mecheng

Hey guys! I've decided to pump up my tires a little bit today for tomorrow's ride (took it off today) and started with the front one. Well, while I was securing the pump on the valve (Presta), it let all the air out. No biggie, I think and try to pump it. After several minutes of vain attempts I figured there may be something wrong with the tube (the pump is almost new). Now, this front tire was giving me some problems getting it to proper pressure ever since I got the bike. So I take the tire off and what do I see? The valve's base got separated from the tube... Just plain effing separated!!! I've checked the inside of the rim and tire surfaces and they seem fine. I don't think I ever had the tube overinflated either. With that in mind, what do you think could've been the cause of the problem? A manufacturing defect? Anyone faced something like that before? The inner tube was a Kenda if you're interested. Now replaced with a Michelin Ultra Light.

UmneyDurak

Over tightening the nut on the valve might do it. Might also be a defective tube.

John Wilke

Agreed. I think once you get the tire mounted, you can throw those nuts away ... they serve no purpose.

jw

Smoothie104

Not using a nut maybe the problem as well, especially if you put some horizontal force on the valve stem.

There is a sharp edge on the inside of the rim where the valve hole is, your rim tape will slide over slightly over time and expose the edge.


I see this happen to newbs with a frame pump, as they hold the rim in one hand, an pump with the other, but all the force of their pumping is pushing sideways on the valve stem.

Theres a way to hold the wheel still, brace it, and take the strain off the valve stem.

If anyone wants it, ill take a photo..

If youre using a floor pump and werent applying any hoizontal force, maybe the hole edge cut it, maybe you just a bad tube. I had one fail like that recently, 3000 miles or so.

Psimet2001 

+1 - also yanking the pump head off of the valve puts a lot of stress on the base. I had one come off in my hand about a month back as I was pulling the pump head off, but unless you're leaving the head engaged (tight) on the stem, and really pulling on it then I would agree that is may have been due to a faulty valve stem installation to the tube by the manufacturer.

the beef

Yeah, it happened to me the first time I pumped up a Presta valve. Just go easy on that stem.

DannoXYZ 

You're not using a HAND-PUMP are you? That first sentence I highlighted is the EXACT cause of your problem. Somehow, you're manhandling the valve-stem a little too much and all that wiggling's gonna rip off the valve-stem. I always think of Jackie Stewart's training practice on driving fast around a track, he lays an egg on a plate on the dash and he tries to get around the track as quickly as possible without lauching the egg off the plate or the plate off the dash... be SMOOTH. Same thing with valve-stems, apply forces in the appropriate directions. Unscrew the valve-tip, but don't wiggle the valve-stem. Tap it lighty to unblock it. Slide the pump-head on in a direction parallel to the valve-stem, no lateral movements or wiggling. Lock the head with the other hand while one hand holds the head stationary on the valve. There should be absolutely no reason to let all the air out while you're just installing the pump head.

If you are using a hand-pump, grab the pump-head AND a surrounding spoke with one hand. That way, the rocking motion that comes from pumping will move the entire wheel along with the pump so the valve-stem won't get wiggled to death (relative to rim).

domestique

How old are the tubes? maybe they are just old...

But everyone elses responses seem really good. I personaly like longer valve stems so I have more to work with and can grab onto the bottom when Im installing the pump head to avoid this kind of situation. It is also nice when on a group ride when on of my buddies has a flat and need sto bum a tube that will fit his deep aero rim wheels.