Bob
The two charts don ‘t agree.
Re.9L Great White as one example - The first says the 9L does have 88 cubic feet at 4500psi. Yours says 97 cu feet at 4500 psi.
Which is correct?
Tom
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Carbon fiber tank size comparison chart
- Thread starter Humdinger
- Start date
Bob
The two charts don ‘t agree.
Re.9L Great White as one example - The first says the 9L does have 88 cubic feet at 4500psi. Yours says 97 cu feet at 4500 psi.
Which is correct?
Tom
Well, I'm going to go with mine, since the chart I made used simple math formulas, not data gleaned from the internet.
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Bob
I found this post and perhaps this explains the discrepancy. Take a look.
Carbon Fiber Air Tank Liter to Cubic Feet Conversion
A friend of mine asked me the other day about carbon fiber air tanks on eBay and how some of this type of HPA tanks that are made here in the USA are measured in cubic feet and not liters. Well I didn’t have a clue what to tell him so I told him I would get back to him when I had the answer. It...
www.airgunnation.com In reading Mojoatomic’s post, It appears the discrepancy ( 97/98 cu ft vs. 86 cu ft ) is due to how you calculate the PSI for 300 BAR. The formula yields a different result using 4351 PSI as 300 BAR vs. when the formula uses 4000 psi for 300 BAR. The post suggests the Chinese chart uses 4000 psi for safety reasons vs. 4351 psi to calculate fill volume.
Technically, 4351 psi equals 300 BAR, but the Chinese conservatively used ‘4000 psi’ as 300 BAR in their formula to calculate the fill volume of 86 cubic feet.
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Well, as I stated above, it's simple math. Disregarding the heat factor, of course. Yes, 4351 psi is 299.99 bar. Always has been, always be. (I cannot speak to what some company from China claims it to be)Bob
I found this post and perhaps this explains the discrepancy. Take a look.
Carbon Fiber Air Tank Liter to Cubic Feet Conversion
A friend of mine asked me the other day about carbon fiber air tanks on eBay and how some of this type of HPA tanks that are made here in the USA are measured in cubic feet and not liters. Well I didn’t have a clue what to tell him so I told him I would get back to him when I had the answer. It...
It appears the discrepancy ( 97/98 cu ft vs. 86 cu ft ) is due to how you calculate the PSI for 300 BAR. The formula yields a different result using 4351 PSI as 300 BAR vs. when the formula uses 4000 psi for 300 BAR. The post suggests the Chinese chart uses 4000 psi for safety reasons vs. 4351 psi
Technically, 4351 psi equals 300 BAR which yields the higher value at 94.07 cu feet.
So, If this post and formula logic is correct, it appears to me that the Manufacturer can quote the higher spec using 4351 psi in the formula.
Also, Boyle's law has been around since the mid-1600s. Can't really argue with them maffs. And the math in your quoted post is as accurate as mine is, but we are talking about 4500 psi, or 310.26 bar, and THAT is what leads us to 97 cu ft as opposed to 88.
To be clear, a 9L/550 cu in tank filled to 4,070 PSI (280.6 bar) will hold 88 cu ft, whereas filling it to 4500 psi (310.3 bar) will result in an air volume of 97 cu ft.
(And that firman's rating... we need to just drop that from our vernacular, as it is useless, even for firemen; anyone should be able to deduce that a 110 lb female firefighter won't draw as much air as a 210 lb male firefighter. And BOTH of those will draw more air, thereby reducing the time a tank lasts, when they are stressed and exerting themselves.)
Thanks for pointing out that post!
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“To be clear, a 9L/550 cu in tank filled to 4,070 PSI (280.6 bar) will hold 88 cu ft, whereas filling it to 4500 psi (310.3 bar) will result in an air volume of 97 cu ft.”
This sentence really explains the discrepancy I noted very well.
Yep. Good explanations. Tx…
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Cubic feet of air at 4500 psi is a really odd unit of measurement.
It should state, cubic feet of air this would produce if full at 4500psi, then emptied into a 14.7psi room.
It should state, cubic feet of air this would produce if full at 4500psi, then emptied into a 14.7psi room.
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I am the author of the chart in this thread. My original version of this chart used simple math which showed higher tank volumes which were incorrect and inaccurate. It's true that just using volume x pressure will yield a tank capacity higher than the current chart accurately shows. For instance, a 9L tank at 310 bar would seem to hold 97CF of air. It doesn't. The reason manufacturers such as Scott and Luxfer use 88CF instead of 97CF as the air capacity of their 9L tanks at 310 bar is that gases don't compress at a linear rate. Once air is compressed to pressures exceeding 3,000 psi air compresses less because air compresses logarithmically. For the technically and scientifically minded, it is calculated using van der Waals equation. If air did compress in a linear manner, simple math would calculate the air capacity. I trust the manufacturers who sell the tanks to divers and firefighters whose lives depend on their calculations. These companies have an understanding of the compressibility of gases. The chart is correct.
Reread this thread from the beginning. This topic has already been discussed previously and explained.
Reread this thread from the beginning. This topic has already been discussed previously and explained.
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It actually does. Think of it this way. If you filled a balloon with a 9L tank filled to 310 bar it would expand to 88 cubic feet of volume. A 6.8L tank would fill a balloon to 66 cubic feet of volume.
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