US2639086A - High vacuum diffusion pump - Google Patents

Description

May 19, 1953 B. B. DAYTON HIGH VACUUM DIFFUSION PUMP Filed Nov. 50, 1951 28 El] /0 p 45 28 5 47 I 2.9 35 i l= as I L 26 28 I I lig 27 l 32 r '5 4? 3/ 34 l3 a; 2 /5 a 5 349 29 l IM 40 2 l 5 u 5 l I I 5? 29 o 1 56 f I 18 IX i l 1.9 /7 l i 1 57 I /5 1 BENJAMIN B. DAYTON INVENTOR.

MA/TQM M A TTOR/VE Y5 Patented May 19, 1953 HIGH VACUUM DIFFUSION PUMP Benjamin B.'Dayton, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application November 30, 1951, Serial No. 259,081

Claims.

This invention relates to vacuum pumps and particularly concerned with fractionating diffusion pumps adapted to operate in the high vacuum range.

Vacuum technology is dependent upon the provision of adequate pumping means for producing the desired degree of vacuum. The well-known high vacuum operations, such as high vacuum distillation, vacuum coating with metals and the like, vacuum dehydration, and similar high vacuum processes, are made possible by vacuum pumps which operate in the range below 100 microns pressure. The so-called fractionating diffusion pumps are particularly adapted for producing the desired high vacuum when employed in conjunction with a mechanical backing pump.

Fractionating diii'usion pumps were evolved to employ organic pump fluids, and in operation, such pumps. separate the components of the pump fluid into fractions of varying vapor pressure. In operation, the pump fluid components having the lowest vapor pressure exert their pumping action in the low pressure or inlet portion of the pump while the higher vapor pressure pump fluid components exert their pumping. action in higher pressure zones of the pump adjacent the forepressure outlet. The effectiveness of a diffusion pump is measured by the degree of vacuum which it will produce, by the pumping speed and by the forepressure breakdown. Highly volatile components of the pump fluid and also decomposition products formed upon prolonged heating of the pump fluid tend to impair the efficiency of the pump unless means are provided for ensuring optimum operation.

It is accordingly an object of this invention to provide an improved diffusion pump for producing high vacuum.

Another object of the invention is to provide a fractionating diiiusion pump of novel design.

Another object of the invention is to provide a diffusion pump having improved means for draining pump fluid therefrom.

Another object of the invention is to provide a vacuum pump including a drainage conduit and including means for ensuring the attainment of high vacuum in spite of possible leakage of air into the pump through the drainage conduit.

Another object of the invention is to provide a difiusion pump including improved means for minimizing the objectionable effects of pumpfluid decomposition.

Another object of the invention is to provide a fractionating diffusion pump comprising a new combination of elements.

I Other objects will be apparent from thedrawings, description and claims.

These and other objects are attained by means of this invention as described more fully hereinafter with reference to a preferred embodiment thereof as illustrated in the drawings.

Of the drawings:

Fig. 1 is a view in elevation, partly broken away and in section, of a fractionating diffusion pump constituting a preferred embodiment of the invention; and

Fig. 2 is a sectional view taken along line 2-2 of Fig. 1.

Referring particularly to the preferred embodiment illustrated in the drawings, a pump embodying this invention comprises a tubular metal casing l0 welded or otherwise secured to boiler ll. Boiler H, which is of metal or other suitable heat-conducting material, has a neckeddown upper portion 12 projecting inside the lower end of casing l0 and forming an annular trough 13' with the lower margin of easing Hi. The bottom Ml of boiler H is a plate which is welded or otherwise secured to side Wall l5 of boiler l 1'. Side wall l5 of boiler l'l extends downwardly beyond bottom M to form an annular skirt 16 which serves as a base for the pump. Heater H which is secured to the lower face of bottom l4 serves, to supply heat to boiler H for vaporizing pump fluid in boiler l'l. I-Ieater ll consists of resistance wire [8 embedded in a ceramic base l9 and current is furnished by connections at binding posts 2 I to a suitable source of electric currentione binding post not shown).

The upper end of easing ID is open to serve as an inlet port 22 from the system to be evacuated; Flange 23 around inlet port 22 is adapted to be bolted or otherwise secured to the system to be evacuated, sealing ring 24 being provided to insure a vacuum-tight connection.

