US 2816702 A
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R. R. WOODCOCK PUMP 3 Sheets-Sheet 1 Filed Jan. 16. 1953 ATTORNEY 3 Sheets-Sheet 2 R. R. WOODCOCK PUMP Dec. .17, .1957
Filed Jan. 16. 1953 FIG 2 f fl%w R ATTORNEY Dec. 17, 1957- R. R. WOODCOCK PUMP . Filed Jan. 16. 1953 .s Sheets-Shej; :5
ATTORNEY United States Patent PUMP Robert R. Woodcock, Danvers, -Mass., assignor to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts Application January 16, 1953, Serial No. 331,572
4 Claims. Cl. 230-152 This invention .relates to rotary mechanical pumps, and more particularly to high vacuum mechanical pumps.
A principal object of the present invention is to provide an improved high vacuum pump of .a very light weight, having long life and ,capable of producing low ultimate pressures.
Another object of the invention is .to provide a pump of the above type which is simple to manufacture and maintain.
Still another object of the invention is to provide a pump of the above type which can be manufactured at a low cost and which can be readily adjusted to obtain the highest possible vacuum.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:
Fig. 1 is an exaggerated, diagrammatic, sectional view of one embodiment of the invention;
Fig. 2 is a fragmentary, cross sectional view taken along the line 22' of Fig. 1;
Fig. 3 is an enlarged, fragmentary view of a portion of Fig. l; and
Fig. 4 is a sectional view taken along the two sectional lines 4a-4a and 4b4b of Fig. 1, the right-hand portion of Fig. 4 being taken along the line 4a4a and the lefthand side of Fig. 4 being taken along the line 4b--.4b.
Numerous workers in the prior art have, for many years, endeavored to provide cheap, lightweight, reliable mechanical vacuum pumps. Many of these attempts have resulted in very complicated designs which involve diflicult machining operations, which are difficult to assemble satisfactorily initially, and which permit essentially no adjustment to compensate for wear in the moving parts of the pump.
The present invention is primarily directed to improvement in such pumps, and embodies the use, wherever possible, of readily available sizes of wrought metal plate, bar stock and tubing which can be easily fabricated and thereby greatly decrease the cost of the pump. Light weight, reliability, ease of maintenance, adjustability, and low ultimate blankoff pressure are prerequisites for vacuum pumps which are to be used in great numbers in connection with automatic machinery, such as radio tube manufacturing equipment and the like. The pump of the present invention is designed particularly for such use.
In the present invention the various improved results and low cost are achieved, without sacrificing the pump in-g speed, or the ultimate high vacuum, by providing a pump which includes a driven rotor, pumping vanes carice ried by the rotor, and a;hard sleeve defining a crescents'haped pumpingchamber with the rotor. The-pump also includes hard, thin endplates which bear directly on the two ends of the hard sleeve. 'For providing additional strength and sufiicient bulk for attaching various components to the pump, thereis also included a lightweight housing which surrounds the chamber-defining hard sleeve. Lightweight thick end plates are included for backing the .thin, hard end plates and also for providing bearings for the .pump rotor.
The lightweight portions of the pump are preferably formed of aluminum or magnesium alloys. These materials provide sufficient bulk-to furnish adequate volume for tapping studs and the like, and for supporting the necessary bearings without unduly adding to the weight of the pump. However, these lightweight materials, such as aluminum or magnesium alloys, have a coefficient of thermal expansion which is considerably greater than the hardened steel sleeve and rotor. Accordingly, the lightweight housing which surrounds the hard sleeve is made slightly shorter than the sleeve to provide a space at each end which permits the lightweight housing to expand with respect to the hard sleeve. In this space a compressible gasket, such as an O ring, is positioned.
In a preferred embodiment of the invention, the thin, hard end plates are held firmly against the ends of the hardened sleeve by means of lightweight end pieces which, in turn, are clamped towards each other by tie rods.
