A company named Klune V makes some, but they will run you about 89 dollars, and it replaces the whole valve stem.
There's also an Australian company that makes valve caps, but the name is not coming to me right now. check the back of Off Road or Four Wheeler, thye advertise in there. They run about 60 though.
For the cost, I'd rather do it manually.
What are you doing that takes 20 min!? A quick way is to get a valve stem core tool, then just unscrew the core. Be careful though, you could lose all pressure quick if you don't screw it back in!
Last edited by buckgnarly; 05-16-2005 at 06:53 AM.