gearing up for fundies

[pants!]

I don't claim to be DIR, but the correct tank is the one that provides you with a balanced rig. In some cases, the AL80 is absolutely the correct tank. In other cases, the Steel LP104 is the correct tank.

What I have read on more than one occasion, is that the HP Steel tanks tend not to be favored. Apparently there is some feeling that the very high pressure of the gas in the tanks, causes undue strain on gear (manifolds, first stages, etc.) so low pressure steels tend to be favored. Also, their size is favorable so that you don't have to pump them up to get a good amount of gas in the tank.

Total bull! Modern first stages are designed with working pressures of that type. Furthermore, as E- and X- and whatever 3442 psi cylinders become more and more popular, LP tanks are slowly disappearing.

There's no reason to buy an LP 95 when you can get an E8-119 or X8-119 that's the same size and weight but holds 20cf more gas at its rated pressure, and doesn't need a + rating!

 

[pants!]

piikki, if higher pressure were that much more failure inducing, cavers wouldn't pump their LP tanks up to 4000 psi to do serious penetrations.

Also, in Europe, "high pressure" is 300 bar... which is over 4000 psi! Standard 200 bar tanks are over 3000 psi as well.

 

[Derek S]

Yes...The ones that match your snorkel.

Thank you Jeff, I needed that.

 

[JeffG]

Thank you Jeff, I needed that.

I aim to please.

 

[PerroneFord]

It may well be bull. Like I said, I am not a DIR diver, and don't claim to be. If you have "the blue book", please refer to comments on P95 in regards to choosing a cylinder. There are other concerns with HP tanks as I understand it that relate to PP mixing and gas laws. Since I am not a gas blender, I'll let someone with more experience tackle the issue, but the jist of it seems to be that as pressure increases inside the tank, the accuracy of the fill becomes harder to achieve with common equipment. Again, this may not be correct, but it is my layman's understanding.

In regards to buying a E8 tank, there is most certainly a reason to favor buying an LP95. The cost gap is nearly $100! Maybe not an issue for you, but it sure is for me!

And burning up that 120 cuft tank is going to put me into mandatory deco. Which means that I have a de-facto overhead and need to be redundant. If I need to be redundant, then I am going to be on doubles. So now I need TWO steel tanks, a manifold, and a new wing. If I am diving steel doubles, I am going to be at least 20 pounds negative at the start of my dive, and doing that with a wetsuit is asking for trouble. So now I need to dive dry. It's a waterfall effect as I see it.

Total bull! Modern first stages are designed with working pressures of that type. Furthermore, as E- and X- and whatever 3442 psi cylinders become more and more popular, LP tanks are slowly disappearing.

There's no reason to buy an LP 95 when you can get an E8-119 or X8-119 that's the same size and weight but holds 20cf more gas at its rated pressure, and doesn't need a + rating!

 

[piikki]

pants:
>>Total bull! Modern first stages are designed with working pressures of that type. Furthermore, as E- and X- and whatever 3442 psi cylinders become more and more popular, LP tanks are slowly disappearing.
There's no reason to buy an LP 95 when you can get an E8-119 or X8-119 that's the same size and weight but holds 20cf more gas at its rated pressure, and doesn't need a + rating!<<

>>piikki, if higher pressure were that much more failure inducing, cavers wouldn't pump their LP tanks up to 4000 psi to do serious penetrations.
Also, in Europe, "high pressure" is 300 bar... which is over 4000 psi! Standard 200 bar tanks are over 3000 psi as well<<

I am relieved to hear these tidbits… (awaiting the inevitable BUT). When I was buying tanks I was not too educated but I sure knew I was not going to be diving for long if I had to dive Al and drag all that extra weight around my waist. So steel it was, and my LDS basically stated that they do not understand why ‘anybody’ would buy LP anymore when the price difference is so minimal (no he aint no techie that is for sure but I had not even heard of technical diving at that time).

Since I’ve lived most of my life in Europe, DIN would have been my choice even if I didn’t opt for HP. I knew I wouldn't be able to haul two tanks unless some medical miracle, so I went for HP to get some air out of my tanks. Boy, I would not want to hear I maxed my chances of gear failures because of the pressure in’em! I did study my reg – I wan’t to attach it to those 5000 PSI nice little yellow Poseidon tanks back at home The guy in the shop assured my stuff is compatible, and I didn't find anythign stating the opposite at the time.

I can’t imagine I ever do but air and nitrox either. Now, this summer steel’s been in short supply and since I wanted to dive THIS summer I had limited choice. Now I realize there are quite a lot of differences between HP 80s even! Or better said – now I understand the differences slightly better than when I first read them without any dives under my belt…

I do anticipate though that if I turned up to fundie course with wetsuit and HP tank, I might get whupped...

 

[PerroneFord]

I don't think turning up to fundies with a wetsuit and a single HP tank would be a bad thing. A single steel tank is not THAT much heavier underwater than an AL80 when both are full. Maybe 5-7 pounds, which means that in temperate waters, it'll reduce your weightbelt nicely. It's when you start to dive doubles that I think the problems occur as you can be VERY negative 8-12 pounds negative per tank, 6 pounds on the plate, a pound on the manifold, jet fins, primary light, etc. You can be 30-40 pounds negative. A buoyancy failure early in the dive could be somehwhat problematic, especially with a deep bottom under you.

Again, I don't think the idea of DIR says "You cannot use HP tanks", because you may weill have an HP tank and only use 3000 PSI in it. Nothing wrong with that at all. To me, the practical problem comes in at some of these local sites where you show up with your small, 120 cuft tank that needs 4000psi to have that volume, and the shop can only push 3100 psi. Now how much gas are you getting? And if you frequent these kids of dive sites regularly (like the springs here in N. FL.), you've spent a lot of money on a tank that give you no more volume than a common AL80.

That LP95 or E7100 sound very good to me both as singles and doubles.

 

[wedivebc]

To me, the practical problem comes in at some of these local sites where you show up with your small, 120 cuft tank that needs 4000psi to have that volume, and the shop can only push 3100 psi. Now how much gas are you getting? And if you frequent these kids of dive sites regularly (like the springs here in N. FL.), you've spent a lot of money on a tank that give you no more volume than a common AL80.

in your example the tank would hold 13cf more.

 

[PerroneFord]

Ok,

With the HP120 hovering around $350-$379, and AL80s around $139-$159, an extra 13cuft just cost me ~$200. Is that good? Now please don't start thinking that I am anti-HP Steel. They have their place just like other tanks do. For *MY* purposes, diving wet with doubles, AL tanks make a lot more sense. For those of you diving dry, or those of you in caves, steels make a lot more sense.

I think I'll end up with a set of AL doubles, a set of steel doubles, and probably just a single steel tank as an all purpose tank. Probabably a few stage/deco tanks as well.

 

[JimC]

From what I have seen these are the "DIR" tanks of choice:

AL 6 or 12 or 18? - Used for drysuit inflation
Luxifer AL40 - Used for deco gas
Luxifer AL80 - Used for deco gas, travel gas and stage gas. Also used for singles or doubles in wetsuits.
PST LP 104 or PST E8-130 - Used for most back gas applications in a dry suit.
PST LP 120 - Used to sandwich an RB80

Keeping the list small makes team gas plans a LOT easier since everyone has the same tanks. I wouldn't by a tank not on this list unless I had a very clear reason not to because they cover basically every application I can think of well.