66g lifejacket cylinder = what volume?

[tim_ber]

I found that the cylinders are pressured at about "Fill pressure: 60 kgf/cm2" (58 atm).

I want to know what volume these cylinders will fill to a pressure of 2 atm, say.

How do I work that out? PV=nRT isn't helping me and that's about the only equation I can remember.

But what pressure is a lifejacket at when inflated do you think?
I think lifejacket pressure should be somewhere around 23 kN/m2 according to a website (http://www.caa.co.uk/docs/33/CASPEC05.PDF) See 7.1.4

But 2300 newton/square meter = 0.022699235134468 atmosphere according to link below. Sounds odd though for a lifejacket pressure?

google says at 1 metre in salt water, pressure exerted is 132psi(=9atm), so a ifejacket at a poor old 0.02atm would not be a lot of good.

Conversion chart here:
http://online.unitconverterpro.com/...alpha/factors.php?cat=pressure&unit=16&val=60

 

[nigelmercier]

I found that the cylinders are pressured at about "Fill pressure: 60 kgf/cm2" (58 atm). I want to know what volume these cylinders will fill to a pressure of 2 atm, say.

Current volume x 58/2

 

[VicS]

I found that the cylinders are pressured at about "Fill pressure: 60 kgf/cm2" (58 atm).

I want to know what volume these cylinders will fill to a pressure of 2 atm, say.

How do I work that out? PV=nRT isn't helping me and that's about the only equation I can remember.

But what pressure is a lifejacket at when inflated do you think?
I think lifejacket pressure should be somewhere around 23 kN/m2 according to a website (http://www.caa.co.uk/docs/33/CASPEC05.PDF) See 7.1.4

But 2300 newton/square meter = 0.022699235134468 atmosphere according to link below. Sounds odd though for a lifejacket pressure?

google says at 1 metre in salt water, pressure exerted is 132psi(=9atm), so a ifejacket at a poor old 0.02atm would not be a lot of good.

Conversion chart here:
http://online.unitconverterpro.com/...alpha/factors.php?cat=pressure&unit=16&val=60

You have gone wrong somewhere in your conversions

23kN/m² = 0.227 atm or about 7.70 ft water (or 7.48 ft seawater)

1 metre water = 0.097 atm ( or 1 metre seawater = 0.100atm)


As Nigel says the cylinder at 58 atm will expand to 29 times its volume at 2 atm

As you say PV= nrT so if T is constant P1V1 = P2V2

OK I'm a chemist and that's more than enough physics for this time of the day

 

[maxi77]

The only lifejacket I have known the pressure of was the submarine escape suit lifejacket which had a relief valve that lifted at 2 psi above ambient. It exhausted into the hood which also had a relief valve which lifted at 4psi above ambient thus giving you a supply of breathing air from 600ft to the surface.

I suspect the normal pressure for most inflated lifejackets will be similar

 

[geoffatstanpit]

The reason they use carbon dioxide in lifejackets is that it has a critical pressure of about 58 atmospheres (at normal temperatures). This means that if you fill a cylinder with CO2 up to 58 ats and then keep filling, the gas turns to liquid and then the gas laws don't apply any more and you can get lots more gas in than you'd expect.

Somebody's law states that 44 grams (molecular weight in grams) of CO2 expands to 22.4 litres at normal pressure (1 at). Guessing that a lifejacket cylinder holds about 10 grams of CO2 that would make about 5 litres of gas which is closer to what actually happens than Mr Boyle & Co would have thought.

Calor gas cylinders work on the same principle - the gas is liquid until you open the tap.

 

[Twister_Ken]

33gm bottle is for 150 newton l/j.

Thus 66gm = 300 newton l/j???

 

[jdc]

Ideal Gas Law

...

Somebody's law states that 44 grams (molecular weight in grams) of CO2 expands to 22.4 litres at normal pressure (1 at). Guessing that a lifejacket cylinder holds about 10 grams of CO2 that would make about 5 litres of gas which is closer to what actually happens than Mr Boyle & Co would have thought.

...

This is the approach I'd take, only I think the 66g in a '66g cylinder' is the amount of gas not the total weight of the cylinder. So it would be 1.5 x 44g, ie 1.5 moles, so 1.5x 22.5l = 33.75l (CO2 = 12 + 2*16 = 44 grammes per Mole).

At a good pressure for a lifejacket (which is nowhere near as much as 1 atmospheres over-pressure I think, given that oral inflation works; I guess it to be more like 0.25 atmospheres) then that makes it 27 litres using PV = nRT.

27 litres of gas displaces 27 litres of water, which weighs 27kg more or less, ie 265N, which all seems to stack up

 

[tim_ber]

Thanks for all that, appreciate it.