Calibrating a pressure gauge

[Maker]

Re "Bespoke" gas mixtures; how often do you inflate and deflate them? Most polymers are surprisingly permeable to gases, so there will be exchange of gas with the atmosphere. I wonder how long it takes to be able to measure changes in composition after the tyres after the tyres have been inflated?

I suspect his bespoke mixture of nitrogen and oxygen won't change too much as it mixes with the atmosphere.

 

[Ross365]

I think you'll find (if you care to get informed) that the main issue with gas mixtures in tyres is the water vapour, not nitrogen nor oxygen .

 

[mike os]

I think you'll find (if you care to get informed) that the main issue with gas mixtures in tyres is the water vapour, not nitrogen nor oxygen .

So irrelevant below 180mph?

 

[Ross365]

I've just done some tests, putting a few gauges on the first inflated tyre I came to.

Budenburg 4" diameter gauge* 30.5psig
Dunlop pencil #1 30.5
Dunlop pencil #2 30.5
Dunlop pencil #3 30.5
Cheap no-name pencil 30.0

Cheap plastic dial guage #1 52
Cheap plastic dial guage #2 27

The Budenburg* is what I described as my "master gauge" earlier on. It's a 4" gauge, 0-150psi bought directly from Budenburg in 1999, last calibrated in 2005, and only ever used to check other gauges.

Dunlop#1 is something I bought when I got my first car in the mid-1970's, when China was making nothing. I suspect that now, there are gauges labelled Dunlop which are nothing to do with Dunlop.

The three cheap things were all off ebay. All of the gauges are marked up in one psi increments, and I've quoted the results to the nearest 0.5 psi as best I could make out. From my point of view, I just take this little exercise as confirming my faith in the genuine Dunlop pencils as being adequate for most motorists, who are usually doing less than 180mph.

 

[voipio]

.... Most polymers are surprisingly permeable to gases, so there will be exchange of gas with the atmosphere. I wonder how long it takes to be able to measure changes in composition after the tyres have been inflated?

If gas exchange is subject to surprising permeability through polymers, how is it that tyres can remain inflated for over a year, with little or no pressure drop?

 

[Ross365]

We're talking relative terms, but note that the OP says he's interested in pressure changes to plus/minus 0.1psi. Moreover, he's got tyres with "a bespoke mixture of nitrogen, oxygen and some trace gases". The rate of permeation of different gases through polymers varies quite a lot, so pretty soon he has a mixture who's composition is different and who's pressure is less than he needs. Ordinary road tyres are thick-walled, and permeation rates are reduced because of it; have you seen a graph of the different rates of deflation on nitrogen versus air-filled tyres; the data is out there on Google and the difference is very appreciable when we start talking 0.1psi.

 

[bricol]

We're talking relative terms, but note that the OP says he's interested in pressure changes to plus/minus 0.1psi. Moreover, he's got tyres with "a bespoke mixture of nitrogen, oxygen and some trace gases". The rate of permeation of different gases through polymers varies quite a lot, so pretty soon he has a mixture who's composition is different and who's pressure is less than he needs. Ordinary road tyres are thick-walled, and permeation rates are reduced because of it; have you seen a graph of the different rates of deflation on nitrogen versus air-filled tyres; the data is out there on Google and the difference is very appreciable when we start talking 0.1psi.

I think his "a bespoke mixture of nitrogen, oxygen and some trace gases" is a reference to those expensive nitrogen fill-ups advertised - ie he's got the same " bespoke mixture of nitrogen, oxygen and some trace gases" that I, you, and probably most of use have in our tyres

ie that stuff known generally as "air"

 

[Ross365]

The OP seems to have lost interest in his thread; maybe he's using "hot air"?

 

[cheb]

The OP hasn't much to add to that that's already been posted.

 

[optima21]

The OP seems to have lost interest in his thread; maybe he's using "hot air"?

best make allowance for that as it cools down to ambient temperature

 

[Ross365]

The OP hasn't much to add to that that's already been posted.

So, are you going to tell us whether or not the "bespoke mixture" is just air and why you want to measure to 0.1psi?

 

[cheb]

Yes, the bespoke mixture is just air. Bespoke because the universe and therefore Earth was created just for me.

The 0.1psi was just my sense of humour and not to be taken literally. The first sentence of the opening post did suggest that this might not be entirely serious.

 

[brightspark]

was thinking its a big deal over nothing and the tire pressures