US3064878A

US3064878A - Method and apparatus for high performance evacuation system

Info

Publication number: US3064878A
Application number: US706947A
Authority: US
Inventors: William H Bayles; Benjamin C Nash
Original assignee: Nash Engineering Co
Current assignee: Nash Engineering Co
Priority date: 1958-01-03
Filing date: 1958-01-03
Publication date: 1962-11-20
Anticipated expiration: 1979-11-20

Description

Nov. 20, 1962 w. H. BAYLES ETAL 3,064,878

METHOD AND APPARATUS FOR HIGH PERFORMANCE EVACUATION SYSTEM Filed Jan. 3, 1958 6 Sheets-Sheet 1 IN V EN TOR. William H. Bay/es an! Ben amin C. Nash .4 T TORNE Y3 Nov. 20, 1962 w. H. BAYLES ETAL 3,064,878

METHOD AND APPARATUS FOR HIGH PERFORMANCE EVACUATION SYSTEM Filed Jan. 3, 1958 6 Sheets-Sheet 2 IN VEN TOR. W/l/lqm 4t fid /EJ and Ben am? C. Nash A TTORNEYJ Nov. 20, 1962 w. H. BAYLES ETAL 3,064,378

METHOD AND APPARATUS FOR HIGH PERFORMANCE EVACUATION SYSTEM Filed Jan. 5, 1958 6 Sheets-Sheet 3 IN VEN TOR.

ATTORNEY Nov. 20, 1962 w. H. BAYLES ETAL 3,064,878

METHOD AND APPARATUS FOR HIGH PERFORMANCE EVACUATION SYSTEM Filed Jan. 3, 1958 6 Sheets-Sheet 4 INVEN TOR. wn/pm H. flay/es and Ben amin C. Nash ATTOfiNE S Nov. 20, 1962 w. H. BAYLES ETAL 3,064,878

METHOD AND APPARATUS FOR HIGH PERFORMANCE EVACUATION SYSTEM Filed Jan. 3, 1958 6 Sheets-Sheet 5 .lil

3 1/ CmAgwrORS 5w n/w'v MLU/ v A. 8/1 YLES M d-% 1 I m5 ATTOZ/S Nov. 20, 1962 w. H. BAYLES ETAL 3, 8

METHOD AND APPARATUS FOR HIGH PERFORMANCE EVACUATION SYSTEM Filed Jan. 5, 1958 s Sheets-Sheet 6 fix 1\ s zi/ INVENTORS flaw/mm C/Vmw BY Mu/4M h. 54 153 ATTO NEYS 3,064,878 METHGD AND APPARATUS FOR HIGH PERFORM- ANCE EVACUATION SYSTEM William H. Bayles, South Norwalk, and Benjamin C. Nash, Noroton, Conn, assignors to Nash Engineering Company, South Norwallr, Conn., a corporation of Connecticut Filed Jan. 3, 1958, Ser. No. 706,947 17 Claims. (Cl. 230-45) This invention relates to a method and means for producing a vacuum, and more particularly to a novel method and apparatus therefor wherein the unique design of equipment involving aerodynamic techniques and the use thereof, under given conditions, controls motion of compressible fluids having a velocity exceeding Mach number unity to create or improve the degree of vacuum in an evacuation system.

This instant application is a continuation-in-part of my co-pending application Serial No. 251,934, filed October 18, 1951, now abandoned.

Ordinarily, the way to improve suction in an evacuation system is to cause the pump or evacuator to be driven faster, even to an overload condition. Further, various ancillary means have been utilized to improve suction, such as a venturi aspirator or a conventional ejector. However, the operating principles involved in the supersonic jet difiuser of the present invention are entirely diiierent from those of a conventional subsonic ejector or venturi tube, and are as different as a fan is from a reciprocating compressor.

The techniques utilized in the method and apparatus of the present invention are based on theoretical and proven principles of aerodynamics. A supersonic jet difiuser has been developed that has its optimum vacuuminducing performance only when utilizing supersonic flow. Consequently, for a high performance evacuation system as in the present invention, the supersonic jet diffuser is available in the system but is not effectively cut in until the vacuum in the system has reached predetermined conditions.

The conventional ejector normally works with fluids which flow at velocities that may vary from somewhat above stagnation condition to a velocity that is definitely subsonic when used for suction purposes. Further, the conventional ejector normally is designed to be operative over a wide range of subsonic flow. Moreover, the degree of vacuum attainable in a vacuum system using the conventional type of ejectors and suction pumps left much to be desired.

It is, therefore, an object of the present invention to provide novel method and means for an improved vacuum system.

Another object of the invention is to provide a novel system utilizing a vacuum pump and supersonic jet diffuser employable when there is suflicient vacuum to provide supersonic flow in the jet ditfuser tube passage.

A further object is the provision of a novel vacuum system employing an evacuator having a direct inlet passage and an alternate by-pass coupling connectable only when the vacuum through the direct inlet passage is sufficient to provide supersonic fiow through the by-pass coupling thereby to increase the vacuum and reduce effort of the evacuator.

