and got home. Next week an AD came requiring vented caps. K.I.S.S.
WhiskeyMike
MEMBER
West Boxford MA
fule tank vents
Hey, now you mention it, if you go to headerless tanks, wouldn't you really would be wise to use FAD vented caps!
DW said:
Hey, now you mention it, if you go to headerless tanks, wouldn't you really would be wise to use FAD vented caps!
FdxLou
BENEFACTOR
Canton, GA
My Smith Cub has 4 fuel tanks. The inboards are 24 gals each and have the fwd facing ram air vented caps(headerless system). The outboard(aux) tanks each hold 12 gals and are a standard vented cap( no raised vent).
When I fill up the aux tanks to the top (12 gals) they vent approx 1 gal overboard. So I only fill them to 11 gals. Anyone else with this setup have a similar experience?
Lou
When I fill up the aux tanks to the top (12 gals) they vent approx 1 gal overboard. So I only fill them to 11 gals. Anyone else with this setup have a similar experience?
Lou
RE87-Zulu
PATRON
Sweetwater, Texas
Yes, caused by a bad gasket on fuel cap, it plugged the vent on cap and caused the tank to collapse a little and fuel stravation on that tank. replaced fuel caps and check condition of caps and gaskets periodically when refueling.
