A pump impeller for a centrifugal pump. The impeller is defined by a shroud rotatable about an axis of rotation. At least two pump vanes extend axially from the shroud, each of the vanes configured as a blunted tear drop shape and having an inside wall and an outside wall, the leading edges of which are interconnected by a blunt wall. The trailing edges of the inside and outside walls merge together. A substantially constant width flow channel is defined between the blunted wall of one vane and a confronting surface defined by an inside wall of the other vane. The vanes are tapered in the axial directions by inclining the inside wall of each vane radially outwardly.

TECHNICAL FIELD

The present invention relates generally to centrifugal pumps and in particular to a new and improved centrifugal pump impeller.

BACKGROUND ART

Centrifugal pumps often use multiple vane impellers to pump fluid such as water from an inlet to an outlet. Pump impellers are currently available which have two or more vanes. In order to pass solids through the pump, it is often desirable to utilize a two or three vane impeller. It has been found that existing two and three vane impellers may operate at reduced efficiencies and/or can be unacceptably noisy especially when run at higher speeds in order to generate higher head pressures.

In the most recognized standard two vane impeller design for solids handling the two vanes are normally relatively perpendicular to the shroud. Each vane usually has a constant width of, for example 0.38 inch. In order to pass the required solids the distance between an inlet leading edge of one vane and a trailing edge at the O.D. of the other vane (the space between the two vanes) may be too far apart for “normal/good” hydraulic design. Due to this spacing, the flow transition from an inside surface of the vane to an outside or working side of the vane in the suction region is unstable, especially at flows to the right or left of the “best efficiency point” (BEP). As the flow enters the working side of the vane it dumps into a “void” (open area) that causes the flow to recirculate back to the underside side of the vane. It is believed that these factors reduce the hydraulic efficiency and cause cavitation/noise.

DISCLOSURE OF THE INVENTION

The present invention provides a new and improved fluid pump which has increased hydraulic efficiency. In particular, the present invention provides a new and improved impeller for a fluid pump such as a centrifugal pump.

According to the invention, the pump impeller is rotatable within a pump chamber defined by the fluid pump and is driven by a source of rotation such as a motor. The impeller includes a shroud that is rotatable about an axis of rotation and at least two pump vanes that extend substantially axially from the shroud. Each vane is defined by an inside wall and an outside wall, the leading edges of which being interconnected by a substantially blunted wall. The vanes are arranged such that a flow channel is defined at least partially between the blunted wall of one vane and a portion of the inside wall of the other vane.

According to a feature of this invention, the flow channel has a substantially constant width, and more preferably, a constant cross-section.

In the preferred and illustrated embodiment, each vane is shaped as a truncated tear drop wherein the outside and inside walls of each vane merge together at a trailing end of each vane. In order to achieve this feature, the radius of the outside wall is greater than the radius of the inside wall.

In the exemplary embodiment, each vane tapers in the axial direction such that a width of a vane at a vane base where a given vane joins the shroud has a greater width than a distal side of the vane which is located near the inlet of the pump when the impeller is located within the pump chamber. In a more preferred embodiment, the tapering is achieved by inclining the inside surfaces of the inside wall of each vane outwardly such that the spacing between the vanes at the distal surface is greater than the spacing of the vanes at the vane base. With this configuration, each flow channel defined between the vanes defines a larger opening near the inlet of the pump and thus facilitates the pumping of entrained solids by the impeller.

According to the illustrated embodiment, the width of each flow channel does not vary by substantially more than 10%.

In the illustrated embodiment, the shroud is attached to a drive shaft forming part of the pump by suitable structure such as a threaded bore which is adapted to receive the threaded end of the drive shaft. According to another feature of the invention, a plurality of pump out vanes or channels are defined on the shroud and urge fluid between the underside of the shroud and a pump housing outwardly during rotation of the impeller.

The “truncated tear drop vane” configuration of the present invention actually extends a working side of the vane into the “void” region described above. As the flow transitions to this “extended” working side of the vane the flow is pushed or directed outward to the “actual” working side of the vane. This increases the hydraulic efficiency and reduces recirculation. The wider vane thickness also helps seal off leakage between the top face of the vane and the wear plate. This improves the efficiency at BEP a little but the largest advantage of this style vane is that it reduces the H.P. required at flows to the right or the left of BEP. It also appreciatively reduces the noise at flows to the right or left of BEP. This allows a pump fitted with the disclosed impeller to be operated at faster speeds and over an increased operating range and still have acceptable noise levels. The faster speeds produce desired higher head pressures while using the same size pump.

Additional features of the invention and a fuller understanding will be obtained by reading the following detailed description made in connection with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1illustrates the overall construction of an impeller embodying the present invention. The illustrated impeller includes two vanes10,12which as viewed inFIG. 1, extend upwardly from a shroud16. The shroud16defines a centrally positioned, threaded bore20by which the impeller is secured to a drive shaft (not shown). The drive shaft typically has a threaded end which is threadedly received by the bore20. Other methods for attaching the impeller to the shaft such as keyways are also contemplated. The impeller typically rotates within an impeller chamber (not shown) which may be formed at least partially by a volute (not shown). Generally, the central portion of the impeller as viewed inFIG. 2communicates with an inlet through which fluid i.e. water is drawn into the impeller chamber. The rotation of the impeller, in the counterclockwise direction, as viewed inFIG. 2causes the water to be discharged, under pressure, to an outlet (not shown) which communicates with a peripheral portion of the impeller.

An example of a centrifugal pump that may utilize an impeller constructed in accordance with the present invention is disclosed in U.S. Pat. No. 6,887,034 which is hereby incorporated by reference. Another example of a pump that may use the impeller shown inFIG. 1is disclosed in U.S. Pat. No. 3,898,014 which is also hereby incorporated by reference.

