Not strictly according to the theoretical definition, the applications with vacuum level from 100 Pa to 0.1 Pa (1 mbar to 1×10-3 mbar) are classified as medium vacuum applications. To achieve such pressure, it is generally to use 2 different types of vacuum pumps to assemble a vacuum system. Here’re some vacuum systems can be found in the market:
• Oil diffusion vacuum pump with mechanical vacuum pump
The oil diffusion pump (also known as oil booster pump) has a working range of 10-2 mbar to 10-4 mbar. Oil booster pump can be used as the main pump in the vacuum system. And oil-sealed rotary vane pump as one of the mechanical pump types, is commonly used as primary pump. Simple structure, high pumping speed and high durability are the features of the system consisting of an oil diffusion pump and a mechanical pump. However, the pre-pumping time is sort of shortage. It’s longer than that of Roots pump system.
• Roots vacuum pump with mechanical vacuum pump
The combination of Roots booster pump and mechanical vacuum pump is very popular to design a vacuum system. For the working pressure range of 10 mbar to 10-2 mbar, the system has high flow rate, short pre-pumping time but a little high working noise.
• Upgrade version of Roots pump and mechanical pump
The combination of a Roots pump with a small Roots pump and a mechanical pump has a wider pressure range of 10 mbar to 10-3 mbar as well as a better compression ratio.
• Roots vacuum pump with liquid ring vacuum pump
More precisely, liquid ring pump is one of mechanical pumps. It is worth mentioning that a vacuum system with liquid ring pump is suitable for dusty and vapory applications. Two main shortages of such system are low efficiency and low vacuum.