Burst Discs

[Cave Diver]

I have heard a lot of controversy over the 'proper' burst disc usage on their cave rigs. Some people use higher pressure discs, I have heard of some doubling the discs up, and still others that just put a solid plug in place of the disc.

I would love to hear from Uncle Pug, et al. regarding their setup and more importantly WHY they choose to do it that way. I am currently running OMS tanks and O2 clean valves with the OMS Isolation manifold (ya, I know, but that was before I heard about DIR and I got too much money invested to just chunk them). My setup is running the factory discs, I have never changed them, but it is something I have given some thought to doing.

Really interested in opinions that include some sort of substantiation or reasoning as to WHY they choose a particular set up vs. someone saying 'because so~n~so does it that way.'

Dive often, but dive safe

John

[Uncle Pug]

Originally posted by Cave Diver
I would love to hear from Uncle Pug, et al. regarding their setup and more importantly WHY they choose to do it that way.
Hi John, sorry but I don't have any real light to offer on the subject... since I don't cave dive I have been content to just run the disc as it came with the tanks (PST LP104s)...

But I have thought about it because we typically fill to 3K... I will inquire at my DIR LDS tomorrow and give you a post.

A friend just had a disc let go on a HP102. The tank might have had a slight overfill and it was a hot day but fortunately it was in the garage and not on a dive.

[Divesherpa]

Problems with burst disks can be fun.
Plug em and go, especially with 4200 PSI cave fills

[WYDT]

Basically the burst disk is an unnecessary failure point. They are weakend on every fill and use by flexing... they will eventually blow with even a normal fill...

You eliminate that failure point by using a shim that won't flex and eventually blow.

Does this happen often? no... Does it happen? yes... Would it suck if it happend to you 4000ft in the cave... YES!

Is this dangerous?? I've been told that the tank neck o-ring will extrude long before the tank blows (unless the tank has a defect).

Bottom line: I don't have shims in my valves *yet* but am planning on doing so asap. I fill my PST LP 104's regularly to 3600psi for cave diving.

DSAO!!

[Rick Murchison]

Originally posted by WYDT
Is this dangerous?? I've been told that the tank neck o-ring will extrude long before the tank blows (unless the tank has a defect).
Any idea if this has been researched at all - or is this just a SWAG?
Rick

[roakey]

Originally posted by Rick Murchison
Any idea if this has been researched at all - or is this just a SWAG?
I believe the specific claim is that in a FIRE the neck O ring will soften/burn to the point that it will extrude before a STEEL cylinder will blow.

I don't know of any specific research.

Roak

[NetDoc]

as for burst discs... useful? Europe does not use them. They are SUPPOSED to be 1.6 the rating of your tanks. That is way more than most overfills would stress it. I does give an idea of just how much "safety" is engineered into our tanks. I think most ratings are way too conservative.

I change burst discs at hydro time. I would not have an issue with someone putting in a higher rated disc... it's their call. Just as overfilling their tank is their call. BTW, I am sure that European valves would fit on US cylinders just fine!

[WYDT]

Originally posted by Rick Murchison

Any idea if this has been researched at all - or is this just a SWAG?
Rick

Well, I don't know... that's why I said "I've been told"... because I don't know the source of the information... though I've heard it on numerous occasions from different people (not just dir). I've also never heard of a steel tank blowing up because of overfilling unless it had other problems like a lot of rust inside. The lined tanks come to mind... :eek:

The way I look at this one is it's your choice... take your chances or not... I was just posting the actual answer to the original question "WHY they choose to do it that way"...

DSAO!!

[Dell]

This practice is almost as old as cave diving itself.
It is one the original methods of eliminating as many of the failure points in your gas supply as possible. It was simply called "double disking" when I was trained. Double disking is the easiest way to accomplish this. Some of the newer manifold designs are trying very hard to make this impossible. Some are resorting to assemblies that cannot be altered, or have integrated disks. This will force people to use bolts or other means to acheive the goal. Hard core tech divers should continue to source manifolds that allow individual disks to be installed.......
Dell Motes

[NetDoc]

We welcome your experience and expertise in the cave diving arena. I hope you find all to your liking, and if there are any questions, please feel free to ask, and by all means we look forward to your continued input!!!

