burst disks vs safety

[scuba_guy]

after aot of debate about DIR and how safe they like to be, why do they like to double disk there PST104's and over fill them??tanks have fill pressure for a reason. why fill them to 3 or 4000 psi?

[WYDT]

Troll....

Even so...

Doubling burst disks or even shiming them in Steel tanks isn't a DIR thing... it's a cave diver thing. Almost ALL cave divers do it DIR or not.

Burst disks are a BS failure point.. tanks in Europe don't have them.

Almost all cave divers overfill their steel tanks as well as shim/double the disks. The faber steel tanks are rated at something like 10,000 cycles at 4,000 psi... Pressed steel are even greater.

DSAO!

[MikeFerrara]

It's not just for overfilling. burst discs sometimes burst, regardless of fill presure. This is something that most could do without in a cave.

[Scubaroo]

Were burst disks originally designed for safe venting of the pressurised tank in say, a house fire, or was this misinformation?

[MikeFerrara]

I believe that is the idea. I have seen them blow but always without the fire.

[NetDoc]

An aluminum tank exposed to a fire (especially one that is only partially filled) will probably rupture the tank and not the disk. An aluminum alloy's properties change with heat (even more so than steel), and the strength can decrease by several factors with only a 100 degree increase in temperature. This is why you should never ever "bake" the paint on AL tanks.

As for overfilling tanks... it is NOT just a DIR practice. Many tech divers (including cave, wreck etc) wishing for more bottom time do it regularly with few accidents. In all actuality, I have not heard of any tanks exploding due to this practice. I am not advocating or defending here, but it does not seem that the statistics support such a cautious rating of tanks. This is one area where the diver and the fill station have to arrive at their own agreement.

[Munin]

Originally posted by scuba_guy
just because people in other countries do it, doesnt make it right. Im sure if you talk to faber or PST they won't tell you to over fill them

Many tanks have higher rated pressures in Europe. It is the country's decision as to what they are rated at, and the DOT is apparently more conservative than its European counterparts. If you have ever seen the expected life cycle of a tank you would know that they are good for more cycles than they could ever possibly see at a pressure greater than most are overfilled to. The number of tank explosions is actually very, very small, especially considering the number in service, and like NetDoc said, I don't know of any caused by overfilling. There is no evidence of any risk that I've seen.

This has all been discussed just two weeks ago anyway here (http://www.scubaboard.com/showthread.php?s=&threadid=9174&highlight=to+what+pressure+are+you+filling) .


Originally posted by scuba_guy
But i forgot WYDT you just do what your told and cant form your own opinion :)
It sounds to me like you're the one who can't form your own opinion about anything. What about evaluating the information and making an informed decision? Or are you just trolling? I don't think that's very :)

[Campana]

Originally posted by scuba_guy
just because people in other countries do it, doesnt make it right. Im sure if you talk to faber or PST they won't tell you to over fill them But i forgot WYDT you just do what your told and cant form your own opinion:)

Faber rates its own tanks for 10,000 fills to 4,000 psi. I don't know about PST.

[JamesK]

According to a reliable source, PST is about to start stamping their tanks to 3500psi anyway. That way they are going to be rated for the pressure to which we are filling them. They will be the same tanks, just rated different.

[WYDT]

Originally posted by scuba_guy
just because people in other countries do it, doesnt make it right. Im sure if you talk to faber or PST they won't tell you to over fill them But i forgot WYDT you just do what your told and cant form your own opinion:)

Yeah, you're right... I just do what I'm told... by people with THOUSANDS of hours of Technical diving.... it's called instruction... or haven't you heard of that??

Look, there's no need to re-invent the wheel here. Pretty much everyone.. DIR or NOT agrees that burst disks are BS.

Someday when you've got some real experience in the techdiving community (if you live that long) you'll see firsthand why we do some of the things we do. There's no need to question every detail.

Much as you'd like to make it one this isn't a DIR vs Not argument.

DSAO!

[MikeFerrara]

Breathing gas = life. More is better. Anything that lets it out before you can breath it is bad.

[Windknot]

The commute is a bit*h, but can I start bringing my LP98's to you to fill????

I've gotta bust chops to get someone just fill my tanks topped at 2640, let alone higher.....

Last good fill I got was to 3100 while hot and that dropped back to 2700 once cooled......NOW THAT WAS A FILL!!!!!!! (that was while I was in Ohio)

Seriously though....for all of us outside of the Cave Belt, We thank you for your understanding of what we NEED.:)

WK

[MikeFerrara]

Windknot,
We can fill them and with whatever gas you might need. If you were on your way to a Missouri cave or the other side of the lake we wouldn't be too far out of the way. All our blending is PP so trimix takes some time to get right. I don't have a booster so you won't get a full tank with 100%. Everything else is a snap.

Mike

[anth]

I was informed that burst discs WERE necessary on the tanks/valves of yesteryear, when the gas was "held in" by plumber's tape in the valve threads.

Now that tanks neck o-rings are the norm, the burst disc is not necessary as most any tank neck o-ring will extrude before a tank's burst pressure is reached. (I recall overhearing that the burst pressure for an oms/faber lp tank was somewhere in the range of 10000 psi anyhow?)

Now... why doesn't this neck o-ring fail due to the heat in a fire?

DSAO,
Anth

P.S. - My burst discs are intact, however I'm a recreational openwater diver at this point. The surface is always a direct ascent away. If i were a few thousand feet in a cave things would be an ENTIRELY different story.