aluminium cylinders?

[aclivity]

<font color='#810541'>I downloaded the GUE overview a couple of weeks ago, and have finally had time to start reading it today.  One question immediately springs to mind.

In one section it states that ONLY aluminium cylinders shall be used as stage cylinders, not steel.  I haven't read far enough to see if this also covers back mounted cylinders (from what  I understand it doesn't) but I'd be interested to know what the thinking is behind this particular rule?

Andy

[RobK]

Originally Posted by [b

Quote[/b] (aclivity @ Sep. 08 2003,12:06)]I downloaded the GUE overview a couple of weeks ago, and have finally had time to start reading it today.  One question immediately springs to mind.

In one section it states that ONLY aluminium cylinders shall be used as stage cylinders, not steel.  I haven't read far enough to see if this also covers back mounted cylinders (from what  I understand it doesn't) but I'd be interested to know what the thinking is behind this particular rule?

Andy

Put simply, Buoyancy.

It's not just that the stage bottles are ally but also that they display the right kind of buoyancy characteristics. Basically they should go from slighty -ve to slightly +ve as you use the gas in them. Obviously you need to factor in the gas that's being carried etc.

It's all again about having a balanced rig. Ally bottles with the right buoyancy characteristics have minimal impact on a divers buoyancy and therefore you don't need to have a wing the size of a liferaft to cope with them.  

HTH
Rob

[aclivity]

<font color='#810541'>Thanks for that RobK - does that mean that Aluminium is required for ALL cylinders (not just stage bottles)?

[Dominic]

No, back bottles are either steel or alu depending on weight requirements.

In a wetsuit with minimal lead, use alu
In a drysuit that needs lots of lead, use steel.

Otherwise you end up being unavoidably negative in a wetsuit or needing masses of lead to get neutral in a dry.

[Mark Chase]

Strange thing is that my 7ltr steel stages go neutrol with 100 bar in and are positive if empty and they are about 1kg negitave when full but they are rareley over 200 bar for deco mix.

I was quite surprised the first itme I took a half full stage off and saw it hover in front of me. When empty they dont float up too badly so I dont have to allow additional weight for this.

I have never dived Ali stages but I always wondered, if they are that boyent, when empty dont you have to carry additional weight in case or do you just un clip them and let them float up (expensive me thinks)


My stages are Faber by the by.

ATB

Mark Chase

[Bob Cooper]

Originally Posted by [b

Quote[/b] (Mark Chase @ Sep. 08 2003,18:04)]Strange thing is that my 7ltr steel stages go neutrol with 100 bar in and are positive if empty and they are about 1kg negitave when full but they are rareley over 200 bar for deco mix.

I was quite surprised the first itme I took a half full stage off and saw it hover in front of me. When empty they dont float up too badly so I dont have to allow additional weight for this.

I have never dived Ali stages but I always wondered, if they are that boyent, when empty dont you have to carry additional weight in case or do you just un clip them and let them float up (expensive me thinks)


My stages are Faber by the by.

ATB

Mark Chase

Originally Posted by [b

Quote[/b] ]Strange thing is that my 7ltr steel stages go neutrol with 100 bar in and are positive if empty and they are about 1kg negitave when full but they are rareley over 200 bar for deco mix.

I was quite surprised the first itme I took a half full stage off and saw it hover in front of me. When empty they dont float up too badly so I dont have to allow additional weight for this.

I have never dived Ali stages but I always wondered, if they are that boyent, when empty dont you have to carry additional weight in case or do you just un clip them and let them float up (expensive me thinks)

Mark
7L Faber steel stages?  Never seen these before.  If the buoyancy characteristics are as you say, then I can't see any problem.

You are quite correct about the buoyancy issues.  When I am carrying a couple of AL80 stages I do carry a little more weight.  When near empty, they do give noticable extra positive buoyancy.  Sometimes, we use this to our advantage......A stage can be breathed down to nearly nothing, clipped to an SMB line and sent up to the surface.  This way we conserve backgas which can be used for another dive.  It's also an economical way of diving for the tight wads.  On a short gas dive, just take a stage full of backgas, breathe it empty and send it up! &nbsp;Make sure the skipper knows to expect this. &nbsp;We've confused one or two recently using this method!

It also has it's disadvantages........Some Czech friends of mine were diving in Ressel this year and one of them &quot;dropped&quot; a stage during a switch at the top of the shaft in the deep section.  The stage floated up to the ceiling and was lost.  One of our team found it a few days later wedged up in the ceiling!

[Dominic]

I can believe it - my steel 7s are very slightly +ve when neutral, and they're amongst the heaviest 7s in Faber's range - if you've got some more lightweight ones, then they could easily become +ve when only half empty.

[Mark Chase]

Originally Posted by [b

Quote[/b] (Dominic @ Sep. 09 2003,07:53)]I can believe it - my steel 7s are very slightly +ve when neutral, and they're amongst the heaviest 7s in Faber's range - if you've got some more lightweight ones, then they could easily become +ve when only half empty.

Dom, I couldent quite understand the +ve -ve referance bit??

My stages are off the shelf nothing special as far as I know. I think they are Faber Lightweights 235 bar but I thaught all Fabers were called Faber Lightweights?? as in the fact that Hyser cylinders are so bloody heavy .

I dived twin 10 Hysers in Gozo and had to take weight off the belt to cope.

ATB

Mark Chase

[Dominic]

+ve = positively buoyant

Not sure what naming convention Faber use, but if you check divefaber.com, you'll see that there are various weights for all the 232 bar cylinders. My 7s are 8.2kg each - in the sea they're 1.8kg -ve full, and 0.1kg +ve empty.

Faber's lightest 7L on their website is 7.6kg, they'd be &nbsp;1.3kg -ve when full, and 0.6kg +ve empty.

I find it interesting to note that Faber 300 bar 7s can weigh as little as 8.2kg - maybe I should start overfilling my twinset to a greater extreme?

[Mark Chase]

OK looks like I have lightweights then as thats about the charictoristics of my stages. I weighed them full (200 bar)using fishing scales in the water of Stony Cove and they weighed a smidge over 1kg.

ATB

Mark Chase