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To start the drying process, the main drying process has to be
activated in the control system. The pressure control valve opens and
the main drying process starts.
Caution:
The frozen samples can only be connected to the valves when a
pressure of less than 1.030 mbar is reached.
Liquids are frozen in flasks according to the shell freezing principle,
manually or with a turning device. Thanks to this freezing process the
layer thickness is reduced and the drying period is considerably
shortened.
Most of the manifolds and valves available allow a continuous
connection and removal of flasks during the drying process. Each
rubber valve is equipped with a closing and aeration valve.
If the rubber valves or stainless steel valves are stiff they must be
dismantled, cleaned, slightly greased with vacuum grease and
reassembled.
It is also possible to connect a distributor for 15 ampoules to every
rubber valve.
Using a distributor a maximum of 15 ampoules can be simultaneously
frozen in the cooling bath and connected to the manifold.
3.4. Separate Freezing and Drying of Liquids in
Ampoules (Process B)
The refrigeration compressor and the vacuum pump are activated via
the control system to start the pre-freezing of the ice condenser and
the warming-up of the vacuum pump. The valve is closed during
warming-up of the pump. In case the unit is not equipped with an
electromagnetic pressure control valve we recommend to use a
manual stop valve. Without such a valve the vacuum pump must not
be warmed up.
The manifold is equipped with blind plugs for connection of a
maximum of 48 ampoules so that it can be pre-evacuated.
The first hose is clamped in the middle with the supplied hose clamp
and the blind plug is removed. The vacuum of the system is
preserved.
The liquid in the ampoule is either frozen under rotation in a cooling
bath or in a deep-freeze.
If shock-freezing is required we recommend that freezing is carried
out in liquid nitrogen or in a cooling bath.
22 • Description of the Freeze Drying Processes
Operating Manual Freeze Dryer ALPHA 1-2 LDplus
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