In the preferred and illustrated embodiment, the vanes10,12and shroud16are integrally formed such as by casting. The raw casting is then generally machined to more precisely define the impeller shown inFIG. 1.

FIG. 3illustrates the underside of the shroud16and as can be seen in this illustration, a plurality of pump out vanes26are defined or cast into the shroud. When the impeller is rotating, these channels drive the fluid and entrained solids between the underside of the impeller and the pump housing outwardly, i.e. towards the outer diameter of the impeller.

Referring again toFIG. 2, the vanes are shaped as truncated or blunted tear drops. In particular, each vane is defined by two curved, sidewalls30,32having different radii so that the vane narrows at a trailing edge indicated generally by the reference character36. As seen best inFIG. 2, the leading edge of each vane is defined by a blunt wall38that joins and interconnects the sidewalls30,32. The blunted wall is shaped and positioned so that a flow channel, indicated generally by the reference character40is defined between the blunt wall38of one vane and at least a portion of the inner sidewall30of the other vane. As seen best inFIGS. 1,2and12-15, the sidewalls30,32have their greatest separation at the blunted wall28. In other words, each vane is widest at the blunted wall38. Consequently, two such flow channels40each having a substantially constant cross section are defined. It has been found, that the illustrated impeller produces less noise in operation especially at higher speeds. The efficiency of the pump is also substantially improved over a wider operating range.

Referring toFIGS. 1,2and7-10, it can be seen that each vane preferably tapers from a vane base44to a top or distal end surface46of the vane. This surface is located near the pump inlet when the impeller is in the pump chamber. This is achieved by inclining the inner sidewalls of each vane. The resulting cross section of each vane at various locations are seen best inFIGS. 7-10. As seen in these Figures, the inclination of the inner walls30of the vanes10,12can vary along their extent. In the preferred embodiment, the outer sidewalls32of each vane are substantially constant and are substantially parallel to an axis of rotation of the impeller indicated by the reference character48inFIG. 3andFIG. 5.

As seen best inFIGS. 1 and 2, the outward inclination of the inner sidewalls30of each vane causes the spacing between the vanes to be larger at the tops46of the vanes (as viewed inFIG. 2) than at their bases44. It has been found that a larger spacing at the tops of the vanes which is nearer the pump inlet (not shown), improves the solids handling capability of the pump.FIGS. 12-15illustrate the variation in cross section of each as one proceeds from the base44of a vane and the top surface46of the vane.

Turning now toFIG. 11, the relationship and configuration of the vanes and the associated flow channels is more clearly illustrated and exampled. The two vanes10,12are designed such that a constant width not varying more than +/−10% forms a “flow channel”40. The channel40is defined by the radius “R1” (2.46 R) forming a working side of the vane “Vw” and the radii “R2” (3.73 R and 4.45 R) forming the vane inside surface “Vu”. (Vu and Vw correspond to the vane surfaces indicated by the reference character30and38, respectively inFIG. 2.) The length of the flow channel is proportional to the distance of the working vane diameter “Dw” (6.80 dia.) minus the vane inner diameter “D1shroud” (2.18 dia.) divided by the overall diameter of the impeller “D2” (9.75 dia.) minus the inner vane diameter “D1shroud” (2.18 dia.). The length of the channel is also proportional to the working vane diameter “Dw” (6.80 dia.) minus the inner vane diameter “D1top” (3.62 dia.) divided by the overall diameter of the impeller “D2” (9.75 dia.) minus the inner vane diameter “D1top” (3.62 dia.). The inlet vane angle formed between the shroud16and the top46of the vane may vary from 0 to 20 degrees. InFIG. 11A, the angle shown is 13 degrees.

Length of Channel Formulas

Bottom of vane ratio=(Dw−D1 shroud)/(D2−D1 shroud)=at least 47%
Top of vane ratio=(Dw−D1 top)/(D2−D1 top)=at least 47%
Note: In the above example the “length of channel bottom of vane ratio”=(6.8 dia.−2.18 dia.)/(9.75 dia.−2.18 dia.)=0.61 or 61%; “length of channel top of vane ratio”=(6.8 dia.−3.62 dia.)/(9.75 dia.−3.62 dia.=0.518 or 52%)

FIG. 16illustrates a prior art impeller design. The prior art impeller includes a pair of vanes10′,12′ and an integrally formed shroud16′. As seen inFIG. 16, the vanes10′,12′ have substantially constant width. The vanes10′,12′ are relatively narrow and define relatively sharp leading edges38′ and terminate at trailing edges36′.

FIG. 17compares the impeller of the present invention to the prior art impeller configuration. The vanes10,12of the present invention are shown in solid line whereas the prior art vanes10′,12′ are shown in dashed line. As can be seen inFIG. 17, the vanes10,12of the present invention are not of constant width and are substantially wider than the prior art vanes10′,12′. The vanes10,12of the present invention extend into and overlap a “void” area indicated generally by the reference character60which is located to the outside of the prior art vanes10′,12′.

It is believed that during operation of the prior art impeller, turbulence (indicated by the circular arrows62inFIG. 17) is generated in the fluid flowing through the void region60of the prior art impeller which reduces impeller efficiency and increases noise. The flow channels40defined by the vanes10,12of the present invention or equivalent structures are absent in the prior art impeller as is apparent inFIG. 17. Each vane10,12of the present invention has a working surface defined by the associated surfaces38and32, which is substantially larger than a working surface32′ defined by the prior art vanes10′,12′.

It is believed that the principles of this invention can be applied to an impeller with three vanes. Although the invention has been described with a certain degree of particularity, it should be understood that those skilled in the art, can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.