US3146722A

US3146722A - Centrifugal pumps and the like

Info

Publication number: US3146722A
Application number: US82552A
Authority: US
Inventors: Warman Charles Harold
Original assignee: Research and Development Pty Ltd
Current assignee: Research and Development Pty Ltd
Priority date: 1960-01-19
Filing date: 1961-01-13
Publication date: 1964-09-01
Anticipated expiration: 1981-09-01

Description

CENTRIFUGAL PUMPS AND THE LIKE Filed Jan. 13, 1961 5 Sheets-Sheet 1 Charles H. Warman INVENTOR v ATTORNEYS 5 Sheets-Sheet 5 INYENTOR ATTORNEYS C. H. WARMAN CENTRIFUGAL PUMPS AND THE LIKE Sept. 1, 1964 Filed Jan. 13, 1961 mm Q Sept. 1, 1964 c. H. WARMAN CENTRIFUGAL PUMPS AND THE LIKE 5 Sheets-Sheet 4 Filed Jan. 13, 1961 Charles H. Warman BY MM, Maw

ATTORN EYS Sept. 1, 1964 c. H. WARMAN 3,146,722

CENTRIFUGAL PUMPS AND THE LIKE Filed Jan. 13, 1961 5 Sheets-Sheet 5 United States Patent 3,146,722 CENTRIFUGAL PUMPS AND THE LIKE Charles Harold Warman, Castiecrag, New South Wales,

Australia, assignor to Research and Development Pty.

Ltd, Perth, Western Australia, Australia, a corporation of Western Australia Filed Jan. 13, 1961, Ser. No. 82,552 Claims priority, application Australia Jan. 19, 1960 3 Claims. (Cl. 103103) This invention relates to centrifugal pumps, blowers, fans, compressors and like centrifugal units which will hereinafter be referred to as centrifugal pumps for convenience.

One object of the invention is to provide more efficient pump components and constructions. Another object is to provide a pump casing which, when the pump is used for pumping abrasive material, is less liable to wear. Other objects are to provide improved components and constructions as hereinafter described.

In any centrifugal pump, whatever its type or construction, the fluid discharged from the impeller into the casing has a variable total energy-variable both as to time and point of discharge from the impeller. In the casing there are losses of fluid energy. These losses are not uniform throughout the fluid and tend further to distort the already uneven distribution of energy of the fluid leaving the impeller. Losses of fluid energy in the casing occur chiefly at the cutwater, adjacent the containing surfaces and in the discharge branch.

In conventional pumps the fluid of higher energy issues from the impeller within a disclike layer substantially normal to the axis of rotation and of less thickness than the axial width of the impeller passages. If the impeller has a single axial intake from one side the disc layer will be towards or against the opposite side wall of the impeller passages. If the impeller is symmetrical in axial section and has axial fluid entry from both sides and flow rates from each side are substantially equal the disc layer will emerge more or less centrally from the periphery of the impeller.

It is a fundamental physical requirement of fluid flow in a curved path that the fluid of higher total energy will move to and displace lower energy fluid from the outer portion of the path. The higher energy fluid within the disclike layer emerging from the impeller consequently moves to the outer portion of the casing where it circulates until either it passes into the discharge branch of the casing or, by shock and turbulence from the cutwater or friction against the casing surfaces, it loses energy suflicient to be displaced toward the axis of the pump by fluid of higher energy. The displaced fluid constitutes a return flow moving towards the impeller and, superimposed on the main flow, gives rise to spiral flows in the casing. If the disc layer of higher energy fluid emerges from the impeller symmetrically with respect to the casing the flow in the casing consists of right and left hand spiral flows of approximately equal strength moving outwards in the center of the casing and inwards adjacent each of the sidewalls towards the axis of the pump. The result of the fluid movements described is that fluid of lower energy is displaced to positions adjacent the peripheries of the running clearances between the impeller and the sidewalls of the casing and portion of it passes into the clearances from Where it either returns to the casing by being re-energized by the side disc friction of the rotating impeller or joins the fluid entering the intake opening of the impeller. If the disc layer of higher energy fluid emerges from the impeller asymmetrically with respect to the casing then the spiral flows will correspondingly differ in size and strength and more or less lower energy fluid will be displaced to each side of the impeller. When the fluid contains solids in suspension the solids, particularly if large and of high density relative to the fluid in which they are transported, lose even more energy than does the fluid by shock and turbulence from the cutwater and friction against the casing surfaces and tend to become concentrated in the lower energy fluid and to pass with it into the running clearances between the impeller and the casing and there cause rapid wear of the parts and consequent reduced performance of the pump. Certain features of this invention provide zones of higher energy fluid adjacent the peripheries of the running clearances between the impeller and the sidewalls of the casing which act as barriers to isolate these clearances from the lower energy fluid in the casing.

