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Scuba Forum / Scuba Equipment / July 2004AL vs. Steel tanks
i have been diving for allmost 1 year now and i want to buy my own tank mainly so that we dont have to be back to the dive shop before they close to return it. I was just wondering what would you guys recomend. I do mainly fresh water diving. One of are friends that we usually go with has a AL 80 and me and my brother just arnt sure what to get. i would kind of like a bigger one because me and my brother both are bigger and use a little more air than the average person. Im about 6'2" and weight about 250 lbs. I was just wondering what would some of the pros/cons of AL vs. Steel and how big of a tank would be to big? I know some of the steel are HP and i can switch my regs over to DIN for about $50 so that wont be a problem. thanks for any info you can give me. Justin Expense is a minor point... it's the "weight at end of the dive" one remains boyant one isn't. Your dive instructor should have gone over all this with you. >i have been diving for allmost 1 year now and i want to buy my own tank >mainly so that we dont have to be back to the dive shop before they close to [quoted text clipped - 15 lines] > >Justin --- Remove x's to send. > Expense is a minor point... > it's the "weight at end of the dive" one remains boyant one isn't. > > Your dive instructor should have gone over all this with you. Which does not answer his question and depends on the tanks themselves. Some steel are positive when empty and some Al are negative. For the most part the difference in most places either adds to or subtracts from the weight belt. Perhaps you shoud review what your instructor said. > >i have been diving for allmost 1 year now and i want to buy my own tank > >mainly so that we dont have to be back to the dive shop before they close to > >return it. There are to many variables to answer your question. However if you spend a lot of time and money at the shop I'd just ask them to let you keep them over night if it makes sense for you. If you are looking at higher pressure make sure the shop can and will fill to the higher pressure. There are lots of shops that will overfill tanks for you to get in a little extra time. http://www.mikepainter.com/dotletter.pdf is a letter that explains that DOT really does not care what you do with a cylinder. >"Josh Assing" <xjoshx@jassing.com> wrote in message >> Expense is a minor point... [quoted text clipped - 6 lines] >For the most part the difference in most places either adds to or subtracts >from the weight belt. Nevermind the fact that what the instructor says can hardly be assumed to be accurate. Sometimes the answer is dictated by the brands stocked by the dive shop. >> >i have been diving for allmost 1 year now and i want to buy my own tank >> >mainly so that we dont have to be back to the dive shop before they close >> >to return it. This was a big motivation for me as well. Given the big price differential and the lack of rust issues, I'd suggest the AL80 for now. I've found the HP steels prone to needing tumbling, and getting a good fill is hard. If I were to buy over again I'd aim for lower pressure steels but keep the din valve. Sometimes you can get great deals buying used tanks.  SignatureJason O'Rourke www.jor.com Mike, which Aluminum tanks are negative when empty? T Signature???`?.?. , . .???`?..><)))?>`?.??.???`?.?.???`?...?><)))?>?. ><)))%>???`?.?. , . .???`?.. ><)))?>`?.??.???`?.?.???`?...?><)))?> > > Expense is a minor point... > > it's the "weight at end of the dive" one remains boyant one isn't. [quoted text clipped - 23 lines] > http://www.mikepainter.com/dotletter.pdf is a letter that explains that DOT > really does not care what you do with a cylinder. > Mike, which Aluminum tanks are negative when empty? The Catalina 60 by .4 pounds and their 6 (six) by 1.1 http://www.mikepainter.com/scubatankweight.html Cool, thanks. T Signature???`?.?. , . .???`?..><)))?>`?.??.???`?.?.???`?...?><)))?>?. ><)))%>???`?.?. , . .???`?.. ><)))?>`?.??.???`?.?.???`?...?><)))?> > > Mike, which Aluminum tanks are negative when empty? > > > The Catalina 60 by .4 pounds and their 6 (six) by 1.1 > > http://www.mikepainter.com/scubatankweight.html > i have been diving for allmost 1 year now and i want to buy my own tank > mainly so that we dont have to be back to the dive shop before they close to [quoted text clipped - 5 lines] > because me and my brother both are bigger and use a little more air than the > average person. Buoyance characteristics and capacity are going to be your deciding factors. Standard 80 aluminum tanks are about 4 lbs buoyant when empty, which is how most tanks are compared. If you carry less than 4 lbs of lead when using one of them, then they are the way for you to go. If you carry more than 4 lbs of lead, you might consider one of the higher pressure aluminum tanks. Catalina and Luxfer both offer them. They're only a little more expensive than the standard 80s. They fill to 3,300 psi and are available with either A clamp or DIN valves. A little web research will tell you the sizes available. These can improve your trim and reduce the lead you carry. Most divers want enough ditchable weight to allow them to become at least slightly buoyant, but not much more. HP 100s are even more negative, but not by much. They have the advantage of holding more gas in about the same space. PST makes some with valves that will work with both A clamp and DIN regulators. They're about twice the cost of aluminum tanks. They also require a bit more care to ensure water does not get into them, particularly salt water. Steel tanks can rust. Lee In news:Lee Bell <leebell@ix.netcom.com> typed: > They also require a bit more care to