Nitrogen vs Oxygen

Jaybird · Mar 17, 2002

I'm curious as to the reason nitrogen is used for shocks. Would oxygen perfom the same as nitrogen IF it were completly dry?

Vic · Mar 17, 2002

Kaboom?:eek:

DKT735 · Mar 17, 2002

Vic is right!

Don't substitute oxygen for nitrogen in your shock bladder. Using oxygen or compressed air to recharge your shock is putting a fuel source and an oxygen source together is a bomb in the making that happens to be between your legs. Can you say ouch?

morph · Mar 18, 2002

the reason for using nitrogen is that it is an inert gas..doesnt react with any thing.And that it is temperature stable increasing the temp hardly increases it's presure unlike most gasses..heat up a sealed container full of air and see what happens...bang

mxneagle · Mar 18, 2002

All gases must abide by the equation PV=nRt. Nitrogen increases pressure just like a combination of N2, O2 & CO2 (ie air)

dodgedogjb · Mar 19, 2002

Pure oxygen is also very reactive to metals and other materials such as seals which could lead to premature failure. Another reason I can think of is the possible formulation of moisture inside the shock. Probably the biggest reason though is that both Nitrogen and Oxygen would perform very much the same but Oxygen is much more difficult and expensive to use in a manufacturing environment and its much more expensive to purchase...so no real advantage.

Just my thoughts.

Jaybird · Mar 20, 2002

OK, on the boom boom theory....:) Oil and air don't mix IF there is an ignition source. I do understand that oxygen can serve as a accelerator and with an ignition source, can ignite oil and even explode....BUT the only ignition source available in a shock ids friction. I highly doubt that there is enough friction from usage to ignite. But I do see where y'all would think that.
I actually have seen an oxygen cylinder completelt explode during fill due to the fact that some idiot painted the threads on the filler with machine oil to make the brass go on easier....big kaboom! (wish I had the picture, it would amaze you)

Now, back to the shock. The only downside I can see by using compressed air (forget pure oxygen for my question) is the moisture. If one were to be able to obtain completely dry compressed air, would it work? I feel it will, but would like some more input here.
Thanks

MX-727 · Mar 20, 2002

O2 is corrosive. No matter how dry it is going in, you are going to pick up some moisture from the oil, which will react negatively with the internals of your shock.

Jaybird · Mar 20, 2002

If there is in fact moisture in the oil, why would it be different than sharing the space with nitrogen? Are you saying the "air" would draw out the moisture from the oil and the nitrogen won't?

dirt bike dave · Mar 20, 2002

Air is about 70% nitrogen. I have filled shocks with air and you cannot feel any difference. It is possible that over time contaminants in the air could weaken the bladder. Air is more explosive than nitrogen, but most shock bodies are aluminum and not prone to sparking, even if something were to hit it hard.

All in all, nitrogen is superior to air for filling your bladder with, but air will work if you have no access to nitrogen or no money.

MX-727 · Mar 20, 2002

No, if any moisture is present, the nitrogen will draw it also. But, O2 is very reactive. Oxygen causes rust, thus the term oxidation. Heck, burning of a material is also a form of oxidation. Oxygen is the catalyst. Without it, no burning, no rust, no corrosion. Those are the real reasons we stick with inert gases. Inert being the keyword. Oxygen is anything but. Oxygen is even corrosive to the human body. Breathing pure oxygen at higher pressures (scuba diving comes to mind) is toxic. One of those too much of a good thing dilemas. :eek:

Road/Dirt Rash · Mar 20, 2002

using dry air is OK, they use it in airplanes when nothing else is available and it is perfectly acceptable. Those accumulators run 1500 to 3000 psi without a problem. Using pure oxygen in any form is not. The major dif is that much higher pressures can be used with nitrogen as most folks air compressors don't get very high. I have been running air for twenty years without incident either on the Boom side or corrision. I usually run only 125 psi because that's all I have and I usually change the oil in my shock three or four times a year. If you burst a bladder, you will know right off that it is time for repair and oil change no matter what it has in it.

Jaybird · Mar 21, 2002

KX-727,
I have always felt that the downside of compressed air (not oxygen, we aren't talking oxygen here folks) is the moisture/dirt content. I think that no matter what, we are going to see a certain level of oxidation with oils occur over time. It's one of the main reasons we change out (or should) our fork oils and also why we open our bleed holes on the forks so the gas created can escape.
Maybe a versed expert could weigh in here and tell me if I'm wrong...but isn't the real reason we opt for nitrogen is that clean/dry air is just not readily available.
btw...isn't the corrosiveness, that we are concerned with here, the oxide that is created when oils oxidate, and not the oxygen in paticular?? ie.aluminum oxide.

MX-727 · Mar 21, 2002

Clean/dry air vs. nitrogen: probably so. We do put unconditioned compressed air in steel and aluminum wheeled tubless tires with little harm. Of course, there are no moving internals to get fouled up. Air vs. nitrogen is probably not as big a deal. I was really only addressing the pure, dry, O2 vs. dry nitrogen.

Something I was neglecting is the fact that in a shock, there is a bladder that seperates the oil and compressed gas.

Jaybird · Mar 22, 2002

KX-727,
I also made the mistake of starting this thread and using the term oxygen, when in fact I had Air in my brain. :confused:

I remember not long ago Jeremy posted a pic of a bursted shock body and asked opinions on what caused this. My guess was that air had been used and the moisture expanded. (not sure if that thread was ever settled)

I've always felt that compressed air that was say .001 micron clean and totally dry (ISO quality) would be fine in a shock. Just wonder if there are downsides I haven't thought of.

marcusgunby · Mar 22, 2002

Jer said dry air is fine to use.