A further object is to provide a supersonic jet diffuser having a convergent m xing entrance, at turbulence reducing or constant-area duct, and a difliuser portion having characteristics and being so proportioned as to provide optimum efficiency of fluid flow therethrough upon predetermined pressure conditions of primary and secondary inlet areas.

A further object is the provision of a supersonic jet diffuser having a housing with first and-second inlet areas, and a diffuser tube connected thereto and characterized by divergent and convergent terminal portions with a discrete turbulence reducing area therebetween to facilitate supersonic flow therethrough.

A further object is the provision of a method for improving evacuation by the steps of coupling the inlet of an evacuator through passages designed for subsonic flow and upon attainment of a predetermined vacuum coupling the inlet to passages designed for supersonic flow to increase the degree of evacuation and reduce the eifort of the evacuator due to fluid velocity inversion upon change from subsonic to supersonic flow.

The present invention contemplates a uniquely designed supersonic jet diffuser including a fluid combining chamber and a jet difiuser element having optimum fluid flow at supersonic velocity which will be in excess of Mach number unity. The jet diffuser is particularly designed for supersonic flow therethrough only after an evacuation system has attained a predetermined degree of vacuum to support the supersonic flow by combining a primary and secondary stream, mixing the streams in a predetermined passage and decelerating said mixed stream to increase the pressure of the system and decrease the jet diffuser fluid flow velocity, thereby reducing the effort or work required to operate the evacuator, or vacuum pump.

In one form of the invention an evacuator represented by a conventional vacuum pump, and at least one supersonic jet diffuser are arranged in a system for extending the useful range of higher vacuums. The novel system of the invention not only obtains higher vacuums than any comparable system but also reduces strain on the apparatus, avoids irregular operation and extends the normal life of the evacuator or vacuum pump or pumps without the expenditure of additional power.

The available operating energy is represented by the difference between the initial atmospheric pressure and the jet diifusers discharge pressure, and since this pressure diiferential is produced by the vacuum pump it is evident that the pump furnishes the energy for operating the supersonic jet diffuser. Since the pump is not required, however, to maintain so high a vacuum at its own intake as before, the energy expended on the supersonic jet diffuser is regained.

When ordinary air expands through a supersonic type nozzle from 14.7 pounds per square inch absolute (p.s.i.a.) to pressures around a half inch of mercury absolute, it attains a velocity several times that of sound. Neglecting friction, the total pressure on the upstream side of the nozzle is equal to that on the downstream side. The upstream pressure is all static and the downstream pressure is all velocity pressure. This high velocity air has the ability to entrain additional air or other gases and vapors, and to accelerate them from stagnation or rest to a relatively high velocity. This part of the process is one of mixing fluids during which the velocity of the motive air and entrained air is still supersonic after mixing, but considerably lower than the velocity of the secondary 'fluid or motive air at the nozzle.

The mixture, still at supersonic velocity, enters a diffuser portion which greatly reduces its velocity and increases its pressure at the discharge end of the tube. The action taking place in the jet diffuser is the reverse of that which takes place in the nozzle. In the nozzle static pressure or head is changed to velocity head, while in the difiuser velocity head is changed to pressure head. The phenomenon can be applied expediently to an atmospheric air operated device discharging into the suction of a vacuum pump.

If, for example, a supersonic jet difiuser of the invention is set up to discharge into the inlet of a two-stage pump of the kind illustratively described herein, the vacuum at the supersonic jet difluser suction may be 29.5 inches of mercury and simultaneously the vacuum at the suction of the two-stage pump may be about twenty seven inches of mercury. This would compare with a normal vacuum at the pump suction for the pump alone of 28.5 inches of mercury, and an efiective vacuum of the same value. The addition of the supersonic jet diffuser increases the effective vacuum and at the s'ametime reduces the pump suction vacuum. At this lower intake vacuum the useful life of the pump or evacuation system and its air handling ability are both greatly increased.

It has been established that a supersonic jet diffuser designed particularly for fluid flow exceeding Mach one (1) and used with atmospheric pressure and in combination with a two-stage hydroturbine pump can actually increase the rate of air handled at high vacuums above that handled by the same pump arrangement alone at high vacuums, and with no increase in power consumption. This net increase in capacity will not take place over the entire range of the pump, but only at relatively high vacuums where supersonic flow is utilized in the jet diffuser designed for such fluid velocities. The design of the jet diffuser element will vary for different evacuation systems.

While reference has been made to air as the motive or operating fluid, and the use of air is regarded as highly advantageous when its use is compatible with the fluid being evacuated, the pump discharge may advantageously be fed to the intake of the supersonic jet diffuser to make a closed system of the pump and jet difiuser combination, when the employment of air is contra-indicated. An instance of this would occur when an explosive gas is being evacuated.

The available vacuum may be still further increased by employing two or more supersonic jet diflusers of appropriately related sizes in series with one another in advance of the pump. In a combination of this kind the suction of the pump is applied to the last jet difiuser as already outlined, and the suction of each, other than the first, is applied to the jet difiuser which precedes it.

