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Old 05-17-2015, 11:43 AM   #1
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1970 31' Sovereign
Springfield , Missouri
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replacing water lines-copper pipes weird size

We have some issues with our water pipes in our 1970 Airstream. We have purchased pex and connections, but are worried that the copper pipes won't be either 3/8 " or 1/2. They seem to be inconsistent and a little bigger than 3/8" yet a little smaller than 1/2. Any ideas?

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Old 05-17-2015, 12:16 PM   #2
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Most likely freeze related swelling of the existing copper


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Old 05-17-2015, 12:19 PM   #3
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If the water lines have frozen, the copper will have stretched to an odd size. We found it impossible to match the existing copper with anything. Worked better to tear out the whole system (after carefully making a diagram) and replace it with 1/2" PEX.
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Old 05-17-2015, 12:38 PM   #4
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Pipe sizes are nominal inside diameters, so 3/8 will be just under 1/2 measured on outside, and 1/2 will be just under 5/8 outside diameter. Varies with wall thickness for different types of copper pipe/tubing as well.
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Old 05-17-2015, 01:02 PM   #5
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I don't know for sure what is in an older Airstream, but type K flexible copper tubing is measured differently than the standard type L tubing. Perhaps that is what is in your trailer. You can find this tubing and fittings at McMaster-Carr.
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Old 05-17-2015, 03:11 PM   #6
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I second Kevin245 and Mimiandrews reply above.

I had the same issues when I redid the '78 Sovereign in my signature line.

I managed to get a flare fitting over some lines after polishing the OD with
emery cloth.

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Old 05-17-2015, 04:33 PM   #7
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I agree with sb55 TUBING

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Old 05-18-2015, 10:41 AM   #8
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There are two scenarios:

1) Some time during your AS's lifetime, the water lines froze and as a consequence, they have expanded.

2) There's copper "pipe" and there's copper "tubing." The sizes are slightly different.

a) In my 77 AS, I've got copper tubing. It took me a while before I figured this out. Get a micrometer and measure OD carefully. When doing a repair, outside diameter is what counts.

FYI - I use "L" tubing for repair and upgrades. It bends easily and without kinking. You'll need a tubing bender. Harbor Freight has cheap ones that work just fine.

b) My lines have also expanded (in places) and split (in 2 places) due to freezing. As a consequence of that, I've learned to choose my repair/upgrade jobs very carefully. There are times when you hafta "make do" with what you've got and leave "well-enough" alone.

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Old 05-18-2015, 03:41 PM   #9
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As I recall, there are two types of copper tubing, hard and soft. I have no hands on experience with the hard type which is usually joined by soldering into similar alloy fittings. The soft type I believe can also be soldered but is often joined by brass compression or flared fittings. It is somewhat maleable and over time, even if not over pressured, can actually "creep" and expand slightly which makes it too tight for compression type fittings. It can sometimes be sanded on the outside slightly to accomodate a flared fitting and if so, may well work ok. Flaring, of course, requires a special tool and care must be taken to cut the end perfectly square.
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Old 05-18-2015, 03:58 PM   #10
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Freeze related expansion as others have noted.

Tricks to try if you are trying to connect to expanded copper.

1) Try to find a join point that isn't as badly expanded. Some areas will be worse than others. Curved areas will usually be worse because the tubing deforms in shape somewhat when it is bent.
2) You may be able to squeeze the pipe back down to size with the clamp part of the flare tool, enough to get a flare nut on. Polishing the pipe with emery cloth may help if it is dirty and corroded, but don't remove too much material or the result will leak.
3) You may find you can place a piece of new 1/2" copper over the existing expanded 3/8" copper, overlapping about 1" or so, and solder the two pipes together. Then you can connect the 1/2" copper using the method of your choice.

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