Patent Description:
An impeller is a rotating component of a centrifugal pump which transfers energy from the power source that drives the pump to the fluid being pumped by accelerating the fluid outward from the center of rotation. The velocity of the impeller translates into pressure when the output movement is confined by the pump casing. Typically, an impeller includes a central hub or eye which is positioned at the pump inlet, and a plurality of vanes to propel the fluid radically. The central hub typically includes an axial bore or opening which may be splined to accept a splined driveshaft.

One of the challenges of centrifugal pumps is providing a generally constant pressure rise at the output of the pump across varying flow rates of the pump. This generally constant pressure rise is desirable for improving a dynamic stability of the system. Indeed, many contemporary high efficiency pumps, despite their high efficiency, have an appreciably lower pressure rise at low flow rates than at higher flow rates. To address this problem, a common solution is to use a less efficient centrifugal pump which does not exhibit as drastic of a pressure rise differential at low flow rates by increasing pump internal leakages. While such a solution has proven to be effective, it is not desirable in many cases, especially those applications where good thermal efficiency and low power consumption is a requirement.

Another approach to maintain a generally constant pressure rise across differing flow rates is to incorporate a stability valve into the system that effectively acts as a fixed orifice at any given flow. Unfortunately, this stability valve consumes extra power and reduces the pressure output of the pump. Further, with such a configuration, the overall size, weight, and cost of the system is increased.

Accordingly, there is a need in the art for a centrifugal pump which provides for a reduced amount of pressure rise variation across varying flow rates. The invention provides such a centrifugal pump. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

<CIT>) describes a self-priming centrifugal pump having an impeller chamber formed integrally with a coaxially disposed impeller bearing housing of less radial dimension, an integral reservoir for priming liquid is located at least in part beneath the said bearing housing and a port is arranged to afford communication between the impeller chamber and the reservoir so that during priming liquid is directed on to the periphery of the impeller which is provided with a series of interruptions or irregularities to increase turbulence on priming. The reservoir extends upwardly around the portion of the impeller chamber and, is connected to the impeller chamber by the port. In operation, liquid is drawn from the reservoir through port and is expelled by the impeller through upper port back to the reservoir.

<CIT> describes a centrifugal pump impeller which comprises a wheel cover plate forming a centrifugal pump impeller. The cover plate is provided with a mounting corresponding side corresponding to a body or pump cover of a centrifugal pump or corresponding to a liquid guide, and is provided with a plurality of cavities on the surface of the corresponding side, and the cavities are evenly and symmetrically arranged on the corresponding side in a surrounding manner.

<CIT> describes a centrifugal impeller wherein the peripheral edges of the shrouds include alternate teeth and recesses which are located between adjacent ones of the vane outer ends to be longitudinally along the arcuate impeller vanes.

In one aspect, embodiments of the invention provide an impeller for a centrifugal pump in accordance with claim <NUM>. An impeller according to such an embodiment includes a disc-shaped shroud which has a central axis and a central hub circumscribing the central axis. The impeller also includes a disc shaped baseplate having a central axis coaxial with the central axis of the shroud. The baseplate has a plurality of vanes extending from a first surface of the baseplate. The shroud includes a plurality of serrations formed circumferentially along a periphery of the shroud. The baseplate includes a plurality of serrations formed circumferentially along a periphery of the baseplate. The shroud is mounted against the baseplate.

The central hub of the shroud has a first outer diameter. The baseplate includes a central hub extending axially from the first surface of the baseplate. The central hub of the baseplate has a second outer diameter which is less than the first outer diameter. A portion of the central hub of the baseplate extends axially into an opening defined by the central hub of the shroud.

The plurality of serrations of the baseplate includes a plurality of major teeth and a plurality of minor teeth arranged such that multiple minor teeth are arranged between adjacent ones of the plurality of major teeth. Each one of the plurality of major teeth has a thickness measured in the circumferential direction. Each one of the plurality of minor teeth has a thickness measured in the circumferential direction. The thickness of each of the plurality of major teeth is greater than the thickness of each of the plurality of minor teeth, respectively.

The plurality of vanes are aligned with the plurality of major teeth such that a radially outer facing surface of each vane is coplanar with a radially outer facing surface of each major tooth, respectively. A combined thickness of each one of the aligned plurality of vanes and plurality of major teeth measured circumferentially is variable in the axial direction.

