Storing a tank in car with 100 degree heat?

[mksmith713]

I like to do two tank dives when I shore dive.
Living in SE,Fla, the heat gets incredible during the summer months.
Does anyone have recommendations on how to store tanks in your car without blowing the burst disk from the elevated heat?

[fire diver]

If your burst disks are in good order, there is no way will blow.

[Rhino]

How far is your dive site from where you live? If more than an hour away, you should pull over to a shade at least once and open your trunk to let the hot air out and allow for cooler air to circulate in. I cover my tanks with a standard car windshield visor to help protect the tanks.

[SkuaSeptember]

Although car interior temps can easily climb to well over 120 deg. even with the windows cracked, you are looking at a pressure increase of only about 5 psi per degree f. A few hundred psi should not cause a burst disk to go on a tank that hasn't been overfilled to begin with.

[mksmith713]

So.....if my wife and I want to do 2 shore dives, and the first dive is 1:20, the second tank can be left in the car with no concerns?
I'm talking West Palm Beach heat.

[fire diver]

That's correct, the heat is NOT going to hurt the tanks in any way. You will noticed a slightly higher tank pressure when you gear up, but that drop within the first minutes of the dive as the tank cools back down.

[petronius]

I'm no physicist, but I think this risk is vastly overstated. Gay-Lussac's Law states that, with constant volume (as in a scuba tank), pressure is directly proportional to temperature (assuming an ideal gas, to be precise). In other words, P1/T1 = P2/T2. We can rewrite that to show that P2 = (P1*T2)/T1.

For my low pressure tank, filled to 2400 psi as an example, and assuming I start off at 70F and warm it to 140F in the car:

T1 = 70F (294 Kelvins)
T2 = 140F (333 K)
P1 = 2400 psi (16,547,400 Pascals)

So, P2 = (16,547,400 * 333)/294 = 18742010 Pa = 2720 psi. I've gotten larger fills than that on more than one occasion.

From the other direction, assuming I had a 4000 psi burst disk, the car/tank would need to warm to a temperature of about 420 F before the disk blew. I'd probably notice that happening...

(Of course, I could have totally screwed up the math or made bad assumptions - and info from the internet is worth exactly what you pay for it. But I'm pretty sure I'm correct... )

[rustyshakelford]

how about just double disk them and call it good?

brett

[navyhmc]

Originally Posted by rustyshakelford

how about just double disk them and call it good?

brett

Not a good idea either. If you double, you are risking a catastrophic tank failure rather than a disk failure. While the risk of tank ka-boom is low, the burst disk to the correct thickness/pressure for the tank will make sure that doesn't happen. This is said knowing that tanks are tested to 5/3 the working pressure during hydro's and the burst disc is usually 4/3 the working pressure-or at least that is what I have been told.

[mitsuguy]

the only other thing you should worry about (other than the already mentioned pressure increase) is that the tank should never be subjected to temps over 180 degrees F... If one was, it should be hydrostatically tested to ensure structural integrity...

as far as the pressure increase, it is definitely P1/T1 = P2/T2, but you don't have to convert pressure to pascal, and its easier to just add 460 to get rankine...

or, easier than that even, its 5 psi per degree F (edit: I just worked out the math and it looks like it comes out to 5.38 psi per degree F change)