Stamp of the day: piston, flywheel, and cylinder

Germany has some really nicely designed stamps, clean and simple.  Here is an engine piston (I think).  Maybe PP can interpret it better?  Looks like a flywheel with gears and a cylinder with a piston inside.  I am not sure if this is from a steam engine, gas engine, or what...

UPDATE: Our friend BV just sent me this, which explains the stamp in detail (thanks!!!!):

If PP hasn't let you know, the engine pictured on the stamp is a Otto
Langen Free Piston Atmospheric Engine, circa 1867.

A small flame, like a pilot light on a stove was at the base of the cylinder.
I do not know the starting procedure, but as the engine was running, if
the wheel started to slow down, a gas, like natural or coal gas, was
admitted into the bottom of the cylinder, and a little trap door would
open next to the base.  The flame would be drawn into the base, igniting
the gas, and drive the piston upward.  This would push the vertical rack
gear attached to the piston and engage the gear on the flywheel shaft,
increasing the speed of the wheel. The inertial energy would be stored in
the rotating wheel, which drove a load attached to it.  As the flywheel
slowed down to a certain speed, a governing mechanism would start the
process over again to keep the engine running until the fuel supply was
removed.

You can see one at the Rough & Tumble Museum at Kinzer, PA.
It is run for exhibition days.