hoses, nuts, fittings, adapters, steel vs alum... torques?!?!

prkaye · #1 08-10-2009, 05:17 PM

I'm a bit baffled that I haven't been able to get a consistent answer anywhere on the issues of torque values for various different types of hoses and fittings. Most people point me to the usual tables, which don't really answer my questions. Surely every builder has to figure this out...

1) For example, the VA-102 hose has a nut on the end that gets tightened onto an AN822-4D elbow. In this case, I would call the nut on the end of the hose "the nut", and I would call the elbow "the fitting". Is this correct terminology?

2) I asked Vans, and the reply was a reference to an Aeroquip technical document. Another generic table! Reading this page that was sent to me, I realise I'm also unclear on terminology. The document starts off by saying "....how tight should the connection between the fitting and the adapter be?". What is the "adapter"? When they say "fitting", which part are they refering to, the nut on the end of the hose, or the thing the nut gets tightened onto?

3) In cases like these hoses onto various steel and aluminum elbows and nipples, how do I determine the correct torque? Is it based on the material of the nut on the hose, or on the material of the elbow/nipple, or on both materials?

4) The nuts on the ends of my hoses (fuel and oil hoses) from Vans FWF kit are not blue. They are a silvery colour, and have a smooth shiney finish and so I would guess they are steel. Is this conclusive evidence that they are indeed steel, or could they be silvery shiney aluminum nuts on these hoses? I don't want to risk putting steel torque values on aluminum nuts!

Guy Prevost · #2 08-10-2009, 05:45 PM

For flared fittings, I let the softer material dominate. In other words, if either part is aluminum, use the aluminum torque spec. If both are steel, I use the steel spec.

The fuel and oil hoses you asked about are (stainless) steel.

prkaye · #3 08-10-2009, 06:12 PM

Thanks Guy, I guess that's what I'll do.

The KB-090-T fitting that goes on the mechanical fuel pump.. it is a brassy colour. Is this steel too?
if a fitting is not blue, is it always safe to assume it therefore must be steel?

But wait, here's a contradiction. Page 183 of hte standard aircraft handbook. For e.g. for fitting bolt or nut size -4, under the column for "auminum alloy tubing, bolt, fitting or nut torque value" it says 40-65. For Hose end fittings and hose assemblies, however, it gives a minimum of 100 (max 250). So if you're attaching the hose to an aluminum AN-822 elbow, the max torque value for the elbow is less than the minimum torque value for hte hose assembly. So what should be used?? Is the lesson here that ONLY steel fittings should be used with these hoses? In that case, Vans FWF plans have some errors (they call for this case of an alum AN-822 elbow with one of their SS oil hoses).

I'm a bit amazed that nobody seems to have an answer to this (either that, or nobody has yet understood my questions). The oil hose to AN-822 elbow is something that EVERY RV builder will have done. Has everyone just blindly picked a value out of a table without examining the basic assumptions invovled with the application of that table?

G-force · #4 08-10-2009, 07:30 PM

"adaptor" is what your calling an elbow. In the case of an 822 it is adapting a female pipe thread to a male AN 37 deg fitting. "Fitting" is a very loose, generic term that can mean several things so it is not as precise a term. Its better to use a more specific term like adaptor, union, hose end, nut, nut sleeve, etc. As mentioned, generally use the torque value for the softest material in the connection. The torque values for steel will always be higher because 1) the threads can take it, and 2) you need more pressure on the joint (the 37 degree tapers) to seal the less malleable steel. So if your threading a hose assemble made with steel hose ends on to an aluminum adaptor, use the aluminum torque value. It should be pretty easy to determine if a hose end or adaptor is steel, just stick a magnet to it. Even stainless will be very slightly magnetic. All aluminum fittings (made to the AN or MS standards) will be anodized. Blue is the most common, but I don't think the color is specified. Automotive grade fittings come in all colors of the rainbow, but its a **** shoot if the are made up the mil spec. standards.

prkaye · #5 08-11-2009, 06:01 AM

Quote:

It should be pretty easy to determine if a hose end or adaptor is steel, just stick a magnet to it. Even stainless will be very slightly magnetic.

Thansk Mike! That is a big help... now i can be sure of the material of all my fittings. For example, the KB-090-T (T fitting for mech fuel pump) which is a brassy colour, I'll just put a magnet and see if it sticks. I did find this additional info on the web...

QUOTE]A basic stainless steel has a 'ferritic' structure and is magnetic. These are formed from the addition of chromium and can be hardened through the addition of carbon (making them 'martensitic') and are often used in cutlery. However, the most common stainless steels are 'austenitic' - these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it non-magnetic[/quote]

So I guess our SS fittings are of the 'ferritic' type and not of the 'austenitic' type.

