Losing air, but no puncture?

Check that the valve itself isn't leaking. Use a valve core tool to
unscrew and remove the guts of the valve. Clean off the valve,
lubricate the gasket part of the valve with spit and screw it back in.
That process will usually solve a leaky valve. You can get various
styles of valve core tools at a local auto parts store.

A common valve core tool looks like this:
29678

The part that unscrews the valve core is the bit at the top of the
image.


+-------------------------------------------------------------------+
|Filename: valvecoretool_76812.jpg |
|Download: http://www.unicyclist.com/attachment/29678 |
+-------------------------------------------------------------------+

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chuckaeronut;1136657 wrote:
I've never personally experienced this, but back a month or so ago on a
ride with Terry, he told me that temperature plays a pretty big role. He
said that car tires inflated to 40 PSI on a cold morning might have 55
PSI in them on a hot afternoon. Now, if air were an ideal gas, this
would be impossible, but it's clearly not, and I don't know enough more
about it to know for sure anything



Temperature can certainly play a big roll in pressure variation. That
said, the temperature change required for the pressure change you
describe is about 135 degrees Fahrenheit. That's a big change in
temperature. That's a REALLY cold morning followed by a REALLY hot
afternoon.

Air is pretty much an ideal gas in the parameter region we're
discussing. Why what you describe would be impossible given an ideal gas
is unclear to me.

Gas temperature/pressure interdependence is not complicated to
approximate. Most folks make mistakes by using the wrong pressure or
temperature scales. To do these problems one must merely know PV=nRT and
that the pressure P is the -absolute- pressure and the temperature T is
the -absolute- temperature. Then reconverting to gauge pressure and
relative temperature gives correct approximate results.

As for JC, although he is the -only- main man and there can be no
other, hungry4uni clearly stated that he submerged his tube in the
bathtub. I'm going to assume the tube was inflated, the tub was full of
water, and the valve stem was under water. A leaky valve stem would have
been apparent. JC rarely plays fast and loose, however.


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harper;1136774 wrote:
As for JC, although he is the -only- main man and there can be no other,
hungry4uni clearly stated that he submerged his tube in the bathtub. I'm
going to assume the tube was inflated, the tub was full of water, and
the valve stem was under water. A leaky valve stem would have been
apparent. JC rarely plays fast and loose, however.



It could be that the valve only leaks when there is more pressure
inside the tube. A tube pumped up and put in a tub of water isn't going
to have much pressure inside. Put the same tube inside a tire and
inflate it to 20 psi and that might be enough to get the valve to leak.

I've had a few leaky valves. It happens so it's something that is
worth checking.

The other possibility is that hungry4uni is pedaling so rapidly that
the reactive centrifugal force is strong enough to depress the valve and
cause air to leak. I leave it as an exercise for the reader to
calculate how fast hungry4uni would need to be pedaling.


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harper;1136774 wrote:
I'm going to assume the tube was inflated, the tub was full of water,
and the valve stem was under water. A leaky valve stem would have been
apparent. JC rarely plays fast and loose, however.



I experienced this a little over a week ago. The valve didn't leak in
the tub because I it's not easy to put 20 psi in the tube without it
being assembled inside the tire, and the valve didn't leak at lower
pressures. Once I reassembled and pumped up the tire to 30+ psi it
became apparent that the valve was leaking.

To check for a leaky valve, just spit on your finger and hold it over
the valve. You'll feel the spittle sputtering if there is air leaking.


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hungry4uni;1136665 wrote:
It's a 20x1.75-2.25 tube, so thats not what it is.

I think it's my incessant checking thats the problem



Why are you so crazy about psi? I mean, who cares what the number
reads as long as it feels fins.


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haha! I'm rubbing off on people again....


My posts don't count they came from MR...would they matter anyways?
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chuckaeronut;1136657 wrote:
Now, if air were an ideal gas, this would be impossible



ideal gas equation:

pv=nrT

if temp goes up, all other things being the same, pressure goes up


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kington99

Dave

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Right; I know about PV = nRT, but I wasn't sure if Air followed that
exactly, or how closely it followed it. I guess it's sufficiently close,
based on all the faith in it I now see in this thread!


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chuckaeronut

Uni to work to eat to live to uni to work to...!
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chuckaeronut;1137024 wrote:
I guess it's sufficiently close, based on all the faith in it I now see
in this thread!



This isn't the only faith-based thread in this forum. Billy starts them
every other day.


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All you have to do is pump up your tire before you go riding. Don't
sweat the small stuff. All is well. Mr. Harper is the man.


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john_childs;1136801 wrote:
It could be that the valve only leaks when there is more pressure inside
the tube. A tube pumped up and put in a tub of water isn't going to
have much pressure inside. Put the same tube inside a tire and inflate
it to 20 psi and that might be enough to get the valve to leak.

I've had a few leaky valves. It happens so it's something that is
worth checking.

The other possibility is that hungry4uni is pedaling so rapidly that
the reactive centrifugal force is strong enough to depress the valve and
cause air to leak. I leave it as an exercise for the reader to
calculate how fast hungry4uni would need to be pedaling.



lol i find a value of 10000rpm using my neuro-estimator calculator.


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