Stoppers Pop Out or Slide Into the Vials

The pop out of stoppers occurs mostly during evacuation. If the product is not completely frozen and contains highly concentrated, but not solidified, inclusions, their water content may evaporate explosively when the vacuum is applied. This abmpt evaporation will also blow some product particles to the walls of the vial, as can be seen in the vials after drying. 

Stoppers may also slide into the vials and cause their virtual closure. This can happen during freezing of the product, especially if the shelf temperatures are very low. The dimensions of the stoppers need to be tested not only for the pressure to close them after drying, but also for shrinking at low temperatures. 

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