Burst disks????

[JS1scuba]

That's very technical and informative but is it really necessary to plug or double discs?
Has there been many burst disc failures? Or is this unfounded paranoia?

If you have a properly serviced safety assembly in your cylinder and it releases then there is probably a good reason for it to release.

In the USA it's required to have a properly rated safety assembly in the cylinder valve. Rendering it inoperable is foolish. We can get into the whole legal and moral discussion about it but that would go on for 30 posts or more. We can address why in the USA it is required but Europe does not require it, and that will run for 30 posts or more as well.

I just serviced some personal valves the other day. I serviced them a year ago as well. Upon inspection of the safety assembly it was indented far enough, and there was some minor corrosion on it that I opted to change it. I use the Thermo type assembly that is the one piece assembly with the pressure rating stamped and the disc held in place with a copper ring. I tossed out the old one and installed the new one to 120 inch pounds torque. I have zero fear that the assembly will blow out under normal use. Next year If it needs replacement I will replace again. It's the cost of diving.

As a DOT facility (we do hydro tests ) it's hard for me to suggest that you overfill cylinders or put improper safety assemblies in cylinders. It's best that you just not do it.

As to the "cave fill" you probably never heard of a Wahoo fill. It may have been 1991 and Dick Long was up on Long Island diving with us. He set up his tanks (twin 80 alum splits) , turned on the gauge and it read zero. He said to me .. Joel this tank is empty. I said not it's not. He said yes it is, I looked at his gauge. It was an older Poseidon SPG that only had readings to 3000 psi and the needle was at Zero .... We put another gauge on it and it read 4,000. He said "you cant fill tanks to that pressure" I asked him if he wanted me to drain it down to 3000... he said no i will keep that extra gas!

FYI when those cylinders got hydro tested a few years later they all failed.

In more than 20 years handling hundreds of thousands of cylinders (yes it adds up) I've had 4 safety release. 2 were on a set of 3442 tanks we were transporting cross country - the guy was using a 300 bar dive rite manifold that had safeties in them for LP tanks (4000 psi release) the cylinders were in a hot trailer box and let go (as they should have) the other was on some old 72s that a customer brought in for filling and it was their time. The valves had not been serviced in 20 years.

..... gotta go fill some tanks

Cheers
JDS

[DaveP]

Phillip,

You don't have to worry about it in the DR since we never get anything over rated tank pressure for fills. Don't want to over fill the alum tanks anyway.

[phillip1]

That's what I thought but was not 100% sure.
Thanks

[FW]

That's very technical and informative but is it really necessary to plug or double discs?
Has there been many burst disc failures? Or is this unfounded paranoia?

I only had one burst, but that was enough for me!

I see a lot of answers here, and many are correct, but the main thing to consider is what you actually fill to, not the "rated" pressure.

[DA Aquamaster]

Absolutely - for purposes of avoiding gas loss in a cave, it should match the fill pressure not the stamped service pressure on the tank. For a 2400 psi tank the test pressure is only 4000 psi - perilously close to the 3600-3800 psi fill pressure in cave country. Add a few cycles on the burst disc and it will fail.

In the case of a 2400 ps tank, you would want a burst disc assembly with a lot more margin over the fill pressure. In this case a burst disc for 3000 psi service will be good to a minimum of 4500 psi, and would be the absolute minimum. A burst disc intended for 3442 psi service will be good to a minimum of 4650 psi and a burst disc intended for 3180 psi service will be good to a minimum of 4770 psi.

[DA Aquamaster]

That's very technical and informative but is it really necessary to plug or double discs?
Has there been many burst disc failures? Or is this unfounded paranoia?

Asked and answered. You apparently did not read this line in post 9.

"Doubling is in my opinion just misguided paranoia as if the burst disc is replaced on a suitable schedule it will be reliable."

[Line Squirrel]

I don't see a reason to do either.

There IS no reason to do either. There are better/safer alternatives.

[lamont]

That's very technical and informative but is it really necessary to plug or double discs?
Has there been many burst disc failures? Or is this unfounded paranoia?

IIRC, there's a few IRAP incidents involving burst disc failures.

[jkdiver]

has anyone used the --- discs? has anyone had issues with them? I dont see why we cant do the european deal? --- so you think there are less ---in europe? thats the only reason --- requires us to use burst discs? at least the --- discs are a middle ground.

I use the --- as I am not --- with the --- discs.

[FW]

I have a recommendation, don't talk about doing something illegal in an open forum on the internet. "Big Brother" may be watching.