It was a mechanism which maintained a crater (cup) full with wine regardless of the quantity which was removed from this. It consisted of a large airtight container full with wine and one horizontal tube that supplied the crater. The tube had a valve that was connected to a pivoted lever with a hollow sphere that was found inside an adjacent vessel. The perforated bottoms of this vessel and crater were connected. When the level of wine in the crater exceeded the predetermined limit, the sphere in the communicating vessel rose and the valve blocked the pipe flow in the large container.

SOURCES: Heron of Alexandria, Pneumatica, B31, Philon of Byzantium, Pneumatica.