Cave divers do it. Others say it is dangerous and against the law. Please give me your opinions/arguments for and against here.
Thanks.
Thanks.
Double Your Burst Disk - Arguments For & Against, Please...
- Thread starter Rick Inman
- Start date
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What is the purpose of a burst disk? When you double them, you defeat their purpose. It's safe right up until the instant you need one to work.
burst disk
A small fixture located on a scuba tank valve that is designed to release pressure from the tank once a certain internal pressure is reached. This is a safety feature that minimizes the risk of tank over pressurization.
A small fixture located on a scuba tank valve that is designed to release pressure from the tank once a certain internal pressure is reached. This is a safety feature that minimizes the risk of tank over pressurization.
matt_unique
Guest
Purpose is to prevent a tank explosion of course. I would rather have to replace the disk and air fill than everything within 20 square feet 
--Matt
--Matt
Rick Inman:
I would like to see a summary of all tank failures that were the result of over pressurizing the tank.
My feeling is that the practice will substantially shorten the life of the tank. The degree to which that life is shortened will depend on several factors. The amount of overfill, the number of times it is overfilled and the pressure used will all affect the life expectency of the tank.
If it was to be my standard practice and I were to do this frequently, I might consider doing a visual twice a year and a hydro every three as a precaution.
If the tank is in good shape and regs are modern and well serviced, I don't have a problem with it.
Here ya go............
=======================================
All compressed gas cylinders used in North America are governed by The US Code of Federal Regulations Title 49. The US Department of Transportation is specifically charged with enforcing Title 49 as well as other sections of the CFR. These aren't optional - they are the law. If a company is found to be out of compliance with these regulations they can be cited and fined by the DOT, OSHA or both. Flagrant violation can be subject to prosecution. In other words, complying with them is not optional.
Section 173.301(a)(1) of Title 49 states:
Except as provided in paragraphs (f)(5) and (f)(6) of this section, a cylinder filled with a gas and offered for transportation must be equipped with one or more pressure relief devices sized and selected as to type, location, and quantity, and tested in accordance with CGA S-1.1 (compliance with paragraph 9.1.1.1 of CGA S-1.1 is not required) and S-7. The pressure relief device must be capable of preventing rupture of the normally filled cylinder when subjected to a fire test conducted in accordance with CGA C-14 (IBR, see § 171.7 of this subchapter), or, in the case of an acetylene cylinder, CGA C-12 (IBR, see § 171.7 of this subchapter).
As you can see from the above, Title 49 refers to CGA S-1.1 as the governing document. Safety assemblies used in North America must be "in accordance with CGA S-1.1". CGA S-1.1 is too big to summarize in a few sentences. But among other things incorporated into CGA S-1.1 is that only manufacturer's original equipment safety assemblies may be used in any particular valve. The most abused aspect of this in the scuba industry is the practice of "double disking" and if one can find an original manufacturer's original equipment that is intentionally double disked, then they may be used with the manufacturer's permission. Since no responsible manufacturer would ever support that practice, it cannot be done legally. If one decides to "improve" a safety assembly by double disking it, then they are not in compliance with Federal law - in addition to being responsible for creating an extremely dangerous situation. If a safety assembly is double disked, the cylinder then becomes the weaker link.
The question of why North America uses safety assemblies and Europe does not is a much longer discussion. It started out as a philosophical difference of the risk/benefit of a safety assembly. But once that decision was made by the governing bodies (and that was a very long time ago), cylinders were then designed based on the knowledge that safety assemblies would either be used or not used. Believe it or not, the primary purpose of a safety assembly is to prevent a cylinder from rupturing in a fire situation - not as an overfill prevention device.
Double Disking a valve is almost obsolete today since the major valve companys have moved to a one piece saftey assembly. Thermo, Sherwood, soon SanoSub, Genesis all use a single piece assembly to prevent double disking.
A properly serviced valve with the saftey replaced with at least each hydro test date ensures that the valve remains in spefication for the cylinder it is used. When we service cylinders in our operation we inspect and replace safteys as routine, if it has been doubled up ... it is no longer.