While certain objects have been set forth above, other and further objects will become apparent upon reading the following specification together with the accompanying drawings forming a part hereof.

In the drawings:

FIG. 1 is a fragmentary view in end elevation of a pump and supersonic jet diffuser combination employing the invention;

FIG. 2 is a horizontal sectional view taken on the line 22 of FIG. 1, looking in the direction of the arrows; FIG. 3 is a longitudinal, sectional, detail view through the ejector proper and section being taken on the line 3-3 of FIG. 2, looking in the direction of the arrows;

FIG. 4 is a view similar to FIG. 1 but illustrating a pump and ejectorcombination in which a plurality of ejectors are employed;

1 FIGS. 5 and 6 are modifications of the supersonic jet diffuser shown in FIG. 3;

FIG. 7 is a modification of one form of the invention wherein the inlet parts of the primary and secondary fluid stream are reversed from that shown for a device of the type presented in FIG. 6; and FIGS. 8 and 9 are modifications of surfaces in respective jet diffuser elements.

' Referring to the drawings, and more particularly to FIGS. ,1 and 2, there is shown a standard two-stage vacuum pump 10 connected in a representative system and includes two'pumps 12 and 14 of the hydroturbine type, c'onnectedin series with one another. Each ofthe pumps .12 and 14 is of the type disclosed in US. Patents Nos.

1,718,294 and 1,797,980. The twov pumps are, mounted upon a common case in axial alignment and are driven by a common motor. Reference may be had to the patents referred to above for a more complete disclosure of the pump structure, and no detailed description will be given importance since useful application of the principle of the invention can be made with any suitable evacuator or vacuum pump.

A cold water main lsupplies water through branches l8 and '20 respectively, to the pumps12 and 14. An intake conduit is connected to the intake side of the pump 12. A conduit 24fconn ects the output of the pump 12 to the input of the pump 14. The pump 14 discharges to a conduit 26.

A supersonic jet difiuser 28 connected to the intake end of the conduit 22 receives motive air through a conduit 30. The conduit 30 may communicate with the atmosphere through a manually operable valve 32, a motive fluid intake conduit 34 and an air filter 36. A conduit 38, equipped with a vacuum gauge 40, communicates at one endwith the chamber or system under evacuation (not shown), and at the other end with the suction of the ejector 28 through a side inlet passage 42 thereof.

Details of the supersonic jet diffuser 28 are illustrated in FIGURE 3. The supersonic jet diffuser 28 comprises a body member 44 formed with a long hollow bore 46 of varying diameter which extends through it from end to end. The body includes a side extension 48 in which the primary fluid inlet passage 42 is provided. The bore 46 intersects the inlet passage 42. Connecting flanges 50' and 52 are provided at opposite ends of the body 44.

A nozzle 54 having a tapered tip is mounted inv line with the entering end of the supersonic jet diffuser housing or body 44. The tip of the nozzle may extend into a flaring mouth of a supersonic flow tube diffuser 56 asshown, or it may terminate short of the jet diffuser mouth. The tube 56 is secured in a predetermined position within the housing or body 44, but the nozzle is movably mounted in the housing for longitudinal adjustment. 7

The supersonic flow tube 56 is formed with a shoulder 58 which bears upward against a shoulder portion of the body 44. At the lower end of the tube there is a shoulder 62 which receives upward pressure from a bushing 60, shims 64, and a split ring 66, the ring being partially received in a groove of the body 44. A sealing ring 68 is lodged in a circumferential groove of the difluser to provide a sealing joint between the difluser and the ejector body 44.

, The flow tube 56 is formed with a convergently tapered portion 56a having a bore which tapers downward roughly for about one-third of its length, a uniform portion 56b which continues of uniform diameter to substantially the midpoint, and a divergent outer portion 56c which flares outwardly for the remainder of its length. The nozzle tip penetrates the bore 70 to a slight extent in the view shown. The nozzle bore has an entrance portion 72 of relatively large, uniform diameter, a constricted portion 74 and a flaring portion 76. i

The nozzle is mounted in the upper end of the body 44 and is movable for axial adjustment. A nut 78, threaded on the nozzle, is adapted to be set in a recess of the body 44 which surrounds the upper end of the bore 46. The thickness of the nut is made equal to the depth of the recess and the nut is formed with a passage which fits onto a pin 84 that stands up from the base of the recess for restraining the nut 78 against turning. The nozzle is provided with a screw driver slot 86 whereby it may be turned while the nut is held against rotation. When a desired adjustment is secured the nozzle is locked against turning relative to the nut. For this purpose the nut 78 is slotted at one side to a considerable depth to divide it into upper and lower segments 88 and 90. A set screw 92 is threaded through the segment 88 and bears against the segment 90. Turning of the set screw 92 in a direction to separate the segments 88 and 9t) cramps the nut threads on the nozzle threads to lock the to the flange 50 of the ejector body 44 by headed screws 96. The plate 94 bears simultaneously against the flange 50 and the nut 78, and holds the nut firmly against movement. Repeated adjustments and trials of the nozzle may be made for securing the best nozzle adjustment before the set screw 92 is operated to lock the nut 78 against turning.

