Which cylinder size/type?

[steveharriss]

I am a bit confused about which size and type of tank to purchase as a new diver. Steel or aluminum, capacity, dumpy or not? I'd like it to be one that I can use either singley, or as a twin, when my skills improve.

The information is a bit confusing to say the least.

Also does anyone have a simple guide to working out air capacity and a guide to dive time (I am aware that air consumption increases at depth and with over exertion).

Cheers

Steve:o

[David Walker]

Unless you're planning anything unusual, and assuming you're diving in the UK, steel 12 or 15's are pretty much standard. A 10l may do if you're small and don't want to do much below about 15-20m. Quite often what people do is start with a 15 and a 12 (15 for first dive, the 12 for the second dive), but there's no reason to particularly. Starting with a tall 12 for example would make it easy to twin them up later.

In general, its good to be diving something similar to your buddies though - if everyone else in your club uses 10's, there's no point you going out and getting a 15 - after your air consumption improves (doesn't usually take that long) you're carrying extra weight for nothing!

Personally, i'd go for a tall 12... :)

David

[Chris Cherrington]

12 litre steel. Faber lightweight 232 bar. Choice of one - all others give em a miss.

100 quid - http://www.kentdiving.com/prod.asp?partno=F12T

To work out consumption you need to know how much you use at the surface. But don't get bogged down in it all. A 12 litre single should be good for no stop dives to 25m. Its the correct choice to twin up (why do people that have been diving ten minutes want twins???? stupid IMO... do some research Steve, not needed yet.)

Chris

[Alan Ewart]

I am a bit confused about which size and type of tank to purchase as a new diver. Steel or aluminum, capacity, dumpy or not? I'd like it to be one that I can use either singley, or as a twin, when my skills improve.

The information is a bit confusing to say the least.

Also does anyone have a simple guide to working out air capacity and a guide to dive time (I am aware that air consumption increases at depth and with over exertion).

Cheers

Steve:o


I'm with David, If you are new to diving I would start with a 12 or 15L steel, depending on how large you are.

A 15 is a good option, roughly the same price to fill and gives you a good reserve in the sports diver range (35M). Remember no one ever died from having too much gas! I wouldnt worry about twinning them up at present, by the time you need to do this you will probably be diving in the 40+ range and you will be spending so much on kit that the price of a twin set will seem superficial :)

[Ben Panter]

Hi Steve,

Welcome to the forums! Like most things, the tank you will want is heavily dependent on your build and preference. Best advice is to try a lot of different tanks first, and see what you like - but bearing that in mind:

Dumpy or Standard?
Some people love dumpies, others (like me) are not fans. How tall are you? Taller people tend to prefer standard tanks, shorter folk sometimes go for a dumpy cylinder. Dumpies are probably unsuitable for twinning, but I'm sure someone out there has done it.

Twinning in the future?
If you're just starting out, I'd give it a year or so before running into diving that requires twins and the like. Having said that, if you get something along the lines of a 10 or 12.2l faber lightweight you'll be able to twin it up in the future with no problem. Often when people get to that stage though, they have a tank for using on easy splashes and a twinset for dives that are a bit more involved. Myself, if I'm doing hardboat diving I'm happy with twins, if I'm in an inflatable or shore diving I think a single is the way forward.

Volume?
If you have low consumption, you might think about a 10 - but I find the extra 2 and a bit litres of air useful. 12/12.2 l tanks are the standard, and give all but the most aggressive gas guzzlers a decent lenght dive at a sensible depth. 15l tanks are also availiable, but they're a bit heavier and if you do plan to twin in the future you'll need to be built like hercules to get them on your back.

Pressure?
There is also the option of a 300 bar tank - much heavier, carries a bit more air (but not quite as much as you might expect, as there is not a simple relation between free-air volume and pressure above 250 bar - covered in exhaustive detail here (http://www.babilim.co.uk/pages/gas_laws.html)). Almost all DIN regs on the market are 300 bar compatable, but if you have a yoke type fitting then it won't work without being converted.

