![United States Patent [19] [1 1] Patent Number: 41,893,497 Danielson [45] Date of Patent: Jan](http://data.docslib.org/img/d80bc2e7345c1630797e3bed8c0963f8-1.webp)
United States Patent [19] [1 1] Patent Number: 41,893,497 Danielson [45] Date of Patent: Jan. 16, 1990
[54] LEAK DETECI'ION SYSTEM cle, “Will Tomorrow’s High-Vacuum Pumps be Uni versal or Highly Specialized?”. [76] Inventor: Philip Danielson, 5620 Main St., “Optimization of Molecular Drag Pumps”, by Louis Downers Grove, 111. 60516 Maurice. [21] Appl. No.: 193,810 Alcatel MDP 5010 (Molecular Drag Pump). [22] Filed: Sep. 12, 1988 Primary Examiner—Hezron E. Williams Assistant Examiner-Joseph W. Roskos [51] Int. Cl.4 ...... 601M 3/20 Attorney, Agent, or Firm-Milton Gerstein; Marvin [52] U.S. Cl...... 73/40.7 Ben [58] Field of Search ...... 73/40.7; 250/288, 289 [56] References Cited [57] ABSTRACT U.S. PATENT DOCUMENTS A leak-detection system for vacuum vessels and con tainers. A probe gas, such as helium, is detected ?owing 4,785,666 11/1988 Bergquist ...... 73/40.7 out of leaks in the vacuum vessel by directing such leaks OTHER PUBLICATIONS to the exhaust of a molecular drap pump providing a high vacuum to a mass spectrometer’s detection cham Jan, 1988, “Physics Today”, p. 2 Advertisement. her. The probe gas is injected with dynamic ?ow hav Alcatel Vacuum Products Advertisement. ing turbulent, laminar and transitional ?ow-characteris Veeco Advertisement for its MS-2O Leak Detector. tics. The helium ?ows rearwardly through the molecu Veeco Instruments, Inc. Brochure on Leak Detectors. lar drag pump by the process of cavitation and dynamic Balsers Advertisement on its HLT 100 Leak Detector. mixing until it is tranformed into molecular ?ow and In?con Brochure on its UL 100 Leak Detector. directed to the detection chamber of the mass spectrom Leybold-Heraeus, Inc. Leak Detection Equipment and eter for detection. A series of support pumps back up Accessories Brochure. the molecular drag pump, between any two of which In?con Ultratest M2ST Helium Sniffer Leak Detector. gross probe gas leaks may be introduced. The system of Thomas Industries, Inc. Brochures on Model Numbers the invention has application to pure gas separation of 2107CA; 2107CB; 2107CB; 004 CA 33; 004 CD 33; 004 one gas from a heavier gas. CD 33M and 004 CC 33. 1987 American Vacuum Society, Jul/Aug, 1987 arti 19 Claims, 1 Drawing Sheet
4,893,497 1 2 tremely low operating pressures. The additional advan LEAK DETECTION SYSTEM tage provided was the fact that turbomolecular pumps will pump heavy gases more readily and easily than BACKGROUND OF THE INVENTION lighter gases, such as helium, so that the technique of The present'invention is directed to a system for “Back-Diffusion” or “Counter-Flow” was developed detecting air leaks in vessels and containers in which a using the turbomolecular pumps, by which the probe vacuum is formed. Leak-detection in vessels and con helium gas to be detected was introduced at the outlet tainers used in a vacuum environment is well-known, of the exhaust of the turbomolecular pump, with the such detection utilizing the detection of leaks of helium probe helium diffused rearwardly through the turbomo previously pumped into the vacuum vessel expressly for p-l lecular pump until it reached the sensor probe of the the purpose of detecting potential leaks. Helium leak mass spectrometer, the heavier air molecules having detection is possible owing to the lightness of the gas been “?ltered out” or selectively eliminated by this and its concomitant small molecular size, allowing de process. The laws governing such diffusion are based on tection of even the smallest hole or tear. The leaking molecular ?ow and statistical thermodynamics. How helium is detected by a simple and conventional mass ever, as stated above, complex throttling valves are still spectrometer that is designed to detect only helium gas. required, owing to the extremely low exhaust pressure However, for such a mass spectrometer to operate ef at the pump outlet. fectively, such must be evacuated to high vacuum, The present invention is directed to a considerably which allows the probe, or leaking, helium to be drawn improved helium-leak detection system by which the into the detecting chamber of the mass spectrometer, detection-sensitivity is increased, oil-vapor diffusion is and detected by the helium-sensing head. However, completely obviated, and the use of a throttling valve is since the probe helium gas is traveling from an essen eliminated. The present invention has achieved such a tially