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

[Diver Dennis]

Hmmmm. I posted pictures of a truck that I was driving to a dive site that caught on fire with a bunch of tanks in the back. I'm still looking for the link but it was not long ago. I've seen burst discs go in a fire and it is amazing the rocket like destruction the air flow caused. I'll keep looking for the thread...

 

[dherbman]

Those were great pictures. I should have snarfed them when I last saw them

 

[Diver Dennis]

Here is the link.

http://www.scubaboard.com/showthread.php?t=129798&page=4&highlight=Scuba+tank+burn

Nice avatar herb!

 

[PvilleStang]

I recall seeing the 10,000 cycles to 4,000psi in some old PSI literature, but it WASN'T a warranty. It was part of the initial qualification tests of the tank design. It is NOT a warranty. It is NOT something that says the rated working pressure is 4,000psi.

Because of tank to tank variations, because of possible unseen defects, and because of possible unnoticed variations in material strength from lot to lot, the rated working pressure of tanks is lower than the pressure at which they are expected to fail.

Ropes usually have an safe working load limit less than 1/10 of the expected breaking strength. You will see similar ratios between the test loads and rated working load on cranes, hooks, and other lifting gear.

Most of the time one can exceed the rated pressures, rated working loads, or accepted oxtox limits and not have a problem. Whether or not is a wise choice is something you have to decide for yourself.

You hit the point on the head, without even knowing it! First off, it wasn't a PST, it was a Faber, made in Italy, where 4,000 isn't a huge deal. But from my whole argument that I've been trying to make: ENGINEERS GIVE WORKING PRESSURES MUCH LOWER THAN FAILURE POINTS! Why? For these exact reasons. Hydro, 5/3rds working pressure... I'll leave the rest to be debated later, cause its time for some FLIED LICE!!!

 

[Dive-aholic]

If you go on a charter boat that is commercial transport and is under DOT juristiction. At least in this country.

I'm not sure, but I think DOT only has jurisdiction on land. Once on water someone else gets it. Also, charter boats don't usually transport interstate. Finally, it's still not me that's responsible for the tanks. The captain is. I'm just a passenger. :14:

 

[wedivebc]

I'm not sure, but I think DOT only has jurisdiction on land. Once on water someone else gets it. Also, charter boats don't usually transport interstate. Finally, it's still not me that's responsible for the tanks. The captain is. I'm just a passenger. :14:

Trust me Transport Canada has everything to do with boats, their crew, their passengers and the items carried on those vessels. I am a licensed marine engineer so I have dealings with TC occasionally.

 

[Dive-aholic]

I'm sure they do, but the US does things a little differently. If the DOT has jurisdiction over boats, they certainly don't have the funding to oversee them like TC. Not much different than any other US govt org.

 

[NTDS]

The whole fire issue is ludicrous the first thing that goes on a tank in a fire that has no burst disc is the seals and seat in the valve assembly, hasn’t one of you ever noticed that these parts are o-rings nylon and teflon the seat is not metal to metal hence the reason for not needing burst discs in the UK, unless fires are different over there.

Let’s see, transport Canada or DOT is going to pull over someone to inspect a scuba tank, what are they going to see, a bolt with 1 or 2 holes in it, or maybe no holes at all. Then they are going to drain the tank, NOT, discharging a compressed gas from a cylinder on a public highway, street or road is an offence in Canada and is probably also in the US, they would have to confiscate the said cylinder and inspect it in a controlled environment, in order to inspect the burst disc/discs. The only way of getting a compressed disc out of most valves especially ones that haven’t been changed on a regular basis is to damage it by digging it out from its seat, or undo the bolt and add pressure to the cylinder until it releases from the seat, this is actually the best option because there is less risk of damaging the seating surface, if you try this method make sure that the disc is facing away from you, you don’t want to get shot by a copper bullet. At this point they are going to have to call in their burst disc CSI to do ballistics on the said offending discs because in a court of law they are going to have to prove that the discs actually came from the said valve. Upon further inspection they will find out that the valve came from the factory with double discs that the manufacturers installed because that’s all they had in stock at the time, many manufacturer's new valves out there at today’s date are like this. If you double up youself maybe they will find your finger prints on the disc and imprison you for valve tampering wear gloves!

As you can see this is absolutely foolish, it is just another instance of deceit and misconception that the scuba industry has created over the years in a hope to sucker gullible people into believing that there are burst disc police out their just waiting to nail some unsuspecting diver because he has a little to much copper in his valve.

Put a good grade stainless shim in the valve, over fill your steel tanks within reason use your aluminum tanks as stage bottles there’s no reason to over fill them and go diving.

Steve
:06:

 

[wedivebc]

As you can see this is absolutely foolish, it is just another instance of deceit and misconception that the scuba industry has created over the years in a hope to sucker gullible people into believing that there are burst disc police out their just waiting to nail some unsuspecting diver because he has a little to much copper in his valve.

Put a good grade stainless shim in the valve, over fill your steel tanks within reason use your aluminum tanks as stage bottles there’s no reason to over fill them and go diving.

Steve
:06:

There are burst disk police out there and they are called insurance investigators. You will see them going over everything with a fine tooth comb in the event of an accident in order to avoid paying out on your policy.
I wish you the best in your new charter business Steve but if you are publicly advocating breaking the law you are not going into business in a very sensible way.

 

[GDI]

For the most part should you decide to overfill your cylinders there is no reason to double disc the valves. The valves are overrated to the working pressure as it is.
In a fire the o-rings would let go but yes the burst disc would release as well because the increasing heat would still cause the expansion of gas to exceed the release rate in fact the valves may themselves pop right off. The cylinder would in any rate become unusable as the metal will heat fatique and become brittle.

A cave fill as some of you are calling it is not that much over the working pressure as a norm but there are those who will go big time so I say don't buy a used tank from a cave diver is the moral of the story here if you have any doubts.
I have seen burst discs blow usually at the filling station or just after getting filled. A few have let loose in the trunk of the car on a hot day. Having a burst disc blow from impact to a overhead is possible but this is the result of impact and dislodgement, My answer to this is have better awareness of your position. This can happen regardles of the pressure in the tank. With increased tank pressure it will make the joint a weaker area of concern so why overfill excessively and then attempt to make it safe or safer by double discing. Carry a stage bottle for extra gas if you want further penetration.

I see no need to double disc