Fuel and oil line torque?

[Desert Rat]

I've reviewed all the previous threads where this question seems to come up frequently, as well as 43.13 table 9.2 and just want to make sure I have a clear understanding of torquing my fuel and oil hoses.

9.2 is clear on the torque values for either aluminum or steel tubing, but am I to presume that I should be using the steel value for steel hose ends onto steel fittings as well? If so, then the values from 9.2 should be as follows;

-4 = 135 -150 in/lbs
-6 = 270-300 in/lbs
-8 = 450-500 in/lbs

Does that look right? Also, for cases where it's impossible to get a torque wrench on the nut, are people just going 2 flats past finger tight or what?

Thanks,

Terry

 

[Avanza]

To be clear, table 9.2 refers to a AN-818 nut.
This type of nut is used on a 37 deg flared tube end. (auto parts has 45 deg).
If you have a ready made hose with a 37 deg steel nut and it fit´s on the male steel nipple then yes, I would use the torque values in table 9.2.
It helps with a drop of oil on the tube end so that the nut does not shear into the flared pipe.
Where it's impossible to get a torque wrench on the nut, put a nipple in a vise and torque the nut with the wrench to get the feeling of how much.
Be care full on soft aluminium pipe not to "crush" the flare.

Good luck

 

[Bcone1381]

Bottom Line: I failed here and it caused me to damage fuel lines using torque charts. AN education was received when I tested and practice on scrap discovering how to mess up an how to succeed.

So I experimented with AN818 nuts & AN919 sleeves on 3003 and 5052 AL tubing.

I used a Parker 37 degree flaring tool for flaring the tube. The flare radius dimension before I torqued the AN818 nut was properly formed and met specifications.

When I tightened my AN818 nut in accordance to the torque chart I had, it resulted in the flare of the tubing being squeezed/smashed. The Flare dimension radius enlarged, bound up the nut thus impeading the nuts free movement. The diameter of the flare was measured before and after in order to see the real data point of the smashing.

When the flare gets smashed Strength is sacrificed and the AL is work hardened and may be prone to cracking. This smashing occurred with both 3003 and 5052 AL tubing. I also saw the Sleeve dimension enlarge slightly. These were real MIL SPEC AN sleeves, not race car fittings.

So practice on some scrap tubing. Use a micrometer or a digital caliper to see how the tubing and the sleeve react to tightening. Tighten it up to your AC43.13 specifcation. Realize There are several types of AL tubing. Versa Tube is 3003 soft aluminum sold in a coil. 5052 is hard and sold in 10' lengths. There is also 6061 and maybe 2024 tubing. Your AC43.13 chart doesn't specify what type of AL tube it applies to. I call that a fault in AC43.13. I don't trust the chart.

I now tighten my AN818 nuts by feel or by counting flats. 1/4" get 1.5 flats past finger tight. The larger the tubing the fewer the flats. If I feel a sudden increase in torque I don t go further. I stop before the flare smashes down.

I'm Still building so they are not leak tested yet in the field but they are leak free to at least 70 PSI so far in the classroom/laboratory/shop.

Here is a good reference. Read the fine print and alternative torque procedures. This post has a chart for flare dimensions and a link to a Parker torque chart and "Alternative Tightening Method" procedure.
https://vansairforce.net/community/showpost.php?p=352788&postcount=6

 

[Desert Rat]

I appreciate the detailed response, but I’m asking specifically about the torque value for stainless hose end fittings, not aluminum flares. Sorry if I didn’t do a good job of explaining that.