US3399826A

US3399826A - Pump with auxiliary vacuum pumping stage

Info

Publication number: US3399826A
Authority: US
Inventors: Andriulis Vytautas
Original assignee: Cenco Instruments Corp
Current assignee: Cenco Instruments Corp
Priority date: 1966-08-26
Filing date: 1966-08-26
Publication date: 1968-09-03
Anticipated expiration: 1985-09-03

Description

7 Sept. 3, 1968 v. ANDRIULIS 3,399,826

I PUMP WITH AUXILIARY VACUUM PUMPING STAGE Filed Aug. 26, 1966 6 Sheets-Sheet l IN VE/VTOR ga 4 @zafr M a'r By W +6244 ATTORNEYS p 1968 v. ANDRIULIS 3,399,826

PUMP WITH AUXILIARY VACUUM PUMPING STAGE Filed Aug. 26, 1966 6 Sheets-Sheet 2 IN VE/V TOR BY wm+ p 3, 1968 v. ANDRIULIS 3,399,826

PUMP WITH AUXILIARY VACUUM PUMPING STAGE Filed Aug. 26', 1966 I 6 Sheets-Sheet 5 I i i 294 v i l V t- A TTORNEYS Sept. 3, 1968 v. ANDRIULIS PUMP WITH AUXILIARY VACUUM PUMPING STAGE 6 Sheets-Sheet 4 EL: "um"! ATTORNEYS Sept. 3, 1968 v. ANDRIULIS PUMP WITH AUXILIARY VACUUM PUMPING STAGE 6 sheetses'neet 5 Filed Aug. 26, 1966 //v vs/v TOR 7,24,424 @zdwkfai:

m T A Sept. 3, 1968 v. ANDRIULIS 3,399,826

PUMP WITH AUXILIARY VACUUM PUMPING STAGE Filed Aug. 26, 1966 e Sheets-Sheet 6 IN VE/V TOR gZbaZa/S BY W A TTORNEYS United States Patent Oihce 3,399,826 Patented Sept. 3, 1968 3,399,826 PUMP WITH AUXILIARY VACUUM PUMPING STAGE Vytautas Andriulis, Chicago, IlL, assignor to Cenco Instruments Corp., Chicago, 111., a corporation of Delaware Filed Aug. 26, 1966, Ser. No. 575,392 33 Claims. (Cl. 230--152) This invention relates generally to mechanical vacuum pumps and more particularly is concerned with a type of mechanical vacuum pump known as a vane type. The invention is directed to a vane type of mechanical pump in which there is an additional pumping stage or additional stages operating at the same time that the principal stage or stages are operating.

The vane type of pump is of well-known construction. Basically the pump comprises a stator having a cylindrical interior chamber with a cylindrical rotor mounted for rotation within the chamber. The rotor is of a diameter substantially less than that of the chamber and its axis of rotation is spaced from the axis of the chamber, but is parallel therewith. In this manner, a crescent shaped pumping chamber is formed in the space defined between rotor and stator, the volume being a function of the size of the chamber and rotor, the spacing between axes and the axial length of the chamber and rotor. The chamber is enclosed on its ends and the rotor carries movable vanes mounted for radial reciprocation in suitable slots or grooves formed in the rotor. The vanes are of a length to extend between the end closure of the chamber and further, during rotation are pressed against the interior of the cylindrical walls of the chamber either by spring pressure, centrifugal force or both.

An intake port is provided at one location on the circumference of the chamber and an exhaust port on another. The ports are separated sufliciently with regard to the operation of the pump so that there is normally no transfer of fluid, either gas or liquid, between them, other than as provided by operation of the vanes.

By suitable geometrical design, the intake port is located to communicate with the chamber at a point on its circumference where the vane rotating past the intake port and continuing from there onward is at the same time moving radially because of the increasing size of the chamber defined between the vane and the intake port. With good efliciency and sealing, the fluid entering the chamber expands, and thus exerts a vacuum on the intake port and any structure with which said intake port communicates. Obviously the same vacuum is exerted on the interstices of the structure, such as the cleft or journalling engagement between the rotor and wall of the stator just on the circumferential side of the intake port opposite the direction in which the vane is moving. Conventional pumps use at least two diametrically mounted vanes, so that while the one vane is moving radially outward, the second vane is moving radially inward because it is 180 displace-d. Being pressed against the stator interior wall also, the second vane attempts to preserve the seal between intake and outlet ports so that all of the vacuum will be exerted on the intake port.

At the circumferential point that the first vane has reached its apogee of contact relative to the axis of the rotor, the second vane has reached its perigee. The volume subtended between the vanes on the intake port side is thereafter decreased but, since such volume is captured between vanes due to the passage of the second vane relative to the intake port, compression will occur and continue to occur until the first vane passes the exhaust port, at which time the pressure will be relieved into the exhaust port. Further, continued movement of the second vane will positively sweep the fluid in the chamber out of the exhaust port in a decreasing volume compressing action.

Of course while this is occurring, the same phenomenon is occurring on the other side of both vanes, so that in effect there is a dual pumping action for each stage of pumping that has two vanes.

In the art of such vane type mechanical pumps, it has become conventional to immerse the entire stage in a bath of oil, so that not only is lubrication more positive and constant, but in addition sealing between points of differential pressure may be achieved. When a pump has been standing for example, the entire chamber will usually fill up with oil, so that the first several rotations of the pump are depended upon to clear the chambers. The exhaust of such pumps is normally within housings carrying the oil and thence such exhaust may be led by tortuous passageways to the atmosphere or other suitable discharge vessels.

The artisan will recognize that the principal discussion herein is and will be related primarily to vacuum pumps in which it is desired to evacuate an external vessel or chamber, but this type of pump may also be used in apparatus for obtaining high pressure within an external vessel, where the intake port is connected to the atmosphere, for example, and the exhaust to the external vessel.

The vane pump described above is typical and conventional of known vane pumps. Multiple stages of such pumps comprise sets of rotor-vane combinations, all mounted in the same bath of oil, and with all of the rotors upon the same shaft, rotated by an external source of power. The swept volume of the respective stages of any multi-stage pump decreases due to the decrease in the volume of fluid being handled from stage to stage.

The auxiliary stage referred to herein in describing the invention is not the type of additional stage which is conventional in that it does not comprise the same type of rotor and stator but instead operates on an entirely different principle, although it is operating simultaneously with the operation of a single stage vane pump.

Pump design for the most part has heretofore been directed to variations of known structures. The desire of pump designers commonly is to achieve the following by way of improvement:

(a) the achievement of as high a vacuum as possible through the use of smaller apparatus utilizing as little power as possible;

(b) the achievement of better lubrication of moving parts with greater durability and reliability;

(0) the achievement of a better seal between points of pressure differential in the pump;

(d) the degassing of the oil which passes through the pump parts so that the vacuum achieved in the intake port is not spoiled due to occluded gasses in the lubricating oil;

(e) the achievement of improved gas ballast control.

As stated above, good engineering may often achieve a small degree of improvement in some of these, and in this respect the application of the teachings of the several arts will contribute some value. For example, improved metals and materials, improved chemicals and efficient hearings will help.

The invention herein also seeks as an important object to provide a pump with the above attributes, that is, improved vacuum, better lubrication, better sealing between points of differential pressure, a degassing of the pump oil and the achievement of better ballast control, but such object is achieved by a novel structure which, it is believed, has not heretofore been used and which produces important and substantial improvement in pump functions.

The invention has as other objects the provision of a pump of the vane type in which the vanes themselves in cooperation with their slots provide an auxiliary pumping stage which is used to great advantage, especially in the reduction of the pressure on the exhaust side of the pump, thereby increasing and improving the vacuum provided by the pump to a degree not heretofore believed capable of achievement with a vane type of pump.

Still another object of the invention is to provide a vane type of pump in which, through the use of the auxiliary stage to be described, seepage of oil is reduced in a novel manner.

Another object of the invention is to provide in a pump of this type novel means for regulating the pressure conditions and the lubrication within the pumping stage.

