Argon vs Nitrogen in Coilovers

[ksagis]

Internet has so much garbage on it that I thought I’d post the question here. It seems other than cost, Argon is fine for coilovers in terms of how the gas performs, no oxygen to promote corrosion, leak rates.

I’d do a couple partial fills and vents to dilute any remaining nitrogen in system before Argon fill. Also, I’m not worried about fill hardware difference like regs, etc. I have plenty of hardware that will work fine for argon at these pressures.

Am I missing anything that Argon is totally fine, any opinions from experts on the forum?

 

[ntsqd]

How does argon differ in it's volumetric change with temperature? My understanding is that N2 was chosen because it is one of the lowest that is economical to procure.

 

[ksagis]

My interpretation of the ideal gas law says the volume change would be the same for the same temperature change. I think it's more complicated since there's work being done (for something like a shock that is cycling back and forth) so maybe one need to look at gas constant as well.

 

[ksagis]

This may be a case of a desert rig with high rate of cycling would prefer nitrogen over argon, but a rock crawler to a street rig falls in the category of it doesn't materially matter.

Edit: this is as much me being a little lazy since I have argon easily available (I would need to get an account at AirGas to get nitrogen), and also just wanting to learn from the experts. The difference in cost for this little Argon is sort of meaningless to me as compared to the hassle factor.

 

[ntsqd]

N2 expands slightly less than does air. No idea where Ar fits in that.

pV=nRT, that "n' is what changes. How many molecules are present in each gas at STP?

I built a whole charging system from a donated (work was literally throwing it away) regulator. A tiny N2 bottle wasn't very much (pre-pandemic) and has lasted for a very long time as I don't charge shocks all that often. Am able to get the whole kit, bottle and all, in a medium sized (16"?) Craftsman tool bag.

 

[ksagis]

Yup, I think we're saying the same thing, n is different for nitrogen and argon. Nitrogen's gas constant is 0.2968 kJ/kg-K and Argon is 0.2081. I think the difference in gas constant would show up as a difference in performance during dynamic cycling.

Here's a model I built for fifteen minutes of cycling at 1 hertz. Is there a difference in gas heating, yes - does it matter, dunno. I'm thinking this is in the realm of theoretically is does make a difference, but in practice it doesn't, particularly for street use or rock crawling. Maybe it does for high speed. Haven't done any validation of the model, but if it's right, it seems to indicate Argon is preferred since it heats up less.

At this link: https://rockkrawler.com/2-25-ifp-shock-info/, they say:

• Why Argon for charging our shocks? Argon has a molecular size that is almost 3 times that of Nitrogen so it does not weep as fast so recharging is not as frequently required, but yet Argon is still readily available at most commercial gas suppliers.

 

[Broncobowsher]

I'll throw more data out there, just to muddy things up even worse.
At the few hundred PSI range, the gasses compress the same. When you start getting over the 3000 PSI mark the gasses start deviating from the ideal gas laws.
Another that may play in is gas density. Argon is a much thicker gas. It doesn't flow as well. It is also a more insulating gas (argon filled windows)
If you go the other way there is more potential. Helium. Also inert. Very small molecule, flows really good. Also a great conductor of heat. I know most of this stuff from scuba diving (rebreathers, trimix gasses, high pressure compressors).
If you want the gas charge to insulate, argon. If you are cheap, nitrogen. If you need help conducting heat away, Helium. But Helium will also leak out the fastest through the smallest of holes. Small than what oil can leak out of.

Keep in mind that conducting heat faster may not actually show up as running cooler. If you conduct the same amount of heat faster, it will be hotter on the cool side because it is cooler on the hot side. You may have to think about that a couple of times. It's hotter because it is cooler, is actually a more even thermal distribution.

Helium is also used on high end Sterling (heat) engines. The Helium conducts heat better and flows through the plumbing better. But a lot harder to seal up against leaks.

 

[ntsqd]

As an aside, past work has used helium for leak checking. Set your helium detection threshold low enough and you can detect helium going thru a 1/4" thick plate of 316 Stainless Steel. I wouldn't have believed it if I hadn't seen it.

 

[JB Fab]

I thought I read something about the a few years ago and it was mentioned that in systems where the gas/oil were not separated by a piston there were gas bubble solubility issues depending on gas type.

 

[ksagis]

Cheap, nitrogen.

