Author Topic: Tank Sizes  (Read 1454 times)

steveoh

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Tank Sizes
« on: September 05, 2018, 09:55:43 AM »
I'm chewing on getting another big tank since the Big Bores chew through the air way too quickly. So I'm looking at used, at Chinese Tanks, and Good Old American tanks that cost a pretty penny.

The Chinese tanks are described in Liters.
Fireman's used tanks are described in 30,45 and 60 minute varieties
The American Airgun tanks are described in Cubic Inches and Cubic Feet.

I am flipping confused since the math doesn't see to make sense. Anyone come across a chart of all of these measurements so I see what is what?

Yeah, I'm math challenged sometimes.


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steveoh

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Re: Tank Sizes
« Reply #1 on: September 05, 2018, 10:01:21 AM »
hmmm maybe I found the answer:

The Chinese tanks are measured in water capacity.  Fireman's tanks measured in minutes. This chart from Dragar lists both.

Now the airgun tank capacity is yet another thing. I suppose a 97CF tank is 97CF of compressed air.  hmmm.
« Last Edit: September 05, 2018, 10:03:22 AM by steveoh »
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Alan

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Re: Tank Sizes
« Reply #2 on: September 05, 2018, 11:02:30 AM »
A nominal large tank has a water capacity of ≈550 cubic inches (≈.318 cubic FEET, ≈9 cubic liters). At its rated pressure, it has ≈97 cubic FEET (≈167,616 cubic inches, 2,747 cubic liters) of air (referenced to STP).

I trust I figured all of this correctly?

By the way.... I didn't look, but recently I saw some large tanks which have been re-certified which were only a couple of hundred. The requisite valves and gauges are reasonable too.
« Last Edit: September 05, 2018, 11:04:44 AM by Alan »
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

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Re: Tank Sizes
« Reply #3 on: September 05, 2018, 11:37:46 AM »
The 60 minute SCBA tanks are indeed 550 CI = 9 litres internal volume.... and the 45 minute tanks are 416 CI = 6.8 litres.... Although Boyle's Law for ideal gasses would predict that a 550 CI tank would hold 97 CF of air, once you surpass about 3000 psi, air no longer acts as a ideal gas, but a "real gas", and calculations must use VanDerWaal's formula, not Boyle's.... In fact that 550 CI tank only holds 88 CF of air (at STP) when filled to 4500 psi, not the 97 CF you sometimes see advertised.... The same holds true for the 416 CI (45 minute / 6.8 litre) tanks, they only hold 66 CF of air at 4500 psi, not 74 CF....

Bob
« Last Edit: September 05, 2018, 11:44:24 AM by rsterne »
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Alan

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Re: Tank Sizes
« Reply #4 on: September 05, 2018, 11:43:08 AM »
True, but I used the same straight calculation, which is obviously a bit of a misnomer. (Reminds me of antenna manufactures who used dBi instead of dBd, and leave of the last digit identifier just to make themselves look better than they are!)

Here are a couple of links of interest:

https://www.phmsa.dot.gov/approvals-and-permits/hazmat/file-serve/offer/SP16320.pdf/2017078089/SP16320  This is the recertification approval.

https://www.digitalwavecorp.com  This is the company which got the recertification.
  • Roswell, New Mexico
Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

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Re: Tank Sizes
« Reply #5 on: September 05, 2018, 11:45:44 AM »
Sorry, but I get very tired of some sellers saying their standard SCBA tanks hold more air than they actually do....  ::)

Bob
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Alan

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Re: Tank Sizes
« Reply #6 on: September 05, 2018, 12:08:12 PM »
I agree—at least, in one very evident case!

I think some of us get hung up on minor differences of a few cubic feet as if that's the only reason to buy one over another. What is more important to me, is how good is the valve, gauge(s), hose, supplied fittings, etc.
  • Roswell, New Mexico
Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

steveoh

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Re: Tank Sizes
« Reply #7 on: September 05, 2018, 12:59:12 PM »
Sorry, but I get very tired of some sellers saying their standard SCBA tanks hold more air than they actually do....  ::)

Bob

Hence part of my confusion.  &^%$@
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caniborrowsomeammo

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Re: Tank Sizes
« Reply #8 on: September 05, 2018, 08:12:16 PM »

By the way.... I didn't look, but recently I saw some large tanks which have been re-certified which were only a couple of hundred. The requisite valves and gauges are reasonable too.
/
Where did you see them? And how many years left you think
I also heard some 15-year tanks were getting recert for 15 more years. Don't remember where I saw that though.
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rsterne

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Re: Tank Sizes
« Reply #9 on: September 05, 2018, 08:26:12 PM »
PA is now selling recertified tanks....

Bob
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Alan

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Re: Tank Sizes
« Reply #10 on: September 06, 2018, 03:42:15 AM »
It may have been PA, but I'm not sure. The price was around $200 without the valve and hose assembly.
  • Roswell, New Mexico
Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.