GB2438702A

GB2438702A - Efficiency maintenance apparatus for a mechanical assembly

Info

Publication number: GB2438702A
Application number: GB0707546A
Authority: GB
Inventors: John Fleming
Original assignee: Weir Pumps Ltd
Current assignee: Weir Pumps Ltd
Priority date: 2006-05-31
Filing date: 2007-04-19
Publication date: 2007-12-05
Also published as: GB0707546D0; GB0610684D0

Abstract

A mechanical assembly, such as a pump 40, comprises a rotary component 46 mounted within a casing 44, wherein an annular space 50 is defined between a portion of the rotary component 46 and a portion of the casing 44. The assembly further comprises an injection apparatus 47 adapted to inject an injectable material 48 into the annular space 50.

Description

1 2438702

EFFICIENCY MAINTENANCE APPARATUS FOR A MECHANICAL

ASSEMBLY

FIELD OF THE INVENTION

The present invention relates to an efficiency maintenance apparatus for a mechanical assembly, and in particular to an efficiency maintenance apparatus for minimising pressure losses across stationary and rotating parts of a pump.

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 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 pressurised. 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. However, permitting some leakage in this manner is done at the expense of pump efficiency and as such it is desirable to maintain fluid leakage to an absolute minimum, with a difficult compromise between pump efficiency and favourable leakage for lubricating/cooling purposes being preferably maintained.

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 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 known in the art to locate wearing components in regions of machinery where tight clearances exist between rotary and stationary parts, such that the clearances may be minimised without risking damage to the machinery components.

However, through use of the mechanical assembly the clearances will increase, reducing efficiency and thus necessitating replacement of the wearing components.

This conventionally requires shut-down and dismantling of the equipment which in many cases is undesirable.

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 comprising: a casing; a rotary component rotatably mounted within the casing, wherein an annular space is defined between a portion of the rotary component and a portion of the casing; and an injection apparatus adapted to inject an injectable material within the annular space.

Preferably, the mechanical assembly defines first and second chambers positioned on either side of the annular space. Advantageously, in use, the injectable material within the annular space will act to minimise fluid leakage across the annular space between the first and second chambers. The material may entirely fill the annular space. Alternatively, the material may be injected into the annular space such that a clearance gap is established between the material and one or both the casing and rotary component.

Conventional rotary machinery, such as pumps and compressors, which incorporate regions of tight clearances between rotary and stationary parts may require leakage of a fluid across the clearance during use. However, such leakage may adversely affect the efficiency of the machinery. Preferably, in the present invention the injectable material is self lubricating and preferably also self cooling.

Accordingly, fluid transfer across the annular space between the first and second chambers is not essential for cooling and lubrication purposes, such that the injectable material may be arranged within the annular space to substantially prevent leakage of fluid across said space, thus increasing the overall efficiency of the mechanical assembly.

Additionally, when in use, the injectable material may prevent or substantially minimise contact between the casing and the rotary component when one or both are deflected or forced together. Additionally, by virtue of the material being injectable, the material is preferably compliant and advantageously is adapted to conform to the shape of the annular space. Furthermore, the injectable material may advantageously deform to accommodate any deflections of the pump casing and impeller, when in use, which will also assist to reduce compressive, shear and other loads applied to the injectable material and transmitted between the parts of the pump assembly.

In one embodiment of the present invention, the annular space extends in an axial direction relative to the mechanical assembly. In this embodiment the rotary component defines a radially inner surface and the casing defines a radially outer surface. Alternatively, or additionally, the annular space extends in a radial direction.

In this alternative embodiment the rotary component and casing define axially separated surfaces.

Preferably, the injectable material, in use, is adapted to be wearable.

Preferably also, the injectable 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 injectable material will be sacrificially worn to substantially prevent or minimise wear of the rotary component and/or the pump casing.

