Structural Characteristics of Vacuum Pump

(1) The general structural type of the pump

The layout structure of the pump body of the vacuum pump determines the overall structure of the pump.

The intake and exhaust ports of the vertical structure are horizontally arranged, and the assembling and connecting lines are convenient. However, the pump has a high center of gravity and poor stability at high speed, so this type of pump is mostly used for small pumps.

The intake port of the horizontal pump is on the top and the exhaust port is on the bottom. Sometimes in order to facilitate the installation and connection of vacuum system piping, the exhaust ports can be connected from the horizontal direction, i.e. the inlet and exhaust directions are perpendicular to each other. At this point, the exhaust port can be opened in either left or right direction, and the other end is blocked or connected with a bypass valve in addition to one end of the exhaust pipe. This pump has a low center of gravity and good stability at high speed. Generally large and medium-sized pumps use this structure.

The two rotor shafts of the pump are installed vertically with respect to the horizontal plane. This structure has easy assembly clearance control, convenient rotor assembly and small pump area. However, the pump has a high center of gravity and inconvenient gear disassembly, so the lubrication mechanism is relatively complex.

(2) Driving mode of pump

The two rotors of the vacuum pump operate in relative synchronization by means of a pair of high-precision gears. The drive shaft is connected to the motor via a coupling. There are mainly two kinds of arrangement in the transmission structure: one is that the electric motor and the gear are placed on the same side of the rotor as shown in the figure. The driven rotor is driven directly by the end gear of the motor. In this way, the torsional deformation of the active rotor shaft is small, and the clearance between the two rotors will not be changed by the torsional deformation of the active shaft, so that the clearance between the rotors is uniform in the running process. The biggest disadvantage of this transmission mode is: a. There are three bearings on the drive shaft, which makes it difficult to process and assemble the pump and inconvenient to disassemble, assemble and adjust the gears; B. The overall structure is not symmetrical and the center of gravity of the pump is on the side of the motor and gearbox.

Characteristic

(1) There is a large pumping speed in a wide pressure range;

(2) The rotor has good geometric symmetry, so it has small vibration and smooth running. There is clearance between the rotors and between the rotors and the housing. Without lubrication, the friction loss is small, which can greatly reduce the driving power and thus achieve a higher speed.

(3) No oil seal and lubrication are needed in the pump chamber, which can reduce the pollution of oil vapor to the vacuum system.

(4) There is no compression and no exhaust valve in the pump cavity. It is simple, compact and insensitive to dust and water vapor in the extracted gas.

(5) Compression is low and the effect of hydrogen extraction is poor;

(6) Rotor surface is a curved cylindrical surface with complex shape, which is difficult to process and inspect.