Steel or Aluminium
I'm a bit out of date on this, but the alu tanks that I have are heavier out the water and lighter in the water than the steel versions, due to their much thicker walls. I like alu for stages, but I wouldn't use them for back gas.

Second Hand?
Second hand might be an option - but get the seller to put it though a test first, and check that it's not an antique cylinder with a low working pressure (find this by looking at the "WP XXX" on the bottle neck). In case you didn't know, the current test cycle is a mechanical pressure ('hyrostatic') test every 5 years, with a visual inspection 2.5 years later. Visual is usually about 20 quid, hydrostatic about 30. Old alu tanks will need a 'crack test' as well, economically even over just a five year cycle it is probably better to buy a new tank.

The standard tank bought by most divers, and visible all over the UK of a weekend, is a 12.2 l steel. That's what I'd go for, but your choice may be different.

Hope that helps,

Ben

[Keith Lawrence]

Personally, i'd go for a tall 12... :)I'm with David on this, 15 is a big lump of metal. IMHO a single 12L is ideal as your first cylinder, get the standard tall as the dumpies don't sit comfortably on the bench when you've kitted up :)

As a very rough guide to duration try this easy method : Let's say you use 25l/min, call it 24L to keep the maths simple. So using a 12L you will need 2BAR to deliver that 24L

On the surface you will breathe 2BAR/min
At 10m it will be 4BAR/min
At 20m it will be 6BAR/min...So, if you've got a 200BAR fill, you want a 50BAR reserve, you're diving to 20m using 6BAR/min - it will give you around 150/6 = 25 minutes of dive time.

That's the quick mental arithmetic check I use as a ready reconer to check my detailed air calculation.

HTH

Keith L

[Jo Brooks]

Also does anyone have a simple guide to working out air capacity and a guide to dive time (I am aware that air consumption increases at depth and with over exertion).

If I remember my training correct the formula used is as follows;

Breathing Rate x Ambient Pressure x time = air required

Whereby;
A conservative breathing rate is 25 litres/min
Ambient pressure is 2 @ 10m, 3 @ 20m, 4 @ 30m etc

So say you have a 12l cylinder filled to 232 bar (2784) and want to dive to 30m you would be able to dive for 28mins......BUT this does not take reserves into account nor decompression penalties etc.

[pugwash]

As previously said, I would select a tall 12 litre steel cylinder.

Just one point to remember when sorting out your weight belt, a steel cylinder compared to a similar capacity aluminium one will be lighter at the end of a dive, so you should allow for this. The following link will help you in your calaculations.

http://www.subaqua.co.uk/cgi-bin/cylinder-buoyancy.cgi?units=metric&material=steel&volume=12.2&pressure=232&weight=17&water=salt

A dumpy cylinder as with a 10 litre cylinder may be too short and with the 10 litre, not enough air capacity for a newbie to diving.

Similar to many divers in the UK, I do not prefer a aluminium cylinders as they are initally heavier when full than steel ones. However, as we are all different, some others will make the case for "allys".

[Ben Thompson]

So, if you've got a 200BAR fill, you want a 50BAR reserve, you're diving to 20m using 6BAR/min - it will give you around 150/6 = 25 minutes of dive time.

The other plan for your reserve is to use the rule of thirds, which means you keep 1/3rd of your air for the reserve (so make it a 210 bar fill to make the maths easy:) you keep 70 bar back, and have 140 for the dive- which gives you marginally less at 23 'n' a bit minutes... So close enough, allowing for breathing rate differences :)

[Woz]

Dumpy 12's are pants unless you are a hobbit. You can pick loads up 2nd hand as people really don't want them. Tall 12's are fine.

However all of our instructors lunge for the 10L when doing shore dives. 12's are a good compromise but I find a 15 a bit heavy. I reckon a 12 and a pony will see you through pretty much any no-deco club dive up to the end of SD and a bit beyond until you start going deeper or longer.

