31 Bearing Failure Bearings fail in general either through contamination of the

31 bearing failure bearings fail in general either

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3.1 Bearing Failure Bearings fail, in general, either through contamination of the bearing oil by water, another liquid, or solid particles or because of high heat, which is often caused by an overload on the bearing or by excessive lubrication [9]. These faults can have various root causes. Moisture contamination in the bearings comes from multiple sources: packing leakage flows back to the bearings, and seeps into the bearing housing; using a water hose to clean a packing leakage, which would allow water to splash into the bearing case and into the housing through the vent or grease seal area; replacing the heated air through the bearing casing vent with cooler atmospheric air when the bearing case cools down; or the leakage of steam, condensate or cooling water from a mechanical seal quench gland and directed at the radial bearing [18]. When the pump is operating at its BEP, the only bearing loads are due to the weight of rotating assembly, the stress caused by the interference fit on the shaft, and any bearing preload that has been specified by the manufacturer. However, most pumps do not work continuously at their BEP, and thus overloading is possible [19]. Overloading of bearings can be a result of many different conditions: an unbalanced rotating element; a bent rotating shaft ; blocked impeller balance holes; cavitation; excessive axial thrust; excessive radial load caused by low flow operation or some mechanical failure inside the pump; excessive heating of bearings due to improper dissipation of heat; improper cooling of the bearings such as cooling the bearing housing with a water hose or some other similar system; increased pump internal running clearances around the wear rings; increasing the speed of the bearing; misalignment between the pump and its driver; operating the pump away from its best efficiency point (BEP), which may create excessive radial forces on the impeller that would felt by the bearing; pipe work exerting strain; pulley driven pump drivers; pumping a high specific gravity fluid such as sulphuric acid, which can almost double the radial load on a bearing; pushing the bearing too far up a tapered sleeve; rusting of antifriction bearings because of water in the bearing housing; having the thermal expansion of the shaft greater than the thermal expansion of the bearing; causing the bearing housing to be out of round; having the impeller located too far away from the bearing; having the wrong interference fit between the bearing and the shaft (the shaft was out of tolerance causing the bearings to be too tight); having the vane passing frequency coincident with the resonance of the pump assembly; having the vibration of almost any form from other parts of the piping system or within the pump; or producing water hammer in the lines [3, 18, 20, 21] .
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