Papakeith · Mar 22, 2002

Originally posted by Jaybird
If there is in fact moisture in the oil, why would it be different than sharing the space with nitrogen? Are you saying the "air" would draw out the moisture from the oil and the nitrogen won't?

Regardless of wether or not you use air or nitrogen it wil not draw moisture from the oil. The gas is kept seperate from the oil by a rubber bladder. Unless the bladder fails the two never meet.
The only place that I believe would show a corrosive consequense of using air would be the resevior cap and valve.

Jaybird · Mar 23, 2002

If the air is moisture free, it should be of no consequence.

NGE · Nov 21, 2003

ok, I have a high pressure air pump... (bought from a bicycle shop for about $20 US... pedal-bikes run air/oil shocks as a regular).. this pump goes to about 300psi with relative ease.

Heres my input... although I realize that bikes do not stress the shock as much as an MX'er can, my observation has been that these shocks are made in the same manner as motorcycle shocks (albeit a bit smaller)... they come in air sprung/oil dampened and nitrogen and coil sprung/oil dampned.... They are ALL made with aluminum bodies with no sign of excess corosion on the air models (I have worked on MANY, and owned MANY for MANY years)...

A company called Fox (perhaps you've heard of them..lol) makes them (and the pumps) for the Mtn Bike industry... They are the company that has the air/oil (not the nitro)...

I have never had the opportunity to substitute air in a nitro shock because the nitro shocks are all sealed.. :( ... while this makes for a better seal, and they literaly almost NEVER leak, they are less adjustable and thus the air ones (which can be adjusted at will) are preferable to most regular riders... The DH riders go with the Nitro-coil spring/oil dampned models..

These pumps are tiny (about the size of a 10" long 3/4"dowel), cheap, and can be carried with... so, you have spring adjustability ON THE TRAIL... or in the garage with ease...

So, there is at least ONE advantage to running air...

Would I use the same pressure for air as I would for nitrogen?

marcusgunby · Nov 21, 2003

PMK · Nov 21, 2003

I think Vic had it right in the very first reply. Kaboom! When using oxygen never use petroleum products as a lube or in contact a it's possible for the grease and O2 to spontaniously combust. Or so I'm told and I'm not one to test the accuracy. For all the O2 servicing and maintenance we use special non petroleum lubes.
PK

muddy226 · Nov 21, 2003

In Eric Gorrs book he says "never use air to pressurize the bladder ", but he doesn't say why, so perhaps this doesn't help much. Could it have anything to do with compression ignition ? ( "Dieseling"). A miniscule amount of oil when compressed in a chamber with air will explode. If you have an airgun and put a bit too much gun oil in the cylinder it makes a big bang until the oil is gone.

James · Nov 21, 2003

Am I missing something or is everybody overlooking the fact that forks use the same oil as shocks and that oil is mixed with "AIR" all of the time? And this is just ordinary "outside" air all full of moisture and whatever. Not only that but is seems like there is a whole lot more moving in there that might ignite the "fuel." I do understand that the max pressure in the bladder is probably higher than that of the forks but as somebody mentioned...the air in the shock only mixes if the bladder breaks.

I only pump mine up to 150 psi (manual says 142) but I think these bladders can handle well beyond 175 cold psi? (implying that the design of the bladder could most likely accomodate the air if it increased in pressure more than nitrogen as a result of heating from use).

In some of these instructions I have for servicing suspension..it says to use compressed "air" to first charge the bladder to 7psi for bleeding, and then to later use air at about 1/2 regular charge to test the assembly before taking it to the shop for charging.

Weren't "Air Shocks" the thing on MX bikes "back in the day"? Matter of fact, I think that has already been mentioned in another of these threads (or is it de ja vue??)

I know I had air shocks on the old Cutlass GT with the 350 Rocket engine and they didn't explode even when I jumped it like Dukes of Hazard. (I know that is completely different application but I was having flashbacks...sorry). But on a similar note...don't they use air assisted suspension in these off road trucks/buggies?

So many questions...so little time. I am not arguing a side...just sharing my confusion. I used air the last few times.

muddy226 · Nov 21, 2003

I think you can still buy air shocks for MXers, Fournales ?, I seem to remember seeing a "shock shootout" in a trail bike magazine, they were rated second to Ohlins on lap times, but first on "feel". I think the diff. might be no oil at all. Re the forks, they don't start off with high air pressure, and the quantity of oil in the mix would probably preclude ignition anyway. Just guessing, need an expert !

"Air shocks" I have just discovered do not have any seperation between oil/air with a floating piston as other types, and I think are best described as an emulsion controlled oleopneumatic shock. There is also a shock called the Air Xo, which has no metal spring but has a totally seperate chamber filled with compressed air. I know this is a bit off the topic but i thought it might be interesting. I think in the air shock combustion is unlikely because of the high amount of oil in comparison to air, as with forks.

WWR · Nov 21, 2003

There are three reasons that Nitrogen is preferred by the Military:

- even "dry" air seems to thermally expand/contract more than pure Nitrogen. I have seen this alot in our aircraft tires. Using Nitrogen, the pressures seem to hold much more stable.
- air also seems to cause more corrosion (at least that is what our superiors tell us).
- Nitrogen is a "safer" gas. In the event of an accident, a blown accumulator (about 3000psi) of Nitrogen will not enhance a fire if it explodes. Air, or anything with oxygen in it, often does.

I think it may be easier to get pure Nitrogen than it is to get purely "dry" air. If you have "dry" air that still has a mix of oxygen and hydrogen gas molecules, the two can mix later due to temperature or pressure changes and create water (condensation). This causes your previously set pressure to drop, and may cause corrosion.

Nitrogen vs Oxygen

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