Plumbing – How to replace PVC Valve

From the way you describe it, it sounds like it's a regular gate valve. You might be able to repair it as you describe by removing the packing nut and replacing whatever is broken or stripped out inside.

The only exception to that would be a ball type valve, but those will just have a handle that makes only a 1/4 turn. Those generally aren't repairable, but then again they almost never fail either.

Personally, I would just remove and replace the gate valve with a good ball valve. Gate valves have a tendency to rot out or seize up from lack of use. I actually had one once that disintegrated in my hand when I tried to turn it off (spraying water everywhere and making a nice mess). Ball valves are just much more reliable.

As Steven says, hit it with some penetrating oil first (WD-40 should work for this). Give it some gentle whacks against a piece of scrap wood in all directions to help break any bonds. Then clamp on to the bottom square part and try to torque the nut on top with a socket. If you still can't get it, you may find it easier to replace the entire thing.