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how to attach high-stress fittings
Posted: Sun Mar 22, 2009 6:23 pm
by FishBoy
I want to attach a fitting to the 3/16" steel (Al?) rigid tubing which is the output on my fridge compressor so that it will have a 1/4" threaded end. It will most likely be used up to around 500 psi and I am not sure as to the best way to attach the fitting.
Ideas-
1. Score the tubing and JB-Weld the fitting on; I do not how strong JB-Weld actually is.
2. Weld it, pretty straightforward.
3. [Submit your possibly better suggestion here]
Posted: Sun Mar 22, 2009 7:21 pm
by jook13
Man, my fridge had 3/16 or 1/8 copper output, which 1/4 inch copper just so conveniently fit nicley over, so I sodered it.
JB Weld (or other appropriate epoxy, I like marine epoxy) would work fine, just make sure to clean and roughen up the surfaces well and give it 24 hours to set up.
Posted: Sun Mar 22, 2009 7:21 pm
by psycix
I used a compression fitting.
But instead of the metal ring, a piece of rubber bike pump hose.
Holds 30 bar without any problems when tightened down firmly.
I believe you can use a 1/4" threaded fitting with an endcap, but then with an hole drilled through the endcap.
Posted: Sun Mar 22, 2009 9:50 pm
by Gippeto
I'll second the recommendation for a compression fitting.
But;
Why would you replace the ferrule (olive to some) with a piece of rubber?
Compression fittings were designed to work with a ferrule, and they do. I routinely use compression fittings to thousands of psi.
Have a little faith in those engineers that were paid to design the thing.
Posted: Mon Mar 23, 2009 5:52 am
by psycix
Because the ferrule only works on a perfectly round pipe with the right OD.
Posted: Mon Mar 23, 2009 10:43 am
by POLAND_SPUD
@ psycix I agree with psycix that using rubber is a good idea..
on my fridge compressor I use a homemade compression fitting made from: two identical 1/2" male-female fitings with several rubber washers squeezed in between them...
washers had a small hole so I put the tube through the washers and then tighthened the fittings as much as I could... seems pretty simple doesn't it ?? suprisingly it has never leaked... not even at 500psi
Posted: Mon Mar 23, 2009 2:53 pm
by FishBoy
I am still unsure as to how a compression fitting works; how is it tightened?
Posted: Mon Mar 23, 2009 3:41 pm
by jimmy101
They are just assembled with a pair of wrenches. For one manufacturer's instructions see
http://www.bulksrl.it/pdf/tube/ing/general_info_ing.pdf
Usually, compression fittings are rated to a higher pressure than is the pipe (or tube) it is designed to be used with.
IIRC, standard compression fittings for standard 1/4" copper pipe is rated to several thousand PSI.