Talk:Diving cylinder

Terminology
12/14/06 Discussion regarding the phrase copied below:

A diving cylinder (the term which tends to be used by divers) or SCUBA tank (more often used colloquially by non-divers)

As a NOWI Certified Diver and a PADI Certified Diver for more than twenty-five years, I can attest to the fact that I have never heard an American diver or American Oceanographer refer to our "Dive Tanks" as anything other than "Tanks." Therefore, the author's statment as prefaced above in parenthesis may be not be valid.

In any case, the reference to "non-divers" seems a bit unnecessary and sounds more like personal opinion rather than an actual fact. I recently, reviewed my old dive manuals whereby, the official terminology used here in the USA is "Tank" and not "Cylinder." The only exception I found was at a PADI web site tonight. However, I noticed the date of birth on the registration page of the website is European I.e. day/month/year as opposed to American month/day/year. Therefore,the term cylinder would be more appropriate coming from European divers. There is also a dive master video on the NOWI website regarding equipment. The term tank is being frequently used by the dive master when referring to the breathing unit.

European divers would generally refer to them as "tanks" - the proper name being a "cylinder" however, its not used in general speaking. Perhaps non-english speakers translate as cylinder? —Preceding unsigned comment added by 89.168.72.84 (talk) 23:05, 9 December 2007 (UTC)

I have seen the same (idiotic) argumnet over the term skeg or fin on a surfboard and have heard some say that only a non-surfer would say skeg. I simply believe this type of commentary detracts from the article in general and is therefore, may not necessary.

PEACE

(LCrockett 04:16, 15 December 2006 (UTC))hope I did this correctly :-(?


 * You don't have to indent paragraphs (screws things up if you do). Otherwise you did fine. I get three times as many Google hits on scuba tank as scuba cylinder. But I do notice that makers and engineers tend to call them cylinders. Perhaps this filters down to those who want to sound like the people who make (and service and hydrotest) the stuff, rather than just use it. S  B Harris 08:23, 15 December 2006 (UTC)


 * Should Diving tank be added as a redirect to this article? -- Armadillo From Hell GateBridge  08:36, 15 December 2006 (UTC)


 * Yes, I think so, and have done so. Along the way I fixed the definitions so that I think everyone will be happy and satisfied. "Gas cylinder" is the generic term used by engineers and the ACGA people who use all kinds of sizes of compressed gas containers, not just the ones for scuba. Even the big H cylinders get called tanks by the non-cognoscenti, but never by people who work on them for a living. The same kind of distinction carries over to scuba. S  B Harris 18:27, 15 December 2006 (UTC)

Diving Oxygen
"Breathing industrial compressed gases can be lethal because the high pressure increases the effect of any impurities in them.". I breath welding oxygen on a regular basis and so do a lot of other people. My research says it's the same oxygen used for both applications. Maybe that should be clarified. 142.165.246.187 16:13, 10 February 2007 (UTC)


 * I would wish to take issue that welding and breathing oxygen can be regarded as the same product. In the UK, USA and Europe there are both civilian and military specifications for welding oxygen and for diving quality oxygen (and medical oxygen). I would suggest that you could safely use diving oxygen and medical oxygen, if you wished, for welding but it would not be sensible to do so as these products are more expensive than welding oxygen. Likewise, you could use industrial grade oxygen (welding oxygen) for diving, however it is not sold (in the UK and Europe) as a breathing gas; and that it would be safer to use one that is sold for that purpose. Perhaps, that partially answers your point.Pyrotec 18:29, 10 February 2007 (UTC)


 * My anecdotal experience comes from talking to someone who worked for BOC (British Oxygen Company) some years ago. He maintained that all of the oxygen sold came from the same source, i.e. there was only one process used. The only exception being "Aviation grade" oxygen which had an extra stage of processing to remove any remaining water vapour because of the low temperatures that this oxygen may be exposed to. So medical, breathing and welding oxygen all came out of the same pipe. The catch was that BOC rented large cylinders to the end-user to hold the oxygen; when empty, these would simply be swapped for a full one. There was no procedure for ensuring that the cylinder was clean for customers who purchased welding oxygen, while the "higher" grades had the cylinders cleaned regularly. All of this seems to make commercial sense to me, so I have no reason to dispute his claims. Bottom line: you have a good chance of getting the same oxygen when breathing "welding grade", but no guarantees. RexxS (talk) 20:09, 6 January 2008 (UTC)


 * "The pipe bit" is not the whole story; as you say an important part of the filling process is ensuring that the cylinder is clean before it is filled. Any hospital or dive shop that "plugs" a patient or diver into a cylinder of welding grade oxygen is going to get a large legal bill if someone suffers as a consequence. If its a proper medical or diving cylinder, then BOC or its competitors carry the consequences of "dirty" product being supplied. Pyrotec (talk) 20:26, 6 January 2008 (UTC)

Gas quantity calculations
To calculate the quantity of gas: quantity of gas = volume x pressure

But: 3 litres * 200 bar = 60 kilojoules Should the article clear this up? Also we might want to include some mention of the energy content (compressed air) of scuba tanks. —Preceding unsigned comment added by Glueball (talk • contribs) 11:55, 12 July 2007(UTC)


 * The formula only works in metric units - it's just Boyle's Law (and subject to the same limitations). Should be


 * "Volume of gas at atmospheric pressure = (cylinder volume) x (cylinder pressure) / (atmospheric pressure)"


 * I'll change it. And it would be of interest to show the energy stored in a cylinder - maybe with some comparisons to TNT, etc.? RexxS (talk) 20:29, 6 January 2008 (UTC)