In conventional pumps the discharge branch forms on the one side a continuation of the casing at its maximum radius and hence it preferentially discharges the higher energy fluid which occupies the outer portion of the easing. The other or cutwater side of the discharge branch is adjacent the periphery of the impeller and extends for the full width of the casing at this point. Consequently the higher energy fluid issuing from the impeller impinges directly on the cutwater and even under the most favourable conditions at best efficiency point, considerable shock and turbulence take place with corresponding loss in efliciency. When the fluid contains solids in suspension, as with slurry or dredge pumps, the shock and turbulence from impingement on the cutwater and resultant production of lower energy fluid with a higher than average concentration of solids is the most potent cause of wear of the pump components. This invention provides a construction in which the cutwater can be of substantially less width than the casing. It also provides that thecutwater may be so positioned that it cuts only fluid of lower energy. In these ways efliciency can be improved and wear reduced.

In conventional pumps a portion of the disc layer 01 higher energy fluid issuing from the impeller enters the discharge branch directly without impinging on any sur face and, having moved the least distance of any fluid in the casing, has the highest energy of all fluid entering the discharge branch. It is flanked on either side in an axial direction by fluid of lower energy entering the discharge branch and this lower energy fluid is held towards the cutwater side by higher energy fluid occupying the outer portion of the discharge branch. conventionally the discharge branch comprises a diverging nozzle with a substantially straight axis and its object is to convert fluid kinetic energy into pressure at the discharge flange. As the axis is straight the pressure over any cross section of the discharge branch is substantially uniform so that variatron m energy level of the fluid entering the branch from the casing appears as variation in kinetic energy and hence as variation in velocity over the cross section, areas of higher velocity corresponding with the areas occupied by fluid of higher energy. It is well known that it is not possible efficiently to convert fluid kinetic energy to pressure in a diverging nozzle when the velocity distribution is sensibly non-uniform and as the conversion cor responds to that to be expected from the lower velocity fluid, substantial loss of energy is sustained by the fluid of higher velocity. Features of this invention enable the fluid to enter the discharge branch with substantially uniform energy and velocity and thereby allow a higher efliciency of conversion of kinetic energy to pressure to be attained than is possible in a conventional pump.

Generally in a pump or blower according to the invention, means are provided for segregating and directing or for producing, segregating and directing fluid of differing energy levels in such a way that in the casing :3 fluid of higher energy level forms an envelope about the' fluid of lower energy level.

As a means of preserving the envelope of higher energy fluid and also of ensuring the greatest uniformity in the level of the energy of the fluid leaving the casing, the entry to the discharge branch from the casing is so located and shaped as to receive preferentially fluid of lower energy level and to exclude fluid of high energy level. As a result fluid energy losses resulting from casing wall contact are borne substantially by the higher energy fluid.

In one specific form the invention comprises an 1mpeller so shaped that its discharge consists of two peripheral side zones of higher energy fluid separated by a zone of lower energy fluid, the zones of higher energy being directed towards the casing sidewalls adjacent the periphery of the impeller.

