Burst Discs

Cave Diver · Jun 27, 2002

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 · Jun 28, 2002

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 · Jun 28, 2002

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

WYDT · Jun 28, 2002

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 · Jun 28, 2002

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 · Jun 28, 2002

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

The Chairman · Jun 28, 2002

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 · Jun 28, 2002

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...

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 · Jun 28, 2002

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

The Chairman · Jun 28, 2002

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!!!

Burst Discs

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Uncle Pug

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Rick Murchison

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