In order to obtain high vacuum, ultra-high vacuum and extremely high vacuum, multiple vacuum pumps are connected in series to form a unit to complete the pumping task. Therefore, it is very important for users to choose an economical vacuum pump to correctly understand the working principle, main performance, structural characteristics and classification of the pump.

A vacuum pump is a device used to generate, improve and maintain a vacuum. According to its working principle, it is basically divided into two types: gas transmission pump and gas capture pump.

The gas transfer pump is a vacuum pump that can continuously suck and discharge gas out of the pump to reach the suction port. This gas transfer pump includes two categories: positive displacement pump and momentum transfer pump.

Positive displacement vacuum pump is a device that uses the periodic change of the volume of the pump chamber to complete suction, compression and exhaust. The gas is compressed before being discharged. This pump is divided into two types: reciprocating and rotary.

(1) The reciprocating vacuum pump uses the reciprocating motion of the piston in the pump chamber to inhale, compress and discharge the gas. Therefore, it is also called a piston vacuum pump.

(2) Rotary vacuum pump uses the rotary motion of the piston in the pump chamber to inhale, compress and discharge the gas. There are many types of pumps that belong to this category.

1) Oil-sealed mechanical pump, which is a rotary positive displacement vacuum pump that uses oil to seal the gaps of various moving parts and reduce harmful spaces. This kind of pump usually has a gas ballast device, so it is called a gas ballast vacuum pump. According to its structural characteristics, it is divided into: rotary vane pump, fixed vane pump, slide valve pump, trochoid pump and multi-chamber rotary vane pump.

2) Dry vacuum pump. At present, the so-called dry vacuum is generally referred to as: a vacuum pump that can work in the pressure range from atmospheric pressure to 10-2Pa; in the pumping air passage (such as the pump cavity), no any vacuum pump can be used. Oils and sealing liquids. The exhaust port is connected to the atmosphere, and the pump that can continuously exhaust to the atmosphere is called a dry vacuum pump. According to its working principle, there are also dry positive displacement vacuum pumps, such as multi-stage roots pump, multi-stage piston pump, claw pump, screw pump, scroll pump, etc.; This kind of pump is no longer polluted by oil, and it is a kind of pump that has been developed recently.

3) Liquid ring vacuum pump, the rotor with multi-blade is eccentrically installed in the pump casing. When the rotor rotates, the liquid (water or oil) is thrown to the pump casing to form a liquid ring concentric with the pump casing. The blades of the vacuum pump form several small volumes with periodic changes in volume to achieve suction, compression and exhaust. Because the liquid ring plays the role of compressing gas, it is also called a liquid piston vacuum pump.

4) Roots vacuum pump, the pump is equipped with two double-leaf or multi-lobe rotors that rotate synchronously in opposite directions, and there is a certain gap between the rotors and between the rotor and the inner wall of the pump casing. It belongs to the vacuum pump without internal compression. According to the purpose, it is divided into wet Roots pump, direct exhaust atmospheric Roots pump and mechanical booster pump.