WO2018049438A1

WO2018049438A1 - Slurry pump and associated impeller

Info

Publication number: WO2018049438A1
Application number: PCT/ZA2017/050061
Authority: WO
Inventors: Siegfried Geldenhuys
Original assignee: Mechanical Engineering Transcendent Technology (Pty) Ltd
Priority date: 2016-09-12
Filing date: 2017-09-12
Publication date: 2018-03-15

Abstract

A slurry pump impeller which has an inlet of diameter D and a machined annular surface of width W around an axis of rotation, and wherein 0,25 ≤ W/D ≤ 0,35.

Description

SLURRY PUMP AND ASSOCIATED IMPELLER BACKGROUND OF THE INVENTION

[0001] This invention is concerned with reducing leakage on a suction side of a slurry pump, and with related constructional aspects of an impeller of the pump. [0002] In a typical slurry pump an impeller bears against an inlet suction liner. The liner and the impeller are generally formed by means of a casting process. Opposing faces of the liner and the impeller often have large tolerances which means that a flow-path, of relatively large size but with varying dimensions, is created between the opposing surfaces of the impeller and the suction liner, which leads to unwanted recirculation flow of the slurry. [0003] An object of the present invention is to address, at least to some extent, this drawback.

SUMMARY OF THE INVENTION

[0004] The invention provides in the first instance that a surface of the suction liner which opposes the impeller is machined after casting. In addition an opposing surface of the impeller which is radially innermost is also machined. In this way a rotating surface of the impeller is as close as is practically possible to an opposed stationary surface of the liner and recirculation leakage is almost eliminated.

[0005] The applicant has established that there is an optimum ratio of the width of the suction seal (i.e. the machined surface on the impeller) to the diameter of an inlet to the impeller. This optimum takes into account suction side leakage and cost of manufacture. The optimum lies in the range of 0.25 to 0.35.

[0006] The impeller may have a set of primary inlet vanes close to an axis of rotation of the impeller and these primary inlet vanes may be surrounded by secondary or auxiliary vanes which are mounted to shrouds. Radial outer surfaces of the auxiliary vanes, extending away from the machined suction seal, may subtend an angle relative to a central axis of the impeller ranging from 90° to greater than 90°.

[0007] The said opposing machined surface of the impeller may be offset in an axial direction relative to the outer surfaces of the auxiliary vanes. This feature on the suction side may be replicated on the opposing drive side.

DESCRIPTION OF DRAWINGS

[0008] The invention is further described by way of example with reference to the accompany drawings in which:

Figure 1 is a plan view of an impeller according to the invention, Figure 2 is a view in cross section of the impeller taken on a line 2-2 in Figure 1 ,

Figure 3 and Figure 4 respectively illustrate on an enlarged scale different aspects of a part of the impeller in Figure 2, enclosed in a circle A,

Figure 5 shows, on an enlarged scale and in in cross section, an impeller and a part of suction liner, Figure 6 shows on an enlarged scale a portion of the impeller in Figure 5 which is enclosed in a circle marked "6", and

Figure 7 graphically depicts a relationship of suction side leakage as a function of different parameters. DESCRIPTION OF PREFERRED EMBODIMENT

[0009] Figure 1 of the accompanying drawings illustrates in plan an impeller 10 which includes a body 12 which has first and second axially spaced apart front and rear shrouds 14 and 16 (see Figure 2) respectively and, between the shrouds 14 and 16, a plurality of primary vanes 18 which are not shown in detail. The vanes 18 are circumferentially spaced apart about a central axis of rotation 24 of the impeller 10 and extend generally radially outwardly towards a periphery 26 of the impeller 10.

[0010] The rear shroud 16 has an outer face 28 which has a centrally positioned mounting formation 30 for a drive shaft (not shown).

[0011] The impeller 10 and the front and rear shrouds 14 and 16 are located in a pump chamber formed inside a pump housing (not shown).

[0012] The front shroud 14, on an outer face 32, carries a plurality of auxiliary vanes 34 which are circumferentially spaced apart from one another and which extend generally from an annular portion 36 to the periphery 26 of the body 12. The annular portion 36 has a machined surface 38 which is at a right angle to the rotational axis 24 of the impeller 10. [0013] Figure 3 illustrates on an enlarged scale a portion of the impeller 10 which is enclosed in a circle marked A in Figure 2. The machined surface 38 is off set (stands proud) by an amount 40 relative to a junction 42 between the annular portion 36 and an outer surface 44 of each auxiliary vane 34. [0014] Figure 4 illustrates that the machined surface 38 is at an acute angle 46 relative to the outer surface 44 of each auxiliary vane 34.

