Comparative pressure measurement between a capacitive pressure gauge and a Pirani sensor can define the endpoint. Whereas the capacitive pressure gauge functions independently of the gas type and always indicates the true pressure in the drying chamber, the Pirani sensor is calibrated to a specific gas and measures only relative figures according to gas type. Calibrated to N2, the Pirani sensor indicates higher values than the capacitive pressure gauge in response to the presence of water molecules in the chamber. As the concentration of water molecules decreases, the detected value of the Pirani sensor reading progressively becomes closer to that of the capacitive pressure gauge until they become equal at the end point.
Pressure rise test is accomplished by closing the valve between the product and condenser chambers. When the two chambers are isolated, the pressure in the product chamber rises due to the on-going sublimation of the water molecules. The pressure rise curve progressively levels off as the water molecule concentration decreases. The end point is the point at which no further pressure rise is dicscernible.
Stoppering to close your vials under required conditions
The height of the shelves in the BUCHI top-mounted Freeze Drying rack is adjustable in a wide range. That enables the use of a unique stoppering system for all shelf drying racks. The system has a self-sealing mechanism and stoppering can be achieved under vacuum and ambient pressure conditions even with inert gas. In contrast to conventional systems, the shelves therefore do not need a hole in the middle of the round shelves.
Cleaning and waste-water handling
Cleaning of the double condensers is carried out automatically when fully loaded. Thus, that the waste water is directly discharged into a drain or collecting vessel. There is a fill level sensor in the collecting vessel that informs the user when the vessel needs to be emptied.