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NoTime58
02-20-2008, 08:56
Ok everyone......I'd like to get your preferences and opinions about the pro's and con's of steel vs aluminum tanks, ie: cost, maintenance, durability, weight, and anything else that you can come up with in as far as comparisions. I've only used steel tanks (so far) in my grand total of 23 dives since August 2007 and want the info for reference for possible future purchase. As of now my Misses and I only dive singles and will probably keep it that way. Any info from anyone will be appreciated :smiley20:.

terrillja
02-20-2008, 09:17
Do a search. The comparisons have already been beaten to death pretty much. I have both HP steel cylinders as well as AL80s. One thing you will hear overwhelmingly is that AL100s are hard to trim out properly.

NoTime58
02-20-2008, 09:27
Do a search. The comparisons have already been beaten to death pretty much. I have both HP steel cylinders as well as AL80s. One thing you will hear overwhelmingly is that AL100s are hard to trim out properly.

I have been checking both types of tanks out....what I would like to get from this forum is other divers opinions and personal preferences and why they prefer what they use as opposed to the other. Really simple.....if you don't want to post then don't ........!

Kingpatzer
02-20-2008, 09:33
I like AL80s for shallow warm salt water or fresh water dives where 80 cf is plenty of air and I don't need a lot of weight to get down in the first place.

But for anything where I'm wearing my dry suit (and particularly if I have an undergarmet on as well) I want a steel tank. In those situations, I need so much weight to be negative, that I'd rather help my cause along by having necessary gear be contributing to solving my buoyancy equation not contributing to the postive imbalance.

For tanks bigger than 80, I have limited experience, but I can see the logic behind the view that AL tanks bigger than 80 are difficult, since they can become very light at the end of a dive.

NoTime58
02-20-2008, 09:57
I like AL80s for shallow warm salt water or fresh water dives where 80 cf is plenty of air and I don't need a lot of weight to get down in the first place.

But for anything where I'm wearing my dry suit (and particularly if I have an undergarmet on as well) I want a steel tank. In those situations, I need so much weight to be negative, that I'd rather help my cause along by having necessary gear be contributing to solving my buoyancy equation not contributing to the postive imbalance.

For tanks bigger than 80, I have limited experience, but I can see the logic behind the view that AL tanks bigger than 80 are difficult, since they can become very light at the end of a dive.

Thanks for the info, I'll keep that in mind about the AL80's

No Misses
02-20-2008, 10:58
I just added 2 steel HP120 cylinders to my collection. I have not dived them yet. Hopefully this weekend the seas will be calm.

Current list
2 HP120 (x7-120 Worthington)
4 AL80 (Luxfer)
1 AL19 (Luxfer)

cmburch
02-20-2008, 13:06
The rentals I used were Steel LP95 for me; and my wife could use a LP75 or LP95. Most of the people I dive with have Al80's. I originally purchased 2 Al80's for my wife and I because of price and I did not know any better. I used the Al80 for about 10 years. My buddies still use them. The dive shop had a good deal on steel HP100's and talked me into buying one. The diameters are the same, the weight is about the same 32/33lb, the HP100 is 2" shorter 24" H - Al80 26"H. The buoyancy characteristics are completely different. My Al tanks gouge easier and maybe oxidize easier. I think the fills are about 3000 for Al and 3400 for HP Steel. And there is a LP Yoke vs HP DIN connection. I love the HP100. I've been using it about 9 years. I was able to drop over 5lb off my belt (Big Plus). It seems like I am carrying less weight when hiking down cliffs to get to the water. Everyone is not getting perturbed at me anymore (Big Plus) because we have to surface early because I sucked up all my air swimming up and down, and around all the rocks and boulders looking for a fish to kill. Now I have plenty of air to spare when we surface vs my buddies. For me, a larger capacity tank would not make sense unless I was diving alone or with someone else with a larger tank. The larger steel tanks weigh more (bad for hiking) and I would not use the additional air because I was surfacing with my buddies who have Al80's. I think I can swim up/down/around rocks and boulders easier, but it may just be my perception.

