US3923424A - Self-cleansing diffusion pump - Google Patents

Self-cleansing diffusion pump Download PDF

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US3923424A
US3923424A US522708A US52270874A US3923424A US 3923424 A US3923424 A US 3923424A US 522708 A US522708 A US 522708A US 52270874 A US52270874 A US 52270874A US 3923424 A US3923424 A US 3923424A
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pump
fluid
foreline
gutter
boiler
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Alvin E Buggele
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Priority to GB43367/75A priority patent/GB1528957A/en
Priority to DE19752550456 priority patent/DE2550456A1/de
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04F—PUMPING OF FLUID BY DIRECT CONTACT OF ANOTHER FLUID OR BY USING INERTIA OF FLUID TO BE PUMPED; SIPHONS
    • F04F9/00—Diffusion pumps

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  • ABSTRACT A diffusion pump capable of separating impurities from its pump fluid during operation is disclosed. Skimming drains are provided in the pump's boiler for periodically skimming the cvaporative surface of the working fluid. This eliminates nearly all contaminants of higher molecular weight than the pump fluid. 1n the foreline of the pump, a series of peripheral gutters are provided for trapping, separating and draining off con densatesi The gutters facilitate the removal of impurities of lower molecular weight than that of the pump fluid.
  • Means are also provided for further removing trace quantities of residual volatile impurities which tend to backstream up the diffusion pump barrel.
  • the highly purified pump fluid allows for a more vigor ously working evaporative surface, thereby increasing the throughput of the diffusion pump Together with the elimination of volatile impurities from the pump barrel. this facilitates the attainment of significantly higher ultimate chamber vacuum.
  • the withdrawn condensates and skimmed residues also form the basis for use of the apparatus as a device for obtaining a high degree of separation between liquids of very close vapor pressures.
  • the invention relates to diffusion pumps for producing high vacuum and more particularly to an improved diffusion pump by which the pump fluid may be separated from its impurities during operation.
  • Diffusion type pumps for producing high vacuum are well known.
  • the original effort of Gaede around 1914 was supplemented by Langmuir in the development of the vertical jet diffusion pump disclosed in U.S. Pat. No. 1,393,350, and the single inverted jet or mushroom pump covered by US. Pat. No. 1,320,874.
  • a multiple jet modification of the mushroom pump is described in US. Pat. No. 1,367,865.
  • Such pumps operate on the principle that a liquid having relatively heavy molecules is vaporized in the pump by raising its temperature. The vapor comprising heavy molecules is directed by suitable nozzles in a direction away from the region to be evacuated, towards a mechanical forepump.
  • the accelerated molecules of vapor compress against molecules ahead of the nozzle, forcing them toward the mechanical forepump and thereby reducing the pressure within the evacuated region.
  • the vapors are recondensed on a cool wall of the pump where the liquid is permitted to return to the bottom of the pump to be reheated and vaporized.
  • the latter means include stirring or otherwise rotating the fluid mechanically, and positioning the applied heat so as to induce circulation (N-boiler of Murakami). Numerous diffusion pump boiler modifications are shown and described at pages 974976 of the first above-referenced Hickman article.
  • Backstreaming also known as reverse fractionation
  • backstreaming constitutes a back migration of some molecules from the jets back into the vacuum chamber and is inherent in a diffusion pumping process.
  • pressure in the chamber being evacuated decreases, the rate of backstreaming increases, and when it equals the throughput of gas, no further decrease in chamber pressure occurs.
  • backstreaming and various suggested remedies therefor, are discussed in Hickman US. Pat. Nos. 3,034,700 and 2,080,421, Scatchard US. Pat. No. 2,905,374, Nelson US. Pat. No. 2,291,054, Bachler U.S. Pat. No. 3,317,122 and Hayashi US. Pat. No.
  • baffles have been helpful in trapping chamber gases and reducing backstreaming, they have not been able to trap all passing gases, and once they are filled with condensate, they lose their effectiveness. If the baffle is warmed, the condensables drip into the boiler and cannot be removed.
  • This system consists of collecting condensed distillate in annular alembics defined in the foreline of the diffusion pump.
  • the distillates comprise light end substances which have escaped the diffusion pump barrel and passed along with vacuum chamber gases into the foreline.
  • the present invention provides a diffusion pump, in-
  • the diffusion pump apparatus of the invention is also capable of achieving a high degree of separation among fluids of slightly different volatility, and thus has utility in the field of refining and other arts involving high purification and separation of fluids.
  • the torpidity phenomena which has been the subject of study for some years as discussed above, is due almost entirely to the presence of heavy end contaminating substances present in the pump fluid.
  • the heavy ends comprise substances of molecular weight higher than that of the pump fluid, and include to a large extent polymerized molecules of lighter substances. These heavy ends tend to collect into nonevaporating islands on the evaporative surface, restraining the release of motive fluid molecules in these areas. Thus, only the working holes in the schizoid evaporative surface release fluid molecules at an appreciable rate.
  • the diffusion pump apparatus of the present invention is capable of almost totally eliminating heavy end substances from the pump fluid during operation of the pump, thereby removing the principal cause of torpidity on the evaporative surface. This helps provide for a vigorous, 100% working surface. resulting in a much greater molecular throughput and greatly improved pump efficiency.
