Originally Posted by mecheng
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. ...
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).