US3243102A

US3243102A - Centrifugal fluid pump

Info

Publication number: US3243102A
Application number: US332087A
Authority: US
Inventors: Kenton D Mcmahan
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-12-20
Filing date: 1963-12-20
Publication date: 1966-03-29
Anticipated expiration: 1983-03-29
Also published as: JPS498961B1; DE1428191A1; GB1045219A

Description

K. D. M MAHAN CENTRIFUGAL FLUID PUMP March 29, 1966 5 Sheets-Sheet l INVENTOR.

KENTON D. MC MAHAN Filed Dec. 20, 1963 ATTORNEY March 29, 1966 K. D. M MAHAN CENTRIFUGAL FLUID PUMP 5 Sheets-Sheet 2 Filed Dec. 20, 1965 INVENTOR.

KENTON D. MC MAHAN ATTORN EY FIG-4.

March 29, 1966 MCMAHAN 3,243,102

GENTRIFUGAL FLUID PUMP Filed Dec. 20, 1963 5 Sheets-Sheet 5 INVENTOR.

KENTON D. MC MAHAN BY W ATTORNEY 5 Sheets-Sheet 4 Filed Dec. 20, 1963 INVENTOR. KENTON 0. MC MAHAN FIG.50.

ATTORNEY K. D. M MAHAN CENTRIFUGAL FLUID PUMP March 29, 1966 5 Sheets-Sheei 5 Filed Dec. 20, 1963 INVENTOR.

KENTON D. MC MAHAN ATTORNEY United States Patent 3,243,102 CENTRIFUGAL FLUID PUMP Kenton D. McMahan, Scotia, N.Y. (Rte. 3, Siry Mountain, Rogers, Ark. 72756) Filed Dec. 20, 1963, Ser. No. 332,987 16 Claims. (-Cl. 230117) The present invention relates to centrifugal fluid pumps and although particularly adapted to centrifugal blowers or fluid movers of the mixed-flow type having an axial discharge as opposed to the type having the usual tangent-ial discharge, some of the features of the invention can be advantageously employed in connection with other types of centrifugal fluid pumps. The present invention is such, that some of the basic concepts used in the reduction of interstage losses in multi-stage centrifugal machines by the use of a plurality of radial jets of balanced momentum and disclosed in US. Patent No. 2,868,440 and copending applications Serial Nos. 175,940 and now Patent No. 3,171,353 and 258,033 now Patent No. 3,188,968 can be advantageously employed in connection with said invention.

In Patent 2,868,440, it was disclosed that if two jets of equal magnitude (jet velocity X mass) created from the discharge of an impeller of an earlier stage unit are directed in opposed directions radially inwardly towards the suction eye in alignment along a radial center plane and in centered position over the axis of the eye, substantially balanced impact of the two jets is effected as they meet in the vicinity of said suction eye and substantially smooth axial deflection of said jets into said suction eye is effected as they merge into a single stream. By creating diametrically opposed jets of equal magnitude from each impeller discharge, the rotational velocity components, turbulences, undesired accelerations, eddies and vacuou-s pockets in the stream flow between the discharge of a volute of one stage and the intake or eye of a succeeding stage, resulting in so called interstage losses, and consequent lowering of overall performance and efficiency of multi-stage machines, are materially reduced.

In cop-ending application Serial No. 175,940, it has been disclosed that the radial jets from the discharge of the volutes need not be diametrically opposed to suppress the rotational components and other undesirable eifects in the said jets, but that these factors disturbing the efficiency of centrifugal machines can be materially reduced if the magnitude of the radial jets and the spacing therebetween is such that the resultant of the radial momentum (jet velocity mass) on one side of any selected radial plane passing through the axis of the inlet suction eye is substantially equal to and in substantial radial alignment with the resultant of the radial jet momentum on the other side of the plane. In accordance with this disclosed concept, an odd number of radial jet passages properly spaced Will provide the desired jet balance to reduce interstage losses. It was further disclosed that the tendency of the jets from the perimetric volutes of one stage when turned radially inward by a conventional elbow to crowd toward the outer bend and away from the inner bend of said elbow, can be compensated for by the use of overbends or overextended bends, whereby a single radial jet of very nearly uniform velocity, mass and direction thereacross and with the resultant of it momentum almost coextensive in position with the radial mechanical centerline of the jet, is produced without the use of inner vanes and the like. Also, by this means, the circumferential spaced confining walls on the circumferential spaced boundaries of the radial jet passages are eliminated. As a result, the radial jets of one stage enter the eye of the next stage with little or no rotational components and without measurable loss.

In the copending application Serial No. 258,033, it has been disclosed that the two overbend elbows may be employed in series for each volute passage, the function of the first being to arrest the tangential component of velocity and direct the resultant jet in an axial path, and the function of the second being to turn the said jet radially inward with balanced momentum toward the inlet suction eye of a successive stage impeller or a common concentric discharge passage with uniform axial velocity.

