C-Forum

I've used nitrogen in my race motorcycles tires as it is much less effected to pressure changes due to temp changes. I am in the middle of an experiment where I replaced all the air in the sledge's air bags with nitrogen. Nitrogen molecules are bigger than air, reducing loss o pressure through seepage through the fabric and so far seem to not be effected by small temp changes. Working on more drastic temp changes to proof the point, but has anyone else tried this?

Where are you getting your information? Not from a physicist or chemist...

Air is 78% nitrogen and 21% oxygen. The rest are trace gases (argon mostly) and water. Both their molecules are almost identical in size, and their expansion rate follows the same formula: PV=NRT (as do all gases). Water vapor will vary from zero at freezing to 4% by weight at 90F and 100% humidity.

Straight nitrogen is used in tires because straight nitrogen does not oxidize rubber, (edit: maybe that's where the oxygen disappears to?...) and there is no water vapor (which does have a very slight effect on pressure because of variable condensation).

Neat idea. I will be interested in your findings.

Isn't 'air' already about 78% Nitrogen? If we're looking for bigger molecules then wouldn't Argon be a better choice. It is even more inert and has an atomic number of 18 vs Nitrogen's puny 7.

Dave

I use helium. It helps me boof.

Tie your boats down well before heading east! If I see you floating over my head at Cheyenne, I'll try to arrange to meet you when you land in Kansas somewhere.

Don't bother with nitrogen. The thermal expansion of any gas at low pressures is approximately the same as an ideal gas, i.e. it will be the same no matter what gas you put in there. The diffusion through the material will also not be affected eityher, particularly since air consists of 78 % nitrogen anyway.

TGG!

I like hellium to, it makes for easyer portage!!

In the aviation industry we use nitrogen because it is more thermally stable and not as prone to unwanted expansion or contraction. back when I owned my own a/c the landing gear shocks were filled with nitrogen to keep performance the same whether at field elevation of 5000+ ft home in Colorado or sea level during a trip. I looked into filling OC1 air bags with N2 but thought it made more sense for c-boats,kayaks, and now maybe decked L'Edges. Any boat that is difficult to check the tension of hot airbags. FYI not many places have nitrogen gas and bottle rental can be pricey. Also, if you are low or slow leak....carrying a pony bottle would be a pain. And what if you are stuck under water and could reach the fill tube for a breather and no air only nitrogen(javascript:emoticon('')probably has never happened but...)
Oh, yes the atmosphere is mostly composed of nitrogen, but the oxygen and water molecules are sufficient to cause significant expansion and contraction

So... ok, maybe the molecules are the same size... but thermal stability as Mike said is one of the reasons nitrogen is used in fire extinguishers... well we will see how they do. I have a huge supply of the stuff, so no worries.

The main reason why nitrogen is used in in aircraft tires is because it's inert, i.e. it does not burn when a tire explodes from overheating.
Fire extingiuishers are usually filled with CO2 (rarely Halon), also because they are inert and displace oxygen.
If you have access to free compressed Nitogen it won't hurt to use it, but there is no benefit to do so. I would not spend a cent on on nirogen for filling em though. No benefit to it.

TGG!

Believe it or not, I actually did try using Helium in the air bags of a whitesell piranha. Made no noticeable difference other than it leaked out faster. Live and learn....

skooks wrote:Believe it or not, I actually did try using Helium in the air bags of a whitesell piranha. Made no noticeable difference other than it leaked out faster. Live and learn....

Yep, me too - same results

I may have to try this, via a new novel technique... calculate the volume of my airbags, add the correct amount of liquid nitrogen, and leave in a warm room for a couple of hours.

Mainly because I'm still enjoying the novelty of liquified gasses though, I might try and get some liquid Helium to do the same thing...

Having some chemistry background, I'm with TGG on this one big time.

Extreme conditions like airplane tires and shocks that goes through huge variations of pressure temperature yeap there is no question there. Also humidity from simple air could rust metal shocks with time.

But seriously for cars I always laught at salesman trying to convince you to blow you tire for some extra bucks. This is such a joke; yes there is a small difference in leaking time but sooo minor you won't ever notice. And perfect gases theory applies to air good enough.

At this point boof'n helium makes more sense. Oh and there is another reason why they use N2 or CO2 and not O2-containing air in fire extinguishers ! Not just expension or leaks...

In canoe air bags the huge temperature gap between the cold water that splashes the bags and half an hour of sun exposure on shore is what kills us and we just have to look for these bags, no shortcut that I know of... Oh but wait... yes! Get into a C1!

I'm going to fill my bags with hydrogen and rename my OC1 the Hindenboat...