 * A liter-bar is 100 J = 0.1 kJ, giving you the energy above, but this assumes that all the volume is delivered at this pressure, which if course is not the case in a scuba tank. As it charges, or as it explodes or discharges, the pressure runs up or down as the volume is delivered, so differential work at each instant changes, and the correct formula integrates the PV work over the whole process. There are two ways to do this: one is to assume that the heat or "cold" stays in the gas during the compression/decompression (a good assumption for charging a cylinder in air (say with fill-whip on a boat), or for one that explodes). The other way is to assume that compression heat leaks out to ambient temp, as in the tank-fill water bath (which is how you figure how much extra energy is, in a tank after it has cooled back down to room temp, and assuming that you discharge the gas so slowly that it has time to absorb surrounding heat which it can convert to work.)  The work to charge a tank VERY slowly and isothermally (or discharge it over an hour where the gas can warm up in the first stage), is W = P(1)V(1)ln (P2/P1). For a typical aluminum 80 at the surface, P1 is 11.3 L, P1 is 1 bar, P2 is 200 bar, so the work is 12,000 L-bar or so, or 1.2 MJ or 1200 kJ. This is 286 Cal, or about as much as in a candy bar. But no small potatoes energy-wise if released quickly, as a stick of dynamite is only 2100 kJ. So only half a stick of dynamite. In fact, for a fast adiabatic release, as in a tank explosion, it will be even less than this, since the gas will cool as it expands and does work on the environment, and thus will not do as much work as if it had been allowed to remain at the same temperature, absorbing heat in a slow expansion. S  B Harris 00:58, 20 September 2009 (UTC)


 * This assumes a ideal gas. Air at 200 or 300bar is NOT an ideal gas. So 10L at 300bar ends up at only about 2700L air, a full 10% shy of the teoretical 3000L! --StefanHuszics (talk) 04:42, 19 May 2010 (UTC)
 * That's true and it's mentioned in the article. At 232 bar, the deviation from ideal gas law linearity is about 5% (assuming temperatures around 300 K). There's an article Compressibility factor that has lots of good data. --RexxS (talk) 05:09, 19 May 2010 (UTC)

Breathing Time
The formula and example are wrong, imho. They miss the point that ambient pressure should include the contribution of the weight of air above the water. In metric terms, you need to add 1 bar (or atmosphere - I know they're strictly not the same). The current formula leads to the conclusion that you can breathe off the cylinder for an infinite time at a depth of 0 metres! I would suggest:

AP = D * g * rho + atmospheric pressure

in proper units. However, gravity and water density are near constant compared to other variables, so this approximates to:

AP = D / 10 + 1

for all practical purposes. Remember that analogue depth gauges and analogue pressure gauges have errors both in linearity and readability, so there's little point in trying for absolute accuracy here when other variables can easily be out by 5% or more. Not forgetting of course that "depth gauges" work by measuring ambient pressure anyway, so correcting for water pressure is pointless as you really ought to correct the depth read by the same factor in the opposite direction - unless somebody has invented a dive computer that knows if it's diving in fresh or salt water. And of course, the biggest variable is breathing rate, which is difficult to keep within +/- 10% even for the most experienced divers.

Finally, there's no point in using the term (CP-AP) when CP is much greater than AP in all practical circumstances. If the purpose of this section is an illustration of how dives may be planned (rather than a sterile demonstration of how long before a cylinder becomes unusable), may I suggest that (CP-RP), where RP is the reserve pressure, would give more real-life information to the beginner and non-diver alike?

RexxS (talk) 21:40, 6 January 2008 (UTC)

Types of pillar valve - EN 144-3:2003
I'm looking at trying to clarify the sentence "From August 2008, these shall be required for all diving equipment used with Nitrox or pure oxygen."

The word that needs clarification is required. Required for what?

EN 144-3:2003 (ISBN: 0 580 41367 5) ''[http://www.standardsdirect.org/standards/standards1/StandardsCatalogue24_view_11748.html Respiratory protective devices. Gas cylinder valves. Outlet connections for diving gases Nitrox and oxygen]'' does not address 'requirements' and is not legislation per se. It is true that if equipment is to be CE certified from August 2008, then it must comply with this European Norm. Note, though, that it says nothing about procedures for filling cylinders or using them safely. It certainly does not make the use of M25x2 connections illegal when used for nitrox or O2.

The EN which deals with requirements is in fact, EN 13949:2003 (ISBN: 0 580 41368 3) ''[http://www.standardsdirect.org/standards/standards1/StandardsCatalogue24_view_11316.html Respiratory equipment. Open-circuit self-contained diving apparatus for use with compressed Nitrox and oxygen. Requirements, testing, marking]''. It is interesting to see what EN 13949:2003 says about cylinder connections:

4.4 Pressure vessel valve(s)

Pressure vessel valve(s) shall comply with appropriate national or European Regulations and shall be approved and tested for use at the rated working pressure and pure oxygen. The threads for connecting the pressure vessel(s) and the valve(s) shall be M 18 x 1,5 or M 25 x 2 as specified in EN 144-1. Safe connection between the pressure vessel valve(s) and the demand regulator shall be ensured by using the connections as defined in EN 144-3.

So a little bit of drafting inexactitude? Both norms published on the same date, but the latter (although mentioning EN 144-3) fails to include M26x2 threads as permissible! --RexxS (talk) 23:13, 27 August 2008 (UTC)

Purposes of diving cylinders
Mark.murphy added the following: "To reduce the diver's high negative buoyancy when carrying many cylinders, divers often use aluminium stage cylinders because they are less dense than steel cylinders." I don't doubt that divers do that, but in most cases it's a mistake. Unless a diver has so much negative buoyancy that they have no weights, then the material of the cylinder is irrelevant: a properly weighted diver will be neutral with empty cylinders - the negative buoyancy at the start of a dive is simply the weight of air in the cylinders. All that aluminium cylinders do is increase the total volume of the diver+equipment, which means that they carry a greater total weight out of the water - not a desirable thing.