  • the elimination of heavy ends is accomplished in part by the periodic skimming of the evaporative surface of the pump fluid in the boiler during operation. Skimming outlets are located around the periphery of the boiler and also toward the center of the boiler in large pumps having concentric annular boiler channels.
  • the skimming openings are provided at various levels on the boiler and are connected, when skimming valves are opened, to a collection vessel existing at lower internal pressure than that of the boiler.
  • the diffusion pump apparatus of the invention also includes means for withdrawing condensed distillate from the forepressure line of the pump.
  • Alembics are provided in the foreline for catching condensates flow ing down the internal walls thereof.
  • Valved lines connect the alembics with a collection vessel of lower internal pressure than that of the foreline.
  • Condensates within the foreline contain high concentrations of light end" substances, and the removal of these light ends prevents their return to the boiler for revaporization and possible polymerization into heavy end molecules. In this way, backstreaming is nearly eliminated, since most light ends are prevented from re-entering the flow of vapors through the diffusion pump jets.
  • Light end contaminants cannot be completely eliminated from the system via the foreline.
  • the heavy light ends not being as volatile as the lighter light ends which may be isolated in the foreline, condense on the diffusion pump barrel walls nearly as readily as does the motive fluid. Therefore, molecules of the heavy light ends are continually present in the diffusion pump barrel and available for backstreaming toward the vacuum chamber and for combining by polymerization to form heavy end contaminants which cause torpidity in the boiler.
  • the uncombined heavy light end molecules tend to backstream more readily than those of the pump fluid, toward the lower pressure of the vacuum chamber. If after separation and removal of most light light ends from the foreline, pressure could be made sufficiently low, with a sharper gradient, and temperature sufficiently high in the foreline, the heavy light ends could be drawn in greater concentration into the foreline before condensation, condensed therein and trapped within the alembics. The substances would thus be present in high concentrations within the condensate and could be drawn off from the alembics. However, to achieve such separation would require an extremely strong roughing or backing pump connected to the foreline, and extremely high temperatures within the foreline.
  • a solution to the problem of the trace quantities of heavy light ends present in the diffusion pump barrel is provided according to the present invention.
  • Valved draw off lines lead from each of the gutters to a collection vessel of lower pressure than the barrel pressure at the level of that particular gutter.
  • Certain of the gutters are provided with draw off lines at more than one level, so that motive fluid condensate, which may be present in the bottom of certain gutters, can be returned to the boiler, while condensates containing heavy light end contaminants can be drawn off from upper levels of the gutters into a collection vessel.
  • one pump having all of the above-discussed modifications can act as a slave pump to the remaining pumps having only boiler and foreline modifications.
  • Boiler fluid would be exchanged between the pumps so that the fluid of each pump would reach a high degree ,of purification.
  • the apparatus of the present invention also has utility as a precision fluid separation device.
  • Apparatus described below for boiler surface skimming and for collecting and separating condensates in the foreline and on the barrel of a diffusion pump can be utilized in other separation arts apart from diffusion pumps, such as those relating to the separation of petroleum fractions, uranium isotopes, metals, and other organic and inorganic chemicals.
  • the diffusion pump apparatus of this invention is illustrated and described herein in connection with an umbrella or mushroom type inverted-nozzle pump of the type shown in US. Pat. Nos. 2,206,093, 2,386,298, 2,436,849, 2,905,374, 3,251,537, 3,317,]22 and 3,536,420.
  • a model diffusion pump embodying some of the improvements of the invention was constructed and operated, the results of such operation being discussed in National Aeronautics and Space Administration Technical Memorandum X-68272, published Nov. 12, I973 and presented at the Seventh Space Simulation Conference, Los Angeles, Ca]., Nov. 12-14, 1973. Remaining improvements according to the invention are discussed in NASA Technical Memorandum X- 2932, to be published in or prior to January, 1975.
  • FIG. 1 is a schematic elevational view showing a vacuum chamber and connected model diffusion pump including apparatus according to the present invention
  • FIG. 2 is an enlarged view of the model diffusion P p
  • FIG. 3 is a sectional elevational view of a typical prior art large mushroom-type diffusion pump
  • FIG. 4 is a sectioned perspective view of the boiler of a typical prior art large diffusion pump
  • FIG. 5 is a sectional elevational view showing modifications to a prior art diffusion pump according to the present invention.
  • FIG. 6 is a sectional plan view taken along the line 6-6 of FIG. 5;
  • FIG. 7 is an enlarged sectional elevational view taken along the line 7-7 of FIG. 6 with parts removed for clarity.
  • FIG. 1 of the drawings shows a vacuum chamber 10 connected to the low pressure side of a model selfcleansing diffusion pump assembly according to the invention, generally indicated by the reference number 11.
  • the assembly 11 includes a diffusion pump barrel 12, a chimney and nozzle assembly 13, a boiler 14, a forepressure line 16 including alembics l7 and valved draw off lines 18, a line 19 leading through a foreline cold trap 21 to a mechanical backing pump 22, vessels 23 and 24 for collecting contaminants removed from the boiler 14 and the foreline 16 respectively, a foreline pressure gauge 26, a blower 27 for cooling the diffusion pump barrel l2, and a boiler contaminant adding device 28.
  • a pressure gauge 29 a chamber contaminant adding device 31 including a valve 32, an auxiliary bleed valve 33, and a chamber bafi'le 34 which may be chilled to provide a refrigerated condensing trap for gaseous substances travelling toward the diffusion pump barrel 12.
