AN Fuel Fitting torque?

[Astro John]

Plenty of posts about this on the vans forum, but I haven’t seen anything here.

There are reports of torquing them to spec and still having leaks.

I have read finger tight, then 1 or 1 1/2 flats.

One post recommends the flat method, but repeating it 3 times.

Another post says to use a sacrificial fitting for the first tightening, and then swap it out for a permanent one.

Another says on the loose end to start, and tighten until they don’t leak.

What’s the Bearhawk builder’s consensus on this?

 

[jaredyates]

I didn't stress too much about it. There are so many rabbit hole opportunities that I have to choose carefully which ones to fall into. I have had fittings that leaked, most often because I forgot to tighten them. Sometimes because I didn't make a good flare. Excepting those cases, it just hasn't been a big problem. Sometimes a fitting seeps a little and I snug it just a little more and that fixes it.

 

[gregc]

Tight but not too tight . Jared is right. the vast majority of AN fittings work fine the first time within a pretty wide range. If not, you can try tightening them a bit. If that fails,you can swap it out.

 

[svyolo]

One annoying thing is avgas is dyed blue. Which does a wonderful job of blending in with blue or black AN fittings. I had 1 leak on a blue union. It leaked so slow it didn't drip - it evaporated and leaked at about the same rate. Show up barely as blue goo in the AN fitting joint.

I use the "flats" method.

 

[Bcone1381]

I didn't stress too much about it. There are so many rabbit hole opportunities that I have to choose carefully which ones to fall into. I have had fittings that leaked, most often because I forgot to tighten them. Sometimes because I didn't make a good flare. Excepting those cases, it just hasn't been a big problem. Sometimes a fitting seeps a little and I snug it just a little more and that fixes it.

It's physics, math, and engineering. Machine it, draft it, build it, test it, break it. Every time something new gets built, the entire world advances." Mike Patey

I've jumped down this hole. What Jared says is real good gouge. Ive never had one leak that was tightened down. its a real good design.

You will learn a lot if you flare a short piece of aluminum tubing, then tighten it up of a fitting at various torques or flats past finger tight. 3000 soft aluminum will smash down and its easy to over torque it. This deformation will be hidden until it is disassembled. It must loose strength. The flared end will flatten and enlarge between the nut and male flare so much that the nut may not easily come off the tube. Tighten it this far to see how it behaves. Its a good shop education. Kind of like Mike Patey. I think of this exercise I did every time I tighten a flare fitting now.