Anyway, I don't want to remove the statement, since I know that divers do use Al cylinders, mistakenly thinking that a less dense cylinder means less total negative buoyancy. But I'm concerned that the article now gives the wrong impression. This article isn't really the right place to present the arguments about buoyancy, correct weighting and choice of equipment. Is there an alternative formulation that would meet my concerns? --RexxS (talk) 15:19, 21 February 2009 (UTC)


 * Rexx, you are right. The explanation was not correct or complete. I have improved it.
 * Mark.murphy (talk) 18:11, 21 February 2009 (UTC)


 * Thanks Mark, you've made a good job of that - it explains well without the complexity I wanted to avoid. Cheers --RexxS (talk) 00:27, 22 February 2009 (UTC)

Spare Air
Although "Spare Air" is a trademark, that doesn't prevent the phrase being used in Wikipedia. Since the Spare Air is the only device of its type that I'm aware of, I'm unable to find a generic term to describe it. A "micro-aqualung" doesn't fit, since googling for that only brings up hits for the magical device used by James Bond in Thunderball or something similar used in Pokemon. I've referred to Spare Air by name and cited the website as the source. I must say that although I regard these devices as almost worthless, they exist and divers do use them, so they deserve a mention in the article. --RexxS (talk) 19:18, 19 September 2009 (UTC)
 * They are Bail-Out Bottles. Regardless of size. — Preceding unsigned comment added by 71.4.236.2 (talk) 14:51, 28 June 2011 (UTC)

Photographs of "J" Valves. 1) incorporated in regulator, and 2) "J" Valve on Diving Cylinder.
These are two photographs which may add clarity and interest to the text of "Diving Cylinder". They are my photographs of my equipment taken yesterday, 2010-07-22, and are made available to you with my blessings. All substantiating paperwork is included in the "Gallery" with the .jpg images themselves.

As was mentioned, "J" Valves are not normally found today on modern equipment. However "J" Valves were incorporated in the earliest SCUBA gear from the time of Jacques Yves Cousteau and Emile Gagnon original invention and were the normal reserve systems until they became obsolete when high quality diving computers incorporating tank pressure gauges made them superfluous.

John W. Goodspeed "TheGoodspeeds (TheGoodspeeds (talk) 17:24, 23 July 2010 (UTC))

EU regulations
It's generally accepted that EU regulations require a diving cylinder to have a label that describes its contents. We know this because dive shops tell us so when we take in an old cylinder for a fill or test. However, here in the UK, it's not well-known what the relevant legislation actually says about diving cylinders, not least because it's not immediately obvious what the actual regulation number is.

There's a good leaflet from the UK Health and Safety Executive (INDG308(rev1) 4/02 C250), which is free to reproduce as long as the HSE is credited. A copy can be found online at http://www.lambaydiving.com/ukhse.pdf and it summarises the regulations that apply to the manufacture, testing, filling, and transportation of gas cylinders.

The standard EN 1089 Gas Cylinder Identification sets out the EU requirements for stamp marking, precautionary labels and colour coding. There's a summary online at http://www.ukdivers.net/equipment/cylinders.htm which is usually pretty accurate, but I wouldn't feel comfortable using it as a Wikipedia reliable source. I'll take a trip to the library this week to see if I can find the wording of the actual regulation. --RexxS (talk) 17:24, 13 November 2011 (UTC)

Orphaned references in Diving cylinder
I check pages listed in Category:Pages with incorrect ref formatting to try to fix reference errors. One of the things I do is look for content for orphaned references in wikilinked articles. I have found content for some of Diving cylinder's orphans, the problem is that I found more than one version. I can't determine which (if any) is correct for this article, so I am asking for a sentient editor to look it over and copy the correct ref content into this article.

Reference named "NOAA": From Scuba diving: NOAA Diving Manual, 4th Edition, Best Publishing, 2001 From Scuba gas planning: National Oceanographic and Atmospheric Administration, ; NOAA Diving Manual, Fourth Edition, U.S. Department of Commerce National Technical Information Service, Springfield, VA  

I apologize if any of the above are effectively identical; I am just a simple computer program, so I can't determine whether minor differences are significant or not. AnomieBOT ⚡ 14:05, 27 November 2011 (UTC)

Poor "advantages" for manifolds
Re. the following text under "Manifolded twin set/doubles with two regulators":

"The pros of this configuration include [1] a large gas supply, [2] no requirement to change regulators underwater, [3] automatic gas supply management, and [4] in most failure situations the diver may close a failed valve or isolate a cylinder in order to leave himself with an emergency supply."

Let me use "manifolds" to mean a twin tank system where the two tanks are joined by a manifold; and "independents" to mean a twin tank system where the two tanks are totally independent.


 * [1], as stated, is just not true as an advantage of manifolds over independents. Two tanks, manifolded, have no more total gas than the same two tanks rigged independently. I suspect the author was actually thinking of [4].


 * [4] is true, but doesn't actually state the critical benefit of manifolds - namely, that closing valves or isolating cyclinders generally lets you retain access to *all* the remaining gas *on both sides* - unlike independents, where a failure on one side will generally result in losing access to all the gas on the failed side.


 * [3] is a poor choice of words. Most technical divers would understand "gas management" as meaning a range of things, such as, choosing the right size tanks for the dive; filling them to adequate pressures; being aware of differing personal gas consumption rates for different members of the team or group; following the "rule of thirds" when entering overhead environments, and so on. None of those things are specific to manifolds. All of them are equally applicable to independents.

I suggest replacing the quoted text with something like this:

"The pros of this configuration include: automatic balancing of the gas supply between the two tanks; thus, no requirement to constantly change regulators underwater during the dive; and in most failure situations, the diver may close a failed valve or isolate a cylinder and thus retain access to all the remaining gas in both the tanks."

