Fore Vacuum for Turbomolecular 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. Such turbo pumps need an auxiliary backing pump, or "roughing pump", as they cannot compress to atmospheric pressure. Using oil-free diaphragm pumps for fore-vacuum generation in connection with state-of-the-art turbo pumps (with "molecular drag" stage) decisively improves the cleanliness of the vacuum generation, and often reduces service requirements as well. In many cases, such an oil-free high vacuum is absolutely mandatory.

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 available backing vacuum. The volume flow rate of the diaphragm pump then only has an impact on the pump-down time.
• Under gas load (process-related gas inlet or gas release), the roughing pump has to be sized so that the maximum permissible backing pressure of the high vacuum pump is safely reached. This requires a diaphragm pump with high pumping speed close to its ultimate vacuum. All VACUUBRAND diaphragm pumps are excellent in this regard because of their planar diaphragm designs.

Pump requirements

• ultimate vacuum of the diaphragm pump sufficient to meet the backing pressure requirements of the high vacuum pump – down to 0.3 mbar, with VARIO® diaphragm pumps
• high pumping speed even at pressures close to ultimate vacuum
• low power consumption
• low anti-suckback leakage rate, no venting during a power failure
• high reliability, designed for continuous operation (24/7)
• good tolerance of condensate
• high ultimate vacuum stability and service intervals comparable to turbo pumps
• reliable starting even under vacuum
• small size, low weight and low vibration