ensure > water does not get into them, particularly salt water. Steel tanks > can rust. Sorry, but I had to but in. Aluminum will oxidize just as fast and even faster than steel under certain circumstances; just leave a penny on deck of an aluminum boat and see how fast it drills trough. It's a recurrent misconception that aluminum doesn't rust, just because the oxide is not red in color. Signaturewww.odysea.ca >Sorry, but I had to but in. Aluminum will oxidize just as fast and even >faster than steel under certain circumstances; just leave a penny on >deck of an aluminum boat and see how fast it drills trough. Put aside the details that belong in ALT.CHEMISTRY_AND_METALURGY. They are not pertinent to SCUBA. Under the actual circumstances encountered in SCUBA diving, observation makes it very clear that AL tanks have far less frequent corrosion problems than do steel tanks. It can be argued that steel tanks are often better than Al, at least for certain types of SCUBA diving. However, steel can cost US$1-200 more for each tank, and corrosion IS a consideration. Given these two factors, it is not surprising that the overwhelming majority of SCUBA tanks you see in actual use are Aluminum. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. In news:Charlie Hammond <hammond@not@peek.ssr.hp.com> typed: >> Sorry, but I had to but in. Aluminum will oxidize just as fast and >> even faster than steel under certain circumstances; just leave a [quoted text clipped - 12 lines] > factors, it is not surprising that the overwhelming majority of SCUBA > tanks you see in actual use are Aluminum. We'll have to agree to disagree. The main factor driving the use of alu over steel is price and then weight; corrosion is not a factor. I've retired, just last year, two steel 72's due to corrosion pitting; yeah, but thoses were 32 years old heavily used cylinder. I very much doubt the two new aluminum one will last that long. Heck, I'm not even sure I will last that long. Signaturewww.odysea.ca > We'll have to agree to disagree. The main factor driving the use of alu > over steel is price and then weight; corrosion is not a factor. I've > retired, just last year, two steel 72's due to corrosion pitting; yeah, > but thoses were 32 years old heavily used cylinder. I very much doubt > the two new aluminum one will last that long. Heck, I'm not even sure I > will last that long. Oh how I wish I still had my first aluminum tank. Alas, it was stolen after only a few years of use. The oldest one I presently have was manufactured in 1988. That makes it approximately 16 years old. It was recently hydro tested, visually inspected and visual plus tested. No corrosion, no pits, it passed hydro and showed no sustained load cracks. Not much of a surprise, it's a Catalina, not a Luxfer or a Walter Kidde. Corrosion was a factor for most of us that bought aluminum tanks so many years ago. It still is. Unfortunately, problems with some alloys suggests that they may fail for very different reasons. Lee > It was recently hydro > tested, visually inspected and visual plus tested. No corrosion, no pits, > it passed hydro and showed no sustained load cracks. Not much of a > surprise, it's a Catalina, not a Luxfer or a Walter Kidde. Funny you should mention Walter Kidde tanks. I have a question about that - was there any warning before the explosion(s) that set off the hullabaloo? Any stress fractures, etc.? I'm just wondering - how long a WK tank (or any of the 6351 alloy tanks) can be expected to remain in good shape and not be a ticking time bomb as some shops seem to think it is. Or are they panicking over nothing at all? > ... I'm just wondering - how long a WK tank (or any >of the 6351 alloy tanks) can be expected to remain in good shape and not be >a ticking time bomb as some shops seem to think it is. Or are they >panicking over nothing at all? SHORT ANSWER -- Yes, they are panicking over nothing. LONGER ANSWER -- The available data are insufficient in both quantity and quality to support a stastically vaild answer to your question. We simple do not know how long 6351 or 6061 tanks can be expected to remain in good shape. (Even though most failures (all?) have come in 6351 tanks, 6061 tanks should also be considered. We also do not know if periodic eddy current testing (a.k.a. "VIP+") is a good test for this -- because we do not know how long it takes for this type of crack to progress from detectable to failure. We DO Know that "VIP+" testing probably results in more false problem detections than in finding truely bad tanks. (This is probably why it is NOT recommended for use on 6061 tanks.) We DO know that an extremely small number of tanks have failed, so the "risk" is probably down around the risk of being struck by lightening -- much less than many risks we accept daily -- like driving on public highways. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > LONGER ANSWER -- The available data are insufficient in both quantity and > quality to support a stastically vaild answer to your question. But, but, I know this guy who says he knew a guy who heard from a friend that they were, like really dangeeeeerous. He says that your statistics don't show nothing and wants me to go in with him on a program to predict winning lottery numbers. > But, but, I know this guy who says he knew a guy who heard from a friend > that they were, like really dangeeeeerous. > He says that your statistics don't show nothing and wants me to go in with > him on a program to predict winning lottery numbers. I'll ask you the same thing I asked Charlie. How many old Catalinas would you like to trade me for Old Luxfers and Walter Kiddes? Ask the kid that was filling the tank in Force E what he thinks about the danger. Lee > > But, but, I