Function and selection of vacuum pump oil, vacuum equipment suppliers often require vacuum pump users to add vacuum pump oil regularly during the use of vacuum pump, and require customers to replace vacuum pump oil every three months. What is the role of vacuum pump oil in mechanical vacuum pump, and the special oil for vacuum pump matched with the selection. 1. Function of mechanical vacuum pump oil (1) The exhaust valve is sealed with pump oil, which can prevent the atmosphere from returning to the pump through the exhaust valve and ensure good air tightness when the exhaust valve is closed. (2) The pump oil penetrates into the pump rubber through the oil circuit, exhaust valve and assembly clearance to lubricate, seal and cool the moving parts of the pump, such as rotor, rotor, bearing, shaft seal and friction surface. (3) The pump oil can fill the harmful space and reduce the high-pressure residual gas, so as to greatly reduce the influence of the harmful space on the limit vacuum. (4) When the vacuum is high, the amount of gas entering the suction space is very small, and the compressed gas pressure still cannot push the exhaust valve plate. At this time, the exhaust valve plate can be forcibly pushed open with the help of pump oil to make the pumped gas discharge smoothly. 2. Selection of mechanical vacuum pump oil (1) Under the working temperature of vacuum pump oil, the pump oil must have a certain viscosity and change little with temperature to ensure good sealing effect. The viscosity is too small, the sealing performance is not good, and the viscosity is too high. It is difficult for the pump oil to enter the gap of the wiping surface, and the lubrication will become worse. At the same time, the rotor rotation is difficult, the power consumption increases, and the pump oil is overheated. Generally, 20 saturated vapor pressure shall not exceed 5.3 * 10-3pa. The viscosity of pump oil at 50 shall be within the range of (47 ~ 57) * 10-6m2 / s, which can meet the requirements. With the increase of temperature, the viscosity of oil decreases, the sealing energy of oil becomes worse, the saturated steam pressure increases and the vacuum degree decreases. Therefore, it is specified that the operating temperature of vacuum pump oil shall not exceed 70 ℃. (2) The saturated vapor pressure of vacuum pump oil is low and the volatile light fraction is less. Because the extreme vacuum of the pump is mainly determined by the vapor pressure of the lightest fraction. The saturated vapor pressure of daluton vm100 vacuum pump oil at 20 is 6.5 * 10-5pa, which is suitable for various mechanical vacuum pumps. In addition to the saturated steam pressure, it can also be expressed by the ignition temperature (flash point) of the pump oil, that is, at this temperature, the steam accumulated on the oil surface begins to ignite. Therefore, the higher the flash point of pump oil, the less volatile light fraction and the lower the saturated vapor pressure. The oil flash point of vm100 vacuum pump is 206 degrees, which fully meets the requirement that the pump oil flash point is not less than 200 degrees. (3) The chemical properties of vacuum pump oil are stable, and the contents of impurities such as water, water-soluble acid and water-soluble alkali are small. 3. Use of mechanical vacuum pump oil In order to reduce the saponification of pump oil during operation, a dryer can be installed at the pump inlet. The dryer contains P2O5 or cold trap and dry ice (solid CO2) to absorb or freeze the water in the gas. Sour oil cannot be used in mechanical vacuum pumps. And avoid pumping corrosive gases and solvents because they will saponify vacuum pump oil. During the use of vacuum pump oil, a few oil molecules split, resulting in the gradual increase of light fraction and the deterioration of limit vacuum. It is necessary to replace fresh, dry and clean vacuum pump oil regularly.