View Full Version : Nitrogen or Compressed Air?

22-06-2017, 09:03 PM
This may seem like a dumb question guys. But someone may know the answer?

Which has the denser composition?
Compressed Air or Nitrogen?
I ask because I know in Fridge work the size of the molecules between Nitrogen and some refrigerants is very relevant when leak checking a system.
Hopefully someone will know the answer?

Cheers Grizzly

22-06-2017, 09:14 PM
normally compressed air has moisture and it is not good for system unless you use dried air

N2 is good but it cost more money ..

also to reach for high pressure more than 8 bars you need 2 stage air compressor with dried air but in N2 you have in N2 cylinders

in large system we need more pressure to test our Peiping

22-06-2017, 09:23 PM
My question was which is denser.
I don't want to nor have ever used Air in a refrigeration system.

In a way it was a trick question!
It's obvious from some of my posts that I don't like scams.
I walked past my wife's elderly parents car earlier tonight to notice the Green Valve Caps.

Which reminded me that they had paid for their car tyres to be filled with Nitrogen.

Which all the major tyre repair and supply companies over here.
Will happily sell the premise that it is better for the environment and the tyres!

I remembered that sometimes we leak test with nitrogen on systems that have a particular refrigerant with smaller molecules than the nitrogen.. Game over!

So I thought... Which has the smaller molecules, hence the question.


22-06-2017, 09:49 PM
we still paying money to fill our tyres with N2 ???

22-06-2017, 09:54 PM
Grizzly you probably know reasons already, but here is one explanation why to use nitrogen.
It indicates nitrogen may have larger molecules.



22-06-2017, 10:26 PM
Thanks Guys.
Yep it seems so! mbc.

Article 1 seems to confirm my thoughts that it is a scam?
And 2 has so many figures it bores me.
Cheers Ranger.
Your archive of data must make my one look puny?

22-06-2017, 11:24 PM
Yes the theory is there regarding molecule size but basically it's BS

N2 size is 300 picometres, O2 is 292 picometres, not a lot is it?

If you've got 17 minutes spare this Australian youtuber goes into it quite well...he calls it like it is.


23-06-2017, 01:12 AM
Is helium better for leak testing?

The Viking
23-06-2017, 01:13 AM
Air is ~79% Nitrogen.
The reason many racing cars / motorcycles got OFN in their tyres is because it doesn't change volume as much as air does when the temperature changes.

This might also be the reason quoted by the tyre fitters to their customers.
But I am getting old and cynical (and also questioned a surprisingly honest tyre fitter on why they used OFN)... Here in UK, a system relying on "portable", rented, OFN cylinders is not covered by the same rules and regulations as a fixed system delivering pressurised air. It (allegedly) doesn't need to be included in planning permissions, doesn't need to be regularly inspected and doesn't jack up the premises' insurance premiums.

The tyre fitter I spoke to had just changed premises and he said that the difference in installation cost between a compressor driven system and a bottled Nitrogen system would pay for the first 5-7 years worth of Nitrogen and after that the reduction in his insurance premiums would be equal to the cost of Nitrogen. Win - Win for him...

But No, of course they use Nitrogen to reduce wear and tear on the tyres, for the environment and so on....


23-06-2017, 01:19 AM
And yes I know it's no laughing matter lol

23-06-2017, 06:32 AM
Thanks Guys.
Yep it seems so! mbc.

Article 1 seems to confirm my thoughts that it is a scam?
And 2 has so many figures it bores me.
Cheers Ranger.
Your archive of data must make my one look puny?

I just Googled it so no guarantee it's correct either.

23-06-2017, 06:52 AM
Brilliant answers Guys.
Thanks Fault Code.
When I am not trying to deal with the Mini Heat wave of the last few days ( Like most I would think?)
I will certainly have a read.
Very interesting.
I too am becoming more cynical which is why I asked the question in the first place.
Your answer makes a lot of sense.
Hi Cadwaladr.
Nitrogen with added Helium IS the future.
My tight bosses have finally realised that the time and effort saved using it more than covers the extra cost.
Thanks, Your archive is indeed greater than mine then!
Is that not the problem now.
We all Google and believe even when the Author could be talking crap!
Bit like me, but at least we all talk about it.
Sorry Guys got to go.

Ps. Try and avoid my part of Somerset.
It's called the Glastonbury Effect apparently! :D

23-06-2017, 06:40 PM
On vacuum insulated co2 and oxygen tanks, we use pure helium.
Where leaks are hard to find, we use nitrogen mixed with helium.
Helium prices are soaring as world stocks are getting low.
Helium [for those who don't know] comes from the ground, not from the air.

23-06-2017, 10:25 PM
Thanks Chemi.
I did not know about the origin of the Helium.

25-06-2017, 06:52 PM
Helium is used to cool the heads on MRI and CAT scanners, indeed it is getting hard to find. That post about the nitrogen not forcing up insurance costs makes perfect sense!!

30-08-2017, 12:17 PM
hi guys, in car tires, i always though it was due to a lower expansion ratio, the pressure doesn't change when the tires are warmed up.
in the way of the refrigeration industry, Agas have a product called Trace-A-Gas. its dry nitrogen + 5% Hydrogen,being the the smallest molecular structure it leaks a lot easier. also they say you can use a heated diode leak detector to locate leaks charged with this trace-a-gas (although i haven't tried this myself). i found it leaked through old gaskets that nitrogen and refrigerant wouldn't leak through.

03-09-2017, 12:02 PM
can you post additional information about that Trace A Gas?

04-09-2017, 09:43 AM

^^^^^^ try this link ^^^^^^

In Australia a major supermarket company woolworths were retrofitting R22 systems with R407C, they specified we used this trace a gas for all pressure testing and leak detection. it leaked very well so it could be picked up easily with bubbles, but it did have a larger expansion ratio. so if you pressure tested at lunch time and checked it the next morning, it would always be less pressure but it would come back later in the day as it warmed up.