Martin Christ Beta 2-8 LDplus - Manual (Page 24)

24 General Information on Freeze-drying Operating Manual Freeze Dryer BETA 1-8 LDplus / BETA 2-8 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.