atmospheric pressure environment to one of very high vacuum in the detecting chamber of the mass spec remarkable and improved leak-detection system by the trometer, complicated and expensive variable-leak use of the relatively recently-developed molecular drag throttling valves are required to allow for the introduc pump instead of the turbomolecular pump above tion of the higher pressure helium into the detection described. The molecular drag pump, which includes chamber of the mass spectrometer so that the helium the Gaede molecular drag pump, as well as the modern sensing head thereof is not adversely affected by a rise and greatly advanced version of the old Holweck in pressure. The complex throttling valve allows for pump, compresses a gas along the axial ?ow-direction, such introduction. In order to sustain the high vacuum in contradistinction to the turbomolecular pump which in the detection chamber of the mass spectrometer, a imparts compression transversely to the ?ow-direction. ' high vacuum pump is required. The original pump used In the disc-type molecular drag pump, such compres was a high-vacuum oil diffusion pump. Since oil vapors sion is achieved by a rotating rotor in which is formed from the pump would contaminate the mass spectrome a series of precisely-aligned and formed spiral grooves ter sensing headgliquid nitrogen traps were employed to that cooperate with several parallel helical grooves freeze‘ out the oil vapors before reaching the sensing formed in the stator. The use of the molecular drag head. The use of liquid nitrogen was and is a dif?cult pump in aleak-detection system has allowed for the and costly process, as well as requiring the maintenance above-noted advantages and improvements as com of an adequate supply. pared to the turbomolecular pump systems, since the An alternative to the use of oil diffusion pumps has outlet or exhaust pressure of the molecular drag pump is been the use of turbomolecular pumps, which has only of the order of one-thousand times that of the turbomo been commonplace within the last few years, owing to lecular pump: 30 torr as compared with 30 millitorr. the re?nement and development of these kinds of pumps. The turbomolecular pump is essentially an axial 45 SUMMARY OF THE INVENTION flow molecular turbine having a plurality of alternately It is, therefore, the primary objective of the present arranged slotted rotating blades and stationary stator invention to provide a leak detection system that elimi blades, with the relative velocity between the two sets nates the need of expensive and complex throttling of blades making it highly probable that a gas molecule valve structure, while also enhancing the overall sensi will be transported from the pump inlet to the pump outlet. Since the gas is compressed only slightly by each tivity of the system to probe-gas, leak detection. It is another objective of the present invention to stage, a series of such blades are required to achieve an effective compression ratio and workable and effective provide such a leak detection system that will allow for pressure differential. The turbomolecular pump deals the detection of ?ne or gross leaks of a vacuum vessel with molecular ?ow, with compression achieved via without any adverse effect on the mass spectrometer momenta-transfer from the high-speed rotating blades sensing head associated with the leak detection system to the gas molecules. The operating exhaust pressure is of the invention. in the range of about 30 millitorr, which extremely low It is yet another objective of the present invention to pressure, like the oil diffusion pump, has required com enhance probe-gas detection sensitivity to the leak de plex and expensive throttling valves to allow for the 60 tection system of the invention by eliminating the possi introduction of the probe helium gas into the sensing bility of oil-vapor contamination in the detection cham probe chamber, as explained above. The use of the ber of the mass spectrometer associated with the leak turbomolecular pump, however, was an advancement detection system of the invention. in that it more effectively prevented the simultaneous It is still a further objective of the present invention to introduction of oil vapors, though such was not com 65 ensure that the leak detection system of the invention is pletely eliminated as a problem, since an oil-sealed me readily capable of being used in repetitive fashion, so chanical pump was required in series with the turbomo that after one leak has been detected, the system may be