US2950046A - High vacuum pump - Google Patents

Description

A. LORENZ HIGH vAcuuuPuu'P Filed Jan. 25, 1957 4 Sheets-Sheet 1 1 INVENTOR. /4Z5K7 [Mil/Z AITMVIKJ' Aug. 23, 1960 Filed Jan. 25, 1957 A. LORENZ HIGH VACUUM PUMP 4 Sheets-Sheet 2 z .20 a; 34 J0 20 I wmm-u mu [J i a Aug. 23, 1960 A. LORE'NZ HIGH'VACUUM PUMP 4 Sheets-Sheet 4 Filed Jan. 25, 1957 INVENTOR flux?" [mm/z BY 524$, mi t/ ArrUIA/[m United States Patent@ 2,950,046 111G1 1 VACU UM PUMP Albert Lorenz, Hanau (Main), Germany, assig'nor to W. C. Heraeus G.m.b.H., Hanau (Main), Germany, a German body corporate Filed Jan. 25, 1957, s61. N0. 636,405 Claims priority, application Germany Jan. 28, 1956 2 Claims, (Cl. 230-139) The present invention relates to new improvements in Rootsdype compressors for producing high vac'ua.

Roots-type compressors which have been well known for many years for the purpose of conveying and compressing gases, and more recently also for producing high vacua are positive displacement pumps operating substantially without friction. The gaps which are necessarily formed in such pumps between the walls of the pump housing and the rotary pistons are sealed on" by dynamic means. When used as a high-vacuum pump, a Roots-type compressor is generally applied in combination with a mechanical pump so as to form a second or high-vacuum stage following the first or fore-vacuum stage of said mechanical pump whereby the gas molecules passing from the first to the second pump have such a mean free path in the evacuated volumes as to seal the mentioned gaps the Roots-type pump effectively and dynamically and prevent any backilow of gas through these gaps.

Prior to this invention, the bearings of the rotating shafts of such Roots-type compressors when used as high-vacuum pumps were merely sealed by a sliding contact and thus constituted the source of serious pressure leaks.

It is one ofthe objects of the present invention to overcome these disadvantages of the known compressor designs by sealing these bearings of the rotating shafts by the application of the dynamic sealing principle by means of a fore-vacuum, and by covering these bearings toward the outside by evacuated chambers.

Depending upon the particularly requirements, these vacuum chambers must according to the invention be evacuated either to the same extent as the suction side of the pump, or the pump itself must be disposed between these chambers and the high-vacuum outlet or the coin tainer or apparatus to which such vacuum is applied so that oil vapors and the like cannot pass from the vacuum chambers to such container or apparatus.

Further objects, features, and advantages of the present invention will be apparent from the following detailed description thereof, particularly whe'n fread with reference to the accompanying drawings of several preferred embodiments'of the invention, in which Fig. 1 shows a cross-section through a Roofs-type highvacuum pump accordingto the invention;

Fig. 2 shows a longitudinal section taken along line A' -B of Fig. 1, showing a pump wherein the vacuum chambers are selectively connected either to the inlet or 'the muster the pump; 1

Fig. 3 shows another longitudinal section taken along line A B-of Fig; l, showing a modification of the-pump wherein the vacuum chambers may likewise be connected either to'tlie inlet 'or to the'outlet of the pump;

Fig. 4 shows-another longitudinalsection taken along line A-FBofFig; l, showing'a pump similar to that of Fig. 2 butprovided' with automatic reversingv means; while Fig. 5 shows a further longitudinal section taken along line A-B of Fig. 1, showing a pump similar to that of Fig. 3 but provided with automatic reversing means.

Referring to the drawings, the Roots-type high-vacuum pump according to the invention consists of a pump hous-' ing 1 having an inlet 2 and an outlet 3. The rotary shafts 4 and 5 on which the pistons and 11, respectively, are secured extend through housing 1. An electric motor 6 connected to a source of current by a cable 9 is connected to the drive shaft 4 for driving the same, and the rotation of shaft 4 is transmitted to shaft 5 by interengaging gears 7 and 8. Rotary pistons 10 and 11 are thus rotated in the direction shown in Fig. l by arrows 12 and 13 so as to displace and convey the gases supplied thereto through inlet 2.

