how tight for the bulkhead coupling nut??

[RV9inIowa]

I posted this on the "big" site, but only got 1 reply.... can you guys help?

I can't find the torque setting for the nut that holds the fuel tank vent fitting to the end rib. The fitting is an AN832-4D bulkhead union and the nut in question is an AN924-4D.

I know the nut that hold the flare tube onto the union should be 40-65 in-lb. Is that the same torque for the nut that hold the union to the rib? Seems like you'd want the flare nut looser (so as not to mush the flare) and the bulkhead nut tighter (so the union wouldn't turn).

I wouldn't ask but the generic torque values for this thread (7/16x20) in aluminum are pretty high (450-500 in-lbs for a "standard" nut or 270-300 in-lbs for a "shear-type" nut). Those values are pretty far from 40-65 for the flare nut.

Also - what is a "standard" nut and what is a "shear" nut???

Any help out there? I can't wait to get this torque value so I can cover the nut in black goo and not think about it anymore!

Having problems with my nuts ,

dave

[captain_john]

Dave, in all honsesty these things need only be mmmmmph tight.

You know, mmmmmph. In German it is "gudentite".

I have a special torque sensitive elbow and it is NEVER WRONG!

Just do what feels good and butter 'em up!

CJ

[tshort]

I have the same elbow as CJ, and mine worked just as well!
Once your nuts are smeared in proseal you won't have anymore problems with them (the AN924s, anyway!)
I also put just a little proseal on the threads of the fitting where the nut would be just to help keep it in place.

Thomas

[captain_john]

Once your nuts are smeared in proseal you won't have anymore problems with them.

<snip>

Thomas

If that is the case, you will have another complete set of problems to deal with!

CJ

[cjensen]

Oh boy... Fuel line fittings boys...

[RV9inIowa]

...Once your nuts are smeared in proseal...

Yikes, just remember this quote about proseal- "there is no known solvent"

I guess tomorrow I'll use my armstrong wrench. What can go wrong?

[Brantel]

Actually Flamemaster states that you can soak your nuts in Methylene Chloride if you want to remove it from them.


Don't know about you but I think that would burn!

[TomNativeNewYorker]

Actually Flamemaster states that you can soak your nuts in Methylene Chloride if you want to remove it from them.

Methylene Chloride is the main component in paint stripper used by the Navy on aircraft.

[RVNewsletter]

I didn't see if the original question got answered but I *think* it's about 115 inch pounds. If you have AC43.15, the torque requirements are actually in the section on brakes and houses, rather than where all the other torque values are (which I think is in bolts and nuts)

[Thermos]

I can't find the torque setting for the nut that holds the fuel tank vent fitting to the end rib. The fitting is an AN832-4D bulkhead union and the nut in question is an AN924-4D.

Don't know if you got your nuts sealed correctly but I just went through the same process. As I read the Standard Aircraft Handbook, those torque values for aluminum fittings are the same for the flare couplings and the b-nuts that hold the bulkhead fittings on.

I used 110-130 in-lbs for the fuel pickup bulkhead pass-through, and 50-65 in-lbs for the vent pass-through. That seemed pretty darn tight, and when covered in proseal I think they're on for the long haul.

Also - what is a "standard" nut and what is a "shear" nut???

I *think* shear nuts are another name for those jam nuts that are used to secure control surface rod ends. They're thin so they support bolt loads in shear, but not in tension.

Dave

[N537TM]

One other thing to watch out for ..... if you use as Crow foot on the end
of your torque wrench ... you must re-calculate the torque deliverd
to the fastener. 100 in-lbs on the dial will deliver 100 + the fastener. The torque wrench is calibrated to deliver the value ... only when the center of the socket is in the center of the bolt. A Crow Foot is off set ..huumm ... 3/4 to one inch from the center. Now you have to use the formula in the Aircraft Handbook to see what the dial needs to be set for .. to deliver 100 in-lbs..

Mine was long, 2" and I rounded the nut on the vent line tube... another $10 lesson learned the hard way...

Mike

[Dan A]

Rule of thumb for flare fittings,. . . . . . snug plus one flat! That's all you usually need. If it is a good flare, then it will not leak. I had to re make most of mine as I tightened them too much!!! Lesson learned!
Dan

[RV9inIowa]

Thanks Dan - but the torque I was lookin for was for the nut holding the union to th bulkhead, not for the flare nut. I did ask Ken at Vans, and I stumped them too! The answer I got was:

We have no good number for this...and haven't found it to be
critical. Our best thought is to use the settings for hose ends,
rather than flare fittings.

In the end, I simply tightened it "gud-n-tite" and covered it with proseal. It will be fine. I'll be more precise on the flare nuts.

[Dan A]

OH, I guess I miss read that. Yeah, the bulkhead part is in the gud-n-tite range. Will work great!
dan

[RV9inIowa]

Woo-hoo! Both tanks are done with no leaks!!!

After 3 days of leak testing there was no loss of pressure on the balloon or the manometer (other than from the temperature swings).


The only problem I had was a leaky valve core in the Vans Fuel Tank Test Kit.

It will be great to be back to "dry" building again. Suddenly priming doesn't seem so bad. It will be hard to catch up to JohnR, though

[Spike]

Looks like you decided to use different screws to hold on the access plate?

[RV9inIowa]

Hi Spike - good eyes, I did use different hardware. For the access plates, I used NAS1352-08-08 screws which are cap screws (9/32" allen key) but are CAD plated steel. This is better than stainless, which could corrode the aluminum of the tank. The cap screws are easier to apply torque to, and will hopefully be easier to get out (which I never want to do)

I also used thin AL washers to get a better seat for the screw and provide more surface area for the sealant. They are NAS1149DN832K. I got them both from www.gen-aircraft-hardware.com which is awesome.

I didn't use the cork gasket or rubber gasket, but I chose to use a different proseal - C3330B2 "access panel sealant" which is supposed to be a "little" easier to remove. It is pink when you get it (but I'm man enough to use it ) but hardens up grey. It cured quicker than the regular stuff and smelled a lot worse. I got it from www.sealpakcoinc.com

Finally, I didn't like the idea of the sender ground return being through 2 prosealed plates to the aircraft structure, so I added a local ground wire. I've heard some builders have this problem and I can see why.

Hope this helps someone. I'm going to write up my tank tips because, now that it's done, it wasn't really that bad. I got a lot of great advice from many places.