I am about to go on liquid oxygen for when I am moving around. In speaking to the oxygen nurse today she said that the setting was going to be 4 lpm because that is what the level was when I was tested. As I am new to the oxygen service I was wondering how long these tanks are actually lasting at 4 lpm. I assume that the settings are fixed when I receive the tank and cannot be changed by me. Also, do they supply more than one tank as with the non liquid tanks?