One function of the shape of an impeller according to the invention is so to control the difference in energy levels of the fluid discharged by the impeller that the energy level of the higher energy fluid is reduced in the casing to substantially that of the lower energy fluid at entry to the discharge branch of the casing.

Some specific forms of the invention are illustrated in the accompanying drawings, wherein:

FIGS. 1, 2A, 2B and 3 are axial sections showing different forms of impeller and easing,

FIG. 4 is a section on line 4-4 of FIG. 1 with supporting shell members removed,

FIG. 5a is a fragmentary section of the casing on line 5a5a of FIG. 4,

FIG. 5b is a fragmentary section of the casing on line 5b5b of FIG. 4,

FIG. 50 is a fragmentary section of the casing on line 5c5c of FIG. 4,

FIG. 5d is a fragmentary section of the casing on line 5d5d of FIG. 4,

FIG. 5c is a fragmentary section of the casing on line 5e5e of FIG. 4,

FIG. 5 is a fragmentary section of the casing on line 5f5f of FIG. 4,

FIG. 6a is a fragmentary section of the casing on line 6a6a of FIG. 4,

FIG. 6b is a fragmentary section of the casing on line 6b6b of FIG. 4,

FIG. 60 is a fragmentary section of the casing on line 6c6c of FIG. 4,

FIG. 6d is a fragmentary section of the casing on line 6d--6d of FIG. 4.

Like parts are illustrated by like characters throughout the specification and drawings.

As shown in the drawings, and especially with reference to FIGS. 1 and 4, the pump comprises a casing C which has axially spaced

opposed walls

34 and 46, which in the embodiment of FIG. 1 are lined with a soft wear resistant material at 33 and 45. The casing C has a peripheral wall 21 made up of the peripheral portions of the casing halves and lined with wear

resistant linings

29 and 31. The axially spaced walls and peripheral wall define a pumping chamber 3, and projecting into the pumping chamber toward the axis of the casing is a ridge 22 which extends around a substantial portion of the periphery of the circumferential wall of the casing. The opposite peripheral ends 24 and 25 of said ridge taper gradually outwardly toward the circumferential wall of the casing in the circumferential direction of said ridge. The ridge 22 has a top surface 2212 which has an axial width substantially less than the axial spacing of the side walls. The ridge 22 and the side walls define between them circumferentially extending concave grooves 23 which are coextensive with said ridge.

An impeller 1 is mounted on a shaft 2 for rotation in the counterclockwise direction (as viewed in FIG. 4) within the pumping chamber 3 of the casing. The impeller has opposed axially spaced

walls

5 and 6 with the peripheral portions of the inwardly opposed surfaces of the

walls

5 and 6 flared smoothly outwardly at 16 toward the respective adjacent opposed walls of the casing. The impeller 1 further has blades 4 between the

walls

5 and 6 which define between them passages 7 leading from an axial inlet 8 to impeller outlets 9. The outside surfaces of the

impeller walls

5 and 6 can have auxiliary side vanes 1t; mounted thereon.

The radially outer trailing ends of the blades 4 have a smooth concave recess 11 in the central portion thereof, the effect of which is to reduce the energy imparted to the fluid in the region of the groove by the impeller. As illustrated, the centerline of the groove 11 is offset in the axial direction from the centerline of the impeller in the direction of the impeller wall 5 which is remote from the intake, in order to counteract the effect of the single axial intake, which would otherwise cause the fluid to issue from the impeller with energy and volume which is greater adjacent the plate 5 than adjacent the plate 6. The extent, shape and position of the grooves 11 and the ends of the vanes 4 depends on the relative energy levels, volumes, positions and flow directions of the fluid energy zones required by a particular pump construction and the point of operation on the pump characteristic performance curve.

The opposed side walls of said casing are curved smoothly at 29a and 31a from adjacent the periphery of the impeller 1 into the grooves 23.

The casing has a discharge branch 20 thereon which opens into the pumping chamber 3 of the casing only through the top surface 22a of the ridge 22 at 19 along a portion of the length of the ridge 22, said portion of the length of the ridge being at radial distances from the center of the casing which are less than the radial distances of the remainder of the top surface 221; from the center of the casing.

