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Conflicting Torque Values

Daniel S.

Well Known Member
Slighly confused here. I'm about to torque the fuel tank AN fittings. the torque chart on Van's site says 270-350in/lb for -8 fittings, AC43-13 (section 9, page 19) sites 230-260 in/lb & The Aircraft Mechanics Handbook sites 150-250 in/lb... Anyone know off hand what is correct for the fuel pick up & vent (-4) line fittings?

Thanks all

BTW I did search VAF & found more conflicting data :confused:
 
I assume you are refering to the 3003 aluminum tube connection to the tank fitting:

Those Vans torque values are for hose fittings (like the FWF fuel hose, oil cooler, ect. Now for soft aluminum tube. The standard for the versatube is one flat past seated. More than that will damage the flare.

Edit: After re-reading your post I'm not sure what fittings you are refering to. You mention -8 fitting, but I can't think of any -8 in the fuel system (RV-8 may be different from the -6).
 
AN fitting torque values

Okay here I go answering my own question :D... After doing some research & talking to Van's, here is the skinny. There are 2 different torque values used for AN fittings. Please chime in if you've heard differenly. I hope this might help others who scratch their head when it comes to installing the fuel tank blue AN fittings.

-Torque Value #1. When the junction includes a flared aluminum tube & sleeve, the values are as follows.(When using the AN 818-** nuts)

-4 min 50 max 65
-6 min 110 max 130
-8 min 230 max 260


- Torque Value #2. When using the AN924-** nut. The plain nut usually used for mounting the fitting through the structure. (Bulkhead and Universal Fitting)


-4 min 100 max 140
-6 min 150 max 195
-8 min 270 max 350
 
I assume you are refering to the 3003 aluminum tube connection to the tank fitting:

Those Vans torque values are for hose fittings (like the FWF fuel hose, oil cooler, ect. Now for soft aluminum tube. The standard for the versatube is one flat past seated. More than that will damage the flare.

A little support for this is in a thread from 2015. Look at my posts (photos) and review by Scott McDaniels. It is always best to use Vans most current documentation, it has improved greatly from older materials.
 
Looking back as a first time builder, "How to torque fluid fittings" has been one of the more confusing questions throughout the build. Information seems to be out there, but it's not all in one place, and some of it doesn't look very authoritative.

For flared tubes with AN-818 nuts, there's table 9-2 in AC43.13, which is for aluminum (and steel) tubing. Pretty straightforward, but it only mentions tube material. Does the fitting material matter? What about 3003 alloy vs 5002 alloy tube?

Then there's AN-924 bulkhead fitting jam nuts. Couldn't find these in AC43.13, but a few VAF threads refer to this rando link, but is this for steel nuts or aluminum nuts? Unclear to me.

Then there's hose end fittings which are usually (always?) stainless steel. For these, Vans offers a link to some Aeroquip document for these torque values. Does it matter if the hose is connecting to a steel or aluminum fitting? Lycoming's Service Table of Limits document mentions flexible hose torque on page 2-30, and includes values for steel and aluminum, but does that refer to the hose end material or the fitting material? Also, the values in Lycoming's document are different from the values in the Aeroquip document.

Then there's the torque vs. flats topic... good grief! Maybe I'm the only one who had trouble finding and digesting all this, but seeing as there are numerous VAF threads discussing this topic, (with these docs spread all about them), I doubt I'm the only one. I wonder how anyone would do this without VAF as a resource.
 
Daniel----you have -8 fittings in the tanks? Normal RVs use -6 so recheck that.
Yes torque 'specs' are kinda all over the place. New vs slightly used fittings, aluminum on aluminum, stainless on aluminum, etc all have varying torques.
I've used the flats method for years. There are just some places where you cant get a torque wrench, without several different adapter bars (F1 Rocket, IO54, Romec fuel pump comes to mind). I've known of several 'torqued to spec' hoses that after a period of time would leak just a little bit. Another 1/2 flat of tightening solved the issue.

Tom
 
#8 hoses for oil cooler. Fuel will be all #6, #4 for brake lines, and #3 are the best for brake flex hoses.

Ed Holyoke
 
Table

I would love it if someone (Vans) would put all these tables together and post. It's very frustrating.
Heck, if they wouls send me the tables, I would be happy to compile into one spreadsheet.
Feels like Mil-Spec part numbers all over again.
 
Just went through this research (and mistakenly screwed up - my fault). But the longer I read up, the better '1 flat' sounds.
 
Rando link--steel or aluminum? <shrug>

Then there's AN-924 bulkhead fitting jam nuts. Couldn't find these in AC43.13, but a few VAF threads refer to this rando link, but is this for steel nuts or aluminum nuts? Unclear to me.

Yes, the table in the rando link doesn't specify steel or aluminum. But the torque values would be pretty darn low for steel.

The AN924-4D nut was 2014 or 2024 aluminum. To make matters more interesting, that material has been obsoleted for the AN924 nuts due to nut cracking problems ;). The new aluminum alloy used to make these nuts is 7075, and the corresponding new designator is 'W', i.e., AN924-4W.

See Version 14 of the AN924 spec at this link.

Another post I found on rivetbangers addresses the AN924 nuts, and a response from Ken (Krueger?) at Van's: https://www.rivetbangers.com/forums/viewtopic.php?p=16907#p16907

I agree with WireJock. Van's should compile the torque values for these fittings into a table and update Manual Section 5. Although some of us are aeronautical engineers, and some of us stayed at a Holiday Inn Express last night, it would be good to have sound and clear advice from the kit manufacturer.
 
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