Silt Pumping Plant Rehabilitation Preliminary Design

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Preliminary Design Memorandum Silt Pumping Plant Rehabilitation Disadvantages: • Pump impeller is above the wet well level. Therefore a priming system is required. • Horizontal pump floor plan requires more floor area than a vertical turbine pump floor plan. Since pumping plant has already been built for a horizontal layout,this disadvantage has no significance. Vertical Turbine Pumps(VTPs) Advantages: • A wide selection of pumps is available to meet the project requirements. • Pump impellers are always submerged;therefore,a priming system is not required. • Net Positive Suction Head requirement is easily met since the initial impeller is submerged. • The minimum submergence requirement to prevent a surface vortex is well defined and can be easily met. • Substructure and superstructure area requirements are small. • Pump motor is above wet well maximum water surface. Disadvantages: • High superstructure is required to pull pumps from the sump. Existing crane height and capacity must be carefully examined to determine if VTPs can be removed without modifications. • Motor must be disconnected and removed to inspect or repair pump. • More shaft bearings are required than other designs. • Pump maintenance is not as simple as split case centrifugal pumps, District will have to train maintenance staff to service VTPs or truck pumps to the nearest service center. • Screening requirements for multi-stage VTPs are typically tighter than single stage centrifugal pump styles since multistage impellers are smaller in diameter with smaller clearances.Existing trashrack must be evaluated to determine if screening modifications are required. • Pump substructure may require structural modifications to support the different weight pattern of the VTPs. • Sump may require modifications to prevent vortex formation from the water 11 FOR OFFICIAL USE ONLY