What do the numbers on scuba tanks mean?

[rhwestfall]

we like complexity in the US....

 

[runsongas]

the test pressure is 3/2 working pressure per the special permit. this is different than the 5/3 used for 3AA vessels.

xs scuba has pretty much all the info listed on their page:

Cylinder Markings — XS Scuba

@JimBlay 3442 psi is to skirt the DOT DIN connection requirement in order to keep standard 3/4 NPS neck sizing. originally, the tanks were 3500 psi, but that forced DIN only valves with a unique 7/8 UNF neck by DOT regulations. as yoke regs were much more prevalent and still more common than DIN, it made more commercial sense to drop the service pressure slightly and allow for convertible valves

 

[Storker]

Filling a HP tank to 3700-4000 I don't (personally) consider a cave fill.

Hot or cold?

I routinely overfill my 300 bar tanks by some 10%. When they've cooled down, they still need topping up to have their rated pressure at the site.

 

[kelemvor]

I've always considered a "cave fill" being the HP filling (3600+) of LP tanks. Filling a HP tank to 3700-4000 I don't (personally) consider a cave fill. I rather consider it good customer service.

That's what I'm used to getting as well.. 3600ish on tanks rated for 2640. 36% more pressure. 3700-4000is only 7%-16% extra in an HP.

 

[Divin'Papaw]

Hot or cold?

I routinely overfill my 300 bar tanks by some 10%. When they've cooled down, they still need topping up to have their rated pressure at the site.

Cold

 

[Scuba_Nick27]

Slight revision, Steel cylinder are regularly overfilled in Florida. Outside of Florida you don't regularly find places doing "cave fills" .

TP = Test Pressure. It is the pressure that the cylinder should be tested at when doing a hydro. This is where you can run into issues with a shop botching a hydro. If they ignore the TP and go with the 5/3s working pressure they exceeded the test pressure and will probably condemn what was a good tank. So you need to watch it when it comes time for a hydro. Avoid bad testers.

Will keep that in mind.

 

[Scuba_Nick27]

That makes some sense ... except for where does 3442 come from? I always wondered that. Seems so random.

Here on the right (pun definitely intended) side of the pond, standard tank pressures are 200, 232 and 300 bar. 200 bar is archaic, I don't think you'll find a new steel tank rated below 232 bar these days.

200 bar = 2900 psi, 3000 psi = 207 bar, close enough for government work.
232 bar = 3365 psi, 3442 psi = 237 bar, close enough for government work.
300 bar = 4350 psi

I have no frikkin' idea why y'all chose 3442 instead of, say, 3400 psi.

I actually know why. I mentioned that I run DIN. 3500 is the maximum working pressure Yoke regulators withstand, past that and you get leaks and your A-clamp can blow off the valve (my instructor told me about that happening once in the shop, where an inexperienced filler was filling a tank). DIN regulators can take pressures way past 3500. But manufacturers don't write "maximum pressure is 3500" because it is easier to overfill if you are using a Yoke. They write 3442 to give some 'wiggle room' so to speak and prevent any damage to people using Yokes on their tanks. The tank itself and the valve can handle a bunch more pressure, the pressure you are allowed to fill to is decided by how you attach your 1st stage to the tank, by a Yoke or a DIN. It's just safety regulations.

By the way, when I filled the tank on monday, I checked with my dive computer and the pressure was 3540. If I was using a Yoke I probably would have had problems.

 

[Scuba_Nick27]

the test pressure is 3/2 working pressure per the special permit. this is different than the 5/3 used for 3AA vessels.

xs scuba has pretty much all the info listed on their page:

Cylinder Markings — XS Scuba

@JimBlay 3442 psi is to skirt the DOT DIN connection requirement in order to keep standard 3/4 NPS neck sizing. originally, the tanks were 3500 psi, but that forced DIN only valves with a unique 7/8 UNF neck by DOT regulations. as yoke regs were much more prevalent and still more common than DIN, it made more commercial sense to drop the service pressure slightly and allow for convertible valves

Here, I found a scuba board thread discussing this Steel HP tank 3500 vs 3442??? . I also replied to @Storker and @JimBlay with the explanation I heard. So I guess that it's not only the DIN/Yoke problem. Its also the type of steel (chromoly vs. galvanized), the neck and valve sizings, buoyancy, and regulations.

 

[Scuba_Nick27]

@runsongas @JimBlay @Storker I also found this HP 83 Cu.Ft 4500 PSI/ 300 BAR Steel Tanks [Archive] - Scuba Forum - Scuba Diving Forums and Discussion Board . The second message on this forum states that Yokes are made for pressures below 3500. So yeah, 3442 is just for peace of mind for the Yoke users out there.

 

[runsongas]

Here, I found a scuba board thread discussing this Steel HP tank 3500 vs 3442??? . I also replied to @Storker and @JimBlay with the explanation I heard. So I guess that it's not only the DIN/Yoke problem. Its also the type of steel (chromoly vs. galvanized), the neck and valve sizings, buoyancy, and regulations.

galvanized refers to the coating, all steel tanks are made from chromoly steel, the older vintage tanks have a slightly different alloy than newer ones.