cu ft in a gas cylinder

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Robatoy wrote:

A Faraday keeps the engineer away -- then we don't have to endure bad puns you see.
-- Will R. Jewel Boxes and Wood Art http://woodwork.pmccl.com The power of accurate observation is commonly called cynicism by those who have not got it. George Bernard Shaw
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THAT will never happen..*WEG*.. btw, I have been meaning to ask you..did you make it to the Muskoka Wood show?
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Robatoy wrote:

Yep -- got a few things -- it was small as usual, but I arranged for some purchases for the next few months so...
-- Will R. Jewel Boxes and Wood Art http://woodwork.pmccl.com The power of accurate observation is commonly called cynicism by those who have not got it. George Bernard Shaw
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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"
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On Thu, 25 Aug 2005 02:01:13 GMT, snipped-for-privacy@yahoo-dot-com.no-spam.invalid (mawtg) wrote:

it's compressed.
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snipped-for-privacy@yahoo-dot-com.no-spam.invalid (mawtg) wrote:

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
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mawtg wrote:

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.
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George E. Cawthon wrote:

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'.
--

FF


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snipped-for-privacy@spamcop.net wrote:

All true. But none of that changes the fact that the question is erroneous.
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George E. Cawthon wrote:

Did you ever see this show called Dr Who?
A gas cylinder is constructed like a tardis you see so that
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George E. Cawthon wrote:

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.
--
Mortimer Schnerd, RN

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Mortimer Schnerd, RN wrote:

No it isn't. The volume of the cylinder is about 0.5 cubic foot, so the amount of gas that it contains is ALWAYS 0.5 cubic foot; it doesn't make any difference what the pressure is. Your 4th sentence is also incorrect. At some pressure and temperature you get liquid air which fills the cylinder and at that point you can't put any more air into cylinder since a liquid is only slightly compressible. Your last point is also incorrect; there was is no assumption about the pressure, and it still matters not a whit since the cylinder volume is 0.5 cubic feet so that is all the air it can hold no matter what the pressure is as long as it is gas.

Your assumption is that we are talking about cylinders of air for scuba diving at specific pressure. The OP did not say anything that would indicate that. He did provide enough information that you could figure out the pressure needed in the cylinder to have 80 cf of gas at one atmosphere. Since it is 80 cf and cylinder is 0.5 cf it needs to be compressed about 160 times. One atmosphere is about 15 psi, so the psi needed is 15 x 160 about 2700 psi. All of which has nothing to do with what I said and the general lack of understanding of states of matter.
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George E. Cawthon wrote:

Within the cylinder, yes. But cylinders aren't sold according to their empty volume; they're sold and rated according to the volume of gas they can hold at their rated pressure.

OK, I'll give you that point. My bad. But I'll bet the tank will blow long before the air liquifies. 3000 psi scuba cylinders will blow the safety disk at around 4000 psi; get hydrotested at 5000 psi, and will catastrophically fail at around 7500 psi. Will air liquify at 500 ATM? What gases would? I pulled out my trusty old CRC Handbook of Chemistry and Physics but couldn't find the information.

But it can certainly be pressurized to hold much more gas than .5 cubic feet. Otherwise there's no way in hell it can hold more than it holds at one atmosphere.
--
Mortimer Schnerd, RN

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Mortimer Schnerd, RN wrote:

No it can't. How can you get more than .5 cubic feet of air inside a cylinder that only has .5 cubic feet of volume? Please explain how you can get more volume inside a cylinder than the volume of the cylinder. Inquiring minds want to know?
And why are you fixated on assumptions about the cylinder? It is just a cylinder. You don't know the purpose or anything else about the cylinder.
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By compressing it, of course, so that the same *mass* of air that occupies 80 cu ft at standard pressure now occupies only 0.5 cu ft and easily fits inside the cylinder.
Do you really have a hard time understanding this concept? Or are you just being pedantic? Inquiring minds want to know....
--
Regards,
Doug Miller (alphageek at milmac dot com)
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The phrase I used was "intentionally obtuse", but "pedantic" fits even better.
todd
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Doug Miller wrote:

Possibly being pedantic, but more like trying to indicate that sloppiness in writing results from faulty thought processes or lack of information. The point I was trying to make was a basic understanding of states of matter would negate that kind of question. The point was, and is, that a gas occupies whatever space it is allowed to occupy. And the volume it occupies, of itself, tells nothing about the mass.
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George E. Cawthon wrote:

Ah, a purist. Also a horse's ass. And please don't shoot the messenger.
--
Mortimer Schnerd, RN

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There's no need to be intentionally obtuse just to try to prove a point. The subject contains the phrase "gas cylinder". Now, maybe in your world, that's any old cylindrical object that contains matter in a gaseous form, but most humans interpret that to mean a (mostly) cylindrical object designed to contain a gas at pressure. It's obvious from the freakin' question that the gas is pressurized...otherwise the question would have never come up.
todd
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Todd Fatheree wrote:

If you don't like the message, don't shoot the messenger.
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