It will thus be seen that the

impeller walls

5 and 6, with the outwardly flared portions 16 thereof, the opposed casing wall portions 29a, the concave grooves 23, and the ridge 22 coact to produce a pair of fluid flows represented by the arrows 12, which flows are outwardly diverging from the periphery of the impeller 1, and then inwardly converging at the sides of the ridge 22. The flows 12 define a low energy central zone 13 into which fluid discharged from the grooved portion of the ends of the impeller vanes is discharged. In this manner the higher energy fluid flows form an envelope about the lower energy fluid, sustaining the losses from friction with the walls and isolating the low energy fluid from the impeller clearance spaces 18 between the impeller and the side walls.

By locating the opening 19 into the discharge branch 20 in the top of the ridge 22 at a smaller radius from the casing axis than the radius of the outer wall 21 of the casing, the higher energy fluid is excluded from the discharge. The ridge 22 and the grooves 23 are shaped so as to minimize the disturbance to the fluid flow in the casing, and the grooves are made of suflieient size to allow the higher energy fluid to bypass the entry 19 to the discharge branch. The ridge 22 is in general symmetrically positioned with respect to the casing as viewed in axial section, but it may be offset to suit some types of pump construction.

The entry 1? to the discharge branch, is in the form of an elongated circumferential slot occupying substantially the whole of the width of the top of the ridge 22 which is substantially less than the width of the casing. One end of the slot forms the cutwater 26 the width of which is consequently also substantially less than the width of the casing. In effect the ridge 22 penetrates the envelope of higher energy fluid l2 and places the entry to the dis charge branch in a position to receive preferentially the lower energy fluid 13. The loss of energy at the cutwater 26 is a minimum because the cutwater has the least possible width and cuts only the fluid of lower energy.

To ensure minimum loss of energy the area and attitude of the entry to the discharge branch are so arranged as to allow the fluid to pass from the easing into the discharge branch with velocity substantially unchanged in both direction and magnitude. The area of cross section of the discharge branch 20 provided at the cutwater section 6a'-6d (FIG. 6d) is such that the velocity of the fluid passing this cross section is substantially the same as at the entry 19 to the discharge branch. The portion of the discharge branch from the cutwater cross section 6d-6d to the discharge flange 27 is of increasing cross sectional area and so shaped that the centers of area of cross sections (FIGS. 6a to 6d inclusive), lie on a straight line substantially normal to the discharge flange, the rate of increase of cross sectional area being low enough throughout to ensure that high eificiency of conversion of the fluid kinetic energy to pressure at the discharge flange 27 is achieved. The shape of the discharge branch 20 is such that the walls are regular in the direction of fluid flow and transition in change of direction and of shape and area of cross section is gradual, as shown in FIGS. 4 and 5a and FIGS. 6a to 6d inclusive.

Within the casing the cross sectional area increases uniformly from the cutwater 26 to the commencement of the discharge branch at 23, in the direction of rotation, to accommodate fluid discharged by the impeller 1. From the commencement of the discharge branch at 28 to the cutwater 26 in the direction of rotation the cross sectional area of the casing decreases so as to maintain a constant average fluid velocity in this portion of the casing as fluid enters the discharge branch 20.

The casing comprises separately renewable sections shaped according to the invention with suitable joints between. For abrasive duty the casing sections are constructed of wear desistant materials and are supported and located by separate shell members. Such constructions are illustrated in FIG. 1 for a low specific speed type pump and in FIGS. 2A and 2B for a pump of higher specific speed. For non-abrasive or very slightly abrasive duty the casing sections are self-supporting and self locating. Such a construction is illustrated in FIG. 3. FIGS. 1 and 2A illustrate abrasion resisting construction in resilient material such as natural or synthetic rubber reinforced where necessary with metal. FIG. 2B illustrates abrasion resisting constructions in hard metal.