In the construction described briefly above, the pump chamber is defined by the hard sleeve and the hard thin end plates, these thin end plates bearing against the complete periphery of the ends of the hard sleeve. For forming a vacuum-tight seal around the pumping chamher, the compressible gasket which is positioned at each end of the lightweight housing is compressed between the thin end plates and the end of the lightweight housing, this compressible gasket thus completely seals the two ends of the pumping chamber Where the hard sleeve bears against the hard end plate. The compressible gasket, due to its compressibility, permits expansion of the lightweight housing with respect to the hard sleeve as this lightweight housing is heated up during the operation of the pump. It should be apparent, of course, that the expansion of the lightweight housing during use must be less than the distance between the end of this housing and the hard end plates.
In addition to the end seal feature of the pump, it also includes an improved arrangement for permitting positive adjustment of the internal clearance of the pump. This is achieved by providing a bridging means which is connected to both lightweight end plates and which carries means for moving the axis of the hard sleeve toward or away from the aXis of the pump rotor. In a preferred embodiment, this adjusting mechanism is arranged to permit positive readings, taken outside of the pump, to be absolutely correlated to internal clearances within the pump.
Referring now to the drawings, wherein like numbers refer to like elements in the various figures, it can be seen wherein the housing, which is generally indicated at 10, comprises a composite structure having an inner hard sleeve 12 and a lightweight outer housing 14. The inner housing 12 is preferably formed of hardened steel tubing which is ground to a high finish. Within the hardened sleeve 12 there is positioned a rotor 16 (see particularly Fig. 2) which defines with the sleeve 12 a crescent-shaped pumping space 18. As can be seen best from Fig. 2, the top part 12a of the sleeve 12 is ground to the same radius as the radius of the rotor 16 so that for an appreciable are (approximately 60) the portion 12 of the sleeve 12 and the surface of rotor 16 are spaced apart by a verysmall, essentially constant, distance.
The rotor 16 carries a plurality of pumping vanes 20, the rotor including a hollow spindle 22 which is supported by bearings 24 (Fig. 1) positioned in lightweight end plates 26. On the inner face of each lightweight end plate 26, there is provided a thin hard endplate 28 (see Figs. 1 and 3). A plurality of tie rods 30 clamp the lightweight end plates towards each other so that the thin, hard end plates 28 are pressed firmly against the ends of the hard sleeve 12. Since the lightweight housing 14, which surrounds the sleeve 12, is slightly shorter than the sleeve 12, there is a gap (indicated at 15 in Fig. 3) between the end of the housing 14 and the end plate 28. In order to prevent the possibility of any leakage between hard end plate 28 and lightweight end plate 26, a thin seal (not shown) may be provided. This seal can be a piece of thin (.0005 inch) oiled kraft paper or a coating of a vacuum grease.
The air to be pumped is admitted to the pumping chamber 18 through air inlet openings 32 (Fig. 2), and is discharged through openings 34, during discharge this air lifting a spring-loaded ball check valve 35. There is also provided a secondary air outlet 36 at the top of the pump. The pump outlet 36 also serves as an oil inlet to provide for a constant film of oil along the arc 12a to seal the space between arc 12a and the rotor 16.
Referring now to Fig. 3, the specific preferred embodiment of the seal at the end of the pumping chamber is shown in greater detail. This seal preferably comprises a compressible gasket 38, such as an O ring, positioned in a groove 40 provided in the end 'of the lightweight housing 14. As can be seen, the space 15 between the end of the housing and the thin, hard end plate 28 provides for expansion of the lightweight housing 14 with respect to the hard sleeve 12. The only result of this expansion is to compress the O ring 38 more firmly into the corner between the outside of the hard sleeve 12, the hard end plate 28, and the lightweight housing 14, thereby sealing this joint to form a vacuum-tight seal.
