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Hi I am looking into getting a Twin set  maybe  two 7lts or more .I am off to the dive show on sun  ,can anyone give me any tips and advice as to the diffrent options and types on the market . I will you useing them for general diving , sometimes  30m + diving .and cavern / cave diving later on, any info would be very helpfull. at the moment I am on Air  I will be doing mixed gas training soon . thanks Fiona.
 

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Amazing...i was just about to post up the same question and for the same reasosn (cavern and cave diving) saw your post Fiona...I'll tag along on the responses.

Also, manifolds? and 232 v 300 bar? and what weight are we looking at for say twin 10s or 12s (for each pressure rating)? and what make is recommended?

Personally, nitrox for me is not important for the limits it imposes on depth but I'm not going deep enough to be worried about trimix etc etc.

Additionally, what pony would be recommended (size and metal type) with twins as described above?

Cheers all and esp Fiona.

Graham
 

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I'm bouncing the idea of twins around my head at the mo. Troubles is at less than 30m I can get to the surface on a pony and a 15+pony would give me almost as much time as twin 10's. 7's - just too small, 12's a bit of overkill really.
So if its just for the gas, as opposed to balance etc I think I'll look real hard at a 15, the pony I already have.
Conclusion I'm coming to is that I will need 12's if I'm going below 30 and/or into deco obligations. I see 10's as giving me 5 maybe 6 minutes more bottom time that a single 12/15 but then the possibility of running into deco which means cutting back on bottom time to ensure enough gas for deco obligations, so its a no-win situation (for me). Add the complication of manifolds etc and I'm finding 10's hard to justify.

Matt
 

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There is no "right answer" just common sense.
cylinder size depends on-
Can you carry them?
 You need to be able to manhandle them about so no point in twin 15's if you can't move them.

What sort of diving will you be doing re SAC?
 You need enough gas for your SAC and the type of dive you are doing. too small is no use.

What size you are for wearing them.
 10's might be long enough or 7's too long. depends on your height and build.

what type of fills you can get re 232 or 300bar.
  If you want compactness then you need to make sure you can get them filled.

Whether you want alloy or steel.
 Some people have a preference one way or the other.

Opinions only but you should look at an isolating manifold (MDE few people will argue they are the most robust and reliable) and steel cylinders (Fabers are very light and good quality,most others like ND ones are very heavy and Cheap/nasty) preferably 232bar unless you dearly wish to have 300bar for the size. (232 is easy to fill and use).
Size- 7 lt 232 are too small for just about anything other than one dive, 7lt 300bars ones are a bit tight for two but possible.
A good size is 10lt 232bar, 12lt 232 bar are even better but see size issues above.
 Basically try a few on and see how heavy they are and whether they are comfortable, then work out how much gas you need and go from there. There are only really a couple of sizes so it shouldn't take to long to work out the best option for you.
ps don't listen to anybody who says you MUST use "this" size, the best size is the one that suits your diving and build. For mix gas use or cave diving IMO 7lt cylinders are too small to be of any use at all.
 

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[b said:
Quote[/b] (MATTBIN @ Nov. 16 2003,18:15)]Conclusion I'm coming to is that I will need 12's if I'm going below 30 and/or into deco obligations. I see 10's as giving me 5 maybe 6 minutes more bottom time that a single 12/15 but then the possibility of running into deco which means cutting back on bottom time to ensure enough gas for deco obligations, so its a no-win situation (for me). Add the complication of manifolds etc and I'm finding 10's hard to justify.

Matt
Even a 10lt set is 40% bigger than a 12lt or 30% bigger than a 15lt. You can't count the pony if it is only for emergencies.
There are no complications with a manifold, you put one reg in your gob and breathe with one SPG, less than you would have with a single and pony. Plus no fiddling around changing cylinders.
 You also have a bigger reserve with twins at 30-50bar than a single/pony.
 

