Ice in my dewar! (Liquid helium transport dewar)
From NMR Wiki
Here is a solution to an iced-up Liquid helium Transport Dewar. This is of special interest to sites which are far from their liquid helium supplier, and wh perform their own liquid helium fils.
Scenario:
The dewar will not pressurize, or pressurizes reluctantly. The dewar will not vent via the regular vent port. Some of the safety valves do not vent any gas.
