Abstract
Many correctly sized centrifugal pump drivers have only limited reserve power at a pump's higher flow rate. When performance declines gradually in such applications, the higher flow demands—at or above best efficiency point (BEP) flow—often result in a power demand beyond the driver's capability, resulting in a motor trip. Severely reduced pump hydraulic performance may also be capable of overloading even an oversized pump driver. When the head rise from BEP to shut-off is shallow, the power demand rises substantially as flow increases. To understand the relevance of the power vs. flow rate relationships, it is necessary to appreciate that the power demand from the driver is a result of the work performed by the pump impeller(s), not the apparent hydraulic power delivered by the pump. A number of simple predictive maintenance techniques help predict the onset of motor overload. Each method must be treated with appropriate cautions, which include—periodic tracking of process control valve position vs. flow rate, periodic recording of motor amperes and voltage, and periodic measurement of pump shut-off head.
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