  • An additional baffle 37 and valve 38 may be provided between the valve 36 and the diffusion pump barrel 12.
  • the contaminant collection vessels 23 and 24 are connected by valved lines 39 and 41 to a source of lower pressure than that existing within the diffusion pump boiler 14 and foreline 16 so that the vessels 23 and 24 will draw liquids from the boiler 14 and the alembics 17, respectively, when the appropriate valves are opened.
  • the vacuum source may be the mechanical backing pump 22 itself or some other suitable source, since the pressure existing within the boiler 14 and foreline 16 during operation of the pump assembly 11 are not extremely low, as is the pressure within the upper end of the diffusion pump barrel l2.
  • Contaminant drain valves 35 and 36 are provided on the vessels 23 and 24 for removing contaminants when the vessels 23 and 24 are appropriately isolated from the source of vacuum and from the boiler and foreline.
  • Atmospheric bleed valves 40 and 45 are also provided on the vessels 23 and 24 for the same purpose.
  • the boiler 14 contains motive fluid 42 up to the level of a skimming drain line 43 which is open to the interior of the boiler.
  • the line 43 can be opened by a valve 44 to a line 46 leading to the collection vessel 23.
  • the contaminant adding device 28 which includes an open-ended graduated tube 47 and a valve 48 for admitting liquids from the tube 47 into the interior of the boiler 14. Such contaminating liquids may be added to determine their effect on pump performance and the ability of the purification apparatus of the model pump to separate the liquids out of the pump fluid, as discussed below.
  • the device 28 may also be used to replenish pump fluid in the boiler 14 as heavy and light end constituents are skimmed and drawn off.
  • the fluid level shown in FIG. 2 should be maintained through all skimming operations, since skimming is provided only at one level in the model pump.
  • the chimney and nozzle assembly 13 includes nozzles or jets 49a, 49b and 490 which are angled downwardly to create, when pump fluid passes therethrough, a low pressure on the high vacuum side 51 of the diffusion pump.
  • several openings 52 are provided around the periphery of the chimney and nozzle assembly 13 so that any fluid condensing on the lower interior of the chimney and nozzle assembly 13 returns to the boiler 14 by passing into the foreline entrance and thence down through a conduit 53, through the line 43 into the boiler 14. Similarly, condensate from the surface of the barrel 12 returns to the boiler via the lines 53 and 43.
  • the foreline 16 of the diffusion pump includes a pair of peripheral alembics 17a and 17b, and lines 18a, 18b and 18c are provided to conduct condensed fluid away from the foreline 16.
  • Each of the lines 18 may be opened by a valve to a light end collection vessel 24 of lower pressure than that of the foreline 16, as shown in FIG. 1.
  • the lower line 53 which remains open to the interior of the boiler 14, returns to the boiler those condensates which have not been removed through the lines 18.
  • Electric heating tape 54 is wrapped around the foreline 16 from just above the line 53 to just below the backing pump line 19, so that temperature within the foreline 16 can be maintained at a predetermined, nearly consistent level along the length of the foreline.
  • a valved bottom drain line 56 is provided in the boiler 14 for draining the pump fluid 42 out of the boiler when the diffusion pump is not operating.
  • the glass walls of the boiler 14 include thermocouple inserts 57 and 58 for monitoring the temperature at various positions within the boiler 14.
  • the thermo-couple inserts 58 extend from the back of the boiler.
  • the foreline 16 also includes a thermocouple insert 59 for monitoring temperature at the position shown. Foreline pressure is monitored via the pressure gauge 26 shown in FIG. 1, while chamber pressure is monitored by the gauge 29, also shown in FIG. 1.
  • the 5 year old DC-705 oil produced a maximum test chamber vacuum of 5 X 10 torr.
  • the reason for the difference in ultimate vacuum between the G-4 test pump and the model pump illustrated in the figures, using the same 5 year old pump oil, is primarily that the model pump including a large number of joints between the diffusion pump barrel- 12 and the vacuum chamber 10 (some of which are seen in FIG. 1). These joints were not perfect but allowed a small amount of gas leakage into the system, consistently raising minimum attainable pressures in the system in all tests with the pump. Outgassing of gasket materials around joints also contributed to the gas load in the system.
  • chamber pressure often varied from about 10 torr to 5 X 10 torr.
  • a torpid evaporative surface appeared approximately of the time. For brief periods the evaporative surface would become 100% working. Between torpid and working periods, a surface previously described as schizoid would appear briefly, with numerous small working holes" present in the otherwise torpid surface.
  • lmproved chamber pressure always accompanied the 100% working periods, often lowering chamber pressure by 0.5 decade (five times). The l00% working evaporative surface appeared about 20% of the time during the first day of operation.
  • chamber vacuum reached improved levels of between 5 X 10 and l X 10 torr.
  • the working evaporative surface now appeared approximately 99% of the time.
  • the lightest most volatile light ends are the first light end contami nants to be collected in the forearm alembics 17a and 17b.
  • the alembics are drained of these lightest light end substances (the drain line 180 may also be opened), and pressure in the foreline progresses downwardly.
  • the next cut of light ends from the foreline occurs when pressure is somewhat lower, so that contaminants contained in the fluid removed from the alembics now comprise somewhat heavier, less volatile light light ends. If any of the lightest, most volatile light ends are still present within the system, they would be likely to be passed completely out of the foreline, through the line 19 toward the mechanical backing pump, under the new conditions.
