What's the biggest standard tank size?

[fisherdvm]

The biggest tank I know of is the LP120 which when filled to 3800psi holds 173cf of air. I actually have two of these doubled which gives me about 350cf of air. They are heavy though, when filled to 3800psi they are roughly 15lbs negative each, and weigh ~55lbs each when empty.

Wow, that's like filling them pass their usual hydro pressure! Do you use burst disk rated for 4000 psi or something? I imagine that this will greatly decrease the life of the tank, and perhaps you'd have to hydro them more frequently than every 5 years.

 

[marchand]

Actually it is 200psi short of hydro pressure, and I have two 3500psi (service pressure) disks on each tank. As far as life of the tank goes, I might be decreasing it from forever to only a few lifetimes.

Overfilling LP tanks is a widely accepted practice in my neck of the woods, and has been shown to have very little if any negative effects on the tanks.

 

[fisherdvm]

Marchand, does it also explain why almost all of the tanks that've exploded were found in Florida in cave diving land?

 

[battles2a5]

I've never heard of a LP steel tank exploding. The only times I have ever heard of blown tanks are w/ AL80s. And proportionally speaking, there are probably a lot more AL80s in FL then there are in other parts of the country. The rest of the world routinely fills our "LP" tanks to high pressures (4000psi) without issue. The LP ratings are a DOT thing, not a manufacter's limit.

As for the big Fabers being bouyant when empty, they most certainly are. The LP108/FX133 and LP120/FX149 are bouyant when empty. They are larger tanks by volume than a Worthington or PST. They are also rolled, not drawn so they do not have the thick bottoms of the others. So the combination of the two makes them pretty "light" tanks in the water.

 

[marchand]

Marchand, does it also explain why almost all of the tanks that've exploded were found in Florida in cave diving land?

Do you have any evidence to back up that statement? Even if there were such evidence, it would also show that almost all of those tanks were made out of Al alloy 6351. Unlike steel aluminum fatigues, looses strength and eventually fails; this is accelerated under higher loads. During the engineering process the fatigue rate of steel is not is hardly considered, as long as there is enough steel to contain a pressure it does not mater how may times it is filled to that pressure.

 

[teknitroxdiver]

Heiser 190s are the biggest made in the past. 4400 psi service pressure, 31" tall, 87lbs out of water, -46lbs negative empty, -62lbs negative full. That's a serious tank right there. Interestingly enough, it's physically not an especially large tank.

 

[marchand]

I heard of a guy that doubled up some 190's and ended up killing two other people besides himself. Took one with him to the bottom and got the other bent.

 

[WD8CDH]

Do you have any evidence to back up that statement? Even if there were such evidence, it would also show that almost all of those tanks were made out of Al alloy 6351. Unlike steel aluminum fatigues, looses strength and eventually fails; this is accelerated under higher loads. During the engineering process the fatigue rate of steel is not is hardly considered, as long as there is enough steel to contain a pressure it does not mater how may times it is filled to that pressure.

Steel fatigues too but not as fast as the old 6351 aluminum alloy. A 6061 aluminum alloy will handle over 100,000 fills and a 7000 aluminum alloy will handle even more.

 

[fisherdvm]

Do you have any evidence to back up that statement? Even if there were such evidence, it would also show that almost all of those tanks were made out of Al alloy 6351. Unlike steel aluminum fatigues, looses strength and eventually fails; this is accelerated under higher loads. During the engineering process the fatigue rate of steel is not is hardly considered, as long as there is enough steel to contain a pressure it does not mater how may times it is filled to that pressure.

I was told that by a cylinder inspector. But when I checked out the data on DOT's report, 6 of 13 reported cases were in florida, confirming his assertion that it is more common down there (also probably more people dives down there). Most of the failure were aluminum tanks.

So you might be very well correct in that steel tank are more reliable in overfills than aluminum. And, if not corroded, might actually last longer??

 

[SCUBAholicEd]

OK, here is the scoope on the biggist tank. I have been diving for 30 years. I'm a big guy and I simply use more air than little people and long distance runners. I got my whole family into diving and all the men use HP 130s and the Faber FX149 also an HP. HPs are filled to 3445. I also use a 19 cuft pony bottle instead of an octo. Yes they are heavy out of the water, but we all can walk around with them and we can climb out of the water on an 8 foot ladder to the deck several times a day while diving from the graet excape dive boat.
I love diving steel tanks. The key is proper weighting. at the end of your dive check your weighting. with 300 to 400 psi [remember these are big tanks] you should be at eye leveal with all the air out of your BC. So at the start of your dive you'll be alittle neg and be neutral at the end. Like I said, we all [10 of us] use the big tanks and love them. I dive 50 to 100 dives a year. As a 6 foot 250 pound man, a big steel tank is the only way to go. If you want to talk more about the big tanks eheiser@amerifirstloan.com I'd be glad to share more info. ED