GB2518173A - Fluid pump - Google Patents

Abstract

A fluid pump comprising first and second impellers 13, 20 mounted in respective cavities 12, 19, the first impeller being configured to provide a low pressure output, the second impeller being a regenerative impeller and being configured to provide a high pressure output. A fluid passage to an inlet 15 of the first impeller cavity is defined through one or more apertures 21 in the second impeller. The second impeller may be located on the inlet side of the first, centrifugal impeller and the aperture located substantially radially centrally within the second impeller.

Description

FLUID PUMP

Technical Field

The invention relates to a multi-pressure pump and particularly but not exclusively to a dual pressure pump suitable for use in fire-fighting applications.

Backciround Multi-pressure pumps have applications across a wide range of industries. One industry that relies heavily on multi-pressure pumps is the fire-fighting industry: the use of multi-pressure pumps enables fire-fighters to employ varied fire-fighting tactics from a single pump.

Typically, pumps used in the fire-fighting industry are configured to provide both high pressure and low pressure outputs. The pump may be operated so as to provide exclusively high pressure output or exclusively low pressure output. In certain circumstances, the high and low pressure capabilities may also be deployed simultaneously, thereby allowing for multiple fire-fighting tactics to be deployed simultaneously. The high pressure output is typically in the region of 20-40 Bar and is output at a flow rate of between approximately 150 litres per minute (1pm) and 600 1pm.

The low pressure output is typically in the region of 6-17 Bar and is output at a flow rate between approximately 500 1pm and 10,000 1pm. These pressure ranges and flow rates are, however, not absolute limits; the pressure ranges and flow rates will vary depending on the application.

The high and low pressure outputs are provided by respective portions of the pump, which are typically housed within a single pump assembly. The assembly is constructed from a plurality of parts, which are typically bolted together. Certain parts may be shared between the high pressure and low pressure stages. The high pressure portion is usually provided on the same driven input shaft as the low pressure portion. Whilst this is not a necessary requirement for the functionality of the pump, it is almost exclusively done as it constitutes an optimal packaging solution that minimises cost. A closing plate is typically provided between the high and low pressure portions for sealing therebetween.

In general, the low pressure portion includes a centrifugal pump comprising at least one centrifugal impeller mounted in an impeller cavity. A curved funnel, known in the art as a volute, is connected to the impeller cavity and provides a pressure boundary for the centrifugal pump. The volute is shaped to appropriately direct the suction and discharge flow. In particular, the cross-sectional area of the volute increases towards the discharge port, thereby reducing the speed of the fluid and increasing the fluid pressure. After suitable priming of a centrifugal pump, the rotation of the impeller within the impeller cavity generates a reduced pressure in the eye of impeller. This pressure reduction is large enough to overcome the head differential and head-loss from pipe friction and hence sustain the drawing of water from a water source lower than the pump. The pump is thus able to operate in situations in which the watel source is many metres below the eye of the impeller. It will be appreciated that this is a critical characteristic for a fire-pump since it may be necessary to use water sources which located significantly lower than the pump.

The high pressure portion may comprise one or more additional centrifugal impellers arranged in a manner well known to those skilled in the art. An alternative arrangement is one in which the high pressure portion to comprise a regenerative impeller mounted in an impeller cavity. A regenerative impeller is typically more compact and lightweight than a centrifugal impeller and hence the use of a regenerative impeller reduces the overall size and weight of the multi-pressure pump. This is particularly important for pumps intended to be mounted on vehicles in view of the requirement to minimise the overall size and weight of the vehicle.

A typical multi-pressure pump includes a bearing housing, from which the pump shaft extends. The bearing housing is mounted to the pump body proximal to the high pressure portion thereof Bearings are provided within the bearing housing and are typically lubricated, for example with water or oil. The bearing housing may incorporate a gearing or other speed adjustment device so that the optimal pump shaft output speed can be attained. Alternatively a gearbox may be externally mounted to the bearing housing to achieve the same result.

Whilst the above-described pump design is well known and widely used, particularly within the fire-fighting industry, it suffers a number of significant drawbacks.

A major drawback is that, unlike a centrifugal impeller, a regenerative impeller is not able to generate a reduced pressure within the pumping cavity and hence has to be supplied with fluid at a sufficiently positive pressure to drive the fluid into the pumping cavity. This positive pressure is typically achieved by diverting a portion of the delivery water from the low pressure output. Accordingly, a multi-pressure pump must include a fluid passage from an outlet side of the low pressure portion to an inlet side of the high pressure portion.

