I have a question regarding a water line from the street to a house. What happens to the pressure in a water line if it goes from a 1" diameter pipe (at street) and increases to a 1.5" diameter pipe for 300 feet from the street to the house and then back down to a 1" pipe inside the house?
[Physics] Pressure change with a pipe diameter change
fluid dynamicshomework-and-exercisespressure
Best Answer
If the flow rate is zero then the pressure is the same everywhere in the pipe.
If there is some flow rate then the pressure drop per unit length of pipe is given by the Hagen-Poiseuille equation if the flow is laminar, or the Darcy-Weisbach equation if the flow is turbulent. The pressure gradient along the pipe is going to look something like:
so the pressure will fall more slowly along the bigger pipe. However to make this quantitative i.e. to calculate the gradients of the $P:L$ lines you will need one of the two equations mentioned above.