Patent Application
20090116958
The present invention relates to a variable pump and a method for operating the same. In particular, but not exclusively, the present invention relates to a centrifugal pump having an interchangeable impeller and an interchangeable cutwater for varying the characteristics of the centrifugal pump.
Centrifugal pumps are used to impart gases and liquids with an increased flow rate or pressure. Referring to
The rotation of the impeller 12 forces gases or liquids from the inlet 14 toward the volute 16, which collects and directs the gases and liquids toward the outlet 18. The volute 16 may be provided as an expanding cross sectional area that forces high-kinetic-energy water flung from the periphery of the impeller to slow down as it travels around the outside of the impeller to discharge from the pump.
To ensure the water does not continue rotating around with the impeller instead of being discharged, a cutwater 19 is typically formed adjacent the discharge area and close to the periphery of the impeller 12.
In some applications, it is desirable to provide some variability to the operation of a centrifugal pump. For example, variability may be provided in the water pressure or flow rate out of the pump. Some prior art systems therefore include the use of a variable speed motor to operate the impeller. Other prior art systems provide variability to the impeller itself, for instance in terms of impeller blade contours or placement. While successful in providing some variability in pump operations, these prior art systems can be prohibitively costly.
The use of a variable cutwater to provide variability in pump characteristics is described in U.S. Pat. No. 3,967,915 to Litzenberg. The cutwater in the Litzenberg patent comprises several plate portions that define a cut-out through which the impeller passes. The cutwater in the Litzenberg patent is made variable by allowing the cut-out shape to be altered to accommodate different impeller sizes.
In this specification, where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or sources of information is not to be construed as an admission that such documents or sources of information in any jurisdiction are prior art, or form part of the common general knowledge in the art.
The object of the present invention is either to provide a cost-effective and improved variable pump or to at least provide the public with a useful choice.
In one aspect, the present invention broadly consists in a centrifugal pump having a pump housing and an impeller, the centrifugal pump comprising one or more grooves provided in the housing adjacent the impeller, wherein the one or more grooves are adapted to removably receive a cutwater.
In another aspect, the present invention broadly consists in a centrifugal pump housing to receive an impeller, the pump housing including one or more grooves to removably receive a cutwater.
In a further aspect, the present invention broadly consists in a centrifugal pump adapted to receive different-sized impellers, the centrifugal pump comprising a housing having one or more grooves to receive a cutwater, wherein the one or more grooves are positioned such that different-sized cutwaters may be interchangeably placed adjacent the periphery of different-sized impellers.
Preferably the pump housing comprises two housing halves that are attached together, with grooves provided in each housing half.
Preferably two or more discrete grooves are provided in the pump housing.
Preferably a single continuous groove is provided in the pump housing. In one form, ridge-like formations are provided in the continuous groove.
Preferably the cutwater comprises a strip of plastic or metal. In one form, the cutwater is provided in a single size from which smaller sizes may be made by machining the cutwater. Alternatively various discrete sizes may be provided. Preferably the various sizes may also be machined.
Preferably the cutwater comprises a pre-curved strip of material. Alternatively the cutwater comprises a flexible strip of material that can be curved for insertion into a groove.
In a still further aspect, the present invention broadly consists in a method for varying the properties of a centrifugal pump, the pump having an interchangeable impeller and one or more grooves to receive an interchangeable cutwater, the method comprising the steps of: selecting an impeller having one or more desired characteristics; selecting a cutwater for use with the selected impeller; and installing the selected impeller and cutwater into the centrifugal pump.
Preferably the step of selecting an impeller comprises selecting an impeller with a desired diameter.
Preferably the step of selecting an impeller comprises selecting an impeller with a desired contour.
Preferably the method further comprises the step of machining the selected cutwater to better suit the selected impeller before the step of installing the cutwater into the centrifugal pump.
Preferably the method further comprises the steps of: removing the selected cutwater from the pump; machining the selected cutwater to better suit the selected impeller; and installing the machined cutwater into the centrifugal pump.
Preferably the method further comprises the steps of: removing the selected cutwater from the pump; selecting a replacement cutwater; and installing the replacement cutwater into the centrifugal pump.
In a still further aspect, the present invention broadly consists in a method for varying the properties of a centrifugal pump, the pump having an interchangeable impeller and a housing provided with one or more grooves to receive an interchangeable cutwater, the method comprising the steps of: disassembling the pump so as to gain access to the impeller and cutwater; removing the cutwater from the one or more grooves; machining or replacing the cutwater; inserting the cutwater into the one or more grooves after being machined or replaced; and reassembling the pump.
Preferably the method further comprises the steps of: removing the impeller; machining or replacing the impeller; and inserting the impeller into the pump after being machined or replaced.
The term ‘comprising’ as used in this specification means ‘consisting at least in part of’, that is to say when interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present.
This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
Preferred forms of the apparatus and method of the invention will now be described with reference to the accompanying figures in which:
Referring to
The impeller 26 is received in the pump in any conventional manner, provided it is removable. The cutwater 28 is received in grooves provided in the two housing halves. An example groove is indicated as 29 in the back casing 24 in
The cutwater 28 is preferably a strip of metal or plastic. A wide range of fixed cutwater sizes may be provided for interchangeable use in the variable pump 20. Alternatively, the cutwater 28 may be provided in a limited size range or a single size that can be machined to a specific smaller size.