TC 203.122.223.123 (talk) 11:15, 26 April 2013 (UTC)


 * Thank you for your well reasoned and constructive comment. It has been used in the article almost as stated. The advantage of a larger gas supply is valid when compared with a single cylinder (in most cases) and has been changed to specify that point. Gas management would include the balancing of available gas during a dive, but your version is unambiguous and an improvement on the original text. Please feel welcome to make further comments on any of the diving articles, and when you have an improvement which is unlikely to be controversial, you are free to edit the article yourself. It will be checked, and may be modified again, that is how this wiki works. Cheers, &bull; &bull; &bull; Peter (Southwood) (talk): 16:45, 26 April 2013 (UTC)

Reader feedback: The web page could benifit f...
132.3.29.79 posted this comment on 1 August 2013 (view all feedback).

"The web page could benifit from US equivalent information, as it caters to metric users. While the Aluminim 80 is mentioned almost as an afterthought, common tank sizes such as a steel 100 and steel 120 are completely missing. Also missing is a discusion of low pressure vs high pressure steel tanks."

This is a good point. Any volunteers? This equipment is not used much in my part of the world. Alternatively point me at a good reference. &bull; &bull; &bull; Peter (Southwood) (talk): 09:11, 17 August 2013 (UTC)


 * Found some refs and added some content. Any comments? &bull; &bull; &bull; Peter (Southwood) (talk): 16:12, 17 August 2013 (UTC)

Table showing the buoyancy of diving cylinders in water when empty and full of air.
The list gives the impression that these are the same for every cylinder of this type. This is frankly not correct. I have several sets of 12l tanks weighing ~14kgs. They generally seem to be about two KGs too heavy. Maybe this can be reworded to make clear that this is an example, because the general message is still true. But overall, I do not see why there even needs to be this full table. I think it might suffice to say that 1L of tank volume at 200 Bars corresponds to ~250 grams of air, and maybe show the common 10/12/AL80s in comparison. --Data2 (talk) 13:10, 8 February 2015 (UTC)

Upgraded to B-class
The article meets the six B-Class criteria: If anyone disagrees, please specify where it falls short, so it can be fixed. Suggestions for upgrade to A-class are welcome. It is probably pretty close already. &bull; &bull; &bull; Peter (Southwood) (talk): 10:04, 5 June 2015 (UTC)
 * 1) The article is suitably referenced, with inline citations. It has reliable sources, and any important or controversial material which is likely to be challenged is cited.
 * 2) The article reasonably covers the topic, and does not contain obvious omissions or inaccuracies. It contains a large proportion of the material necessary for an A-Class article.
 * 3) The article has a defined structure. Content is organized into groups of related material, including a lead section and all the sections that can reasonably be included in an article of its kind.
 * 4) The article is reasonably well-written. The prose contains no major grammatical errors and flows sensibly.
 * 5) The article contains supporting materials where appropriate. Illustrations are adequate. Diagrams and an infobox etc. are included where they are relevant and useful to the content.
 * 6) The article presents its content in an appropriately understandable way. It is written with a broad audience in mind. The article does not assume unnecessary technical background and technical terms are explained.
 * Thanks, Peter. We don't have A-class criteria for WikiProject Scuba - only the big projects like Military History have the resources to undertake rigorous reviews like that. However, it would certainly be a good experience for you to look at taking this article through the Good Article Nomination process - the six Good article criteria are not too different from the B-class criteria, but you have an external reviewer who makes the final judgement. It's a fast way to iron out the minor wrinkles that may be present and helps maintain consistency of quality across different topics in Wikipedia. Having been through it a few times myself, I'd be more than happy to lend a hand if you decide to go down that route. --RexxS (talk) 16:54, 5 June 2015 (UTC)
 * Thanks, I will give it a go. &bull; &bull; &bull; Peter (Southwood) (talk): 20:26, 5 June 2015 (UTC)
 * There are a few outstanding citations, some for things for which I have no references, but are probably true and uncontroversial, just uncited. How do we deal with this? &bull; &bull; &bull; Peter (Southwood) (talk): 15:15, 6 June 2015 (UTC)
 * Ask, of course! If sources exist, I'm willing to bet that Gene knows where to find them. If he can't find sources, take out the cn tags that you placed for anything you think is uncontroversial. Should facts then be challenged at GA review, the correct action would be to remove the text (and put it on the talk page, pending sources being found). Take a look at the three GA reviews at Talk:Oxygen toxicity/Archive 1 and you'll get some idea of the process of refinement that a review provides for the article (and how valuable it is to have Gene as a collaborator). What I learned there allowed me to take the oxygen toxicity article to Featured Article status soon after. --RexxS (talk) 15:50, 6 June 2015 (UTC)
 * A few of the unreferenced items relate to EU requirements/standards, which tend to be rather expensively paywalled, so I will just remove the cn for things that are unlikely to be challenged, like the Hydro test period in Norway. &bull; &bull; &bull; Peter (Southwood) (talk): 16:32, 6 June 2015 (UTC)

Weight of gas consumed
Peter's expansion of this section is very useful but I wonder about the following: I'm pretty certain that the decrease in external volume is almost non-existent. If that were not so, my twinset would be dropping out of its steel bands every time the cylinders were empty - and that's with 300 bars of internal pressure to change their diameter. I agree that the lack of change of external dimensions is worth mentioning, but perhaps the simpler "The decrease in external volume of the cylinder owing to reduction of internal pressure is negligible." would be better? --RexxS (talk) 10:57, 6 June 2015 (UTC)
 * "The decrease in external volume of the cylinder due to reduction of internal pressure is relatively small, and can be ignored for practical purposes."
 * I am OK with that, but have actually noticed a change in tightness of tankbands between full and empty cylinders. Still a trivial change of volume. &bull; &bull; &bull; Peter (Southwood) (talk): 15:10, 6 June 2015 (UTC)
 * You've got to stop over-blowing your cylinders, Peter. :D I can't say I've ever noticed, but if you've seen a small effect, leave the wording as it is for accuracy. I suspect that for most rigs the cam-bands used have enough stretch to swamp any possible effect of cylinder shrinkage. Cheers --RexxS (talk) 15:35, 6 June 2015 (UTC)
 * Yes, I rely on my tank bands to prevent the cylinders from bursting, but they do tend to bulge a bit after a while.
 * More seriously, bear in mind that the modulus of the cylinder material is nearly the same as that of the bands, for steel cylinders, and at full pressure the stress in the cylinders is probably in the order of 200MPa. If there is no soft material between the cylinder and band, the strain in the band will be a significant fraction of that in the cylinder (if the clamping plates are reasonably rigid), so quite a bit of tension will be induced. However, I did a rough estimate and the volume change is negligible.
 * I have managed to find some references and fix a few discrepancies. Time to nominate? &bull; &bull; &bull; Peter (Southwood) (talk): 19:42, 6 June 2015 (UTC)

Illustrations wanted
Starting a list of illustrations which could improve the article. Just in case it encourages people to upload them to Commons.