lecular pump in order to achieve and sustain such ex used immediately again to detect another leak. 4,893,497 3 4 It is also an objective of the present invention to compared with prior art systems where even with com allow the detection system of the present invention to plex throttling, gross leaks are not detectable, since the be used for detecting other gases besides helium in other introduction of the probe gas leakage would destroy the applications besides vacuum-vessel leak detection. high-vacuum requirement of the exhaust port of the Toward these and other ends, the leak detection sys high-vacuum turbomolecular or diffusion pump. Also in tem of the present invention incorporates a molecular accordance with the present invention, in order to drag pump as the ?rst vacuum-forming pump for evacu allow for quick, repetitive use of the detection system ating the detection chamber of the mass spectrometer for detecting another leak in a vacuum-vessel or con whose probe detects the pressure of the probe gas he tainer, an air-purge valve is provided at the molecular .lium leaking from a hole or crack of a vacuum vessel or drag pump outlet, which air purging valve is operated container. The exhaust or outlet of the molecular drag after each leak-detection. This is necessary, since the pump is of the order of 30 torr, as compared with 30 helium is pumped at very slow speeds by the molecular millitorr of the turbomolecular pump or diffusion pump. drag pump and its supporting pumps, which tends to The very much greater exhaust pressure of the molecu saturate the system with helium, the air purge eliminat lar drag pump has obviated the need for complex throt ing the remaining helium so that the next test may be tling of the helium probe gas, as the pressure differen carried out. tials from atmospheric (760 torr) to the exhaust of the turbomolecular pump are minute as compared to that of BRIEF DESCRIPTION OF THE DRAWINGS the turbomolecular or diffusion pump. In accordance The invention will be more readily understood with with the present invention, the probe gas is introduced 20 reference to the accompany drawing, wherein: at the exhaust of the high vacuum pump—the molecular FIG. 1 is a schematic of the prior-art leak-detection drag pump—for ?ne or minute leaks, just as in the case system for detecting leaks in a vacuum-vessel or con of the turbomolecular pump system. However, whereas tainer; in the turbomolecular pump system, the helium pene FIG. 2 is a schematic of another prior art leak-detec trates into the mass spectrometer detection chamber via 25 tion system for detecting leaks in a vacuum-vessel or molecular ?ow called molecular counter-?ow or back container; and diffusion, the probe helium gas penetrates into the mass FIG. 3 is a schematic of the leak-detection system of spectrometer detection chamber via turbulent mixing or the present invention for detecting leaks in a vacuum cavitation, since the outflowing helium probe gas is not vessel or container. molecular flow but a combination of turbulent, laminar and transitional flow. The present invention is also DETAILED DESCRIPTION OF THE based on the discovery that light gases are very slowly INVENTION ~ pumped by a molecular pump, which discovery also has Referring now to the drawing in greater detail, import to the general concept of separation of gases, FIGS. 1 and 2 show two prior-art leak-detection sys and, therefore, to applications outside of helium, gas tems. The one shown in FIG. 1, which was the ?rst probe leak detection, to any application requiring the helium probe gas, leak-detection system in widespread detection or separation of one gas relative to others use, like all leak-detection systems, utilized a conven mixed therewith, which change of application is en tional mass spectrometer analysis cell 10, which is tuned abled by simple changes in systemic pressures associ for the mass of helium (m/e=4, atomic weight). The ated with the exhaust port of the molecular drag pump, probe gas, helium, is pumped into a vacuum vessel or and the inlet and outlet pressures of the associated, container to be tested, with the sensing probe of the back-up supporting pumps of the present invention for mass spectrometer 10 being used about the entire outer the high-vacuum, molecular drag pump of the inven circumferential surface of the vessel or container to tion. The present invention has substituted complex gas detect any out?ow of helium, which would then indi flow for the complex and expensive valving of the prior 45 cate an origin of a leak in the