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At 11:57 AM 3/12/99 -0500, Craig Waldman wrote: >The first possible advantage is that the valves are much easier to reach. >If you can scratch your butt you can turn a valve. This comes in especially >handy for doubles with an isolation manifold. This configuration requires that you have all non-standard length hoses and that they be routed non-DIR. The tanks will be very awkward to handle on most boats which are set up to hold tanks in the upright position. Your rig will be so unusual and unfamiliar to your buddies (if you can find any) that they will have a hard time figuring out your system and helping you if there's a problem. If your gear is properly set up, you should have no trouble reaching all the valves. >A second possible advantage. When using round bottom (now top) tanks, you >are even more streamlined, and have greater clearance around your head. >It's easier to look up or forward with NO obstructions behind your head. You will be unable to hear gas flowing through the hoses thus making it harder to detect a leak. Besides, if your tanks are properly set up, you shouldn't have a problem with clearance behind your head. >A third possible advantage. Your manifold is less likely to get banged >during a "Push" though an overhead environment. If you're frequently banging your manifold, you should solve the problem with better diving skills, not by rearranging your gear. >And here is a big one for the Remove all excess potential failure points >fans: > >The Royal navy divers do not use a pressure gauge. That's one less hose. Aaaaccckkk! The operant word above is *excess*. Removing failure points applies to unnecessary items like extra drings, webbing clips, and such. It doesn't apply to SPGs. >They employ an interesting method of gas management. The word 'interesting' isn't the one that comes to mind. >1- They start with two full tanks Isolated. >One on, one off Thus defeating the isolation valve entirely. The valve is there to allow you to deal with a blown burst disk (which you shouldn't have) or an extruded tank o-ring, not to manage your gas. That's what SPGs and dive planning are for. >2- They breath the first tank to empty, >then open the second tank >The tanks then equalize so each tank is now at %50 capacity. >They then shut off the second tank, isolating it. What happens when they've breathed down one tank, then lose the o-ring on the stand-by tank? What happens if they have an undetected leak on the stand-by tank (a likely scenario since they can't hear gas flowing through their hoses which are down near their butt) and find nothing left in it when they open the isolation valve? >3- They breath the first tank to empty again, >They then open the second tank >The tanks then equalize so each tank is now at %25 capacity. >This is the reserve point, so begin ascent procedures. And if they lose track of how many times they've done this? What happens if they lose their deco bottle and have to bail-out on back-gas? How will they know if enough gas is left? It's hard to believe anyone would dive this way. -Mike -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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