In the vacuum electron beam welding machine, roots pump is often used in the vacuum system as the booster pump for differential pumping. roots pump is a two-rotor volumetric molecular pump. Besides volume action, the working principle of molecular pump is also applied.
Under high pressure, because the average free path of the gas is smaller than the clearance, the gas will return in large quantity, so the vacuum pump cannot work well. In order to make this kind of vacuum pump work normally, the rotary plate-type mechanical pump is generally used as the front vacuum pump.
When the current pressure at the outlet of the pump drops to about 100Pa, the roots pump starts to work, and its maximum pumping rate appears at 1.33pa, at which time the average free path of the gas significantly exceeds the width of the clearance, greatly increasing the flow resistance of the returned gas, and its inlet pressure is directly related to the front vacuum pressure at the outlet.
The roots pump has a high pumping speed of up to 40000L/S within the pressure range of 1.33 * 10-2~1.33Pa, and can rapidly expel the gas suddenly released. The speed of the rotary mechanical pump within this pressure range is already very small, while the oil diffusion pump is just starting to work, so the disconnection between the two pumps in the pumping rate can be solved by the addition of the first-stage rotz vacuum pump, so it is also called the booster pump.
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