In connection with the immediately preceding object, the invention contemplates the provision of a novel automatically operated valve which is extremely sensitive and reliable for preventing oil and gas suck back, thereby further improving the efficiency of the pump.

Still a further object of the invention is to provide a vane pump of the character described in which the advantages and objects of the invention are achieved by means which are extremely simple and effective, hence economical and reliable.

In connection with the object set forth immediately above, again it is recognized that one desirable characteristic which is sought by engineers in the pump field as well as in practically every field of endeavor is to design structures in such a way that they are simple and economical. In the present case, the invention utilizes a structure which is multi-functional and which provides many advantages and benefits never heretofore achieved. This structure is radically different, it is believed, from any which have been used in vane pumps prior to this time, an yet, in practicing the invention, the only important component which need be different from the components of conventional pumps is a single end plate. Means to preserve pressure in the vane chambers is a simple additional requirement, but one not being difficult or expensive to achieve.

As stated above, the principal structure which is characteristic of the invention is means for enabling the vanes to produce pumping action within their slots while at the same time producing pumping action in cooperation with the crescent shaped pumping chamber. All of the features and structure of the invention are built into the end plate over the pumping chamber; however, the configuration and contours of this novel end plate are practically conventional. Thus, conventional end plates may be modified simply and economically to achieve the benefits of the invention.

It will be understood from a study of the structure to be described that the modifiactions made to what would otherwise be a conventional end plate comprise the forming of certain arrangements of grooves, passageways, bores and connections therein. Certain valve structures are also mounted on this same end plate, so that almost every other element of the pump may be considered conventional. Again, it is emphasized, the novel structure of the end plate enables the pump to function in a manner not contemplated for any known vane pump.

Although the preferred embodiment has all of the principal structure which enables the new functions to be performed incorporated into the end plate, the broader aspect of the invention includes the feasibility of using pump components in addition to or other than the end plate for carrying the passageways, grooves, valves and the like. For example, the rotor may carry some of these means and the center mounting plate may likewise have some of this structure. The opposite end plate may also be used.

The objects and advantages pointed out above are not the only ones which result from the use and practice of the invention. Those who are skilled in this field with pumps of this nature will immediately recognize many attributes which are not specifically mentioned. Likewise, as the description of a preferred embodiment is set forth hereinafter, many ways will become apparent in which the invention and the various aspects thereof may be used to great and unusual advantage.

In the description of the preferred embodiment which follows an effort will be made to be as complete as possible, but in the interests of lucidity, certain explanations of details already known in this art will be curtailed. In the drawings, like reference numerals will be used Wherever feasible to designate the same or equivalent structures.

In the said drawings:

FIG. 1 is a side elevational view of a vane type mechanical pump constructed in accordance with the invention.

FIG. 2 is a sectional view taken generally along the line 22 of FIG. 4 and in the direction indicated, but portions are cut away and the section is not taken along the line 2--2 directly in order to show and enable the explanation of certain details.

FIG. 3 is a perspective view of a pumping stage somewhat diagrammatic in nature and with parts cut away, illustrating the construction contemplated by the invention, this view being used primarily to explain the principles of construction and operation of the invention.

FIG. 4 is a sectional view of the pump of FIGS. 1 and 2, taken generally along the line 4-4 of FIG. 2 and in the direction indicated, but with parts broken away and portions removed to show details.

FIG. 5 is a fragmentary perspective exploded view showing especially the inner end plate of the exhaust stage of the pump of FIG. 1.

FIG. 6 is an elevational view of inner aspect of the end plate of the exhaust stage of the pump of FIG. 1, such stage being the one that is constructed in accordance with the invention, certain parts being in section, and other parts of the same stage being shown in phantom.

FIG. 7 is an elevational view of the outer aspect of the end plate of FIG. 6 with parts broken away and shown in section.

FIG. 8 is an exploded perspective view of the intake stage of the pump of FIG. 1.

FIG. 9 is an exploded top plan view of the pump of FIG. 1.

FIG. 10 is a perspective view of the stator of the exhaust stage of the pump of FIG. 1.

Generally, as previously stated, the invention is characterized by the provision of an auxiliary stage in a vane type of mechanical pump, such stage being achieved by utilizing the movement of the vanes within their slots to acquire a pumping action additional to that which the vanes exert outside of their slots. In moving from a position fully withdrawn into the slot in the rotor to a position fully extended, the vane contact with the stator moves from its perigee relative to the axis of the rotor to its apogee. At the same time, the radially inward end of the vane travels in its slot from a condition in which the volume of the slot is minimum to a condition in which the slot volume is maximum. The volume of the pumping chamber lagging the exterior portion of the vane in the crescent is also increasing and the intake port is connected with this space, as previously explained.

According to the invention, the vane slot of the vane which is acting to decrease the pressure of the intake port is connected by suitable passageways to the exhaust port. In a high efiiciency pump, the slightest improvement of the vacuum is important. What the decrease in pressure in the exhaust port does is to decrease the pressure differential between the intake and exhaust ports, thereby decreasing the likelihood of oil being passed through the interstices or joints of the pump back to the intake stage. Such backstreaming of oil will spoil the vacuum ultimately achieved. Furthermore, decreasing the pressure differential between the intake and exhaust ports will decrease the occlusion of gas Within the oil circulating through the pump since the gas at the exhaust port will have less tendency to become dissolved in the oil.

Other functions performed will be described with the description of the invention. Included in these are the novel structure for achieving a good seal, and the novel valving means for divers purposes described hereinafter.

Although described in connection with a two-stage pump, in which the first stage is a conventional intake stage using a vane pump, and the exhaust stage has the invention associated therewith, the structure of the invention may readily be applied to single stage pumps which do not have a prior intake stage.

Attention is first invited to the diagrammatic structure of FIG. 3 for a simplifiedversion of the invention and a discussion of the principles of operation and theory thereof.

In FIG. 3 there is illustrated in perspective exploded view a simple stator 20, rotor 22 and an end plate 24 which is constructed in accordance with the invention. The three components together with a front closure or end plate that is not shown will form the basic structure of a single stage vane type mechanical pump. The rotor is cylindrical and is journalled in the front closure by having the shaft 26 mounted in suitable bearings therein. The shaft 26 is also mounted in a bearing 28 the end of which may be seen mounted in the end plate 24.

The rotor 22 rotates within the cylindrical bore of the stator 20 but with its axis spaced from and parallel with the axis of said cylindrical bore so that a crescent shaped pumping chamber 30 is formed between the rotor and stator. Such crescent shaped pumping chamber will be referred to hereinafter as a crescent chamber 30 in order to distinguish it from the slot pumping chambers presently to be described.

The rotor 22 has axially extending

radial slots

32 and 34 on diametrically opposite sides thereof, each slot extending from a location quite close to the shaft 26 to the outer periphery of the rotor, so that in effect the

slots

32 and 34 are open at their radially outward ends. Each slot has a vane slidably mounted therein, the vane 36 being snugly but freely reciprocable within the slot 32 and the vane 38 being snugly but freely reciprocable within the slot 34. The

vanes

36 and 38 are substantially the same length as the radial depth of the slots, and are pressed outwardly when the rotor 22 rotates, by centrifugal force or by spring pressure or both.

Reference will be made hereinafter to slot pumping chambers and these are designated 40 and 42, being located radially inward of the

respective vanes

36 and 38 and defined by the radial inward edge of the vanes and the remaining portion of the respective slots not filled by the vanes. Obviously the

slot pumping chambers

40 and 42 will vary in volume, depending upon the relative rotative disposition of the rotor 22 and stator 20.

Assuming for the moment that the face 44 of the end plate 24 is imperforate, that is, without grooves or holes, the action of the pump is conventional. With rotation of the rotor 24 in the direction of the arcuate arrows, gas or other fluid is drawn in through the intake pipe 46 which opens at the top of the stator 20, passes through the intake port 48 of the stator 20 and into the left side of the crescent chamber 30. The pumping action which has been described as conventional occurs as the gas moves in a counterclockwise direction through the crescent chamber 30 with the movement of the rotor 22 and its reciprocating vanes, and finally passes out of the exhaust port 50, up the exhaust passageway 52 and out of the top of the stator 20 by way of the flutter valve 54. This flutter valve 54 is a simple flexible metal flap and if it is assumed that the exhaust passageway terminates below the level of oil in a pump casing, the valve 54 is needed to prevent entrance of oil into the crescent chamber 30.

