GB2414278A

GB2414278A - Pump assembly with driving means located in a pump casing

Info

Publication number: GB2414278A
Application number: GB0507540A
Authority: GB
Inventors: John Fleming
Original assignee: Weir Pumps Ltd
Current assignee: Weir Pumps Ltd
Priority date: 2004-05-18
Filing date: 2005-04-14
Publication date: 2005-11-23
Also published as: GB0411040D0; GB0507540D0

Abstract

A pump assembly 10 comprises a pump casing 12, a drive assembly 44 mounted within the casing 12 and impellers 32, 38. The casing 12 may define an inlet 14, an outlet 16 and an annular inter-stage flow passage 46 between two impellers 32, 38. The flow passage 46 may surround the drive assembly 44, which may be supported in the passage 46 by ribs 48. The drive assembly 44 may be adapted to drive each impeller 32, 38 at a different rotational speed. The rotational speed of the impellers 32, 38 may be controlled by a control system, such that overall pump efficiency can be managed. The drive assembly 44 may include two separate driving means, each having a motor 50, 52 which drives an impeller 32, 38.

Description

, 2414278

PUMP ASSEMBLY

FIELD OF INVENTION

The present invention relates to a pump assembly, and in particular, but not exclusively, to a pump assembly incorporating a low speed inlet impeller in fluid communication with a high speed discharge impeller within a single pump unit.

BACKGROUND OF INVENTION

The limiting factor in many high speed single stage pump designs with optimum specific speed is often suction performance. Increases in operating speed results in an increase in the Net Positive Suction Head Required (NPSHR). If the Net Positive Suction Head Available (NPSHA) is less than that required this will cause cavitation of the fluid at the impeller inlet. Cavitation results when the pressure of a liquid falls below its vapour pressure which causes the sudden formation and collapse of low pressure bubbles or cavities. This cavitation produces noise and vibration and can damage the internal pump components. Cavitation also affects the performance of the pump due to the fact that the pumped fluid exists in two phases, a condition which most conventional pumps are not designed to accommodate. It is necessary for optimum pump performance and longevity to ensure that the pressure of the liquid being pumped does not fall below its vapour pressure at the pump suction port or inlet. That is, an adequate Net Positive Suction Head (NPSH) must be achieved and maintained.

The most common approach to ensuring that pumps have adequate NPSH is to set the operating speed such that available suction pressure exceeds pump requirements. This, however, often results in pumps being selected with non optimum specific speed hydraulics, with resultant efficiency reduction, and being physically larger pumps operating at lower speeds with resultant increases in pump and driver costs. On pump duties involving higher discharge pressures to satisfy suction requirements by operating at lower speeds will result in the pump type having to be of a multi-stage as opposed to a single stage design An alternative conventional approach to ensure that an adequate NPSH is achieved involves the use of a booster pump, fitted in series into the hydraulic system, wherein the booster pump pressurises the fluid to the required head prior to the fluid entering the main pump. However, this approach may be difficult to accomplish in locations where space is restricted, for example. Additionally, a booster pump includes separate suction and discharge ports and associated flanges and seals which increases the line losses in the hydraulic system as a whole, resulting in a loss in efficiency. Furthermore, a booster pump conventionally requires dedicated monitoring and control equipment, increasing the required plant space and cost.

It is among the objects of the present invention to obviate or at least mitigate

the aforementioned problems with the prior art.

SUMMARY OF INVENTION

According to a first aspect of the present invention, there is provided a pump assembly comprising: a pump casing; two pump impellers mounted within the pump casing; and a drive assembly mounted within the pump casing and being coupled to the pump impellers.

Thus, the pump assembly of the present invention provides an integrated unit including both pumping means and driving means.

it should be understood that the pump assembly of the present invention may include two or more pump impellers, and references herein to two impellers should be construed accordingly.

Preferably, the pump casing defines a fluid inlet, generally defined as a pump suction port, and a fluid outlet, generally defined as a pump discharge. A flow path is defined between the pump casing fluid inlet and outlet. Advantageously, the two pump impellers are located within the flow path. The pump casing inlet may be a tangential inlet. Preferably, the pump casing inlet is an axial inlet. The pump casing outlet may be tangential or axial. For example, the pump outlet may be of a double volute tangential discharge arrangement, a diffuser style tangential discharge arrangement, an axial discharge diffuser style bowl arrangement or the like.

