GB2414768A

GB2414768A - Centrifugal pump with deformable seal

Info

Publication number: GB2414768A
Application number: GB0510220A
Authority: GB
Inventors: John Fleming
Original assignee: Weir Pumps Ltd
Current assignee: Weir Pumps Ltd
Priority date: 2004-06-02
Filing date: 2005-05-19
Publication date: 2005-12-07
Also published as: GB0412231D0; GB0510220D0

Abstract

A mechanical assembly, such as a centrifugal pump 20, comprises a stationary part, such as a pump casing 22, a rotary part, such as an impeller 26, and a deformable element 40 situated between the stationary and rotary parts. In use, the deformable element 40 may act as a seal, reducing fluid leakage between the stationary and rotary parts. The deformable element 40 may also prevent or reduce collisions caused by relative deflections between the stationary and rotary parts. The deformable element 40 may be ring shaped and may be attached to the stationary part. The deformable element may combine deformable rings, resilient rings and wearable rings (see figures 7-9) and O-ring seals may be provided between the deformable element and a stationary part (see figure 11).

Description

24 1 4768

MECHANICAL ASSEMBLY AND DEFORMABLE ELEMENT THEREFOR

FIELD OF THE INVENTION

The present invention relates to a mechanical assembly and a deformable element therefor, and in particular, to a deformable element for locating between stationary and rotating parts of a centrifugal pump, wherein the deformable element is also wearable.

BACKGROUND OF THE INVENTION

Pumps have wide-ranging applications and are regularly used both in industrial and domestic applications for transporting or pressurising fluids for various purposes. Numerous types of pump exist and are most commonly classified as either positive displacement or rotodynamic: positive displacement pumps displace a volume of fluid by applying a force to a moveable boundary encompassing the fluid, and include reciprocating, metering and rotary pumps, among others; rotodynamic pumps impart energy to a fluid resulting in an increase in the fluid pressure, and include centrifugal and turbine pumps, among others.

A number of pumps, primarily rotodynamic pumps, consist of rotary and stationary parts, and careful consideration must be given to ensure that the interaction 2 0 of the rotary and stationary parts will not adversely affect the operation of the pump or cause damage to key pump components. Such considerations may be illustrated with reference to a conventional centrifugal pump, as described below.

Centrifugal pumps include a pump casing within which is mounted a shaft carrying one or more pump impellers which define a corresponding number of pump stages. In use, the shaft and impellers are rotated and draw fluid through a suction branch into a low pressure chamber within the casing. The fluid enters the first stage impeller from the low pressure chamber through a central impeller eye, is pressurised by being driven through the impeller, with pressurised fluid exiting the first stage impeller into a high pressure chamber. From this high pressure chamber the fluid may be discharged from the pump through a discharge branch, or alternatively may be directed to a successive pump stage to be further pressurized. The low and high pressure chambers are separated by closely interfacing portions of the stationary pump casing and rotary impeller. More specifically, the arrangement between the casing and impeller is such that an outer surface portion of a neck of the impeller is located adjacent an inner surface portion of the casing, wherein a small gap is defined between the respective surfaces, which gap, or surface separation, is required to prevent contact between the rotary surface of the impeller and stationary surface of the casing. In order to minimise leakage of fluid between the high and low pressure chambers and thus maximise pump efficiency, it is preferred to provide a minimal surface separation or operational clearance. However, while leakage from the high pressure chamber to the low pressure chamber should be minimised to optimise pump efficiency, some leakage may be tolerated in order to provide lubrication and cooling of the rotating and stationary surfaces. Nevertheless, it is desirable to maintain fluid leakage to an absolute minimum, and achieve and maintain an optimum compromise 2 0 between pump efficiency and favourable leakage for lubricating/cooling purposes.

Centrifugal pumps are, in use, subjected to considerable thrust forces, both axial and radial, which cause deflections of the shaft and associated impeller(s). The magnitude of the deflections can vary considerably depending on operating conditions and may cause contact between the surfaces of the impeller and casing which can 2 5 result in excessive wear or even damage, not only to these parts, but also to bearings and seals and the like due to transmission of impact loading. These shaft deflections generally require a larger clearance between the respective surfaces of the casing and impeller to accommodate much of the variable deflections and thus minimise contact, which as a result increases the level of fluid leakage and reduces pump efficiency.

