Hello, I guess this is something of a fluid dynamics problem. I'm having some trouble understanding non-backpressure compensated variable orifice flowmeters (NBPCVOF) used with medical gas tanks. Regarding a non-backpressure compensated flowmeter, I'm being told that adding partial obstruction/restriction (i.e. oxygen tubing) to the system would increase pressure in the tube, and thus increase the flow rate of gas through the system. The diagrams below may help to clarify. Issues: 1) I'm not understanding how adding restriction would increase the flow rate, if it would at all? I'm currently under the impression that the flow would remain constant. 2) I'm also not sure if the ball in the tube would move up or down or at all when the restriction is added. Our notes are as follows: What am I missing??