Some, not all tubes, have replaceable valves. You can ask at your LBS, but they may prefer to just sell you a new tube.

Quote Originally Posted by AnnieBikes View Post
You might actually be able to replace the valve itself. A few weeks ago, I unscrewed the cover cap on the valve of my road bike, and it was after riding my touring bike for two weeks, so the valve was sort of "stuck". The cap unscrewed the valve itself, a completely separate thing from the tube. So your LBS may be able to replace the valve separately from the tube.