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Old 05-21-12, 11:33 AM   #1
AndreyT
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Presta valve base failure

Yesterday, as I was standing next to my bike at home, I suddenly heard the sound of air escaping the tube. Turns out my rear tube suddenly developed a large leak, right out of the blue on stationary and unloaded bike. I immediately replaced the tube with a spare. Inspection showed that the reason for failure was the rupture at the base of the smooth-stem Presta valve. Obviously, the main reason for this failure was the repetitive stress experienced by the rubber at the base of the valve from the pump head, as it was attached to and detached from the valve. Fortunately, my new tube has a threaded stem with a nut, which will protect the tube from experiencing this sort of wear.

My front tube also has a smooth-stem Presta valve, it was installed at the same time as my rear tube and it was pumped up with the same frequency. Taking this into account, I wonder if I should preventatively replace the front tube as well...

Anyway, a question to people who use smooth-stem Presta valves: what steps you take to prevent or minimize stressing the tube as you attach or detach the pump head? Is there some sort of technique the would allow one to attach the pump without pushing the stem in?

Last edited by AndreyT; 05-21-12 at 11:49 AM.
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Old 05-21-12, 11:38 AM   #2
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Riding under inflated, tire creeps around the rim, carries the tube with it,
shear forces build up, because the stem in the hole in the rim
does not move with tire/tube movement, and the stem tears out of the tube.

I use a Silca track pump, I push the air chuck seal no further down than just below
the threads for the cap.

even on stems with the ring nut, there is a smooth band between the 2 threaded portions.

that is where the Air seal is best, and effort to remove pump head , reasonable.

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Old 05-21-12, 11:42 AM   #3
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Why do these oddball things happen with Presta and not Schrader though? For years and years, never a problem with Schrader. Now I have some bikes that use Presta valves, and I've had several failures of the valve itself.
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Originally Posted by bragi "However, it's never a good idea to overgeneralize."
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Old 05-21-12, 11:44 AM   #4
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Originally Posted by AndreyT View Post
Anyway, a question to people who use smooth-stem Presta valves: what steps you take to prevent or minimize stressing the tube as you attach or detach the pump head? Is there some sort of technique the would allow one to attach the pump without pushing the stem in?
1. Do not use hand-pumps.

2. when loosening the valve, tap it lightly to break the seal, should hear a momentary >PFfsst<

3. Depending upon pump-chuck, you can loosen the chuck cap lightly to make rubber-seal looser (works on Silca heads)

4. push chuck onto valve-stem straight (inline with stem) only far enough to seal, about 1/4 to 1/2" max

5. tighten pump-chuck cap to tighten rubber-seal (some pump-heads have a lever to does this)

6. pump up to recommended pressure for your weight and tyre-size

7. loosen pump-chuck cap or lever

8. pull pump-chuck straight off, not at an angle and do not wiggle.
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Old 05-21-12, 11:48 AM   #5
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Quote:
Originally Posted by fietsbob View Post
Riding under inflated, tire creeps around the rim, carries the tube with it,
shear forces build up, because the stem in the hole in the rim
does not move with tire/tube movement, and the stem tears out of the tube.
My bike is a 32mm cyclocross setup used on paved roads. I keep the pressure at 100 psi, which is actually more on the overinflated side.

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Originally Posted by fietsbob View Post
I use a Silca track pump, I push the air chuck seal no further down than just below the threads for the cap. even on stems with the ring nut, there is a smooth band between the 2 threaded portions. that is where the Air seal is best, and effort to remove pump head , reasonable.
With my Topeak floor pump that is insufficient. Grabbing just that smooth portion does not provide enough seal to pump the tire to 100 psi. I absolutely have to grab the "main" portion of the valve stem for that.
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Old 05-21-12, 11:50 AM   #6
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1. Do not use hand-pumps.