With the particular mechanism chosen for illustration there is no advantage in usin the supersonic jet difiuser 28 until a vacuum of substantially 28.5 inches has been obtained at the primary fluid inlet. Accordingly, a bypass conduit 98, equipped with a manually operable valve 109, is arranged to connect the conduit 33 directly with the pump intake conduit 22. When the pump is to be put into operation, the valve 101% is opened and the valve 32 is closed, the path of ingress t0 the pump being through the conduit 98. When the gauge 4% shows a vacuum of 28.5 inches, the valve 1410 is closed and the valve 32 is opened. This causes the vacuum in the conduit 22 to fall to about 27 inches and the vacuum in the conduit 38 to rise to about 29.5 inches. No increase of power consumption attends this change. In fact, since the pump is not required to pull so high a vacuum at its intake, it operates more evenly and smoothly, without cavitation and without undue strain and wear. There is a gain in operating eifect and efliciency since a higher vacuum is obtained with the same expenditure of power, and at the same time a gain in operating characteristics.

In the operation which has just been described, the secondary fluid or motive fluid employed in the tube 56 is drawn through the filter 36 from the atmosphere. The air discharged by the pump through the conduit 26 passes freely to the atmosphere through a conduit 102, in which a manually operable valve 104 is provided, the valve 164 being open under the conditions described.

As has been pointed out, it is necessary under some conditions to avoid mixing secondary fluid or air with the primary fluid or gas drawn from the system under evacuation. For that purpose provision is made to enable the pump discharge to furnish the motive fluid for the jet diffuser. A conduit 186, equipped with a manually operable valve 188, is accordingly provided for connecting the conduit 26 to the conduit 39. When air is to be excluded, the

valves

32 and 104 are closed. The valve 193 may be initially closed and the valve 109 open. When the gauge 40 shows a vacuum of about 28.5 inches, however, the valve 108 is opened and the valve 100 is closed. In order to avoid the building up of a fluid pressure at the discharge side of the pump, a bleeder bypass 110 is provided around the valve 104. A check valve 112, normally maintained closed by spring 114, is provided in the bypass 110. The spring loading of the check valve is very light, being just suflicient to maintain a slightly superatmospheric pressure in the conduit 26. Gas which reaches the conduit 102 through the bypass 110 is conducted to a safe point of discharge.

FIGURES and 6 of the drawings, refer specifically to the supersonic jet diffuser and are modifications of the jet diffuser shown in FIG. 3.

Referring specifically to FIG. 5, there is shown a chamber body or housing 1511 having a difluser tube 151 connected thereto by means of a flange 152, which flange is formed on and adjacent one end of the diffuser tube 151. The diffuser tube, by means of the flange 152, is

. held in fixed relation to the body or housing 150 by means of bolts 153. The housing 156 has an inlet flange 155 on one side thereof having a primary stream inlet 156 formed therein leadia into the primary stream chamber 157.

-A secondary stream chamber 158 in the housing has a vented cap 169 which covers an opening 161 in communication with the secondary stream chamber 158. The vented cover is removably attached to the secondary chamber housing portion 162 forming the chamber 158. Three projections 164 are equally spaced from each other and formed on the underneath surface of the vented cover,

so that the cover is spaced from the opening 161 to permit air to enter the chamber. This cover arrangement for chamber 158 is used when the system is employed without the use of a filter, such as filter 36 shown in FIG. 1. The vented cover keeps out dirt and foreign matter generally, and yet permits suificient air to enter the device when it is in operative condition. When the filter is employed in this system with a device such as shown in FIG. 5, the vented cap is removed and the filter is properly connected to the threaded portion 165 in the housing portion 162.

A secondary stream nozzle 166 has a threaded portion 168 which is threadably connected into a complementary threaded portion formed in a partition having a communicating passage between the primary stream chamber 157 and the secondary stream chamber 158. A nozzle shoulder 17% formed on the secondary stream nozzle 166 engages the partition between the primary and secondary stream chambers.

The secondary stream nozzle 166 has a flare 172 at one end thereof leading into the nozzle sub-chamber 173, which sub-chamber leads into a convergent portion 174, which in turn leads into a restricted area portion 175, and then into a divergent portion 176 terminating in the primary stream chamber 157.

The nozzle 166 is axially aligned with the diffuser tube 151, with the outlet end of the secondary stream nozzle being spaced from the flare 178 which forms a terminal area at the convergent inlet mixing portion 180 of the diffuser tube 151. The diffuser tube 151 has a central portion which is a tubulence reducer or constant-area duct 169 having a uniform cross-sectional area throughout its length. A divergent difiuser portion 183 has a passage therethrough which merges with the outlet portion of the turbulence reducer duct formed in the diffuser tube 151 on the end opposite the entrance flare 178. The outlet end of the divergent diffuser portion '183 terminates in a passage formed in an outlet flange 185.

