The old compression nut and ferrul (olive ) maybe very hard to remove.
DO NOT reuse the one that is on there. I have seen others do this and a few days pass when, POP! The new valve came out of the old nut and
.
Now imagine what it would look like with the water flowing out of the pipe at full pressure and how long it will take you to shut of the main water. Not pretty
They do make a ferrul puller to make it easier.
Yesterday a guy just paid me $237 US to change 3. after hours on OT.
he was remodeling a kitchen. ripped out his sink and counter top.
Thought he could do it himself. Could NOT do it. Waited until 4:30pm to call.
I just got home. I charge travel for after hour calls. 30 min job just turned into a 1.5 hr job.
The reason for the long reply
I seen a lot of talented craftsmen/tradesmen but when it comes to replacing stop valves they cringe and hire a pro. They look simple and in most cases are but they can get ugly sometimes for the novice