The Relationship Between Foam and Vacuum Degree in Vacuum Oil Purifiers
In the use of vacuum oil purifiers, there is a common misconception about the vacuum degree, namely: "The higher the vacuum degree of the oil purifier, the better." The reason for this belief is that, theoretically, the higher the vacuum degree inside the vacuum tank, the more conducive it is to water vaporization, thereby more effectively extracting water vapor. In this way, the oil purifier is more effective in removing water from the oil.
This is actually an incorrect method of using a vacuum oil purifier. Usually, the manufacturer's manual for the vacuum oil purifier will state: when there is too much foam in the oil sight glass, open the air inlet valve to reduce the vacuum degree slightly, allowing the foam to subside, then close the air inlet valve. Let's briefly analyze the reason for this operation.
We know that the vacuum oil purifier operates based on the significant difference in boiling points between oil and water. Under high vacuum, the boiling point of water decreases greatly (because the oil temperature cannot be operated at high temperatures, the vacuum state is used to evaporate a large amount of water while the oil remains liquid, hence the choice of vacuum state to achieve oil-water separation). Not considering altitude, generally when the oil temperature is 65 degrees, and the vacuum degree is 0.06 MPa, the oil-water separation effect is optimal. If the vacuum degree is not suitable, for example, too high, the boiling points of oil and water may become close, causing a large amount of oil to evaporate along with the water (this is also why there is a condenser after the vacuum tank; it is mainly used for oil recovery and automatic drainage). Additionally, when there are too many bubbles, the oil level in the separation chamber becomes too high, and the upper oil foam can easily be drawn away by the vacuum pump, resulting in a decrease in oil volume. Moreover, this itself is harmful to the vacuum pump.
Generally speaking, online operation of the oil purifier is a good choice. The national standard requires that the water content in oil be below 100 ppm to ensure the normal lifespan of the unit. Exceeding 100 ppm can seriously cause emulsification and acidification of the oil, and servo valve sticking is inevitable sooner or later. The circulating oil will be contaminated by steam leaking from the turbine, as well as by water dissolved from the air. Ordinary filter elements cannot effectively separate water from oil, which is why the oil purifier needs to operate online to ensure the water content meets the standard.
