Maybe a strange question, but how low can the pressure go in an O2 cylinder and still have the regulator operate properly? My 20 cubic foot O2 bottle has lasted almost two years with pretty regular jewelry torch use (Meco midget and Little Torch). The cylinder pressure is now down to about 475 lbs on the gage -- how low before I should consider it empty and get it refilled, as I don't want to run out in mid-project?
Regards,
Bob