vessel, which may then be art systems. The high-vacuum, molecular drag pump of repaired. Connected to the mass spectrometer 10 is a the invention is supported by a series of supporting high-vacuum oil-diffusion pump 12, which creates a pumps; A ?rst pair of conventional diaphragm pumps, very high vacuum in the analysis cell’s chamber, which and a second pair of conventional piston pumps, all of high vacuum is typically less than 0.0002 millibar. The these support pumps being series-connected together 50 diffusion pump 12 typically has an exhaust pressure of and with the molecular drag pump. Such an arrange 30 millitorr. Owing to the very high vacuum required, ment achieves a continual rebalancing of pressures and the probe helium cannot be allowed to enter freely into flows, and gradually brings the last exhaust up to atmoé the analysis cell of the mass spectrometer, since such spheric pressure. By this very arrangement, very large probe gas is exiting the vacuum vessel at or near atmo and gross leaks may be detected, which hitherto has not spheric pressure, which would destroy the high vacuum been possible, by simply introducing the helium probe of the cell, and would, thus, render such cell inopera gas leakage at one of the other exhaust outlets of the tive. To overcome such problems, the prior art system other pumps, rather than the exhaust outlet of the mo of FIG. 1 utilizes a specially-designed, complex and lecular pump. The helium probe gas, by the same princi expensive throttling valve structure 14, which meters ple of turbulent mixing or cavitation, will flow rear the flowing helium and allows for the transition from wardly through the pumping system until it ?nally atmospheric to high vacuum to take place without ad reaches the mass spectrometer detection chamber for versely affecting the functioning of the analysis cell. detection in the usual fashion. Since the exhaust pres The probe helium is directly introduced, via the throt sure at any of the other support pumps is considerably tling valve structure, into the analysis cell of the mass greater than that of the exhaust of the molecular drag 65 spectrometer. A mechanical support pump 16 is con pump, and, of course, that of the turbomolecular pump nected to‘ the exhaust of the oil-diffusion pump to bring of prior art systems, not only is probe gas detection the exhaust up to atmospheric. The drawbacks with the possible, but even complex throttling is unnecessary, as system of FIG. 1 is not only the requirement for com 4,893,497 5 6 plex and expensive throttling valve structure, but the thereof, it is possible to introduce the probe helium gas contamination from oil vapors effused into the system at the exhaust of the molecular drag pump without the via the oil diffusion pump 12, which also necessitated requirement of first throttling, since molecular ?ow at the provision of liquid nitrogen traps to freeze out the the exhaust of the high-vacuum pump is not an issue, as oil vapors before reaching the cell’s sensing head. This it is in the systems of FIGS. 1 and 2. Thus, in the present had meant that a large supply of liquid nitrogen must be invention, the helium probe gas may be introduced into provided and maintained, which is costly and dif?cult. the detection system at the exhaust of the molecular The system of FIG. 1 is still in use to this day. drag pump without the need of expensive and complex A more recent prior-art leak-detection system is throttling valve structure, and without the need of spe shown in FIG. 2. This system utilizes a turbomolecular cial helium-selective gas barriers, the equivalent of the pump 22 to create the high vacuum in the analysis cell complex throttling technique, but is introduced by sim of the mass spectrometer 20. The turbomolecular 22 ple and conventional tubing. The molecular drag pump also operates at exhaust pressures of approximately 30 32 is backed by a series-connected, oil-free, dry, support millitorr. The turbomolecular pump 22 must be backed pumps to gradually bring the system up to atmospheric by a mechanical pump 24, which is an oil-sealed pump, at the outlet of the system. These support pumps are a posing the potential problem of oil-vapor contamination pair of series-connected diaphragm pumps 34, 36 such as in the system of FIG. 1. The main difference between as those manufactured by Thomas Industries, Inc. of the system of FIG. 2 with respect to the system of FIG. Sheboygan, Wisconsin, Model Nos. 2107CA, 2l07CB, 1 is that the probe helium gas is not introduced directly 2lO7CD, and a pair of