know this guy who says he knew a guy who heard from a friend > > that they were, like really dangeeeeerous. [quoted text clipped - 6 lines] > Ask the kid that was filling the tank in Force E what he thinks about the > danger. You must be the guy I'm talking about. Asking a person involved in any accident if he would do it again is meaningless and is at best anecdotal information. >Ask the kid that was filling the tank in Force E what he thinks about the >danger. You mean the kid who apparantly had no formal training and who was under age to be working with hazzardous material? (Yes, pressure cylinders are HAZMAT!) O.K. that is beside the point, but this is clearly a poor example if you're looking for a "poster child". More to the point, try this: Seek out people who have had an in-water failure of a ScubaPro regulator and interview then regarding the quality of ScubaPro. I'll but you come up with a MUCH different opinion of ScubPro than that high opinion which generally prevails in this newsgroup. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > >Ask the kid that was filling the tank in Force E what he thinks about the > >danger. > > You mean the kid who apparantly had no formal training and who was > under age to be working with hazzardous material? (Yes, pressure cylinders > are HAZMAT!) Yep, the one that did nothing but reach out to check where the bubbles were coming from. The one who had not even started to add gas to the tank. > More to the point, try this: Seek out people who have had an in-water > failure of a ScubaPro regulator and interview then regarding the > quality of ScubaPro. I'll but you come up with a MUCH different > opinion of ScubPro than that high opinion which generally prevails > in this newsgroup. How many of them are missing parts of their bodies? Lee >> >Ask the kid that was filling the tank in Force E what he thinks about the >> >danger. [quoted text clipped - 6 lines] >Yep, the one that did nothing but reach out to check where the bubbles were >coming from. ... Would a properly trained technicain have done that? I've never been able to answer that question to my satisfaction. > ... The one who had not even started to add gas to the tank. And I've never fully believed that part of the story. >> More to the point, try this: Seek out people who have had an in-water >> failure of a ScubaPro regulator and interview then regarding the [quoted text clipped - 3 lines] > >How many of them are missing parts of their bodies? Irrelevant. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > >Yep, the one that did nothing but reach out to check where the bubbles were > >coming from. ... > > Would a properly trained technicain have done that? > I've never been able to answer that question to my satisfaction. I don't know that it was a training issue. I think it's pretty much natural for anybody in the same circumstances. You put a tank in the water and hook a whip up to the tank, opening the tank's valve to check the pressure already in the tank. The Force_E event was a top off, not a fill from empty. You notice a few bubbles and reach out to see why. Who, back then, would have suspected an explosion? I know that hearing gas escape from my tank on a dive boat, under almost identical conditions, makes me think of a bad O ring first. I'd reach out to check. Why would I expect it to be different in a dive shop? > > ... The one who had not even started to add gas to the tank. > > And I've never fully believed that part of the story. We'll never know. That's what was released to the press, included in the internet and was what Skip, the owner of Force-E told me shortly after the accident. As I recall, the statement was backed up with photos of the accident scene showing the fill valve in the off position. Problem is, that could either be because it was off at the time or because it was turned off after the explosion, which it certainly would have been in this case. The liability issues are far different if the valve was on than they are if it was off. > >> More to the point, try this: Seek out people who have had an in-water > >> failure of a ScubaPro regulator and interview then regarding the [quoted text clipped - 5 lines] > > Irrelevant. Not when you're talking about risk of injury, it's not. I have swam myself up OOA from 128 feet deep at the back of Blue Springs and lived to tell about it. Most divers with more sense than I had way back then, have a buddy around somewhere to help in case of an OOA or regulator failure situation. There's no escaping an exploding tank, unless, of course, you can run faster than the fragments travel. I can't. If my gun goes off unexpectedly and kills you, is it OK because it only happened once? Lee .. >> Would a properly trained technicain have done that? >> I've never been able to answer that question to my satisfaction. > >I don't know that it was a training issue. I think it's pretty much natural >for anybody in the same circumstances. ... Natural? I agree. That is the whole point of training -- to learn NOT to do the "natural" thing when it is wrong/dangerous. e.g. We learn NOT to hold our breath when SCUBA diving. Pilots learn NOT to pull up when an airplane stalls. Firearems classes teach us NOT to put our finger on the trigger until we are ready to shoot. Etc., etc. >> >How many of them are missing parts of their bodies? >> >> Irrelevant. > >Not when you're talking about risk of injury, it's not. .. Yes, but that was not the topic. We were talking about analysis of the risk, not the risk itself. ... but this has become a rathole in any case. Lee, I think you and I mostly agree that 6351 SCUBA tanks should be phased out, if not taken out of service immediately. However, neither of us can claim that our opinion is based on sound analysis of the risk. FWIW, I also subscribe to your opinion that Luxfer could/should have been more open about this issue, and that they also could/should have offered a more aggressive trade/exchange program to get the 6351 tanks out of service. By dumb luck, our tanks, which were purchased well before this SLC/VIP+ issue, are all Catalina. I won't trade the for Luxfers, even if you had Luxfers to trade. But if I had bought Luxfer tanks and knew that I had treated them very well all there service lives, I don't know that I would be willing to just junk them and buy replacements at a cost of ~$800 out of MY pocket. I do wish Luxfer -- or SOMEbody -- could make data available. There is a B*I*G differnce between a risk that is 1 in several million, and one that is one in several thousand. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > Lee, I think you and I mostly agree that 6351 SCUBA tanks should be > phased out, if not taken out of service immediately. However, neither > of us can claim that our opinion is based on sound analysis of the risk. Yes, I think they should be phased out, but I disagree that it's not based on sound analysis of risk. If the risk were better defined and more predictable, I'd be insisting that the tanks be removed from service. As it is, I only think they should be and, personally, would chose to follow up on that. If I had one, I'd destroy it. I would not use it and I would not sell it to somebody who would. That, however, is simply my conclusion, not something I have sufficient basis for to insist others agree with. > FWIW, I also subscribe to your opinion that Luxfer could/should have been > more open about this issue, and that they also could/should have offered > a more aggressive trade/exchange program to get the 6351 tanks out of > service. Truth be told, I don't think they could have done that. There are way too many of them in service for Luxfer to have survived taking them all out of service at once. I'd be a lot more understanding if we didn't have to pay for the test, that uses the machine that they designed and marketed, to determine if we have a problem they caused. > By dumb luck, our tanks, which were purchased well before this SLC/VIP+ > issue, are all Catalina. It was not dumb luck on my part. I bought Catalina tanks quite intentionally. There were rumors about problems with Luxfer tanks from the start. What those problems were, was not clear, but it was enough for me to look for something more to my liking. When I bought my last two aluminun tanks, I couldn't find Catalinas anywhere. I ordered them through Brownies rather than settle for Luxfers. > I won't trade the for Luxfers, even if you > had Luxfers to trade. But if I had bought Luxfer tanks and knew that I > had treated them very well all there service lives, I don't know that I > would be willing to just junk them and buy replacements at a cost of > ~$800 out of MY pocket. Different levels of risk tolerance . . . part of what makes the world go around. > I do wish Luxfer -- or SOMEbody -- could make data available. > There is a B*I*G differnce between a risk that is 1 in several million, > and one that is one in several thousand. I suspect the current Visual Plus program will take them out of circulation reasonably quickly. We'll see how much Luxfer does for those whose tanks fail. The ones that worry me the most are those that are in the hands of people that don't get them inspected. More than a few people have their own compressors and many of my police and fire department friends get their tanks filled whenever they like. When I went on a houseboat trip with two other couples, one of them had several old Luxfer tanks that were years out of visual and barely in hydro. He thought I was kidding when I told him that if those tanks went on the boat, Jayna and I would not. He learned differently. I loaned him a couple of mine. Lee >I suspect the current Visual Plus program will take them out of circulation Lee, by "them" do you mean ALL 6351 tanks or "faulty" 6351 tanks? (Whatever "faulty" means!) I rather suspect that the attitude or most diver against 6351 will have a greater effect. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > >I suspect the current Visual Plus program will take them out of circulation > > Lee, by "them" do you mean ALL 6351 tanks or "faulty" 6351 tanks? > (Whatever "faulty" means!) It that's mine and not something quoted from somebody else, I'm not sure what I meant. I can only imagine that I was referring to tanks with sustained load cracks in the neck area. > I rather suspect that the attitude or most diver against 6351 will > have a greater effect. Maybe. I have my doubts. Very few divers are going to scrap a tank they bought and have been using for years until some form of test convinces them that it's not safe to continue using. It's easy for me to say I would since I've never had one of the 6351 tanks. I think I'd scrap them, but talk is cheap. Buying new tanks wouldn't slow me down much, but it's not free. Lee .. >> I rather suspect that the attitude or most diver against 6351 will >> have a greater effect. [quoted text clipped - 4 lines] >I've never had one of the 6351 tanks. I think I'd scrap them, but talk is >cheap. Buying new tanks wouldn't slow me down much, but it's not free. Tell me! I'd love to replace our AL 80s, even though they're 6061 Catalinas, with HP 100's or 120's (probably 2 of each size). However, at a total cost of over US$1500.00 (including H vavles -- wanna do it RIGHT) -- well, I'm not finding myself in a great rush. {sigh} SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > > ... I'm just wondering - how long a WK tank (or any > >of the 6351 alloy tanks) can be expected to remain