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Leaking Schrader Valves


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I've been having this same issue for months and can't seem to get it resolved.  When I first bought my '04 230F back in May, both tires were flat, so I replaced both tubes and both tires and installed new schrader valves.  However, the tires still lose 3 psi to 5 psi over a one to two week period of not riding it (with the bike sitting on a stand).  I tried tightening the valves and eventually replaced both of them, but I am still having the same issue.  I took both tubes out, inflated them, and soaked them in a tub of water and there were no bubbles.  I always thought schrader valves were supposed to be spring loaded, but all of the ones I have seen are not.  The center pin is loose and wiggles around.  The valves that came with the new tubes were loose like this and a pack I picked up at the auto parts store are also loose.  What the hell is going on?  How is a tire supposed to maintain pressure if the atmospheric pressure is greater than that inside the tube if there is no spring to keep the valve sealed shut? 

Edited by mossman77
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Just a little tidbit of info on gauges and pressure. Atmospheric pressure at sea level is 14.7 pounds per square inch. Most gauges are calibrated to read zero at 14.7, this is called psig or pounds per square inch gauge. Very few gauges are calibrated to what is called psia or pounds per square inch atmosphere. This would lead us to the fact that the pressure in the tire is actually higher than atmospheric pressure. All I can say about the schrader valves is they don't make em like they used to.

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Oh gees the old nitrogen thing. Granted you can get higher % into a tube than a car tire, so I'll give you that. Most people don't know that air is already 80% nitrogen. You can get a tire to maybe 95% at most. Most likely 90%. So, you're increasing the percentage a whole 10% and that's only if you start with a vaccum in the tire to begin with. But we know the tire is at atmospheric pressure to begin with, so...

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And whenever your tires get low on pressure, you have to add more.

And every time you add more Nitrogen, the percentage goes up.

Eventually you notice that your pressure stays up to specs longer and doesn't change as much with the outside temperature fluctuations.

All the tubes that I have purchased over the years are completely empty of any air. I have never checked for a vacuum but if I removed the valve stem in the past, air would enter the tube and expand it slightly.

I do not remove the stems any more just because of that.

Edited by adnohguy
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IMO the only advantage to using N2 or CO2 for tires is the available supply is a dry gas.  Both N2 and CO2 are major components of the air we breathe, along with  O2 and moisture (plus a few other gases). It is the moisture in air that causes problems with tires if they are high pressure and operate over a wide temperature range like airplane tires, but at 0-15psi for dirt bike tires  you are only making the bike faster because your wallet is lighter. 

 

Also tubes do leak air, some worst than others.  I have some motorcycle wheels that hold air for a long time, others that leak down enough that I must check before each ride. :banghead:

I have a motor home that uses 120psi tubeless tires and they hold pressure for a year or more. 

 

I've found a wide range of quality in Schrader valves so be careful about what you have, or what you buy.  I've found that the high temp ones with a red "rubber" seal seem to hold up better than the black "rubber" versions.  A truck tire shop will have the best quality Schrader valves.

Edited by Chuck.
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  How is a tire supposed to maintain pressure if the atmospheric pressure is greater than that inside the tube if there is no spring to keep the valve sealed shut? 

 

  your gauge shows the difference between pressure inside the tube and atmospheric pressure.

a flat tire is at atmospheric pressure. when your gauge shows 0.8bar/12psi inside the tube there are 0.8bar+atmospheric pressure: an inflated tube always provides a force pushing against the spring.

 

a gauge measures pressure of tube + total volume of the gauge.  when this volume is large (for example a bicycle floor pump with raised handle) you loose air from the tube at every check. you can verify how much air you loose at every check, just recheck after a few seconds.

imho 4 psi over 2 weeks is normal for natural rubber

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  your gauge shows the difference between pressure inside the tube and atmospheric pressure.

a flat tire is at atmospheric pressure. when your gauge shows 0.8bar/12psi inside the tube there are 0.8bar+atmospheric pressure: an inflated tube always provides a force pushing against the spring.

 

Right.  That should have occurred to me 🤦 .  Still doesn't explain why the schrader valves I have don't have springs in them.

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Ok, it makes since but when I buy a new tube in a box and spread it out on the bench, it's 18" or 21"round in circumference" but the (100x100) diameter is not round, it's flat.

If I were to remove the valve core, air rushes into the tube causing it to "fluff up" slightly. (Like I said earlier, I don't remove the core, when the tube is new)

So it had less than atmospheric pressure in it, correct?

Does that mean it "was" under a vacuum?

If so, How would you measure the amount of vacuum? (Not that it really matters)

I asking because I always use dry nitrogen in all tires on everything.

(Because it pleases me)

Does that mean that my tires have 100% dry Nitrogen without any moisture inside the tube?

My Understanding is:

Nitrogen molecules are larger than most others in the air we breathe so they don't escape as rapidly, causing a longer amount of time they are holding pressure and because of no moisture, the pressure is more consistent regardless of outside air temps, water crossings, hot pavement, etc.

A full bottle (2,000 psi) last me about a year and cost is about $35.00 to Refill it.

I welcome all Thoughts?

Now if I used Helium in my tires, my Bike(s) would be lighter, correct? Lol

Edited by adnohguy
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Ok, it makes since but when I buy a new tube in a box and spread it out on the bench, it's 18" or 21"round in circumference" but the (100x100) diameter is not round, it's flat.

If I were to remove the valve core, air rushes into the tube causing it to "fluff up" slightly. (Like I said earlier, I don't remove the core, when the tube is new)

So it had less than atmospheric pressure in it, correct?

Does that mean it "was" under a vacuum?

If so, How would you measure the amount of vacuum? (Not that it really matters)

I asking because I always use dry nitrogen in all tires on everything.

(Because it pleases me)

Does that mean that my tires have 100% dry Nitrogen without any moisture inside the tube?

My Understanding is:

Nitrogen molecules are larger than most others in the air we breathe so they don't escape as rapidly, causing a longer amount of time they are holding pressure and because of no moisture, the pressure is more consistent regardless of outside air temps, water crossings, hot pavement, etc.

A full bottle (2,000 psi) last me about a year and cost is about $35.00 to Refill it.

I welcome all Thoughts?

Now if I used Helium in my tires, my Bike(s) would be lighter, correct? Lol

When tubes are packaged for shipping they suck out the air to reduce the size for shipping, the rubber will try to return to original shape when the tube is unpacked.

 

I'm not sure I buy the molecule size with tube air loss since Carbon, Nitrogen, and Oxygen are adjacent to each other on the Periodic Table of Elements so their size and atomic weights are very close. As gases they are bonded to one or more atoms to form a molecule; CO2, N2, and O2;   Carbon Dioxide is the largest with 3 atoms.

 

IMO air loss is from air leaks, and as others have posted natural rubber seems to be more porious than synthetic rubbers.

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