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  #11  
Old 02-13-2018, 05:16 AM
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DanH DanH is online now
 
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Quote:
Originally Posted by VA Maule View Post
So here's the question, what's the point of coils.
It's a good question. There are enough contributing variables that I suspect there is no absolute answer. The conventional thinking is that they serve as a reservoir...if some small amount of fuel gets pushed out into the vent line, it may trap there and get pushed back in later.

Sometimes it is reasonable to try a new thing by first assessing the possibility of harm. If the experiment can't hurt (i.e. unquestionably satisfies the primary requirement), a trial installation to see if a secondary factor is better or worse becomes a reasonable choice. So, if you're sure a no-loop vent will in fact vent the tank, give it a try. If it dumps too much fuel on the ramp when parked in the sun with a full tank, it's easy to drop the root fairing and retrofit as many loops as desired.

Be aware that standard RV-8 vents, even with a high point all the way to the top of the gear towers, will barf fuel if the tanks are filled in the sun. A no-loop vent would just be a much shorter version.

I'm told some states and/or airports have become militant about fuel spills, so I may make a simple addition which should eliminate the problem. It's an 8oz header tank added to the vent line in the very top of each tower. It won't change venting, but it should temporarily hold expansion fuel, while allowing air bubbles to pass through and out the vent.

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  #12  
Old 02-13-2018, 05:55 AM
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f1rocket f1rocket is offline
 
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Quote:
Originally Posted by mfleming View Post
Sooo...is this the rocket style vent??

Yes. That is a picture of my first F1 Rocket wing going together.
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  #13  
Old 02-13-2018, 06:02 AM
bobnoffs bobnoffs is offline
 
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good idea dan, will be very easy for me to put this into my venting on the bulkhead.
my tank is a custom behind the seat of a 12. vent line is at front pilot side of tank top side. the top right side has a 1/4npt flange in it also. painless to put a small valve in that flange. like a valve you find on the bottom of an air compressor tank. never a problem to have the vent not doing its job in flight...........if you could keep it together enough to remember to open the valve!
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  #14  
Old 02-13-2018, 06:05 AM
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maniago maniago is offline
 
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Default Couple of solutions

Theres an old thread around here (unfort couldnt find it just now) where a check valve is T'ed into the vent line. I did this - T'ed into the top of the vent line before it turns down and overboard. The check valve allows air in, but not vapor out and is hidden inside a wing bay so its protected. A mesh screen over the end of the check valve prevents trash from getting into the tube. I used a check from McCarr Master that has a very low opening vacuum (I think its .5 psi) and is speced for vapor as well as liquid fuel.

Also, when I went to punch the skin hole for the vent, I didnt like just the tube sticking out, so I went with a JDAir streamlined vent, which also incorporates a secondary ice hole. http://www.jdair.com/fuel-vents-for-...s-rv-aircraft/
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Last edited by maniago : 02-13-2018 at 06:10 AM.
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  #15  
Old 02-13-2018, 06:39 AM
pa38112 pa38112 is offline
 
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Quote:
Originally Posted by DanH View Post
I'm told some states and/or airports have become militant about fuel spills, so I may make a simple addition which should eliminate the problem. It's an 8oz header tank added to the vent line in the very top of each tower. It won't change venting, but it should temporarily hold expansion fuel, while allowing air bubbles to pass through and out the vent.

I like This !!! I am thinking the tank would need to have slightly more volume than the length of vent line leading to it. I am tired of linemen telling me I have a leak. I once came back to find two buckets under my vents...
Have you identified a supplier for the header tank ?
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  #16  
Old 02-13-2018, 06:46 AM
rv7charlie rv7charlie is offline
 
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Have any of you guys who are talking about vent check valves and/or shutoff valves done the math on the air pressure change from, say, a 30 degree night temperature to a 80+ degree daytime temp, in a partially full tank?

I haven't, but I'd want to know before trapping that air in the tank.

