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Nitrogen in Rear Shock. Can air be used?

52 posts in this topic

I was curious to see why Nitrogen is put into the rear shock. Does plain ole air just get contaminated?

Would it be harmful to put air in the rear shock?

My mountain bike stuff just uses air from my shock pump.

Just curious cause i want to check the pressure, but i know it will probably lose a lot of pressure and it will probably be $$ at my local shop to refill the Nitrogen.

But before i check it i just wanted to know why Nitrogen is used and if air could be substituted.

Thanks for any info.

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Nitrogen is an inert gas which remains a gas at extremely high pressures. Shop air from a compressor has moisture in it which leads to internal corrosion of the shock over time.

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Believe me it's nitrogen for a reason and it's usually just a few $$$ to get it charged.

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Air and oil under pressure can diesel.

A good proctologist would be needed after and episode like that.

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Nitrogen is not an inert gas. It is, however, very inactive, chemically, and does not at all readily involve itself in chemical reactions. You could say it's somewhat inert. Air, on the other hand, contains oxygen, one of the original busy bodies of chemistry, along with carbon dioxide and several other gases, and even if it were dried , it's more reactive than nitrogen by itself, so the point made is the same.

Nitrogen is also more compressible than other air gases are, which allows it to be put in a smaller space at a higher pressure, and compressed to a higher degree without the pressure rising to a dangerous level.

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Using air rather ethan nitrogen is dangerous due to the small volume of highly compressed gas. When the air expands due to heat, it could explode the reservoir. A nitrogen recharge is only about $15 at a dealer.

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Gotta agree with Gray, I couldn't have said it better. Air is mostly nitrogen, but the low percentage of oxygen (12%?) will cause rubber seals to oxidize, moisture in the oil to oxidize, etc.

Just make sure the shop is reputtable (sp?)....and doesn't just put in compressed air.

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Gotta agree with Gray, I couldn't have said it better.
But I did omit the fact concerning the thermal expansion of air, too.

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Also, by its nature, nitrogen doesn't absord water vapor as much as O2 or air, has less partial pressure (more compressable and purges heavier gases)....also if we look at nuclear-phyllic attacks with a N2 compounds........don't get me started...

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I was ALSO thinking they put in nitrogen because the nitrogen molecules are bigger than air molecules. The larger molecules have a harder time going through the rubber seal, so the charge lasts longer. That is why they put nitrogen in airplane tires. Atleast that is what I have heard.

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The main reason Nitrogen is used is because it is less likely to change when heated. ie. if air was used and you started with a pressure of 140#, by the end of the moto the pressure could be as high as 160#, where the Nitrogen filled shouck might only gain 5#. The same reason we run Nitrogen in our tires on the Mile ovals. Tdub

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I was ALSO thinking they put in nitrogen because the nitrogen molecules are bigger than air molecules. The larger molecules have a harder time going through the rubber seal, so the charge lasts longer. That is why they put nitrogen in airplane tires. Atleast that is what I have heard.

:thumbsup:

I was gonna say the same thing. Tire stores also use N2 because people are too lazy to check the air pressure in their tires, and low tires lead to blowouts.

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The main reason Nitrogen is used is because it is less likely to change when heated. ie. if air was used and you started with a pressure of 140#, by the end of the moto the pressure could be as high as 160#, where the Nitrogen filled shouck might only gain 5#. The same reason we run Nitrogen in our tires on the Mile ovals. Tdub

I've always heard Nitrogen was used in aircraft struts because it is thermally stable in addition to it's cleanliness.

What is the normal precharge of the shock on the 450, should it be checked more than annually? Or any bike for that matter I would imagine they leak down some over time.

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Nitrogen is bigger than air? Nitrogen is found in the form of N2, thus its 14 daltons in weight (or weight, however you want to look at it), "Air" is (approx) 76% Nitrogen, 15% Oxyegen (O2 = 18 daltons) and the rest is a mix of other gases (CO2, etc). Add it up, "Air's" average size is just larger than N2 alone.

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It would also be tough to find a compressor that would charge a shock at 150-175 PSI.

Any scuba diving shop can do 5000 psi air

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if you put standard air from a compressor in your shock I'm guessing the hike in pressure when its warm would blow the seals out. Argon is inert but I'm not sure whether it would react to heat change as well as nitrogen :thumbsup::thumbsup:

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The main reason Nitrogen is used is because it is less likely to change when heated. ie. if air was used and you started with a pressure of 140#, by the end of the moto the pressure could be as high as 160#, where the Nitrogen filled shouck might only gain 5#. The same reason we run Nitrogen in our tires on the Mile ovals. Tdub

I agree :thumbsup:

Contrary to some claims, nitrogen does not diffuse through tire rubber more slowly than air. Air is mostly a mixture of nitrogen and oxygen, and the nitrogen molecules are smaller. All else being equal, smaller molecules diffuse through porous substances more quickly.

Pure Nitrogen is an inert gas, meaning it does not change state very easily or chemically react with other materials very easy. :thumbsup:

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