A half outer casing section liner shaped according to the invention is shown in resilient material construction as 29a in FIGS. 1 and 2A. It carries half of the ridge liner 22b and half of the discharge branch 20 and has a flange 30 adapted to be joined on the plane of symmetry of the casing to a half outer casing section liner 31a of opposite hand. The outer half casing section liners each have a side flange 32 adapted to make a joint in the manner shown with the casing side section.

The intake side casing section is made up of liner 33 which is a disc-like member formed of wear resistant material such as resilient natural or synthetic rubber bonded to a metal reinforcing wall 34 which carries a hollow cylindrical metal portion 35 to which is bonded the rubber lining 6 to form the intake 8. The cylindrical metal reinforcement 35 is provided with an annular shoulder 38 against which bear tapered cotters 39 driven through slots in the supporting intake side shell member 40. Qriving of the cotters 39 draws the intake side casing section liner 33 tightly against the resilient flange 32 of the outer casing section liner 2% which is supported by the shell member 40 and a fluid-tight joint is thus made with the resilient facing 41 of the side casing section liner. The rubberlined intake branch 8 of the side casing section liner 33 projects slightly beyond the face of the flange 42 of the shell member 40 and is adapted to make a fluid-tight joint with an intake pipe bolted to the flange. The intake side casing section liner 33 may be bevelled as at 43 in FIG.

2A to conform with the direction and facilitate the move ment of the higher energy fluid flow from the impeller. A conical projection 44 to which the impeller conforms, is provided about the intake branch 8 to facilitate the entry of abrasive slurry into the impeller and direct abrasive particles away from the side clearance space 18 between the impeller and the casing side section.

The shaft side casing section liner 45 is a disc-like member formed of resilient material such as natural or synthetic rubber bonded to a metal reinforcing wall 46. It has an annular projection 47 to the outer surface of which the auxiliary vanes 10 on the impeller conform with suitable running clearance, the purpose of the projection being to return to the vanes fluid leakage from the running clearance between the impeller and the casing side section. The reinforcing Wall 46 is provided with threaded bosses 48 into which studs 49 are screwed. The studs pass through holes in the shell member 50 and are provided with nuts 51 which may be tightened to draw the casing section liner 45 against the flange 32 of the outer casing section liner 31a and against the face 52 of the seal member 53, where fluid-tight joints are thus made. The shaft side casing section liner 45 may be bevelled as at 54 in FIG. 2 to conform with the direction and facilitate the movement of the higher energy fluid flow from the impeller.

The shell members 4-0 and 50 which locate and support the casing sections are drawn together by suitable bolts not shown in the figures and press together the resilient flanges 3t of the outer casing sections to make a fluidtight joint. The shell member 50 is adapted to locate and support interchangeably various forms of impeller shaft sealing means and to attach to a frame not shown in the figures for supporting the shaft bearings and maintaining alignment of the various parts.

An outer casing section shaped according to the invention is shown in two piece hard metal construction in FIG. 213. It has raised armula-r faces 56 which may be rough ground and are adapted to make fluid-tight joints with annular rings 57 of resilient material supported by the shell members 40 and 55 respectively. The

half sections

58 and 59 are of opposite hand and have flanges 60 between which a fluid-tight joint is made by means of a gasket 61 of resilient material. The hard metal outer casing sections are shaped and sized externally so as to be everywhere clear of the shell members 44) and Stl from which they are supported, and have joint sealing pressure applied, through the joint rings 57.

The hard metal intake side casing section 62 shown in FIG. 2A is similar in shape and size to the corresponding sections in rubber covered construction illustrated in FIGS. 1 and 2A. The raised annular face 63, which may be rough ground, is pressed against the resilient ring 57 to make a fluid-tight joint by driving the tapered cotters 39 which pass through slots in the shell member 40 and bear on the annular shoulder 38.

