I think I've found a nice 3d printing chalenge for myself

Discussion
1

I came across this document while looking up what a moineau pump was.
Found some interesting shapes on thingiverse people were trying to print.
And that led me to this interesting pump structure.
I found myself completely engrosed with it for my bedtime reading.
Water lifting devices for irigation and drainage
There are some fantastic machines and engineering described in its pages.

Id love to have a go at taking them off the pages and turning them into working models.
Looks like a fun challenge.
But that document is well worth a read if you are of a mechanical mind.

2

A working archimedes screw would be awesome. They are mesmeric to watch too.

3

The whole section on different types of pump attracted me.
From hand buckets all the way through to turbines.

I liked the combustion engine type especially. Using gas spark combustion and the water as the piston.