1. Field of the Invention
This invention relates to centrifugal pumps of the type used in industrial processing of abrasive slurries, and is specifically related to pump casings which are structured to withstand high abrasive wear.
2. Description of Related Art
Centrifugal pumps are commonly used in a variety of industries to process liquid mixtures containing particulate solids, commonly known as slurries. The mineral processing and dredging industries are common examples of applications in which centrifugal pumps are used to process slurries. Centrifugal pumps used in such applications are subject to severe erosion and wear by the particles in the slurry flow, which leads to the need to repair or replace the pump. Substantial economic consequences result. Therefore, considerable effort is expended by pump manufacturers and users to try to ameliorate the problem of wear in centrifugal pumps.
Centrifugal pumps generally comprise an impeller housed within a casing. An inlet in the pump casing directs fluid into the rotating impeller. The rotation of the impeller ejects the fluid outwardly toward the volute of the pump casing and eventually through an outlet formed in the pump casing. The pump casing therefore provides a pressure vessel which serves the dual function of collecting the slurry expelled by the impeller and converting the high kinetic energy flow at the impeller exit into potential (i.e., pressure) energy at the discharge outlet of the pump casing.
The pump casing of a conventional centrifugal pump is further comprised, in general, of a volute, a drive side liner and a suction side liner. In some pump casing constructions, the volute and one of the sides (either the drive side or suction side) are integrally formed as one piece and are joined to a separate side liner in a two piece construction. In other pump casing constructions, the volute is a separate piece from the two side liners and are all joined together in a three piece construction.
While the particular shape of the casing may vary by manufacturer and specific application, pump casing side liners are universally configured with a circular peripheral edge which joins to the volute of the pump casing. The diameter of the side liner or liners is selected to permit movement of the impeller into and out of the pump casing to thereby facilitate assembly and maintenance of the pump.
With continuous use of centrifugal pumps in the processing of abrasive slurries, wear will occur within the pump casing at the periphery of the impeller near the cutwater of the pump. The cutwater is that internal portion of the pump casing that is adjacent the discharge of the pump in the direction of rotation of the impeller. The most significant wear occurs at the cutwater because of the interaction of the flow streams around the impeller shrouds, the discharge neck of the casing and the cutwater. Typically, the greatest wear occurs between the drive side liner and the volute of the casing at or near the cutwater. When sufficient damage has occurred that the integrity of the casing is compromised, the pump casing, or even the entire pump, must be replaced.
Changes in the shape of the pump casing have been employed in the past in an attempt to ameliorate the wear on the casing. For example, the shape of the volute, or the shape of the casing at the cutwater, has been modified to compensate for the wear. More specifically, the radius of the pump at the cutwater (as measured from the center line of the pump radially toward the cutwater) has been increased to direct the wear more toward the side wall of the pump casing. However, modifications in the pump casing often compromise pump performance and a trade-off occurs where pump efficiency may be sacrificed in the interest of reducing or re-directing the wear.
Thus, it would be advantageous in the art to provide a pump casing design which reduces loss in pump efficiency while directing wear to the side liners of the pump so that wear can be localized, thereby reducing repair costs.