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[SNIP stuff about running out of gas with either system] > > *BUT* in OW there is a difference! I don't know about others, but I > > retain not thirds, or exact halves, or halves + 200, but the amount > > of gas needed to reach the first stop from the wreck. Hence if my > > second cylinder should "just stop" be it from failure, or from > > breathing it dry, there "should" be enough gas in the first cylinder > > to get me back to the anchor, and up to my first stop. I think > > that this is a major advantage for indies, over manis. > > A cave dive is to thirds. When you dive with a buddy, especially one you > dive with regularly, your buddy should have an idea where your turn would > be as well. Example, I sometimes dive with a guy who just doesn't breath at > all, he's inhuman. He knows if he gets close to his third then I'm over > mine for some reason. Another guy I dive with I know when to expect him > to hit his third. If your brain doesn't function properly on a particular > dive, at least with a buddy you have some form of backup. This sounds like very bad backup. When you are diving with the inhuman who doesn't breathe at all, you do realise that when he has reached thirds, there isn't enough gas in his system to get you both back if yours blows up? Do you also realise that when you are diving with the air hog, if he misses his thirds, and then has a problem, you won't have enough gas to get you both back? With a mani he will breathe your system down till there isn't enough to get either of you back. With an inde, you can give him a reg (which is supposed to get him back). If he breathes that dry, well tough, he don't get seconds! You're going to need that to get out yourself! (note to anyone who gets into this difficult situation. Be DAMN sure that you don't arrive back alone with half a cylinder still left. Drain it before you surface!) With an independent system (be it in cave or OW) other peoples mistakes won't do you in. > > The other point that I can remember concerned burst disks. I haven't [snip me seeing burst disks go] > <some real interesting math snipped out> > > Ok, first. Some manifolds have two burst disks, yes. However, just > because one blows doesn't mean both will. Quite often burst disks blow > because they've been sitting in a valve for a long period of time and > just get weak. I'd be willing to bet that only one of the two burst disks > on those manifolds will go at a time. Those figures were based on *one* disk failing in a manifolded set. The pressure remaining, was the pressure in both cylinders and the time was the time to closing the isolation valve. Then the pressure remaining was the pressure left in the cylinder with the "good" disk. The other one will drain to nothing, and there is no way to stop it. I mentioned two holes because there are two types of burst disk plug in common use. I measured, and did the figures for the one with the *lowest* flow. The *single* hole plug. These are now falling into disfavour due to liablity concerns with cylinders flying around when the disk goes. They are being replaced with "reactionless" plugs, which have *two* holes in each plug (nothing to do with there being two plugs in a manifolded pair) This type of plug will flow twice as fast as the older single hole type, because it has two holes! > > I've only seen about three burst disks blow. All were on single tanks. If > I remember correctly they took at least 5 minutes to drain. They make a > very loud noise and a mess out of a room with papers laying around in it. > Maybe longer. > > We could run a test. Fill a tank all the way. Now open the valve wide > open and time how long it takes for the tank to drain. I bet a burst disk > doesn't go that fast. Well you'd be half right. I just measured the hole in a valve, and it is 3 mm, giving an area of 7mm. Larger than the area of a single hole burst disk plug (5mm) but smaller than a two hole plug (10 mm). I'd love to donate $100 worth of TMX to the cause of science, and see how fast I can dump it through a 3mm hole, but I don't have any mixed at the moment <grin> > > If I've missed anything, or if you can think of anything else, I'll > > have a go at that. It seems that Carl is going to *make* me use > > a manifold if anyone can find any advantage to them for OW TMX. > > > Jason, next you'll be telling me you want to do trimix fills based on > a set flow psi over <x> minutes ;-) > Isn't that how ANDI mixes NTX? ;) > ================================================================== > Ken Sallot "Your trim goes to hell when you run out of air" Cheers Jason =:)
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