The present invention contemplates the application of some of the basic concepts of the aforesaid patent and copending applications to the design of a com-pact axial blower having the high flow and pressure head characteristics of conventional centrifugal blowers without the necessity of using the comparatively large and awkward volute collector scrolls with tangential discharges, and further contemplates the possible instfllation of such blower units in'series to thereby create multi-stage blowers in the manner disclosed in the aforesaid copending application Serial No. 175,940, which is not now feasible with conventional blowers.

Another object of the present invention is to provide a new and improved centrifugal fluid pump, which is compact, which has a high flow capacity and high efficiency, and which is so designed as to be capable of being molded of plastics or made of any other suitable material with a minimum of tooling and unit piece cost.

A further object of the present invention is to provide a new and improved centrifugal fluid pump, which is designed to reduce overall noise level particularly by the elimination of or material reduction in blade frequency, or harmonics thereof, or noise components, such as those normally present in centrifugal blowers operating with conventional scrolls.

To carry out the last object, the discharge from the impeller is divided into a plurality of volutes serving as diffusing passages and especially shaped to reduce the magnitude of the fluid shock at each volute inlet cut-off. To further reduce the noise level of the pump, the number of such cut-offs are chosen so that the ratio of the number of impeller blades to the number of cut-offs is not a whole number. Also, each such cut-off is axially askewed with respect to the impeller blades by an angle greater than that of the blade spacing of said impeller.

Still another object of the present invention is to provide a new and improved centrifugal fluid pump designed to attain compactness notwithstanding its high flow capacity. To attain this objective, the diffuser or volute passages extend not only radially and circumferentially but also axially to materially reduce the normally large ratio of external diameter to impeller diameter of centrifugal machines and to substantially eliminate or materially reduce the radial overlap of such passages and substitute therefor a large axial overlap along the axial casing of the driving motor. To attain this large axial overlap andsmall or null radial overlap, the radial diffuser of the aforesaid copending applications has been reduced in radial extent to a mean diameter only slightly larger than that of the impeller, and each volute passage has been axially shifted abruptly but uniquely around the next succeeding volute, and has been continued in diverging helical form of extended length around the driving motor. Each volute passage terminates in an elbow which is desirably overextended and which directs the fluid radially inwardly as circumferentially wall free, jets of balanced momentum, in accordance with the teachings of said copending applications. The radial jets can be diverted and merged for axial discharge or for injection into the axial impeller of a succeeding pumping stage.

A still further object of the present invention is to provide a new and improved generally circular fan or blower unit designed for simple mounting in the wall panel of to electronic or other devices to replace vane-axial, tubeaxial or multi-stage axial fans or blowers.

It is well known that presently existing designs of highly eflicient centrifugal fluid pumps of the multi-stage type have a comparatively large outer diameter as compared to their impeller diameter and hence are unsuitable for many applications. To simply employ one stage from such machines and use it as a blower or fan would be beyond reasonable design consideration for a great number of applications because of size, weight and cost factors, in spite of their very high efiiciency and low noise characteristics. It is further well known that certain designs, having a comparatively small ratio of outer diameter to impeller diameter and making use of mere turning vanes at the periphery outside the impeller, have both low fluid flow and efliciency characteristics coupled with high comparative noise levels, and thus are also not feasible for such design purposes. Even with the improved designs disclosed in the aforesaid applications, the outer diameter of the casings are over twice the diameter of their respective impellers and notwithstanding the fact that both the flow and pressure factors are high for such machines, neither would be a suitable replacement for an axial fan or blower in the mass market for small inexpensive blowing or cooling devices as hereinafter further described.

To explain the relative nature of the volume flow capacity of various known types of centrifugal machines from liquid pumps through compressors to blowers and fans, reference is made to a well recognized dimensionless quantity, Q/ND where Q represents the inlet flow volume in cubic feet per minute, N represents the speed in revolutions per minute, and D represents the diameter of the impeller in feet. In simplified form, this factor is the cubic feet of fluid handled per revolution of a one foot diameter impeller measured under its inlet conditions. Typical flow factors for some well known types of machines may be given as follows:

Water and liquid pumps .02 to .10 Radial blade centrifugal compressors .10 to .20 Radial blade centrifugal blowers .15 to .30 Improved mixed-flow compressors .25 to .50 Propeller fans .40 to 1.1 Vane axial fans .50 to 1.1 Mixed-flow blowers with tangential scroll housings .60 to 1.5 Squirrel cage blowers with tangential scroll housings .50 to 2.0

The foregoing tabulation of the dimensionless flow factor, Q/ND for various typical fluid moving devices serves to better bring into focus the stated objectives of the present invention and to point up the magnitude of the improvements required to attain such objectives. It further permits a more detailed explanation of the first named objective. The term mixed-flow is a generic term applied to fluid impellers having axially directed blading at their inlet eyes, sometimes referred to as axial inducers, followed by significant centrifugal blading whereby the fluid particles are acted upon both axially and radially in varying degrees depending upon the flow factor and pressure requirements. The impellers disclosed in the copending application Serial No. 175,940 fell within the meaning of the term and are represented in the foregoing tabulations as improved mixed-flow compressors having a flow factor in the range of .25 to .50. On the other hand, mixed-flow blowers of the present invention are intended for flow factors in the range of .60 to 1.5 to match the flow with tangential scrolls and hence have a relatively larger inlet eye and a greater percentage of axial blading.

