MATERIALS HANDLING
they are running. Manufacturers provide performance data for their motors on rating plates that show, amongst other things, the efficiency at 50%, 75% and full load. Although an undersized motor will not provide optimum performance, oversizing it is also not desirable as it affects the overall efficiency of the pump set.
DRIVE COMPONENTS A pump is not generally considered on its own, but as a complete set to include the driver and drive components, such as couplings, gearboxes and belt and pulley systems. Tere are inherent inefficiencies in gearboxes and particularly belt drive systems. Incorrectly fitted and maintained belts can be very inefficient. Electronic variable speed drives (VSDs) have been developed to be extremely efficient now and should always be considered as they allow direct-driven pumps to be used with minimal losses. ln addition, VSDs can be used to control the pump speed to maintain the operating point as close to the best efficiency range as possible.
MATERIALS OF CONSTRUCTION Te operating life of components in contact with a pumped fluid will be compromised due to corrosion or abrasion if not selected to suit the application. Te consequences can be the premature failure of parts, which causes unplanned downtime, as well as the increased cost of replacement parts and associated labour.
TIMELY PARTS REPLACEMENT As parts start to deteriorate due to corrosion or erosion, their performance is also compromised. A pump selected based on its as-new efficiency will eventually begin to consume more energy. At some point, a decision needs to be made regarding the correct time for parts replacement as the cost of rising energy consumption must be
A pump is considered as a complete set that includes other components
offset against the cost of parts replacement; remembering that each breakdown incurs spare parts replacement, labour, warehousing and inventory handling costs.
TIMELY MAINTENANCE A pump’s useful part life can be extended by regular maintenance. Although gland seal and bearing maintenance are common to all pumps, slurry pumps are susceptible to increased wear due to recirculation within the casing. Tis tends to increase as parts begin to wear and clearances become enlarged. Te most affected components are the impeller and the suction side of the casing, where recirculation from the high to the low-pressure side of the casing is present. It is common practice to maintain a small gap between the impeller and the suction side of the casing, effected by
Deciding when to replace parts is crucial to a successful operational strategy
either adjusting the impeller, the casing or suction liner. ln high wear applications, the extension to wear life can be significant. So, in terms of calculating and managing
the TCO of a pumping system, we need to look beyond the most obvious cost components, i.e. capital, spare parts, energy and labour, and consider the impact pump and motor selection, materials of construction and maintenance regime to get a full picture of the true cost of the assets.
Performance and reliability curves 28
www.engineerlive.com Pump performance curve
Harvinder Bhabra is head of segment Fertilisers, Metals, Mining and Chemical Process lndustries at Sulzer.
www.sulzer.com
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