High Vacuum Pumping Unit

Compared with the low vacuum unit, the high vacuum unit operates in the molecular flow state, which is characterized by low working pressure (10-2-10-6 pa), minimum exhaust and high pumping speed. The main pumps of the unit are usually diffusion pumps, diffusion booster pumps, molecular pumps, titanium sublimation pumps, cryogenic condensation pumps and so on. These pumps can not work directly on the atmosphere. Therefore, pre-pumps and front-stage pumps need to be equipped. Some high vacuum pumping units of diffusion pumps are equipped with front-stage maintenance pumps or gas storage masts to prevent pressure fluctuations and improve the performance of the unit.

(1) Pre-pumping. Pre-pumping (rough pumping) is mainly used to extract a large number of gases from the vacuum chamber, so that the gas pressure in the vacuum chamber can be reduced from atmospheric pressure to the vacuum degree when the main pump can start working. Therefore, the pressure of the pre-pumping is required to be less than the starting working pressure of the main pump. The pumping speed of the pre-pumping unit is determined by the rough pumping time. In order to improve the utilization rate of the vacuum unit, the pre-pumping unit is required to achieve a higher pumping speed. It can also be used as a front-stage pump. Vacuum valves are used to separate and switch between the two different functions.

(2) Maintenance pump. Due to the long start-up time of diffusion pump and oil booster pump, when loading and unloading in the vacuum chamber, the main pump is often closed in order to shorten the working cycle, so that the main pump is still in working state. Because the valve always has a very small amount of air leakage and surface bleeding, after a certain period of time, the pressure in the main pump chamber increases, which exceeds the maximum allowable pressure of the pump working yeast and causes the oxidation of the pump oil vapor. In order to solve this problem, one way is to use the front pump to continue pumping out the gas in the main pump, but at this time the gas discharged from the main pump is very small, there is a large horse cart of the front pump, which wastes energy. For this reason, another method can be adopted to stop the work of the front pump, close the valve of the front pipeline, and install a maintenance pump or gas storage inlay at the outlet of the main pump, so as to ensure that both the gas in the main pump can be discharged and the energy consumption can be saved. Gas storage tanks can not be made very different, they can only be used in small vacuum units with diffusion pumps as the main pumps, while maintenance pumps can be used in vacuum units with large main pumps.

(3) Gas storage tank. Small diffusion pump high vacuum pumping units are usually equipped with gas storage tanks, which are set between the diffusion pump and the front pump to store the gas discharged by the diffusion pump.

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