Question

In an aerosol can used for spray paint, a highly compressed "propellant" helps move the liquid into a "dip tube" so that it can be sprayed out. the valve through which the liquid sprays is usually closed, but when it is pressed down, it opens and allows material to pass through.

Answer 1

The liquid rise up through the dip tube when the valve is opened.  The propellant gas wants to expand as much as it can, so if the valve is open, the propellant expands and pushes the spray up out of the can making more room for itself to expand.

Answer 2

"The propellant gas wants to expand as much as it can, so if the valve is open, the propellant expands and pushes the spray up out of the can making more room for itself to expand"