The lower valve is closed.
Why is the lower valve closed?
So as to prevent the water from being forced back again into the well.
How is the upper valve?
The upper valve is open.
Why is the upper valve open?
So that the water may pass up through the valve, while the valve is descending.
What does [Fig. 18] represent?
It represents a pump when the handle is being lowered.
How is the upper valve?