An additional drawback of known multi-pressure pumps is that the regenerative impeller is mounted within the part of the pump body proximal to the bearing housing. A mechanical seal must therefore be provided between the bearing housing and the high pressure portion of the pump body. The seal must be capable of withstanding a high pressure differential, which places rigid constraints of the structure of the seal and increases the likelihood of failure of the seal.

Furthermore, it is common for pump manufacturers to manufacture both multi-pressure pumps and low pressure only pumps, the low pressure only pumps utilising the low pressure portion of the multi-pressure pumps. The manufacturer must theretore either provide different pump bodies for use with the different pump variations or must supply low pressure only pumps in an unnecessarily large body. In the latter case, a spacer is usually provided to occupy the space within the pump body of a low pressure only pump that would be occupied by the regenerative impeller of a multi-pressure pump.

Lastly, the transit of fluid through the pump acts to erode the fluid passages of the pump.

This is particularly prevalent when the fluid source contains small particulates and/or when the fluid is at high pressure. The portions of the pump that define fluid passages must therefore be formed of a suitably wear resistant material such as stainless steel.

Where these portions also form part of the low pressure stage, these portions are over-specified and costly.

Summary of the rresent invention

In accordance with the present invention, as seen from a first aspect, there is provided a fluid pump comprising: a first impeller mounted in a first impeller cavity and configured to provide a low pressure output; a second impeller mounted in a second impeller cavity and configured to provide a high pressure output, the second impeller being a regenerative impeller, characterised in that a fluid passage to an inlet of the first impeller cavity is defined through one or more apertures in the second impeller.

The applicant has recognised the fact that a regenerative impeller, unlike a centrifugal impeller, can be optimally designed to use only a periphery. Accordingly, one or more apertures may be formed through a radially central part of the regenerative impeller to allow fluid to pass to the first impeller. It will be appreciated that a pump formed in this way has the potential to be significantly more compact and light-weight than known pump designs.

Preferably the first impeller is a centrifugal impeller.

The second impeller is preferably located on the inlet, suction, side of the first impeller.

The first and second impellers are preferably mounted coaxially. The first and second impellers may be mounted on a shaft configured to drive said impellers. The pump may comprise a gearbox configured for driving of the first and/or second impeller at a rotational speed not equal to the rotational speed of the shaft.

The first and second impellers are preferably mounted within a pump body. The pump body is preferably formed of at least two portions: a first body portion comprising the first impeller cavity and a second body portion comprising the second impeller cavity. The first and second body portions are preferably detachably engageable, for example by means of a bolt arranged to pass through the second body portion and into the first body portion. Advantageously, forming the pump body in separate portions permits the use of the first, low pressure, impeller and first impeller cavity within low pressure only pumps, thereby creating a modular pump assembly.

The first impeller cavity is preferably substantially open at one axial side of the impeller, said side defining the inlet, suction, side of the impeller and said opening defining the inlet of the first impeller cavity. The first cavity may be substantially circular in cross-section and the axis of the impeller may be mounted in an offset position with respect to the axial centre of the cavity. A spiralled funnel portion is preferably defined around a periphery of the first impeller when the first impeller is mounted in the first impeller cavity.

Preferably the second impeller cavity is substantially annular in cross-section and arranged to enclose a peripheral edge of the second impeller. Preferably the second impeller cavity is configured to fit closely against the axially facing surfaces of the second impeller. The inlet and outlet of the second impeller cavity are preferably circumferentially spaced apart. The fluid conduits connected to the inlet and outlet of the second impeller cavity preferably extend from the impeller cavity in a substantially radial direction.

The second body portion is preferably formed of a wear resistant material such as stainless steel or hard-anodised aluminium. The first body portion may be formed of the same material or may be formed of a material having a lower wear resistance. It will be appreciated that the first body portion houses the low pressure impeller only and thus the abrasive effect of the fluid is substantially lower within the first body portion than within the second body portion. Accordingly, forming the first body portion out of a material having a lower wear resistance than the second body portion may reduce manufacturing costs.

Preferably a first outlet conduit is arranged for conveying fluid from the outlet, pressure, side of the first impeller. The first outlet conduit preterably extends tangentially to the first impeller cavity. An acutely angled divider, herein a cutwater, is preferably defined at the opening of the first cavity to the first outlet conduit. At least a portion of the first outlet conduit may comprise a cross-sectional that increases with increasing distance from the cutwater.