  • the initial light end cut should be sufficient to remove nearly all of these most volatile substances, particularly if separation and salvage of the substances is desired.
  • light end contaminants continue to be removed.
  • the heaviest, least volatile light end substances can be largely removed from the foreline.
  • the pressure varies from lowest at the upstream end of the foreline to the highest at the downstream end adjacent the backing pump line 19. Light end substances of varying volatilities can thus be drawn from the lines 18a, 18b and 18c during operation of the pump.
  • the model self-cleansing diffusion pump system shown in FIGS. 1 and 2 was also tested using new DC 705 oil.
  • the vacuum chamber pressure gauge 29 indicated chamber pressure to be a consistent 5 X 10 torr.
  • a working evaporative surface existed about 10% of the time.
  • 6 ml of fluid containing light end impurities were removed from the foreline, 2 ml from each of the drain lines 18a, 18b and 18c, chamber pressure fell by 0.6 decade.
  • the evaporative surface became l00% working 25% of the time.
  • the three phthalate contaminants added were: di-isodecyl phthalate (DlOP-39O molecular weight); di-isodecyl phthalate (DlDP-446 M.W.); and di-octyl phthalate/di-2-ethylhexyl phthalate (DOP/DEHP-39O M.W.).
  • 2 ml of each contaminant were added directly into the pump fluid through the boiler contaminant adding device 28. The effect was an immediate, sharp rise in chamber pressure from about if) torr to about 2 X l0 torr, with chamber pressure stabilizing at about 7 X 10 torr.
  • chamber pressure dropped to 2.5 X 10 within 1 hour.
  • l0 ml of new DC-705 was added through the device 28 to prevent depletion of the boiler fluid supply during the pending cleansing period.
  • 2 ml of fluid containing light end fractions were 1 I removed from the upper alembic 17a of the forearm 16. This operation was repeated again within 30 minutes.
  • chamber pressure was reduced 3 decades, from 3 X torr to 2.5 X 10 torr. hours later, a chamber pressure of 8.5 X l0 torr was achieved.
  • model diffusion pump assembly established that a high level of motive fluid purity can be attained and maintained by utilization of the contaminant removal apparatus shown and described.
  • model pump further demonstrated that once heavy end contaminants have been initially skimmed from the evaporative surface in the pump boiler, heavy and light end contaminants both can be controlled to a large extent merely by periodic withdrawal of condensates from the foreline. This is due to the fact that after an initial skimming most recurring heavy ends in the boiler comprise polymerized molecules made up of light end molecules or light end molecules in combination with molecules of the basic motive fluid.
  • the model diffusion pump was subject to a number of limitations. Among these limitations were the large number of joints employed in the vicinity of the diffusion pump barrel and the foreline, and the size of the model diffusion pump. Nonetheless, the separation and purification capabilities of the model pump demonstrated that greatly improved pump performance can be attained employing the two types of modifications shown. An even higher degree of purification and contaminant separation can be attained with a third diffusion pump modification described below in connection with large existing pumps.
  • the third modification which could not be incorporated in the glass model pump, relates to apparatus within the diffusion pump barrel itself for separating out the extremely small quantities of light end substances which are only slightly below the molecular weight and slightly above the vapor pressure of the motive fluid itself. The separation of this type impurity cannot be completely accomplished within the diffusion pump foreline.
  • FIG. 3 A typical large diffusion pump 65 of the mushroom or inverted-nozzle type is shown in FIG. 3.
  • the pump 65 includes a concentric channel boiler 66, disposed at the bottom of a chimney and nozzle assembly 67.
  • the boiler 65 includes electrical resistance heating elements 68 disposed between concentric boiler channels for providing a large heating area, and a metal dome 69 receives conductive heat from the electrical heating elements 68 for assuring the vaporization of pump fluid striking it.
  • the boiler includes a valve drain line 71.
  • Surrounding the chimney and nozzle assembly 67 is a barrel 72 about which a cooling jacket 73 containing cooling lines 74 is usually wrapped.
  • the pump includes a foreline elbow pipe 75 leading through a foreline (not shown) to a mechanical backing pump (not shown).
  • the boiler 66 of the typical prior art diffusion pump 65 of FIG. 3 is shown in greater detail.
  • the boiler 66 includes three separate concentric annular boiler channels 78a, 78b and 78c.
  • the electrical resistance heating elements 68 are enclosed within conductive metal heating rings 79a and 79b, and 78b and 780. Communication is provided among all the boiler channels 78 by a break in the heating rings 79a and 79b. As seen at the left in FIG. 4, the rings 79a and 79b terminate in the vicinity of the drain line 71 and thus are C-shaped.
  • An annular flange 81 extends into the boiler from the chimney and nozzle assembly 67 above to prevent the travel of vaporized pump fluid directly into the diffusion pump barrel 72 rather than through the chimney 57 (see FIG. 3).
  • the flange 81 does not reach the boiler bottom.
  • the boiler 66 is designed to maximize contact between the motive fluid and heated surfaces. Some boilers include additional heating fins extending through several of the boiler channels 78 in zigzag fashion for additionally increased surface contact.
  • FIG. 5 shows a diffusion pump assembly 85 similar to the prior art diffusion pump 65 shown in FIGS. 3 and 4 but including self-purification and separation modifications according to the invention.
