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Fuel Vent line question

Stockmanreef

Well Known Member
A couple questions:

1. Does the fuel line flare fitting get any tank sealant? The reason that I ask the question is that at the bottom of the page in bold it says "Double check that the vent line is clear and has not become clogged with sealant." How would sealant get into the line if it was not put on the connection between the aluminum tube flare and the fitting.

2. How does one torque down the fitting with a torque wrench? The only way I can figure it out is to go to HD and buy the correct size open ended wrench to fit on the torque wrench, since a socket won't work.

3. Should I cover the vent line bulkhead union fitting, nut, and tubing with sealant to ensure that not leaks will occur?

Thanks
Ken
 
What you need is what is called a flare nut socket or sometimes a crowsfoot. I bought a set of craftsman sockets on ebay. They have an opening that allows you to slide it on over the line. Here is a link at Sears.

http://www.craftsman.com/craftsman-10-pc-fractional-crowfoot-flare-nut-wrench/p-00942049000P

You can find these as sets of different sizes or as singles.

Once you get these you can use your torque wrench. Be aware that you need to make an adjustment for the torque that is read off of the wrench since you have adjusted the lever arm of the wrench. That calculation is available in the Aircraft Mechanics Handbook.
 
The sealant Van's is probably referring to would be uncured sealant used in the construction of the tanks. They are saying to make sure you don't put the end of the tubing into it and create a blockage.
You may want to apply sealant to the outside of the nut on the vent line to make sure it will not back off as it is just about impossible to reach after the tank is closed. So #3 would be a yes for me.
 
Be aware that you need to make an adjustment for the torque that is read off of the wrench since you have adjusted the lever arm of the wrench. That calculation is available in the Aircraft Mechanics Handbook.

If possible, you can also just attach the crow's foot at a 90 degree angle to the torque wrench and no change or calculation is required.
 
KC-

I bought a crows foot today. So even thought you extend the arm on the torque wrench, you don't need to recalculate?

I did the calculation and it does not change much with the crows foot on it any way. 40-65 in-lbs changed to 37-62 in-lbs.

Thanks for the replies.

ken
 
I did the calculation and it does not change much with the crows foot on it any way. 40-65 in-lbs changed to 37-62 in-lbs.

Correct. It has been reported here that some military guidelines ignore small changes in arm length. Personally, I think that it is kinda' slack. I'd rather do the calculation as you have, and then choose a value that cannot be wrong (like 55 for instance), or use the 90 degree trick.

So even thought you extend the arm on the torque wrench, you don't need to recalculate?

If you assemble the crows foot at 90 degrees to the handle of the torque wrench, you are NOT extending the arm. This geometry trick allows one to use the unmodified torque values.
 
First of all, I apologize for the bad drawing. I don't have much to work with on my home computer.

In the picture below, the torque wrench (purple line) and the crows foot (red line) are at a 90 degree angle to each other. The important thing for torque is the "cross product" between the vector and the force applied... ie the moment arm. That's shown in the drawing here and is the same length as the original torque wrench...no corrections necessary. Bottom line is that the only important thing is the distance at a right angle to the force vector from the force vector to the fastener...times the amount of force applied. Torque = r "cross" F
33wt993.png


In this drawing, the torque wrench and crows foot are in line. You can see how the moment arm between application of force and the fastener is longer for this case. In technical terms, the length of the crows foot itself is included in the cross product. So in this case you would have to compensate for the additional moment arm using the calculations given earlier.
2ryfr13.png


Sorry if I've bored most and confused the rest....
 
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How many people use these fittings between the aluminum tubing and the fittings?

http://www.aircraftspruce.com/search/search.php?s=DEL FITTINGS

Thanks
Ken

Not needed.
The alum tubing supplied in the kit is soft enough to conform to the fitting and get a good seal.
The Del seals from Spruce can be used in situations where you are having difficulty getting a seal, but I know of no one that spends the cash to use them everywhere (particularly with flared aluminum tubing)
general tip -
Don't over think the build process. Particularly with things like this where thousands have gone before you and not used them ( did a quick search in the forum and got only two hits )
 
What Scott says.

I bought a few of each -3,-4.-6 when doing the plumbing on my 10 "just in case"...........never used a single one.
 
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