Transient results can best be viewed with the Transient Results Viewer (Analysis > Transient Results Viewer).

Under the profiles tab, picking any Graph Type that includes Air/Vapor Volume will show the amount of air/vapor in the pipe at the location where it occurs.

Under the Time Histories tab, picking any Graph Type that includes Air/Vapor volume will show the air/vapor in the air valve selected as Time History. The plot of Pressure and Air Volume should show that, air will be drawn into the pipe when pressure becomes negative if the valve is open, or a vapor pocket may form if the valve is closed and the pressure drops below vapor pressure.

The Transient Thematic Viewer can be used to color code the model based on Air or Vapor Volume.