Compression Fittings: Does this look right?

[alpinelakespilot2000]

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



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

[Captain_John]

Great questions, Steve!

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



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

CJ

[Ironflight]

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

[sf3543]

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.

[alpinelakespilot2000]

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

[Rick6a]

Originally Posted by alpinelakespilot2000

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

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"

[Kahuna]

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

[Captain_John]

Rick, my elbow has been calibrated in Newtons, inch and feet pounds.

You should have yours done too!

CJ

[redbeardmark]

Originally Posted by alpinelakespilot2000

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

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.

[rv8ch]

Has anyone ever used these? They seem like a pretty good idea,
but I've never heard of them before a day or two ago.

http://www.aircraftspruce.com/catalo...37fittings.php

Thanks for any feedback.