Double Burst Disk LP Steel Tanks?

[Major Restriction]

I would be interested to know how many of you use, or have used, low pressure steel tanks with double burst disks.

Comments and rationales (either way) are encouraged.

[Slüdge]

No, I use 3500 (working pressure) disks on my LP95s and LP80s, and fill them to 3500psi.

[LiteHedded]

mine are doubled up

[outofayr]

+1 on using 3500 psi discs

[jimdiverman]

Okay, maybe I'm missing something here. If two burst disks are in series (on top of each other) and the pressure in the tank is X psi, and the burst disks are rated for X+ psi, how does it help to have more than one, if theoretically, they both burst at the same pressure (X+ psi) anyway?

[Line Squirrel]

You guys do know the way a burst disks works right <rhetorical - obviously not>...if you double them up it essentially is the same as a solid plug.

It's not as simple as taking the burst rating and multiplying it by the amount of disks.

[jimdiverman]

You guys do know the way a burst disks works right <rhetorical - obviously not>...if you double them up it essentially is the same as a solid plug.

It's not as simple as taking the burst rating and multiplying it by the amount of disks.

This sounds like a potentially dangerous situation.

[Puttzer]

When I recently bought another set of dbl LP 95's, I asked about using double burst disks.

The shop owner told me: when tanks are tested they go way over our my pressures of 3600 psi (4500 psi?)and if they don't burst then, they aren't needed at my lower fill pressures.

That said, I did have one "blow" in my garage years ago.

Are the disks "aging" and do we or don't we want to double them?

[Slüdge]

You need a new shop. When tanks are hydroed, the valves are removed. That's where the burst disks are located.

If your shop owner doesn't know that, well...

[fixxervi6]

Bust disks are copper and need to be replaced from time to time, not only does the copper break down aka rot aka rust aka oxidize (pick your term) it also flexes.

[Line Squirrel]

Are the disks "aging" and do we or don't we want to double them?

I had a shop in Michigan that charged $15 for a VIP and this was in 2001.

Expensive to be sure until you understood what they did.

Part of the VIP was to replace the burst disk.

Now, I think this is excessive but they claimed they did it. None the less, I went someplace else after that. I personally don't feel replacing burst disks on an annual basis is warranted. Feel free to correct me, always willing to learn but I would hope you have some facts to back it up :)

Another thing about burst disks, once a new one is installed and fill pressure applied they should not be removed and reused (ie: O2 cleaning) You will never get them to re-seat the exact same way. That's not to say you can't reuse it without it leaking...just not spec.

[fixxervi6]

I check them once per year, just look in to see if they are getting all green or whatever, but every year seams too frequent. I wouldn't use the same disks past a hydro for sure, but I think my last set where in for like 4 years or something like that before I changed them.

[chimie007]

This sounds like a potentially dangerous situation.

That's why folks die in Europe every year from lack of burst disks ;)

[Line Squirrel]

That's why folks die in Europe every year from lack of burst disks ;)


Ouch...I thought it was warm beer and socialized medicine :sucker or lack there of.

[JahJahwarrior]

Double disking is far too dangerous, one should use steel plugs to be safe! ;)

[aw]

I use double SS discs from EE on all my tanks. Don't care if they are LP, E8-130's, AL80's, etc. I WANT them plugged solid. All of them. I've had a buddy have a single disc burst twice in a very short period of time (no, not on a dive). He doubled them, and ain't had no problem since.

[Line Squirrel]

Double disking is far too dangerous, one should use steel plugs to be safe! ;)

Well...at least your not kidding yourself because it's essentially the same thing.

I have no opinion one way or the other about plugging. At least not one I'm willing to publish on an internet forum.

[sdenney]

I double-disc my steel tanks, and run single 3500s in my aluminums. I will be switching to single stainless steel discs in my steel tanks on the next vip, but will stick with the 3500 in my aluminums. (I usually run my doubles at 3600psi cold, but I don't overfill my aluminum tanks).

[curtschu]

Wouldn't it just be easier to use 237 bar manifold and properly maintain it?

[Gary]

I've seen disks go on the park bench, in the garage, soon after being replaced (badly installed or defective parts) but between the chance of one going after I've started draining the tank and independent gas supplies I'm not worried about double disking etc.

