Diagnosis from Visual Examination of Damage

bearing damage Static radial loads in excess of the bearing rating will cause cracking of the balls or rollers and the races in rolling element bearings. In the case of sleeve bearings, the bearing metal will be worn in one direction only and the journal will be worn uniformly. If the opposite is true (that is, the bearing is worn uniformly and the journal excessively in one direction), the cause of the failure is most likely unbalance or a bent shaft and not excessive bearing loads.

shaft failures Shaft failures from excessive radial loads usually occur at the midpoint of the shaft span in double-suction or multistage pumps. In the case of end-suction pumps, shaft failures usually occur at the shoulder of the shaft, where the impeller hub joins the shaft sleeve, or at the location of the highest stress concentration, if elsewhere.

Instrumentation It is difficult to devise instrumentation to determine excessive radial loading of the shaft and bearings. Temperature rise of the bearings may or may not be symptomatic of excessive radial loading. High bearing temperatures may occur from misalignment, inadequate lubrication, or excessive axial loading of the thrust bearing. These causes should be eliminated before concluding that the radial loads are excessive.

Corrective Procedures Most bearing and shaft failures caused by excessive radial loads occur when the pump operates at low flow rates. Radial loads can be reduced by operating the pump at higher capacities or by installing a bypass from the pump discharge back to the pump suction or suction source. For pumps handling water, the life of the shaft may be extended by substituting a martensitic stainless (13% chrome) steel shaft for carbon steel. If there are signs of corrosion as well as fatigue failure, an austenitic stainless steel shaft may also be considered. Physical properties should be evaluated carefully, as the endurance limit of the 300 series steels may be lower than that of chrome steels in fresh water. For liquids other than water, the endurance limit of the shaft material in the liquid being pumped may be a significant determining factor in the life of the shaft in the presence of high dynamic loading.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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