The 'NPSH' (Net Positive Suction Head) for a centrifugal pump is important because:
Choose the correct answer
Only the efficiency of the pump impeller
Prevents cavitation — available NPSH must exceed required NPSH; cavitation causes impeller pitting and performance loss
Determines the discharge pipe diameter
Controls the pump speed only
Correct Answer
B. Prevents cavitation — available NPSH must exceed required NPSH; cavitation causes impeller pitting and performance loss
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NPSH: total head available at pump suction above vapour pressure. NPSHa (available) = hatm − hf_suction − hs − hv. NPSHr (required, from manufacturer). Condition: NPSHa ≥ NPSHr. If NPSHa < NPSHr: cavitation occurs (vapour bubbles form in low-pressure zone → collapse → pitting, vibration, noise, damage to impeller). Limit suction lift and pipe losses. Pumping hot liquids or at altitude: lower NPSHa.
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