Charlie
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  #17  
Old 02-13-2018, 06:47 AM
bobnoffs bobnoffs is offline
 
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''downside to everything''.........if you forget the conditions are right for your ''header tank'' to be full and you open your gascap.............
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  #18  
Old 02-13-2018, 07:30 AM
SgtZim SgtZim is offline
 
Join Date: May 2015
Location: Crittenden, ky
Posts: 173
Default jd vents on an 8?

I'd really like to have the nice JD vents, but I don't see a reasonable way to use them on the RV-8. I have the fuselage mostly done and the vents per plans pass through the landing gear cover/inspection plates. There is no way to attach and tighten the vent line to the fitting on the JD product without a lot of severe bending of the tubing? Anyone do this? JDair did not sell these for the RV-8 the last time I looked, but now they are for "all RVs", but no specific guidance on how to.

I also would not want a check or release valve anywhere in the cabin, or a check valve in the line inside the tank - would not want to tear apart the tank to fix a stuck valve, and do not want any potential source of fuel vapor in the cabin.



Quote:
Originally Posted by maniago View Post
Theres an old thread around here (unfort couldnt find it just now) where a check valve is T'ed into the vent line. I did this - T'ed into the top of the vent line before it turns down and overboard. The check valve allows air in, but not vapor out and is hidden inside a wing bay so its protected. A mesh screen over the end of the check valve prevents trash from getting into the tube. I used a check from McCarr Master that has a very low opening vacuum (I think its .5 psi) and is speced for vapor as well as liquid fuel.

Also, when I went to punch the skin hole for the vent, I didnt like just the tube sticking out, so I went with a JDAir streamlined vent, which also incorporates a secondary ice hole. http://www.jdair.com/fuel-vents-for-...s-rv-aircraft/
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  #19  
Old 02-13-2018, 07:42 AM
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Carl Froehlich Carl Froehlich is offline
 
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Post The vent must always vent

Quote:
Originally Posted by rv7charlie View Post
Have any of you guys who are talking about vent check valves and/or shutoff valves done the math on the air pressure change from, say, a 30 degree night temperature to a 80+ degree daytime temp, in a partially full tank?

I haven't, but I'd want to know before trapping that air in the tank.

Charlie
Never trap air in the tank. The fuel vent must always vent.

I view the two major risk that will lead to a collapsed tank and/or fuel starvation are:
- Vent clog by insects (mud dauber)
- Vent line block from ice forming on the vent overboard

Ive done two things for this:
- The last few inches of the vent line transition to 3/8 line. The 3/8 line is out in the breeze but the line is terminated on a angle cut, the cut itself has a small piece of aluminum screen epoxied on. This is the mud dauber mitigation.
- The vent line in the wing root (RV-10) or in the line running up the tower leg (RV-8) has a vacuum breaker check valve. Air can go in as the tank sucks, but fuel cannot come out. This is the ice mitigation. The vacuum breaker I use is: https://www.mcmaster.com/#catalog/124/528/=1bjw7gf (Part 5492K51)
Add AN fittings as needed.

To keep fuel from venting out the tank:
- Fill on a level surface
- Fill as the last step before departure.

Carl
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  #20  
Old 02-13-2018, 07:47 AM
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airguy airguy is offline
 
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Quote:
Originally Posted by RV7A Flyer View Post
Rocket-style vents here...500+ hours, no issues other than once or twice, with very full tanks, they "burped" a bit of fuel out when the hangar got hot during the summer.
Same here, just over 200 hours with several flights in rain and I regularly cruise in freezing temps. So far I'm stubbornly refusing to die. In this world there are plenty of "solutions in search of a problem", perhaps it's more effective to concentrate our time and effort on actual problems with a higher likelihood of occurrence. If you're flying in icing conditions in an RV, you've got higher priority problems than worrying about a fuel vent getting blocked. Your iced-up tailplane is going to kill you before the blocked vent does.
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Last edited by airguy : 02-13-2018 at 07:57 AM.
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