1 hour ago, OldBoyScout said:

This is how it's done:

 

He puts a bit of nitrogen into the tyre and lets it out again. Then he inflates the tyre to full pressure with the nitrogen. He ends up with just over 98% of nitrogen in the tyre, and calls it a good fill.

 

 

This doesn't stack up.

 

The 'empty' tyre contains air at about 15psi absolute (~1 bar, atmospheric pressure). He adds 99% pure nitrogen to 'about 5 pounds' (presumably gauge) pressure, so now we have 20psi absolute of which three quarters is air and one quarter the added 99% nitrogen. Then he refills with 99% nitrogen to say 2 bar gauge so the atmospheric pressure mixture of three-quarters air and one quarter nitrogen is added to with 2 more atmosphere's (30psi gauge) worth of nitrogen.

There's no way I can see that that removes as much of the non-nitrogen components as claimed.

My calculations suggest that after the refill to 2 bar you've now got (2.25/3)0.99 + (0.75/3)*0.78 = 0.937 or 93.7% nitrogen

The meter is clearly fiddled with, or the process wasn't as he described it.

 

 

On 20/08/2019 at 15:59, Wino said:

(2.25/3)0.99 + (0.75/3)*0.78 = 0.937 or 93.7% nitrogen

My maths confirm this.

38 minutes ago, KenONeill said:

My maths confirm this.

Conclusion never trust an expert AKA You Tube video.

Maybe you need to allow for the amount of air or nitrogen contained in the tyre. When the 5 pounds has been let out there is not much air / nitrogen left in the tyre. Say for arguments sake that what you have in the tyre  at this point is 90% nitrogen. That is 90% of a relatively small amount of gases.  To raise the pressure of the tyre to the normal operating pressure, a relatively larger amount of almost pure nitrogen is pumped into the tyre. What you then have in the fully inflated tyre is a small amount of air and gas which is 90% nitrogen and a larger amount which is almost 100% nitrogen. I am thinking that the nitrogen content for the total amount could then average out to 98%. The gauge appears not to have been fiddled with, as it starts off at 78.5 before registering what is in the tyre.

 

1 hour ago, Wino said:

My calculations suggest that after the refill to 2 bar you've now got (2.25/3)0.99 + (0.75/3)*0.78 = 0.937 or 93.7% nitrogen

You seem to be saying that one quarter of the final contents of the tyre (your figure 0.75/(2.25+0.75)) is resulting from the first blast of nitrogen, and that the other three quarters (your figure 2.25/(2.25+0.75)) have come from the final inflation to 2 bar. I am thinking that the first blast of nitrogen and subsequent deflation will account for a much smaller portion of the final contents than one quarter, and the final inflation to the full 2 bar will account for much more than three quarters of the total contents. Also your figure of 0.78 is too low, as this would have been the original nitrogen content of the air, and the nitrogen content in the tyre after filling to 5 pounds and letting some of the contents out would be higher.

 

If we substitute one tenth for one quarter and 0.9 for 0.78 into your calculation we get (9/10)*0.99 + (1/10)*0.9 = .981 or 98.1% nitrogen.

 

I'll walk you through my numbers a little later. You seem to be picking ones that give you the answer you want to see.

34 minutes ago, Wino said:

You seem to be picking ones that give you the answer you want to see.

Not at all, I explained why I thought your calculation was flawed in my previous post but one, and suggested the 90% as a hypothetical figure. I only decided to do the maths when I saw that I had caused a confused reaction in another poster, and was quite surprised when the result came out as 98.1%.

 

In my opinion the guy in the youtube video is greatly overstating the benefits of tyre inflation with nitrogen, but I can't believe he would take the risk of faking the actual inflation process, given that it is very important to his business and someone out there would be bound to catch him out.

VW Group. 

11 Million minimum defeat devices, billions in fines and losses in business and reputation, bound to be caught out but all is well and they are thriving.

 

If you are going to lie and cheat lie and cheat big.

Ok, this is way way overthinking it and its beyond silly but I do like a maths conundrum.

 

Original content is 78%

Add the additional n2, you take it to to 83%.  Drop to 0 pressure gauge.

Add in 2 bar of n2 and you have 41.1 psi of the total 43.5psi in there being nitrogen.

That's  94.5%

 

It's not worth worrying about though... Just stick air in and notice absolutely bugger all difference.  

