I want to replace this old shutoff valve under my sink, but I don't know what kind to get or what precautions to take

Question

I have this valve under my sink that is meant for a dishwasher, but it has a weird size to the outlet and its old, and I want to replace it. The two lines above this one lead into the sink (hot/cold)
A few specific questions:

Is the water supply line going into it a PEX supply line or pvc? I'm not sure how to tell.
Is what is there currently there compression with a ferrule? What can I expect to see when I remove it?
Can I, should I, reuse the ferrule (if that's what is under this old one)? If not what is the safe way to remove it without damaging the pipe?
What should I do if I reach some point of no return and can't attach a valve? I don't want to leave my house's water off forever, and because of covid calling a plumber CAN happen but I want to try and prevent that. Can I cap it off temporarily if something goes wrong?
Is there a specific type of valve I should get? I know quarter turn are preferred. I also don't want to get the wrong kind of connection for this kind of supply line

Edit: I realize I have another question about this same valve,  but that question was "what kind of outlet fitting can I get" and the answer was "you probably can't get it, so replace it". This question is about replacing it without making a mess of things, because its hard to tell what kind of pipe is there (appears to be painted copper)

Alaska Man · Accepted Answer

Is the water supply line going into it a PEX supply line or pvc? I'm
not sure how to tell.

It is painted copper, a compression fitting is used on copper, not pex or pvc. Scrape it with a  screwdriver or utility knife to reveal the copper.

Is what is there currently there compression with a ferrule? What can
I expect to see when I remove it?

Yes. You can take the valve off by using two wrenches, one one the body of the valve and the other on the nut. Once the valve is off You will see that the ferrule and the nut will be left on the pipe.

Can I (should I) reuse the ferrule (if that's what is under this old
one)? If not what is the safe way to remove it without damaging the
pipe?

NO, Ferrule's can not be re-used. They are crimped onto the pipe when the nut is tightened and will have to be cut off by cutting off the end of the pipe, then the nut will slide off.

What should I do if I reach some point of no return and can't attach a
valve? I don't want to leave my house's water off forever, and because
of covid calling a plumber CAN happen but I want to try and prevent
that. Can I cap it off temporarily if something goes wrong?

Have a back plan, I.E. a different type valve. It looks like you have just enough room to install another compression valve or a solder on valve. If those fail, having a push to connect (sharkbite is one brand) valve as a back up could save your bacon.

is there a specific type of valve I should get? I know quarter turn
are preferred. I also don't want to get the wrong kind of connection
for this kind of supply line

See the answer to the previous question. Yes it should be a quarter turn valve.
Replace all of the valves while you are at it.

BrianK · Answer

I can't say I have seen those before. Does it looked like they are glued on? Then it would be PCV or CPVC (if its hot water). You could try going to home depot (yes, they can help) during the day when the best plumbing associate will be there. Also you could try a plumbing supply store.
Have you heard of the SharkBite system? Those may help you out. You can get a valve that will slide onto to the pipe if you can get the old one off. Also, you can get cap that will slide on. I recommend buying the sharkbite removal tool if you put on a cap and want to take it off.

DMoore · Answer

That is certainly a compression fitting.   Most are these days for sinks and toilets.
You know what you get...
NOTHING
You need to get into good DIY habits...
Easy Rule - you do not replace or touch good working plumbing unless there is a bigger project justifying it.
You don't like this valve?   What?   It's under your sink.   It works.   Why are you wasting your time and others thinking about this?   This isn't meant to be mean, but you need someone that will be honest.   You do not "fix" things that work.   So for your time and effort, the reward is you introducing risk on your home - either defective product or install.

I want to replace this old shutoff valve under my sink, but I don't know what kind to get or what precautions to take

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