Patent Description:
One form of centrifugal slurry pumps generally comprises an outer pump casing which encases a liner. The liner has a pumping chamber therein which may be of a volute, semi volute or concentric configuration, and is arranged to receive an impeller which is mounted for rotation within the pumping chamber. A drive shaft is operatively connected to the pump impeller for causing rotation thereof, the drive shaft entering the pump casing from one side. The pump further includes a pump inlet which is typically coaxial with respect to the drive shaft and located on the opposite side of the pump casing to the drive shaft. There is also a discharge outlet typically located at a periphery of the pump casing. The liner includes a main liner (sometimes referred to as the volute) and front and back side liners which are encased within the outer pump casing. The front side liner is often referred to as the front liner suction plate or throatbush. The back side liner is often referred to as the frame plate liner insert.

The impeller typically includes a hub to which the drive shaft is operatively connected, and at least one shroud. Pumping vanes are provided on one side of the shroud with discharge passageways between adjacent pumping vanes. The impeller may be of the closed type where two shrouds are provided with the pumping vanes being disposed therebetween. The shrouds are often referred to as the front shroud adjacent the pump inlet and the back shroud. The impeller may also be of the open face type which comprises one shroud only.

One of the major wear areas in the slurry pump is the front and back side liners. Slurry enters the impeller in the centre or eye and is then flung out to the periphery of the impeller and into the pump casing. Because there is a pressure difference between the casing and the eye, there is a tendency for the slurry to try and migrate into a gap which is between the side liners and the impeller, resulting in high wear on the side liners.

As the slurry pump operates, the slurry is energized by rotary motion of the impeller. The slurry flows centrifugally and is collected by the main liner which directs the slurry towards the discharge outlet. Due to the main liner shape, the cut water area influences the flow pattern of recirculating slurry passing by. The side liners are in contact with the slurry within the cavity of the impeller shrouds. The proximity of the impeller outer shroud, or expeller vanes typical in the case of centrifugal slurry pumps, and the main liner cutwater to the frame plate liner may influence erosion rates endured by the side liners. In mill circuit duties, which are typically operated at low flow, erosion rates on the side liners is increased due to the increased rates of internal recirculation, which lead to the side liner eventually being a component with a short life span due to localized wear, sometimes referred to as "gouging".

In order to try and reduce wear in the region of the gap, it has been the practice for slurry pumps to have auxiliary or expelling vanes on the front shroud of the impeller. Auxiliary or expelling vanes may also be provided on the back shroud. The expelling vanes rotate the slurry in the gap creating a centrifugal field and thus reducing the driving pressure for the returning flow, reducing the flow velocity and thus the wear on the side liner. The purpose of these auxiliary vanes is to reduce flow re-circulation through the gap. These auxiliary vanes also reduce the influx of relatively large solid particles in this gap.

The reference in this specification to any prior publication (or information derived from the prior publication), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from the prior publication) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

<CIT>discloses a centrifugal pump with a housing having a bottom wall with a central inlet opening arranged with at least one spirally extending back flow affecting means on the side facing a lower cover disc.

One embodiment describes an impeller for a centrifugal pump, the impeller comprising: an inlet through which fluid passes into the impeller; pumping vanes for pumping the fluid from the inlet and expelling the fluid into a pumping chamber of the centrifugal pump in which the impeller operates; and at least one shroud extending radially from an axis of rotation for the impeller and attached to the pumping vanes, the at least one shroud having an outer surface facing away from the pumping vanes, wherein the outer surface includes a planar portion located near a centre of the impeller and a tapering portion located towards an outer edge of the shroud, characterised by the tapering portion being a compound shape with contiguous concave and convex regions.

In one embodiment the tapering portion of the at least one shroud has a thickness variation greater than outside the tapering portion.

In one embodiment the tapering portion reduces thickness of the at least one shroud on an outer face of the shroud.

In one embodiment the at least one shroud has auxiliary vanes.

In one embodiment the auxiliary vanes extend into the tapering portion.

In one embodiment the auxiliary vanes are tapered in the tapering portion.

In one embodiment the auxiliary vanes are absent in the tapering portion.

In one embodiment the convex region is located closer to the outer edge than the concave region.