series-connected piston pumps, into the analysis cell of the mass spectrometer 20, but is 38 40, such as those manufactured by Thomas Indus introduced at the exhaust of the turbomolecular pump tries, Inc., Model Nos. 0O4CA33, 004CD33M, 22. The helium thus introduced ?ows back into the 004CD33, and 004CC33. The molecular drag pump analysis cell chamber of the spectrometer 20 via what is 1 may be that manufactured by Alcatel Vacuum Prod called “counter-?ow” or “back-diffusion” through the ucts, Inc., of Hingham, Massachusetts, model MDP turbomolecular pump 22. The helium probe gas is intro 25 SOlO, which includes a Gaede-stage and a Holweck duced at the exhaust of the turbomolecular pump 22 via stage in series. The use of these support pumps is that on the same type of throttling valve structure 26 as that of the way to becoming atmospheric, the ?owing media of the system of FIG. 1, such being a prerequisite to the the system experiences a continual rebalancing of ?ow operation of the system of FIG. 2, since the exhaust and pressure between the pumps as the transition from pressure of the turbomolecular pump is so low, that any high vacuum to atmospheric is achieved. The use of introduction of the gas without such metering would oil-free pumps also prevents the potential hazards of make the system of FIG. 2 inoperative. The counter oil-vapor contamination, prevalent in prior-art systems. ?ow of the helium probe gas is possible since the ?ow of In accordance with the present invention, the system the helium from the throttling valve 26 is molecular of FIG. 3 introduces the helium probe gas between the ?ow. Statistical thermodynamics governs such flow, exhaust outlet of the molecular drag pump 32 and the ensuring the great probability that some of these mole inlet port of the diaphragm pump 34. In this manner, cules will ?ow backward through the pump and ?nally there is a semblance to that of the system of FIG. 2, in reach the sensing chamber of mass spectrometer for that the helium probe gas is introduced between the detection thereby. However, as explained, the system of high vacuum pump and a support pump. However, in FIG. 1 still requires the expensive and complex throt the present invention, such introduction of the helium tling of the gas into molecular flow, and still poses the probe gas is achieved without costly and complex throt same risk of oil-vapor contamination via the oil-sealed tling valve structure, but introduced with the all of the mechanical support pump 24, though the introduction naturally-occurring, complex flow characteristics of the probe gas at the exhaust of the high-vacuum thereof: Turbulent, laminar and transitional. According pump 22 rather than directly into the sensing chamber to the present invention, the helium is allowed to flow of mass spectrometer decreases the chances of such oil back into the sensing cell of the mass spectrometer 30 contamination and of inoperativeness of the sensing ~ by the processes of cavitation and turbulent mixing. chamber. Thus, the complex flow patterns of the helium stream The leak-detection system of the present invention is will ensure by these processes that some helium gas will shown schematically in FIG. 3, and includes a conven travel rearwardly through the molecular pump and into tional mass spectrometer 30 with helium sensing cell, as the sensing cell of the mass spectrometer 30. Such ?ow in the prior-art systems. However, the high-vacuum is not molecular flow, as in the case of the “back-diffu pump for creating and sustaining the high vacuum in the sion” or “counter-flow” of the system of FIG. 2, but is sensing cell is a molecular drag pump 32, which is quite complex flow that includes turbulent ?ow and the ensu different from the oil diffusion pump 12 and turbomo ing mixing and cavitation achieved thereby, which lecular pump 22. The flow through the molecular drag forces some helium rearwardly through the molecular pump is axially, as compared to the transverse flow of drag pump 32 by dynamic mixing. The molecular drag the turbomolecular pump, and has an operating exhaust pump will pump heavier gases, such as air, quite easily pressure of approximately 30 torr, as compared to the and readily. However, it will pump only very slightly 30 millitorr of the diffusion pump and turbomolecular 60 light gases, such as helium. Thus, the high vacuum, pump, which is of the order of one-thousand times molecular drag pump 32 creates and sustains the high greater. This much greater exhaust pressure of the mo vacuum in the sensing cell of the mass