I just put an old set of tires and tubes back on the rims, and on one wheel, as I tightening down the Presta retaining nut (the nut that goes onto the valve after it's gone through the rim), I heard a loud hiss and the tire went flat.
I took the tire and tube back off the rim, and found the tube had separated from the valve right at the base:
It pulled away like that on both sides of the valve.
The tube was pretty old - I'd guess minimum 5 years of service.
The nut was tightened by hand only, specifically end of index finger and thumb. No tools, and no hand-tightening torque boosters like a cloth wrapped around it.
What I'm wondering is, does this indicate over-tightening of that Presta nut, or just an old tube that was ready to fail there?
To put it a different way, if I had a brand new tube with no manufacturer defects, would it still be possible to make it fail like this by tightening that nut just with my fingers? If so, how tight should that nut be to avoid such a failure?