Preferably, each pump impeller defines a fluid inlet, typically an impeller eye, and a fluid outlet, wherein, in use, each impeller is formed to impart energy to a fluid flowing from the impeller fluid inlet to the fluid outlet. The impellers may be mounted within the pump casing such that, in use, fluid exiting the fluid outlet of one impeller is directed towards the fluid inlet of the other impeller. Advantageously, each impeller defines, or at least partly defines a pump stage. Preferably, fluid is directed from one impeller stage to the other via an inter-stage fluid passage defined within the pump casing. Preferably, one impeller corresponds to a first or low pressure stage, and the other pump impeller corresponds to a second or high pressure stage. It should be understood that the terms "low" and "high" as used above relate to the pressure of one impeller stage relative to the other. Advantageously, the first or low pressure stage, in use, is adapted to provide and maintain an adequate Net Positive Suction Head (NPSH) to the second or high pressure stage, while the high pressure stage provides a fluid discharged in accordance with the pump assembly duty requirements. Thus, the second or high pressure stage may be utilised to produce higher pressures than would be achievable with conventional single stage pump assemblies, while optimising impeller specific speed, as the first stage impeller will maintain the required NPSH for the second stage impeller to operate efficiently.

Preferably, the drive assembly is adapted to drive one pump impeller at a first rotational speed, and the other impeller at a second rotational speed, greater than the first rotational speed. Advantageously, the first or low pressure stage is driven at the first rotational speed, and the second or high pressure stage is driven at the second rotational speed. Thus, the impeller of the second or high pressure stage may be operated at higher speeds while maximising pump performance than would otherwise be achievable using a conventional single stage pump.

Preferably, the drive assembly is adapted to vary the rotational speed of the impellers. This would allow a wide duty range to be achieved while maintaining an adequate NPSH, and would also permit the pump assembly to be tuned to operate at optimum efficiency for the particular duty requirement.

Preferably, the pump assembly further comprises a control system adapted to optimise operation thereof. The control system may be manually operated.

Alternatively, or additionally, the control system may be automatically operated. For example, the control system may be of a closed loop control or condition monitoring system such that the control system may monitor the conditions of the pump assembly and adjust these accordingly to optimise efficiency. Advantageously, the control system, in use, permits management of the overall pump assembly efficiency by varying impeller speeds to achieve optimum individual impeller performance, and also ensures that the first or low pressure stage impeller achieves and maintains adequate NPSH to itself and the second or high pressure stage impeller. The provision of a suitable control system provides a pump assembly with "smart pump" capability.

Advantageously, the drive assembly is interposed between the pump impellers. In this arrangement, the inter-stage fluid passage may extend at least partially around or over the drive assembly. This advantageously assists in cooling the drive assembly when in use.

Advantageously, the drive assembly defines a substantially uniform outer diameter. Preferably, the drive assembly is provided in a housing defining a substantially uniform outer diameter. The housing may be constructed as a single assembly. Alternatively, the housing is preferably constructed in two separate assemblies, each accommodating a respective drive assembly, the separate housings being directly connected together to form a single pump unit when assembled with the pump components. This preferred arrangement allows a spool piece with one or more inlet/outlet connections to be fitted between the first and second drive units and forming an integral part of the pump casing. This allows the pump assembly to be applied into hydraulic systems where the flow from the first impeller stage does not match the flow from the second impeller stage. By the optional fitting of a spool piece, as noted above, flow can be bled off at the first stage pressure or flow can be introduced at the first stage pressure.

Preferably, the drive assembly is concentrically mounted within the pump casing. In this arrangement, an annular inter-stage fluid passage may be formed between the drive assembly and the inner wall surface of the pump casing.

Alternatively, the drive assembly may be eccentrically mounted within the pump casing. In one embodiment of the present invention, the drive assembly is mounted in the pump casing by at least one, and preferably a plurality of ribs extending between the pump casing and the drive assembly.

In a preferred embodiment, the ribs are located within the inter-stage fluid passage. Preferably, the ribs are circumferentially arranged within the inter-stage fluid passage and in use assist to stabilise the flow of the fluid therethrough.