The injectable material may be supported on the casing. Alternatively, the injectable material may be supported on the rotary component. Alternatively further, the injectable material may be supported on both the casing and rotary component.

Preferably, at least a portion of the injection apparatus is mounted externally of the casing and is adapted to inject the injectable material through a wall of the casing. Alternatively, the injectable material may be injected into the annular space from within the casing.

Advantageously, the injection apparatus may be mounted on the casing, and may be either permanently or removeably mounted on the casing.

The injection apparatus preferably comprises an injector, such as an injector comprising a plunger slidably mounted within a hydraulic cylinder defining an outlet nozzle, wherein the plunger, in use, forces injectable material outwardly from the hydraulic cylinder via the nozzle. In such an arrangement the injector preferably comprises an actuator adapted to move the plunger within the hydraulic cylinder. The actuator may be a linear actuator coupled to the plunger and adapted to directly depress the plunger within the cylinder. Alternatively, the actuator may be a rotary actuator rotatably coupled to the plunger and adapted to indirectly depress the plunger within the cylinder. The nozzle is preferably adapted to be engaged with a port on the casing.

The injection apparatus may be activated to inject material into the annular space manually. Alternatively, the injection apparatus may be adapted to be automatically activated.

Preferably, the injection apparatus is adapted to periodically inject the injectable material into the annular space. The material may be injected cyclically in accordance with a predetermined pump running time, for example. Alternatively, or additionally, the material may be injected in accordance with a pump operational condition. For example, the injection apparatus may be activated in response to a measured operational condition, such as thermometric efficiency. For example, the mechanical assembly may comprise a sensory feedback control system adapted to measuie operational conditions of the mechanical assembly and provide an input signal to activate the injection apparatus the when a measured operational condition falls below a predetermined value.

Advantageously, the injection apparatus may be activated after the mechanical assembly is first commissioned and reaches a steady operational duty.

The mechanical assembly may comprise retaining means adapted to retain the injectable material within the annular space. The retaining means may comprise at least one and preferably at least two retaining plates located within the annular space.

The retaining plates may be mounted on one or both of the casing and rotary component. In a preferred arrangement the retaining plates are mounted on the casing. The retaining means may comprise a pair of retaining plates, which may be in the form of annular plates or rings, located within the annular space, between which plates the injectable material is injected. Preferably, the retaining plates are mounted on the casing and may define a small clearance with the rotary component, or alternatively may engage the rotary component The retaining plates may be adapted to engage the rotary component at least during installation and initial commissioning, wherein use of the mechanical assembly causes the retaining plates to wear and thus define a clearance between the plates and the rotary component. Accordingly, the retaining plates may be wearable, and may form part of a wear ring component located within the annular space. The retaining plates may comprise a metal, polymer, composite, elastomer or the like, or any suitable combination of materials.

The injectable material may comprise a polymer, such as PTFE or the like.

Preferably, the injection apparatus is adapted to be activated when the mechanical assembly is operational. This advantageously permits an optimum efficiency of the mechanical assembly to be maintained without requiring the assembly to be shut down.

In a preferred embodiment the mechanical assembly is a pump and the casing is a pump casing. Preferably also, the rotary component comprises a pump impeller, such as a centrifugal pump impeller. Preferably, the annular space is defined between a neck portion of the impeller and the pump casing. Alternatively, or additionally, the annular space may be in the region of a pump throttle bush.

The mechanical assembly may alternatively be a compressor or other rotary machine.

According to a second aspect of the present invention, there is provided a method of maintaining operational efficiency of a mechanical assembly having a casing and a rotary component mounted within the casing, said method comprising: mounting an injection assembly on a casing of the mechanical assembly; and injecting an injectable material through a wall of the casing and into an annular space defined between a portion of the rotary component and a portion of the casing.

Preferably, the method comprises the step of periodically injecting the material into the annular space. This advantageously permits the volume of material within the annular space to be maintained at an optimum quantity to thus achieve optimum efficiency.

