Compression washers - remove or reuse?

I'm replacing a multi-turn stop with a 1/4-turn. The old one is fastened onto a stub of 1/2" copper with a compression fitting. I can get the valve off easily enough, but now what? Can I just slide the new valve on (they're both BrassCraft) and reuse the compression washer? Or should I take off the washer and nut and use new? If the latter, how do I get the compression washer off without ruining the pipe? Is there a -- dare I say it -- new tool I need ? I've experimented with scrap pieces and with careful sawing and Dremeling and using a screwdriver to pry the washer apart I've been able to get the washers off OK most of the time, but there must be a better way, particularly working in the confined space under a lavatory.

I have had a lot of success using a Channel lock to slide the Ferrel off. I also have used a hacksaw blade, very carefully. Don't be afraid to go after it.

I believe Terry had a picture of a tool like a wheel puller to slide the Ferrell off .

A pulller is the best tool to remove it. If the ferrule and nut are in good shape, I reuse them. This leaves the ferrule at the exact same spot on the copper where it originally made it's impression. If you pull it and install a new one, and if the original was overtightened to where it made a significant divot on the copper, you can have trouble with the seal.

If your old valve was coarse thread, it will be harder to find, so you may be forced to remove the old ferrule to install the new nut.

The fallback is to solder a copper male adapter and use a female IPS valve.

Thanks, guys. I'll reuse the old ferrule (that was the word I was looking for) and nut for now -- they're only a week old -- but I'll be on the lookout for the puller.