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The invention relates to a pump casing for a centrifugal pump, a centrifugal pump including a casing and a method of manufacturing a centrifugal pump and casing.
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Centrifugal pumps commonly employ a casing called a volute. This is a well known structure which functions both to house the pump's impeller and to provide a flow path by which liquid is moved by the impeller from the pump's inlet to its outlet. The flow path so provided sometimes has an increasing volume between the inlet and the outlet which results in an increase in static pressure and a reduction in velocity of liquid in the path. There are two types of volute casing commonly in use in centrifugal pumps; single volutes and double volutes.
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A problem that has been experienced with existing centrifugal pumps employing volutes to feed more than a single liquid outlet is that of unequal liquid flow velocity. In most use cases it is desirable to have an equal liquid flow velocity from each outlet, however it has been found unexpectedly that with existing volutes feeding more than a single outlet this is not the case, and that where a volute is provided with two or more outlets, such as in a so called double volute, liquid flow velocity from the outlets can be unequal. It is an object of the present invention to seek to mitigate problems such as this.
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According to a first aspect of the invention, there is a provided a casing for use in a centrifugal pump, the casing including an inlet for liquid, an internal volume defining a curved circumferential flow path, and a flow path outlet for liquid to exit from the flow path into an outlet conduit of the casing, the internal volume including a first cutwater disposed to direct liquid from the flow path into the outlet conduit, and a second cutwater disposed within the outlet conduit so as to divide the outlet conduit into first and second outlet branches, the second cutwater being disposed in a plane substantially perpendicular to the plane of the first cutwater. It has been found that with this arrangement, a substantially equal liquid flow velocity is obtained for liquid flowing from each outlet branch.
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In a preferred embodiment, the casing comprises a volute. It is further preferred that the first cutwater is disposed in a plane substantially perpendicular to the flow path.
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The position of the second cutwater within the outlet conduit relative to the location of the first cutwater can be varied according to need during manufacture. The outlet conduit has an upstream or proximal end and a downstream or distal end, and the second cutwater may be located at the proximal end of the outlet conduit, in other words directly at or adjacent to the first cutwater. It has been found however, that locating it distally within the outlet conduit, in other words, remote from the first cutwater, results in a more stable liquid flow through the outlet branches and therefore to outlet valves of the pump of which the casing forms a part.
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According to a second aspect of the invention, there is provided a centrifugal pump including a pump casing as described above, the pump comprising at least two liquid outlet valves.
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It is preferred that the centrifugal pump includes a liquid pressure measurement device and a display, such that an operator can monitor the performance of the pump. It is particularly preferred that the liquid pressure measurement device is disposed in the outlet conduit of the casing, between the first and second cutwaters. Surprisingly, it has been found that locating the pressure measurement device in the outlet conduit between the first and second cutwaters gives a truer indication of pump performance than locating sensors at the outlet valves themselves.
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It is preferred that the outlet valves are provided substantially in the same plane relative to the axis of rotation of the impeller. This provides for an efficient use of space.
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It is preferred that the pump includes a support frame to support the components of the pump. Advantageously, the support frame may be partly or wholly demountable to facilitate ease of access to the components of the pump for maintenance and replacement, and further, the support frame may include formations to assist in manual movement of the pump by a user.
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It is preferred that the support frame defines an external boundary beyond which components of the pump do not extend or protrude. This is a safety feature which helps ensure that users are not impacted by hot or moving parts.
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According to a third aspect of the invention, there is provided a method of manufacturing a pump casing, including the step of casting a wall of the casing integrally with an outlet therefrom. It is preferred that the method includes the step of forming a second cutwater within an outlet conduit of the casing.
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The invention will further be described by way of example and with reference to the accompanying drawings, in which,
- Figure 1 is a front perspective view of a pump casing in accordance with an aspect of the invention;
- Figure 2 is a top view of the casing illustrated in Figure 1;
- Figure 3 is a transverse sectional view taken along lines C-C in Figure 2;
- Figure 4 is a part sectional view taken along lines F-F in Figure 1;
- Figure 5 is a front view of a centrifugal pump according to a further aspect of the invention;
- Figure 6 is a top view of the pump shown in Figure 5;
- Figure 7 is a right hand side view of the pump shown in Figure 5; and
- Figures 8a to 8d are schematic views showing flow lines within the casing shown in Figures 1 to 4.
