Difference Between Vacuum Pump and Air Compressor

Air Compressor  

  1. Air compressor is the main body of the air source device. It is a device that converts the mechanical energy of the prime mover into gas pressure energy, and is a pressure generating device for compressed air.  


  1. There are many types of air compressors, which can be divided into positive displacement compressors, centrifugal industrial compressors, and piston compressors according to their working principles.  

  • The working principle of the positive displacement compressor is to compress the volume of the gas, so that the density of the gas molecules in the unit volume increases to increase the pressure of the compressed air.

  • The working principle of the centrifugal compressor is to increase the moving speed of the gas molecules, so that the kinetic energy of the gas molecules is converted into the pressure energy of the gas, thereby increasing the pressure of the compressed air.  

  • The working principle of the piston compressor is to directly compress the gas and discharge it when the gas reaches a certain pressure.  


  1. The commonly used air compressors are piston air compressors, screw air compressors, centrifugal compressors, sliding vane air compressors, and scroll air compressors.  


The selection of the air compressor is mainly based on the working pressure and flow of the pneumatic system. The working pressure of the air source should be about 20% higher than the maximum working pressure in the pneumatic system, because the loss along the way and the loss of the air supply pipeline should be considered. If the working pressure requirement is lower in some parts of the system, a pressure reducing valve can be used to supply air. The rated discharge pressure of the air compressor is divided into low pressure (0.7~1.0MPa), medium pressure (1.0~10MPa), high pressure (10~100MPa) and ultra-high pressure (above 100MPa), which can be selected according to actual needs. Common pressure is generally 0.7~1.25MPa.  


Vacuum Pump  

Vacuum Pump Structure and Principle  

"Vacuum" refers to a gaseous space with a pressure of less than 101.3 kPa. Any device that can extract gas from the container and reduce the gas pressure can be called a vacuum pump. The vacuum pump commonly used in lab is an oil-sealed mechanical vacuum pump, and the vacuum degree is generally 101~1Pa.

This kind of vacuum pump has a steel cylindrical stator, in which there is an eccentric steel solid cylinder as a rotor, and a sliding vane with a spring is embedded in the diameter of the rotor. When the motor drives the rotor to rotate, the sliding vane is in the cylindrical shape. It operates in the cavity of the pump, so that the pump cavity is divided into two regions, and its volume expands and contracts periodically. After connecting the gas container to be pumped to the air inlet of the pump, when the space of the pump cavity increases, the gas to be pumped is inhaled, and as the rotor rotates, the gas is compressed and discharged from the exhaust port. The rotor rotates continuously, the process of suction, compression and exhaust is repeated continuously, the gas in the container is continuously reduced, and the air pressure is continuously reduced. The whole vacuum pump is immersed in a box containing lubricating oil, and the vapor pressure of lubricating oil is very low, which plays the role of lubrication, sealing and cold action.  


Vacuum Pump Usage

The vacuum pump is mainly used in the following aspects in a lab:  

  1. Vacuum Drying

The vacuum pump is connected to the drying oven, and the sample can be removed from the moisture and non-volatile high-boiling impurities in the sample at a lower temperature in the vacuum drying oven so as not to decompose the sample at high temperature.  

  1. Vacuum Distillation

Vacuum distillation is the distillation of pressure, which can reduce the boiling point of the material and enable it to be distilled at a lower temperature. It is suitable for the distillation of organic substances that are easily decomposed at high temperature.  

  1. Vacuum Filtration

For special materials that are difficult to filter, vacuum filtration can speed up the filtration speed. It can also be used for tests that require vacuuming.  


Vacuum Pump Usage Precautions

  1. Before starting the vacuum pump, check whether the oil level in the pump is at the marking line of the oil hole. If there is too much oil, it will splash out with the gas from the exhaust hole during operation. If the oil is insufficient, the pump casing cannot be completely immersed, the sealing and lubrication effect cannot be achieved, which will damage the pump casing.  

  2. The vacuum pump is driven by the motor, and the power supply voltage should be consistent with the voltage required by the motor during use. For a three-phase motor, remove the belt before powering on, check whether the motor rotation direction is consistent, and do not reverse the motor to cause the pump oil to spray out. After checking, attach the belt again.  

  3. The vacuum pump cannot directly pump condensable vapors.

  4. Pay attention to the motor temperature when the vacuum pump is running, and it should not exceed the specified temperature. There should be no friction and metal bumping. If there is any abnormality, please stop the vacuum pump and ask a professional to repair it.  

  5. Before stopping the vacuum pump, the air inlet of the vacuum pump should be vented to the atmosphere and then the power supply should be cut off to prevent the pump oil from returning to the pumping system. For this reason, it is better to connect a three-way piston at the air inlet. Before stopping, the three-way piston should be in a position that not only keeps the system in vacuum, but also allows the pump casing to open to the atmosphere.  

  6. The vacuum pump should regularly clean the spun gauze at the air inlet to prevent small solid particles from falling into the pump and damaging the pump casing.



Doctor Pump Tips

After the vacuum pump has been used for half a year or a year, the oil must be changed.

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