Looking at FIG. 3, in the pumping stage there illustrated, there is an end plate engaged over the front of the stage, in a gas tight connection, and it has a journal through which the shaft 26 extends. An outside source of rotative power, such as an electric motor or the like is coupled to this shaft at either end thereof to drive the pump. Suitable conduits and connections therefor are coupled with the pipes 46 and 52. The end plate 24 is also engaged against the surface of the stator 20 in a gas tight connection.

As the

vanes

36 and 38 move radially inward and outward of their respective slots, the

slot pumping chambers

40 and 42 vary in volume in synchronism with the variation in volume of the crescent chamber 30 subtended between vanes. For example, in the disposition shown, as the portion of the chamber 30 to the right of the vanes is decreasing, the volume of the slot pumping chamber 40 is increasing, while the volume of the slot pumping chamber 42 is decreasing. The other relationships are believed obvious from this explanation.

According to the invention, the two

slot pumping chambers

40 and 42 are sealed from one another by any suitable means. If, for example, only centrifugal force were used to drive the

vanes

36 and 38 radially outward, there would be no need for a connection between them, and in this respect the differential pressure in the slot pumping chambers would be preserved. Individual springs suitably seated in the respective bottoms of the

slot pumping chambers

40 and 42 would also preserve the differential pressure and could be used with the invention. A common type of vane mounting utilizes a pin or tube and spring arrangement which extends fully through the shaft much like that structure shown in U.S. Patent 2,877,946 so that a single pin and a single spring will apply the spring bias to both vanes simultaneously. If such a struc- 'ture is used with the invention, it is necessary to prevent escape of fluid or gas between the slot pumping chambers. Actually, since it is believed that no prior structure uses these spaces for pumping it is probably incorrect to refer to them as such, but for the purpose of identification of these spaces in the prior art with the spaces of the structure of the invention, one may refer to them as slot pumping chambers.

In the preferred embodiment, to be described in more detail later, a single pin is used with hollow ends, a partition in the center, and individual springs disposed in each hollow end, the pin passing fully through the shaft. Thus, in FIG. 2, which is a detailed sectional view through a practical pump, the vanes are shown at 36 and 38, the slot pumping chambers at 40 and 42 and the shaft at 26. The portion of the rotor between the pumping chambers and the shaft 26 is designated 56 in both FIGS. 2 and 3, this being as narrow as practical in a radial direction, to permit as great a stroke as possible for the

reciprocating vanes

36 and 38, but with the view of maintaining the strength and rigidity of the rotor 22. The greater the stroke, the more eccentricity can be built into the pump.

A passageway through the shaft at 58 aligns with

passageways

60 and 62 extending through the portions 56 of the rotor 22, and a single tubular pin 64 is disposed in these passageways. The shaft 26 is keyed to the rotor as shown at 66 in FIG. 4. The pin has a central transverse partition 68 and otherwise is hollow, so that there are hollow bores formed at 70 and 72 opening to opposite ends of the pin 64. Helical coiled springs 74 and 76 carried in the respective hollow bores press the

respective vanes

36 and 38 radially outward. The total length of the tubular pin 64 must be less than the radial distance between the inner ends of the vanes.

Returning now to the discussion of the invention, in connection with the diagrammatic view, FIG. 3, it should be understood that each of the slot pumping chambers opens at its axial ends. Assuming that the front end cover which is not shown has a planar inner surface, the

slot pumping chambers

40 and 42 will have no communication with one another by way of the front end cover. As for the other end plate 24, the invention contemplates that the variation of pressures achieved by confining and controlling the slot pumping chambers will be used to advantage.

In the surface 44 of the end plate 24 there is provided an arcuate groove 80* Which is located radially outward of the shaft 26 so that it is in communication with the far end of the slot pumping chamber 40 as the vane 36 is passing over the general area of the surface 44 in the vicinity of the groove 80. This location is the left side of the pumping stage as shown in FIG. 3. Obviously, when the second vane comes over that area, the slot pumping chamber 42 will be in communication with the groove 80. In each case, the slot pumping chamber that is in communication with the groove 80 is in the process of increasing its volume, with a reduction of pressure of the gas contained within the respective slot pumping cham bers. Where a pump has more than two vanes, the slot pumping chambers will consecutively communicate with a groove like the one shown at 80.

This decrease of pressure is communicated to the exhaust pipe 52 for the purpose of reducing the pressure at the exhaust side of the pumping stage, and such pressure-reducing action occurs continuously and repeatedly with each passage of a vane relative to the groove 80. The communication is achieved by any suitable arrangement of grooves or passageways or bores. In FIG. 3 there is an arcuate passageway 82 illustrated confined within the end plate 24, with one end opening at 84 within the groove 80 and the other end opening at 86 in the end plate surface 44. A lateral branch passageway 88 connects the exhaust pipe 52 with the rear surface of the stator at the port 90 and when the stator 20 is tightly engaged against the surface 44, these

openings

90 and 86 will be in alignment and communication with one another.

It should be appreciated that the illustration in FIG. 3 is merely a diagram. It is quite difficult, if not impossible to drill a passageway like 82, although if the end plate 24 were cast the passageway could be cored. Likewise, split built-up sections could be joined into a unitary whole, in which case the passageway 82 as well as others to be described, could be grooved into interior faces prior to joining the sections.

The decrease in pressure at the exhaust pipe 52 is a very important function. When a pump exhausts to the atmosphere at a pressure which is substantially higher than that at the intake port of the stage, condensible vapors in the gas tend to condense and in this condition mix with the oil that must always be present in these pumps. Even the films of oil existing on the surfaces of the moving parts can take on occluded gases. In this gascarrying condition, oil tends to seep or move past the rotational parts toward the intake port, where the occluded gases tend to come out of solution in the oil, mixing with the incoming gas, thereby increasing its pressure and spoiling the vacuum. Reducing the pressure at the exhaust port tends to lower the differential pressure between the intake and exhaust sides, but also tends to decrease the amount of condensible vapors that will be absorbed into the oil. This in effect substantially decreases internal gas leakage of the pump.

Continuing with the discussion of FIG. 3, after the end of the groove has been passed, the slot pumping chamber 40 is contained. This occurs just before the vane 36 reaches its apogee of contact at the bottom of the crescent chamber 30, and immediately thereafter the vane 36 commences to move radially inward, decreasing the volume of the slot pumping chamber 40. A compression of gas will occur within this chamber as its volume decreases. The first use of the decrease in volume occurs when the slot pumping chamber 40 reaches the beginning of another arcuate groove 92 located in the surface 44 of the end plate 24. This groove must also be suitably located radially with respect to the shaft 26 to provide for such communication while the slot pumping chamber 40 is decreasing its volume. It is on the right hand side of the end plate 24 as viewed in FIG. 3.

If the groove 92 were long enough circumferentially its pressure would eventually rise with decrease of the volume of the vane pumping chamber 40, for example and probably exceed atmospheric pressure by the time the vane pumping chamber had moved a substantial arcuate distance along its length. Obviously the groove must be in communication with the slot pumping chamber. Under these circumstances a connection from the groove 92 to the atmosphere or the oil sump by Way of a unilateral valve would exhaust the groove 92 and the vane pumping chamber passing the same. The groove 92 is, however, quite short. It occurs quite close to the apogee of vane contact with the rotor. Its pressure is thus normally sub-atmospheric, and it thus affords a novel method of furnishing gas ballast to the pump. This will be explained shortly. There is an opening 96 in the groove 92 communicating with a passageway leading to the exhaust ballast valve 100. The exhaust passageway opening through the connection 140 to a flutter valve 142 on the rear face of the end plate 24 is for oil discharges as will be explained.