  • the modified pump 85 includes a boiler 86 with electrical resistance heating element rings 87, a dome 88, a filling and drain line 89, a chimney and nozzle assembly 90, a barrel 9] encircled by cooling jackets 92 and a foreline 93 connected through an opening 94 to a mechanical backing pump (not shown).
  • Heating means is provided about the foreline 93, and may comprise electric heating tape 95 wrapped around the foreline and covered by an insolating jacket 950.
  • the boiler 86 of the diffusion pump 85 is modified to provide evaporative surface skimming means from inner and outer positions.
  • skimming tubes 96a, 96b, 97a, 98a and 99a communicating through openings in the base of the dome 88 with the interior of the boiler at preferably four different levels.
  • Opposite skimming tubes 97b, 98b and 99b at the levels of 97a, 98a and 99a, respectively, are seen in FIG. 6. All of the skimming tubes are connected through valves 100 with a heavy end collection vessel 101.
  • the vessel 101 is connected through a valve line 102 with a source of lower pressure than that within the boiler 86.
  • a valved drain line 103 and a valved atmospheric bleed line 104 are also provided for periodically draining the liquid from the collection vessel 101.
  • Several outer skimming lines 106a, 106b, 107a and 108a are also seen in FIG. 5. These outer skimming lines are connected to a separate heavy end collection vessel 109.
  • the vessel 109 like the vessel 101, has valved lines 111, 112 and 113 connected to a vacuum source, a drain sump and the atmosphere, respectively.
  • FIGS. 6 and 7 indicate the various positions of the boiler skimming lines.
  • An additional valved outer line 114a not seen in FIG. 5, connects with the back side of the boiler 86, with a frontal line ll4b at the same level.
  • Lines 107b and l08b extend from the front of the boiler 86 at the level of lines 1070 and 108a, respectively.
  • the inner and outer skimming lines provide for boiler surface skimming at preferably four different levels, as indicated in FIG. 7.
  • Inner lines 960 and 96b and outer lines 106a and l06b are preferably positioned at the level of full boiler capacity, which is the 4 gallon level in many typical diffusion pumps.
  • An opening 105 is provided in the chimney flange 110 (similar to flange 81 of FIG.
  • the 4 pump) of the pump 85 to provide for surface communication throughout the boiler 86, as seen in FIG. 6.
  • the tubes 98a, 98b, 107a and 107b are preferably about l millimeters below the capacity level, while the tubes 99a, 9912, 108a and 108b are at about l millimeters below the capacity boiler level.
  • the multiple skimming levels provide for surface skimming when the pump fluid is at various levels below full, as well as at the full level. This allows for the loss of portions of the pump fluid after various stages of contaminant removal.
  • Means can be provided for automatically opening the proper skimming lines in correlation with the boiler fluid level, which can be ascertained by a sensor. Means (not shown) can also be provided for determining when skimming is required, by sensing evaporative surface behavior and/or vacuum chamber pressure.
  • the foreline 93 of the modified diffusion pump 85 is shown with purification and separation modifications.
  • the interior surface of the foreline 93 includes a series of alembic-like gutters or troughs 116, 117, 118, 119 and 120.
  • an elbow 122 of the foreline includes traps 123, 124 and 125 for catching condensates as they flow down along the elbow wall toward the boiler. The varies levels for condensate removal, from the top to the bottom of the foreline, provide for trapping of condensates of varying volatility, as discussed in connection with the model pump, and separate collection thereof.
  • Two valved lines extend from an upper level and from the bottom of each gutter and trap, respectively.
  • the reason for the bi-level fluid outlets is that the bottom of each gutter or trap, particularly in the traps and lower gutters, will usually contain nearly pure motive fluid.
  • the upper levels of the gutters and traps will contain fluid having high concentrations of condensed light end substances.
  • the lines 116b, 117b, 118b, etc. which lead into a collection vessel 127, are used primarily for recovering the basic motive fluid from the gutters and traps.
  • the vessel 127 includes a valved drain line 128 and valved lines 129 and 130 connected to a source of lower pressure than that of the foreline and to the atmosphere, respectively.
  • the valved lines 116a, 117a, 1 18a, etc., from the upper levels of the gutters and traps may be connected to separate collection vessels (not shown) if separation of fluids containing light end contaminants of varying volatilities is desired.
  • Each collection vessel would be provided with a drain line, a line leading to the source of lower pressure, and a bleed line to the atmosphere, as with the vessel 127. If separation is not desired, the upper level gutter and trap line may lead to a common collection vessel.
  • each of the gutters 116 through 120 can be provided with a condensing baffle above (not shown for clarity).
  • packing (not shown) can be provided in each gutter to increase effective condensing area.
  • packing might comprise, for example, stainless steel or another inert material in wire mesh or finely spun form.
  • a heating jacket 132 is positioned about the entire foreline 93 and functions in the same manner as the heating tape described above in connection with the model diffusion pump assembly 11. In addition to this function of bringing light end substances to high enough levels within the foreline for condensation and trapping in appropriate gutters, the heating jacket 132 also aids in the separation of light ends from the motive fluid within the gutters and traps, and their withdrawal through the lines 116a, 117a, 1180, etc.