Another aspect of the invention, which is shown best in Fig. 4, is directed to the adjustment of the hard sleeve 12 with respect to the rotor 16. This is achieved by providing a bridging means extending between the end plates. This bridging means comprises a saddle block 42 positioned across the top of the pump. This block straddles the pump body and is rigidly fastened, by means of studs 44 and nuts 46, to the lightweight end plates 26. The spacing of the block 42 with respect to the axis of the rotor is rigidly controlled by the shoulders 48 on the ends of the block which bear on the tops 50 of the lightweight end pieces 26 (see right-hand side of Fig. 4). The top 50 of the end plate 26 is machined to a very close tolerance with respect to the axis of bearing 24. Consequently, the axis of the rotor 16 is positively fixed with respect to the top 50 of the end plate 26. This dimension between the rotor axis and the top 50 is indicated at A on Fig. 4. This block 42 also controls the position of lightweight housing 14 by means of an adjusting mechanism, preferably comprising a plurality of studs 52 which are tapped into housing 14 (see lefthand side of Fig. 4). Between the block 42 and the outer periphery of the lightweight housing 14, there is positioned a resilient gasket 54 which provides for relat1ve vertical movement between the lightweight housing 14 and the block 42. Since the lightweight housing 14 and the hard sleeve 12 are integrally connected together, a vert1cal movement of the lightweight housing 14 achieves the same vertical movement of the sleeve 12.
When gasket 54 is partially compressed, the top 50 is spaced from the inner surface 12a by the dimension B. When the difference between dimensions A and B equals the radius of the rotor 16, there is no spacing between arcuate surface 12a and rotor 16. While zero clearance might be desirable, it cannot be achieved with practical manufacturing techniques, since even the most minute imperfections in the surface of rotor 16 would 4 prevent rotation of the rotor. Additionally, it is highly desirable that there be sufficient clearance between the arcuate surface 12a and rotor 16 so that a film of 011 may be maintained between the top of the rotor and the arcuate surface 12a. This film of oil has the dual function of lubricating the pump rotor with respect to the surface 12a, and also of furnishing a vacuum seal which extends along substantially the whole arcuate sur face 12a.
Accordingly, dimension B is shortened by lifting studs 52 (rigidly connected to housing 14), this lifting being accomplished by rotating adjusting nuts 56 on the studs 52. This compresses gasket 54 and decreases dimensiori B sufficiently so that the spacing between surface 12a and the rotor 16 is on the order of afew ten-thousaiidths' of an inch. The optimum spacing will, naturally, depend on the viscosity of the oil used for the pump seal, the operating temperature, and the rotational speed.
The described construction also permits adjustmeijlt to decrease the spacingbetween arcute surface 12a and the rotor 16. This is achieved by a downward rriovemen't of the studs 52 which increases the spacing between the saddle block 42 and the body 14; This allows the resilf ient gasket 54 to expand, thereby decreasing the spacing between the rotor 16 and the are 12 1. Since the resiliency of the gasket 54 alone may not be quite adequate to force the housing 14 downwardly towards ifotot 16, particular ly whenthe tie b'olts 30 are clampedtig htly, it is desir able to include an additional means for positively fore ing this housing 14 downwardly. This may be accord: plished by providing studs 52a which are similar to studs 52, one of these being indicated in dotted lines in Fig. l. Studs 52a are preferably threaded in the saddle block 42 and bear against, rather than being threaded into, the top of the lightweight housing 14. The studs 52a may be provided at their upper ends with recesses for receiving an allen wrench or the like to permit rotation of the studs 52a. They may also be provided with lock nuts 56a.
The saddle block 42 also includes an oil reservoir 55 Within which a supply of lubricating oil 57 may be confined. The preferred embodiment of the illustrated pump also includes several other features which are shown in some detail in the various drawings. Among these are a spring 58 which bears lightly on the ball check valve 35 which seals the principal exhaust opening of the pump. Other details involve the use of pins 60 for supporting the pump vanes 20, these pins 60 being surrounded by lightweight springs 62 which press the pump vanes 20 outwardly to assure good contact with the inner face of the hard sleeve 12.