spectrometer, but lecular drag pump not only allows for the creation of will not readily pump out the helium flowing back the necessary vacuum in the analysis cell, but, also wardly therein, so that detection of the helium and the means that the ?ow at the exhaust thereof is not molecu 65 leak may be readily and very accurately achieved. lar but a combination of turbulent (viscous), laminar, The helium, as mentioned above, is introduced into and transitional ?ows. Thus, owing to this much greater the system of the invention between the molecular drag exhaust pressure, and ensuing nonmolecular flow pump 32 and the diaphragm pump 34. This is for ?ne or 4,893,497 7 8 small leaks. The helium thus introduced will experience and helium is the probe gas. However, the system of complex flow, including turbulence, which turbulence FIG. 3 may be used in other environments and applica arises from viscous flow conditions, vortex conditions tions, such as, for example, the separation of gases, such within the tubing connecting the helium to the system as hydrogen, from other gases; for separating gases proper, and due to the mechanical action of the pumps. from holes bored in the earth; and in nuclear reactors Before such helium is introduced, the system is in equi for separation of gases. This is accomplished since the librium with a no-flow state existing between the molecular drag pump will pump light gases very pumps. Upon the introduction of the helium stream, slowly, if at all, while readily and speedily pumping such equilibrium is destroyed, and a new “mixing” equi heavier gases. By selecting the appropriate operating librium will result, with the helium now dispersed along pressures and pumping speeds of the pumps 32-40 of the all of the different components of the system. The system of the invention, a chosen light gas may be sepa greater the pressure drop in any part of the system, the rated from ambient gas or carrier-gas by the same pro less helium present, although every part of the system cess of dynamic mixing and reverse ?ow, as described will have helium present. Thus, it is possible to intro above. In simple gas separation applications, the mass duce the helium probe gas at any juncture in the system spectrometer 30 is not needed, and is replaced with a of FIG. 3, and still have some helium mix via dynamic storage container for storing the separated gas. Depend mixing and flow rearwardly until it is present within the ing upon the ?ow conditions of the injected stream, sensing cell of the mass spectrometer. As mentioned such injected stream may be inputted or introduced above, for ?ne leaks, the helium is introduced between between two adjacent pumps of the series of pumps the exhaust of the molecular drag pump 32 and the inlet 32-40. In the preferred embodiment of leak-detection, port of the diaphragm pump 34. However, for large or the gas inputted or introduced is helium mixed with air, gross leaks, hitherto not possible of detection by the prior-art systems, the helium probe gas is introduced and the separation that occurs is the helium from the air, which is readily achieved since the molecular drag between the exhaust port of one of the support pumps and the adjacent inlet port of the next support pump, pump will readily and quickly pump air but will not do such as, for example, between the exhaust of the dia so for helium. The same principle applies in all other phragm pump 36 and the inlet port of the piston pump applications, where the one gas to be separated by the 38, as shown in FIG. 3. Owing to the greater amounts system of FIG. 3 is not readily pumped by the molecu being mixed with gross leaks as compared with ?ne lar drag pump or is pumped at least slower than the leaks, introduction further upstream of the helium probe remaining gas or gases from which separation is occur gas is possible in the system of the present invention, ring. Each application of the present invention will where the line pressures thereof are considerably require its own unique set of operating pressures for the greater than the exhaust port of the molecular drag inlets and outlets of the pumps 32-40, as well as unique pump 32, whereby the exhaust pressure, and thus the pumping speeds thereof, whereby these pressures and operation, of the high vacuum molecular drag pump 32 speeds will vary depending upon the particular gas will not be adversely affected by a sudden introduction being separated and the environment in which the gas is of a large volume of turbulent ?ow. For large or gross found. Thus, it may