Why Doesn't IV Flow Rate Increase Through a Constriction?

[Roshan Patel]

I know I am over thinking this but it's bugging me...

When giving patients fluid through an IV giving set, we set the flow rate by adjusting a rolling clamp on the tubing line. This is in effect creating a construction.

Reading about flow, I am told over and over that flow is conserved. That is, fluid increases its velocity through a constriction to maintain flow.

Clearly this doesn't happen when I clamp the tubing - the flow rate decreases...

I know that Poisuelles law states that flow is directly proportional to radius to the power 4 so that halving r would lead to 16x less flow. But still I though flow was conserved?

I would really appreciate someone explaining this to me...

 

[Drakkith]

Reading about flow, I am told over and over that flow is conserved. That is, fluid increases its velocity through a constriction to maintain flow.

I don't know much about fluid dynamics, but I'd guess they mean that the flow through any given hose/tube/whatever is conserved, and that when you change the system, by adjusting the clamp in your case, you create a different system with a different flow rate that is conserved throughout the tube.