Hello guys.

As we all know, it's easier to think about electrical circuits like water, and therefore it is easier to think about water like circuits.

So what I'm wondering is if there is any equation to determine the resistance caused by a sudden change in diameter size. So I have accounted for Poiseuille's equation and all that. But what I'm looking for is like the suddenly you have a very thin 90 degree wall with a smaller opening blocking your flow and then it opens back up to your normal diameter again kinda thing.

Assumptions: Newtonian incompressible flow ok. Near water viscosity is ok but the equation should have that variable in there somewhere. Standard room temperature. etc etc. I'm using a gate valve so technically the resistance isn't like suddenly changing to a smaller diameter pipe but I think it's a safe assumption. Please cite your sources. Please don't say navier stokes.