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July 16, 1946. 2,404,023 P. ALEXANDER ET AL VAPOR VACUUM PUMP Filed May 26, 1945 §\\\\\\\\\\\\\\\\\\\\\\\§ C S6 IL \^//l AE'Y By n \ A orney 2,404,023 Patente-d July 16, 1946 UNITED 'STATE S PATENT OFFICE 2,404,023 VAPOR VACUUM PUMP Paul Alexander, Berkhamsted, and Cecil Whiley, London, England ` Application May 26, 1945, Serial No. 596,036 In Great Britain April 21, 1945 1 Claim. (Cl. 23o-101) l Mercury is the liquid usually vaporised in vapor pumps, but other liquids, such as oils, are em ployed. In the usual type of mercury vapor pump, mercury vapor from a boiler ascends a central tube and enters an annular jet at the top of the tube. Mercury vaporissues from the jet down wards into the annular space between the central tube and a water-cooled outer tube. The upper end of the outer tube is the inlet of the pump and the outlet is a pipe connecting the lower part of the annular space between the central and outer 2 The outlet of the pump is the pipe I6 connect ing the space I l to the usual backing pump. The This invention relates to vapor vacuum pumps. tube 5 is surrounded by a water jacket I1 to con dense the mercury vapor which falls into the seal I8, and thence returns through holes I9 into the boiler l. In operation the mercury vapor issuing from the oriñce 8 into the space II causes air to be withdrawn from the inlet 6 and is driven down 10 wards by the vapor towards the >outlet IS which is connected with a backing pump. As described and claimed in co-pending applica tion No. 596,034 the tube 5 diminishes in diameter by the inclusion of a conical wall just below the from the jet is condensed by contact with the 15 jet 1, which conical wall joins up with the par cooled outer tube and returns to the boiler. allel walls of the lower part of the tube 5, so that The molecules of mercury vapor collide with the tube 5 diminishes in diameter at a point near , _the air molecules in the annular space driving jet oriiice level so that the length of vapor jet them downwards, thus drawing air from the inlet measured along a line B with angle l5 degrees and driving it towards the outlet. The eñìciency from the general pumping direction, indicated 20 of the pump depends on the downward velocity of by the line I I, does not exceed 2.6 times the width the molecules of the mercury vapor issuing from A of the annular space at jet oriiice level. tubes to the backing pump. The mercury vapor . the jet as well as on the density of the vapor. The object of the invention is to improve the The air pressure is a minimum in the annular space II just below the jet oriñce and from this point rises rapidly with increasing distance down wards from the jet oriñce, till it reaches a pressure above that in the outlet tube I6. The air at points of high pressure tends to ñow backwards up the tube over a length thereof from just below the annular space and through the mercury vapor jet orifice downwards. 30 to the inlet E, and any air which does so flow In the accompanying drawing, which shows backwards diminishes the eiiiciency of the pump. in a single ñgure by way of example a form of Such backward flow of the air can be prevented pump embodying the invention, in vertical sec only by ensuring that every air molecule is struck tion, the mercuryboiler I, containing mercury 2 by downwardly directed molecules of mercury with an electric heater in the space 3, supports 35 vapor and driven downwards. The efficiency of the central vapor tube 4 and the outer tube '5, the pump therefore (assuming adequate density forming the body of the pump, which terminates of the mercury vapor) depends on the downward above the inlet 6 of the pump. The annular jet velocity of its molecules, and the Velocity is par 1, with annular orifice 8, is mounted on the ticularly important in the annular space from the upper end of the tube Il. The tube 4 may either 40 neighborhood of the reference Figure 11 down extend right up to the annular jet as illustrated wards and past the portion of the outer tube 5 in co-pending application No. 596,035 or, as shown which is shown conical in the drawing, because in the embodiment illustrated in the accompany it is over this length of space that the gradient of ing drawing, the tube 4 terminates below the an the air pressure is most steep. nular jet, and the latter is fixed on a tube 9 45 It has been found that the eñiciency of the adapted to slide over the upper end of the tube 4. pump is increased by surrounding that portion of The Vapor from the mercury 2, passing up the the central tube 4 which passes through this tube 4, enters the jet 'I through holes I0 in the length of space by a Water jacket 25, supplied with central body of the jet, and issues from the orifice water by the pipes 26. The water jacket is out 8 into the annular space Il between the tubes 4 50 of contact with the tube ll, since any appreciable and 5 in which the pumping action takes place, cooling of the tube is disadvantageous. The rea the pumping direction being 4indicated by the son for the resulting increase in efficiency is that, dotted line I2. without the jacket 25, vapor molecules which hit The jet is adjustable in height relatively to the tube 5 by means of the screw I3 engaging a nut CTI Cl the hot wall of the tube lose their downward ve locity and rebound with random velocity, equally I4 carried by a spider l5 ñxed to the tube 5. eíñciency of the pump by maintaining this down ward velocity of the molecules. According to the invention, a water-.cooled jacket surrounds, but does not touch, the central 3 2,404,023 distributed in al1 directions. These rebounding ¿i , ascending the tube 4 to the jet 1 is appreciably cooled. We claim: molecules collide with the molecules of the vapor issuing from the jet and diminish the downward component of their velocity. Since this is the A vapor vacuum pump comprising a central component effective for pumping, the pumping 5 tube and an outer tube surrounding the same and eñìciency is diminished as the result of molecules striking the ‘not wall of the tube 4. forming therebetween an annular space, an an nular jet on said central tube having a jet ori When the molecules are prevented by the water ñce arranged to project vapor therefrom down jacket 25 from striking the hot wall, this harm wardly into said annular space, and a water~ ful eiïect is avoided, and the eñiciency of the 10 cooled jacket surrounding and spaced from said pump is increased. central tube and extending downwardly over a The extent of the tube 4 surrounded by the length thereof from just below said jet oriñce. Water jacket may be increased beyond that shown in the drawing, but the advantage gained is small, while some disadvantage results if the vapor 15 PAUL ALEXANDER. CECIL WHILEY.