It is among objects of embodiments of the present invention to obviate or at least mitigate the aforementioned problems.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a mechanical assembly having a stationary part and a rotary part, and an element located between the stationary and rotary parts, wherein at least a portion of the element is deformable.

Preferably, the stationary and rotary parts are arranged such that a surface of the stationary part is positioned adjacent or in close proximity to a surface of the rotating part, wherein the element is positioned between the respective surfaces.

Thus, the element is preferably located in a gap defined between the stationary and rotary parts.

Thus, when the mechanical assembly of the present invention is in use, the element will prevent or substantially minimise contact between the stationary and rotary parts when one or both are deflected or forced together. Additionally, the element will deform to accommodate any deflections, which will also assist to reduce compressive, shear and other loads applied to the element and transmitted between the parts of the assembly.

It should be noted that the description and statements provided herein, for clarity, predominately refer to deflections of the rotary part with respect to the stationary part. However, it should be understood that the scope of the present invention also extends to deflections of the stationary part with respect to the rotary part.

In a preferred embodiment of the present invention, the element may be mounted and secured to the stationary part of the mechanical assembly. The element may be mounted and secured to the stationary part by adhesive bonding, interference fitting, direct moulding, bolting, clamping, welding or any other suitable securing means. In an alternative embodiment, the element may be mounted on and secured to the rotary part of the mechanical assembly.

Preferably, at least a portion of the element is resiliently deformable.

Accordingly, the element may be capable of deforming to accommodate any movement between the stationary and rotary parts while preventing any surface contact therebetween, and will substantially revert to its original form when any loading is removed. This feature of the present invention is particularly advantageous where respective surfaces of the stationary and rotary parts must be closely positioned together, for example, where fluid leakage between the stationary and rotary parts is to be prevented or at least minimised. In conventional mechanical assemblies, a gap may be required between respective surfaces to substantially accommodate the expected maximum relative displacement of the stationary and rotary parts when in 2 0 use. In some instances, this gap or separation between the surfaces of the respective parts may be quite large which may adversely affect the operation and efficiency of the mechanical assembly due to excessive fluid leakage through the gap, from one part of the assembly to another. Minimising the gap between surfaces of stationary and rotary parts may be difficult to achieve without the surfaces coming into contact 2 5 as a result of any deflection of the respective parts. Providing a deformable element, which is preferably resilient, and locating this within any gap between the surfaces effectively reduces the gap and prevents direct contact between the surfaces while being deformed, preferably resiliently, to accommodate relative deflections of the stationary and rotary parts, allowing the effective small gap to be maintained, and minimising any impact loading and damage to the components of the assembly.

In a preferred embodiment of the present invention, the element is substantially ring shaped.

Advantageously, the element is adapted to be located in an annular gap defined between the stationary and rotary parts. In this embodiment, the element may define inner and outer circumferential surfaces, wherein one circumferential surface is adapted to be secured to one of the stationary and rotary parts, and the other circumferential surface is adapted to engage with the other of the stationary and rotary parts upon relative deflection therebetween.

Alternatively, the element may be adapted to be located in an axial gap defined between the stationary and rotary parts of the assembly. In this embodiment the element advantageously defines first and second axially displaced annular surfaces, wherein one annular surface is adapted to be secured to one of the stationary and rotary parts, and the other annular surface is adapted to engage with the other of the stationary and rotary parts upon relative deflection therebetween.

In one embodiment of the present invention, the element may be mounted directly on the surface of the relevant part of the mechanical assembly. The element may be mounted within a recess, such as an annular channel, step or the like, formed in the relevant part of the mechanical assembly. This arrangement may assist to retain the element in position and prevent or limit unwanted deformation or movement of the element. Mounting the element on or in the surface of the relevant part of the mechanical assembly may reduce the requirement for fine machine finishing of the part surface as the element may accommodate for surface irregularities or the like produced by, for example, a casting process.

Advantageously, one or more seals which may be in the form of O-ring seals may be provided between the element and the part of the mechanical assembly upon which the element is mounted in order to prevent or minimise leakage therebetween.

Preferably, at least a portion of the element comprises a wearable material.

