Compressed air vs Nitrogen - gas shock refill

**MotoKuzzi** · 3rd July 2012, 20:08

The original marzocchi rear shocks on my '97 California are hydraulic oil over gas if that makes sense. I recently had them apart to change the oil and in the process dumped the compressed gas in the reservoir.

When I reaasembled them I put a charge of compressed air in to see what effect it had ( not reinstalled to the bike ) and was pleasantly surprised how well they seemed to work.

My question is, apart from the obvious effect of reduced gas loss to the system that nitrogen offers (which I could over come by regular topping up with air) what advantage would refilling with Nitrogen give me? Is there any potential damage that compressed air could cause, e.g. damage to rubber / metal parts through moisture and corrosion?

The compressor I'm using is one of those small battery powered electric jobs so I would have thought the air would be less laden with the oil etc that a larger compressor would produce.

**OllyMoto** · 3rd July 2012, 21:05

My understanding of it would be that the main benefit in this situation would be thats Nitrogen gas is affected less by the heat build up through use. Works on the same principles of why some cars are reccomended to have tyres filled with nitrogen.

Olly

**CookMySock** · 3rd July 2012, 21:50

Originally Posted by MotoKuzzi

damage to rubber / metal parts through moisture and corrosion?

Yes, this. If you could find a way to dry the gas and consume the oxygen out of it...

**ducatilover** · 3rd July 2012, 21:59

The air we breathe is around 78% nitrogen.
The moisture content of the gas has a greater effect on its expansion rates as it heats than the fact that it is nitrogen, or 78% nitrogen.
Unless you're running in Le-Mans where the incredibly extreme temps of constant shock oscillations is a factor, than I very highly doubt you will ever notice the difference between the two... what you should do, is fill 'em in the driest/least humid conditions you can.

**Coldrider** · 3rd July 2012, 22:14

Nitrogen is an inert gas, so doesn't "normally" have any chemical reactions, which includes oxidation etc. Nitrogen is also used to dispel oxygen and thus moisture.

If you have one shock charged with air and onther charged with nitrogen, after five or so years if you pull them apart you would probably find why the sealed shocks used nitrogen.

**Pussy** · 3rd July 2012, 22:32

Originally Posted by Coldrider

Nitrogen is an inert gas, so doesn't "normally" have any chemical reactions, which includes oxidation etc. Nitrogen is also used to dispel oxygen and thus moisture.

If you have one shock charged with air and onther charged with nitrogen, after five or so years if you pull them apart you would probably find why the sealed shocks used nitrogen.

Nitrogen is not an inert gas.

**Coldrider** · 3rd July 2012, 22:35

Originally Posted by Pussy

Nitrogen is not an inert gas.

It is not a noble gas, but has the properties of an inert gas, which is why it is cheap.

**slowpoke** · 3rd July 2012, 22:50

Bad move, the compressed air will oxidise and degrade the oil, which will ultimately affect the damping qualities of the shock.

We use oil as a heating medium where I work and have a gas "blanket" on the large storage vessel to remove oxygen and stop the oil oxidising. We also have a nitrogen plant that produces 98% pure Nitrogen, yet even that isn't adequate to stop the oil degrading so use dehydrated natural gas to blanket the oil and ensure it isn't oxidised.

**Robert Taylor** · 4th July 2012, 08:00

Originally Posted by MotoKuzzi

The original marzocchi rear shocks on my '97 California are hydraulic oil over gas if that makes sense. I recently had them apart to change the oil and in the process dumped the compressed gas in the reservoir.

When I reaasembled them I put a charge of compressed air in to see what effect it had ( not reinstalled to the bike ) and was pleasantly surprised how well they seemed to work.

My question is, apart from the obvious effect of reduced gas loss to the system that nitrogen offers (which I could over come by regular topping up with air) what advantage would refilling with Nitrogen give me? Is there any potential damage that compressed air could cause, e.g. damage to rubber / metal parts through moisture and corrosion?

The compressor I'm using is one of those small battery powered electric jobs so I would have thought the air would be less laden with the oil etc that a larger compressor would produce.

Dry / purified air you will get away with, meaning it has to come from a cylinder supplied by one of the gas supply companies. But if you do that its as well to use the PROPER INTENDED GAS, nitrogen. Filling it from a small electric compressor means there is 100% chance that you are drawing in lots of moisture and given that theres a lot of rainfall at present we have high humidity content.
I disagree totally with someone else who said to the effect ''this is not LeMans, dont worry''. Given that we have a high ratio of bumpy roads it challenges the suspension moreso than relatively smooth racetracks. You get lots of suspension shaft movement so therefore lots of gas pressure fluctuation and heat buildup.
If there is a seperating bladder oil contamination is not so much of a risk but given the above you dont need to risk the possibility of bursting an often hard to source bladder for want of having the extra security of installing a more suitable and purified gas. If it is emulsion type then yes Slowpokes comments about oil contamination and corrosive elements is very valid.
The danger of asking such questions on such forums is too often you will get ''she'll be right'' answers, the number 8 wire mentality doesnt cut it.

**bogan** · 4th July 2012, 09:12

Shit, thats what I forgot to do, 8 months ago! Gassed up my shock from the compressor when I was pissing about with different oil viscosities and forgot to replace it with nitrogen afterwards. Cheers for the reminder!

**MotoKuzzi** · 4th July 2012, 19:40

Thanks for all the comments - taking everything into consideration Nitrogen appears to be the safest option, if it was simply a case of pressure loss I would take the punt and refill more often which can be done easily with the tire valves fitted at the base.

**ducatilover** · 4th July 2012, 22:16

Originally Posted by bogan

Shit, thats what I forgot to do, 8 months ago! Gassed up my shock from the compressor when I was pissing about with different oil viscosities and forgot to replace it with nitrogen afterwards. Cheers for the reminder!

Did your shock explode and kill you?

**Icemaestro** · 4th July 2012, 22:31

I had my cbr600 shock re oiled and gassed just recently - when he pulled it apart there was just air in it...it wasn't performing great but I'm still in one piece (just 1 small crash...)