Different liquids have different saturated vapor pressures. At a temperature of 70°C, water starts to boil at a pressure of about 30kPa, while oil can only boil at a low pressure of 5Pa. At the same temperature, the saturated vapor pressure of oil is much lower than that of water. Therefore, when the pressure of the oil liquid surface is reduced below the saturated vapor pressure of water by vacuuming, the water in the oil liquid will violently vaporize and overflow from the oil in the form of steam. Through the suction of the vacuum, the oil enters the vacuum tank from the top and sprays down through the nozzle. The water in the oil is vaporized in the vacuum chamber and pumped out by the vacuum pump, and the oil after dewatering is discharged from the bottom. The middle part of the vacuum chamber is filled with lipophilic material, so that the sprayed oil is dispersed on the surface of the filling material to form a thin oil film, so as to increase the interface area of the gas-liquid two-phase and prolong the residence time of the oil in the gas-phase space. .
The effect of vacuum water removal is mainly related to the working vacuum degree and oil temperature. The lower the vacuum degree, the higher the temperature, the better the water removal effect. The oil temperature is generally around 60°C, and if the temperature is too high, the oxidation of the oil will be accelerated. For hydraulic oil, the vacuum degree is generally 600~700Pa, which can reduce the water content in the oil to below 0.01%. For transformer insulating oil, a higher vacuum degree can be used, and the water content can be reduced to 0.001%.