Roots vacuum pump is a rotary volumetric vacuum pump. Its structure is evolved from roots blower. It first appeared in Germany in 1944 and used as a supercharging pump to adapt to a vacuum melting system with large pumping speed within the pressure range of 10 to 1000Pa.

The two rotors of Roots vacuum pump are operated by a pair of high-precision gears. The active shaft is connected to the motor through a coupling. In the layout of the transmission structure, there are two main types:
One is that the motor and gear are placed on the same side of the rotor as shown in the following figure (a). The driven rotor is driven by the end gear of the motor directly, so the torsion deformation of the active rotor shaft is small, and the gap between the two rotors will not be changed greatly by the torsion deformation of the active axis, so the clearance between the rotor is even in the process of operation.
The biggest disadvantage of this transmission mode is that there are three bearings on the A. drive shaft, which increases the processing and assembly difficulty of the pump, and the disassembly and adjustment of the gear is inconvenient; the overall structure of the B. is unsymmetrical, and the center of gravity of the pump is biased toward the motor and the side of the gear box.
The other is that the motor and transmission gear are mounted on both sides of the rotor respectively, as shown in the following figure (b). This form makes the overall structure of the pump symmetrical, but the active shaft has large deformation. In order to ensure that the clearance of the rotor is uniform during operation, the shaft should have enough stiffness, and the connection between the shaft and the rotor should be fastened (the structure of the rotor and the shaft is welded or cast in one). This structure is very convenient to assemble and disassemble, so it is widely used.