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Scuba Forum / Scuba Equipment / June 2007My first Tanks
Hi All. Just purchased my first set of tanks (Worthington X7-120)'s Steels, rated at 230bar/3442psi as part of my new RAS setup (also purchased an AL30 Pony). They came from the LDS charged at 3500 PSI. But upon filling at Dutch, the gas blender indicated he would fill them to 4000 PSI and they'd cool down to 3500 PSI or thereabouts (actually, there down to 3100 PSI now so perhaps I got rooked for a high pressure fill). Question being, for a steel 120 rated at 230bar/3442 PSI, is there any margin for "overfilling" and what would be the max to which it could be filled without any danger to the tank or the 1st stage (which in the case of my 2 regs, are rated to 3500PSI each as well)? 2nd Question - The LDS recommended converting the regs to DIN for these tanks but I hear from other shops that it is not necessary. Thoughts? BTW, doing much better on buoyancy. THe steel 120's actually help. ____________________________________________ Regards, Arnold > Hi All. > [quoted text clipped - 4 lines] > cool down to 3500 PSI or thereabouts (actually, there down to 3100 PSI now > so perhaps I got rooked for a high pressure fill). Typical. At Dutch, they can't afford to fill slowly enough to avoid a large temperature rise. To keep the temperature rise to a minimum, they'd have to fill at 60-80 psi per minute. That means it would take 45 minutes to fill your cylinder. Imagine them doing that on a busy day! At 3100 psi, you still have around 100 cubic feet of gas in that cylinder. Don't think you'll use that up on a single dive at Dutch, do you? > Question being, for a steel 120 rated at 230bar/3442 PSI, is there any > margin for "overfilling" and what would be the max to which it could be > filled without any danger to the tank or the 1st stage (which in the case > of my 2 regs, are rated to 3500PSI each as well)? Those cylinders, new or in like-new condition, should be able to handle an occasional overfill to 4000 psi without a problem. > 2nd Question - The LDS recommended converting the regs to DIN for these > tanks but I hear from other shops that it is not necessary. Thoughts? The 300 bar DIN fitting is nominally rated to handle higher pressures (there is also a 200 bar DIN - both ratings are very conservative). Modern "A-Clamp" or "yoke" fittings should be able to withstand 3500 psi without problem. To a large degree, this is a matter of personal preference. I prefer 300 bar DIN, even on low-pressure cylinders. I do have a few with 200 bar DIN on them. I don't like the clamp knob of the yoke sticking out behind me, where it is subject to snagging or entanglement in a place I can't see or reach well to clear it. > BTW, doing much better on buoyancy. THe steel 120's actually help. Why? Were you underweighted before? You don't need big cylinders to fix that.  SignatureArt Greenberg artg at eclipse dot net > The 300 bar DIN fitting is nominally rated to handle higher pressures > (there > is also a 200 bar DIN - both ratings are very conservative). Modern > "A-Clamp" > or "yoke" fittings should be able to withstand 3500 psi without problem. There seems to be three DIN valves available in the US, 300 BAR, 232 BAR and 200 BAR. The rating does not indicate the valve's ability to handle high pressure. Instead, it refers to the ability of the regulators it will attached to to withstand pressure. You can hook a 300 BAR regulator to any of the three, but can not hook a regulator rated for 200 or 232 BAR to a 300 BAR valve. The tanks he has most likely have the 232 BAR valves, the newer ones that come with slugs to convert to an A clamp system. If he had anything else, he would not be asking about whether to convert, he'd be asking how. The slugs, by the way, won't work in the 300 BAR valves either. >> BTW, doing much better on buoyancy. THe steel 120's actually help. > > Why? Were you underweighted before? You don't need big cylinders to fix > that. I'll take that a step further. The 120's can't help buoyancy. The increased weight shift during the dive increases the amount of adjustment required during the dive. As Art suggests, if your buoyancy is better with the 120s, there was something wrong with your weighting to begin with. Lee > I'll take that a step further. The 120's can't help buoyancy. The > increased weight shift during the dive increases the amount of adjustment > required during the dive. As Art suggests, if your buoyancy is better with > the 120s, there was something wrong with your weighting to begin with. It gets weight off your hips and onto your back, which can improve trim, which Arnold might be confusing with buoyancy. >> I'll take that a step further. The 120's can't help buoyancy. The >> increased weight shift during the dive increases the amount of adjustment >> required during the dive. As Art suggests, if your buoyancy is better >> with >> the 120s, there was something wrong with your weighting to begin with. > It gets weight off your hips and onto your back, which can improve > trim, which Arnold might be confusing with buoyancy. Good point. Lee >> I'll take that a step further. The 120's can't help buoyancy. The >> increased weight shift during the dive increases the amount of adjustment [quoted text clipped - 3 lines] >It gets weight off your hips and onto your back, which can improve >trim, which Arnold might be confusing with buoyancy. Perhaps so. Let's put it this way. Prior to the 120's, I could not begin to submerge properly without at least 22lbs in fresh water with a 7.0mm. With the 120's (and with dumping my ankle weights) I'm now down to 16-18lbs, leaning toward 16. Dumping the ankle weights helped a lot with trim in fresh water, but I need to see if they might be required in salt water. I recall some issues with salt water this past January in Bradenton Beach Fl. Next salt water opportunity is back in Bora Bora in another month where I'll be taking Rescue Diver as well as some other "enjoyment" dives, and practicing with the Ikelite housing. After that, back to the NJ Shore for the two ocean dives I need to do for my Wreck/Deep Diver specialties. BTW, Lee, I'll be back in Bradenton Beach in mid-January for a week visiting Dad. If you want to set something up, perhaps I can hook up with some of you FL. folks. ____________________________________________ Regards, Arnold > BTW, Lee, I'll be back in Bradenton Beach in mid-January for a week > visiting Dad. If > you want to set something up, perhaps I can hook up with some of you FL. > folks. Check back when it's closer to January. You never know. Lee >> Hi All. >> [quoted text clipped - 12 lines] >At 3100 psi, you still have around 100 cubic feet of gas in that cylinder. >Don't think you'll use that up on a single dive at Dutch, do you? Well, I didn't at all in 5 dives over this weekend. Apparently, I fared much better at Dutch. They did high pressure fills for the first two fills which cooled to just over 3200 PSI each time. Unfortunately, It was a very hectic Sat. Evening. They had over 200 tanks to fill at 5pm when they were closing. But they expedited mine as I was taking them home (apparently some people leave them at the fill station overnight and collect them in the morning for Sunday dives). They did have some difficulty today though. They have a "triple bank" air repository which apparently was still depleted at 1pm this afternoon from all the overnight activity. The compressor was non-stop all day yesterday and today. They didn't give me a high pressure fill this afternoon, but at least they admitted it to me and they didn't charge me extra. As for me, I completed all the requirements of both the Wreck Diver and Deep Diver specialty ratings this weekend, except for the two North Atlantic Ocean dives I have to do after I come back from Bora Bora. I'll be doing those off of Barnegat light, NJ. Once done, I'll have both specialty ratings. >> BTW, doing much better on buoyancy. THe steel 120's actually help. > >Why? Were you underweighted before? You don't need big cylinders to fix that. And I'm doing even better now. I'm down to 12lbs when using a 30CF Pony with those steel 120's and a 7mm in fresh water. I put a little more on the side opposite the pony for balance. ____________________________________________ Regards, Arnold > But upon filling at Dutch, the gas blender indicated he would fill them > to 4000 PSI and they'd cool down to 3500 PSI or thereabouts (actually, there down to 3100 PSI > now so perhaps I got rooked for a high pressure fill). That pressure drop represents a drop in temperature of about 125 degrees F. What did they do, fill them from dead empty in 30 seconds in the back of a black pickup truck in the sun? When a DSM in NY, NJ or PA opens his mouth, it's a pretty good bet he's either clueless himself or feeding you bullshit. I don't dive at all up here, and I wouldn't buy an O ring from any shop I've been in. If I do decide to start diving here, I'll buy a compressor and dive from my brother's boat. >> But upon filling at Dutch, the gas blender indicated he would fill them >> to 4000 PSI and they'd cool down to 3500 PSI or thereabouts (actually, there down to 3100 PSI [quoted text clipped - 3 lines] >degrees F. What did they do, fill them from dead empty in 30 seconds in >the back of a black pickup truck in the sun? Well, they have a hut so it's not directly in the sun, but they have no water bath at all, and it was a fast fill (I'd say no more than 10 minutes). The tanks were scorching