I think this is ultimately the reason N2 is used

It is also a more insulating gas (argon filled windows)

If you want the gas charge to insulate, argon. If you are cheap, nitrogen.

I think although N2 heat conductivity is maybe 50% more than Ar, in this use case I don't think heat conduction through gas is dominant, so this consideration is a push. i.e. the majority of the heat is being generated in oil flow and shearing, with the much stronger heat conduction path being through the metal case to ambient (versus across the piston, to the gas, to the reservoir, and then out)

As an aside, past work has used helium for leak checking. Set your threshold low enough and you can detect helium going thru a 1/4" thick plate of 316 Stainless Steel. I wouldn't have believed it if I hadn't seen it.

Helium is a leak waiting to happen. The only place it would make any sense to me for a race machine that is setup just prior to a race. But for an oring sealed system and dynamic sliding seals (versus static seals), I wouldn't think it would fare well.

Appreciate all the feedback.

 

[ntsqd]

Helium won't wait to leak, it'll just do it and be gone.

Tongue firmly in cheek someone on another forum once proposed that he fill his tubular frame with helium to make the vehicle lighter. LOL.........

Oil emmulsionability or miscibility of a gas isn't something that occurred to me, but depending on what works best I can see that being a potential problem.
To my thinking the most ideal situation would be that the gas doesn't mix with the oil at all, it stays as a bubble 'above' the oil. It is bubbles in fluids that cause the erosion of the fluid containing surfaces (cavitation). Best would be that bubbles aren't going thru the valving of a damper.

 

[ksagis]

I've never debuilt a coilover, isn't there a piston between the oil and gas? Particularly with a reservoir type system?

 

[ntsqd]

Not in everyone of them, no. When there's an external reservoir then there is a divider piston, but when there is no external reservoir they may or may not have a piston. As far as I know, Fox is the only damper mfg to offer "Emulsion" versions, I won't claim to know all of the different mfg product lines.

Other than cost I'm not understanding why anyone would want an emulsion damper.

 

[Yeller]

Other than cost I'm not understanding why anyone would want an emulsion damper.

Going slow, not knowing better, the biggest is cheap price point that drives volume, giving other manufacturers the “Fox Shock equipped” marketing.

 

[JB Fab]

Not in everyone of them, no. When there's an external reservoir then there is a divider piston, but when there is no external reservoir they may or may not have a piston. As far as I know, Fox is the only damper mfg to offer "Emulsion" versions, I won't claim to know all of the different mfg product lines.

Other than cost I'm not understanding why anyone would want an emulsion damper.

Our remote reservoir ORI struts don't have a divider....

 

[ksagis]

Good point on the possibility of either gas being more prone to emulsifying with the shock oil (though in my case with remote reservoir its possibly a non issue but need to confirm if I have a piston)

Poked around a bit, seems that nitrogen is more prone to emulsify in oil. Couple of snippets:

Nitrogen has a slightly higher solubility in oils than argon. This is due to:

• Polarity and molecular interactions: Nitrogen (N₂) is more compatible with the molecular structure of oils than noble gases like argon.
• Size and polarizability: Argon is a noble gas, monatomic, and less polarizable compared to nitrogen, which affects how well it can interact with oil molecules.

and

Property	Nitrogen (N₂)	Argon (Ar)
Solubility in water	Lower than Ar	~2.5× higher than N₂
Solubility in mineral/ester oil	~7–14 volume % (25 °C)	Likely lower or similar, but data sparse
Effect of temperature	↑ solubility with ↑ temperature	Likely follows similar trend

 

[ksagis]

Our remote reservoir ORI struts don't have a divider....

Do you mean in shock body or in the reservoir? Feels like having a remote reservoir without a piston would create an orifice flow at the choke point of smaller diameter of line connections, unless the reservoir is always mounted so the fluid drains down.

 

[JB Fab]

Yes, the required reservoir mounting angle is noted in the instructions.
The reservoir orifice is externally adjustable with a rotary valve attached to different lengths of tubing inside of the reservoir.
ORIs have two chambers, one pushing up, and one pushing down both are emulsion. (most likely to be replaced soon with a more maintenance friendly coil-overs)

 

[ntsqd]

ORI's have always been a little odd compared to most everything else, but they're more than just a damper so the rules that they need to play by are different.

 

[ksagis]

Look's like I need to read up on ORIs!