Casing Ill is apertured adjacent its lower end to provide an. outlet port '26 opening into forepressure arm 21 which is welded to casing It around port 26. Forepressure arm 21, which is adapted to be connected to a mechanical backing pump, projects outwardly and upwardly from outlet port 26. A coil. 28 of copper tubing wound around casing I0 and forepressure arm 21 is adapted to be connected. to a. source of cooling fluid by means of fittings 2.8, 29 for cooling casing l0 and forepressure and 21 to a sufficient degree to condense pump fluid vapors contacting them. A hemispherical dam 3i is mounted inside forepressure arm 21 to collect condensate forming in the forepressure arm and drain 32 opening out of forepressure arm 21 is arranged for draining condensate collected behind dam 3i, drain 32 being closed by threaded plug 33 and gasket 34.

Concentric vapor chimneys 35, 36 and 31 are disposed inside casing 10. and the two inner chimneys 36 and 31 extend downwardly to the bottom of boiler ll. Chimneys 36 and 31 thus divide boiler ll into concentric boiler compartments 38, 39 and 46. The lower end of chimney 35 extends into annular trough 13. Chimney 35 is secured to chimney 35 by means of element 42 whereby chimney 35 is supported by chimney 36 with the lower end of chimney 35 out of contact with the walls of trough I3. Chimneys 36 and 3'1 rest on and are supported by the bottom I4 of boiler ll. Chimney 31 extends upwardly to a zone adjacent inlet 32 of casing and is provided with an umbrella cap 43 over its upper end, cap 43 forming with theupper margin of chimney 31 a downwardly-directed jet nozzle. The outer vapor chimney terminates in a zone slightly above outlet 26 and is provided with a cap 44 welded to the outer face of chimney 36 to form a jet nozzle with chimney 35. Chimney 36 terminates in an intermediate zone between inlet port '22 and outlet port 26, and cap 45 welded to chimney 31 forms a jet nozzle with chimney 36. Spacers 41 and 48 maintain the proper spacing between chimneys 35, 36 and 31. Spider 43 welded to chimney 31 maintains the chimney assembly approximately concentric with casing l3. Wire spring clip is pinned within casing ill above cap 43, spring clip 56 being wound around post 5| which is welded to and projects upwardly from cap 43. Spring clip 50 does not touch either post 5| or cap 43 and is maintained in position by spring pressure exerted by the ends of clip 53 against casing 10. Clip 50 serves to prevent dislodging of the jet assembly, composed of the chimneys and caps, if a backward blast of gas should enter through forepressure arm 21 or if the pump is accidentally inverted. Both spider 49 and clip 50 are constructed and arranged so as not to constrain the jet assembly in any way which might prevent the bottoms of chimneys 36 and 31 from resting flat on bottom 14 of boiler II and forming a liquid tight seal therewith.

Chimneys 36 and 31 are notched at their lower ends to provide fluid passageways 52, 52 interconnecting the boiler compartments in series. The notches 52, 52 are spaced on the adjacent chimneys to form as long a path of travel as possible from one boiler compartment to the next. Boiler II is provided with a cooling coil 53, including suitable fittings 28, 29 for controlling the wall temperature of boiler II. A drainage conduit 54 is bored through threaded plug 56 which is screwed into a threaded opening extending through heater l1 and the bottom I4 of boiler ll. Threaded cap 55 screwed into the lower end of plug 56 closes conduit 54, gasket 59 serving as a seal for cap 55. Plug 56 is locked in place by nut 51. Tube 58 extends from immediately above drainage conduit 54 through chimney 31 and opens into the space between chimneys 36 and 31 above the normal level of pump fluid, tube 58 being secured at its upper end to chimney 31 and suspended from chimney 31 with a flared lower end immediately above conduit 54. Tube 58 thus forms an innermost boiler compartment inside compartment 46, such innermost compartment being vented, however. into chimney 38 communicating with the jet in the intermediate pressure zone of the pump.