Advantageously, the ribs define one or more passages extending between the pump casing and the drive assembly. The passages may provide conduits for allowing access for power or control cables or the like to the drive assembly.

to Additionally, or alternatively, one or more of the passages may provide a conduit for allowing a fluid, such as a cooling fluid or a lubricant to be supplied to or removed or drained from the drive assembly. This is discussed in more detail below.

Advantageously, any fluid supplied to or removed from the drive assembly may be monitored by a suitable control system, such as that discussed above.

Preferably, the drive assembly comprises a motor unit, and preferably an electric motor unit. Advantageously, the drive assembly is coupled to the pump impellers using a drive shaft.

In a preferred embodiment of the present invention, the drive assembly comprises two motor units, one coupled to one pump impeller, and one coupled to the other pump impeller. Advantageously, the motor units are coupled to their respective pump impeller via a drive shaft. Each drive shaft may be supported at either end thereof, for example, by the respective motor unit at one end, and by the pump casing at an opposite end, with the respective pump impeller being mounted on the shaft at a location between the ends thereof. Alternatively, and in a preferred embodiment, each drive shaft is cantilevered from a respective motor unit, with each pump impeller being mounted on a free end of a respective drive shaft.

Preferably, the motor units are mounted within the pump casing in a backto back arrangement. That is, each motor unit is arranged such that each drive shaft extends from a respective motor unit in opposite directions.

Advantageously, each motor unit is mechanically and electrically autonomous from the other motor unit. In a preferred embodiment, the pump assembly comprises a single control panel for controlling the motor units. As noted above, the drive assembly may, however, be controlled by a suitable control system. Preferably, the pump assembly is coupled to a single electrical power supply, such as an A.C.

electrical power supply. Advantageously, the single electrical power supply may be converted into two separate supplies, one for each motor unit, such as separate D.C.

electrical power supplies.

Preferably, the motor units are mounted within a single motor housing defining a substantially uniform outer diameter. Alternatively, each motor unit is mounted in a respective motor housing.

Advantageously, each drive shaft is mounted within each motor unit via suitable bearings. The bearings may be cartridge sealed bearings or the like.

Preferably, each motor unit comprises a shaft sealing arrangement to prevent ingress of fluid into the motor units. For example, mechanical seals may be provided.

Preferably, a seal leakage chamber is provided and is associated with each motor unit.

A single seal leakage chamber may be provided, or alternatively each motor unit may comprise an individual seal leakage chamber. In use, the or each seal leakage chamber may collect any fluid which may have leaked past each shaft seal; it should be noted that some leakage past the shaft seals may be tolerated in order to lubricate and/or cool the respective shaft and seal. Prcferab]y, the or each seal leakage chamber comprises drainage means to allow any fluid to be dramed therefrom. The drainage means may be conduits or the like extending *om the or each seal leakage chamber to the exterior of the pump casing. Advantageously, and as noted above, the drainage means may be provided by passages formed in ribs used to mount the drive assembly within the pump casing.

The pump casing is preferably formed in separate sections which are subsequently secured together, thus allowing the pump assembly to be more readily assembled. In one embodiment, the pump casing may be axially split. Alternatively, the pump casing may be laterally split. In one embodiment, the pump casing may be formed in three separate sections; a first end portion incorporating the pump casing inlet, a centre portion accommodating the drive assembly, and a second end portion incorporating the pump casing outlet. In this arrangement, the sections of the pump casing are circumferentially joined at two axially spaced locations. In an alternative embodiment, the pump casing may be formed in four separate sections; a first end portion incorporating the pump casing inlet; two centre portions for accommodating the drive assembly; and a second end portion incorporating the pump casing outlet.

According to a second aspect of the present invention, there is provided a pump assembly comprising: a pump casing; a first pump impeller rotatably mounted in the pump casing and being coupled to first variable speed drive assembly; and a second pump impeller rotatably mounted in the pump casing and being coupled to a second variable speed drive assembly, the second pump impeller being in fluid communication with the first pump impeller.

Preferably, at least one of the first and second variable speed drive assemblies is mounted in the pump casing. More preferably, both first and second variable speed drive assembhes are mounted within the pump casing.

Advantageously, the first and second drive assemblies are mounted within the pump casing and are interposed between the first and second impellers.

Preferably, the first and second variable speed drive assemblies are individually controlled by a suitable control system, such as a closed or open loop feedback system.

