If these are charter boats you're mostly doing, many include AL80s in the fare.
When to buy tanks?
- Thread starter thomasj1107
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thomasj1107
Contributor
What is a “good deal” on steel 100s these days? And if I’m going to use for nitrox should I just wait til I’m ready to fill with nitrox so I’m not switching back and forth
Price is around $350 for the painted version if you can find one and around $400 for hot dip galvanized. This normally includes the valve and a boot, but not shipping.
Nitrox doesn't factor into it. Air fills are just as clean as nitrox fills at any place that does both.
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thomasj1107
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thomasj1107
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Also… when looking at tanks, they have an LP and a HP in the steel fabers. Why would I want one vs the other?
broncobowsher
Contributor
Nitrox to air and back, no problem so long as the air is clean. Just get a 21% Nitrox fill.
Unless you live in an area (Florida) that they will do a 'cave fill' the LP tanks won't hold as much as the HP tanks. Considering that most dive shops in the 49 normal states only fill to the rated pressure, you are throwing away a lot of capacity. The HP tanks will hold more air since they are filled to a higher pressure. They cost a little bit more and are a touch heavier. But since you live in Florida, the LP tank and just get it overfilled. Works great so long as you stay local. There is also the issue that some shops don't have the limit switch set correctly for a HP fill, they are set to do AL80s and 3000 PSI is all you are going to get out of them.
Unless you live in an area (Florida) that they will do a 'cave fill' the LP tanks won't hold as much as the HP tanks. Considering that most dive shops in the 49 normal states only fill to the rated pressure, you are throwing away a lot of capacity. The HP tanks will hold more air since they are filled to a higher pressure. They cost a little bit more and are a touch heavier. But since you live in Florida, the LP tank and just get it overfilled. Works great so long as you stay local. There is also the issue that some shops don't have the limit switch set correctly for a HP fill, they are set to do AL80s and 3000 PSI is all you are going to get out of them.
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thomasj1107
Contributor
In other places, besides Florida, do they not overfill a HP tank by the same percentage as an LP is overfilled? Or is that not possible?
I guess I’m asking why is one overfilled routinely in a certain place but the other is not?
Why were two different types even made, what was the goal?
Yeah, it's complicated. Many places (outside of FL) will only fill an HP tank to 3000 psi (because that's what their compressor is set at for aluminum tanks and they don't know the difference). Not many places will knowingly overfill anything. My VERY non-comprehensive survey says most of cave country in FL and a few places around the Great Lakes will fill an LP tank to 3300-3800 psi. The one place on the FL coast (Key Largo) I've been to used AL tanks (perhaps because of the reduced maintenance with salt water), and I was lucky to get 3100 psi when I distracted the guy filling the tanks. I suspect the HP steels are treated the same in cave country (nicely overfilled).
You should understand that an LP85 and an HP100 is very nearly the same volume tank -- they only seem different due to the naming convention in the US. An HP100 holds 100 cuft at its service pressure of 3442 psi. An LP85's holds 81.1 cuft at its service pressure of 2640 psi, but it holds 103 cuft at 3442 psi. The HP100 is about 3 lbs less buoyant.
There is usually a slight premium for HP100s, which basically gives you license to complain of an underfill rather than have to bring doughnuts for the privilege of an overfill.
You should understand that an LP85 and an HP100 is very nearly the same volume tank -- they only seem different due to the naming convention in the US. An HP100 holds 100 cuft at its service pressure of 3442 psi. An LP85's holds 81.1 cuft at its service pressure of 2640 psi, but it holds 103 cuft at 3442 psi. The HP100 is about 3 lbs less buoyant.
There is usually a slight premium for HP100s, which basically gives you license to complain of an underfill rather than have to bring doughnuts for the privilege of an overfill.
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thomasj1107
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So if they were both to be overfilled the same percentage (for lack of a better term) then the 100 will still hold more than the 85, it’s just less likely for a place to overfill a HP as compared to an LP?
Why are there even two different types? Is there a specific function or intent of either type?
To break it down simply, At the same pressure, they hold the same amount of gas. If both tanks are filled to 3600 psi, you have the same volume of gas to use. The issue stems with an LP tank is rated at a lower pressure, so if filled "correctly," it holds less gas.
The reason for the two different styles has to do with costs and the DOT.
DOT regulates pressure vessels in the United States. If you want to manufacture tanks, you have a few ways to do it. One is use an established method, you make a tank that meets the requirements for a DOT-3aa pressure vessel. Submit them for testing and evaluation, and start manufacturing tanks. This gives you the ability to quickly and cost effectively manufacture tanks for sale. It also limits what you can make them out of, what wall thickness, weight for a given pressure, lots of things.
The other way is to design an exemption tank. You engineer it, submit it for testing, lots of testing, and submit a proposal for a special exemption from the DOT. They don't have to accept it, even if the tank is good. At that point, you can start making tanks, but it isn't over, you have to renew that exemption every so many years or every tank you ever made under that exemption becomes ineligble for retesting.
Exemption (HP) tanks cost more to design, produce, and keep active. They are also a better scuba tank in that you can get them filled to their rated pressure anywhere, not just a few places in the United states.
I know that is a lot, but we are just starting down this rabbit hole. If you have any more tank questions, feel free to ask.
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