Question About Scuba Tanks - At Ambient Temperature

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eng123 Member Join Date: Dec 2007 Posts: 5	Question About Scuba Tanks - At Ambient Temperature 12/28/2010 9:18 AM
	Most recreational scuba tank specifications state the amount of air and the maximum pressure. They do not seem to state the temperature of the air in it which seems too important to be left out. The place where I fill the tank is at 80 deg F. The ambient temperature at dive location is usually around 50 deg F. Following the general gas law, I could have the tank filled at the diving location with air at 50 deg F, and have much more (80/50 = 1.6 times) air available to me under water, than filling it at 70 deg F. Conversely, it wouldn't be safe if I fill the tank at 50 deg F to the maximum pressure and take the tank out to a dive spot at 70 deg F. Is my understanding correct?
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#1 Re: question about scuba tanks - at ambient temperature 12/28/2010 9:24 AM
	I'd disregard the ambient air temperature when doing my calculations. Do the math on compressing air from 1 atmosphere to 200 atmospheres. I'd say the air inside the tank is going to be hot, no matter what the temperature of the air going into the compressor is. Oh, and the manufacturer isn't going to sell you a tank that isn't idiot proof, too.
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farmatt Power-User Join Date: Jun 2010 Location: Brownsville, Oregon, USA Posts: 345 Good Answers: 10	#2 Re: question about scuba tanks - at ambient temperature 12/28/2010 9:37 AM
	If what you are talking about is true, then the SCBA tanks firefighters use would have major problems going into fires. I do not know much about such tanks, but they seem similar to me, I have seen both side by side at our fire hall as we are a very small community and the fire department is the underwater rescue in our county. __________________ Give me enough duct tape and I can fix anything!
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kramarat Guru Join Date: Jun 2008 Location: Raleigh, NC USA Posts: 13529 Good Answers: 468	#3 Re: Question About Scuba Tanks - At Ambient Temperature 12/28/2010 10:01 AM
	Here's a pretty good article. http://www.dtmag.com/Stories/Dive%20Physiology/09-97-feature.htm __________________ Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
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Usbport Guru Join Date: Apr 2010 Location: Trantor Posts: 5363 Good Answers: 647	#4 Re: Question About Scuba Tanks - At Ambient Temperature 12/28/2010 10:03 AM
	You need to use Kelvin temperatures, not Fahrenheit. 80F = ~ 300 K; 50F = ~ 283 K; 300/283 = 1.06. __________________ Whiskey, women -- and astrophysics. Because sometimes a problem can't be solved with just whiskey and women.
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34point5 Guru Join Date: May 2010 Location: in optimism Posts: 4050 Good Answers: 130	#6 In reply to #4 Re: Question About Scuba Tanks - At Ambient Temperature 12/29/2010 1:11 AM
	GA ^{_{(though you might have applied the 6% to the fill pressure, but oh dear, the OP didn't cite one)}} __________________ There is no sin except stupidity. (Oscar Wilde, Irish dramatist, novelist, & poet (1854 - 1900))
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dgibson Power-User Join Date: May 2009 Location: Amarillo, Texas, USA Posts: 188 Good Answers: 10	#5 Re: Question About Scuba Tanks - At Ambient Temperature 12/28/2010 10:12 AM
	First your math is wrong, you would not end up with 1.6 X more air. I have seen tanks that were cool in the early morning sit in the sun, warming and gain 100 psi. pressure from a 40 degree rise , that is 1/30 of the air with a 3000 psi fill. The tanks are hydro-tested at over 5000 psi. We usually fill the tank to 3200 psi since it is so hot when it is filled, when it cools it is between 2900 and 3000 psi. With a few variables thrown in 2800 psi is considered a complete fill.
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34point5 (1); dgibson (1); farmatt (1); kramarat (1); lyn (1); Usbport (1)

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