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VDL (E3.1) 10/2020 Page 93/196
9.8 Evacuation
Starting situation: The vacuum pump / vacuum system is connected and ready for operation.
Preparation:
• Make sure that the “Manual ventilation” plug (7) for emergency ventilationin case of a power failure,
which is located on the chamber rear, is closed
• Make sure that the pressure control is activated.
• Turn on the vacuum pump. The pump shall continue running during the entire drying procedure.
• Set the desired pressure set-point on the controller (chap. 10).
• Monitor the internal pressure on the controller display
As long as there is a vacuum, never try to open the oven by force.
9.9 Breaking the vacuum (flooding)
9.9.1 Ventilation after completing the drying procedure (flooding with ambient air or
inert gas)
The duration of the drying procedure can be determined via the pressure display on the controller. When
the decreasing pressure reaches the set-point value, the drying process is completed. If the drying moni-
toring (chap. 11.6) is activated, a corresponding message is displayed.
To break the vacuum (ventilation) after completing the drying procedure, set the desired pressure set-point
to atmospheric pressure (chap. 10). The ventilation valve opens, and ambient air or inert gas flow into the
inner chamber.
Regularly the universal connection for inert gas / ambient air “GAS/AIR” (4) is used for ventilation.
Chambers can be equipped as an option with an additional universal connection for inert gas / ambient air
“GAS/AIR2” (5), which can be used alternatively. To do this, the controller function “GAS/AIR 2” serves to
close the valve of the standard connection “GAS/AIR” (4). Then the valve of the optional connection
“GAS/AIR 2” (5) is used for ventilation (chap. 11.2). This allows convenient switching when both connec-
tions are used differently (e.g., for inert gas and ambient air).
Ambient air is sucked in through the universal connection for inert gas / ambient air (4) or (5). The ambient
air is introduced into the lower part of the rear panel of the inner chamber and is evenly distributed in the
inner chamber. This supply of ambient air by under-flooding prevents turbulence of pulverized drying ma-
terial.
Following ventilation, remove the loading material.
If no further drying process is to be carried out, switch the chamber to standby mode on the controller or
pull the mains plug to switch off the chamber completely.
9.9.2 Operation with inert gas
When operating the VDL vacuum drying oven with inert gas, correctly follow the technical ventilation
measures, as described in the DGUV guidelines 213-850 on safe working in laboratories, issued by the
employers’ liability insurance association (for Germany).
During operation with inert gas, the chamber is supplied with an oxygen displacing gas (e.g. N
2
). Inert gases
in high concentrations are hazardous to health. They are colorless and almost odorless and therefore prac-
tically imperceptible. Inhalation of inert gases can cause drowsiness up to respiratory arrest. When the O
2
content of the air decreases below 18%, there is risk of death from lack of oxygen. Any gas that might
escape has to be led out via good room ventilation or a suitable exhaust system.
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