[Paul Morris]

I am a bit confused about which size and type of tank to purchase as a new diver. Steel or aluminum, capacity, dumpy or not? I'd like it to be one that I can use either singley, or as a twin, when my skills improve.

Based on that, and it you're in any way serious about twinning up in future, has to be Faber tall 12l steel. If you want to be really clever you could ask the shop to change the cylinder valve for an MDE modular valve which will allow a manifold to be added later (will cost a little more). Although, given the fact you say you're a new diver, probably best to wait until you're ready to manifold twins, just in case the MDE system changes in future!

In either case, you can still use your 12l steel with another as independant twins, without needing a manifolded system. Though as valves are often "handed" to say the knob is usually on the RHS when facing the air outlet (please ask a shop to check this!), it may pay to get an MDE modular with the Valve on the reverse side (LHS I think - don't have mine in front of me at work!), so in the future you can beg/borrow/buy any normal 12l tall cylinder and mount them as independant 12s, still allowing you to reach back and operate both valves.


=O O= <---- Note valve knobs '=' on opposite sides
( ) ( )
| | | |
| | | |
| | | |
| | | |
---- ----

Also does anyone have a simple guide to working out air capacity and a guide to dive time (I am aware that air consumption increases at depth and with over exertion).
Your Ocean Diver lectures will cover this subject, but in brief you need to know your Suface Air Consumption (SAC). For planning purposes at Ocean Diver level a SAC of 25l/min usually covers most individuals. Although on your first few open water dives it may be well above this, though your instructor will be aware of this and manage the dive accordingly. Over time, experience and fitness will bring this down significantly - mine is somewhere between 14-16 l/min depends on the dive (currents) and how much kit I'm carrying!

As an example, diving to 20m. If your SAC is 25 l/min, at 20m the pressure is 3 bar, so your air consumption at 20m will be 3 x 25 = 75 l/min.

A 25min dive to 20m (total dive time back to 6m) would need 1,875 litres of gas (75 x 25), which would be about 156bar in a 12l cylinder (1,875/12). You must remember a reserve of 50 bar minimum, which takes you to 206bar. If your cylinder is filled between 220-230 bar you have plenty of air for this dive.

I've simplyfied the process slightly, ignoring the small ascent to surface from 6m, and assuming all the descent time was at 20m, but you get the idea.

Oh, and don't get too hung up on the calculations at this stage. Its useful to work out what cylinder size you need, and how long you can expect to be in for, but at Ocean Diver level you will be taught BSAC Rule of Thirds for air planning. Assume 210 bar fill (makes the sums easy), you have 70 bar for the descent and first part of the dive, when you reach 140bar (1/3rd used) you turn around and swim back for the second part of the dive. When you reach 70bar you ascend to 6m, safety stop, and then to the surface. Which diving within Ocean diver limits, by no co-incidence will usually get you back to the surface with your 50bar reserve. :D

Hope that helps.

Regards,
Paul.

[Woz]

I'd ignore all this cobblers about twinning up. Big twinsets are fine for what they do but complete overkill for 99.9% of club dives and will just make you struggle. 1/2 the people who dive them just do it for the "look at me I'm all technical" cudos. And then sit out the 2nd dive of the days bacause "I really can't be arsed lugging that around again".

I've got a single cylinder setup on a stab jacket that is a pleasure to dive and a twinset setup on a wing that with twin 7's is an utter joy but with twin 12's is a bit of a misery unless you are hard boat diving and doing the dives that warrant 35kg of steel on your back. Have seen people walk from the top car park in Stoney in twin 12's and you do ask yourself "why?"

Keep your eyes out for a 2nd hand 12L tall cylinder. Loads come up for sale, especially if you ask around the internet forums like here or www.yorkshire-divers.co.uk (http://www.yorkshire-divers.co.uk). Experienced divers usually have 1 or 2 hanging around the garage then don't want any more.

Alternatively if you really are a hobbit then I know somewhere that may have a cheap 12L dumpy for sale.

