Nitrogen filling

[sirbike]

I have a three year old, 25,000 mile Penske shock that is mostly likely low on nitrogen.
This has me wondering is it normal to loose pressure over time when all else is in fine condition. I assume this is probable while asking from someone with more experience.
As I call cycle shops and not finding any nitrogen after a few calls, I find that I can buy a tank and regulator nearby and order a no loss schrader valve. For about $650 I can have my own fill service for the four nitrogen shocks in my fleet.
If low nitrogen automatically means it’s time for a rebuild I would skip the tank idea and send the shock for service.
Opinions on inflating with air are all over the place on the rest of the internet, ranging from devastating explosions to ok but not ideal. Seeing this I figure nitrogen is the worthwhile safe bet.

 

[klaproth]

Since the air we breathe is 80%+ nitrogen, couldn’t you just add a good air drier on your compressor, and use it to fill the shocks?

I often smile when I see claims of “ more mileage, smoother ride” from nitrogen filled tires….

 

[dwalby]

@klaproth a regular 125psi air compressor isn't enough pressure for this application, something closer to 200psi is needed.

@sirbike how do you know that it is "most likely low on nitrogen"

 

[Slammer]

Since the air we breathe is 80%+ nitrogen, couldn’t you just add a good air drier on your compressor, and use it to fill the shocks?

I often smile when I see claims of “ more mileage, smoother ride” from nitrogen filled tires….

Got into a discussion a while back with one guy.... 3 series black BMW with toned windows, you know the type. I commented on the green valve nubbles on the tires and I was informed that it is because he paid top Euro for nitrogen. 60 Euro a tire.... "Why?" I ask all innocent. "It´s technology from the aeronautical and spaceflight industry, Nitrogen molecules are larger that oxygen molecules so you keep a filling longer.... All the other guys in the group nodded. "Best there is" I was assured.
"Well" I say. The reason it is used in the aeronautical industry is that at the operating hight of jets the air is -50, -60° and normal air would freeze, that´s the only reason. Then oxygen molecules are in fact larger that those of Nitrogen, and lastly the air that you breath is already 80% Nitrogen, so I would have just bought the green nubbles and be done with it.
Needless to say I was not popular.

 

[dwalby]

Yikes, Costco gives it away for free if you bought your tires from them. €60 per tire is insane, I guess there's one born every minute.

 

[Superdirk]

Intersting, I also heard that N2 molecules are supposedly bigger than O2 and therefore have a benefit maintaining tyre pressure. according to a website :

Molecular size a bit tricky. As a quick comparison, we can use the covalent radius defined as 1/2 the distance between to identical covalently bonding nuclei. This is measured in picometers (1 pm= 1x 10-12 m). Nitrogen's covalent radius is 75pm so the length of a nitrogen (N2) molecule ought to be 4 X 75pm or 300 pm. A molecule of oxygen (O2) ought to be just a shade smaller 4 X 73pm or 292pm. So an oxygen molecule is a little less than 3% smaller than a nitrogen molecule.

So that is evidence that due to the increased size of the molecules, N2 filled tyres maintain their pressure much longer and this effect is much more significant than any negligable effect of rim damage, leaky valve stems or cheap green valve nubbles or nails on the road... It's on internet therefore must be true (just like everything we post here)

 

[dwalby]

Having already known all of this, I specifically shop for tires made from rubber with molecular gaps no bigger than 70.0pm. Its a bit of a chore to lug the electron microscope around from store to store, but I have no issues with deflation over time.

 

[Slammer]

Intersting, I also heard that N2 molecules are supposedly bigger than O2 and therefore have a benefit maintaining tyre pressure. according to a website :

Molecular size a bit tricky. As a quick comparison, we can use the covalent radius defined as 1/2 the distance between to identical covalently bonding nuclei. This is measured in picometers (1 pm= 1x 10-12 m). Nitrogen's covalent radius is 75pm so the length of a nitrogen (N2) molecule ought to be 4 X 75pm or 300 pm. A molecule of oxygen (O2) ought to be just a shade smaller 4 X 73pm or 292pm. So an oxygen molecule is a little less than 3% smaller than a nitrogen molecule.

So that is evidence that due to the increased size of the molecules, N2 filled tyres maintain their pressure much longer and this effect is much more significant than any negligable effect of rim damage, leaky valve stems or cheap green valve nubbles or nails on the road... It's on internet therefore must be true (just like everything we post here)

I did find this..:

"A nitrogen molecule measures roughly 300 picometers while an oxygen molecule measures 292 picometers. That's only a 2.6% difference in size. One picometer is equal to one trillionth of a meter (1 m / 1,000,000,000,000)."

Basically same difference.

 

[Al st1100]

hey guys he is talking about a shock not tires !

 

[Al st1100]

Oh by the way tires are not made out of rubber

 

[SMSW]

The reason it is used in the aeronautical industry is that at the operating hight of jets the air is -50, -60° and normal air would freeze, that´s the only reason.

If normal air freezes at the operating height of jets, what do they use to combust the fuel? Maybe abnormal air?