Please feel free to add to this list and strikethrough items as they become available on commons, even if not actually used in this article. &bull; &bull; &bull; Peter (Southwood) (talk): 06:48, 25 September 2015 (UTC)
 * Photos of diving cylinders at various stages of manufacture.
 * Exotic or unusual cylinders and configurations.

Water in cylinder
- Warning: Anecdote.

"it is not possible for water to get in during the dive". Actually, it is. Some years ago, a buddy of mine was diving a wreck lying on a slope, using twin independents. The shot line used for descent had dropped onto the deepest part of the wreck. He was so interested in the wreck he failed to monitor his gauges and ran one cylinder out of air when he had worked his way to the highest point. He then switched to his other cylinder - without turning off the 'empty' one - and finished the dive by working his way back down the wreck to the shot line and made his ascent. Back on the boat, none of us were surprised when we could hear water sloshing around in the cylinder that had run out of air.

Of course there was air left in the cylinder when he ran out of air - at least the water pressure at that depth - but taking that cylinder back down to greater depth can provide sufficient reverse pressure. The upstream valve that he was diving with ("I prefer it because it doesn't freeflow"), was the final piece of the jigsaw needed to ensure that we spent that evening emptying and drying out the cylinder before it could be refilled. It seems that nothing's impossible. --RexxS (talk) 14:03, 14 July 2016 (UTC)
 * Yes, agreed. unless the cylinder had been submerged deeper than where the last gas was used it is not possible for water to get in during the dive is how I put it, which is exactly what happened to your friend. Nothing is foolproof. He was actually lucky that enough got in to be noticeable, otherwise he would probably have lost the cylinder at the next inspection. Water does get in from time to time, but probably more often when third world compressor operators fill cylinders that have been transported under dripping wet gear and don't check the inlet opening is clean before connecting up. That way only a small amount gets in, so not easily noticed, but enough to accelerate corrosion severely
 * Do you think I should make that statement more clear?. &bull; &bull; &bull; Peter (Southwood) (talk): 15:56, 14 July 2016 (UTC)
 * Nah,, you need a peculiar set of circumstances, and almost all second stages are downstream these days, so chances are very slim that anybody reading the article will be mislead. My experience with third-world filling stations is that the likeliest source of water is the compressor itself when they neglect to maintain it regularly. You obviously have the luxury of working with better trained operators than I do :P Cheers --RexxS (talk) 16:37, 14 July 2016 (UTC)
 * Maybe you just have slightly different third world experience. My anecdote is from Mozambique, where the resort management are usually reasonably conscientious and are often foreigners with some experience of how things should be done, usually PADI instructors or the like, but they hire locals to do the grunt work and don't train them properly, or the locals don't actually care, or both. So the filters get changed by the boss, who stands to lose custom if the air is dodgy, but the cylinders get filled by the uneducated local who is in a hurry and doesn't understand the problem, and doesn't pay for the damage, and is in any case at a higher risk of being blown up by an old landmine in the bush than by a corroded cylinder, so may take a somewhat cavalier attitude to the whole personal risk issue.
 * Any of the servo-assisted Poseidon second stages could leak back through the second stage under a reverse pressure differential, as they rely on interstage pressure to keep the second stage valve closed. While we are on anecdotes, on the same trip that my friend had his new 15l steel contaminated with seawater to the extent that it failed visual later that year, I did my last dive with a Posiedon Jetstream, which free-flowed on me at 30m when I sent up my DSMB and basically emptied my cylinder in seconds. I got octo from my buddy and we surfaced without problems, safety stop and all, but I removed the Jetstream that day and replaced it with an Apeks, and have never gone back. &bull; &bull; &bull; Peter (Southwood) (talk): 07:02, 15 July 2016 (UTC)
 * Nah,, you need a peculiar set of circumstances, and almost all second stages are downstream these days, so chances are very slim that anybody reading the article will be mislead. My experience with third-world filling stations is that the likeliest source of water is the compressor itself when they neglect to maintain it regularly. You obviously have the luxury of working with better trained operators than I do :P Cheers --RexxS (talk) 16:37, 14 July 2016 (UTC)
 * Maybe you just have slightly different third world experience. My anecdote is from Mozambique, where the resort management are usually reasonably conscientious and are often foreigners with some experience of how things should be done, usually PADI instructors or the like, but they hire locals to do the grunt work and don't train them properly, or the locals don't actually care, or both. So the filters get changed by the boss, who stands to lose custom if the air is dodgy, but the cylinders get filled by the uneducated local who is in a hurry and doesn't understand the problem, and doesn't pay for the damage, and is in any case at a higher risk of being blown up by an old landmine in the bush than by a corroded cylinder, so may take a somewhat cavalier attitude to the whole personal risk issue.
 * Any of the servo-assisted Poseidon second stages could leak back through the second stage under a reverse pressure differential, as they rely on interstage pressure to keep the second stage valve closed. While we are on anecdotes, on the same trip that my friend had his new 15l steel contaminated with seawater to the extent that it failed visual later that year, I did my last dive with a Posiedon Jetstream, which free-flowed on me at 30m when I sent up my DSMB and basically emptied my cylinder in seconds. I got octo from my buddy and we surfaced without problems, safety stop and all, but I removed the Jetstream that day and replaced it with an Apeks, and have never gone back. &bull; &bull; &bull; Peter (Southwood) (talk): 07:02, 15 July 2016 (UTC)
 * Any of the servo-assisted Poseidon second stages could leak back through the second stage under a reverse pressure differential, as they rely on interstage pressure to keep the second stage valve closed. While we are on anecdotes, on the same trip that my friend had his new 15l steel contaminated with seawater to the extent that it failed visual later that year, I did my last dive with a Posiedon Jetstream, which free-flowed on me at 30m when I sent up my DSMB and basically emptied my cylinder in seconds. I got octo from my buddy and we surfaced without problems, safety stop and all, but I removed the Jetstream that day and replaced it with an Apeks, and have never gone back. &bull; &bull; &bull; Peter (Southwood) (talk): 07:02, 15 July 2016 (UTC)