In one embodiment a thickness of the at least one shroud decreased by at least half in the tapering portion.

In one embodiment the planar portion of the at least one shroud has a variable thickness.

In one embodiment the planar portion of the at least one shroud is thinner near the outer edge than near the centre of the impeller.

In one embodiment the at least one shroud is two shrouds located on either side of the pumping vanes and the fluid is pumped between the two shrouds.

In one embodiment, each of the two shrouds have a tapering portion.

One embodiment discloses a pump having an impeller as described above.

In one embodiment the pump has a patterned side liner.

In one embodiment the patterned side liner is selected from the set of side liner comprising a front side liner and a back side liner.

In one embodiment the patterned side liner is a grooved side liner.

In one embodiment the patterned side liner is has a radially swirling pattern.

Example embodiments are provided in the following description, which is given by way of example only, of at least one preferred but non-limiting embodiment, described in connection with the accompanying figures.

The following modes, given by way of example only, are described in order to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments.

Described is an impeller for a centrifugal pump having shrouds that are tapered at one end of the shroud. Each shroud of the impeller has a tapered region, located near an outer edge of the shroud. The tapered region reduces a thickness of the shrouds, with the shrouds getting thinner towards the outer edge of the shrouds. The tapered portion is a compound shape and having a concave and a convex region. The tapered portion may reduce wear of a liner of the pump, when the pump has a patterned side liner, compared to a pump using a flat side liner.

The impeller for a centrifugal pump has an inlet through which fluid passes into the impeller. The impeller has pumping vanes for pumping the fluid from the inlet and expelling the fluid into a pumping chamber of the centrifugal pump in which the impeller operates. The impeller also has one or more shrouds extending radially from an axis of rotation for the impeller and attached to the pumping vanes. The one or more shrouds have a planar portion located towards a centre of the impeller and a tapered portion located towards an outer edge of the shroud.

Referring to <FIG>, <FIG> and <FIG> of the drawings, there is generally illustrated a pump apparatus comprising a pump <NUM> and pump housing support in the form of a pedestal or base, not shown, to which the pump <NUM> is mounted. Pedestals are also referred to in the pump industry as frames. The pump <NUM> generally comprises an outer casing that is formed from two side casing parts or sections (sometimes also known as the frame plate and the cover plate) which are joined together about the periphery of the two side casing sections. The pump <NUM> is formed with side openings one of which is an inlet hole <NUM> there further being a discharge outlet hole <NUM> and, when in use in a process plant, the pump is connected by piping to the inlet hole <NUM> and to the outlet hole <NUM>, for example to facilitate pumping of a mineral slurry.

The pump <NUM> further comprises a pump inner liner arranged within the outer casing and which includes a main liner <NUM> and two side liners <NUM>, <NUM>. The side liner <NUM> is located nearer the rear end of the pump <NUM> (that is, nearest to the pedestal or base), and the other side liner (or front liner) <NUM> is located nearer the front end of the pump and inlet hole <NUM>. The side liner <NUM> is also referred to as the back side part or frame plate liner insert and the side liner <NUM> is also referred to as the front side part or throatbush. The main liner comprises two side openings therein. As shown in <FIG> the back side liner <NUM> comprises a disc like main body <NUM> having an inner edge <NUM> and an outer edge <NUM>. The main body <NUM> has a first side <NUM> and a second side <NUM>.

In some embodiments the main liner <NUM> can be comprised of two separate parts which are assembled within each of the side casing parts and brought together to form a single main liner, although in the example shown in <FIG> the main liner <NUM> is made in one-piece, shaped similar to a car tyre. The liner <NUM> may be made of materials such as rubber, elastomer or of metal.

When the pump is assembled, the side openings in the main liner <NUM> are filled by or receive the two side liners <NUM>, <NUM> to form a continuously-lined pumping chamber <NUM> disposed within the pump outer casing. A seal chamber housing encloses the side liner (or back side part) <NUM> and is arranged to seal the space or chamber between drive shaft and the pedestal or base to prevent leakage from the back area of the outer casing. The seal chamber housing takes the form of a circular disc section and an annular section with a central bore, and is known in one arrangement as a stuffing box (not shown). The stuffing box is arranged adjacent to the side liner <NUM> and extends between the pedestal and a shaft sleeve and packing that surrounds drive shaft.