I was doing the same calculation in Excel, but using absolute pressures.

 

Normal air is 80% N2, 20% O2 at say 15 PSI.

N2O2

Ie123

Inflate to  20 PSI with N2, IE add 5

173

So that's now 17/20 parts N2, Ie 85%

Release new mix back to 15 PSI, removing 1/4 of the mix.

12.75    2.25

Inflate to 45 PSI using N2, IE Add 30

42.75    2.25

Percentage N2 is 42.75/45

0.95

6 hours ago, OldBoyScout said:

I watched that video too. I think most of what he says there makes sense and is correct, except nitrogen is heavier than air, not lighter.

 

I have to ask ...  What?

 

Air is mostly nitrogen, as we know.

Most of the rest is oxygen, which is denser than nitrogen.

Air also contains water vapour, which as we also know is a liquid and is denser than nitrogen.

So, dry air should be denser, wet air certainly is.

 

Or, to put it more simply, if nitrogen was heavier than air, we'd all be dead as the oxygen filled air would be sitting high up in the atmosphere and we'd have no air to breathe.

 

I don't really have the energy this evening, but I invite anyone else with an interest to explain better

.

Basically, the tyre when seemingly empty has much the same internal volume as when at full pressure. So when at zero gauge pressure it still contains a volume of air at atmospheric pressure (1 bar/~15psi absolute). So when you add 99% pure nitrogen to bring the pressure up to 5psi gauge (20psi absolute), you still have 3/4 (15/20) of the internal volume filled with the original air (@78% nitrogen).

After you let that 5psi gauge pressure mixture down to atmospheric pressure again, you can reasonably assume that the proportions of the original air and the added nitrogen that are released are not affecting the internal composition, so 3/4 air at 78% N2, 1/4 added nitrogen at 99%.

 

Add 2 bar/30psi (gauge) to bring it up to working pressure and you have effectively increased the gas content by 200% (15psi absolute to 45psi absolute) that's where I get my divides by 3 in my earlier post.

So my earlier (2.25/3)0.99 + (0.75/3)*0.78 = 0.937 or 93.7% nitrogen breaks down like this

2.25/3 is the 2bar of final adding nitrogen plus the 1/4bar that was added when 'purging', all at 99%N2

The three-quarters of the original air proportion (now 1/3 of the whole content) was 78% nitrogen

Add these together to get the final proportion.

 

 

Simple?

@Alex-W @Wino - Well, that's 3 of us did the same basic calculation using slightly different proportions of N2 and O2 and methodologies, and we all came up with pretty much the same answer, Enough said?

26 minutes ago, Alex-W said:

Or, to put it more simply, if nitrogen was heavier than air, we'd all be dead as the oxygen filled air would be sitting high up in the atmosphere and we'd have no air to breathe.

By this logic, if nitrogen was lighter than air we would all be dead from excess oxygen sitting low down in the atmosphere being too rich to breathe and causing fires and explosions to break out all over the place, or maybe not...

 

In fact I was wrong again, and nitrogen is lighter than air but only very slightly. However, we are not all dead because the nitrogen and oxygen in the air do not spontaneously separate out.

 

The reason I was thinking that nitrogen was heavier than air was due to health and safety warnings that I have been given in the past regarding the danger of nitrogen asphyxiation.

 

1 hour ago, Alex-W said:

Ok, this is way way overthinking it and its beyond silly

I thought that we were all overthinking it, as various people were coming up with clever theories about how tyres could be fully inflated with nitrogen, rather than trying to find out how it was actually done in real life. That was why I went looking for details of what really happened and posted the link to the youtube video. I was hoping that someone might find it helpful, but instead of that the veracity of the process shown in the video was called into question.

50 minutes ago, KenONeill said:

Well, that's 3 of us did the same basic calculation using slightly different proportions of N2 and O2 and methodologies, and we all came up with pretty much the same answer, Enough said?

So, should we accept a theoretical calculation where 3 people have come up with similar results, and another person has come up with something else, rather than video evidence which appears to show how the actual process is carried out in real life? I don't see what the video presenter would have to gain by showing a fake process.

On 20/08/2019 at 22:49, OldBoyScout said:

nitrogen was heavier than air was due to health and safety warnings that I have been given in the past regarding the danger of nitrogen asphyxiation.