Preferably, the material injected into the annular space prevents or minimises fluid leakage across the annular space between first and second chambers located on either side of the annular space.

Advantageously, the step of injecting may be performed when the mechanical assembly is in use.

According to a third aspect of the present invention, there is provided an injection system for use with a mechanical assembly, said system comprising: an injectable material; an injector adapted to be mounted on a portion of a mechanical assembly, said injector being adapted to inject the injectable material into an annular space defined between a stationary component and a rotary component of the mechanical assembly.

According to a fourth aspect of the present invention there is provided a pump assembly comprising: a pump casing; a pump impeller rotatably mounted within the casing, wherein an annular space is defined between a portion of the pump impeller and a portion of the pump casing; and an injection apparatus adapted to inject an injectable material within the annular space.

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 part of a known centrifugal pump; and Figure 2 is a diagrammatic view of a portion of a mechanical assembly, namely a centrifugal pump, in accordance with an embodiment of an aspect of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring initially to Figure 1, there is shown a diagrammatic cross-sectional view of a known centrifugal pump 10. The pump 10 includes a pump casing 12 within which is mounted on a shaft 14 carrying one or more impellers 16 (only one shown) which define a corresponding number of pump stages. In use, the shaft 14 and impellers 16 are rotated and draw fluid through a suction branch (not shown) into a low pressure chamber 18 within the casing 12. The fluid enters the first stage impeller 16 from the low pressure chamber 18 through a central impeller eye 20, is pressurised by being driven radially through the impeller 16, with high pressure fluid exiting the first stage impeller 16 into a high pressure chamber 22. From this high pressure chamber 22 the fluid may be discharged from the pump casing 12 through a discharge branch, or alternatively may be directed to a successive pump stage to be further pressurised. The low and high pressure chambers 18, 22 are separated by closely interfacing portions of the stationary pump casing 12 and rotary impeller 16, shown generally by reference numeral 24. More specifically, the arrangement between the casing 12 and impeller 16 is such that an outer surface portion of a neck 26 of the impeller 16 is located adjacent an inner surface portion 28 of the casing 22.

An annular space or clearance 30 is defined between the respective surfaces of the casing 12 and impeller 16 to prevent or minimise contact therebetween, for example when the impeller is deflected by varying thrust forces. This annular space 30 results in fluid leakage from the high pressure chamber 22 into the low pressure chamber 18 which reduces overall pump efficiency. However, it should be noted that in some cases minimal leakage may be tolerated in order to cool and lubricate the respective surfaces of the impeller 16 and casing 12. 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 or annular space 30 and thus fluid leakage between the pump casing 12 and impeller 16, while preventing/minimising contact therebetween, it is known in the art to located a deformable or wearable element 32 between the casing 12 and impeller 16. Thus, the deformable element 32 will prevent or substantially minimise any contact between the impeller 16 and casing 12.

Additionally, the deformable element 32 minimises the flow path between the high and low pressure chambers 22, 18. However, due to the sacrificial wearing properties of the element 32, the use of the pump 10 will result in the gap between the impeller 16 and element 32 increasing, thus permitting an increasing volume of fluid to leak from the high pressure chamber 22 to the low pressure chamber 18. This therefore results in a reduction in pump efficiency. In order to seek to maintain an acceptable operational efficiency, it is necessary to shut-down the pump 10 and remove and replace the element 32. Such level of maintenance is undesirable.

Reference is now made to Figure 2 of the drawings in which there is shown a diagrammatic view of a portion of a pump assembly 40 in accordance with an embodiment of the present invention. The portion of the pump 40 shown in Figure 2 is generally the same portion identified by region 42 in the known pump 10 of Figure 1.