in good shape and not be > >a ticking time bomb as some shops seem to think it is. Or are they > >panicking over nothing at all? > > SHORT ANSWER -- Yes, they are panicking over nothing. How many old Catalinas would you like to trade me for old Luxfers and Walter Kidde's? Lee > > > ... I'm just wondering - how long a WK tank (or > any [quoted text clipped - 7 lines] > How many old Catalinas would you like to trade me for old Luxfers and Walter > Kidde's? How many you got? > > How many old Catalinas would you like to trade me for old Luxfers and > Walter > > Kidde's? > How many you got? None, but I'm willing to bet that I can get as many as I want for less than what others can buy comparable Catalinas for. I used to be able to say that I'd never owned a Luxfer. Just because it was convenient and I was vulnerable, I let Dave Carmichael sell me one as my emergency O2 tank. It's been filled once and not empted since. Even a Luxfer, particularly a newer one, is good for more than one fill cycle . . . I hope. Lee > It can be argued that steel tanks are often better than Al, at least > for certain types of SCUBA diving. To the best of my knowledge, and I'm not claiming exceptional knowledge here, the only advantage of steel tanks is that they can be overfilled by a greater amount, more times, without failing that aluminum ones can. Lee > In news:Lee Bell <leebell@ix.netcom.com> typed: > [quoted text clipped - 5 lines] > faster than steel under certain circumstances; just leave a penny on > deck of an aluminum boat and see how fast it drills trough. Aluminum oxidizes almost instantly but forms a coat that stops further oxidation. A penny on an aluminum boat has nothing to do with oxidation but with the fact that you now have a battery and electrolysis is the factor. Keep them both dry and they will be happy until somebody picks up the penny. > > In news:Lee Bell <leebell@ix.netcom.com> typed: Which is heavier an aluminum or steel tank, given that they both hold the same amount of air at the same pressure? > Which is heavier an aluminum or steel tank, given that they both hold the same amount > of air at the same pressure? Damned if I know. Mostly, we worry about buoyancy, which is affected not only by weight, but also by outside diameter. A steel tank of the same internal size and pressure capacity, will have thinner walls than a comparable aluminum one. It will be have a slightly smaller external size and, in my experience, will be slightly more negative, all else being equal. A standard aluminum 80 is about 4 lbs positive when it's as empty as I'll ever get it. My Catalina Compact 80s and the Luxfer Neutral 80s are both neutral when empty. My HP 100 is smaller than either of the other tanks mentioned, fills to a higher pressure, allowing it to hold more gas, and is 1 to 2 pounds negative when empty depending on which of my 100's it is. The new ones aren't quite as negative as the older ones. Lee > > > In news:Lee Bell <leebell@ix.netcom.com> typed: > > Which is heavier an aluminum or steel tank, given that they both hold the same amount > of air at the same pressure? I can't find an exact match but in general the aluminum would be heavier because it is so much weaker than steel. So it weighs more than steel and displaces more, just the opposite of what we want. I've posted a comparison at http://www.mikepainter.com/scubatankweight.html > > Which is heavier an aluminum or steel tank, given that they both hold the > > same amount of air at the same pressure? > > I can't find an exact match but in general the aluminum would be heavier because it is so much weaker than > steel. So it weighs more than steel and displaces more, just the opposite of what we want. Would be, or is? Information on weight, size and displacement is not all that hard to find. I'm not sure it's appropriate to say that aluminum is so much weaker than steel. The fact is, each metal's strength is manifested differently. Aluminum tanks have to be rigid. They do not respond well to stretching, which is why many recommend against over filling them. Steel, on the other hand, stretches and returns to, or very near to, it's original size and shape. Steel can be allowed to stretch a bit more without compromising their safety. While it's true that the walls of an aluminum tank are thicker than the walls of a comparable steel tank, aluminum is also lighter than steel. It's the net effect that matters. As for displacement, that's not always a problem. Aluminum tanks are normally used for stage tanks specifically because they are less negative in the water. Hang a bunch of them on yourself and the 5 or more lb difference in buoyancy adds up pretty quickly. When empty, they return themselves to the surface. Most steel tanks don't. Lee > > > Which is heavier an aluminum or steel tank, given that they both hold > the [quoted text clipped - 7 lines] > Would be, or is? Information on weight, size and displacement is not all > that hard to find. Is and I posted the comparison. > I'm not sure it's appropriate to say that aluminum is so much weaker than > steel. The fact is, each metal's strength is manifested differently. [quoted text clipped - 5 lines] > thicker than the walls of a comparable steel tank, aluminum is also lighter > than steel. It's the net effect that matters. And the net effect is that the Aluminum tank for the same volume and pressure weighs more than a steel tank out of the water and displaces more in the water. That means you carry a lighter tank to the water and have less on your weight belt. > As for displacement, that's not always a problem. Aluminum tanks are > normally used for stage tanks specifically because they are less negative in > the water. Hang a bunch of them on yourself and the 5 or more