The cutwater 28 may be made flexible to allow the cutwater to be bent to conform to a curved groove. Alternatively, the cutwater 28 may be pre-curved or permanently curved to suit a curved groove.
Referring to
In one preferred form of assembly, clips or clamps are provided around the periphery of the pump housing to securely couple the two housing halves together. In an alternative form the pump housing halves are attached together using a combination of nuts, bolts and washers. This alternative form of the assembly is shown in
The operation of the variable pump assembly of
One variability in the variable pump of the present invention is the interchangeability of the impeller. In one form, the variable pump allows the use of impellers of differing diameters. Given that impellers with different diameters produce different flow rates and water pressures, the interchangeability of the impeller allows the variable pump to be tailored to suit a range of applications. For example, if the variable pump is desired to supply water to a household in a neighbourhood with a generally low mains water pressure, a large diameter impeller may be used to provide both high flow rate and high water pressure to the household.
An example of three different sizes of impellers and their respective operating characteristics are shown below in Table 1.
When the impeller of the variable pump is changed, the cutwater in the variable pump should also be changed. As noted earlier, the cutwater functions to divert water from the impeller to the discharge or the outlet.
It is important for the cutwater to remain close to the periphery of the impeller to effectively divert the water. If the impeller is changed to a lower diameter impeller with no change in cutwater, the cutwater will no longer be in close proximity to the periphery of the impeller, and the operating characteristics of the pump will be adversely affected. If the impeller is changed to a large diameter impeller with no change in cutwater, the rotating impeller may come into contact with the cutwater, causing damage to the impeller, cutwater and the housing.
The present invention addresses the above by providing a removable cutwater in the variable pump. As noted earlier, the cutwater is placed in grooves in the pump housing halves. Referring to
In one form, various sizes of cutwaters can be interchangeably fitted into one or more of the discrete grooves. For instance, if a large diameter impeller is used, a cutwater may be placed in an outer discrete groove. If a small diameter impeller is used, the cutwater may be placed in an inner discrete groove, or alternatively, in both inner and outer discrete grooves. In the form shown in
The specific position of the discrete grooves will depend on the variable pump application and the range of impellers that are to be used in the pump. Skilled persons will appreciate that the groove arrangement can be modified to suit the variable pump and impeller range.
As an alternative to discrete grooves, a single continuous groove may be provided in the pump housing. The continuous groove may securely receive fixed-length edges of a cutwater. The variability of the cutwater in this embodiment will be in the variability of the material between the fixed-length edges of the cutwater.
In one embodiment, ridge-like formations are preferably provided in the continuous groove. The provision of ridge-like formations allows the use of cutwaters that comprise a simple length of material, without any fixed-length edges. The ridge-like formations serve to prevent any cutwater that is shorter than the groove length from moving within the continuous groove. As with the groove design, the ridge-like formations may be tailored to suit the application of the variable pump and the range of impellers that may operate in the pump.
The use of the variable pump of the present invention with different-sized impellers will now be described with reference to
In
The ease with which the characteristics of the preferred form pump may be varied and maintained will now be explained. In terms of varying the pump characteristics, a skilled technician may first determine the pump characteristics that are desired, such as a certain water flow rate and/or pressure. Based on the desired characteristics, the skilled technician then selects an impeller that will provide the desired characteristics. The technician then notes the impeller size or contour, and selects an appropriate cutwater. This may be done via a printed chart or table, or a computer program. Once the technician has chosen the impeller and the cutwater to suit, the technician installs the same into the centrifugal pump housing, and begins operating the pump.
Where only a fixed sized cutwater is available, or where the cutwater size does not meet the technician's requirements, the technician can easily machine the cutwater to a suitable size. Where better suited replacement cutwaters are available, the technician may opt to simply replace the cutwater.
In terms of maintenance, a skilled technician first disassembles or opens the pump housing to access the impeller and cutwater. If servicing is required for the cutwater, the technician removes the cutwater and either machines or replaces the cutwater, depending on the state of the cutwater and the purpose of servicing the pump. Once the cutwater is machined or replaced, the technician installs the cutwater and reassembles or closes the pump housing. The above maintenance process also applies to servicing impellers in the preferred form variable pump, or changing impellers to vary the pump performance characteristics such as water flow rate and/or pressure.
In addition to the ease with which the characteristics of the variable pump may be varied, the present invention also provides the benefit of a cost-effective solution to the variability of centrifugal pumps. The cost-effectiveness of the present invention stems from the simple yet robust design of the pump housing and cutwater.
The foregoing describes the invention including preferred forms thereof. Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated within the scope hereof. For example, although the interchangeability of the cutwater has been described with reference to different impeller diameters, the interchangeability of the cutwater may also be based on different impeller blade contours. Also, while specific shapes and placements of the interchangeable cutwater have been illustrated, persons skilled in the art will appreciate the numerous other cutwater shapes and placements that may be employed instead.
| Number | Date | Country | Kind |
|---|---|---|---|
| 544309 | Dec 2005 | NZ | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NZ2006/000313 | 12/1/2006 | WO | 00 | 9/26/2008 |
