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alpinelakespilot2000

Well Known Member
Knowing very little about the fuel system compression fittings, I reasoned out the order of the parts shown in the following picture.

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1. Do I have the right order for the fuel vent fittings on the tank? (Obviously, I don't have the inboard rib in there, but are the fittings--particularly the tubing, sleeve, and that big nut on the left side of the picture--themselves in the right order/orientation?)

2. The only other experience I've had with compression fittings were on my dishwasher. I had to wrench REALLY REALLY hard to get rid of a water leak on that application. How tight should I tighten these fuel fittings?

3. Is there any way to check whether they are leak free prior to sealing up the tank?

Thanks for anyone's help.

Steve
 
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Great questions, Steve!

Looks like the way I am about to do it... but I am going to install the rib too!

:D

Looking forward to hearing what the pro's have to say!

:rolleyes: CJ
 
Torque for fluid fittings

There is a torque table for fluid fittings in the little black book (the aircraft mechanics handbook), and I know that because I just used it the other night - but it's in my shop, and I'm at the computer, so you'll have to look it up. But it is definitely NOT "really, really tight..." ;)

Paul Dye
 
I believe the correct terminology for these fittings are flare fittings. Compression fittings have a ring that slips on to the tubing which is compressed as the nut is tightened on to the fitting.
That being said, you do have the correct sequence shown; however the bulkhead fitting could be turned either way, in relation to the rib.
I don't know what the actual torque values are for each size fitting, but it isn't good to over tighten since you could flatten out the flare, or worse crack or break the tubing. Lubricating the face of the fitting and tubing with FUELUBE, or comparable, helps.
Make sure the tubing and fitting are in perfect alignment during installation. This isn't a place where you can tighten it into place and expect it to straighten itself out and still make a good seal.
Good luck.
 
Thanks Paul and sf3543. Anybody know where I can get fuelube or equivalent locally? Is this something that might be available at an autoparts store?

Steve
 
alpinelakespilot2000 said:
Knowing very little about the fuel system compression fittings...........I had to wrench REALLY REALLY hard to get rid of a water leak on that application. How tight should I tighten these fuel fittings?.........................
Steve
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Steve,

Without aid of a torque wrench set to the correct value (like most of us, be honest), I'd tighten the fitting "just snug." If it leaks, you can always retighten with caution. The last thing you want to do is overtighten the fitting which will surely stress or even crack the flare on the aluminum tubing. A dead giveaway of a cracked flare (this DOES happen) to an experienced mechanic is the fitting leaking even more with increased tightening.

Rick Galati RV-6A "Darla"
 
How Tight

Only snug enough to stop the leaks. Snug everything and put system under pressure, then snug the leaking ones till they stop.
Kahuna
:rolleyes:
 
fuel lube

alpinelakespilot2000 said:
Thanks Paul and sf3543. Anybody know where I can get fuelube or equivalent locally? Is this something that might be available at an autoparts store?

Steve
Click to expand...


Try EZ-Lube. Available from Aircraft Spruce. Also works well to smear a little bit on the fuel tank cap O-rings.

It's a little thick for use as a lip balm. ;)
 
They work fine but are totally unnessessary. If your fittings are done correctly they will seal with no problems. Just another place to spend $$$.
Mel...DAR
 
Del 37 degree AN fitting seals

Mel said:
Just another place to spend $$$.
Click to expand...
Kind of what I thought. I've added a couple to today's ACS order just to have a look. They are pricey!
 
Flared Fittings

All:

The correct way to tighten an AN Flared Fitting is to tighten it finger tight then turn the B Nut one flat which is 60 degrees. No more, no less, and dry , dry dry. These fittings do not require any lubricant. They also do not need any washers or fancy spacers. The key to a good tight seal is to make sure that there are not any marks or scratches in the tubing flare. After the flaring is complete clean it with some scotch brite. (The MAROON ones, not the Home Depot crap.

I've been in this business for more than 30 years and have made thousands of flares that have held forever. Take a look at Tony's book Firewall Forward or check out the AC 43-13. There's a ton of information in these publications.

Tom Emery
WPA RV BUILDERS
 
tomsrv said:
All:

The correct way to tighten an AN Flared Fitting is to tighten it finger tight then turn the B Nut one flat which is 60 degrees. No more, no less, and dry , dry dry. These fittings do not require any lubricant. They also do not need any washers or fancy spacers. The key to a good tight seal is to make sure that there are not any marks or scratches in the tubing flare. After the flaring is complete clean it with some scotch brite. (The MAROON ones, not the Home Depot crap.

I've been in this business for more than 30 years and have made thousands of flares that have held forever. Take a look at Tony's book Firewall Forward or check out the AC 43-13. There's a ton of information in these publications.

Tom Emery
WPA RV BUILDERS
Click to expand...

Tom,
Thanks for your very informative tips. You bring up an issue or two that frankly, never occured to me. There is always room for improvement!
Rick
 
Why are the fuel faired fittings not secured to prevent them from loosening due to vibration? All other critical bolts and nuts are.
 
finger tight, then one flat

tomsrv said:
The correct way to tighten an AN Flared Fitting is to tighten it finger tight then turn the B Nut one flat which is 60 degrees. No more, no less, and dry , dry dry. ...
Click to expand...
Thanks for this hint. Perhaps I'm not making my flares right, but when I tried to go one flat, it felt *really* tight. Maybe my flare tool is making the flare too flat, and there is not enough meat to compress. Perhaps my calibrated elbow is just getting wimpy.
 
slight problem

I recently swapped out an old fuel selector valve. Everything tightened up ok and didn't leak under pressure. A couple of test flights, still no problem.

Then the plane sat for 2 weeks. The joint(s) weeped while it sat and there is the tell tale bue stain under the floor boards. Very annoying. I have tightened things slightly more. We'll see if that helps. Any ideas ?

John
 
Spruce sells some little teeny seals that go on the sealing surface between the flair and the AN fitting. It's supposed to stop leaking from imperfect or scratched surfaces.

Steve Zicree
 
I wouldn't use any half-measures like those little seals. If you don't have a good seal after the retightening, take it apart and check for nicks on the flares and on the fittings. If it has some fix um. either with scotchbrite on the flare, or new fittings if it's scratched.
 
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