A vacuum pump refers to a device or equipment that utilizes mechanical, physical, chemical, or physicochemical methods to extract gas from a container to obtain a vacuum. Simply put, a vacuum pump is a device that improves, generates, and maintains a vacuum in a closed space using various methods.
Overall Pump Structure
The layout of the pump body determines the overall structure of the vacuum pump.
In a vertical structure, the intake and exhaust ports are set horizontally, making assembly and connection of the pipelines relatively convenient. However, the center of gravity is higher, leading to poor stability during high-speed operation; therefore, this type is commonly used for small pumps.
In a horizontal pump, the intake port is on top, and the exhaust port is at the bottom. Sometimes, to facilitate the installation and connection of vacuum system pipelines, the exhaust port can be connected horizontally; thus, the intake and exhaust directions are perpendicular to each other. In this case, the exhaust port can open to either the left or right, with one end connected to the exhaust pipeline and the other end blocked or connected to a bypass valve. This pump structure has a low center of gravity, providing good stability during high-speed operation. This structure is commonly used in large and medium-sized pumps.
The two rotor shafts are installed perpendicular to the horizontal plane. This structure makes it easy to control assembly gaps and install the rotors, and it occupies a small floor space. However, the center of gravity is high, and disassembling and assembling gears is inconvenient, with a relatively complex lubrication mechanism.
Pump Transmission Method
The two rotors of the vacuum pump achieve relative synchronous operation through a pair of high-precision gears. The drive shaft is connected to the motor through a coupling. The main transmission structure arrangements are as follows: one is placing the motor and gears on the same side of the rotors, as illustrated in the diagram. The driven rotor is directly driven by the gears from the motor end, minimizing the torsional deformation of the drive rotor shaft, thus keeping the gap between the two rotors from changing due to significant torsional deformation of the drive shaft. As a result, the gap between the rotors remains uniform during operation. The main drawbacks of this transmission method are: a. The drive shaft has three bearings, increasing the difficulty of pump machining and assembly, and the gears' disassembly and adjustment are also inconvenient; b. The overall structure is asymmetrical, with the center of gravity leaning towards the motor and gearbox side.
It has a high pumping speed over a wide pressure range;
The rotor has good geometric symmetry, resulting in low vibration and stable operation. There are gaps between the rotors and between the rotor and the casing, eliminating the need for lubrication, reducing friction losses significantly, and potentially achieving higher rotational speeds;
The pump chamber does not require oil for sealing and lubrication, reducing oil vapor contamination in the vacuum system;
There is no compression in the pump chamber, and no exhaust valve is needed. Its structure is simple and compact, and it is not sensitive to dust and water vapor in the gas;
It has a low compression ratio, making it less effective for hydrogen gas extraction;
The rotor surface has a complex curved surface, making processing and inspection relatively difficult.
The performance of a vacuum pump depends on its mechanical structure and oil quality, and it must be well protected during use. When distilling volatile organic solvents, the organic solvent might be absorbed by the oil, increasing the vapor pressure and thereby reducing the extraction efficiency. Acidic gases can corrode the oil pump, and water vapor can turn the oil into an emulsion, damaging the vacuum pump.
Therefore, attention must be paid to the following points when using a vacuum pump:
An absorption device must be installed between the distillation system and the vacuum pump.
Before distillation, the vapor of the organic solvent in the system must be thoroughly extracted using a water pump.
Use a water pump to extract gas if possible. If the distillate contains volatile substances, use a water pump for initial reduction and then switch to an oil pump.
The vacuum system must be airtight without any leaks; all rubber stoppers should fit well, and rubber hoses should be vacuum-grade. Apply vacuum grease to the ground glass joints.
