Diagrams.ink / Everyday engineering
Inside a moka pot: steam pressure lifts the water
Heat the lower chamber and trapped steam pushes hot water up the funnel, through the coffee and into the top. Open side view: turn the heat, run a brew and follow the numbered path.
01 · Cutaway of a moka potReady
1Steam pressure2Funnel stem3Coffee bed4Column5Upper chamberVSafety valveHHeatRulers show liquid levels
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Try it: drag Heat while it brews, or switch on the clogged-bed demo.Cutaway · not to scale
Gentle pressure, not espresso
The only force is steam above the water, so a moka pot works at roughly 1–2 bar. An espresso machine pumps water through a much finer, denser bed at about 9 bar. That is why moka coffee is strong but not true espresso. More heat gives a faster, hotter brew; less heat is gentler.
The safety valve must stay free
The valve (V) is the pot's pressure relief. In normal use it stays closed. If the coffee bed jams, steam can build until it opens and vents. Never block, plug, tape or modify the valve, and keep the pot clean and the grounds level, never tamped.