Claw pump and oil-free screw vacuum pump are both mechanical equipment used to pump liquid, gas and other substances. Although their working properties are similar, there are still some obvious differences. For example, the pipeline length of the oil-free screw vacuum pump is relatively short, while the pipeline length of the claw pump is relatively long, so the oil-free screw vacuum pump can easily discharge solid particles, while the claw pump can not. The pump body and rotor of oil-free screw vacuum pump are single, so it is easy to carry out anti-corrosion treatment. The diaphragm between stages of claw pump can hardly be treated externally, and the anti-corrosion coating on the surface of rotor is also simple, which is damaged during installation. The shaft and rotor of oil-free screw vacuum pump are processed and formed after integral casting, which is completely integrated, and there is no installation problem. Claw vacuum pump because of the existence of stage diaphragm, rotor and pump shaft can not be integrated, the rotor is installed on the shaft, for the convenience of device and disassembly, cooperation can not be too tight, so after work, it simply presents the scene of rolling key and rotor loose. Only the gap between the exhaust end and the rotor determines the performance of the oil-free screw vacuum pump, and the gap between the rotor and the rotor is interrelated, so the working reliability is very high. There are many gaps in claw vacuum pump, such as: the gap between rotor and rotor, the gap between rotor and pump body, the gap between rotor and end cover and diaphragm, and each gap is independent. If only one gap presents a problem, the pump can not operate normally.