Every pump datasheet carries a curve called NPSH, and it is the line buyers skip most. It is also the line that determines whether the impeller survives the installation. NPSH stands for Net Positive Suction Head: the pressure margin at the pump inlet that keeps water from boiling into vapour.
Required versus available
NPSH splits into two numbers. Required is the pump's appetite: how much inlet pressure it needs at a given flow to avoid cavitation; the manufacturer publishes it as a curve that rises steeply with flow. Available is your installation's offer: atmospheric pressure minus suction lift, pipe friction and vapour pressure of the liquid. The rule is blunt: available must exceed required, with a sensible margin.
Why installations fail quietly
Cavitation rarely announces itself as a datasheet problem. It arrives as a gravelly rattle, a pump that never quite reaches its curve, and an impeller that pits away over months. The causes are always suction-side: a lift a metre too tall, a line a size too small, a strainer slowly blinding, hot water raising the vapour pressure.
The practical discipline
When evaluating a pump, take your real suction conditions, subtract lift and friction, compare against the required curve at your duty flow, and demand margin. And remember that required NPSH climbs at the right-hand end of the curve: a pump selected to run past its best efficiency point may be quietly cavitating while still "on curve".