The plurality of serrations of the shroud includes a plurality of major teeth and a plurality of minor teeth such that multiple minor teeth of the plurality of minor teeth are interposed between adjacent ones of the plurality of major teeth. The plurality of major teeth of the shroud are aligned with the plurality of major teeth of the baseplate. The plurality of minor teeth of the shroud are aligned with the plurality of minor teeth of the baseplate.

Each one of the plurality of serrations of the shroud has a first width measured axially and each one of the plurality of serrations of the baseplate has a second width measured axially. The first width is less than the second width.

In yet another aspect, embodiments of the invention provide a centrifugal pump. An embodiment of such a centrifugal pump includes a pump casing that defines an inlet, an outlet, and an internal cavity disposed between the inlet and the outlet. The pump also includes a drive shaft. A portion of the drive shaft is rotatably disposed within the internal cavity. The pump also includes an impeller as claimed in claim <NUM> as its dependencies disposed within the internal cavity.

Turning now to the drawings, an embodiment of a centrifugal pump and its associated serrated impeller according to the teachings of the present invention are illustrated. As will be explained in greater detail below, the serrated impeller overcomes problems with existing impeller designs by reducing the variance of pressure rise across differing flow rates. Indeed, the serrated impeller imparts additional momentum and velocity to a working fluid of the pump at low flow rates such that, even at such low flow rates, there is a satisfactory pressure increase in the working fluid. At higher flow rates, the velocity of the working fluid approaches that of the impeller itself, and as such, the serrated impeller has less of an impact on the pressure rise of the working fluid. As a result, the pump maintains a significantly "flatter" pressure rise characteristic of the working fluid across a broad spectrum of flow rates. As a result, the need for a stability valve as well as the need to utilize a less efficient pump is eliminated.

With particular reference to <FIG>, a centrifugal pump <NUM> incorporating the aforementioned impeller is illustrated. More specifically, <FIG> illustrates a <NUM>-stage centrifugal pump. Two of the stages employ serrated impellers according to the teachings of the present invention. While a <NUM>-stage centrifugal pump is illustrated, it will be readily recognized that the advantages of the serrated impeller as described herein may be employed in other embodiments of centrifugal pumps, e.g. a single stage centrifugal pump.

Centrifugal pump <NUM> includes an outer casing <NUM>. Centrifugal pump <NUM> also includes a number of inlets and outlets for each of its respective stages. Indeed, for one of the aforementioned stages, there is an inlet <NUM> and an outlet <NUM>. An internal cavity <NUM> is defined between inlet <NUM> and outlet <NUM>. A serrated impeller <NUM> is situated within internal cavity <NUM>. Impeller <NUM> is utilized to pump or convey a working fluid from inlet <NUM> to outlet <NUM>. In another one of the stages of centrifugal pump <NUM>, there is another inlet <NUM> and outlet <NUM>. Another internal cavity <NUM> is positioned between inlet <NUM> and outlet <NUM>. A serrated impeller <NUM> is situated within internal cavity <NUM>. This second serrated impeller <NUM> is identical to serrated impeller <NUM>, except that it is a mirror image.

Turning now to <FIG>, a cross-section of centrifugal pump <NUM> is shown taken through the plane extending through outlet <NUM>. This cross-section illustrates the relative positioning of impeller <NUM> within internal cavity <NUM>. Impeller <NUM> is mounted on a shaft <NUM> (See also <FIG>). Rotation of shaft <NUM> results in a like rotation of impeller <NUM>. A peripheral edge <NUM> of impeller <NUM> includes a plurality of serrations <NUM> as shown.

In the particular configuration shown in <FIG>, as impeller <NUM> rotates clockwise relative to a working fluid disposed within internal cavity <NUM>, the plurality of serrations <NUM> impart extra momentum and power to the fluid causing the fluid to locally spin in a direction opposite to the rotation of impeller <NUM>, i.e. counterclockwise. At low flow rates, this results an additional pressure rise. As a result, the relatively small pressure rise at low flows of existing designs is overcome by such a configuration.

As the flow rate is increased, the impeller circumferential velocity and the velocity of the working fluid within the internal cavity <NUM> approach one another. As a result, there is less momentum and power transfer to the working fluid from the plurality of serrations <NUM>. Accordingly, the pressure rise of the working fluid at a low flow rate is closer to the pressure rise at a high flow rate than in non-serrated impeller designs. Therefore, the undesirable variance of pressure rise across varying flow rates is substantially reduced with such a configuration.

