The upper valve is closed.
Why is the upper valve closed?
So as to lift up the water which is above it.
What becomes of the water which is lifted up?
It runs out of the spout of the pump.
As the upper valve is raised up, what is produced under it?
A vacuum is produced under it.
How is this vacuum filled?
The water below the lower valve is forced up, so as to fill the vacuum.
How is the lower valve?