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>> From: Andy Feifarek [mailto:bufclown@pa*.ne*] << >> If the ambient pressure of the bladder and the water were the same, the bag would not deflate. Thus water pressure is greater than air pressure << Fascinating statement - never expected to have THIS conversation HERE! (Although I've been maintaining for years that 99% of self-proclaimed technical divers should stop dreaming about rebreathers and mixed gases, and first figure out how scuba and air works!) >> Doesn't air have a tendancy to rise while in water??? << Yep - but because of lesser DENSITY! >> Hence to empty a bladder doesen't the deflator need to be the highest point of that system?? << Yep - no-one stated anything to the opposite. >> Take a bladder under water. Fill it fully with air. Now press the deflate button.. it deflates to a certian degree right? << Depends on where you hold the deflator. Unless you give the air a route to a "higher" point (by raising the opening of the deflator/mouthpiece above the deepest point of the bladder) it will NOT leave the bladder. In fact, you can take a water bucket upside-down, totally open on the lowest point, fill it with air and then bring it down. The air is trapped in the upside-down bucket and will NOT escape (but be reduced in volume). >> now move the bladder around to where the inflator/deflator is at the highest point and press the deflate button again... WOW more air comes out!!! << Actually - in that scenario ALL the air will come out as long as your deflator hose is pretty much a straight line allowing no air to get trapped in a higher point and you make sure that there are no "higher" pockets in your bladder. >> the outside pressure of the water does deflate the bag... If the ambient pressure of the bladder and the water were the same, the bag would not deflate. Thus water pressure is greater than air pressure << Nope, air and water pressure are the same if you take a bladder under water. This is the very basic of Boyle's Law, 1st session in any basic class. During descent, the water will exert pressure against the bladder and continuously "collapse" it to the EXACT point, where the air molecules have been pushed close enough together to exert the SAME absolute pressure as the ambient water. (That's why you have to add more air to your BC to maintain its volume during descent.) The reason why the air escapes is NOT because the pressure is different, but because the density is. Any more doubts? Time to visit your friendly PADI/NAUI/NASDS/SSI instructor for a refresher. Best Regards Andy EMail: Andy@Sc*.AS* http://www.Schmidt.AS/ -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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