The assistant engineer reports an installed centrifugal pump has a history of running higher than normal amperage since new construction. Capacity and discharge head for the pump are more than adequate. All other system parameters are normal. The best way to reduce the pump load is to do which of the following?
• Centrifugal pump performance curves – how head, flow, and power change with impeller diameter • Pump affinity laws – how brake horsepower (BHP) relates to impeller diameter and speed • Differences between changing the pump itself, changing the impeller, adding bypasses, or adding pumps in parallel
• Which option directly changes the pump’s power demand at the same speed and system conditions, according to the pump affinity laws? • How does installing a bypass line affect the flow through the pump and therefore the power it draws? • What happens to total load on the system if you add another pump in parallel instead of changing the operating point of the existing pump?
• Review the pump affinity law for power: power varies with the cube of impeller diameter and speed • Consider whether a bypass line causes the pump to do more or less work overall at the same discharge pressure • Think about whether adding a second pump in parallel reduces, increases, or leaves unchanged the load on the original pump at the same system head
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