Various other objects, features, and advantages of the present invention will be apparent from the following description and from the accompanying drawings, in which:

FIG. 1 is a cut-away side elevation of a centrifugal pump, shown in the form of a blower embodying the present invention;

FIG. 2 is a fragmented transverse discharge end view of the blower shown in FIG. 1;

FIG. 3 is a transverse section of the blower of FIG. 1 taken along the lines 3-3 of FIG. 1 and FIG. 4 and shows a half-section of the axial portion of the volute passages and a half-section at the impeller back plate and the radial portion of the volute passages at the discharge side of the impeller;

FIG. 4 is a circumferential section taken along the lines 4-4 of FIG. 3 and FIG. 5 and shows the axial contour of the volute passages;

FIG. 5 is a transverse section of the blower of FIG. 1 taken along the lines 5-5 of FIG. 1 and FIG. 4 and shown fragmented to show one complete volute passage and its discharge opening;

FIG. 5a is a fragmentary transverse section of the blower similar to that of FIG. 5 but showing the axial overlap attained with the present invention;

FIG. 6 is an enlarged fragmented portion of FIG. 3 to show the askew or oblique angle of one cut-off and the angular spacing of the impeller blades;

FIG. 7 is an enlarged sectional view of one cut-off similar to that of FIG. 4 but showing the radial overlap of the volute passages;

FIG. 8 is a fragmented side elevation view of the blower of FIG. 1 modified to permit it to be mounted in panel walls and the like;

FIG. 9 is a fragmented and cut-away side elevation of a modified blower designed to attain maximum flow rates,

' and FIG. 10 is a fragmented transverse view of one cut-off of the blower of FIG. 9 viewed in the same direction as that of FIG. 6 of the blower of FIG. 1.

Referring to FIGS. l6 of the drawings, there is shown a centrifugal fluid pump 10 and more specifically a single stage centrifugal blower unit for handling air or gases at comparatively low pressure heads and intended for installation in a simple duct or pipe of uniform size and crosssection, although as far as certain aspects and features of the invention are concerned, the blower with minor variations may have any number of stages mounted concentrically on a single shaft or any number of complete singlestage blowers may be used in series to form a multi-stage assembly.

The blower unit 10 comprises a skeleton type motor 11 mounted axially of the unit in suitable elastic mountings 12 and having a shaft 13 on which is mounted an impeller 14 secured to shaft 13 by a set screw 15. The blower 10 also comprises a circular impeller casing 16, an axial diffuser casing 17 and a discharge casing 13, these casings being secured end to end. The axial diffuser casing 17 contains as its inner periphery a cylindrical motor compartment housing 20, with an inner end motor support 21 for receiving one of the elastic mountings 12. Similarly, an opposite end motor support 22 is adapted to receive the other elastic mounting 12. The mountings 12 are restricted against rotation in the

supports

21 and 22 by suitable lugs 23 respectively, and are cemented or otherwise rigidly attached to motor bearing shields 25. The support 22 is secured to the end wall of the casing 17 by screw studs 26 and the discharge casing 18 is likewise secured to the casing 17 by means of screw studs 27 threaded into tapped stud spacers 28 and into bosses 29 on said casing 17.

While the motor 11 is shown mounted in elastic mountings 12, it is understood that such mountings may not be needed where the

entire blower casing

16, 17 and 18 is molded with any one of several comparatively flexible plastic materials as contemplated. In such cases, the

motor may be rigidly secured to support 22 or otherwise mounted.

The support 22 contains a circumferential row of holes 30 to permit free circulation of air or gas around the motor windings 31 for cooling. Motor leads 32 pass through a suitable grommet 33 in the support 22 ad a similar grommet 34 in the wall of casing 17. The discharge casing 18 contains on its inner periphery a discharge flange 35 upon which a suitable discharge duct or a hose and clamp (not shown) may be attached. Similarly, the impeller casing 16 contains on its inner periphery an inlet flange 36 on which is pressed or shrunk an inlet orifice 37 having the same outer flange diameter as the opposite end flange 35 for the same or similar connection.

The impeller 14 comprises a backplate 40, an inlet shroud 41 and a plurality of circumferentially spaced blades 42 mounted therebetween and so shaped that they are concave on their leading faces and generally forwardly curved at their outer peripheries or discharge ends 43 as respects their direction of rotation. The impeller blades 42 have inlet portions 44 inclined outwardly and forwardly to form an axial inducer section and to efiiciently receive the flow from the eye of inlet orifice 37 in a shock free manner. The blades 42 so designed also serve to increase greatly the flow factor of such mixedflow impellers. The impeller blades 42 receive the flow from the inlet orifice 37 in a substantially axial direction at their inlet portions, impel it first in a generally axial direction and then change it gradually, by the centrifugal action and the shape of the blades, to a generally radial direction until it is discharged at the discharge end 43 of the blades in said radial direction. Depending upon the desire-d flow-pressure head characteristics, the discharge ends 43 of the blades 42 need not have the same diameter at the backplate 40 as at shroud 41 and the flow discharge from said blades need not be in a radial direction as regards the axis of the impeller but may contain an axial component as well as a radial component.

