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I can't pinpoint what I'm doing wrong while inflating my tubes. I use presta valves and have a "Joe Blow" Topeak pump. I put the tube stem at 12 o'clock, I unscrew the tip of the tube stem (but not too hard), press to let out some air, place the pump head on, lock it on, inflate to 120 psi (as recommended on the tire), then reverse all procedures, trying to keep everything straight (not wiggling the pump head too much).

I inflate before every ride but didn't think that was a problem as long as I'm letting some air out before pumping and am not inflating beyond the max. psi.

Still, after a couple weeks (riding about 3 times per week), the part of the tube stem that screws up and down is gone, and a few weeks later, after inflating, all the air rushes out when I take the pump off, then it won't hold air again.

The last time I replaced a tube for this reason, I decided to keep the little nut in place at the base of the stem near the tire (though my mechanic says it's unnecessary) and to keep the dust cap on the stem. I'm thinking these two items might not be necessary to most folks, but they'll perhaps protect against whatever I'm doing wrong.

Any other advice?

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    I've hear people say to put the stem at 12 o'clock, but I've always found that 6 o'clock works much better. Having the ground to push against when mounting the pump seems to make it much easier to attach the pump head to the valve. – Kibbee Nov 7 '14 at 17:54
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Use those two items - retaining screw and cap.

On the valve there are actually two sets of threads

  • One to open and close
  • Two to remove the core

If you unscrew to far / hard the core comes out.

You probable loosened the core and then it blew out.

Some sets of tubes just don't have the core very tight.

Get a tool to remove the core - it is also used to tighten it. Tighten the core. I even use a dab of locktite but don't get it in the rubber mechanism.

Some tubes do not have serviceable cores (won't come out). You would probably be better off with those type of tubes.

When I get a flat I save the core, retaining nut, and cap so I have spares.

  • I don't understand parts of your comment (removing/saving the core), but I think you're probably right that I was unscrewing it too far. Thanks for the help! – Mary B Nov 9 '14 at 21:29
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I also use a Joe Blow on my prestas. After I had a couple valve stems bend and/or break, I started making sure I only unscrew the stem a little bit. My theory was that by unscrewing the stem all the way up, it was easier to bend or break when pulling the pump head off. Haven't had it happen again since.

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The retaining nut will help keep the valve in one position, which might solve a part of the problem. As for the cap, I don't think it's necessary - it will only protect the valve from weather conditions and dirt.

With a shop pump like Joe Blow a bit more reliable option is to place the valve at 6 o'clock position for pumping. When it's at 12 o'clock the hose comming from the bottom might exert some force on the valve stem bending it slightly every time you pump the tire.

Personally I've only broken the valve stem a few times and it was only because of wobbling around the pump (a compact hand pump) when removing it. I use retaining nuts, but I don't put caps on the valves, and haven't had any problems for the past 2 years.

  • Thanks! I'm going to switch to 6:00 and make sure I'm not unscrewing it too far. And that sounds right - I'll keep the nut in place but won't worry about the cap. I really appreciate your taking the time to reply! – Mary B Nov 9 '14 at 21:27

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