Superglue can save your arse.
 

I was 15 miles out when I noticed the front flat. Pulled it apart and noticed it was leaking around the valve stem. As luck would have it, the spare inner tube was also leaking around the stem. Unbelievable.

I was about to resort to the cell phone when I decided to do try to repair the area with the "Superglue Gel" and some tube scraps I keep in my pack.

I cleaned the area around the stem an tilted the stem to open up the tear. I applied the glue into the crack and surrounding area and then placed a 3/8" round tube scrap over it and squeezed it for about 40 seconds.

Finished out the ride and made it back home.

I am now going re-enforce all my tubes around the stem by taking a nickle size patch and punch a hole in the center and slide it over the valve stem and gluing it in place.

The tubes often seem delicate in the area around the stem. Outside of snake bite flats this is my second most common failure.

Check the valve hole in the rim for flash, then file the flash away.

Not normal for tubes to fail like this. It's indicative of faulty tubes or some issue with the rim or installation. Better to diagnose and address the root cause.

BTW. It's also not normal to carry super glue gel and tube scraps when riding.

I have come across the same problem.
Super glue comes in handy sometimes.
I carry a small tube.

Or... scissors and a hole punch.

Tube/valve joint failure has become a serious source of frustration. Valves used to have large base flanges against which the tube eas sandwiched with a nut and washer. That gave way to bonding a rubber flange to the valve and vulcanizing it to the tube, which when done right was very reliable.

However, valve base flanges started to become an issue as rims got narrower, and the gap between the tire's beads kept valves from seating properly. Also there's a perception that valves threaded all the way down were superior to those with a conical rubber base.

These days many makers use a valve without a base flange per se, but a short base of slightly bigger diameter against which the tube is glued. If the rim's valve hole is slightly oversize as is common on the inner hold of double wall rims this extrudes through the hole slightly tearing the tube away.

I've addressed the issue on my commuter by using a tight fitting washer on the rims inner surface, held in place by the rim tape, and also pre-mounting a punched feather edge patch as a valve reinforcement to all my tubes before packing them as spares. That's solved the issue for myself, but I continually run into folks on the road who've flatted, and were stranded because the valve joint on the spare tube let go as did the OPs.

I should have made it clear in the original post. There is nothing wrong with the rim around the stem hole.
"Not normal for tubes to fail like this." BS! Like FBinNY, I see it happen all the time not only to myself but to others.

After 30 min ride Monday, bike sat in sun for an hour then big bang as tube blew at valve stem. Last winter same problem different wheel after bike sat in warm room after cold ride.

one potential cause:
Under-inflation, thus, tire creep, carrying the tube with it, shear forces result,
since the hole in the rim is fixed.
a benefit of Talc in the tire is, tube sticks to the inside of the tire, less..

Thanks for the tip. This has happened to me a few times, generally on tubes that have been mounted for a long time and have been pumped many, many times. The little stress from pumping adds up. I wonder if this would prolong their life.

OK, but happening all the time to you and others isn't normal. Maybe it's Bermuda triangle type of thing or something...the Altoona Triangle?

No Altoona triangle is involved. This issue is commonplace, though more so with some brands of tubes than others, but it's happening all over. Almost every dealer has run into it, and it's commonly discussed on various forums.

I visit lots of shops in the course of my business, and am finding it harder and harder to find tubes that aren't prone to the problem.

Does it happen to everyone all the time, of course not, but is isn't rare either. Different rims, and different rim/tire combinations worsen the problem, but it's something that didn't happen at all 5 years ago, and is now commonplace.

I also work in a bike shop, and we recently had problems with a batch of tubes (from a major brand) that had problems at the valve hole very soon after installation. I'd be keen to hear if anyone knows of a brand that is still managing to avoid this problem.

I've seen this on tubes which were unused, but which had been lying in the garage for a few years. The tubes appeared absolutely normal when I removed them from their boxes, but the surface of the brass valves had started to corrode. Although the corrosion was very slight - invisible unless you were looking closely - it had got into the rubber-metal join and weakened it.

I haven't seen this problem on tubes with nickel-plated valves.

A business opportunity. Package up and sell little kits of rubber washers and super glue.

I think one of the tubes was a Performance "Lunar Lite". I'm never going to buy them again. Too much trade off with the weight.
I believe the other was a Continental.

Both of these tubes had more than a season on them. I patch my tubes, so sometimes my spare tube is a used patched tube. I do think that pressure cycling is a contributing factor to the failure around the stem. I probably do about 100 miles a week during the season and ride 25 mile weekends in the off season. I guess I average around 4-5 flats during the year. I'm really keen on this stem reinforcing idea. I think its going to go a long way in preventing stem failures. We'll see how it pans out.

I've had the problem with Kenda tubes sold as REI's brand. The Michelin Airstop tubes I now use have a reinforced area at the stem base about twice as large as the Kenda's. I've had no problem with the Michelins.

I've had this problem with MEC tubes, so much in fact that I have stopped using MEC tubes (a number of years ago now) and use, almost exclusively, Continential.

Now, it CAN happen with the Continentials, but it is infrequent and if it does happen the tube is getting long in the tooth anyway or was caused by a poor pumping method.

With the MEC tubes, it happened almost immediately, or very soon after installing.

As a side note, do not buy the MEC patch kits either. The patches don't stick, or perhaps its the glue.

Just a few tips regarding the use of Super Glue Gel.

I buy it at the dollar stores. Three tubes in a foil pack.
I use a 3/8" punch to cut out small patches from an old inner tube.
Place these and the Superglue tube in a small plastic ziploc bag.

When you have a flat, clean the area around the puncture with a little spit and rub it dry.
Apply the superglue to the patch and use the plastic ziploc bag to press the patch to the tube.
The plastic bag will keep the glue from getting on your hands. You want to apply pressure for about 40 seconds.

Cyanoacrylate glue actually bonds very well to rubber. Moisture absorbed in the rubber actually helps to catalyze the glue.
The problem is that it does not stretch very well, so you want to keep the patches small. 3/8" seem to be perfect for
snakebite flats.

Another cause for this not yet mentioned is a pump jack that is difficult to remove. Over time the motion of pulling and wiggling the jack to remove it and damage the tube in this area.
Be gentle when jacking your valve.

And due to what FBinNY said, more and more pumps are coming out with air hoses instead of direct connection to relieve stress on the valve stem.

I always carry Superglue in my bag because it can be used for many things from what you did to repairing slices in tires from the outside to even putting your skin back together.

+1 Mihelin Airstops are the only tubes I use on my road bike.