cu ft in a gas cylinder

[mawtg]

does anybody know how a gas cylinder measuring 6" dia and 32" tall can have 80 cu ft of gas? how is this figured?

[Rick M]

"mawtg" wrote

Yes ... the gas volume (in your case 80 cubic feet) is when it is at atmospheric pressure. By compressing the gas, you can make it fit into a smaller volume, but the pressure goes up accordingly.

Take a look at this page (hint ... I did a google search using the search term ' gas cylinder volume ' without the quotes):

some old dead fellow (before he died) came up with Boyle's Law (betcha his name was Boyle).

Simply put, if you squeeze 80 cubic feet of gas at atmospheric pressure into a vessel with a volume of 40 cubic feet, the pressure in that vessel will be twice atmospheric pressure.

Hope this helps, but I'm still trying to figure out what this has to do with woodworking, other than it's a gas when it goes well!

Regards,

Rick

[bridger]

it's compressed.

[Lew Hodgett]

You are referred to a high school chemistry text for a detailed explanation of Boyle's Law.

The same text will also give you the density of the gas in question at standard pressure and temperature specifications.

Next you weigh the cylinder to get a gross weight, then subtract the cylinder weight to get net weight of the compressed gas.

After that, it is a basic math problem.

Lew

[Roy]

The Engineering Gods will smite you for that one.

[Guess who]

..it can also be liquified, depending upon the gas; e.g. propane. CO2 doesn't liquify under pressure, it becomes solid [dry ice.] Either way a lot can be fit into a little space.

[fredfighter]

ISTR that CO2 will liquify under pressure at room temperature.

It won't condense into liquid at atmospheric pressure though, goes straight to solid.

Water does the same, gas to solid, solid to gas (sublimation) with no liquid phase at very low presssure.

[George E. Cawthon]

The answer is that it can't. It can only hold about 1/2 cubic foot (if I did the math correctly). Doesn't matter what the gas is, doesn't matter what the pressure is, it is always the same volume because gases expand to fill the volume of the container. The question is illogical probably based on a statement that was incomplete, or part of which was ignored in stating the question.

And by the way, any amount of gas in the cylinder can have a volume of 80 cu ft if the pressure is sufficiently lower that the gas in the cylinder.

If you want to measure the amount of gas, you have to give a volume and a pressure, or something by which the number of atoms/molecules of the gas can be calculated.

It is unfortunate that school don't teach, or the students don't learn, the states of matter and the basic properties of those states. Seems to me that would be more important that the colors of the rainbow and a few other things kids are taught.

[fredfighter]

A standard measure of gas is the _standard cubic foot_ which is the amount of gas that will occupy a volume of one cubic foot at standard temperature and pressure, usually abbreviated SCF. You see it most often in reference to volumetric flow as through a blower or a fan, SCF/minute or whatever.

The standard pressure is one atmosphere. Unfortunately the standard temperature is either 0 degees C or 'room temperature' (which I think is around 70 degrees F) depending on which standard is used, though that makes only a small difference.

So when you buy gas by the cubic foot, you are buying by the standard cubic foot, the seller usually omits the word 'standard'.

[Robatoy]

as does the temperature

[Robatoy]

...errrrmmm...is this why we 'boyle' water?

...could be where that word came from...

A faraday keeps the doctor away?

Back to sleep.

[Mortimer Schnerd, RN]

Not quite. Your statement is incomplete as well. That .5 cubic foot that you suggest only holds true at atmospheric pressure. If you compress the gas within, you can hold virtually any amount up to the bursting pressure of the tank. On 80 cf scuba cylinders which are only a little bigger than his example, you'd charge them to about 200 atmospheres (3000 psi) to get the 80 cubic feet packed in there. It is understood that the 80 cf measurement is what the cylinder holds under pressure, not empty.

AGA Divator used to make twin 40 cf systems that required them to be pumped up to 4400 psi. Now that is one hell of a lot of pressure. They were little things that fit closely to your back but they were ungodly expensive and most dive shops couldn't fill them. But they packed the same 80cf as the larger cylinders.

[Doug Miller]

Not correct. CO2 cannot be *solidified* under pressure unless the temperature is below -57 degrees C.

The triple point of CO2 is -57 deg C and 5.1 atmospheres: it can exist as a solid, liquid, or gas at that temperature and pressure. It cannot exist in the solid phase above -57 degrees, nor in the liquid phase below that point, regardless of pressure.

[WillR]

A Faraday keeps the engineer away -- then we don't have to endure bad=20 puns you see.

--=20 Will R. Jewel Boxes and Wood Art

power of accurate observation is commonly called cynicism by those=20 who have not got it.=94 George Bernard Shaw

[Robatoy]

THAT will never happen..*WEG*.. btw, I have been meaning to ask you..did you make it to the Muskoka Wood show?

[Lawrence Wasserman]

The volume of the cylinder is piR^2H, so (roughly) 3.14X3X3X32=904 cu inches. Divide by 12X12X12=1728 to convert cu in to cu feet=.523, lets say 1/2 a cubic foot for convenience and to allow for cyl wall thickness, etc. If it's a common gas cylinder it will usually be compresssed to about 2500psi, so if we let that 1/2 CF expand by releasing it tio atmospheric pressure of roughly 15psi, it would take up .5X2500/15=83 cu ft, which is about right.

[Leon]

The gas compresses and will until it turns to a liquid.

[Robert Bonomi]

measuered as 80 cu ft, at _one_atmosphere_. Compressed to *much* higher levels, to fit in the limited space. :)

[Robert Bonomi]

Sir Arthur Conan Boyle concluded that such gas behavior was "elementary, my dear Watson, elementary!" < *groan* >

[Robert Bonomi]

Beware, the EE types have some that are real joules! Which they tell without reluctance. Until people cry "no mho!"

However, an engineer did *not* commit the following atrocity -- An inmate of the insane asyslum, escaped, raping the window-cleaing lady on the way; wherepon the local scandal-sheet rag ran a headling about it: "Nut Screws Washer And Bolts"