In FIG. 6 of the drawings, portions of the supersonic jet diffuser similar to portions of FIG. 5, are given the same reference numeral. While a device of that shown in FIG. 6 has a similar function to a device of that shown in FIG. 5, the two devices have specific design changes.

The diffuser tube 151 of the device shown in FIG. 6 has an annular flange 152A formed as a part thereof, and the flange is employed in conjunction with a collar which engages the annular flange and holds the diffuser tube 151 against the housing 150 by bolts 153. A jet ditfuser outlet flange 191 is threadedy connected to the divergent diffuser or outlet portion of the difluser tube 151.

While FIG. 5 shows a nozzle connected to the partition of the secondary stream chamber housing 162, FIG. 6 shows a somewhat different arrangement employing a nozzle 192 having a shoulder 193 thereon abutting a complementary shoulder of a nozzle coupling 194, which nozzle coupling has a shoulder thereon engaging the partition in the secondary chamber housing and is threadedly connected thereto.

The nozzle coupling 194 has a fiare 195 at the inlet end thereof adjacent the secondary stream chamber. The nozzle 192 has a flare 197 at one end thereof which forms a convergent portion merging into a restricted portion 198, which restricted portion in turn merges with a divergent portion 199, with the large end of the divergent portion being spaced from the flare 178 formed at the inlet end of be made if desired. A two-stage pump 10a, the same as the pump 19 of FIGURES 1 and 2, is provided. The pump draws in air through a conduit 22a and a supersonic jet diffuser 28a, similar to that shown in FIGURE 3. Motive air enters the jet dilfuser nozzle through a filter 36, a conduit 340, a manually operable Valve 32a and a conduit a.

The side extension 48a of the supersonic jet diffuser 28a is connected to the discharge end of a further jet diffuser 2812 into which secondary fluid or motive air is drawn from the atmosphere through a filter 3612, a conduit 34b, a manually operable valve 32b, and a conduit 30b.

The side extension 48b of the jet difiuser 28b is connected to the discharge end of a still further jet diifuser 280 into which motive air is drawn from the atmosphere through a filter 36c, a conduit 340, a manually operable valve 32c, and a conduit 300. The side extension 48c of the ejector 28c is connected to the discharge end of a conduit 38a, the other end of which is connected to the chamber or system undergoing evacuation. The details of the several jet difiusers may be the same as those heretofore described in connection with FIGURE 3. The interior part of the ejectors may, however, be varied in size with relation to one another as required for the tandem or series operation.

As before, there is no advantage in employing the supersonic jet diffusers until the pump has directly produced a vacuum of about 28.5 inches. A bypass conduit 98a, equipped with a manually operable valve 100a, is accordingly provided. Before setting the pump into operation the valves 32a, 32b and 32c are closed and the valve 106%; is opened. When a gauge a shows a vacuum of about 28.5 inches in the conduit 38a the valves 32a, 32b and 320 are opened in the order named, and the valve liltla is then closed. This will cause the vacuum in the conduit 22:: to fall to about 27 inches but will produce a vacuum of about 29.5 inches in the outlet end of the evacuator 281), a vacuum of about 0.1 inch in the outlet end of the supersonic jet diffuser 23c, and a vacuum of about 500 microns in the conduit 38a. As 'in the former case, the operating conditions of the pump itself will be considerably improved by the addition of the jet diflusers.

In FIG. 7, there is shown a modification of the supersonic jet difiuser presented in FIG. 6. However, in FIG. 7 the primary stream is connected to the supersonic jet diffuser by inlet opening 260 which is aligned axially with the opening in the difiuser tube or element 251. The secondary stream which is connectable to the atmosphere enters the device through the port 2%., and then passes through the passage 262 out through the nozzle 203, where the atmosphere is entrained by the gas drawn in through the primary stream inlet 200 and is carried through the difiuser tube or element 251 having divergent portion 252. The divergent portion of the diffuser tube has its free end connected to the flanged coupling 253. In FIG. 7 the nozzle 263 of the seconary stream is centrally aligned with the convergent portion 254 of the jet diffuser tube or element 251.

In FIGS. 8 and 9 there are two modificaions showing the longitudinal cross-sectional portions of jet diffuser tubes. In FIG. 8 the surface 275 has a gradual contour of which the central portion is curved and parallel to a similar portion spaced therefrom between the

points

276 and 277. Further, the form shown in FIG. 8 has convergent and divergent portions connected with the constant area portion 260 and operates substantially similar to that shown for corresponding portions of the jet tube shown in FIG. 6.

In FIG. 9 it will be seen that'there is a convergent portion A, a divergent portion B, and a central portion C, but all three of the portions are made from surfaces defined by

gradual curves

280 and 281.

The ideal tube would preferably have no sharp corners or edges which could cause turbulence in the air stream. Consequently, FIG. 9 is one form of a tube having no sharp edges throughout its interior jet diffuser tube portion, whereas the surfaces such as 275 and 278 in FIG. 8 have only surface portion 275 which is completely free V greater advantages.

of sharp edges, while the opposed surface portion 278 has merged edges but not entirely a smooth flowing curve comparable with curve 281 shown in FIG. 9, for equivalent portions.

