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About:
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High wear applications usually call for closed-type impellers. In applications with coarse particles, expelling vanes on the face of the front shroud make sense. These vanes prevent large particles from becoming trapped between the impeller and suction side liner and minimize recirculation. The benefit is reduced gouging and recirculation wear at the expense of a 2–3% drop in efficiency. In addition, expelling vanes often are used on the back shroud of the impeller in coarse particle applications to prevent the trapping of large particles between the impeller and back liner. In this location, they also serve to decrease the forward axial load by lowering the pressure acting on the back shroud and beneficially reducing the pressure at the hub. The decreased axial load improves bearing life. All these effects also cut the pressure differential at the shaft seal and reduce the tendency for slurry leakage from the pump. As with expelling vanes on the front shroud, back vanes usually absorb 2–3% of efficiency.
To combat wear and allow for passing large diameter solids, many slurry pump impellers feature fewer but thicker main pumping vanes. Both of these factors further contribute to reduced efficiency compared with clear liquid impellers. While a clear liquid impeller usually has five to nine vanes, most slurry pump impellers have two to five. Applications requiring large particle passing often employ pumps with two or three vanes. Slurry pumps use short blocky vanes in contrast to the thin long-length, long-wrap vanes found on high efficiency pumps for clear liquids.
Sumps And Storage Tanks
Slurry pumps usually require sumps or suction tanks to act as suction source or intermediate storage for slurries. However, lack of detailed knowledge about the slurry pump’s behavior and sump hydraulics often leads to oversizing. The larger the sump or storage tank, the more likely it may become a settling tank for solids. For some services, the accumulation of solids leads to other problems, for instance, the build-up of harmful gases, and requires periodic desludging of the sump or tank, which increases operating costs and reduces overall safety and reliability. The optimal volume of suction storage, in this context, should prevent the settling of solids while avoiding problems for pump operation.
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