Nitrogen in Rear Shock. Can air be used?


51 replies to this topic
  • Fastest1

Posted April 21, 2006 - 02:29 PM

#41

Straight from the Boeing website.

In addition, Boeing has received reports of three confirmed cases and other suspected cases in which a wheel/tire assembly exploded when the oxygen in air-filled tires combined with volatile gases given off by a severely overheated tire. In one case, the tire became overheated as a result of a dragging brake, and the wheel/tire assembly exploded when it reached the auto-ignition temperature. In another case, a wheel/tire assembly explosion in the wheel well during flight was suspected in the catastrophic loss of one airplane. A similar explosion caused severe damage to two others.

As a result, the U.S. Federal Aviation Administration issued Airworthiness Directive 87-08-09 requiring that only nitrogen be used to inflate airplane tires on braked wheels. However, tires may be topped off with air in remote locations where nitrogen may not be available if the oxygen content in the tire does not exceed 5 percent by volume.

  • FZ1426

Posted April 21, 2006 - 02:46 PM

#42

The nitrogen or air if that was used would be contained in a bladder causing no corrosion. From my experience roadracing where quite a few people filled their tires with Nitrogen, it was because the pressure remained closer to the original setting hot or cold, and it was cheap. Would a tire mounted at sea level and pressurized stay together at 30,000 ft? I dont see why a gas contained inside the tire makes any difference until the tire burned all the way thru and released the gas.

Gasses do have different adiabatic pressure rates. Nitrogen's is less than that of say, oxygen, or air. Compressed nitrogen may be cheap, but not cheaper than compressed air. The only place you'll find compressed air is in home and industrial shop compressors and usually at no higher a pressure than about 120psi. Nobody will store air in a bottle (safely) for long at higher pressures because the moisture and oxygen in the air will corrode the bottle (unless it's a composite bottle) and go boom (or just leak out slowly if you're lucky). 200psi. aircraft tires (wheels) can and do to stay together all day long at 30K and higher. It's not that much of a pressure differential. Of much higher concern is the heat generated by the brakes which could explode the wheel if not for fuse plugs designed to melt and release the pressure at about 400 degrees F.

  • Numskull

Posted April 21, 2006 - 04:02 PM

#43

I see that I should have said "naturally occurring compounds" containing the 5 inert gases. There are none, where as nitrogen compounds are extremely commonplace in nature. Which brings us back to the original point that nitrogen is not inert.


Nitrogen placed in the shock has created an inert atmosphere, displacing oxygen and the moisture that oxygen contains and absorbs. In another words, there will be no chemical reactions with other elements; there will be no oxidation; there will be no degradation of the nitrogen gas. So in this application, it is referred to as an inert gas. :thumbsup:

  • Numskull

Posted April 21, 2006 - 04:20 PM

#44

They have also used nitrogen as an inert gas in aircraft ,not only in tires, but to prevent fuel tanks from exploding.

I think probally the biggest thing about useing air rather than nitrogen in the shock is the fact that air contains moisture (h2o). Its the moisture that will reak havoc on the pressure stabilty. With such a small resevoir for the charge, alittle will go along way as far as unstabilty.

  • grayracer513

Posted April 21, 2006 - 04:40 PM

#45

Nitrogen placed in the shock has created an inert atmosphere, displacing oxygen and the moisture that oxygen contains and absorbs. In another words, there will be no chemical reactions with other elements; there will be no oxidation; there will be no degradation of the nitrogen gas. So in this application, it is referred to as an inert gas. :thumbsup:

They have also used nitrogen as an inert gas in aircraft ,not only in tires, but to prevent fuel tanks from exploding.

I think probally the biggest thing about useing air rather than nitrogen in the shock is the fact that air contains moisture (h2o). Its the moisture that will reak havoc on the pressure stabilty. With such a small resevoir for the charge, alittle will go along way as far as unstabilty.

1) Any non free oxygen bearing gas, such as CO², can be used for the suppression of oxidization by displacing oxygen or air in a confined environment. But then, anything will react with nothing if it's isolated from everything else. That does not make it inert.

2) Air can be rendered anhydrous as easily as nitrogen.

3) Neither of these points matters a wit relative to the corrosivity question in a typical rear shock because the gas is separated from virtually everything except the inside of the bladder cap by the bladder.

The manufacturer's stated reason for the use of nitrogen in a shock of this type is to reduce the pressure rise caused by frictional and compressive heating.

  • Numskull

Posted April 21, 2006 - 04:55 PM

#46

1) Any non free oxygen bearing gas, such as CO², can be used for the suppression of oxidization by displacing oxygen or air in a confined environment. But then, anything will react with nothing if it's isolated from everything else. That does not make it inert.

2) Air can be rendered anhydrous as easily as nitrogen.

