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Valve separating from tube, but there is no leaking. This was a strange tube. It went flat on me while I was descending Page Mill Rd. There was no noise, just a softening tire, then flat, probably over a few minutes. When I re-inflated the tube it held air. I have this tube hanging in my garage, inflated and bulging, for several days now with no apparent loss of air. I'm suspicious that this gap at the valve leaks intermittently. I've tried wiggling the valve stem, but this doesn't cause any leaking. The only thing I can't easily simulate in the shop is to apply heat as if it were on a wheel with a hot rim. (When the tire went flat on the Page Mill descent I singed my fingertips and had to wait several minutes before I could touch the rim.