 This is a problem because nitrogen is sometimes used as a means of excluding air from large tanks during cleaning processes.

 

Quote

3 people have come up with similar results, and another person has come up with something else, rather than video evidence which appears to show how the actual process is carried out in real life?

OK, I've not watched the video, but how is the partial pressure actually sensed?

10 hours ago, OldBoyScout said:

The reason I was thinking that nitrogen was heavier than air was due to health and safety warnings that I have been given in the past regarding the danger of nitrogen asphyxiation.

 

Possibly down to the fact that large amounts of nitrogen gas might be introduced into a room rapidly by a liquid nitrogen spill; there the fact that the nitrogen gas is very cold initially would be the reason for its higher density.

 

10 hours ago, OldBoyScout said:

rather than video evidence which appears to show how the actual process is carried out in real life? I don't see what the video presenter would have to gain by showing a fake process.

 

The video evidence is by a seller of the product, telling us how 'in theory' it is done. In practice, it's quite hard to believe that the whole removing and replacing tyre valve stuff and 'purging' with a whiff of nitrogen would actually be followed, unless someone was watching. The video presenter would hope to gain trade at his business, which he introduces in writing and verbally right at the beginning.

Not really an impartial standpoint.

Thanks to everyones contributions in this debate , which I probably stirred up. No one has yet mentioned the selective permeation of the oxygen from the tyres. Ducks. 🤕

9 minutes ago, gregoir said:

No one has yet mentioned the selective permeation of the oxygen from the tyres

 

If that really happens to any significant extent, then you'll gradually increase the proportion of nitrogen in your tyres every time you pump them up (with common or garden air) a bit.

Edited 21 August, 20196 yr by Wino

@gregoir @Wino - I'd expect the rate of permeation of nitrogen to be higher because the molecules are smaller.

2 minutes ago, KenONeill said:

because the molecules are smaller

Are you sure about that Ken?

I tried helium in the front tyres once, but it made the steering too light.

 

Sorry , couldnt resist. 😂

 

 

On 21/08/2019 at 10:55, Wino said:

Are you sure about that Ken?

Pretty sure, based on density at STP.

 

N2 1.2506 g/L, O2 1.429

2 hours ago, Wino said:

The video evidence is by a seller of the product, telling us how 'in theory' it is done. In practice, it's quite hard to believe that the whole removing and replacing tyre valve stuff and 'purging' with a whiff of nitrogen would actually be followed, unless someone was watching. The video presenter would hope to gain trade at his business, which he introduces in writing and verbally right at the beginning.

Not really an impartial standpoint.

He is not telling us in theory, he is giving a practical demo. If he was giving us the theory, I would expect to have a more detailed explanation of how he could get the content up to 98% by doing what he is doing. Now you seem to be saying that he is doing the correct process here, but would not be doing it if no one was watching. It only takes about 90 seconds from removing the valve to completion of the fill. If he was an employee he might cut corners, but this would be more unusual in an owner of the business.

 

After watching the video a few more times I think I know what is really happening. Mr. Striegel starts off by telling us how he fills the tyres of all his vehicles with nitrogen, even his tractor. The vehicle he is using for the demo is clearly one of his. It has sign writing which he is taking the opportunity to show off. The tyre has previously been filled with nitrogen, and he is not starting off with regular air. Simple.

On 21/08/2019 at 12:01, OldBoyScout said:

he could get the content up to 98%

Er, 3 of us have independently calculated that the process as described doesn't go past 95% by volume. Since O2 is denser, I'd expect the percentage of N2 to be lower than than the volume.

16 minutes ago, OldBoyScout said:

The tyre has previously been filled with nitrogen, and he is not starting off with regular air. Simple.

That's quite believable.

 

@KenONeill, I think your density figures disprove your idea, but I can't quite get my head around it just now.  Is it that proportionally, the difference in density is greater than the difference in molecular weight?, so that means there are more oxygen molecules per unit volume, therefore they are smaller? Actually that is a load of tosh. The numbers come to the same if you press the calculator buttons right. I was forgetting Avogadro for a sec there.

 

Haven't read this properly, but try it on yourself if you want: https://www.getnitrogen.org/pdf/graham.pdf

(Non-impartial source, to be fair!)

Edited 21 August, 20196 yr by Wino