lb difference > in buoyancy adds up pretty quickly. When empty, they return themselves to > the surface. Most steel tanks don't. Aluminum tanks are used by the vast majority of divers. It is very rare to see anything but an aluminum tank on the beaches at Monterey where a huge percentage of divers in Northern California are certified. Most of their instructors wear them and they buy or rent them because of the price. Most people dive in fairly shallow water and swim around a lot enjoying themselves looking. The idea of having to sit at stages for a long time because they spent a short time where it is dark and cold does not appeal to them. The only time I do anything close to that is when I get paid lots of money to do it. > And the net effect is that the Aluminum tank for the same volume and > pressure weighs more than a steel tank out of the water and displaces more > in the water. That means you carry a lighter tank to the water and have less on your > weight belt. With my C-80 aluminum tanks, I use no lead. How much less should I hope for? Lee > > And the net effect is that the Aluminum tank for the same volume and > > pressure weighs more than a steel tank out of the water and displaces more > > in the water. That means you carry a lighter tank to the water and have > less on your > > weight belt. > With my C-80 aluminum tanks, I use no lead. How much less should I hope > for? Most of the people I know wear wet suits so that is of little interest. If you wear a steel plate then you could shave 7 pounds off , go to a 3000 pound 80 CF tank which gives a bit more air and save 10 pounds off the tank. You could also add .4 pounds of buoyancy to your self, stay with about the same tank weight and go to a 120 steel. C80 Alum 77.4 10.2 3300 7.25 25.1 35.0 15.9 40.80 18.5 -5.8 0.0 35.0 31080 Steel 80 3000 7.25 20.1 32.4 14.7 38.30 17.4 -13.2 -7.3 25.1 Steel 120 3500 7.25 27.87 36.0 16.4 45.00 20.5 -9.4 -0.4 35.6 > Most of the people I know wear wet suits so that is of little interest. Most people you know don't use stages tanks. Most people you know wear wet suits. Most people you know don't understand the DIR prohibition on diving wet and using steel tanks. You have a limited circle of acquaintances. > > Most of the people I know wear wet suits so that is of little interest. > > Most people you know don't use stages tanks. > Most people you know wear wet suits. > Most people you know don't understand the DIR prohibition on diving wet and > using steel tanks. Most people don't care. They dive for pleasure. They don't plan for several hours, then play soap on a rope for long periods to see how deep they can go. Those that I know that do such things do it for a lot of money and not for fun. Most people ask honest questions. >Which is heavier an aluminum or steel tank, given that they both hold the same amount >of air at the same pressure? For all practical purposes, Al tanks are heavier at equal capacities. There are some LP steels that don't fit the mold though. safe diving, bullshark >Which is heavier an aluminum or steel tank, given that they both hold >the same amount of air at the same pressure? This is a difficult question because there are few direct comparisons. i.e. It is hard to find aluminum and steel tanks with the same capacity and rated pressure. Because steel is stronger than aluminum, and because steel has better elastic properties, the amount (thickness) of steel is less than the amount of aluminum. It is enough less that steel tanks can be both noticably smaller and noticably lighter than aluminum. The smaller size results in a reduced displacement, which is often enough to make the steel tank more negatively bouyant than the aluminum, even though the steel weighs less. This leads to the confusing situation that the steel may be "ligher" in weight (mass, if you prefer), but "heavier" in bouyancy. Confusing or not, this is the consideration that can make steel a better choice -- in some situations and according to some opinions. Thus, if you switch from a 3000 PCSI Al 80 to a 2500 PCSI steel 80 you can take off about 4-6 lbs of weight and loose an additional 3 lbs or so because the steel tank weighs less. This comparison is very similar if you substitue a "classice" steel 72 lp tank for the hp steel 80. Or you can carry a HP steel 100 and experience 25% more air with overall weight and bouyancy considerations that are almost identical to the AL 80. You can find some data for Steel and Aluminum tanks at http://www.diveriteexpress.com/gas/steel.shtml http://www.diveriteexpress.com/gas/aluminum.shtml Here is some information I have on a couple "classic" LP steel tanks. Please note that I have not verified and do not guarantee this! -----without-valve------ Length Weight -Buoyance- Matl vol Mfg/dist PSI OD Empty Full ----- ---- ---------- ---- ---- ---- ----- ---- ---- Steel 95.1 Faber/ 2640 8.02 23.82 37.62 -1.2 -8.5 Steel 72.0 (std) Scubapro 2640 6.90 25.0 29.0 -1.0 -6.0 You should also note that there are variations in the manufaturing of SCUBA tanks. It is not uncommon for an idividual tank to vary by a pound or two from its "standard" weight/bouyancy. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > >Which is heavier an aluminum or steel tank, given that they both hold > >the same amount of air at the same pressure? [quoted text clipped - 17 lines] > you can take off about 4-6 lbs of weight and loose an additional 3 lbs > or so because the steel tank weighs less. That's a significant advantage to steel tank if you have to lug 8lbs less (when shore diving) from the beach to the car. If I were buying my tank again I would go with high pressure steel for the weight advantage. .. >> Thus, if you switch from a 3000 PCSI Al 80 to a 2500 PCSI steel 80 >> you can take off about 4-6 lbs of weight and loose an additional 3 lbs [quoted text clipped - 3 lines] >diving) from the beach to the car. If I were buying my tank again I would go with >high pressure steel for the weight advantage. I pretty much agree. When I bought our tanks, HP steel tanks were more than twice the price of AL 80s. I looked at http://www.diveritexpress.com and found AL-80 -- $179.00 -- Aluminum, 300PSI, available today E7-80 -- $204.00 -- Steel, 3442 PSI, available in Jul If that $25 price diference holds up when they are actuall avaialable, I may soon have some excellent use AL80s for sale! Unfotunately, the E7-100 and E7-120 are a lot more -- $336 and $384. Even the E7-65 is $281! SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > AL-80 -- $179.00 -- Aluminum, 300PSI, available today > E7-80 -- $204.00 -- Steel, 3442 PSI, available in Jul [quoted text clipped - 4 lines] >Unfotunately, the E7-100 and E7-120 are a lot more -- $336 and $384. >Even the E7-65 is $281! I don't think the E7-80 is a realistic choice, unless you are petite. It's not the air consumption that's a problem, its the height of the BC sitting on a rack behind the bench, and the balance when you're in the water. The damned thing is only 20 inches tall. The beauty of the E7-100 is that it is the same size/weight (about) as an S80. The cost is going to be an increasing problem I fear. China's appetite for steel is voracious and it's impacting just about everyone. Are you *sure* it was an E7-80? I ask because PST still makes an LP-80 that has been remarkably inexpensive (by comparison). Just about the price you quote. safe diving, bullshark >> AL-80 -- $179.00 -- Aluminum, 300PSI, available today >> E7-80 -- $204.00 -- Steel, 3442 PSI, available in Jul .. >I don't think the E7-80 is a realistic choice, unless you are petite. >... its the height of the BC sitting on a rack behind the bench... >.... The damned thing is only 20 inches tall. I don't see this as a serious problem, but I do see your point. >The beauty of the E7-100 is that it is the same size/weight (about) >as an S80. Yep. That is almost as true for the E7-120, too. >Are you *sure* it was an E7-80? I ask because PST still makes an LP-80 >that has been remarkably inexpensive (by comparison). Just about the >price you quote. Yep. Look at www.diveriteexpress.com and see for yourself. More specifically, http://www.diveriteexpress.com/gas/steel.shtml They even claim to offer free shipping. SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. > > They also require a bit more care to ensure > > water does not get into them, particularly salt water. Steel tanks > > can rust. > Sorry, but I had to but in. Aluminum will oxidize just as fast and even > faster than steel under certain circumstances; just leave a penny on > deck of an aluminum boat and see how fast it drills trough. > > It's a recurrent misconception that aluminum doesn't rust, just because > the oxide is not red in color. Aluminum oxidizes relatively quickly, but it's a self limiting process. The oxide blocks off the aluminum underneith relatively quickly, causing no significant structural damage. That's not the case with steel tanks which, of course, is why aluminum ones rarely have to be tumbled and steel ones often have to be. Ever see a piece of steel rust through? Me too. Ever see a piece of aluminum oxidize through? Me neither. Electrolysis doesn't count. Lee Sure, an Aluminum will oxidize all the way through when the oxidation is under the paint. I've condemned several Aluminum tanks with excessive exterior pitting. T Signature???`?.?. , . .???`?..><)))?>`?.??.???`?.?.???`?...?><)))?>?. ><)))%>???`?.?. , . .???`?.. ><)))?>`?.??.???`?.?.???`?...?><)))?> > > > They also require a bit more care to ensure > > > water does not get into them, particularly salt water. Steel tanks [quoted text clipped - 17 lines] > > Lee > i have been diving for allmost 1 year now and i want to buy my own tank > mainly so that we dont have to be back to the dive shop before they close to [quoted text clipped - 13 lines] > > thanks for any info you can give me. I had two basic reasons for choosing a steel tank over an aluminum tank. 1) I live near the Puget Sound in Washington State. Diving requires either a fairly thick wetsuit or a drysuit. Instead of diving with 16-18 lbs of lead I required (at the time of the purchase) nearly 40 lbs of lead. The steel tank is negatively bouyant when empty which allowed me to remove about 4-6 lbs of lead. 2) I have what is called a barrel chest, I have big lungs. In otherwords I suck air bigtime. It does not matter how shallow or deep, I am the first to ascend, average dive time on a 60' dive is 35 minutes. Sometimes 40. I got the steel tank for extra capacity - it's a 100cuft, and can be preasurrized to 3500 psi. Those were my two reasons behind purchasing a steal tank. Walter > I had two basic reasons for choosing a steel tank over an aluminum tank. > [quoted text clipped - 3 lines] > steel tank is negatively bouyant when empty which allowed me to remove about > 4-6 lbs of lead. Yep. > 2) I have what is called a barrel chest, I have big lungs. In otherwords I > suck air bigtime. It does not matter how shallow or deep, I am the first to > ascend, average dive time on a 60' dive is 35 minutes. Sometimes 40. I got > the steel tank for extra capacity - it's a 100cuft, and can be preasurrized > to 3500 psi. Sound enough thinking as far as it goes. The size of your lungs probably has some effect on your consumption, but not nearly as much as you might think. I know more than one large person whose consumption is as low as anybody else's. The single most significant factor effecting gas consumption, is how relaxed you remain while underwater. Any