According to a third aspect of the present invention, there is provided a pump assembly comprising: a pump casing defining a fluid inlet and a fluid outlet and a flow path therebetween; a pump impeller rotatably mounted within the flow path of the pump casing; and a drive assembly mounted within the flow path of the pump casing and being coupled to the pump impeller.

According to a fourth aspect of the present invention, there is provided a pump assembly comprising: a pump easing; and first and second pump impellers rotatably mounted within the pump casing, wherein the first pump impeller is adapted to operate at a different rotational speed than the second pump impeller.

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 I is a diagrammatic longitudinal cross-sectional view of a pump assembly in accordance with an embodiment of the present invention; and Figure 2 is a diagrammatic lateral cross-sectional view of the pump assembly of Figure 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to Figure 1, a pump assembly, generally indicated by reference numeral 10' is diagrammatically shown in longitudinal cross-section. The pump assembly 10 comprises a pump casing 12 having an axially arranged inlet 14 and an tangentially arranged outlet or discharge 16. As shown, the casing 12 is split into three separate sections; a first end portion 18 incorporating the pump casing inlet 14, a centre portion 20, and a second end portion 22 incorporating the pump casing outlet lS 16. The three separate sections 18,20,22 of the pump casing 12 are circumferentially joined at two axially spaced locations 24,26 using a flange and bolting arrangement 28,30.

Mounted within the pump casing 12 is a first stage impeller 32 having a central fluid inlet 34 and a circumferential fluid outlet 36, and a second stage impeller 38 having a central fluid inlet 40 and a circumferential fluid outlet 42. The first and second impellers 32,38 are coupled to a variable speed drive assembly 44 which is also mounted within the pump casing 12. An annular inter-stage fluid passage 46 is defined between the drive assembly 44 and the pump casing 12, wherein the inter stage fluid passage 46 provides fluid communication between the outlet 36 of the first stage impeller 32 and the inlet 40 of the second stage impeller 38. This arrangement is advantageous in that any fluid flowing through fluid passage 46 will assist to cool the drive assembly 44.

In the embodiment shown, the first stage Impeller 32 operates at a lower rotational speed and pressure than the second stage impeller 38. In use the first stage impeller 32 provides and maintains and adequate Net Positive Suction Head (NPSH) to the second stage impeller 38, while the second stage impeller 38 provides a fluid discharged in accordance with the pump assembly duty requirements. The provision of variable speed drive assembly 44 allows a wide duty range to be achieved while maintaining an adequate NPSH, and also permits the pump assembly 10 to be tuned to operate at optimum efficiency for the particular duty requirement.

The drive assembly 44 is mounted within the pump casing 12 by ribs 48 which extend across the inter-stage fluid passage 46. This is better shown in Figure 2 which is a lateral diagrammatic cross-sectional view of the pump assembly 10. Referring to Figure 2, four ribs 48 are provided and are circumferentially distributed within the fluid passage 46 in a cruciform arrangement. The ribs 48 extend axially along the fluid passage 46 and assist to stabilise the flow of fluid therethrough.

Referring again to Figure 1, the drive assembly 44 comprises two independent electric motor units 50,52 mounted within a single motor unit housing 53 having a uniform outer diameter. The first motor unit 50 is adapted to operate at a lower speed than the second motor unit 52. The first stage impeller 32 is coupled to the first motor unit 50 via a first drive shaft 54, and the second stage impeller 38 is coupled to the second motor unit 52 via a second drive shaft 56.

The first motor unit 50 comprises a rotor 58 mounted on drive shaft 54, and a stator 60. Similarly, the second motor unit 52 comprises a rotor 62 and a stator 64.

Each drive shaft 54,56 is mounted within its respective motor unit by cartridge sealed bearings 66,67. Each motor unit 50,52 further comprises a mechanical seal 68,69 to prevent ingress of fluid. Additionally, each motor unit 50,52 comprises a seal leakage chamber 70,72 to collect any fluid which may have leaked past each shaft seal 68,69; it should be noted that some leakage past the shaft seals 68,69 may be tolerated in order to lubricate and/or cool the respective shaft 54,56 and seal 68,69. Each seal leakage chamber 70,72 comprises one or more drainage ports 74, 76 to allow any fluid to be drained therefrom. The drainage ports 74,76 are provided in the ribs 48.