With reference now to <FIG>, the structural attributes of impeller <NUM> will be described in greater detail. As discussed above, but for being a mirror image, impeller <NUM> is identical to impeller <NUM> shown in <FIG>. Therefore, the description provided for impeller <NUM> applies equally well to impeller <NUM> introduced above.

With particular reference to <FIG>, impeller <NUM> includes a shroud <NUM> and a baseplate <NUM>. Shroud <NUM> is mounted directly to baseplate <NUM>. This mounting may be achieved by any mechanical connection. Shroud <NUM> and baseplate <NUM> are concentrically arranged about an axis <NUM> of impeller <NUM> passing through a center thereof. As can also be seen in <FIG>, the plurality of serrations <NUM> extend radially outward and define the outer periphery of impeller <NUM>. As will be understood from the following, both shroud <NUM> and baseplate <NUM> include their own serrations which are aligned with one another such that when fully assembled they form the aforementioned plurality of serrations of impeller <NUM>. It will be recognized, however, that such an alignment is not necessary. In other embodiments, the plurality of serrations on shroud <NUM> may be misaligned with the plurality of serrations of baseplate <NUM>.

With reference now to <FIG>, shroud <NUM> includes a central hub <NUM> defining a central opening <NUM>. A plurality of serrations <NUM> define the outer periphery of shroud <NUM>. This plurality of serrations <NUM> includes a number of major teeth <NUM> and minor teeth <NUM>, as will be discussed in greater detail below.

Baseplate <NUM> also includes a central hub <NUM> with an opening <NUM> therethrough. Openings <NUM>, <NUM> are sized such that shaft <NUM> (See <FIG>) may extend therethrough. Additionally, opening <NUM> is also sized such that the working fluid flows from internal cavity <NUM> and subsequently contacts baseplate <NUM>.

A plurality of vanes <NUM> extend axially outward from a first surface <NUM> of baseplate <NUM>. As can be seen from inspection of <FIG>, these vanes are arcuate in shape and extend from a diameter which is greater than an outer diameter of central hub <NUM> to an outer periphery of baseplate <NUM>. In other embodiments, vanes <NUM> may extend radially inward such that they contact central hub <NUM>. Also in other embodiments, vanes <NUM> may not extend radially to the outer periphery of impeller <NUM>, but instead may stop short of this outer periphery.

As was the case with shroud <NUM>, baseplate <NUM> also includes a plurality of serrations <NUM>. As can also be seen in <FIG>, each one of the plurality of vanes <NUM> includes a radially outer facing surface which is generally coplanar with a radially outer facing surface select ones of the plurality of serrations <NUM>. As discussed in greater detail below, this plurality of serrations <NUM> includes a number of major teeth <NUM> and a number of minor teeth <NUM>.

Turning now to <FIG>, an additional hub <NUM> extends axially outward from a second surface <NUM> of baseplate <NUM> for the reception of shaft <NUM> (See <FIG>). Although not shown, hub <NUM> as well as hub <NUM> may also include dynamic seals mounted thereon to sealingly engage an interior surface of pump casing <NUM>.

With reference now to <FIG>, the particular structural details of the aforementioned plurality of serrations will be discussed. Turning first to the plurality of serrations of shroud <NUM>, the same includes a number of major teeth <NUM> and minor teeth <NUM>. Major teeth <NUM> are distinguishable from minor teeth <NUM> in that they have a thickness t<NUM> measured in the circumferential direction which is greater than a thickness t<NUM> measured in the circumferential direction of minor teeth <NUM>. As can also be seen in this view, major and minor teeth <NUM>, <NUM> have a uniform width measured in the axial direction.

In a similar manner, the plurality of serrations of baseplate <NUM> include a number of major teeth <NUM> and minor teeth <NUM> as shown. Major and minor teeth <NUM>, <NUM>, are distinguishable in that a thickness t<NUM> measured in the circumferential direction of major teeth <NUM> is greater than a thickness t<NUM> measured in the circumferential direction of minor teeth <NUM>. It will also be recognized from inspection of <FIG> that thickness t<NUM> is equal to thickness t<NUM> and thickness t<NUM> is equal to thickness t<NUM>. As such, when the respective plurality of serrations of shroud <NUM> and baseplate <NUM> are aligned as shown they generally form a combined plurality of serrations with a number of major teeth and minor teeth. As described above, however, such an alignment is not necessary.