Lubricating oil passages 64 are provided for communication between the reservoir 55 and lubricating dimples 66 on the ends of the hollow spindle 22. These dimples carry small quantities of oil into lubricating passages 67 in the bearings 24, this oil passing to the ends of the hollow rotor spindle 22. Thence the oil passes into an oil passage 68 within the rotor spindle 22 and outwardly through lubricating holes 69 to the vanes 20.
The oil reservoir 55 also preferably includes a transparent plastic top 72 through which the condition of the oil and its level may be observed, and a vent 70 for the final discharge of all pumped air.
In a preferred embodiment of the pump, as mentioned briefly before, the sleeve 12 is preferably formed of hardened SAE 52100 steel which has been heat-treated, in one preferred example, to give a Rockwell of C60 plus. The rotor is preferably formed of a high alloy carburizing steel, such as SAE 8620, which may be case hardened to a Rockwell C-60. The hard, thin end plates 28 are preferably formed of hardened spring steel, and the lightweight portions of the pump (e. g., 14, 26 and 42) are preferably formed of wrought aluminum or magnesium alloys. The pump vanes are preferably formed of graphite or mixtures of carbon and graphite. The pump vanes may have lubricating slots (not shown) in the sides thereof to assist the passage of oil from behind the vanes sgsieg'rce .5 out to the'purnpingchamberi The" pump' vanes and the rotor are of essentially the same length. and are about .OOZ-inch shorter than the hardened sleeve 12. Due to thisspacing (.OOIinch at each end), the rotor doesnot acthally touch the hardened end plates 28 when in operation. However, the film of oil fed to the end bearings travels inwardlyto'the pump chamber and'forms a vacuum-tight seali between the rotor ends and the end plates.. In this connection, itvis preferred that'the hardened sleeve 12L be ground absolutely flat at its two ends so that it bears, accurately, throughout its thickness, on the end plate 28.
In assembling the pump described above, the rotor 16 and the vanes 20 are first assembled and are then slid into the composite structure formed 'by pressing the hardened sleeve 12 into the lightweight housing 14. The 0 rings 38 are then inserted in the grooves 40 in the two ends of the lightweight housing 14. The hardened steel end plates 28 and the lightweight end plates 26 are then assembled on the rotor spindle 22 and clamped together by means of the tie bolts 30. At this point the housing 14 and sleeve 12 are moved downwardly so that there is essentially no clearance between the inner surface 12a and the rotor 16 (i. -e., dimension B of Fig. 4 is maximum). The studs 52 are then fastened to the top of the outer housing 14. The gasket 54 is now placed in position, and the saddle block 42 is lowered into position over the studs 52. The saddle block is then securely bolted to the two end plates 26 by means of the studs 44 and nuts 46. This automatically compresses the gasket 54 and holds the hard sleeve 12 downwardly against rotor 16 so that the arcuate surface 12a is in metal-to-metal engagement with the rotor 16 throughout its length. At this point the rotor 16 cannot and should not be turned. Attempts to turn it would undoubtedly result in scoring of either the rotor or the arcuate surface 12a.
In order to accurately obtain the desired operating clearance, a pair of dial indicator gauges are mounted at each end of the saddle block 42, the probes of these dial indicator gauges being placed on the top of the lightweight housing 14. In order to permit contact of the probes with the metal surface of the housing 14, the gasket 54 is cut away along its central portions, this being most clearly indicated in Figs. 1 and 4. When the dial gauges have been set, the studs 52 are gradually lifted by operating adjusting nuts 56. This Permits positive measurement of the decrease in dimension B, and the consequent increase in the spacing between the top of the rotor 16 and the arcuate surface 12a.
As a result of this construction, the internal clearance in the pump may be positively gauged while the pump is sealed and only external adjustments are made. During the above described adjustment of the pump clearance, the stude 52a are backed off so that they do not interfere with the lifting of the housing 14 and the compression of the gasket 54.
After the pump has been initially adjusted, as described above, the ball check valve 35 and the spring 58 may be placed in position. Cover 72 may then be fastened to the top of the saddle block 42, and the oil reservoir may be filled with a supply of suitable pump oil.