I was thinking about a steel HP119 tank that I could use for LP fills on boat dives and for HP fills for shore diving. Does anyone have experience using the same steel tank for LP and HP? Thanks.

cummings66
02-20-2008, 13:24
I have doubled HP120's and 2 single HP100's soon to be doubled. I have experienced LP (IE short fills) and normal fills on the same tank. There is no problem getting short fills, it is way to easy in fact and certainly won't damage the tank.

I prefer steel tanks except I use AL for stage bottles and pony bottles. I dive dry almost 100% of the time, and since I'll be in doubles from now on more than likely I won't dive my wetsuit again unless I pick up another steel tank.

Why do I use steel? Simple, weight and buoyancy characteristics. In the cold waters I dive you'll most likely have a 7mm all the time and/or a drysuit. That means a lot of lead on a belt which I don't care for because it pulls on you and for me makes me trim out wrong.

Using steel tanks means I can put more of that weight over my lungs which helps trim, it's also one reason I've used a BP for a long time now. Even on singles it makes the trim easier for me.

There isn't a big deal to using AL tanks, it just means you'll have about 4 lbs of extra lead to compensate for the empty tank, and that's not a big deal.

Once under water they all pretty much behave the same, if you do the work and figure the amount of weight you need that is. You could not tell the difference between an AL80 and an HP100 for example.

No Misses
02-20-2008, 13:26
Here is the cf compareson for different fills. Worthington X-Series SCUBA Diving Tanks (http://diveriteexpress.com/gas/steel.shtml)
Cylinder.........2640 psi.....3000 psi.....3442 psi
X7 Steel 80......64 cu. ft......72 cu. ft........80 cu. ft.
X7 Steel 100....80 cu. ft......89 cu. ft.......100 cu. ft.
X7 Steel 120....96 cu. ft......107 cu. ft......120 cu. ft.
X8 Steel 119....95 cu. ft......107 cu. ft......119 cu. ft.
X8 Steel 130...104 cu. ft......117 cu. ft......130 cu. ft.

CompuDude
02-20-2008, 14:27
I like bigger tanks. Bigger tanks means more bottom time. Yes, I can get an hour out of an Al.80 no problem... but why dive an hour when you can dive 2 hours? And Al.100s just suck. So why dive Aluminum? It's cheap. And you don't have to take good care of your tanks. Other than that, I'd rather dive big steel tanks every time. I consider an HP100 to be a minimum. I only dive aluminum during pool sessions, where the shop is supplying the tanks, and when traveling, when I have no big steel option.

Locally in cold water, buoyancy considerations blow Al. tanks out of consideration, even aside from their puny capacity.

Side point, for those who are unaware: An Al.80 tank actually holds 77.4 cf of gas at 3000 psi. Not the "80" cf you would otherwise expect.

NoTime58
02-20-2008, 15:22
I'd like to thank all of you for posting your comments and preferences to this posting. I have a better perspective on these two types of tanks. I'll get a chance to talk to other divers about their preferences once I get to Florida this weekend. Thanks Again everyone !!

SkuaSeptember
02-20-2008, 18:03
While I won't dispute anything the steel tank fans have to say, I will put in a good word for the lowly Al tank. Cost. I've got 6 tanks that I keep filled and never miss out on a dive invite because the shop might be closed and my buddies don't miss out on any dives because I consider an extra tank or three to be part of my save a dive kit.

cummings66
02-20-2008, 18:58
And you don't have to take good care of your tanks.

I don't know about that. A pit that's .03 inches deep will fail an AL tank on the vis. That's pretty shallow and easily done in salt water. Get just a bit in the tank via a sloppy fill and you may very well condemn an AL tank.