In operating the pump shown in the drawings, a suitable organic pump fluid is charged into boiler I I. Forepressure arm 21 is then connected to a suitable backing pump and flange 23 is bolted to a suitable port on the system to be evacuated. Cooling fluid is circulated through coils 29 and 53 and heater I1 is energized to vaporize the pump fluid in boiler H. The pump fluid vapors formed in compartments 38, 39 and 40 as cend through chimneys 35, 36 and 31 and are discharged through the jet nozzles downwardly towards the forepressure end of the pump. The discharged vapors condense on casing 10 which is cooled by coil 28 and the condensed pump fluid flows downwardly along the inner wall of easing [0 into trough 13. The condensate collecting in trough l3 forms a liquid seal around the lower end of chimney 35 and overflows into boiler compartment 38. The extremely volatile constituents of the pump fluid which do not condense in the pump casing are drawn out into forepressure arm 21 together with the gases being evacuated from the system to which the pump is connected. Such volatiles are condensed in forepressure arm 21 and collected behind dam 3| so that such volatiles are segregated irom the main body of pump fluid. Periodically the condensed volatiles are drained of! through drain 32 by removing plug 33.

The condensed pump fluid returning to the boiler l l is first heated in boiler compartment 38. The higher vapor pressure components of the pump fluid are immediately revaporized and ascend inside chimney 35 to exert their pumping action in the high pressure zone of the pump adjacent the forepressure outlet. The remaining pump fluid flows through passageway 52 into boiler compartment 39 wherein the next lower vapor pressure components are vaporized and ascend the chimney 36 to exert their pumping action in a zone intermediate the high and low pressure ends of the pump. The remaining low vapor pressure components of the pump fluid flow into the boiler compartment 43 and are vaporized and ascend inside chimney 31. These low vapor pressure components exert their pumping action in the low pressure end of the pump adjacent inlet 22.

In operation, certain high boiling fractions and decomposition products formed due to the prolonged heating of the pump fluid tend to collect in the innermost boiler compartment formed by tube 58. Upon prolonged heating, such fractions and decomposition products evolve gases which, if discharged through chimney 31 into the low pressure end of the pump adjacent inlet 22, would greatly impair the eiiectiveness of the pump. These evolved gases are channeled into chimney 36 by tube 58 in the pump embodying this invention and are thus discharged in an intermediate pressure zone wherein their eiIect is not particularly objectionable. These decomposition products and high boiling fractions which collect within tube 58 can be drained off through conduit 54 by removal of plug 55. Such drainage of pump fluid cannot, of course, be accomplished while the pump is in operation, and cooling coil 53 around boiler ll serves to speed up the cooling of the pump fluid in the boiler before such draining is carried out. Since it is not practical to interrupt the operation of the pump and drain out such heavy fractions, and decomposition products as they accumulate, tube 5.3 formingthev innermost boiler compartment isolates. such materials, and collects and channels evolved gases into. a chimney. other than the inner chimney 31, where such gases do not adversely affect the. operation of the pump. Tube 5.8 also serves to channel any air leaking in through conduit: 5.4 out. of the innermost boiler compartment and into a chimney not communicating with the lowest pressure zone of the pump.

Thus, in the pump embodying this invention, the highly volatile components of the pump fluid are segregated from the mainbody of pump fluid by means of the dam in the forepressure arm and are readily drawn oil through conduit 32. The effect of high boiling impurities and decomposition products formed by prolonged heating OI the pump fluid is minimized by the inclusion of tube 58 which serves as innermost boiler compartment for collecting such products and impurities and which channels evolved gases to a zone of the pump where such gases are not particularly objectionable. The use of tube 58 also permits the inclusion of a drainage conduit for the innermost boiler compartment without the danger of air leakage impairing the efficiency of the pump. The drainage conduit 54 serves a dual function in that it can be employed for draining only a portion of the pump fluid containing the highest concentration of undesirable high boiling impurities and decomposition products from the innermost compartment or it can be employed for draining all of the pump fluid from the pump.

This invention thus provides a pump particu larly adapted for producing a high degree of vacuum. The pump successfully obviates the objectionable eifects of volatile components of the pump fluid as well as non-volatile products which are particularly subject to decomposition during operation of the pump to form undesirable volatile products.

The invention has been described in considerable detail with reference to a preferred embodiment as illustrated in the drawings, but it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove, as illustrated in the drawings and as defined in the appended claims.

I claim:

1. A fractionating difiusion pump comprising Wall means defining a boiler and a pump casing extending upwardly from said boiler, spacedapart inlet and outlet ports in said casing, a plurality of generally concentric vapor chimneys disposed within 'said Wall means and being arranged to divide said boiler into a plurality of generally concentric boiler compartments, the upper ends of said chimneys being in said casing between said inlet and outlet ports, jet nozzle means communicating with the upper ends of said chimneys, centrally disposed means for draining pump fluid from said boiler compartment formed by the inner vapor chimney, removable closure means for said draining means, and means disposed Within said inner chimney for channeling gases from the region of said draining means into a vapor chimney other than said inner vapor chimney.

