What are the reasons for the low vacuum of a vacuum pump?There are two ways to mark the vacuum degree. One is to mark it with absolute pressure (i.e., absolute vacuum), and the other is to mark it with relative pressure (i.e., relative vacuum).The so-called "absolute pressure" means that the vacuum pump is connected with the test vessel, after enough time and continuous pumping, the pressure in the container no longer continues to drop and maintain a certain value, and then the gas pressure value in the container is the absolute pressure of the pump.If there is absolutely no gas in the container, then the absolute pressure is zero, which is the theoretical vacuum state.In practice, the absolute pressure value of the vacuum pump is between 0 and 101.325KPa.Absolute pressure value need to use absolute pressure meter, at 20 ℃ altitude of 0, instrument of the initial value of 101.325 KPa.In short, the pressure indicated by the reference of "theoretical vacuum" is called "absolute pressure" or "absolute vacuum".
The "relative vacuum degree" of a vacuum pump refers to the difference between the pressure of the object under test and the atmospheric pressure at the measuring point.Measure with a common vacuum gauge.In the absence of vacuum, the initial value of the table is 0.When measuring a vacuum, its value is between 0 and -101.325KPa(generally negative).For example, a measurement of -30kpa indicates that the pump can be pumped into a vacuum of 30KPa lower than the atmosphere at the location of the measurement.When the same pump is measured at different locations, its relative pressure value may be different, because atmospheric pressure at different measurement sites is different, which is caused by different objective conditions such as altitude and temperature.In short, the pressure indicated by the reference to "measuring the atmospheric pressure at the place" is called "relative pressure" or "relative vacuum".The international vacuum industry general "vacuum degree", is also the most scientific is with the absolute pressure mark;It refers to "ultimate vacuum, absolute vacuum, absolute pressure" (our company is in agreement with it), but "relative vacuum" (relative pressure, vacuum table pressure, negative pressure) has been widely used due to its simple method of measurement, the fact that measuring instruments are very common, easy to buy and cheap.Can be mutual conversion between them in theory, the conversion method is as follows: relative limiting vacuum of vacuum = (absolute pressure) - measuring the location of air pressure, for example: there is a kind of miniature limiting vacuum of vacuum pump PK4512 45 kpa, it's relatively vacuum degree about = 45-100-55 kpa, on commonly used relative to the vacuum table shows about 0.055 Mpa (because has something to do with the local atmospheric pressure), which is why some customers bought a pump in the back with vacuum gauge measurement, misunderstanding manufacturers parameters is not up to what they said.