At present, the pressure range involved in vacuum technology is 105Pa~10-13Pa. Such a wide pressure range cannot be achieved by any kind of vacuum equipment—vacuum pump alone, so it needs to be realized by vacuum pumps of different structures. According to the working principle, several types of vacuum pumps are described.

Pumps that use mechanical motion such as rotation or sliding to obtain vacuum are called mechanical vacuum pumps, which can be divided into the following types:
(1) Reciprocating vacuum pump. It is a volumetric vacuum pump that compresses and discharges the gas by the reciprocating motion of the piston in the pump chamber. Ultimate vacuum: single-stage about 103Pa; double-stage about 10Pa. The pumping rate is 45m3/h~20000m3/h.

(2) Water ring vacuum pump. It is a vacuum pump that uses a water ring to rotate and change its volume. Ultimate vacuum: single-stage about 103Pa; double-stage about 102Pa. The pumping rate is 0.25m3/h~500m3/h.

(3) Oil-sealed rotary vacuum pump. It is a pump that maintains the seal with oil and uses a rotating eccentric cam to rotate in the cylinder to pump air, including stator vacuum pump, rotary vane vacuum pump, slide valve vacuum pump and trochoid vacuum pump. In the vapor deposition technology, the rotary vane vacuum pump is used a lot, and the ultimate vacuum degree is about 10-1Pa (single stage) and 10-2Pa (dual stage). The pumping rate is 1L/s~500L/S. In addition, a slide valve vacuum pump is also used, and the ultimate vacuum degree is about 10Pa (single-stage) and 10-1Pa (two-stage). Pumping rate 1L/S~600L/s.

(4) Roots vacuum pump. It is a rotary variable volume vacuum pump with two double-lobed or multi-lobed rotors that rotate in opposite directions in the pump, and a certain gap is maintained between the rotors and between the rotors and the inner wall of the pump casing. The pump has a large pumping speed between 102Pa and 1Pa, which can completely make up for the insufficient pumping speed of the rotary mechanical pump and oil diffusion pump in this pressure range. pressure pump. Its ultimate vacuum is about 10-2Pa. The pumping rate is 15L/s~40000L/s. The roots pump cannot be used alone, and must be used in series with the backing pump.

(5) Turbo molecular pump. It is a mechanical high vacuum pump fitted with a slotted disc or a vaned rotor. The rotor rotates between the corresponding discs of the stator, and the linear speed rotates at the same order of magnitude as the gas molecules. The normal operation of the pump is suitable for the molecular flow state. The ultimate vacuum is about 10-8Pa or higher, and the pumping rate is generally below 5000L/s.