Flow through a pipe along a reduced diameter

[TSN79]

Imagine a pipe of d=50mm with water flowing through. The pipe's diameter is reduced along a small section to 40, and then returned to 50. If I have a flow of x l/s along the first 50mm piece, will I also get x l/s along and after the reduction? Will the only change be more speed through the reduced section and then back to normal, accompanied by a big pressure loss?

 

[Mech. Engineer]

actually the flow rate will be constant if it is one stream...

the velocity will increase in the 40...pressure will reduced...

then velocity will come back to its normal...

but with very long pipes the pressure will drop due to friction...

so it is not a must that the velocity and the pressure will be same at the

second 50 mm pipe...