3) Neither of these points matters a wit relative to the corrosivity question in a typical rear shock because the gas is separated from virtually everything except the inside of the bladder cap by the bladder.

The manufacturer's stated reason for the use of nitrogen in a shock of this type is to reduce the pressure rise caused by frictional and compressive heating.


1) CO² is considered inert

2) air is like 75% nitrogen its the oxygen that is so reactive. Nitrogen is anhydrous where as air is not.

3)The manufacturer's stated reason for the use of nitrogen in a shock of this type is to create an inert atmosphere to reduce the pressure rise caused by frictional and compressive heating.

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  • MotoGoalie

Posted April 22, 2006 - 07:24 AM

#47

So huffing Nitrogen will render me inert? :thumbsup: :thumbsup:

  • FFRacing79

Posted April 22, 2006 - 11:31 AM

#48

1) The manufacturer's stated reason for the use of nitrogen in a shock of this type is to reduce the pressure rise caused by frictional and compressive heating.


Finally greyracer....this the SOLE reason it is used in shocks. Thank you very much...Tdub

  • FFRacing79

Posted April 22, 2006 - 11:32 AM

#49

So huffing Nitrogen will render me inert? :thumbsup: :confused:

Inept...maybe lol Tdub :thumbsup:

  • FFRacing79

Posted April 22, 2006 - 11:46 AM

#50

Short funny story...
Just before BikeWeek '04, I was helping out DTer National #42 Bryan Smith. We were getting the bikes ready for the ST National. Many DTers carry a Nitrogen tank on board to not only fill tires but to power air tools as well. Well, the Nitrogen tank was low for a full weeks of racing so I sent Bryan to the "gas store" to get it refilled. He came back and we strapped the tank in the back of the hauler. I never bothered to look at the tanks label.
ell bryan had a pretty good week leading up to the ST Hotshoe and National. We ended up winning the Hotshoe and podiumed the National. Everyone was happy as we headed home.
Once we got back to the race shop at home, we noticed Bryan's MX practice bike had a blown shock. I proceeded to rebuild it for him, then went out to the truck to charge the shock from the "nitrogen" tank. When I got to the truck, I noticed the label on the tank that I had apparently not noticed all week in Florida. Instead of charging the shock, I went back into the shop and grabbed an ineer tube which I then filled from the "nitrogen" bottle. I went back into the shop and asked Bryan about the refill. After he told me he was sure he got the "right" stuff, I took a big hit from the inner tube and then talked like Minnie Mouse! They had exchanged a Nitrogen bottle with a HELIUM bottle!!! We then all laughed at how we had found a NEW secret!! This "secret" has never been leaked before this...just hope Bryan doesn't see this post, cause I wasn't suppose to tell of our "screwup"! Tdub :thumbsup:

  • DaveJ

Posted April 22, 2006 - 01:37 PM

#51

So I think we agree that pressure increases between nitrogen and outside air are the same, however, it is noted that 200PSI of heated outside air will feel different than 200PSI of heated nitrogen. Is that right? And if so, why?

I also hope that the message got out that nitrogen runs cooler (dare I say it like that). Meaning that a nitrogen filled tire or shock will remain at a lower or more consistant pressure than one filled with outside air.

I would assume this is the primary reason for the popularity of nitrogen in truck and RV applications as well.

Personally, I had set out one day to test pressure rises between two similar shocks, one with nitrogen and the other with outside air. Based on my crude instrumentation, they both rose at the same rate when heated, (temps to PSI). However, at a certain point, I was not able to get the shock filled with nitrogen anywhere near as hot as I could get the shock filled with outside air. And I was able to get the shock far hotter than the shock would get at an advanced track.

Therefore, it became obvious that the nitrogen filled shock would stabilize (even under the most severe motocross application) at a much lower PSI.

And of course, you're still going to be dealing with operating PSI verses static or cold PSI, if you tune to that level.

  • grayracer513

Posted April 22, 2006 - 05:24 PM

#52

So I think we agree that pressure increases between nitrogen and outside air are the same,

In a strict sense, maybe, but not in a practical one.

Personally, I had set out one day to test pressure rises between two similar shocks, one with nitrogen and the other with outside air. ... However, at a certain point, I was not able to get the shock filled with nitrogen anywhere near as hot as I could get the shock filled with outside air. And I was able to get the shock far hotter than the shock would get at an advanced track.

Therefore, it became obvious that the nitrogen filled shock would stabilize (even under the most severe motocross application) at a much lower PSI.

One of the two stated reasons for the use of nitrogen to fill tires, and the reason it's used in shocks, is the lower pressure rise under exposure to heat. The fact is that nitrogen will not retain heat as well as air will, even dry air.

BTW, clean, dry air is more expensive to produce than the cost of isolating nitrogen from air.





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