  • the foreline wall is warmer than the gutter itself and other points within the interior of the foreline. This causes fluids contacting the foreline wall to convect upwardly along the foreline wall, thus creating a circulation pattern within the gutter.
  • the fluid circulation pattern is up along the wall, inward along the surface of the fluid, and then downward and outward along the bottom of the gutter toward the wall. This circulation pattern aids in bringing the lighter fluids toward the surface of the collected condensate. Since the light end fluid within each gutter is at conditions very close to its liquid-vapor equilibrium conditions, the light end condensate tends to move toward the liquid surface for incipient vaporization and actual vaporization to some extent. Polymerization of these light end fractions at gutter surfaces may also play an important part as to the ease in which a specific fraction is drawn from the surface into a vessel of lower pressure.
  • the preferred procedure for light end contaminant removal is the sequential opening of the a skimming lines, beginning with the trap line 1250 and ending with the uppermost gutter line 116a.
  • the withdrawn condensates of each gutter or trap can then be analyzed to determine the distribution pattern of light end contaminants for a given pump fluid and a given set of chamber conditions after a given period of time of pump operation. This operation can then be repeated after various periods of time, and the results can be used to automate the removal of foreline light end contaminants.
  • valves of the lines 125a, 124a, etc., through 116a can be programmed to be opened at predetermined times and for predetermined time periods for maximum light end contaminant removal and minimum withdrawal of the basic motive fluid.
  • fluid removal from the upper gutter line or lines can be timed to occur periodically according to past performance and analysis of withdrawn foreline condensates, or such removal can be made responsive to changes in vacuum chamber pressure. For example, if chamber pressure rises and is sustained at the higher level, fluid could be removed from the uppermost gutter line 1160 for several seconds, since such increased pressure would indicate the presence of volatile contaminants.
  • a sensor determines that chamber pressure is fluctuating, indicating the probable occurrence of alternate periods of working and torpid evaporative surface, the presence of heavy end contaminants within the boiler would be indicated.
  • the foreline skimming valves can again be programmed to remove fluid from the uppermost gutter 1160. If the pressure fluctuations then persist, a second boiler skimming operation from the appropriate level could be mandated by the automatic system.
  • each gutter fills with condensate and overflows into the next gutter or trap, and so on, eventually flowing through the elbow 122 of the foreline and returning to the boiler.
  • the waterfall effect prevails continually, involving all gutters except those being drained at any given time.
  • the withdrawn condensates can be separated by another means, such as a centrifugal molecu- 16 lar still as described in the above-referenced NASA Technical Memorandum X-68272.
  • diffusion pump barrel modifications shown in FIG. 5 may also be made.
  • the diffusion pump barrel 91 may include around its inner periphery condensate collection gutters 140, 150, 160 and 170. Between the gutters on the outside of the diffusion pump barrel 9] are the cooling jackets 92 which cool the barrel 91 for condensing the motive fluid and various contaminating fluids thereon.
  • the cooling jackets 92 are interrupted at the level of each gutter for the provision of a heating band 134 which extends around each gutter and is broken only at the location of draw off lines described below.
  • the bands 134 may comprise electric heating tape employed to heat the foreline 93, around the barrel wall at each gutter.
  • the modified diffusion pump barrel 9 acts as a high purification-separation still, as does the modified foreline 93.
  • the modified barrel 91 is capable of attaining a much higher degree of purification and separation than is the foreline 93, after the appropriate separation has been made by fluid withdrawal from the foreline gutters. After such separation, virtually the only remaining light end contaminants should be those very close in volatility to the basic motive fluid itself.
  • foreline modifications can only remove a portion of these heavy light end contaminants, leaving the rest to backstream within the pump barrel and reduce ultimate attainable chamber vacuum to some extent.
  • the diffusion pump barrel modifications described herein are designed to separate out extremely minute quantities of contaminants within the diffusion pump barrel, possibly in the parts per billion range. Foreline purification is conducted first in order that substantially only heavy light end contaminants remain in the barrel along with the motive fluid.
  • the ultra-high purification capability of the modified diffusion pump barrel 9] depends in part on the existence therein of large variations in pressure at different levels.
  • pressure above the top gutter after foreline purification may be around 10 torr, but around 10 torr near the gutter 150, in the 10 or ID torr range adjacent the next lower gutter 160, and around 10 torr near the lowest gutter 170.
  • the high degree of separation discussed can be achieved by utilizing this strong pressure gradient to condense heavy light end substances at varying levels depending upon volatility, and to separate such contaminants from the motive fluid itself.
  • the operation is very similar to that of the modified foreline 93.
  • the barrel gutters 140, 150 can be provided with packing (not shown) for increased condensing area.
  • packing can increase separation capabilities in the pump barrel 91.
  • a valved low pressure line 135 extends from the diffusion pump barrel 91 at a point above the highest gutter 140, where pressure is lower than that existing anywhere below in the diffusion pump barrel. This low pressure line 135 extends downward to serve a fluid collection system for each gutter in the manner described below.
  • a valved line 136 extends from the lower end of the line 135, leading to a holding vacuum pump (not shown) which may be the same mechanical backing pump that is connected to the foreline 93. This pump provides preliminary pressure reduction for the collection system and in fact can serve one or several of the lower gutters by itself, since these gutters are at higher pressure ranges.
  • a valved fluid draw off line 141 is positioned to deliver fluid into a collection vessel 142.
