Since I got good results from my pressure test experiment I thought I'd go ahead and build the actual pump. I upgraded the 500ml bottle to a 2 litre bottle, added the one way valve and an output pipe that I ran up to the top of the hill.
This pump runs well, pumping about 0.6 litre/min with a working pressure of about 25psi. With the output valve closed it gets up to about 40psi before beginning to struggle.
