Quantcast Figure 6-23.Impeller, impeller wearing ring, and casing

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Figure 6-23.—Impeller, impeller wearing ring, and casing wearing ring for a centrifugal pump. bearings-laminated phenolic material grade FBM (fabric-based Bakelite or Micarta), high lead content bronze, graphite bronze, and lignum vitae. The  condition  of  all  types  of  internal  water- lubricated bearings should be checked frequently to guard against excessive wear which can result in misalignment and shaft failure. As for oil-lubricated sleeve or shell-type bearings, the bearing clearances should be measured following procedures described for the pump, and clearances should be maintained within the limits specified in the manufacturer’s technical manual. The  clearance  between  the  impeller  wearing  ring and  the  casing-wearing  ring  (fig.  6-23)  must  be maintained, as shown in the manufacturer’s plans. When clearances exceed the specified figures, the wearing rings must be replaced. This replacement requires  the  complete  disassembly  of  the  pump. Information on disassembly of the unit, dimensions of the wearing rings, and reassembly of the pump is in the manufacturer’s  technical  manual.  (Wearing  rings  are located on the main feed pump, as shown in figure 6-24.) When  deciding  whether  the  wearing  rings  need renewing, you must consider the capacity of the pump and the discharge pressure of the pump. On low- pressure  pumps,  the  wearing  ring  diametrical clearance may be 0.015 to 0.030 inch more than the designed  amount  without  any  appreciable  effect  on  the capacity of the pump. For pumps with a discharge pressure up to 75 psi, a wear of 0.030 to 0.050 inch is permissible. The percentage of capacity loss with a 0.030-inch wearing ring clearance in excess of standard may be large with a small pump but comparatively small with a large pump. For high-pressure boiler feed pumps, the effect of increased wearing ring clearance is readily noticeable in the efficiency and maximum capacity of the pump. For high-pressure pumps, the wearing rings should be renewed when the clearance shown on the manufacturer’s plans is exceeded by 100 percent. It is usually not necessary to renew wearing rings uniess the wear is at least 0.015 inch. If a pump has to be disassembled because of some internal trouble, you should check the wearing rings for clearance. Measure Figure 6-24.—Two-stage centrifugal pump. 6-24

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