The first outlet conduit is preferably fluidly connected to a pump discharge member and an inlet of the second impeller cavity such that, in use, fluid that exits the first impeller cavity is directed to the pump discharge member and/or the second impeller. The pump may comprise means for varying the proportion of fluid that is directed from the first impeller to the second impeller, preferably from 0% to 100%. The fluid that exits the first impeller and is not directed to the second impeller is preferably directed to the pump discharge member. It will be appreciated that the pump will provide a solely low pressure output if 0% of the fluid that exits the first impeller is directed to the second impeller. Conversely, the pump will provide a solely high pressure output if 100% of the fluid that exits the first impeller is directed to the second impeller. The pump will provide a dual pressure output if the proportion of fluid that exits the first impeller and is directed to the second impeller is not equal to 0% or 100%.

The pump preferably comprises a second outlet conduit arranged for conveying pressurised fluid from the second impeller to the pump discharge member. The second outlet conduit is preferably distinct from the first outlet conduit, although one component may house both conduits.

The first and/or second outlet conduits are preferably defined by elongate cavities formed within the body.

The pump body may comprise a pump inlet portion, which is preferably mounted to the second body portion. The pump inlet portion and second body portion are preferably detachably engageable. In a preferred embodiment, a bolt is arranged to pass through the pump inlet portion, through the second body portion and into the first body portion.

The pump inlet portion preferably comprises a substantially tubular member, the fluid passage to the inlet of the first impeller cavity preferably extending from the tubular member and through the one or more apertures in the second impeller. An end of the tubular member distal to the second body portion preferably comprises a radially outwardly depending lip for engaging with other tubular members or other pipe work.

The pump preferably comprises a bearing housing. The pump body may comprise a pump front arranged to abut the bearing housing. The shaft preferably extends from the bearing housing to the first and second impellers. The first, low pressure, impeller is preferably axially disposed between the second, high pressure, impeller and the bearing housing. In known dual pressure pump designs, the high pressure impeller is adjacent the bearing housing, thereby demanding that the mechanical seal between the high pressure impeller and pump body is capable of withstanding a large pressure differential. In the present invention, it is preferably the low pressure impeller that is adjacent the bearing housing, thereby reducing the pressure differential across of the mechanical seal.

A surface of the first impeller on the inlet, suction, side thereof preferably comprises a plurality of outwardly protruding vanes. The vanes may be substantially radial.

Alternatively, the vanes may be forwards curved blades or may be backwards curved. A shroud may be provided over the vanes so as to define a plurality of bounded fluid passages between respective vanes.

The second impeller preferably comprises an outer peripheral portion arranged for imparting energy to the fluid. The outer peripheral portion is preferably substantially annular in cross-section. The one or more apertures are preferably defined radially inwardly of the outer peripheral portion. The outer peripheral portion of the second impeller preferably comprises a plurality of vanes, each vane extending substantially radially outwardly from an outer peripheral edge of the impeller. The vanes may be curved backward or forward with respect to the radial position in order to modify the pump pressure output characteristics.

The outer peripheral portion of the second impeller may be provided with a plurality of vanes arranged to extend radially inwardly into at least one of the one or more apertures. It has been found that, in use, such vanes impart a pumping effect to the fluid prior the fluid entering the first impeller.

The second impeller may be mounted directly to the first impeller. The second impeller is preferably mounted to the shroud of the first impeller. The inner tubular wall of the outer peripheral portion preferably blends smoothly into the shroud of the first impeller such that the inner tubular wall of the peripherally portion constitutes an extension to the shroud of the first impeller.

Alternatively, or in addition thereto, the second impeller may comprise a support portion arranged for supporting the outer peripheral portion. It will be appreciated that the support portion permits independent mounting of the first and second impellers on the shaft. The support portion may comprise a plurality of spokes arranged to extend radially from the shaft.

Brief description of the drawings

Figure 1 is a diagrammatic longitudinal sectional view of part of a dual pressure pump according to an embodiment of the present invention.

Detailed description

With reference to figures 1 of the drawings, there is illustrated a dual pressure pump 10 in accordance with an embodiment of the present invention. The pump 10 comprises a pump body ii, which is divided into four portions: a pump inlet portion ha, a low pressure portion lib, a high pressure portion lic, and a pump front lid. The various body portions are arranged axially from the inlet, suction, side of the pump 10 in the following order: the pump inlet portion ha, the high pressure portion hic, the low pressure portion lib, and lastly the pump front lid. The various body portions are detachably mounted to adjacent body portions by means of bolts or the like. This enables the modular construction of pumps, for example the high pressure portion hic could be removed and the pump inlet portion ha mounted directly to the low pressure portion hib in order to produce a low pressure only pump.

The high pressure body portion 1 lc is formed of a wear resistant material such as stainless steel or hard-anodised aluminium. The other body portions ha, lib, lid may be formed of the same material or may be formed of a material having a lower wear resistance.