hot when I got them. I should have checked the pressure then but I was wanting to get home. The ambient temp outside during the fill was low 80's as well. After 2 days in my air conditioned basement (70F) they were down to between 3000 - 3100 PSI. Maybe they'll perk up a bit when I get them back outside again. ____________________________________________ Regards, Arnold > Maybe they'll perk up a bit when > I get them back outside again. LOL - but what's going to happen when they hit the freezing cold water? > Well, they have a hut so it's not directly in the sun, but they have no water bath > at all, and it was a fast fill (I'd say no more than 10 minutes). You don't want a water bath. Ever. That's stroke stuff. It doesn't do anything except increase risk of getting water in your tanks. Heat within reason is just fine. This isn't the 60's anymore. The O-rings and lubricants in your valves aren't adversely affected by a little heat. It certainly won't affect the tank unless you get it up to temperatures that affect temper, and I don't think that's happening. 10 minutes isn't all that fast (400 psi/min). They would be hot, but that's OK. Tanks always get hot when you fill them, and as long as it doesn't fry bacon, it's not a big deal. My steels, which get filled at least once a week (x4), are routinely too hot to lay my hand on comfortably and keep it there for long. If it really took 10 minutes. they should have been fine, 33-34 at the worst. Maybe your valves weren't shut tight. Next time you fill, squirt a little water on the burst discs to see if they bubble. They might not be tight. After all, they *are* new. Sometimes people roll the valves open (just a little) when they carry them. Point the valve handle forward in the right hand, and aft in the left. That way they can only roll more tightly closed. bullshark The tanks were scorching > hot when I got them. I should have checked the pressure then but I was wanting to get home. > The ambient temp outside during the fill was low 80's as well. After 2 days in my air conditioned > basement (70F) they were down to between 3000 - 3100 PSI. Maybe they'll perk up a bit when > I get them back outside again. > That's stroke stuff. Your scaring me. > > That's stroke stuff. > > Your scaring me. Me too! SignatureArt Greenberg artg at eclipse dot net > Your scaring me. Relax, it was a *little* 's', not a big one. Strokes are still very, very handsome. bullshark > > Well, they have a hut so it's not directly in the sun, but they have no water bath > > at all, and it was a fast fill (I'd say no more than 10 minutes). [quoted text clipped - 11 lines] > least once a week (x4), are routinely too hot to lay my hand on > comfortably and keep it there for long. It's faster than the DOT spec I saw back in the mid 90's. 300 psi/min for the first 2/3 and 100 psi/min to the top. Does anybody know for sure if that has changed? > If it really took 10 minutes. they should have been fine, 33-34 at the > worst. Maybe your valves weren't shut tight. Next time you fill, squirt [quoted text clipped - 12 lines] > > basement (70F) they were down to between 3000 - 3100 PSI. Maybe they'll perk up a bit when > > I get them back outside again. > It's faster than the DOT spec I saw back in the mid 90's. A DOT spec for filling? I don't think there is such a thing. Are you sure it wasn't some pamphlet from PSHigh? 20 minutes to fill a tank is ridiculous. bullshark > > It's faster than the DOT spec I saw back in the mid 90's. > > A DOT spec for filling? I don't think there is such a thing. Are you > sure it wasn't some pamphlet from PSHigh? > > 20 minutes to fill a tank is ridiculous. I'd suspect that it would have been a "one size fits all" that would have also covered the filling of Aluminum tanks. Compared to steel, Aluminum alloys are vastly less immune to thermal excursions, which can cause unhealthy metallurgical changes. -hh > That pressure drop represents a drop in temperature of about 125 degrees F. > What did they do, fill them from dead empty in 30 seconds in the back of a > black pickup truck in the sun? Almost. Have you seen the fill station at Dutch? They do kinda jam the gas in there. If it takes 10 minutes, that's because they're letting the thing "soak" for 8 minutes after the fill is done. > When a DSM in NY, NJ or PA opens his mouth, it's a pretty good bet he's > either clueless himself or feeding you bullshit. Ouch! Kinda harsh, Al. FYI, the people manning the fill station at Dutch are kids, who probably don't dive themselves. Nowhere close to a DSM. > I don't dive at all up here, and I wouldn't buy an O ring from any shop > I've been in. I've trained the local guy, he's a smidge better. Not exactly DIR, though. But most of the time, I know what's BS and what is