Flaring Hydraulic Line End

Rob58

Rob58

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Planning to replace some hydraulic hard lines (3/16 OD alum). In reviewing all of the videos it seems that they all talk about a double flare, however the old lines that I am replacing all have single flare ends. Also, most of the dies in my flaring tool say "double flare". I do have a 37 deg cone insert but no die that specifically says for a single flare. What's the best practice: single flare or double flare? Thanks in advance!
 
Rob58 said:
What's the best practice: single flare or double flare?
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The rule of thumb is a double flare for certain soft aluminum alloys on lines up to 3/8" if I recall. All others to include harder aluminum alloys a single flare is okay. But given double flare tools can be quite expensive (different than single flare tools) its not uncommon to see single flares everywhere.
 
Rob58 said:
Planning to replace some hydraulic hard lines (3/16 OD alum). In reviewing all of the videos it seems that they all talk about a double flare, however the old lines that I am replacing all have single flare ends. Also, most of the dies in my flaring tool say "double flare". I do have a 37 deg cone insert but no die that specifically says for a single flare. What's the best practice: single flare or double flare? Thanks in advance!
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I have always used double flares for steel lines that are electrically welded together and have that seam running down the side.

Aluminum tubing gets single flares with a AN 819 sleeve coupling and nut.

I use the same flaring tool to make both 37 and 45° flares. Once you tighten it down the flare will seat in the fitting with soft aluminum.

Aluminum lines for hydraulic use?
 
dtuuri said:
AC 43.13-1B - Acceptable Methods, Techniques, and Practices Aircraft Inspection and Repair (w/Change 1) (faa.gov)
Part 9-30(b)
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b. Tube Connections. Many tube con nections are made using flared tube ends with
standard connection fittings: AN-818 (MS 20818) nut and AN-819 (MS 20819) sleeve. In forming flares, cut the tube ends square, file smooth, remove all burrs and sharp edges, and thoroughly clean. The tubing is then flared using the correct 37-degree aviation flare forming tool for the size of tubing and type of fitting. A double flare is used on soft aluminum tubing 3/8-inch outside diameter and under, and a single flare on all other tub ing. In making the connections, use hydraulic fluid as a lubricant and then tighten. Over- tightening will damage the tube or fitting, which may cause a failure. Under-tightening may cause leakage which could result in a system failure.
CAUTION: Mistaken use of 45-degree automotive flare forming tools may result in improper tubing flare shape and angle; causing misfit, stress and strain, and probable system failure.

And all that said, my -3 aluminum lines are single flared and work just fine.
 
Great feedback - thanks!
 
I can see nothing good coming from using a 45° tool to produce a 37° flare.
 
Gary Ward said:
Aluminum lines for hydraulic use?
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My Cessna has -3 aluminum lines running from bulkhead fittings on the fuse down the gear legs and connected to short flex hoses for the brakes. It also has -3 aluminum lines running down the gear legs for the hydraulic skis. Brake lines that are internal (under the floor) are all aluminum.
 
Gary Ward said:
I knew I would get flamed for that, should have never said that.
Sorry for misleading people with bad information.
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I do not judge you harshly, Gary.
It's just something we have been taught.
If anything I offer a gentle direction, sir!
 
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