Re: shutn off valve
My suspicion is that you're referring to a compression style angle stop. With a compression fitting, there is a nut, a brass ring, and the angle stop (valve ). The nut crushes the ring against the pipe as the nut is tightened to the angle stop. I personally don't like this style of fitting as it's difficult for the average DIY'r to change out without leaks and problems. That is not to say that you can't change it, it just takes a little effort. The easiest way to change a compression angle stop is to turn off the water main, remove the angle stop valve and leave behind the ring and nut. Take the angle stop to the hardware store and match up the threads to a new unit, negating the need to remove the existing nut and ring.
The next best thing is that there's enough pipe hanging out of the wall to convert the compression fitting to a standard threaded nipple (my preference ). With a threaded nipple you will be able to change the angle stop with ease at any point in the future without problems.
Sticking with a compression fitting, you'll either need to cut or split the existing ring off the pipe stub. Cutting back the supply stub would be better if there's enough pipe stub to install a new fitting. Barring that, you'll have to remove the existing ring and nut so that the new nut and ring can be installed and tightened to a point to prevent leakage.
Again, if you can convert to a threaded nipple, you're better off in the long run. Also, if you can convert to a ball valve type angle stop you'll likely never have to deal with these valves again.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!