New question about tanks and heat

[Hoosier]

I only did TILT the sunroof window, not open and cover the tank with "Sun Shield" like this (http://www.streetbeatcustoms.com/wihesh.html). It is only $10 at Wally world and covers four tanks. Keep it simple and stupid...... I don't like too much worry. Yes, my car is also black tinted every windows except the front one.....

If I left them sit in the car during the work day, it would be in the back of a SUV with tinted windows and also would leave all the windows cracked about 1" to let out heat.

How would this work?

-mike

 

[doos]

From experience, storing full tanks in cars on warm days can cause problems. The problem is not that the tank is not rated for the increased pressure due to temperature, it's the o-rings. I had tanks in my car on about a 32 C day (90 F or so), and the heat inside the car deteriorated the o-ring in the neck of the tank (where the valve screws into the tank). It was enough that you could see where the o-ring had been pushed out of the threads.

Just for informations sake, when pressure vessels (scuba tanks, propane cylinders, oil/gas equipment, etc) are pressure rated, it is not as simple as "rated to 300 psi". It is always rated to "3000 psi @ 100 F". As temperature increases, pressure rating decreases.

I would be carfeull about storing tanksin a car on warm days. Not so much for damage to the vehicle, just for the loss of a dive.

 

[PapaBob]

First, understand that your tank is hydrostatically tested to approx. 160% of the maximum working pressure (MWP) of the tank (let's say MWP is 3000 psi). Second, the failure point of the tank is typically greater than 300% of the MWP. Scuba tanks have a burst disk so that failure, while catastrophic, is not, umm, spectacular.

So, just for argument's sake, suppose you didn't feel comfortable with a tank pressure greater than 3400 psi (approx. 13% overpressure). Well, we've got to do a little math. (PV/T)=constant, where P is the pressure, V is the volume, and T is the absolute temperature (e.g. Kelvin or Rankine, depending on your preference). Let's say 70 F is about 530 R, and 140 F is about 600 R. If your tank has approx. 3000 psi at (70 F) 530 R, at 140 F, because the volume is constant, the pressure will have gone up by (600/530), or your new pressure will be about 3400 psi (3396 if you use a calculator, but I'm only working to 2 digits here).

That said, I wouldn't be concerned. I might not leave the tank in the hot sun day after day after day because the heat might affect the valve packing, but I would not at all be concerned about the heat affecting either the aluminum temper, or causing overpressure in the tank.

Hdtran:

Wow! You are the first person I have seen in a long time that understands Boyle's law. I have a dive buddy who cant grasp the concept of calculations involving absolute zero. He insists that a tank filled in a chilly 60 deg f tub to 3,000 psi will pressure up to 6.000 psi in 120 deg car trunk. He also insists that two identical dive boats crashing "head on" bow to bow at 30kts is the equivalent of one dive boat hitting a concrete jetty at 60kts. Go figure.

---Bob

 

[pasley]

A local diver here in Los Angeles was on his way to an after work dive 2 summers ago. The burst disk failed and acording to him "made quite a mess inside the car" . I will bet his pants did not fare all that well either. :11:

 

[FredT]

A local diver here in Los Angeles was on his way to an after work dive 2 summers ago. The burst disk failed and acording to him "made quite a mess inside the car" . I will bet his pants did not fare all that well either. :11:

I'd be willing to bet the burst disk needed manitenance BEFORE it blew. There is a good reason to change them at least at every hydro.

FT

 

[scubatoys]

Yes, I have seen a burst disc go-and it sent the tank spinning!

Then that was probably a very old steel 72 tank with an improper burst disk. I the goood 'ole days, they had a straight shot out burst disk, so the air went out in one direction, and could knock the tank over and spin it. Today is it mandatory that burst disks divert the air in opposite directions at the same time, so the tank won't even tip over if you blow a burst disk.

And I know all that PV/T this is a lot of fun... but to make your life easy... an al80 will pick up about 5 psi per degree F.

 

[Heffey]

I got this link off another thread a while back.
http://www.searover.com/rca/scuba/opinions/scuba_opn_burst_disks.shtml
It may give you the answers you are looking for.
Jeffrey

 

[pasley]

I'd be willing to bet the burst disk needed manitenance BEFORE it blew. There is a good reason to change them at least at every hydro.

FT

Agreed.

 

[Leadking]

Burst disc by law must be @ hydro to -10%

 

[FredT]

oops