be seen that the present invention leaks, the probe gas may be injected between any two of has a wide application, applicable not only to vacuum the support pumps, depending upon the intensity of vessel leak-detection, but broadly to the separation of such leak. Since the helium is not readily pumped by the 40 gases in general, as long as the gases being separated molecular drag pump, there is provided an air purge via have different molecular weights. valve 44. This valve is used after each leak-detection, While a speci?c embodiment of the invention has and “flushes” the system clean from accumulated he been shown and described, it is to be understood that lium. If this air purge were not used, it would take days numerous changes and modi?cations may be made or even weeks for the molecular drag pump to pump 45 therein without departing from the scope, spirit and out all of the helium accumulated in the sensing cham intent of the invention as set forth in the appended ber. Operation of the conventional valve 44 provides a claims. stream of atmospheric air into the system, entraining all’ What I claim is: of the helium molecules, and allowing for the pumping 1. In a leak-detection system for detecting leaks in thereof, since air is readily pumped by the molecular vacuum vessels and containers, which system comprises drag pump 32, carrying along with it the entrained helium-detection means for sensing the presence of helium molecules. In the preferred embodiment, the air helium, which helium is a probe gas injected into a purge valve 44 is located at the exhaust of the molecular vacuum vessel or container being tested for leaks, high drag pump, where its effect is more immediate. vacuum pump means connected to said helium-detec In the preferred embodiment of the invention, in use 55 tion means for forming a high vacuum in said helium for detecting leaks in vacuum vessels via the probe gas detection means, means for directing helium probe gas helium, the equilibrium pressure at the exhaust of the from a leak to the outlet of said high-vacuum pump molecular drag pump and at the inlet to the diaphragm means, and support pump means connected to the outlet pump 34 is 3.4 torr; the pressure at the exhaust outlet of of said high-vacuum pump means for exhausting the the diaphragm pump 34 and the inlet port of the dia system to the environmental surroundings, the improve phragm pump 36 is 11 torr; the pressure at the exhaust ment comprising: port of the diaphragm pump 36 and the inlet of the said high-vacuum pump means comprising a molecu piston pump 38 is 30 torr; the pressure at the exhaust of lar drag pump having an inlet in ?uid communica the piston pump 38 and the inlet of the piston pump 40 tion with the interior of said helium-detection is 350 Torr; and the exhaust pressure of the outlet of the 65 means, and an outlet in fluid communication with piston pump 40 is, of course, 760 torr, atmospheric. As said means for directing. stated, there are the operating pressures when the sys 2. The improvement according to claim 1, wherein tem of FIG. 3 is used as a vacuum leak-detection system said means for directing introduces the helium probe 4,893,497 9 10 gas from a leak to said outlet of said molecular drag a third pump means having an inlet port connected to pump in a flow having turbulent ?ow characteristics. said outlet port of said second pump means, and an 3. The improvement according to claim 2, wherein outlet port, said second and third pump means said How also comprises laminar and transitional ?ow supporting said molecular drag pump; characteristics. means for introducing leaking probe gas into at least 4. The improvement according to claim 2, wherein one of said exhaust port of said molecular drag said means for directing comprises conduit means in pump and said exhaust port of said second pump ?uid communication with said outlet of said molecular means, whereby the probe gas by dynamic mixing drag pump for ?uidly coupling said outlet with the ?ows backwardly into said detecting chamber of leaking helium. said mass spectrometer. 5. The improvement according to claim 1, wherein 12. The leak-detection system according to claim 11, further comprising a fourth pump means having an inlet said support pump means comprises'at least one oil-free port connected to said exhaust port of said third pump pump having an inlet ?uidly coupled to said outlet of means, and an outlet port; and a ?fth pump means hav said molecular drag pump; said means for directing ing an inlet port connected to said exhaust port of said directing the leaking helium probe gas between said fourth pump means and outlet port, said fourth and ?fth outlet of said molecular drag pump and said inlet of said pump means serving also as support pumps, for bringing at least one oil-free pump. the exhaust of the system up to atmospheric. 