The apertures 41, 42, 51, and 52in the walls of housing 1 through which the rotating shafts 4 and 5 pass into the housing and containing ball bearings, not shown, are sealed by vacuum chambers 14 and 15 directly adjacent to the end walls of housing 1. These vacuum chambers may, however, also be connected to each other. They are formed by hollow cap members 16 and 17, respectively, and parts of the end walls of housing -1 to which they are firmly secured so as to seal chambers 14 and 15 toward the outside. Vacuum chamber 15 contains gears 7 and 8 on the ends of shafts 4 and 5, respectively. As

, shown in the embodiments according to Figs. 2 and 4, cap

member 16 of chamber 14 is further provided with an aperture 43 for the passage of drive shaft 4 therethrough toward the motor 6 which is kept under the outer atmospheric pressure. In the embodiments according to Figs; 3 and 5, however, cap member 16 has an extension 19 thereon enlarging the size of chamber 14 and enclosing motor 6 so that the latter will also be under a vacuum. The lead-in wires 9 connecting the current supply with motor 6 are passed through the wall of extension 19 through a suitable aperture which is hermetically sealed. Since the Roots-type'pump according to these embodiments in which the motor is sealed-in within one of the vacuum chambers does not need any bearing, bushing or the like within the outer walls of its vacuum'chambers 14 and 15 for the passage of a rotating shaft which 0011- nects the inside of these chambers with the outer atmosphere, there is no possibility of any leak of pressure in these pumps.

Vacuum chamber 15 of the embodiments as shown in Figs. 2 and 3 is connected by two airtight conduits 20 and 21 with the inlet 2 and the outlet 3, respectively, while vacuum chamber 14 is likewise connected with the inlet and outlet by conduits 22 and 23, respectively. These conduits may either consist of pipe lines, as indicated in the drawings, or, if vacuum chambers 14 and 15 border directly on inlet 2 and outlet 3 and are merely separatedtherefrom by wall portions common to both, they may simply be formed by apertures in these wall portions.

Conduits 20 and 22 to inlet 2 and conduits 21 and 23 to outlet 3 terminate inscrew-threaded apertures 30, 31, 32,

and 33, respectively. Prior to starting the operation of thepump, these apertures either in the inlet 2, as shown in Fig. 2, or in outlet 3, asshown in Fig. 3, may be closed by screws 34 and 35.

In the embodiment of the invention as shown in Fig. 4, conduits 20, '21, 22, and 23 do not lead from vacuumchambers 14 and 15 directly to inlet 2 or outlet 3, respectively, but are interposed by electromagnetically operated valves 24, 25, 26, and 27, respectively, which,

in turn, are thenconnected-to the inlet and outlet by conduits 36, 37, 38, and 39, respectively. The operation of these valves is control-led by the vacuometer 44 through an electric control apparatus 18 so that, if

there isa poor vacuum in the fore-vacuum conduit 45 leading to the fore-pump, that is, at pressures there-' in above 10 Hg, vacuum chambers 14 and 15 will be connected with inlet 2, while if there is a higher vacuum, they will be connected with outlet 3.

In the embodiment as shown in Fig. 5, vacuum chambers 14 and 15 are each onlyprovided with one conduit 20 or 22 leading to valves 47 and 48, respectively. These valves may either produce a connection to inlet 2 through conduits 36 and 38 or to outlet 3 of pump housing 1 through conduits 37.and 39. Valves 47 and 48 are electromagnetically controlled by a vacuometer 744 through a control apparatus 18 as above described with respect to Fig. 4. The vacuometer is a pressure'controlled switch device which may be set to open or close the switch as the pressure rises or falls belowany predetermined absolute. pressure at the pump outlet.

The reversal of the position of valves 24, 25, 26, and 27- in the embodiment as shown in.Fig. 4 or of valves 47 and 48 in the embodiment. according to Fig. 5, or the insertion of screws 34 and .35 either into the, apertures 30 and 32 as shown in Fig. 2, or into apertures 31 and 33 as shown in Fig. 3 hasthe following advantages: 1 It is one of the greatest advantages of Roots-type high-vacuum pumps that they do not need any lubrication and operate entirely dry and without oil. Conserequired by the respective is being evacuated. If they are inserted into apertures 30 and 32 in inlet 2, the pressure range in which the oil might be forced into the interior of housing 1 will generally be passed so quickly that there will be no causes for any trouble.

Furthermore the vacuum, chambers 14. and 15 can be directly interconnected. As a consequence the connecting conduits and 21 may be left out; the conduits 22 and 23 will do in this particular case.

Eventually the vacuum chambers 14 and 15 can be connected to form a single vacuum chamber by means of joining pieces. Such a single vacuum chamber is e.g. shown in'Fig. l'to 5 of my previous pending application No. 490,316, filed February. 24,1955, now abandoned.