In connection with the description of the assembly of the pump, it should be pointed out that the dimension B can be decreased even through the tie rods 30 are pressing the hard end plates 28 against the ends of the hardened steel sleeve 12, since a tremendous mechanical advantage is obtained by the use of the adjusting units 56. If desired, a final adjustment of the dimension B may be made while the pump is in operation, this adjustment being arranged to give the highest ultimate vacuum.
As will be apparent from the above description of the operation, construction and adjustment of the pump, it can be readily disassembled and reassembled. When wear takes place in the pump, the dimension B can be increased by lowering the studs 52. This lowering is achieved by backing off the adjusting nuts 56, and the tightening down isresilient, it wille-xpand during this downward move= ment of the housing-and will maintain anadequate seal at the top of the pump,
Sincecertain changes may bemade in the above appa ratus without: departing from the scope" of th'e inventionherein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.
What is claimed is:
1. A mechanical vacuum pump including a rotor, pumping vanes carried by the rotor, a hard sleeve defining a crescent-shaped pumping chamber with the rotor, hard thin end plates bearing directly on the two ends of the sleeve, the sleeve and hard end plates having appreciably harder surfaces than the pumping vanes, a lightweight housing surrounding said sleeve, lightweight end plates backing the thin hard end plates, the housing being slightly shorter than the sleeve and having a higher coefiicient of thermal expansion than the sleeve, bearing means supported by said lightweight end plates for supporting the rotor, fastening means for clamping said lightweight end plates towards each other, a circumferential groove in each end of said lightweight housing adjacent the ends of the hardened sleeve, 0 rings in the grooves forming vacuum-tight seals at the junctions between the hard sleeve, the hard end plates, and the lightweight housing means bridging said end plates, studs connected to said lightweight housing, means carried by the bridging means for moving the studs and the limited sealing area away from the axis of the pump rotor, and a resilient gasket between the bridging means and the lightweight housing, the gasket being sufficiently compressible to permit moving of the lightweight housing.
2. A mechanical vacuum pump including a rotor, pumping vanes carried by the rotor, a hard sleeve defining a crescent-shaped pumping chamber with the rotor, hard end plates bearing directly on the two ends of the sleeve,
a lightweight housing surrounding said sleeve, bearing means associated with the end plates for supporting the rotor, fastening means for clamping said end plates towards each other, said sleeve throughout most of its inner circumference having a radius greater than the radius of the rotor, said sleeve having a limited sealing area where its radius is substantially equal to the radius of the rotor, means bridging said end plates, studs connected to said lightweight housing, means carried by the bridging means for moving the studs and the limited sealing area away from the axis of the pump rotor, and a resilient gasket between the bridging means and the lightweight housing, the gasket being sufliciently compressible to permit moving of the lightweight housing.
3. The pump of claim 2 wherein said bridging means includes studs for positively forcing the limited sealing area towards the axis of the rotor.
4. A mechanical vacuum pump including a rotor, pumping vanes carried by the rotor, a hard sleeve defining a crescent-shaped pumping chamber with the rotor, hard thin end plates bearing directly on the two ends of the sleeve, a lightweight housing surrounding said sleeve, lightweight end plates backing the thin hard end plates, bearing means supported by said lightweight end plates for supporting the rotor, fastening means for clamping said lightweight end plates towards each other, said sleeve throughout most of its inner circumference having a radius greater than the radius of the rotor, a circumferential groove in each end of said lightweight housing adjacent the ends of the hardened sleeve, and an 0 ring in each groove forming a vacuum-tight seal at the junction between the hard sleeve, the hard end plate and the lightweight housing, said sleeve having a limited sealing area References Cited in the file of this patent UNITED STATES PATENTS Van Beresteyn June 28, 1904 Shore Sept. 14, 1915 Malbay Feb. 28,1928 King July 10, 1928 Curtis et a1 Nov. 30, 1948 Larsh Mar. 29, 1949 De Lancey et al. Feb. 16, 1954