Patent GB-1011256-A (GB)
Title: An improved method and apparatus for producing high vacua
IPC: F04F9/04
Filed: 1962-05-16
Abstract: 1,011,256. Diffusion pumps. NIHON SHINKU GIJUTSU KABUSHIKI KAISHA. May 16, 1962 [May 16, 1961; May 2, 1962], No. 18942/62. Heading F1E. In a method of producing a high vacuum in a chamber c, Fig. 1, with a diffusion pump 40, the working fluid is continuously fractionally distilled to obtain fluid, substantially free from components of high vapour pressure, which is delivered past the inlet 27 to trap vapour having such high vapour pressure components to prevent back streaming into the chamber c. The backstreaming check device 10 has a heater 14, an outer cylinder 15, a coaxial cylindrical ejector 16 and a jet chamber 25, formed by an inclined plate 24 in upper chamber 18 and corrected by a return tube 28 to a lower chamber 19 which communicates through opening 21 with an evaporation chamber 20. Outer cylinder 15 and casing 12 have cooling means 23, 26, e.g. water or refrigerator cooling or a thermoelectric cooling element. A first pipe 30, a distillation pipe 33 which passes through a heater 31 and cooling means 32, and a second pipe 34 connect with the diffusion pump 40. The pump casing 41 has cooling means 43, an outlet 44 to a backing pump, heating means 47, outer and inner cylinders 45 and 46 which communicate through openings 55, 56. Vapour produced from the working fluid within an outer chamber 50 is directed through an annular opening 51 into a pumping chamber 57 and vapour within inner cylinder 46 is directed through openings 53, 54. Operation. Vacuum chamber c, the backstreaming check device 10 and diffusion pump 40 are firstly evacuated by the backing pump and cooling means 26, 23, 32 and 43 and heating means 14, 47, 31 are brought into operation. Heating of liquid working fluid in chamber 19 causes its component having a high vapour pressure and a smaller molecular weight to be first evaporated leaving a work fluid rich in a main component having a low vapour pressure and larger molecular weight. This working fluid flows through opening 21 into chamber 20 where it is evaporated the vapour passing through ejector 16 where it may also act as a side vapour jet of a diffusion pump in a multistage jet assembly. The main part of the ejected vapour condenses on the inclined plate 24 where any lighter components present are subject to evaporation and migration through tube 30 to diffusion pump 40, the remaining condensate, consisting of the low vapour pressure main component, flows downwardly along the cooled casing, past inlet 27 and through the return pipe 28 into chamber 19. The working liquid in chamber 19 when heated is fractionally distilled so that the components which have a high vapour pressure and low molecular weight rise in pipe 33 and are successively heated at 31 and condensed by cooling means 32 to flow into the bottom of pumping chamber 57 together with the main working fluid vapour flowing from openings 51, 53, 54, and the vapour passing through pipe 30. The fluid in chamber 57 contains a relatively large amount of light distillate which is mainly re-evaporated during its roundabout passage through openings 55, 56 into the inner chamber 52 where the working fluid is rich in the low vapour pressure main component and is returned to chamber 19 through pipe 34. The effect of the condensation plate 24 can be amplified by using an additional condensation tower. In another embodiment, the working fluid consisting of the main low vapour pressure component is drawn by an electromagnetic pump 61, Fig. 2, into conduit 62 and forced into conduit 63, after being cooled at 64, and discharged at distributor 66 from where it flows along shoot 67 into annular channel 69 and overflows into the casing 41 through opening 70. The stream of downwardly flowing working fluid takes into solution the light distillate vapours tending to backstream from the openings 51, 53 and 54. In a modification, the distributor 66 is omitted and the fluid is supplied directly to the overflow means. In a further modification a cooled cylindrical member is disposed coaxially within the opening 70 to prevent backstreaming.