water dynamics help

lalababa

I've posted this on the physics forum but to no avail. I have a water well and a run of around 250m to a proposed trough. It's a long run with a few ups and downs and a big up followed by a bigger 100m run down. The overall fall of the total run is about 3m. If I plum the last 100m with a slightly larger diameter pipe (and prime it) will I get a better continuous gravity feed. (I imagine I will):) Any thoughts?, many thanks in advance.

Donelson

Yes, but only a small increase due to lower friction losses in the 100m pipe work.

lalababa

It's good to hear there will be slightly less friction on the larger diameter, but I though that there would be more gravitational pressure from using the larger pipe aswell. From hydraulics : force of liquid is increased when diameter decreases. i.e from big pipe to small pipe, so reversing that the gravity force is 'pulling' a greater volume in the larger pipe increasing the pressure in the smaller pipe? no?yes?

Donelson

The additional force due to the larger volume of water in the large cross section pipe will be carried by the transition section between the two diameters.
you could thing of it like having one long small diameter pipe and a second 100m dead end pipe.