As shown in <FIG>, <FIG> and <FIG>, an impeller <NUM> is positioned within the main liner <NUM> and is mounted or operatively connected to the drive shaft which is adapted to rotate about a rotation axis X-X. A motor drive (not shown) is normally attached by pulleys to an exposed end of the shaft, in the region behind the pedestal or base. The rotation of the impeller <NUM> causes the fluid (or solid-liquid mixture) being pumped to pass from a pipe which is connected to the inlet hole through the pumping chamber <NUM> which is within the main liner <NUM> and the side liners <NUM>, <NUM> and then out of the pump via the discharge outlet hole.

The impeller <NUM> includes a hub <NUM> from which a plurality of circumferentially spaced pumping vanes <NUM> extend. A central nose portion <NUM> extends forwardly from the hub <NUM> towards a passage in the front liner <NUM>. The impeller <NUM> further includes a front shroud <NUM> and a back shroud <NUM>, the vanes <NUM> being disposed and extending therebetween and an impeller inlet <NUM>. The hub <NUM> extends through a hole, formed by the inner edge <NUM> of the back liner <NUM>. The front shroud <NUM> and the back shroud <NUM> extend radially from an axis of rotation, rotation axis X-X, of the impeller <NUM> and are attached to the pumping vanes <NUM>. The front shroud <NUM> and the back shroud <NUM> are two shrouds located on either side of the pumping vanes <NUM> with a slurry being pumped between the two shrouds.

The impeller front shroud <NUM> includes an inner face <NUM>, an outer face <NUM> and a peripheral edge portion <NUM>, also referred to as an outer edge. The back shroud <NUM> includes an inner face <NUM>, an outer face <NUM> and a peripheral edge portion, or outer edge <NUM>. The front shroud <NUM> includes the inlet <NUM>, being the impeller inlet and the vanes <NUM> extend between the inner faces of the shrouds <NUM>, <NUM>. The shrouds are generally circular or disc-shaped when viewed in elevation; that is in the direction of rotation axis X-X.

Also shown on the front shroud <NUM> and the back shroud <NUM> are shroud tapers <NUM>. The shroud tapers <NUM> are located on the outer face <NUM> of the back shroud <NUM> and the outer face <NUM> of the front shroud <NUM>. Each of the shroud tapers <NUM> is a tapered portion of the shroud where thickness of the shroud is reduced. As shown, the reduction in thickness of the shroud at the tapered portion occurs on the outer surface of the shroud. In some embodiments the thickness of the shroud may be reduced for the outer and inner portions of the shroud. The shroud tapers <NUM> are located closer to the peripheral edge portion <NUM> and the peripheral edge portion <NUM>, also referred to as the outer edge of the shrouds. The shroud tapers <NUM> are located near planar portions <NUM> of the outer faces <NUM>, <NUM>. The planar portions <NUM> are located closer to, or towards, a centre of impeller <NUM> while the shroud tapers <NUM> are located closer to, or up to, the outer edge of the impeller <NUM>.

For the impeller <NUM>, the thickness of the front shroud <NUM> and the back shroud <NUM> varies to more in the shroud tapers <NUM> than for other portions of the shrouds <NUM>, <NUM> such as the planar portions <NUM>. For some impellers, the shroud tapers <NUM> may reduce, or vary, the thickness of the shroud by at least half in the tapered portion. That is, the thickness at the thicker end of the shroud tapers <NUM> is at least twice the thickness of the shroud tapers <NUM> at the thinner end. For some impellers the thickness reduction of the shroud tapers <NUM> may be approximately <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>%. For example, if the shroud thickness is <NUM> at the start of the tapered portion, the thickness at the outer edge may be <NUM> for a <NUM>% reduction.

Each impeller shroud may have a plurality of auxiliary or expelling vanes <NUM> on the outer faces <NUM>, <NUM> thereof. A shape of the auxiliary vanes may also be subject to the shroud tapers <NUM> with the end of the auxiliary vanes, located near an outer edge of the shrouds, conforming to the shaped of the shroud tapers <NUM>. Auxiliary vanes are an optional feature of the impeller.