Another distinguishing factor between the major teeth <NUM>, <NUM> and minor teeth <NUM>, <NUM> is that between each major tooth <NUM>, <NUM> an end of one of the aforementioned vanes <NUM> is disposed. As introduced above, each vane <NUM> includes a radially outer facing surface which is generally coplanar with a radially outer facing surface of each major tooth <NUM> on baseplate <NUM>. The same holds true for each major tooth <NUM> of shroud <NUM>. From inspection of <FIG>, however, it will be recognized that the aforementioned radially outer facing surfaces of vanes <NUM> and major teeth <NUM> form a generally continuous and uninterrupted radially outer facing surface <NUM>.

It will also be recognized from inspection of <FIG> that major teeth <NUM>, <NUM> are annularly spaced apart at an angle θ<NUM> which is greater than an angular spacing between θ<NUM> between adjacent minor teeth <NUM>, <NUM>. In the particular configuration shown in <FIG>, there are two minor teeth <NUM>, <NUM> positioned between adjacent major teeth <NUM>, <NUM>. Further, the spacing or gaps formed between adjacent ones of major teeth <NUM> and minor teeth <NUM> as well as adjacent ones of minor teeth <NUM> is constant. The same holds true for major and minor teeth <NUM>, <NUM> of baseplate <NUM>. It will be recognized from the teachings herein that any number of teeth may be utilized. Further, it is also contemplated that rather than using major teeth and minor teeth of differing thicknesses taken in the circumferential direction, all teeth may have a uniform thickness.

Turning now to <FIG>, a cross-section of impeller <NUM> is illustrated. The aforementioned concentric alignment of shroud <NUM> and baseplate <NUM> is shown. Hub <NUM> of baseplate <NUM> extends axially into opening <NUM> of hub <NUM> of shroud <NUM>. Working fluid enters opening <NUM> as illustrated generally by flow directional arrows, and then encounters vanes <NUM> as it is propelled radially outward to the outer periphery of impeller <NUM>.

As discussed above, the plurality of serrations of impeller <NUM> are configured to impart additional momentum and power to the working fluid at lower flow rates. Indeed, FIG. <NUM> illustrates a comparative example of a centrifugal pump employing a serrated impeller and a centrifugal pump which does not include a serrated impeller, i.e. a baseline impeller.

As can be seen from this graph, the difference in pump pressurize at a low flow rate of <NUM> gpm and a high flow rate of <NUM> gpm for a pump employing a serrated impeller is considerably less than a baseline impeller. As a result, the system produces a more desirable pressurize across low flow rates. This advantageously reduces or entirely eliminates the need to use a less efficient pump, or additionally or in the alternative, a stability valve to ensure that there is a sufficient pressurize at lower flow rates.

Claim 1:
An impeller (<NUM>, <NUM>) for a centrifugal pump, the impeller comprising:
a disc-shaped shroud (<NUM>) having a central axis, and a central hub (<NUM>) circumscribing the central axis, wherein the central hub of the shroud has a first outer diameter and defines an opening (<NUM>);
a disc-shaped base plate (<NUM>) having a central axis coaxial with the central axis of the shroud, the base plate having a plurality of vanes (<NUM>) extending from a first surface of the base plate, wherein the base plate includes a central hub (<NUM>) extending axially from the first surface of the base plate, the central hub of the base plate having a second outer diameter which is less than the first outer diameter and defining a second opening (<NUM>);
wherein the shroud includes a plurality of serrations (<NUM>) formed circumferentially along a periphery of the shroud, wherein the plurality of serrations of the shroud includes a plurality of major teeth and a plurality of minor teeth such that multiple minor teeth of the plurality of minor teeth are interposed between adjacent ones of the plurality of major teeth;
wherein the base plate includes a plurality of serrations (<NUM>) formed circumferentially along a periphery of the base plate, wherein the plurality of serrations of the base plate includes a plurality of major teeth (<NUM>) and a plurality of minor teeth (<NUM>) arranged such that multiple minor teeth are arranged between adjacent ones of the plurality of major teeth, wherein each of the plurality of vanes are aligned with each of the plurality of major teeth such that circumferential sides on an end of each vane are disposed between circumferential sides of the major teeth of the base plate and the major teeth of the shroud,
wherein the shroud is mounted against the base plate, and
wherein each one of the plurality of serrations of the shroud has a first width measured axially and wherein each one of the plurality of serrations of the base plate has a second width measured axially, wherein the first width is less than the second width.