The Key of this coffee machine is the inner system to production of pressure.
Look particularly at 16 & 18.
16 is a outgrowth of the aluminum "one-body" it has small openings at its summit.
18 is a close tube, introduced throughout the opening 14, that covers the outgrowth 16.
Here in RED is the electrical heat plate:
(you have to imagine that the bakelite knob is on!)
Water expands through the heat...
An inside pressure is created...
... that press the water in the direction of the only pressure relieving space (the tube system):
After going up outside the inner tube, the water goes direction outwards through the inner of the inner tube (my english is real appalling):
and go direction coffee grind:
... coffee pours out... that was actually the aim...