The pump assembly 40 comprises a pump casing 44, a pump impeller 46 rotatably mounted within the casing 44, and an injection system, generally identified by reference numeral 47. The injection system 47, in use, injects an injectable material 48 into an annular space 50 defined between a neck portion 52 of the impeller 46 and an inner surface portion 54 of the casing 44. The injectable material 48 is retained between two annular plates 56, 58 which are mounted on the inner surface portion 54 of the pump casing 44. The annular plates 56 define a very small, and in some embodiments a zero, clearance with the neck portion 52 of the impeller 46.

In the embodiment shown the material 48 substantially entirely fills the annular space 50, such that the injectable material 48 may substantially prevent leakage of fluid from a high pressure chamber 60 to a low pressure chamber 62.

Additionally, when in use, the injectable material 48 will prevent or substantially minimise contact between the pump casing 44 and impeller 46. Additionally, by virtue of the material 48 being injectable, the material 48 is compliant and advantageously conforms to the shape of the annular space 50. Furthermore, the injectable material 48 deforms to accommodate any deflections of the pump casing 44 and impeller 46, when in use.

The injection system 47 comprises an injector having a hydraulic cylinder 64 defining an outlet nozzle 66, and a plunger 68 slidably mounted within the cylinder 64, wherein the plunger 68, in use, forces injectable material outwardly from the hydraulic cylinder via the nozzle 66. The pump casing 44 defines a port 70 adapted to receive the nozzle 66 of the injector. The injector comprises an actuator 70 adapted to move the plunger 68 within the hydraulic cylinder 68. The actuator 70 in the embodiment shown is hand operated. Accordingly, material 48 may be periodically injected into the annular space 50 in order to maintain an optimum volume of material 48 and to thus maintain an optimum efficiency.

It should be understood that the embodiment shown and described is merely exemplary of the present invention and that various modifications may be made thereto without departing from the scope of the invention. For example, in the embodiment described the material may be injected cyclically in accordance with a predetermined pump running time, for example. Alternatively, or additionally, the material may be injected in accordance with a pump operational condition. The injection system may alternatively be operated automatically.

The annular space in the embodiment shown extends in an axial direction.

However, in an alternative embodiment the annular space may extend in a radial direction.

Claims

CLAIMS: 1. A mechanical assembly comprising: a casing; a rotary

component rotatably mounted within the casing, wherein an annular space is defined between a portion of the rotary component and a portion of the casing; and an injection apparatus adapted to inject an injectable material within the annular space.

2. The mechanical assembly of claim 1, wherein first and second chambers are defined on either side of the annular space.

3. The mechanical assembly of claim 2, wherein the injectable material within the annular space is adapted to minimise fluid leakage across the annular space between the first and second chambers.

4. The mechanical assembly of any preceding claim, wherein the injectable material entirely fills the annular space.

5. The mechanical assembly of claim 1, 2 or 3, wherein the injectable material is adapted to be injected into the annular space such that a clearance gap is established between the material and one or both the casing and rotary component.

6. The mechanical assembly of any preceding claim, wherein the injectable material is self lubricating.

7. The mechanical assembly of any preceding claim, wherein the injectable material is self cooling.

8. The mechanical assembly of any preceding claim, wherein the injectable material is adapted to minimise contact between the casing and the rotary component when one or both are deflected or forced together.

9. The mechanical assembly of any preceding claim, wherein the injectable material is compliant and is adapted to conform to the shape of the annular space.

10. The mechanical assembly of any preceding claim, wherein the annular space extends in an axial direction relative to the mechanical assembly.

11. The mechanical assembly of any preceding claim, wherein the rotary component defines a radially inner surface and the casing defines a radially outer surface.

12. The mechanical assembly of any preceding claim, wherein the annular space extends in a radial direction.

13. The mechanical assembly of any preceding claim, wherein the rotary component and casing define axially separated surfaces.

14. The mechanical assembly of any preceding claim, wherein the injectable material, in use, is adapted to be wearable.

15. The mechanical assembly of any preceding claim, wherein the injectable material is selected to have a pv factor which is lower than that of the part of the mechanical assembly which induces material wear.

