Heidolph VAC control automatic - Manual (Page 54)

54
E
- requires detailed knowledge about thermal dynamic substance parameters
particularly for all standard processes
9.1.1. Settings in "Manual" regulation mode
- pressure "p" (Set Vac) and the hysteresis

p (Set

p) are set.
- choose pressure "p" as to locate boiling point of the substance to be distilled in the limits
defined by Chapters 9 and 10 (bath temperature and coolant temperature). To this end make
reference to reference chart (page 60) and nomogram (page 60).
- hysteresis

p defines temperature rise in mbar, required to open the vacuum valve.
Extended valve opening times equals high losses due to repeated gas transport.
- Low-boiling substances prefer a higher

p (5 - 10 mbar), whereas we recommend a lower
value (1 - 5 mbar) for high-boiling substances.
9.2. "Auto Mode" vacuum regulation mode
The "Auto Mode" is distinguished by the following parameters:
-
Find distillation point automatically
- Distillation pressure once found will be maintained permanently, integrating hysteresis

p (h).
- Separate mixes within physical limits
- No need to know about thermal dynamic substance data.
9.2.1. "Auto Mode" settings
-
The only item to be set is h hysteresis

p (h).
10. Solvent data
Examples for using reference table and nomogram:
This reference table details substance data needed for distillation, whereas the nomogram reflects
relationship between pressure and boil temperature of some solvents. Go by the Clausius-
Clapeyron equation and plot 1/T against log p.
10.1. at boil temperature of 40°C
LABOROTA 4002/4003 control: in column "vacuum for boil temperature" use the "Set Vac"
nominal value as depicted for 40°C.
10.2. at boil temperatures deviating from 40°C
4. On temperature axis of the nomogram mark boil point wanted.
5. Draw a line to the right and determine intersection with the solvent line.
6. From this intersection draw a straight line down to determine the vacuum pressure needed.
10.3. solvents not depicted
-
The following items might help in determining the right vacuum pressure: