Silt Pumping Plant Rehabilitation Preliminary Design

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Preliminary Design Memorandum • Silt Pumping Plant Rehabilitation make the electrical evaluation is not typically available until 30%design. Hydraulic Transient Mitigation Alternatives Considered: Flywheels or an Air Chamber Existing System The current pumping plant uses flywheels mounted on the motor shafts for hydraulic transient mitigation on the 2 large pumps and the medium pump. This type of system is effective for shorter pipelines with a rising profile. The existing motors have been custom designed for the flywheels since additional bearing loads are introduced by the additional rotating mass.Additionally, hydraulic transients are also prevented by operating the discharge gate valves according to the prescribed timing in the Designers' Operating Criteria. Proposed System Our experience with the existing plant shows that for pumps and motors of these sizes and rotating masses and for this particular pipeline, hydraulic transients must be evaluated. The worst hydraulic transient case is typically loss of power when all pumps are operating at capacity.A hydraulic transient model will be developed early in the design process to determine if hydraulic transient mitigation is required for the new pumps and motors. If required,the transient model will be used to size flywheels for the three larger pumps. If the flywheel mitigation scheme works sufficiently well,then an inquiry will be put forth to selected motor manufacturers to confirm that the custom designed motor and flywheel combination can be reasonably acquired. If the flywheel mitigation scheme does not provide adequate protection to the pumping plant and discharge piping or if the custom flywheel motor design cannot be reasonably acquired,the addition of an air chamber located outside of the plant will be evaluated using the hydraulic model. The model will be used to optimize the size of the air chamber using proven Reclamation criteria. Advantages/Disadvantages Flywheel Advantages: • No additional maintenance, only maintenance to motor bearings. • Proactive hydraulic transient mitigation(immediately reduces hydraulic transient pressure wave development in the pipe when a change in velocity occurs) for normal, emergency and loss of power pump shutdowns. Disadvantages: • The function of the flywheels is not apparent to most operators and some 23 FOR OFFICIAL USE ONLY