I have had at least a big dozen tube blow off because the valve was ripped off.
My 29er has had 4 such blow-out lately but this morning the tube on my 26er just expired. 
When are they going to build tubes that can withstand Muni riding?
I use a Schwalbe tube in my 29er, but have used Specialized and a couple of other makes. Never had anything like that happen to me, I’ve had a few thorn punctures but never split the tube like that - perhaps I’m not a knarly enough rider 
My 26" muni usually runs a 3" Duro tyre with whatever big heavy tube came with the Nimbus muni a few years ago (Cheng Shin?). I’ve never even had a puncture on that. I’m also using a Schwalbe 29er tube in my 36er and never had a problem.
Perhaps you’ve just been unlucky - or are you getting pinch damage from running too low a pressure? Or could it have been pinched under the tyre bead when fitting? What size tyre are you using on your 26? Perhaps the tube was over stretched and the seam gave up.
Rob
I run a 3in duro tube in mine its heavy but gets the job done 100% of the time so simplicity wins!
That doesn’t look like a flat caused by the valve, or a pinch or thorn or whatever - something like that happens when the tube gets exposed to the air with no support from the rim/tire. So yeah, tube squeezed between the tire and rim when you put the tire on, or you rolled the tire off the rim on a sidehop or off camber landing or something.
Bottom line, it’s not the tube to blame.
I had a series of blow-outs on my 29" riding street, using tubes I bought at a LBS, and then switched to buying tubes from UDC and the problem went away. Not really sure what the problem was.
Tubes do get bad after a lot of use, esp if the valave is getting worked against the hole in the rim, so be sure and deburr the hole. I use the Maxxis Freeride tubes and have yet to have one fail, they are 26" tubes, but I use them in my 29, 26 x 4, and 26 x 3.
Once had a spate of tube failures on a new set of wheels, turned out that rim liner was cutting through the tubes, so you might want to look at the lip of the rim to see if it’s sharp and your liner to see if it has gotten old and hard. My liner was hard enough that the edge was slicing the tubes.
You shoudln’t have that many flats due to bad tubes, in four years I’ve had two bad tubes from valves getting cut at the base, all were the big heavy DH tubes from Duro, so that may be part of the problem…
possibly not possibly yes: those tubes are Continental made in China.
I blew the 3 I had!
this last one came with my new Muni and it just tore apart along a neat line.
It is fairly hard to find good tubes in bike stores: I had to order 2 Schwalbe through the internet. On My 24 things settled when I found a Torque 24x3 which (until now) withstood valve ripoff. But it is nearly impossible to find good MTB tubes in your local bike shop!
Good day to all.
Did you tried this one? Maxxis DH Tube are actualy on my bike and muni - I can not destroy it… No puctures, no raptures it’s just swllowing all hits. On MTB it lasts almost two years.
The tube shown in the pic is a presta valve. I’ve had a problem with valves tearing off of those in the past.
I believe the problem is one of my pumps. The presta side of the pump head seats really tightly. Too tightly. The valve stem/ rubber interface gets stressed after inflation.
I switched pumps and the problem has subsided.
That doesn’t explain the blowout in the pic, however. I’ve had problems with some lightweight 29er tubes in the past. They were labeled as thin. A switch to a thicker 26" tube solved the problem. I couldn’t find non-thin walled 29er tubes at my local shop.
It is a frustrating situation. Best of luck.
There really aren’t any good 29er tubes, which is why I use 26er tubes. I haven’t used anything but 26er tubes for 29", as well as my fat tired 26 x 4", no flats, no tears, no probelms.
You could also go tubeless…
Tires?
Have you considered that there’s something wrong with your tires? Stretched bead perhaps?
happened with 3 different munis with 5 different tires… but the latest blowout in the picture is special … I’ll investigate.
Really? I bought some Schwalbe 29er tubes which appear identical (apart from being larger) to the 26er tubes I bought at the same time. Fairly sure I’ve used Schwalbe branded tubes before with no problems, though admittedly I have very little in the way of recent experience of using wide tubes of any size - I only use them on my road bikes and the kids bikes - my MTB has been tubeless for 10 years. Yet to have a puncture on the muni, though I’ve only been riding that for ~8 months and not huge amounts of mileage.
Usually when I tear a valve it is from my tire spinning on the rim at low pressure.
You could try using tubular glue to glue one bead like the fatbikers do.
I may try that on my trials. i got 4 flats in a day
sorry my english is sometimes inadequate (and automatic translation does not help): what is a “bead” ?
thanks
edit: ok found (through google images)