Rotary vane vacuum pump working principle demonstration diagram

The rotary vane vacuum pump (referred to as rotary vane pump) is an oil-sealed mechanical vacuum pump. Its working pressure range is 101325~1.33×10-2 (Pa), which belongs to low vacuum pumps. It can be used alone or as a forepump for other high vacuum or ultra-high vacuum pumps. It has been widely used in metallurgy, machinery, military industry, electronics, chemical industry, light industry, petroleum, and pharmaceutical production and research departments.

　　The rotary vane pump can extract dry gases from sealed containers, and if equipped with a gas ballast device, it can also extract a certain amount of condensable gases. However, it is not suitable for extracting gases that are too high in oxygen, corrosive to metals, chemically reactive with pump oil, or contain particulate dust.

　　The rotary vane pump is one of the most basic vacuum obtaining devices in vacuum technology. Rotary vane pumps are mostly medium and small-sized pumps. There are single-stage and double-stage rotary vane pumps. The so-called double-stage means that two single-stage pumps are connected in series in structure. Generally, they are mostly made as double-stage to achieve a higher vacuum degree. The relationship between the pumping speed of the rotary vane pump and the inlet pressure is specified as follows: at inlet pressures of 1333 Pa, 1.33 Pa, and 1.33×10-1 (Pa), the pumping speed values must not be lower than 95%, 50%, and 20% of the nominal pumping speed of the pump, respectively.

　　The rotary vane pump mainly consists of a pump body, rotor, vanes, end caps, springs, and other components. An eccentric rotor is installed in the cavity of the rotary vane pump, with the outer circle of the rotor tangent to the inner surface of the pump cavity (there is a very small gap between the two). Two vanes with springs are installed in the rotor slots. During rotation, the centrifugal force and the tension of the springs keep the tips of the vanes in contact with the inner wall of the pump cavity, and the rotation of the rotor drives the vanes to slide along the inner wall of the pump cavity.

　　The two vanes divide the crescent-shaped space enclosed by the rotor, pump cavity, and two end caps into three parts: A, B, and C, as shown in the figure. When the rotor rotates in the direction of the arrow, the volume of space A, which is connected to the suction port, gradually increases, indicating the suction process. Meanwhile, the volume of space C, which is connected to the exhaust port, gradually decreases, indicating the exhaust process. The volume of the central space B also gradually decreases, indicating the compression process. As the volume of space A gradually increases (i.e., expands), the gas pressure decreases, and the external gas pressure at the pump's inlet is greater than the pressure in space A, thus drawing in the gas.

　　When space A is isolated from the suction port, i.e., when it rotates to the position of space B, the gas begins to be compressed, and the volume gradually decreases until it is connected to the exhaust port. When the compressed gas exceeds the exhaust pressure, the exhaust valve is pushed open by the compressed gas, allowing the gas to pass through the oil layer in the oil tank and be discharged into the atmosphere. Through the continuous operation of the pump, the goal of continuous gas extraction is achieved. If the discharged gas is transferred through a gas path to another stage (low vacuum stage), it is extracted by the low vacuum stage and then compressed by the low vacuum stage before being discharged into the atmosphere, thus forming a double-stage pump. At this time, the total compression ratio is borne by two stages, thereby improving the ultimate vacuum degree.