stress, be it nervousness (very common even among relatively experienced divers) or physical exertion, increases consumption dramatically. Slow down, calm down and relax in the water and you'll be amazed at how low your consumption will get. When it gets low, don't get rid of those 100 cubic foot tanks. What is very cool about them is that they look, to the casual observer, just like a standard 80. Imagine the surprise when you come up a half hour after everybody else, including Greg who, by that time, will be puking over the side of the boat. Imagine my surprise the first couple of times I dove with Mike Gray, when I looked at my guage and realized that, for the first time (but not the last), somebody was going to stay down longer, on the same dive, than I could. The stinker was using a 120. I'll give him his due, Mike didn't keep me on the hook long. He confessed to his low consumption secret. After diving with him a while, it does not surprise me that he has excellent consumption. He's about as relaxed in the water as anybody I know . . . at least anybody that doesn't use a plate and wing. 8^) Before he says it. Bullshark's wife also has exceptionally low consumption, possibly the best of our relatively close knit group. His ain't too bad either . . . which explains why we enjoy diving together as much as we do. Lee > I know some of the steel are HP and i can switch my regs over to DIN for > about $50 so that wont be a problem. > > thanks for any info you can give me. I have a couple LP steel 104s I will sell you. Kimber > > I know some of the steel are HP and i can switch my regs over to DIN for > > about $50 so that wont be a problem. [quoted text clipped - 4 lines] > > Kimber Really? What would you sell them for? >I know some of the steel are HP and i can switch my regs over to DIN for >about $50 so that wont be a problem. If your regs are stamped "CE" and meet EN250 specifications, then you don't have to have DIN for HP. The EN250 A-Clamp is rated to 250 bar (3625 psig) and good for quite a bit more. The new E series tanks from PST are delivered with convertible valves that are DIN or yoke. It's the money. Steel is 2 times the cost. Around these parts we have no problems getting fills of any kind or pressure. Your dive shop might suck but don't despair, you don't have to fill them all the way up. It's perfectly OK to underfill. PST E7-100 Pressure Cu Ft ---------------- 3500 ~102 3300 ~98 3000 ~90 2640 ~80 Any shop should be able to give you 3300 fills and you'll be at 96% of capacity, big deal. BTW, with your own tanks you'll have to stop by the shop before it closes to get them filled. safe diving, bullshark Thanks for all the replies. On my reg. it has CE0078 and EN 250 but on the yoke part of it it says USA 3000 PSI and 232 BAR MAX. So that is good to 3410 PSI right? Thats close enough to full for me. Thanks Justin > >I know some of the steel are HP and i can switch my regs over to DIN for > >about $50 so that wont be a problem. [quoted text clipped - 28 lines] > > bullshark >Thanks for all the replies. On my reg. it has CE0078 and EN 250 but on the >yoke part of it it says USA 3000 PSI and 232 BAR MAX. So that is good to >3410 PSI right? Thats close enough to full for me. Talk about yer mixed messages... 232 bar is about 3364 psig. It's pretty strange that the yoke says 232 bar and also "USA 3000 PSI". Thats a 10% difference. Does the metal get weaker when you cross the ocean? It also implies that the reg is not suitable for Medium pressure tanks (3300) like the S-100, or C-80. I just rechecked and I erred in the first reply. EN250 implies CGA 850 which is, as your regulator says: 232 bar, not 250. That, is according to "harrier": http://groups.google.com/groups?selm=426ec785.0403230749.31c9799b%40posting.goog le.com&output=gplain At any rate, that is certainly good enough for me, too. We've been slapping our EN 250 yokes on 3500 PSI tanks for over a year now...so far not even one has broken loose and shot through the back of my head...at least not that I *remember*. safe diving, bullshark >Does the metal get weaker when you cross the ocean? ... I don't know. If you find out, let us know. This coudl be related to understanding why tanks designed for 4000 PSI are DOT approved for only 2400/2640. ...said Charlie, with tongue planted firmly in cheek. ;-) SignatureCharlie Hammond -- Hewlett-Packard Company -- Ft Lauderdale FL USA (hammond@not@peek.ssr.hp.com -- remove "@not" when replying) All opinions expressed are my own and not necessarily my employer's. Justin, Getting your own tank is a great idea. I started with AL80's, and, overall, I think these are still a very good choice and the most universal tanks. I still have and use my original AL80's. I have also owned some LP steel cylinders that I have used for single-tank diving, but I prefer to only use these with a drysuit as they are quite heavy when full (too much non-ditchable weight with a wetsuit). Some steel tanks are very negative even when empty. These should be avoided in my opinion. I would highly recommend starting with the AL tanks. You can always get steel tanks later when you have more exerience. LP vs HP steel tanks is a whole other issue. It has been my experience that the popularity of HP tanks is somewhat regional. They are popular in some areas and almost unknown in other parts of the country. Also getting HP fills can be a problem in some areas. I use DIN fittings and valves with all my regulators and tanks, none of which are the HP variety. -bob >i have been diving for allmost 1 year now and i want to buy my own tank >mainly so that we dont have to be back to the dive shop before they close to [quoted text clipped - 15 lines] > >Justin |
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