Generally, the vacuum is obtained by pumping of the vacuum system. According to the required degree of vacuum and cleanliness, different vacuum systems are used. The general vacuum system can be divided into: low and medium vacuum systems, high vacuum systems, ultrahigh vacuum systems, and extremely high vacuum systems based on vacuum degree.
These vacuum systems consist of different main pumps, auxiliary systems and other corresponding vacuum parts. The medium and low vacuum system consists of mechanical pump or a mechanical pump and a roots pump. In order to prevent oil contamination, a molecular sieve trap can also be installed. However, the molecular sieve solid particles must be prevented from being sucked into the mechanical pump during operation.
The high vacuum system is mainly composed of diffusion pump, baffle plate, cold trap, gate valve, mechanical pump and other parts. The main pump can also be turbo molecular pump or a cryogenic pump. To further reduce oil pollution, a sputter ion pump can be used together with a titanium sublimation pump as well as a low-temperature baffle to form an oil-free high-vacuum suction unit, the backing pump of which is adsorption pump.
The most important sign of the ultra-high and extremely high vacuum systems is the high degree of cleanliness. Ultra-high and extremely high vacuum can be obtained by using high-performance ion pumps, cryogenic pumps, turbo molecular pumps, cold traps and other parts.
The turn on, turn off, operation, protection from pollution when a fault occurs of the various vacuum systems all have strict requirements. And operators must comply with the operating procedures.
For example, the mechanical pump can only pump the pressure of 15Pa-20Pa or higher, otherwise the pollution of the backflow is serious. The diffusion pump has great pollution of the oil vapor before operation and during 20 mins after stop working, so it should not be connected to the vacuum chamber or the cold trap, so the cold trap should be isolated from the vacuum chamber and after nitrogen is removed and the temperature is restored, the high vacuum pump can be stopped. The adsorption pump should be equipped with an anti-pressure blasting device to prevent accidents after reheating.
If the vacuum cannot be obtained, it is first necessary to check whether the air extractor is working properly, and secondly, check if there is an unallowable of gas release source. Now, take the multilayer heat insulation cryogenic vessel Vacuum parts should be subjected to strict cleaning, drying and leak detection before assembly. It is also necessary to check whether the sealing ring of the removable part is clean and good, whether the sealing surface is scratched or not, or whether the connection is tight.