In Reply To:
One way to open it back (while leaving the tires on) is to put the extender in up-side-down and see if you can open it back up, but this may then be a reoccurring problem.
You just saved my day. I'm getting my bike ready for a ride in the morning and I could not air up my tire. (Zipp Tangente on a 404 with a valve extender)
I was getting ready to remove the tire and be forced to ride my other bike when I decided a quick search on Slowtwitch was in order...low and behold I found this old post.
I tried the trick of inverting the extender and unscrewing the valve and it worked. Now I can go on my ride tomorrow, but I'll have to remove, repair and reinstall the tire afterward so that this does not happen again.
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Michael