I think an AL tank requires the same level of care, perhaps more because of the nature of AL tanks. A very shallow dent can be caused by banging them together and it doesn't take much to condemn them, a dent so small you need to use a straight edge to detect is enough to fail them on a vis. Steel tanks are tougher in that regards.

CompuDude
02-20-2008, 19:18
While I won't dispute anything the steel tank fans have to say, I will put in a good word for the lowly Al tank. Cost. I've got 6 tanks that I keep filled and never miss out on a dive invite because the shop might be closed and my buddies don't miss out on any dives because I consider an extra tank or three to be part of my save a dive kit.

There's no disputing that Al. tanks are the low cost king! Steel can get closer than you might think, however, especially considering their potentially long life span, the rising cost of aluminum, and the used steel tank market.

Once you decide it's worth the cost, however, things change. I can match each of your Al.80s with an HP100 from my collection. You paid less, but I get more BT... and so do the friends I loan tanks to! ;)

Come visit SoCal, dive with me, and you can decide for yourself. :smiley20:

CompuDude
02-20-2008, 19:20
And you don't have to take good care of your tanks.

I don't know about that. A pit that's .03 inches deep will fail an AL tank on the vis. That's pretty shallow and easily done in salt water. Get just a bit in the tank via a sloppy fill and you may very well condemn an AL tank.

I think an AL tank requires the same level of care, perhaps more because of the nature of AL tanks. A very shallow dent can be caused by banging them together and it doesn't take much to condemn them, a dent so small you need to use a straight edge to detect is enough to fail them on a vis. Steel tanks are tougher in that regards.

Perhaps. But I see a rather large number of boats in warm water dive destinations that are filled to the brim with Al.80s that LIVE on the boat... they rarely see dry land. A steel tank stored at sea like that is going to have a very short life indeed. (I'm sure there are exceptions, but you see my point.)

JFH
02-22-2008, 15:53
I think it really depends on your needs. If your just a recreational diver then AL80s are great. If you do technical, spearfish or other specialties the need for added weight and more air come into play. I do multiple drops spearfishing up to a 150ft so the extra air comes into play. The added weight for the winter wetsuits comes in handy also.
I prefer and love AL80s but my style has pushed me towards LP 120s. I will still use the AL80s shallow or during the summer.

cummings66
02-22-2008, 16:47
The only absolute certainty is that a scuba cylinder needs care or it will never last as long as it could.

texdiveguy
02-22-2008, 16:55
Some good replies as usual. I like several have said think both St. and Al. have merit to almost every diver based on their needs. I use St. as back gas tanks only now....and both Al. and St. for deco/stage bottles....Al. for my argon needs. Al. is cheaper than steel but steel will generally last longer with equal care because of the nature of the material.

jeepbrew
02-25-2008, 10:56
I prefer steel tanks in just about any environment. I like them for bounancy characteristics (I can dive w/o any weights when diving with my steel 130s) as well the fact that they hold more air...

cmburch
02-25-2008, 11:45
I prefer steel tanks in just about any environment. I like them for bouncy characteristics (I can dive w/o any weights when diving with my steel 130s) as well the fact that they hold more air...
How do you like your HP130's. I currently have an HP100, but was considering getting an HP130 for easy access shore dives and boat dives. What do you think about the size, weight out of water, and handling in the water? Thanks.

texdiveguy
02-25-2008, 13:00
I prefer steel tanks in just about any environment. I like them for bouncy characteristics (I can dive w/o any weights when diving with my steel 130s) as well the fact that they hold more air...
How do you like your HP130's. I currently have an HP100, but was considering getting an HP130 for easy access shore dives and boat dives. What do you think about the size, weight out of water, and handling in the water? Thanks.

I have a steel PST HP130/H-valved I use for my single tank...it's wonderful! Easy to handle and trim out in the water....course a bit heavy on land but I am used to diving steel doubles so its a relief. Mega amount of gas filled to rated psi and if tech filled it just keeps on going--lol. Great tank for serious sport divers.....doubled up I can't even lift them.