Although the invention has been described in detail with reference to certain now preferred examples and embodiments thereof, itwill be understood by those quently, they are totally unafiectedbydust as the lat,

ter is not retained by any oil film, and also by vapors as they cannot dissolve in any pump liquid, for example, oil, and will pass through the pump without forming any condensate therein. pump as such is entirely dry and free of oil, it is necessary to lubricate gears 7 and 8, as well as the ball bearings (not shown) in the apertures 41, 42, 51, and 52 in the walls of housing 1. For this purpose, an oil of a very low vapor pressure is used. appreciable gas current should occur, it might fiowalong apertures 41, 42, 51, and 52'toward the inside of pump housing 1 and thereby force the oil from the ball bearings into the housing. In order to avoid this, the present invention further proposes to connect vacuum chambers 14 and 15 with the inlet of the pump whenever there is a noticeable difference of pressure between chambers 14and 15 and the interior of housing 1, that is, whenever there 'is a poor vacuum or higher pressure. At such time, there will always be the same .or-a lower pressure in vacuum chambers 14 and 15 than atthe inside of pump housing 1.v Any oil vapors which might then be drawn into the pump from the vacuum chambers through the conduits 20 and 22 respectively will not be condensed in the pump. Therefore, if the pump is intended to operate within such highpressure range, screws 34 and 35 should then .be inserted into aper-. tures 31 and 33 in outlet 3 of housing 1, while apertures 30 and 32 in inlet 2 should be left open, as shown in Fig. 3, and valves 24, 25, 26, and 27 or 47 and 48, respectively, should then be adjusted by the vacuometer 44 so that conduits 36 and 38"will be open and conduits 37 and 39 willbe closed.

' If, however, the respective container or apparatus which is connected to inlet 2 is to be very highly evacuated, the oil vapors which penetrate into inlet 2 from vacuum chambers 14 and 15. could then continue to pass into such container or apparatus. At such times, it will be better if screws 34 and 35 be inserted into inlet 2, as shown in Fig. 2, and to allow the mentioned valves to connect the vacuum chambers'only with outlet 3. However, within this pressure range there is a very small difierence in pressure between outlet 3 and inlet 2 (even though the pressure ratio may increase far beyond 100), and therefor there is then very little danger that any oil might be forced out of the ball bearings in apertures 41, 42, 51, and 52 into the interior of housing 1.

1 This reversal of valves 24, 25, 26, and27 in the embodiment according to Fig. 4or of valves 47 and 48 as shown in Fig. 5 is carried out by them, automatically. Screws 34 and 35 in the embodiments shown in Figs. 1' and 2 are inserted into those apertures as'may' be Althoughthe inside of the If, however, an

skilled in. the art that various changes and modifications may be made without departing from, the spirit and scope of the invention as defined in the appended claims.

The invention having now been fully described and disclosed, that which is claimed as new is:

1. A Roots type vacuum pumpcomprising a pump casing 'havingan inlet and an outlet, a pair of impellers rotatable within the casing, a pair of shafts journaled in the casing and rotatably supporting the impellers in intermeshing relationship, theshafts extending outside the casing, gear means secured to the shafts outside the casing for intercoupling the two shafts, means secured to one of the shafts outside the casing for driving the impellers, means in combination with the casing defining a chamber enclosing the ends of the shafts projecting outside the casing, means defining passages connecting the chamber to the inlet and to the outlet, valve means in said passages for selectively connecting the chamber to the inlet or the outlet, pressure sensing meansconnected to the outlet of the pump casing, and means responsive to the pressure sensing means for operating said valve means to open up one or the other of said passages depending on the outlet pressure of the pump. 2. Apparatus as defined in claim 1 wherein said valve 7 operating means includes means for operating the valve References Cited in the file of this patent UNITED STATES PATENTS Re. 21,189 Price Aug. 29, 1939 1,038,075 Berrenberg Sept. 10, 1912 1,531,607 Green Mar. 31, 1925 1,641,840 Enyart Sept. 6, 1927 1,656,917 Kucher Jan. 24, 1928 1,669,050 Grant May 8, 1928 1,732,871 Wilsey Oct. 22, 1929 1,816,508 Wilsey July 28, 1931 1,898,914 Vickers Feb. 21, 1933 1,934,189 Grier Nov. 7, 1933 2,062,035 McCormack Nov. 24, 1936 2,062,045 Van Deventer Nov. 24, 1936 2,246,276 Davidson June 17, 1941 2,302,966 MacNeil et a1. Nov. 24, 1942 2,413,035 De Lancey Dec. 24, 1946 2,440,593 'Miller Apr. 27, 1948 2,444,773 Gondek July 6, 1948 2,525,619 Roth et a1. Oct. 10, 1 950 2,545,600 Berry Mar. 20, 1951 2,596,640 Berry May 13, 1952 2,620,124 Brill et a1. Dec. 2, 1952 2,690,291 Taylor Sept. 28, 1954 2,697,402 Lindquist Dec. 21, 1954 2,721,694 Van Atta Oct. 25, 1955 2,767,658. 1956 M r a g a- 2;.

container or apparatus which

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