西南航空同美国其他大多数航空公司一样，多年来有一条正式规定要求身体容积超过一人座的乘客应购买双人机票。

Southwest, like most of the major United States carriers, has had a formal policyin place for years requiring that passengers who can’t physically fitinto a single airline seat must buy two.

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且尺寸体积远小于同流量的容积式压缩机，稳定性和压比也比同流量的条件下的叶轮式压气机有所提高。

But it has smaller volume than displacement compressor at the same mass flow rate; and higher pressure ratio and efficiency than impeller compressor.

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