Around the impeller 14 is a radial receiver passage 45 of minimum radial extent and comprising an inlet wall 46 and a backplate wall 47 mounted on a rabbeted surface 48 of the motor support 21. Around the receiver passage 45 are a plurality of cut-offs 50, five being shown equally spaced and of equal dimensions, forming the inlets to combined radial volute and axial diffuser passages 51 formed by vane assemblies 52 within the impeller cas ing 16 and axial casing 17. Each vane unit 52 comprises .a proportionate section of the backplate wall 47, a. corresponding-cut-oif 50, a radial volute section 53 within the impeller casing 16, an axial diffuser section 54 between the outer and inner circumferential walls of axial diffuser casing 17 and a wedge-shaped filler 55 to serve the dual purpose of gradually reducing the inner diameter of the volute passage from that of the backplate wall 47 down to that of the motor compartment housing 20 and to facilitate the divergence of the passage inwardly and thus effectively reduce the required outer diameter of the casing. Each of said vane units 5-2 is secured to the casing 17 by a screw stud 56 passing through the end wall of said casing and by two screw studs 57 threaded into the motor support 21, and is also secured to the impeller casing 16 by a screw stud 58 passing through the end wall of the casing 16. The vane assemblies 52 thereby serve not only as flow passages but also as a means of securing casing 17 to casing 16 with the assistance of a rabbeted joint 59 between

casings

16 and 17. While the vane assemblies 52 are shown made up of separate units, they could just as well be formed as a single multi-vaned assembly and inserted within the blower casing in the same or similar manner. Additionally, each said vane assembly 52 contains a dead space between the outer walls of radial volute section 53 and the inner" circumferential and end walls of casing 16 (shown seetionally in FIG. 8), which simplifies the design and construction of casing 16 and the molding of the vane assemblies but could be eliminated by appropriate shaping of the end wall of casing 16.

The aforesaid dead space serves as an area adjusting means for controlling the rate of divergence of the radial volute section 53 in conformity with the design characteristics of impeller 14, and further serves to distinguish the present invention from prior art machines such as represented by U.S. Patent No. 3,069,071 which shows a circumferential receiver, outside the impeller discharge, devoid of any form of radial volute passages.

Located at the inner ends of volute passages 51 around the impeller 14 are the cut-offs 50 radially spaced by a minimum clearance from the discharge ends 43 of the impeller blades 42. In the preferred form of the invention shown, this clearance is approximately 3% of the impeller diameter but as far as certain aspects of the invention are concerned, may vary from the least allowable operating clearance to that of a vaneless diifu-ser between

walls

45 and 47, such as described in the copending applications. The inlet edges of the cut oifs 50 are axially askewed from the inlet wall 46 to the backplate wall 47, i.e. the inlet edges of the cut-offs 50 extend obliquely with respect to a plane at right angles to the impeller axis. These cut-oifs 50 are axially askewed by a circumferential cut-ofi spanning angle (FIG. 6)

' defined as the angle between a radial plane, passing through the impeller axis and through the tip of the cutofi 50 at its junction'with inlet Wall 46 and a similar radial plane passing through the other tip of the cut-off at the point of junction of the cut-off with its section of backplate wall 47. This angle p is greater than the radially outer impeller spacing angle 0 measured similarly be tween the radial planes of successive impeller blades; In the specific form shown, the angle is approximately 26 while the angle 0 between sucessive blades is approximately. The ratio between the angle 3 and the angle 0 must be at least one but desirably less than 2.0, except that angle :1: should be at least 20.

it is well known that the cut-off of centrifugal blowerhousings is a major source of noise of such devices and various means have been employed to reduce or absorb such noise at its source. Reference is made to U.S. Patents 2,107,897, 2,160,666, 2,171,341 and 2,171,342. These various methods and others have hadvaried success in reducing in blowers the blade frequency and their harmonics to acceptable levels. However, any and all these known methods require a comparatively large clearance between such cut-off and the impeller blades ranging from a minimum of 5% of the impeller diameter to upwards of 8% or more and further require that these cut-offs be comparatively blunt. These factors are a cause of both reduced performance and efiiciency over a closely spaced, sharp edged cut-01f. It has been 'found in accordance with the present invention that this objectionable type of noise is substantially eliminated by askewing said cut-off by a cut-off spanning angle equal to or greater than the radially outer impeller spanning angle 6 necessary to span the space between successive impeller blades and that with this invention, the requirements for clearance, bluntness and all the other means employed in the prior art to control noise are eliminated.

This permits a cut-off designed solely for performance and ease of manufacture.

Since the ratio between the number of impeller blades (nineteen) and the number of cut-offs 50 (five) is not a whole number, this mix number relationship further tends to .cut down harmonics and resonances tending to create noises.