[MikeFerrara]

Dell,
Which ones are which. I don't have mine double disked yet but the next time I drain them I will. Halcyon has stainless replacement disks available for theirs. What about the others. I would imagine the Diverites can be plugged otherwise there wouldn't be so many using them. We have both and none are plugged yet.

[Aviatrr]

The burst discs in manifolds by Dive Rite, Halcyon, Sea Elite, Scubapro, and OMS can all be changed. I have burst discs from high pressure steel tanks in my manifolds(which are 300BAR manifolds anyways, so they came with HP burst discs). I have been told by a couple people at different shops that discs meant for LP steel tanks(marked for 2640PSI fills) will let go around 4500PSI, the discs for 3000PSI fills(such as the discs that come in valves for aluminum tanks) will let go around 5000PSI, and discs for HP steel tanks(3500PSI fills) will let go at around 5800PSI. Of course, these are probably estimates, and these are based on brand new discs.....not discs that have been subject to 200 fill cycles.

I, personally, feel that changing burst discs each year at VIP is a good idea if you use single discs.

Mike

[Dell]

Thanks for the welcome NetDoc.
I was participating for a brief time up until several weeks ago.
I had a change of employment status, mainly, I left Dive Rite and now work for Halcyon. I just "re-upped" to the board on Friday.
This is one of the more diverse and interesting boards, so I think I'll stick around for awhile.
To answer some questions;
The burst disk issue is purely DOT, it does not exist anywhere else. It has been common practice in cave diving to "fortify" disks for as long as I can remember. The metal in a single disk will certainly fatique eventually. While it is most likely to go when filling, (at the highest pressure and temperature), I certainly would not want one to go on me in a cave. Not only is it catastropic loss, (unless you have an isolation manifold, hence the popularity), it is incredibly scary, especially since it is right behind your head. I've had one go in a fill vat, and it cleared the entire area of about 20 people who were hanging around.

The Dive Rite, Halcyon, Sea ELite and some older Sherwood all use individual disks. These are the ones I am sure of, the rest you should check before purchasing. These valves all consist of a simple brass threaded plug, a disk, and a metal or plastic washer, either one is effective. The age old standard practice has been to just double the disk. The overall design that these particular valves all use is truly the best in so many ways. I suggest anyone who just wants to get what they really need to buy one of these makes, then you can concentrate on other things that may seem more subjective. This valve design has a proven track record that cannot be ignored.


Dell Motes

[Laurence Stein DDS]

Dear Dell,

You know Ken Bonde? I dive with him...it was either you or your partner who when with Ron Caplan to the Keys last week.

Looking forward to taking Nitrox with him.

He'll be profiled on Shark Week on the Discovery Channel in August.

Regards,

Larry Stein

[DNAXdiver]

Hmmmmm.....
This could be interesting. Tell us, what do you think about Halcyon vs DiveRite products now? ;-)

This is a good board isn' t it lot of refugees from techdiver I bet.


Originally posted by Dell
Thanks for the welcome NetDoc.
I had a change of employment status, mainly, I left Dive Rite and now work for Halcyon.
Dell Motes

[Tegg]

Well, I would have never worried about doing this until I was getting my tanks filled by Bill Rennaker... We got up to 2300psi in one of my Faber 104s and all of a sudden the burst disc went... :eek:

There is no sound like the one of a bursting disc less than 2 feet away. After the initial shock, we all cut the air supply to the tank and he mentioned doing a "double disc". After what I just saw, I said disc it to whatever you can to prevent that from happening...

I can't imagine that taking place in a cave at 3000ft penetration only inches from my head... it was very violent.

Let's just say I am not as worried about it happening now... on either of my tanks... (double HP discs). After seeing it first hand, I am a firm beliver in eliminating that problem.:)

[Hobbs]

Tegg once bubbled...


I can't imagine that taking place in a cave at 3000ft penetration only inches from my head... it was very violent.



hmm I wounder what the "chances" are that this happens in a cave with the water cooling the bottle and thus shrinking the pressure on the tank itself and thereby the burst disc.

Does anyone have any information on the subject of this happening during a dive and not on fill or when left the bottle in the sun?

But what do I know, basically we dont use them where I dive wich means very limited experience with them.
but I find it interesting.