The hard metal shaft side casing section 64 is similar in most respects to the corresponding sections in rubber covered construction. The raised annular face 63, which may be rough ground, is pressed against the resilient ring 57 by tightening the nuts of bolts 65 which pass through the shell member 50 in the manner of the studs 49 and which engage by means of square heads 66 and locknuts 67 suitable lugs 63 cast integrally with the side casing section 6

Resilient gaskets

69 and 70 serve to make fluid-tight joints between the casing side section 64 and adjacent seal member '71.

The self supporting casing construction illustrated in FTGJ 3 comprises two

casing sections

72 and 73 facejointed with a gasket at 74 and held together by studs 75 and nuts 76. Casing section 72 is flanged as at 77 for at taching to any suitable supporting frame and is provided with sealing means 78 where .the shaft 2 supporting the impeller 1 passes through the casing. Casing section 72 has a cylindrical opening 79 co-axi-al with the impeller and of diameter sufficiently large to permit easy removal of the impeller when the casing section 73, which closely fits the opening, is removed. The axial dimensions of the casing sections are such that when assembled the faced annular projections 80 and 81 on the respective sections are a close running fit with corresponding faced

annular projections

82 and 83 on the sides of the impeller. The casing section 73 is provided with the intake branch 8 which may be flanged as at 85 or otherwise adapted for connection to an intake pipe. Casing section '72 is provided with integral discharge flange 86 or other suitable means for connection to a discharge pipe.

As depicted in FIG. 3 the impeller and casing are for a pump of medium specific speed. Beyond the diameter of the impeller the walls of the casing diverge as at 87 and the outward flare of the impeller side plates and the dimensions and location of the groove 11 in the periphery of the impeller vanes are such as to project the streams 12 of higher energy fluid leaving the impeller adjacent and parallel to the diverging walls of the casing. The outer portion and discharge branch of the casing section '72 is shaped on its internal surface substantially as previously described with reference to FIGS. 4, 5 and 6.

What I claim is:

1. A centrifugal pump, comprising a casing having axially spaced opposed walls and a peripheral wall defining a pumping chamber, said peripheral wall having a circumferentially extending ridge extending around a substantial portion of the periphery of said circumferential Wall and projecting inwardly toward the axis of the casing, the opposite peripheral ends of said ridge tapering grad ually outwardly toward said circumferential wall in the circumferential direction of said ridge, said ridge having a top surface having an axial width substantially less than the axial spacing of said side walls, said ridge and spaced side walls defining between them circumferentially extending concave grooves coextensive with said ridge, an impeller in the pumping chamber of said casing rotatable about the axis of said casing, said impeller having opposed axially spaced walls with the peripheral portions of the inwardly opposed surfaces thereof flared smoothly outwardly toward the respective adjacent opposed walls of said casing, said impeller further having blades between said walls, the radially outer trailing ends of said blades having a smooth concave recess in the central portion thereof, said opposed walls of said casing curving smoothly from adjacent the periphery of said impeller into said grooves, and a discharge branch on said casing and opening into said pumping chamber of said casing only through the top surface of said ridge along a portion of the length of said ridge, said portion of the length of the ridge being at radial distances from the center of the casing which are less than the radial distances of the remainder of the top surface from the center of the casing, whereby said impeller walls and blades, said opposed casing walls, the concave grooves in said peripheral wall and said ridge coact to produce a pair of fluid flows which are outwardly diverging from the periphery of said impeller and then inwardly converging at the sides of said ridge, and said flows defining a lower energy central Zone at said discharge opening in said top surface of said ridge.

2. A centrifugal pump as claimed in claim 1 in which the said ridge is symmetrically positioned on the peripheral wall of said casing.

33. A centrifugal pump as claimed in claim 1 in which said opposed walls of said casing are inclined outwardly at an angle to the casing axis adjacent the periphery of said impeller.

