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三十多年来，随着蒸汽流泵，特别是油扩散泵技术的进展，国外和国内围绕蒸汽返流这个课题做了不少的试验。发表了许多研究文章，分析了蒸汽返流来源，提出了减少返流的措施。但是，现在尚没有能够从理论上对返流问题给予定量的解释。此文根据气体分子热运动的麦氏分布律，推导出了离开蒸汽射流的油蒸汽分子速率的计算式，利用角系数概念，计算了喷咀出口平面以上的泵体内壁和测试罩内壁各表面上的返流率数值，证明了油蒸汽分子对表面需要碰撞十数次才能被俘获。由这些计算，提出了蒸汽返流模型。此外，又导出了由于蒸汽返流对抽速减小量Ｓｂ的计算式，分析了蒸汽返流与极限压力的关系，最后，还提出了减少蒸汽返流的一些措施。
Over the past 30 years, with the steam flow pump, especially the progress of oil diffusion pump technology, foreign and domestic steam reflux around the subject made a lot of tests. Published a number of research articles, analyzed the source of steam backflow, and proposed measures to reduce backflow. However, it is not possible to give a quantitative explanation for the problem of regurgitation theoretically. Based on the Maxwellian distribution law of gas molecules’ thermal movement, the formula of molecular velocity of oil vapor exiting the steam jet is deduced. Using the concept of angle coefficient, the inner wall of the pump body and the inner surface of the test hood above the nozzle exit plane are calculated. The value of regurgitant flow on the surface proves that the vapor molecule needs to collide with the surface ten times before it can be captured. From these calculations, a steam backflow model is proposed. In addition, the relation between the steam return flow and the ultimate pressure was also deduced because of the calculation formula of steam return flow rate decreasing Sb. Finally, some measures were put forward to reduce the steam backflow.