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mksmith713
06-07-2009, 18:22
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
06-07-2009, 18:29
If your burst disks are in good order, there is no way will blow.

Rhino
06-07-2009, 18:39
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
06-07-2009, 18:41
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
06-07-2009, 18:46
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
06-07-2009, 19:18
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
06-07-2009, 20:11
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
06-07-2009, 20:30
how about just double disk them and call it good?

brett

navyhmc
06-07-2009, 20:42
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
06-07-2009, 21:32
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)

BubblesMcCoy
06-07-2009, 22:33
There is an article on this in the june Dive Training. I just skimmed it, but I think the jist of the article was a recommendation to cover with a reflective sunshade.

The physics calculations certainly look right, but it's not that hard to cover them from direct sunlight, so why take the chance. May not be an issue, I can't imagine that the abrupt temp change from hot car to water would be good as far as the tank is concerned. Just a thought.

chilly willy
06-07-2009, 22:46
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?
I've had tanks in the trunk of a car in Bullhead City, AZ in July and never had a problem. The ambient temp was at least 115F so I think you'll be fine.

nrembis
06-08-2009, 01:15
You'll be fine, I carried 5-6 tanks with me in the back of a pickup truck all day long for a long time when I cleaned boats in Stuart, FL....they were always in direct sunlight, some were new tanks, some were 20 years old, never had any issues.

UCFKnightDiver
06-08-2009, 08:13
also keep in mind if there is no direct sunlight getting into your trunk than the trunk should stay relatively cool compared to the rest of the car, and like others have said I wouldnt worry about it.

mike_s
06-08-2009, 11:20
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.

w.t.f. ?

where the heck do you get that crazy information from?

If this was true, then you'd see tanks blowing up all over Florida, Arizona, California and anywhere else that the heat got above 100 degrees.

You're going to have to get your car up to over 400 degrees internally for it to make a difference in a good quality tank.

yes a few have blown up in cars, but there were other issues involved such as cracks in the SLC in 6351T alloy tanks, etc.



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.

exactly



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... :))



We did the math on this a few years a back and come up with a temp that was in the 400 something degree range.

also there was another thread with the math on it on Scubaboard that came up with 400 something degree also.

MSilvia
06-08-2009, 11:33
The "theoretically this and probably thats" are all well and good, but I have an interesting first-hand experience to share. I used to have a set of perfectly good AL80s that I doubled and more-or-less stored in the car for a season. The only came out for dives and fills, and were otherwise left in what occasionally became a very hot car.

Because they were doubled, they weren't able to roll at all, and the same side of the tanks were always in the sun, and the opposite side in the shade. When I brought the tanks in for vis at the end of the season, it was brought to my attention that both tanks (long since cooled to room temperature) had taken on a slight curve... the "sunny side" of my (now banana-shaped) yellow tanks was a fraction of an inch longer than it used to be. It wasn't enough to cause them to fail, but it was enough to cause me to change my practices (and sell the doubles with full disclosure).

The burst disks never failed, but the tanks were clearly affected by the heat. Catastrophic explosions are not the only danger... apparently deformation of filled tanks can occur as well, and at temps much lower than 400 degrees.

in_cavediver
06-09-2009, 11:40
The "theoretically this and probably thats" are all well and good, but I have an interesting first-hand experience to share. I used to have a set of perfectly good AL80s that I doubled and more-or-less stored in the car for a season. The only came out for dives and fills, and were otherwise left in what occasionally became a very hot car.

Because they were doubled, they weren't able to roll at all, and the same side of the tanks were always in the sun, and the opposite side in the shade. When I brought the tanks in for vis at the end of the season, it was brought to my attention that both tanks (long since cooled to room temperature) had taken on a slight curve... the "sunny side" of my (now banana-shaped) yellow tanks was a fraction of an inch longer than it used to be. It wasn't enough to cause them to fail, but it was enough to cause me to change my practices (and sell the doubles with full disclosure).

The burst disks never failed, but the tanks were clearly affected by the heat. Catastrophic explosions are not the only danger... apparently deformation of filled tanks can occur as well, and at temps much lower than 400 degrees.

See - that is why you need to break doubles down each year and rotate tanks. That way, you can put the 'sunny side' down next year and have flat tanks after 2 years............

Seriously, I would never store tanks in a car. A simply accident could get exciting depending on how/where things were hit, rollover etc and that is enough for me to only carry them when I dive.