As for torque values, the general feel I'm getting from responses on my local RV webgroup is that people often do these by "feel", and then just tighten them if they leak. I guess it is standard practice before first flight to run the engine for a while with the cowling off to visually inspect all fittings for leaks?

LettersFromFlyoverCountry · #6 04-25-2010, 12:24 PM

I've resurected this thread because I notice that Phil never got an actual answer to his questions, and now I'm having the same frustration he had. This is airplane-building weather and instead I'm going out to the hangar, getting confused and then leaving because I can't seem to figure out the answer. All the charts and tables I have for torques are starting to blur.

Here's the T-fitting Phil described above. I can't quite recall if it's a 1/2" fitting or a 1/4" fitting, but it doesnt' matter. I'm confused about both when it comes to looking up the torque value. So whatever that value is, I presume I crank it into the fuel pump until I reach that value. But this is also has a nut on it. What happens with this nut.

I have the same questions on VA-102. The little Aeroquip chart lists a value for -4 where the nut is concerned. This, I presume, is actually referring to the fitting, right? -4. Because the nut itself is something like a 7/16" (don't quote me, but it's not 1/4")

apkp777 · #7 04-25-2010, 12:46 PM

Bob - Having just installed the fitting in your photo, I can tell you that I am not in love with such a device.

If you look closely at the fitting, you will see how it works. The fitting is threaded into the fuel pump completely, then the "nut" is tightened to compress the "O"-ring against the fuel pump port. As a rule with ALL fluid fittings, torque should be the minimum necessary. More problems come from over torquing than under. All fluid lines have to be "leak checked" so tighten the nut on your fitting to the point where it begins to compress the o-ring, but not enough to smoosh it completely. When you do your leak check later on you will focus your attention on that fitting and others similar.

The dash numbers for fluid fittings are based on pipe fitting standards and don't follow any intuitive sense (IMO). When it comes to torquing aeroquip stuff. Tighten the "B"-nut until snug, then ONE additional flat. Try to use a "fitting" wrench if you can (craftsman sells them). I doubt it makes any difference, but they do prevent distortion of the "b" nut.

G-force · #8 04-25-2010, 12:51 PM

That is a unique fitting. I am not familiar with them, but it appears the part with the nut is designed to allow the fitting to be clocked to a desired position, then the nut, with this sealing o-ring, tightened to seal the connection. Can you tell if that is a straight thread or a tapered NPT thread? My guess is a straight thread. If so, you would turn it into the pump as far as it goes, it should just turn by hand, then back it out untill it is aligned in the direction you want. Then hold the body in that position with a wrench and tighten the lock nut with another wrench. And your right, the "dash" sizes of hose or tube refer to the I.D. and have nothing to do with the size of wrench it takes to turn the fittings. As I recall, most -4 nuts use a 9/16 wrench.

LettersFromFlyoverCountry · #9 04-25-2010, 12:54 PM

Quote:

Originally Posted by apkp777

The dash numbers for fluid fittings are based on pipe fitting standards and don't follow any intuitive sense (IMO). When it comes to torquing aeroquip stuff. Tighten the "B"-nut until snug, then ONE additional flat. Try to use a "fitting" wrench if you can (craftsman sells them). I doubt it makes any difference, but they do prevent distortion of the "b" nut.

It's weird, actually. I would think companies would want to be very specific in these sorts of things. If a -4 is some kind of Ouija board notation that you have to have the clue book for, what's the value of it in the first place.

I did try the 1+1 flat today. No good. I could get it to about 1/4 to 1/2 an extra flat. But it was too touch getting a wrench on the An fitting in that location and if you don't, you'll rip the transducer manifold right off the firewall.

I'm starting to figure out why there are so many engine problems in light airplanes.

rvbuilder2002 · #10 04-25-2010, 01:02 PM

Quote:

Originally Posted by G-force

That is a unique fitting. I am not familiar with them, but it appears the part with the nut is designed to allow the fitting to be clocked to a desired position, then the nut, with this sealing o-ring, tightened to seal the connection. Can you tell if that is a straight thread or a tapered NPT thread? My guess is a straight thread. If so, you would turn it into the pump as far as it goes, it should just turn by hand, then back it out untill it is aligned in the direction you want. Then hold the body in that position with a wrench and tighten the lock nut with another wrench. And your right, the "dash" sizes of hose or tube refer to the I.D. and have nothing to do with the size of wrench it takes to turn the fittings. As I recall, most -4 nuts use a 9/16 wrench.

It is designed the way it is for the exact reason that Mike mentioned....to allow clocking the fitting in what ever direction you wish. It is straight thread, not tapered (NPT).