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Chris >Are you suggesting that a stage cylinder is OK minus a gauge if >'thirds' is not being applied? Yes. With deco bottles it is a one direction journey - you use the gas from its MOD to the MOD of the next deco gas. You calculate the gas required and add contingency to this. You do not need to know what pressure is in the cylinder at any point during the dive as you have planned to have enough. You only need to know the contents prior to entry. If shit happens (neck O-ring failure) you share with your buddy as he is carrying your reserve (or other measures e.g. signalling DSMB, deco out on a lower O2 gas). A SPG does not prevent shit happening it merely adds a further point of failure. Also, A SPG does not increase the amount of gas you are carrying - you have to do the homework and plan correctly. >>My stuff snipped >Pony cylinders have a very limited application in non mandatory deco >diving at (dependant on your views) 0 to 30 metre range. They 'arrived' >on the scene as an emergency piece of equipment to enable a return to >the surface in the event of a total failure on the primary cylinder (we >are talking single cylinder, single pillar valve). Not sure where this >scenario you are advocating has come from - it sure looks like a recipe >for disaster to me and would smack of bad dive planning and conduct. In this context we are talking single cylinder diving in the approximate range you state. I would not advocate going deeper, longer BT, doing more deco or changing a yellow BC for a black one just because someone carries a pony. For me there is not enough gas in a pony to cause me to reply on it at depth. However, with a twinset, there are some limited applications for a small 3l *stage bottle*, but this is going beyond what was being discussed here. >>The need for a pony pressure gauge is even more reduced if the diver >>adopts an incorrect procedure and breaths the primary dry before >>switching to the pony - you either have enough gas or you don't - a >>pressure gauge really doesn't help. > >Hmmmm.... see my comment above on dive planning & conduct. This was my point - improper dive conduct. > >> >>The pressure gauge on the pony is a comforter and nothing else! > >I thought the pony was the comforter! You have already stated that there is an application for Pony cylinders, "Pony cylinders have a very limited application in non mandatory deco diving at (dependant on your views) 0 to 30 metre range". In that scenario they are not a comforter but a viable means of carrying a redundant gas supply sufficient for the dive. Going beyond this scenario is FAS as it provides the illusion of safety whereas in reality the user is now on the slippery slope awaiting the first little problem that increases their breathing rate, which leads to the next little problems which rapidly ends up with dead diver(s). My preferred choice is a set of doubles. However, someone else pointed out that diving with hired cylinders abroad, a pony may be your only choice and then we come back to limiting the dive to match the equipment carried. A wise person once said, "Pony cylinders have a very limited application in non mandatory deco diving at (dependant on your views) 0 to 30 metre range". :) In this case, the holiday maker must limit the dive to the equipment available (and be cautious with hired equipment). <snip> All the best. David Shimell Project Manager, Sequent Computer Systems Ltd, Weybridge, UK Email: shimell@se*.co* -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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