A first impeller cavity 12 is defined within the low pressure portion hib of the pump body ii. A centrifugal impeller 13 is housed within the first cavity 12, the centrifugal impeller 13 being configured to provide a low pressure output. The centrifugal impeller i3 is mounted on a drive shaft 14, the drive shaft 14 being configured for driving the impeller 13. The first impeller cavity 12 is substantially open at a first axial end to define an inlet 15 to the cavity 12. The end at which the cavity 12 is open defines the inlet, suction, side of the centrifugal impeller 13. The first impeller cavity 12 is substantially circular in cross-section, the impeller 13 being mounted in an axially offset position with respect to the centre of the cavity 12. A spiralled funnel portion, herein a volute 16, is thus defined around the periphery of the centrifugal impeller 13 when the impeller 13 is mounted in the cavity 12. A plurality of radially extending vanes are provided on the face 17 of the centrifugal impeller 13 on the inlet, suction, side thereof. A shroud 18 is provided over the vanes so as to define a plurality of bounded fluid passages between respective vanes.

A second impeller cavity 19 is defined within the high pressure portion lic of the pump body 11. A regenerative impeller 20 is housed within the second cavity 19, the regenerative impeller 20 being configured to provide a high pressure output. The regenerative impeller 20 is mounted directly to the shroud of the centrifugal impeller 13.

The regenerative impeller 20 is substantially annular in cross-section, the clear central portion 21 of the impeller 20 defining a fluid passage to the inlet 15 of the first impeller cavity 12. The regenerative impeller 20 is provided with a plurality of vanes 22 that extend radially from a peripheral edge of the impeller 20. The second impeller cavity 19 is substantially annular in cross-section and arranged to enclose a peripheral edge of the regenerative impeller 20. The walls of second impeller cavity 19 are configured to fit closely against the axially facing surfaces of the regenerative impeller 20. A fluid inlet (not shown) and a fluid outlet (not shown) are provided at circumferentially spaced apart locations of the second impeller cavity 19.

A first outlet conduit 23 is defined within the body 11 and arranged for conveying fluid from the centrifugal impeller 13. The first outlet conduit 23 extends tangentially to the first impeller cavity, constituting an extension to the spiral of the volute 16. An acutely angled divider, herein a cutwater (not shown), is defined at the opening of the first cavity 12 to the first outlet conduit 19. The first outlet conduit 23 is fluidly connected to a pump discharge member (not shown), the exact nature of which may vary depending on the intended application of the pump 10. In addition, the first outlet conduit 23 is fluidly connected to the inlet of the second impeller cavity 19.

A second outlet conduit (not shown) is defined within the body 11 and arranged for conveying fluid from the regenerative impeller 20 to the pump discharge member.

The pump 10 comprises means (not shown) for varying the proportion of fluid that is directed from the outlet of the first impeller cavity 12 to the inlet of the second impeller cavity 19. The fluid that exits the first impeller cavity 12 and is not directed to the inlet of the second impeller cavity 19 is directed to the pump discharge member. The proportion of fluid that is directed to the inlet of the second impeller cavity 19 may be varied from 0% to 100% of the fluid exiting the first impeller cavity 12. It will be appreciated that the pump 10 will provide a solely low pressure output if 0% of the fluid that exits the first impeller cavity 12 is directed to the inlet of the second impeller cavity 19, whilst the pump 10 will provide a solely high pressure output if 100% of the fluid that exits the first impeller cavity 12 is directed to the inlet of the second impeller cavity 19. The pump 10 will provide a dual pressure output if the proportion of fluid that exits the first impeller cavity 12 and is directed to the inlet of the second impeller cavity 19 is not equal to 0% or 100%.

The pump inlet portion ha comprises a substantially tubular member of substantially equal internal diameter to the internal diameter of the annular regenerative impeller 20.

An axial end of the tubular member distal to the second body portion preferably comprises an outwardly depending lip 24 for engaging with other tubular members or other pipe work.

The pump 10 further comprises a bearing housing 25, the pump body front lid being arranged to abut the bearing housing 25. The drive shaft 14 is mounted in the bearing housing 25. A first end of the drive shaft 14 protrudes outside distal end of the bearing housing 25. Drive attachments (not shown) may be attached to the second end of the drive shaft 14 to provide rotational drive to the drive shaft 14. A second end of the drive shaft 14 protrudes into the pump body 11, the centrifugal impeller 13 being fastened to the drive shaft 14 by means of an impeller nut 26. A mechanical seal 27 is provided between a mechanical seal housing portion 28 of the body 11 and the bearing housing 25. Tightening the impeller nut 26 has the effect of compressing the mechanical seal 27 and hence ensuring the sealing between the pump body hi and the bearing housing 25.

