Close Call at the LDS and a High Pressure Reminder...

[KDAD]

I recall the thread were the op tattooed his hand putting it in front of the valve.

I had to double check on one of my tanks - this discussion has had me fearing a burst disk failing while the tank is on my back. Seems that they point away from your head when properly oriented in the harness. Would still probably take you for a ride if it failed under water.

 

[runsongas]

unlikely to be an issue by the time you hit the water. only seen them go during filling or occasionally while being in a very hot car. those are the two times when the tank encounters the highest temps and pressures.

 

[guruboy]

Okay, these guys don't understand physics. Burst discs are designed to burst at about 140% of rated pressure. 140% of 2400 psig is 3360 psig. I don't have time right now to go through the Universal Gas Law equation, but they caused this themseleves. More later...

Repeated overfilling of tanks causes damage. In steel, it is in weakened walls. In aluminum, especially the earlier AL 80 tanks, it lead to sustained load cracks (SLC) in the threads. Overfilling is not a good idea. Get a larger capacity tank, or sling more (although I don't like the streamlining of this configuration).

SeaRat

Where is your 140% number from? DGX sells 5000psi discs for 3000psi service pressure.

 

[CuzzA]

I recall the thread were the op tattooed his hand putting it in front of the valve.

I had to double check on one of my tanks - this discussion has had me fearing a burst disk failing while the tank is on my back. Seems that they point away from your head when properly oriented in the harness. Would still probably take you for a ride if it failed under water.

Although highly uncommon I would be curious to hear a first hand account of a disc going at depth right by your ear. I imagine it would be painfully loud, but I doubt there would be a high risk of it actually happening other than a big temperature swing from the environment above and below water as @kelemvor mentioned earlier. I doubt the gas would be able to penetrate skin underwater as well.

 

[runsongas]

Where is your 140% number from? DGX sells 5000psi discs for 3000psi service pressure.

the pressure stamped on the disc is the hydro pressure and service pressure for the tank you use it on. the actual burst pressure for the disc is lower than the hydro pressure, 90% iirc.

 

[guruboy]

Maybe, maybe not?

Below taken from this website-
PRD Safety Assembly (Burst Disk Kit) | Dive Gear Express®

Ratings are release pressure

Type of Cylinder/Service/PRD
Argon Bottles/2015/3360
Low Pressure Steels/2400/4000
Most Aluminums/3000/5000
High Pressure Steels/3442/5250

All US cylinder valves are required by the Department of Transportation (DOT) to have a pressure release device (PRD) that operates if the pressure exceeds the cylinder test specifications.

 

[CuzzA]

Here's the thread. I misspoke about the garage. He lived in an apartment.

Show and tell at the ER

 

[Bob DBF]

Why did the Burst disc let go? Was the tank overfilled? Burst disc loose? Installed too tight?

Old will do it as well, I've taken some out that were quite corroded. I replace mine when I rebuild the valve, or find one of the old school one hole reliefs.


Bob

 

[John C. Ratliff]

Where is your 140% number from? DGX sells 5000psi discs for 3000psi service pressure.

Here it is:

...A burst disk consist of a thin copper disk held in place with a gasket and a vented plug. If the pressure inside the tanks rises to 140% of the working pressure, the disk ruptures, and the air escapes thought the vented plug...
What is a Burst Disk ?

Just because someone sells something, doesn't mean it's necessarily correct. I've also seen this in regulations somewhere, and I believe that the disc cannot burst greater than 10% deviation from that 140% of cylinder rated pressure. That is why my LDS had to get different discs for my 1800 psig tanks, as the ones for 2250 psig rated tanks really were not correct.

SeaRat

 

[clownfishsydney]

I have had two burst disks go, both on the same tank. The first one happened while I was at work. When I came home I thought that someone had broken in and trashed my back room where I stored my dive gear. Took me a while to figure out what had happened. The tank had moved all over the room, knocking things over.

I replaced the disk with the recommended one. The second time it failed was night time and I was asleep. The noise was amazing and again, it took me a while to figure out what was going on. I ran out the back and the tank was moving all over the place, rolling around.

The burst disk had two outlets, so theoretically it should have balanced everything out. I also suspect that it is more violent when a burst disk goes compared to opening a valve as the opening is much smaller. Also, around this time quite a few people I know had disks go, all supplied by the same dive shop. Obviously a faulty batch or wrongly labelled.