not. I was forced to learn. I don't have my own fill station, and I do buy parts at the LDS form time to time. > If I do decide to start diving here, I'll buy a compressor and dive from my > brother's boat. Need a buddy? SignatureArt Greenberg artg at eclipse dot net > Ouch! Kinda harsh, Al. Perhaps a bit, but I got really spoiled in FL and SC. There are, of couse, plenty of idiots there too. I am willing to belive that there may be a good shop here. but I haven't seen it yet. > I've trained the local guy, he's a smidge better. Not exactly DIR, though. > But most of the time, I know what's BS and what is not. I was forced to learn. > I don't have my own fill station, and I do buy parts at the LDS form time to > time. The best shops I know are not DIR, but they just do exactly what you ask, tell really funny stories while you're waiting, and charge a fair price. > > If I do decide to start diving here, I'll buy a compressor and dive from my > > brother's boat. > > Need a buddy? I'm not planning on anything right now, but if I do, I'll be in touch. > Question being, for a steel 120 rated at 230bar/3442 PSI, is there any margin for "overfilling" Of course. Misunderstood in general, pressure ratings are in psig at 20C. This *automatically* translates to higher pressures at higher temperatures. The cylinder specification incorporates all this. DOT cylinder specifications are for industry and transport, not for scuba. As such, they are overbuilt by orders of magnitude. They are expected to be stored in steel mills and left baking in Death Valley sun for months on end. They're also expected to be run over by trucks, dropped from buildings and slammed into bridge abutments at high speeds. The 3AA cylinder standard has been unblemished since the 40's. My fill station always fills these to 4200 psig, which cools to about 35-3700 depending on how fast they filled them. The faster they fill them, the hotter they get, and the more they drop. It really doesn't make much difference. Other shops here routinely fill for 4000 psig (cool). Knowledgeable shops aren't very concerned about steel tanks in good condition. 1) they can't hurt them with shop compressors 2) even if they could, steel wouldn't have the drama of aluminum when it fails > and what would be the max to which it could be filled without any danger to the tank or the > 1st stage (which in the case of my 2 regs, are rated to 3500PSI each as well)? Your shop doesn't have a powerful enough compressor to hurt your steel tanks. > 2nd Question - The LDS recommended converting the regs to DIN for these tanks but I hear from > other shops that it is not necessary. Thoughts? I wouldn't do it, unless you like to fiddle fart around with crossthreads and 90 sizes/styles of o-ring. I've had mine(A-clamp) at 4000 psig without incident, but I don't make it a habit and that was not on purpose. Your cylinders came with the new valves right (they have removable inserts)? Some people just like DIN. They like to screw things. It gives them a woodie. I *way* prefer A-clamp to DIN. I travel dive a lot, and wouldn't want the adapter shoving the thing into the back of my head on the inevitable AL80s. Diving locally, I swap tanks in half the time it takes DIN guys. That counts for something when the seas a running big. I own native DIN assemblies for my regs, but haven't used them in years...In steel tanks, I think yoke is also less apt to get water in the tank. It sure as hell has less to blow out. Then there's all that fun when some prankster opens your valve with the dust caps in... 300 Bar is a *really* big fill (4350psig). I guess if that's what you dived with all the time, then DIN would probably be the way to go. I only know one company that makes that tank (Luxfer) and I've only seen two of them. Who wants glass wrapped Aluminum? If you decide to convert, make sure you convert to 300 bar DIN, not 200 Bar DIN. SP has both possibilities (or at least they used to). The difference is the length of the post. If you rent DIN tanks somewhere, they will likely be 300 bar DIN valves, and it's a real drag to find your post is too short to fill the hole. About a year ago we had a guy on the boat in that predicament, and the dive monkey tried to fix things with a pair of channel locks....it wasn't pretty bullshark >> Question being, for a steel 120 rated at 230bar/3442 PSI, is there any >> margin for "overfilling" [quoted text clipped - 18 lines] > condition. > 1) they can't hurt them with shop compressors Actually, in the shop where I help out occasionally, we have a 300 bar compressor and the storage banks are at 300bar. Putting that in a 232bar cylinder would not do it any good. More importantly, it puts a strain on the burst disk(s). Over time these become more likely to