为了最小化油蒸汽的回流，一些冻干机在真空泵和前箱间设计了弯曲的管路。
In order to minimize oil vapor migration, some lyophilizers are designed with a tortuous path between the vacuum pump and chamber.
由于罗茨泵是一种无内压缩的真空泵，通常压缩比很低，故高、中真空泵需要前级泵。
As the Roots pump is a non-vacuum inside the compression, the compression ratio is usually very low, so high, medium and vacuum pumps need to pump before.
本机组采用罗茨泵作为主泵，以旋片式真空泵作为前级泵。
The set takes Roots pump as its main pump and spinning vacuum pump as pre-stage pump.
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