Now, in the upper part of the surface 44 of the end plate 24 there is provided an arcuate groove 102 which is so located that it is not in communication with the slot pumping chambers as they pass, and which is also located between the opening 86 as well as the exhaust port 50 and the bearing 28. On the inside of the arc defined by the groove 102 there are also located the groove 92 and a second exhaust recess 106 for a purpose to be described. These latter two small chambers formed in the face 44 are at much higher pressure than the exhaust port 50 and the opening 86, so that it is essential to seal these two

chambers

92 and 106 from the low pressure parts of the stage. This is done by maintaining oil under pressure in the groove 102 so that any tendency for leakage will be prevented by the presence of the cushion of oil in the interface space between surface 44 and the rear surfaces of the stator 20 and rotor 22.

Oil is admitted to the oil seal groove 102 through a small opening 108 that communicates by an internal branch passageway 110 and a long internal passageway 112 with an opening 114 in the plug 116 at the top of the end plate 24. This plug 116 is a part of the novel valve 120 reference to which has already been made. Since the stage is immersed in oil, oil enters the opening 114, and flows past the O-ring 122 only if the cap 124 has been raised on the piston portion 136. The oil flows down the passageway 112 directly to the bearing 28 to lubricate the same. It flows into the groove 102 and is maintained there, seeping out to lubricate and seal the interface space between rotating and sliding parts.

Referring now to the operation of the recess 106 in conjunction with the groove 92, note that the recess 106 communicates through the opening 128 with the passageway 130 that enters the center of the plug 116, passes through the top end by means of a small axial opening 132 and has a much larger side opening 134 that is normally covered by the cap 124. Note that the cap 124 is capable of riding freely up and down on the cylindrical piston portion 136 of the plug 116, being limited in its upward movement by the arm 138 of the stop bracket 139 fastened to the top of the end plate 24.

The vertical relationship between the

openings

114 and 134 is such that when the cap 124 starts to rise from a seated condition on the O-ring 122 at which condition no openings are uncovered, first the opening 114 will be uncovered and oil enters to lubricate the bearing 28 and provide the seal by means of the groove 102. Thereafter the side opening 134 is uncovered to permit oil and/ or air to be discharged.

The normal operating position is with the cap 124 fully up and both

openings

114 and 134 wide open. Oil can flow int-o the pump and air and/or oil can be exhausted from the pump during this condition. When the pump stops, oil is prevented from flowing back into the pump and air will not be sucked back into the pump since the cap moves int-o sealing engagement with the O-ring 122 in a single movement. The opening 132 provides the control for the valve 120, since by adjusting its size the movement of the cap may be controlled. The exhaust flow from the recess 106 is metered by the size of the opening 134.

As previously mentioned, the pump of the invention has novel structure for providing gas ballast. The groove 92 occurring at the location just after the apogee of contact of the vane 36 with the bottom inside surface of the stator is intended for a function primarily different from relief of the compressed gas in the slot pumping chamber 40. In the early phases of the pumping operation, oil will accumulate in all of the chambers of the pump, including the slot pumping chambers, and hence this groove 92 will primarily capture and expel oil in such early phases of pumping. In the practical device, there is a discharge opening with a flutter valve in the passageway that is equivalent to passageway 98. In FIG. 3 there is illustrated a short passageway 140 leading to the rear face of the end plate 24 where the discharge port is covered by some form of valve 142 which is unilateral.

Thus, after the pump has been started, while there is still considerable oil in the chambers, such oil will be flushed out of the groove 92 by way of the flutter valve 142. The pressure in the slot pumping chamber, such as for example 40, as it passes from the left to the right around the bottom of the stator 20, is still at sub-atmospheric, since the compression action of decrease of the slot pumping chamber has not yet fully commenced. Thus, there will be some air sucked in from the gas ballast valve 100 to aid in gas flushing. The important function of this groove, however, is additional. To appreciate this added function, the operation of the gas ballast in the ordinary vane type pump should be understood.

In the conventional vane type pump, there is a connection directly to the atmosphere from the exhaust port or the exhaust chamber. When the moving vane sweeps around the bottom of its crescent chamber, passing the apogee of contact with the interior of its stator, the pressure in the now-contracting portion of the chamber is quite low. Normally for a multi-stage pump, this could be below atmospheric. The atmospheric pressure from external of the pump is effective to introduce a quantity of gas into the exhausting side of the pump cycle, ahead of the sweeping vane. By the time the vane has reached the exhaust port, the chamber defined ahead of said vane and the point of closest engagement of the rotor and stator is considerably reduced in volume, and the pressure Within the chamber has risen considerably, normally increasing at the end of the cycle to above atmospheric. When the pressure in this last defined chamber rises to a predetermined value, the gas ballast valve will automatically close, preventing exit of gas through this valve, while also stopping the admission of gas. Most gas ballast valves have spring-pressed ball arrangements with adjustment of the maximum flow provided by a suitable needle valve. The spring pressure is chosen so that only a slight sub-atmospheric pressure is required to open it.

For the period of time that the conventional gas ballast valve is open admitting additional gas into the compressing chamber, there will be a larger quantity of gas within the chamber than provided by pumping action alone. Oil normally exists in the pump. Such oil will tend to foam and capture condensible vapors and gas, and the foam together with such gas remaining in the chamber will be flushed out the exhaust port. It is noted that oil will be forced out, whether foamed or not. The exhaust port normally is below the level of oil in the housing carrying the pump mechanism.

This theory of operation for conventional pumps has produced good results in the past, but problems of internal leakage and backstrearning of oil through interstices is a concomitant of increased pressure in the exhaust side of the last stage. Recall that the objects of the invention included providing a structure in which the pressure differential between the exhaust and intake ports of the pump was decreased. Any attempt to decrease the pressure in the exhaust area of a conventional vane type pump provided with gas ballast is a self-defeating act, since the action of the gas ballast is to increase the pressure.

Accordingly, that object of the invention and the structure which is used to accomplish the same is wholly unobvious to the skilled pump artisan since practically all high vacuum pumps of the vane type utilize gas ballast structures. In the invention, while gas ballast is used, it is not applied in the crescent chamber. In the structure according to the invention, the gas ballast is applied in a novel and unconventional manner, there being a valving action preferably, which is not readily apparent from a cursory examination of the drawings, but which will be clear with a short explanation.

The small groove 92 occurring as it does immediately after the

vane

36 or 38 has passed its apogee of contact at the bottom of the pump, when connected with the slot pumping chamber of the respective vane, will have very low pressure. Thus, the valve 100, which may be assumed to have a ball and spring arrangement to prevent discharge from it, will open and introduce a quantity of air into the groove 92. It may be assumed that this is occurring some time after the pump has been operating so that the oil in the slot pumping chamber and hence the groove 92 is normal. This gas is under atmospheric pressure and hence the pressure in the slot pumping chamber is raised at that point, say for example, in the chamber 40 passing around the bottom. The groove 92 is small, and hence, it is passed with little movement of the vane 36 in its counter-clockwise rotation. Accordingly, unlike the conventional vane pump in which the total pressure of the exhaust area is raised, there is no effect of such introduction of gas upon the crescent chamber 30. Instead, the movement of the rotor 22 disconnects the slot pumping chamber passing the groove 92 from that groove and its interconnected passageways.

Further rotation of the rotor 22 compresses the confined gas in the slot pumping chamber, increasing its pressure sooner to the exhaust valve limit pressure than it would have occurred without the introduction of air from the gas ballast system. By the time the vane has rotated around to the nearly vertical position, the slot pumping chamber is placed in communication with the recess 106, and the gas within this chamber is expelled through the opening 128 up the passageway 130 and out through the lateral passageway 134 in the plug 116. This results in a considerable flushing of the slot pumping chamber, but most importantly there is little or no effect upon the exhaust port 50 or the crescent chamber 30. Accordingly, the method described of re- 1 1 ducing the pressure in the exhaust port is very effective to decrease the pressure ditferential between exhaust and intake ports.

