There is increased turbulence at the vane tips as the impeller is trimmed because the shroud to casing clearance (Gap “A”) is increasing.This is true only in low specific speed pumps. The affinity laws assume the impeller shrouds are parallel.The affinity laws accounting for the impeller trimming is the key relation to determine the pump performance with a trimmed impeller anyway they are not as accurate as we would like them to be, especially if we are making more than a 10% reduction in impeller diameter. Impeller trimming is a proper way to alter the performance of a centrifugal pump with a constant speed so as to meet the demand on the specified flow rate and head in pumping systems. Therfore it will undoubtedly provide helps for the improving of existing mehtods to fully master the existed successful experience. Impeller trimming refers to the reduction of the impeller diameter, and thus a reduction of the circumferential speed at the impeller outlet of a centrifugal pump. At present a set of wholly mature design methods of impeller theory based on existential experiences do not exist, because of the complexity of internal flow characteristics of centrifugal fan.
Theory bites are a collection of basic hydraulic theory and will touch upon pump design and other areas of pump industry knowledge.
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