While specific views shown herein embrace a jet diffuser tube having a convergent portion, a constant area portion, and a divergent portion, very good results have been obtained in tests under certain conditions, wherein the convergent portion has been appreciably reduced in axial length. In other instances, the constant area portion adjacent the nozzle has only a flare portion, and the opposite end of the constant area portion of the tube merges with the divergent portion which may be somewhat of the general nature shown for other devices represented in the drawings.

The length of the straight portion or constant area portion of he tube should be suflicient to appreciably reduce the turbulence of the fluid flow through the tube after the mixing of the primary stream with the secondary stream.

In the operation of the present device, when the degree of evacuation is attained suitable to provide supersonic flow when the secondary stream or atmosphere is entrained by the flow of the primary stream, the supersonic jet diffuser is cut into the system. In other words, the valves which were closed in the system prior to attainment of the proper degree of vacuum are now opened to permit the fluid flow through the supersonic jet diffuser. In the specification, 28.5 inches of mercury has been referred to as an ideal degree of evacuation to cut in the supersonic jet difiusers as the ancillary device for increasing the vacuum beyond that normally attainable in the particular system shown. 28.5 inches of mercury has been mentioned because this degree of evacuation is attainable with two stage pumps of a type manufactured by the inventor of the present invention. However, 28.5 inches of mercury is not necessary to produce supersonic flow through jet diffusers of the type set forth herein. Eighteen inches absolute or higher velocity of gas produced flow less than Mach unity. Certain of the supersonic jet difiusers have been designed to operate well on 26 inches of mercury.

Supersonic jet diffusers of the present invention may be of any of the general type of design presented herein. it is to be understood that any type of supersonic jet difuser may be employed or cut into the system at any time when the degree of evacuation is sufiicient to establish supersonic flow through the jet diffuser. Normally, in operation, when the air enters the entrance portion of the jet diffuser tube, the initial mixing takes place in part in the convergent portion of the tube, and at this time there is an increase in velocity and a decrease in pres sure. While the flow through the constant area portion of the tube is an added mixing, there is also a reduction in turbulence, the length of the constant area portion being sufficient to reduce turbulence the desired amount. The

divergent portion of the diffuser actually increases the pressure and reducees the velocity so that the fluid flow now becomes subsonic as it leaves the jet diffuser. It is this increase in pressure and decrease in velocity that causes the increase in evacuation due to tr e supersonic jet diffuser action.

While the invention has been illustrated in connection with a duplex pump of the liquid ring, hydro-turbine type, and the illustrative figures are applicable to the illustrative mechanism only, supersonic jet diffusers may generally be combined with almost any vacuum producing element with substantially equal, or in some cases, even An example of an increased advan tage would occur when the supersonic jet difiuser is combined with an oil sealed vacuum pump of the displacement type. The capacity of such a pump at very high vacuum would be increased considerably more than the capacity of the liquid ring pump can be.

Operation suction pressures for the combination of a 9 single supersonic jet diffuser with a two-stage liquid ring vacuum pump of between .5 inch and 1.5 inches absolute yield the most satisfactory results.

The field of application of the atmospheric air ejectorvacuum pump combination is a wide one. It comprehends air, gas and vapor removal in processes such as drying, evaporating, distilling, deaerating, cooking, etc., that require vacuums of 28.5 inches and higher.

The use of quiescent atmosphere instead of a stream jet ordinarily calls for a larger size vacuum pump, but against this disadvantage to the user many advantages accrue, such as elimination of steam equipment and simplified operation resulting therefrom, as well as greater life expectancy of the pump. The use of a fluid jet stream instead of quiescent fluid as the motive fluid is also contemplated, however, as included within the scope of the invention.

The device of the invention can handle condensable gases. Because of the condensing ability of the liquid ring pump, the performance of the unit will be improved when loads consisting partly or wholly of condensable vapors are handled. Oil sealed vacuum pumps of the displacement type, under certain conditions, cannot handle condensable gases without special attention to the oil seal. For service involving condensable gases, therefore, the liquid ring pump and supersonic jet diffuser combination has advantages over such displacement pumps.

While specific drawings have been presented herein, it is to be understood that the various views are for the purpose of illustration, and that changes and modifications may be made in apparatus of the invention without departing from the spirit of the subjoined claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A system for producing vacuum comprising a liquid ring pump primary evacuation apparatus having inlet conduit means and ejector ancillary evacuation means coupled in series in said inlet conduit means for increasing the vacuum therein, said ancillary evacuation means being motivated by the vacuum produced by said primary evacuation apparatus and including a fluid combining chamber, means for introducing a secondary fluid stream into said fluid combining chamber for entraining same with the primary fluid stream of the system, and supersonic jet difiuser means through which the entrained fluid stream flows, said last means including a portion for decreasing the velocity to subsonic flow and increasing the absolute pressure and reducing the vacuum, said liquid ring pump primary evacuation apparatus being constructed and arranged to produce the major portion of the total vacuum produced by said system, said ancillary evacuation means being constructed and arranged to produce but a minor portion of the total vacuum produced by said system.