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Referring to the drawings, in particular Figures 1 to 4, there is illustrated a casing 1 for use in a centrifugal pump 100, the casing including an inlet 2 for liquid, an internal volume 3 defining a curved circumferential flow path 4, and a flow path outlet 5 for liquid to exit from the flow path into an outlet conduit 6 of the casing, the internal volume including a first cutwater 7 disposed in a plane perpendicular to the flow path, to direct liquid from the flow path 4 into the outlet conduit, and a second cutwater 8 disposed within the outlet conduit 6 so as to divide the outlet conduit 6 into two outlet branches 6a, 6b, the second cutwater 8 being disposed in a plane substantially perpendicular to the plane of the first cutwater 7.
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As mentioned, the pump casing 1 is intended for use in a centrifugal pump 100 as illustrated in Figures 5 to 7. As is well known in the art, the casing houses the pump's impeller (not shown), which is located on a shaft mounted for rotation about central axis Z-Z as shown in Figure 2. In the described embodiment the pump 100 is a portable pump used in firefighting and also sometimes is pumping out flooded areas, which is a known type of centrifugal pump that often includes multiple liquid outlet valves 101 to enable a plurality of hoses to be connected for use at the same time. Particularly in the case of a firefighting pump, it is desirable that the velocity of liquid flowing from the outlets is equal so that connected hoses are equally effective in combating a fire. The pump 100 is of generally known type and includes casing 1, outlet valves 101, support 102, motor 103 and heat shield 104. The support 102 is demountable in this embodiment, meaning that it can be removed partially or entirely for maintenance and replacement. The support 102 comprises circular section tubing that is formed into two rectangular side frames, each rectangular side frame being sized and mounted to the sides of the pump such that the support thus defines an external boundary beyond which components of the pump do not extend or protrude. In the present embodiment this is further assisted by the heat shield 104. The rectangular side frames 102 are each provided with hinged parts 105 which assist in their partial or complete removal, and the side frames further provide a user with convenient hand holds by which the pump may be moved.
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A particular feature of the pump 100 is the provision of a sensor and display device to enable a user to monitor the performance of the device in use. A user is primarily interested in ensuring that flow from the outlet valves 101 is sufficient for the intended purpose. It is possible to provide each outlet valve 101 with a dedicated sensor, to measure a value such as fluid pressure. In the present embodiment however, the pump is provided with a sensor 106 that is located to obtain a reading in the outlet conduit of the casing, as will be described in greater detail below.
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Referring to Figure 1, the pump casing 1 of this embodiment comprises a volute, which is a structure that is well known in the art. The term "volute" is often used to describe the structure as a whole, as well as only a part of the structure, particularly that part of the structure that in some devices increases in cross sectional area around the central axis Z-Z, but for the purposes of this exposition it will be understood that all such meanings are encompassed. It is a generally circular, longitudinally compressed disk viewed front to back as shown in Figure 1 and includes a front face 9, a rear face 10, and a circumferential rounded edge, the faces and edge together forming a continuous casing wall 11. As mentioned, internally the casing 1 includes internal volume 3, which is a generally circular hollow chamber having a liquid inlet 2, a flow path outlet 5, and a flow path 4 for liquid flow therebetween. The shape of the chamber is defined by and within continuous wall 11, which corresponds internally in shape to the external shape of the casing. Thus, the internal surface of the wall 11 is correspondingly curved and rounded and defines the curved circumferential liquid flow path 4. The liquid inlet 2, as shown in Figure 5, includes an aperture capped off by a removable cap 2a. It is provided centrally on the casing 1 to provide an entrance for liquid into the volume 3 so that liquid may pass centrally into the impeller mounted therein, before being passed by centripetal force generated by rotation of the impeller outwardly from the centre towards the wall 11, into flow path 4. Under the influence of the impeller the liquid passes outwardly and around the flow path in an anticlockwise direction as viewed, until it meets flow path outlet 5.
