High-vacuum pump

Application filed September 22, 1922. Serial No. 589,788.

To all whom it may concern:

Be it known that I, Dr. Wolfgang Gaede, a citizen of Germany, residing at Karlsruhe, in the State of Baden, Germany, have ins vented certain new and useful Improvements in High-Vacuum Pumps; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which io it appertains to make and use the same.

My invention relates to improvements in high vacuum pumps, and more particularly in pumps of the type in which a jet of a suitable vapor such as mercury vapor is 11 made to flow across an opening through which there is communication from the chamber to be evacuated,· the gas or air-being carried away by the jet to a condensing chamber, and the mercury vapor which gets 20 into the chamber to be evacuated being condensed and removed from said chamber. One of the objects of the improvements is to provide a pump of this type in which the requisite pressure of the vapor is relatively 23 low. With this object in view means are provided for condensing the mercury vapor immediately after passing across the said opening, for which purpose I cause the said jet to flow after passing across the opening 30 through a cooled metallic tubular member the internal diameter of which is substantially the same as that of the nozzle through which the jet of mercury is discharged. Thus the mercury vapor is brought in intimate 35 contact with an effectively cooled surface. Another object of the improvements is to provide a pump in which a plurality of sectional pumps all connected to the same vapor supply are arranged in series, the chamber 40 upon which an earlier sectional pump of the series exerts its evacuating effect being the condensing chamber of the next succeeding sectional pump. Thereby the vacuum attained is of progressively increasing value, 15 from the first sectional pump of the series to that directly connected with the chamber to be evacuated. Other objects of the improvements will appear from the following description of the pump.

In order that my invention be more clearly understood an example embodying the same has been shown in the accompanying drawing, in which—

Fig. 1, is a diagrammatical sectional view 55 showing a nozzle constructed according to my invention, and

Fig. 2, is a vertical section showing the improved apparatus.

Referring at first to the view shown in Fig. 1, the suction member proper consists of a nozzle a from which a jet of mercury vapor may be impelled and directed downwardly, and a metallic member δ having an axial bore c in alignment with the nozzle a spaced at an interval from nozzle a and constituting with the nozzle a. vapor ejector. The member b is fitted within a water jacketed cylinder d so as to be in thorough cooling contact therewith. I have found that an exceedingly effective cooling is in- TO sured by discharging the. jet of mercury vapor through a cooled metallic body having a passage c of a diameter substantially equal to that of the rim of the nozzle. Said metallic body b is in good heat transmitting TO contact with the jacket d by forming the body with a comparatively narrow flange e and filling the annular channel / formed by and between the main part of the member and the wall of the cylinder with liquid mer- 80 cury, insuring a thorough transmission of heat. Preferably the mercury is supplied by condensation in the chamber above the member b. An important feature of this construction resides in that the member b 86 can readily be withdrawn from the cylinder d.

The jet of mercury vapor rushing from thq nozzle a passes into the bore c of the cooling member where it is immediately cooled. As long as the Sir pressure within the chamber above the member b exceeds that of the jet of vapor passing into the bore c the air is drawn by suction through _;the narrow space between the rim of nozzle ⁰⁰a and the adjacent rim of member b and into the jet of vapor and carried along by the said jet, the pump having the function of an ordinary.ejector. If after some time the pressure of the air within the chamber to be evacuated has been reduced until it is equal to or smaller than the pressure of the vapor passing across the annular slot between the nozzle a and the core c, the air can not be drawn into the jet by suction, a flow 105 of a fluid from a space of lower pressure into a space of higher pressure being impossible. Nevertheless air continues to be carriedi along, now by diffusion, and the pump has the function of a diffusion pump. no

By constructing the operative parts of the pump so as to be readily removed there1.460,318 from, the said parts can easily be cleaned. Further, a plurality of nozzles a and members & can be placed one above the other for subdividing the pump into several stages 5 and providing every one of them with a nozzle of the most appropriate form.