fail. > 2) even if they could, steel wouldn't have the drama of aluminum when > it fails [quoted text clipped - 12 lines] > I wouldn't do it, unless you like to fiddle fart around with > crossthreads and 90 sizes/styles of o-ring. Never seen one crossthread. And there's only one size of O-ring in the regs and I've got a couple of different brands. > I've had mine(A-clamp) at > 4000 psig without incident, but I don't make it a habit and that was [quoted text clipped - 3 lines] > Some people just like DIN. They like to screw things. It gives them a > woodie. Ummm... I wouldn't know about that. But my setup *is* all DIN because with the O-rings in the reg instead of the cylinder, it is much simpler. As a DM, I carry a kit with O-rings for cylinders and fro my regs in any case. And I've got a set of twin 12 litre cylinders with a a 300 bar manifold and cylinders rated at 300 bar. The only downsides of 300 bar cylinders are the weight (17kg each (38lbs)) and that the gas laws start to change somewhere around 250 bar. So, while the theory says that 300bar at 24 litres should be 7200 litres of back gas, the reality is somewhat less. > I *way* prefer A-clamp to DIN. I travel dive a lot, and wouldn't want > the adapter shoving the thing into the back of my head on the > inevitable AL80s. I've got a couple of Titan regs with both DIN and yoke backs - I can convert them to yoke for travel use- takes about 5 minutes. > Diving locally, I swap tanks in half the time it > takes DIN guys. I don't see this happening. I'm as quick as anyone else getting set up. > That counts for something when the seas a running big. > I own native DIN assemblies for my regs, but haven't used them in > years...In steel tanks, I think yoke is also less apt to get water in > the tank. It sure as hell has less to blow out. I just keep the valves dry- not particularly difficult since they have regulators in them most of the time. > Then there's all that fun when some prankster opens your valve with the > dust caps in... My dust caps have vent holes in them. It would be noisy but that's about all. > 300 Bar is a *really* big fill (4350psig). I guess if that's what you > dived with all the time, then DIN would probably be the way to go. I > only know one company that makes that tank (Luxfer) and I've only seen > two of them. Who wants glass wrapped Aluminum? Faber makes a steel 300 bar cylinder. See above comments about weight. (But Italian cylinders may be hard to get in the USA) > If you decide to convert, make sure you convert to 300 bar DIN, not 200 > Bar DIN. SP has both possibilities (or at least they used to). The [quoted text clipped - 3 lines] > on the boat in that predicament, and the dive monkey tried to fix > things with a pair of channel locks....it wasn't pretty Yeah, I bought a Mk25 DIN reg on the net thinking that as a technical regulator it would *of* *course* have a 300 bar fitting. I forgot that the USA generally uses lower cylinder pressures. And clearly the DM on the boat had little clue. The difference is fairly obvious and if you're putting things together correctly you should feel the insert "bottom" on the O-ring in the valve. The bottom line for me is that it's better to get cylinders that allow you the option of using either DIN or yoke regulators. I personally believe that there are enough good reasons to use DIN that it is worth the little extra hassle that is involved in using them. But if your cylinder valves go either way you do not need to commit to one style or the other. -Don > Actually, in the shop where I help out occasionally, we have a 300 bar > compressor and the storage banks are at 300bar. Putting that in a 232bar > cylinder would not do it any good. More importantly, it puts a strain on > the burst disk(s). Over time these become more likely to fail. I don't believe the question was about what does them good, but what will cause them to fail. There is a difference. As for burst disks, unlike tanks, they are designed to fail and yes, the higher the pressure, the more likely they are to fail. Importantly, burst disks almost never fail in the water. They fail on land, in conditions that heat the tank, increasing the pressure still further. Even so, burst disk failures are rare and nothing more than a bit of adrenaline rush and inconvenience. In more than 40 years of diving, I've never had even a burst disk fail and I've witnessed less than half a dozen failures, all on tanks filled substantially over rated pressure. These days, my tanks are filled the same place Bullsharks are. On the other hand, I'm slowly, but surely converting to DIN connections. Three are sufficient advantages to me to more than compensate for the few disadvantages. Lee |
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