CompuDude
02-25-2008, 13:13
I prefer steel tanks in just about any environment. I like them for bouncy characteristics (I can dive w/o any weights when diving with my steel 130s) as well the fact that they hold more air...
How do you like your HP130's. I currently have an HP100, but was considering getting an HP130 for easy access shore dives and boat dives. What do you think about the size, weight out of water, and handling in the water? Thanks.

I have a steel PST HP130/H-valved I use for my single tank...it's wonderful! Easy to handle and trim out in the water....course a bit heavy on land but I am used to diving steel doubles so its a relief. Mega amount of gas filled to rated psi and if tech filled it just keeps on going--lol. Great tank for serious sport divers.....doubled up I can't even lift them.

Agreed. Although I don't bother with them on land, only boat dives. Shore dives I make do with an HP100 or I schlep the doubles if that's not enough gas.

(I have an HP119, not a 130, but they're close to the same specs)

texdiveguy
02-25-2008, 13:38
I prefer steel tanks in just about any environment. I like them for bouncy characteristics (I can dive w/o any weights when diving with my steel 130s) as well the fact that they hold more air...
How do you like your HP130's. I currently have an HP100, but was considering getting an HP130 for easy access shore dives and boat dives. What do you think about the size, weight out of water, and handling in the water? Thanks.

I have a steel PST HP130/H-valved I use for my single tank...it's wonderful! Easy to handle and trim out in the water....course a bit heavy on land but I am used to diving steel doubles so its a relief. Mega amount of gas filled to rated psi and if tech filled it just keeps on going--lol. Great tank for serious sport divers.....doubled up I can't even lift them.

Agreed. Although I don't bother with them on land, only boat dives. Shore dives I make do with an HP100 or I schlep the doubles if that's not enough gas.

(I have an HP119, not a 130, but they're close to the same specs)

I dive shore sites in my neck of the woods that are pretty much off limits for toting double steels both from the actual hike and water in/egress stand points. The single HP130 is a good option for those.

cummings66
02-25-2008, 19:11
I've hiked 1/10 of a mile with a Steel HP120 and drysuit, even that was not pleasant. I'm going to do that same dive this year in double steel HP120's but I'm going to use a cart of some sort to get the tanks there. No way I'm carrying them that far.

texdiveguy
02-25-2008, 19:16
I've hiked 1/10 of a mile with a Steel HP120 and drysuit, even that was not pleasant. I'm going to do that same dive this year in double steel HP120's but I'm going to use a cart of some sort to get the tanks there. No way I'm carrying them that far.

I have been known to dolly in tanks over terrain that 2 of us to manage the labor on one dolly. I prefer though if the entry and exit are steep/dangerous to use a large steel single. Sometime 'this having fun' is a lot of work!

dmg893
03-09-2008, 18:39
After many years of diving, I feel most comfortable diving with steel tanks, trim and control is the best with steel. good luck

Crimediver
03-09-2008, 21:30
I have a bunch of tanks both steel and aluminum. I like steel. Stay away from AL 100. I have a few of them. I will probably sell them to paintballers one day... They love 'em.

RoyN
03-09-2008, 21:34
I'm ready to get a set of steel soon! :D Time to upgrade now!

BoomerNJ
03-10-2008, 03:10
I am planning on buying a pair of steel HP119's this week from ST... I have dived both & prefer steel though I have only a few dives to judge by. My biggest two points are less weight on my belt & the amount of BT provided by the larger size, plus you don't get that positive buoyancy turn at 500psi when using steel...

jeepbrew
03-10-2008, 08:53
I prefer steel tanks in just about any environment. I like them for bouncy characteristics (I can dive w/o any weights when diving with my steel 130s) as well the fact that they hold more air...
How do you like your HP130's. I currently have an HP100, but was considering getting an HP130 for easy access shore dives and boat dives. What do you think about the size, weight out of water, and handling in the water? Thanks.