2. A system for producing a vacuum as set forth in claim 1, wherein said ancillary means includes a plurality of supersonic jet diffuser means coupled in series.

3. The method of improving the efliciency and extending the useful application range of a liquid ring pump evacuation system, said pump employing a seal liquid therein, comprising the steps of employing the liquid ring pump to produce a major percentage of the desired total evacuation in a primary fluid stream, entraining a secondary fiuid with the primary fluid stream of the evacuation system to produce an entrained fluid stream of supersonic velocity when the primary fluid reaches a predetermined minimum degree of evacuation, and simultaneously reducing the velocity of the entrained supersonic fluid stream and increasing the pressure, whereby the degree of evacuation producible by the system is extended to produce an absolute pressure lower than the vapor pressure of the seal liquid and the efficiency of the system is improved.

4. The method of improving the efliciency and extending the useful application range of an evacuation system as set forth in claim 3, wherein when the supersonic fluid i6 stream velocity is reduced, it is reduced to a velocity of subsonic flow.

5. The method of improving the efiiciency and extending the useful application range of an evacuation system as set forth in claim 3, and wherein after the velocity of the entrained fluid stream has been reduced, it is again subjected to a secondary fluid and again produces an entrained fluid stream having a velocity greater than that of the first entrained fluid stream.

6. The method of extending the useful application range or" a liquid ring pump employed to eflect a major portion of a desired high vacuum to absolute pressure levels below the vapor pressure of the liquid within the pump comprising providing ancillary vacuum producing means to produce a relatively small incremental degree of vacuum, connecting said ancillary means to the volume to be evacuated and connecting the liquid ring pump in series with the ancillary vacuum producing means so that the ancillary vacuum producing means is operated by the vacuum produced by the liquid ring pump and the absolute pressure at the inlet of the liquid ring pump exceeds the vapor pressure of the liquid within said pump.

7. The method of operating liquid ring pump means for producing a major portion of a desired high-degree of evacuation in combination with jet diffuser pump means for producing a minor portion of a desired high degree of evacuation to produce a subsatrnospheric absolute pressure below the vapor pressure of the liquid within the liquid ring pump means comprising the steps of withdrawing vapor directly from the volume to be evacuated with said first mentioned pump means until a substantially high vacuum is obtained, and thereafter utilizing the substan- -tial vacuum thus obtained to provide the pressure differential necessary to operate said second mentioned pump means by withdrawing the inlet vapors pumped by said first mentioned pump means through said jet difiuser pump means, whereby an absolute pressure may be obtained within the evacuated volume which is less than the vapor pressure of the liquid in the liquid ring pump means.

8. A high vacuum producing system comprising a rotary hydroturbine liquid ring vacuum pump adapted for producing substantially the entire portion of the desired high vacuum, said pump having an inlet conduit connected to an area to be evacuated and an outlet, and an ejector adapted for producing the small remaining portion of the high vacuum desired, said ejector including an inlet and a discharge connected in said vacuum pump inlet conduit, said ejector including an interior tubular flow portion communicating with said inlet conduit, a nozzle portion arranged to discharge into said tubular flow portion, and a secondary fluid inlet connected to said nozzle portion, said tubular flow portion being of a configuration to produce a higher pressure at the discharge of said ejector than at said inlet, whereby said ejector is operated by the vacuum produced by the liquid ring pump to effect a reduction in pressure in said inlet conduit between said ejector and the area to be evacuated and an increase in pressure at the inlet of said pump.

9. A vacuum producing system according to claim 8, wherein said pump includes a discharge conduit connected between said pump outlet and said secondary fluid inlet whereby said pump discharge may be used as a secondary fluid.

10. A vacuum producing system according to claim 8, including a bypass conduit connected in said inlet conduit and extending around said ejector and valve means in said by-pass conduit.

11. The combination with a vacuum pump capable of developing at its intake a low subatmospheric pressure substantially less than 15.9 inches of mercury absolute, of an aeroform fluid motivated supersonic jet difluser capable of maintaining a much lower absolute pressure when subjected to the intake suction of the pump and motivated by aeroform fluid at atmospheric pressure or above, said supersonic jet difluser having an intake end 1 l for motive fluid, a nozzle, a diffuser in alignment with the nozzle, a discharge end, and a chamber to be evacuated,,means connecting the discharge end of the jet difiuser to the pump intake, and means forming a returnsystem for aeroform fluid handled, said. last mentioned means connecting the pump discharge to the motive fluid intake end of the jet difiuser and including means automatically limiting pressure in said return system to substantially atmospheric pressure or above, while providing for the safe disposal of surplus fluid.