6. The improvement according to claim 5, wherein 13. The leak-detection system according to claim 12, said support pump means comprises a plurality of oil 20 wherein said means for introducing leaking probe gas free dry pumps, at least one thereof being a dry dia further comprises means for introducing the leaking phragm pump and at least one thereof being a dry piston probe gas at the exhaust port of at least one of said third pump. and fourth pumps. 7. The improvement according to claim 6, wherein 14. The leak-detection according to claim 13, said support pump means comprises a pair of series-con 25 wherein each of said second and third pump means nected diaphragm pumps, and a pair of series-connected comprises a diaphragm pump, and each of said fourth piston pumps, said diaphragm pumps being positioned and ?fth pump means comprises a piston pump. upstream and closer to said molecular drag pump as 15. The leak-detection system according to claim 11, compared to said piston pumps, each said pump of said further comprising air purging means for injecting am support pump means comprising an inlet and an outlet. 30 bient gas into the exhaust port of one of said pump 8. The improvement according to claim 7, further means for purging the system of any accumulated probe comprising means for introducing leaking helium probe gas. gas between one said outlet of one said pump of said 16. The leak-detection system according to claim 15, support pump means and one said inlet of another, di wherein said probe gas is helium; and said means for rectly adjacent pump of said support pump means for 35 introducing the probe gas comprises means for injecting detecting gross leaks. helium to a respective said exhaust port such that the 9. The improvement according to claim 5, wherein helium has turbulent, laminar, and transitional ?ow support pump means comprises a plurality of dry pumps characteristics. connected in series, each of said plurality of pumps 17. A method of detecting leaks in a vacuum vessel or having an inlet and an outlet; and means for introducing container, into which a probe gas has been injected, leaking helium probe gas between one said outlet of one comprising: of said plurality of pumps and one said inlet of another, directing the out?ow of a leaking probe gas to the exhaust of a molecular drag pump; directly adjacent pump of said plurality of pumps, said step of directing comprising introducing the whereby gross leaks may be detected. out?ow such that it has dynamic flow properties of 10. The improvement according to claim 1, further turbulent, laminar, and transitional ?ows; comprising means for injecting a stream of higher-pres allowing the probe gas after said of directing to ?ow sure ambient gas into said outlet of said molecular drag upstream through the exhaust of the molecular pump for purging said helium-detection means and the drag pump toward the inlet of the molecular drag remainder of the system of accumulated helium. 50 pump whereby dynamic ?ow is converted to mo 11. A leak-detection system for detecting leaks in lecular ?ow; vacuum vessels and containers, comprising: sensing the molecular ?ow of the probe gas emanat a mass spectrometer comprising a detecting chamber ing from the inlet of the molecular drag pump, and means for sensing the presence of a probe gas whereby the probe gas is detected thereby. in said detecting chamber, said detecting chamber 55 18. The method according to claim 17, wherein said being evacuated to a high vacuum; step of directing comprises directing helium probe gas; ?rst pump means connected to said detecting cham and said step of sensing comprises sensing the presence ber for forming a high vacuum therein; of helium with a mass spectrometer. said ?rst pump means comprising a molecular drag 19. The method according to claim 17, further com pump having an inlet port coupled connected to prising the step of introducing an out?ow of probe gas said detecting chamber, and an outlet exhaust port; to the exhaust outlet of another pump supporting the second pump means having an inlet port connected to molecular drag pump, whereby gross leaks may be said exhaust port of said molecular drag pump, said detected. ’ second pump means also having an outlet port; * it * * 1k 65