This is a model of a donkey pump to a design by Elmer Verburg.  Donkey pumps were the 1/4 horsepower motor pumps of the age of steam.  They were hung on walls in factories to supply oil and water to various pieces of machinery.

The engine is double acting and, like any good pump, drives the pump piston directly for maximum power transfer.  The two aluminum cylinders near the bottom contain ball check valves to prevent backflow.