Burst discs: Yes they burst when they shouldn't

[NAM001]

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.

On that i agree with you. that is why i have not seen a 200 bar fill connector. the instructor said they are hard to find and often was used in systems that had different regulated outputs. The prutruded pin items protects the tank and the thread system protects teh regulators when they made 200 bar regs.

 

[JamesBon92007]

3/8" UNF is 24 threads per inch (chart).



No, in fact, it is a recommended practice to do that.



All (oddball exceptions aside) LP72s are 3AA-2250, not 3AA-2400 like most newer LP steels. The correct choice is a 3750 burst disc, which has been discontinued. Some dealer/distributor stock still exists but they are getting hard to find. The usual choices are 3360, which is what you probably encountered, or 4000. Which of those is safer is debatable. I have 3750s in mine so I don't have to choose.

Several times I came across "$6" as the going rate for a burst disc however I am finding them at around twice that. The best price I've found is about $11. Should I keep looking or is that likely to be the lowest price I will find?

 

[tbone1004]

Several times I came across "$6" as the going rate for a burst disc however I am finding them at around twice that. The best price I've found is about $11. Should I keep looking or is that likely to be the lowest price I will find?

I linked to Northeast Scuba Supply where the prices are about $3.50 for the actual disc and $0.50 for the washer if you stay with 3 piece assembly. If you switch to 1-piece, they're $8 for non-sherwoods, and $11 for Sherwood 5000 valves and manifolds.

 

[JamesBon92007]

I linked to Northeast Scuba Supply where the prices are about $3.50 for the actual disc and $0.50 for the washer if you stay with 3 piece assembly. If you switch to 1-piece, they're $8 for non-sherwoods, and $11 for Sherwood 5000 valves and manifolds.

Thanks! That reminds me of how much they used to cost.

Are the Sherwoods a different thread? Some of my valves are Sherwoods, some are not.

 

[tbone1004]

Thanks! That reminds me of how much they used to cost.

Are the Sherwoods a different thread? Some of my valves are Sherwoods, some are not.

some are, John wouldn't differentiate if there wasn't a difference. I haven't pulled burst disc assemblies on the Sherwood 5000's in a long time. I'm about to, but haven't in quite a while

 

[JamesBon92007]

some are, John wouldn't differentiate if there wasn't a difference. I haven't pulled burst disc assemblies on the Sherwood 5000's in a long time. I'm about to, but haven't in quite a while

I just went and looked and I have at least one Sherwood 5000 on an AL80. It attaches at the end opposite of the valve knob. Most of my other burst discs (on the steel 72s) are opposite of the valve opening/regulator connection. One of the valves on an old 72 is opposite the knob which makes me suspect that the previous owner switched valves and it may have a higher pressure burst disc. It is also a Sherwood valve and has a sticker that says 3000 psi service pressure so I guess that confirms it.

I'm going back and forth as I'm writing this so this is a "discovery" post.

 

[BRT]

2air

a little correction . I believe the burst disk used is required to blow between 90-100% of test pressure. an al80 tests at 5k so the disk should blow about 4600 psi a little over the 90%. Picky perhaps but i have had one blow. It was on a lp95 pumped to 3200 on the gage , however teh gage was in error and off about 250 psi. It actually had about 3500 in it and the heat raised it to a little over 3600 EST. and it blew. tp was 4000 on a lp tank. 35 degree increase in temp at 5 psi per is about 175 psi increase from temp. I have never crossed paths with a blown disk since. Over filling was the cause of the rupture. BTW i believe the vis and hydro is to include verification that the burst disk is undamaged and the correct size for the tank application. I have 3000 psi valves on my lp's (they have burst disks for 4500#) and I do not give the valves to the hydro shop. In the above diagram item 11 is not always an item the the disk can be separated from the bolt. If they insist on valves i put on the original 2400 psi thermo valves. Item 11 is not a cheap item (5-7$ a piece) when you vis a dozen tanks a year.

I just had 7 hydro'd and didn't even send the valves along.

 

[tbone1004]

I just went and looked and I have at least one Sherwood 5000 on an AL80. It attaches at the end opposite of the valve knob. Most of my other burst discs (on the steel 72s) are opposite of the valve opening/regulator connection. One of the valves on an old 72 is opposite the knob which makes me suspect that the previous owner switched valves and it may have a higher pressure burst disc. It is also a Sherwood valve and has a sticker that says 3000 psi service pressure so I guess that confirms it.

I'm going back and forth as I'm writing this so this is a "discovery" post.

location shouldn't matter on where it is. The Sherwood 5000 is a series of valves but there were several in the series

 

[Jay]

I've come across several postings about burst discs bursting on land, but not yet to find any incidents whilst diving. Are there any stats on this, even anecdotal? And how seriously injured was the diver?

If a burst happens underwater wouldn't the tank take some time to fully flood? (Reason for Q: OOA and kicking up 11+kg for an AL80 to your buddy would be hard, but if you're aware that 11kg of negative was happening over the next x minute(s) ...)

Am I correct in assuming the ubiquitous AL80 tanks that are used around Asia have burst discs?

If a disc bursts whilst diving, assuming the diver's still conscious/reasonably uninjured, is there likely to be 'shrapnel' from it? Just thinking through a what-if the wing's also punctured.

 

[TrimixToo]

I do actually replace mine at hydro time, so when they get replaced they get either the right ones or blanking plugs. I have a bunch of blanking plugs about to go in

I likewise replace mine at hydro time. The valve is taken apart, O2 cleaned, the seat inspected or replaced, and the burst disc replaced. I have had one failure, ever, and it was a tank sitting in the car on a hot day before a planned dive trip. (As pointed out upthread, it doesn't get hot enough to reach the burst pressure, but I guess that one was just a bit weaker than usual.)