Pressure in Hammer transient simulation

Hi,

During hammer simulation two issues occured:

1- the pressure , the first 400 sec  in simulation HGL fluctuate near the upper value - max pressure (No.1), after that HGL moves to position No.2 for little time then it moves to position No.3 till the end of the simulation (1200 sec).

2- when I reduce time interval of simulation from 0.05 sec to 0.01 sec the vapor volume disappears. 

Kindly I need illustration for possible causes for these events.