The rotor of oil-free screw air compressor is not in direct contact, and there is a certain gap between the two. The outer rotor drives the inner rotor to rotate through the synchronous gear to ensure the rotor clearance when transferring power. The so-called "oil-free" means that the gas does not come into contact with the oil at all during the compression process, but the bearings and synchronous gears of the compressor still need lubricating oil, but only between these lubricating parts and the compression chamber. Use effective seal isolation oil injection screw compressor. A large amount of lubricating oil is injected into the compressed gas medium for lubrication, sealing, cooling and noise reduction. Oil-filled screw compressor without synchronous gear. The anode rotor directly drives the rotation of the cathode rotor. In addition to reducing exhaust temperature, lubricating oil also provides lubrication for bearings, mechanical seals, sliding valves, etc.

Because the rotors of the oil-free screw air compressor do not contact each other, the medium gas and the lubricating oil are separated by the shaft seal, so there is no direct contact. Therefore, oil-free screw air compressors have been widely used in waste gas recovery. There are dust and liquid in the medium gases such as coke oven gas recovery, CBM pressurization and pressure swing adsorption, and the gas composition changes greatly. Oil-free screw compressors can meet the long-term continuous operation requirements of industrial production, and the continuous uninterrupted operation time is 24,000 hours. The volumetric efficiency of oil-free screw air compressor is lower than that of oil-filled screw air compressor. Generally speaking, the pressure ratio of a single stage does not exceed 10.

The rotor of the oil injection screw compressor is directly engaged and transmitted, and the volume efficiency is high. Single stage pressure ratio can reach more than 10. However, due to the direct contact between the lubricating oil and the process medium, the medium gas should be relatively clean, and a large number of impurities and water can not be included, otherwise it will affect the influence of the lubricating oil. In addition, it is necessary to select a lubricating oil that does not react with the medium gas during the process, usually a special synthetic oil. Therefore, oil-filled screw air compressors are usually medium pressure gases used in a single working state, such as air compressors, refrigeration compressors, etc.