Fluid Dynamics Question

[KenRexford]

Suppose that you have, say, a run of 1-inch diameter pipe running from a pump to something. Suppose you then replaced 90% of the pipe with say 1.25-inch pipe but the tied into the last 10% with a reduction fitting. Would having 90% of the run increase pressure or would that last 10% ruin things for the entire run? What if that last 10% were just an adapter (1%?)?

 

[Pistondog]

The pressure drop would be less over the 1.25" pipe length. Larger diameter, helps, even if partial.