The volute passages 51 starting at the cut-offs 50 continue, in a diverging manner to. convert the high velocity at the impeller discharge into static pressure head, at first in a generally radial direction within the radial volute section 53. Then the volute passages 51 are gradually directed and shunted axially between the outer circular Wall of casing 17 and the outer surface of wedge-shaped filler 55 and the circumferential motor compartment housing 20, separated by the axial diffuser section 54 of the vane assembly 52 and terminate in overbends or overextended elbows containing an inner bend 61 having a protuberance 62 and an overextended outer bend 63. The resultant fluid jets issue substantial axially from the elbows 60 and are then directed radially inwardly by a second overbend elbow, containing in combination the curved surface 64 of casing 18 with its concentric protuberance 65 forming an overextended outer bend, and a slightly overextended intermediate vane 66, to direct the jets over the concave surface 67 of the motor support 22 and to the common axial discharge orifice 68 within the discharge flange 35.

As fluid goes through an elbow, it tends to crowd towards the outer bend of the elbow and away from the inner bend due to centrifugal action, so that the resultant momentum of the jet, ie the jet velocity times its mass, is offset from the positional centerline of the jet passage at the outlet of the elbow. This adverse condition is substantially nullified by shaping each elbow 60, so that the momentum of the elements of each jet emerging from the elbow is substantially uniform across the elbow from the inner bend to the outer bend. For that purpose, the inner bend 61 on the upstream side of the elbow 60 from which the stream tends to break away as it flows through said elbow, turns through an angle only sulficiently to direct the stream from the corresponding volute passage 51 in an axial direction but the outer bend 63 at the downstream side of the elbow has an overbend, i.e. turns through an angle greater than that sufficient to direct the stream in an axial direction. The effect of this overbend in the elbow 69 is to compensate for the tendency of the stream to crowd towards the outer bend 63 and to cause thereby the resultant momentum'of the jet entering the passage at the outlet of the elbow to be almost coincident with the centerline of the passage. The function of the overbend elbow 60 is described in detail in the aforesaid copending applications.

Another aid in preventing the stream passing through the elbow 60 from breaking away from the inner bend 61 of the elbow is the protuberance 62 on said bend to deflect the approach stream away from the immediate area of the bend to crowd said stream around and over said protuberance into the sides of the passage at the outlet of the elbow and thereby increase the actual and effective radius of the inner bend. The function of this protuberance 62 is also described in detail in the aforesaid application.

The overex-tension of the outer bend in the casing 18 with its concentric protuberance and its slightly overextended intermediate vane 66 serves a function similar to that described with reference to the elbow 60 with its overextended outer bend 63 and its protuberance 62 on its inner bend.

As a result of the construction described, the five equally spaced balanced streams of equal magnitude free from confining circumferentially spaced stream separating walls course radialy inwardly in the casing 18 and merge as they meet near the inlet of the axial discharge orifice 68. As a result of the construction described, the rotational velocity components, turbulences, undesired accelerations, eddies and vacuous pockets in the stream are reduced materially before and as they enter the axial discharge orifice 68, so that the merging of the streams in this orifice is accomplished smoothly with minimum loss of efiiciency.

The functions of the overbend elbows and the Wall means for the production of radial jets of balanced inward momentum and their combination into a single axial dis charge stream are similar to those described in detail in the aforesaid copending applications, except that the second overbend in this invention contains the intermediate vane 66 of lesser overbend proportions to further contribute to the efiicient turning of the jets from axial to radially inward. The need for such a vane or vanes arises because of the high aspect ratio (ratio of the depth of the stream perpendicular to the axis of the bend to that of its width parallel to said axis) of the bend and the desirability of minimizing the axial space required to accomplish the reduction in discharge diameter. As far as certain applications and uses are concerned, the intermediate vane 66 may be omitted, and further it is within the broad scope of the invention to dispense entirely with the second overbend elbow and make use of a single overbend elbow at the terminus of each passage to direct the jets radially inward or at any angle from an axial direction to radial inward direction with balanced momentum in accordance with the teachings of copending application Serial No. 175,940 to thereby obtain any desired discharge convergence.

Cne of the important objectives of the present invention is to reduce the normally large outer diameter of centrifugal blowers, while at the same time permitting a greater than two fold increase in the flow factor normal for such machines. This is accomplished in the present invention by the substitution of combined radial-axial volute and diffusing passages for the usual overlapping radial volute passages together with the use of the axial space over the driving motor which would otherwise be wasted. This is possible in the present invention as an added result of and in combination with the askewed cut-off 50 previously described in detail. This askewed cut-off 5% permits a gradual and orderly conversion of the normal radial volute to an axial passage with substantially little or no radial overlap of successive volutes. For purposes of describing this feature of the invention and to distinguish from prior art machines, consider a radial plane rotatable about the axis of the impeller and having an axial width equal to the spacing between the inlet wall 46 and backplate wall 47, or the equivalent, radial overlap may be considered to occur when any radial element of, or radial line on, the said plane intercepts any wall separating any portion of one jet from the adjacent jet. The term radial overlap as herein used is expressed as the percentage of the total projections of said intercepted areas on the total cylindrical surface having the mean diameter and axial width of the fluid receiver 45, or its equivalent. Similarly, axial overlap may be considered to occur when any axial element of a radial plane rotatable about the impeller axis, or any line on said plane parallel to the axis, intercepts any wall separating any portion of one jet from an adjacent jet having common directional components. The term axial overlap as herein used is expressed as the percentage of the total of the projections of the said intercepted areas on the total circumferential area between the impeller backplate diameter and the outer contour of the housing inner wall.