If I were starting out all over again I would get, in this order:

Buddy BCD
Single 12L tall (Faber or Beaver)
3L aluminium pony (Luxfer)
Twin 7's (Faber or Beaver)

Then I'd get a wing and backplate and finally get:
Twin steel 12's (Faber or Beaver)
AL40 aluminium stage (Luxfer)

Small progression each time and you end up with an extremely flexible set of kit you can use for any dive you like, from a 6m shore pootle to a 50m wreck dive with 30 mins of deco and more.

[Paul Morris]

I'd ignore all this cobblers about twinning up. Big twinsets are fine for what they do but complete overkill for 99.9% of club dives and will just make you struggle.
True, agree 100% but if he wants to plan ahead.. I've only had to use twin 12s twice for the diving I do, I usually manage on my twin 300bar 7s to 40m minimal deco. If I need the big ones, then its easy to put independants together quickly using blocks and cambands. Having a suitable opposite-handed 12l is an advantage, as I then just need to borrow a standard tall 12l from the club!

5-10 mins head scratching on how to thread the blocks, and I have a twinset. Taking it apart again is a 1 minute job, and we're back to singles again.

I bought a 12l dumpy as my first cylinder, and its a pain. Avoid, though everyone in our club at the time was raving about them. Damn the midget D.O. :p

For the rest of my diving I have a 10l steel (nice for instructing, or as a big deco stage), 3l pony (bail-out or deco), 7l 300bar twinset, 12l dumpy :mad: and 12l tall.

So, whatever happens if your diving expands, you will inevitably start buying more kit :cool:

[Chris Cherrington]

Dumpy 12's are pants unless you are a hobbit. You can pick loads up 2nd hand as people really don't want them. Tall 12's are fine.


My missus used to use them (dumpties) although I would describe her more as gnome-like than hobbitish :D See the pointy hat??

http://www.filelodge.com/files/room16/410175/chrisekelly.jpg

Since doing her trimix ticket and using a wing she has changed her mind and uses the tall ones. (Our LDS has a 12 stubby for sale 2nd hand.....)

Given the recent fall in prices tanks are nearly a throw-away item now.....

Chris

[steveharriss]

Thanks everyone....I guess I'll go for a 12l steel cylinder then.

Excellent forum

[Matt-75]

As mentioned earlier, you can pick up 12L cylinders secondhand (ebay/personal ads) for not much, and in test. I picked one up a couple of months back for £40, in test until october this year.

So dont just go new for the sake of it, look here as well:

http://sports.search.ebay.co.uk/scuba_SCUBA-Snorkelling_W0QQcatrefZC12QQfmcZ1QQfromZR10QQfsooZ 1QQfsopZ1QQfstypeZ1QQftrtZ1QQftrvZ1QQga10244Z10425 QQsacatZ16052

[Chris Cherrington]

But they are only 100 quid new and then you get 2.5 years trouble free, a £15 test and another 18 months then sell it on ebay for 30 notes.....

Chris

[Chris aka divingchef]

All very good advice.
But beware of 300bar cylinders, filling stations outside the UK are virtually none existant.
I use 15L steel with a 3L pony for most dives but I also have two 10L for the shallower dives, I can also twin these with a buddie stab jacket or use then as stage.
Have a look on www.acsac.co.uk
:D

[Chris Cherrington]

.... 300bar .....filling stations outside the UK are virtually none existant.
.....

Upon what evidence do you ascert this viewpoint? My LDS here can pump to 300 bar as do at least 2 other places in Luxembourg. My old local shop in Italy also would give 300 bar as did the school in Lake Garda that I did my trimix course with and also the school we used in Belgium to do the CMAS 3 star. Ok I haven't been everywhere I admit, but of the places I have at least 50% will (if pressed) blow to 300.

That said, 300 bar tanks are rubbish.

Chris

[Richard Whitcombe]

Ive got a steel 15 and a 12l dumpy.

