AN Fitting Leak

CWizard · #1 (**permalink**) 09-13-2006, 10:36 AM

I hooked up my oil cooler a couple of weeks ago, and there is a persistent small leak at one of the connections to the cooler. It's the standard SPF setup with AN-10 90 degree fittings at the cooler connection. I've tightened to about 12 ft-lbs, which I found recommended as the max torque for -10 fittings. Still leaked, so I added a soft aluminum cone (similar to Earls Conoseal; got it at a local aircraft shop) on top of the tapered nipple on the cooler. Still leaks. I can't see any imperfections on either the 90 deg fitting or the cooler nipple. I know the threads are not supposed to form the seal, but I'm considering adding some teflon tape or something similar. Suggestions, anyone?
Thanks a bunch.
Jerry

xlr8or · #2 (**permalink**) 09-13-2006, 10:45 AM

Are you sure the leak is between the two fittings and not between the hose and fitting?

MrMagoo · #3 (**permalink**) 09-13-2006, 11:38 AM

Thread sealer? I used the white permatex goo. I woudnt use teflon tape since it can break off and get into the lines. That fixed my seepage.

Rick Parker · #4 (**permalink**) 09-13-2006, 01:05 PM

CWIZARD: I had this very thing happen to me too. I didn't have any specific torque specs to refer to but I knew it was tight enough to seal if it was going to. Here is what I did to solve it. I too used the soft aluminum cones in an effort to seal it. Remove the cones carefully or have a replacement available. Remove the hose from the cooler. Look at the male nipple for a "scuffed ring" on the tapered face. THis is how it actually seals. This will be about .025 width. Look at the female part for any roughness on the mating tapered surface. Retighten the "B" nut on the fitting at the hose. Reinstall the cone and hose end, being carefull not to dislodge the cone and then just as it begins to get snug rotate the fitting back & forth to create a scribed sealing surface internally, then torque it down. I have found personally that the fittings that do not use a hose cutter design will tend to seep a minor amount internally. I fought this separate issue for quite a while until I replaced the fittings with those that used a cutter design. Recheck the toque after a few heat cycles. The threads have nothing to do with the sealing, dismiss the idea of Teflon tape or thread sealing compunds. Those are for tapered pipe threads only.
Good luck

Roscoe · #5 (**permalink**) 09-13-2006, 02:34 PM

What brand of AN fittings are you using.????

Roscoe

CWizard · #6 (**permalink**) 09-13-2006, 03:53 PM

xlr8or - Yep, it's definitely from the fittings and not the hose/fitting interface. Since I put the hose together, that's the first thing I checked, thinking I'd made a mistake.
Roscoe - Aeroquip. I read Carroll Smith's book on fasteners, and took his advice to heart. So I use only Earls or Aeroquip.
Rick - Sounds like a good suggestion. I'll give it a try tomorrow. And I'm glad your close call wasn't any closer!
Jerry

Michael C Henry · #7 (**permalink**) 09-14-2006, 09:27 PM

Earl's makes conical seals for 37° AN fittings. They are a soft silver metal cone that fits exactly over the fittings tapered cone . They are so thin and soft that they come in little plastic boxes to keep them from getting misshapened. They come in different sizes and are available individually or in assortments. Not shown in paper catalog but still available on line. I incountered them when working on M1 turbine engines. They came with the different fuel componet kits. Lots of SS and you don't want a nineteen year old with large wrenches tightening those fittings. And you don't want leaks. I used them almost everywhere oil lines, fuel connections, anywhere I used AN fittings. I think it was Summit but it may have been Jeg's.

Jerry Clayton · #8 (**permalink**) 09-15-2006, 10:10 AM

You are never going to get a metal fitting to not leak at 12 ft lbs torque on the nut--tighten it up to maybe 80-95 lbs.

Jerry

CWizard · #9 (**permalink**) 09-15-2006, 11:15 AM

Jerry - 80-95 ft-lbs of torque on an aluminum fitting? That's the kind of torque used for 3/8 inch head bolts and other similar heavy duty bolts. Seems a bit much for a fitting. Typo maybe?
Thanks,
Another Jerry

Fred Hamilton · #10 (**permalink**) 09-15-2006, 11:43 AM

I just checked my books at work and we call out 360 inch pounds or 30 ft lbs.

xlr8or · #11 (**permalink**) 09-15-2006, 12:06 PM

You will rip the fittings off the oil cooler with 85 ft. lbs.
I tightened mine up to about 25 - 30 and they seal fine.

Jerry Clayton · #12 (**permalink**) 09-15-2006, 04:34 PM

3/8 bolts should be around 35-45

I've never seen a torque chart for AN fittings---but if I had a leak I'd tighten it.

Jerry

Fred Hamilton · #13 (**permalink**) 09-15-2006, 05:57 PM

I work for an Aerospace Co and we have the torque for all the AN fittings.

Jerry Clayton · #14 (**permalink**) 09-15-2006, 06:13 PM

I did a search for AN fitting torque and found numbers all over the place--none as low as 12 lbs or even as low as 30 for a -12

Please post a link to where I can access the values, preferbly with types of thread lube for the tightening

I did work for an airline company and have been in racing for several years, dealing with Earl's, aeroquip and others and have NEVER seen a chart that they published--not saying that they don't exist, but I haven't seen one.

Jerry

CWizard · #15 (**permalink**) 09-16-2006, 07:20 AM

A couple of things: 1. I did the "twist during tightening" thing suggested by Rick and also tightened the fitting a bit harder, and it does not leak anymore. 2. I agree with Jerry C. that a reference, preferably online, for AN fitting torque would be useful. So if you know of one, please post! And Fred, I suspect that your source is a vendor manual, which probably isn't going to be available online, right?
Thanks again to all who responded.
Jerry

Fred Hamilton · #16 (**permalink**) 09-16-2006, 12:19 PM

I found this on the web, its different than our books but its a start.

http://www.advancedfluidconnectors.com/resources.html