Use of nitrogen gas in modern shock absorbers

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Discussion Overview

The discussion revolves around the use of nitrogen gas in modern shock absorbers, specifically focusing on its role in preventing cavitation and enhancing ride comfort. Participants explore the mechanisms involved, the design of shock absorbers, and the implications of using nitrogen in this context.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that nitrogen gas prevents cavitation in shock absorbers, contributing to a more comfortable ride.
  • One participant explains that nitrogen is used to prevent oil aeration by being contained in a plastic bag within the shock absorber, allowing for oil volume changes without mixing with the oil.
  • A question is raised regarding the necessity of a floating or separating piston in monotube shock absorbers when nitrogen can be used in a plastic bag.
  • Another participant argues that nitrogen in a plastic bag acts as a spring and piston due to its compressibility.
  • One participant challenges the idea that nitrogen prevents cavitation, suggesting that while it may help, cavitation can still occur at high piston speeds.
  • Another participant proposes that cavitation prevention is linked to maintaining a higher pressure within the shock assembly, making it harder for cavitation to occur.
  • A reference to a shock dyno is made as a method to determine the cavitation point in shock absorbers.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of nitrogen in preventing cavitation, with some supporting its role while others question its efficacy under certain conditions. The discussion remains unresolved regarding the exact mechanisms and necessity of nitrogen in shock absorbers.

Contextual Notes

There are unresolved assumptions regarding the conditions under which cavitation occurs and the specific design choices in shock absorber construction. The discussion also highlights the dependence on pressure levels and piston speeds.

vinay ks
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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?
 
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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.
 
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??
 
I do not understand what you ask
 
Nitrogen filled in a plastic bag will act as a spring as Nitrogen is compressible. Therefore it will act as a piston as well.
 
vinay ks said:
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.
 
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.
 
We find the cavitation point on a shock dyno. this attached PDF file should help explain a lot.
 

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Excellent article Mike!
 
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