The front side liner <NUM> has a cylindrically shaped inlet section <NUM> leading from an outermost end <NUM> to an innermost end <NUM>. When the pump <NUM> is in operation, the outermost end <NUM> may be connected to a feed pipe, not shown, through which slurry is fed to the pump <NUM>. The innermost end <NUM> has a raised lip <NUM> which is arranged in a close facing relationship with the impeller <NUM> when in an assembled position. The front side liner <NUM> has a surface <NUM>, facing in towards the pumping chamber <NUM>, which is in contact with the pump <NUM> during pump operation as well as an outer edge <NUM>.

An impeller <NUM>, as may be used in pump <NUM>, will now be described with reference to <FIG>. The figures show the impeller <NUM> with <FIG> showing a view of a back shroud <NUM>, <FIG> showing a view of a front shroud <NUM>, <FIG> showing a cross section through the impeller <NUM> and <FIG> showing a slice through the impeller <NUM>.

The pump inlet is coaxial with respect to a drive shaft and is located on the opposite side of the pump casing to the drive shaft. The drive shaft attaches to the impeller <NUM> through a hub <NUM>. The impeller <NUM> has circumferentially spaced pumping vanes <NUM> with a leading edge <NUM>. The circumferentially spaced pumping vanes <NUM> take slurry from an inlet, such as the cylindrically inlet section <NUM> of pump <NUM>, of a centrifugal pump.

Located on an outer face of the front shroud <NUM> are auxiliary vanes <NUM>. The auxiliary vanes <NUM> are located on a front side surface of the impeller <NUM>, the front side surface being the surface closest to a front side liner of the pump. The circumferentially spaced pumping vanes <NUM> are normally referred to as backwards-curving vanes when viewed with a direction of rotation of the impeller <NUM>. The auxiliary vanes <NUM> are also curved and are shown with curvature in the same direction as the circumferentially spaced pumping vanes <NUM>.

The auxiliary vanes <NUM> may assist in pumping slurry in a centrifugal pump. The auxiliary vanes may work in conjunction with other vanes, such as circumferentially spaced pumping vanes <NUM> of impeller <NUM> to move slurry from the inlet of the centrifugal pump to an outlet. In one embodiment, the back shroud <NUM> may also have auxiliary vanes.

Each shroud of the impeller <NUM> has a tapered portion <NUM> located at an outer edge <NUM> of the shroud. The tapered portion <NUM> is a region of the impeller <NUM> where a thickness of the impeller <NUM> is reduced. As shown in <FIG>, the tapered portion <NUM> has a concave region of taper <NUM>, located closer to the axis of rotation of the impeller <NUM>, and a convex region of taper <NUM> located at an edge of the shrouds. The two concave regions may have different radius of curvature or even varying curvature within a region. For example, the concave region of taper <NUM> and/or the convex region of taper <NUM> may have a varying radius of curvature.

The thickness of the front shroud <NUM> and the back shroud <NUM> is approximately halved for the impeller <NUM> with the reduction in the thickness occurring only from the outside face of the shrouds. Each shroud of the impeller <NUM> also has a planar portion <NUM> located on the outer face and located between the tapered portion <NUM> and a centre of the impeller <NUM>. The planar portion <NUM> includes the region of the impeller <NUM> where the auxiliary vanes <NUM> are located. The planar portion <NUM> may be a region where thickness of the front shroud <NUM> and the back shroud <NUM> may also decrease, but at a slow rate than the tapered portion <NUM>.

An impeller <NUM> will now be described in relation to <FIG> and <FIG>. The impeller <NUM> is similar to the impeller <NUM> and the impeller <NUM> described above. The impeller <NUM> has a hub <NUM> for receiving a drive shaft. Circumferentially spaced pumping vanes <NUM> are located between a front shroud <NUM> and a back shroud <NUM>. Located on the front shroud <NUM> are auxiliary vanes <NUM> that extend from a centre of the impeller <NUM> to tapered portion <NUM>. The auxiliary vanes <NUM> are located on a planar portion <NUM>, or substantially planar portion, of the front shroud <NUM>. The back shroud <NUM> also has a planar portion <NUM>, or substantially planar portion, located between the centre of the impeller <NUM> and the tapered portion <NUM>. The tapered portion <NUM>, extending to an outer edge <NUM> of the impeller <NUM> from the planar portion <NUM>, has a concave region <NUM> and a convex region <NUM>. As shown, the auxiliary vanes <NUM> are absent from the tapered portion <NUM>. The concave region <NUM> is located towards the centre of the impeller <NUM> and the convex region <NUM> is located towards the outer edge of the impeller <NUM>. As will be discussed below, the tapered portion <NUM> is a compound shape having the concave region <NUM> and the convex region <NUM>. The auxiliary vanes <NUM> have a tapered portion of the auxiliary vanes <NUM> which transitions from the planar portion <NUM> to the tapered portion <NUM>. In some embodiments the auxiliary vanes <NUM> may extend in to the tapered portion <NUM>. The auxiliary vanes <NUM> may be tapered in a similar manner to the tapered portion <NUM>.

