Engineering · Pumps — Priming
A centrifugal pump loses suction (will not pump) when it becomes air-bound because:
- AAir increases its discharge head
- BThe low density of air cannot generate enough pressure differential to draw liquid up the suction✓ Correct
- CAir lubricates the impeller
- DIt raises the NPSH available
Explanation
A centrifugal impeller develops head proportional to fluid density. Air is far less dense than liquid, so an air-bound casing cannot create the pressure differential needed to lift liquid — the pump must be primed (filled) or fitted with a self-priming arrangement.
Authority: Modern Marine Engineer's Manual; pump operation
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