I love em. As everyone else chimed in and said, they have great buoyancy characteristics and are easy to trim. If overfilled, they hold a TON of air. I use mine for both shore and boat dives and if I could only own one tank, it would be a steel 130. I will be taking my steel 130 on the Juliet with me again this May.

WD8CDH
03-10-2008, 16:19
I use both. In general, I prefer aluminum for 40cf and smaller and I usually prefer steel for larger tanks. If cost (and the DOT) were no object, titanium would be the best material. I used to dive with a double set of titanium tanks. A titanium ~65cf tank was about the size and weight of an aluminum 30.

What I am really waiting for is 7000 series aluminum SCUBA tanks. 7000 series alloy is about 80% stronger than 6061-T6 so the wall thickness would only need to be 56% as thick for the same pressure. That would give about the same volume as steel tanks but with less weight and better corrosion resistance. Sure, you would have to add a weight to bring them to the same buoyancy as steel tanks but the tank plus the weight would weigh the same as a steel tank but you would only have to carry one weight for multiple sets of tanks. So far, the largest DOT 7000 series tank is 32 cf. I dive a set of quad 7000 series 20s. When weighted to the same buoyancy as an HP80 the rig is about one or two pounds less than an HP 80 but it is much more trim and easier to dive with.

Current tanks:
Triple AL 40s
Double AL 40s
Triple AL 35s
Double AL 35s
Quad AL 20s
Single AL72
Single AL 50
AL 13 pony
AL 14 pony
AL 19 pony
AL 30 pony

Double HP80 steel
Single HP80 steel
Single HP120 steel
steel 20 pony
steel 25 pony

several not really SCUBA carbon fiber tanks

PS, if I only owned one tank, it would be an HP120. If I only owned one rig, it would be the Quad AL20s or the Triple AL40s

cummings66
03-10-2008, 21:25
Where did you find titanium cylinders?

WD8CDH
03-11-2008, 14:11
It was from when I was actually making a living as a comercial diver (back in the 70's). The tanks were made in Russia and had a fill pressure of 500 bar, a little over 7,200psi. The tanks came from Rockwell Aerospace and were intended to be nytrogen accumulators. I used a Posidon regulator on the tanks with no problem. They of course were not DOT and the only place I could get them filled was a research facility that I did some work for. They could pump to 12,000psi. At that time Cousteau was using some 5000psi French titanium tanks.

mark44883
03-11-2008, 14:23
poly carbin there much lighter and hold more psi

skdvr
03-11-2008, 14:25
I would love to see some pics of the Triples and Quads? Do you have any that you can share?

Phil

Gombessa
03-11-2008, 15:52
There's a guy around with an online Cousteau museum with pictures of all manner of triples and quads...pretty far out stuff.

Hollywood703
03-11-2008, 19:47
I use and recommend a HP120, My wife dives an AL80 as I got a killer deal on it, and when we travel thats what she'd have to use....I wont buy a new aluminum.....i would buy steel.

CompuDude
03-11-2008, 19:58
poly carbin there much lighter and hold more psi

It's been tried. Too light, is the problem. They're WAY buoyant. Takes so much lead to sink them there's no point, because there's no savings in overall weight. MORE overall weight, actually.

mark44883
03-11-2008, 22:13
poly carbin there much lighter and hold more psi

It's been tried. Too light, is the problem. They're WAY buoyant. Takes so much lead to sink them there's no point, because there's no savings in overall weight. MORE overall weight, actually.
i'm a big guy :smilie40::smilie39:

WD8CDH
03-17-2008, 07:06
poly carbin there much lighter and hold more psi

It's been tried. Too light, is the problem. They're WAY buoyant. Takes so much lead to sink them there's no point, because there's no savings in overall weight. MORE overall weight, actually.

