Picked up the tank this morning. I'm pretty sure it's a 20lb tank. It's about 23" tall to the neck and about 8" in diameter. It's a steel tank, a little rusty, but in pretty good shape, nothing a little BKF won't take care of. Painted red at the top with a label and stamping from some carbonics company from Chicago. Hydro stamps from '84, '89, and '94, so it's WAY overdue for hydro testing.
Other than that, it's got ICC-3AA180, 88934CE, and AWK stamped on the neck. Don't see anything else on it. The valve is made by Thermo.
Is the fact that it has a company name stamped on the neck going to cause a problem. I can get it hydro tested and filled for about $30 at one of the local fire extinguisher companies. Anyone know what Praxair charges for a tank exchange? It's a nice steel tank, I'm a bit loathe to give it up for a crappy aluminum tank if I don't have to...