Patent Application
20090208336
The invention concerns a pump impeller and more precisely a pump impeller for centrifugal-or half axial pumps for pumping of fluids containing pollutants.
In literature there are lot of types of pumps and pump impellers for this purpose described, all however having certain disadvantages. Above all, this concerns problems with wear, clogging and low efficiency.
Sewage water contains a lot of different types of pollutants, the amount and structure of which depend on the season and type of area from which the water emanates. In cities plastic material, hygiene articles, textile etc are common, while industrial areas may produce wearing particles. Experience shows that the worst problems are rags and the like which stick to the leading edges of the vanes and become wound around the impeller hub. Such incidents cause frequent service intervals and a reduced efficiency.
In agriculture and pulp industry different kinds of special pumps are used, which should manage straw, grass, leaves and other types of organic material. For this purpose the leading edges of the vanes are swept backwards in order to cause the pollutants to be fed outwards to the periphery instead of getting stuck to the edges.
Different types of disintegration means are often used for cutting the material and making the flow more easily. Examples are shown in SE-435 952, SE-375 831 and U.S. Pat. No. 4,347,035.
In literature the designs of the pump impellers are described very generally, especially as regards the sweep of the leading edges of open impeller wheels. Attempts to define the sweep of the leading edges for an open impeller wheel are described in e.g. EP 0916851 and EP 0916852.
During pumping where high lifting heights are required, for example in mines, closed pump impellers are often used, i.e. such with two cover discs, an upper and a lower as well as intermediate vanes, because these types of impellers reduce the axial load on the pump in comparison to the open type impellers. On the other hand, closed impellers have a lesser lead-through, which means higher risk for clogging.
EP 0395604 discloses an impeller wheel, which is arranged with one or several vanes that are attached to cover discs on each side forming a so called closed impeller wheel. The leading edges of the vanes are placed generally in a plane perpendicular to the axis of rotation of the impeller, at the inlet opening in one of the cover discs.
Regarding closed impeller wheels they are generally designed with leading edges placed in the central inlet such that they are rather straight as seen in the flow direction. It has been found that during use, and in particular when the liquid contains rather large quantities of abrasive pollution, there is considerable wear on the leading edges of the vanes. There is further a risk that pollutants such as rags, plastic bags and other elongated objects get stuck on the leading edges, thereby requiring cleaning of the pump.
The aim of the present invention is to remedy the above mentioned problems and in particular in connection with closed impeller wheels.
This aim is solved according to a main aspect of the invention by what is characterized in claim 1. Preferable embodiments of the invention form the dependent claims.
According to a main aspect of the invention, it is characterized by an impeller wheel of a centrifugal or half axial type to be used in a pump for pumping liquids, wherein the impeller is arranged with one or several vanes, that the vanes are attached to cover discs on each side, forming a so called closed impeller wheel, characterized in that the leading edges of the vanes are swept backwards at the inlet opening in one of the cover discs of the impeller.
According to a further aspect of the invention, it is characterized in that the leading edges co-operate with cutting means arranged in a central inlet opening of the pump,
Preferably the leading edges protrude somewhat out of the inlet opening, and that the cutting means constitute at least one narrowing section of the gap between the central inlet opening of the pump and the leading ledges of the impeller, whereby, when the leading edges sweep past these sections during operation, a cutting action is obtained there between.
By designing the leading edges of the vanes strongly backswept it has been found that the wear on these edges are reduced drastically. The design also reduces the risk of material getting stuck on the edges. Rather such material are fed towards the periphery.
The material that however tends to get stuck on the edges at the inlet opening of the impeller will be cut by the cutting means. In a preferred embodiment the leading edge of the vanes co-operate with two narrowing parts of the inlet opening of the pump housing.
For a good performance regarding the pump function and transportation of material towards the periphery, the sweep angle α should be in the region 40-60° and the sweeping of the leading edges may generally follow the curvature of a logarithmic spiral.
In all an impeller wheel with improved performance and wear resistance is obtained, leading to long operation cycles between maintenance and service.
These and other aspects of and advantages with the present invention will become apparent from the following detailed description and from the drawings.
In the following detailed description of the invention, reference will be made to the drawings, of which
a is a perspective view from above of an impeller wheel comprising the present invention,
b is a view corresponding to
According to the principles for a centrifugal pump, the liquid is sucked in axially through the inlet 24 and leaves the pump through the outlet 26 according to flow arrows A, B and C.
According to the present invention the vanes 18 are designed such that the leading edges 40 are swept strongly backwards at the inlet opening 42 of the impeller wheel, in relation to the direction of rotation R. The sweep angle could be increased from the hub and outwards. The sweep of the leading edges could be defined by a logarithmic spiral where the sweep angle α is π/2−β, where β is the angle of the logarithmic spiral. Preferably the sweep angle should be in the region 40-60°.
At the inlet opening of the impeller the leading edges are placed generally in a plane perpendicular to the axis of rotation 10 of the impeller. The advantage with this design is to make sure that pollutants slide towards the periphery instead of getting stuck on the edges. It has further been shown that the wear on the leading edges are reduced when they have this configuration instead of the conventional design.
Further, the leading edges protrude somewhat out of the central opening of the impeller,
In total the design of the leading edges being swept and protruding somewhat, and co-operating with the opening of the bottom plate, greatly reduces the risk of pollutants getting stuck and reduces the wear on the leading edges.
It is to be understood that the embodiment described above and shown in the drawings is to be regarded as a non-limiting example of the invention and that it may be modified within the scope of the patent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0402840-3 | Nov 2004 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/55726 | 11/3/2005 | WO | 00 | 5/5/2009 |
