[rawcatslyentist]

>"what is the difference between a "sweat" connection and a compression connection and an iron connection? Also, the part of the valve into which the pipe stub goes appears to be unthreaded. How, then, does the valve stay on the pipe? Thanks."

A sweat is a solder connection, with a blowtorch.
A compression literally compresses a brass doughnut ring around the pipe end, the force of this compression holds the conection together and prevents leakage.
An iron stub, or MIP shouldn't apply as you have copper pipes, not iron.

The sweat is actually the easiest to do. Just heat then lay the solder to the joint, capilary action does the rest.

[rudy45]

Thanks. However, if I install a sweat connection, then I need a soldering iron and solder, right? I haven't used those things since junior high. Why is sweat connection easier than compression? seems with the latter, all I need is a wrench? Thankx. What are some advantages of sweat over compression?

[rudy45]

Another issue: I would be replacing a valve that's already there. What if is sweat connection? Will I even be able to remove it?