Working Principle of Rotary Vane Vacuum Pumps

The rotary vane vacuum pump (commonly referred to as the rotary vane pump) is an oil-sealed mechanical vacuum pump. Its operating pressure range is from 101,325 to 1.33 × 10^-2 Pa, classifying it as a low-vacuum pump. It can be used independently or as a forepump for other high-vacuum or ultra-high-vacuum pumps. It has been widely applied in various production and research sectors, including metallurgy, machinery, military industry, electronics, chemical engineering, light industry, petroleum, and pharmaceuticals.

A rotary vane pump can evacuate dry gases from sealed containers. If equipped with an oil-seal device, it can also handle a certain amount of condensable gases. However, it is not suitable for pumping gases that are excessively oxygen-rich, corrosive to metals, capable of chemically reacting with the pump oil, or containing particulate dust.

The rotary vane pump is one of the most fundamental vacuum-generating devices in vacuum technology. Rotary vane pumps are typically medium- and small-sized. There are two types of rotary vane pumps: single-stage and double-stage. A "double-stage" pump refers to a design in which two single-stage pumps are connected in series. Double-stage pumps are generally preferred because they can achieve higher vacuum levels. The relationship between the pumping speed of a rotary vane pump and its inlet pressure is specified as follows: At inlet pressures of 1333 Pa, 1.33 Pa, and 1.33 × 10⁻¹ Pa, the pumping speed must be no less than 95%, 50%, and 20% of the pump’s nominal pumping speed, respectively.

The figure illustrates the working principle of a vane pump. A vane pump mainly consists of a pump body, a rotor, vanes, end covers, springs, and other components. Inside the pump cavity, a rotor is mounted eccentrically. The outer circumference of the rotor is tangent to the inner surface of the pump cavity (with a very small clearance between them). Two spring-loaded vanes are housed in slots on the rotor. As the rotor rotates, centrifugal force and the tension of the springs keep the tips of the vanes in contact with the inner wall of the pump cavity. The rotation of the rotor drives the vanes to slide along the inner wall of the pump cavity.

Two vanes divide the crescent-shaped space formed by the rotor, pump cavity, and two end covers into three sections—A, B, and C—as shown in the figure. As the rotor rotates in the direction of the arrow, the volume of space A, which is connected to the intake port, gradually increases, indicating that the suction process is underway. Meanwhile, the volume of space C, which is connected to the exhaust port, gradually decreases, signaling that the exhaust process is taking place. The middle space B also sees its volume gradually decrease, meaning that the compression process is under way. Since the volume of space A is gradually increasing (i.e., expanding), the gas pressure within it drops. Consequently, the external gas pressure at the pump’s inlet becomes higher than the pressure inside space A, thus drawing gas into the pump. When space A becomes isolated from the intake port—that is, when the rotor moves into the position of space B—the gas begins to be compressed, its volume gradually shrinks, and finally it connects with the exhaust port. Once 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 reservoir and then vent into the atmosphere. With the pump running continuously, this ensures a continuous pumping action. If the discharged gas is routed through a gas passage into another stage (the low-vacuum stage), where it is further pumped out and then compressed again before being exhausted into the atmosphere, such a system constitutes a two-stage pump. In this case, the overall compression ratio is shared between the two stages, thereby significantly improving the ultimate vacuum level.