Do taper threads eventually wear out?
Since tank valves need to be periodically removed for internal visual inspection, do the US/Imperial taper threads on the tank or valve eventually wear out from repeated removal and reattachment?

The main intent of the US/Imperial National Pipe Thread (NPT) taper is apparently to mechanically squish and deform the metal pipe threads, to make a permanent metal-to-metal gas-tight seal between two potentially imperfect hand-threadings. Repeated disassembly does not seem to be intended, or even desirable with torqued taper threads.

Though I suppose if the metal alloy of the valve side is softer than the tank alloy, the tank threads would be less likely to deform from repeated disassembly, but the valve may need to be discarded or reshaped with a threading die periodically. -- DMahalko (talk) 18:21, 2 August 2016 (UTC)
 * I'm pretty certain that the valve thread is noticeably harder than the cylinder thread. But as I understand it, taper threads on dive cylinders are always sealed with thread seal tape, so the PTFE ensures the seal against imperfect machining, rather than deforming a metal-to-metal contact. You just renew the tape after visual inspection and as long as you don't exceed the recommended torque, the cylinders don't suffer from thread failure, in my experience. That's anecdotal, of course, but I don't know of a reliable source that addresses the issue. --RexxS (talk) 19:43, 2 August 2016 (UTC)
 * The threads do wear out. In the case of a steel cylinder the threads on the valve usually wear out faster as the valve is almost always brass. This is cheaper to fix as a new valve is usually cheaper than a new cylinder. Aluminium tank threads are softer than the valve and will wear out first, or may bind and gall, which damages both threads at the same time. Taper threads on aluminium cylinders are less common in my experience, but this may be a regional thing. In general, taper threads are now less often found on scuba cylinders than in the past, probably for this reason, but in some cases for legal reasons too. In South Africa it is no longer legal to market new cylinders with taper threads for scuba, though the large steel storage cylinders still use them. As RexxS mentions, taper threads on HP cylinders are fitted using either thread tape (usually PTFE) or soft lead covers (not seen on scuba cylinders by me), both of which are much softer than the metal of the threads, and which deform to fill the gaps and make a seal while lubricating and preventing the threads from coming into direct metal to metal contact over most of the surface. This both provides a better seal and reduces the thread deformation to an acceptable level so that the valve can be removed and replaced several times before wear is excessive. Re-threading is usually not possible as the refurbished thread will be smaller than the permitted tolerances and will fail the gauge tests. There are international and national standards for thread form, and manufacturers specifications for torque. Also training manuals and procedures for visual inspection of cylinders. These would be reliable sources. How much of this do you think is in scope for this article? &bull; &bull; &bull; Peter (Southwood) (talk): 05:26, 3 August 2016 (UTC)
 * The lead caps are not for use on aluminium cylinders. &bull; &bull; &bull; Peter (Southwood) (talk): 12:11, 5 August 2016 (UTC)
 * Wikipedia_is_not_paper and so there is no problem with the article being as long and detailed as is necessary to fully cover any relevant topic area. -- DMahalko (talk) 12:36, 3 August 2016 (UTC)
 * My point is whether it is still relevant to this topic to go into thread standards. I guess I will put stuff in and if it gets too much, split it off. Been there, done that. &bull; &bull; &bull; Peter (Southwood) (talk): 15:46, 3 August 2016 (UTC)
 * Thanks, Peter. The only taper thread cylinder I've used was an old aluminium one, but as you say, it may be a regional thing. I appreciate that we could get sourcing on the background to cylinder/thread construction and maintenance, but to address the original question, I've been looking for sources concerned with the failure of taper threads, particularly for examples of the mechanism and for some idea of how common such failures are. I've not yet had any luck. Perhaps you or might have come across some? --RexxS (talk) 15:21, 3 August 2016 (UTC)
 * I will dig around in my paper files. There should be something somewhere. &bull; &bull; &bull; Peter (Southwood) (talk): 15:45, 3 August 2016 (UTC)
 * I found a mention in SANS 1825:2005 Table 3. Basic equipment for test stations: Gauging is mandatory to ensure the integrity of parallel threads. In the case of taper threads where the gauge exceeds the maximum gauge limit remachining may be considered at the discretion of the competent person. The same document references SANS 6406/ISO 6406 Periodic inspection and testing of seamless steel gas cylinders and SANS 10461/ISO 10461 Seamless aluminium alloy gas cylinders - Periodic inspection and testing. Unfortunately I don't have either, but I will make inquiries. &bull; &bull; &bull; Peter (Southwood) (talk): 18:12, 3 August 2016 (UTC)
 * Somewhat to my surprise I found pdfs of both on the net. https://law.resource.org/pub/us/cfr/ibr/004/iso.6406.2005.pdf, and https://ia800306.us.archive.org/21/items/gov.law.iso.10461.2005/iso.10461.2005.pdf I will get back after I have had a read. &bull; &bull; &bull; Peter (Southwood) (talk): 18:26, 3 August 2016 (UTC)
 * With these references it should be possible to create an article on Testing and inspection of diving cylinders. &bull; &bull; &bull; Peter (Southwood) (talk): 18:44, 3 August 2016 (UTC)
 * I have added a fairly comprehensive section on inspection and testing as specifically relates to diving cylinders - left out the stuff for other applications. Open for comment and suggestions., I cant work out how best to use sfn for ISO documents, as they don't really have a useful author name (written by a committee), Do you know a workaround or better option? &bull; &bull; &bull; Peter (Southwood) (talk): 10:22, 5 August 2016 (UTC)
 * I will dig around in my paper files. There should be something somewhere. &bull; &bull; &bull; Peter (Southwood) (talk): 15:45, 3 August 2016 (UTC)
 * I found a mention in SANS 1825:2005 Table 3. Basic equipment for test stations: Gauging is mandatory to ensure the integrity of parallel threads. In the case of taper threads where the gauge exceeds the maximum gauge limit remachining may be considered at the discretion of the competent person. The same document references SANS 6406/ISO 6406 Periodic inspection and testing of seamless steel gas cylinders and SANS 10461/ISO 10461 Seamless aluminium alloy gas cylinders - Periodic inspection and testing. Unfortunately I don't have either, but I will make inquiries. &bull; &bull; &bull; Peter (Southwood) (talk): 18:12, 3 August 2016 (UTC)
 * Somewhat to my surprise I found pdfs of both on the net. https://law.resource.org/pub/us/cfr/ibr/004/iso.6406.2005.pdf, and https://ia800306.us.archive.org/21/items/gov.law.iso.10461.2005/iso.10461.2005.pdf I will get back after I have had a read. &bull; &bull; &bull; Peter (Southwood) (talk): 18:26, 3 August 2016 (UTC)
 * With these references it should be possible to create an article on Testing and inspection of diving cylinders. &bull; &bull; &bull; Peter (Southwood) (talk): 18:44, 3 August 2016 (UTC)
 * I have added a fairly comprehensive section on inspection and testing as specifically relates to diving cylinders - left out the stuff for other applications. Open for comment and suggestions., I cant work out how best to use sfn for ISO documents, as they don't really have a useful author name (written by a committee), Do you know a workaround or better option? &bull; &bull; &bull; Peter (Southwood) (talk): 10:22, 5 August 2016 (UTC)

