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  #1  
Old 02-12-2018, 05:40 PM
bobnoffs bobnoffs is offline
 
Join Date: Jul 2012
Location: n. wi
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Default vent lines again

a month ago i asked about running a vent line with a low point before it ran up to the siphon break. someone posted that it might be a point for ice and i thought that idea had merit. then someone posted about the vent lines in some wings that have one or several loops to prevent leaking fuel and what about ice in those loops. the question about the loops was never answered and i brought it up in another recent thread without any response. so the question still remains to me.........are low spots a danger for icing and what do the builders think of this that have loops in their vent lines. any takes on this would be appreciated.
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  #2  
Old 02-12-2018, 06:20 PM
scsmith scsmith is offline
 
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It would seem pretty difficult to get any water in there. The vent tube starts out as high as it can get in the tank - water would never float up into that corner to get carried into the vent line.

All our vent lines have a low point, at the wing root, before either entering the fuselage for a single big loop or before starting the multi-loop "rocket-style" vent, because of the wing dihedral.

I suppose heavy rain could somehow get enough water into the drain end of the vent line and held in with pitot pressure that as the tank fuel is withdrawn, it could conceivably suck a blob of water in far enough to land at the low spot?

I don't really know, seems unlikely.
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  #3  
Old 02-12-2018, 06:31 PM
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9GT 9GT is online now
 
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The RV-10 per plans vent line comes straight out of the tank a couple inches and then 90* bend down and out of the wing root fairing. No issues with icing there so I don't see why it would be any different in other models.
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  #4  
Old 02-12-2018, 06:49 PM
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Ironflight Ironflight is offline
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We have “rocket-style” vent loops on the RV-3, and aside from burping a little more fuel out if you park sideways on a steep slope, we haven’t had any issues. I was told by a DAR that he refused to license an RV because it had loops for the vent, and I asked what he thought about the Rockets - he was unaware that there are hundreds flying around that way. He said “but what about ice?!”, and I asked how water could get in there (see Steve Smith’s thoughts on that above...I agree), and his response was “well ..... it could!”

Not unless someone drove it there with a pressure line. Impossible? No. Improbable? Yes, in my studied opinion. Many more things that are probable to go wrong in our airplanes....

Paul
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  #5  
Old 02-12-2018, 07:49 PM
cajunwings cajunwings is online now
 
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Default Vent lines.

I fully intend to go with the rocket style fuel vent plumbing on my 9 project. Seems like its well proven. Perhaps as continuing maintenance and to alleviate any concerns about water these vents could be blown out on a interval like annually or semiannually or any time plane flies in rain.

Don Broussard
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  #6  
Old 02-12-2018, 09:29 PM
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RV7A Flyer RV7A Flyer is offline
 
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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.
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  #7  
Old 02-12-2018, 10:46 PM
VA Maule VA Maule is offline
 
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Default Venting?

Pardon my ignorance hear and this is NOT to start a fight. Due to a one piece gear and using a wider gear web because it needs to be somewhat taller for the nonstandard engine I'm using , plan standard vent routings won't work for my build so the " Rocket coils " are my best option. So here's the question , what's the point of coils . The vent is in the highest point in the tank with an air gap unless the tank is overfilled the air gap in the tank will stop any siphon and even if overfilled the resulting vacuum of a sealed ( leek free) fule system will shortly stop the ground based siphon situation. In flight with the vent on the bottom of the wing in the area of high pressure siphoning should not be able to occur. So other than possibly preventing some sloshed venting of fuel in flight what purpose does making the coils do other than a setup like a " P-trap under the sink "?
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  #8  
Old 02-12-2018, 11:07 PM
lr172 lr172 is offline
 
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I believe the risk with icing is at the opening of vent line that is hanging out in the open air. Anything that can get wet from moisture in the atmosphere has a risk of freezing. The fact that ice forms faster on small protrusions makes the small vent protrusions, common on our RV's, a high risk area. I have no concerns about ice in any of my vent tubing, but I have a great fear of ice forming at vent exit out in the free air. For this reason, I installed a check valve and interior vent exit that can only draw air in from the cabin if a vacuum exists in the tank and the main vent is clogged. It cannot let air from vent into the cabin, assuming the valve doesn't fail.

Larry
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Last edited by lr172 : 02-12-2018 at 11:11 PM.
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  #9  
Old 02-12-2018, 11:49 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by VA Maule View Post
Pardon my ignorance hear and this is NOT to start a fight. Due to a one piece gear and using a wider gear web because it needs to be somewhat taller for the nonstandard engine I'm using , plan standard vent routings won't work for my build so the " Rocket coils " are my best option. So here's the question , what's the point of coils . The vent is in the highest point in the tank with an air gap unless the tank is overfilled the air gap in the tank will stop any siphon and even if overfilled the resulting vacuum of a sealed ( leek free) fule system will shortly stop the ground based siphon situation. In flight with the vent on the bottom of the wing in the area of high pressure siphoning should not be able to occur. So other than possibly preventing some sloshed venting of fuel in flight what purpose does making the coils do other than a setup like a " P-trap under the sink "?
I think perhaps to try to avoid the "burping" due to fuel expansion by creating more space for the fuel to expand into? As noted, even with 2 or 3 coils, some people have this occasionally happen, so it might be much more common with fewer coils. Dunno for sure, though.
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  #10  
Old 02-13-2018, 05:44 AM
bobnoffs bobnoffs is offline
 
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Location: n. wi
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thanks for all the replys guys. after reading i am comfortable with a low point in my vent line.
in the original post where a concern was expressed maybe that concern was related to a fuel line. low spots in fuel lines [at least in cars] are a spot for ice. entirely different for vent lines. thanks again.
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