Steel tank ?..again

[o2diver]

Sorry Jon, Rick, Yes I agree with you on the weight difference. I guess my point was more that it would be better for warhammers other half to wear the weight on her back than on her hips. Choosing the steel would put the weight on her back, choosing the AL would put the weight on her hips.
Sorry for the confusion.
o2diver

 

[Ladydiver]

Ok peeps,

I have been thinking about investing in a steel tank for the same reason Warhammer is thinking of getting one for his better half. I have a hard time handling the weight of the AL80 plus what I have to wear on my belt to be neutral at the end of the dive.

I understand the neutrality benefits of using a steel instead of an AL. Where I get confused is when it comes to the different sizes and the HP vs. LP information.

Can someone please explain the differences and the benefits or drawbacks of each.

Thanks for the help.

Cheers,

 

[Rick Murchison]

In general, for any given capacity (filled capacity, not internal volume) e.g. 80CF...
Both have excellent buoyancy characteristics (they sink)
HP tanks are lighter and smaller than LP tanks.
LP tanks can use yoke or DIN adapters; HP tanks require DIN.
LP tanks can be filled anywhere; HP tanks can be filled most places.
HP tanks cause more wear & tear on your regulator first stage.
So, if weight per CF is the main consideration then the HP is the way to go. I prefer LP myself because I can fill 'em with my little portable compressor on site and they're easier on the equipment.
Rick

 

[Warhammer]

I'm probably not the best one for this, but I'll give it a shot.

HP steels tend to be smaller in size, weight less, and have more negative bouyancy than an Aluminum tank of the same size. That takes a load off your back and belt! There draw back is that unless you have a place that can fill them to their rated pressure, you loose a good bit of air. For example, a Catalina AL80 holds 77.4cf of air when filled to 3000PSI, a Pressed Steel HP80 holds 82.1cf when filled to 3500PSI but only 70.4cf when filled to 3000PSI. So if you get a short fill, it has more effect. Also with HP steels you have to use a DIN fitting vs Yoke. That's not a bad thing, but since most rentals that you'd use on vacations would be Yoke, you'd have to either afix an adapter or have another reg with a Yoke fitting. Some people don't like the adapters and that's one of the things my wife will have to see for herself before making a final decision.

LP steels tend to be heavier, larger, and have less negative bouyancy than HP steels but more than AL tanks. They also have a lower pressure rating (usually 2400PSI + 10%, making it 2640PSI) that can be filled to capacity almost anywhere. And in alot of cases "overfilled" to give you more air for the same rated volume than HP or AL. For instance, compared to a HP80s 82.1cf @ 3500PSI and an AL80s 77.4cf @ 3000, the LP80 would have 91.6cf @ 3000PSI. Course at the same time it would be overfilled by 360PSI. The fact that they have more cf of air per PSI is what makes them so popular for cave divers. They also tend to be Yoke, with some exceptions, espeacially for cavers.

AL aluminum tanks tend to be heavier than and larger than HPs, but smaller and lighter than LPs, while at the same time have positive bouyancy, (with a few exceptions) when empty, compared to an HP or LP's negative bouyancy. But they are the most common found in the US and are usually always Yoke.

 

[Warhammer]

I meant to post this link, but forgot. Diverlink has a great chart on the various tanks available with up to date specs. Check it out:
http://diverlink.com/gear/tanks.htm

 

[Ladydiver]

Ok, so let me make sure I am getting this straight.

An LP is lighter than an AL but heavier than an HP and more negatively buoyant than an AL but less than an HP.

I would probably be able to use the first stage I currently have with and LP but not and HP. I would also be able to get an LP filled practically anywhere and filled at least to the correct capacity or even "overfilled", which would mean greater bottom times based on air consumption. With an HP, I would have to be more diligent in making sure the place where I get my fills could do it properly.

So with an LP I probably wouldn't get the benefit of losing the weight from my belt like I would with the HP, but I could possible gain the benefit of additional air.

So, for my purpose, I would be better off going with an HP even though I would have to purchase either another reg or an adaptor.

Did I get that right?

 

[Warhammer]

Nope...An LP is heavier than an HP or AL for the same capacity tank. Here's how it would break down for me with an HP80, LP80, and AL80:

With an AL80 I require 10lbs of lead to be neutral with 500PSI in salt water. The AL80 weighs 31.6lbs when empty and 37.8 when full, giving me a total weight of 47.8lbs (tank + lead) when full.

With a Pressed Steel HP80, I'd require 3.5lbs of lead to be neutral @ 500PSI, due to the HP80 having a -2.5lb bouyancy when empty vs the AL80's +4.1. The HP80 weighs 26lbs when empty and 32.4 when full. So I'd have a total weight of 35.9lbs when the tank is full. That's nearly 11lbs lighter than the AL80!

With a Pressed Steel LP80, I'd require 6.5lbs of lead to be neutral @500PSI, due to the LP80s +0.5lb bouyancy when empty. The LP80 weighs 32lbs when empty and 38.4lbs when full. So I'd have a total weight of 44.9lbs. That's still 3lbs lighter as a whole than the AL80, but a long ways from the HP80 setup. That's even with the LP80 weighing a tad more than the AL80 by itself.

If loosing weight is your main goal then HP is the way to go. If you want more potentional air for about the same weight, then LP is the way to go. Course that's only if you overfill and that's a whole other can of worms. And you also have to consider the weight of the air, so if your overfill that LP80 it will end up weighing slightly more than the AL80. FYI, air weighs approximately 8/100s of a pound per cubic foot. And all tanks are different wih different characteristics, so it will take some figuring and research to find out which one suits you the best.

 

[Ladydiver]

Thanks so much for the great explanations and for your patience. I think I understand now and, as Warhammer said, I will be doing some more research and figuring before I make my purchase.

Cheers,

 

[Iguana Don]

LD,

Unless you are using a regulator from the Lloyd (Bow and face the West) Bridges era, all modern high quality regulators will handle the increased air pressure. If they wouldn't they wouldn't be offered in DIN.

I think there is a misconception when it comes to "additional wear and tear" on your regulator, if that was a problem, wouldn't the manufacturers advise agianst using H/P tanks so as to reduce their liability? Also if you have it serviced on a regular basis, there shouldn't be any problems whatsoever.

As for the adaptor, you could go back to the shop where you purchased it or maybe Rainreg, could do it for you, and order a DIN 1st stage housing. Would be a lot cheaper than buying a whole new reg.

ID

 

[Warhammer]

I here that a new Yoke fitting that is good up to 3500PSI is just around the horizon. That may eliminate the need for DIN altogether. I'm not so sure that's a good thing, but then again, I've turned my air on several times to find I had as much as 3400PSI in an AL80 with a Yoke fitting.