Nitrogen Shock Fill

sandhills
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6/11/2022 6:58am Edited Date/Time 6/11/2022 10:29am
Take two shocks at 70f / 150psi one filled with nitrogen and one filled with air and then warm both up to 150f. Guess how much difference there would be in pressure?

Basically none, it's a fraction of a PSI too small to measure with a shock filling gauge.

Edit: Before someone thinks I am confused, both shocks would rise to about 175psi at 150f, it's the difference between them that would be too small to measure, 174.8 vs 174.9 maybe.

If you're the manufacturer or a high volume shop where nitrogen only adds 10 cents or whatever to the cost of each shock fill then sure, the tiny benefits are worth it. But DIYers don't need to worry about using an air shock pump.
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Berni
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6/11/2022 9:38am Edited Date/Time 6/15/2022 3:11am
I have been filling my shocks for some time with a MTB pump and it has worked great. No issues at all and I cannot feel the difference... What I can feel is that a rebuild shock with air from the MTB pump is much better than a non rebuilt shock filled with nitrogen....

For those of you that have your doubts.... Just try you have nothing to lose.... Fill with regular air, try and if you really feel any difference... Empty and then look for the nitrogen..... I really doubt you will do the last
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40
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6/14/2022 7:14pm
Air is 78% nitrogen to begin with.
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The Shop

bvm111
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6/15/2022 7:14am
If the manufacturers could get away with just pumping air in the bladder … why don’t they?
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FGR01
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6/15/2022 9:56am
bvm111 wrote:
If the manufacturers could get away with just pumping air in the bladder … why don’t they?
Maybe they do ???? Do we have any independent lab analysis of OEM shock gas? hahaa

Seriously, though, I always run nitrogen since I have a setup and have been doing it for decades, but I doubt there's much harm or difference in using air. Keep in mind, the air only touches the bladder and bladder cap. So it's not like there's much risk of corrosion from the moisture content. And, as pointed out, the pressure stability across the normal operating range is likely negligible.
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6/15/2022 10:17am
bvm111 wrote:
If the manufacturers could get away with just pumping air in the bladder … why don’t they?
FGR01 wrote:
Maybe they do ???? Do we have any independent lab analysis of OEM shock gas? hahaa Seriously, though, I always run nitrogen since I have a...
Maybe they do ???? Do we have any independent lab analysis of OEM shock gas? hahaa

Seriously, though, I always run nitrogen since I have a setup and have been doing it for decades, but I doubt there's much harm or difference in using air. Keep in mind, the air only touches the bladder and bladder cap. So it's not like there's much risk of corrosion from the moisture content. And, as pointed out, the pressure stability across the normal operating range is likely negligible.
when i was at college many many years ago, from memory, nitrogen has a bigger molecule than air, and air contains moisture vapour, its the vapour content that causes the difference in expansion,it also slows leakage through shock bladders by about 30 percent? (please do correct me if i'm wrong as it was a long time ago) i've always used n2 as i have my own kit, pals of mine have used argon etc and say its just as good,
sandhills
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6/15/2022 10:16pm
bvm111 wrote:
If the manufacturers could get away with just pumping air in the bladder … why don’t they?
Because Nitrogen is a just a tiny bit better and it costs them almost nothing.