One might ask whether it is not true that the use of the gas ballast in the slot pumping chambers as opposed to the crescent chamber provides no flushing action in the crescent chamber. The fact is that the function of reducing the pressure in the exhaust port 50 substantially decreases the need for the flushing action, since the likelihood of vapors condensing is not as great as in conventional structures. It is further noted that the entrance of oil into the interstices will occur closer to the shaft 26 and hence there will be better opportunity for gas occlusion at points closer to the axis. Thus, the use of a rather high pressure flushing arrangement as described is quite effective, and no concern need be had that such gas ballast operation will adversely affect the ultimate vacuum, since the flushing system is insulated, as it were, by an arcuate wall of interface oil furnished by the groove 102, from the principal pumping chambers.

In considering the gas ballast function as described, one might liken the operation to the groove 92 being the instrumentality for enabling the passing slot pumping chamber to inhale a gulp of air, to hold it as the groove 92 is passed, to increase its pressure as the slot pumping chamber decreases in volume, and finally to expel it by way of the recess 106.

In the practical structure there is at least one intermediate groove between the recess 106 and the groove 92 together with passageways and valving arrangements to give substantial control over the operation of the gas ballast function, and to increase the efiiciency of the pumping action of the slot pumping chambers.

A consideration of the discussion just had and a study of the operation of the pump will indicate that a highly simplified version of the invention would have the groove 92 connected with the recess 106 so that there is no valving action. Such structure will provide at least some of the important advantages of the invention, either with or without the gas ballast structure. Considerable variation in the passageway arrangement and exhaust valves for the groove system can be made.

Having explained the principles of the invention and simplified structure in connection with the diagrammatic view of FIG. 3, a detailed description of a preferred practical embodiment will follow. The same reference numerals used in FIG. 3 will be used for equivalent structure wherever feasible.

The general structural concept of the practical pump 200 is that of a central plate 202 that serves as the standard for the entire structure. Right and left

casings

204 and 206 are bolted to the central plate 202 through suitable openings formed in the right and left casings. Such bolts are shown at 210 in FIG. 9 which is an exploded top plan view of the structure. The casing halves 204 and 206 are hollow and form the reservoir for the oil in which the entire pump mechanism is immersed. An oil level sight glass 212 is provided in the casing half 204 as shown in FIG. 2. As seen in FIG. 9 the pump mechanism comprises two stages, a first or intake stage 214 and a second or exhaust stage 216. These stages are secured to the central plate 202, which thus forms the end plate for each of the pumping stages, as will be explained. The securement is effected by the

bolts

218 and 220 so that the actual pumping mechanism in both cases hangs from the center plate 202. Usual gaskets are used in all interface engagements, but none are shown. When the

casings

204 and 206 are removed, the main mechanism of the pump is still fully assembled. This arrangement and the advantages which result are described in some detail in US. Patent 2,877,946 previously mentioned. While of considerable use in the construction of a practical pump according to the invention, any other method of construction may be used, such as for example, securing the parts to the housings, or to end stands, etc.

The pump 200 comprises two

stages

214 and 216, as stated, and in the structure illustrated little will be said about the intake or first stage since it is assumed to be of conventional vane type construction. The exhust stage 216 is constructed in accordance with the invention. It is desired to point out that although the discharge from the intake stage 214 is the intake of the second stage, it is a simple matter to construct a pump which has only a single stage constructed in accordance with the invention, in which case, the intake to the pump will be from the vacuum system. Likewise, if desired, both stages may be constructed in accordance with the invention.

In the drawings, the only views which show any details of the intake stage are the sectional view through the pump 200, namely FIG. 2 and the exploded view FIG 8. In FIG. 2 the stator 224 is shown bolted to the surface 226 of the central plate 202 through an end cover plate 228 of conventional construction, with the intake stage rotor 230 keyed at 232 to the shaft 26 for rotation within the stator 224. A crescent chamber 234 is formed in the stage 214 on the left side of FIG. 2 and the right side of the center plate 202 in FIG. 9. Vanes 236 reciprocate in suitable slots formed in the rotor 230, and a central pin and spring arrangement designated generally 240 urges the vanes radially outward. The construction of this latter means is of no consequence since the end plate 228 has a central cavity 242 which equalizes pressure in what would be the slot pumping chambers of both vanes.

Looking at FIG. 8, the central plate is hollow in places, such hollow formations being provided during the casting of the plate 202 by suitable cores. The intake fitting 244 (FIG. 4) is mounted in a port 246 which leads to a large cavity 248 formed in the upper part of the plate. The large cavity 248 beside saving weight forms an oil storage chamber to accumulate oil and prevent possible back-up of such oil into the system which is being evacuated. This fitting 244 will be connected to a vessel or system from which gas is to be pumped. The chamber 248 opens to a port 250 which may be seen in FIG. 8 on the surface 226 of the center plate 202. The stator 224 has crescent shaped recesses 254 in its front and rear surfaces, connected by a through passageway 256, these recesses 254 being in communication with the opening 250 so that for a considerable portion of the rotation of the rotor, as a vane 236 passes the recesses 254, there will be communication between the crescent chamber portion lagging the vane and the intake opening 250. Since the volume of gas being handled at this time is a maximum, it is best to have a large intake passage leading to the pumping chamber. This arrangement is conventional, and is best seen in FIG. 8.

Similar crescent shaped recesses 258 and a through passageway 260 are provided on the exhaust side of the stage 214 in the stator 224 to exhaust the gases. This is shown in FIG. 8 also, although the size of the recesses 258 is considerably less than the recesses 254. The entrance recesses 254 and the exhaust recesses 258 have configurations which are a matter of design, respectively, but the geometry with respect to the rotor 230 and its vanes 236 must be such that there is never communication directly between them across the top of the stator 224. The direction of rotation assumed in FIG. 8 is indicated by the arrows.

The rear one of the recesses 258 is engaged against the surface 226 in aligment with the opening 262. This opening 262 leads to an S-shaped passageway 264 in the center plate 202, the other end of the passageway 264 opening at 266 on the surface 268 of the center plate 202. Thus, the exhaust gases from the first stage 214 will pass through the passageway 264 to the second stage to become the intake of that stage.

As thus far described the stage 214 may be considered conventional. It operates as an intake stage, to eliminate the majority of gases from the system being evacuated. It also will act to discharge oil from the pumping chamber 235 in the beginning of the pumping action. For this purpose one or more large vertical risers 268 extend from the transverse passageway to the top of the stator 214 and are covered by a spring-pressed flutter valve 270 which opens to discharge oil and some gases during the earlier stages of the pumping action. If the pressure is high enough, even large quantities of gas may be expelled at this point prior to entering the finishing stage 216. This makes it much easier to start the pump and get the earlier phase of the pumping completed quickly since this would go slowly and require considerable power unless incompressible fluids could be thrown off without requiring them to pass completely through both stages.

It will be noted that an outgassing arrangement is provided in the intake stage. There is a groove 272 formed in the face 226 of the center plate 202 which leads to an annular recess 274 surrounding the shaft 26 at the large bearing 276 which is set into the center plate 202 Oil is supplied to the intake stage during operation by the clearances of the bearing 276. Oil will always tend to seep at this point during operation, and since all of the oil carries some occluded gases, the circulation of a portion of the exhaust gases around the annular recess and their subsequent withdrawal by the second stage tends to outgas the oil in that area. This is a simple structure which is capable of being utilized with conventional vane type pumping stages. Its use with the pump of the invention is preferred.

As mentioned previously the entire mechanism is immersed in a bath of oil. The discharge of gas and incompressible fluids by the flutter valve 270 and by other valve arrangements will normally occur below the level of the oil. The oil permeates the entire mechanism and finds its way into the needed interstices and clearances for lubrication and sealing, or is deliberately drawn or led into these locations. In FIG. 2 especially it will be seen that the oil chamber 280 is formed between the stages and the casing. The bottoms of the casing halves 204 and 206 are joined as shown to provide for continuous circulation of the oil while combining to form feet or a base for support of the pump. From time to time the oil may be drawn off at the bottom through a petcock 282. Additiona l oil is easily poured into the chamber 280 by way of the exhaust port 284 this being done by removing the exhaust silencer 286 while the pump is not operating. The construction of the casing and the center plate 202 provides considerable leeway for the formation of hollow spaces and cavities to lighten the metal castings used to form such parts, and to increase the oil capacity of the pump. These for the most part are not given reference characters since their configurations are matters of design dictated by good foundry and molding practice and by previous experience with other pumps of this general type.

