Martin Christ Alpha 2-4 LDplus - Manual (Page 22)

22 General Information on Freeze-drying Operating Manual Freeze Dryer ALPHA 1-4 LDplus / ALPHA 2-4 LDplus
2.5. Final Drying
The final pressure in the drying chamber depends on the ice
condenser temperature according to the vapour pressure curve
above ice :
e. g. 1.030 mbar correspond to -20°C
0.370 mbar correspond to -30°C
0.120 mbar correspond to -40°C
0.040 mbar correspond to -50°C
0.011 mbar correspond to -60°C
The unit is in operating condition if the temperature of the ice
condenser is lower than -50°C and the pressure is lower than 0.120
mbar.
The final pressure measured by the vacuum sensor when there is
no product in the unit and its corresponding ice temperature value is
mainly determined by the warmest place of the ice on the ice
condenser chamber. Moreover, this value is affected by residues or
parts of solvents in the product with a higher vapour pressure.
2.6. End of Drying and Aeration
A rough indication of the end of drying are the vacuum and the ice
condenser temperature. The ice condenser is no longer loaded and
reaches the final temperature of approx. -55°C to - 85°C. The
pressure in the drying chamber decreases according to the ice
condenser temperature.
The vacuum pump is switched off and the drying chamber is vented
via a rubber valve or the aeration valve on the left side of the unit.
The aeration valve can also be used to “flood” the unit with nitrogen
or another inert gas instead of using air.
CAUTION! Maximum overpressure 0.2 bar!
Then the unit is switched off and the product is removed.
2.7. Defrosting
If the freeze-dryer is not equipped with a defrosting device,
defrosting of the ice condenser is carried out at room temperature
or with warm water. At a maximum the ice condenser chamber may
be half filled with water.
When defrosting the ice condenser with (warm) water, it is of crucial
importance that no water gets into the pipe connection for the
vacuum pump and the vacuum sensor (see figure)!
The condensate as well as the defrosting water are drained through
the drain valve at the left side of the unit. To do this, a hose is put
onto the nozzle. The condensate and the defrosting water are
collected in a vessel.