Preferably also, the wearable material is selected to wear at a greater rate than the part of the assembly inducing the material wear. That is, the wearable material is selected to have a pv factor which is lower than that of the part of the mechanical assembly which induces material wear. In this way, the wearable material will be sacrificially worn to substantially prevent or minimise wear of the part or parts of the mechanically assembly.

Advantageously, the element is manufactured from a material which provides both the required deforming and wearing properties. Alternatively, and in a preferred embodiment, the element is manufactured from a first material having the required deforming properties, and a second material having the required wearing properties.

In this preferred embodiment, the element may be formed by a deformable ring secured to a wearable ring, wherein the deformable ring is adapted to be secured to 2 0 one of the stationary and rotary parts, and the wearable ring is adapted to engage with the other of the stationary and rotary parts. On account of the wearable ring being secured to the deformable ring, any contact of the wearable ring with the stationary or rotary part of the mechanical assembly during deflection thereof will result in the wearable ring being displaced in the same direction. Accordingly, the wearable ring 2 5 may be described as a "floating wear ring".

In one embodiment of the present invention, the wearable ring and deformable ring may be of substantially similar widths so as to produce an element having a substantially uniform width. Alternatively, the deformable ring may be of a greater width than the wearable ring, wherein the wearable ring may be flush mounted on a surface of the deformable ring, or alternatively may be mounted within an annular recess such as a channel, step or the like in the deformable element. Alternatively, the deformable ring may be of a smaller width than the wearable ring, wherein the wearable ring may be flush mounted on a surface of the deformable ring, or alternatively the deformable ring may be mounted within an annular recess such as a channel, step or the like in the wearable element.

Preferably, the mechanical assembly is a centrifugal pump. Preferably also, the stationary part of the mechanical assembly is a pump casing and the rotary part of the mechanical assembly is a pump impeller. For example, the element may be located between a portion of the pump casing and a neck of the impeller. Preferably further, the element is mounted on the pump casing.

According to a second aspect of the present invention, there is provided an element for use between a stationary part and a rotary part of a mechanical assembly, wherein at least a portion of the element is deformable.

According to a third aspect of the present invention, there is provided an 2 0 element for use between a stationary part and a rotary part of a mechanical assembly, said element comprising a deformable ring secured to a wearable ring, wherein, in use, the deformable ring is adapted to be secured to one of the stationary and rotary parts of a mechanical assembly.

The element of the second and third aspects may be suitable for use as the element of the mechanical assembly of the first aspect. Accordingly, preferred features of the element defined in the first aspect noted above may also apply to the elements of the second and third aspects. For clarity and brevity, however, these preferred features have not been repeated.

According to a fourth aspect of the present invention, there is provided a wear ring for locating between stationary and rotary parts of a mechanical assembly, said wear ring comprising a wearing surface located on a resilient backing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-sectional view of a rotary body rotating within a stationary body; Figure 2 is a diagrammatic crosssectional view of part of a mechanical assembly, namely a centrifugal pump, in accordance with an embodiment of an aspect of the present invention; Figure 3 is an enlarged cross-sectional view of a portion of the mechanical assembly of Figure 2; Figure 4 is a diagrammatic crosssectional view of a portion of a mechanical assembly, namely a centrifugal pump, in accordance with an alternative embodiment 2 0 of an aspect of the present invention; Figure 5 is a cross sectional view of a wear ring element, in situ, in accordance with an embodiment of aspects of the present invention; Figure 6 is a diagrammatic cross- sectional view of a rotary body rotating within a stationary body incorporating the wear ring element of Figure 5; Figures 7 to 9 are diagrammatic cross-sectional views of three alternative wear ring elements, in situ, in accordance with three alternative embodiments of aspects of the present invention; Figure 10 is a diagrammatic cross- sectional view of a wear ring element according to an aspect of the present invention, shown secured to a stationary part of a mechanical assembly; and Figure 11 is a diagrammatic cross-sectional view of a wear ring element incorporating a sealing arrangement.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring initially to Figure 1, there is shown a diagrammatic crosssectional view of a rotary part 10 and a stationary part 12 of a mechanical assembly, wherein the rotary part 10 is rotating within the stationary part 12. The mechanical assembly may be a centrifugal pump such that the rotary part 10 may be a pump impeller and the stationary part 12 may be a pump casing. As shown, the rotary part 10 is subject to a radial thrust force, represented by arrow 14, which causes the rotary part to be deflected; such radial thrust forces are common in mechanical assemblies such as centrifugal pumps when in use. Such deflections may result in surface contact between the rotary and stationary parts 10,12 which can result in excessive wear or 2 0 even damage not only to these parts, but also to bearings and seals and the like due to transmission of impact loading.