Nice work, Peter. You can use sfn with any identifier you want as long as you explicitly refer to that identifier using a matching sfnRef in the full definition of the reference (instead of harv . For example in Oxygen toxicity, I used sfn to cite the U.S. Navy Diving Manual in the text like this:

etc. and then in the Sources section, made the full definition like this: The short references show up in the References section where the reflist template is placed and link to the full definition in the Sources section. The sfnRef template takes a number of "authors" (or whatever you want) and a year to match the ones you used in the sfn. Does that make sense? --RexxS (talk) 16:02, 5 August 2016 (UTC)
 * Thanks, that looks perfect. I will see if I can get it to work when I get back from diving. Cheers, &bull; &bull; &bull; Peter (Southwood) (talk): 04:52, 6 August 2016 (UTC)
 * Done. Works as advertised. Thanks, &bull; &bull; &bull; Peter (Southwood) (talk): 18:07, 6 August 2016 (UTC)
 * Done. Works as advertised. Thanks, &bull; &bull; &bull; Peter (Southwood) (talk): 18:07, 6 August 2016 (UTC)

Please use SI units
Please use (or at least include) SI units. E.g. ..maximum working pressure rating from 184 to 300 bars (2,670 to 4,350 psi).
 * 1 bar = 100 kPa=0.1 MPa, so conversion should not require a calculator.
 * In this case kPa would probably be the most familiar.
 * So the pressure would be 18400 kPa to 30000 kPa or 18.4 to 30 MPa (would probably be easier to read under water. )  — Preceding unsigned comment added by 75.73.1.89 (talk) 22:27, 4 November 2016 (UTC)
 * What advantage would this have? I know of no diving equipment making use of any pressure units other than psi (USA) or bar (elsewhere). I've never seen a submersible pressure gauge marked in MegaPascals: have you? Sources use psi or bar (sometimes atmospheres absolute, ATA, or feet/metres of sea water, fsw, msw) as do all the training materials that I'm familiar with. Not one uses Pascals that I'm aware of. For what it's worth, SI_derived_unit specifically mentions the bar, which is by definition 100 kPa - as you say, it's easy for anyone used to SI units to understand. --RexxS (talk) 23:30, 4 November 2016 (UTC)
 * I agree with RexxS on all points mentioned above, but I am also willing to consider any carefully reasoned argument which takes into consideration the realities of industry standards and potential usefulness to the reader of all levels. &bull; &bull; &bull; Peter (Southwood) (talk): 18:04, 5 November 2016 (UTC)
 * I agree with RexxS on all points mentioned above, but I am also willing to consider any carefully reasoned argument which takes into consideration the realities of industry standards and potential usefulness to the reader of all levels. &bull; &bull; &bull; Peter (Southwood) (talk): 18:04, 5 November 2016 (UTC)
 * I agree with RexxS on all points mentioned above, but I am also willing to consider any carefully reasoned argument which takes into consideration the realities of industry standards and potential usefulness to the reader of all levels. &bull; &bull; &bull; Peter (Southwood) (talk): 18:04, 5 November 2016 (UTC)

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OK Here is the scoop
I know, most divers use the term "tank", which is incorrect usage, but we all know what they mean, and I use it myself simply because it doesn't sound as "geeky" as cylinder.