The 15 is nice for ~40m diving or the longer first dive.
12l for most diving though is more than enough.

Dumpy i find is the perfect height for balancing on the tubes whilst kitting up on a RIB (which is 99% of my diving).

[Chris aka divingchef]

Upon what evidence do you ascert this viewpoint? My LDS here can pump to 300 bar as do at least 2 other places in Luxembourg. My old local shop in Italy also would give 300 bar as did the school in Lake Garda that I did my trimix course with and also the school we used in Belgium to do the CMAS 3 star. Ok I haven't been everywhere I admit, but of the places I have at least 50% will (if pressed) blow to 300.

That said, 300 bar tanks are rubbish.

Chris

Hello Chris
I stand corrected ,,,,,,,,I dont know of anywere around here that does 300bar.
Lucky to get 200 !!!!
Chris

[Helen (AKA Hellvet)]

12l are fine for me, but i personally much prefer the dumpy, as most of the women in my club do, whereas i find the blokes prefer the standard tall 12l, or 15l.

Try one of each if you can, before you buy - i found the dumpy much more comfortable to carry and dive, especially off a RIB as previously mentioned. I find it much more comfy to sit down, stand up and walk in. This seems to be a bit to do with back length - though i'm 5"7' i have a relatively short back and long legs. I find they're easier to carry in/out of the shop too as i find a standard 12l is just that little bit too long to be comfortable!

Incidentally surely you can twin dumpy 12l's if you can twin 15l's as they're the same diameter aren't they? Happy to be corrected...

[Woz]

Yes you can twin dumpty 12's and as an added bonus they make your bum look smaller.

[Martyn Ward]

and as an added bonus they make your bum look smaller.

My bum looks just perfect as it is thank you.

To be honest, it looks so good in a mirror that I really want to make love to myself. Trouble is, I just can't get round to it :D

[Janos]

Incidentally surely you can twin dumpy 12l's if you can twin 15l's as they're the same diameter aren't they? Happy to be corrected...

Yes you can. I have done so on holiday. It's painful though as they stick out a fair way behind you, and were way to short for me. I have also twinned a 12 with a 15 (they brought a 15 and 12 on board instead of 2 12s). That was odd, but managable once I was in the water.

Janos

[Paul Oliver]

OK then, we as a Rhib diving club use 15L Steel, as 12L are too small for our diving (especially the new divers with high air consumption rates) which is mainly Wrecks in the 30m range out of Dover. We actually consider 12L a waste of time other than for dive 2 (when we do one).

If i am shore diving or training i prefer a 12L, and despite being 6' i much prefer a 12L Steel Dumpy. If its set right on me BC its VERY comfortable.

I have twin 12L and they are for deeper/longer diving off of Hardboats, not something you need to rush into, despite what many techie weenies will tell you on the interwebbythingy :)

[Matt-75]

For a good starter kit, get a 12L or 15L.

Then get a 3L Pony to cover any bailout options you want.

Beyond that its up to personal choice.

[Ant Slegg]

Someone recently said:

First you buy a 10l because the club you dive with has one and it seems OK.
Then you buy a 3l as a deco stage or pony.
Then you buy another 10l because you want to twin them.
Then you buy twin 12s for deeper stuff and a 7ltr for deco.
Then you buy another 7l for trimix type diving.
Then if you push things really deep the 10s become stage cylinders.
Then you twin the 7s for the shallower stuff because carrying 2x12 all the time is hardwork and you can't sell two old 7s.
Then you sell the lot and buy a rebreather.
Then you realise your mistake and buy a 7l as a bail out.


Ant S

[Matt-75]

So an ideal setup is likely a 12L primary, and a 5L or 7L bailout. More than enough air for most dives.

Then when you have a few dives under your belt. Get a twin 10 setup.

If you never go onto trimix, you probably wont need much more than those 4 cylinders.

[Woz]

So an ideal setup is likely a 12L primary, and a 5L or 7L bailout. More than enough air for most dives.

