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

[CT-Rich]

I had a burst disc go and my parents never let me keep a full tank at their house again. It did stay upright and did't move. A restraining bungy cord would be cosmetic at best. If the tank wants to move, it will. a venting tank is going to be unpredictable (what it is supposed to do is not the same what it will do), follow your instinct and get clear fast (I doubt you would need to be told). Most times it will be scarier than dangerous.

 

[2airishuman]

Now, back to the cost/repair issue. I left feeling a little disappointed. Not at all about the money for the new knob and valve stem, although I do wonder if I should have been responsible for that. Of course I expect to pay for the new burst disc, but this is where I question whether tanks should be secured in some way when filling.

What was the rating on the burst disc? It appears from the photos to be one-piece style, which means that the rating should be stamped on the head of the plug. To what pressure were the cylinders being filled?

 

[CuzzA]

What was the rating on the burst disc? It appears from the photos to be one-piece style, which means that the rating should be stamped on the head of the plug. To what pressure were the cylinders being filled?

Rated 4000, intent to fill to 3500 which normally cools to about ~3200.

 

[2airishuman]

That clarifies things a little, I think.

4000 PSI burst discs are used in low pressure steels (3AA-2450). These cylinders have a hydro test pressure of 4083 PSI (2450 * 5/3). A fill to 3500 would have been 85% of hydro test pressure and 87% of the rating of the burst disc. Burst discs have a tolerance of +0% and -10%. Put another way, they are supposed to release somewhere between 90% and 100% of their rated pressure. It is not hard to believe that repeated fills to 87% of rated pressure could cause a burst disc to rupture.

I get air at 3 places depending on circumstances, and none of them will fill a cylinder in excess of its rated capacity, though they will sometimes fill a + stamped cylinder to 10% over. If a cylinder is hot from filling they will wait for it to cool and top it off, but they will not fill it to a higher pressure in anticipation of the pressure dropping as the cylinder cools, even though this is an approved practice. None of these places have fill stations that are separated from customer areas. None of them secure cylinders before filling.

Whether burst discs provide added safety on scuba cylinders is a difficult question. In a fire, typically the walls of the cylinder will fail before the burst disc does. As pointed out upthread, burst discs aren't used -- indeed, aren't allowed -- in Europe. But from what I understand they don't practice "cave fills" there, either, and there are mechanical safety controls in place to prevent overfilling a cylinder, accidentally or otherwise.

 

[DogDiver]

The same fabers sold here and Europe are rated the same. DOT restricts them to 3450. The cylinders are filled to 4000 in Europe (and cave country) to 3800

 

[KevinNM]

Fabers catalog shows only a few 300 bar cylinders, most of the ones with European approvals are 232 bar.

 

[Storker]

How many do you need? 300 bar is pretty common around here, but so far I've only seen 6, 7, 10, 12 and 15L. The two former in twinsets, the latter as singles.

300 bar tanks get heavy pretty quickly. A 10L 300 bar weights about the same as a 15L 200 bar. IMO, the largest 300 bar tank worth considering is a 12L; I had a 15L and it was just too heavy. If I need that kind of gas capacity, I'd rather use a small twinset like a D7x300 or a D8.5x232. They balance much better on your back.

 

[bergersau]

This discussion of burst discs brings up a question some divers I know were discussing/arguing around the bar recently.
If a recreational Nitrox fill <=40% was to rupture a burst disc in the sun in a boat. How much of a hazard would that create in regards to fire on board? Bearing in mind oils, fuel and electrics etc.

 

[cerich]

[QUOTE although I had them VIPed and O2 cleaned, I did not have the burst discs replaced..[/QUOTE]

let me fix that for ya

You paid to have them O2 cleaned, if the valve as taken apart properly for a O2 clean, the disc would have been replaced.

You didn't get what you thought you got.

Really glad your child wasn't injured.

I have had burst discs go many times in my career, never saw a tank hit the ceiling I have however had the escaping gas do a good job of blowing the dust off, moving stuff off shelves etc. I would bet the ceiling tile was hit by air, not the tank. I could be wrong.

 

[cerich]

I keep reading in this thread "tank flying around the shop" I doubt that it actually flew around the shop and would bet that it tipped over and the valve knob hit something to cause it to bend. The "blown out ceiling tile" I'm sure was just the air escaping and the air pushed the light weight tile out of the way. I have had a disk blow on one of my tanks, yes it was loud and I'm sure some of the customers may have soiled their pants. The air did blow a picture off the wall and the glass broke when it hit the floor. But no tank flying around the shop.

just saw this post, and as in my post, mirrors my experiences