If I was worried about safety margins an additional bottle in the water would be 1000 times more useful then double disks. :)

Not that I'm against double disks but it'd be nice if double meant they were redundant - not disabled. :)


Of course I refuse to dive with a manifold so I guess we all have our hang ups. :smt102

[bletso]

I don't double disk, but I do use higher rated disks. The problem with double disking is you really don't know what pressure they would burst, say in a fire and cause serious property damage when the cylinder explodes.


Dale

[Gary]

I've seen disks go on the park bench, in the garage, soon after being replaced (badly installed or defective parts)

Come to think of it most of those were manifold leaks... the disks I've only seen two: in the garage (time and heat) and defective/poorly installed.

[JahJahwarrior]

Well...at least your not kidding yourself because it's essentially the same thing.

I have no opinion one way or the other about plugging. At least not one I'm willing to publish on an internet forum.

Would be interesting to see a study though, does an SS or double brass disk go first?


Agreed on the opinion on the internet thing...Rich at CEE has a funny story about that which he's shared at the fill station once or twice whenever the topic of double disking comes up.

[Pete]

That's why folks die in Europe every year from lack of burst disks ;)

Yes you are correct in thinking that in Europe we do not use burst disks. However, I am not aware of any fatality/accident that has resulted from this.

Worth remembering that gas cylinders are designed to fail in a 'safe' manner if exposed to extreme pressure and actually split rather than explode. Still not nice to be around but provided the bottle was 'sound' before being exposed to such extremes you would either have had to be an idiot to charge the bottle to such an over pressure (probably well in excess of double the rated pressure) or the bottle would have had to be exposed to such an extreme of temperature that you would have cooked before the bottle failed. The other failure mode is the valve but provided that the threads are correct and not damaged the bottle will probably split before the valve becomes a missile.

I feel far more secure diving with a set of 300bar, 12 litre doubles here in the UK than with rented doubles with the unavoidable failure point inherent in burst discs whenever I visit Florida or Mexico.

Peter

PS. leaving a set of tanks in a hot car may raise the pressure the few bar necessary for a burst disc to fail but will not cause the bottle to fail. Remember, when using the gas laws it is absolute temperature you have to use and so the hot car scenario is unlikely ever to result in even a 10% increase in pressure.

[stairman]

Mine are double disked.I snug em up every once in a while and will change em out at hydro.I dont want a disc going out in a cave.If the house is on fire Ill tell the firemen about the tanks as well as all the live ammo.

[jj1987]

Would be interesting to see a study though, does an SS or double brass disk go first?


Agreed on the opinion on the internet thing...Rich at CEE has a funny story about that which he's shared at the fill station once or twice whenever the topic of double disking comes up.
There was a thread on TDS about this. Lots seem to think the tank neck oring would come out long before a they burst in a fire or explode. I have no idea, I've never tested it, so I'm not going to even attempt to comment on it other than stating the theory exists.

[sdenney]

This would be a cool one to see on MythBusters!

Which will blow first:

1. Tank neck o-ring
2. Double burst disc
3. SS burst disc
4. something else?

[Rich]

Agreed on the opinion on the internet thing...Rich at CEE has a funny story about that which he's shared at the fill station once or twice whenever the topic of double disking comes up.

LOL......you'll never know who you might actually meet in person :)

Safe diving,

Rich

[mfascuba]

Single SS discs from EE on steel cylinders, "stock" brass burst discs correctly rated on Aluminum cylinders. Never overfill anything beyond what is safe.....

Mark

[stairman]

I watched an aluminum 80 blow a disc at ginnie and rocket across the grass.A class had them laid out on a tarp.No reg was on it yet.When I first got my doubles,I left them in the truck and they had the stock discs in them still.The gas in them expanded enough to blow one.I was in the house and it sounded like a semi tire blowing out.Luckily the deivers window was down or may have blown out the windshield.I took it backto the DS and told them to put in some bigger ones.I dont jack em too high unless Im hitting the water soon even now.

[Puttzer]

I read somewhere that the burst disk in a 300 bar manifold is significantly higher than a 200 bar manifold.

Is this true and if so, how much higher?

[chimie007]

I read somewhere that the burst disk in a 300 bar manifold is significantly higher than a 200 bar manifold.

Is this true and if so, how much higher?

There is not one higher than the other. They both sit about an inch above the tank neck.

Joke aside for more info: http://thedecostop.com/forums/showthread.php?t=30140

[jpdiver]

I would be interested to know how many of you use, or have used, low pressure steel tanks with double burst disks.

Comments and rationales (either way) are encouraged.

I don't double disk but do use higher rated disks. You can get 200 bar din valves with 5500 psi disks