The vacuum unit is composed of various vacuum components, and it is an exhaust system without a vacuum chamber. The vacuum units are named after the main pump. At present, domestic vacuum units mainly include oil diffusion pump units, oil booster pump units and Roots pump units.

The main pumps of the low vacuum pumping unit are commonly used reciprocating vacuum pumps, oil-sealed vacuum pumps, water vapor jet pumps, water ring pumps, molecular sieve adsorption pumps, oil vapor jet pumps, Roots pumps, etc. The main features of the low vacuum pumping unit are high working pressure and large exhaust basin, but the pumping speed is relatively low. It is mostly used for rough pumping of vacuum chambers, and vacuum conveying, vacuum impregnation, vacuum filtration, vacuum drying, vacuum degassing and other devices with large air release and high working pressure. When using a low-vacuum extraction unit, it is also necessary to match the necessary dust collectors, dryers and other components according to the cleanliness, humidity or other special requirements of the extracted gas.

The medium vacuum oil booster pump unit is used to obtain the working pressure of 1~10-1Pa. The ultimate vacuum degree is 10-2Pa. It consists of oil booster pump, vacuum valve, trap, low vacuum shut-off valve, air release valve, pipeline, electrical control panel, water pressure relay and other components.

The working vacuum degree of the medium vacuum Roots pump unit is 1~103Pa. The ultimate vacuum degree is 10-1Pa. Other components are the same as the oil booster pump unit.

The working vacuum degree of the high vacuum pumping unit is 10-2~10-3Pa, and its ultimate vacuum degree is 10-4Pa. The main pump of the unit is usually oil diffusion pump, diffusion booster pump, molecular pump, titanium pump, low temperature condensate pump, etc. These pumps cannot work directly with the atmosphere and require a pre-pump or fore-maintenance pump. Some diffusion pump high vacuum extraction units are also equipped with a pre-stage air storage tank to prevent air pressure fluctuations and improve the performance of the unit.

The ultra-high vacuum pumping unit works at 10-6~10-8Pa. In addition to the requirement that the material of the vacuum chamber has a very low outgassing rate, a small air leakage rate, and can withstand high temperature baking at 200-450℃, the requirements for the unit are as follows: the ultimate vacuum of the main pump should be high, at least 10-7~ Above 10-8Pa. The main pump has a certain pumping speed within the working pressure range of ultra-high vacuum. The partial pressure of the reflux gas from the main pump should be low enough; the main pump with strong selectivity to the gas to be pumped should be equipped with a sufficiently large auxiliary pump; the material selection and sealing of the pipes, valves and other components above the air inlet of the main pump of the unit Be especially careful. Generally, stainless steel with a lower gas outlet rate and metal sealing rings are used.