In Fig. 2 I have shown an example of my improved pump in which four nozzles are arranged in succession one above the other, io The lower part of the pump consists of a vaporizing chamber h formed within a cylindrical casing the lower portion 1 of which is formed with a thick wall and has a closed bottom, and the upper part of which has a 15 thin wall 2 provided at its top with a flange 3. In the operation of the pump the chamber h is filled about to a level indicated by a dotted line 4 with mercury. On the shoulder formed at the top of the thick wall 1 a 20 partition 10 is supported through the intermediary of a conical ring or seat 11. The upper surface of partition 10 inclines funnelwise to an eccentrically placed bore which extends vertically through the partition. 25 Into this bore telescopically arranged pipes 5 and 6 are fitted which extend downwardly therefrom and to a point near the bottom of the casing 1, where they are connected to a plug 9 having an axial bore. The space be>0 tween the pipes 5 and 6 is closed both below and above, and constitutes a heat-insulating air space in the double wall so dividing the space within the bore of pipe 5 and the chamber h. Into the inner pipe 5 there ex55 tends downwardly from above a cooling rod 7 made from iron or another suitable metal. The pipe 5 is provided for allowing the condensed mercury to flow back into the casing 1, which mercury is normally at a level « within pipe 5 indicated by the character 8. Reevaporization of the mercury within pipe 5 is prevented by the heat-insulating wall 5. 6 and the heat-absorbing iron rod 7.

In an axial bore through the partition 10 a pipe 12 is secured. It extends downwardly and into the casing 1 and upwardly into the upper pajrts of the pump. The said pipe serves to cairy the vaporized mercury upwardly and to the different operative 50 parts of the pump, as will presently be described. The pipe 12 is disposed within a pipe 13 fitted in the said axial bore through the partition 10 and insulating the pipe 12, for preventing condensation of the mercury 55 vapor therein. Further, the pipe 13 is used for returning condensed mercury into the casing 1. Preferably the pipe 12 is provided at its lower end with a hood 14 preventing the condensed mercury falling from 60 the pipe 13 from being carried along by the rising mercury vapor. The drops of condensed mercury fall from the hood 14 at points remote from the current of mercury vapor flowing into the pipe 12. The pipe 12 ; is provided with holes 15,16, and 17 through which it communicates with the nozzles of the sectional pumps, as will be described hereafter.

From the flange 3 a cylinder 20 rises which is surrounded by a jacket 21, and 70 through the annular chamber provided between the cylinder 20 and the jacket 21 a cooling medium such as water is circulated which is supplied thereto and withdrawn therefrom through nipples 22 and 23. With- 75 in the said annular chamber a pipe 24 is located which communicates with the cylinder 20 at a point near the bottom thereof and which is connected at its top end with a nipple 25 adapted to be connected with a 80 suction pump for producing a vacuum within the pipe 24 and the part k of the cylinder immediately connected therewith. The pipe 24 is also in communication with an annular chamber 26 which will be described herein- 85 after. Substantially at the height of the flange which carries cylinder 20 and below the bottom end of the pipe 24 a cooling body 18 is fitted in the cylinder 20. Tight engagement with the cylinder is afforded by ¹ , a leather cup 19. At intervals above body 18 and within cylinder 20 similar cooling bodies 27, 28, and 29 are arranged, each similarly provided with a leather cup 19. The upper surface of the body 18 inclines funnel- ¢5 wise to a vertically extending eccentrically situated bore, and in this bore the rod 7 already mentioned is carried. The rod extends vertically downward through chamber i and its lower end extends as has been said loo within pipe 5. The rod 7 is in its upper part provided with a bore 33 which leads from the chamber k above and opens below to the chamber I.

Above the leather cups 19 the bodies 27, 105 28, and 29 are reduced in diameter, and in the operation of the pump the annular channels thus provided between the bodies and . the wall of the cylinder are filled with mercury, providing effective heat transmission 110 from the bodies to the cooled wall of the cylinder 20.

The pipe 13 carries hollow members 30 and 35 held in position by pipes 34 and communicating with the inner pipe 12 through 115 the openings 15 and 16 respectively. The member 30 carries a nozzle 31 discharging into a bore 32 eccentrically placed and vertically extending through the cooled body 27. In a similar way the member 35 is equipped 120 with a nozzle 36 discharging into a bore of the cooled body 28. The upper surfaces of bodies 27 and 28 are conically shaped and slope downwardly from the points where the bores just mentioned are drilled. Through 125 the bodies 27 and 28 opposite the bores just mentioned and near the lower rims of the conical upper surfaces are drilled aligned and vertically extending bores. In the bore in the upper body 28 a pipe 37 is secured

1,480,91« ο through which the mercury condensed in the chamber n above, overflowing from the annular channels mentioned above, flows downwardly and into the next chamber m. The δ body 27 carries a similar pipe 38 conducting condensed mercury into the next lower chamber k, from which it flows through 33 and through an opening 51 formed through the lower .pipe section 34 and through the io annular passage afforded between the pipes 34 and 13 into the casing 1.

To the top ends of the pipes 12 and 13 members 39 and 40 are secured. The member 39 is formed with an axial recess hav13 ing a conical side wall, and the member 40 is formed with a conical outer face. The members 39 and 40 are so placed one within the other as to provide an annular outwardly flaring nozzle for the mercury vapor so coming from the top end of pipe 12, the relative distance of the walls at the narrowest part of the passage of the nozzle being about .1 or .15 millimeters. Below the said annular nozzle a fourth nozzle is se provided by a body 43 formed with an annular chamber 42 communicating through the holes 17 with the pipe 12, said chamber discharging downwards through a narrow annular passage 52 provided between the S® body 43 and the outer wall of the pipe 13, The major part of the said nozzle, and more particularly its, tip 41, projects into a funnel shaped axial opening through the cooling ring 29, and discharges through a ring³⁸ shaped orifice formed between body 29 and pipe 13 and into the condensing chamber n, which chamber encloses the nozzle 36. The parts 29 and 43 may be dispensed with.

The member 39 carries a disk 53 formed 40 with a hole 45 and acted upon by a spring 44 forcing all the nozzles and the pipes carrying the same downwardly and on the annular seat 11. To the top of the cylinder 20 a high vacuum pipe 46 having a flange 45 47 is secured, which pipe is made tight by a packing ring 48 of leather or the like. At its lower end the(pipe 46 extends beyond flange 47 and is there provided with a flange 49 tightly fitting in the cylinder 20. 50 Above the flange 49 and between the lower part of the pipe 46 and the upper part of the cylinder 20 the annular chamber 26 is formed which is partly filled through a hole normally closed by a screw 50 with 53 mercury constituting a tight closure of the low vacuum chamber 26 as against the high vacuum chamber 46.

In the operation of the pump the mercury confined within the receptacle 1 is heated ⁰⁰ and a low vacuum pump connected to the nipple 25 is set in operation. The mercury vapor rises from the receptacle 1 through the pipe 12 and to the individual nozzles connected therewith. The vapor flowing ⁶⁵ through the hole 15 and into the chamber rushes through the nozzle 31 and into the cooled bore 32, and it evacuates the chamber m situated between the bodies 27 and 28. The condensed mercury falls on the cup shaped cooling body 18 from which a 70 part flows through the axial bore 33 of the cooling rod 7 to chamber i and thence through pipe 5 into the chamber h of the receptacle 1. The remaining part flows through the hole 51 and the annular pas- 75 sage formed between the pipes 34 and 13 to chamber i. Simultaneously, a portion of the vapor which rises in pipe 12 flows through the hole 16 into the chamber 35, from which it rushes through the nozzle ⁸⁰36 into the cooled bore of the body 28, thus evacuating the chamber arranged above and between the bodies 28 and 29. The condensed mercury collecting in and overflowing from the annular channel which sur- ⁸⁵rounds body 27 flows through the pipe 38 into the chamber k, mingling there with the mercury condensed from the jet from nozzle 31, whose course has already been described. In a similar way other portions of ⁰⁰the mercury vapor which rises in pipe 12 flow through the nozzles provided respectively by the bodies 43 and 39, 40. Any vapor which condenses in chambers 30, 35, 42, and the chamber formed within mem- ®⁵ber 39 will be returned by pipe 13 to chamber h.

It will be perceived that the succession of chambers k, m, n, etc. arranged as described, with' evacuation nozzles directed ¹⁰⁰into the passageways which open from chamber to chamber, constitutes apparatus by which in a succession of steps air may be exhausted from the ultimate chamber, the chamber communicating with pipe 46. The ¹⁰⁵degree of attenuation so achieved is very high indeed. Each of the lower chambers constitutes a preliminary vacuum chamber for the chamber located next above. The pressure attained within - the successive ¹¹⁰chambers is gradually reduced from the lowermost to the uppermost chamber, and in the pipe 46 a vacuum is produced, attenuated to a degree which can not be measured by known apparatus. ¹¹⁵

The heat is effectively transmitted from the bodies 18, 27, 28, and 29 through the rings of mercury surrounding the same and providing a good metallic contact.

All the parts of the pump can readily be 7-° takin apart.

Whije in describing the invention reference has been made to a particular example embodying the same I wish it to be understood that my invention is not limited to ¹²⁵the construction shown in the drawings, and that various changes may be made in the general arrangement of the apparatus and the construction of its parts without departing from the invention. ¹³⁰

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