Roots vacuum pump It is one of many vacuum devices. Its structure is crucial to ensuring the device’s performance and usability. Therefore, before use, users typically familiarize themselves with the device’s structure and operating principles in order to maximize its efficiency.

　　The Roots vacuum pump is a type of variable-displacement pump. It is equipped with two rotor blades that rotate in opposite directions and simultaneously. The Roots vacuum pump has undergone extensive operational training and proven its reliability in various applications, including chemical plants, plastics processing, fertilizer production, dynamic balancing of turbine-generator rotors, aerospace cabin space simulation, and other similar equipment. Moreover, it is widely used in industrial production processes such as oil extraction at high altitudes, chemical plants, metallurgical industries, and textile manufacturing. Vacuum pump components are also utilized as vacuum pump silencers to mitigate the noise generated by the pump.

　　1. Principle of Roots Vacuum Pump

　　The Roots vacuum pump is a type of vacuum pump that features no internal compression. Typically, the pump has a very low compression ratio; therefore, it serves as a forepump for both high-vacuum and medium-vacuum pumps. This vacuum pump operates by using the propulsion effect of a pair of blade-shaped rotors that rotate in the same direction within the pump chamber and in opposite directions, thereby moving vapor and maintaining a vacuum. The Roots vacuum pump refers to a mechanical vacuum pump equipped with a pair of shoe-shaped rotors that run simultaneously at high speed. This pump cannot achieve vacuum extraction on its own; it requires a front-stage unit fitted with a skeleton seal and a water ring to directly exhaust air.

　　 Roots vacuum pump Its structure and operating principle are similar to those of a Roots blower. During operation, its suction port is connected to either a vacuum packaging container or the main pump of an ultrafiltration device. Due to the continuous rotation of the rotors, the extracted vapor is drawn in through the inlet port into the chamber v0 located between the rotor and the pump housing, and then discharged through the outlet port. Since the chamber v0 is completely sealed after intake, the vapor within the pump cavity does not undergo compression or expansion. However, when the top of the rotor rotates around the edge of the outlet port and the chamber v0 becomes connected to the outlet pipe side, a portion of the vapor will flow back through the outlet pipe due to the higher air pressure on that side, causing a sudden increase in pressure within the chamber v0. As the rotor continues to rotate, the vapor is expelled from the pump. Inside the Roots pump’s pumping chamber, there are two “8”-shaped rotors mounted vertically on a pair of parallel shafts. These rotors are driven by a set of transmission gears that rotate them at opposite speeds with a specific reduction ratio. In the middle of each rotor, a small clearance exists between the rotor and the inner cavity of the pump, allowing for high-speed rotation.

　　2. Construction and Composition of Roots Vacuum Pumps

　　The arrangement of the two rotors within the pump casing determines the overall structure of the Roots vacuum pump. Generally, there are three common structural layouts for Roots vacuum pumps worldwide:

　　Column-type: In this design, the central axes of the two rotors are mounted horizontally, yet the plane formed by the central axes of the two rotors is perpendicular to the horizontal plane. With this configuration, the pump’s inlet and outlet ports are arranged horizontally, making assembly and connection piping relatively convenient. However, a drawback of this design is that the pump’s center of rotation is positioned too high, leading to poor reliability at high speeds. Therefore, apart from small-sized pumps, this structural form is rarely adopted in practice.

　　Vertical Type: In this design, the central axes of the two rotors are installed horizontally, and the plane formed by the central axes of the two rotors lies in a horizontal direction. In pumps of this configuration, the inlet is located at the top of the pump, while the outlet is situated directly below the pump (or, more precisely, at the bottom). Typically, the lower outlet is oriented horizontally, so the inlet and outlet ports are arranged perpendicular to each other. The outlet is connected to a three-way pipe that opens in two directions—one end connects to the exhaust pipe, while the other end is either sealed or fitted with an intake valve when in use. A key feature of this design is its low center of gravity and excellent operational stability at high speeds. This type of construction is widely adopted for medium- and small-sized Roots vacuum pumps around the world.

　　Vertical-axis: Available overseas Roots vacuum pump The two rotors are mounted with their centerlines perpendicular to the plane. This type of construction features very easy-to-control assembly clearances, convenient rotor assembly, and a compact footprint. However, the transmission mechanisms—such as gears—are cumbersome to assemble and disassemble, and the lubrication system is relatively complex.

　　Once the overall structural design is finalized, the structure and shape of the Roots vacuum pump casing are also relatively determined.

　　Roots pump with a flow-control valve: To prevent overloading that could lead to safety hazards, the Roots pump is equipped with a reliable safety protection device—a flow-control valve installed on the bypass valve pipeline.

　　Roots pump with a vapor cooler: Under conditions where fat is being pumped, the pump needs to be equipped with a cooler to cool the vapor. This cooler can be installed either before or after the pump. It is mounted directly onto the pump casing of the Roots pump. Under certain conditions, special catalysts that promote endothermic reactions can help reduce overheating in the Roots pump. When the upper limit vacuum is reached, the total flow rate of incoming air through the pump passage drops to zero, meaning the pump’s specific pumping efficiency becomes zero.