  • the line 141 when opened, withdraws condensates only from adjacent the upper surface of the fluid in the gutter 140, for reasons similar to those discussed in connection with the foreline modifications above.
  • the collection vessel 142 Since the collection vessel 142 must be at lower pressure than the pressure within the barrel 91 adjacent the gutter 140 in order to withdraw fluid from the gutter 140, it is connected by a valved line 143 to the low pressure line 135.
  • the vessel 142 like all low pressure collection vessels previously described, is also provided with a valved drain line 144 and an atmospheric bleed line 145, which must be opened in order to drain the vessel 142.
  • Extending from the bottom level of the gutter 140 is a valved gutter drain line 146 which connects into a lower gutter draw off line 151.
  • the line 143 is first opened to lower the pressure in the vessel 142. Then the line 141 is opened to draw fluid into the vessel 142. To drain the vessel 142, the lines 141 and 143 are closed, and the lines 144 and 145 are opened.
  • the fluid collection structure for the next lower barrel gutter 150 is similar to that above, with the reference numbers 151-156 describing similar elements.
  • Fluid drained from the lower portion of the gutter 140 through the line 146 may be drawn into the collection vessel 152 along with fluid from the top of the gutter 150 or drained into the gutter 150 to enrich the concentration therein of the particular fraction present in the gutter 140 bottom. This can be accomplished by sizing of the line 146 such that liquid is able to drip down therethrough, even though there is a slight pressure differential between the gutters 140 and 150.
  • the gutter 140 may be allowed to overflow into the gutter 150, thereby enriching the gutter 150 in the condensates of the gutter bottom 140.
  • the remaining diffusion pump barrel gutters 160 and 170 have fluid collection apparatus similar to that of the gutters 140 and 150 and numbered accordingly.
  • the valved gutter drain line 176 leading from the lower-most gutter 170 is connected into a collection vessel 182 having a valved line 183 leading to the low pressure line 135 and having drain and bleed lines 184 and 185 similar to those above.
  • a valved auxiliary boiler fluid add line 187 is provided, the purpose of which is described below.
  • the drain line 146 may be opened to drain the lower portion of the gutter 140 into the collection vessel 152 (or admitted to the next lower gutter as discussed above, for further enrichment processing). This would be accomplished by opening only the line 153 to lower the pressure within the vessel 152 below that adjacent the gutter 140, then opening the line 151 with the valve 157 closed, and opening the line 146.
  • the vessel When the fluid is collected in the vessel 152, the vessel could then be drained through the line 154 for analysis by closing the lines 151 and 153, opening the bleed line and then opening the line 154. If this condensate comprises nearly pure motive fluid, it can be re-admitted to the barrel and the boiler via the line 187. Condensates from the lower portions of the gutters 150 and can be drained similarly.
  • the gutter drain line 176 for the gutter is of course provided with its own collection vessel 182. During periods when the gutters are not being drawn from, the various condensates overflow successive gutters in a waterfall effect.
  • the pressure gradient within the diffusion pump barrel 91 is from lowest at the top to highest at the bottom, opposite that of the foreline 93, the lightest of the heavy light end substances would be expected to be found in the gutter 170, with the heaviest found in the gutters 140 and 150.
  • the lower three gutters, particularly the gutters 160 and 170 would also contain very small concentrations of the lightest of the heavy end contaminants in the fluid spectrum, which may escape the boiler skimming process.
  • the automatic operation of the diffusion pump barrel purification and separation apparatus described above may be programmed according to results of initial analysis. Variations in the type of pump fluid used, in the exact specifications of the pump boiler and fore-line, and in the conditions within the vacuum chamber will dictate drastically different results in the collection gutters 140-170. After such analysis, the opening of the fluid withdrawal lines can be sequenced and duration timed in order to provide maximum withdrawal of heavy light end and light heavy end contaminants with minimum withdrawal of basic motive fluid.
  • the diffusion pump assembly 85 including boiler, foreline and barrel modifications can be used as a slave" pump to a group of additional diffusion pumps serving the same vacuum system.
  • Each of the additional master pumps would have boiler and foreline modifications only.
  • the slave-master" relationship between the pumps would simply be one of boiler fluid exchange.
  • the slave pump shown in FIG. would dispense portions of its highly purified pump fluid from its boiler drain line 89 into the boilers of each of the master pumps. Such fluid would be admitted to each master pump through an auxiliary fluid adding line such as the line 187 shown in FIG. 5.
  • fluid from the boilers of the master pumps very pure but not to the extent of the fluid in the fully modified slave pump 85, would be taken from the boiler drain lines of each of the master pumps and delivered through the auxiliary fluid add line 187 into the slave pump 85 of FIG. 5.
  • Such circulation between the pumps could be accomplished slowly and continuously, but would preferably be done periodically, with the slave pump 85 exchanging fluid with only one other pump at a time.
  • the fluid purification and separation apparatus of the above-described difiusion pump including boiler, foreline and barrel modifications, can also be applied, in total or in part, purely as means of fluid separation in other disciplines apart from diffusion pumps and high vacuum production.
  • the surface heavy end skimming modifications of the invention can be employed in a fractionating column for the refining of petroleum.
  • Surface skimming such as that described herein can be employed at all evaporative surfaces in the refining process in the boiler and at each distillation plate in the fractionating column (not shown in the drawings).
