Centrifugal pumps use centrifugal force to move liquids from a lower pressure to a higher pressure and employ an impeller, typically consisting of a connecting hub with a number of vanes and shrouds, rotating in a volute or casing. Liquid drawn into the center of the impeller is picked up by the vanes and accelerated outwardly by rotation of the impeller toward the periphery of the casing, where it is then discharged at a higher pressure.
Centrifugal pumps are conventionally used in applications involving mixtures of solids and liquids, solids-laden mixtures, slurries, sludge, raw unscreened sewage, miscellaneous liquids and contaminated trashy fluids. These mixed mediums are encountered in industrial or commercial applications including sewage plants, sewage handling applications, paper mills, reduction plants, steel mills, food processing plants, automotive factories, tanneries, and wineries.
The nature of the conveyed medium poses significant challenges to continuous operation of the pumps. Of particular concern is the clogging of the impeller by debris in the pumped medium including but not limited to long rags, fibers, and like debris which are able to wrap around the impeller vanes, stick to the center of the vanes or hub, or lodge within the space between the impeller and the housing. Clogging severely impacts the efficiency of the pump.
U.S. Pat. No. 6,464,454 issued to Kotkaniemi on Oct. 15, 2002, discloses as shown in FIGS. 1(a)–(b), grooves 4, 16 at an inside wall of housing 1–1A, which extend from the outer outlet channel in the housing along the whole of the part of the wall adjacent to the vanes and some distance further. Kotkaniemi discloses slits 5, 15 provided between a vane and the housing, wherein the slits widen continuously outwards from the shaft in the direction of the flow so as to improve conveyance of fluid and matter therein. However, widening of the clearance between the impeller and wear plate or housing toward the outer diameter of the impeller reduces the efficiency of the impeller, such as by recirculation from the top side of the vane to the underside of the vane. In fact, worn pump impellers typically exhibit wear toward the outer diameter of the impeller, such as provided as the starting point in Kotkaniemi.
U.S. Pat. No. 6,139,260 issued to Arbeus on Oct. 31, 2000, discloses a pump housing comprising feeding grooves 8 in a wear surface opposed to the impeller vanes, as shown in FIG. 2. Arbeus discloses that such grooves 8 cooperate with the leading edges of the vane or vanes in such a way as to feed pollutants in the direction of the pump outlet, as opposed to an attempted disintegration of the pollutant by a cutting means. Groove 8 is shown to extend radially outwardly from an inner edge of the pump housing 7 to an outer edge thereof along the direction of rotation 9 of the impeller. Groove 8 is also shown to continuously widen along its length.
Some pumps designed for handling mixtures of solids and liquids displace the impellers from the wear plate, such as vortex pumps. U.S. Pat. No. 4,575,308 provides a vortex pump configured to minimize or reduce jamming or clogging of the pump by providing a swirl chamber adapted to redirect the pumped liquid thereabout as the impeller is rotated, whereby the liquid and suspended solid materials are formed into a swirling vortex of increased rotational velocity to substantially prevent the solid materials from adversely interfering with the impeller. A significant problem with these designs is that the pumps deliver a relatively low head to the fluid and the efficiency of these pumps is poor. Other pump designs, such as shown in U.S. Pat. No. 4,932,837, favor a closer, but still sizable, clearance between the impeller and the housing. However, the clearance between the impeller vanes and the interior wall of the pump housing is typically one quarter inch or more, which still suffers from reduced head and efficiency. This approach yields a compromise between pumping pressure and efficiency, on one hand, and minimization of pump clogs caused by solid objects jamming between the impeller vanes and the housing, on the other hand.
However, despite the above-noted improvements to pump and impeller design, additional structural and performance improvements may yet be realized.