Referring to FIG. 7, the projection of the total intercepted area of each volute passage by radial elements of a radial plane passing through the axis of the impeller is bounded by the construction lines around area X, and for the purpose of the present invention shown, the radial overlap need not exceed 15 to 25% to effect an orderly axial shift of one volute passage around the next succeeding passage and could with slightly reduced performance be entirely eliminated. In the specific form shown, the radial overlap is approximately 17%. This radial overlap is exceedingly low as compared to the usual to 200% radial overlap found in conventional multi-volute centrifugal pumps. The radial overlap of the invention shown in copending application Serial No. 175,940 is approximately 100%.

Referring to FIG. 5a, the projection of the intercepted area of a preceding passage with respect to a chosen passage by axial elements of or lines on a radial plane passing through the impeller axis is represented within the construction lines around area Y and the additional intercepted area of the succeeding passage is represented within the construction lines around the smaller area Y the total axial overlap is represented by an area equal to area Y plus area Y This axial overlap is desirably above 75 In the specific embodiment of the invention shown, the axial overlap is approximately 78%, compared to substantially in the machines of the aforesaid copending applications.

The combined radial and axial overlaps must exceed 75% and desirably should total approximately 100% or higher for maximum conversion of the high velocity head at the impeller discharge into static head for elficient overall performance. In the preferred form of the present invention, the ratio of axial overlap to that of the radial overlap must be greater than 2.0 and desirably should be as high as 4.5 or higher.

Thus, there has been created in accordance with the present invention, a diffuser for converting velocity head to static head that is the exact converse of the mixedflow impeller in that it receives the stream at high radial velocity from the impeller discharge and gradually changes its direction into an axial one while at the same time reducing its velocity.

Referring to FIG. 8, the blower of FIG. 1 with discharge casing 18 removed is shown mounted in a metal panel 70, such as might represent the outer wall of a cubical enclosure, by five symmetrically spaced servo mounts 71, each comprising a screw 72, a nut 73, a lock-washer 74 and a heavy washer 75 having a milled out crescent recessv 76 forming a crescent shaped tongue extending into a correspondingly milled recess 77 formed-in the casing 16 (FIG. Similar recesses 77a are likewise milled in casing 17 to permit a similar mounting in a panel 70 at the opposite end, to permit a reversal of the flow direction by turning the complete blower unit around or other mounting considerations, To further facilitate the mounting of the blower unit in the panel 70, circular rabbeted flange 78 is provided at the endtof casing 16 to fit conveniently into a round hole in the panel 70, and a like rabbeted flange 78a is also provided on casing 17 for like panel mounting but is used additionally for the mounting of casing 18 to casing 17. comes an axial blower having centrifugal performance and 'efliciency and suitable as replacements for vane-axial or similar devices of lower efiiciency and much higher noise levels. Although the milled recesses 77 and 77a are shown as symmetrically spaced, it is understood that any spacing or number could be used, or continuous circumferential grooves might be substitutedtherefor without departing from the broad concepts of the present invention.

Referring to FIGS. 9 and 10, there is shown a modified form of the present invention affording the highest possible flow factor with the same outside diameter and employing an impeller of larger inlet diameter and blading of larger diameter at the inlet shroud than at the backplate. In the modified form, impeller 14a is driven by motor 11a through shaft 13a in the same manner as described for the blower of FIG. 1 and comprises a backplate 40a, an inlet shroud 41a and a plurality of blades 42a therebetween. The outer diameter of the inlet shroud 41a and the outer discharge ends 43a of the blades 42a at the said shroud is larger than that of the backplate 40a thus providing a conical shaped discharge which permits the largest possible radial space between the impeller backplate 40a and the other wall of casings 16a and 17a to handle the higher flow from said impeller in an efficient manner. Around the outside of the impeller 14a is located a plurality of cut-offs 50a, five being used, askewed by the cut- The blower so mounted be off spanning angle a of higher value than the radially.

outer impeller spacing angle 0a between successive blades 42a, and further radially askewed between

passage walls

46a and 47a by an amount equal to the difference between r and r sufiicient'to maintain a constant radial clearance between said cut-offs and the discharge ends 43a of the blades 42a. The cut-offs 5011 form the entrance to radialaxial volute passages 51a separated by vane assemblies 52a which'terminate in overbend elbows 60a in the same man: ner as previously described.

Further in the modified form of the present invention shown in FIG. 9, the cylindrical motor compartment housing 20 of the blower of FIG. 1 has been eliminated for the combined purposes of (1) conserving radial space over the motor, (2) providing a maximum of ventilation for the said motor, and (3) eliminating the additional weight and cost of the said housing. Thecentrifugal forces on the fluid particles due to their circumferential motion in the radial volute and axial diffusing passages 51a tend to keep the streams confined to their respective passages with out the need for the inner confining wall. Hence, the inner periphery ofthe axial diffusing passages may be wall-free in the manner of the previously described circumferential wall-free stream passages within discharge casing 18, or the outer diameter of the driving motor 11a may partially serve as such a confining wall.

