Imperial vs Metric specifications for AL tanks

[JohnN]

So. . if I look up the Imperial specifications of an AL80 tank (lets say Luxfer) I get an volume of 77.4 cuft @ 3000 PSI.

If I look up the same tank, the metric specifications give an "internal volume" of 11.1 l @ 207 bar.

(11.1 * 207) * 0.035315 = 81.1 cu ft

However if I use the "true capacity" (2192 l) I get the 77.4 I've come to know and love.

WTF?

 

[runsongas]

true capacity is lower due to the z value (for compressibility) of air deviating from that of an ideal gas at high pressure.

 

[JohnN]

true capacity is lower due to the z value (for compressibility) of air deviating from that of an ideal gas at high pressure.

That's not how I read the data:

	Pressure, bar (absolute)
Temp, K	1	5	10	20	40	60	80	100	150	200	250	300	400	500
75	0.0052	0.0260	0.0519	0.1036	0.2063	0.3082	0.4094	0.5099	0.7581	1.0125
80		0.0250	0.0499	0.0995	0.1981	0.2958	0.3927	0.4887	0.7258	0.9588	1.1931	1.4139
90	0.9764	0.0236	0.0453	0.0940	0.1866	0.2781	0.3686	0.4681	0.6779	0.8929	1.1098	1.3110	1.7161	2.1105
100	0.9797	0.8872	0.0453	0.0900	0.1782	0.2635	0.3498	0.4337	0.6386	0.8377	1.0395	1.2227	1.5937	1.9536
120	0.9880	0.9373	0.8860	0.6730	0.1778	0.2557	0.3371	0.4132	0.5964	0.7720	0.9530	1.1076	1.5091	1.7366
140	0.9927	0.9614	0.9205	0.8297	0.5856	0.3313	0.3737	0.4340	0.5909	0.7699	0.9114	1.0393	1.3202	1.5903
160	0.9951	0.9748	0.9489	0.8954	0.7803	0.6603	0.5696	0.5489	0.6340	0.7564	0.8840	1.0105	1.2585	1.4970
180	0.9967	0.9832	0.9660	0.9314	0.8625	0.7977	0.7432	0.7084	0.7180	0.7986	0.9000	1.0068	1.2232	1.4361
200	0.9978	0.9886	0.9767	0.9539	0.9100	0.8701	0.8374	0.8142	0.8061	0.8549	0.9311	1.0185	1.2054	1.3944
250	0.9992	0.9957	0.9911	0.9822	0.9671	0.9549	0.9463	0.9411	0.9450	0.9713	1.0152	1.0702	1.1990	1.3392
300	0.9999	0.9987	0.9974	0.9950	0.9917	0.9901	0.9903	0.9930	1.0074	1.0326	1.0669	1.1089	1.2073	1.3163

Figure 300 oK approximates the temperature, @ ~200 Bar, Air doesn't deviate that much from an ideal gas

 

[runsongas]

80 cf / 1.0326 = 77.474 cf

 

[Divetech99]

If using Luxfer AL80, SAC rate in cubic feet is computed using tank capacity of 77.4 cf. vs 80. This will lower your sac rate .

 

[Chugwhump]

I cannot believe how often these algebra/physics tank capacity fights start.
But please carry on.
It is always a good knowledge review.
And sometimes very funny.

Chug
Does not accept the word low, on low pressure tanks.