Tank overfill

[OneBrightGator]

The low presssure PST 95 & 120's (2400) that I use in Cozumel routinuely show 2800-2900 and they get dove almost everyday. In Florida cave country this would be considered a good fill.

Actually, this would be considerd a short fill in Cave Country, hell, I've ended dives with more then that in my LP 104s.

We've been round and round this argument, on this board and every other, the fact of the matter is there is only one recorded incident of a steel tank exploding, but it was badly rusted 72 that was out of hydro and no sane person overfills 72s or any other "old" tank for that matter.

 

[markfm]

I'll go away on this topic, then, since you must know something that mere designers don't. Diving is supposed to be pretty safety oriented, the tech areas even more so. To arbitrarily exceed design points is not the sign of a reasoned approach. Sorry if engineering is inconvenient, I was simply trying to educate slightly, since most people do not understand specifications, what they are meant to convey.

(Not meaning to imply that a 10% overfill matters, though at 20% it's a bit high. This thread had gotten to talking a 3500 fill on a 2400 tank, which is a real push.)

Where I live, a good person is embarrassed to significantly overfill someone's tank.

Good luck, have fun, please don't fill your tanks anywhere near me.

 

[OneBrightGator]

The problem is it's not designers or engineers that make the specs, it's politicians. Everything is over-designed, which is obvious from the such small number of scuba cylinder explosions (I've heard that CO2 cylinder explosions are 1000x more frequent), not to mention that a hydrostatic test measures the "flex" in a cylinder not if it will explode from the next fill or not, theoretically, a cylinder could come within 1% of failing and still be safe for at least the next 5 years. There's a big difference between "design specs" and real world use, even lowly non-engineers know that.

Just don't come down to Gainesville, they get filled about every other day.

 

[markfm]

I hear you on practical use vs. theory, just that it bites when you hit the margins. People really do purposefully over-design, to take into account tolerances and real-world use (that bit of banging around that things get). The vast majority of the time a given product will greatly exceed design, but another copy, theoretically exactly the same, might hit the low end on all the tolerances.
Being an engineer isn't all that special, just means I'm good at math and paid to think and write in certain ways. I try to be careful around specs only because it's so easy to get wrapped around the axle, innocently misinterpret them.
I couldn't handle that warm Gainesville air -- we're use to brisk stuff near the Great Lakes (actually, a week of 90+, a rarity this early in the year)

 

[D_B]

It surprises me to hear , in a sport that advocates saftey first , that you fill 2400(+2600) psi rated tanks to 4000psi .... who was first to do it? ... if the thinking is there grossly over engineered , why not more pressure? how about 4500? ... first stages? ... K valves?

Sarcastic I know ... sorry to put it that way, but I'm just really surprised, as I said

DB

Oh, Kestrell , don't worry about that 3000psi, not any chance that It's going to hurt anything

 

[scubafanatic]

Okay, I just got my tank filled and my wife's tank too, a few days ago.

As an aside,to my knowlewdge, my wife has yet to pay for anything related to diving. I'm not sure how she does this.

Anyway, the guy filling the tanks hands me my tank and says, I filled it to 3800 so when it cools down you should be right around 3400-3500. That's cool. I have a PST E8 130 so I have a complete fill.

Well when he gave me my wife's tank he said something similar, but I didn't really hear what he said. I assumed he put in a bit of an overfill so when the tank cools it will be at max pressure.

Max pressure for my wife's tank is 2400 since she has a Faber LP 85.

Well, afew days later, just for the fun of it, I decided to see how close the guy got to filling the tanks to their max.

I checked mine and the pressure gauge was reading just bekow 3500. Great.

When I checked my wife's tank it the needle was right on 3000. By my calculations that is a 25% overfill.

Is this going to damage her tank? Its been at that pressure for a few days now. Is it even safe? If so, how long can it stay like that?

I also own a Faber LP 85.......it's actually rated to be full @ 2640 psi, so you are getting 85 cu. ft. of gas @ 2640 psi ( 2400 psi + another 10%= 2640 psi) so your 3000 psi fill was only a -- 13 % -- overfill.....rather trivial and absolutely nothing to worry about....you should thank your lucky stars you've got a dive shop that does decent fills.....I know plenty of shops that would give you a 2640 psi 'hot fill' and you'd be down to 2300-2400 psi after cool down = a 'short ' fill.

Karl

 

[DA Aquamaster]

It surprises me to hear , in a sport that advocates saftey first , that you fill 2400(+2600) psi rated tanks to 4000psi .... who was first to do it? ... if the thinking is there grossly over engineered , why not more pressure? how about 4500? ... first stages? ... K valves?

Sarcastic I know ... sorry to put it that way, but I'm just really surprised, as I said

DB

Oh, Kestrell , don't worry about that 3000psi, not any chance that It's going to hurt anything

Explosives are for also pretty stable as long as they are handled properly, properly stored etc, but you still do not screw with them as all it takes is once to really screw up the millisecond that remains of the rest of your life.

I would not go beyond a 10% overill in a steel tank because it is illegal, it is reducing the safety factors designed into the tank and because it would over time erode my confidence in the tank.

I am also struck by the tendency if not outright preference of cave divers to do relatively massive overfills of 20% or more when in every other regard they to seek to minimize the potential for failuire whenever and wherever possible.

Obviously the choice is being made to accept a long term threat in order to reduce the more immediate and tangible threat of running out of gas. If a lot of gas is good, even more gas must be great. Right?

Of course I also hear a lot of these same folks advocating getting rid of the tank after the second hydro, so obviously my confidence is not the only one being eroded over time. The concern I have is that many if not most of these tanks are probably being sold rather than scrapped and are consequently remaining in service with owners who may not know their history of chronic overfills. Personally, I would never buy a used tank from a cave diver or from anyone who lived anywhere near cave country.

 

[Leadking]

It is this mis-information that will cause someone to get injured or killed. Another company in the scuba industry advertised that Faber cylinders have had 10,000 hydro cycles without fail. This is a half truth. ALL cylinders, by ANY manufacturer, in order to be approved by DOT must pass 10,000 hydro cycles before failure. This test is done on a new cylinder without corrosion or age issues and is done between 6-10 time a minute until it fails and it must do a minimum of 10,000 cycles. When it fails, it must split and not fragment.

This test ensures virtually all cylinders have the same level of safety regardless of manufacturer. If a cylinder manufacturer overbuilt it's cylinders to a point where they would not fail they could never finish the test.

 

[lamont]

given that there's a lot of experience with overfilling LP cylinders, and most of them pass hydro year after year, it does seem like they're overdesigned and that overfilling (within reason) is reasonably safe. you may be reducing the lifetime of the tank before it fails hydro, but the risk of catastrophic failure seems very minimal.

it seems more like a cost decision than a safety decision and a tradeoff between service pressure and fill cycles. the more you overfill, the sooner your tanks will fail hydro, and the more you'll be spending on replacement tanks.

if we didn't have hydro testing to catch tanks which were marginal, i think it would be a whole different question...

 

[Dan Gibson]

I guess I will being going to jail.

I would not go beyond a 10% overill in a steel tank because it is illegal, ...