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How an espresso machine drives water
The pump makes the pressure. The coffee bed resists the flow. Open the side of the machine and follow the water into the cup.
01 — The hydraulic circuitPaused · heater ready
1ReservoirWater supply
2PumpAdds pressure
3Boiler / heaterHeats water
4Group headSpreads water
5Coffee puckResists flow
6CupCollects brew
0% of model maximum
0% of free-flow rate
Illustrative 60 mL capacity
More openMore resistant
Try higher resistance while brewing.Cutaway · not to scale
Less flow. More pressure.
A more resistant puck makes water harder to push through. On this simplified pump curve, the operating point moves toward higher upstream pressure and lower flow. The gauge, stream and cup share that same model.
A teaching model, not a recipe.
The heater is already ready. Pump pressure falls linearly with flow; the puck has a fixed hydraulic resistance. Pausing immediately removes modeled pressure. Real machines have changing resistance, valves and thermal dynamics. Pressure alone does not determine coffee quality.
Flow fraction = 1 / (1 + resistance)