If you're making thousands of them, and most of them are going to people who won't check the pressure for 5+ years, then yes it's worth an extra penny for N2.
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btroxler
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6/16/2022 9:54am Edited Date/Time 6/16/2022 9:54am
The benefit of [b]Nitrogen[/b] is the [i]stability[/i] of the gas. With using [b]Air [/b]you get oxygen (an oxidizer on parts) and some hydrogen, being moisture. As...
The benefit of Nitrogen is the stability of the gas. With using Air you get oxygen (an oxidizer on parts) and some hydrogen, being moisture. As temperatures rise very high in the shock, the pressure will increase in the shock bladder higher with Air over Nitrogen. I don't know how much. In road racing, only Nitrogen is used in tires for pressure stability/ consistency. May not want air in a shock long term for seasons or years.
Chuck_Below hit the nail on the head. Nitrogen provides stability. Using air the pressure can vary 5-10% during a extreme temperature change or really fast cycling of the shock or fork.
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sandhills
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6/16/2022 7:30pm
btroxler wrote:
Chuck_Below hit the nail on the head. Nitrogen provides stability. Using air the pressure can vary 5-10% during a extreme temperature change or really fast cycling...
Chuck_Below hit the nail on the head. Nitrogen provides stability. Using air the pressure can vary 5-10% during a extreme temperature change or really fast cycling of the shock or fork.
The temperature pressure change difference of nitrogen vs. air is less than 1%, more like .1%
Leeham
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6/18/2022 2:27pm
Perhaps running 30+ min motos in sand rollers or pro national you probably dont want air. I bet some of the guys say never use air but run a shock for 70-80 hours on SPENT oil.
Kidkawie
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6/19/2022 11:06am
Late 90's RM service manual calls for compressed air.
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Lasse
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6/22/2022 3:10pm
This discussion is slightly ridiculous, the mass of nitrogen you add to increase the pressure sufficiently is minuscule and on top of that you still have atmospheric air in the bladder from the assembly.
FGR01
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6/23/2022 7:17am
Lasse wrote:
This discussion is slightly ridiculous, the mass of nitrogen you add to increase the pressure sufficiently is minuscule and on top of that you still have...
This discussion is slightly ridiculous, the mass of nitrogen you add to increase the pressure sufficiently is minuscule and on top of that you still have atmospheric air in the bladder from the assembly.
Not trying to counter your take, but when I charge a shock with nitrogen I first purge it with the nitrogen for a few secs to flush the ambient air out before I close it up and set the final pressure. I understand most typical charging setups people are using don't allow for this but I modified mine a little to be able to do this. But, I agree, that I doubt it would make a monumental difference either way.
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UFOpilot
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4/9/2024 9:31am
DuroTools wrote:
Air forks we will fill with Air and is somewhat similar in function so maybe we are idiots for not using nitrogen up front. If I...
Air forks we will fill with Air and is somewhat similar in function so maybe we are idiots for not using nitrogen up front. If I get my own fill nozzle and tank I'll definitely be trying that.
i really hope you dont think i was saying anyone is a idiot for using air buddy, there seems to be a lot that use it...
i really hope you dont think i was saying anyone is a idiot for using air buddy, there seems to be a lot that use it and i was just genuinely curios why, i do prolly 15 to 20 shocks a month as im a breaker and do a bit of cerakoting, and i fill up with air when i seat the res cap, but always drain and fill with n2, id heard of people using argon etc ie other inert gases but never straight air, hope i didnt offend anyone
DuroTools wrote:
I personally wasn't offended and I was genuinely just thinking that with the stability of nitrogen it really makes sense to use it up front so...
I personally wasn't offended and I was genuinely just thinking that with the stability of nitrogen it really makes sense to use it up front so not sure why I've never thought or heard of anyone doing it before. I'm not one that messes with my forks air pressure but I do notice the forks get firmer as the day goes on so I bet there is an increase in pressure that wouldn't happen with nitrogen. But about the shock, I've done it once, was selling the bike and was under a time crunch to get the shock rebuilt and back on the bike so the buyer could test ride it. Taking it to get filled would have been a half day ordeal since the closest place was am hour away and I'd have to wait a half hour at least. I'm assuming the only reason people would use air is for the same reason I did , strictly convenience and nothing else. Oh and in case anyone was wondering I did disclose to the buyer that it needed nitrogen eventually. I honestly couldn't feel the difference on the track though.

Hi, sorry for the intrusion.  I'm building a 1981 Suzuki RM465.  Have a problem with the shock. Hose is a bit worn near to the shock inlet but just checked reservoir and its got nitrogen.  Problem is its not lifting or returning. There is some resistance when pulling it back up manually but it then slowly drops back down. Shock seems to be in rather good condition, no oil leaking, good chrome, even retains its original paint. 

Have you guys any idea why it's not returning?