Although not shown, additional ports may be provided in the ribs 48 allowing access for power or control cables or the like to the drive assembly 44.

A control system (not shown) is provided which, in use, optimises the operation of the pump assembly 10. That is, the control system monitors the conditions of the pump assembly 10 and adjusts these accordingly to optimise efficiency. Specifically, the control system permits management of the overall pump assembly 10 efficiency by varying impeller 32,38 speeds to achieve optimum individual impeller performance, and also ensures that the first stage impeller achieves and maintains adequate NPSH to itself and the second stage impeller. The provision of a suitable control system provides the pump assembly 10 with "smart pump" capability.

A single control panel (not shown) is provided in association with the pump assembly 10, wherein the single control panel is used to control both motor units 50,52. Additionally, the single control panel converts a single A.C. power supply into two D.C. power supplies for each motor unit 50,52.

It will be understood by those of skill in the art that the embodiment described above and shown in the accompanying drawings is merely exemplary of the present invention and that various modifications may be made thereto without departing from the intended scope of the present invention. For example, a pump assembly may be provided with more than two impellers. Additionally, the geometry of the pump casing inlet and outlet may be varied and are not restricted to and axial inlet and a tangential outlet. Furthermore, the casing may be axially split. Additionally, the motor units 50,52 may be encased within separate housings which are subsequently secured together. In this alternative arrangement, a spool piece may be located between each motor to permit flow to be bled omin between the first and second impeller stages. Where separate motor unit housings are provided, the pump casing may be formed in four separate sections, as opposed to three shown in Figure 1. That is, the pump casing may comprise; a first end portion incorporating the casing inlet; two central portions for accommodating a respective motor unit housing, and a second end portion incorporating the casing outlet.

