Double Your Burst Disk - Arguments For & Against, Please...

[H2Andy]

Actually, before I got my top on my truck, my LDS cautioned me not to carry my tanks standing up so they can't be seen by the Law folks.

He said if they can see the tanks, they can pull you over and do a DOT inspection.

not your local metropolitan or sheriff's office.

some of your state DOT officers might (but they don't have the manpower to
do anything but high-volume sting operations). however, they'll be enforcing
state law, not federal tank law.

as far as i know, there are no federal dot officers tasked with random stop
enforcement. generally speaking, the dot tank regulations are left to the
industry to enforce, and except for rare spot visits to commercial establishments,
the dot folks leave us alone (yes!)

so, your chances of being stopped for a "DOT violation" are slim to none, and
then your state probably doesn't even have a law concerning the transportation
of scuba tanks to begin with.

this is not intended as legal advice. for legal advice, please
consult an attorney licensed to practice in your state.

 

[in_cavediver]

Cave divers do it. Others say it is dangerous and against the law. Please give me your opinions/arguments for and against here.

Thanks.

As A cave diver, here's my answer.

Yes, it is illegal to double disk the valve. How applicable this is to a personally owned tank not taken over interstate transit is up for debate but that legaleaze and I am not a lawyer so call it illegal.

Second, unless you have a lot more to loose by not doubling your disks, why do it? If you are planning to overfill you tanks, then you either need to get a 300 bar manifold/300 bar disks or double disk your 200 bar manifold. (for a while, stainless steel burst disks were available through back channels). If you never plan to overfill your tanks, then I wouldn't double disk them.

Cave divers double disk and overfill for two main reasons:

1) Many take fill pressures on LP tanks as merely a suggestion. (or an easy way to get your turn pressure with the stamped 2400). Why you might ask, more gas means more distance. A set of PST LP104's at 2640 have 208cft. At 3600-3700, they have 285-290 cft. (or a built in 80cft stage bottle)

2) Blowing a burst disk in a cave several hundred to several thousand feet in would really ruin your day. (or end it for that matter). Doubling the disk prevents this from happening.

Now, is it safe? Well, there has been a lot of years where the steel tanks have been overfilled and never burst. Does that mean it can't happen, well no, it just means that for the last 10-15 years, it hasn't. And yes, overfilling tanks will shorten thier service life. At one time, I saw the PST data for cycles at hydro pressure prior to failure and it was in the 5-10 thousand range. (at service pressure, it was in the 50-150 thousand cycle range. I don't have it in front of me so take it as mere recollection.

 

[OneBrightGator]

So do you walk your tanks to the dive site?

Faber, the manufacturer, warranties their tanks for 10,000 fills to 4,000 PSI.

Lugging your tanks on your back does not constitute transport

Do you have references for that warranty? I hear that all the time but have never seen it in official documentation.

 

[OneBrightGator]

state DOT officers might (but they don't have the manpower to
do anything but high-volume sting operations).

FDOT officers regularly patrol state maintained roads and actually have more authority to pull vehicles over then any other state law enforcement agency and they definitely do, believe me

 

[OneBrightGator]

Or use them because;
a. it's the law
b. in the highly unlikely event a tank should blow up. The widow of the poor tank monkey who agreed to overfill the tanks is left penniless because the insurance is void because the investigator found doubled burst disk.
c. because there could be any number of other eventuallities that you may not see but because of a. the pitfalls are probably numerous.

I have filled thousands of tanks and never seen a burst disk fail.

a. Only for commercial transport
b. A steel tank has never exploded (don't DD alums) and good luck finding the valve after a tank does.
c. Like what?

I haven't filled thousands of tanks and I've had enough (4ish I think) fail.

 

[H2Andy]

FDOT officers regularly patrol state maintained roads and actually have more authority to pull vehicles over then any other state law enforcement agency and they definitely do, believe me

i've never seen them (lucky me, i guess)

do they enforce anything to do with scuba tanks? i can't seem to find
any state law regarding scuba tanks.

 

[Quarrior]

2) Blowing a burst disk in a cave several hundred to several thousand feet in would really ruin your day. (or end it for that matter). Doubling the disk prevents this from happening.

I've seen this reason given many times for taking the risk of double disking, however, I've never seen any evidence of it actually happening.

It just makes no sense to me and the phsyics don''t support it on properly maintained equipment.

 

[H2Andy]

i think the genesis of the double-disk thing was to be able to pump more
air into a tank... not so much a safety thing as a "let's go further" thing

 

[JS1scuba]

I may be way off base here, and maybe Joel has something when he says that European cylinders are different (he does seem to know his ***** )

But Burst disks are alien to us in the UK and we don't have exploding cylinders (99% steel - Faber, Heiser or ECS) all over the place.

Dom

Thanks -- yes the specs on European cylinders are different. Most are heavier and can take a higher pressure. So much so that the elevated pressure generated from heat will most probably extrude the o-ring before the cylinder lets loose. Also in Europe even though they fill cylinders to higher pressures than we do here in the states you will rarely have a dive centre overfill a cylinder. With all the regulations they have there for cylinder handling they are a bit more careful than most DSM are here.

Cheers

 

[OneBrightGator]

do they enforce anything to do with scuba tanks? i can't seem to find any state law regarding scuba tanks.

No. Typically officers pull over personal vehicles for speeding, some as part of drug interception, but scuba tanks, legal or illegal would not even cross the radar.