Compression ratio

[sputnick]

There is a question that I have been wondering for a while, and that is, What is the compression ratio of air at 100 psi VS air at just normal atmospheric pressure? as in, one liter of 100 psi is the equivalent of how many liters of uncompressed air?

This is all I need to know to measure how much wasted air is being blown out the barrel of my many inefficient airguns, and any help would be appreciated

[skyjive]

If you compress a given amount of air to double the pressure, it will occupy half the volume. Atmospheric pressure is 14.7 psi, so 1 liter of air at 100 psi is equal to 100/14.7=6.8 liters at atmospheric pressure.

[sputnick]

So you mean to say, that 6.8 litres of just regular pressure air compressed to 100 psi would be 1 liter? are you sure of this?

[Hotwired]

A standard atmosphere (atm) is 14.696psi.

100/atm = 6.805

So thats 6.805 litres of air in a 1 litre chamber if pressurised to 100psi.


If you want to be unreasonably accurate then find out your local atmospheric pressure and recalculate.


Blarg. Beaten to the post.

[sputnick]

Thanks for the reassurance, so then a ratio of 7 to 1 is all I really need, since none of my devices are that precise

[POLAND_SPUD]

I know it's kind of offtopic but it good to be able to use different units.. both imperial and metric... answering this quesiton is very easy if you can switch to atm instead of PSI...

1L of air at 2 atm equals 2L of air at 1 atm

seems simple doesn't it ?

the same thing aplies to measuring lenght and weight
US, UK and commonwealth countries use imperial units not becasue they are better but becasue of tradition... personally I preffer to use PSI though - somehow it's easier for me to imagine how much is 700 psi than 50 bar/atm...

[btrettel]

The ratios people have posted are accurate for constant temperature, which may or may not be a reasonable assumption (GGDT will show if it is). If the air temperature changes things'll get a little more complicated. You should look at air mass, not volume, if you want to know how much you are wasting. The ideal gas law will give you a good idea of how much air mass you are using if you know the temperatures. I don't use the version of the number of moles. Scroll down a bit to see the version with the total mass of the gas and use that.