Introduotion to the Aerodynamioal Theory 01 the Vapor Jet highVaouum Pump. - Results obtained with three glass pumps of 2 and 3stages, two of them used with mercury and with oil, 11110w to dis·entanglethe factors governing tlieir functioning. It is founa that the lesser effieiencyof mercury at 'low pressures is due to a higher Gaede's flow andthat its reported hig4er efficiency at relatively high pressures is duemainly to the fact that the same Watt imput develops larger boiler p!essureswith mercúry. A valve and a compressor effects can be conceptualIyseparated. A quantitative first aproximation aerodynamicl11 theory ofthe first is developed. It shows that Bupersonic Bpeeds of vapor jets arecommon and that Mach'a number is larger for mercury. Backing pressuresof the order of millimeters can be obtained with oil aB well as with mer'cury. With increasing gas flux the apead decreases at firBt and growslater to a "secondary" maximum. The reason, for this iB found in thebehavior of Gaede's flow. The volume swept by themain vapor currentis several times larger tllan the apead at low pressures, but it builds upthe main resistance at lligher pressures under dynamical conditions. The"second diffusioJl" limits the speed at higher pressures under static·condictions. The factor of Sears constitutes the main resistance at theIow pressure end' of the velocity curve
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