bar
Hot water, pushed by the pumpOne inlet, a few dispersion holes, about 97 screen holes, the puck, around 640 basket holesThe pump moves the water, not gravity. It pushes about 9 bar into a sealed head. The gap above the shower screen fills first, and from then on every hole gets the same push, which is why they all release water at once. The tamped coffee is the real brake: almost all of the 9 bar goes into forcing water through it, and that keeps the flow near 1.5 ml/s. A precision 58 mm basket then lets the coffee out through around 640 holes of 0.3 mm, about 3.3 cm/s through each. The layers are spread apart so you can see between them; in a real machine they are clamped together.