GB182090A - Improvements in high vacuum pumps of the aspirator type - Google Patents

Abstract

182,090. Western Electric Co., Ltd., (Assignees of Houskeeper, W. G.). June 20, 1921, [Convention date]. Aspirating-apparatus, ejector.-In order to overcome the objection to mercury-vapour-jet air and gas ejectors, that by reason of the considerable vapour pressure of mercury at room temperatures, a liquid air-cooled trap between the ejector and the vessel to be exhausted is necessary, substitution is made of the vapour of substances having a vapour-pressure at ordinary temperatures of less than 10<-6> m.m. of mercury, which is the usual pressure within a vacuum tube of the pure electron discharge type, and at higher temperatures a vapour-pressure above 10<-3> m.m. of mercury, which is that usually obtained with rough pumps. When lead, bismuth, or tin are used, the rough pump 10 is operated to reduce the pressure to that value, the metal in a chamber 14 is vaporized by an electric heater 18, and the vapour rising in the pipe 12 exhausts air from the bulb 11 by ejector action, being at the same time maintained at slightly above melting temperature by an electric heater 20, the condensed particles returning by gravity to the vaporizing- chamber. If zinc or cadmium is employed, sublimation temperatures below the melting point are chosen, the pipe 12 is not heated during exhausting, but subsequently the heater 20 is used to melt the solid zinc &c. that has condensed on the walls thereof, so that it may return to the vaporizer. Passages 12 and 13 are of pyrex glass and are connected to lead-glass tubing 16 by sleeves of platinum.