Too light is not really a problem, you can always add weight. The key is maximum air in minimum volume (i.e. thinnest walls or highest reasonable pressure). If two tanks were the same volume externally and held the same amount of air the lightest tank would be the best one because once weighted to the same buoyancy, they would both weigh the same but you only need to carry one extra weight for the rig that you are diving. You wouldn't have to carry the extra weight for each and every tank. Interspero uses this technique with their carbon fiber SCUBA tanks. You just carry one V weight per diver.

http://www.interspiro.com/_downloads/98607C01_Divator_Lite_product_leaflet_L.pdf


Unfortunatly, there are no DOT approved composite SCUBA tanks available and the availabilty of 7000 series aluminum tanks is very limited so the "lightest" practical choice in the US is steel.

cummings66
03-17-2008, 07:13
Look for a post from me, a long time ago I posted a link to a real scuba tank that was composite. It's real, it's here, it's buoyancy characteristics are actually not bad. I think Luxfer makes it, if I recall right.

Nobody I know has one, never even seen one, and deny they're made until they see the tank specs from luxfer. It's like a ghost, you'll never see one in captivity.

Thanks for the interspiro post, I've been looking for that flyer. My LDS has one and I wanted it too.

I found the link, here it is.
http://www.luxfercylinders.com/news/releases/20021022b.shtml

in_cavediver
03-17-2008, 11:09
poly carbin there much lighter and hold more psi

It's been tried. Too light, is the problem. They're WAY buoyant. Takes so much lead to sink them there's no point, because there's no savings in overall weight. MORE overall weight, actually.

Too light is not really a problem, you can always add weight. The key is maximum air in minimum volume (i.e. thinnest walls or highest reasonable pressure). If two tanks were the same volume externally and held the same amount of air the lightest tank would be the best one because once weighted to the same buoyancy, they would both weigh the same but you only need to carry one extra weight for the rig that you are diving. You wouldn't have to carry the extra weight for each and every tank. Interspero uses this technique with their carbon fiber SCUBA tanks. You just carry one V weight per diver.


Not quite. If two tanks were the same physical volume and held the same amount of air but different only in empty out of the water wieght, then you have to look carefully at the buoyancy figures. (your rig plays into optimal choice here) For instance, 2 tanks, 1 is 4lbs positive the other is 2lbs negative. If you need 6lbs of weight (no tank) to be neutral, with one tank you add 4 more lbs where the other lets you shed 2lbs of wieght. In this case, the heavier tank translates to a 6lb lighter rig. If you needed 0lbs of wieght, you would be overwieghted by 2lbs with the heavier tank whereas the lighter tank would allow you to carry ditchable weight. Different optimums based on your specific gear.

Still, small volume high pressure tanks would be nice. (except I would want large volume high pressure tanks - say double 200's or 250's....)

CompuDude
03-17-2008, 15:28
Look for a post from me, a long time ago I posted a link to a real scuba tank that was composite. It's real, it's here, it's buoyancy characteristics are actually not bad. I think Luxfer makes it, if I recall right.

Nobody I know has one, never even seen one, and deny they're made until they see the tank specs from luxfer. It's like a ghost, you'll never see one in captivity.

Thanks for the interspiro post, I've been looking for that flyer. My LDS has one and I wanted it too.

I found the link, here it is.
http://www.luxfercylinders.com/news/releases/20021022b.shtml

Joel, the owner of TDL, has a couple of the composite tanks. IIRC, he says he tried them a few times and didn't care for them.

In the real world, however, even ignoring the issue of needing a ton of lead to sink the tanks, it's going to be tough to find a shop who is willing to run their compressor hard enough to fill a 4000-4500+ psi tank. I realize Florida is a little different, but around here, it's hard enough convincing them to hot fill your 3500psi tank to 3800 so it cools to a reasonable pressure. And as for boats with compressors, there are precious few that can actually deliver 3500 psi, let alone more than that, so one dive and you're stuck with 3300psi fills (or worse, on some boats).

So seriously... what's the point of owning these tanks, unless you have access to someone else's $60k fill station that will fill them for you without question?

cummings66
03-17-2008, 20:00
What happened to the webpage, it was there this morning.