 

[SMSW]

I have a three year old, 25,000 mile Penske shock that is mostly likely low on nitrogen.

A couple of points here. Normal life of a shock is what, 50K miles? Over that lifetime, the seals wear very slightly, but they do wear. What are the relative costs of a suspension shop's charge for boosting the N2 pressure vs. rebuilding the shock? If you have lost pressure, I'd go for the rebuild, unless you can talk to a knowledgeable guy about your shocks. How about calling RaceTech? I found their guys to be very helpful.

 

[bdalameda]

The basic argument of 100% nitrogen vs regular air is:
Air from a compressor though 80% Nitrogen can hold moisture from the air. Pure Nitrogen from a bottle is dry. With any moisture entering the shock, the potential for expansion from heat is ever present. Oxygen will also expand more rapidly from heat. Basically the idea of using dry nitrogen vs. regular air insures that the shock damping will perform consistently with temperature changes so dry nitrogen is preferred. Moisture can also increase the possibility of corrosion on the internal shock components. It is pretty amazing how much heat can be generated inside a shock when riding on a bumpy road.

 

[dwalby]

If normal air freezes at the operating height of jets, what do they use to combust the fuel? Maybe abnormal air?

he was half right, its the water vapor in normal compressed air that would freeze.

water vapor in compressed air is the thing that is avoided by using Nitrogen instead, since its dry. Apparently a fair amount of water vapor exists from regular air compressors and as the tire heats up it can turn from liquid to gas under extreme uses like racing, and changes the pressure inside the tire more than a dry gas like Nitrogen.

 

[dwalby]

The basic argument of 100% nitrogen vs regular air is:
Air from a compressor though 80% Nitrogen can hold moisture from the air. Pure Nitrogen from a bottle is dry. With any moisture entering the shock, the potential for expansion from heat is ever present. Oxygen will also expand more rapidly from heat. Basically the idea of using dry nitrogen vs. regular air insures that the shock damping will perform consistently with temperature changes so dry nitrogen is preferred. Moisture can also increase the possibility of corrosion on the internal shock components. It is pretty amazing how much heat can be generated inside a shock when riding on a bumpy road.

There may be some very small real-world differences, but generally all gases will follow the ideal gas law pretty closely, so I doubt there's any real difference in expansion rates between N2 and O2 molecules.

question about the pressurized chamber in the shock. I think I've read somewhere that its purpose is to prevent the oil from entering places its not wanted, not to provide any performance related aspect to the shock, is that correct? If so, then it probably doesn't matter what the actual pressure is exactly, just that its high enough to do the job. I think the main risk of using plain air is the moisture aspect you mentioned, where the water vapor molecules could corrode internal surfaces, especially if they're made of steel.

 

[bdalameda]

There may be some very small real-world differences, but generally all gases will follow the ideal gas law pretty closely, so I doubt there's any real difference in expansion rates between N2 and O2 molecules.

question about the pressurized chamber in the shock. I think I've read somewhere that its purpose is to prevent the oil from entering places its not wanted, not to provide any performance related aspect to the shock, is that correct? If so, then it probably doesn't matter what the actual pressure is exactly, just that its high enough to do the job. I think the main risk of using plain air is the moisture aspect you mentioned, where the water vapor molecules could corrode internal surfaces, especially if they're made of steel.

The problem with the moisture in the shock is that as the fluid is compressed through the shock valve and orifices the pressure spikes and the moisture rapidly vaporizes and reduces the shock damping effect. Much like how moisture in a brake system causes brakes to fail as the water vaporizes under pressure.

 

[SMSW]

Basically the idea of using dry nitrogen vs. regular air insures that the shock damping will perform consistently with temperature changes so dry nitrogen is preferred.

Seriously, if one can buy dry compressed N2, why can one not use a desiccant in an in line filter on a compressor? Last I read, you want dry air for spraying a flawless finish on a mc tank or auto body. Is that not dry enough? We are, of course, ignoring that most residential and small shop type compressors will not reach the 200 psi mentioned in a post above.

 

[bdalameda]

Seriously, if one can buy dry compressed N2, why can one not use a desiccant in an in line filter on a compressor? Last I read, you want dry air for spraying a flawless finish on a mc tank or auto body. Is that not dry enough? We are, of course, ignoring that most residential and small shop type compressors will not reach the 200 psi mentioned in a post above.

I'm just saying what is preferred and suggested by most if not all suspension specialists. I am not telling anyone what they can or cannot do. I'm not arguing here, anyone is free to make their own choices.
.

 

[dwalby]

We are, of course, ignoring that most residential and small shop type compressors will not reach the 200 psi mentioned in a post above.

I think this is the primary reason for the shock application.

For tires, it seems that its not as easy as you claim to get compressed air that's dry enough, because none of the race teams do that, they all use Nitrogen.

 

[rogo]

I work on stockpickers (warehousing) that utilize a nitrogen filled accumulator in the hydraulic system for cushioning.
Maybe a local forklift shop would be able to fill it.