Step 5 · Remove Old Compression Nut and Ferrule
With the valve removed, you will see the old compression nut and a brass ring called a ferrule on the copper pipe. Both must be removed. The nut should slide off. The ferrule can be stubborn. The best method is to use a dedicated ferrule puller tool, which grips behind the ferrule and pulls it off without damaging the pipe. Alternatively, you can carefully cut a slot into the ferrule with a small hacksaw or rotary tool, being extremely careful not to cut into the copper pipe itself. Once cut, you can pry it open with a flathead screwdriver and remove it.