Cheers
=======================================
All compressed gas cylinders used in North America are governed by The US Code of Federal Regulations Title 49. The US Department of Transportation is specifically charged with enforcing Title 49 as well as other sections of the CFR. These aren't optional - they are the law. If a company is found to be out of compliance with these regulations they can be cited and fined by the DOT, OSHA or both. Flagrant violation can be subject to prosecution. In other words, complying with them is not optional.
Section 173.301(a)(1) of Title 49 states:
Except as provided in paragraphs (f)(5) and (f)(6) of this section, a cylinder filled with a gas and offered for transportation must be equipped with one or more pressure relief devices sized and selected as to type, location, and quantity, and tested in accordance with CGA S-1.1 (compliance with paragraph 9.1.1.1 of CGA S-1.1 is not required) and S-7. The pressure relief device must be capable of preventing rupture of the normally filled cylinder when subjected to a fire test conducted in accordance with CGA C-14 (IBR, see § 171.7 of this subchapter), or, in the case of an acetylene cylinder, CGA C-12 (IBR, see § 171.7 of this subchapter).
As you can see from the above, Title 49 refers to CGA S-1.1 as the governing document. Safety assemblies used in North America must be "in accordance with CGA S-1.1". CGA S-1.1 is too big to summarize in a few sentences. But among other things incorporated into CGA S-1.1 is that only manufacturer's original equipment safety assemblies may be used in any particular valve. The most abused aspect of this in the scuba industry is the practice of "double disking" and if one can find an original manufacturer's original equipment that is intentionally double disked, then they may be used with the manufacturer's permission. Since no responsible manufacturer would ever support that practice, it cannot be done legally. If one decides to "improve" a safety assembly by double disking it, then they are not in compliance with Federal law - in addition to being responsible for creating an extremely dangerous situation. If a safety assembly is double disked, the cylinder then becomes the weaker link.
The question of why North America uses safety assemblies and Europe does not is a much longer discussion. It started out as a philosophical difference of the risk/benefit of a safety assembly. But once that decision was made by the governing bodies (and that was a very long time ago), cylinders were then designed based on the knowledge that safety assemblies would either be used or not used. Believe it or not, the primary purpose of a safety assembly is to prevent a cylinder from rupturing in a fire situation - not as an overfill prevention device.
Double Disking a valve is almost obsolete today since the major valve companys have moved to a one piece saftey assembly. Thermo, Sherwood, soon SanoSub, Genesis all use a single piece assembly to prevent double disking.
A properly serviced valve with the saftey replaced with at least each hydro test date ensures that the valve remains in spefication for the cylinder it is used. When we service cylinders in our operation we inspect and replace safteys as routine, if it has been doubled up ... it is no longer.
Cheers
Well, I've *seen* several dive days ruined by having burst discs blow at inopportune times for no apparent reason.. yet I've never even *heard* of a modern steel tank blowing up due to overpressurization.
*shrug* I don't, and I won't, but to say that it's incredibly dangerous is a bit of a stretch, I think.
*shrug* I don't, and I won't, but to say that it's incredibly dangerous is a bit of a stretch, I think.
H2Andy
Contributor
it's probalby pretty safe, so long as you are willing to accept the remote possibility
that the tank will give before the doubled-up burst disks do
assuming a doubled-up pressure just shy of 8,000 psi, how likely is tank failure
anyway? i ask cause i know nothing of this subject
that the tank will give before the doubled-up burst disks do
assuming a doubled-up pressure just shy of 8,000 psi, how likely is tank failure
anyway? i ask cause i know nothing of this subject
strongbow
Guest
You might want to increase you life insurance.....ponder that.
H2Andy
Contributor
why? how dangerous is it really?
do you know? or do you just think it is more dangerous?
can 8,000 psi really compromise the integrity of a tank's material?
do you know? or do you just think it is more dangerous?
can 8,000 psi really compromise the integrity of a tank's material?
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