| 摘要 |
A diffusion pump for a leak detector of helium or other light gases includes a foreline, responsive to gases from vacuum equipment being monitored for leak detection, and an inlet, connected to a mass spectrometer or other similar high vacuum gas measuring instrument. The diffusion pump includes two diffusion stages. The second stage has a diffuser throat with a relatively narrow width and small cross-sectional area so that the velocity of diffusion oil vapor flowing through it causes the light gases to be easily back diffused from the foreline to the inlet, while substantially preventing the flow of air or other relatively heavy gases between the foreline and the inlet. Fluid is returned to the pool by a conduit having a vertically extending, longitudinal axis aligned substantially with the center of the pool and an outlet orifice in proximity to the bottom of the pool, whereby the oil is returned to the coolest part of the pool at its bottom, central portion.
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