Due to deflections of the rotary part 10, a sufficient clearance must be provided in an attempt to prevent or at least minimise any surface contact with the stationary part 12. However, the clearance can often result in a large gap 16 between the rotary and stationary parts 10,12, which may provide a leak path for fluid, which in many mechanical assemblies may adversely affect efficiency.

Reference is now made to Figure 2 in which there is shown a crosssectional view of part of a mechanical assembly, namely a centrifugal pump 20, in accordance with an embodiment of an aspect of the present invention. The pump 20 includes a pump casing 22 within which is mounted a shaft 24 carrying one or more impellers 26 (only one shown) which define a corresponding number of pump stages. In use, the shaft 24 and impellers 26 are rotated and draw fluid through a suction branch (not shown) into a low pressure chamber 28 within the casing 22. The fluid enters the first 1 0 stage impeller 26 from the low pressure chamber 28 through a central impeller eye 30, is pressurised by being driven radially through the impeller 26, with high pressure fluid exiting the first stage impeller 26 into a high pressure chamber 32. From this high pressure chamber 32 the fluid may be discharged from the pump casing 22 through a discharge branch, or alternatively may be directed to a successive pump stage to be further pressurized. The low and high pressure chambers 28,32 are separated by closely interfacing portions of the stationary pump casing 22 and rotary impeller 26, shown generally by reference numeral 34. More specifically, the arrangement between the casing 22 and impeller 26 is such that an outer surface portion of a neck 36 of the impeller 26 is located adjacent an inner surface portion 38 2 0 of the casing 22. A gap or clearance is defined between the respective surfaces of the casing 22 and impeller 26 to prevent or minimise contact therebetween when the impeller is deflected by varying thrust forces, as generally discussed above with reference to Figure 1. This gap results in fluid leakage from the high pressure chamber 32 into the low pressure chamber 28 which reduces overall pump efficiency.

2 5 However, it should be noted that some leakage may be required in order to cool and lubricate the respective surfaces of the impeller 26 and casing 22. Nevertheless, it is generally desirable to maintain fluid leakage to an absolute minimum, and achieve and maintain an optimum compromise between pump efficiency and favourable leakage for lubricating/cooling purposes.

In order to minimise the gap and thus fluid leakage between the pump casing 22 and impeller 26, while preventing/minimising contact therebetween, a deformable element 40 is located between the casing 22 and impeller 26, and is mounted on the inner surface portion 38 of the casing 22. An enlarged view of the encircled portion 42 of Figure 2 is shown in Figure 3. The deformable element 40 is located in an annular gap formed between the inner surface portion 38 of the casing and a portion of the neck 36 of the impeller. Thus, the deformable element 40 will prevent or substantially minimise any contact between the impeller 26 and casing 22.

Additionally, the deformable element 40 minimises the flow path between the high and low pressure chambers 32,28. Furthermore, the deformable element 40 will 1 5 deform to accommodate any deflections, which will also assist to reduce compressive, shear and other loads applied to the element 40 and transmitted between the impeller 26 and casing 22.

In the embodiment shown in Figures 2 and 3 the deformable element is located in an annular gap between the impeller 26 and pump casing 22. However, in an alternative embodiment shown in Figure 4, the deformable element 40 may be located in an axial gap defined between the impeller 26 and casing 22.

Reference is now made to Figure 5 in which there is shown one form of a deformable element for use as described above. The deformable element, which for convenience is generally represented by reference numeral 40, comprises a deformable ring 44 directly flush mounted on an inner surface portion 38 of the casing, and a wearable ring 46 mounted on the deformable ring 44. Thus, the deformable ring 44 accommodates any deflection of an impeller while the wearable ring 46 is adapted to be engaged by the impeller when deflected. The wearable ring 46 is manufactured from a material which wears at a greater rate than the pump impeller. That is, the wearable ring 46 has a lower pv factor than the pump impeller such that the wearable ring 46, in use, will be sacrificially worn to substantially prevent or minimise wear of the impeller.

