BACKGROUND OF THE INVENTION

[0001] This invention relates to a centrifugal pump and more particularly to a seal between opposing surfaces of an impeller and an inlet liner of the pump.

[0002] In a centrifugal pump, apart from a primary slurry flow, recirculation slurry flow takes place between a front shroud of the impeller and front secondary pump-out vanes, and an inlet of the pump. The recirculating slurry flow is abrasive and degrades the pump-out vanes and the inlet liner, resulting in component wear, a loss in pumping efficiency and an increase in energy consumption.

[0003] The situation is illustrated in Figure 1 of the accompanying drawings which shows in cross section a part of a typical centrifugal pump 10 in which recirculation of slurry leads to component wear.

[0004] The pump 10 includes an impeller 12, with vanes 14, which is mounted on a shaft in a volute 16 of a casing 18. A suction inlet 20 in use directs slurry in the direction of an axis 22 into a circular entrance area into the impeller, referred to as an eye 24 of the impeller. A clearance 30 (marked by xxx for ease of identification) is formed between a surface 32 of the impeller around the eye 24 and a spaced apart surface 34 of a front liner 36. The clearance 30 forms a vertical or near-vertical (i.e. at about 90 degrees relative to the axis 22) so-called “labyrinth sealing arrangement” particularly on the radial innermost portion thereof, through which the slurry is recirculated. The opposing surfaces 32 and 34 are abraded by the slurry flow, leading to the aforementioned negative consequences. In order to improve this aspect an adjustment of the front liner 36 relative to the impeller 12, in an axial direction, is required. This type of adjustment can be difficult to achieve .

[0005] The invention is concerned with the aforementioned situation.

SUMMARY OF THE INVENTION

[0006] The invention provides a centrifugal pump which includes a casing, a volute inside the casing, an impeller mounted on a shaft in the volute for rotation about an axis, the impeller including a centrally positioned eye and a plurality of vanes which extend radially outwardly from the eye, and a structure which supplies a medium to be pumped into the eye, and wherein the structure includes an outer seal surface which extends circumferentially and concentrically around the axis, which is parallel to and concentric with the axis and which extends, at least partly, into the eye, and the impeller includes an inner seal surface which extends circumferentially and concentrically around at least a part of the eye, and which is radially spaced from and which opposes the outer seal surface, whereby an axially extending, annular sealing clearance is formed between the outer seal surface and the inner seal surface.

[0007] A second sealing clearance may extend outwardly from the axially extending annular sealing clearance at an acute angle relative to the axis.

[0008] The axially extending annular sealing clearance may be substantially cylindrical i.e. with outer and inner surfaces which are spaced apart and which are parallel to each other and coaxial with the axis.

[0009] The structure may supply the medium in an axial direction into the eye. [0010] As used herein “sealing clearance” refers to an arrangement in which a seal is formed between opposing surfaces of at least two components. Such seal does however form a gap between the opposing surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 2 illustrates in cross section and from one side an end suction centrifugal slurry pump according to one form of the invention.

Figure 3 is a side view in cross section and on an enlarged scale of a front liner used in the pump of Figure 2 (Item 80 in figure 2),

Figures 4A and 4B depict, schematically, parts of the pump enclosed in a circle 4 in Figure 2, with different spacings between the parts, and

Figure 5 depicts performance curves of a conventional slurry pump and a slurry pump of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

[0012] Figure 2 of the accompanying drawings illustrates from one side and in cross section a part of an end suction slurry pump 50 according to the invention.

[0013] The pump 50 includes a casing 52 which defines a volute 56. An impeller 58 is mounted on a shaft 66 inside the volute for rotation about an axis 62. The impeller 58 has a drive end 64 which is connected to the shaft 66, which in use drives the impeller.

[0014] The impeller 58 defines a centrally positioned impeller eye 68, primary pump-out vanes 70, and secondary pump-out vanes 72 on a front shroud 74. [0015] An axially directed inlet structure 78 is mounted to the casing 52. The structure 78 includes a tube 80 which is centred on the axis 62. A radially extending flange 82 on the tube forms a front liner 84 for the pump. An inner surface 86 of the front liner opposes the vanes 72.