<FIG> shows a pump <NUM>, similar to the pump <NUM> of <FIG> and <FIG>. The pump <NUM> has many of the same features as the pump <NUM> and the same features are marked with the same reference numerals as used for the pump <NUM>. However, the pump <NUM> has a different style of side liner with a grooved front side liner <NUM>. The front side liner <NUM> has grooves <NUM> cut in to the surface <NUM> that is in contact with the material or fluid pumped by the pump <NUM>. The grooves <NUM> may reduce a rate of wear of the front side liner <NUM>. When used in conjunction with the shroud tapers <NUM> of the impeller <NUM>, the grooves <NUM> in the front side liner <NUM> may combine to further reduce a rate of wear of the front side liner <NUM> when compared to a flat surfaced side liner. A grooved side liner, also referred to as a patterned side liner, such as the grooved front side liner <NUM> , will be described in more detail in relation to <FIG>.

<FIG> and <FIG> show a cross section of a portion of a pump <NUM> with an impeller <NUM>. The impeller <NUM> has a front shroud <NUM> and a back shroud <NUM>. Each of the shrouds have a tapered portion <NUM> located near an outer edge <NUM> of the shrouds with a planar portion <NUM> located between the tapered portion <NUM> and a centre of the impeller <NUM>. The tapered portions <NUM> are located on an outer surface <NUM> of the front shroud <NUM> and an outer surface <NUM> of the back shroud <NUM>. <FIG> has a smooth front side liner <NUM> and a smooth back side liner <NUM>. <FIG> shows the pump <NUM> using the smooth back side liner <NUM> and a patterned front side liner <NUM>. The patterned front side liner <NUM> may be a grooved side liner, such as will be described in relation to <FIG> or have other patterns on the liner.

A side liner will now be described in relation to <FIG> which shows a patterned side liner <NUM>, more specifically a back side liner having a radially swirling pattern for use in a centrifugal pump such as pump <NUM>. While the side liner <NUM> is described as a back side liner, a patterned side liner may also be used for the front side liner. As discussed above, the radially swirling pattern on the side liner <NUM> may reduce localised wear on the side liner, compared to a flat surfaced side liner. The decreased wear may increase an operational lifespan of the patterned side liner. Typically, a side liner such as the side liner <NUM> is a replaceable part in a centrifugal pump made out of a suitable material such as rubber, elastomer or metal. The side liner <NUM> operates in a manner similar to the side liner <NUM> of <FIG>.

The side liner <NUM> has a centrally located aperture <NUM>. The aperture <NUM> allows passage of a shaft into a pumping chamber of a centrifugal pump to rotate an impeller, such as the impeller <NUM> or the impeller <NUM> described above. The side liner <NUM> has a surface <NUM> that is placed facing towards the pumping chamber and may be in contact with slurry pumped by the centrifugal pump. The surface <NUM> has an inner edge <NUM>, forming an edge of the aperture <NUM> and seals with the drive shaft, such as the drive shaft described above. An outer edge <NUM> of the surface <NUM> may form a seal with a main liner, such as main liner <NUM> described above.

Located on the surface <NUM> are a plurality of grooves <NUM>. The grooves <NUM> are formed into the surface <NUM> and may extend radially from the inner edge <NUM> to the outer edge <NUM>, as shown in <FIG>. The grooves <NUM> may be considered to be in a plane parallel to the surface <NUM>. Depth of the grooves <NUM> may vary over the surface <NUM>. One example of a depth profile for the grooves <NUM> is for the grooves <NUM> to be shallower closer the inner edge <NUM> and the outer edge <NUM>. With such a depth profile a deepest part of the grooves <NUM> may be located at, or near, a mid-region <NUM> located between the inner edge <NUM> and the outer edge <NUM>. The depth profile of the grooves <NUM> may vary.

