pressure and quantity

[Julian]

Hi All,

At work it is assumed that because I am a model engineer I am also the authority on all technical matters......I wish!!!!!

We have had a colleague injured by a lorry tyre exploding as she walked past it and the question was inevitably asked of me....." At 120psi how much air was in there?"

This will also relate to a mk2 compressor I am building. How do I work out how much air at normal atmospheric pressure is compressed into a rigid volume at higher pressures. For example how many litres atmospheric fit into a litre tank at 120psi? I assume there must be a formula for it.

Thanks

Julian.

 

[Jasonb]

At 120psi how much air was in there?"

That would depend on the volume of the tyre

I think its Boyles law that gives pressure/volume of gasses.

Jason

 

[scoop]

It is Boyles law you need.

original volume X original pressure = final volume X final pressure

Allowing for 1bar = 15 psi this gives 120 psi / 15 psi as the ratio = 8

so i think you end up with 8 litres of air in your 1 litre bottle.

waiting for the HMEM science department to shoot me down soon so use this answer very carefully.

best regards Steve C.

 

[IanN]

Hi,

I can never remember Boyle's Law - I thought it was either:

If you heat a gas, it Boyles

or

Watt's pots never Boyle

;D

Ian

 

[malcolmt]

Hi Julian

Non technical answer is a hell of a lot.

As an example lorry tyres are these days inflated in a steel cage when installing a new tyre The tube that the cage is made from is approx 2" diameter. This is due in no small part to an accident that occurred 25 odd years ago when a tyre fitter was killed when inflating a newly installed tyre and leant over it just when the bead of the tyre popped onto the rim and the incorrectly installed locking ring came off with huge force and splattered him over the ceiling some twenty feet above. this story was written up in a trade magazine at the time.

So as you can see your colleague was very lucky.

Kind regards

Malcolm

 

[steamer]

Scoop,

Assuming Isothermal conditions....you are correct.

That means the temperature of the air in the container is at the temperature of the surroundings, and at the pressure stated.


Dave

 

[Kermit]

29.4 1000
---- = ----
14.7 500


58.8 500
---- = ----
29.4 250 etc.

pressure(2)/pressure(1) = Volume(1)/Volume(2)

With no assumptions or care of the temperature, or course.


Just expand the volume of the tire by doubling and halving pressure until the pressure in the tire is close to one atm. Rough check estimate.