[0016] In use slurry is supplied in an axial direction through the tube 80 to a discharge outlet 88 and then into the eye 68 of the impeller. The discharge outlet 88 has a rounded inner surface 88A - see Figure 3 which shows the inlet structure 78 from one side and in cross section, on an enlarged scale.

[0017] A section 90 of the tube 80 which protrudes to the left of the flange 82 has an outer seal surface 92 which is planar, which is parallel to the axis 62 and which extends circumferentially around the axis.

[0018] In this embodiment a junction 94 between the section 90 and the flange 82 has a junction seal surface 96 between the outer seal surface 92 and the inner surface 86 of the front liner 84 which is at an acute angle 98 with respect to the axis 62.

[0019] The section 90 extends into the eye 68 which is enlarged, compared to a conventional, known, design, to accommodate this feature. The impeller 58 at the eye 68 has a circular inner seal surface 100 which is centered on the axis 62 and which is concentric (maybe rather use coaxial - meaning same axis) with the outer seal surface 92. The inner seal surface 100 which is centred on the axis 62 and which is concentric with the outer seal surface 92. The inner seal surface 100 opposes the outer seal surface 92. An axially extending annular sealing clearance 102 is thereby formed between the inner seal surface 100 and the outer seal surface 92 of the section 90. [0020] A sloping surface 106 which is adjacent the inner seal surface 100 and which is spaced from and parallel to the junction seal surface 96 extends at the acute angle 98, relative to the axis 62, to the secondary pump-out vanes 72. An inclined extension sealing clearance or seal gap 110 is thereby formed between the surfaces 106 and 96.

[0021] In the Figure 1 construction the recirculation gap 30 is established at an interface between the impeller 12 and the front liner 36 and extends in a radial direction. In the Figure 2 case the axially extending annular sealing clearance 102 extends circumferentially around and is parallel to the axis 62. Thus the sealing clearance 102 is coaxial with the axis 62. The axially extending annular sealing clearance 102 is followed by the extension sealing clearance 110, between the surfaces 106 and 96, which inhibits slurry entering through the tube 80 from readily flowing to the secondary pump-out vanes 72 on the front shroud of the impeller.

[0022] The prior art arrangement shown in Figure 1 has a vertical labyrinth seal which extends in a radial direction relative to the pump axis. In contrast the sealing clearance 102 is established circumferentially around and coaxially with the axis 62 and thus provides a horizontal static labyrinth seal.

[0023] In the pump 50 (Figure 2) adjustment of the front liner 84 in an axial sense relative to the impeller 58 is not called for. The pump 50 is less sensitive to dimensional changes in the axial width of the extension sealing clearance 110. Wear effects at the impeller 58 and on the front liner 84 are significantly reduced due to the axially insensitive arrangement. The flow across the impeller vane passage, (opposing the vanes 72) during flow recirculation, is smoother as the pump is operated across its intended performance range.

[0024] Figure 4A illustrates schematically a portion of the pump 50 enclosed in a circle 4 in Figure 2. The extension sealing clearance 110 has a cross sectional dimension of X in the axial direction. In Figure 4B the axial dimension of the extension sealing clearance 110 is increased to 3X. However in each case the thickness of the annular sealing clearance 102 in a radial direction is the same. It has been established that the pump performance is largely unaffected as the size of the extension sealing clearance 110 varies. Also similar wear patterns are maintained.

[0025] Figure 5 shows performance curves of head in meters, and efficiency, versus flow rate (litres per second) of two pumps under test. The solid lines show the performance curves of a conventional pump. The dots indicate the performance curves of a pump according to the invention. An improved head is obtained with a pump according to the invention. Also the efficiency of a pump according to the invention is increased relative to the efficiency of a conventional pump. These benefits arose due to a redesign of the impeller primary pump-out vanes which was necessary due to the increase in the size of the impeller eye. The increased efficiency is demonstrated at higher flow rates. This is also the case with the head increase. These factors translate into better overall wear and potential energy savings.

[0026] The invention offers an improvement of wear life of from 10% to 50% of the impeller and of the front liner of a centrifugal pump. The hydraulic performance of the pump is increased. The operation of the pump is not sensitive to the size of the axial front gap either as established during assembly or as may occur during usage. There is an overall improvement of wear life and a reduction in energy consumption.

[0027] It is possible to implement the principles of the invention in a retrofit manner i.e. to install an impeller and suction inlet structure which embody the described concepts, in a conventional pump.