Cylinder Pressures and Reg Fittings [Archive]

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AllynCarter

23-12-2008, 10:41

Nigel Hewitt

23-12-2008, 10:51

Chris W

23-12-2008, 11:14

I went for DIN fitting - make sure that the first stage is 300bar rated and it'll work on either 300 or 232 bar cylinders. I've got a 232 12L at the moment but may got to 300's in the future.
Where as a 232 bar DIN won't work on a 300 bar cylinder.
I think it's to do with the number of threads (7 on a 300 and 5 on a 232 IIRC).

tony J

23-12-2008, 13:00

I know this is a regular topic and I have visited a large number of threads discussing these topics, but what I'm really looking for is a concise, impartial discussion of the pros and cons of different cylinder pressures (232 and 300 bar) and then the related regulator fittings DIN, A-Clamp.

I'm really not trying to start any kind of flame war, but I am in the market for my first cylinder and thoroughly confused about what I should be looking for.

If you can throw in any comments on cylinder size, that would be appreciated, too.
Impartial is quite hard, as many of us dive certain kit because it works for us.

For back gas I dive 10 litres 232 (as singles and indy twins). These are too small for many others as they use more air than me. I probably use in a 10 what friends use in a 12 or 15. The only cylinders I do not like are small manifolded sets (7's and 5's) as shutdown has to be very quick to prevent loss of gas (though many are very happy diving them)

I don't like heavy cylinders and 10l 232 is really light. If I bought a 300 bar it would very often be at 232 and heavier than I need.

I use A clamps - why, I have 6 or so A clamp regs (some up to 20 years old) which I mix and match depending on whether I'm in the pool, sea , stage or spares. My cylinders are DIN with an a clamp insert
I have been told by many that DIN is safer. I have never had a problem with A clamps, so I can't get safer than safe, so I can not be bothered to spend 40 quid a reg to convert, then convert back to go to the red sea.

When I have borrowed DIN (or used a draeger) I find DIN harder to do up / undo when cold and tired so will need a real incentive to convert. DIN may be a better (German system) but A clamp is good enough (for me)

I would expect the average (mode) diver to have 12's 232 and Din

Tony

ChristianG

23-12-2008, 13:09

I know this is a regular topic and I have visited a large number of threads discussing these topics, but what I'm really looking for is a concise, impartial discussion of the pros and cons of different cylinder pressures (232 and 300 bar) and then the related regulator fittings DIN, A-Clamp.

I'm really not trying to start any kind of flame war, but I am in the market for my first cylinder and thoroughly confused about what I should be looking for.

If you can throw in any comments on cylinder size, that would be appreciated, too.
As for your last comment, mine are 7.7 litres and 260 bar, itty bitty baby ones then about halfway in pressure from those commonly in the UK.

Nigel is being a tad unfair in his comment because he has his own compressor. 300 bar cylinders require topping up, and quite possibly topping up again, and quite possibly again after they have cooled each time. So do my 260s to a slightly lesser extent. That requires time and if you don't have it (and/or the compressor facility cannot accommodate you) chances are that you will get a "short fill". There's some Law involved there that I can't remember the name of as I write which Nigel reminded me of, I think it was a Dutchman or at least he has a Dutch name. Nigel?

I can tell you that anyone who even considers A Clamp (today) as against DIN, never mind the tank pressure, has rocks in their head. A Clamp has a conventional O Ring, visible, which can extrude (it has happened to me twice in the past when I didn't have a choice) whereas a DIN O Ring is "captured" - it has nowhere to go.

A Clamp is used by Americans (as a generality) who don't know better and places like the Red Sea (and the Pacific, amongst others) where they're still using "ancient" tanks and cannot see the significance of converting (other than the cost of it). You can easily get a conversion plug for DIN to A Clamp but it's not so easy the other way. Conversely you will not be able to find an A Clamp plug which will fit 300 bar tanks because they're not designed for that pressure, well, not legally anyway. They're around but I would definitely not advise it, that's an accident waiting for somewhere to happen.

I'm sure I'm only paraphrasing what Nigel says on his (excellent) website, but there you go.

deveugle

23-12-2008, 13:34

The real answer here is to talk to the people you're diving with regularly and test their solutions out until you find one that you are happy with for how you think you will be diving (depths/lengths/locations/...).
Nonetheless a couple of musings that might help you focus your mind (or completely confuse you):

DIN versus A-clamp: Nigel’s page explains the differences. Unless you exclusively dive in places where only A-clamps are used (only your own tanks, only in the US, Carribean, …) I cannot see any rationale to prefer an A-clamp over a DIN fitting when buying a new reg. If your club only has A-clamp tanks or a fill whip for A-clamps, it might make sense to stick with an A-clamp for convenience (don’t have to use adaptors). These days a 300 bar DIN fitting would be preferred for a new first stage, especially if you're also buying your own tanks.

