AN hose fittings - what is this tiny hole on the fitting?

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See that tiny hole on one of the nuts? What is it and is there something you have to do to it?
I noticed a leak (again!) and seems to be coming from these little holes. They are only on one nut per fitting and have no idea what they are for. there is something in there but maybe its not doing it's job...

I am SO DONE with AN fittings! Never again
someone help me out
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Fits a little pin the holds the collar on. How old are the fittings? Is the sealing surface clean?

I've never had issues with any of the AN fittings I've used, some being 15-20 years old.
 
Thanks GarageRat,
At least I know I didn't install incorrectly.

Had surplus fittings before that leaked so bought the new ones pictured. Clean surfaces, went back and used AN alloy crush washers... really fed up with it.

Right now I can't tell where it's leaking from.
The old ones leaked from the back side of the nuts - not from the threads.

I used thread sealant so I think it's leaking from the back side again or from that little pin hole.
I didn't over torque, kept it clean.... this will be about the 4th or 5th time messing with it.... jeez.

Any ideas?

It's just barb fittings for me from now on. Those actually go on and don't leak!
 
What sort of hose are you using with the fittings? Using the incorrect hose will effect the crimping of the hose material when the fittings are assembled.

What is the crush gasket you're referring to? flare saver?

Another dumb question...are you using all 37* fittings? I ask because some of the online stores don't do a very good job stating whether or not the fittings are 37* or 45*.

I'm sure you have a bunch of info handy but here's a link, check out page 25/75 - 30/75

AC43.13-1B Section 9

Good visual aid pics
Common Mistakes when fabricating Aircraft Hose Assemblies
 
What sort of hose are you using with the fittings? Using the incorrect hose will effect the crimping of the hose material when the fittings are assembled.
it is the 90° fitting pictured in my first post. There is no hose connection- all hardline. It is leaking from the backside of the nuts on that 90° hard line connector.

What is the crush gasket you're referring to? flare saver?

it is a thin aluminum washer that is 3-d shaped exactly like the male end of the 37° connecting area.

Another dumb question...are you using all 37* fittings? I ask because some of the online stores don't do a very good job stating whether or not the fittings are 37* or 45*.
yes all 37° fittings


thanks for the links, i'll take a look.
I have no idea why it's leaking at this point.
 
WOw havent seen a 43.13 in a while its for safety wire so the B nut has a lower chance of backing off
 
That is a strange fitting in the pic. I have never seen one like that on any plane I've worked on.

Do you have a picture showing your installation in a situational type shot? I don't mean like the pics in the links more like a visual of how you're using it in application? I know you can make something work but it may require different fittings to get to a leak free install.

The 3D washer is a flare-saver or conical seal and normally used if one of the flare faces has become slightly buggered up (scored, scratched, etc). They are one time use soft aluminum that will aid in sealing a less than flare face.
 
The old ones leaked from the back side of the nuts - not from the threads.

I used thread sealant so I think it's leaking from the back side again or from that little pin hole.

The nut and the treads do not provide the seal. The seal is formed between the two flared surfaces, male and female. All the nut does is hold the two sides together. You don't use thread sealant or teflon tape with these fittings. If the fitting leaks, then you have not tightened the nut enough or one side of the flare is damaged.
 

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