References Cited in the file of this patent UNITED STATES PATENTS 873,923 Cousans Dec. 17, 1907 1,166,257 Rees Dec. 28, 1915 1,967,182 Allen July 17, 1934 2,465,625 Aue Mar. 29, 1949 2,992,617 Kroeger July 18, 1961 FOREIGN PATENTS 28,997 Finland Sept. 30, 1957 529,613 France Sept. 13, 1921 698,340 France Nov. 8, 1930 752,623 France July 24, 1933 62,505 Germany June 2, 1842 251,696 Great Britain May 6, 1926 323 Great Britain of 1868 68,264 Netherlands June 16, 1951 1,059,289 Germany Jan. 16, 1959

Claims

1. A CENTRIFUGAL PUMP, COMPRISING A CASING HAVING AXIALLY SPACED OPPOSED WALLS AND A PERIPHERAL WALL DEFINING A PUMPING CHAMBER, SAID PERIPHERAL WALL HAVING A CIRCUMFERENTIALLY EXTENDING RIDGE EXTENDING AROUND A SUBSTANTIAL PORTION OF THE PERIPHERY OF SAID CIRCUMFERENTIAL WALL AND PROJECTING INWARDLY TOWARD THE AXIS OF THE CASING, THE OPPOSITE PERIPHERAL ENDS OF SAID RIDGE TAPERING GRADUALLY OUTWARDLY TOWARD SAID CIRCUMFERENTIAL WALL IN THE CIRCUMFERENTIAL DIRECTION OF SAID RIDGE, SAID RIDGE HAVING A TOP SURFACE HAVING AN AXIAL WIDTH SUBSTANTIALLY LESS THAN THE AXIAL SPACING OF SAID SIDE WALLS, SAID RIDGE AND SPACED SIDE WALLS DEFINING BETWEEN THEM CIRCUMFERENTIALLY EXTENDING CONCAVE GROOVES COEXTENSIVE WITH SAID RIDGE, AN IMPELLER IN THE PUMPING CHAMBER OF SAID CASING ROTATABLE ABOUT THE AXIS OF SAID CASING, SAID IMPELLER HAVING OPPOSED AXIALLY SPACED WALLS WITH THE PERIPHERAL PORTIONS OF THE INWARDLY OPPOSED SURFACES THEREOF FLARED SMOOTHLY OUTWARDLY TOWARD THE RESPECTIVE ADJACENT OPPOSED WALLS OF SAID CASING, SAID IMPELLER FURTHER HAVING BLADES BETWEEN SAID WALLS, THE RADIALLY OUTER TRAILING ENDS OF SAID BLADES HAVING A SMOOTH CONCAVE RECESS IN THE CENTRAL PORTION THEREOF, SAID OPPOSED WALLS OF SAID CASING CURVING SMOOTHLY FROM ADJACENT THE PERIPHERY OF SAID IMPELLER INTO SAID GROOVES, AND A DISCHARGE BRANCH ON SAID CASING AND OPENING INTO SAID PUMPING CHAMBER OF SAID CASING ONLY THROUGH THE TOP SURFACE OF SAID RIDGE ALONG A PORTION OF THE LENGTH OF SAID RIDGE, SAID PORTION OF THE LENGTH OF THE RIDGE BEING AT RADIAL DISTANCES FROM THE CENTER OF THE CASING WHICH ARE LESS THAN THE RADIAL DISTANCES OF THE REMAINDER OF THE TOP SURFACE FROM THE CENTER OF THE CASING, WHEREBY SAID IMPELLER WALLS AND BLADES, SAID OPPOSED CASING WALLS, THE CONCAVE GROOVES IN SAID PERIPHERAL WALL AND SAID RIDGE COACT TO PRODUCE A PAIR OF FLUID FLOWS WHICH ARE OUTWARDLY DIVERGING FROM THE PERIPHERY OF SAID IMPELLER AND THEN INWARDLY CONVERGING AT THE SIDES OF SAID RIDGE, AND SAID FLOW DEFINING A LOWER ENERGY CENTRAL ZONE AT SAID DISCHARGE OPENING IN SAID TOP SURFACE OF SAID RIDGE.