Use of the deformable element 40 of Figure 5 is shown in Figure 6 which is a diagrammatic cross-sectional view of a portion of a pump incorporating the deformable element 40. When an impeller 26 is deflected by a thrust force in the direction of arrow 50, for example, the impeller 26 will engage the wearable ring 46 which by virtue of the deformable ring will be deflected in the same direction as the impeller 26. Thus, the deformable element 40 permits a relatively small gap 52 to be achieved and maintained, which in turn minimises fluid leakage through the gap 52.

An alternative arrangement is shown in Figure 7, wherein the deformable element, generally represented by reference numeral 54, is located in a gap 60 formed between an inner surface portion 58 of a pump casing and a neck 62 of an impeller.

The element 54 is mounted within an annular step 56 formed in the inner surface portion 58 of a pump casing. The deformable element 54 comprises a radially outer deformable ring 64 and a radially inner wearable ring, wherein the inner and outer rings are of the same width.

Another alternative arrangement is shown in Figure 8 of the drawings wherein a deformable element 70 is located in a gap 72 formed between an inner surface portion 74 of a pump casing and a neck 76 of an impeller. The element 70 comprises 2 5 an outer deformable ring 78 mounted within an annular step 80 in portion 74, and a wearable ring 82, smaller in width than the deformable ring 78, wherein the wearable ring 82 is mounted within an annular step 84 within the deformable ring 78.

A further alternative arrangement is shown in Figure 9, in which a deformable element 86 is located in a gap 88 formed between an inner surface portion 90 of a pump casing and a neck 92 of an impeller. The deformable element 86 comprises a radially outer deformable ring 94 and a radially inner wearable ring 96, wherein the outer deformable ring 94 is mounted between the inner surface portion 90 and the inner wearable ring 96, in respective annular channels 98,100.

Reference is now made to Figure 10 in which a deformable element 102 1 0 according to an embodiment of an aspect of the present invention is shown mounted on an inner surface portion 104 of a pump casing. The provision of a deformable element 102 in this manner eliminates the requirement to machine finish the surface 106 of the inner surface portion 104 of the pump casing, with the required surface finish being provided on the inner surface 108 of the deformable element 102.

Referring now to Figure 11, there is shown a deformable element 110 in accordance with an embodiment of the present invention, secured to an inner surface portion 112 of a pump casing. O-ring seals 114 are provided in respective annular channels 116 formed in the outer surface 118 of the element 110, wherein, in use, the O-ring seals assist to prevent leakage between the surface 120 of the inner surface 2 0 portion 112 of the pump casing and the outer surface 118 of the element 110.

It should be appreciated that the embodiments hereinbefore described are merely exemplary of the present invention and that various modifications may be made thereto without departing from the scope of the invention. For example, a deformable element may be provided which is composed of a single ring which is made of a material which provides both the required deformable and wearable properties. Additionally, each of the embodiments shown in Figures 5 to 11 may be utilised in an axial gap, such as that shown in Figure 4. Furthermore, the deformable ring in the embodiments shown are mounted on the stationary pump casing.

However, the deformable ring may alternatively be mounted on the rotary impeller.

