DIR and stage bottles

[Jay]

Ok, not that I am going DIR or anything like that but I am interested in knowing what diving practices work and, more importantly, why. I currently use a steel 7l stage for nirox backup gas and would use the same for deco bottle when I complete my TDI courses but I notice that DIR advise only the use of ali stages. Why? Is it an absolute no-no (I know there is no such thing as almost-DIR but does it REALLY make that much difference). I don't want to have to sell my 7l just to buy an ali stage (especially with all the new testing rules etc) so comments please!

[andy2tanx]

I'm sure someone will be along to tell me i'm wrong, but i think ally cylinders are used for stage because they are neutral underwater and can be jettisoned when empty as they are then slightly positive.  Isn't that right Jarrod!!

[Jay]

They won't be neutral all the time, but I can jettison steels too surely? Just means I'd have to recover it another time?

[Davey Willo]

The problem is Jay, if you've dived deep enough or long enough to of incurred a decompression obligation, then at no time would you want to jettison the deco bottle... you'll need it to make sure you don't start fizzing at the surface bro...

The reason for them being Ali (I believe) is that you want at all times to have a fairly balanced rig (i.e. be able to swim it up from depth should you lose bouyancy) Steel deco bottles would weigh you down excessively and not allow you to the surface without dropping the bottle(s) Not good

[Dominic]

And another reason is that DIR states all stages are carried on the left, so you need the most neutral cylinders you can get to stop you spending your whole dive on your side

[Jay]

Ok - starting to make more sense now. Aren't the UK laws relating to ali bottles and testing going to make using ali bottles a real pain in the ass though?

Which, btw, are you all aware that under new regulations, cylinders that have had the paint chipped to the metal will no longer be valid for testing until they have been sandblasted and repainted???

[Dominic]

Probably. Especially since it's going to become very hard to get the neutrally-buoyant types over here, AIUI.

As far as the paint goes: If you have any chips like that, nip to any decent DIY or decorating store and get some Hammerite paint.
I've used it to colour my D-weight a nice shade of yellow, and I'll be putting the black & white quartering onto my cylinder neck with it later as well. There's no law against repainting your own cylinders, after all. So long as you don't use heat...

[Driftwood]

</span>

Originally Posted by [b

Quote[/b] ]Quote: from Dominic on 10:13 am on Oct. 17, 2002
Probably. Especially since it's going to become very hard to get the neutrally-buoyant types over here, AIUI.

<span =''>Why?

Go-Dive sells Luxfers from 1.5l Argons to 12l (at £159!!!) with everything inbetween?

[Dominic]

It was something on the DIS list about new EU/HSE regs IIRC - basically, the cylinders are going to be heavier, therefore loosing the buoyancy properties that made them popular as stages.

So yeah, you can still get Luxfer cylinders, but there won't be any point, they'll be no different to steels. In fact, you might well be better off with a lightweight steel.

There's even been talk of importing US Alu cylinders...

[Driftwood]

Luxfer</span>

Originally Posted by [b

Quote[/b] ]The cylinder when empty has a buoyancy of 18.7 kg - 16.6 kg = 2.1 kg
The cylinder when full has a buoyancy of 18.7 kg - 16.6 kg - 3.3 kg = -1.1 kg

<span =''>Faber</span>

Originally Posted by [b

Quote[/b] ]The cylinder when empty has a buoyancy of 14 kg - 12.8 kg = 1.2 kg
The cylinder when full has a buoyancy of 14 kg - 12.8 kg - 3.3 kg = -2 kg

<span =''>Gee.... 900g in it. Same swing, both end up positive - an arguement for the sake of bolloxs as it is now anyway - with a heavier Luxfer (18.0Kg) you will have the exact same bouyancy characteristics as a steel Faber.

Hmmm