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Steel Swivel AN fittings

claycookiemonster

Well Known Member
Playing 3D Tetris assembling fuel and oil and sensor hoses now. Can anyone explain why some of the fittings on the engine are direct AN fittings, and some have a swivel so that they can be oriented in any direction and still tightened? My humble pilot brain wonders why they all aren't swivel fittings? I suspect there is an additional risk factor and failure mode to include the swivel. A bit more weight and more money, no doubt.

It would certainly assist in hose routing if I could change out some of the simple fittings for ones that included swivels. Any reason not to?
 
The engine is vibrating. Anything connected to the engine will vibrate too.
Metal is subject to fatigue.
My concern would be to keep the mass as low as possible.
This is more important when using aluminium fittings.
Some times you need a swivel.
Supporting the hose is important because it "hangs" on the fitting.

Good luck
 
research

You might want to give Tom at tsflightlines a call and talk to him about the advantages/disadvantages of swivel fittings...
 
Swivel fittings

The steel fuel pump fittings are unique in that they have a jam nut to allow orientating the fitting on the side that mates with the pump. Perhaps those are the fittings in question?
 
Google "SAE Staight Thread O-Ring Boss". It's a straight thread fitting with a face-seal oring that requires a precision triangular oring cavity and spotface machined into the the housing it screws into. Orientable, no sealant required, no oring extrusion gap (in contrast to radial seal oring cavities).

Other fittings have tapered pipe threads.

One can imagine straight thread versus tapered pipe design tradeoffs of legacy, cost, reliability, form factor, availability, etc but as the assembly technician your choice is simple because it has been decided by the manufacturer of the component that receives the fitting.
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Last edited:
Clay----I think youre refering to hose ends and not AN adapters. While having a swivel stem hose end can solve a 'few' issues with wither install or orientation with another angled hose end, you have to understand what makes it swivel to begin with. The stem of the hose end is attached to the hose, via a crimp collar or a reusable collar. The body of the fitting, where the bend and the flare head is, connects to the stem. That is generally via a lock wire pressed into grooves machined into the stem and the body. There is a short, inserted section of the body that fits inside the stem, and is normally sealed by a single o'ring. The body, now sealed by the oring, and secured by the lock pin, is now free to rotate.

While this seemingly is fabulous, especially for those hose assemblies that have 2 angled hose ends that need orientation, there is a trade off. That trade off is the sealing of the body insert to the stem. Its generally great at working pressure due to some expansion. The issue is a very low, or no pressure, you can get some seepage. Fuels in particular, especially IF the internal oring is not necessarily fuel compatible.

In addition to potential seepage, you can get air leaks. The big disadvantage is that over time, the oring looses its pliablity or deteriorates, and the joint gets alot of movement in it. Movement mean lack of sealing, which in the wrong place could be catastrophic.

Here is an excellent example of a live swivel. Stem/body rotates on ball or needle bearings (ball in this pic), sealed by a fluid compatible oring backed up by a teflon seal, similar to what you might see in a hydraulic cylinder. Components are stainless,or titanium, very precision built, and expensive. I guess if we were to have live swivel stems, they would be like this, but you guys would cringe at the costs. Another drawback of 'industrial live swivels' are the bodies are generally large, and heavy.

So---'probably' the best solution is to use solid stem/body hose ends and orient them correctly as the hose will be installed.

Tom
 
OOPS----forgot to post the pic of the live swivel. Must be a Saturday.

Tom
 

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