What is the meaning of the "Vaporization Grade Line" in the Data tab of a profile in the Transient Results Viewer?
The Vaporization Grade line is the HGL elevation below which water will turn to vapor (a vapor pocket will form). If the HGL falls below the value, vapor will form.
Negative values indicate that this grade line is below sea level. In the transient calculation options, the default vapor pressure limit field is -97.9 Kpa, which is -10 m or -1 bar. This is sometimes referred to as "full vacuum" - the water changes phase to gas at room temperature and "column separation" occurs. In the example screenshot below, many of the elevations are around 3.7 m, hence with the default vapor pressure limit of -10, the vaporization grade line is -6.3 m.
Assumptions and limitations of tracking air or vapor pockets in HAMMER