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Proper fitting torque

Mike Miller

Active Member
I have searched the forums but perhaps not well enough. I am trying to determine what the appropriate torque is for a particular fuel line fitting. I am using an Andair fuel valve on my RV-9A, and TS Flightlines braided fuel lines (great product). I know what the required torque is for the AN fittings that supply fuel from the wings to the valve (75 to 125 inch pounds for 3/8" tubing). What torque value do I use for the stainless TS Flighlines braided hose fitting that goes from the fuel valve to the electric fuel boost pump? The reason I ask is because I know that the male fitting on the bottom of the Andair fuel valve is aluminum and the fitting on the stainless hose is steel. Is the flair inside the stainless fitting aluminum? If so, is it 3003 soft aluminum that "we" would typically use, or is it 5052 aluminum? I don't want to use too high of a torque and damage the Andair male fitting or not enough torque which would create a leak.

Certainly this is an easy answer for somebody who has been in the same situation before? What says you?

Thanks,

Mike
 
Send me your email and I will send you couple of PDF files showing torque values for all aircraft hardware including fuel line fittings.
 
I have searched the forums but perhaps not well enough. I am trying to determine what the appropriate torque is for a particular fuel line fitting. I am using an Andair fuel valve on my RV-9A, and TS Flightlines braided fuel lines (great product). I know what the required torque is for the AN fittings that supply fuel from the wings to the valve (75 to 125 inch pounds for 3/8" tubing). What torque value do I use for the stainless TS Flighlines braided hose fitting that goes from the fuel valve to the electric fuel boost pump? The reason I ask is because I know that the male fitting on the bottom of the Andair fuel valve is aluminum and the fitting on the stainless hose is steel. Is the flair inside the stainless fitting aluminum? If so, is it 3003 soft aluminum that "we" would typically use, or is it 5052 aluminum? I don't want to use too high of a torque and damage the Andair male fitting or not enough torque which would create a leak.

Certainly this is an easy answer for somebody who has been in the same situation before? What says you?

Thanks,

Mike

Ask Tom directly.. He helped me with the brake lines.
 
Mike and all---
our hose ends are all 304 stainless, -3 through -8. Not just a stainless nut over a brass, aluminum or steel insert. As such, YES it does take a little extra torque to seal the connection. HONESTLY----I use 2 stubby wrenches and tighten them about 1 flat after snug. There are just some places where you cant get a torque wrench no matter how clever you are. Rocket guys with Romec pumps know what I'm talking about.

Torque specs can sometimes be misleading. Ever 'torqued' a fitting to 'specs' and had a leak? We hear of it all the time. Even have had new mil spec certified fittings that took more 'torque' to seal them.
Stainless on aluminum will be on the lower part of the scale, stainless to steel or stainless steel on the higher part. AC43-13 has a good reference table 9-2. Aeroquip has one too, and the flats method.

Our brothers using the German spec seem to have no issues. That spec is
'Goodentight'.

Oh Parker has a 40 page installation guide that covers all of this. Page 23 lists stainless fittings. https://www.parker.com/literature/Tube Fittings Division/Assembly_Installation.pdf

Tom
 
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Torqued up

Gents, thank you all for the information. I will do as Tom says and go one flat after snug.

I've got to hand it to Tom...as others have said...his customer service is the best in the business.

Mike
 
Mike and all---
our hose ends are all 304 stainless, -3 through -8. Not just a stainless nut over a brass, aluminum or steel insert. As such, YES it does take a little extra torque to seal the connection. HONESTLY----I use 2 stubby wrenches and tighten them about 1 flat after snug. There are just some places where you cant get a torque wrench no matter how clever you are. Rocket guys with Romec pumps know what I'm talking about.


Tom, are your fittings the stainless with the silver plated threads for lubrication? If not, what do you recommend to prevent galling of the stainless/stainless joint on installation?
 
Dave, ours are not coated. Commercially available AN818 nuts generally are not, nor are Stratoflex stainless hose ends.
That being said, some builders have applied a light film of moly lube to the threads, some used differing sprays, some nothing at all. A coating of anything will change the torque required. Most all the specs are for clean, dry fittings.

Tom
 
To back up Tom's statements with practical observations... I've installed a fair number of aluminum fittings over the years. When assembling our aircraft using the same stainless fittings that Tom uses (hoses provided by his colleague Steve at Aircraft Specialties), all those fittings were mated with steel AN fittings. Using "standard" AN fitting torque I had three small leaks. Additional torque was required to produce a leak-free assembly. The fittings have remained leak-free for the first 50 hours of flight so I'm reasonably certain they will continue to do so.
 
Good to get Tom's take on this. I was just wondering the same thing. The Aeroquip hose chart calls for over 100 in lb even on the 1/4 lines to an al fitting, and the Lycoming overhaul manual I reference only calls for 45 in lb on 1/4 and 3/8 lines. That sounds really low.
 
case in point---in my pressure tester, I can take 2 stubby wrenches and snug the fittings then 1 flat depending on the size and get 3000 psi. Tester goes to 7500.
For what this is worth, torque specs on tightening fittings is an average. NEW fittings, clean threads, even temperature can affect torque. And yes sometimes you have to add some to stop a little seeping because of dissimilar metals or some small debris on the flare. I'm probably the worst at it, because I tend to 'tighten' things up, which is a nice way of saying I over tighten. Bad habit from the industrial days dealing with high pressure lines of +6500 psi working pressures.

Torque wrenches are great, if they are accurate and calibrated. And used with the proper torque adapters that will yield an accurate reading. And yes there are someplace that you can get a torque wrench in place to tighten something. Lee's Rocket with the Romec pump is a great example. You can hardly see the pump much less get to it to torque something.

So--making something exactly 130 inch lbs by the "book" may not be what it takes for your fittings.

Tom
 
agree with this 1 flat tightening method. some places you can't get a torque wrench. I used the triple torque method for -6 fuel lines, meaning torque 1 flat after finger snug, loosen, repeat twice more. five years, no leaks.
 
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