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Flow path outlet 5 comprises an aperture 5a defined in wall 11. At one side, the aperture 5a includes first cutwater 7, which is a structure well known in the art and which includes a lip 7a that guides a proportion of liquid from the flow path 4 into outlet conduit 6. The lip includes a straight edge that extends in a line from the front face 9 to the rear face 10, parallel with the central axis Z-Z. Opposite the lip, the aperture 5a is further defined by the wall 11 which extends smoothly tangentially outward from the volume 3 and assists in guiding liquid into the outlet conduit 6. Outlet conduit 6 here takes the form of a tangentially mounted curved and branched cylinder, the radius of curvature of which, advantageously, matches that of the casing. Outlet conduit 6 includes through bore 12. Conveniently, the casing 1 and the conduit 6 are formed by casting to have a common wall 13, the through bore 12 of the outlet conduit 6 being in liquid communication with the internal volume 3 via flow path outlet 5.
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Figures 2 and 3 show, respectively, a top view and a transverse sectional view of casing 1. From these it can be seen that each of the first and second outlet branches, 6a, 6b, includes an internal liquid passage 14a, 14b, both passages being in liquid connection with through bore 12 of outlet conduit 6. Each outlet branch 6a, 6b further includes a circumferential mounting plate 15 at its distal end, for attachment to a valve such as a tap 101, for connection of a hose or other take-off device. As can be seen particularly from Figure 3, first outlet branch 6a is longer than second outlet branch 6b, extending as it does, further around the circumference of the wall 11. Although this is the case, the distal ends of the outlet branches 6a, 6b are still provided in side by side configuration, in the same plane relative to the axis Z-Z, which is the axis of rotation of the pump's impeller. This is a desirable configuration because it is an efficient use of space in apparatus that is advantageously as compact as possible, but with known designs of pump that include multiple outlets, such as double volute designs, is difficult to achieve. In contrast, the novel expedient of including a second cutwater 8 disposed in orientation perpendicular to the first cutwater 7 enables one outlet branch to be formed and to pass either behind (as here) or in front of, the other, before returning to the same plane in order to achieve the desired position of the outlet valves. It is preferred that the longer outlet branch, in this case the first outlet branch 6a, is smoothly curved.
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As described above and shown in Figure 3 and Figure 4, the second cutwater 8 is located within the outlet conduit 6 in an orientation that is perpendicular to the orientation of the first cutwater 7. In this embodiment the second cutwater 8 takes the form of a bifurcation of the outlet conduit 6, the point of bifurcation being a narrow lip 8a that, as the name suggests, cuts the liquid flow in two. It is positioned in this embodiment towards the distal end of the outlet conduit 6, in other words the end remote from the first cutwater 7, as this has been found to result in a more stable liquid flow in the branches 6a, 6b.
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As mentioned above, in this embodiment the casing 1 is provided with a sensor 106 (Figure 7 and Figures 8a,) that here takes the form of a liquid pressure sensor located in and through the wall 11 of the outlet conduit 6. The sensor is thus disposed to obtain a liquid pressure reading in the outlet conduit between the first and second cutwaters. The reading from the sensor can be displayed on any known type of display device located on the pump 100, or can report to a remote display device, such as a user's mobile phone, to alert the user to pump failure or reduced performance.
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In use in a pump such as the pump shown in Figures 5 to 7, liquid such as water is passed into casing 1 via inlet 2 into a rotating impeller (not shown). The impeller directs the liquid into and around the flow path 4. As it travels around the flow path the liquid encounters first cutwater 7, which directs a proportion of it into flow path outlet 5 and thence to outlet conduit 6. In its passage along outlet conduit 6 the liquid stream then encounters second cutwater 8 which splits the liquid flow into two, into branches 6a, 6b. The orientation of the cutwater 8, perpendicular to the orientation of the first cutwater 7, ensures that the liquid flows from the two branches have substantially equal velocity, and its location within outlet conduit 6, spaced from first cutwater 7, helps to promote a more stable, less turbulent flow. This can be seen from Figures 8a to 8d, which show graphical representations of the liquid flows in the casing and in the branches. Figure 8a is a cut away perspective view of a casing 1 in accordance with the invention, Figure 8b is a transverse sectional view of the casing 1, and for the purposes of further clarification, Figure 8c is a rendering of Figure 8b with the physical structures of the casing 1 removed so that flow in the two outlet branches can be seen. Figure 8d is a schematic view of a further casing in accordance with the invention. In Figures 8a to 8c, the arrows indicate flow, with higher density of arrows indicating areas of higher flow. Thus it can be seen particularly from Figures 8b and 8c that arrow density is substantially equal in the two outlet branches 6a, 6b. In Figure 8d, the length of the arrows denotes fluid velocity, and again, it can be seen that arrow length in the outlet branches is substantially equal.