Cryopumps are made according to the principle of gas condensation, cryogenic adsorption, cryogenic trapping or suction to obtain vacuum.
1. According to the working pressure of the pump, it can be divided into cryopump for continuous flow range, cryopump for molecular flow range, usually condensate pump plus an adsorption stage or a cryogenic capture stage.
2. According to the cooling method, it can be divided into storage tank cryopump, evaporative cryopump and refrigeration cryopump. Among them, the storage tank cryopump and the evaporative cryopump both use liquid refrigerant for refrigeration, the cooling shield surface is commonly used liquid nitrogen, and the cryogenic surface is commonly used liquid helium or gas helium for refrigeration. Due to the flammability, explosiveness and high price of liquid hydrogen, it is still rarely used despite its higher evaporation enthalpy than liquid helium.
Refrigeration cryopump refrigerators are commonly used by Gifford. McMahon type (referred to as G.M refrigerator) and Stirling type (referred to as St refrigerator). For refrigeration cryopumps with large pumping speed, a liquid helium temperature-grade refrigerator can be used, and a J-T valve can be set to form a liquid circulation refrigeration device, and sometimes liquid nitrogen in a liquid storage tank or nitrogen liquefaction machine is used to cool the baffle and shield surface.
The main performance of cryopump
①Higher than the pumping speed, better than all other types of pumps.
②There are no restrictions on the shape, it can be immersed in the vacuum chamber or fixed on the wall of the vacuum chamber with a flange.
③It can provide a completely clean vacuum without pollution to the vacuum system.
④Vacuum degree of extremely low pressure can be obtained, such as below 10-12Pa. Moreover, the operation of the cryopump is reliable, and when the pumping speed is relatively large, the operating cost of its investment is lower than that of the traditional vacuum pump, and it is easy to realize automation.