Pressure through the coffee bed.
What creates pressure in an espresso machine?
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What creates pressure in an espresso machine?
Fit pump, boiler, shower screen and coffee basket
The pump sends heated water through the shower screen and compact coffee bed. The bed resists flow, so pressure rises; changing its resistance changes both pressure and delivery rate.
Illustrative pump curve P=12−1.5Q (bar, mL/s), coffee-bed resistance P=RQ, 0.3 kg boiler water, cp=4180 J/(kg·K), 20 °C start. A 0.05 bar·s/mL bypass returns water in parallel with the bed. Thermostat caps water at its setting. No boiling, heat loss, coffee chemistry or detailed extraction yield.
Deliver 30–50 mL at 90–96 °C with 8–10 bar brew pressure.
Compare brew pressure, temperature and shot volume.