In the event the system is open to the atmosphere while either the cold trap is cold or a temporary leak occurred, water vapor from the air around the machine can condense on the cold trap, forming ice. When a vacuum is applied, this ice will slowly sublimate (or turn into vapor) causing the vacuum to not go below the mid-to-low negative 1’s (between 1 mbar and 0.1 mbar).
This can easily be fixed by simply leaving the vacuum pump on with the gas ballast open. In addition, you can accelerate this process by changing the temperature of the setpoint of the cold trap chiller to 0 degrees C, and then changing the temperature back down to the minimum setting once it reaches 0 degrees.
The elevated temperature will supply the thermal energy necessary for the sublimation of the water and will reduce the time for the ice to disappear.
More information can be found in SOP – Vacuum Troubleshooting.
If you need additional assistance, please call technical support at +1 (206) 452-1130.