The structure of rotary vane mechanical pump is shown in Figure 1, which is mainly composed of cylindrical cavity stator, eccentric rotor, rotary vane, spring, top cover and exhaust valve. The top end of the eccentric rotor always keeps in contact with the inner cavity of the pump stator, and when the eccentric rotor rotates, it always slides along the inner wall of the stator. There are two chutes on the rotor, and a rotating blade with a spring is installed in the middle. When the rotating blades rotate with the rotor, the two rotating blades slide on the inner wall of the stator under the action of spring tension and centrifugal force. The whole cavity is placed in the oil tank.

The two rotating blades divide the crescent-shaped space surrounded by the rotor, the stator cavity and the fixed cover into three parts, namely, a suction cavity, a compression cavity and an exhaust cavity. When the rotor rotates in the direction shown in the figure, the volume of space A communicating with the air inlet increases continuously, and the pressure in space A decreases continuously. When the pressure in the space A is lower than that in the pumping container, the pumping gas is continuously pumped into the suction chamber A according to the principle of gas pressure balance. At this time, the volume of the compression chamber B gradually decreases, the gas pressure increases, the volume of the exhaust chamber C communicating with the air outlet further decreases, and the space pressure of the exhaust chamber C further increases. As shown in Figure 2, during the continuous operation, the pump continuously performs the processes of suction, compression and discharge, thus achieving the purpose of continuous pumping. Obviously, the faster the rotor speed, the greater the pumping speed of the pump. The rotating speed of mechanical pump is generally between 450~ 1400r/min, and sealing is extremely difficult because of the high rotating speed. The exhaust valve is immersed in oil to prevent a large amount of airflow from entering the pump. In order to ensure that there is no air leakage between the suction cavity and the discharge cavity, in addition to ensuring close contact, special machinery with low steam pressure and a certain salary is used to pump oil, and the oil enters the pump cavity through the gap on the pump body, the oil hole and the discharge valve, so that all moving surfaces in the pump cavity are covered with oil and a seal is formed between the suction cavity and the discharge cavity. In addition, mechanical pumping also plays a role in lubricating and helping to open the exhaust valve when the gas pressure is low. At the same time, mechanical pumping can also fill all harmful spaces and eliminate their influence on extreme vacuum.

The mechanical pump discussed above has only one rotor, which is called single-stage rotary vane vacuum pump, and its limit pressure is 1Pa. In order to improve the ultimate pressure, two-stage pump structure is usually adopted, that is, two single-stage pumps are connected in series, which can make the ultimate pressure reach Pa level.