A gearbox (not shown) is provided facilitating effective driving of the impellers 13, 20 through a range of shaft rotational speeds.

The performance of the pump is optionally further improved by the use of wear rings 29, 30. The wear rings 29, 30 restrict the area by which fluid of a boosted pressure can leak back to areas of lower pressure.

In use, the pump 10 is initially primed by any one of a number of known priming means.

Priming is required in order to fill the pump 10 with the fluid to be pumped such that the centrifugal impeller 13 can function. Once primed the rotation of the centrifugal impeller 13 is sufficient to draw fluid into the pump 10 and sustain the pump function. Fluid is drawn into the pump at A through the pump inlet portion ha. The fluid passes through the open central area 21 of the regenerative impeller 20 in area B before passing into the inlet 15 of the first impeller cavity 12. Upon entering the first impeller cavity 12, the fluid is pumped by the centrifugal impeller 13 in a manner know to those skilled in the art, eventually exiting the centrifugal impeller 13 at the periphery thereof into the volute l6at region C. The volute 16, i.e. region C, is fluidly connected to the first outlet conduit 23 at D, which is fluidly connected to the pump discharge member and the inlet of the second impeller cavity 19. If the pump 10 is configured to provide a solely low pressure output, all of the fluid that exits the first outlet conduit 23 at D is directed to the pump discharge member.

Conversely, if the pump is configured to provide a solely high pressure output, all of the fluid that exits the outlet conduit 23 at D is directed to the inlet of the second impeller cavity 19.

Any fluid that is directed to the inlet of the second impeller cavity 19 is directed around the periphery of the regenerative impeller 20 at region E to the outlet of the second impeller cavity 19. This process acts to further boost the pressure of the fluid and thus provide a high pressure output. The fluid then passes from the outlet of the second impeller cavity 19 to a pump discharge member, which may be the same pump discharge member as that connected to the first output conduit 23 or may be a separate member

Claims (20)

1. Claims 1. A fluid pump comprising: a first impeller mounted in a first impeller cavity, the first impeller being configured to provide a low pressure output; and, a second impeller mounted in a second impeller cavity, the second impeller being a regenerative impeller and configured to provide a high pressure output, characterised in that a fluid passage to an inlet of the first impeller cavity is defined through one or more apertures in the second impeller.
2. 2. A fluid pump according to claim 1, wherein the second impeller is located on the inlet, suction, side of the first impeller.
3. 3. A fluid pump according to claim 1 or claim 2, wherein the first impeller is a centrifugal impeller.
4. 4. A fluid pump according to any preceding claim, wherein the first and second impellers are mounted coaxially on a drive shaft.
5. 5. A fluid pump according to any preceding claim, wherein the first impeller cavity is defined within a first body portion.
6. 6. A fluid pump according to any preceding claim, wherein the second impeller cavity is defined within a second body portion.
7. 7. A fluid pump according to claim 6 when dependent upon claim 5, wherein the first and second body portions are detachably engageable.
8. 8. A fluid pump according to claim 6 or claim 7, wherein the second impeller cavity is substantially annular in cross-section.
9. 9. A fluid pump according to any preceding claim, further comprising a pump discharge member.
10. 1O.A fluid pump according to claim 9, wherein a fluid passage is defined from an outlet of the first impeller cavity to the pump discharge member.
11. 11.A fluid pump according to claim 9 or claim 10, wherein a fluid passage is defined from an outlet of the second impeller cavity to the pump discharge member.
12. 12. A fluid pump according to any proceeding claim, wherein a fluid passage is defined from an outlet of the first impeller cavity to an inlet of the second impeller cavity.
13. 13. A fluid pump according to claim 12, further comprising means for varying the proportion of fluid directed from the outlet of the first impeller cavity to the inlet of the second impeller cavity.
14. 14.A fluid pump according to any preceding claim, wherein the pump comprises a bearing housing and wherein the first impeller is axially disposed between the second impeller and the bearing housing.
15. 15. A fluid pump according to any preceding claim, wherein the one or more apertures are located substantially radially centrally within the second impeller.
16. 16. A fluid pump according to any preceding claim, wherein the second impeller is substantially annular in cross-section.
17. 17. A fluid pump according to claim 16, wherein the second impeller comprises one or more vanes arranged to extend radially inwardly into the one or more apertures.
18. 18.A fluid pump according to any preceding claim, wherein the second impeller is mounted directly to the first impeller.
19. 19. A fluid pump according to claim 18, wherein the second impeller is mounted to a shroud of the first impeller.
20. 20.Afluid pump as hereinbefore described with reference to, and as illustrated in, the accompanying figure.