Then when you have a few dives under your belt. Get a twin 10 setup.

If you never go onto trimix, you probably wont need much more than those 4 cylinders.Twin 10's not really big enough for 2 biggish dives and the short 10's are a pain to kit up in unless you are Ronnie Corbett.

Single 12 and 3L pony will see you thorough lots up to little deco dives.

5L ally stage cyl is lovely, 7L ally is quite big. Personally I would try stuff out first before buying.

[Matt-75]

This thread seems to have gone on a bit.

I think the answer is their is no definitive answer.

Each individual is different and you have to customise what you buy to the sort of diving you are doing and likely to do.

We can only give you advice, its up to you what you do with it.

[Paul Morris]

Twin 10's not really big enough for 2 biggish dives and the short 10's are a pain to kit up in unless you are Ronnie Corbett.

Single 12 and 3L pony will see you thorough lots up to little deco dives.

5L ally stage cyl is lovely, 7L ally is quite big. Personally I would try stuff out first before buying.

However, 10l faber steels are quite light and surprisingly floatly for greedy stage cylinders, so perhaps those twin 10s' were a useful progression after all! :D

[tony J]

However, 10l faber steels are quite light and surprisingly floatly for greedy stage cylinders, so perhaps those twin 10s' were a useful progression after all! :D

The larget set I've ever dived twin 10's (I'm 6ft 4, so two Ronnie corbets). They seem to last Ok for two dives aswell. I find twin 12's too heavy (they give me backache underwater). They seem to last me two dives Ok as the more serious the first dive, the more numpty the second.

I never spend more than an hour in water on a dive (I get cold...) so I do not need loads of Gas.

It would be nice to have slightly taller 10's, but as they are light its not a great problem.

Tony

[Woz]

Dumpy 12's are pants unless you are a hobbit. You can pick loads up 2nd hand as people really don't want them. Tall 12's are fine.

I take back everything I said about dumpy 12's. Just did a week diving with them and they are absolutely fine, even twinned up with Buddy blocks on my Commando. Being wide they even made my arse look small.

[R.Burgess]

For the first year most dives will probably be non deco, shallow and short say 30-40 min max. Many of us rarely dive below 40m and most dives are less than 30m. At first breathing rates are high. In time Sac rates of 25 litres per min or more, come down to 16 and 15 litres per min and small framed light weight people can be breathing less. Steel cylinders are cheaper than ali in the U.K. Steel Faber 232bar cylinders weigh around 1.2 kg per litre. Some steel cylinders like Roth 232's and Faber 300 cylinders weigh more. At first you'll probably want a large cylinder like a 15 litre, in time your ideal size cylinder will change.
E.G. On my average 30-40min non deco recreational shore dive I use +- 1800 litres of air and if I have a 1/3 reserve of 600 litres I need a cylinder with 2400 litres capacity. Hot fills and cold water often means a 232 cylinder has 200 bar so a 232 12 litre is the cheapest option. If your small, weak or getting old and saving the all up weight is critical. You could cut about 4kg of ballast from your weight belt by getting a 9 or 10 litre 300 bar cylinder. It would cost more, the cylinder will take longer to fill and you need to ensure you get a cool fill for there to be an advantage. You may also have to pay slightly more for a 300 bar fill. The cylinder will be just as heavy, but because it displaces less you need slightly less weight on the belt and that means slightly less all up weight to carry on the surface. I'm not sure if this will also improve your SAC rate.
Regards the choice of long or short 12. The fatter 12 faber dumpy is generally a 12.2 litre and although I've never measured them and it seems negligable, I get better air consumption than with a long 12. The long 12 however can be carried lower on the back is often more comforable for sitting whilst kitted up and the balance is a help in getting a horizontal trim. Good luck.

[scubadiver]

I started diving with a 12l, but always had my eye on the gauge as I breathed the air quickly. Although my breathing rate is now good and a 12l is OK I find having a 15ltr is a real confidence builder with that extra air.