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The Roots pump is a two-rotor, volumetric vacuum pump. There are two symmetrical rotors in the pump chamber, and the rotor has two-leaf, three-leaf and four-leaf shapes. The two rotors rotate in opposite directions to each other and are driven to rotate synchronously by the shaft end gears. The rotors are not in contact with each other, and the rotor and the pump chamber wall are also not in contact, and there is usually a gap of 0.15 to 1.0 mm therebetween, and the pump chamber is sealed by the gap.

Since there is no friction in the pump chamber of the Roots pump, the rotor can run at high speed, generally 1500~3000r/min, and it is not necessary to use lubricating oil, which can realize the oil-free cleaning process. The lubrication of the pump is limited to bearings and gears, as well as to the dynamic seal. The pump has no reciprocating parts, so a good dynamic balance can be achieved. Therefore, the Roots pump runs smoothly, the rotation speed is high, and the size is small to obtain a large pumping speed.

At present, most of the Roots pumps at home and abroad are horizontal structures. The intake port of the pump is on the top and the exhaust port is on the bottom. This horizontal structure has a low center of gravity and good stability at high speed. The two rotors of the Roots pump are relatively synchronously rotated by a pair of high precision gears. Pumps are mostly direct-coupled, while large pumps are belt-driven. The motor and the transmission gear are arranged on both sides of the rotor shaft for easy installation and disassembly. The drive shaft transmits a large torque, the shaft has sufficient strength and rigidity, and the shaft and the rotor are firmly fixed. The sealing of the Roots pump is critical. The outer shaft of the drive shaft, the bearing of the two rotors and the pump chamber are provided with a dynamic seal, and the pump chamber and each end cover are provided with a static seal.

In order to avoid the misoperation of the Roots pump, a bypass relief valve is generally provided. According to the special needs of the Roots pump, the oil gear box, bearing and other components are separated from the pump chamber. The heat generated during the compression of the Roots pump is transferred to the rotor and the pump body. It is difficult for the rotor to transfer heat to the outside of the pump, and the heat of the pump body is easily lost to the surrounding atmosphere. Thus, a temperature difference occurs between the rotor and the pump body. The thermal expansion of the rotor is exacerbated. When the pump load increases, the rotor expands and the gap disappears and is stuck. Therefore, an air-cooled Roots pump has emerged, which uses a cooled gas or atmosphere to directly cool the hot rotor, thereby reducing the temperature difference between the rotor and the pump casing, and improving the heat resistance of the Roots pump.

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