Laboratories often use vacuum pumps to create a vacuum. Since the pressure span from rough vacuum to extremely high vacuum is as high as more than ten orders of magnitude (Pa), different types of vacuum pumps need to be selected when different vacuum degrees are required in experiments. To obtain high vacuum or ultra-high vacuum, it is generally necessary to use a combination of several pumps to achieve it.

Vacuum pumps can be divided into two categories: compression type vacuum pumps and adsorption type vacuum pumps according to the mechanism and method of obtaining vacuum. Compression type pumps compress the gas from a specific container and then discharge it out of the container. Such as water flushing pump, mechanical pump, diffusion pump, molecular pump, etc. The other type is the adsorption pump, which relies on the adsorption of gas molecules in a specific space to reduce the pressure to obtain a vacuum degree. Such as titanium pump, cryogenic pump, adsorption pump, etc.

Mechanical pumps and diffusion pumps are inexpensive and have high pumping rates. They are the most commonly used vacuum pumps in laboratories, but they all use special oils as working substances, which cause certain contamination to experimental objects. Mechanical pumps can only generate a low vacuum of 1~10-1Pa. When the diffusion pump is used, a mechanical pump must be used as the fore pump, and a high vacuum or ultra-high vacuum of 10-1~10-7Pa can be obtained. Diaphragm pumps, adsorption pumps and titanium pumps are all oil-free pumps, and there is no contamination problem with oil vapor. They can be used in tandem to obtain ultra-high vacuum better than 10-6Pa. The molecular pump relies on the high-speed mechanical movement of the inner cylinder to make the gas flow in a directional manner. Generally, it must be combined with the backing pump to obtain a high vacuum. The cryopump is the vacuum pump with the highest pumping speed and can reach extremely high vacuum.