Apart from economic considerations, two primary selection considerations for dredge pump operation are no settlement of sediments in the pump and minimum amount of wear and tear in the pump due to the flow operation. The key design parameters to keep in mind to satisfy the primary requirements are the type of installation, critical flow rate, total discharge head, and the pump design material.
Before moving on to estimating the design parameters of ‘your’ slurry pump, an extremely crucial step is being familiar with the material that needs to be transported. Therefore, estimation of pH and temperature of the slurry, the specific gravity of slurry and concentration of solids in the slurry is the first crucial step towards the direction of ‘your’ ideal pump selection.
Critical flow rate is the transition flow rate between a laminar and a turbulent flow and is calculated based on grain diameter (size of slurry particles), the concentration of solids in the slurry and the pipe diameter. For minimal settlement of sediments, the actual pump flow rate of ‘your’ pump should be higher than the calculated critical flow rate for your application. However, it is important to be careful with the selection of the pump flow rate as the increase in flow rate will increase the wear and tear or abrasion of the pump material and hence reduce the lifetime of the pump. Hence, for an uninterrupted performance and extended lifetime, the pump flow rate should be optimized.
Total discharge head is a combination of static head (actual elevation difference between the surface of the slurry source and the discharge) and friction loss in the pump. Along with dependence on the geometry of the pump (pipe length, valves or bends), friction loss is also affected by the pipe roughness, flow rate and slurry concentration (or percentage of solids in the mixture). The friction losses increase with the increase in pipe length, the specific gravity of the slurry, concentration of the slurry or the slurry flow rate. The pump selection procedure requires that discharge head of ‘your’ pump is higher than the calculated total discharge head. On the other hand, it is crucial to note that the discharge head should be kept as low as possible to reduce the pump abrasion due to slurry flow.
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