The remainder of the description hereinafter relates to the second or exhaust stage 216, which as mentioned, is constructed in accordance with the invention.

The equivalent of the end plate which was referred to in connection with the discussion of FIG. 3 and not there illustrated is the center plate 202 since the stage 216 is engaged directly against the surface 268.

The exhaust or second stage of the practical pump comprises the stator within which the rotor 22 is arranged to rotate on the shaft 26. The rotor 22 is keyed to the shaft at 66. A description of the means for pressing the

vanes

36 and 38 radially outward has already been given, and just to review, there is a hollow-ended tubular pin 64 which engages in suitable passageways in the shaft 26 and the respective margins 56 of the rotor, carrying springs 74 and 76 in said ends pressing outward against the vane inside edges, there being a partition 68 in the center of the pin 64 to prevent transfer of gas between the two slot pumping chambers. Since the operation of the exhaust stage 216 is basically the same as the operation described in connection with FIG. 3, only the differences need be discussed.

First, the intake port 48 of the practical structure is in the form of crescent shaped recesses on opposite sides of the stator 20 shown in FIG. 4, these recesses opening along a portion of the circumference of the cylindrical bore of the stator. This is best shown in FIG. 10. Accordingly, the equivalent of the intake passageway may be considered the opening 266 on the face 268 of the center plate 202 and the crescent shaped recesses designated 48 and the through passageway 49. This latter type of construction, as noted by comparison with the ports of the stator 224 of the first stage 214 is conventional.

As for the exhaust port 50 of FIG. 3, its equivalent is found in the three openings 50 shown in FIG. 10 which open to risers 52 terminating in suitable ports at the top of the stator 20 as shown in FIG. 2. These ports are covered by a flutter valve 54 that is springpressed, and discharge occurs below the oil level which is indicated at 290. The flutter valve is also shown in FIGS. 4 and 9. The connecting passageway 88 from the face of the stator 20 to one of these risers is shown in FIGS. 2 and 10. It should be appreciated that the passageway 88 in effect may be said to connect with the exhaust port, or exhaust port area.

For a good understanding of the practical construction of the end plate 24, reference may be had to FIGS. 5, 6 and 7. FIG. 5 shows an elevational perspective view, FIG. 6 shows a front aspect elevational view but with certain parts of the stage in phantom to show the relationship, and FIG. 7 is a rear aspect elevational view with parts in section to illustrate details.

From a comparison with FIG. 3, it will be apparent that there is no internal passageway similar to the passageway 82. Instead, the groove has an elongate connecting groove portion 82 which is formed in the surface 44 of the end plate 24. This groove portion extends from the lower 'left hand area of the end plate 24 upward and across to the upper right hand area where it terminates at 86. In this construction there is no need for forming internal passageways, this long groove being the full equivalent of internal passageway 82. The movement of the

principal pumping vanes

36 and 38 will affect this groove very little, if at all, because the groove passes over the outer cylindrical path of the vanes as indicated at 292 at the point where the rotor 22 meets the stator. Here the stator and rotor practically touch, and in view of the good lubrication afforded because of the oil film described, there will be no practical communication between either the right or left halves of the crescent chamber 30. If anything, since the actual crossing of the line 292 occurs slightly to the right of the vertical center line, if there is leakage at this point, it will function to lower the pressure in the exhaust side, and hence be beneficial.

The groove 92 and the opening 96 are equivalents in the practical structure of the respective similarly identified elements of FIG. 3. In this case, however, the opening 96 connects with a horizontal passageway 98 opening from the right side (FIG. 6) and plugged at 294. The vertical passageway 99 intersects the horizontal passageway 98 and extends to a threaded socket 298 opening to the top of the end plate 24. Into this socket there is installed the gas ballast valve 100 which is best shown in FIG. 4. Its operation being known and well understood, it may be simply described. The body 300 is screwed into the socket 298. It has a ball valve element 302 pressed against a seat by a spring 304. A needle valve element 306 controlled by a hand wheel 308 mounted on a threaded shaft 310 provides a pre-set adjustment. The body extends through a fluid tight grommet 312 mounted in a suitable opening formed in the casing 206. Only a small piece of this casing is shown in FIG. 4.

The passageway 99 also connects by way of a transverse opening 140 with the outer wall of the end plate, and over this opening is the flutter valve 142. Fluid will be relieved through this passageway 140 and the flutter valve 142 only at the beginning phase of pumping when oil will be driven out of the pump.

The oil groove 102 and its passageways are clearly identified and related to the same structure of FIG. 3, while the groove 106 functions exactly as the recess 106 of FIG. 3. The passageway 130, of the practical srtucture, however, opens also to the rear face of the end plate 24 under the flutter valve 142 thereby providing an additional relief and control of the discharge from the slot pumping chambers at the end of their exhaust stroke.

The remaining groove 316 is intermediate the

grooves

92 and 106 and it has a connecting passageway 318 extending to the rear surface of the end plate and also opening under the flutter valve 142. This is another structure for relieving the oil from the slot pumping chambers near the beginning of the pumping action. Also, if pressure in the slot pumping chambers is high enough to cause the flutter valve to raise when the passing slot pumping chamber connects at the groove 316, the relief of gas pressure is advantageous. This structure therefore provides additional control of the gas ballast.

In all other respects, the practical structure is the equivalent of that described in connection with FIG. 3.

As seen in the illustrations of the practical structure, the plug 116 of the valve 120 is screw threaded into a socket 320 formed at the upper end of the passageway 130. This valve 120 takes the place of several valves since it has the multiple function of admitting oil and discharging gas. Variations can readily be made of the finishing stage, utilizing all of the benefits of the decrease of pressure in the exhaust area through the use of slot pumping chambers, without utilizing the particular multi-function valve 120.

The gas ballast valve is controlled from the exterior of the pump. As noted, the valve 100 passes through the casing 206 and into the socket 298 formed at the top of the end plate 24. Thus, it must be understood that the entire pump is fully assembled, but for the gas ballast valve, after which such valve is inserted into the grommet 312 and screwed home, using the flats formed at 322 on the body 300 to obtain a purchase.

The various flutter valves described, the gas ballast valve 100, the valve 120 and the sizes of holes and passageways of the pump as well as the dimensions of the functional components of these valves give a broad basis for adjustment to achieve complete control of the operation of the pump for various requirements and purposes. An attempt has been made to draw the parts of the practical pump to scale, but the dimensions will not be assumed by those skilled in this art to provide any critical basis for operation. Indeed, the pump operates over a wide range of variations in some of these factors with great reliability, and achieves results which indicate a substantially higher efiiciency of pumping than deemed feasible for prior mechanical pumps of the same size. Detailed and complex study of the sizes and dimensions of the various passageways and valves and their location could no doubt increase the efiiciency of the pump, but the basic improvement is substantial and a direct result of the structure described and claimed herein. Accordingly, a pump of a given capacity when constructed according to conventional methods will be substantially larger in size, weight and cost than a pump constructed according to the invention and having the same capacity.

Some of the details of the practical structure have not been described to any extent where they relate to conventional pump practice. These details, while of course necessary for the actual operation of the pump, do not relate directly to the novel aspects of the invention.

Some advantage in appreciating the nature of this invention will be obtained by studying such prior patents as the one already mentioned, namely, 2,877,946 and in addition another U.S. Patent 3,237,851. This latter patent relates especially to a novel outgassing method and one technique of construction which is capable of being used with the invention herein. In said patent, one stage is carried in a standard from which the entire pump is supported so that the second stage is carried upon the end plate covering the one stage. The invention herein may be applied to a pump construction of this type as well.

