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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*
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