In the world of vacuum-creation, there are several different ways to achieve high vacuum. One of the most popular methods is to use a turbo pump in conjunction with a roughing pump.
The broad category of “turbo pumps” can be broken down into several sub types, including molecular drag, turbomolecular, and turbo drag pumps. The three different designs all have their advantages, and can achieve different vacuum levels:
Molecular Drag Pumps: low pumping speed • can be backed by smaller, less powerful roughing pumps • achieves around 4-5 scale vacuum examples: Pfeiffer/Alcatel MDP series
Turbomolecular Pumps: high pumping speed • must be backed by robust roughing pump which can pull to 2 scale plus vacuum • can achieve up to 11 scale vacuum examples: Leybold TMP series | Pfeiffer TPH series
Turbo Drag Pumps: most common design in modern turbo pumps • combination of molecular drag stages & turbomolecular rotor • allows for less powerful roughing pump, while creating high compression ratios and deep ultimate vacuum • achieve around 8-9 scale vacuum examples: Varian/Agilent TV series | Pfeiffer TMH & HiPace Series | Leybold MAG W series