In FIG. 2, it will be seen that there is a seal 330 in the outer face of the end plate 24 surrounding the shaft 26 to attempt to preserve the pressure conditions within the exhaust stage when the pump is shut down. The air above the oil bath just outside of the end plate 24 is at atmospheric pressure. If the oil can be prevented from entering the exhaust stage due to atmospheric pressure when the pump is stopped for a while, it will be much easier to start up once more. The bearing and seal 332 for the shaft 26 at the point where the shaft passes through the casing 206 is set into a suitable boss 334 formed in the wall of the casing. Such bearing and seal assembly 332 is substantially the same as the equivalent construction of the pump of U.S. Patent 2,877,946.

In order to enable those skilled in this art to appreciate the invention, some of the specifications of the practical pump illustrated would be of value. The vertical height of the pump measured at the level of the boss 284 carrying the exhaust port is about 10% inches. The thickness of the center plate 202 is 1% inches. The width of the center plate at its base is about 8% inches. Each of the casing halves is about 3% inches wide so that the total length of the complete pump is about 9 inches. The principal rotor, stator, vane and pumping chamber dimensions are the same for both stages, The rotor diameters are approximately 4% inches, their thickness about 2% inches, the stator chambers have a diameter of about 4% inches, so that the eccentricity is about inch. The vanes have a length equal to the length of the rotors, and a thickness of about inch. Their radial length is about 1% inches, and the slot depths are the same as the radial length of the vanes. The end plate 24 of the finishing stage is inch. No fabrication difiiculties were encountered in having all of the described grooves, passageways and openings formed in this plate. It will also be noted that the multiple function valve 120, the flutter valve 142 and th gas ballast valve are all also mounted to this plate, so that to all intents and purposes, this is the only important major component of the pump which differs from conventional construction. This is true in the structure illustrated, but is a benefit and advantage flowing from the invention, and is not a requirement, as previously mentioned.

The pump having the above dimensions, and formed of a pair of stages, one constructed according to conventional practice and the other constructed in accordance with the invention had the following ratings and capacities.

Using a general purpose, one-half horsepower alternating current electric motor operating through a suitable power transmission to drive the shaft 26 at about 600 r.p.m., the capacity of the pump is rated at liters per minute for atmospheric pressure. This rating is based upon the pump intake being subjected to the atmosphere and the pump pumping air. With the pressure at the intake being one millitorr, the pump will handlee 75 liters per minute. Conventional vane type pumps of this same atmospheric pressure rating will take a considerably greater length of time to achieve the ultimate pressure capability of the pump. Conventional pumps are very much more noisy than the pump constructed according to the invention. The pump of the invention easily attains a vacuum at the intake of .05 millitorr and even better. This extent of vacuum is not readily obtained by a pump of the same atmospheric pressure rating, certainly not with ordinary production pumps. A conventional pump, specially constructed with high precision ,joints and bearings, with highly finished sliding surfaces and special seals might achieve this vacuum, but only at great expense. The same effort applied to a pump constructed according to the invention will produce better ratings and an even greater vacuum. The figures given are for a pump produced by ordinary factory production methods. a

Reference may be made in the claims to a stationary pump assembly in order to provide a designation for the combination of an assembled stator with two end plates. For example the stationary pump assembly of the exhaust stage comprises the stator 20, end plate 24 and the center plate 202. Since elements claimed could be in one or the other end plate, with or without also being in the stator, or could be in the stator and not in either end plate, this designation of stationary pump assembly is used generally to cover all variations.

Considerable variations in the details of the invention may be made without departing from the spirit thereof. For example, the groove system described and illustrated may be augmented with other grooves and passageways to achieve the desired results; it may be made more sophisticated by using a series of curved instead of straight grooves or a group of round recesses and so on; it may be arranged in the center plate in addition to or instead of being in the end plate; portions of the system might be provided in the stator, etc. The principal concepts are the manner of using the slot pumping chambers for decreasing the pressure in the exhaust area of the pump stage, the novel manner of introducing gas ballast, the novel discharge arrangements, the novel multi-function valve structure, and other described aspects of the structures.

What it is desired to secure by Letters Patent of the United States is:

1. A mechanical vacuum pump of the rotary, fluidse'aled, internal vane type mounted within a housing and having intake and exhaust connections on said housing and comprising,

(a) a stationary pump assembly on the interior of the housing and including a central stator and end plates and a cylindrical bore within the stator,

(b) an eccentrically mounted cylindrical rotor journalled for rotation within the stator and forming a crescent pumping chamber in said bore and having a plurality of slots and a vane in each slot, the vanes adapted to reciprocate within the respective slots during rotation of the rotor and engage the inner cylindrical wall of the bore to sweep the crescent chamber,

(c) an intake port and an exhaust port in the assembly on opposite sides of the perigee point of engagement of the vanes with the bore, rotation of the rotor acting to decrease the pressure of the intake port by action of the vanes moving through the crescent chamber,

(d) means isolating the inner ends of the slots from one another pressure-wise so that the reciprocation of the vanes produces a pressure variation in each slot in synchronism with the rotor, thereby constituting each of said inner ends a slot pumping chamber,

(e) passageway means in the pump assembly connected between a first location where the slot pumping chambers which consecutively pass will be in communication with said passageway means while passing said first location and will be expanding during passing, and a second location in the vicinity of the exhaust port, whereby to reduce the pressure of gas in said exhaust port during operation of the pump by action of the vanes moving in the slot pumping chambers.

2. The pump of claim 1 in which the said passageway means comprise a groove formed in the face of one of said end plates, said first location is at a point on said 18 end plate at which the vane of each slot which communicates while passing is close to its maximum extent of radially outward movement.

3. The pump of claim 2 in which the second location is spaced a distance substantially radially outward of the bore, and the groove passes the crescent chamber adjacent said perigee point.

4. The pump of claim 1 in which second passageway means are provided in the pump assembly connected from a third location where the slot pumping chambers which consecutively pass will be in communication with said second passageway means while the said chambers are decreasing in volume, respectively, to the interior of said pump assembly independently of said exhaust port.

5. The pump of claim 4 in which there is a unilateral valve in said second passageway means permitting discharge from but not intake to said second passageway means.

6. The pump of claim 4 in which the second passageway means has a gas ballast connection with the exterior of the pump at a portion of said third location immediately after the respective vanes pass the apogee point of engagement with said bore, and said connection to the exterior of the pump assembly comprising a fluid discharge path from a later-reached portion of said third location having unilateral valve means therein.

7. The pump of claim 6 in which the two portions of said third location are isolated fluid-wise from one another.

8. The pump of claim 7 in which there is an intermediate portion of the third location between the other two portions having another connection with the exterior of the pump assembly independently of said exhaust port.

9. The pump of claim 1 in which second passageway means are provided in the pump assembly and having at least two separate parts, one part including a first exposed opening at a third location where the slot pumping chambers consecutively passing will be in communication therewith immediately after the vane of the respective slot has passed its apogee point of engagement, the second part including a second exposed opening at a fourth location where the slot pumping chambers consecutively passing will be in communication therewith a substantial time after the vane of the respective slot has passed its apogee point of engagement and the pressure with'm the slot pumping chambers has substantially increased, the first part including a uni-lateral gas ballast connection from said first exposed opening extending to the exterior of the pump, the second part including a unilateral discharge connection extending from said second exposed opening to the exterior of said pump assembly.

10. The pump of claim 4 in which there is an oil seal in the pump assembly between the exhaust port and said third location.

11. The pump of claim 10 in which said oil seal comprises a groove in the end plate and a feed passageway from said groove to exterior of said pump assembly for enabling oil to be applied to said groove.

12. The pump of claim 4 in which the second passageway means comprise at least one recess formed in one end plate and there is an arcuate oil groove generally concave toward the axis of the rotor also formed in the said one end plate with the said recess on the concave side of the said groove, the exhaust port being on the convex side of said groove, and there being means to feed oil from exterior of said pump assembly to said groove.

13. The pump of claim 1 in which there are two vanes arranged in respective slots on diametrical opposite sides of the rotor, in which the first location in an arcuate area along which the slot pumping chambers are expanding in communication with said passageway means, and in which the second location is approximately diametrically opposite the first location but located at a substantially greater radial distance from the axis of the rotor than said first location.