The grooves <NUM> of <FIG> are not straight lines, but are arced or curved. The direction of curvature of the arc may play a role in reducing gouging of the side liner <NUM>. The grooves <NUM> are formed in an arc with curvature in a direction opposite to a direction of curvature of the main pumping vanes of the impeller of the centrifugal pump. The curvature of the grooves <NUM> is also in a direction opposite to curvature of the auxiliary vanes of the impeller, if auxiliary vanes are fitted. As a result, the direction of the curvature will differ between the front and the back side liners, when looking at the grooved surface of the liners. The front and side liners have grooves that may be referred to as forwards-curving grooves when viewed with a direction of rotation of the impeller, as compared to the backward-curving vanes of the impeller.

<FIG> show simulation results for a speed of a material, such as a slurry, flowing over a pump liner when operating with an impeller having tapered portions and auxiliary vanes only on a front shroud, such as the impeller <NUM>. <FIG> shows a pump liner <NUM> with a flat front side liner. Pumped material exits the pump liner <NUM> via an outlet <NUM>. A high velocity region <NUM> is located at a centre of the pump liner <NUM>, transitioning to a medium velocity region <NUM> before the material velocity drops to a low velocity region <NUM>. <FIG> show material velocities in a pump liner <NUM> when a grooved front side liner is used, with an outlet <NUM>. The grooved front liner dissipates more of the material velocities when compared to the pump liner <NUM> with a flat front side liner. A medium velocity region <NUM> is located near a centre of the pump liner <NUM>, with material velocity dropping to a low velocity region <NUM> away from the pump centre.

<FIG> show an opposite side of the pump liner <NUM> and the pump liner <NUM>, respectively. <FIG> shows a pump liner <NUM>, including a back side liner, including an outlet <NUM>. The pump liner <NUM> uses a flat front side liner, not shown in <FIG>. A very low velocity region <NUM> is located towards a centre of pump liner <NUM>. The material velocity increases to a low velocity region <NUM> and then a medium velocity region <NUM>. Outside of the medium velocity region <NUM> is a low velocity region <NUM>. <FIG> shows a pump liner <NUM> with an outlet <NUM>. <FIG> shows flat back side liner. The pump liner <NUM> has a grooved front side liner, not shown. The pump liner <NUM> has a very low velocity region <NUM> located near a centre of the pump liner <NUM>. The very low velocity region <NUM> transitions to a low velocity region <NUM>, then a medium velocity region <NUM>. The outer edge of the liner has a low velocity region <NUM>. The medium velocity region <NUM> is smaller than the comparable medium velocity region <NUM> of the pump liner <NUM>.

Simulation results for a speed of a material, such as a slurry, flowing over an impeller, operating inside a pump, will now be described in relation to <FIG>. The figures show a front shroud of an impeller, such as the impeller <NUM>. Located on the front shroud are auxiliary vanes. <FIG> shows an impeller <NUM> modelled in a pump liner with a flat front side liner. The impeller <NUM> has auxiliary vanes <NUM> on an outer face of a shroud of the impeller <NUM>. The impeller <NUM> has a low velocity region <NUM> located near a centre of the impeller <NUM>. A very low velocity region <NUM> extends across most of the area covered by the auxiliary vanes <NUM>. A low velocity region <NUM> is located near an outer edge of the impeller <NUM>, where a tapered portion <NUM> is located.

<FIG> shows an impeller <NUM> modelled in a pump liner with a grooved front side liner. The impeller <NUM> has auxiliary vanes <NUM> on an outer face of a shroud of the impeller <NUM>. The impeller <NUM> has a low velocity region <NUM> located near a centre of the impeller <NUM>. A very low velocity region <NUM> extends across most of the area covered by the auxiliary vanes <NUM>. A low velocity region <NUM> is located near an outer edge of the impeller <NUM>, where a tapered portion <NUM> is located. The low velocity region <NUM> of the impeller <NUM> is lower than the low velocity region <NUM> of the impeller <NUM>.

