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Oil contamination freeze dryer

In our freeze dryer silicone oil is used for cooling/heating of the plates. The oil is fed to the plates using flexible metal hoses. These hoses are used world wide for this purpose because of the wide temperature range -60 to +70°C, and because the plates must be movable for stoppering of the vials.

These hoses are supposed to be fail safe, however until now we have had three hoses ruptured. At first no leakage will be visible, but still oil contaminents are measured in the product. At a certain moment the rupture expands and oil droplets will become visible.

We have some questions.
-What is an acceptable oil contamination level for freeze dryers, and what is the basis for this requirement.
-Are there other users who have experience with ruptured silicone oil hoses.
-What cleaning method would be advised after breakdown.
-What preventive actions would you advice.
-What methods for measuring of oil contamination are available.
-Are there any in line methods for measuring oil contamination

Of item
-What requirements are used for leak testing
-What is the basis for this requirement