14. The pump of claim 13 in which there are second passageway means having communication between a third location in an arcuate area along which the slot pumping chambers are compressing in communication with said second passageway means and the exterior of the pump assembly, but independent of said exhaust port.

15. The pump of claim 14 in which said passageway means include recesses in one of said end plates at said locations.

16. The pump of claim 1 in which the pump is of the oil-sealed variety, the housing is oil-filled, and the rotor is adapted to be driven from exterior of said housing, in which said pump assembly comprises an exhaust pumping stage, there being an intake pumping stage also disposed within the housing and mechanically coupled with said finishing stage, the intake on said housing being connected to the intake of said intake stage, the exhaust of said intake stage being connected to the intake port of said exhaust stage, the exhaust port of said exhaust stage being connected to the exhaust connection of said housing.

17. The pump of claim 4 in which the pump is of the oil-sealed, oil-filled variety, in which there is an oil groove formed in one end plate between the exhaust port and the third location, an oil-conducting passageway to the exterior of the pump assembly opening into said housing below the level of the oil in said housing, a valve member closing said oil-conducting passageway and means to move said valve member to open condition when the pump is operating.

18. The pump of claim 17 in which the second passageway means includes a gas discharge conduit, said valve member also closing said conduit, a jet extending from said gas discharge conduit against the interior of the valve member to move the same to open condition for both the gas discharge conduit and the oil conducting passageway, whereby when the pump is operating oil will enter the pump assembly and gas will leave by way of said valve member, but when the pump is quiescent, neither oil nor gas will enter the pump assembly.

19. A vacuum pump of the vane type including a stator, a pair of opposite end plates secured to the stator, a cy lindrical bore in the stator, a rotor eccentrically mounted in the stator for rotation and forming therewith a crescent pumping chamber and adapted to be coupled with a rotary power source, a plurality of vanes mounted in slots radially formed in the rotor and having their radially outer ends engaging the interior of the bore during rotation while sweeping the crescent chamber, an intake port in the stationary parts of the pump on one side of the narrowest point of the crescent chamber and an exhaust port in the stationary parts of the pump on the other side of the narrowest point of the crescent chamber, slot pumping chambers formed within the slots by action of the radially inner ends of the vanes in reciprocating in said slots during rotation of the rotor, means for connecting the slot pumping chambers respectively with the exhaust port while the slot pumping chambers are increasing in volume, and means for exhausting the slot pumping chambers externally of the pump independently of the exhaust port while the slot pumping chambers are decreasing in volume.

20. The vacuum pump of claim 19 in which means are provided for introducing gas ballast to the slot pumping chambers at the beginning of the portion of their action that they are decreasing in volume.

21. The pump of claim 19 in which there is an oil seal between the exhaust port and the slot pumping chambers.

22. The pump as claimed in claim 21 in which means are provided operated by the exhausting of the slot pumping chambers to introduce oil to said oil seal while the pump is operating, but acting to block the entrance of oil when the pump is quiescent.

23. The pump as claimed in claim 19 in which the means for connecting the slot pumping chambers with the exhaust port comprise a groove in one end plate commencing at a point where the passing slot pumping chambers have reached approximately their maximum value during expansion and extending in a generally curved path to the exhaust port.

24. The pump as claimed in claim 19 in which the means for exhausting the slot pumping chambers comprise at least one recess in an end plate at a point where the volume of the slot pumping chambers has decreased substantially, a passageway leading to the exterior of the pump, and a unilateral valve in the passageway.

25. The pump as claimed in claim 20 in which the means for exhausting the slot pumping chambers comprise at least one recess in said one end plate at a second point where the volume of the slot pumping chambers has decreased substantially, a passageway leading to the exterior of the pump and a unilateral valve in the passageway.

26. The pump as claimed in claim 23 in which the exhaust port opens on the interior of said bore and includes a connecting conduit extending to an edge of said stator, there being a transverse channel extending from the face of the stator which is in engagement with said one end plate to said connecting conduit, and in which the groove end opposite said point is in alignment with said channel.

27. The pump as claimed in claim 26 in which there is a unilateral valve blocking said conduit at said stator edge.

28. The pump as claimed in claim 24 in which there is a second recess in said end plate at a second point where the volume of the slot pumping chambers is just commencing to decrease, a gas ballast intake system connected to said second recess, and means for discharging incompressible fluid from said second recess.

29. The pump of claim 19 in which the last means comprise at least two independent recesses formed in one of said end plates consecutively along the path taken by the slot pumping chambers during the pumping cycle while they are decreasing in volume, one or both recesses being connected to discharge incompressible fluid through a flutter valve during the early pumping phases, the first having a gas ballast connection with unilateral entrance for bringing in exterior air to said slot pumping chambers, the second recess having a connection through a unilateral discharge valve for exhausting compressed gas and flushing fluids from said slot pumping chamber but only during operation of the pump whereby to deny entrance of fluids through said last connection when the pump is quiescent.

30. A multi-function valve for a vane-type, oil-sealed rotary pump, in which there is a pump assembly mounted in a housing immersed in oil, the pump assembly has a fluid discharge conduit requiring relief of fluid below the oil level, and has an internal structure requiring the introduction of oil thereinto, said valve comprising a pair of telescopic members, one being secured to the pump assembly and having three passageways therein, the second member being movable between two positions, one engaged against the pump assembly and the other raised from it, one passageway extending to said internal structure and having a lateral entrance closed during the engaged position, but opened during the raised position, the second and third passageways connected to said exhaust conduit, the second having a lateral entrance closed during the engaged position but opened during the raised position, the third passageway opening in an end of said first member in a confined space formed between telescopic members and serving to raise the second member by fluid discharged through said third passageway during pump operation.

31. The valve of claim 30 in which there are means limiting the raising movement of said second member.

32. The valve of claim 30 in which there is a sealing member on the pump assembly pressed by said second member when engaged against said pump assembly to seal the passageways.

21 33. A valve as claimed in claim 30 in which the structure requiring introduction of oil thereto comprises at least an oil seal between ports of said pump assembly.

References Cited UNITED STATES PATENTS 1,245,691 11/1917 Deysher 103-136 1,558,696 10/1925 Marion 103-136 1,854,692 4/1932 Cooper 230-207 Jones 230-45 Links 103-136 Garrison et a1 230-153 Wessling 230-152 Wessling et a1 230-153 FRED C. MATTERN, JR., Primary Examiner. WILBUR J. GOODLIN, Examiner.

Claims

1. A MECHANICAL VACUUM PUMP OF THE ROTARY, FLUIDSEALED, INTERNAL VANE TYPE MOUNTED WITHIN A HOUSING AND HAVING INTAKE AND EXHAUST CONNECTIONS ON SAID HOUSING AND COMPRISING, (A) A STATIONARY PUMP ASSEMBLY ON THE INTERIOR OF THE HOUSING AND INCLUDING A CENTRAL STATOR AND END PLATES AND A CYLINDRICAL BORE WITHIN THE STATOR, (B) AN ECCENTRICALLY MOUNTED CYLINDRICAL ROTOR JOURNALLED FOR ROTATION WITHIN THE STATOR AND FORMING A CRESCENT PUMPING CHAMBER IN SAID BORE AND HAVING A PLURALITY OF SLOTS AND A VANE IN EACH SLOT, THE VANES ADAPTED TO RECIPROCATE WITHIN THE RESPECTIVE SLOTS DURING ROTATION OF THE ROTOR AND ENGAGE THE INNER CYLINDRICAL WALL OF THE BORE TO SWEEP THE CRESCENT CHAMBER, (C) AN INTAKE PORT AND AN EXHAUST PORT IN THE ASSEMBLY ON OPPOSITE SIDES OF THE PERIGEE POINT OF ENGAGEMENT OF THE VANES WITH THE BORE, ROTATION OF THE ROTOR ACTING TO DECREASE THE PRESSURE OF THE INTAKE PORT BY ACTION OF THE VANES MOVING THROUGH THE CRESCENT CHAMBER,