16. The mechanical assembly of any preceding claim, wherein the injectable material is supported on the casing.

17. The mechanical assembly of any preceding claim, wherein the injectable material is supported on the rotary component.

18. The mechanical assembly of any preceding claim, wherein at least a portion of the injection apparatus is mounted externally of the casing and is adapted to inject at least a portion of the injectable material through a wall of the casing.

19. The mechanical assembly of any preceding claims, wherein at least a portion of the injectable material is adapted to be injected into the annular space from within the casing.

20. The mechanical assembly of any preceding claim, wherein the injection apparatus is mounted on the casing.

21. The mechanical assembly of any preceding claim, wherein the injection apparatus is removably mounted on the casing.

22. The mechanical assembly of any preceding claim, wherein the injection apparatus comprises an injector.

23. The mechanical assembly of claim 22, wherein the injector comprises a plunger slidably mounted within a hydraulic cylinder defining an outlet nozzle.

24. The mechanical assembly of any preceding claim, wherein the injection apparatus comprises an actuator.

25. The mechanical assembly of claim 24, wherein the actuator comprises a linear actuator.

26. The mechanical assembly of claim 24, wherein the actuator comprises a rotary actuator.

27. The mechanical assembly of any preceding claim, wherein the injection apparatus is adapted to be activated to inject material into the annular space manually.

28. The mechanical assembly of any preceding claim, wherein the injection apparatus is adapted to be automatically activated.

29. The mechanical assembly of any preceding claim, wherein the injection apparatus is adapted to periodically inject the injectable material into the annular space.

30. The mechanical assembly of any preceding claim, wherein the injectable material is adapted to be injected cyclically in accordance with an operational condition of the mechanical assembly.

31. The mechanical assembly of claim 30, wherein the operation condition is a measured condition.

32. The mechanical assembly of claim 30 or 31, wherein the mechanical assembly comprises a sensory feedback control system adapted to measure operational conditions of the mechanical assembly.

33. The mechanical assembly of claim 32, wherein the feedback control system is adapted to provide an input signal to activate the injection apparatus when a measured operational condition falls below a predetermined value.

34. The mechanical assembly of any preceding claim, wherein the injection apparatus is activated after the mechanical assembly is first commissioned and reaches a steady operational duty.

35. The mechanical assembly of any preceding claim, further comprising retaining means adapted to retain the injectable material within the annular space.

36. The mechanical assembly of claim 35, wherein the retaining means comprises at least one retaining plates located within the annular space.

37. The mechanical assembly of claim 36, wherein the retaining plates are mounted on one of the casing and rotary component.

38. The mechanical assembly of any preceding claim, wherein the injection apparatus is adapted to be activated when the mechanical assembly is operational.

39. The mechanical assembly of any preceding claim, wherein the casing comprises a pump casing and the rotary component comprises a pump impeller.

40. The mechanical assembly of claim 39, wherein the annular space is defined between a neck portion of the impeller and the pump casing.

41. A method of maintaining operational efficiency of a mechanical assembly having a casing and a rotary component mounted within the casing, said method comprising: mounting an injection assembly on a casing of the mechanical assembly; and injecting an injectable material through a wall of the casing and into an annular space defined between a portion of the rotary component and a portion of the casing.

42. The method of claim 41, further comprising the step of periodically injecting the material into the annular space.

43. An injection system for use with a mechanical assembly, said system comprising: an injectable material; an injector adapted to be mounted on a portion of a mechanical assembly, said injector being adapted to inject the injectable material into an annular space defined between a stationary component and a rotary component of the mechanical assembly.

44. A pump assembly comprising: a pump casing; a pump impeller rotatably mounted within the casing, wherein an annular space is defined between a portion of the pump impeller and a portion of the pump casing; and an injection apparatus adapted to inject an injectable material within the annular space.