TrimixToo
Contributor
Yep. Forgot to divide by two. Still plenty of thrust to make the tank spin, though.
Scuba Cylinder kills fire fighter
- Thread starter akdeepdiver
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Yep. Forgot to divide by two. Still plenty of thrust to make the tank spin, though.
This is exactly why multiport burst disks were created.
Back when I took my PSI course (12-13 yrs ago) I remember being advised to loosen the burst disk if the valve was otherwise stuck. There was an implicit assumption that the multiport plug would distribute the exiting gas forces so no mention of strapping the tank down. Or if there was discussion, it didn't stick in my head.
Before doing a valve overhaul I actually often vent most of the cylinder and then loosen the burst disk slightly near the end. The remaining tank pressure dislodges the burst disk which is sometimes corroded into the hole a little bit. Going to start being more diligent about how I do that in light of this accident.
Back when I took my PSI course (12-13 yrs ago) I remember being advised to loosen the burst disk if the valve was otherwise stuck. There was an implicit assumption that the multiport plug would distribute the exiting gas forces so no mention of strapping the tank down. Or if there was discussion, it didn't stick in my head.
Before doing a valve overhaul I actually often vent most of the cylinder and then loosen the burst disk slightly near the end. The remaining tank pressure dislodges the burst disk which is sometimes corroded into the hole a little bit. Going to start being more diligent about how I do that in light of this accident.
Rred
Contributor
Oh. Thanks for clearing that up, Bob. Even if the rocket science (thrust) part is debatable, yeah, I'd be loathe to just take a fitting off a possibly fully pressurized tank. And if I absolutely HAD to, I think I'd make Real Damn Sure it was chained down first. But then again, I'm lucky, in junior high I had a really good shop teacher who taught us that machines sometimes like to snack on people. I prefer not to be lunch!
The more I think about this, the more I convince myself that an intact burst disk will rarely vent through the multidirectional ports if loosened rather than bursting. Pretty sure it will find its way out through the threads, and direction will be random. All the more reason to vent VERY slowly, and not be in a rush to empty the cylinder quickly. A fast venting of the disk assembly may also be violent enough to rattle the part out the rest of the way, which may be another explanation of unexpected mishaps.
The threads are not lubed and there is no way to rinse the thread to valve interface. So after years of use (typically 5+) the plug part is usually well corroded into the female valve thread side. They don't just wiggle out. The corrosion on the valve in the report is certainly extensive. Much more likely that the nut end sheared off and that turned the multiport outlet into a single port outlet. The plugs are soft brass and the 3 vent holes weaken the nut to threaded section connection.
Rred
Contributor
AFAIK with the new style disks, where the disk and plug are one fused assembly and the disk itself no longer can be replaced separately, there's no way in hell that the valve is going to vent through the multiple holes UNLESS THE DISK RUPTURES.
Physically impossible any other way, because they've sealed the assembly.
And still pretty unlikely on the old style, where the disc would be compressed up against the plug by tank pressure, in any case.
That's like discussing safe ways to stick a hairpin in a live electrical socket. The safe way? Yeah, just don't do that.
Physically impossible any other way, because they've sealed the assembly.
And still pretty unlikely on the old style, where the disc would be compressed up against the plug by tank pressure, in any case.
That's like discussing safe ways to stick a hairpin in a live electrical socket. The safe way? Yeah, just don't do that.
They are not fused or sealed assemblies
The disk is held onto the end of the plug with a cup shaped plastic washer. The copper disk itself isnt any different than the copper disks used when you have the separate washer/disk/plug. If you back one of the "integrated" burst disk units out 1 or 2 turns the gas pressure pushes the disk outwards which breaks the seal formed by the plastic washer and the gas vents via the multiport plug just like with any other burst disk.
Rred
Contributor
Thanks, rjack. I guess I've been misinformed, I was told the discs were integral to the new plugs so that the whole assembly had to be changed. From what you say, the copper disc itself CAN be changed, even if no one bothers to.
I used to change my own burst discs, and apply food-grade grease to both sides of them, so any moisture inside the tank, or salt water on the outside, couldn't pinhole the copper and cause a disc failure. Then a professional went and replaced the originals with the new ones and said that's no longer possible.
I used to change my own burst discs, and apply food-grade grease to both sides of them, so any moisture inside the tank, or salt water on the outside, couldn't pinhole the copper and cause a disc failure. Then a professional went and replaced the originals with the new ones and said that's no longer possible.
AfterDark
Contributor
Lots of power
First, it is still possible to find sources for some 3 pc burst discs. The newer 1pc burst disc assemblies may not be "fused," but they are NOT intended to be disassembled at any point. At least Sherwood and Thermo specify to replace the single assembly (or ALL 3 individual pieces) every 5 years, not to re-use anything. I have seen many copper burst discs deformed but not ruptured at the service interval, on cylinders that were never over filled. Waiting for it to fail instead of replacing on schedule is very much "penny wise and pound foolish" in my opinion.
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