Fore-vacuum generation for Turbo pumps

Many analytical applications (such as mass spectrometry, electron microscopy or surface analysis) are carried out in high vacuum. Turbomolecular pumps are typically used to generate the needed vacuum. Turbo pumps need an auxiliary backing pump as they cannot compress to atmospheric pressure. Using oil-free diaphragm pumps for fore-vacuum generation in connection with state-of-the-art turbomolecular pumps (with "molecular drag" stage) decisively improves the cleanliness of the vacuum generated. In many cases, such an oil-free high vacuum is absolutely necessary.

Process requirements

• if the high vacuum system is operated without any gas load, the ultimate vacuum of the diaphragm pump may be assumed as the backing vacuum. The volume flow rate of the diaphragm pump then only has an impact on the pump-down time.
• in case of a noticeable gas load, the backing pump has to be appropriately dimensioned to guarantee the maximum acceptable backing pressure of the high vacuum pump. For these applications, it is important to select a diaphragm pump with high flow rates even near ultimate vacuum. All VACUUBRAND diaphragm pumps are excellent in this regard due to their planar diaphragm design.

Demands made of the vacuum pump

• the required ultimate vacuum of the diaphragm pump depends on the maximum permissible backing pressure of the high-vacuum pump; VARIO^® diaphragm pumps offer an ultimate vacuum up to 0.3 mbar
• high volume flow rate even close to the ultimate vacuum
• low energy consumption
• low back-streaming leakage rate to prevent venting of the application in the event of power failure
• continuous-duty rated, 24/7
• not sensitive to condensate
• high long-term ultimate vacuum stability and diaphragm lifetime
• reliable start-up even under vacuum
• small size, low weight and very low vibration

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