When there is low or no pressure, the o-ring of the flow regulator is relaxed (position 1).
As soon as water is flowing and the pressure is rising, the o-ring starts changing shape and is pressed into the core's indentations (position 2). The openings for the water become smaller, less water flows through.
The higher the pressure, the more the o-ring changes shape and the smaller the openings (position 3). Thus no matter how high the pressure is, the water flows at a regulated, virtually constant rate that is comfortable and ecologically sound at the same time.
When the pressure decreases, the o-ring gradually goes back to its regular shape, while the water openings become larger again (back to positions 2 and 1).