2. when loosening the valve, tap it lightly to break the seal, should hear a momentary >PFfsst<

3. Depending upon pump-chuck, you can loosen the chuck cap lightly to make rubber-seal looser (works on Silca heads)

4. push chuck onto valve-stem straight (inline with stem) only far enough to seal, about 1/4 to 1/2" max

5. tighten pump-chuck cap to tighten rubber-seal (some pump-heads have a lever to does this)

6. pump up to recommended pressure for your weight and tyre-size

7. loosen pump-chuck cap or lever

8. pull pump-chuck straight off, not at an angle and do not wiggle.
For a Schrader valve, it's

1. Attach chuck to valve.

2. Pump it up.

3. Detach and ride bike.
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Old 05-21-12, 12:01 PM   #7
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Many people prefer smooth stems. Reasons include less wear on pump head. Also, some that use threaded stems don't bother using the nut.

When you inspected the failed tube, did you also inspect the rim's valve hole for roughness or a less-than-smooth edge?

Presently, I use threaded stems w/ or w/o nuts. Rim hole is smooth. I also place another small square of tube over the base of each valve, inside rim. Belt & suspenders, but my tubes die from other causes.
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Old 05-21-12, 12:03 PM   #8
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check for burrs on the rim at the stem hole and sand or file them down, if you haven't already.
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Old 05-21-12, 12:12 PM   #9
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check for burrs on the rim at the stem hole and sand or file them down, if you haven't already.
I have, however, I don't see how it might matter in my case.

With the new tube only about half of the Presta stem is sticking out of the rim. Another half is actually inside the rim. It is not possible to pull the stem out any further. Apparently, the rigid valve base is wedged between the sides of the rim, which prevents it from seating fully against the inner surface of the rim. This means that the actual base of the valve remains pretty far from the hole. Whatever irregularities I might have around the hole, they can't really come in contact with the tube.
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Old 05-21-12, 12:24 PM   #10
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I actually started using smooth valve specifically because I found threaded valves were more prone to this issue. My pump head disengages more easily from smooth valve (less tugging), and I have fewer instances of failure around the valve stem as a result (I think one since I made switch).

Secondly, you indicate you ride an pretty hi pressure. I think that may be an issue too. Besides switching to smooth stem, I also began riding with lower prerssure in my tires (I lost a lot of weight). My therory is that combination of high pressure in tube and tugging on valve is what would couase the occasional failure. So you might try backing off a few pounds since 100psi is a tad hi for 32mm tires.

And lastly, another thing that helps is grabbing the base of the valve stem itself with your fingers to stabilize it as you pull the pump head off.

edited to add: I wrote above in response to OP before I read post #9 about tube not seating all the way. Something's not right there.

Last edited by DOS; 05-21-12 at 12:42 PM.
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Old 05-21-12, 12:27 PM   #11
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I've got threaded and smooth presta stems on various rims. I haven't had any such issues with longevity of the valve base or with pumping, whether it's with portable pump (Zefal HP-X classic frame pump) or floor pump. Both work. I tend to buy whatever tubes I can get on sale, and sometimes, those are smooth stem, 60mm variety with a lot of stem showing for a semi-aero profile rim.

I'm am a bit confused why the tube is not seating correctly. If you don't have a tire, and just have the tube around the rim, will the valve stem/base seat correctly and give you more extension out of the rim? If that's the case, then maybe the tube you have with combination of rim/tire bead makes it unsuitable for your tube. You may want to revert back to some other brand of tire or tube. Or maybe use a rim with wider internal ISO width spec?
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Old 05-21-12, 12:29 PM   #12
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check for burrs on the rim at the stem hole and sand or file them down, if you haven't already.
+1
not on the outside but on the Inside of the rim
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Old 05-21-12, 12:30 PM   #13
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I have, however, I don't see how it might matter in my case.

With the new tube only about half of the Presta stem is sticking out of the rim. Another half is actually inside the rim. It is not possible to pull the stem out any further. Apparently, the rigid valve base is wedged between the sides of the rim, which prevents it from seating fully against the inner surface of the rim. This means that the actual base of the valve remains pretty far from the hole. Whatever irregularities I might have around the hole, they can't really come in contact with the tube.

Not really sure how this is possible and this might be the reason for your tube wear.
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Old 05-21-12, 12:38 PM   #14
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I have, however, I don't see how it might matter in my case.

