This can be prevented by keeping the stuffing box temperature within the

This can be prevented by keeping the stuffing box

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elastomer, the seal faces or the metal parts) becomes destroyed, or the coated hard faces crack. This can be prevented by keeping the stuffing box temperature within the specified limits. In addition, by controlling the pressure in the stuffing box, one can control the temperature and prevent the fluid from vaporizing in the stuffing box or across the seal faces [19]. 3.3 Lubrication Failure The purpose of lubrication is to decrease the friction between two moving parts, thus decreasing their wear, and prolonging the life of the parts of the system. Non-contaminated oil cannot wear out and has a useful life of about thirty years at 30 o C. This life span is halved for every 10 o C rise in the temperature of the oil [18]. Overloading bearings can cause excessive heat to be generated within the bearings. The temperature rise will result in a decrease in the viscosity of the lubricant, which then leads to generation of more heat as it loses its ability to support the load. A varnish residue forms which then cokes at the elevated temperature. This coking will destroy the ability of the oil or grease to lubricate the bearing, as well as introduce solid particles into the lubricant [18]. Infrared thermography can be used to determine whether or not the bearing is overloaded by the amount of heat that is produced [23]. 3.4 Excessive Vibrations Excessive vibrations, or otherwise unsatisfactory or unacceptable vibrations, are classified, according to ISO 10816, to have amplitudes larger than 2.80 mm/s for small machines, 4.50 mm/s for medium machines, 7.10 mm/s for large machines with rigid foundations, and 11.2 mm/s for large machines with soft foundations. Vibrations result from unbalanced moving parts found within the pump system, interactions of the fluid and its particles with the pump and the connecting pipes, and movements of the pipelines themselves. There are numerous reasons that can lead to unwanted vibrations in a pump system, such as impeller unbalance, hydraulic imbalance, problems in the bearings, movement in the baseplate, component run-out, cavitation, air or vapour lock, and hydraulic excitation. Impeller imbalance usually appears in the vibration signature as a 1x running speed frequency vibration, and may result from either a mechanical problem, such as a mechanical seal or bearing failure, or a hydraulic problem. Mostly, inspections to determine if an impeller is balanced are not performed until heavy pitting is found on the impeller. The degree of etching or pitting is usually used as an indicator that the impeller needs balancing. Unbalanced forces which result from loose fit impellers could results in large amplitude vibrations. Impellers may shift due to the decrease in residual stresses that are created when the impeller is cooled and contracted around the shaft. Shaft vibrations and flexing tend to result in the impeller cocking or bowing the shaft, which removes it from its original balance along its centreline. Hence, when balancing an impeller, it is imperative that it must be balanced at the
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