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lenbud@ac*.mo*.ne* wrote: > > The simple way to look at it is that each molecule has a mass and therefore > a weight in this gravity well called earth. the high pressure tanks hold > more molecules in the same volume, and this volume of gasses weighs more at > the higher pressure (when full) because of the much higher number of > molecules in the same volume. This higher density produces more change in > weight from full to empty, and it results in more of a change in bouyancy > for the high pressure tanks. > > > > > >At 06:29 PM 2/15/97 -0900, you wrote: > >>Hello folks: > >> > >>I have sitting in front of me the 1997 US Divers catalog and I am looking > >>at the tank specifications chart. US Divers now appears to be carrying the > >>entire Pressed Steel line of low pressure and high pressure tanks as well > >>as aluminum 80s. For your reference, I have duplicated parts of the chart > >>as an ASCII table below (Sorry you metric folks, this probably won't mean > >>too much) > >> > >>---------------------------------------------------------------------- > >> > >>Tank/Size LP95 LP104 LP120 HP80 HP102 HP120 AL80 > >>---------------------------------------------------------------------- > >>PSI 2400 2400 2400 3500 3500 3500 3000 > >>Diameter (in) 8.0 8.0 8.0 7.25 7.25 7.25 7.25 > >>Wt. empty w/o > >> valve (lbs) 41 46 52 27 33 38 33 > >>Height (in) > >> (w/valve) 27.3 29.5 33.0 23.0 27.25 30.38 29.0 > >>Buoyancy > >> full -4.74 -4.17 -3.8 -8.0 -8.2 -10.0 -1.9 > >>Buoyancy > >> empty -1.75 -1.0 0.0 -1.0 +0.5 +1.0 +4.1 > >>---------------------------------------------------------------------- > >> > >>What strikes me immediately when viewing this chart is that the change in > >>buoyancy for low pressure tanks is far less than for high pressure tanks. > >>According to the chart, each tank changes in buoyancy as follows: > >> > >>----------------------------------- > >> Buoyancy change from > >>TANK full to empty > >>----------------------------------- > >>LP95 3 > >>LP104 3.17 > >>LP120 3.8 > >>HP80 7.0 > >>HP102 8.7 > >>HP120 11.0 > >>AL80 6.2 > >>----------------------------------- > >> > >>I was under the impression that breathing a set volume of air....say 100 cf > >>will add the same amount of buoyancy to your tank regardless of the tank > >>you are using, but I haven't had a physics class for over a decade. So > >>unless US Divers blew their own tank specs it appears that the wet volume > >>of the tank and/or the starting pressure are also factors. So, I pose the > >>following questions > >> > >>1. Can anyone out there explain the relationship between tank volume, and > >>buoyancy at various pressures and why low pressure tanks do not change > >>nearly as much as high pressure tanks when releasing the same volume of air? > >> > >>2. Is this one of the reasons that low pressure tanks are so preferred in > >>cave and tech diving? The tradeoff seems to be a heavier tank on the > >>surface for less change in buoyancy. > >> > >>3. And finally, does anyone happen to know the exact buoyancy of aluminum, > >>steel, and lead in sea water? In other words, if you are 1 lb positive in > >>sea water, how many lbs of aluminum, steel, and lead, respectively, would > >>be required to bring you back to neutral buoyancy. > >> > >>Regards, > >>---------------- > >>Kent Lind > >>klind@al*.ne* > >> > >> > >>-- > >>Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > >>Send list subscription requests to `techdiver-request@aquanaut.com'. > >> > >> > > > > -- The real Handicapped people are the ones that refuse to see their own. -- > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send list subscription requests to `techdiver-request@aquanaut.com'. Perhaps the reason for this change in bouyancy is to to the internal volume, the length, and the circumfrence. If you look at the equation for the area of a cylinder, then perhaps the change in bouyancy is a function of the displacement of water by air. As with any bouyancy, there is a pos. a neg. and a neutral. If you look at the height, the diameter, and the volume of air, that can give clues. Also, a factor to consider, is how much lift does the empty tank create? Also, is the weight of the tank a counterbalance to any bouyancy properties? What is the minimum reccomended amount of air remaining? Etc.. That may shed some light on this subject... A 2000 psi 100 lb tank that is 35" tall and 10" dia. Would probably sink even full. Whereas a 2000 psi tank weighing 25 lbs. of the same dia and height would probally exhibit positive bouyancy in this example. Dbrown.. I'm no expert, but this seems to make sense. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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