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Preliminary Design Memorandum <br /> Silt Pumping Plant Rehabilitation <br /> the irrigation system so that the Contractor can order long lead equipment items in advance.No <br /> recreational or environmental concerns related to the construction schedule are anticipated. <br /> FEATURES FOR EVALUATION <br /> There are five significant features that require an understanding and agreement before initiating <br /> final design. Those features are pump type,pump priming system, fixed-speed or variable speed <br /> pumps,hydraulic transient mitigation, motor control center features,and facility power supply. <br /> Each feature with options will be discussed. <br /> Pump Type <br /> Alternatives Considered: Vertical Turbine Pumps or Horizontal Centrifugal Pumps <br /> Description <br /> The current pumping plant is designed for horizontal, split-case centrifugal pumps. Over the last <br /> 46 years of operation,the District has become familiar and proficient at maintaining the pumps. <br /> The pumps do require a priming system that has proven to be troublesome for the District. <br /> Consequently,the District would like to evaluate their pump type options. Two options seem to <br /> be apparent,the existing pump type and vertical turbine pumps. <br /> Advantages/Disadvantages <br /> Horizontal,Split-Case Dual Suction Centrifugal Pumps <br /> Advantages: <br /> • Pumps are available to meet the project requirements. <br /> • Horizontal, split-case pumps are considered to be robust, simple and reliable. <br /> • The existing pumping plant was designed specifically for horizontal, dual suction, <br /> centrifugal pumps. Substructure and superstructure modifications are therefore <br /> not expected. <br /> • District has developed an expertise to service horizontal centrifugal pumps. <br /> • Maintenance of this style of pump is simpler than vertical turbine pumps since <br /> pump internal components are easily accessed from the pump bay floor without <br /> lifting the pump from its base. <br /> • Motors are above wet well level and easily accessible for maintenance. <br /> • Clearances to pass sticks are larger for a single-stage centrifugal pump than for a <br /> multi-stage vertical turbine pump. <br /> 10 <br /> FOR OFFICIAL USE ONLY <br />