Claims

CLAIMS: 1. A pump assembly comprising: a pump casing; two pump impellers

mounted within the pump casing; and a drive assembly mounted within the pump casing and being coupled to the pump impellers.
2. A pump assembly as claimed in claim l, wherein the pump casing defines a l O fluid inlet and a fluid outlet.
3. A pump assembly as claimed in claim 2, wherein a flow path is defined between the pump casing fluid inlet and fluid outlet.
4. A pump assembly as claimed in claim 3, wherein the pump impellers are located within the flow path.
5. A pump assembly as claimed in claim 2, 3 or 4, wherein the pump casing inlet is a tangential inlet.
6. A pump assembly as claimed in claim 2, 3 or 4, wherein the pump casing inlet is an axial inlet.
7. A pump assembly as claimed in any one of claims 2 to 6, wherein the pump casing outlet is tangential.
8. A pump assembly as claimed in any one of claims 2 to 6, wherein the pump casing outlet is axial.
9. A pump assembly as claimed in any preceding claim, wherein the impellers are mounted within the pump casing such that, in use, fluid from one impeller is directed towards the other impeller.
10. A pump assembly as claimed in any preceding claim, wherein one impeller defines a first pump stage, and the other impeller defines a second pump stage.
11. A pump assembly as claimed in claim 10, wherein an inter-stage fluid passage is defined within the pump casing.
12. A pump assembly as claimed in claim 11, wherein the inter-stage passage is annular.
13. A pump assembly as claimed in claim 10, 11 or 12, wherein the first pump stage is adapted to provide and maintain an adequate Net Positive Suction Head (NPSH) to the second pump stage.
14. A pump assembly as claimed in any preceding claim, wherein the drive assembly is adapted to drive one pump impeller at a first rotational speed, and the other impeller at a second rotational speed, greater than the first rotational speed.
15. A pump assembly as claimed in claim 14 when dependent on any one of claims 10 to 13, wherein the first pump stage is driven at the first rotational speed, and the second pump stage is driven at the second rotational speed.
16. A pump assembly as claimed in any preceding claim, wherein the drive assembly is adapted to vary the rotational speed of the impellers.
17. A pump assembly as claimed in any preceding claim, further comprising a control system adapted to optimise operation thereof.
18. A pump assembly as claimed in claim 17, wherein the control system is adapted to permit management of the overall pump assembly efficiency by varying impeller speeds.
19. A pump assembly as claimed in any preceding claim, wherein the drive assembly is interposed between the pump impellers.
20. A pump assembly as claimed in claim 19 when dependent on any one of claims 11 to 18, wherein the inter-stage fluid passage extends at least partially around the drive assembly.
21. A pump assembly as claimed in any preceding claim, wherein the drive assembly defines a substantially uniform outer diameter.
22. A pump assembly as claimed in any preceding claim, wherein the drive assembly is provided in a housing defining a substantially uniform outer diameter.
23. A pump assembly as claimed in claim 22, wherein the housing is constructed as a single assembly.
24. A pump assembly as claimed in claim 22, wherein the housing is constructed in two separate assemblies, each accommodating a respective drive assembly.
25. A pump assembly as claimed in any preceding claim, wherein the drive assembly is concentrically mounted within the pump casing.
26. A pump assembly as claimed in any one of claims I to 24, wherein the drive assembly is eccentrically mounted within the pump casing.
27. A pump assembly as claimed in any preceding claim, wherein the drive assembly is mounted in the pump casing by at least one rib extending between the pump casing and the drive assembly.
28. A pump assembly as claimed in claim 27 when dependent on any one of claims 11 to 26, wherein the ribs are located within the inter-stage fluid passage.
29. A pump assembly as claimed in claim 27 or 28, wherein a plurality of ribs are provided, said ribs being circumferentially arranged within the inter-stage fluid passage.
30. A pump assembly as claimed in claim 27, 28 or 29, wherein at least one rib defines one or more passages extending between the pump casing and the drive assembly.
31. A pump assembly as claimed in any preceding claim, wherein the drive assembly comprises a motor unit.
32. A pump assembly as claimed in any preceding claim, wherein the drive assembly is coupled to the pump impellers via a drive shaft.
33. A pump assembly as claimed in any preceding claim, wherein the drive assembly comprises two motor units.
34. A pump assembly as claimed in claim 33, wherein one motor unit is coupled to one pump impeller and one motor unit is coupled to the other pump impeller.
35. A pump assembly as claimed in claim 33 or 34, wherein the motor units are coupled to their respective pump impeller via a drive shaft.
36. A pump assembly as claimed in claim 35, wherein each drive shaft is supported at either end thereof with the respective pump impeller being mounted on the shaft at a location between the ends thereof.
37. A pump assembly as claimed in claim 35, wherem each drive shaft is cantilevered from a respective motor unit, with each pump impeller being mounted on a free end of a respective drive shaft.
38. A pump assembly as claimed in any one of claims 33 to 37, wherein the motor units are mounted within the pump casing in a back-to-back arrangement.
39. A pump assembly as claimed in any one of claims 33 to 38, wherein each motor unit is mechanically and electrically autonomous from the other motor unit.
40. A pump assembly as claimed in any one of claims 33 to 39, wherein each motor unit comprises a shaft sealing arrangement to prevent ingress of fluid into the motor units.
41. A pump assembly as claimed in claim 40, wherein the shaft sealing arrangement comprises a seal leakage chamber associated with each motor unit.
42. A pump assembly as claimed in claim 41, wherein a single seal leakage chamber may be provided.
43. A pump assembly as claimed in claim 41, wherein each motor unit comprises an individual seal leakage chamber.
44. A pump assembly as claimed in any one of claims 40 to 43, wherein the seal leakage chamber comprises drainage means to allow any fluid to be drained therefrom.
45. A pump assembly as claimed in any preceding claim, wherein the pump casing comprises separate sections which are adapted to be secured together.
46. A pump assembly comprising: a pump casing; a first pump impeller rotatably mounted in the pump casing and being coupled to first variable speed drive assembly; and a second pump impeller rotatably mounted in the pump casing and being coupled to a second variable speed drive assembly, the second pump impeller being in fluid communication with the first pump impeller.
47. A pump assembly comprising: a pump casing defining a fluid inlet and a fluid outlet and a flow path therebetween; a pump impeller rotatably mounted within the flow path of the pump casing; and a drive assembly mounted within the flow path of the pump casing and being coupled to the pump impeller.
48. A pump assembly comprising: a pump easing; and first and second pump impellers rotatably mounted within the pump casing, wherein the first pump impeller is adapted to operate at a different rotational speed than the second pump impeller.
49. A pump assembly substantially as described herein and as illustrated in the accompanying figures.