On the other hand - I have a D bottle or O2 I keep in my car as part of my tec kit. I'll have to keep an eye on it and see if it develops issues.

MSilvia
06-09-2009, 11:55
that is enough for me to only carry them when I dive.
Sure, but at the time I was averaging 3-4 dives per week, so they were usually either getting transported to or from a fill station or dive site, and removing them from the car seemed like more trouble than it was worth... unless I was going to be parking somewhere "risky".

divinginn
06-09-2009, 14:59
I had a disc burst on a steel 72,it was overfilled to 3600,I drained it down to 3200 and then left it in the truck in the sun. I came out to the truck and it looked like a tornado had gone through my truck,it took me a minute or two to figure out what happened. It was a old disc that needed changing out anyhow.

petronius
06-09-2009, 15:28
I had a disc burst on a steel 72,it was overfilled to 3600,I drained it down to 3200 and then left it in the truck in the sun. I came out to the truck and it looked like a tornado had gone through my truck,it took me a minute or two to figure out what happened. It was a old disc that needed changing out anyhow.

When are burst disks typically changed? At hydro? When they seem to be 'getting old'?

And what does it look like when it fails? Does the little hexagonal nut just pop out like a turkey-timer, or does it come shooting out with force? Or does it not move at all?

WaScubaDude
06-09-2009, 16:23
The hex bolt does not move at all. Behind it is a thin disc (copper I think) that actual fails, rips open into the cavity of the hex bolt. The bolt has a few little holes on the sides that let the air exit relatively safely.

In the very old days they used a bolt with a lead plug that would fly out like a bullet, the next gen had a bolt with a single hole drilled thru with the copper disk, when either of these plugs blew the tank would dance around and cause some damage to stuff in the way. I watched one dance and roll about 12 ft across a concrete floor.

JahJahwarrior
06-09-2009, 18:02
MSilvia-- are you saying that one side of the tank was longer than the other--ie: the sides of the tank no longer made a perfect 90 degree angle with the bottom? Or that the entire tank was longer than the other tank? Do you have pictures or proof of this event?

The Great Kazoo
06-09-2009, 18:20
I dive four to five times a week due to a lack of work. Not sorry. pretty happy, as I have prepared myself for. I NEVER leave my tanks in my truck/vehicle ALL Week. I will leave them for a day or two at most. I have dove in Az. Ca. Utah... In 125' weather. Maybe it is just me....dont think so. I do cover my stuff and vent my trunk every 10 miles. LOL

petronius
06-09-2009, 18:32
The hex bolt does not move at all. Behind it is a thin disc (copper I think) that actual fails, rips open into the cavity of the hex bolt. The bolt has a few little holes on the sides that let the air exit relatively safely.

In the very old days they used a bolt with a lead plug that would fly out like a bullet, the next gen had a bolt with a single hole drilled thru with the copper disk, when either of these plugs blew the tank would dance around and cause some damage to stuff in the way. I watched one dance and roll about 12 ft across a concrete floor.

Thanks - I was picturing something a lot more explosive (obviously I'm glad to be wrong). I guess it must take a fairly long time for the tank to finish draining through those small holes...

MSilvia
06-10-2009, 10:28
MSilvia-- are you saying that one side of the tank was longer than the other--ie: the sides of the tank no longer made a perfect 90 degree angle with the bottom? Or that the entire tank was longer than the other tank? Do you have pictures or proof of this event?
Yeah, that's exactly what I'm saying... both tanks took on a curve, so that "the backplate side" was a smidge longer than it used to be. If you rested them on a level table, either the middle would have a mm or two of clearance, or the middle would touch and the ends would have clearance, depending on which side was up. I don't have pictures, (It didn't occur to me to bother, as they still passed inspection) but I sold them to Leo Laskin (Lord1234 on the decostop) if you want to ask him about them.

mike_s
06-10-2009, 16:51
he didn't want picture of that oddness of the tanks before he bought them?

JahJahwarrior
06-10-2009, 23:37
Msilvia-- That's an interesting story...I'm confused about why that happened like that, I wish someone could run experiments to show how much tanks will expand over time based on heat...

actually I'm going to start leaving my doubles out in the yard sunning, if I flip them once a day, I'll be able to get more gas in them in a few months! :D


I wish you had some pictures, I'd love to see how dramatic the shift was.