Liquid nitrogen dewars can be divided into two categories, one for storing liquid nitrogen + samples, and the other for rehydration of cryogenic containers!
The former has no pressure, but the latter has a low pressure within 0.1MPa!
The key point is actually “sample storage”!
The liquid nitrogen storage Dewar needs to store samples, so there is an opening for the sample to enter, which is what we often call the caliber; there are large and small calibers, but they are all for sample storage. Also because of the caliber, even if the liquid nitrogen evaporates, it can be discharged quickly, and there will be no pressure accumulation in the container.
You may ask, liquid nitrogen storage Dewar has a neck plug, but even if the neck plug covers the neck, there is no pressure, why?
It is still considered for sample storage!
In order to avoid the explosion caused by the accumulated pressure of liquid nitrogen evaporation, resulting in the death of cells or semen, the neck plug of the liquid nitrogen Dewar has an air outlet. It does not completely clamp the neck, but covers it loosely. The evaporated nitrogen will Leaks out through small “openings”, keeping the storage Dewar pressurized at all times.
As for the liquid nitrogen Dewar used for infusion, although there is no opening for storing samples, there is also an emptying valve. When the liquid nitrogen is stored statically, there is still no pressure. Only when the liquid nitrogen needs to be output can the low pressure be increased!
All for the safety of users and samples! This is why there is no pressure in the liquid nitrogen storage Dewar!