In recent years, dry vacuum pumps are popular and have the potential to start a prairie fire. Several companies in Shandong, Beijing and Shenyang have successively launched dry vacuum pumps and formed commercial production. Dry vacuum pump has high added value and the profit space is unmatched by water ring and oil pump. Throughout the development and production of dry vacuum pumps, they can be divided into contact seal type and non friction gap seal type. The common models of contact sealing type include oil-free piston and oil-free rotary plate, and the common models of friction clearance free sealing type include oil-free claw type, oil-free screw type and oil-free scroll type. The contact sealed dry vacuum pump has high failure rate, short maintenance cycle and low vacuum degree. It can not extract gas and saturated steam containing dust or entrained liquid, and can not provide clean vacuum. It has low technical content and small profit space. Many domestic manufacturers have produced it. Because of its low price, it has a certain market share in China. The non friction gap sealed dry vacuum pump is a new type of machine that has just sprung up in China in recent years. Their common characteristics are that the working chamber is not worn, the failure rate is low, the vacuum degree is high, and it can provide clean vacuum. The claw type and screw type can also deal with gases containing a small amount of dust or liquid, especially the vertical claw vacuum pump, because it has good liquid and dust discharge performance, In chemical drying and vacuum distillation process, it is more like a fish in water. These dry vacuum pumps have high technical content, high requirements for processing equipment and manufacturing process, and their market prices are high. They are the object of competitive research and development by various manufacturers. Dry screw vacuum pump: at present, the pumping speed of commercial products is 15 ~ 150L / s, and the limit vacuum degree can reach 1pA. It is generally of horizontal structure. They are suitable for use in relatively clean environment, such as electronics, vacuum coating and other industries, and have a high failure rate in chemical and pharmaceutical industries. High precision machining equipment such as NC screw milling and NC screw grinding are popular abroad, and the machining accuracy of screw rotor is high and the quality is good. The vast majority of domestic enterprises do not have foreign processing conditions. They often use CNC lathes to process screw rotors, which greatly reduces the machining accuracy and quality of screw rotors. The quality and service life of the whole machine are different from those of foreign products. Claw rotor dry vacuum pump: at present, the commercialized product of this dry vacuum pump has a pumping speed of 4 ~ 150L / s and a limit vacuum degree of 1 up to 3PA. It is divided into horizontal and vertical structures. The horizontal structure is suitable for relatively clean environment, such as electronics, vacuum coating and other industries; Vertical structure is suitable for extracting dust, entrained liquid gas and condensable gas. For example, Edward EDP Series in Britain has a very high share in petroleum, chemical and pharmaceutical industries. The equipment requirements for the production of claw vacuum pump are relatively low. CNC machining center, wire cutting machine tool, cylindrical grinder and surface grinder can process qualified parts, but there are many parts and components, which have high requirements for assembly. Scroll dry vacuum pump: at present, the commercialized product of this dry vacuum pump has a pumping speed of 1 ~ 15L / s. At present, there is no product exceeding 15L / s, and its limit vacuum degree can reach 1pA. The pump is suitable for use in a clean environment and cannot be used to extract gas containing dust and liquid. Vortex disc production has high requirements for equipment and complex process. It is difficult for domestic machining centers to meet their accuracy requirements, and its assembly and commissioning procedures are very complex and difficult.