Unsweating a pipe fitting?

I bought an unused water-hammer arrester at an estate sale for a dollar, without looking very carefully at it.
It has some 3/8" compression fittings sweated on. I wanted to sweat it onto an existing 1/2" stub.
Can I unsweat the compression fitting and then use it like I want? My experience is that it takes a lot more heat to unsweat than to sweat, and I am concerned about damaging it. Can I wrap a wet towel around it, or something like that?
What do you suggest, other than not buying stuff without looking at it first?
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toller wrote:

There are a couple of reasons why it appears to take "more heat" to unsweat a copper joint...
First:
You have to have the joint at the melting point of the solder all the way around at the same time, or it won't come apart.
Second:
The molten solder forms metallic compounds with the copper (I forget just what they are called.) Those compounds have a significantly higher melting point that virgin solder does, so you have to get the joint hotter.
You can usually get a joint apart if you plan ahead and have some slip joint pliers or the like ready to twist and pull things apart as soon as they are hot enough to move, 'cause the longer you keep it hot the more of those metallic compounds form.
Keeping the back end of the arrester cool with a wet cloth isn't a bad idea, and a bucket of water to toss them into just as soon as you get those fittings off wouldn't hurt either.
You may have scrape solder off or out of the fitting end of the arrestor with a pocketknife or machinist's triangular scraper to get a slip fit with whatever you are going to sweat it onto.
HTH,
Jeff
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My name is Jeff Wisnia and I approved this message....

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This is Turtle.
You never said what type torch you had to know how bad it would be to take it off with.
Now use a wet towel or hang the body in a bucket of water and just have the solder joint above the water. Heat it and let the body fall in the water when it come loose. Don't use a piece of wood or rope to hold it with.
TURTLE
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