2. A fractionating difiusion pump comprising boiler means for vaporizing pump fluid, casing means joined to said boiler means and defining a pumping chamber communicating with said boiler means, spaced-apart inlet and outlet ports in said casing means, jet. nodule means disposed in said pumping chamber between said ports, chimney means connecting said jet nozzle means with said-boilermean-s, said chimney meansdividing said boiler means into a plurality of concentric boiler compartments, a drainage conduit arranged ior draining pump. fluid from the boiler compartment formed by the inner chinmey, removable closure means for said drainage conduit, and means disposed in said inner chimney and forming an innermost boiler compartment immediately above said drainage conduit for collecting high boiling fractions and decomposition products from the pump fluid and for channel- 111g cases from the region of said drainage conduit into a, boiler compartment other than said boiler compartment formed by said inner chimney.

3., A fractionating; diffusion pump comprising boiler means, pump casing means associated with said boiler means, vapor chimney means extending from the bottom of said boiler means into said pump casing means, said chimney means dividing said boiler means into a plurality of generally concentric boiler compartments, spacedapart inlet and outlet ports for said casing means, jet nozzle means mounted in said casing means between said inlet and outlet ports and communicating with said chimney means, fluid passageways interconnecting said boiler compartments in series for permitting flow of pump fluid from the outermost boiler compartment inwardly through said boiler compartments in series, a drainage conduit for draining pump fluid from the boiler compartment formed by the inner chimney, closure means for said drainage conduit, and tube means disposed in and communieating with said boiler compartment formed by said inner chimney, said tube means forming an innermost boiler compartment for collecting high boiling fractions and decomposition products from said pump fluid, said tube mean communicating with a chimney other than said inner chimney for channeling evolved gases into a chimney other than said inner chimney, said tube means being disposed over said drainage conduit.

4. A fractionating diflusion pump comprising wall means defining a boiler and a pump casing extending upwardly from said boiler, an inlet port in an upper zone of said casing, an outlet port in a lower Zone of said casing, a plurality of generally concentric vapor chimneys disposed within said wall means and being arranged to divide said boiler into a plurality of generally concentric boiler compartments, fluid passageways interconnecting said boiler compartments in series, said chimneys extending from said boiler into said casing, the upper ends of said chimneys being between said inlet port and said outlet port, a jet nozzle mounted on the u per end of each said chimney and being arranged to receive pump fluid vapors from said chimney, a drainage conduit arranged for draining pump fluid from the central zone of said boiler within the inner chimney, removable closure means for said conduit, and means in said inner chimney for channeling gases from said drainage conduit into a vapor chimney other than said inner vapor chimney, said means for channeling gases comprising tube means forming an innermost boiler compartment within said inner chimney and opening into a chimney other than said inner chimney, the lower end of said tube means being 7 flared and disposed immediately above said drainage conduit.

5. A fractionating diffusion pump comprising wall means defining a boiler and a pump casing extending upwardly from said boiler, spacedapart inlet and outlet ports in said casing, a forepressure conduit communicating with said outlet port, means for collecting condensate in said iorepressure conduit, means for withdrawing condensate from said collecting means, a plurality 10 of generally concentric vapor chimneys disposed within said wall means and being arranged to divide said boiler into a plurality of generally concentric boiler compartments, fluid passageways interconnecting said boiler compartments in series, the upper ends of said chimneys being in said casing between said ports, jet nozzle means communicating with the upper ends of said chimneys, means forming an innermost boiler compartment within the inner vapor chimney, the last said means comprising a tube disposed in said inner chimney and opening out of said inner chimney into another of said vapor chimneys at a point above the normal level 01 pump fluid in said boiler compartments, means for draining pump fluid from said innermost boiler compartment formed by said tube, and removable closure means for said draining means.

BENJAMIN B, DAYTON.

References Cited in the file of this patent UNITED STATES PATENTS 15 Number Name Date 2,291,054 Nelson July 28, 1942 2,395,552 Johnson Feb. 26, 1946 2,585,139 Lawrance Feb. 12, 1952

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