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Just not enough dive time.
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Rupert we have bounced this one around a few times so its probably getting a bit boring by now but, 10's require 60bar to get you to the surface (same as a pony volume of 200 x 3l = 600ltrs) and if you only have one cylinder due to a big failure then I dont see how twin 10's really do have that reserve over a 12/15 & pony. (20 ltr x 140 bar = 2800ltrs, 15ltr x 150 = 2250 diff = 550bar at consumption  rate of 100l/min (30 odd mtrs) = 5 mins bottom time). But a 15 would just about get you into deco obligations, so twins 10's definitely would.
Manifolds - I agree that they arent any more difficult to breath from but again there are more failure point and you may need to isolate, possibly by inverting and then having to get longer hoses etc.
Even with the supposed extra gas, much of it will be used on a 30m dive to satisfy deco obligations caused by just a few extra minutes on the bottom. I do agree that sub 30m its a different issue, but that would probably requires 12's.
Absolutely right re tank size etc. - the one thats right for you may not be right for someone else or vice versa.

Matt

ps convince me otherwise and they'll be on my Xmas pressie list quicker than you can say, we have a spare set going free.

Matt
 

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I'd argue that 7s are a good set for caves and penetration. You can get through some evry small holes with them, and there is quite a lot of gas in there, certainly enough to get me as far into and out of a cave as I'm prepared to go right now!

I like 300 bar tanks because they're heavy, and they suit me. That said, I've met a fair few who they don't suit at all, who find the weight of the tanks make it very difficult to add lead in other places. I don't have that problem, and like having everything on my top half and no lead needed. All of this is IMO, many others milage will vary.
 

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If you need 300bar for a particular reason then fair enough (have had 8lt, 10lt and 12lt 300bar sets over the years) but if you don't need it the 232bar is far superior in use and easier to get a good fill in. You can get through some small holes but the difference between 7lt and 12lt cylinders is minimal and is it such a good idea to go through holes quite as tight as that?
 
 (He says knowing full well he does the same
)

I don't understand the argument about deco obligations, cylinders don't do that, only the diver. You seem to be arguing for a single dive on twins where they are normally used for one technical dive or two "normal" dives. A 10lt twinset having 600lt in it would be at 30 bar not 60. Since you can isolate the faulty reg and still breathe the cylinder it follows that 50bar reserve gives you more than 60% more than a pony would.
 

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Just not enough dive time.
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Rupert
30 bar in a twin 10 would in theory give you 600 ltr (ignoring that you need 10bar IP as a minimum), but what happens if you get a catastrophic failure you only have 300 ltrs.
I'm not being pedantic but I dont see how you can justify going down to 30bar. I agree its the diver re: deco but the whole reason for carrying more gas is to get more bottom time. Two dives from twins? Really, doesnt that just mean you are carrying a spare tank of 10ltrs in effect on the first dive and an empty 10 on the second in real terms. So wouldnt it be better to do each dive with a single instead?
Have I missed the point of a twin set, is it to do two dives from the one rig in <30m situations. I accept the extra size of the cylinders will give you redundancy on >30m dives whereas a pony probably wont.
So do you need a twin-set for 30m dives?

Matt
 

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A regulator will give air right down to empty, not just at 10 bar and above.
The only catastrophic failure that would get you onto one cylinder is the manifold or tank valve blowing up and how likely is that (see previous polls on here)?
 The whole point of a manifold is to give access to all gas in case of reg failure and is balanced against this more likely possibility. this type of failure would be as likely as on a single.
You mentioned 30 bar as the amount of gas needed although you have to remember that reserve on twins is larger, my 30 bar on my 12's is far larger than 50bar on a single.
 I don't agree that you carry more gas to get more bottom time, I carry the gas to allow me to do the bottom time I wish to do and hardly ever use all the air carried even over two dives.
For example yesterday. used 70bar from my twins on a 15min bottom time and deco at 40m on a wreck. jumped straight in several hours later and did a wall with a maximum depth of about 35m for around 40m using another 60bar. both dives allowed me to carry enough reserve to rescue me and my buddy at any time during the day even at the very last min of the second dive.
 For an non deco dive I would have no problem  surfacing with  30bar if I wanted to stay in and still have more than enough gas for any emergencies.
 Doing two dives is one of the whole points of having them. You are also not carrying an empty tank but one large one at whatever pressure you have left and more of it is useable than two singles as you only need one "reserve"
 

