@irenea8 I am referring to tanks you pull around on carts . I use the E size . It is 27” high 4 .35 in diameter . I use 4 ltrs when active . This tank lasts me 2.3 hours. Of course longer if I turn it down to 3 when not active . So riding in a car , I turn it down . Sitting at a diner, or waiting , I turn it down . Walking, I have it on 4 ltrs . It is a continuous flow. Easy to control with the regulator at the top. The numbers on the regulator represent ltrs . The numbers on your Inogen do not. They are only numbers on a dial. I had an Inogen also . I rented mine from Apria . It did not keep up . I didn’t get around very well .I had to stop and sit . Use my oximeter to know when it finally caught up. I had it about 2 weeks . Terrible . Now I know that those numbers are not ltrs . That machine is not what they want people to believe. If you don’t use much oxygen. They have a large concentrator that you can have in your home . That machine actually can fill smaller bottles / tanks that you can carry in a bag . I spoke with a lady who was using one . She says even at home she uses those small bottles because they free her from an oxygen line. I was offered one when I got my consentrator. I prefer the larger tanks . The cart doesn’t bother me . I get 2 hours from one tank . I carry spare . I like continuous flow. I get all I need . It is simple. No playing with my oxygen level . When your oxygen level goes below 88 your body is being damaged. All those few moments under 88 add up. I want the best flow I can have . I’m not caring about stares from people . I just smile. That Inogen I had was noisy , actually people stared at it more . Best to you , Crystalena