Originally Posted by
Andrew R Stewart
With no images or better descriptions I don't see how we can tell you what EXACTLY happened.
Have some pictures.
Originally Posted by
Andrew R Stewart
As to what might cause this I can only think of two reasons. One is a faulty stem molding, not unheard of but fairly uncommon and far less to be repeated by the next tube.
I discarded the bad stem hypothesis after the second occurrence.
Originally Posted by
Andrew R Stewart
The other is bad valve use. If the valve stem is wagged or pulled a bunch its internal bonding to the rest of the tube can be damaged.
As I noted, I've been installing tubes for 60 years. I know I've damaged some through carelessness and riding through tough brush. I've been careful with these, haven't ridden in brush. It also hasn't happened to the rear tube.
The pump, a 15-year-old Serfas FP-50 has gotten hard to remove: could a problem with the pump head cause this?
This is the valve that separated. I had to tear the remaining attached bit to remove the tube from the rim. It didn't cut at the base as I initially reported.
This is the valve that split. The split is hard to see.
This is the valve that split with a toothpick opening the split.