By CGA, PSI, DOT, and OSHA standards, all of which govern the scuba cylinder industry, a "TANK" is a permanently attached vessel. A "CYLINDER" is a portable, mobile vessel. For example: My RV burns LP gas. It has a TANK that is mounted to the vehicle frame. It can't be easily removed and is considered to be an integral part of the vehicle. When I get ready to fill the tank, I drive to the truck stop and fill the RV tank up with LP gas. A forklift that runs on LP gas uses a CYLINDER. It's strapped onto the back of the forklift, and when it's empty, I don't take the whole fork lift to the gas station. I take the 30 lbs cylinder off and just replace it with a full one that's stored in the supply room. When they're empty, I throw them on the back of the truck and go get them filled. My gas grill uses a 20 lbs CYLINDER. When it;s empty, I take it off and go have it filled. I don't take the entire grill with me to the fill station. A car has a fuel TANK. It isn't detachable.

Since I'm PSI/PCI certified, I go by their terminology when in formal conversation. Hanging around the dive shop It doesn't matter, tank or cylinder's is all the same to most people. — Preceding unsigned comment added by 71.51.248.75 (talk • contribs)


 * It is not clear what point you are trying to make here. Cheers, &middot; &middot; &middot; Peter (Southwood) (talk): 07:47, 13 June 2018 (UTC)

Reverted unverifiable edits
, I reverted your recent edits which had some problems I was unable to fix.

You added: As at early 2019, scuba cylinders can be got for higher pressures:
 * 300 bar:
 * 350 bar:
 * 400 bar:

At high pressure, the simple ideal gas law ($$PV = nRT$$) cannot always be relied on exactly. For more information see Van der Waals equation and this link.


 * Firstly, 300 bar cylinders have been available and in use since the 1980s, so not new.
 * The Google search links provided in lieu of references failed to provide me with any reliable evidence that 350 bar and 400 bar working pressure cylinders are available for legal scuba use. This does not necessarily mean that they do not exist, but it demonstrates why such links are not suitable for use as references. There is no guarantee that the user will be able to find the information, not even which of the search results is most likely to be worth examining in detail. I checked a few. Most of the results referred to non-scuba service or to test pressure, not working pressure. If you found a site which actually shows 350 and 400 bar working pressure cylinders available for scuba service, please at the very least link to that specific page, not the search, and preferably provide a properly formatted reference to whichever accepted style you prefer, not a bare url, which is more susceptible to linkrot.
 * As we have not established whether these higher pressure cylinders are actually available, is it necessary to go into van der Waal's equation? (or any of the other non-linear gas equations for higher pressures)? I will look into linking to relevant Wikipedia articles, but we do not use inline links to external websites in the body of a rated "good article". Cheers, &middot; &middot; &middot; Peter Southwood (talk): 16:02, 1 February 2019 (UTC)
 * What cylinder valves and regulators would be used on higher pressure cylinders? I do not know of any rated for more than 300 bar. &middot; &middot; &middot; Peter Southwood (talk): 16:52, 1 February 2019 (UTC)


 * I have modified Diving_cylinder to mention the limitations of the ideal gas laws and a link to the Van de Waals equation. I will look into getting a graph to illustrate the difference. &middot; &middot; &middot; Peter Southwood (talk): 16:48, 1 February 2019 (UTC)


 * Thanks, sorry. Anthony Appleyard (talk) 17:08, 1 February 2019 (UTC)
 * I have to agree with Peter's points about linking directly to websites rather than Google results per Search engine test.
 * Tangentially, the theory behind non-linearity of gases under compression isn't really relevant to diving cylinders. It's enough to note three empirical results (for air or nitrox):
 * a cylinder at 300 bar will contain roughly 10% less free gas than an ideal gas would;
 * a cylinder at 232 bar will contain roughly 5% less free gas than an ideal gas would;
 * a cylinder pressurised to less than 200 bar will not deviate significantly from the ideal gas law.
 * That's off the top of my head, so I'll have to go and find a reliable source for the figures if we want to use them, but that would be far more practical information for a diver than a link to the Van der Waals equation article. --RexxS (talk) 17:18, 1 February 2019 (UTC)
 * Or you could calculate the difference between ideal and v d Waals values for those pressures:-) Actually a graph would say it all. It is more of a problem for partial pressure blending to high pressures, but that would be more at home in gas blending for scuba diving, if not already mentioned. I will check. &middot; &middot; &middot; Peter Southwood (talk): 20:27, 1 February 2019 (UTC)
 * I added a bit in gas blending. &middot; &middot; &middot; Peter Southwood (talk): 20:27, 1 February 2019 (UTC)
 * I added a bit in gas blending. &middot; &middot; &middot; Peter Southwood (talk): 20:27, 1 February 2019 (UTC)

Expand section tag
Hi. I am going through Good Articles with clean up tags on them. Currently we have an expand section tag under the "Surface finish, colour-coding and labeling" sub heading asking for more info on Refinishing, problems with powder coating aluminium, corrosion under attachments etc.. Looking at the article we are sitting at 68KB readable prose. We are into the probably should be divided territory (and considering this is an article on one piece of Scuba equipment an argument could probably be made that it falls short focus wise). Anyway I was wondering whether we really need more info on surface finish. From a bigger picture point of view, has there been any thought to splitting this? AIRcorn (talk) 09:34, 20 January 2020 (UTC)

Proposed split

 * , I have been considering splitting out the content on valves to scuba cylinder valve. &middot; &middot; &middot; Peter Southwood (talk): 19:35, 22 March 2020 (UTC)
 * Sorry for late reply. I would encourage any splitting you see necessary here to keep this more aligned with summary style. AIRcorn (talk) 03:38, 17 April 2020 (UTC)
 * Better late than never. I will try to remember to get round to it soonish. Splitting out Scuba cylinder valve would remove about 18KB, but the summary would put a bit back. Cheers, &middot; &middot; &middot; Peter Southwood (talk): 09:59, 21 January 2021 (UTC)
 * ✅ &middot; &middot; &middot; Peter Southwood (talk): 15:50, 21 January 2021 (UTC)