[0015] Figure 5 shows the impeller 10 in cross section in an installed configuration, a portion of a suction liner 50 and a portion of a drive liner 52. The liners 50 and 52 define an operating volume 56 within which the impeller 10 is located. The drive liner 52 defines an inlet 58 for the drive shaft (not shown) which is engaged with the formation 30. The suction liner 50 defines a suction inlet 60 for slurry flow to take place in an axial direction 62 to a central region of the impeller 10 which is positioned between opposing faces 50A and 52A of the suction liner 50 and of the drive liner 52 respectively.

[0016] The face 50A faces the outer face 32 of the front shroud 14. An annular section 68, of the face 50A, which bounds the suction inlet 60 is machined so that it can fit as close as is practically possible to the machined surface 38 of the impeller 10.

[0017] To the extent which may be necessary an annular section 70 of the face 50A which surrounds the annular section 68 and which, in use, faces outer surfaces 72 of the auxiliary vanes 34, is also machined so that these surfaces 72 present no impediment to the annular section 70. [0018] An outer face 74 of the rear shroud 16 has an annular surface 76 which is machined so that it can be brought as close as is practical to a surface 78 of the inner side 52A of the drive liner 52. An intention in that respect is to provide a seal which is as effective as is possible under these circumstances, between a pressurized region in a pump chamber which is occupied by the impeller 10, and atmosphere. This means that in practice there is a maximum pressure difference between the interior of the pump chamber and atmosphere.

[0019] Figure 6 shows in enlarged detail further aspects of the relationship between the machined surface 38 and each primary vane 18. A radial inner edge 38A of the machined surface 38 is spaced by a distance 80 from the leading inner edge 82 of each primary vane 18. The size of the distance 80 is variable, for it depends on the particular configuration. Typically, as the impeller 10 rotates, a complex flow regime is established at the radial inner edge 38A of the machined surface 38. This leads to inefficiency in the operation of the pump. However, by axially spacing the inner edge 38A relative to the primary vanes 18 by the offset distance 80 the flow regime at this location is simplified. It has been found, that due to the offset 80, a portion of the incoming slurry flow which otherwise would tend to flow over the outer face 32 of the first shroud 14 and thereby lead to inefficiencies and leakage, is much reduced. The offset 80 thus helps to eliminate this unwanted factor and therefore helps to increase pumping efficiency.

[0020] Figure 2 shows that the impeller 10 has an inlet diameter D while the radial width of the machined surface 38 is marked W. This is on the suction side of the impeller 10. For convenience the ratio W/D is referred to as R. [0021] The applicant has investigated the cost of manufacture of a slurry pump, of the type described, as a function of suction side leakage (which contributes to operating inefficiencies) and of the sizes of critical components of the pump, when constructed in accordance with the aforegoing factors i.e. in order to reduce, as far as is practically possible, the suction side leakage. The outcome of such investigation is reflected in Figure 7 which graphically depicts the relationship of suction side leakage (Q) as a function of R; the cost of manufacture of the liners 50 and 52 and of the impeller 10 (C) as a function of R; and the ratio of the cost of manufacture (C) to leakage (Q) as a function of the ratio R.

[0022] A reduction in leakage can be achieved at an increased cost of manufacture, but the substantial elimination of suction side leakage requires a prohibitively expensive pump. However, an inspection of Figure 7 shows that a good and effective compromise can be struck when the cost to leakage ratio lies in the marked range of 0,25 < 0,35.

Claims

1. An end suction slurry pump which includes a housing within which is located an impeller (10) which is rotatable about an axis (24), a drive liner (52) with an inner surface (52A), a suction liner (50) which is axially spaced from the drive liner (52) and which has an inner surface (50A) with a machined annular section (68) which has a radial width W and which surrounds an axially directed slurry inlet (60) of diameter D to the impeller (10), the impeller (10) including a front shroud (14) with an outer face (32) which has a machined surface (38) at an annular portion (36) thereof which opposes the annular section (68), a rear shroud (16) which is axially spaced from the front shroud (14), a plurality of primary vanes (18) between the inlet shroud (14) and the rear shroud (16), and a plurality of auxiliary vanes (34) on the outer face (32), and wherein 0.25 < W/D < 0.35.

2. An end suction slurry pump according to claim 1 wherein the rear shroud (16) has a formation (30) for engagement with a drive shaft, and an outer face (74), wherein at least an annular surface (76A) of the outer face (74) is machined and opposes an annular machined surface (78) of an inner surface (52A) of the drive liner (52).

3. An end suction slurry pump according to claim 1 wherein each primary vane (18) has a respective leading edge (82) which is displaced in an axial direction from the suction liner (50) towards the drive liner (52) away from a radial inner edge (38A) of the machined surface (38)

4. A slurry pump impeller which has an inlet of diameter D and a machined annular surface of width W around an axis of rotation, and wherein 0,25 < W/D < 0,35.