7 While the modified blower of FIG. 9 operates efliciently at the extremely high flow factors for mixed-flows blow-t ers within a minimum outside diameter of easing, it has limited suitability and efliciency for multi-stage operation because some of the requirements for suppressing eddies, turbulences and vacuous pockets in the discharge stream have been traversed in this modified specie of the invention Any simple and inexpensivelmeans for reducing the required number and/or complexity of sizes is of extreme economic importance. It is believed that the present invention fulfills that desideratum.

The improved blower of the present invention affords simple and inexpensive means for varying the performance over a wide range Within the same housing and the same basic impeller by reducing its outer diameter in convenient'steps, usually by reducing the diameter of the backplate 40 by a greater percentage than that of inlet 41,

and still maintain its inherent high efiiciency. As the outer diameter of the impeller is reduced, the inlet wall 46 and the backplate wall 47 form a vaneless difiuserfor partially converting the high velocity at the impeller discharge into static head in an efiicient manner prior to reaching the cut-offs 50. It is to be. understood that the broad concepts of the invention permit such latitude in impeller design within the same housing or the cut-offsSt] may be extended into said diffuser to form a vaned diffuser askewed in the manner described to obtain any desired I performance characteristics. Further, while the improved axial housing is shown for a mixed-flow type impeller and it is particularly well suited to this type due to its high flow factor, other impeller designs having a relatively low ratio of discharge width to impeller diameter, of the order of .25 or less, would operate satisfactorily.

In'the following claims, radial overlap and axial overlap are intended to mean the overlaps hereinbefore described.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended presenting an inlet cut-off edge near the discharge periphcry of said impeller extending obliquely with respect to a plane at right angles to the impeller axis.

r l l centrifugal fluid pump as described in claim 1, wherein the volute passages have radial, circumferential and axial flow components, the circumferential flow components being in the direction of rotation of the impeller, each of said cut-off edges extending obliquely from the inlet side of the pump in a direction having a circumferential component in the direction of rotation of the impeller.

3. A centrifugal fluid pump comprising an impeller having a plurality of equally spaced blades, and means forming a plurality of volute passages extending around the discharge periphery of said impeller and each presenting an inlet cut-off edge near the discharge periphery of said impeller extending obliquely with respect to a plane at right angles to the impeller axis, the ratio between the number of blades in said impeller and the number of cutoff edges being other than a whole number.

, 4. A centrifugal fluid pump having an inlet and an outlet and comprising an impeller having atplurality of spaced blades, and means forming a plurality of volute passages extending around the discharge periphery of said impeller and each presenting an inlet cut-off edge near the discharge periphery of said impeller extending obliquely with respect to a plane at right angles to the impeller axis, the radius of the blades to the outer tips thereof on the sides of the blades nearest the inlet ofthe pump being substantially the same as the radius of the blades to the outer tip thereof on the side of the blades furthest from the inlet of the pump, whereby the outer discharge edges of the blades conjointly define a cylindrical outline.

, 5. A centrifugal fluid pump having an inlet and an outlet and comprising an impeller having a plurality of spaced blades, and means forming a plurality of volute passages extending around the discharge periphery of said impeller and each presenting an inlet cut-01f edge near the discharge periphery of said impeller extending obliquely with respect to a plane at right angles to the impeller axis, the radius of the blades to the outer tips thereof on the sides of the blades nearest the inlet of the pump being greater than the radius of the blades to the outer tips thereof on the side of the blades furthest from the inlet of the pump, whereby the outer discharge edges of the blades conjointly define a substantially conical outline.

6. A centrifugal fluid pump comprising animpeller having a plurality of equally spaced blades, means forming a radial receiving passage around said impeller and comprising an inlet wall and a back Wall, means forming a plurality of volute passages extending around the discharge periphery of said impeller and each presenting an inlet cut-off edge in said receiving passage located between said walls near the discharge periphery of said impeller and extending at an oblique, angle with respect to a plane at right angles to the impeller axis, each of said cut-oif edges terminating at its tips near said walls respectively, the cut-off spanning angle between two radial planespass: ing through the impeller axis andthe tips respectively of said cut-off edge being greater than the radially outer impeller blade spacing angle between two radial planes pass ing through the corresponding radially outer edge sections respectively of successive impeller blades. 7

7. A centrifugal fluid pump comprising an impeller having a plurality of equally spaced blades, means forming a radial receiving passage around said impeller and comprising an inlet Wall and a back wall, means forming a plurality of volute passages extending around the discharge periphery of said impeller and each having radial, circumferential and axial flow components, the circumferential flow components being in the direction of rotation of the impeller, each of said volutes presenting an inlet cut-01f edge in said receiving passage located between said walls near the discharge periphery of said impeller and extending at an oblique angle with respect to a plane at right angles to the impeller axis from said inlet wall in a direction having a circumferential component in the direction of rotation ,of the impeller, each of said cut-off edges terminating at its tips near said walls 12 respectively, the cut-off spanning angle between two radial planes passing through the impeller axis and the tip respectively of said. cut-off edge being greater than the radially outer impeller blade spacing angle between two radial planes passing through the corresponding radially outer edge sections respectively of successive impeller blades, the ratio between the number of blades in said impeller and the number of cut-0ff edges being other than a whole number.

