Oh no! My 72s are too small for tech classes! :(

[tbone1004]

Burst discs... Never seen one. Are they common in the US?

they are a federal requirement for all pressure vessels.
When they burst there is no shrapnel, just a loud noise and a very cold valve. They burst by being punctured by a needle. They are consumable devices and must be replaced. It's a sporty experience I've witnessed 3x in the last decade. Usually from valves that did not have them replaced at hydro time since they do wear out over time from constant cycling, though one was from a 2250psi burst disc *designed to blow around 3300psi* being installed on an AL80 for some reason which are filled to about 3500psi to cool to about 3000 and it went off. That caused me to jump.

The history goes back to boiler explosions at the turn of the last century and they are required on all pressure vessels regardless of use. In the EU they are required for pressure vessels for the same reason however they are actually banned on breathing vessels which is a nice exception they've made. Unfortunately I do not see that happening in this country.

Outlined in the image below as "one-piece safety" though there are 3-piece designs.

 

[Gone for diving]

Basically it looks like a small piece of copper,
I have made one out of brass shim stock

 

[jtsfour]

What happens when they burst? Aside from a bang and disc shrapnel thrown across the room! Can you just push the disc back in?

Seriously, have never seen one!

Every tank in the US (that I am aware of) has a burst disk.

It is a machined disk that plugs a hole that bypasses the valve. It is used to prevent tanks from exploding from overpressure.

The disks are in threaded plugs that go into the valve. I have never seen one go off but I would assume you would hear a loud pop. Then the entire tank will drain and you cannot stop it.

That is why my above comment is significant. I had overfilled the tanks and the burst disks were no longer disk shaped. They could have failed. If that happened underwater it would have been a "catastrophic gas lost" we always plan for.

On one hand that is a pretty significant failure point in the valve design. On the other hand I don't have to worry about my tanks exploding if my house/car catches fire.

You can replace the burst disk assembly with closed plugs instead of burst disks. I honestly have no idea if that is legal. I assume burst disks are part of DOT regulations.

 

[jtsfour]

they are a federal requirement for all pressure vessels.
When they burst there is no shrapnel, just a loud noise and a very cold valve. They burst by being punctured by a needle. They are consumable devices and must be replaced. It's a sporty experience I've witnessed 3x in the last decade. Usually from valves that did not have them replaced at hydro time since they do wear out over time from constant cycling, though one was from a 2250psi burst disc *designed to blow around 3300psi* being installed on an AL80 for some reason which are filled to about 3500psi to cool to about 3000 and it went off. That caused me to jump.

The history goes back to boiler explosions at the turn of the last century and they are required on all pressure vessels regardless of use. In the EU they are required for pressure vessels for the same reason however they are actually banned on breathing vessels which is a nice exception they've made. Unfortunately I do not see that happening in this country.

Outlined in the image below as "one-piece safety" though there are 3-piece designs.

I didn't know there was a needle... So they burst when the disk expands like a bubble into the needle?

 

[PfcAJ]

they are a federal requirement for all pressure vessels.
When they burst there is no shrapnel, just a loud noise and a very cold valve. They burst by being punctured by a needle. They are consumable devices and must be replaced. It's a sporty experience I've witnessed 3x in the last decade. Usually from valves that did not have them replaced at hydro time since they do wear out over time from constant cycling, though one was from a 2250psi burst disc *designed to blow around 3300psi* being installed on an AL80 for some reason which are filled to about 3500psi to cool to about 3000 and it went off. That caused me to jump.

The history goes back to boiler explosions at the turn of the last century and they are required on all pressure vessels regardless of use. In the EU they are required for pressure vessels for the same reason however they are actually banned on breathing vessels which is a nice exception they've made. Unfortunately I do not see that happening in this country.

Outlined in the image below as "one-piece safety" though there are 3-piece designs.

Never seen this needle contraption you speak of.

It’s a thin piece of copper. Nothing punctures it’s, it just fails when the pressure gets too high and vents out the plug.

 

[tbone1004]

Never seen this needle contraption you speak of.

It’s a thin piece of copper. Nothing punctures it’s, it just fails when the pressure gets too high and vents out the plug.

some of the older valves have a small pin that pushes against the disc, don't think most of the newer ones have. I have one laying around somewhere I'll try to get a picture of. Many of the industrial bottles have them on there, they're weird. The pin presses against the disc and punctures it.

@jtsfour plugging them not legal, so is doubling them up, so is putting a burst disc that is not 90% of test pressure. Not to say it's not common practice, but it's not legal. Ironic given that it is illegal to have them installed on scuba tanks in the EU though

 

[parzdiver]

What happens when they burst? Aside from a bang and disc shrapnel thrown across the room! Can you just push the disc back in?

Seriously, have never seen one!

Saw a freshly filled black tank that was left in the sun on a hot day burst its disk. There was a pop and the tank started spinning around like crazy sending gravel flying all over the place. Let me just say, thank goodness for pee valves.....

Once it bursts, it needs to be replaced, as others have said, it is a copper disk that breaks.

 

[boulderjohn]

Years ago I picked up my LP 108 doubles at a South Florida shop where they were filled to service pressure for a routine deco dive. The person who filled them told me that he had detected a slight leak in my burst disk, and he had fixed it. I assumed he meant he had used a wrench to tighten it.

Two months later I was at Cave Adventurers in Marianna, Florida, and I left them at the shop to be filled for a day of cave diving. When I came back, the shop was a mess. It looked as if a tornado had gone through it. "What happened here?" I asked. "Didn't anyone tell you?" someone asked in return.

It seems that the South Florida tank filler who "fixed" my burst disk had replaced the whole thing with a new disk suitable for a low pressure tank.

So if you want to know what it is like when a burst disk goes, just ask anyone who was at Cave Adventurers that day. I am sure the tale will be one to remember.

 

[Jack Hammer]

Somebody shared a video several years ago from, IIRC, a dive shop security camera showing a burst disc let go. The tank knocked stuff over and spun around making a mess. It was impressive.

 

[rjack321]

In really old valves the burst disk was actually a lead plug that was designed to soften in high temps and then pop out. Those were used more in O2 valves than the scuba industry.