Hello All. This is my first post, and I hope it is not too simplistic, but I am out of my normal line of work here. I am trying to understand the relationships between flow, velocity, and cross sectional area with gases and fluids(air and water). Imagine a large vertical, cylindrical tank filled with water. It has two pipes coming out the side, at the same elevation, and they are the same length(24") with a ball valve to open and close water to them. They terminate in free air. One pipe is 1" diameter, the other is 6" diameter. If I open both ball valves, water will come out both pipes and spill onto the floor. My question is this: Will the velocity, flow or pressure of the water be significantly different between the two pipes?(if all measurements are taken halfway from the tank to the end of the pipe) My feeling is that the larger pipe will have greater flow, lower velocity, and increased pressure, vs the smaller pipe. Is this accurate? What about the same scenario, but with the tank being filled with air instead of water, and being kept at a constant pressure of say 50 psig? Would the air react any differently than water? I realize air is just a less dense "fluid", right? I feel it would behave the same. My second scenario, is with air supplied through a heating duct. Imagine a constant pressure of say 15"H2Og on one side of a piece of sheet-metal duct. This duct has 2 holes in it. One is 1" diameter, the other is 3" diameter. Will the flow, or velocity of air be any different between the two holes?(If measured with a meter held 1" from hole on exit side) I feel the velocity would be slightly greater measure at the smaller hole, but flow would be the same? Is this correct? I apologize, as I'm sure this is basic stuff, but I am not a mechanical guy. Thanks to all who reply!