Regards 

Gaz

motomind00132
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4/9/2024 10:37pm

The biggest reason the oems run nitrogen in the bladder vs super dry air is that the nitrogen doesn't bleed through the bladder as fast as air. They know that most peolple aren't going to rebuild their suspension often enough if at all. An the for people that dont ride often and the bike sits. Nitrogen just keeps it alive longer. If your using dry air at about halfway to when you should do a rebuild check it's pressure it's likley low. Proably around 80-100psi. Shock will feel a bit better for the last few hours. Thats at least what ive noticed using air for a couple years and looking into a little of the science behind the gasses and air.

Now i just use a mtb nitrogen tire cartridge get it up to 150psi or 100-125psi and finish it off with dry air or mtb pump if its a,used cartridge.  They seems to alway die around 100-125 psi so the little air is negligible as theres alot of nitrogen in air to begin with.

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UFOpilot
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4/10/2024 1:58am Edited Date/Time 4/10/2024 2:00am
The biggest reason the oems run nitrogen in the bladder vs super dry air is that the nitrogen doesn't bleed through the bladder as fast as...

The biggest reason the oems run nitrogen in the bladder vs super dry air is that the nitrogen doesn't bleed through the bladder as fast as air. They know that most peolple aren't going to rebuild their suspension often enough if at all. An the for people that dont ride often and the bike sits. Nitrogen just keeps it alive longer. If your using dry air at about halfway to when you should do a rebuild check it's pressure it's likley low. Proably around 80-100psi. Shock will feel a bit better for the last few hours. Thats at least what ive noticed using air for a couple years and looking into a little of the science behind the gasses and air.

Now i just use a mtb nitrogen tire cartridge get it up to 150psi or 100-125psi and finish it off with dry air or mtb pump if its a,used cartridge.  They seems to alway die around 100-125 psi so the little air is negligible as theres alot of nitrogen in air to begin with.

Cheers for the information. Very helpful. The reservoir has no valve cap and I'm hoping someone's simply been messing with it, letting the nitrogen out. It could explain why it's still got nitrogen.  I've had the shock about 6 years myself. Still fitted to the old frame.  I'll look onto the MBT nitrogen canisters and probably give it a go, either that or pop it into the bike shop and top it up. 

Thanks again for your help. 

Kind regards Gaz 

DejaMoto
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4/18/2024 7:36am

My understanding is that it's not really about the nitrogen, it's more about the oxygen. Oxygen is reactive with both the rubber parts as well as the fluid. The byproducts of the reaction effect lubricity and viscosity. Advances in synthetics and additives helps fight the oxidation of the fluid, but heat and agitation are two major accelerators to the oxidation process. so while air is mostly nitrogen, reducing the reactive element of oxygen should prolong oil life, especially in the case of bladder equipped shocks due to a MUCH more rapid permeation rate. Oxygen reacts with the bladder membrane as well.

Like many things, there's many ways to skin a cat. so the good/better/best compromise probably applies here, as well as "the enemy of good is perfection", which from my understanding suggests that the inability to do it perfectly results in nothing being done at all. If access to a nitrogen charging setup is the barrier keeping you from regular service intervals, then I guess compressed air will have to do.. but again, considering all of the other hurdles involved in obtaining and riding a motocross bike and servicing the shock yourself up to the point of charging it.. finding n2 is a small hurdle. 

Dry air is better to reduce/eliminate water vapor content which condenses and obviously affects lubricity (especially in the case of a separating piston setup) , nitrogen is best to eliminate water vapor content and reduce oxygen content. You could go one step further in saying that a bladder equipped shock will have a greater benefit from nitrogen over a separating piston shock, simply due to the permeation rate and resulting gas contamination in the fluid. 

There are plenty of suspension applications where air is utilized, It's important to realize HOW the air is utilized. MFG's offering Infinite adjustability and weight reduction are HUGE selling features. . The end user is given hand pumps to make those adjustments, so the system is designed accordingly, and service intervals recommended accordingly (and hopefully support networks) to mitigate those potential performance or reliability compromises. 

If you do suspension work commercially or begin doing a higher volume of suspension you'll realize VERY quickly that mitigating variables is paramount. So for me, the N2 setup is a small price to pay for knowing that whatever problem we are trying to solve, is not due to the charging gas. 

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