8. A centrifugal fluid pump. comprising an impeller .With an axial inlet, a motor coaxial with said impeller for driving said impeller,,an axial discharge, means forming a plurality of volute passages extending around the discharge periphery of said impeller and each presenting an inlet cut-off edge near the discharge periphery of said impeller, each of said volute passages having radial, circumferential and axial flow components, said passages extending helically around said motor and terminating in respective elbows turned to direct the fluid radially inwardly towards said axial discharge, said passages extending with streamline continuity from the discharge periphery of said impeller to said elbows respectively.

9. A centrifugal fluid pump comprising an impeller of the mixed flow type, and means forming a plurality of volute passages extending around the discharge periphery of said impeller and having streamline continuity along their full lengths, said passages having radial and circum- :ferential flow components as well as axial flow components, said pump having an axial overlap substantially greater than the radial overlap.

It A centrifugal fluid pump comprising an axial impeller of the mixed flow type, a casing surrounding said impeller and extending axially a substantial distance beyond said impeller, said pump having an axial inlet for said impeller near one end of said casing and an outlet near the other end of the casing, and means forming a plurality of diffusing volute passages extending with streamline continuity from regions near the discharge periphery of said impeller radially, circumferentially and axially along said casing to said outlet, said ump having an axial overlap substantially greater than the radial over-lap.

r 11. A centrifugal fluid pump as described in claim 10, wherein said outlet .is anaxial one, and said casing has means for directing the streams from the discharge ends of said volute passages radially inwardly towards said axial outlet. 1

12. A centrifugal fluid pump having an inlet and an outlet and comprising an axial impeller, and means form- .ing a plurality of ditfusing volute passages around the discharge periphery of said impeller, said volute passages extending from the discharge side of said impeller to said outlet with streamline continuity radially, circumferentially and axially and having less than 25% radial overlap and more than 75% axial overlap.

. 13. A centrifugal fluid pump as described in claim 12, wherein said pump includes a casing with said inlets and outlets coaxial and extending at opposite ends of said casing.

14. A centrifugal fluid pump comprising a peripheral casing, an inlet and an outlet near opposite ends of said casing, an impeller on the discharge side of said inlet located between said inlet and said outlet, a motor in said casing for driving said impeller located between said impeller and 'said outlet and having its outer periphery spaced radially inwardly from said casing, means forming a plurality of volute passages extending around the discharge periphery and around the motor towards said outlet withstreamline continuity and having radial, circumferential and axial flow components, with said volute passages having an axial overlap substantially greater than the radial overlap.-

15. A centrifugal .fluid pump as described in claim 14,

wherein the inner peripheries of the parts of said volute passages extending around said motor are provided with W W p pher l Walls around said motor separating the :chamber enclosing said motor from said volute pas- 2,139,112 12/1938 Catranis 230130 sages. 2,331,299 10/1943 Blorn 103109 16. A centrifugal gas pump as described in claim 14, 2,474,611 6/1949 Wylie 230-42 wherein the inner peripheries of the parts of said volute 2,476,692 7/1949 Bernstein 230-42 passages extending around said motor are wall-free, 5 2,868,440 1/1959 McMahan 238130 whereby the inner peripheries of the parts of the volute passages extending around said motor are in free eorn- FOREIGN PATENTS munication with the chamber enclosing said motor. 75 347 12/1954 h 1 3 222 2 ifi g ifggfig 10 ROBERT M. WALKER, Primary Examiner.

DONLEY J. STOCKING, MARK NEWMAN,

1,275,672 8/1918 Goss 230127X 2,002,907 5/1935 Sessions 103 s7 V

Claims

8. A CENTRIFUGAL FLUID PUMP COMPRISING AN IMPELLER WITH AN AXIAL INLET, A MOTOR COAXIAL WITH SAID IMPELLER FOR DRIVING SAID IMPELLER, AN AXIAL DISCHARGE, MEANS FORMING A PLURALITY OF VOLUTE PASSAGES EXTENDING AROUND THE DISCHARGE PERIPHERY OF SAID IMPELLER AND EACH PRESENTING AN INLET CUT-OFF EDGE NEAR THE DISCHARGE PERIPHERY OF SAID IMPELLER, EACH OF VOLUTE PASSAGES HAVING RADIAL, CIRCUMFERENTIAL AND AXIAL FLOW COMPONENTS, SAID PASSAGES EXTENDING HELICALLY AROUND SAID MOTOR AND TERMINATING IN RESPECTIVE ELBOWS TURNED TO DIRECT THE FLUID RADIALLY INWARDLY TOWARDS SAID AXIAL DISCHARGE, SAID PASSAGES EXTENDING WITH STREAMLINE CONTINUITY FROM THE DISCHARGE PERIPHERY OF SAID IMPELLER TO SAID ELBOWS RESPECTIVELY.