The upper parts of the two balls communicate with each other by means of a brass pipe (diameter 1.5 cm). Another brass pipe of the same diameter places in communication the base of the recipient and the lower ball into which it projects to about 1 cm from the bottom. A brass pipe (diameter 0.8 cm, length 28.5 cm) is screwed to the base of the recipient with a watertight seal and penetrates into the top ball almost to its bottom. At the top of the pipe there is a series of six small holes from which water jets out when the fountain is working.
Basically, we can consider Hero's fountain a compression fountain in which the air is compressed by a column of water.