The operation is a continuous two-stroke process: the Downstroke (dispensing) and the Upstroke (priming).
You press down on the actuator.
This pushes the piston down into the chamber, compressing the spring and increasing the pressure inside.
The inlet valve closes, sealing the chamber from the dip tube.
The pressurized liquid-air mixture inside the chamber is forced through the fine mesh of the foaming screen.
This action aerates the mixture, creating a consistent, low-density foam.
The foam exits through the nozzle.