What's caused this?

[jammy]

ah even that varies ...... a hot tyre can show 220psi but when cooled can show 195psi ok it is better but u still have to watch out for temp increases

 

Isn't dry Nitrogen an inert gas not influenced by heat or cold

 

 

that's what i was thinkin

[Sagitar]

ah even that varies ...... a hot tyre can show 220psi but when cooled can show 195psi ok it is better but u still have to watch out for temp increases

 

Isn't dry Nitrogen an inert gas not influenced by heat or cold

 

 

that's what i was thinkin

 

 

It depends upon what you mean by "inert". Any gas that does not react with its surroundings is inert in those circumstances. The gases recognised as generally inert are the "noble" gases such as argon or xenon. Nitrogen is certainly not one of those.

 

Several substances are compounds of nitrogen e.g. ammonia, nitrate and nitrogen dioxide and that is only possible if nitrogen reacts with the other substances that form the compounds i.e. it is not inert in their presence. Various microorganisms can make these materials by reacting with nitrogen in the atmosphere. It's how nitrogen rich fertiliser is formed naturally at the roots of leguminous plants.

 

PS - even if nitrogen was inert, it still wouldn't be exempt from the normal gas laws. We have been here before!

 

In any gas, "pressure" times "volume" is proportional to "temperature", so if you raise the temperature of a fixed volume of gas its pressure must rise.

[Tony]

ah even that varies ...... a hot tyre can show 220psi but when cooled can show 195psi ok it is better but u still have to watch out for temp increases

 

Isn't dry Nitrogen an inert gas not influenced by heat or cold

 

 

that's what i was thinkin

 

 

It depends upon what you mean by "inert". Any gas that does not react with its surroundings is inert in those circumstances. The gases recognised as generally inert are the "noble" gases such as argon or xenon. Nitrogen is certainly not one of those.

 

Several substances are compounds of nitrogen e.g. ammonia, nitrate and nitrogen dioxide and that is only possible if nitrogen reacts with the other substances that form the compounds i.e. it is not inert in their presence. Various microorganisms can make these materials by reacting with nitrogen in the atmosphere. It's how nitrogen rich fertiliser is formed naturally at the roots of leguminous plants.

 

PS - even if nitrogen was inert, it still wouldn't be exempt from the normal gas laws. We have been here before!

 

In any gas, "pressure" times "volume" is proportional to "temperature", so if you raise the temperature of a fixed volume of gas its pressure must rise.

 

I don't understand why Nitrogen is mandatory in all commercial aircraft and used in F1 for example?

[Sagitar]

I don't understand why Nitrogen is mandatory in all commercial aircraft and used in F1 for example?

 

Hi Tony

In the days when I designed high pressure hydraulic systems for aerospace we were concerned mainly about safety. Nitrogen does not support combustion, it is reasonably easy to get hold of (more than three quarters of the earth's atmosphere is nitrogen), it is not of itself toxic (though it can suffocate you) and so it presents no real problems if it leaks. We did actually put air into some mobile military systems for convenience, but generally the greater safety of nitrogen is preferable. Its behaviour as say, the charging fluid in a high pressure hydraulic accumulator is not that different from dry air, except when you get a leak and a fire.

 

I assume that the F1 people do not mind spending a lot of money to get exactly the tire conditions that they want and that they go to a lot of trouble over inflation pressures etc. but my experience of tyre inflation for common or garden road cars is that it is not a very exact science. The variations generated by poor calibration of guages, by failure to take account of differences in ambient and tyre carcass temperatures when checking inflation pressures etc are likely to lead to bigger variations than those resulting from using either nitrogen or air to fill tyres. Putting nitrogen into tyres in the belief that there will be NO change in the tyre pressure given a change in ambient or running conditions is flying in the face of established science. The best that can be hoped for is a very marginal reduction in the level of change as compared with a tyre filled with air.

[ROB]

ah even that varies ...... a hot tyre can show 220psi but when cooled can show 195psi ok it is better but u still have to watch out for temp increases

 

Isn't dry Nitrogen an inert gas not influenced by heat or cold

 

 

that's what i was thinkin

 

 

It depends upon what you mean by "inert". Any gas that does not react with its surroundings is inert in those circumstances. The gases recognised as generally inert are the "noble" gases such as argon or xenon. Nitrogen is certainly not one of those.

 

Several substances are compounds of nitrogen e.g. ammonia, nitrate and nitrogen dioxide and that is only possible if nitrogen reacts with the other substances that form the compounds i.e. it is not inert in their presence. Various microorganisms can make these materials by reacting with nitrogen in the atmosphere. It's how nitrogen rich fertiliser is formed naturally at the roots of leguminous plants.

 

PS - even if nitrogen was inert, it still wouldn't be exempt from the normal gas laws. We have been here before!

 

In any gas, "pressure" times "volume" is proportional to "temperature", so if you raise the temperature of a fixed volume of gas its pressure must rise.

 

I don't understand why Nitrogen is mandatory in all commercial aircraft and used in F1 for example?

 

 

Hi Tony,

 

sorry not looked at this for ages - its law that nitrogen or any other inert gas that contains less than 5% oxygen is used in commercial aircraft wheel assys because nitrogen does not support combustion - important when there is a brake fire or overheat ( AKA numpty pilot slammed the brakes on and tried to take first exit when plane is at max landing weight/speed)

 

but on a serious note the criteria is aircraft with a MTOW ( max take off weight) of over 5700kg with retractable landing gear that have braked wheel assys. The main reason is to reduce inflight fires from a burst tyre.

 

a quick copy paste from the EASA regulations:

 

The majority of in-flight tyre bursts have been attributed to the tyre carcass being weakened by foreign object damage, scuffing, etc., such that a rapid release of pressure takes place. Such failures are usually experienced when the gear has been retracted for some time and the effects of brake heat transfer, internal tyre temperature and differential pressure are combined.

 

A fatal accident involving cabin decompression and fire has highlighted another mode of tyre failure in flight where a tyre may fail explosively without any significant prior degradation. A tyre inflated with air and subjected to excessive heating, possibly caused by a dragging brake, can experience a chemical reaction resulting in release of volatile gases. Such a chemical reaction in the presence of the oxygen in the contained air may result in a tyre explosion in a landing gear bay and/or in-flight fire since it appears that the

protection normally afforded by conventional pressure relief devices in the wheel would be incapable of responding adequately to the rapid increases in temperature and gas pressure associated with auto-ignition.

 

Other potential benefits may accrue from the use of nitrogen as it will tend to reduce wheel corrosion, tyre fatigue and the risk of fire when fusible plugs melt due to brake overheating.

[Tony]

Thank you everyone for the technical assistance regarding the properties of dry nitrogen.

 

I have done some research online and the past claims that the nitrogen is resistant (inert) to heat expansion has been removed.

 

It appears that the pioneering benefits are not as promised