Almost finished this simple boiler feed pump (excuse the temporary screws and the oily handle!) which is a variation on one in an old book. Works ok even with oiled string (!) rather than graphited yarn in the stuffing box, will shift half a pint in thirty seconds or so and squirt about 10 foot
It has a design fault in that it's too easy to pull the plunger out completely; it needs some sort of stop
What I learned: how to make a neat container for the inlet valve, how the delivery pipe orifice needs to keep away from the outlet valve, the effect of water hammer and why there's an air chamber on old pumps!
EDIT: It's about 5" tall (that's a UK penny)