As I recall, they essentially had the buoyancy characteris of an AL80, it was not a cylinder that needed a lot of lead to make neutral, far from it in fact. They are 3 lbs positive empty. Not too bad is it? It certainly doesn't need as much lead as an AL80 would and aside from the fill pressures and cost it's a pretty decent tank.

WD8CDH
03-18-2008, 06:57
poly carbin there much lighter and hold more psi

It's been tried. Too light, is the problem. They're WAY buoyant. Takes so much lead to sink them there's no point, because there's no savings in overall weight. MORE overall weight, actually.

Too light is not really a problem, you can always add weight. The key is maximum air in minimum volume (i.e. thinnest walls or highest reasonable pressure). If two tanks were the same volume externally and held the same amount of air the lightest tank would be the best one because once weighted to the same buoyancy, they would both weigh the same but you only need to carry one extra weight for the rig that you are diving. You wouldn't have to carry the extra weight for each and every tank. Interspero uses this technique with their carbon fiber SCUBA tanks. You just carry one V weight per diver.


Not quite. If two tanks were the same physical volume and held the same amount of air but different only in empty out of the water wieght, then you have to look carefully at the buoyancy figures. (your rig plays into optimal choice here) For instance, 2 tanks, 1 is 4lbs positive the other is 2lbs negative. If you need 6lbs of weight (no tank) to be neutral, with one tank you add 4 more lbs where the other lets you shed 2lbs of wieght. In this case, the heavier tank translates to a 6lb lighter rig. If you needed 0lbs of wieght, you would be overwieghted by 2lbs with the heavier tank whereas the lighter tank would allow you to carry ditchable weight. Different optimums based on your specific gear.

Still, small volume high pressure tanks would be nice. (except I would want large volume high pressure tanks - say double 200's or 250's....)

Hi Cavediver,

If two tanks had the same exterior volume and the same air capacity but different weights, their buoyancy differances would be the same as the differance in weight. So once weight was added to the lighter tank, the total weight would be the same. Plus, as I mentioned before, you only need to carry one extra weight per diver that is underwater, not one for each rig. That can add up to a lot of total weight savings if you are taking tanks for multiple dives.

If you want lot's of air in a small OC rig, you would have loved my old titanium tanks. I could fit almost 160 CF (two tanks) in a briefcase and still have room for my lunch and mask.:icon_smile_big:

cummings66
03-18-2008, 07:17
The page is working again, so here's the specs, the 4350 psi tanks are the composite ones. It appears that the 106 is the only one left now. Same as the AL80 but has more air, not a bad deal IMO, except for fill pressure.

http://www.luxfercylinders.com/products/scuba/specifications/us_imperial.shtml

in_cavediver
03-18-2008, 11:30
poly carbin there much lighter and hold more psi

It's been tried. Too light, is the problem. They're WAY buoyant. Takes so much lead to sink them there's no point, because there's no savings in overall weight. MORE overall weight, actually.

Too light is not really a problem, you can always add weight. The key is maximum air in minimum volume (i.e. thinnest walls or highest reasonable pressure). If two tanks were the same volume externally and held the same amount of air the lightest tank would be the best one because once weighted to the same buoyancy, they would both weigh the same but you only need to carry one extra weight for the rig that you are diving. You wouldn't have to carry the extra weight for each and every tank. Interspero uses this technique with their carbon fiber SCUBA tanks. You just carry one V weight per diver.


Not quite. If two tanks were the same physical volume and held the same amount of air but different only in empty out of the water wieght, then you have to look carefully at the buoyancy figures. (your rig plays into optimal choice here) For instance, 2 tanks, 1 is 4lbs positive the other is 2lbs negative. If you need 6lbs of weight (no tank) to be neutral, with one tank you add 4 more lbs where the other lets you shed 2lbs of wieght. In this case, the heavier tank translates to a 6lb lighter rig. If you needed 0lbs of wieght, you would be overwieghted by 2lbs with the heavier tank whereas the lighter tank would allow you to carry ditchable weight. Different optimums based on your specific gear.

