A vacuum pump refers to a device or equipment that uses mechanical, physical, chemical, or physicochemical methods to evacuate a container to obtain a vacuum. Simply put, a vacuum pump is a device that uses various methods to improve, generate, and maintain a vacuum in a closed space.

According to the working principle of vacuum pumps, they can be basically divided into two types, namely gas capture pumps and gas transfer pumps. It is widely used in industries such as metallurgy, chemical, food, and electronic coating.

Structural characteristics

(1) Overall structural type of pump

The arrangement structure of the pump body of a vacuum pump determines the overall structure of the pump.

The horizontal setting of the inlet and outlet of the vertical structure makes assembly and connection of pipelines relatively convenient. But the center of gravity of the pump is relatively high, and its stability is poor during high-speed operation, so this type is mostly used for small pumps.

The inlet of the horizontal pump is on top and the outlet is on the bottom. Sometimes, in order to facilitate the installation and connection of vacuum system pipelines, the exhaust port can be connected horizontally, that is, the inlet and outlet directions are perpendicular to each other. At this point, the exhaust port can open from both left and right directions, except for one end connected to the exhaust pipe, the other end can be blocked or connected to a bypass valve. This pump structure has a low center of gravity and good stability during high-speed operation. This structure is commonly used in large and medium-sized pumps.

The two rotor shafts of the pump are installed perpendicular to the horizontal plane. This structure is easy to control the assembly clearance, the rotor assembly is convenient, and the pump occupies a small area. But the pump has a high center of gravity and the gears are difficult to disassemble, and the lubrication mechanism is relatively complex.

(2) The transmission mode of the pump

The two rotors of a vacuum pump operate in relative synchronization through a pair of high-precision gears. The active shaft is connected to the motor through a coupling. There are mainly two types of transmission structure arrangements: one is to place the motor and gear on the same side of the rotor as shown in the figure. The driven rotor is directly transmitted and driven by the motor end gear, so that the twisting deformation of the active rotor shaft is small, and the gap between the two rotors will not change due to the large twisting deformation of the active shaft, thus making the gap between the rotors uniform during operation. The advantages and disadvantages of this transmission method are: a There are three bearings on the drive shaft, which increases the difficulty of pump processing and assembly, and the disassembly and adjustment of gears are also inconvenient; b. The overall structure is uneven, and the center of gravity of the pump is biased towards the side of the motor and gearbox.

characteristic

(1) Has a larger pumping speed within a wider pressure range;

(2) The rotor has good geometric symmetry, resulting in low vibration and smooth operation. There are gaps between the rotors and between the rotor and the housing, which do not require lubrication and have low friction loss. This can greatly reduce the driving power and achieve higher speeds;

(3) The pump chamber does not require oil sealing and lubrication, which can reduce the pollution of oil vapor to the vacuum system;

(4) There is no compression in the pump chamber and no exhaust valve. Simple and compact structure, insensitive to dust and water vapor in the extracted gas;

(5) Low compression ratio results in poor hydrogen extraction efficiency;

(6) The surface of the rotor is a complex curved cylindrical surface, which is difficult to process and inspect.

Maintenance and upkeep

The quality of a vacuum pump depends on its mechanical structure and the quality of the oil, and it must be protected when using it. If volatile organic solvents are distilled, they will be absorbed by the oil, resulting in an increase in vapor pressure and a decrease in evacuation efficiency. If it is acidic gas, it will corrode the oil pump. If it is water vapor, it will make the oil into an emulsion and damage the vacuum pump.

Therefore, when using a vacuum pump, the following points must be noted:

An absorption device must be installed between the distillation system and the vacuum pump.

Before distillation, it is necessary to thoroughly remove the vapor of organic solvents from the system using a water pump.

If it is possible to use a water pump to extract air, try to use a water pump as much as possible. If volatile substances are present in distilled materials, first use a water pump to reduce pressure and then switch to an oil pump.

The pressure relief system must be kept tight and leak proof, and all rubber plugs should be of appropriate size and holes. The rubber tubes should be vacuum rubber tubes. Apply vacuum grease to the ground glass.

According to the scope of use and pumping efficiency, vacuum pumps can be divided into three categories:

(1) A typical water pump can achieve a pressure of 1.333 to 100kPa (10 to 760mmHg) for a "coarse" vacuum.

(2) Oil pump, with a pressure of up to 0.3 Pa (0.001 mmHg) as the "second highest" vacuum.

(3) Diffusion pump, pressure can reach below 0. Good Pa, (10-3mmHg) is a "high" vacuum.