Patent GB-514820-A (GB)
Title: Improvements in high vacuum condensation or diffusion pumps
IPC: F04F9/00
Filed: 1938-05-11
Abstract: 514,820. Vacuum pumps. KODAK, Ltd. (Eastman Kodak Co.). May 11, 1938, No. 13334/37. [Class 71] In high vacuum condensation pumps of the type producing a high rate of evacuation at low pressures, e.g., less than 0.001 mm. of mercury and in which heated vapour is projected from an umbrella nozzle on to a condensation surface passing across a space with a backing pump the gap between the wall of the pump and the jet mouth is at least one half inch while the fore vacuum of the jet is maintained at less than 0.01 mm. of mercury. As shown in Fig. 2, an umbrella jet comprises a plate 10 and flange 12 and surmounts a vapour tube 6 contracted at 14. The vapour passes through openings 16 into the jet. A conical guard 17 protects the plate 10 from the gases. The main casing has a ground edge 4 and a plate 18 forming a boiler for pump fluid 20. The tube 6 is enlarged at 22 and supported by a spinder 21. Additional intermediate and low-pressure jets are arranged at 36, 30. Skirts 34, 26, 28 are mounted upon the tube 6. Openings 38 feed the jet 36 and openings 32 the jet 30. The lower portion of the casing 2 is connected to a conduit 40 with fractionating rings 44. Conduits 46, 48 permit the removal of light fractions, and the supply and removal of pump liquid. Vapour issuing at 8 passes downwardly towards the axis of the pump and increases pumping speed. A backing pressure below about 0.01 millimetres may be obtained with a rotary oil pump. In the construction shown, intermediate and low-pressure jets are used to obtain a sufficient low back pressure for the jet 8. Di-amyl-pthalate is used in the pump. The jet 30 operates against a rather high backing-pressure. The skirt 26 preserves the jet as a high-density stream, and the element 28 streamlines the jet after it passes into the pumping zone. The jet 36 has a clearance intermediate that of the jets 30 and 8, and operates against an intermediate pressure. Light fluid fractions and gases pass into the outlet 40. The pump may be made of artificial resin, glass, and/or a metal. The main casing may be glass, the jets, spun aluminium. The constriction 14 may be parabolic, hyperbolic. or formed of two cones. Two or more jets and cooling fins or fluid, may be used. Mercury and low-vapour pressure, organic liquids may be used.. A horizontal pump is shown in Fig. 3. The boiler comprises three compartments A, B, C spaced from the floor and provided with baffles 56. High, intermediate, and low-vacuum jets are shown at 51, 54, 58 respectively. Mixed condensate from jets 51, 54 is passed through pipe 57 to chamber 59 which also receives the condensate from jet 58. Parts of the condensate pass to chambers A, B, C respectively. Low-boiling point condensates pass to the low-vacuum jet compartment. Fractionation of the liquid occurs. In another horizontal construction the casing is slightly conical and the narrower end at the lowvacuum side. The base comprises adjustable boiler compartments connected by small gaps. The intermediate and low-pressure jets are of horse-shoe shape and a restricted throat is arranged behind the high-pressure jet. Baffle trays may be inserted in front of the highpressure jet to condense vapours tending to diffuse back. Additional concentric baffle rings which may be hollow and cooled may be employed.