Diffusion Pump Edwards

Exhibit no. 166

It is important that the ions have a free run through the mass spectrometer without hitting air molecules. To achieve this, a vacuum must be generated in the instruments. The vacuum systems of many mass spectrometers consist of a differentially pumped system with a foreline pump establishing a rough vacuum and a high vacuum pump. The high vacuum can be created and maintained by diffusion pumps. Diffusion pumps operate by boiling fluid and forcing the dense vapor stream through central jets angled downward to give a conical curtain of vapor. Gas molecules that randomly enter the pump inlet are pushed toward the boiler and the pump walls by momentum transfer from the more massive fluid molecules. At the air- or water-cooled pump walls, the working fluid condenses and returns under gravity flow downward into the boiler.