>A 47.6 pound rated propane bottle was filled with 20 pounds of propane back
>in the oldy days but is now filled by most vendors with 17 pounds of
>propane. I don't think propane bottles are standard volume.
> That said, I doubt that there are very many manufacturers and any variance
> would be minimized by using bottles from the same general time period from
> the same manufacturer. Like SCUBA tanks, they're stamped, but on the top
> Then, you'll have to do the Archimedes thing: fill a barrel to the brim
> with water, submerge the tank, and use your wife's measuring cup to
> replace the displaced water. Every pint is a pound of buoyancy, minus the
> tare which I'll guess at about 18.5 pounds.
The thought of using these is that they will be readily available up there,
so CHEAP! And they will hold no pressure. They can be left open for a few
weeks, then drilled, and a fill stem/valve inserted, or welded shut. Bad
valves can be epoxied shut. They are just to hold air under no pressure for
buoyancy purposes underwater to help the diver take some of the weight off
the hoses and device. Enough of them would make an airlift, but different
than airlift, these could not expand as they rise. If one wanted to use an
actual airlift up there, they could get one.
Tares are ring stamped, and different with manufacturer. The site I went to
had a constant 47.6 for inner volume on different manufacturers for the 20#
tank. I'm satisfied with the 35# calculation number so far.