A Tympanum is basically just a sectioned
cylinder which is rotated. It has a number of pie-slice shaped chambers, each
of which has an intake hole at the outer edge and an outlet hole near the center.
The outer slot or hole is on the leading edge in the direction the cylinder
is rotated. When the leading edge dips into the water, the section fills and when
it rises out of the water the hole is above the water line.
As the cylinder
rotates the liquid sloshes to the center and empties out the center hole.
Tympanums were used in ancient Greece and have been used throughout the world
for thousands of years. They might be powered by horses or humans or even by the
force of a stream from which the pump takes its water.