Hogarthian rig balancing

[rjack321]

Confirmed. Have sucked a few tanks totally empty before.

Ditto.
Although once I take the tank out of the water and set it in the sun there's often a liter or two of gas "left" in there. Enough to go pffft for a second or two before its completely done. Being at ambient pressure and warming up ever so slightly "makes" half a breath of gas.

 

[rjack321]

It goes without saying to most folks, nevertheless (for posterity).... I think we all agree that this talk of breathing a tank down to 30psi (or pick your really-low-practically-empty number) is based on the presumption that the 1st and 2nd stage regs are both balanced regs. I think, with an unbalanced piston 1st stage (for example), you would not get very close to the 30psi (or whatever) like you could with a balanced reg.

You can suck an unbalanced reg down too. Just only works shallow, like using an O2 bottle at 5ft. At least empty enough to have no needle movement on the gauge and unscrew the (DIN) reg without any purging required.