<FIG> show projected fluid velocities inside a pump using an impeller with a tapered portion. <FIG> shows a pumping chamber <NUM> with an impeller <NUM>. A flat back side liner <NUM> and a flat front side liner <NUM> are located on either side of the impeller <NUM>. The impeller <NUM> has tapered portions <NUM> on an outer surface of the impeller <NUM>. There is a lower velocity region <NUM> of fluid near the tapered portion <NUM> and a higher velocity region <NUM> located near an outer edge of the impeller <NUM>. An advantage of an impeller with a tapered portion is that a higher velocity region, such as the higher velocity region <NUM> is located further away from a side liner. The result may be that fluid velocity near an outer edge of an impeller may have greater dissipation before reaching the side liner compared to an impeller without a tapered portion. As a result, one or both of the side liners may wear slower when an impeller has a tapered portion, compared to an impeller without a tapered portion.

<FIG> shows a lower portion of pumping chamber <NUM> with the impeller <NUM> with the flat front side liner <NUM> and the flat back side liner <NUM>. The motion of the impeller <NUM> in the pumping chamber <NUM> creates a higher velocity region <NUM> near an outer edge of the impeller <NUM> and a lower velocity region <NUM> between the tapered portion <NUM> and the back side liner <NUM>. Similar regions are present around the other shroud of the impeller <NUM>.

<FIG> shows an upper portion of a pumping chamber <NUM> with a flat back side liner <NUM>, a grooved front side liner <NUM> and an impeller <NUM>. The impeller <NUM> has a tapered portion <NUM>. A higher velocity region <NUM> is located near an outer edge of the impeller <NUM> and a lower velocity region <NUM> is located between the tapered portion <NUM> and the flat back side liner <NUM>. Similarly, a higher velocity region <NUM> and a lower velocity region <NUM> are located on a front shroud of the impeller <NUM>. <FIG> shows a pumping chamber <NUM> with the flat back side liner <NUM>, the grooved front side liner <NUM> and the impeller <NUM>. The impeller <NUM> generates the higher velocity region <NUM> and the lower velocity region <NUM> for the back shroud in the pumping chamber <NUM> as well as the higher velocity region <NUM> and the lower velocity region <NUM> for the front shroud. As with the impeller <NUM>, the tapered portions <NUM> of the impeller <NUM> may result in slow wear of side liners when compared to an impeller without tapered portions for the reason described above.

<FIG> show possible profiles for the tapered portion of an impeller shroud. Each of the <FIG> show a section of an impeller shroud with an outer face <NUM> and an inner face <NUM>. Each of the outer faces of the impeller shrouds have a planar portion <NUM> leading to the tapered portion on the outer face of the shroud. The tapered portion is located at, or leads to, an outer edge <NUM> of the impeller. <FIG> shows a convex taper portion <NUM> at an outer edge of the shroud. <FIG> shows a concave taper portion <NUM>. <FIG> shows a tapered portion with two concave sections, an inner concave region <NUM> and an outer concave region <NUM>, where inner is located closer to a centre of the impeller and outer refers to a location closer to the outer edge <NUM>. The tapered portion of <FIG> may be considered to be a compound shape made up of two simpler shapes, in this case two concave regions.

<FIG> shows a straight taper portion <NUM>. While the straight taper portion <NUM> forms a point with the inner face <NUM> at the outer edge <NUM>, variations may have the straight taper portion <NUM> ending further away from the inner face <NUM> to a flat region on the outer edge <NUM> of the impeller shroud. Such an arrangement may provide a stronger outer edge <NUM> design than a straight taper that extends across the thickness of the shroud. <FIG> shows a tapered portion with a compound shape made of an inner convex region <NUM> and an outer concave region <NUM>. <FIG> shows a tapered portion with an opposite profile to <FIG> with an inner concave region <NUM> and an outer convex region <NUM>. The outer convex region <NUM> is located closer to the outer edge than the inner concave region <NUM>. In one embodiment, the taper may be based on an <NUM>% trim, or thickness reduction, based on standard thickness of the shroud versus the taper. It may also be that the inner concave region <NUM> and the outer convex region <NUM> have an equal radius. The size of the radius may be determined based on the size of the impeller with the radius increasing as the size of the impeller increases. The tapered portion profiles shown in <FIG> are some examples that may be used on the shroud of an impeller. Other profiles may also be used including other compound shapes. For example, the tapered portion may have an inner straight region and an outer concave portion. Alternatively, the tapered portion may have an inner convex region and an outer convex region.