Claims

CLAIMS: 1. A mechanical assembly having a stationary part and a rotary

part, and an element located between the stationary and rotary parts, wherem at least a portion of the element is defonnable.
2. The mechanical assembly of claim 1, wherein the stationary and rotary parts are arranged such that a surface of the stationary part Is positioned adjacent a surface of the rotating part.
3. The mechanical assembly of claim 2, wherein the element is positioned between the respective surfaces.
4. The mechanical assembly of claim 1, 2 or 3, wherein the element is located in a gap defined between the stationary and rotary parts.
5. The mechanical assembly of any preceding claim, wherem the element is mounted and secured to the stationary part of the mechanical assembly.
6. The mechanical assembly of any of claims I to 4, wherein the element is mounted on and secured to the rotary part of the mechanical assembly.
7. The mechanical assembly of any preceding, claim, wherein at least a portion of the element is resiliently deformable.
8. The mechanical assembly of any preceding claim, wherein the element Is capable of deforming to accommodate any movement between the stationary and rotary parts while preventing any surface contact therebetween.
9. The mechanical assembly of any preceding claim, wherein the element Is substantially ring shaped.
10. The mechanical assembly of any preceding claim, wherein the element is adapted to be located in an annular gap defined between the stationary and rotary parts.
11. The mechanical assembly of any preceding claim, wherem the element defines inner and outer circumferential surfaces.
12. The mechanical assembly of claim 11, wherein one circumferential surface is adapted to be secured to one of the stationary and rotary parts' and the other circumferential surface is adapted to engage with the other of the stationary and rotary parts upon relative deflection therebetween.
13. The mechanical assembly of any one of claims 1 to 9, wherein the element is adapted to be located in an axial gap defined between the stationary and rotary parts of the assembly.
14. The mechanical assembly of any preceding claim, wherein the element defines first and second axially displaced annular surfaces.
15. The mechanical assembly of claim 14 when dependent on 13, wherein one annular surface is adapted to be secured to one of the stationary and rotary parts, and the other annular surface Is adapted to engage with the other of the stationary and rotary parts upon relative deflection therebetween.
16. The mechanical assembly of any preceding claim, wherein the element is mounted directly on the surface of the relevant part of the mechanical assembly.
17. The mechanical assembly of any preceding claim, wherein the element is mounted within a recess.
18. The mechanical assembly of any preceding claim, wherein one or more seals are provided betwocn the element and the part of the mechanical assembly upon which the element is mounted.
19. The mechanical assembly of claim 18, wherein the one or more seals are in the form of O-ring seals.
20. The mechanical assembly of any preceding claim, wherein the element comprises a wearable material.
21. The mechanical assembly of claim 20, wherein the wearable material Is selected to wear at a greater rate than the part of the assembly inducing the material wear.
22. The mechanical assembly of claim 2() or 21, wherein the wearable material is selected to have a pv factor which is lower than that of the part ot the mechanical assembly which mduces material wear.
23. The mechanical assembly of any preceding claim, wherem the element is manufactured from a material which provides both required deforming and wearing properties.
24. The mechanical assembly of any one of claims I to 22, wherein the element is manufactured from a first material having the required deforming properties, and a second material having the required wearing properties.
25. The mechanical assembly of any preceding claim, wherein the element is formed by a deformable ring secured to a wearable ring.
26. The mechanical assembly of claim 25, wherein the deformable ring is adapted to be secured to one of the stationary and rotary parts, and the wearable ring is adapted to engage with the other of the stationary and rotary parts.
27. The mechanical assembly of claim 25 or 26, wherein the wearable nag and deformable ring are of substantially similar widths.
28. The mechanical assembly of claim 25 or 26, wherein the deformable ring is of a greater width than the wearable ring.
29. The mechanical assembly of any one of claims 25 to 28, wherem the wearable ring is flush mounted on a surface of the deformable ring.
30. The mechanical assembly of claim 25, 26 or 28, wherein the wearable ring is mounted within an annular recess in the deformable element.
31. The mechanical assembly of claim 25, 26 or 29, wherein the deformable ring is of a smaller width than the wearable ring.
32. The mechanical assembly of claim 25, 26 or 31, wherein the deformable ring is mounted within an annular recess in the wearable element.
33. The mechanical assembly of any preceding claim, wherein the mechanical assembly is a centrifugal pump.
34. The mechanical assembly of any preceding claim, wherein the stationary part of the mechanical assembly is a pump casing and the rotary part of the mechanical assembly is a pump impeller.
35. The mechanical assembly of claim 34, wherein the element is located between a portion of the pump casing and a neck of the impeller.
36. The mechanical assembly of claim 34 or 35, wherein the element is mounted on the pump casing.
37. An element for use between a stationary part and a rotary part of a mechanical assembly, wherein at least a portion of the element is deformable.
38. An element for use between a stationary part and a rotary part of a mechanical assembly, said clement comprising a deformable ring secured to a wearable ring.
39. The element of claim 38 wherein, in use, the detonnablc ring is adapted to be secured to one of a stationary part and a rotary part of a mechanical assembly.
40. (he element of claims 37 or 38 adapted for use in the mechanical assembly of any one of claims I to 36.
41. A wear ring for locating between stationary and rotary parts of a mechanical assembly, said wear ring comprising a wearing surface located on a resilient backing.
42. A mechanical assembly substantially as described herein and shown in the accompanying drawings.
43. An elcmcut for rise between a stationary part and a rotary part of a mechanical assembly substantially as described herein and shown in the accompanying drawings.