Experimental Investigations on Oil and Mercury Diffusion Pumps with Differing Nozzle Geometries

Abstract

Experimental investigations with commercial oil diffusion pumps are reported, where the top nozzle of the four stage nozzle system was replaced by dual nozzles with variable throat widths. Certain changes of pumping speed characteristics could be observed when varying the heater input for different throat widths but, in general, a lower maximum pumping speed was measured for dual nozzles. Even when taking into consideration the pump fluid backstreaming the use of dual nozzles in commercial oil diffusion pumps does not show any advantages. In addition, results of measurements of the pumping speed and of the compression ratio in single-stage mercury diffusion pumps for different nozzle geometries but with identical nozzle throat areas in dependence on mass flow are reported. Here, too, the dual nozzle gave only a slight improvement in the compression ratio. The results are discussed applying familiar principles of the diffusion pump theory.