12. In an evacuation system, the combination of liquid ring a vacuum pump employing seal liquid as the working liquid therein for developing at its intake a major portion of a desired low subatmospheric pressure, said major portion comprising evacuation to an absolute pressure approaching the vapor pressure of the seal liquid employed in said pump, with an air motivated, superacoustic ejector capable of developing a still lower absolute pressure below the vapor pressure of the seal liquid when subjected to the intake suction of the pump, said ejector including a nozzle in communication with a source of aeroform motive fluid at atmospheric pressure, through which aeroforrn motive fluid is drawn by the pump from said source, said nozzle being sized and shaped to increase the velocity of fluid passing therethrough, a difiuser in alignment with the nozzle but spaced from it, to define with the nozzle a suction inlet which surrounds the nozzle at the mouth of the diflfuser, said difl'user being flared outwardly to increase the pressure of said fluid to an amount in excess of the pressure at the inlet of said ejector and a discharge end connecting the diffuser to the pump intake, the construction and arrangement being such that aeroform fluid may be drawn through the suction inlet and into the difa still lower absolute pressure when subjected to the intake suction of the pump, said ejector having a motive fluid intake portion open to the atmosphere, a nozzle sized and shaped to increase the velocity of fluid passing therethrough to a super-acoustic velocity, a diffuser in alignment with the nozzle but spaced from it, said difluser being flared outwardly to increase the pressure of said fluid to an amount in excess of the pressure at the inlet of said ejector, a suction inlet in communication with the ejector at the inlet mouth of the diffuser, through which aeroform fluid may be drawn from the volume to be evacuated into the diffuser at super-acoustic speed by entrainment, a conduit connecting the diflFuser to discharge into the intake of the vacuum pump and valve means to render said nozzle inoperative during periods when the pressure differential created by the liquid ring pump operating alone is insuflicient to cause super-acoustic flow through said nozzle, said liquid ring vacuum pump when operating in series relation with said ejector being constructed, arranged and eifective to produce the major percentage of the subatmospheric evacuation, said ejector being employed for producing a very minor percentage of the subatmospheric evacuation in the range of absolute pressure approximating the vapor pressure of the seal liquid employed in the liquid ring vacuum pump.

14. A high efficiency evacuation system comprising a liquid r ng pump having an outlet conduit, and an inlet conduit connecting said pump to a container to be evacuated, shut-off valve means in said inlet conduit, a supersonic jet diffuser, said diffuser including an intake passage for motive fluid, a nozzle in communication with said intake passage, a discharge end, and a chamber to be evacuated, conduit means connecting said chamber to the inlet conduit on the container side of said shut-off valve means, conduit means connecting said discharge end of said supersonic jet difluser to the inlet on the pump side of the valve means, and second valve means in said motive fluid passage which is closed during the start-up of the evacuation system until the pressure difierential between the pump inlet conduit and the motive fluid intakepassage is suflicient to cause supersonic flow within said jet 15. A system according to claim 14 including passage means between said pump outlet conduit and said motive fluid inlet passage whereby a portion of said pump discharge may be used as the motive fluid.

16. A high efficiency evacuation system according to claim 14 including a second supersonic jet diffuser connected in series relation with the first-mentioned supersonic jet diffuser.

17. An evacuation system for producing a low subatmospheric absolute pressure comprising a liquid ring primary evacuation apparatus employing a seal liquid as the Working liquid therein and having inlet conduit means aid primary evacuation apparatus constructed and adapted for producing a major portion of the desired total evacuation to a low subatmospheric pressure approaching the vapor pressure of the seal liquid employed therein, ancillary evacuation means coupled in said inlet conduit means .for effecting a relative small increase in the vacuum theresolute pressure and reducing the vacuum, and valve means -to render said ancillary evacuation means inoperative during the start-up of said system until the pressure differential between the secondary fluid stream and the primary fluid stream is suflicient to cause supersonic flow in said jet difiuser.

References Cited in the file of this patent UNITED STATES PATENTS 299,267 Richter -a May 27, 1884 741,270 Parsons Oct. 13, 1903 1,010,456 Schaller Dec. 5, 1911 1,055,210 Morison Mar. 4, 1913 1,134,215 Morse Apr. 6, 1915 1,472,874 Krick Nov. 6, 1923 1,575,770 Kennedy u Mar. 9, 1926 1,718,294 Jennings June 25, 1929 1,797,980 Jennings Mar. 24, 1931 1,845,969 Hueber Feb. 16, 1932 2,095,534 Schmidt Oct. 12, 1937 2,096,883 Clason Oct. 26, 1937 2,231,090 Ross Feb. 11, 1941 2,268,656 Haltmeier I an. 6, 1942 2,493,387 Campbell Jan. 3, 1950 2,631,774 Plumrner Mar. 17, 1953 FOREIGN PATENTS 647,707 Germany July 10, 1937 711,791 Germany Oct. 7, 1941 800,086 Germany Sept. 1, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,064,878 November 20 1962 William H Bayles et ale.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column ll, line 11 strike out "a"; column' 12, line 27, for "aid" Signed and sealed this 30th day of April 1963.

after "of" insert a line 12,

read said (SEAL) Attestz' DAVID L. LADD ERNEST W. SWIDER Attesting Officer Commissioner of Patents