  • the extremely high purification and separation capability of the foreline and barrel modifications described above can be employed, in total or in part, for the separation of the isotypes of uranium.
  • Raw feedstock uranium slurry would be heated in a boiler similar to the boiler 86 of the diffusion pump shown in FIG. 5.
  • means would preferably be provided for increasing condensing area, such as baffles over the foreline gutters and stainless steel packing within the foreline and barrel gutters (not shown).
  • baffles slow pump throughput but increase separation capabilities.
  • Gutter packing also increases separation capabilities.
  • the high vacuum and pressure gradient present in the diffusion pump barrel can be utilized to aid in the separation/enrichment of the isotopes of uranium.
  • Separation of metals from one another and from impurities can also be effected using the purification and separation apparatus described hereinabove, in total or in part.
  • the methods and apparatus of the invention are particularly adaptable for the separation of metals in the low and intermediate melting point range, such as those metals melting below about 2500F.
  • a diffusion pump for producing high vacuum including a boiler, a pump barrel, at least one nozzle downstream of and operatively associated with the boiler and cooperating with the barrel, a foreline operably connected to the barrel downstream of the nozzle and a roughing vacuum pump operably connected to the downstream end of the foreline, the improvement of a conduit providing communication between the interior of the pump at the level of the surface of fluid in the boiler and a low pressure source exterior of the pump, a valve in said conduit, means within the foreline for collecting liquid flowing down the walls thereof, a conduit providing communication between liquid in said collecting means and a low pressure source exterior of the pump, and a valve in said last-named conduit.
  • the apparatus of claim 1 which further includes means within the pump barrel for collecting and dis- 21 charging liquid flowing down the walls thereof.
  • the apparatus of claim 1 which further includes means positioned on the interior surface of the pump barrel for substantially isolating liquids of lower volatility than that of the pump fluid flowing down such interior surface, and means for discharging such liquid into a collection vessel external to the difi'usion pump.
  • the apparatus of claim I which further includes means positioned on the interior surface of the pump barrel for substantially isolating liquids of higher volatility than that of the pump fluid flowing down such interior surface, and means for discharging such liquid into a collection vessel external to the diffusion pump.
  • said isolating means comprises at least one liquid trapping gutter on the internal periphery of the pump barrel
  • said discharging means comprises a conduit providing communication between the gutter and the external collection vessel, a valve in last-named conduit, and means for lowering the pressure of said external collection vessel below that in the pump barrel at the level of the gutter.
  • the apparatus of claim 5 which further includes a second conduit extending from the barrel adjacent the gutter and providing communication between the gutter and a second conduit, said first-named gutter conduit being positioned at the level of the surface of fluid in the gutter and said second conduit being positioned at the bottom of the gutter, and means for lowering the pressure of said second external collection vessel below that in the pump barrel at the level of the gutter.
  • a method for purifying the fluid of a diffusion pump comprising withdrawing from the body of the fluid in the boiler at least a substantial portion of the upper surface thereof after vaporization from the body of the liquid has occurred; collecting and discharging from the foreline of the pump at least a portion of liquid flowing down the internal surface thereof: and collecting and discharging from the diffusion pump barrel at least a portion of liquid flowing down the internal surface thereof.
  • thermo-couple should be thermocouple.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
US522708A 1974-11-11 1974-11-11 Self-cleansing diffusion pump Expired - Lifetime US3923424A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
US522708A US3923424A (en) 1974-11-11 1974-11-11 Self-cleansing diffusion pump
US05/620,245 US4170522A (en) 1974-11-11 1975-10-06 Fluid refining method
CA238,019A CA1043286A (en) 1974-11-11 1975-10-21 Self-cleansing diffusion pump
GB43367/75A GB1528957A (en) 1974-11-11 1975-10-22 Method and apparatus for separating fractions of a liquid
DE19752550456 DE2550456A1 (de) 1974-11-11 1975-11-10 Verfahren und vorrichtung zum reinigen des arbeitsmittels einer diffusionspumpe

Applications Claiming Priority (1)

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US522708A US3923424A (en) 1974-11-11 1974-11-11 Self-cleansing diffusion pump

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US61980775A Division 1975-10-06 1975-10-06
US05/620,245 Division US4170522A (en) 1974-11-11 1975-10-06 Fluid refining method

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US3923424A true US3923424A (en) 1975-12-02

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CA (1) CA1043286A (de)
DE (1) DE2550456A1 (de)
GB (1) GB1528957A (de)

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DE4037935A1 (de) * 1990-11-23 1992-05-27 Mannesmann Ag Strahlverdichter fuer gasfoermige medien

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2080421A (en) * 1935-06-21 1937-05-18 Eastman Kodak Co Vacuum pump
US3034700A (en) * 1960-03-11 1962-05-15 Rochester Inst Tech Method of producing high vacuum
US3536420A (en) * 1969-04-01 1970-10-27 Atomic Energy Commission Condensate purifier for diffusion pump

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2080421A (en) * 1935-06-21 1937-05-18 Eastman Kodak Co Vacuum pump
US3034700A (en) * 1960-03-11 1962-05-15 Rochester Inst Tech Method of producing high vacuum
US3536420A (en) * 1969-04-01 1970-10-27 Atomic Energy Commission Condensate purifier for diffusion pump

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CA1043286A (en) 1978-11-28
DE2550456A1 (de) 1976-05-13

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