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[b said:
Quote[/b] (MATTBIN @ Nov. 17 2003,15:13)]Have I missed the point of a twin set, is it to do two dives from the one rig in <30m situations. I accept the extra size of the cylinders will give you redundancy on >30m dives whereas a pony probably wont.
So do you need a twin-set for 30m dives?
You don't need any of them but manifolded twins give better redundancy and are better all rounders in that they are more capable than a single and pony.
I have one 12lt twinset now as I have sold everything else. These are perfect for going and doing my two "normal dives" on a normal diving day with everyone else like yesterday or for my trimix/deep doing in conjunction with stages.
My wife has a 10lt twinset and only dives what would be classed as club diving (ie two dives in day to a max of around 30m or so)
 the main advantages are -
Kit gets set up at home so very few failures as it has been put together in no rush and checked.
I only pay £2 for a fill for a full days diving.
The kit gets put on the boat and is not touched except to dive, no messing about changing cylinders etc.
Lots of redundancy and plently of air
Easy to dive, one SPG, one reg getting used.
With a long hose on the main and going onto the backup reg, one SPG to monitor.
One set of kit does all.
And many other minor ones.
ps I only boat dive so I can see the advantages of a single if shore diving a lot
 

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Just not enough dive time.
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[b said:
Quote[/b] ]I only pay £2 for a fill for a full days diving
so 7.50 & 6.00 for two 12l fills was bit pricey?
36% Nitrox.

It still looks to me as though you are carrying around one bloody great big tank where a smaller one would do the dive i.e. in your wife's case but I concede that the advantages are there and might outweigh the disadvantages.
More thought required,  


Cheers
Matt
 

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[b said:
Quote[/b] (MATTBIN @ Nov. 17 2003,16:03)]so 7.50 & 6.00 for two 12l fills was bit pricey?
36% Nitrox.
We were both diving 27% nitrox,
Total cost of both twinsets including air fills about £2.50 each
That is mixing myself but even a pure 02 fill locally is only about 6-7 quid a cylinder.
 

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I find my 300 twin 7s far more comfortable than any single tank setup I've encountered so far. That includes everything from a single 10 to a single 18 plus pony (though that was a ludicrous setup for the dive, and didn't do any of the things I wanted it to).

I like the simplicity of singles diving, but I can't get on with it. Having the twins, I'm more compact (I can get into and out of holes better than a 12 and pony, either side-slung or back-mounted) and more stable.

All in, twins is the way to go. I've now got a 5.8l twinset (232s), and people look at you real funny in that, but it's much better than a single 10, and has a lot more redundancy. It's also a real pain to try and sidemount singles, as I've discovered. 2 little tanks much better than one big one.
 

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[b said:
Quote[/b] (Digger @ Nov. 17 2003,16:11)]I've now got a 5.8l twinset (232s),
<font color='#000F22'>does that mean that your 7s are in need of a good home  
 

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Nice try. It just means that now, instead of faffing around putting a single tank on, I just take off one set, and place the other on instead. No annoying filling tanks at lunchtime for this bunny. And they only cost me £60 for the 2, including testing the things!
 

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[b said:
Quote[/b] (Digger @ Nov. 18 2003,10:14)]And they only cost me £60 for the 2, including testing the things!
bah! beat me and my sevens! though thanks to very nice people on this forum i've found a lovely man to test them for £8 each  
 

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I am looking into a twin set for my wife - though the main reason is all to do with total weight / weight distribution and comfort rather than underwater time - which is not a problem.  The main question is 7ltr 300 bar / 232 bar - as twin 10s would I think be too heavy and probably way more air than necessary.  I believe that by going the 300 bar route it gives the best option, as the extra weight just means that you carry less elsewhere, while the extra air gives a better margin.  Anyone with any further thoughts on the weight / comfort side rather than deco issues and bottom time
 

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300 bar fills are no problem locally - even Nitrox - and I think 300 bar is becoming more popular around the country.  Would love to hear from people around and about if 300 bar is available in their areas
 
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