When the actuator is depressed, it pushes the valve stem down against the spring.
The valve stem moves down through the inner gasket, and when the hole is below the level of the gasket liquid flows up through the dip tube into the valve housing, then through the valve stem to the actuator.
The liquid will continue to flow due to the internal pressure
exerted by the propellant, until the valve is closed when the
operator releases the pressure on the actuator and the valve stem
is pushed upwards by the spring.