Analysis and Discussion on the Breakage of the Pump Shaft in Centrifugal Pumps with Direct Motor Connection
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One centrifugal pump, with circulating water as the medium and normal temperature. Installed 14 years ago; it’s been about three years since then. One pump is in use while the other serves as a backup. The pump in use makes noise, so the backup pump is switched on – but no flow occurs. The inlet filter was found to be in good condition, so the only option left was to disassemble the pump ； Fracture surface on the impeller side, fracture surface on the pump shaft side with a mechanical seal; the pump shaft has been removed from the impeller. Please analyze the following image – what could be the cause?
Looking at the cross-section, it seems the shaft itself has defects
The fracture of the shaft is almost certainly due to a defect, and specific testing and analysis can be carried out
To save material, manufacturers of such shafts sometimes weld two sections of the shaft together.
Is the standby pump rotated regularly? Is pump switching performed regularly? Then investigate the cause within the pump itself. You should know better than us. The reason I gave is that the pump was not in use for a long time, the impeller rusted together with the pump casing, and the shaft broke at the moment of startup. Is the fracture site on the pump shaft a new mark? I envy your company for installing filter screens at the pump inlet – it’s a quite proper approach. Our company has a vertical pump; when it was started without rotating the pump first, the coupling broke. After replacing the coupling, the pump exhibited high vibration levels during operation. Upon stopping the pump for inspection, it was found that insulation sheeting was stuck to the impeller; once this was removed, the noise and vibration returned to normal levels. Regular maintenance of the equipment must be proper, and in the event of an accident, a thorough analysis is required; it is not sufficient to attribute it solely to one particular factor.
Let’s look at it from the perspective of eliminating pump body vibration.
The moderator’s explanation was excellent! Give a like
1. The pump shaft itself has defects; 2. There are impurities inside the pump, which cause the impeller to get stuck and lead to the breakage of the pump shaft
First, check whether the motor shaft is overheating, and whether there is abnormal vibration with loud noise from the motor. Second, determine if the head pressure selected for the pump is too high; this pressure buildup causes the impeller and shaft to exert more force, resulting in increased shaft torque that exceeds the shaft’s tolerance limits. Third, it could be a problem with the material of the shaft itself, caused by defects in its forging process
I’ve seen this situation for the first time. Congratulations, the original poster has won the big prize.