With the new tube only about half of the Presta stem is sticking out of the rim. Another half is actually inside the rim. It is not possible to pull the stem out any further. Apparently, the rigid valve base is wedged between the sides of the rim, which prevents it from seating fully against the inner surface of the rim. This means that the actual base of the valve remains pretty far from the hole. Whatever irregularities I might have around the hole, they can't really come in contact with the tube.
hmm, interesting. So the stem never seats down fully on the rim when fully inflated? and you run it at 100psi?
It could be that the stem is getting wedged when it shouldn't.
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Old 05-21-12, 12:49 PM   #15
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Not really sure how this is possible and this might be the reason for your tube wear.
No, actually all my previous tubes were smooth-stem Presta ones. And as far as I remember, I never had (or never noticed?) this "wedging" issue with them. The entire (or almost entire) Presta stem would go through the rim. That's how it was with the tube that failed yesterday.

The new tube is an ordinary Specialized Standard Tube (700 x 28c-38c) with threaded Presta

http://mikesbikes.com/product/specia...resta-4480.htm

This tube has a fairly rigid area around the base of the valve, which gets wedged between the sides of the rim, preventing the valve stem from going all the way through. I can, of course, slowly tighten the outside nut to force more and more of the stem out of the rim, but that will probably eventually destroy the tube. So, I inserted the stem as far as it would go without forcing it, pumped my tire to 100 psi and then lightly tightened the nut. I believe about half of the valve stem (or 1/3) is still inside the rim.

I'd say that this could be perfectly normal, depending on the profile of the rim.

I'll get another tube of the same kind today and compare the valves. I'll try to post a picture of what it looks like.

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Old 05-21-12, 05:32 PM   #16
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Why do these oddball things happen with Presta and not Schrader though? For years and years, never a problem with Schrader. Now I have some bikes that use Presta valves, and I've had several failures of the valve itself.
Most shrader valve tubes are heavier. Thicker rubber means more resistant to tearing. I've seen plenty of shraeder valves fail at the joint between the valve and the tube, though.
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Old 05-21-12, 06:15 PM   #17
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From your description, it sounds like you might have a single wall rim with a fairly narrow well. Some of these rims are so narrow that the valve, with the reinforcing around it, has a hard time seating at the bottom of the well. If the valve sits up a bit, the tube balloons down at the edge of the reinforcement and eventually fails.

If you have rim tape that covers the sides of the well, remove the tape from the sides for an inch or so in either direction of the valve hole to allow maximum room for the valve to seat at the bottom of the well.
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Old 05-21-12, 06:27 PM   #18
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I prefer non-threaded presta valves. the pump head releases much easier from a smooth stem than a threaded stem. Those nuts are worthless and won't prevent you from pulling too hard on a stem and causing a rupture.
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Old 05-21-12, 06:51 PM   #19
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I prefer non-threaded presta valves. the pump head releases much easier from a smooth stem than a threaded stem. Those nuts are worthless and won't prevent you from pulling too hard on a stem and causing a rupture.
With a shallow profile rim, where the tube is seated against the rim, "pulling too hard" is not really an issue. The real issue is actually pushing too hard, which is exactly what those nuts prevent. Moreover, even with deep profile rims, pulling is significantly less likely to damage the tube than pushing.

So no, they are not worthless.
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Old 05-23-12, 09:20 AM   #20
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With a shallow profile rim, where the tube is seated against the rim, "pulling too hard" is not really an issue. The real issue is actually pushing too hard, which is exactly what those nuts prevent. Moreover, even with deep profile rims, pulling is significantly less likely to damage the tube than pushing.

So no, they are not worthless.
I've never had an issue with pushing too hard; in fact pump heads all slide on effortlessly whether stem is threaded or smooth so no pushing involved. Its getting them off that threaded stem made more difficult and I have pulled stem straight out of the tube. That said, Mr Brandt seems to think the cause is niether pushing nor pulling, but manufacturing defect.

http://www.sheldonbrown.com/brandt/tube-failure.html

"In a self accusative manner, riders often place blame for this failure on errant inflation, the use of the anchor nut on the stem, or some other feature of the rim that they failed to ameliorate. On close inspection, separated stems show that the rubber peeled away leaving only a slight black trace on the stem where the leak began. This isn't caused by any of the usually believed mechanisms. It is a manufacturing flaw."

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