300 bar cylinders
Cons
- Weight: all 300 bar sizes weigh more than their 232 bar equivalent hence less easy to manipulate on a boat, in a car, etc.. However subjectively I feel a 12l 300 bar weighs less than a 15l 232 bar for almost the same gas …
- Filling difficulties: depending on how good and where you’re nearest compressor is, you might not be able to get them filled properly to 300 bar – check with the person who will most often be filling your tanks before you buy. Also a quick refill between two dives off Swanage pier, on a live aboard, in Stoney Cove or similar is unlikely to get you 300 bar after cooling
- Gas volume: 300 bar is not so much more than 200 bar as it sounds due to non-ideal gas behaviour (read Nigel’s explanations)
- Twinning: 12l300bars are really too heavy to twin up, so you can’t buy one now and dive it single for a while thinking you might buy a second one later and twin it up (2x12L300bar is a mind-blowing heavy combination I grudgingly have to admit after stubbornly trying it out in spite of what everyone was telling me). A 2x7l 300 bar or 2x10L 300bar might make sense if you’re happy with the volumes for your diving and can get them filled (a 2x7l300 bar for instance is a great choice instead of a single 15l 232 bar because of its inherent redundancy, of course you’ll need a second first stage, but then again you would need that too for a pony set-up etc …)
Pros:
- Weight: a heavier cylinder allows you take some weight off your weight belt –think about implications for your diving before you decide this is a good or bad thing – or look up some of the ditchable weight threads as this is a whole can of worms. Personally I like to have a heavy SS backplate and a heavy tank so I can have as light as possible a weight belt.
- Streamlining: a 12l 300 bar is smaller than a 15l 232 bar and combined with my wing it feels a lot easier to move around with it on my back, both above and below the water. Also a 12l is slightly longer, but a lot thinner a 15l which distributes the weight for me (6’4”) a lot better around my body than a 15l. Some body types might prefer shorter tanks or even a dumpy. In my experience these tend to be shorter people

My personal preference:
I have and will continue to dive almost any tank I can get my hands on. If I had a load of money to spend and get whatever I want for my diving I would prefer a 2x7l300bar for an average British sea dive to max 40m with no more than a couple of minutes mandatory decompression stops and a single 12l 300 bar tank with 32% in it for poodling around to 25ish meters. For anything deeper or longer I would keep a 12l232 bar twinset (or bigger if my diving evolves that way) and a couple of Alu stages. Having said that, I currently have a 15l232bar and 12l232 bar because I “inherited” them from someone who left the dive club and I happily dive them until they run out of test. All my valves are DIN (300 bar), no questions asked. I do have a convertor for when diving in American influenced parts of the world (where they might have only A-clamp cylinders) so I can still use my own regs.

Hope that helps a little,
Peter

PeteM

23-12-2008, 14:10

There's some Law involved there that I can't remember the name of as I write which Nigel reminded me of, I think it was a Dutchman or at least he has a Dutch name. Nigel?

Van de Waal

In simple terms says that a cylinder pumped to 300bar does not have twice as much gas in it as one pumped to 150bar.

Effectively the law of diminishing marginal returns applied to pumping cylinders

Nigel Hewitt

23-12-2008, 14:59

Van de Waal
Me again :D
Van de Waal (http://www.nigelhewitt.co.uk/diving/maths/vdw.html)

I'm glad I wrote them all up once and web-sited them as redoing it in a forum post every time never quite worked.

tony J

23-12-2008, 15:16

I can tell you that anyone who even considers A Clamp (today) as against DIN, never mind the tank pressure, has rocks in their head. A Clamp has a conventional O Ring, visible, which can extrude (it has happened to me twice in the past when I didn't have a choice) whereas a DIN O Ring is "captured" - it has nowhere to go.
twice it happened and both times you lived ?

Only time its happened to me is on turning on a cylinder when it makes a nice bang.

Tony (rocks in head)

ChristianG

25-12-2008, 17:36

twice it happened and both times you lived ?

Only time its happened to me is on turning on a cylinder when it makes a nice bang.
Both times on the same dive trip in the Solomons on the Spirit of Solomons. I had, as I do (so should everyone else), exchanged the O Ring on the tank with a brand new one that I had brought with me. No, it had nothing to do with incorrect sizes, I don't do incorrect sizes in O Rings. Both new ones extruded, one at thirty metres and the other at twenty (thereabouts). Guess what? I'd also brought my pony along - no dramas at all, especially since my buddy was me old mate Nik (as usual).

Edit: the picture in my avatar is of me on that trip. You can easily see the offending tank and you should just be able to see the base of the pony sticking up at my left shoulder, the brightish yellow thingie. Nik is (thankfully) obscuring my face.

AllynCarter

28-12-2008, 11:48

Thanks to everyone for all the words of wisdom. One follow up question, if I may...

What about aluminium cylinders?

PeteM

28-12-2008, 13:46

Thanks to everyone for all the words of wisdom. One follow up question, if I may...

What about aluminium cylinders?

In the UK for back gas generally considered horrible. Out of the water they weigh about the same so no advantage, in the water they weigh considerably less so you have to put a lot more weight on your belt which is a worse place to have it than on your back.

Plus I believe the testing intervals are smaller

As stage cylinders or for use with thin wetsuits where little or no weight is carried then the arguments are different

ChristianG

29-12-2008, 14:36

In the UK for back gas generally considered horrible. Out of the water they weigh about the same so no advantage, in the water they weigh considerably less so you have to put a lot more weight on your belt which is a worse place to have it than on your back.

As stage cylinders or for use with thin wetsuits where little or no weight is carried then the arguments are different
Ummmm, I would have to say "kind of".

I use steel, mostly for the reasons you describe above and when in twin tank mode all of my weight is on my back.

Most diving in this country is done with aluminium tanks, and al tanks tend to become positively buoyant once they have little to no gas in them to weight them down. Thus I would quite certainly not use them as stage cylinders for reasons which should be fairly obvious. In fact in my favourite (warm) parts of the Pacific where I would be supplied with an al tank (I bring my own al pony) I wear a skinsuit and no BCD delighting in the freedom that this offers. If I were to need buoyancy on the surface I'd dump the remaining pressurised air in the tanks which will then give me perfectly adequate floatation. Mind, that reminds me, I've never tested whether the pony will float when empty. :eek: