US2211329A - High vacuum pump - Google Patents

Description

K. c. D. HICKMAN HIGH VACUUM PUMP -iled Aug. 9, 1938 2 Sheets-Sheet l Mooofo o noun KEMVETH CDHICKMAN I NVEN'T 0R ATTORNEYS Patented Aug. 13, 1940 TATE PA if HIGH VAGUUM P Application August 9, 1938, Serial l lo. 223,925

8 Claims.

This invention relates to improved apparatus for producing high vacua and in. particular relates to improved condensation or diffusion pumps.

In my U. S. Patent 2,080,421 I have described improved condensation pumps adapted to employ an organic working fluid. These pumps are adapted to fractionate the organic pump fluid during use and deliver the vapors of the various fractions to appropriate jets in the pump. The pumps described in 'this patent are a big improvement over pumps of the prior art. However, even with the fractionating features, these pumps do not give pressure reductions corresponding to theory. This has been found to be particularly true in connection with vertical fractionating pumps wherein a plurality of boiler compartments are formed in the base by concentric tubes which deliver vapors to, appropriately located jets at the upper ends of the concentric tubes.

An object of my invention is to provide improved fractionating condensation or diffusion pumps. A further object is to provide improved fractionating condensation pumps of the vertical concentric tube type. A still further object is to provide fractionating condensation pumps which will yield pressure reductions corresponding to theory. A still further object is to provide condensation pumps which will yield pressure reductions approximately as low as the vapor pressure of the lowest vapor pressure constituents of the pump fluid which can be vaporized without decomposition. Other objects will appear hereinafter.

These and other objects are accomplished by my invention which in general comprises arranging the boiler compartments or the vapor conduits between the boiler compartments and the jetnozzles so that the lowest vapor pressure components of the pump fluid, which cannot be vaporized without decomposition, are delivered to a jet nozzle at least once removed from the highest vacuum jet nozzle so that the next lowest vapor pressure components, which can be vaporized without appreciable decomposition, are delivered to the highest vacuum jet.

The reason why theoretical pressure reductions were not obtained in the earlier constructions has been found to be due to the fact that the lowest vapor pressure constituents cannot be vaporized without at least partial thermal decomposition. Heretofore, the vapors from the lowest vapor pressure constituents were delivered to the highest vacuum jet. Therefore, these volatile decomposition products were released at a point in the pump where they could do most harm. ,By bypassing these harmful constituents to a low vacuum or intermediate vacuum jet they are prevented from exerting their harmful action and are, in fact, caused to perform useful pumping 5 action.

In the following description I have given numerous examples of the preferred embodiments of my invention. However, it is to be understood that these are given for the purpose of illustration and not as limitations thereof. 1

In the accompanying drawings:

Fig. l is an elevation in section of a vertical concentric pump embodying the principles of my invention wherein vapors from the lowest vapor s pressure constituents are by-passed to the lowest vacuum jet;

Fig. 2 is a horizontal section on line- 2--2 of Fig. 1;

Fig. 3 is an elevation in section of a vertical concentric pump wherein the lowest vapor pressure constituents of the pump liquid are bypassed from the boiler supplying the high vacuum jet to the boiler supplying vapors to a jet operating against an intermediate vacuum;

Fig. 4 is a horizontal section on line Qt of Fig. 3;

Fig. 5 is a sectional elevation of a horizontal fractionating pump wherein the vapors are bypassed;

Fig. 6 is a vertical section on line 66 of Fig. 5 and is shown on a slightly reduced scale;

Fig. 7 illustrates in sectional elevation a modified horizontal fractionating pump wherein the lowest vapor pressure constituents are by-passed in liquid form from the lowest vapor pressure boiler to an intermediate boiler supplying vapors to the next lowest vacuum jet;

Fig. 8 is a vertical section on line t8 of Fig. 7.

Referring to Fig. 1, numeral 2 designates a cylindrical pump casing, the base of which is closed by an integral plate t, the center of which is connected to ,a withdrawal conduit 6. The top of the casing 2 is provided with a flange 8 which facilitates connection to the system which is to be evacuated. The upper end, therefore, represents the high vacuum or intake side of the pump.

The low vacuum side, or exhaust side of the pump is indicated by conduit Ill which connects to the backing pump (not shown). Numerals l2, l4 and I6 designate approximately concentric cylinders, the base ofeach of which is in close, and preferably liquid-tight contact with the base plate d. Concentric cylinder l2 is provided with a collar I8 atits base which extends into close proximity to the inner wall of pump casing 2. Cylinder I2 is truncated at the top and the truncated portion is extended to, and integral with, concentric cylinder I4. Concentric cylinder I4 is similarly truncated at I9. Cylinder I6 is truncated at 20 as illustrated in order to form a chimney for vapors passing to the highest vacuum jet.

Numerals 22, 24 and 26 designate annular jet lips integral with the periphery of cylinders I2, I4 and I6 respectively, so as to form low, intermediate and high vacuum jet nozzles. Numerals 28, 30 and 32 designate openings through which vapors issue into the jet nozzles from the spaces between the concentric cylinders. Numeral 34 designates the annular boiler formed at the base by concentric cylinders I2 and I4 which supplies working vapor to jet nozzle 22. Numeral 35 designates an annular boiler which Sup lies working vapor to jet nozzle 24. Numeral 38 designates an annular boiler which supplies working vapor to jet nozzle 26. Numeral 40 designates a conduit, the lower end of which is integral with and penetrates through concentric cylinders I4 and I6. This conduit covers a circular central portion 42 which serves as a boiler for the lowest vapor pressure constituents.

Numeral 44 designates a collar which supports the entire pump assembly and which provides a circular space, closed by plate 46 within which is mounted a plurality of heating units as illustrated. Each of these heating units is adapted to heat the boiler compartments 34, 36, 38 and 42 to separate and independent temperatures.

Referring particularly to Fig. 2, numeral 41 designates an opening in the base of concentric cylinder I2. This opening is sufiiciently low that its upper portion is well covered by the pump liquid in the boiler. Numeral (l8 designates a similar opening in the base of cylinder I5. Numeral 50 designates a small opening in the base of concentric cylinder I6. Numeral 52 designates a similar opening in the base of cylinder 40.

Referring to Figs. 3 and 4, concentric cylinders I2, I4 and I6 are mounted within the main cylindrical casing as described in connection with Figs. 1 and 2. These cylinders are in liquidtight contact with the base 0 and cylinders I2 and I4 are truncated as previously described. However, cylinder I6 extends, without constriction directly to the high vacuum jet 26. Numeral 60 designates a conduit integral with concentric cylinders 4 and I6 which provides a passageway for the flow of pump liquid from boiler compartment 34 into boiler compartment 38. A bafile 62 in 1 he shape of an annular ring is located in the boiler 38 and is split at 64 as indicated. Passage 60 is sufficiently low that its top portion is well covered by pump liquid. A similar passageway 66 connects the inside of bafile 62 with boiler compartment 36. An electrical heating element 68 is mounted in the base. It is not shown as being controllable so as to heat each boiler compartment to an independent temperature. However, the amount of heat supplied to each boiler compartment can be regulated by varying the proportion of heating unit placed under each compartment.

Referring to Figs. 5 and 6, numeral 00 designates a cylindrical pump casing which is adapted to be connected at the high vacuum end by flange 82 to the chamber to be exhausted, and at the low vacuum end by conduit 86 to a backing pump (not shown). The low vacuum end of is closed by a plate integral with conduit 80. The base of cylinder 80 in the vicinity of the low vacuum end is cut away and the extended walls.85 and 81, closed by a base plate 88 so as to form a recessed pump fluid boiler. A similarly shaped cylinder 90 is located within the main casing 80 and more or less concentric therewith. The portion of this cylinder adjacent the low vacuum end of the pump is cut away and provided with an extension corresponding to that of the pump liquid boiler. The end of the cylinder 90 is closed by a plate 92 which is integral with a conduit 93 which extends slightly into conduit 84 as illustrated. Plate 92 extends to the base plate 88 of the boiler. A similarly shaped plate 94 located inside the cylinder 90 .extends from the top inside wall of the cylinder to the base plate 88. Plate 96 is similarly shaped and likewise extends to the base plate 88. Plate 98 is integral with the lower wall of cylinder 90 and extends to the base plate 88 of the boiler. Two bent plates I00 and I02 integral with the lower wall of the cylinder 90, extend transversely to plates 92, 94, 96 and 98 and are integral therewith. They serve to segregate the pump liquid boiler into a plurality of compartments, A, B and C. Cylinder 90 is truncated at 99 and the truncated portion is extended to, and becomes integral with conduit I04. Jet nozzle I06 is mounted at the high vacuum end of conduit I04. Jet nozzle I08 is similarly located at the end of cylinder 90. Holes I09 and H0 provide a passageway for Working vapors to issue into jets I06 and I08 respectively. Numeral II2 designates a series of staggered bafiles which are located in the various boiler compartments. They cause the pump fluid to flow in a tortuous path or at a slow rate in passing through the boiler compartments.

Numeral H4 designates a semi-circular opening in the base of plate 98. It is sufficiently small that it is well covered by pump fluid. These openings are two in number. Numerals H6, H8 and I20 designate similar openings in the base of plates 92, 94 and 96 respectively. Numeral II5 designates a conduit which extends along the base of the boiler through openings in the various baffle and partition plates. These openings are preferably small so that a tight fit results. Conduit H5 is bent upward at II! and terminates at the bottom central portion of the casing 80. The other end of the conduit terminates at the low pressure end of the boiler.

Numeral I2I designates a series of fractionating rings integral with the wall of conduit 84. Conduit I23 connects the space between the last two rings I2I with the low pressure portion of the boiler. Numeral I22 designates a cooling coil integral with the external wall of the pump casing. Cooling fluid is introduced at I24 and with drawn at I26. Numeral I28 designates a sightglass whereby the level of the pump fluid can be readily determined.

Referring to Figs. '7 and 8, numeral I50 designates an approximately cylindrical pump casing, the high vacuum end of which is provided with a flange I52 which is adapted to be connected to the chamber to be evacuated and the low vacuum end of which is shown is connected to a conduit I54 which is in turn connected to a backing pump (not shown). The base of pump casing I50 is cut out at a point beginning at the central portion to the low vacuum end. The walls of the base near the cut out area are extended to form an elongated reservoir having walls I58 and I5? and base I58. A cylindrical element IE0 is located inside the pump casing sponding to the location of the reservoir in the and has its base cut away in a position correbase of casing I50. Internal cylindrical element I60 is divided into a plurality of compartments D, E, F and G by partitions I62, I66, I64 and I65 which extend to the base plate I58 of the titions I62 and I63 are provided with a plurality I I02 and I'I4 which permit pump liquid to of small notches I68 which are well below the level of the pump liquid in the boiler. Partition I64 extends entirely to the base plate I58 and makes substantially liquid-tight contact therewith. Partition I 65 is provided at its base with a plurality of notches H0. The walls of cylindrical element I60 are extended to the base of the boiler at I12 and H4 which are at a suflicient distance from walls I56 and I61 to just permit pump liquid to flow therebetween. Numeral I16 designates a plurality of minute notches, in walls flow back into the boiler compartments.

Referring particularly to Fig. 8, it will be noticed that partitions I64 and I65 do not extend to wall I I4. They are shortened, as shown, and are connected by a plate I16 soas to form a passageway I60 from the boiler of compartment E directly into the boiler of compartment G.

Reference numerals I62, I64, I66 and I66 designate jet nozzles which communicate with compartments D, E, F, and G by openings I90, I92, I64 and throat I96, respectively. Numeral 200 designates a bafile constructed of a metal conduit wound in the form ofa helix. Cooling fluid is supplied to this baiile by introduction at 202 and withdrawal at 204.

, In operating the apparatus illustrated in Fig. 1, an organic pump fluid is introduced into the pump. It should be filled to a height suflicient to at least cover the openings 46, 66 and 52. Flange'6 is connected to the system to be evacuated and conduit I0 is connected to a backing pump in the usual manner. Conduit 6 is closed or is connected to a small air-tight sump. The base of the pump is then heated by the electrical heating element. It is best that the temperature uniformly increase toward the center of the pump. Vapor produced in boiler section 64 rises in the annular space between concentric tubes I2 and I4 and passes through holes 28 and issues from jet nozzle 22. The jet entrains gases in known manner which are removed by the backing pump through conduit III. The jet vapors condense on the walls of casing 2, flow by gravity into the space between I6 and 2 and arrive back into the boiler compartment 24 from which they were derived by way of opening 41. The unvaporized liquid in compartment 64 flows in a circular path to opening 46 and into boiler compartment 86. When the liquid arrives in compartment 66 it has traveled in a tortuous path through boiler 34 and has, therefore, been thoroughly deprived of high vapor pressure constituents before passing through opening 46.

In compartment 66 the next lowest, below the high vapor pressure constituents are vaporized and pass upwards between concentric cylinders I4 and I6. These vapors issue through openings 30 and pass out through jet nozzle 24. Vapors are condensed on the inside wall of easing 2 and the condensed liquid flows back into boiler compartment 24. The pump fluid which .is not vaporized in compartment 26 passes ima circular or tortuous path to passage 60 and into boiler compartment 68. Here the next lowest, to the lowest 'vapor pressure components are vaporized and rise and issue through openings 32 and pass from jet nozzle 26., Jet 26 is the highest vacuum jet and it is desirable that it be supplied with the best portion of the pump fluid vapors. Vapors issuing from jet 26 are condensed on the walls 02 casing 2 and flow by gravity back into boiler Pump fluid which is not vaporized in boiler compartment 38 then flows through opening 62 into boiler compartment 42. These pump fluid constituents are the lowest vapor pressure components. However, they have such a low vapor pressure thatthey cannot beefliciently vaporized without some thermal decomposition. The vapors derived therefrom are, therefore, not suitable for delivery to the high vacuum jet 26. These vapors rise through L-shaped conduit 40 and pass into the annular space between concentric tubes I2 and I6 and eventually pass ou through jet 22.

It is apparent that eflicient fractionation of the pump fluid takes place in the operation of this apparatus. The pump fluid is segregated into components of gradually increasing vapor pressure as in prior constructions but the lowest vapor pressure component is segregated and is not permitted to be vaporized and delivered to the highest vacuum jet. The harmful effects of its decomposition products are thereby avoided. A further feature of novelty which also adds to the eflicient operation of the vertical concentric fractionating pump is illustrated in Figs. 1 and 2. 7

It will be noted that the boiler area in boiler compartment 36 is increased so that it is approximately the same as the boiler areas in each of, the other compartments. This permits effective vaporization of pump fluid in ample quantities for operation of the high vacuum jet without overheating.

The feature of causing the pump fluid to pass in a tortuous path through each boiler compartment is also of decided advantage and can be used in fractionating pumps of all types. If the pump fluid is permitted to flow too quickly from one compartment to another it is not efiiciently stripped of its lighter constituentsand these will be vaporized at a point where they may adversely affect the pumping action. By causing liquid to pass in a tortuous, path removal of. all volatile constituents before it reaches the next boiler compartment is assured During operation of the apparatus illustrated in Figs. 3 and 4, fractionation and the action of the jet is similar to that of the apparatus illustrated in Fig. 1. However, the pump liquid in boiler 64 flows directly into boiler compartment 38 through conduit 60. The highest vapor pressure constituents are, therefore, vaporized in compartment 34 and issue through jet 22. The intermediate vapor pressure constituents are vaporized in boiler compartment 66 and in the area within ring 62. These vapors rise and issue through high vacuum jet 26. The lowest vapor pressure constituents remain unvaporized and pass through passageway 66 into intermediate boiler compartment 66. Here the lowest vapor pressure components which undergo more or less decomposition are vaporized and the vapors delivered to jet 24 which operates against a lower v vacuum.

In both concentric pumps illustrated in Figs. 1

mulate. These can intermittently be withdrawn by suitably located. conduits such as conduit 8.

In operating the apparatus illustrated in Figs. 5 and 6, pump fluid is introduced into the boiler compartment. The pump fluid is indicated at I and is shown as it would be retained by the boiler during operation of the pump. It will be noted that the pump casing 80 and the base oi the boiler 88 slant upwardly toward the high vacuum end. This is to cause the pump liquid to flow back into the boiler compartments. Flange 82 is connected to the chamber to be evacuated and conduit 84 is connected to any suitable backing pump. The boiler containing the pump fluid is heated in any suitable manner, such as by gas. The highest vapor pressure pump fluid constituents vaporize and pass into compartment A and thence through jet nozzle 93. The jet of vapors passes into conduit 84 where it is condensed and entrained gases removed by the backing pump connected thereto. The condensed pump liquid flows back over fractionating sure so that the pump fluid is caused to flow more or less up-hill into compartment B. In compartment B the intermediate fraction representing the most useful components of the pump fluid is vaporized and passes into conduit I04 and thence to jet I06. Vapors from this jet condense on the cooled walls of 80 and flow to the base and into conduit I I5. They then flow through conduit H5 to the lowest portion of the boiler as indicated at I21. The lowest vapor pressure constituents are not vaporized in compartment B, but flow into compartment C. vapor pressure, decomposable substances are vaporized and issue through the intermediate jet I08. Vapors from this jet condense on the walls of casing 80 and flow by gravity back into conduit H5 and eventually return to compartment I21.

The staggered baflies H2 in each of the boiler compartments cause the pump fluid to pass in a tortuous path as explained above. Sight-glass I28 permits accurate determination of the level of the pump fluid in the boiler.

It will be noted that in the apparatus illustrated in Figs. 1, 3 and 5 the conduit conveying vapors to the highest vacuum jet is more or less completely surrounded by heated vapors which pass to an intermediate jet. This eflectively prevents the low vapor pressure constituents passing to the highest vacuum jet from condensing before they reach the jet. The eificiency of the jet is thereby increased.

In operating the apparatus illustrated in Figs. '7 and 8 conduit I54 is connected to a backing pump and flange I52 is connected to a receptacle to be evacuated. The boiler compartments are filled with an appropriate pump fluid to a level well above the top of openings H0 and I16, etc. In the boiler of compartment D, the highest vapor pressure constituents are vaporized, rise through compartment D, pass through openings I90 and issue from jet I82. The vapors condense on the wall of easing I50, flow by gravity into the space between wall I56 and wall H2 and thence through Here the low.

openings I16 back into the boiler compartment. Liquid which is not vaporized in compartment D then flows through openings I68 in partition I63 and are vaporized in compartment E and issue from jet nozzle I84. The remaining unvaporized liquid then by-passes compartment F through passage I80 and directly flows into the boiler 01 compartment G. Here the most useful vapor pressure constituents for the high vacuum Jet nozzle I88 are vaporized and pass through that jet. Unvaporized residue then passes backwards through openings H0 in the base of partition I65 and into the boiler of compartment 1. Here non-volatile residues accumulate and low vapor pressure constituents which cannot be vaporized without decomposition are vaporized and delivered to jet nozzle 88 where they perform useful pumping action. Vapors from each of the jets are returned to the boiler compartments in the same manner described in connection with compartment D.

Any vapors which might diffuse backwards into the zone under evacuation are condensed upon baflle 200. This bafiie may be constructed in other ways well known in the art but the shape shown has been found to have high efficiency. A bafile should present as little resistance to the flow of gases into the pump as is possible.

The apparatus illustrated in Figs. 7 and 8 may be provided with a tilting device so that the level of the pump fluid in the various boilers may be appropriately controlled. The base of the boiler may likewise be slanted as illustrated in connection with Fig. 5.

The apparatus illustrated may be constructed of any suitable materials. Any of the apparatus illustrated may be constructed entirely of metal. The apparatus of Figs. 1 and 3 can be conveniently constructed partly of glass so that the operation of the pump can be observed. The jet nozzles can be conveniently spun from aluminum and the standpipes and other parts can also be constructed of this metal, although steel, iron, copper, etc., may be used.

This application is a continuation in part of my U. 8. application 143,305 filed May 18, 1937. now Patent 2,153,189, granted April 4, 1939.

What I claim is:

1. In a multi-stage fractionating vacuum pump provided with a plurality of Jet nozzles adapted to operate in series and a plurality of boiler compartments adapted in operation to arrange the low vapor pressure components of the pump fluid so that they exert their pumping action toward the high vacuum side and the high vapor pressure components toward the low vacuum side, the improvement which comprises a vapor passage conduit connecting the boiler compartment containing the lowest vapor pressure components to a jet nozzle intermediate the lowest and highest vacuum jet nozzles, and a vapor passage conduit connecting the boiler compartment containing the next lowest to the lowest vapor pressure components to the highest vacuum jet, whereby the lowest vapor pressure components of the pump fluid are not vaporized and passed to the highest vacuum jet where they would do harm but instead are utilized in a lower' vacuum jet where they do not exert harmful effects.

2. In a multi-stage fractionating vacuum pump provided with a plurality of jet nozzles adapted to operate in series and a plurality of boiler compartments adapted in operation to arrange the low vapor pressure components of the pump fluid so that they exert their pumping action toward upper end with one of said nozzles and. termithe high vacuum, side and the high vapor pressure components toward the low vacuum side. the improvement which comprises a restricted pump liquid passage directly connecting the boiler compartment supplying working vapors to the high vacuum jet with the boiler compartment supplying vapors to a jet at least once removed from the high vacuum-jet, and a restricted pump liquid passage between the boiler compartment supplying the high vacuum jet with working vapors, and the boiler compartment supplying working vapors to the jet next to the high vacuum jet whereby the lowest vapor pressure compo-- nents of the pump fluid are not vaporized and passed to the highest vacuum jet where theywould do harm, but instead are utilized in a lower vacuum jet where they do not exert harmful effects.

3. In a multi-stage fractionating vacuum pump provided with a plurality of jet nozzles adapted to operate inseries and a plurality of boiler compartments adapted in operation to arrange the low vapor pressure components of the pump fluid so that they exert their pumping action toward the high vacuum side and the high vapor pressure components toward the low vacuum side the improvement which comprisesa vapor passage conduit "connecting the boiler compartment containing the lowest vapor pressure components to a jet nozzle intermediate the lowest and highest vacuum jet nozzle and a vapor passage conduit connecting the boiler compartment containing the next lowest vapor pressure components with the highest vacuum jet whereby the lowest vapor pressure components of the pump fluid are not vaporized and passed to the highest vacuum jet where they would do harm, but instead are utilized in a lower vacuum jet where they do not I exert harmi'ul efl'ects.

4. In a multi stage iractionating vacuum pump 1 provided with a plurality of jet nozzles adapted to operate in series and a plurality of boiler compartments adapted in operation to arran e the low vapor pressure components of the pump fluid so that they exert their pumping action toward the high vacuum side and the high vapor pressure components toward the low vacuum side the improvement which comprises a vapor passage conduit connecting the boiler-compartment containing the lowest vapor pressure components to a jet nozzle at least .once removed from the h ghest vacuum jet nozzle, and a vapor passage conduit connecting the boiler compartment containing the next lowest vapor pressure component with the highest vacuum jet whereby the lowest vapor pressure components of the pump fluid are not vaporized and passed to the highest vacuum jet where they would do harm, but

instead are utilized in a lower vacuum jet where they do not exert harmful eflects.

5. A multi-stage fractionatiug vacuum pump adapted in operation to arrange the components of the pump fluid so that the low vapor pressure components exert their pumping action toward the high vacuum side and the high vapor pressure components toward the low vacuum side 01 the pump, comprising in combination a tubular chamber with an outlet port near the lower end and an inletport above the outlet port, means to heat the base of the tubular chamber, a plurality of nozzles in series from the high vacuum to the low vacuum side mounted one above the other between said ports and directed toward the outlet port, a plurality of approximately concentric conduits each communicating at the hating at the bottom of the chamber to form a plurality of boiler compartments in the chamber below the outlet port, restricted passages in sequence between adjoining boiler compartments, except those supplying vapors to the two highest vacuum Jets, a, restricted pump liquid passage between the boiler compartment supplying working vapors to the high vacuum jet and the boiler compartment supplying vapors to a jet at least once removed from the highest vacuum jet and a restricted pump liquid passage from the boiler compartment supplying the high vacuum jet with working vapors to the boiler compartment supplying working vapors to the jet next iii the series to the high vacuum jet whereby the lowest vapor pressure components of the pump fluid are not vaporized and passed to the highest vacuum jet where they would do harm, but instead are utilized in a lower vacuum jet where they do not exert harmful effects.

6. A multi-stage fractionating vacuum pump adapted in operation to arrange the components of the pump fluid so that the low vapor pressure components exert their pumping action toward the high vacuum side and the high vapor pressure components toward the low vacuum side of the pump, comprising in combination a tubular chamber with an outlet port near the lower end and an inlet port above the outlet port, means to heat the base 01' the tubular chamber, a plusure components, to a jet nozzle at least once removed from the highest vacuum jet nozzle and a vapor passage from the boiler compartment containing the next lowest to the lowest vapor pressure components to the highest vacuum jet whereby the lowest vapor pressure components of the pump fluid are not vaporized and passed to the highest vacuum jet where they would do harm, but instead are utilized in a lower vacuum Jet where they do not exert harmful efl'ects.

'I. In a multi-stage tractionating vacuum pump provided with a plurality of jet nozzles arranged in horizontal series and adapted to operate in series and a horizontal boiler divided into a plurality of compartments by approximately vertical partitions and adapted in operation to ar- 7 range the low vapor pressure components of the pump fluid so that they exert their pumping action toward the high vacuum side and the high vapor pressure components toward the low vacuum side, the improvement which comprises a vapor passage conduit connecting the boiler comment containing the next lowest to the lowest vapor pressure component with the highest vacuum jet whereby the lowest vapor pressure components oi the pump fluid are not vaporized and passed to the highest vacuum jet where they would do harm, but instead are utilized in a lower vacuum, jet where they do not exert harmiul eflects.

8. A multi-stage fractionating vacuum pump adapted in operation to arrange the components of the pump fluid so that the low vapor pressure components exert their pumping action toward the high vacuum side and the high vapor pressure components toward the low vacuum side of the pump, comprising in combination a tubular chamber with an outlet port near the lower end and an inlet port above the outlet port, means to heat the base of the tubular chamber, a plurality 01' nozzles mounted one above the other between said ports and directed toward the outlet port, and a plurality of approximately concentric conduits each communicating on the upper end with. one of said nozzles and terminating at the bottom of the chamber to form a plurality of boiler compartments in the chamber below the outlet port. the concentric conduits being of such diameter that approximately the same area of the bottom of the chamber is enclosed between each pair of 10 conduits.

KENNETH C. D. HICKMAN.

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