Loosening a cold water kitchen valve for reverse osmosis

[Osmosisjones]

Hi, I bought a reverse osmosis kit. i have sparse instructions in the manual. I know I need to add a feed water adapter to my cold feed water pipe (first picture ...253.jpg) under the kitchen sink.
Based on some YouTube videos(for a different, similar model), I need to remove the cold water pipe (silver hexagonal end to the brass pipe) so I can add the reverse osmosis feed pipe before it reaches the cold water feed piece. (I did turn off the main shome valve with a bowl for collecting water.) My brass pipe and/or the silver hexagonal part) is a little rusty-the silvery greenish pipe seems to rotate and unscrew when I use the wrench but I can't determine if the end is spiraling out and if it can be removed. I spent more than an hour loosening it but I might need to use two wrenches to keep the brass pipe in place while loosening the cold feed pipe. Putting the faucet tube back onto it and tightening one part in caused a leak so I seem to have loosened it but I don't know how much more/how I need to rotate it off. When it's removed, then I will add the feed water adapter (...430.jpg) so it looks like the third picture (kimg0181.jpg).

Any help is greatly appreciated. Thanks in advance.

 

[journeyman]

That is a compression angle stop to remove you put a wrench on valve and nut behind it do not turn pipe it is copper and you will brake off in wall

 

[Osmosisjones]

That is a compression angle stop to remove you put a wrench on valve and nut behind it do not turn pipe it is copper and you will brake off in wall

Thanks so much. I'll try to use a wrench on the both the valve and the nut. The plumbing is less than 40 years old. I have some leftover Teflon tape and wonder if it may help here.

 

[journeyman]

No Teflon tape

 

[journeyman]

Or you can leave valve and buy an easy tee

 

[Osmosisjones]

i was able to remove the compression angle stop but the ferrule is still stuck. i will be able to remove it with a tool but there's a female thread on the the RO feed adapter whereas the cold water valve uses a male thread with a nut over the farrule.

It appears that I need to install this one (pic 2) "backwards"- some systems have the RO feed on the copper pipe with the blue shutoff facing the cabinets, whereas this one seems it will face the wall. I think the copper pipe needs to be filed or sanded down a bit to fit the new piece. That or the new adapter itself is a little tight (right male thread in the 2nd pic) and its inside needs to be filed with an outer reamer.

 

[Osmosisjones]

do i need a new ferrule ring and nut? or could i use the existing one? the nut is still stuck on the ferrule and i suppose i could just use the outer reamer so the new adapter fits on the copper with the old nut over the ferrule.