Use of nitrogen gas in modern shock absorbers

[vinay ks]

nitrogen gas is said to prevent cavitation in shock absorbers and thus provide a comfortable ride.. i want to know what actually happens in a shock absorber when nitogen gas is used. how does it prevent cavitation?

 

[Ranger Mike]

gas shock use nitrogen to prevent oil aeration. a plastic bag filled with nitrogen is placed in the oil reservoir space between the inner and outer tube of a single tube shock. Since it is compressible it permits oil volume change during shaft movement and since it is in its own separate bag, it does not mix with the shock oil. Shock oil is special oil for high temperature use.

without this the oil would become aerated – filed with air bubbles and performance would suffer.

 

[vinay ks]

but what is the use of a floating or separating piston in a monotube shock absorber when u can use a plastic bag of nitrogen between the inner and outer tubes??

 

[Ranger Mike]

I do not understand what you ask

 

[Luxman]

Nitrogen filled in a plastic bag will act as a spring as Nitrogen is compressible. Therefore it will act as a piston as well.

 

[J Mc]

nitrogen gas is said to prevent cavitation in shock absorbers and thus provide a comfortable ride.. i want to know what actually happens in a shock absorber when nitogen gas is used. how does it prevent cavitation?

In short, it doesn't prevent cavitation(Essentially boiling the shock oil due to low pressure behind piston). If it could then my job would be a lot easier. If anything it HELPS to prevent cavitation, but if the piston is moving fast enough you will always encounter cavitation(Race cars can see piston speeds upwards of 1m/s). Nitrogen is the gas of choice in motorsport for everything from shock absorbers to filling the tyres. It's inert and expands at a constant rate, compared to atmospheric air when its heated.

 

[Rx7man]

I think the prevention of cavitation occurs because the entire assembly is at a MUCH higher pressure than atmospheric.. Any time you have an instantaneous, localized pressure of close 0 ATM, (especially at higher temperatures) the risk of cavitation increases greatly.. If you pressurize the entire assembly to 50ATM, it will be VERY much harder for any cavitation to occur.

 

[Ranger Mike]

We find the cavitation point on a shock dyno. this attached PDF file should help explain a lot.

 

[Rx7man]

Excellent article Mike!