Some impellers may have a taper on one or more shrouds that extends along the shroud. For example, where the thickness of the shroud decreases from a centre, near the impeller inlet, along the planar portion of the shroud. Such impellers have a planar portion that may be tapered from being thicker closer to the centre of the impeller to thinner near the outer edge. The planar portion has a variable thickness and is thinner near the outer edge than near the centre of the impeller. In such an example, the tapered portion is an additional taper where a rate of thickness reduction is higher than the planar portion. That is, the rate of change of the shroud thickness may increase for the tapered portion, compared to other regions of the shroud. For some impellers, a reduction in thickness of the tapered portion is greater than a reduction thickness in the planar portion. For some impellers the tapered portion of the shroud has a thickness variation greater than for regions of the shroud outside the tapered portion.

The tapered portion is also located closer to the outer edge of the impeller when compared to the planar portion. That is, the planar portion is located closer to a centre of the impeller than the tapered portion. The planar portion may be located directly adjacent to the tapered portion, or there may be another section between the planar portion and the tapered portion. The planar portion may be flat or may be substantially planar.

The tapered portion may be used only on the front shroud of the impeller, only on the back shroud of the impeller, or on both the front and back shrouds of the impeller. Although the pumps described above have a flat back side liner, a grooved or patterned back side liner may be also be used in addition to a grooved or patterned back side liner. Alternatively, the back side liner may be grooved or patterned, and the front side liner may be flat.

The side liner <NUM> described above has arced grooves, other designs are also possible. For example, the grooves may extend radially or have arcs curving in an opposite direction. Alternatively, the side liners may have overlapping grooves, such as a cross hatched pattern. Further, the shaped of the grooves or patterns of the back and the front liner may be different.

As described above, one advantage of an impeller with one or more tapered portions is that wear of the side liners may be slower than for an impeller without tapered portions. Wear of the main liner may also be slow for pumps using impellers one or more tapered portions. While some of the pumps described above used patterned side liners, the patterned side liners are not required to gain an advantage when using an impeller with a tapered portion. However, using one or more patterned side liners may provide an additional benefit in reducing a rate of wear of the liners of the pump.

Claim 1:
An impeller (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>) for a centrifugal slurry pump (<NUM>, <NUM>, or <NUM>), the impeller (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>) comprising:
an inlet (<NUM>) through which fluid passes into the impeller (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>);
pumping vanes (<NUM>, <NUM>, or <NUM>) for pumping the fluid from the inlet (<NUM>) and expelling the fluid into a pumping chamber (<NUM>) of the centrifugal pump (<NUM>, <NUM>, or <NUM>) in which the impeller (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>) operates; and
at least one shroud (<NUM> or <NUM>; <NUM> or <NUM>; <NUM> or <NUM>; or <NUM> or <NUM>) extending radially from an axis of rotation for the impeller (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>) and attached to the pumping vanes (<NUM>, <NUM>, or <NUM>), the at least one shroud (<NUM> or <NUM>; <NUM> or <NUM>; <NUM> or <NUM>; or <NUM> or <NUM>) having an outer surface (<NUM> or <NUM>; <NUM> or <NUM>) facing away from the pumping vanes (<NUM>, <NUM>, or <NUM>), wherein
the outer surface (<NUM> or <NUM>; <NUM> or <NUM>) includes a planar portion (<NUM>, <NUM>, <NUM>, or <NUM>) located near a centre of the impeller (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>) and a tapering portion (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>) located towards an outer edge (<NUM> or <NUM>, <NUM>, <NUM>, or <NUM>) of the shroud (<NUM> or <NUM>; <NUM> or <NUM>; <NUM> or <NUM>; or <NUM> or <NUM>), characterised by the tapering portion (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>) being a compound shape with contiguous concave (<NUM> or <NUM>) and convex (<NUM> or <NUM>) regions.