Burst discs: Yes they burst when they shouldn't

[NAM001]

Burst disks are apparently a carryover from steam boilers, the regulations apparently started with them. Since I don't hear of the horrible death rate from exploding cylinders in Europe I suspect burst disks are more dangerous than not having them.

My under standing is the burst discs are a USA thing for fire fighting purposes. the disk will blow before that tank explodes in a burning building the rupture factor in the US if i remember is a 4x factor. rupture psi divided by 4 is working pressure burst blow is shy of 2x working pressure.

 

[NAM001]

Trying to learn here. Due to Scubaboard I am aware they exist. As a vacation diver I do not own tanks. I also have not noticed them on the tanks I rent in the Caribbean. I could be blind (or stupid).

So: where are they "required" and what do they look like?

they are a USA thing to protect fire fighters in theatthe plug will blow before the tank ruptures and flying metel injurs te fire fighters. look at teh valve picure in another post and it is item 11. the disc is a little wafer about 3/8 in diameter it goes in a hole in hte valve and a bolt is screwed in hte threaded hole to hole it in. the bolt has a hole up the middle of it and out the side of the HEX sides (2). when the disc blows the air exits up the hole in the bolt and out the sides of htehex surface.

the disc is the silver part surrounded by the copper. you can see the holes in the sides of the hex, It looks lke the disc on this one is recessed into the plug and may not be replacable.



On this valve it is item 4122-4135e (tothe right ) the large piece is the plug and the small parts to teh left are the disc. In this one the disc is replaceable with out the plug. And yes it is often opposite the the valve operator. the disc is basically a thin piece of metal like a mini coin that has a thickness that will rupture at a set pressure that is well below the rupture pressure of the tank walls. the parts list for this one calls it a safety assembly and is 5.35 in cost.

 

[tbone1004]

I think you have it backwards. a 300 bar whip will seal on a 300 and a 200 bar valve. the 200 bar regulator will not seal on the 300 bar valve, insuring the lower rated reg is not connected to the higher pressure source.

In Europe the 300bar whips will not seat against 200bar valves. Look at the link in post #24 to see what it looks like.

 

[Storker]

I think you have it backwards. a 300 bar whip will seal on a 300 and a 200 bar valve.

No, I don't. Things may be different on your side of the pond, but over here a 300 bar whip won't seal on a 200/232 bar tank valve. I've filled enough tanks to be pretty darned certain about that.

 

[NAM001]

It's a grey area and varies from one state to the next.

USDOT PHMSA's jurisdiction begins when hazardous materials used in commerce are loaded into or onto a vehicle (or vessel or aircraft) and ends when the materials are unloaded. It is the compressed gas, not the cylinder or valve, that is considered a hazardous material. Anything over approximately 40 PSI is considered hazardous.

So, if you have a bunch of cascade cylinders, and you never transport them full, USDOT PHMSA's rules don't apply. Or if you have a cylinder that is never transported in commerce, the rules don't apply. If the transportation is on a commercial vessel (dive boat), or incidental to commerce (teaching), then you have to play by the rules. There's a "materials of trade" exemption to some of the rules, but not the ones that govern packaging of gasses (i.e. cylinders and valves).

Even then, be careful, because many states and localities require pressure vessels to be inspected and certified under state and local rules, and have an exception for DOT cylinders. That's true in Minnesota, and the inspection and insurance requirements are more onerous than USDOT. There's a separate exception for SCBA cylinders, but not for SCUBA cylinders. Whether the SCBA provision applies to SCUBA is the sort of question lawyers make their money on. Whether a DOT cylinder has to be in full compliance with DOT rules to be exempt from state law is another question of the same sort.

Of course, no one will known unless there is an accident related to the blanking plug, and it won't affect you unless you survive it...

There is a lot more to it than that. In a dive shop you are engaging in commerce. Whether DOT covers it or OHSA says you will not have hazzardous material unless it is treated like it will be transported. The insurance has a bunch of say what you can do also. IE your tanks have to be standing up and secured per osha. Just like if you were transporting them. Burst discs are a fire issue so they are probably covered under the fire marshall cloke. just like too many people in your store at one time. I would not push those limits in a public forum. like a business.

 

[NAM001]

Interesting. IIRC our yoke adapters can only be fitted to a 232 bar fill whip (or adapter).

There's also a difference in the number of threads. A 300 bar DIN fitting has 7 threads, a 200/232 bar has only 5. Not an issue for regs, since they're designed to fit both 200/232 bar valves and 300 bar valves, but the fill whips are designed to make it physically impossible to screw a 300 bar fill whip into a 200/232 bar tank valve.

Older din regs did not have the 300 bar 7 thread fitting. Now as far as Inow all regs are made to work on 300 bar. But some older ones are still out there. To be honest i have not seen a 200 bar fill whip. Only 300 bar whips. I have seen 200 bar din regs and they will not seal on a 300 bar valve.

 

[NAM001]

No, I don't. Things may be different on your side of the pond, but over here a 300 bar whip won't seal on a 200/232 bar tank valve. I've filled enough tanks to be pretty darned certain about that.

our 300 and 200 are the same except for the number of threads.

 

[Storker]

I have seen 200 bar din regs and they will not seal on a 300 bar valve.

I took my OW in '12, and by that time every DIN reg was 300 bar. So I've never seen a 200/232 bar DIN reg, but I've filled quite a few 200, 232 and 300 bar tanks the last five years.

 

[Storker]

our 300 and 200 are the same except for the number of threads.

They're not here on the right side of the pond.

 

[NAM001]

No, I don't. Things may be different on your side of the pond, but over here a 300 bar whip won't seal on a 200/232 bar tank valve. I've filled enough tanks to be pretty darned certain about that.

You are correct about that fitting it prevents a 300 bar high source from being connecting to a 200 bar tank. I have seen those.

Here is what i have on my fill station it will mate to both 200 and 300 bar valves.

Our 200 bar valves are many times refered to as combo valves as they have an insert to allow use with a yoke reg and a 300 bar valve does allow the insert to function. You can count the threads. these do work on on 300 and 200 and are the common fill whip item. I will say I have only seen one time a tank that was a 300 bar tank. but i have seen many 300 bar valves. they have a pit n the bottom of them that the 200's do not have for that probe to extend in on the other valve you referenced. Our 300 bar regs look like this also.