Another Burst Disc Question

[in_cavediver]

As I understand it, cave divers like to have double discs to prevent failure.

What I don't understand is why? Is it because of transport or because of disc failure underwater?

I can almost see it being a problem on-land since most cavers like a "cave fill".

However, I don't understand it if the issue is underwater bursting of the disc. The reason I don't understand it is because from the time you go under, the pressure in the tank is being reduced continually, thus eliminating the potential of the disc letting go.

I've been around to see two burst disks go, one was on land during the fill and the other was while cave diving. The one on land let go a little over 1000psi while getting filled. I was traced back to improper installation. (IE, it wasn't seated in the valve). The second one was on another poor diver in cow. He lost a burst disk 600 feet in upstream cow. He isolated and exitted. If I recall, his pressure at 'burst' was around 3000 in a set of 112's.

 

[Quarrior]

I've been around to see two burst disks go, one was on land during the fill and the other was while cave diving. The one on land let go a little over 1000psi while getting filled. I was traced back to improper installation. (IE, it wasn't seated in the valve). The second one was on another poor diver in cow. He lost a burst disk 600 feet in upstream cow. He isolated and exitted. If I recall, his pressure at 'burst' was around 3000 in a set of 112's.

Regarding the second burst, that's the first time I've actually seen someone say anything about personally knowing of one that let go underwater.

Now, this brings another question, was the tank and valve properly maintained? I dive HP130's and have my disks replaced every year when I have the vis done. I don't know what the rule on it is, if there is one.

 

[OneBrightGator]

You'd need to fill a E8-130's to almost 3900 to get that and who wants to mess with thirds on 3900? 3900 seems like such a weird number; I prefer 3600.

Uh... 3900/3=1300... :06:

 

[Thalassamania]

Regarding the second burst, that's the first time I've actually seen someone say anything about personally knowing of one that let go underwater.

I second that.

 

[in_cavediver]

Regarding the second burst, that's the first time I've actually seen someone say anything about personally knowing of one that let go underwater.

Now, this brings another question, was the tank and valve properly maintained? I dive HP130's and have my disks replaced every year when I have the vis done. I don't know what the rule on it is, if there is one.

Don't know what the maintance on the manifold was. I only spoke with the diver breifly after he surfaced and changed his wetsuit. He was a bit shaken up about it for some reason.

 

[Quarrior]

Don't know what the maintance on the manifold was. I only spoke with the diver breifly after he surfaced and changed his wetsuit. He was a bit shaken up about it for some reason.

If it were me, the wetsuit would be in the water without me and inside out at that.

 

[loosebits]

Uh... 3900/3=1300... :06:

Uhh, stop confusing me; I'm from Texas.

 

[H2Andy]

i'm from florida and i'm confused

look... OneBrightGator forgot to take off the initial dividend from the
main figure (3900) which in this case is 100 psi to bring it down to
3800 -- the nearest even number.

so... 3800 doesn't go into 3, so you have to go down to 3600, which does,
but don't forget the intial 100 psi you took out, so put it back in,
which gets you back to 3700

but, again, 3700 doesn't work, so you have to go down to 3600. so,
that's 1200 thirds, plus the 100 you took out to get to 3600, which is
1300...

so.. here's the trick, you deduct the 1300 FROM THE ORIGINAL 3900, so
you end up with 2600 as your turn around point.

easy

 

[loosebits]

i'm from florida and i'm confused

look... OneBrightGator forgot to take off the initial dividend from the
main figure (3900) which in this case is 100 psi to bring it down to
3800 -- the nearest even number.

so... 3800 doesn't go into 3, so you have to go down to 3600, which does,
but don't forget the intial 100 psi you took out, so put it back in,
which gets you back to 3700

but, again, 3700 doesn't work, so you have to go down to 3600. so,
that's 1200 thirds, plus the 100 you took out to get to 3600, which is
1300...

so.. here's the trick, you deduct the 1300 FROM THE ORIGINAL 3900, so
you end up with 2600 as your turn around point.

easy

Uh, I assume all that mess was a joke. Round down to the nearest number divisible by 300.

Turn for 3900 is 2600 (3900 - 3900 / 3).
Turn for 3800 is 2600 (3800 - 3600 / 3).
Turn for 3700 is 2500 (3700 - 3600 / 3).
Turn for 3600 is 2400 (3600 - 3600 / 3).
Turn for 3500 is 2400 (3500 - 3300 / 3).

 

[H2Andy]

round down to the nearest number divisible by 300? bah, anyone can do it
that way

i'd like to see you work it the dividend way