Still, small volume high pressure tanks would be nice. (except I would want large volume high pressure tanks - say double 200's or 250's....)

Hi Cavediver,

If two tanks had the same exterior volume and the same air capacity but different weights, their buoyancy differances would be the same as the differance in weight. So once weight was added to the lighter tank, the total weight would be the same. Plus, as I mentioned before, you only need to carry one extra weight per diver that is underwater, not one for each rig. That can add up to a lot of total weight savings if you are taking tanks for multiple dives.

If you want lot's of air in a small OC rig, you would have loved my old titanium tanks. I could fit almost 160 CF (two tanks) in a briefcase and still have room for my lunch and mask.:icon_smile_big:

Your right. I missed the same exact dimensions bit in my thought process. My mind was stuck in the steel is smaller than AL for same capacity mindset. So rare to think of identically sized tanks since we can't get them in the context of diving.

In the end, though, we can all agree the smaller the tank volume for a given air capacity, the smaller the displaced water will be and the 'lighter' the tank can be out of the water and be neutral.

As for the weights - you'll never achieve one weight per diver since divers and exposure protection vary significantly. You'll still need the standard weights to make the diver neutral with no tank. Then add the weight for the tank. Sometimes I think it would be nice to teach weighting as a tank independent measure rather than simply total weight needed.

And you right - I'd have loved the small Ti tanks that held 160cft in a briefcase. Figure about 6 of them for a nice long dive....... 320cft going in, 320cft going out and 320cft in reserve. Yea - Nice long dive.....

WD8CDH
03-21-2008, 13:08
I would usually dive with them as triples. Two were manifolded and the third was independant. Two Poseidon regulators with independant shutoff on the manifolded pair. No isolator valve. Third Poseidon on the independant reserve tank. I used these tanks a lot on confined space diving.

I usually prefer a non-isolated manifold except sometimes on triples I like an isolator valve between tank 2 and tank 3. I would open or close the isolator depending on the dive plan. For most dives the isolator would be closed and the third tank would be a redundant air supply. On shallow but long down time dives, the isolator would be open and I would carry a smaller 4th tank reserve.

cummings66
03-21-2008, 13:29
What's your reason for no isolator? I know it's how it used to be and it's not the current preferred method, but I'm curious why you prefer it now.

WD8CDH
03-26-2008, 11:10
What's your reason for no isolator? I know it's how it used to be and it's not the current preferred method, but I'm curious why you prefer it now.

There are pros and cons to either.

The isolator allows you to save 1/2 of the remaining air if you blow a tank o-ring. But, I have NEVER seen a tank o-ring blow that couldn't have been seen as a gap between the valve and tank neck.

Some of the problems with an isolator that I have seen are:
1. Isolator closed durring a fill and only getting a 1/2 fill.
2. Isolator closed durring a dive causing diver to run ot of air early.
3. Isolator stem leaking.
4. Isolator not shutting off compleatly.


With a non-isolator there are less mechanical failure points and less operator error faults while still having the ability to shut off the most common failure, a regulator failure.

Since I always carry sufficient redundant air (usually 1/3), I am still covered for the very rare tank o-ring failure.

cummings66
03-26-2008, 14:43
OK, normal choices, I respect that.

doczerothree
03-26-2008, 15:06
End of dive bouyancy, quanity of breathing gas in smaller cylinders. They cost more. durability? I have dual 95's for 8 years and a set of 112's I've had for 5-6 years. (LP Fabers.) deco: use aluminum. :smiley2:

WD8CDH
03-26-2008, 15:44
OK, normal choices, I respect that.

If I have the choice, I will pick non-isolator. If I don't have a choice, I will accept an isolator without much worry. It's a somewhat close choice to me.