What does NPSH stand for and what does it indicate in pump systems?

• A. Net Positive Suction Head; the minimum pressure at the suction required to avoid cavitation
• B. Negative Pressure Suction Head
• C. Normal Positive Suction Head
• D. Net Pressure Suction Head

Answer: (A)

NPSH means Net Positive Suction Head, a measure of the suction pressure available at the pump inlet expressed as a height of liquid. It indicates the margin against cavitation—the tendency of the liquid to vaporize when the local pressure falls below its vapor pressure. Cavitation creates vapor bubbles that collapse and can damage the impeller and degrade performance. In pump systems you compare the available NPSH (NPSHa) with the pump’s required NPSH (NPSHr): if NPSHa is at least equal to NPSHr, the pump operates without cavitation; if not, cavitation risk increases. The other terms listed don’t reflect the standard meaning of NPSH.